WO2008066061A1

WO2008066061A1 - Brushless motor

Info

Publication number: WO2008066061A1
Application number: PCT/JP2007/072908
Authority: WO
Inventors: Noboru Niguchi; Hirohide Inayama; Naotake Kanda; Masaru Horikawa
Original assignee: Jtekt Corporation
Priority date: 2006-11-30
Filing date: 2007-11-28
Publication date: 2008-06-05
Also published as: JP2008141803A

Abstract

A brushless motor comprises a rotor including ten permanent magnets, and a stator including twelve teeth (or salient poles) having twelve wires individually wound thereon. Here, the twelve wires include such two wire groups for each phase as are composed of wires of the same number and connected in series and as are so connected in parallel that their individual induced voltages are substantially identical in magnitude and phase. These connections can suppress the generation of a circulating current, and the constitution of ten poles and twelve slots can reduce the impedance of the motor, thereby to deter and suppress the loss torque in the brushless motor and to suppress the cogging.

Description

Specification

Brushless motor

Technical field

TECHNICAL FIELD [0001] The present invention relates to a brushless motor including a permanent magnet for forming a field, and more particularly to a brushless motor used in an electric power steering apparatus that applies a steering assist force to a steering mechanism of a vehicle.

Background art

Conventionally, there has been used an electric power steering device that gives a steering assist force to a steering mechanism by driving an electric motor such as a brushless motor in accordance with a steering torque applied to a steering wheel (steering wheel) by a driver! / RU

[0003] A brushless motor normally used in such an electric power steering apparatus has windings.

Permanent magnet electric motors having a stator (stator) provided with (coils) and a rotor (rotor) provided with permanent magnets, many of which are driven by three-phase power!

[0004] Further, a plurality of stator windings are usually provided for each phase. These windings are typically connected in series for each phase. For example, the number of poles of a permanent magnet (hereinafter simply referred to as “number of poles!”) Is 8, and the number of salient poles (teeth) provided on the stator (stator) (this number is the gap between the salient poles) In the conventional electric motor used in the electric power steering apparatus with 9), three windings are connected in series for each phase. (See JP 2001-275325 A).

[0005] However, in the configuration in which the windings are connected in series as in the above-described conventional electric motor, since the connecting wire becomes long, the impedance increases, and as a result, the copper loss increases. Therefore, there is a conventional electric motor in which a plurality of windings are connected in parallel for each phase. FIG. 6 is a circuit diagram showing the connection of the U-phase winding in the conventional 10-pole 12-slot electric motor with the windings connected in this way. As shown in FIG. 6, the first to fourth coils 90;! To 904 as four U-phase windings are connected to the U-phase terminal 910 at one end and the other end is connected to the other end. It is connected to the neutral point terminal 920, which is the neutral point of each phase.

Disclosure of the invention Problems to be solved by the invention

[0006] However, when parallel connections are made as shown in FIG. 6, a loss (loss torque) that does not occur when connecting in series occurs. That is, when the induced voltage in the first coil 901 is Ec l = sin (Θ), the induced voltages Ec2 to Ec4 in the coins 902 to 904 from the second force to the fourth are expressed by the following equations (1) to (1) to It can be expressed as (3).

Ec2 = sin (Θ— π / 6)… hi)

Ec3 = sin (θ) '' (2)

Ec4 = sin (Θ— π / 6)…)

[0007] As described above, the phase shift of π / 6 is caused between the first coinore 901 and the second coinore 902 and between the third coinole 903 and the fourth coil 904, respectively, in the induced voltage. Therefore, currents II and 12 (that is, circulating currents) shown in FIG. 6 flow between these coils. Such circulating current generates a loss torque of the electric motor. As a result, there is a decrease in operational feeling such as deterioration of steering wheel return in the electric power steering apparatus.

[0008] In addition, when the number of poles of the permanent magnet is increased as described above, the width of the salient pole (tooth) is relatively narrow, so that its rigidity is lowered and noise and vibration of the electric motor may be generated. . Focusing only on this point, it is preferable to increase the width of the salient pole (teeth), but generally the inductance of the electric motor increases as the magnetic flux density of the salient pole (tooth) decreases. A motor with a large inductance has a large copper loss, and a copper loss causes the electric motor to generate heat and generate a loss torque. As in the case where the circulating current is generated, an operation such as lack of assist force in the electric power steering device results. The feeling is reduced.

Accordingly, an object of the present invention is to provide a brushless motor that suppresses or suppresses generation of loss torque without connecting windings of respective phases in series, and an electric power steering apparatus including the brushless motor.

Means for solving the problem

[0010] A first invention is an annular stator that includes a plurality of windings that are driven by three-phase power, and that is arranged inside the stator and is rotatable with respect to the stator. And a rotor including a permanent magnet that forms a plurality of poles in the circumferential direction. And

The stator is

The plurality of windings are provided one by one, and a plurality of teeth portions of the same size disposed at equal intervals along the circumferential direction so as to protrude toward the rotor,

An annular yoke portion to which the plurality of teeth portions are coupled;

Including

The plurality of windings are a plurality of winding groups composed of the same number of windings connected in series, and the plurality of winding groups selected so that the magnitudes and phases of the induced voltages substantially coincide with each other. Connected in parallel and included for each phase,

The number of poles of the permanent magnet is smaller than the number of the tooth portions provided with a multiple of 3 that is 9 or more and more than 2/3 of the number of the tooth portions.

[0011] The second invention is the first invention,

The plurality of winding groups are provided in the same number as one of the divisors of the absolute value of the difference between the number of the tooth portions and the number of poles formed by the permanent magnet.

[0012] A third invention is the first invention,

Twelve teeth are provided,

The permanent magnet forms 10 poles.

[0013] A fourth invention comprises the brushless motor according to the first invention,

Thus, a steering assist force is applied to the steering mechanism of the vehicle.

The invention's effect

[0014] According to the first aspect of the invention, the number of poles of the permanent magnet is smaller than the number of teeth portions, whereby the impedance can be reduced, and the number of poles of the permanent magnet is less than 2/3 of the number of teeth portions. In addition, cogging can be suppressed. In addition, the plurality of windings is a winding group composed of the same number of windings connected in series, and the plurality of winding groups selected so that the magnitudes and phases of the respective induced voltages substantially coincide with each other. By connecting and including each phase, the generation of circulating current can be suppressed. As described above, the generation of loss torque can be suppressed or suppressed, and cogging can be suppressed. [0015] According to the second aspect of the present invention, since the number of winding groups is the same as one of the divisors of I (the number of teeth and the number of poles of the permanent magnet) I, the generation of circulating current is suppressed. The generation of loss torque can be suppressed or suppressed.

[0016] According to the third aspect of the invention, in a practical brushless motor, in particular, the generation of loss torque can be suppressed or suppressed, and cogging can be suppressed.

[0017] According to the fourth aspect of the invention, an electric power steering apparatus including a brushless motor that exhibits the same effect as the first aspect of the invention can be provided.

Brief Description of Drawings

FIG. 1 is a schematic diagram showing a configuration of an electric power steering apparatus according to an embodiment of the present invention together with a vehicle configuration related thereto.

FIG. 2 is a vertical sectional view with respect to the rotation axis of the brushless motor in the embodiment.

FIG. 3 is a circuit diagram showing connection of U-phase windings in the brushless motor in the embodiment.

FIG. 4 is an enlarged view of a main part of a yoke and teeth of a brushless motor in the embodiment.

FIG. 5 is a diagram showing a combination of the number of slots and the number of poles suitable for suppressing cogging while suppressing or suppressing the generation of loss torque in the embodiment.

FIG. 6 is a circuit diagram showing U-phase winding connections in a conventional 10-pole 12-slot brushless motor.

Explanation of symbols

2 ... Rudder angle sensor

3… Torque sensor

4… Vehicle speed sensor

5… Electronic control unit

6… Brushless motor

61… Stator

65… Rotor

66… Motor shaft 611a ~ 6111… Teeth

612a ~ 6121 ... Winding

613 ... υ phase terminal

614

615 ... York

651a ~ 651j… Permanent magnet

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

<1. Overall configuration>

FIG. 1 is a schematic view showing a configuration of an electric power steering apparatus according to an embodiment of the present invention, together with a vehicle configuration related thereto. This electric power steering apparatus has one end fixed to a steering wheel (steering wheel) 100 as an operating means for steering, a pinion mechanism 104, a steering angle sensor 2 for detecting a steering angle indicating a rotational position of the steering wheel 100, A torque sensor 3 for detecting a steering torque applied to the steering shaft 102 by the operation of the handle 100, a brushless motor 6 for generating a steering assist force for reducing a driver's load in the steering operation (steering operation), and Power is supplied from the reduction gear 7 that transmits steering assist force to the steering shaft 102 and the in-vehicle battery 8 through the revolution switch 9, and sensor signals from the steering angle sensor 2, torque sensor 3, and vehicle speed sensor 4 are received. And an electronic control unit (ECU) 5 for controlling the drive of the brushless motor 6 based on the above-mentioned number.

[0021] When the driver operates the steering wheel 100 in a vehicle equipped with such an electric power steering device, the steering torque by the operation is detected by the torque sensor 3, and the steering angle is detected by the steering angle sensor 2. Then, the brushless motor 6 is driven by the ECU 5 based on the detected steering torque and steering angle and the vehicle speed detected by the vehicle speed sensor 4. As a result, the brushless motor 6 generates a steering assist force, and this steering assist force is applied to the steering shaft 102 via the reduction gear 7, thereby reducing the load on the driver during the steering operation. In other words, the steering torque applied by the steering wheel operation and the The sum S with the torque by the steering assist force generated by the lacyless motor 6 and the output torque are given to the rack and pinion mechanism 104 via the steering shaft 102. Thus, when the pinion shaft rotates, the rotation is converted into the reciprocating motion of the rack shaft by the rack and pinion mechanism 104. Both ends of the rack shaft are connected to a wheel 108 via a connecting member 106 composed of a tie rod and a knuckle arm, and the direction of the wheel 108 changes according to the reciprocating motion of the rack shaft.

[0022] <2. Configuration of brushless motor>

FIG. 2 is a vertical sectional view with respect to the rotation axis of the brushless motor 6. As shown in FIG. 2, the brushless motor 6 has a rotor (rotor) 65 that rotates around the rotation axis of the motor shaft 66 and a narrow gap (air gap) that surrounds the rotor 65. And a stator (stator) 61 provided.

[0023] The rotor 65 has ten poles in the circumferential direction by arranging ten permanent magnets 651a to 651j in the circumferential direction. These permanent magnets 651a to 651j are rare earth neodymium magnets that are magnetized in the radial direction (perpendicular to the rotation axis), and are arranged so that N and S poles are alternately arranged in the circumferential direction. It has been. As described above, the number of poles of the permanent magnet is simply called “number of poles”.

Stator 61 includes a cylindrical yoke 615 and twelve teeth (saliency poles) 611a to 6111 that are provided to protrude from the inner peripheral surface of the yoke 615 toward the motor shaft 66. Corresponding windings 612a to 6121 are wound around these teeth 611a to 6111, and a predetermined current flows through these windings, so that the stator 61 has 12 poles in the circumferential direction. It becomes a state. As described above, the number of teeth (that is, the number of windings) corresponding to the number of poles of the stator 61 is referred to as the “slot number”. Therefore, the brushless motor 6 is a 10-pole 12-slot motor and has a feature that the number of slots is larger than the number of poles.

[0025] Here, the windings 612a to 6121 are suitably used as a three-phase power source (not shown) so that four sets of four windings are driven by U-phase, V-phase, or W-phase power. It is connected. Here, as will be described later, the Y connection method is adopted. The three-phase power source includes, for example, a pulse width modulation (PWM) that is a voltage signal with a pulse width controlled corresponding to each phase. The rotation of the brushless motor 6 is controlled by outputting a signal. Such a winding configuration is well known except for the connection (connection relationship) of each phase of the winding, which is devised to suppress or suppress the generation of loss torque. Details and explanations other than the above are omitted, and the wire connections unique to the brushless motor 6 will be described below with reference to FIG. The three sets of windings corresponding to the three phases are Y-connected as described above, and each set of windings is called a U-phase winding, a V-phase winding, and a W-phase winding. .

FIG. 3 is a circuit diagram showing the connection of the U-phase winding in the brushless motor 6 having 10 poles and 12 slots. As shown in Fig. 3, out of the four first to fourth springs 612a to 612d that function as U-phase windings, they are connected to the first and second springs 612a and 612b. The third and fourth windings 612c and 612d are connected in series, and the two windings connected in series are connected in parallel. In addition, one end of each of the first and third windings 61 2a and 612c is connected to a neutral point terminal 614 that is a neutral point of each phase, and the second and fourth windings 612b and 612d One end is connected to U-phase terminal 613. By connecting the windings in this way, the impedance can be made smaller than the conventional connection in which all the windings are connected in series, and as a result, the copper loss can be reduced.

[0027] Even if the wiring is made in this way, loss torque due to circulating current does not occur. That is, when the induced voltage in the first winding 612a is El = sin (Θ), the induced voltages E2 to E4 in the second to fourth windings 612b to 612d are expressed by the following equations (4) to (6) It can be expressed as

E2 = sin (Θ— π / 6) (4)

E3 = sin (θ)

E4 = sin (θ— π / 6) (6)

[0028] Therefore, the magnitude and phase of the voltage (E 1 + E2) across the first and second windings 612a and 612b connected in series are the same as the third and fourth windings connected in series. Since the voltage (E3 + E4) across the lines 612c and 612d matches the magnitude and phase, there will be no circulating current between these windings. Therefore, the brushless motor is not lost due to the circulating current, so that it is possible to prevent a decrease in operation feeling such as a deterioration of the steering wheel return in the electric power steering apparatus. [0029] Next, referring to FIG. 4, the number of poles is smaller than the number of slots! /, And the details of the windings are that a brushless motor has a smaller impedance than a brushless motor with more poles than the number of slots. This will be described together with the configuration.

FIG. 4 is an enlarged view of main portions of the yoke and teeth in the brushless motor. As shown in FIG. 4, for example, a winding 612a is wound around the teeth 61la. More specifically, the winding 612a is wound around a cylindrical bobbin having a jaw at the bottom, a winding restraining plate is press-fitted into the tip of the bobbin, and the bobbin around which the winding 612a is wound is teethed. The winding 612a is wound around the teeth 611a by inserting it into 611a. In this manner, the windings 612a to 6121 are wound around the teeth 611a to 6111. Such a concentrated winding method is also called salient pole winding. In this way, by performing concentrated winding without performing distributed winding that is distributed over a plurality of slots, it is possible to eliminate almost no winding portion that does not form an effective magnetic flux, thereby reducing copper loss.

[0031] As can be seen from FIG. 4, the brushless motor 6 has 10 poles and 12 slots, and the number of poles is smaller than the number of slots, so the density of magnetic flux passing through one tooth is increased. . For this reason, since the magnetic flux density of the teeth increases, the inductance decreases and the impedance decreases. A motor with such a low impedance has a small copper loss, so it is possible to control lost nore due to heat generation.

[0032] However, in order to suppress cogging of the permanent magnet motor (specifically, to reduce the magnitude of cogging torque and its fluctuation range), the least common multiple of the number of slots and the number of poles is increased. It is known that setting a value is effective. In this regard, this brushless motor 6 has 10 poles and 12 slots and the least common multiple is sufficiently large, and therefore can suppress cogging. A combination of the number of slots and the number of poles suitable for suppressing cogging while suppressing or suppressing the occurrence of loss torque will be described with reference to FIG.

FIG. 5 is a diagram showing a combination of the preferred number of poles and number of slots. The X mark shown in Fig. 5 is a combination of the number of poles and the number of slots, which is known to have a high efficiency but is greatly affected by cogging. Specifically, the ratio between the number of poles and the number of slots ( That is, the number of poles: the number of slots) is 2: 3 or 4: 3. In addition, the 〇 mark shown in Fig. 5 This is a combination in a practical brushless motor whose ging is known to be relatively small. Furthermore, the symbol ◎ shown in FIG. 5 represents a combination of the number of poles and the number of slots in the brushless motor 6.

[0034] Referring to FIG. 5, the upper limit and the lower limit of the combination indicated by ◯ are substantially the same as the combination indicated by X. In other words, the number of poles in the combination indicated by a circle is driven by three-phase power, and is less than 4/3, more than 2/3 of the number of slots that is a multiple of 3.

[0035] However, in order to suppress or suppress the occurrence of rostroke due to heat generation by reducing the impedance of the brushless motor, it is preferable to reduce the number of poles rather than the number of slots as described above. The number of poles in the preferred combination taking into account is less than the number of slots greater than 2/3 of the number of slots. If the number of poles and the number of slots are the same, there is no need to consider because the rotor does not rotate.

[0036] Here, a combination of the number of poles and the number of slots capable of suppressing the generation of loss torque due to the circulating current flowing between the windings will be considered. First, when the number of slots is 9 (that is, when the above ratio is 8: 9), when the phase of the induced voltage for one of the three windings in one phase is 0 °, The phase of the induced voltage for the remaining two windings in the phase is 20 ° and + 20 °, respectively. Therefore, all three windings can only be connected in series to prevent circulating currents. When the above ratio is 10: 9, the number of poles is larger than the number of slots, so it is not considered here.

[0037] Next, when the number of slots is 12 (that is, when the above ratio is 10:12), the phase of the induced voltage generated for one of the four windings in one phase is 0 °. Then, the phases of the induced voltages generated for the remaining three windings in the phase are + 30 °, 0 ° and + 30 °, respectively. Therefore, in order to prevent the generation of circulating current, connect all these windings in series or one winding with the above phase 0 ° and one winding with the above phase + 30 °. It can be considered that one set connected in series is connected in parallel with one set connected in series with the remaining windings. The connection connected in parallel is the connection in the brushless motor 6 as shown in FIG. [0038] Subsequently, when the number of slots is 15 (that is, when the ratio is 14:15), the phase of the induced voltage generated for one of the five windings in one phase is 0 °. Then, the phase of the induced voltage generated for the remaining four windings in the phase is + 12 °, -12 °, + 24 ° and -24 °, respectively. Therefore, to prevent the generation of circulating current, all these windings must be connected in series.

[0039] When the number of slots is 21 (that is, when the ratio is 20:21), the phase of the induced voltage generated in one of the seven windings in one phase is 0 °. Then, the phases of the induced voltage generated for the remaining 6 windings in the phase are + 8.6 °, -8.6 °, + 17.1 °,-17.1 °, and +25.7, respectively. And 15.7 °. Therefore, the only way to prevent the generation of circulating current is to connect all these windings in series.

[0040] Thus, the number of winding sets is the same as one of the divisors of the absolute value of the difference between the number of teeth, which is the number of slots, and the number of poles formed by the permanent magnet. Will be provided. That is, in the case of 8 poles and 9 slots, the above divisor is only 1, and the windings are connected in series, that is, in parallel number 1. The same applies to the case of 14 poles and 15 slots and the case of 20 poles and 21 slots. In the case of 10 poles and 12 slots, the above divisors are 1 and 2, and the combinations connected in parallel number 2 all have lower impedance than when they are all connected in series. Therefore, it can be seen that, among the combinations shown in FIG. 5, the combination in which the number of poles employed in the brushless motor 6 is 10 and the number of slots is 12 is extremely suitable for a practical brushless motor.

[0041] <3. Effect>

As described above, in the brushless motor 6, the number of poles of the permanent magnet formed by the 10 permanent magnets 651a to 651j is equal to the number of the 12 windings 612a to 6121! /, 12 The impedance is reduced by being less than the number of teeth 61 la to 6111, and cogging can be suppressed by being more than 2/3 of the number of teeth. In addition, the windings 612a to 6121 are connected in parallel so that the magnitudes and phases of the induced voltages substantially coincide with each other, and the first and second springs 612a and 612b and the third and fourth springs 612c are connected. , 612d, a winding group consisting of the same number of windings connected in direct IJ, and connected in parallel so that the magnitude and phase of each induced voltage are substantially the same. By including groups for each phase, Generation of ring current can be suppressed.

Therefore, the electric power steering apparatus according to this embodiment equipped with the brushless motor 6 in which the generation of the loss torque is suppressed or suppressed and the cogging is suppressed in this manner reduces the operation feeling such as deterioration of the steering wheel return. Can be suppressed.

[0043] <4. Variation>

In the above embodiment, the first winding 612a is wound around the tooth 61 la, the second winding 612b is wound around the tooth 611b, the third winding 612c force is wound around the S tooth 611c, and the fourth winding. Force that is configured so that wire 612d is wound around teeth 61 Id.For example, the third winding 612c is wound around teeth 61 lb and the second winding 612b is It may be configured to be wound around the teeth 61 Id. Also, the second winding 612b is wound around the teeth 611d, the third winding 612c is wound around the teeth 6l lg, and the fourth winding 612d is wound around the teeth 61lj, that is, For each phase, the winding may be wound in the clockwise direction every three teeth.

Claims

The scope of the claims

[1] An annular stator including a plurality of Y-connected windings driven by three-phase power, and an inner side of the stator that is rotatably supported with respect to the stator. A brushless motor comprising a rotor including a permanent magnet that forms a plurality of poles in a direction, the stator comprising:

An annular yoke portion to which the plurality of teeth portions are coupled;

Including

The number of poles of the permanent magnet is less than the number of the tooth portions provided with multiples of 3 or more and 3 and more than 2/3 of the number of the tooth portions. .

[2] The plurality of winding groups are provided in the same number as one of divisors of absolute values of differences between the number of teeth and the number of poles formed by the permanent magnets. The brushless motor according to claim 1.

[3] Twelve teeth are provided,

The brushless motor according to claim 1, wherein the permanent magnet forms ten poles.

[4] The brushless motor according to claim 1,

The electric power steering apparatus according to claim 1, wherein the brushless motor is driven in accordance with an operation by an operation means for steering the vehicle to apply a steering assist force to a steering mechanism of the vehicle.