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WO1994028613A1 - Battery powered permanent magnet direct current motor - Google Patents

Battery powered permanent magnet direct current motor Download PDF

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Publication number
WO1994028613A1
WO1994028613A1 PCT/AU1994/000257 AU9400257W WO9428613A1 WO 1994028613 A1 WO1994028613 A1 WO 1994028613A1 AU 9400257 W AU9400257 W AU 9400257W WO 9428613 A1 WO9428613 A1 WO 9428613A1
Authority
WO
WIPO (PCT)
Prior art keywords
motor
direct current
permanent magnet
armature
turns
Prior art date
Application number
PCT/AU1994/000257
Other languages
French (fr)
Inventor
Colin Edward Cartwright
Original Assignee
Colin Edward Cartwright
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from PCT/GB1993/002291 external-priority patent/WO1994011941A1/en
Priority claimed from PCT/GB1993/002293 external-priority patent/WO1994011162A1/en
Application filed by Colin Edward Cartwright filed Critical Colin Edward Cartwright
Priority to AU67178/94A priority Critical patent/AU6717894A/en
Publication of WO1994028613A1 publication Critical patent/WO1994028613A1/en

Links

Classifications

    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02KDYNAMO-ELECTRIC MACHINES
    • H02K23/00DC commutator motors or generators having mechanical commutator; Universal AC/DC commutator motors
    • H02K23/26DC commutator motors or generators having mechanical commutator; Universal AC/DC commutator motors characterised by the armature windings
    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02JCIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J7/00Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02KDYNAMO-ELECTRIC MACHINES
    • H02K23/00DC commutator motors or generators having mechanical commutator; Universal AC/DC commutator motors
    • H02K23/02DC commutator motors or generators having mechanical commutator; Universal AC/DC commutator motors characterised by arrangement for exciting
    • H02K23/04DC commutator motors or generators having mechanical commutator; Universal AC/DC commutator motors characterised by arrangement for exciting having permanent magnet excitation

Definitions

  • This invention relates to improvements to permanent magnet
  • Direct Current (D.C.) electric motors Such motors are generally used in battery powered hand-held tools such as screw drivers and drills and certain propulsion vehicles. These motors may have permanent magnets situated around the yolk of the motor (providing stationary magnetic field) and a split commutator which distributes electric power to electro-magnet armature pole-pieces. Such motors are known as permanent magnet direct current motors.
  • a further problem with battery driven permanent magnet motors is that they are designed such that the battery and motor are not ideally matched, therefore the performance of such tools can be improved by suitable matching.
  • an arrangement including: a permanent magnet direct current motor; and a battery means for providing electrical power to the permanent magnet direct current motor, wherein the resistance of the permanent magnet direct current motor is substantially greater than that of the internal resistance of the battery means.
  • an arrangement including: a permanent magnet direct current motor; and a battery means for providing electrical power to the permanent magnet direct current motor, wherein the resistance across the battery means is substantially greater than that of the internal resistance of the battery means.
  • an arrangement including: a permanent magnet direct current motor; and a battery means for providing electrical power to the permanent magnet direct current motor, the battery means having a low internal resistance whereby it is possible to damage the battery means by drawing excessive currents, wherein the arrangement is adapted such that the current drawn by the motor will not cause damage to occur to the battery means when the motor is in a stalled condition for a substantial period of time.
  • an arrangement including:
  • SUBSTITUTE SHEET (Rule 2o> a permanent magnet direct current motor; and a battery means for providing electrical power to the permanent magnet direct current motor, wherein the total circuit resistance of the battery means and permanent magnet direct current motor is such that the magnetic saturation of at least one armature pole-piece is saturated to a maximum imit when the permanent magnet direct current motor's output shaft is stalled.
  • the maximum limit is 25% of saturation.
  • an arrangement including: a permanent magnet direct current motor; a battery means for providing electrical power to the permanent magnet direct current motor; and, a current limiting means adapted to limit the current flowing from the battery to the armature of the permanent magnet direct current motor, wherein the current limiting means limits the current so that the magnetic saturation of at least one armature pole-piece is saturated to a maximum limit when the permanent magnet direct current motor's output shaft is stalled.
  • the maximum limit is 25% of saturation.
  • an arrangement including: a battery means having an output voltage of at least 5 volts; and a permanent magnet direct current motor adapted to be electrically connected to the battery means, the permanent magnet direct current motor having an efficiency of greater than 40% when the motor drives a variable load over at least 15% of the total output torque range at the output of the motor, wherein the efficiency is calculated by: where output power is the power at the output of the motor's shaft and input power is the input power to the motor.
  • an arrangement including: battery means having an output voltage of at least 5 volts; and permanent magnet direct current motor adapted to be electrically connected to the battery means, the permanent magnet direct current motor having an efficiency of greater than 50% when the motor drives a variable load over at least 15% of the total output torque range at the output of the motor, wherein the efficiency is calculated by: where output power is the power at the output of the motor's shaft and input power is the input power to the motor.
  • an arrangement including: a battery means having an output voltage of at least 5 volts; and a permanent magnet direct current motor adapted to be electrically connected to the battery means, the permanent magnet direct current motor having an efficiency of greater than 55% when the motor drives a variable load over at least 15% of the total output torque range at the output of the motor, wherein the efficiency is calculated by: where output power is the power at the output of the motor's shaft and input power is the input power to the motor.
  • an arrangement including: a battery means having an output voltage of at least 5 volts; and a permanent magnet direct current motor adapted to be electrically connected to the battery means, the permanent magnet direct current motor having an efficiency of greater than 60% when the motor drives a variable load over at least 15% of the total output torque range at the output of the motor, wherein the efficiency is calculated by: efficiency ⁇ ] output power / input power x 100 where output power is the power at the output of the motor's shaft and input power is the input power to the motor.
  • a battery means having an output voltage of at least 5 volts; and a permanent magnet direct current motor adapted to be electrically connected to the battery means, the permanent magnet direct current motor being wound such that each individual coil between two armature commutator segments has more than 30 turns.
  • the direct current permanent magnet motor is wound such that when it is connected to a 12 Volt battery means the motor's stall current does not exceed 4 amps.
  • the battery means comprises at least one Nickel Cadmium battery.
  • the battery means has an internal resistance of less than 250 milli Ohms per cell.
  • the arrangement is part of a portable power tools such as a drill or screwdriver.
  • a direct current permanent magnet motor having an efficiency of greater than 40% when the motor drives a variable load over at least 15% of the total output torque range at the output of the motor, wherein the efficiency is calculated by: e ffi ci en cy- Joutput power / input power x 100 where output power is the power at the output of the motor's shaft and input power is the input power to the motor.
  • each individual coil between two armature commutator segments has between 35 to 400 turns.
  • each individual coil between two armature commutator segments has between 50 to 400 turns. in another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 75 to 400 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 100 to 400 turns.
  • each individual coil between two armature commutator segments has between 125 to 400 turns.
  • each individual coil between two armature commutator segments has between 35 to 375 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 50 to 375 turns.
  • each individual coil between two armature commutator segments has between 75 to 375 turns.
  • each individual coil between two armature commutator segments has between 100 to 375 turns.
  • each individual coil between two armature commutator segments has between 125 to 375 turns.
  • each individual coil between two armature commutator segments has between 35 to 350 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 50 to 350 turns.
  • each individual coil between two armature commutator segments has between 75 to 350 turns.
  • each individual coil between two armature commutator segments has between 100 to 350 turns.
  • each individual coil between two armature commutator segments has between 125 to 350 turns.
  • each individual coil between two armature commutator segments has between 35 to 325 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 50 to 325 turns.
  • each individual coil between two armature commutator segments has between 75 to 325 turns.
  • each individual coil between two armature commutator segments has between 100 to 325 turns.
  • each individual coil between two armature commutator segments has between 125 to 325 turns.
  • each individual coil between two armature commutator segments has between 35 to 300 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 50 to 300 turns.
  • each individual coil between two armature commutator segments has between 75 to 300 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 100 to 300 turns.
  • each individual coil between two armature commutator segments has between 125 to 300 turns.
  • each individual coil between two armature commutator segments has between 35 to 275 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 50 to 275 turns.
  • each individual coil between two armature commutator segments has between 75 to 275 turns.
  • each individual coil between two armature commutator segments has between 100 to 275 turns.
  • each individual coil between two armature commutator segments has between 125 to 275 turns.
  • each individual coil between two armature commutator segments has between 35 to 250 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 50 to 250 turns.
  • each individual coil between two armature commutator segments has between 75 to 250 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 100 to 250 turns.
  • each individual coil between two armature commutator segments has between 125 to 250 turns.
  • each individual coil between two armature commutator segments has between 35 to 225 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 50 to 225 turns.
  • each individual coil between two armature commutator segments has between 75 to 225 turns.
  • each individual coil between two armature commutator segments has between 100 to 225 turns.
  • each individual coil between two armature commutator segments has between 125 to 225 turns.
  • each individual coil between two armature commutator segments has between 35 to 200 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 50 to 200 turns.
  • each individual coil between two armature commutator segments has between 75 to 200 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 100 to 200 turns.
  • each individual coil between two armature commutator segments has between 125 to 200 turns.
  • each individual coil between two armature commutator segments has between 35 to 175 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 50 to 175 turns.
  • each individual coil between two armature commutator segments has between 75 to 175 turns.
  • each individual coil between two armature commutator segments has between 100 to 175 turns.
  • each individual coil between two armature commutator segments has between 125 to 175 turns.
  • the wire gauge of each individual coil is the thickest that can be wound upon the armature for the given number of turns.
  • an arrangement including: a permanent magnet direct current motor; a battery means for providing electrical power to the permanent magnet direct current motor; and, a current limiting means adapted to limit the current flowing from the battery to the armature of the permanent magnet direct current motor, wherein the current limiting means limits the current so that the magnetic saturation of at least one armature pole-piece is saturated to a maximum limit when the permanent magnet direct current motor's output shaft is stalled.
  • the maximum limit is 25%.
  • the diameter if the armature is less than 50mm.
  • the length of the armature is less than 35mm.
  • the wire gauge of each individual coil is less than 0.4mm.
  • capacitors are connected across each pole- piece winding. This offers the additional advantage of substantially reducing radio frequency interference. This is not achievable with motors currently used for example in commercially available power tools. With such tools the excessive currents required by the armature and physical size capacitor constraints do not readily allow for such capacitors to be connected across each pole winding.
  • the invention can be illustrated by reference to one form of electric motor namely a small direct current electric motor although the applicability of the discoveries may extend beyond this specific application.
  • the invention will be described with respect to small electric motors in which the armature has a plurality of poles established by reason of a laminated ferromagnetic core and insulated wire wound around, as a coil, each of the poles of the common core.
  • Each of the coils is connected electrically to appropriate segments of a commutator and there are brushes engaging the commutator to supply current to the respective coils as they rotate relative to a yoke.
  • the yoke is comprised of a permanent magnet or magnets with which the magnetic field created within each of the coils of the armature interact in a consecutive way.
  • This describes a conventional small permanent magnet direct current (D.C.) motor of a type of which millions exist.
  • D.C. permanent magnet direct current
  • Such motors are generally used in battery powered hand-held tools such as screw drivers and drills; or propulsion vehicles that are powered by Solar Cells, batteries or a combination of both.
  • These motors may have permanent magnets situated around the yoke of the motor (providing a stationary magnetic field) and a split commutator which distributes electric power to electro-magnet armature pole-pieces.
  • Such motors are known as permanent magnet direct current motors.
  • an electrical motor comprising two parts, these being adapted to be caused to have relatively reacting forces between the respective parts upon the supplying of electrical current into at least a first one of the parts to effect a magnetic field to react magnetically with the other of the parts, wherein the first one of the parts includes a plurality of coils of electrically conducting insulated wire around a former, and a second one of the parts has a magnetic field adapted to interact with a field from the coils, the number of turns of windings around the former for each of the coils on the first one of the parts being substantially greater than the number of turns that would conventionally exist hitherto in respect of motors which are otherwise the same.
  • the electrical motor is a direct current motor. In preference, the electrical motor is a permanent magnet motor.
  • an electric motor having a permanent magnetic field or fields and a plurality of coils wound upon a former or formers to provide an electromagnetic field for provide a relative mechanical movement between the permanent magnetic field and the electromagnetic field, wherein the coils for providing the electromagnetic field are wound such that when the motors rated voltage is applied thereto the electromagnetic field and its associated former are substantially magnetically saturated under stall conditions of the motor.
  • an electric motor having a permanent magnetic field or fields and a plurality of coils wound upon a former or formers to provide an electromagnetic field for effecting a relative mechanical movement between the permanent magnetic field and the electromagnetic field, wherein the coils for providing the electromagnetic field are wound such that when the motor's rated voltage is applied thereto the electromagnetic field and its associated former are within the non linear portion of their magnetization curve when the motor is under stall conditions such that the amount of flux density attributable to the non linear portion is at least 20% of the total flux density of the electromagnetic field and its associated former.
  • a direct current supply means electrically connected to an electric motor having a permanent magnetic field or fields and a plurality of coils wound upon a former or formers to provide an electromagnetic field for effecting a relative mechanical movement between the permanent magnetic field and the electromagnetic field, wherein the coils for providing the electromagnetic field are wound such that under stall conditions the current flowing from the direct current supply and into the coils is such that the amount of flux density attributable to the non linear portion of the coils' and core's magnetization curve is at least 20% of the total flux density of the coils and core.
  • an electric motor comprising a yoke and an armature, the armature being adapted to be supplied with direct electrical current through a commutator to each of a plurality of poles, the armature having a magnetically permeable core providing a former for each of the plurality of poles for the armature, there being a coil wound around the former in respect to each pole, the arrangement being characterised in that the number of turns in the windings of each coil for a respective pole, their location and other characteristics are such that there will be effected, at stall, a magnetic field which is substantially greater than required when supplied with a current supply at the motors rated voltage such that the magnetic field is in the non linear portion of the magnetization curve of the core acting as the former.
  • the motor is a direct current motor.
  • the coils and core are in the form of an armature.
  • the amount of flux density attributable to the non linear portion of the magnetization curve is at least 20% but no more than 25% of the total flux density of the coils and core.
  • the amount of flux density attributable to the non linear portion of the magnetization curve is at least 25% but no more than 30% of the total flux density of the coils and core.
  • the amount of flux density attributable to the non linear portion of the magnetization curve is at least 30% but no more than 35% of the total flux density of the coils and core. In preference, the amount of flux density attributable to the non linear portion of the magnetization curve is at least 35% but no more than 40% of the total flux density of the coils and core.
  • the amount of flux density attributable to the non linear portion of the magnetization curve is at least 40% but no more than 45% of the total flux density of the coils and core.
  • the amount of flux density attributable to the non linear portion of the magnetization curve is at least 45% but no more than 50% of the total flux density of the coils and core.
  • the amount of flux density attributable to the non linear portion of the magnetization curve is at least 50% but no more than 55% of the total flux density of the coils and core.
  • the amount of flux density attributable to the non linear portion of the magnetization curve is at least 55% but no more than 60% of the total flux density of the coils and core. In preference, the amount of flux density attributable to the non linear portion of the magnetization curve is at least 60% but no more than 65% of the total flux density of the coils and core. In preference, the amount of flux density attributable to the non linear portion of the magnetization curve is at least 70% but no more than 80% of the total flux density of the coils and core.
  • the amount of flux density attributable to the non linear portion of the magnetization curve is at least 80% but no more than 100% of the total flux density of the coils and core.
  • the amount of flux density attributable to the non linear portion of the magnetization curve is at least 90% but no more than 95% of the total flux density of the coils and core. In preference, the amount of flux density attributable to the non linear portion of the magnetization curve is at least 95% of the total flux density of the coils and core.
  • non linear portion of the magnetization curve is above the knee of the magnetization curve.
  • non linear portion of the magnetization curve is further characterised by:
  • the armature has a core comprised of a ferromagnetic material.
  • each coil is formed from wire having a gauge which offers substantial resistance to current flowing there through at the motors rated voltage.
  • each of the coils of the armature have a resistance such that the resistance across the brushes is no less than greater than 1.2 ohms.
  • the motor is connected to an electric power supply with a voltage which is the motors rated voltage.
  • an arrangement including: a permanent magnet direct current motor; and a direct current supply means for providing electrical power to the permanent magnet direct current motor, wherein the resistance of the motor is when connected across the direct current supply means is no less 20% of the internal resistance of the direct current supply means.
  • an arrangement including: a permanent magnet direct current motor; and a direct current supply means for providing electrical power to the permanent magnet direct current motor, the direct current supply means having a low internal resistance whereby it is possible to damage the direct current supply means by drawing excessive currents, wherein the arrangement is adapted such that the current drawn by the motor will not cause damage to occur to the direct current supply means when the motor is in a stalled condition for a substantial period of time.
  • an arrangement including: a permanent magnet direct current motor; and a direct current supply means for providing electrical power to the permanent magnet direct current motor, wherein the windings of the armature of the motor are such that under stall conditions the current flowing in the armature does not exceed the current rating of the battery.
  • an arrangement including: a permanent magnet direct current motor; and a direct current supply means for providing electrical power to the permanent magnet direct current motor, wherein the windings of the armature of the motor are such that under stall conditions the current flowing in the armature is between the range of 100% to 110% of the current rating of the battery.
  • an arrangement including: a permanent magnet direct current motor; and a direct current supply means for providing electrical power to the permanent magnet direct current motor, wherein the windings of the armature of the motor are such that under stall conditions the current flowing in the armature is between the range of 95% to 100% of the current rating of the battery.
  • an arrangement including: a permanent magnet direct current motor; and a direct current supply means for providing electrical power to the permanent magnet direct current motor, wherein the windings of the armature of the motor are such that under stall conditions the current flowing in the armature is between the range of 90% to 95% of the current rating of the battery.
  • an arrangement including: a permanent magnet direct current motor; and a direct current supply means for providing electrical power to the permanent magnet direct current motor, wherein the windings of the armature of the motor are such that under stall conditions the current flowing in the armature is between the range of 85% to 90% of the current rating of the battery.
  • an arrangement including: a permanent magnet direct current motor; and a direct current supply means for providing electrical power to the permanent magnet direct current motor, wherein the windings of the armature of the motor are such that under stall conditions the current flowing in the armature is between the range of 80% to 85% of the current rating of the battery.
  • an arrangement including: a permanent magnet direct current motor; and a direct current supply means for providing electrical power to the permanent magnet direct current motor, wherein the windings of the armature of the motor are such that under stall conditions the current flowing in the armature is between the range of 75% to 80% of the current rating of the battery.
  • an arrangement including: a permanent magnet direct current motor; and a direct current supply means for providing electrical power to the permanent magnet direct current motor, wherein the windings of the armature of the motor are such that under stall conditions the current flowing in the armature is between the range of 65% to 75% of the current rating of the battery.
  • a direct current supply means having an output voltage of at least 5 volts; and a permanent magnet direct current motor adapted to be electrically connected to the direct current supply means, the permanent magnet direct current motor being wound such that each individual coil between two armature commutator segments has more than 60 turns.
  • the direct current supply means is a battery.
  • the direct current supply means is a solar cell.
  • the battery comprises at least one Nickel Cadmium battery cell.
  • the battery has an internal resistance of less than 250 milli Ohms per cell.
  • the arrangement resides in a portable power tools such as a drill or screwdriver. In preference, the arrangement resides in a propulsion vehicle.
  • each individual coil between two armature commutator segments has between 75 to 200 turns.
  • each individual coil between two armature commutator segments has between 100 to 200 turns.
  • each individual coil between two armature commutator segments has between 125 to 200 turns. In another preferred form, and referring to any of the above forms, each individual coil between two armature commutator segments has between 75 to 175 turns.
  • each individual coil between two armature commutator segments has between 100 to 175 turns.
  • each individual coil between two armature commutator segments has between 125 to 175 turns.
  • each individual coil between two armature commutator segments has between 75 to 150 turns. In another preferred form, and referring to any of the above forms, each individual coil between two armature commutator segments has between 100 to 150 turns.
  • each individual coil between two armature commutator segments has between 105 to 150 turns.
  • each individual coil between two armature commutator segments has between 110 to 150 turns.
  • each individual coil between two armature commutator segments has between 115 to 150 turns.
  • each individual coil between two armature commutator segments has between 120 to 150 turns. In another preferred form, and referring to any of the above forms, each individual coil between two armature commutator segments has between 100 to 125 turns.
  • each individual coil between two armature commutator segments has between 100 to 120 turns. In another preferred form, and referring to any of the above forms, each individual coil between two armature commutator segments has between 105 to 120 turns.
  • each individual coil between two armature commutator segments has between 100 to 105 turns.
  • each individual coil between two armature commutator segments has between 105 to 115 turns. In another preferred form, and referring to any of the above forms, each individual coil between two armature commutator segments has between 110 to 115 turns.
  • the useful flux densisty of the yoke's magnetic field is approximately 900 Gauss (this may vary depending upon the type of permanent magnets used).
  • the current can be increased resulting in thicker windings or an increased voltage.
  • very high currents would be required (eg at least 30 to 40 Amps) which may destroy the armature's windings.
  • the number of turns of the coils can be increased and the cross-sectional area or gauge of wire used can be preferably decreased resulting in an increase in the resistance of the windings. This quite simply, at first sight, appears to be contrary to every known guiding principle in the design of these types of motors.
  • an electric motor having a permanent magnetic field or fields and a plurality of coils wound upon a former or formers to provide an electromagnetic field for provide a relative mechanical movement between the permanent magnetic field and the electromagnetic field, wherein the coils for providing the electromagnetic field are wound such that when the motors rated voltage is applied thereto the flux density of the electromagnetic field and its associated former are substantially identical to the flux density of the permanent magnetic field or fields when the motor is stalled.
  • a direct current supply means electrically connected to an electric motor having a permanent magnetic field or fields and a plurality of coils wound upon a former or formers to provide an electromagnetic field for effecting a relative mechanical movement between the permanent magnetic field and the electromagnetic field, wherein the coils for providing the electromagnetic field are wound such that the current flowing from the direct current supply and into the coils is such that the flux density of the electromagnetic field and its associated former have a similar value of flux density to that of the permanent magnetic field or fields when the motor is stalled.
  • an arrangement including: a permanent magnet direct current motor; and a direct current supply means for providing electrical power to the permanent magnet direct current motor, wherein the flux density of the armature has a similar value of flux density to that of the permanent magnetic field or fields when the motor stalled.
  • the coils and core are in the form of an armature.
  • the said flux density is the useful flux of the armature poles and permanent magnet.
  • similar value has the meaning no more than 20% difference.
  • similar value has the meaning no more than 2% difference. In preference, similar value has the meaning no more than 1% difference.
  • the armature has a core comprised of a ferromagnetic material.
  • each coil is formed from wire having a gauge which offers substantial resistance to current flowing therethrough at the motor's rated voltage.
  • each of the coils of the armature have a resistance such that the resistance across the brushes is no less than greater than 1.2 ohms.
  • the motor is connected to an electric power supply with a voltage which is the motor's rated voltage.
  • the direct current supply means is a battery.
  • the direct current supply means is a solar cell.
  • the battery comprises at least one Nickel Cadmium battery cell.
  • the arrangement resides in a portable power tools such as a drill or screwdriver.
  • the arrangement resides in a propulsion vehicle.
  • each individual coil between two armature commutator segments has between 75 to 200 turns.
  • each individual coil between two armature commutator segments has between 100 to 200 turns.
  • each individual coil between two armature commutator segments has between 125 to 200 turns. In another preferred form, and referring to any of the above forms, each individual coil between two armature commutator segments has between 75 to 175 turns.
  • each individual coil between two armature commutator segments has between 100 to 175 turns.
  • each individual coil between two armature commutator segments has between 125 to 175 turns. In another preferred form, and referring to any of the above forms, each individual coil between two armature commutator segments has between 75 to 150 turns.
  • each individual coil between two armature commutator segments has between 100 to 150 turns.
  • each individual coil between two armature commutator segments has between 105 to 150 turns.
  • each individual coil between two armature commutator segments has between 110 to 150 turns.
  • each individual coil between two armature commutator segments has between 115 to 150 turns. In another preferred form, and referring to any of the above forms, each individual coil between two armature commutator segments has between 120 to 150 turns.
  • each individual coil between two armature commutator segments has between 100 to 125 turns. In another preferred form, and referring to any of the above forms, each individual coil between two armature commutator segments has between 100 to 120 turns.
  • each individual coil between two armature commutator segments has between 105 to 120 turns.
  • each individual coil between two armature commutator segments has between 100 to 105 turns. In another preferred form, and referring to any of the above forms, each individual coil between two armature commutator segments has between 105 to 115 turns.
  • each individual coil between two armature commutator segments has between 110 to 115 turns.
  • This invention also relates to a portable multi purpose power tool powered by direct current power supply.
  • Direct current multi purpose power tools have been developed so that for example they can be used both as a drill or a screwdriver. Such tools have gearing to reduce the output speed from the direct current motor which is an integral part of the tool. The reason for the gearing is due to the design and type of motor which generally has an output shaft speed requiring speed reduction. Furthermore, such motors impose demands upon the direct current power supply (battery) and therefore the motor can rapidly drain the stored battery charge.
  • power tools are generally in the shape of a pistol. Hence, when working in tight corners or in confined spaces the pistol shape may not be suitable and therefore it may be impractical to use such power tools in these circumstances.
  • a portable power tool including: a first direct current storage means adapted to be electrically connected to a direct current motor by a switch means; and a circuit modification means adapted to allow a second direct current storage means to be inserted in series with the first direct current storage means.
  • the portable power tool has a means of changing the turning direction of the motor.
  • the second direct current storage means is contained within an attachment means adapted to engage the portable power tool.
  • the attachment means has an circuit modification means activator, wherein when the portable power tool is engaged by the attachment means the circuit modification means activator, in conjunction with the circuit modification means, inserts the second direct current storage means in series with the first direct current storage means.
  • the attachment means has a switch means adapted to electrically connect the first direct current storage means and second direct current storage means to the direct current motor.
  • an attachment means adapted to engage a power tool having a first direct current storage means, the attachment means having a second direct current storage means adapted to be inserted in series with the first direct current storage means.
  • the attachment means has a switch means adapted to provide a series connection of the first direct current storage means and second direct current storage means to a direct current electrical motor adapted to drive the power tool.
  • a portable power tool arrangement including: a power tool having a first direct current storage means adapted to be electrically connected to a direct current motor by a first switch means; a second direct current storage means contained within an attachment means, the attachment means engaging the power tool such that the second direct current storage means is inserted in series with the first direct current storage means, wherein the attachment means is adapted to disengage the power tool such that when disengaged the second direct current storage means is removed from being in series with the first direct current storage means.
  • the second direct current storage means is adapted to be removed from being in series with the first direct current storage means such that the first direct current storage means remains adapted to be electrically connected to the direct current motor by the switch means.
  • the portable power tool has a means of changing the turning direction of the motor.
  • the attachment means has a second switch means adapted to electrically connect the first direct current storage means and second direct current storage means to the direct current motor.
  • the attachment means has an interlock means adapted to activate the first switch means when the attachment means engages the power tool such that the second switch means provides the electrical connection between both the first direct current storage means and second direct current storage means and the direct current motor.
  • the motor is a permanent magnet direct current motor; and the first and second battery means for providing electrical power to the permanent magnet direct current motor have a low internal resistance whereby it is possible to damage either of the battery means by drawing excessive currents, wherein the arrangement is adapted such that the current drawn by the motor will not cause damage to occur to either of the battery means when the motor is in a stalled condition for a substantial period of time.
  • the direct current permanent magnet motor is wound such that when it is connected to a 12 Volt battery means the motors stall current does not exceed 4 amps.
  • the direct current permanent magnet motor has an efficiency of greater than 45% when the motor drives a variable load over at least 15% of the total output torque range at the output of the motor, wherein the efficiency is calculated by: efficiency - ⁇ output power / input power x 100 where output power is the power at the output of the motor's shaft and input power is the input power to the motor.
  • the direct current permanent magnet motor has an efficiency of greater than 50% when the motor drives a variable load over at least 15% of the total output torque range at the output of the motor, wherein the efficiency is calculated by: efficiency ⁇ ,] output power / input power x 100 where output power is the power at the output of the motor's shaft and input power is the input power to the motor.
  • each individual coil between two armature commutator segments has between 35 to 400 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 50 to 400 turns.
  • each individual coil between two armature commutator segments has between 75 to 400 turns.
  • each individual coil between two armature commutator segments has between 100 to 400 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 125 to 400 turns.
  • each individual coil between two armature commutator segments has between 35 to 375 turns.
  • each individual coil between two armature commutator segments has between 50 to 375 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 75 to 375 turns.
  • each individual coil between two armature commutator segments has between 100 to 375 turns.
  • each individual coil between two armature commutator segments has between 125 to 375 turns.
  • each individual coil between two armature commutator segments has between 35 to 350 turns.
  • each individual coil between two armature commutator segments has between 50 to 350 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 75 to 350 turns.
  • each individual coil between two armature commutator segments has between 100 to 350 turns.
  • each individual coil between two armature commutator segments has between 125 to 350 turns.
  • each individual coil between two armature commutator segments has between 35 to 325 turns.
  • each individual coil between two armature commutator segments has between 50 to 325 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 75 to 325 turns.
  • each individual coil between two armature commutator segments has between 100 to 325 turns.
  • each individual coil between two armature commutator segments has between 125 to 325 turns.
  • each individual coil between two armature commutator segments has between 35 to 300 turns.
  • each individual coil between two armature commutator segments has between 50 to 300 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 75 to 300 turns.
  • each individual coil between two armature commutator segments has between 100 to 300 turns.
  • each individual coil between two armature commutator segments has between 125 to 300 turns.
  • each individual coil between two armature commutator segments has between 35 to 275 turns.
  • each individual coil between two armature commutator segments has between 50 to 275 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 75 to 275 turns.
  • each individual coil between two armature commutator segments has between 100 to 275 turns.
  • each individual coil between two armature commutator segments has between 125 to 275 turns.
  • each individual coil between two armature commutator segments has between 35 to 250 turns.
  • each individual coil between two armature commutator segments has between 50 to 250 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 75 to 250 turns.
  • each individual coil between two armature commutator segments has between 100 to 250 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 125 to 250 turns.
  • each individual coil between two armature commutator segments has between 35 to 225 turns.
  • each individual coil between two armature commutator segments has between 50 to 225 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 75 to 225 turns.
  • each individual coil between two armature commutator segments has between 100 to 225 turns.
  • each individual coil between two armature commutator segments has between 125 to 225 turns.
  • each individual coil between two armature commutator segments has between 35 to 200 turns.
  • each individual coil between two armature commutator segments has between 50 to 200 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 75 to 200 turns.
  • each individual coil between two armature commutator segments has between 100 to 200 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 125 to 200 turns.
  • each individual coil between two armature commutator segments has between 35 to 175 turns.
  • each individual coil between two armature commutator segments has between 50 to 175 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 75 to 175 turns.
  • each individual coil between two armature commutator segments has between 100 to 175 turns.
  • each individual coil between two armature commutator segments has between 125 to 175 turns.
  • the wire gauge of each individual coil is the thickest that can be wound upon the armature for the given number of turns.
  • the wire gauge of each individual coil is less than 0.4mm.
  • capacitors are connected across each pole- piece winding. This offers the additional advantage of susbtantially reducing radio frequency interference. This is not achievable with motors currently used for example in commercially available power tools. With such tools the excessive currents required by the armature and physical size capacitor constraints do not readily allow for such capacitors to be connected across each pole winding.
  • the armature is "excited” in conventional manner, prior to being inserted into the permanent magnetic field during assembly of the motor. Exciting of the armature is preferably achieved by mounting the armature in a test block and passing an electric current therethrough. This is found to reduce any tendency towards mismatching of the magnetic poles of the motor and avoids high eddy current formation during running of the motor.
  • Figures 1a to 1d illustrate a 3 pole-piece direct current permanent magnet motor
  • Figures 2a to 2d illustrate a 7 pole-piece direct current permanent magnet motor
  • Figure 3 (a,b,c,d) to Figure 17 (a,b,c,d) illustrate the characteristics discovered by increasing the number of windings of an armature
  • Figure 18 is a comparison of the number of turns per coil and the current required to provide a torque of 1 Newton metre;
  • Figure 19 illustrates a standard magnetization curve
  • Figure 20 illustrates the circuitry used to obtain the test results
  • Figure 21 illustrates what is meant by usefil flux
  • Figure 22 illustrates a portable power tool
  • Figure 23 illustrates an attachment to the power tool which provides additional voltage to the power tool;
  • Figure 24 illustrates the switch mechanism of the power tool
  • Figure 25 illustrates the electrical circuit of the power tool and the attachment means.
  • a direct current electric motor containing permanent magnets may also act as an electrical generator.
  • the generated electro-motive force (e.m.f.) is proportional to the rate of rotation of the armature. This is because the induced e.m.f. in an armature pole-piece is proportional to the rate of change of magnetic flux through the pole-piece, which in turn is proportional to the angular velocity of the pole- piece as it sweeps past the permanent magnet.
  • the armature rotates, the
  • SUBSTTTUTE SHEET (Rule 26) induced e.m.f. in each pole piece is intrinsically an A.C. signal containing sign reversals and maximum and minima voltages (the minima being zero volts).
  • the position of brushes in contact with the motor's armature, which are also electrically connected to external terminals, are arranged so that the induced e.m.f. at the terminals is always of the same electrical polar sense for a given armature rotation direction.
  • At least one of the pole pieces has a non-zero induced e.m.f. as the armature rotates.
  • the brushes are positioned to capture this non-zero e.m.f.
  • the r.p.m. of a free running motor is defined by the generated induced e.m.f. equalling the supplied e.m.f.
  • the r.p.m. is dependent upon the permanent magnet field, the geometry of the brushes, the armature and the supply e.m.f.
  • the free running r.p.m. is a little less than the theoretical value.
  • the rotational velocity of the ideal motor described above is independent of the electrical resistance of the pole piece windings, brushes and commutator.
  • the induced e.m.f. in the pole-pieces is approximately proportional to the number of windings on each pole-piece for a given motor and armature r.p.m.
  • the free running r.p.m. is approximately inversely proportional to the number of windings for a given supply voltage. That is the fewer the turns the greater the free running r.p.m.
  • the free running r.p.m. is proportional to the supply voltage.
  • M and r1 can be assumed constant, there is an optimum number of turns which is a function of the chosen mass of conductor and internal resistance of the supply plus commutator and brushes. Note that this is optimum is not a function of supply voltage. This maximizes the torque at heavy loads for given internal supply resistance and given brushes and commutator. In general this is approximately true of the efficiency as well at high loads, so long as no magnetic saturation occurs.
  • the current drain is approximately; 5 V(1-rpm/rpmfree)/R, and the power is approximately proportional to rpmV(1 -rpm/rpmfree)/R, where V is the supply voltage, rpm is the angular velocity and rpmfree is the free running angular velocity for supply voltage ⁇ o v.
  • V and R should be chosen to not allow too much saturation or too excessive heating to occur.
  • the more turns per pole-piece will improve the motor's efficiency. This is basically because the generated magnetic field is proportional to the number of turns for a given current. That is the more turns, the smaller the battery current drain required to produce a given torque. Also, the smaller this current, the smaller the power inefficiency losses from the internal resistance of the battery and resistive losses of the brushes, armature and conductors feeding the motor via the switch. However, there is a limit to the number of turns providing improved efficiencies. This related to the insulation of the wires in which the insulation affects the flux within the armature and therefore there is a range of turns which are suitable for a specific application.
  • the 0.28mm gauge motor at 125 turns per pole-piece illustrates that once the number of turns per-pole is determined then the thickest wire gauge that can be used improves the efficiency of the motor. Furthermore, motors having a small number of turns and thick windings are inefficient. (This inefficiency may, be due to magnetic saturation of the armatures poles or because the magnetic field within the armatures poles exceeds that of the flux provided by the permanent magnetic field or fields).
  • the above efficiency results were measured and calculated by coupling the shaft of a HC683G of 22 turns and 0.9mm gauge (adapted to be used as a generator) to the output shaft of the motor being tested. Thus by varying the current in the HC683G generator by means of a variable resistor across the generators output, and measuring its generated voltage across the variable resistor, the efficiency was calculated as follows:-
  • FIGs 1 a to 1d The physical dimensions of the HC683G are illustrated in FIGs 1 a to 1d, this motor as sold has 22 turns and 0.9mm gauge wire per pole-piece.
  • This motor again as sold has 22 turns and 0.9mm gauge wire per-pole-piece.
  • This motor as sold has 24 turns and 0.9mm gauge wire per-pole-piece.
  • the motor illustrated in FIGs 2a to 2d is a 7 pole-piece D.C. permanent magnet motor, this motor as sold has 9 turns and 0.9mm gauge per pole and each pole is wound around 3 pole pieces.
  • capacitors can be connected across each pole-piece winding (if required). This offers the additional advantage of substantially reducing radio frequency interference. This is not achievable with motors currently used for example in commercially available power tools. With such tools the excessive currents required by the armature and physical size capacitor constraints do not readily allow for such capacitors to be connected across each pole winding.
  • FIGs 3 to 18 the motor used to obtain these results was a Johnson 50274 D.C. permanent magnet motor having a 3- tooth armature.
  • the results of FIGs 3 to 18 were obtained using the same motor and rewinding the armature with the different number of turns and wire gauges.
  • FIG 3 (a,b,c,d) relates to a 32 turn per pole wound Johnson 50274 motor, each of the wound poles having a 0.75 gauge wire of 0.2 ohms across the brushes
  • FIG 7 (a,b,c,d) has relates to the same motor wound with 110 turns of 0.34 wire gauge having a resistance of 1.4 ohms across the brushes.
  • a conventionally wound motor usually has approximately 32 turns of relatively thick wire gauge (eg. 0.75).
  • stall armature currents that are above the current rating of the supply (battery, solar cell or other similar supplies) may result (typically substantially greater than 110% of the battery's current rating) due to the reduced back electro motive force (emf) effects. Accordingly, this can rapidly discharge the battery, or reduce the effectiveness of the supply. Furthermore, it may also damage the supply.
  • SUBSTTTUTE SHEET (Rule 26) solar cell technology) and have not addressed the issue of increasing the number of turns to decrease the voltage reduction under load whilst providing a motor with suitable torque characteristics.
  • This increase in the number of turns reduces the current drain from the supply and therefore it is desirable but not essential to operate below the supply's current rating when the motor is at or near stall (a preferable range is between 110% to 65% of the supply's current rating).
  • the increase in the number of turns preferably reduces the possibility of damage occurring to the supply.
  • a preferable feature is that the resistance across supply is at least 20% of that of the internal resistance of the supply.
  • the supply is a Nickel Cadmium battery of 250 milli Ohms per cell then for a 24 volt battery the internal resistance is 6 Ohms, therefore preferably the resistance of the armature should be at least 1.2 Ohms.
  • Johnson 50274 show (FIG 18) that at approximately 100 to 110 turns per pole of 0.34 wire gauge an optimum occurs for a required torque output (note a different optimum number of turns may result for a different permanent magnet motor). Hence, upon deciding upon a required torque output and a wire gauge then the optimum number of turns can be determined by non inventive experimentation. However, it should be noted that the number of turns is limited by the physical dimensions of the armature and air gap.
  • the motor under high loads (or at stall) is magnetically saturated. That is it is operating above the knee point in the area of the magnetization curve known as the non linear portion of the curve.
  • SUBSTTTUTE SHEET (Rule 26) standard theoretical magnetization curve is illustrated in FIG. 19. This shows the three commonly known parts of the magnetization curve: the instep, knee point and the non linear portion.
  • the flux density limit (saturation) of Gauss is shown by Bs and the non linear portion can be approximately defined by Frohlic's equation:
  • the increased Gauss attributable to non linear portion of the magnetization curve results from the combination of the number of turns and the current therethrough. Accordingly, by increasing the number of turns of the armature coils this increase in Gauss can result. However, there is a limit to this as shown in FIG 13b which shows a reduced Gauss at stall.
  • SUBSTTTUTE SHEET (Rule 26) 105 turns per pole armature the flux density at stall is 860 Gauss (see FIG 6b) and for the 110 turns per pole armature (see FIG 7b) the flux density at stall is 900 Gauss.
  • the Flux density (useful flux) of the permanent magnet was measured to be 900 Gauss (see FIG 21 ). Hence, when comparing the results as illustrated in FIG 18, and the corresponding Gauss measurements, it is apparent that there is an optimum in the motor's performance. This occurs when flux density of the armature's magnetic field (or fields) is substantially identical to the flux density of the permanent magnetic field or fields when the motor is at stall.
  • an improved motor performance can be achieved when the the substantially identical matching is not accurately achieved but is within specified limits. These limits being preferably no greater than a 20% difference.
  • the results conducted on the Johnson 50274 D.C. permanent magnet motor illustate this difference (for this motor) is 180 Gauss, therefore when the armature's flux density is below 720 Gauss or above 1080 Gauss there is a considerable reduction in the motor's performance.
  • the Gauss at stall is 998 (11 % difference) and provides an improved performance over what has perviously been known.
  • the 100 turn armature has a Gauss at stall of 763 (15% difference) and provides an improved performance over what has perviously been known. Terpolating these results it is estimated that at approximately 20% difference the improvements over previously known D.C. permanent magnet motors is not substantially significant.
  • the values of flux densisty and the corresponding percentage difference values preferably relate to the useful flux as illustrated in FIG 21. Furthermore, the above results were obtained by using the circuit as illustrated in FIG. 20. it should be noted that the Torque measurements were taken with the same Torque meter and therefore any errors in the accuracy of this meter are common to all the results. To emulate the supply (battery, solar cell or otherwise) two variacs VRI and VR2 were used to model the internal resistance of the supply. The ammeter Am measured the armature current la, the Torque was measured with the Torque meter Tm and the tachometer Rm measured the speed of the motor's shaft under different loads from free running to stall.
  • FIG. 22 there is illustrated a self contained power tool 1 having a push button switch 3, ten 1.2 volt rechargeable batteries 12, recharged via the recharging socket 4.
  • the motor 5 drives the gearbox 6 which turns the chuck 7.
  • the chuck is attached to a spindle and the chuck can be removed from the spindle such that a screwdriver means can be inserted directly into the spindle as opposed to the screwdriver means being gripped by the chuck 7.
  • the push button switch 3 is adapted to move within the slot 34.
  • the push button switch 3 is in the centre of the slot 34, as shown in FIG. 22, no power can be applied to the motor 5 by depressing the push button switch 3.
  • the push button switch 3 when the push button switch 3 is in its top position within the slot 34 the motor 5 turns in a clockwise direction.
  • the push button switch 3 is in the down position within the slot 34 the motor 5 will turn in an anticlockwise direction.
  • the self contained power tool 1 is shown inserted in the attachment means 2.
  • the interlock 16 is pulled downwards by
  • the attachment means further has a hollow handle 18 within which are located ten 1.2 volt batteries 17 that are adapted to be recharged via the socket 35.
  • FIG. 24 and FIG. 25 there is illustrated the switch mechanism and the electrical circuitry of both the self contained power tool 1 and attachment means 2.
  • the turning handle 8 is adapted to rotate the inner body 9 such that push button switch 3 will be activated by either the cam 32 or cam 33 of the interlock 16. This therefore connects the spring means 24 to the positive of the battery 12.
  • both the spring means 23 and 24 are mechanically connected to the inner body 9, therefore when the turning handle 8 is pushed clockwise the spring means 23 makes contact with the pin 22 and the spring means 24 makes contact with the pin 21. Note if the turning handle 8 was pushed in an anticlockwise direction then the spring means 23 would be connected to pin 21 and the spring means 24 would be connected to the pin 22. This provides a simple mechanism for reversing the direction of the motor 5 which is electrically connected to the pins 21 and 22.
  • the push button switch 3 Upon the turning handle 8 being pushed either clockwise or anticlockwise the push button switch 3 will close its contacts by either being activated by the cam 32 or the cam 33. However, the motor 5 will not turn until the switch 13, located upon the handle 18, is closed.
  • the switch 13 is inserted into the circuit by the circuit modification means 20 which includes a jack plug 10 having an inner conductor 31 surrounded by an insulator 30 and an outer conductor 29.
  • the circuit modification means 20 which includes a jack plug 10 having an inner conductor 31 surrounded by an insulator 30 and an outer conductor 29.
  • an electrical circuit is completed at the circuit modification means 20 by the cylindrical conductor 26 making contact with the cylindrical conducting piston 27 which is spring loaded by the conducting spring 28.
  • an electrical circuit is made via the negative of the battery 12 through the conducting spring 28, through the cylindrical conducting piston 27 and the cylindrical conductor 26 to the spring means 23.
  • the cylindrical conducting piston 27 is pushed away from the cylindrical conductor 26 which therefore breaks their direct electrical contact between the negative of battery 12 and the spring means 23.
  • the outer conductor 29 of the jack plug 10 is connected to the switch 13.
  • the other side of the switch 13 is connected to the negative of the battery 17 and the positive of the battery 17 is connected to the inner conductor 31 of jack plug 10.
  • the inner conductor 31 makes electrical contact with the cylindrical conducting piston 27 and the outer conductor 29 makes contact with the cylindrical conductor 26.
  • the insertion of the jack plug 10 reconfigures the circuit such that the battery 12 and battery 17 are in series and power can only be supplied to the motor when both the contacts of the push button 3 and switch 13 are closed.
  • the motor preferably embodies at least one of the improvements described herein for direct current electric motors.
  • the particular forms described above with reference to FIGs 1 to 21 may be especially mentioned. Attention is also directed to the associated discussions of "Theory” and “Results”.
  • motors of improved efficiencies can be designed and manufactured by determining an output speed of the motor which is preferably less than the desired application for which the motor is to be used.
  • the output speed is proportional to 1/n, hence this determines the number of windings (turns) per armature pole-piece.
  • n it is preferable to select the thickest wire gauge that can be wound upon the armature.
  • the Force or Torque is proportional to n.l (until
  • the more turns per pole-piece will improve the motors efficiency. This is basically because the generated magnetic field is proportional to the number of turns for a given current. That is the more turns, the smaller the battery current drain required to produce a given torque. Also, the smaller this current, the smaller the power inefficiency losses from the internal resistance of the battery and resistive losses of the brushes, armature and conductors feeding the motor via the switch. However, there is a limit to the number of turns providing improved efficiencies. This related to the insulation of the wires in which the insulation affects the flux within the armature and therefore there is a range of turns which are suitable for a specific application.
  • FIGS. 22-25 there is illustrated a multi purpose tool which can be powered by either a 12 volt battery supply or 24 volt battery supply. It should be noted that other battery voltages can be used and variations of the embodiments described can be substituted without diverting from the invention. Throughout this specification various indications have been given to the scope of the invention but the invention is not limited to any one of these indications.

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Abstract

A permanent magnet direct current motor (5) and a battery means (12) for providing electrical power to the permanent magnet direct current motor is disclosed, where the resistance of the permanent magnet direct current motor is substantially greater than that of the internal resistance of the battery means. The electric motor has a permanent magnetic field or fields and a plurality of coils wound upon a former or formers to provide an electromagnetic field for effecting a relative mechanical movement between the permanent magnetic field and the electromagnetic field, wherein the coils for providing the electromagnetic field are wound such that the current flowing from the direct current supply and into the coils is such that the flux density of the electromagnetic field and its associated former have a similar value of flux density to that of the permanent magnetic field or fields when the motor is stalled.

Description

ELECTRIC MOTORS
Battery powered permanent magnet direct current motor
This invention relates to improvements to permanent magnet
Direct Current (D.C.) electric motors. Such motors are generally used in battery powered hand-held tools such as screw drivers and drills and certain propulsion vehicles. These motors may have permanent magnets situated around the yolk of the motor (providing stationary magnetic field) and a split commutator which distributes electric power to electro-magnet armature pole-pieces. Such motors are known as permanent magnet direct current motors.
PRIOR ART
Commercially available permanent magnet direct current motors can be inefficient owing to inappropriate choices in the armature windings. The general practice in designing most commercial D.C. permanent magnet motors is to design and manufacture a motor with a fast output shaft speed and then reduce the output speed by suitable gearing. To achieve this the motor's are typically wound with typically less than 30 turns of wire per pole-piece. In general to provide a useable or high torque output from such motors the wire is typically greater than 0.45 mm gauge such that the current flowing in the armature is substantially excessive (typically 8 amps or more for a motor under load). Thus, if the motor is supplied by a battery the current drawn by the motor results in a substantial demands upon the battery. For example, large battery packs for power tools have been manufactured to increase the duration of a battery before it has to be recharged or replaced. This has the disadvantage of increasing the cost of the battery required to drive the motor, furthermore due to its excessive size and weight this solution is cumbersome and provides difficulties when, for example, used up a ladder or on a roof.
A further problem with battery driven permanent magnet motors is that they are designed such that the battery and motor are not ideally matched, therefore the performance of such tools can be improved by suitable matching.
Other problems with D.C. permanent magnet motors is that their torque output may not be sufficient for certain applications. This is due to torque being proportional to the number of turns per pole-piece and the current flowing in each pole-piece. Thus over a limited current range the torque will increase with a increase in current flowing in the pole-piece. However, at a certain current value the motor reaches or approaches an approximate saturation point which has a limiting effect upon the torque of the motor. To reduce battery drain current limiters have been developed but these restrict the current rather than improve the torque characteristics of the motor.
The design of D.C. permanent magnet motors are such that their efficiencies are usually no greater than 40% over a wide load range. Certain motor manufacturers may claim higher efficiencies than this but their efficiency calculations are not given; or ideal conditions and a specific ideal load are used; or their efficiency calculations may be non-standard or ambiguous. However, the efficiencies over a wide load range for D.C. permanent magnet motors is, according to our measurements, no greater than 40% over a significant output torque range which can be provided at the output of the motor when using the calculation: efficiency = \J output power / input power x 100 where output power is the power at the output of the motor's shaft and input power is the input power to the motor. Hence, the are substantial losses in such motors which are generally tolerated by users and manufacturers alike.
It is the intended object of the invention to alleviate the above problems or at least provide the public with a useful alternative. DESCRIPTION OF THE INVENTION
According to one form of this invention, although this need not be the only or indeed the broadest form, there is proposed an arrangement including: a permanent magnet direct current motor; and a battery means for providing electrical power to the permanent magnet direct current motor, wherein the resistance of the permanent magnet direct current motor is substantially greater than that of the internal resistance of the battery means.
Alternatively according to another form of this invention, although this need not be the only or indeed the broadest form, there is proposed an arrangement including: a permanent magnet direct current motor; and a battery means for providing electrical power to the permanent magnet direct current motor, wherein the resistance across the battery means is substantially greater than that of the internal resistance of the battery means.
Alternatively according to another form of this invention, although this need not be the only or indeed the broadest form, there is proposed an arrangement including: a permanent magnet direct current motor; and a battery means for providing electrical power to the permanent magnet direct current motor, the battery means having a low internal resistance whereby it is possible to damage the battery means by drawing excessive currents, wherein the arrangement is adapted such that the current drawn by the motor will not cause damage to occur to the battery means when the motor is in a stalled condition for a substantial period of time. Alternatively, according to another form of this invention, although this need not be the only or indeed the broadest form, there is proposed an arrangement including:
SUBSTITUTE SHEET (Rule 2o> a permanent magnet direct current motor; and a battery means for providing electrical power to the permanent magnet direct current motor, wherein the total circuit resistance of the battery means and permanent magnet direct current motor is such that the magnetic saturation of at least one armature pole-piece is saturated to a maximum imit when the permanent magnet direct current motor's output shaft is stalled.
In preference, the maximum limit is 25% of saturation.
Alternatively, according to another form of this invention, although this need not be the only or indeed the broadest form, there is proposed an arrangement including: a permanent magnet direct current motor; a battery means for providing electrical power to the permanent magnet direct current motor; and, a current limiting means adapted to limit the current flowing from the battery to the armature of the permanent magnet direct current motor, wherein the current limiting means limits the current so that the magnetic saturation of at least one armature pole-piece is saturated to a maximum limit when the permanent magnet direct current motor's output shaft is stalled.
In preference, the maximum limit is 25% of saturation.
Alternatively, according to another form of this invention, although this need not be the only or indeed the broadest form, there is proposed an arrangement including: a direct current permanent magnet motor wound such that flux produced by an electrical current, supplied by a battery means, flowing in a pole of the motor's armature and interacting with the permanent magnet flux does not exceed that of the flux provided by the permanent magnetic field or fields. Alternatively according to another form of this invention, although this need not be the only or indeed the broadest form, there is proposed an arrangement including: a battery means having an output voltage of at least 5 volts; and a permanent magnet direct current motor adapted to be electrically connected to the battery means, the permanent magnet direct current motor having an efficiency of greater than 40% when the motor drives a variable load over at least 15% of the total output torque range at the output of the motor, wherein the efficiency is calculated by:
Figure imgf000007_0001
where output power is the power at the output of the motor's shaft and input power is the input power to the motor. Alternatively according to another form of this invention, although this need not be the only or indeed the broadest form, there is proposed an arrangement including: a battery means having an output voltage of at least 5 volts; and a permanent magnet direct current motor adapted to be electrically connected to the battery means, the permanent magnet direct current motor having an efficiency of greater than 45% when the motor drives a variable load over at least 15% of the total output torque range at the output of the motor, wherein the efficiency is calculated by: efficiency =
Figure imgf000007_0002
x 100 where output power is the power at the output of the motor's shaft and input power is the input power to the motor.
Alternatively according to another form of this invention, although this need not be the only or indeed the broadest form, there is proposed an arrangement including: battery means having an output voltage of at least 5 volts; and permanent magnet direct current motor adapted to be electrically connected to the battery means, the permanent magnet direct current motor having an efficiency of greater than 50% when the motor drives a variable load over at least 15% of the total output torque range at the output of the motor, wherein the efficiency is calculated by:
Figure imgf000008_0001
where output power is the power at the output of the motor's shaft and input power is the input power to the motor.
Alternatively according to another form of this invention, although this need not be the only or indeed the broadest form, there is proposed an arrangement including: a battery means having an output voltage of at least 5 volts; and a permanent magnet direct current motor adapted to be electrically connected to the battery means, the permanent magnet direct current motor having an efficiency of greater than 55% when the motor drives a variable load over at least 15% of the total output torque range at the output of the motor, wherein the efficiency is calculated by:
Figure imgf000008_0002
where output power is the power at the output of the motor's shaft and input power is the input power to the motor. Alternatively according to another form of this invention, although this need not be the only or indeed the broadest form, there is proposed an arrangement including: a battery means having an output voltage of at least 5 volts; and a permanent magnet direct current motor adapted to be electrically connected to the battery means, the permanent magnet direct current motor having an efficiency of greater than 60% when the motor drives a variable load over at least 15% of the total output torque range at the output of the motor, wherein the efficiency is calculated by: efficiency^ ] output power / input power x 100 where output power is the power at the output of the motor's shaft and input power is the input power to the motor.
Alternatively according to another form of this invention, although this need not be the only or indeed the broadest form, there is proposed an arrangement including: a battery means having an output voltage of at least 5 volts; and a permanent magnet direct current motor adapted to be electrically connected to the battery means, the permanent magnet direct current motor being wound such that each individual coil between two armature commutator segments has more than 30 turns.
In preference, referring to any of the above alternative forms, the direct current permanent magnet motor is wound such that when it is connected to a 12 Volt battery means the motor's stall current does not exceed 4 amps.
In preference, referring to any of the above forms, the battery means comprises at least one Nickel Cadmium battery.
In preference, referring to any of the above forms, the battery means has an internal resistance of less than 250 milli Ohms per cell. In preference, referring to any of the above forms, the arrangement is part of a portable power tools such as a drill or screwdriver.
Alternatively, according to one form of this invention, although this need not be the only or indeed the broadest form, there is proposed a direct current permanent magnet motor having an efficiency of greater than 40% when the motor drives a variable load over at least 15% of the total output torque range at the output of the motor, wherein the efficiency is calculated by: e ffi ci en cy- Joutput power / input power x 100 where output power is the power at the output of the motor's shaft and input power is the input power to the motor. Alternatively, according to one form of this invention, although this need not be the only or indeed the broadest form, there is proposed a direct current permanent magnet motor having an efficiency of greater than 45% when the motor drives a variable load over at least 15% of the total output torque range at the output of the motor, wherein the efficiency is calculated by: efficiency = ι]output power / input power x 100 where output power is the power at the output of the motor's shaft and input power is the input power to the motor.
Alternatively, according to one form of this invention, although this need not be the only or indeed the broadest form, there is proposed a direct current permanent magnet motor having an efficiency of greater than 50% when the motor drives a variable load over at least 15% of the total output torque range at the output of the motor, wherein the efficiency is calculated by: efficiency = ] output power / input power x 100 where output power is the power at the output of the motor's shaft and input power is the input power to the motor.
Alternatively, according to one form of this invention, although this need not be the only or indeed the broadest form, there is proposed a direct current permanent magnet motor having an efficiency of greater than 55% when the motor drives a variable load over at least 15% of the total output torque range at the output of the motor, wherein the efficiency is calculated by: efficiency = ι]output power / input power x 100 where output power is the power at the output of the motor's shaft and input power is the input power to the motor.
In preference, referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 35 to 400 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 50 to 400 turns. in another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 75 to 400 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 100 to 400 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 125 to 400 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 35 to 375 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 50 to 375 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 75 to 375 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 100 to 375 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 125 to 375 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 35 to 350 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 50 to 350 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 75 to 350 turns.
SUBSTITUTE SHEET (Rule 2t>, In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 100 to 350 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 125 to 350 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 35 to 325 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 50 to 325 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 75 to 325 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 100 to 325 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 125 to 325 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 35 to 300 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 50 to 300 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 75 to 300 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 100 to 300 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 125 to 300 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 35 to 275 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 50 to 275 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 75 to 275 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 100 to 275 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 125 to 275 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 35 to 250 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 50 to 250 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 75 to 250 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 100 to 250 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 125 to 250 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 35 to 225 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 50 to 225 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 75 to 225 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 100 to 225 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 125 to 225 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 35 to 200 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 50 to 200 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 75 to 200 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 100 to 200 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 125 to 200 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 35 to 175 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 50 to 175 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 75 to 175 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 100 to 175 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 125 to 175 turns.
In preference, referring to any of the above forms, the wire gauge of each individual coil is the thickest that can be wound upon the armature for the given number of turns. Alternatively, according to another form of this invention, although this need not be the only or indeed the broadest form, there is proposed an arrangement including: a permanent magnet direct current motor; a battery means for providing electrical power to the permanent magnet direct current motor; and, a current limiting means adapted to limit the current flowing from the battery to the armature of the permanent magnet direct current motor, wherein the current limiting means limits the current so that the magnetic saturation of at least one armature pole-piece is saturated to a maximum limit when the permanent magnet direct current motor's output shaft is stalled. In preference, the maximum limit is 25%.
In preference, referring to any of the above forms, the diameter if the armature is less than 50mm.
In preference, referring to any of the above forms, the length of the armature is less than 35mm. In preference, referring to any of the above forms, the wire gauge of each individual coil is less than 0.4mm.
In preference, capacitors are connected across each pole- piece winding. This offers the additional advantage of substantially reducing radio frequency interference. This is not achievable with motors currently used for example in commercially available power tools. With such tools the excessive currents required by the armature and physical size capacitor constraints do not readily allow for such capacitors to be connected across each pole winding.
The invention can be illustrated by reference to one form of electric motor namely a small direct current electric motor although the applicability of the discoveries may extend beyond this specific application.
The invention will be described with respect to small electric motors in which the armature has a plurality of poles established by reason of a laminated ferromagnetic core and insulated wire wound around, as a coil, each of the poles of the common core. Each of the coils is connected electrically to appropriate segments of a commutator and there are brushes engaging the commutator to supply current to the respective coils as they rotate relative to a yoke.
Conventionally, the yoke is comprised of a permanent magnet or magnets with which the magnetic field created within each of the coils of the armature interact in a consecutive way. This describes a conventional small permanent magnet direct current (D.C.) motor of a type of which millions exist. Such motors are generally used in battery powered hand-held tools such as screw drivers and drills; or propulsion vehicles that are powered by Solar Cells, batteries or a combination of both. These motors may have permanent magnets situated around the yoke of the motor (providing a stationary magnetic field) and a split commutator which distributes electric power to electro-magnet armature pole-pieces. Such motors are known as permanent magnet direct current motors. Commercially available permanent magnet direct current motors can be inefficient owing to inappropriate choices in the armature windings. The general practice in designing commercial D.C. permanent magnet motors is to design and manufacture a motor with a fast output shaft speed and then reduce the output speed by suitable gearing. To achieve this the motors are wound with typically less than 32 turns of wire per pole- piece.
The discovery of this invention is that by changing at least the characteristics of the coil from that which is traditionally used, significantly improved characteristics of the motor can be achieved. In a first instance, it has been discovered that if, contrary to all known design expectations, one increases the number of turns of wire around each pole as compared to that which has previously been used, then unexpected advantages result.
Implicit in increasing the number of turns however is that, as there is a limited space on the common core, the cross-sectional area or gauge of wire used has to be decreased and further, with a larger number of turns and smaller cross-sectional area, the resistance within each winding will also be increased.
This quite simply, at first sight, appears to be contrary to every known guiding principle in the design of these types of motors.
According to conventional expectations, a number of problems arise by proceeding in the way described.
SUBSTITUTE SHEET (Rule 2bj For instance, one of the significant difficulties associated with reduction of the gauge of wire is that this will then have less capacity to handle large currents without undue heating so that one would expect when the motor has its armature stalled relative to the yoke, that this would make the coils very much more vulnerable to overheating and of course effective destruction through burning of the insulation between the windings and melting of the wire.
Further, even if one could overcome the heating problem, one would expect that increased resistance would implicitly increase losses. The very surprising discovery has been that, contrary to every expectation, these difficulties do not appear in fact to be a major difficulty at all, and the marked improvement achieved by having a somewhat larger number of turns for each coil than has hitherto been used, has resulted in motors which are able to provide higher output torque for a given input as compared to traditional motors of similar apparent characteristics, and improved overall efficiencies.
In experiments conducted thus far, an increase in the number of turns by a factor of approximately 2 to 3 times or greater with a reduction in gauge of the wire and then experimentation through a range of number of turns have found to provide preferred combinations which will vary depending upon whether an overall efficiency improvement is being sought, a minimal current for a given output is being sought or a desirable speed and output at a selected torque.
Examples of experiments conducted so far will be later given showing how changes in the number of turns and the gauge of the wire will change these criteria but in each case, there is disclosed an improvement in the performance characteristics of the motor by reason of the increase in number of turns as compared to that which has been the case given conventional design criteria in existing motors. It is the intended object of this invention to improve the performance of a direct current motor when powered by a battery or solar cell means or at least provide the public with a useful alternative to currently available direct current motors.
According to one form of this invention, although this need not necessarily be the only or indeed the broadest form, there is provided an electrical motor comprising two parts, these being adapted to be caused to have relatively reacting forces between the respective parts upon the supplying of electrical current into at least a first one of the parts to effect a magnetic field to react magnetically with the other of the parts, wherein the first one of the parts includes a plurality of coils of electrically conducting insulated wire around a former, and a second one of the parts has a magnetic field adapted to interact with a field from the coils, the number of turns of windings around the former for each of the coils on the first one of the parts being substantially greater than the number of turns that would conventionally exist hitherto in respect of motors which are otherwise the same.
In preference, the electrical motor is a direct current motor. In preference, the electrical motor is a permanent magnet motor.
Alternatively, according to another form of this invention, although this need not be the only or indeed the broadest form, there is proposed an electric motor having a permanent magnetic field or fields and a plurality of coils wound upon a former or formers to provide an electromagnetic field for provide a relative mechanical movement between the permanent magnetic field and the electromagnetic field, wherein the coils for providing the electromagnetic field are wound such that when the motors rated voltage is applied thereto the electromagnetic field and its associated former are substantially magnetically saturated under stall conditions of the motor.
Alternatively, according to another form of this invention, although this need not be the only or indeed the broadest form, there is proposed an electric motor having a permanent magnetic field or fields and a plurality of coils wound upon a former or formers to provide an electromagnetic field for effecting a relative mechanical movement between the permanent magnetic field and the electromagnetic field, wherein the coils for providing the electromagnetic field are wound such that when the motor's rated voltage is applied thereto the electromagnetic field and its associated former are within the non linear portion of their magnetization curve when the motor is under stall conditions such that the amount of flux density attributable to the non linear portion is at least 20% of the total flux density of the electromagnetic field and its associated former.
Alternatively, according to another form of this invention, although this need not be the only or indeed the broadest form, there is proposed an arrangement including: a direct current supply means electrically connected to an electric motor having a permanent magnetic field or fields and a plurality of coils wound upon a former or formers to provide an electromagnetic field for effecting a relative mechanical movement between the permanent magnetic field and the electromagnetic field, wherein the coils for providing the electromagnetic field are wound such that under stall conditions the current flowing from the direct current supply and into the coils is such that the amount of flux density attributable to the non linear portion of the coils' and core's magnetization curve is at least 20% of the total flux density of the coils and core.
Alternatively, according to another form of this invention, although this need not be the only or indeed the broadest form, there is proposed an electric motor comprising a yoke and an armature, the armature being adapted to be supplied with direct electrical current through a commutator to each of a plurality of poles, the armature having a magnetically permeable core providing a former for each of the plurality of poles for the armature, there being a coil wound around the former in respect to each pole, the arrangement being characterised in that the number of turns in the windings of each coil for a respective pole, their location and other characteristics are such that there will be effected, at stall, a magnetic field which is substantially greater than required when supplied with a current supply at the motors rated voltage such that the magnetic field is in the non linear portion of the magnetization curve of the core acting as the former.
In preference, the motor is a direct current motor. In preference, the coils and core are in the form of an armature.
In preference, the amount of flux density attributable to the non linear portion of the magnetization curve is at least 20% but no more than 25% of the total flux density of the coils and core.
In preference, the amount of flux density attributable to the non linear portion of the magnetization curve is at least 25% but no more than 30% of the total flux density of the coils and core.
In preference, the amount of flux density attributable to the non linear portion of the magnetization curve is at least 30% but no more than 35% of the total flux density of the coils and core. In preference, the amount of flux density attributable to the non linear portion of the magnetization curve is at least 35% but no more than 40% of the total flux density of the coils and core.
In preference, the amount of flux density attributable to the non linear portion of the magnetization curve is at least 40% but no more than 45% of the total flux density of the coils and core.
In preference, the amount of flux density attributable to the non linear portion of the magnetization curve is at least 45% but no more than 50% of the total flux density of the coils and core.
In preference, the amount of flux density attributable to the non linear portion of the magnetization curve is at least 50% but no more than 55% of the total flux density of the coils and core.
In preference, the amount of flux density attributable to the non linear portion of the magnetization curve is at least 55% but no more than 60% of the total flux density of the coils and core. In preference, the amount of flux density attributable to the non linear portion of the magnetization curve is at least 60% but no more than 65% of the total flux density of the coils and core. In preference, the amount of flux density attributable to the non linear portion of the magnetization curve is at least 70% but no more than 80% of the total flux density of the coils and core.
In preference, the amount of flux density attributable to the non linear portion of the magnetization curve is at least 80% but no more than 100% of the total flux density of the coils and core.
In preference, the amount of flux density attributable to the non linear portion of the magnetization curve is at least 90% but no more than 95% of the total flux density of the coils and core. In preference, the amount of flux density attributable to the non linear portion of the magnetization curve is at least 95% of the total flux density of the coils and core.
In preference, the non linear portion of the magnetization curve is above the knee of the magnetization curve. In preference, the non linear portion of the magnetization curve is further characterised by:
H/(a + bH); where a is the "hardness" constant and is a measure of the value of H necessary to attain a given fraction of saturation; b= 1/(the maximum attainable flux density); and H has its known meaning to a noninventive person skilled in the art.
In preference, the armature has a core comprised of a ferromagnetic material.
In preference, the winding of each coil is formed from wire having a gauge which offers substantial resistance to current flowing there through at the motors rated voltage.
In preference, each of the coils of the armature have a resistance such that the resistance across the brushes is no less than greater than 1.2 ohms.
In preference, the motor is connected to an electric power supply with a voltage which is the motors rated voltage.
Alternatively according to another form of this invention, although this need not be the only or indeed the broadest form, there is proposed a method of operating an electrical motor as characterised in any one of the above forms which comprises effecting a connection to the motor of a current source at the motors rated voltage and such that there is thereby caused a magnetic inductance with respect to each coil that substantially exceeds that which is required to reach the non linear portion of the magnetization curve of the core.
Alternatively according to another form of this invention, although this need not be the only or indeed the broadest form, there is proposed an arrangement including: a permanent magnet direct current motor; and a direct current supply means for providing electrical power to the permanent magnet direct current motor, wherein the resistance of the motor is when connected across the direct current supply means is no less 20% of the internal resistance of the direct current supply means. Alternatively according to another form of this invention, although this need not be the only or indeed the broadest form, there is proposed an arrangement including: a permanent magnet direct current motor; and a direct current supply means for providing electrical power to the permanent magnet direct current motor, the direct current supply means having a low internal resistance whereby it is possible to damage the direct current supply means by drawing excessive currents, wherein the arrangement is adapted such that the current drawn by the motor will not cause damage to occur to the direct current supply means when the motor is in a stalled condition for a substantial period of time.
Alternatively according to another form of this invention, although this need not be the only or indeed the broadest form, there is proposed an arrangement including: a permanent magnet direct current motor; and a direct current supply means for providing electrical power to the permanent magnet direct current motor, wherein the windings of the armature of the motor are such that under stall conditions the current flowing in the armature does not exceed the current rating of the battery.
Alternatively according to another form of this invention, although this need not be the only or indeed the broadest form, there is proposed an arrangement including: a permanent magnet direct current motor; and a direct current supply means for providing electrical power to the permanent magnet direct current motor, wherein the windings of the armature of the motor are such that under stall conditions the current flowing in the armature is between the range of 100% to 110% of the current rating of the battery.
Alternatively according to another form of this invention, although this need not be the only or indeed the broadest form, there is proposed an arrangement including: a permanent magnet direct current motor; and a direct current supply means for providing electrical power to the permanent magnet direct current motor, wherein the windings of the armature of the motor are such that under stall conditions the current flowing in the armature is between the range of 95% to 100% of the current rating of the battery.
Alternatively according to another form of this invention, although this need not be the only or indeed the broadest form, there is proposed an arrangement including: a permanent magnet direct current motor; and a direct current supply means for providing electrical power to the permanent magnet direct current motor, wherein the windings of the armature of the motor are such that under stall conditions the current flowing in the armature is between the range of 90% to 95% of the current rating of the battery. Alternatively according to another form of this invention, although this need not be the only or indeed the broadest form, there is proposed an arrangement including: a permanent magnet direct current motor; and a direct current supply means for providing electrical power to the permanent magnet direct current motor, wherein the windings of the armature of the motor are such that under stall conditions the current flowing in the armature is between the range of 85% to 90% of the current rating of the battery.
Alternatively according to another form of this invention, although this need not be the only or indeed the broadest form, there is proposed an arrangement including: a permanent magnet direct current motor; and a direct current supply means for providing electrical power to the permanent magnet direct current motor, wherein the windings of the armature of the motor are such that under stall conditions the current flowing in the armature is between the range of 80% to 85% of the current rating of the battery.
Alternatively according to another form of this invention, although this need not be the only or indeed the broadest form, there is proposed an arrangement including: a permanent magnet direct current motor; and a direct current supply means for providing electrical power to the permanent magnet direct current motor, wherein the windings of the armature of the motor are such that under stall conditions the current flowing in the armature is between the range of 75% to 80% of the current rating of the battery. Alternatively according to another form of this invention, although this need not be the only or indeed the broadest form, there is proposed an arrangement including: a permanent magnet direct current motor; and a direct current supply means for providing electrical power to the permanent magnet direct current motor, wherein the windings of the armature of the motor are such that under stall conditions the current flowing in the armature is between the range of 65% to 75% of the current rating of the battery.
Alternatively according to another form of this invention, although this need not be the only or indeed the broadest form, there is proposed an arrangement including: a direct current supply means having an output voltage of at least 5 volts; and a permanent magnet direct current motor adapted to be electrically connected to the direct current supply means, the permanent magnet direct current motor being wound such that each individual coil between two armature commutator segments has more than 60 turns.
In preference, the direct current supply means is a battery.
In preference, the direct current supply means is a solar cell.
In preference, referring to any of the above forms, the battery comprises at least one Nickel Cadmium battery cell.
In preference, referring to any of the above forms, the battery has an internal resistance of less than 250 milli Ohms per cell.
In preference, the arrangement resides in a portable power tools such as a drill or screwdriver. In preference, the arrangement resides in a propulsion vehicle.
In another preferred form, and referring to any of the above forms, each individual coil between two armature commutator segments has between 75 to 200 turns.
In another preferred form, and referring to any of the above forms, each individual coil between two armature commutator segments has between 100 to 200 turns.
In another preferred form, and referring to any of the above forms, each individual coil between two armature commutator segments has between 125 to 200 turns. In another preferred form, and referring to any of the above forms, each individual coil between two armature commutator segments has between 75 to 175 turns.
SUBSTTTUTE SHEET (Rule 26) In another preferred form, and referring to any of the above forms, each individual coil between two armature commutator segments has between 100 to 175 turns.
In another preferred form, and referring to any of the above forms, each individual coil between two armature commutator segments has between 125 to 175 turns.
In another preferred form, and referring to any of the above forms, each individual coil between two armature commutator segments has between 75 to 150 turns. In another preferred form, and referring to any of the above forms, each individual coil between two armature commutator segments has between 100 to 150 turns.
In another preferred form, and referring to any of the above forms, each individual coil between two armature commutator segments has between 105 to 150 turns.
In another preferred form, and referring to any of the above forms, each individual coil between two armature commutator segments has between 110 to 150 turns.
In another preferred form, and referring to any of the above forms, each individual coil between two armature commutator segments has between 115 to 150 turns.
In another preferred form, and referring to any of the above forms, each individual coil between two armature commutator segments has between 120 to 150 turns. In another preferred form, and referring to any of the above forms, each individual coil between two armature commutator segments has between 100 to 125 turns.
In another preferred form, and referring to any of the above forms, each individual coil between two armature commutator segments has between 100 to 120 turns. In another preferred form, and referring to any of the above forms, each individual coil between two armature commutator segments has between 105 to 120 turns.
In another preferred form, and referring to any of the above forms, each individual coil between two armature commutator segments has between 100 to 105 turns.
In another preferred form, and referring to any of the above forms, each individual coil between two armature commutator segments has between 105 to 115 turns. In another preferred form, and referring to any of the above forms, each individual coil between two armature commutator segments has between 110 to 115 turns.
I have also discovered that if under stall conditions the flux densisty (or Gauss) of the interacting fields are of a similar value then previously unexpected advantages result.
In general when considering permanent magnet motors, the useful flux densisty of the yoke's magnetic field is approximately 900 Gauss (this may vary depending upon the type of permanent magnets used). To achieve such a Gauss from the armature either the current can be increased resulting in thicker windings or an increased voltage. However, this is impractical as very high currents would be required (eg at least 30 to 40 Amps) which may destroy the armature's windings. Alternatively, and contrary to standard motor design principles the number of turns of the coils can be increased and the cross-sectional area or gauge of wire used can be preferably decreased resulting in an increase in the resistance of the windings. This quite simply, at first sight, appears to be contrary to every known guiding principle in the design of these types of motors.
According to conventional expectations, a number of problems arise by proceeding in the way described. For instance, one of the significant difficulties associated with reduction of the gauge of wire is that this will then have less capacity to handle large currents without undue heating so that one would expect when the motor has its armature stalled relative to the yoke, that this would make the coils very much more vulnerable to overheating and of course effective destruction through burning of the insulation between the windings and melting of the wire. Further, even if one could overcome the heating problem, one would expect that increased resistance would implicitly increase losses.
The very surprising discovery has been that, contrary to every expectation, these difficulties do not appear in fact to be a major difficulty at all, and the marked improvement achieved by having a somewhat larger number of turns for each coil than has hitherto been used, has resulted in motors which are able to provide higher output torque for a given input as compared to traditional motors of similar apparent characteristics, and improved overall efficiencies when the Gauss of the interacting fields are of a similar value. Examples of experiments conducted so far will be later given showing improvements in the performance characteristics of a permanent magnet motor when the interacting fields are of a similar Gauss value. To achieve this it is preferable to increase the number of turns of the armature coils as compared to that which has been the case given conventional design criteria in existing motors.
It is the intended object of this invention to improve the performance of a direct current motor when powered by a battery or solar cell means or at least provide the public with a useful alternative to currently available direct current motors. According to one form of this invention, although this need not be the only or indeed the broadest form, there is proposed an electric motor having a permanent magnetic field or fields and a plurality of coils wound upon a former or formers to provide an electromagnetic field for provide a relative mechanical movement between the permanent magnetic field and the electromagnetic field, wherein the coils for providing the electromagnetic field are wound such that when the motors rated voltage is applied thereto the flux density of the electromagnetic field and its associated former are substantially identical to the flux density of the permanent magnetic field or fields when the motor is stalled.
Alternatively, according to another form of this invention, although this need not be the only or indeed the broadest form, there is proposed an arrangement including: a direct current supply means electrically connected to an electric motor having a permanent magnetic field or fields and a plurality of coils wound upon a former or formers to provide an electromagnetic field for effecting a relative mechanical movement between the permanent magnetic field and the electromagnetic field, wherein the coils for providing the electromagnetic field are wound such that the current flowing from the direct current supply and into the coils is such that the flux density of the electromagnetic field and its associated former have a similar value of flux density to that of the permanent magnetic field or fields when the motor is stalled.
Alternatively according to another form of this invention, although this need not be the only or indeed the broadest form, there is proposed an arrangement including: a permanent magnet direct current motor; and a direct current supply means for providing electrical power to the permanent magnet direct current motor, wherein the flux density of the armature has a similar value of flux density to that of the permanent magnetic field or fields when the motor stalled.
In preference, the coils and core are in the form of an armature. In preference, the said flux density is the useful flux of the armature poles and permanent magnet.
In preference, similar value has the meaning no more than 20% difference.
In preference, similar value has the meaning no more than 15% difference.
In preference, similar value has the meaning no more than 10% difference.
SUBSTTTUTE SHEET (Rule 26) In preference, similar value has the meaning no more than 5% difference.
In preference, similar value has the meaning no more than 2% difference. In preference, similar value has the meaning no more than 1% difference.
In preference, the armature has a core comprised of a ferromagnetic material.
In preference, the winding of each coil is formed from wire having a gauge which offers substantial resistance to current flowing therethrough at the motor's rated voltage.
In preference, each of the coils of the armature have a resistance such that the resistance across the brushes is no less than greater than 1.2 ohms. In preference, the motor is connected to an electric power supply with a voltage which is the motor's rated voltage.
In preference, the direct current supply means is a battery.
In preference, the direct current supply means is a solar cell.
In preference, the battery comprises at least one Nickel Cadmium battery cell.
In preference, the arrangement resides in a portable power tools such as a drill or screwdriver.
In preference, the arrangement resides in a propulsion vehicle.
In another preferred form, each individual coil between two armature commutator segments has between 75 to 200 turns.
In another preferred form, and referring to any of the above forms, each individual coil between two armature commutator segments has between 100 to 200 turns.
In another preferred form, and referring to any of the above forms, each individual coil between two armature commutator segments has between 125 to 200 turns. In another preferred form, and referring to any of the above forms, each individual coil between two armature commutator segments has between 75 to 175 turns.
In another preferred form, and referring to any of the above forms, each individual coil between two armature commutator segments has between 100 to 175 turns.
In another preferred form, and referring to any of the above forms, each individual coil between two armature commutator segments has between 125 to 175 turns. In another preferred form, and referring to any of the above forms, each individual coil between two armature commutator segments has between 75 to 150 turns.
In another preferred form, and referring to any of the above forms, each individual coil between two armature commutator segments has between 100 to 150 turns.
In another preferred form, and referring to any of the above forms, each individual coil between two armature commutator segments has between 105 to 150 turns.
In another preferred form, and referring to any of the above forms, each individual coil between two armature commutator segments has between 110 to 150 turns.
In another preferred form, and referring to any of the above forms, each individual coil between two armature commutator segments has between 115 to 150 turns. In another preferred form, and referring to any of the above forms, each individual coil between two armature commutator segments has between 120 to 150 turns.
In another preferred form, and referring to any of the above forms, each individual coil between two armature commutator segments has between 100 to 125 turns. In another preferred form, and referring to any of the above forms, each individual coil between two armature commutator segments has between 100 to 120 turns.
In another preferred form, and referring to any of the above forms, each individual coil between two armature commutator segments has between 105 to 120 turns.
In another preferred form, and referring to any of the above forms, each individual coil between two armature commutator segments has between 100 to 105 turns. In another preferred form, and referring to any of the above forms, each individual coil between two armature commutator segments has between 105 to 115 turns.
In another preferred form, and referring to any of the above forms, each individual coil between two armature commutator segments has between 110 to 115 turns.
This invention also relates to a portable multi purpose power tool powered by direct current power supply.
Direct current multi purpose power tools have been developed so that for example they can be used both as a drill or a screwdriver. Such tools have gearing to reduce the output speed from the direct current motor which is an integral part of the tool. The reason for the gearing is due to the design and type of motor which generally has an output shaft speed requiring speed reduction. Furthermore, such motors impose demands upon the direct current power supply (battery) and therefore the motor can rapidly drain the stored battery charge.
When used as a drill a relatively high speed is often required (but motor gearing speed reduction is still used), whereas with a screwdriver the speed generally required is much lower. Because the screwdriver must turn in both a clockwise and anti-clockwise direction the motor adapted to turn the screwdriver must be bi-directional so that screws can be screwed in or alternatively unscrewed. To achieve the slower drill speeds interchangeable gearing can be used or variable pressure on the power tool switch can be used to provide alternative voltage supplies across the motor. The above approaches to varying speed offer problems. For instance, gear changing can be expensive due to the high gearing ratios and interchanging mechanisms that may be required. The switch sensitive approach requires skill by the operator and it is possible to apply too much pressure causing the screwdriver to jump out of the screw head.
In addition to the above problems, power tools are generally in the shape of a pistol. Hence, when working in tight corners or in confined spaces the pistol shape may not be suitable and therefore it may be impractical to use such power tools in these circumstances.
It is the intended object of this invention to overcome the abovementioned problems or at least provide the public with a useful alternative. According to one form of this invention, although this need not be the only or the broadest form, there is proposed a portable power tool including: a first direct current storage means adapted to be electrically connected to a direct current motor by a switch means; and a circuit modification means adapted to allow a second direct current storage means to be inserted in series with the first direct current storage means.
In preference, the portable power tool has a means of changing the turning direction of the motor. In preference, the second direct current storage means is contained within an attachment means adapted to engage the portable power tool.
In preference, the attachment means has an circuit modification means activator, wherein when the portable power tool is engaged by the attachment means the circuit modification means activator, in conjunction with the circuit modification means, inserts the second direct current storage means in series with the first direct current storage means. In preference, the attachment means has a switch means adapted to electrically connect the first direct current storage means and second direct current storage means to the direct current motor.
Alternatively according to another form of this invention, although this need not be the only or the broadest form, there is proposed an attachment means adapted to engage a power tool having a first direct current storage means, the attachment means having a second direct current storage means adapted to be inserted in series with the first direct current storage means. In preference, the attachment means has a switch means adapted to provide a series connection of the first direct current storage means and second direct current storage means to a direct current electrical motor adapted to drive the power tool.
Alternatively according to another form of this invention, although this need not be the only or the broadest form, there is proposed a portable power tool arrangement including: a power tool having a first direct current storage means adapted to be electrically connected to a direct current motor by a first switch means; a second direct current storage means contained within an attachment means, the attachment means engaging the power tool such that the second direct current storage means is inserted in series with the first direct current storage means, wherein the attachment means is adapted to disengage the power tool such that when disengaged the second direct current storage means is removed from being in series with the first direct current storage means.
In preference, the second direct current storage means is adapted to be removed from being in series with the first direct current storage means such that the first direct current storage means remains adapted to be electrically connected to the direct current motor by the switch means. In preference, the portable power tool has a means of changing the turning direction of the motor.
In preference, the attachment means has a second switch means adapted to electrically connect the first direct current storage means and second direct current storage means to the direct current motor.
In preference, the attachment means has an interlock means adapted to activate the first switch means when the attachment means engages the power tool such that the second switch means provides the electrical connection between both the first direct current storage means and second direct current storage means and the direct current motor.
In preference, referring to any of the above forms: the motor is a permanent magnet direct current motor; and the first and second battery means for providing electrical power to the permanent magnet direct current motor have a low internal resistance whereby it is possible to damage either of the battery means by drawing excessive currents, wherein the arrangement is adapted such that the current drawn by the motor will not cause damage to occur to either of the battery means when the motor is in a stalled condition for a substantial period of time. In preference, referring to any of the above alternative forms, the direct current permanent magnet motor is wound such that when it is connected to a 12 Volt battery means the motors stall current does not exceed 4 amps.
In preference, referring to any of the above forms, the direct current permanent magnet motor has an efficiency of greater than 40% when the motor drives a variable load over at least 15% of the total output torque range at the output of the motor, wherein the efficiency is calculated by: efficiency =■ ] output power / input power x 100 where output power is the power at the output of the motor's shaft and input power is the input power to the motor. In preference, referring to any of the above forms, the direct current permanent magnet motor has an efficiency of greater than 45% when the motor drives a variable load over at least 15% of the total output torque range at the output of the motor, wherein the efficiency is calculated by: efficiency -^output power / input power x 100 where output power is the power at the output of the motor's shaft and input power is the input power to the motor.
In preference, referring to any of the above forms, the direct current permanent magnet motor has an efficiency of greater than 50% when the motor drives a variable load over at least 15% of the total output torque range at the output of the motor, wherein the efficiency is calculated by: efficiency^,] output power / input power x 100 where output power is the power at the output of the motor's shaft and input power is the input power to the motor.
In preference, referring to any of the above forms, the direct current permanent magnet motor has an efficiency of greater than 55% when the motor drives a variable load over at least 15% of the total output torque range at the output of the motor, wherein the efficiency is calculated by: efficiency = y] output power / input power x 100 where output power is the power at the output of the motor's shaft and input power is the input power to the motor.
In preference, referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 35 to 400 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 50 to 400 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 75 to 400 turns.
In another preferred form, and reforring to any of the above alternative forms, each individual coil between two armature commutator segments has between 100 to 400 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 125 to 400 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 35 to 375 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 50 to 375 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 75 to 375 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 100 to 375 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 125 to 375 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 35 to 350 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 50 to 350 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 75 to 350 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 100 to 350 turns.
SUBSTITUTE SHEET (Rule 2t>, In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 125 to 350 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 35 to 325 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 50 to 325 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 75 to 325 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 100 to 325 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 125 to 325 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 35 to 300 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 50 to 300 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 75 to 300 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 100 to 300 turns.
SUBSTITUTE SHEET (Rule 26 In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 125 to 300 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 35 to 275 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 50 to 275 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 75 to 275 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 100 to 275 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 125 to 275 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 35 to 250 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 50 to 250 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 75 to 250 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 100 to 250 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 125 to 250 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 35 to 225 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 50 to 225 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 75 to 225 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 100 to 225 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 125 to 225 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 35 to 200 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 50 to 200 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 75 to 200 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 100 to 200 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 125 to 200 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 35 to 175 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 50 to 175 turns. In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 75 to 175 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 100 to 175 turns.
In another preferred form, and referring to any of the above alternative forms, each individual coil between two armature commutator segments has between 125 to 175 turns.
In preference, referring to any of the above forms, the wire gauge of each individual coil is the thickest that can be wound upon the armature for the given number of turns.
In preference, referring to any of the above forms, the wire gauge of each individual coil is less than 0.4mm.
In preference, capacitors are connected across each pole- piece winding. This offers the additional advantage of susbtantially reducing radio frequency interference. This is not achievable with motors currently used for example in commercially available power tools. With such tools the excessive currents required by the armature and physical size capacitor constraints do not readily allow for such capacitors to be connected across each pole winding.
In preference, referring to any of the above forms, the armature is "excited" in conventional manner, prior to being inserted into the permanent magnetic field during assembly of the motor. Exciting of the armature is preferably achieved by mounting the armature in a test block and passing an electric current therethrough. This is found to reduce any tendency towards mismatching of the magnetic poles of the motor and avoids high eddy current formation during running of the motor.
BRIEF DESCRIPTION OF THE DRAWINGS
For better understanding of the invention, embodiments, results and theory will now be discussed and described, without limitation and with reference to the accompanying drawings, in which:
Figures 1a to 1d illustrate a 3 pole-piece direct current permanent magnet motor;
Figures 2a to 2d illustrate a 7 pole-piece direct current permanent magnet motor;
Figure 3 (a,b,c,d) to Figure 17 (a,b,c,d) illustrate the characteristics discovered by increasing the number of windings of an armature;
Figure 18 is a comparison of the number of turns per coil and the current required to provide a torque of 1 Newton metre;
Figure 19 illustrates a standard magnetization curve; Figure 20 illustrates the circuitry used to obtain the test results; Figure 21 illustrates what is meant by usefil flux; Figure 22 illustrates a portable power tool; Figure 23 illustrates an attachment to the power tool which provides additional voltage to the power tool;
Figure 24 illustrates the switch mechanism of the power tool; and
Figure 25 illustrates the electrical circuit of the power tool and the attachment means.
It should be noted that Figures 10d, 14d, and 15d do not exist.
SUBSTITUTE SHEET (Rule 26; DETAILED DESCRIPTION OF THE DRAWINGS
Referring to FIGs 1a to 1d there is illustrated a 3 pole-piece direct current permanent magnet motor having the approximate dimensions: armature diameter a = 23mm; commutator diameter b = 7.5mm; pole core thickness c = 4.3mm; core end depth d = 3.2mm; shaft diameter e = 3.1 mm; core gap f = 4.3mm; shaft length g = 71 mm; commutator length h = 1 Omm; core and commutator gap i = 4.5mm; core length j = 22.5mm; permanent magnetic yolk inner diameter k = 23.5mm; permanent magnetic yolk outer diameter I = 35.5mm; length of the permanent magnetic yolk m = 29mm; motor casing length n = 48mm; bearing housing diameter p = I2.5mm; and bearing housing depth o = 4mm.
Referring to FIGs 2a to 2d there is Illustrated a 7 pole-piece D.C. permanent magnet motor having the approximate dimensions: armature diameter z = 33mm; commutator diameter t =
71Omm; pole core thickness y = 3mm; core end depth dd = 2mm; shaft diameter u = 5mm; core gap aa = 2mm; shaft length s = 97mm; commutator length w = 14.75mm; core and commutator gap ii = 12 mm; core length v = 29mm; permanent magnetic yolk inner diameter r = 34.25 mm; permanent magnetic yolk outer diameter q = 50mm; length of the permanent magnetic yolk cc = 40mm; motor casing length ee = 68.5mm; bearing housing diameter bb= 18mm; and bearing housing depth dd = 6mm.
THEORY
It is well known that a direct current electric motor containing permanent magnets may also act as an electrical generator. Furthermore, the generated electro-motive force (e.m.f.) is proportional to the rate of rotation of the armature. This is because the induced e.m.f. in an armature pole-piece is proportional to the rate of change of magnetic flux through the pole-piece, which in turn is proportional to the angular velocity of the pole- piece as it sweeps past the permanent magnet. As the armature rotates, the
SUBSTTTUTE SHEET (Rule 26) induced e.m.f. in each pole piece is intrinsically an A.C. signal containing sign reversals and maximum and minima voltages (the minima being zero volts). The position of brushes in contact with the motor's armature, which are also electrically connected to external terminals, are arranged so that the induced e.m.f. at the terminals is always of the same electrical polar sense for a given armature rotation direction. For armatures of more than two poles, at any time, at least one of the pole pieces has a non-zero induced e.m.f. as the armature rotates. The brushes are positioned to capture this non-zero e.m.f. for all positions of the armature. When direct current is supplied to a motor the armature rotates. However, as stated above, the rotation itself causes an induced e.m.f. in the pole-pieces. This generator effect produces an e.m.f. Thus, if the effects of mechanical friction, wind resistance and eddy currents are ignored, the r.p.m. of a free running motor is defined by the generated induced e.m.f. equalling the supplied e.m.f. In other words, for a given supply voltage ignoring mechanical friction, wind resistance and eddy current losses, the r.p.m. is dependent upon the permanent magnet field, the geometry of the brushes, the armature and the supply e.m.f. For a real motor with friction, wind resistance and eddy current losses, the free running r.p.m. is a little less than the theoretical value. However, it is important to establish the above basic concept as a background to aid with the understanding of this invention.
It should be noted that the rotational velocity of the ideal motor described above is independent of the electrical resistance of the pole piece windings, brushes and commutator. Hence, as the induced e.m.f. in the pole-pieces is approximately proportional to the number of windings on each pole-piece for a given motor and armature r.p.m., it follows that in the ideal motor the free running r.p.m. is approximately inversely proportional to the number of windings for a given supply voltage. That is the fewer the turns the greater the free running r.p.m. Furthermore, when considering an ideal motor the free running r.p.m. is proportional to the supply voltage.
SUBSTTTUTE SHEET (Rule 26) When a motor is under load, that is made to do work, the friction, wind resistance, eddy currents, electrical resistance of the windings, brush resistance and commutator have an effect upon the motor's performance. In the extreme case where the motor is so loaded that the rotational velocity is much less than the free running speed, the induced e.m.f. can be considered as insignificant. Furthermore, the motor dynamics are now a function of the said resistances and electrical supply's effective internal series resistance, the flux of the permanent magnets, the geometry of the pole pieces, and the number of windings per pole. I have discovered that direct current permanent magnet motors used for instance in commercially available appliances such as hand held battery operated power tools (including drills and screw drivers) are poorly interfaced with their supply. The motors have thick copper wire armature windings of a small number of turns which results in high a r.p.m. for reasons given above. Consequently, such tools have a gearbox for reducing the output speed of the tool. However for reasons which follow, this results in inefficiency when the motor is heavily loaded, and it is my experience that most battery operated hand held screw drivers and drills are most often heavily loaded when used in practice. It seems that as this practice of small number of thick armature conductors has been universally adopted for permanent magnet direct current motors, there is probably a misconceived "rule of thumb" used in the design process.
I will now show that the practice of a few thick turns found in these electric motors is not optimal, and in fact a thinner wire and more turns can provide a more useful motor. Furthermore, it should be noted that there is an optimum range of wire thickness for a given set of criteria.
Considering a heavily loaded motor: If - the internal resistance of the supply plus commutator and bushes is r1 ,
- the resistance of the windings is r2,
- then r1 +r2=R which is the total effective resistance,
SUBSTTTUTE SHEET (Rule 26) - the number of windings is n,
- the cross-sectional area of the conductor of windings is a,
- the supply voltage is V,
- the armature electro magnet flux is F, - the current flowing through the conductor is i, then for a given conductor mass M M = klan, r2 = k2n/a, i = V/R=V/(r1 +k2n/a) F = k3in=k3Vn/(r1 +k2n/a)=k3Vn/(r1 +k1 k2n2/M) where the k1 , k2 and k3 are constants. If the constant k4=k1 k2 then: dF/dn V/(r1 +k4n2/M)-2k4Vn2/(M(r1+k4n2/M)2) =
V{Mr1+k4n2-2k4n2} V{Mr1 -k4n2}
M(r1 +k4n2/M)2 M(r1 +k4n2/M)2
F is a maximum when dF/dn=O, that is when MM =k4n2. As M and r1 can be assumed constant, there is an optimum number of turns which is a function of the chosen mass of conductor and internal resistance of the supply plus commutator and brushes. Note that this is optimum is not a function of supply voltage. This maximizes the torque at heavy loads for given internal supply resistance and given brushes and commutator. In general this is approximately true of the efficiency as well at high loads, so long as no magnetic saturation occurs.
The flux at the optimized torque is
Figure imgf000047_0001
Thus, the greater the mass of conductor the greater the torque at low r.p.m. For example, to double the torque, all else being equal, the mass need increase by 4 times and both n and a by 2 times. However, this will approximately halve the free running r.p.m. and it should be remembered
SUBSTTTUTE SHEET (Rule 26) that the work done is proportional to the torque multiplied by the angular velocity. Hence, at heavily loaded low r.p.m. the greater the mass of conductor the better (until magnetic saturation occurs).
For an intermediate load, the current drain is approximately; 5 V(1-rpm/rpmfree)/R, and the power is approximately proportional to rpmV(1 -rpm/rpmfree)/R, where V is the supply voltage, rpm is the angular velocity and rpmfree is the free running angular velocity for supply voltage ι o v.
The optimum output power is delivered when at half the free running rpm. However, most users stress the tool beyond this optimum. Under these circumstances, there is a danger that significant magnetic saturation will occur. If this happens, then extra non useful current is drawn
1 5 compared to the non-saturated case and usually the motor's windings will overheat. Hence, this can also be a criteria in the design. That is V and R should be chosen to not allow too much saturation or too excessive heating to occur.
A simplified summary of the above is that motors of improved
20 efficiencies can be designed and manufactured by determining an output speed of the motor which is preferably less than the desired application for which the motor is to be used. The output speed is proportional to 1/n, hence this determines the number of windings (turns) per armature pole- piece. Once n is determined it is preferable to select the thickest wire gauge 5 that can be wound upon the armature. However, there are constraints upon the maximum thickness of wire gauge, these are basically that the Force (or Torque) is proportional to n.l (until magnetic saturation occurs). Thus, consideration of magnetic saturation and demands upon power supplies should be taken into account. 0 RESULTS
When considering devices such as battery powered hand held power drills and screw drivers having which are commonly sold with motors having typically between 12 and 22 turns per armature pole-piece. Efficiencies at mid-range loads are typically less than 35% for these tools. By changing the turns to 125 and using the thickest wire that can fit on the armatures, we have increased this efficiency to approximately 60%). This is attributable to the improved match between the number of windings and rl and r2.
In general, the more turns per pole-piece will improve the motor's efficiency. This is basically because the generated magnetic field is proportional to the number of turns for a given current. That is the more turns, the smaller the battery current drain required to produce a given torque. Also, the smaller this current, the smaller the power inefficiency losses from the internal resistance of the battery and resistive losses of the brushes, armature and conductors feeding the motor via the switch. However, there is a limit to the number of turns providing improved efficiencies. This related to the insulation of the wires in which the insulation affects the flux within the armature and therefore there is a range of turns which are suitable for a specific application.
When considering a battery powered motor in which the battery' has a low resistance per cell (as is the case with Nickel Cadmium batteries which have typically less than 250 milli Ohms per cell) and the motor stalls or is so loaded that the r.p.m. is very low, the current drawn from the batteries may cause battery damage. In contrast, with a 125 or more turn motor, using relatively thin wire of approximately less than 0.4mm gauge, the resistance of the armature windings is several ohms and the near stalled current will not cause much heating or battery stress in practice owing to reasonable currents of a few amperes.
The following results illustrate the performance of this invention.
SUBSTTTUTE SHEET (Rule 26) Considering the motor of FIGs 1a to 1d which is a Johnson Motor HC683G which when obtained had 22 turns per pole-piece and a wire gauge of 0.9mm. This motor is generally used in battery powered drills and battery powered small vacuum cleaners. Using available data sheets (although our own tests differed and showed a worse performance), this motor at maximum efficiency draws 8.17 amps at 17700 r.p.m and produces a torque of 26.12 mNM. Comparing this with the same motor (HC683G) rewound, using the invention disclosed in this specification, with 125 turns per pole-piece and a wire gauge of 0.145mm the following results were obtained:
SHAFT SHAFT
SUPPLY ARMATURE SPEED TORQUE
VOLTAGE CURRENT RPM mNM
2.4v 19OmA (NO LOAD) 990 N.A.
35OmA 693 24.91
93OmA STALL 73.04
4.8v 22OmA (NO LOAD) 1905 N.A.
66OmA 1248 49.02
1720mA STALL 131.89
7.2v 260mA (NO LOAD) 2899 N.A.
640mA 2004 81.07
15OOmA 1088 203.04
21OOmA STALL 293.13
12v 330mA (NO LOAD) 4727 N.A.
670mA 3432 132.82
1570mA 2472 254.08
3500mA STALL 403.1
SUBSTTTUTE SHEET (Rule 26) 24v 450mA (NO LOAD) 9185 N.A.
1000mA 6404 389.57 2373mA 4048 572.04
4700mA STALL 985.47
The above results were obtained using 125 turns and 0.145mm gauge wire. However, this is not the optimum gauge. As stated above by changing the turns to suit a desired r.p.m. and using the thickest wire that can fit on the armature higher efficiencies can be achieved. Thus when considering the motor dimensions of FIGs 1a to 1d (Johnson HC683G) the following was observed when the armature was wound as follows:- wire gauge turns per efficiency pole-piece
0.145mm 125tums = 52% efficiency
0.28mm 125tums = 65% efficiency
0.9mm 22turns = 33% efficiency
The 0.28mm gauge motor at 125 turns per pole-piece illustrates that once the number of turns per-pole is determined then the thickest wire gauge that can be used improves the efficiency of the motor. Furthermore, motors having a small number of turns and thick windings are inefficient. (This inefficiency may, be due to magnetic saturation of the armatures poles or because the magnetic field within the armatures poles exceeds that of the flux provided by the permanent magnetic field or fields). The above efficiency results were measured and calculated by coupling the shaft of a HC683G of 22 turns and 0.9mm gauge (adapted to be used as a generator) to the output shaft of the motor being tested. Thus by varying the current in the HC683G generator by means of a variable resistor across the generators output, and measuring its generated voltage across the variable resistor, the efficiency was calculated as follows:-
SUBSTTTUTE SHEET (Rule 26) effi ciency = ,]ou tpu t power / inpu t power x 100 where output power = Vg2/Rg, Vg being the output voltage of the generator and R the resistance across the generator's output; and input power = Vs. Is, Vs being the supply voltage to the motor under test and Is the supply current to the motor's armature. The above results and theory illustrate that small D.C. permanent magnet motors having a small number of turns and thick windings are inefficient. In general, D.C. power tools use such motors, to emphasize this point the following examples are described:
1 ) The physical dimensions of the HC683G are illustrated in FIGs 1 a to 1d, this motor as sold has 22 turns and 0.9mm gauge wire per pole-piece.
2) The Johnson HC615L is similar in shape to the motor illustrated in FIGs 1a to 1d but some of its dimensions are slightly larger than the HC683G, for instance the armature diameter a=23mm, the shaft length g = 71 mm and the core length j = 31 mm. This motor again as sold has 22 turns and 0.9mm gauge wire per-pole-piece.
3) The Johnson HC783G is similar in shape to the motor illustrated in FIGs 1a to 1d but some of its dimensions are again slightly larger than the HC683G, for instance the armature diameter a=27mm, the shaft length g = 86mm and the core length j = 86mm. This motor as sold has 24 turns and 0.9mm gauge wire per-pole-piece.
4) The motor illustrated in FIGs 2a to 2d is a 7 pole-piece D.C. permanent magnet motor, this motor as sold has 9 turns and 0.9mm gauge per pole and each pole is wound around 3 pole pieces.
It should be noted that capacitors can be connected across each pole-piece winding (if required). This offers the additional advantage of substantially reducing radio frequency interference. This is not achievable with motors currently used for example in commercially available power tools. With such tools the excessive currents required by the armature and physical size capacitor constraints do not readily allow for such capacitors to be connected across each pole winding.
Referring to the results as illustrated in FIGs 3 to 18 the motor used to obtain these results was a Johnson 50274 D.C. permanent magnet motor having a 3- tooth armature. The results of FIGs 3 to 18 were obtained using the same motor and rewinding the armature with the different number of turns and wire gauges. For instance, FIG 3 (a,b,c,d) relates to a 32 turn per pole wound Johnson 50274 motor, each of the wound poles having a 0.75 gauge wire of 0.2 ohms across the brushes, whereas FIG 7 (a,b,c,d) has relates to the same motor wound with 110 turns of 0.34 wire gauge having a resistance of 1.4 ohms across the brushes.
A conventionally wound motor, the results of which are illustrated in FIG 3 (a,b,c,d), usually has approximately 32 turns of relatively thick wire gauge (eg. 0.75). Hence, at or near stall armature currents that are above the current rating of the supply (battery, solar cell or other similar supplies) may result (typically substantially greater than 110% of the battery's current rating) due to the reduced back electro motive force (emf) effects. Accordingly, this can rapidly discharge the battery, or reduce the effectiveness of the supply. Furthermore, it may also damage the supply.
Referring to FIG 3 (a,b,c,d) at stall the current flowing in the armature is approximately 20 amps (which may damage the motor). The voltage (line V) has dropped from 10 Volts (no load) to 4 volts at stall this being a 60% reduction in the voltage supplied to the motor. In contrast the results of FIG 7 (a,b,c,d) show that the reduction is from 24 Volts to 19 Volts, this being a reduction of 21 %.
Analysis of the results illustrates that when the voltage is reduced the current increases which can result in battery damage or unduly rapid discharge of the battery. Accordingly, motor designers and manufacturers have primarily relied upon improving battery technology (or
SUBSTTTUTE SHEET (Rule 26) solar cell technology) and have not addressed the issue of increasing the number of turns to decrease the voltage reduction under load whilst providing a motor with suitable torque characteristics. This increase in the number of turns reduces the current drain from the supply and therefore it is desirable but not essential to operate below the supply's current rating when the motor is at or near stall (a preferable range is between 110% to 65% of the supply's current rating).
In addition to improving the performance of the motor the increase in the number of turns preferably reduces the possibility of damage occurring to the supply. Accordingly a preferable feature is that the resistance across supply is at least 20% of that of the internal resistance of the supply. For example, if the supply is a Nickel Cadmium battery of 250 milli Ohms per cell then for a 24 volt battery the internal resistance is 6 Ohms, therefore preferably the resistance of the armature should be at least 1.2 Ohms.
As can be seen from the results, the characteristics (even when taking into account gearing) for high turns per armature pole with smaller wire gauge provides an improved performance, taking into account the current required to achieve a specific torque, over the standard type of motor of FIG 3 (a, b,c,d). Further the results for the
Johnson 50274 show (FIG 18) that at approximately 100 to 110 turns per pole of 0.34 wire gauge an optimum occurs for a required torque output (note a different optimum number of turns may result for a different permanent magnet motor). Hence, upon deciding upon a required torque output and a wire gauge then the optimum number of turns can be determined by non inventive experimentation. However, it should be noted that the number of turns is limited by the physical dimensions of the armature and air gap.
As shown by the results of the FIGs (especially FIGs 3b, 4b, 5b, 6b and 7b) the motor under high loads (or at stall) is magnetically saturated. That is it is operating above the knee point in the area of the magnetization curve known as the non linear portion of the curve. A
SUBSTTTUTE SHEET (Rule 26) standard theoretical magnetization curve is illustrated in FIG. 19. This shows the three commonly known parts of the magnetization curve: the instep, knee point and the non linear portion. The flux density limit (saturation) of Gauss is shown by Bs and the non linear portion can be approximately defined by Frohlic's equation:
B-H = H/(a + bH); where a is the "hardness" constant and is a measure of the value of H necessary to attain a given fraction of saturation; b= 1/Bs; and H has its known meaning to a non-inventive person skilled in the art. Hence, referring to the results, in particular FIGs 3b, 4b, 5b,
6b and 7b, it is apparent that the motor's performance improves under load when the armature at stall has a flux density within the non linear portion of the magnetization curve. For instance in FIG 5b when the motor is under stall conditions the non linear portion of the magnetization curve NL=280 Gs, and the portion not attributable to NL is 475. Hence, the total Gauss is 288 + 475 = 763 and therefore the percentage of flux density attributable to non linear portion of the magnetization curve (288/763) x 100 = 37% of the total flux density of the coils and core. Similarly, in FIG 3b this virtually 0%, in FIG 6b this is 45%, FIG 7b this is 47%). The increased Gauss attributable to non linear portion of the magnetization curve results from the combination of the number of turns and the current therethrough. Accordingly, by increasing the number of turns of the armature coils this increase in Gauss can result. However, there is a limit to this as shown in FIG 13b which shows a reduced Gauss at stall.
As noted above (in particular FIG 18) at approximately 100 to 110 turns per pole of 0.34 wire gauge an optimum occurs for a required torque output for the Johnson 50274 (note a different optimum number of turns may result for a different permanent magnet motor). To achieve this optimum the flux density of the armature's magnetic field (or fields) is substantially identical to the flux density of the permanent magnetic field or fields when the motor is at stall. For instance, when considering the
SUBSTTTUTE SHEET (Rule 26) 105 turns per pole armature the flux density at stall is 860 Gauss (see FIG 6b) and for the 110 turns per pole armature (see FIG 7b) the flux density at stall is 900 Gauss. The Flux density (useful flux) of the permanent magnet was measured to be 900 Gauss (see FIG 21 ). Hence, when comparing the results as illustrated in FIG 18, and the corresponding Gauss measurements, it is apparent that there is an optimum in the motor's performance. This occurs when flux density of the armature's magnetic field (or fields) is substantially identical to the flux density of the permanent magnetic field or fields when the motor is at stall.
Although the optimum is preferable an improved motor performance can be achieved when the the substantially identical matching is not accurately achieved but is within specified limits. These limits being preferably no greater than a 20% difference. Thus, the results conducted on the Johnson 50274 D.C. permanent magnet motor illustate this difference (for this motor) is 180 Gauss, therefore when the armature's flux density is below 720 Gauss or above 1080 Gauss there is a considerable reduction in the motor's performance. For example, for the 125 turn armature the Gauss at stall is 998 (11 % difference) and provides an improved performance over what has perviously been known. Similarly, the 100 turn armature has a Gauss at stall of 763 (15% difference) and provides an improved performance over what has perviously been known. Terpolating these results it is estimated that at approximately 20% difference the improvements over previously known D.C. permanent magnet motors is not substantially significant.
The values of flux densisty and the corresponding percentage difference values preferably relate to the useful flux as illustrated in FIG 21. Furthermore, the above results were obtained by using the circuit as illustrated in FIG. 20. it should be noted that the Torque measurements were taken with the same Torque meter and therefore any errors in the accuracy of this meter are common to all the results. To emulate the supply (battery, solar cell or otherwise) two variacs VRI and VR2 were used to model the internal resistance of the supply. The ammeter Am measured the armature current la, the Torque was measured with the Torque meter Tm and the tachometer Rm measured the speed of the motor's shaft under different loads from free running to stall.
In view of the above there is a range of number of windings at a given gauge for a given motor that will result in an improved performance. This range may vary depending upon the specific materials, dimensions and shape of the motor's component parts. The results conducted thus far, when terpolated, indicate that when the percentage of flux density attributable to non linear portion of the magnetization curve is above 0% (and preferably at least 20%) the characteristics of the motor improves.
Referring to FIG. 22 there is illustrated a self contained power tool 1 having a push button switch 3, ten 1.2 volt rechargeable batteries 12, recharged via the recharging socket 4. The motor 5 drives the gearbox 6 which turns the chuck 7. The chuck is attached to a spindle and the chuck can be removed from the spindle such that a screwdriver means can be inserted directly into the spindle as opposed to the screwdriver means being gripped by the chuck 7. The push button switch 3 is adapted to move within the slot 34. When the push button switch 3 is in the centre of the slot 34, as shown in FIG. 22, no power can be applied to the motor 5 by depressing the push button switch 3. However, when the push button switch 3 is in its top position within the slot 34 the motor 5 turns in a clockwise direction. Alternatively, when the push button switch 3 is in the down position within the slot 34 the motor 5 will turn in an anticlockwise direction.
Referring to FIG. 23 the self contained power tool 1 is shown inserted in the attachment means 2. To assist in correct location there are two location guides 11 and a jack plug 10 which, when inserted, modifies the circuitry of the self contained power tool 1. When inserting the self contained power tool 1 the interlock 16 is pulled downwards by
SUBSTITUTE SHEET (Rule 26; force acting upon the spring 19 which moves the pivotable arm 14 which therefore acts upon the shaft 15 to move the interlock 16. Hence, when the self contained power tool 1 is inserted into the attachment means 2 pressure can be removed from the spring 19 which therefore allows the interlock 16 to be located in the slot 34. The attachment means further has a hollow handle 18 within which are located ten 1.2 volt batteries 17 that are adapted to be recharged via the socket 35.
Referring to FIG. 24 and FIG. 25 there is illustrated the switch mechanism and the electrical circuitry of both the self contained power tool 1 and attachment means 2. The turning handle 8 is adapted to rotate the inner body 9 such that push button switch 3 will be activated by either the cam 32 or cam 33 of the interlock 16. This therefore connects the spring means 24 to the positive of the battery 12. Furthermore, both the spring means 23 and 24 are mechanically connected to the inner body 9, therefore when the turning handle 8 is pushed clockwise the spring means 23 makes contact with the pin 22 and the spring means 24 makes contact with the pin 21. Note if the turning handle 8 was pushed in an anticlockwise direction then the spring means 23 would be connected to pin 21 and the spring means 24 would be connected to the pin 22. This provides a simple mechanism for reversing the direction of the motor 5 which is electrically connected to the pins 21 and 22.
Upon the turning handle 8 being pushed either clockwise or anticlockwise the push button switch 3 will close its contacts by either being activated by the cam 32 or the cam 33. However, the motor 5 will not turn until the switch 13, located upon the handle 18, is closed.
The switch 13 is inserted into the circuit by the circuit modification means 20 which includes a jack plug 10 having an inner conductor 31 surrounded by an insulator 30 and an outer conductor 29. Before the portable power tool 1 is inserted into the attachment means 2 an electrical circuit is completed at the circuit modification means 20 by the cylindrical conductor 26 making contact with the cylindrical conducting piston 27 which is spring loaded by the conducting spring 28. Thus, an electrical circuit is made via the negative of the battery 12 through the conducting spring 28, through the cylindrical conducting piston 27 and the cylindrical conductor 26 to the spring means 23.
When the jack plug 10 is inserted into the circuit modification means 20 the cylindrical conducting piston 27 is pushed away from the cylindrical conductor 26 which therefore breaks their direct electrical contact between the negative of battery 12 and the spring means 23. The outer conductor 29 of the jack plug 10 is connected to the switch 13. The other side of the switch 13 is connected to the negative of the battery 17 and the positive of the battery 17 is connected to the inner conductor 31 of jack plug 10. When the jack plug 10 is inserted the circuit modification means 20 the inner conductor 31 makes electrical contact with the cylindrical conducting piston 27 and the outer conductor 29 makes contact with the cylindrical conductor 26. The insertion of the jack plug 10 reconfigures the circuit such that the battery 12 and battery 17 are in series and power can only be supplied to the motor when both the contacts of the push button 3 and switch 13 are closed.
The motor preferably embodies at least one of the improvements described herein for direct current electric motors. The particular forms described above with reference to FIGs 1 to 21 may be especially mentioned. Attention is also directed to the associated discussions of "Theory" and "Results".
A simplified summary of the above is that motors of improved efficiencies can be designed and manufactured by determining an output speed of the motor which is preferably less than the desired application for which the motor is to be used. The output speed is proportional to 1/n, hence this determines the number of windings (turns) per armature pole-piece. Once n is determined it is preferable to select the thickest wire gauge that can be wound upon the armature. However, there are constraints upon the maxuimum thickness of wire gauge, these are basically that the Force (or Torque) is proportional to n.l (until
SUBSTTTUTE SHEET (Rule 26) magnetic saturation ovccurs). Thus, consideration of magnetic saturation and demands upon power supplies should be taken into account.
When considering devices such as battery powered hand held power drills and screw divers having which are commonly sold with motors having typically between 12 and 22 turns per armature pole-piece. Efficiencies at mid-range loads are typically less than 25% for these tools. By changing the turns to 125 and using the thickest wire that can fit on the armatures, we have increased this efficiency to approximately 60%. This is attributable to the improved match between the number of windings and rl and r2.
In general, the more turns per pole-piece will improve the motors efficiency. This is basically because the generated magnetic field is proportional to the number of turns for a given current. That is the more turns, the smaller the battery current drain required to produce a given torque. Also, the smaller this current, the smaller the power inefficiency losses from the internal resistance of the battery and resistive losses of the brushes, armature and conductors feeding the motor via the switch. However, there is a limit to the number of turns providing improved efficiencies. This related to the insulation of the wires in which the insulation affects the flux within the armature and therefore there is a range of turns which are suitable for a specific application.
When considering a battery powered motor in which the battery has a low resistance per cell (as is the case with Nickel Cadmium batteries which have typically less than 250 milli Ohms per cell) and the motor stalls or is so loaded that the r.p.m. is very low, the current drawn from the batteries may cause battery damage. In contrast, with a 125 or more turn motor, using relatively thin wire of approximately less than 0.4mm gauge, the resistance of the armature windings is several ohms and the near stalled current will not cause much heating or battery stress in practice owing to reasonable currents of a few amperes.
Using the invention disclosed in this specification with the assistance of FIGS. 22-25, there is illustrated a multi purpose tool which can be powered by either a 12 volt battery supply or 24 volt battery supply. It should be noted that other battery voltages can be used and variations of the embodiments described can be substituted without diverting from the invention. Throughout this specification various indications have been given to the scope of the invention but the invention is not limited to any one of these indications.

Claims

WHAT IS CLAIMED IS:
1. An arrangement including: a permanent magnet direct current motor; and a battery means for providing electrical power to the permanent magnet direct current motor, wherein the resistance of the permanent magnet direct current motor is substantially greater than that of the internal resistance of the battery means.
2. An arrangement including: a permanent magnet direct current motor; and a battery means for providing electrical power to the permanent magnet direct current motor, wherein the resistance across the battery means is substantially greater than that of the internal resistance of the battery means.
3. An arrangement including: a permanent magnet direct current motor; and a battery means for providing electrical power to the permanent magnet direct current motor, the battery means having a low internal resistance whereby it is possible to damage the battery means by drawing excessive currents, wherein the arrangement is adapted such that the current drawn by the motor will not cause damage to occur to the battery means when the motor is in a stalled condition for a substantial period of time.
4. An arrangement including: a permanent magnet direct current motor; and a battery means for providing electrical power to the permanent magnet direct current motor, wherein the total circuit
SUBSTTTUTE SHEET (Rule 26) resistance of the battery means and permanent magnet direct current motor is such that the magnetic saturation of at least one armature pole- piece is saturated to a maximum limit when the permanent magnet direct current motor's output shaft is stalled.
5. An arrangement including: a permanent magnet direct current motor; a battery means for providing electrical power to the permanent magnet direct current motor; and, a current limiting means adapted to limit the current flowing from the battery to the armature of the permanent magnet direct current motor, wherein the current limiting means limits the current so that the magnetic saturation of at least one armature pole-piece is saturated to a maximum limit when the permanent magnet direct current motor's output shaft is stalled.
6. A direct current permanent magnet motor wound such that flux produced by an electrical current, supplied by a battery means, flowing pole of the motor's armature and interacting with the permanent magnet flux does not exceed that of the flux provided by the permanent magnetic field or fields.
7. A permanent magnet direct current motor having an efficiency of greater than about 40% when the motor drives a variable load over at least about 15% of the total output torque range at the output of the motor, wherein the efficiency is calculated by: efficiency -^output power / input power x 100 where output power is the power at the output of the motor's shaft and input power is the input power to the motor.
8. An arrangement including: a battery means having an output voltage of at least about 5 volts; and a permanent magnet direct current motor electrically connected to the battery means, the permanent magnet direct current motor having an efficiency of greater than about 40% when the motor drives a variable load over at least 15% of the total output torque range at the output of the motor, wherein the efficiency is calculated by: efficiency-sjoutput power / input power x 100 where output power is the power at the output of the motor's shaft and input power is the input power to the motor.
9. A permanent magnet direct current motor wound such that each individual coil between two armature commulator segments has more than about 30 turns, for example more than about 35 turns, more particularly more than about 60 turns.
10. An arrangement including: a direct current supply means having an output voltage of at least about 5 volts; and a permanent magnet direct current motor electrically connected to the battery means, the permanent magnet direct current motor being wound such that each individual coil between two armature commutator segments has more than about 30 turns, for example more than about 35 turns, more particularly more than about 60 turns.
11. An electrical motor comprising two parts, these being adapted to be caused to have relatively reacting forces between the respective parts upon the supplying of electrical current into at least a first one of the parts to effect a magnetic field to react magnetically with the other of the parts, wherein the first one of the parts includes a plurality of coils of electrically conducting insulated wire around a former, and a second one of the parts has a magnetic field adapted to interact with a field from the coils, the number of turns of windings around the former for each of the coils on the first one of the parts being substantially greater than the number of turns that would conventionally exist hitherto in respect of motors which are otherwise the same.
12. An electric motor having a permanent magnetic field or fields and a plurality of coils wound upon a former or formers to provide an electromagnetic field for providing a relative mechanical movement between the permanent magnetic field and the electromagnetic field, wherein the coils for providing the electromagnetic field are wound such that when the motor's rated voltage is applied thereto the electromagnetic field and its associated former are substantially magnetically saturated under stall conditions of the motor.
13. An electric motor having a permanent magnetic field or fields and a plurality of coils wound upon a former or formers to provide an electromagnetic field for effecting a relative mechanical movement between the permanent magnetic field and the electromagnetic field, wherein the coils for providing the electromagnetic field are wound such that when the motor's rated voltage is applied thereto the electromagnetic field and its associated former are within the non-linear portion of their magnetization curve when the motor is under stall conditions such that the amount of flux density attributable to the non-linear portion is above 0%, for example at least about 20%, of the total flux density of the electromagnetic field and its associated former.
14. An arrangement including: a direct current supply means electrically connected to an electric motor having a permanent magnetic field or fields and a plurality of coils wound upon a former or formers to provide an electromagnetic field for effecting a relative mechanical movement between the permanent
SUBSTTTUTE SHEET (Rule 26) magnetic field and the electromagnetic field, wherein the coils for providing the electromagnetic field are wound such that under stall conditions the current flowing from the direct current supply and into the coils is such that the amount of flux density attributable to the non-linear 5 portion of the coils' and core's magnetization curve is above 0%, for example at least about 20%, of the total flux density of the coils and core.
15. An electric motor comprising a yoke and an armature, the armature being adapted to be supplied with direct electrical current o through a commutator to each of a plurality of poles, the armature having a magnetically permeable core providing a former for each of the plurality of poles for the armature, there being a coil wound around the former in respect to each pole, the arrangement being characterised in that the number of turns in the windings of each coil for a respective pole, their 5 location and other characteristics are such that there will be effected, at stall, a magnetic field which is substantially greater than required when supplied with a current supply at the motor's rated voltage such that the magnetic field is in the non-linear portion of the magnetization curve of the core acting as the former. 0
16. A motor according to claim 9, 11 , 12, 13 or 15, wherein the winding of each coil is formed by wire having a gauge which offers substantial resistance, for example greater than about 1.2 ohms, to current flowing therethrough at the motor's rated voltage.
17. A method of operating an electrical motor which comprises effecting a connection to the motor of a current source at the motor's rated voltage and such that there is thereby caused a magnetic inductance with respect to each coil that substantially exceeds that which is required to reach the non-linear portion of the magnetization curve of the core.
SUBSTTTUTE SHEET (Rule 26)
18. An arrangement including: a permanent magnet direct current motor; and a direct current supply means for providing electrical power to the permanent magnet direct current motor, wherein the resistance of the motor when connected across the direct current supply means is no less than about 20% of the internal resistance of the direct current supply means.
19. An arrangement including: a permanent magnet direct current motor; and a direct current supply means for providing electrical power to the permanent magnet direct current motor, the direct current supply means having a low internal resistance whereby it is possible to damage the direct current supply means by drawing excessive currents, wherein the arrangement is adapted such that the current drawn by the motor will not cause damage to occur to the direct current supply means when the motor is in a stalled condition for a substantial period of time.
20. An arrangement including: a permanent magnet direct current motor; and a direct current supply means for providing electrical power to the permanent magnet direct current motor, wherein the windings of the armature of the motor are such that under stall conditions the current flowing in the armature does not exceed the current rating of the battery.
21. An arrangement including: a permanent magnet direct current motor; and a direct current supply means for providing electrical power to the permanent magnet direct current motor, wherein the windings of the armature of the motor are such that under stall conditions the current flowing in the armature is in the range of about 65% to 110% of the current rating of the battery.
SUBSTTTUTE SHEET (Rule 26}
22. An electric motor having a permanent magnetic field or fields and a plurality of coils wound upon a former or formers to provide an electromagnetic field for providing a relative mechanical movement between the permanent magnetic field and the electromagnetic field, wherein the coils for providing the electromagnetic field are wound such that when the motor's rated voltage is applied thereto the flux density of the electromagnetic field and its associated former are substantially identical to the flux density of the permanent magnetic field or fields when the motor is stalled.
23. An arrangement including: a direct current supply means electrically connected to an electric motor having a permanent magnetic field or fields and a plurality of coils wound upon a former or formers to provide an electromagnetic field for effecting a relative mechanical movement between the permanent magnetic field and the electromagnetic field, wherein the coils for providing the electromagnetic field are wound such that the current flowing from the direct current supply and into the coils is such that the flux density of the electromagnetic field and its associated former have a similar value of flux density to that of the permanent magnetic field or fields when the motor is stalled.
24. An arrangement including: a permanent magnet direct current motor; and a direct current supply means for providing electrical power to the permanent magnet direct current motor, wherein the flux density of the armature has a similar value of flux density to that of the permanent magnetic field or fields when the motor stalled.
25. A portable power tool including: a first direct current storage means adapted to be electrically connected to a direct current motor by a switch means; and
SUBSTTTUTE SHEET (Rule 26) a circuit modification adapted to allow a second direct current storage means to be inserted in series with the first direct current storage means.
26. An attachment means adapted to engage a power tool having a first direct current storage means, the attachment means having a second direct current storage means adapted to be inserted in series with the first direct current storage means.
27. A portable power tool arrangement including: a power tool having a first direct current storage means adapted to be electrically connected to a direct current motor by a first switch means; a second direct current storage means contained within an attachment means, the attachment means engaging the power tool such . that the second direct current storage means is inserted in series with the first direct current storage means, wherein the attachment means is adapted to disengage the power tool such that when disengaged the second direct current storage means is removed from being in series with the first direct current storage means.
PCT/AU1994/000257 1993-05-20 1994-05-19 Battery powered permanent magnet direct current motor WO1994028613A1 (en)

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AUPL890293 1993-05-20
AUPL890393 1993-05-20
AUPM224293 1993-11-08
PCT/GB1993/002291 WO1994011941A1 (en) 1992-11-06 1993-11-08 An electrical motor
PCT/GB1993/002293 WO1994011162A1 (en) 1992-11-06 1993-11-08 A power tool
AUPM224193 1993-11-08
US17091393A 1993-12-17 1993-12-17

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0111740A1 (en) * 1982-11-13 1984-06-27 Hitachi, Ltd. Permanent magnet field type DC machine
EP0237935A2 (en) * 1986-03-17 1987-09-23 Hitachi, Ltd. Permanent magnet field DC machine
EP0312290A2 (en) * 1987-10-13 1989-04-19 Magneti Marelli Electrical Limited Permanent magnet rotary dynamo electric machines
EP0339584A1 (en) * 1988-04-25 1989-11-02 Hitachi, Ltd. DC rotary electric machine of permanent magnet field type
US5175460A (en) * 1991-01-29 1992-12-29 Asmo Co., Ltd. Flat yoke type DC machine

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0111740A1 (en) * 1982-11-13 1984-06-27 Hitachi, Ltd. Permanent magnet field type DC machine
EP0237935A2 (en) * 1986-03-17 1987-09-23 Hitachi, Ltd. Permanent magnet field DC machine
EP0312290A2 (en) * 1987-10-13 1989-04-19 Magneti Marelli Electrical Limited Permanent magnet rotary dynamo electric machines
EP0339584A1 (en) * 1988-04-25 1989-11-02 Hitachi, Ltd. DC rotary electric machine of permanent magnet field type
US5175460A (en) * 1991-01-29 1992-12-29 Asmo Co., Ltd. Flat yoke type DC machine

Non-Patent Citations (4)

* Cited by examiner, † Cited by third party
Title
(JAMES R. IRELAND), "Ceramic Permanent Magnet Motors", Published 1968, by MCGRAW HILL BOOK COMPANY (NEW YORK), pages 38-47, 52-56. *
(M.G. SAY et al.), "Direct Current Machines", Published 1980, by PITMAN PUBLISHING LTD (LONDON), pages 345-348. *
(T. KENJO et al.), "Permanent Magnet and Brushless DC Motors", Published 1985, by OXFORD UNIVERSITY PRESS (OXFORD et al.), pages 25-31. *
PROCEEDINGS OF THE 34TH INTERNATIONAL POWER SOURCES SYMPOSIUM, 25-28 June 1990, Sponsored by the Industry Applications Society of the Institute of Electrial and Electronics Engineers, HARVEY N. SEIGER, "Lithium/Cobalt Sulfide Pulse Power Battery", pages 334-338. *

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