GB2620149A

GB2620149A - Unbalanced coil winding

Info

Publication number: GB2620149A
Application number: GB2209497.3A
Authority: GB
Inventors: Boubaker Nadhem
Original assignee: Safran Electrical and Power SAS
Current assignee: Safran Electrical and Power SAS
Priority date: 2022-06-29
Filing date: 2022-06-29
Publication date: 2024-01-03
Also published as: GB202209497D0

Abstract

A stator 100 for an electric machine comprising: a plurality of teeth 22, 24,26, 28, defining a plurality of slots 32, 34, 36, 38 which contain windings 52, 54, 56, 58. Around a first tooth 22 there is a larger winding 52, 102, and around a second tooth 24 a smaller winding 54. A third tooth 26 may have a larger winding 56, 104 again; this may continue around the stator. In this way, gaps left by the width of a winding needle may be filled by the additional coils 104 to improve the fill factor. The extra copper coil may simply be part of the first winding, with all of the small coils wound first before the larger coils. Alternatively, the added copper winding may be a layer may be added after all the teeth have an identical small winding applied, in which case the additional wire may be connected to the existing wire. The additional winding may be a single layer, with the winding nozzle withdrawn as the slot fills. The winding may take two rotations of the stator in the winding machine, with the winding needle orbiting a first axis (A2, Fig. 1) and the stator rotating about a second axis (A1, Fig. 1).

Description

Unbalanced Coil Winding

Field of the Invention

This invention relates to a stator for an electric machine and to a method of winding the stator.

Background

Electric machines commonly have a rotor having permanent magnets, or non-permanent, magnetisable elements such as rotor windings, and a stator having electromagnetic coils or windings wound around teeth of the stator. The electromagnetic coils may be wound either automatically using a needle or by hand. Winding by hand may provide a high density of coil windings. However, manual winding may be time consuming and may provide low levels of consistency.

By comparison, automated winding of a stator may be faster and more consistent. The drawback of automated winding is that a certain level of clearance is required in order to allow a winding needle to pass through gaps between teeth of the stator in order to carry out the winding. The space required for the needle may be reduced by the windings and so the present inventors have considered a winding arrangement that may allow a higher coil density to be achieved using an automated winding needle.

Summary of the Invention

According to a first aspect of the invention, there is provided a stator for an electric machine comprising: a stator core having a plurality of teeth, the teeth defining a plurality of slots extending longitudinally in a direction of a longitudinal axis of the stator to receive windings of the stator; the plurality of teeth comprising a first tooth and a second tooth adjacent to the first tooth, the first tooth having a single first tooth winding wound therearound, and the second tooth having a single second tooth winding wound therearound; wherein the first tooth winding comprises: a first portion that is the same as the second tooth winding, and a second portion wound over the first portion. With such an arrangement, the stator may be wound automatically using a winding needle and the stator may have a high fill factor of coil windings. Generally, the first portion of the first tooth winding and the second tooth winding may be arranged such that there is a sufficient distance between them for a winding needle to pass and the second portion of the first tooth winding may be wound as a final step in the manufacturing, meaning that a high fill factor may be provided.

The first portion of the first tooth winding and the second tooth winding may be recognised as being the same by having the same number of turns, the same number of layers and the same number of turns in each layer. Where the winding is automated, it may be recognised that instructions for winding the first portion of the first tooth winding are the same as the instructions for winding the second tooth winding.

The first and second tooth windings may be the only windings on each tooth, meaning that the second tooth has a winding around, the entirety of which is identical to the first portion of the first tooth winding. Further, the first tooth winding may have a greater number of turns than the second tooth winding since the first tooth winding comprises the entirety of the second tooth winding (i.e. the first portion) and also one or more further turns wound over the first portion (i.e. the second portion).

The first and second portions of the first tooth windings may be formed from separate sections of wire connected by a joining section. In this case, the first portion of the first tooth winding and the second tooth winding may be wound in a first pass, i.e. a single rotation of the stator, and the second portion of the first tooth winding may be wound in a second path. The joining may be made via soldering or brazing of the wire. The cross sectional areas of the wires and/or the diameters of the wires may also be varied between the first and second portions of the first tooth windings where the first and second portions of the first tooth windings are wound in separate passes.

The first portion may comprise two wound layers. The two wound layers may each have at least 2, 3, 4, 5 or more turns of wire, and the two layers may be recognised by one layer being wound on top of, radially outside, another layer. By providing a first portion of the first winding that is larger, and a corresponding second winding that is larger, the balance of the rotor may be improved. This may reduce cogging as compared to a stator having more asymmetric first and second windings.

The second portion may consist of one wound layer. Put another way, the second portion may have only one layer. The second portion may provide additional density of the electromagnetic coils, while limiting the size may avoid unduly reducing the balance of the coils. Further, one wound layer may be the difference between there being space for a needle to pass and there being insufficient space for a needle to pass. Therefore, having exactly one wound layer of asymmetry or imbalance between the first and second windings may be desirable.

According to a second aspect of the invention, there is provided a method of constructing a stator for an electric machine, the method comprising: providing a stator core having a plurality of teeth, the teeth defining a plurality of slots extending longitudinally in a direction of a longitudinal axis of the stator to receive windings of the stator, the plurality of teeth comprising a first tooth and a second tooth adjacent to the first tooth; winding a first tooth winding about the first tooth; and winding a second tooth winding about the second tooth; wherein the first tooth winding comprises: a first portion that is the same as the second tooth winding, and a second portion wound over the first portion. Such a method may allow automated winding with a needle while providing a high fill factor and good balancing of a rotor.

Winding the coils may comprise moving a needle relative to the stator core to orbit a first axis. The first axis may be aligned with the first tooth and/or the second tooth. It will be understood that winding the coils may comprise rotating the stator core relative to the needle about a second axis and that the first axis may therefore register with and be aligned with each tooth of the stator core at a different time during winding.

Winding the first tooth winding about the first tooth may comprise: winding a first coil about the first tooth, the first coil being the first portion; winding a further coil about the first tooth, the further coil being the second portion and being layered over the first coil; and joining the further coil to the first coil. This may allow a first winding step to be winding of the same coil onto all teeth of the stator core, simplifying manufacture.

The winding of the first portion of the first coil and the winding of the second coil may be performed during a single rotation of the stator core. This may allow a faster overall construction of the stator by reducing the number of rotations of the stator core required. It will also be understood that the needle may be moved relative to the stator core, and that it may be considered that an orbit of the needle about the stator core is equivalent to a rotation of the stator core relative to the needle.

The second coil may be the only coil wrapped around the second tooth. This may allow a sufficient space for the needle in between the first portion of the first tooth winding and the second coil for winding of the further coil, while maximising the size of the second coil in order to improve winding density.

The stator core may further comprise a third tooth, the third tooth being adjacent to the second tooth such that the second tooth is between the first and the third teeth, and the method may further comprise winding the second tooth winding before winding the first tooth winding and before winding the third tooth winding.

In this case, the second tooth winding may be wound while leaving sufficient space around the second tooth for winding of the first and third tooth windings and a larger first and second tooth winding may subsequently be wound around adjacent to the second tooth to increase the winding density. A fourth tooth winding, identical to the second tooth winding, may also be wound before the winding of the first and third tooth windings. The fourth tooth may be adjacent to the third tooth such that the third tooth is between the second and fourth teeth.

The winding of the first and/or third coil may be performed during a single rotation of the stator core and the winding of the second coil may be performed during a second rotation of the stator coil.

According to a third aspect of the invention, there is provided a method of constructing a stator for an electric machine, the method comprising: providing a stator core having a plurality of teeth, the teeth defining a plurality of slots extending longitudinally in a direction of a longitudinal axis of the stator to receive windings of the stator, the plurality of teeth comprising a first tooth and a second tooth adjacent to the first tooth; winding a first coil about the first tooth; winding a second coil about the second tooth, the second coil being identical to the first coil; winding a further coil about the first tooth, the further coil being layered over the first coil; and joining the further coil to the first coil. In this arrangement, the stator may have a first winding formed of the first coil and the further coil and a second winding comprising the second coil. The winding of the first and second coil may be made during a single rotation of the stator, with the first and second coils being wound identically and a further coil may be wound in a second pass of the stator. As described above, this method may provide a higher density of winding due to the provision of the further coil while allowing the winding to be made with a needle due to the first and second coils being wound before the further coil.

According to a fourth aspect of the invention, there is provided a method of constructing a stator for an electric machine, the method comprising: providing a stator core having a plurality of teeth, the teeth defining a plurality of slots extending longitudinally in a direction of a longitudinal axis of the stator to receive windings of the stator, the plurality of teeth comprising a first tooth and a second tooth adjacent to the first tooth; winding a first coil about the first tooth; winding a second coil about the second tooth, the second coil comprising more turns than the first coil. With such a method, a stator may be constructed where there are no joins required within the coils and the first and second coils may each be wound on a separate rotation of the stator about a stator axis.

Brief Description of The Drawings

Figure 1 shows a stator core; Figure 2 is a detail view of a stator core; Figure 3 is a detail view of a partially wound stator; Figure 4 is a detailed view of a wound stator; Figure 5 is a detail view of an alternative partially wound stator; Figure 6 is a detail view of an alternative wound stator.

Detailed Description

Figure 1 shows a stator core 10. The stator core 10 is annular and has a stator axis Al. It will be understood that the stator core 10 may be elongated along the stator axis Al, although the cross section may be substantially constant. As is shown more clearly in Figure 2, the stator core 10 has a back iron 12 and a plurality of stator teeth 22, 24, 26, 28 extending radially inwardly from the backiron 12.

In alternative arrangements, the stator teeth may extend radially outwardly from the backiron or may extend axially.

A needle N is provided, which is arranged to insert wire into gaps in between the stator teeth and to wind the wire around the teeth. The needle is therefore arranged to orbit an axis A2, which is aligned with one of the teeth of the stator. The needle N may therefore orbit a stator tooth and wind wire around the stator tooth while it orbits.

During the winding of the stator, the stator may be rotated about its axis Al and the needle axis A2 may be aligned with each respective stator tooth in turn, such that wire is wound around each stator tooth.

A complete revolution of the stator 10 about the axis Al may be referred to as a single pass or passage of the needle. It may be desirable to reduce the number of passages of the needle in order to simplify manufacture and to allow faster manufacturing.

It can also be seen that the needle N has an appreciable width and that, in order for the needle N to wind wire around a tooth, sufficient space must be provided between the tooth being wound and adjacent teeth in order to accommodate the needle. In particular, there is a conflict between the desire to fill as much of the gap between the teeth with wire as possible, while also leaving sufficient space in the gap for the winding needle to pass, avoiding the needle being impeded by the wire it has already wound around the tooth or around an adjacent tooth.

Looking to Figure 2, it can be seen that the stator teeth may each have a portion with a relatively constant cross section extending away from the back iron 12 and a flanged end having a cross section that is greater than the cross section of the rest of the tooth. The flanged end may assist in preventing windings from slipping off the tooth, while the constant cross section may provide a support for the windings. The stator core 10 may be formed of soft magnetic material, which may be laminated, in order to direct magnetic flux from the windings and to reduce energy loss due to eddy currents within the stator core.

The teeth may be referred to as a first tooth 22, a second tooth 24, a third tooth 26 and a fourth tooth 28. It will be understood that a stator core may have any number of teeth and that the number of teeth shown in the figures is purely exemplary. Further, the labelling of first, second, third and fourth teeth is merely for explanation purposes and any tooth of the stator may be considered as a first or any other tooth.

Between the stator teeth 22, 24, 26, 28 there are gaps 30, 32, 34, 36, 38 for receiving wires wound around the teeth. There is provided a first gap 30 adjacent the first tooth 22, a second gap 32 between the first tooth 22 and the second tooth 24, a third gap 34 between the second tooth 24 and the third tooth 26, a fourth gap 36 between the third tooth 26 and the fourth tooth 28 and a fifth gap 38 adjacent the fourth tooth 28. It will be understood that, while only a small number of the teeth and gaps have been labelled, the invention may be applied to all teeth of the stator and that the winding patterns described may be repeated in around the entire circumference of the stator.

Figure 3 shows a partially wound stator 50. The partially wound stator 50 has a winding arranged about each stator tooth. For example, a first coil 52 is wound around a first tooth 22. The coil 52 may be wound by a needle orbiting the first tooth 22 and passing through the first gap 30 and the second gap 32. The coil 52 may be formed by the needle orbiting the first tooth 22 while moving along the first tooth 22, such that the coil 52 is wound in a helix about the tooth 22. In order to form two layers within the coil 52, the needle may move in a helix along the length of the tooth 22 twice, such that the coil 52 comprises two layers, a first helix moving towards the end of the tooth 22 distal from the back iron 12 and a second helix where the needle orbits the tooth 22 while moving back towards the back iron 12. Once the first tooth 22 has been wound with the first coil 52, the stator core 10 may be rotated about the stator axis Al such that the needle axis A2 is aligned with the second tooth 24, and the needle may then orbit the second tooth 24 in order to wind a second coil 54 around the second tooth 24 in the same manner as the coil 52 wound about the first tooth 22. This may be repeated for the third and fourth teeth 26, 28 to form third and fourth coils 56, 58. The winding process may then be repeated for all teeth of the stator until every tooth has an identical winding.

This may be considered as a first pass of the stator, since the stator may be rotated in a substantially full revolution in order to wind a coil around every tooth, using the needle.

It is notable that the coils 52, 54, 56, 58 leave sufficient space therebetween to allow a needle to pass through the respective gaps 30, 32, 34, 36, 38. Preferably, the coils may fill as much space as possible without preventing passage of the needle.

Figure 4 shows a wound stator 100 in which a further winding step has been carried out on the partially wound stator 50 shown in Figure 3. In the further winding step, a further coil has been wound onto every other tooth, that is every second tooth, of the stator 100. A further coil 102, is wound around the first tooth 22 on top of the first coil 52. The first coil 52 and further coil 102 may be referred to in combination as a first winding, wound around the first tooth 22.

In this case, the further coil 102 may fill the first and second gaps 30, 32 such that a needle may not pass between the further coil 102 and the adjacent coils of the adjacent teeth 54. Fundamentally, the windings that are common to all teeth may fill as much space as possible without preventing passage of the needle, and a further winding is then introduced onto every other tooth, which prevents a needle passing between adjacent coils.

A further coil 104 is wound over the third coil 56 of the third tooth 26, the third tooth 26 being spaced from the first tooth 22 by the second tooth 24, which may be referred to as an intermediate tooth, the intermediate tooth not having a further coil upon it. Therefore, the second tooth 24 may have a winding that consists of the first coil 54, and the second tooth winding may be is identical to the first coil 52 on the first tooth 22.

It will be understood that, in order for a current to be used to magnetise the stator to provide the correct polarity, a joining step may be required to join the further coils 102, 104 to the previously wound coils 54, 58. The joining step may be made via braising or soldering for example and the joint may be outside the region of the stator. The joint between the coils will be recognisable to a skilled person and may provide an indication of the method by which the windings were constructed.

The winding arrangement of Figure 4 may provide an improved stator having a high fill factor, i.e. a high number of turns considering the gap size between adjacent teeth, and good balancing of the different coils, i.e. a relatively small difference in winding between the different teeth. These desirable properties may also be obtained by an alternative winding method as explained below with reference to Figures 5 and 6.

Figure 5 shows a partially wound stator 150. The partially wound stator 150 has a stator core 10 that is substantially similar to the stator core 10 described above with reference to Figures 1 to 4 and the partially wound stator core 150 also comprises windings 154, 158 wound around the second and fourth teeth 24, 28 and no winding about the first and third teeth 22, 26. Put another way, every other tooth of the stator core has a coil 154, 158 wound around it while the remaining teeth have no windings. The coils 152 and 156 may be the only windings on their respective teeth. The winding process may therefore be finished for the second and fourth teeth 24, 28 after a first pass of the stator. The windings of the second and fourth teeth 24, 28 may therefore be substantially the same as those described above for the same teeth in respect of Figures 3 and 4.

Notably, after the first pass, at the stage shown in Figure 5, significant portions of the gaps 32, 34, 36, 38 are left open for the needle to access such that further windings may be wound around the remaining teeth.

As shown in Figure 6, the respective first and third teeth 22, 26 may be wound with a further coil 152, 156 by passing a needle through the respective gaps 30, 32, 34, 36. The further windings 152, 156 may each have two portions. The winding 152 has a first portion 152a which is substantially identical to the winding 154 on the second tooth 24 and a second portion 152b that is wound over the first portion 152a, the first and second portions 152a, b being formed of a continuous wire with no joint.

The same may be true of the third winding 156, which has a first portion 156a and a second portion 156b. Since both the first portion 156a and second portion 156b may be wound during a single pass of the stator, the first and second portions 156a, b may be wound from a single continuous wire. This may be advantageous as it may avoid the requirement for a joining step after the winding.

It will be understood that the first and second portions 156a, 156b may be the same as the first coil 54 and second coil 104 described above with reference to Figure 4 respectively.

Claims

Claims 1. A stator for an electric machine comprising: a stator core having a plurality of teeth, the teeth defining a plurality of slots extending longitudinally in a direction of a longitudinal axis of the stator to receive windings of the stator; the plurality of teeth comprising a first tooth and a second tooth adjacent to the first tooth, the first tooth having a single first tooth winding wound therearound, and the second tooth having a single second tooth winding wound therearound; wherein the first tooth winding comprises: a first portion that is the same as the second tooth winding, and a second portion wound over the first portion.
2. The stator of claim 1, wherein the first and second portions of the first tooth windings are formed from separate sections of wire connected by a joining section.
3. The stator of claim 1 or 2, wherein the first portion comprises two wound layers.
4. The stator of any preceding claim, wherein the second portion consists of one
5. A method of constructing a stator for an electric machine, the method comprising: providing a stator core having a plurality of teeth, the teeth defining a plurality of slots extending longitudinally in a direction of a longitudinal axis of the stator to receive windings of the stator, the plurality of teeth comprising a first tooth and a second tooth adjacent to the first tooth; winding a first tooth winding about the first tooth; and winding a second tooth winding about the second tooth; wherein the first tooth winding comprises: a first portion that is the same as the second tooth winding, and a second portion wound over the first portion.
6. The method of claim 5, wherein winding the first tooth winding about the first tooth comprises: winding a first coil about the first tooth, the first coil being the first portion; winding a further coil about the first tooth, the further coil being the second portion and being layered over the first coil; and joining the further coil to the first coil.
7. The method of claim 6, wherein the winding of the first coil and the winding of the second tooth winding is performed during a single rotation of the stator core.
8. The method of claim 7, wherein winding of the further coil is performed during a second rotation of the stator core.
9. The method of claim 5, 6, 7 or 8, wherein the second tooth winding is the only tooth winding wrapped around the second tooth.
10. The method of claim 5, wherein the stator core further comprises a third tooth, the third tooth being adjacent to the second tooth such that the second tooth is between the first and the third teeth, the method further comprising winding a third tooth winding about the third tooth, the third tooth winding being identical to the first tooth winding, and wherein winding the second tooth winding occurs before the winding of the third tooth winding and before the winding of the first tooth winding.
11. The method of claim 10, wherein the winding of the second tooth winding is performed during a first rotation of the stator core, and wherein the winding of the first and third tooth windings is performed during a second rotation of the stator core.
12. The method of any one of claims 5 to 11, wherein winding the coils comprises moving the needle relative to the stator core to orbit a first axis.
13. The method of any one of claims 5 to 12, wherein winding the coils comprises rotating the stator core relative to the needle about a second axis.