GB2460404A - Winding the rotor of a 24v DC motor - Google Patents

Abstract

A rotor for an electric machine comprises a commutator having a plurality of electrically conductive segments 22, a rotor core having a plurality of rotor poles 16, and an electrically conductive winding 30. The poles 16 are wound in groups, with each group of poles supporting two coils 34 and as disclosed the groups may comprise one pole per group. The number of segments 22 is twice the number of rotor poles 16 and the winding 30 has each coil 34 connected to two adjacent segments 22. A method of winding is discloses with reference to an eight pole rotor have three poles per group with sixteen coils associated with sixteen segments. In this arrangement eight pole groups are defined, the first pole group comprising the first, second and third poles, the second group comprising the second, third and fourth poles, the groups continuing to the last group which comprises the eighth, first and second pole. The first coil wound about the first group connects to the first and second segment and the second coil wound about the first group connects to the second and third segments.

Description

A WOUND ROTOR

Background of the Invention

The present invention relates to a winding anangement of a rotor for an electric machine, in particular for a DC commutator motor.

The shift to a 24 volt electrical system for the automotive industry, from the current 12 volt system, is causing a big strain on the life of the small electric motors used to drive accessories within the vehicles. For example, there is a requirement for a 24 volt electric motor driven fuel pump with a rated working life of at least 5000 hours. Testing was undertaken using various DC electric motors with 10 segment or bar commutators with different graphite grades, such as EK23, HE5S, 2200KAS, but all failed to reach even 2000 hours due to overloading of the brush commutator interface at the increased voltage leading to excessive sparking and electrical erosion. Therefore, a commutator, rotor core and winding combination needs to be provided which can consistently meet the required rated working life.

Summary of the Invention

The present invention seeks to provide a novel winding arrangement for the above combination to overcome or mitigate the above-mentioned problem.

According to a first aspect, the present invention provides a rotor for an electric machine comprising: a commutator having a plurality of electrically conductive segments, a rotor core having a plurality of rotor poles, and an electrically conductive winding, the number of segments being twice the number of rotor poles, and the winding having a plurality of coils wound about groups of poles, each group of poles supporting two coils and the coils are connected to sequentially placed segments.

Preferably, the coils of each group of poles are wound sequentially and are connected to a common one of the segments.

Preferably, the number of poles in each group of poles is one.

Preferably, the rotor has eight poles with three poles in each group of poles, the winding has sixteen coils with each coil connected to two segments, and the commutator has sixteen segments.

Preferably, the two segments are adjacent segments.

Preferably the winding is formed in two parts.

Preferably the two parts of the winding are each formed by a single piece of wire.

Preferably, the winding includes at least one turn made about a neck of the commutator, the turn being formed between a connection to the commutator and one of the coils, the turn extending about the neck for at least 360°.

According to a second aspect, the present invention provides a 24 volt DC electric motor comprising: a housing; a permanent magnet stator supported by the housing; and a rotor as described above.

According to a third aspect, the present invention provides a method of winding a rotor for an electric motor, the method comprising the steps of: taking a rotor having a core with n poles and a commutator with 2n segments; grouping the poles into n groups of poles; attaching a conductive member to a first segment and winding the conductive member a predetermined number of times about a first group of poles to form a first coil; connecting the conductive member to a second segment and winding the conductive member a predetermined number of times about the first group of poles to form a second coil, and connecting the electrical member to a third segment; winding the conductive member a predetermined number of times about a second group of poles to form a third coil, connecting the conductive member to a fourth segment and winding the conductive member a predetermined number of times about the second group of poles to form a fourth coil, and connecting the electrical member to a fifth segment; and continuing on in like manner until all groups of poles support two coils and each segment is connected to two coils with the conductive member connecting the last coil to the first segment.

Preferably, the winding is formed in two parts and both parts are wound simultaneously.

Preferably, the method includes the step of making a turn of a portion of the winding about a neck portion of the commutator, the turn being at least 360°.

Brief Description of the Drawings

The present invention will now be more particularly described, by way of a non-limiting example only, with reference to the accompanying drawing, in which: Figure 1 is a perspective view of a wound rotor for an electric motor according to the prefened embodiment of the present invention; and Figure 2 is a winding diagram for the rotor of Figure 1.

Detailed Description of the Preferred Embodiment

Referring to the drawings, the preferred embodiment is the wound rotor of Figure 1, sometimes called an armature. The rotor 10 has a shaft 12, a rotor core 14 having a number of poles 16, a commutator 20 having a number of segments 22 and a winding formed of electrically conductive material such as copper or aluminium wire 32 wound about the poles 16 of the rotor 10 and connected to terminals 24 of the segments 22. The rotor 10 shown has eight poles 16 and sixteen segments 22.

Figure 2 is a winding diagram showing the winding arrangement for the rotor 10 of Fig. 1. In the winding diagram, the poles 16 of the rotor core 14 are labelled 1' through 8', while the commutator segments 22 are labelled A' through Q'. (The letter I has been omitted to avoid any confusion with the number 1.) Thus, the rotor core 14 has eight poles 16 and the commutator 20 has sixteen segments 22. As will be appreciated, the number of segments 22 is twice the number of rotor poles 16, and although in this embodiment it is preferable that the number of segments is sixteen and the number of poles is eight, other numbers which are higher or lower can be used.

The winding provides the electrical path about the poles to form electromagnets. The winding is formed as a number of coils wound about groups of the poles. The number of poles in each group of poles is preferably the same and in the preferred embodiment there are three poles 16 in group of poles. Each coil is formed by a number of turns of the wire around the group of poles. Preferably, each coil has the same number of turns but this can depend on the desired operating characteristics of the motor. Each group of poles supports two coils, with the leading and trailing ends of each coil being connected to sequentially spaced segments and the coils being wound sequentially such that the trailing end of one coil is connected to the leading end of the next coil and joined together at the terminal of the common segment. The individual poles may be part of more than one group of poles and in the preferred embodiment each pole is a part of three groups of poles.

As can be understood from Fig. 2, the winding is formed by winding armature wire about the poles of the rotor. At first, the free end of the wire is hooded about a terminal of a first segment 22, segment A'. The wire is then wound about a group of three rotor poles, poles 1, 2 & 3. Once the wire has been wound a predetermined number of turns about the group of poles, to form the first coil, the wire is connected to the sequentially next segment B' and then wound around the same group of three poles, i.e. poles 1, 2 & 3, a further predetermined number of turns to form the second coil, at which time the wire is connected to the terminal of the next segment C'. The wire is then wound about the next group of three poles 2, 3 & 4, which are two of the poles of the first group of poles plus the next sequentially adjacent pole. Once the wire is wound about this group of poles, forming a first coil of the second group, it is connected to the next sequentially adjacent segment, segment D' and then wound about the same group of poles again, forming a second coil on the second group of poles. The wire is then connected to the sequentially next segment i.e. segment E'. The winding is thus continued, forming coils between adjacent segments, with the coils being formed wrapped about groups of poles, three poles per group with each group supporting two coils and the groups of poles being disposed about the rotor core shifting sequentially around the core, one pole at a time.

The winding may be a single continuous wire from start to finish. Preferably though, the winding comes in two parts which start at diametrically opposed segments and are wound simultaneously in the same direction and terminating at the start of the other part of the winding. This is conveniently achieved by use of a double fly winding machine which uses two wires to wind the two parts simultaneously, plus significantly reducing the winding time over a standard single wire winding machine. This is illustrated in the winding diagram of Fig. 2 by a first winding part which forms coils between segments A' to J' and a second winding part which forms coils between segments J' to A'.

Note, on segment J the winding is discontinuous. This represents the end of the first winding part and the start of the second winding part. Segment A is shown twice, once in solid lines to represent the start of the first winding part and once in dashed lines to represent the end of the second winding part but in practice there is only one segment A on which two wire ends are connected.

As some motors subject their rotor windings to high G'-forces, depending on the application, it may be desired to strengthen the support for the lead wires, those parts of the winding extending between the segment terminals and body of the coils on the rotor core. This can be done by wrapping the lead wires about the neck of the commutator, by at least 360°. While this may be done for every lead wire, this will increase the amount of wire used and satisfactory results may be achieved by wrapping just the leading lead wires or just the trailing lead wires. For rotors subject to less forces, just the last trailing lead wire or last pair of trailing lead wires (in the case of two part winding) being wrapped about the neck of the commutator may be sufficient. In this arrangement the lead wires may make several turns about the neck of the commutator to give good support to the lead wires by binding them.

Alternatively, or in addition, the rotor windings may be over moulded with plastics material to give excellent support for the lead wires and to protect the winding from a harsh environment, such as may be found within a motor of a fuel pump.

The number of turns of each coil is selected depending on the requirements of the motor application. However, it is presumed that the number of turns of each coil is substantially the same.

While the number of poles of each group of poles is described and selected in the prefened embodiment as three, it could be more or less and the group of poles may be a single pole. The number of poles in each group, which represents the pole span of the coils, is a design choice and in influenced by the number of poles of the rotor.

The above described winding arrangement is beneficial for use in a 24 volt DC electric motor. The motor has mainly standard components, and in particular a motor housing, a stator housed in the motor housing, and a rotor having a shaft rotatably mounted in the housing, a rotor core fixedly provided on the shaft to be juxtaposed to the stator, and a commutator. Brush gear is also provided in or on the housing to be in electrical contact with the commutator. However, as already mentioned, the commutator has twice the number of segments as the rotor core has poles, preferably sixteen segments and eight poles, in accordance with the example shown in the winding diagram of Figure 2.

The benefits of being able to utilise the commutator and winding arrangement described above for a 24 volt DC electric motor are that electrical resistance is lowered and the required 5000 hour or more working life is achieved. A high rated 24 volt DC electric motor allows a 24 volt fuel pump and other 24 volt systems to be developed, thus dispensing with the need for a 12 volt equivalent in conjunction with a heavy and expensive transformer to step the voltage down to the required 12 volts. This not only reduces cost, but also saves weight and space.

Typical applications for a 24 volt DC electric motor is within any 24 volt system, such as found in trucks, tractors, earth moving vehicles, and generator setups. 24 volt systems are now being introduced into passenger vehicles.

The embodiments described above are provided by way of examples only, and various modifications will be readily apparent to the skilled person without departing form the scope of the invention as defined by the appended claims.

Claims (14)

1. CLAIMS1. A rotor for an electric machine comprising: a commutator having a plurality of electrically conductive segments, a rotor core having a plurality of rotor poles, and an electrically conductive winding, the number of segments being twice the number of rotor poles, and the winding having a plurality of coils wound about groups of poles, each group of poles supporting two coils and the coils are connected to sequentially placed segments.
2. 2. A rotor as claimed in Claim 1, wherein the coils of each group of poles are wound sequentially and are connected to a common one of the segments.
3. 3. A rotor as claimed in Claim 1 or 2, wherein the number of poles in each group of poles is one.
4. 4. A rotor as claimed in Claim 1, 2 or 3, wherein the rotor has eight poles with three poles in each group of poles, the winding has sixteen coils with each coil connected to two segments, and the commutator has sixteen segments.
5. 5. A rotor as claimed in Claim 4, wherein the said two segments are adjacent segments.
6. 6. A rotor as claimed in any one of the preceding claims, wherein the winding is formed in two parts.
7. 7. A rotor as claimed in Claim 6, wherein the said two parts are each formed by a single piece of wire.
8. 8. A rotor as claimed in any one of the preceding claims, wherein the winding includes at least one turn made about a neck of the commutator, the turn being formed between a connection to the commutator and one of the coils, the turn extending about the neck for at least 3600.
9. 9. A rotor having an electrically conductive winding wound substantially as hereinbefore described with reference to the accompanying drawings.
10. 10. A 24 volt DC electric motor incorporating a rotor according to any one of the preceding claims.
11. 11. A method of winding a rotor for an electric motor, the method comprising the steps of: taking a rotor having a core with n poles and a commutator with 2n segments; grouping the poles into n groups of poles; attaching a conductive member to a first segment and winding the conductive member a predetermined number of times about a first group of poles to form a first coil; connecting the conductive member to a second segment and winding the conductive member a predetermined number of times about the first group of poles to form a second coil, and connecting the electrical member to a third segment; winding the conductive member a predetermined number of times about a second group of poles to form a third coil, connecting the conductive member to a fourth segment and winding the conductive member a predetermined number of times about the second group of poles to form a fourth coil, and connecting the electrical member to a fifth segment; and continuing on in like manner until all groups of poles support two coils and each segment is connected to two coils with the conductive member connecting the last coil to the first segment.
12. 12. A method according to Claim 11, wherein the winding is formed in two parts and both parts are wound simultaneously.
13. 13. A method according to Claim 11 or 12, including the step of making a turn of a portion of the winding about a neck portion of the commutator, the turn being at least 3600.
14. 14. A method of winding a rotor for an electric motor, substantially as hereinbefore described with reference to the accompanying drawings.