GB2594734A

GB2594734A - Winding for electrical machine

Info

Publication number: GB2594734A
Application number: GB2006689.0A
Authority: GB
Inventors: Abduallah Ahmed
Original assignee: IMRA Europe SAS
Current assignee: IMRA Europe SAS
Priority date: 2020-05-06
Filing date: 2020-05-06
Publication date: 2021-11-10
Also published as: GB202006689D0

Abstract

A rotor 200 for an electrical machine, comprising a hub 220, and one or more windings 212 attached to the hub. The windings comprise a peripheral portion 214 extending in an axial direction of the rotor, and one or more side portions 216 extending radially inward from the peripheral portion towards an axis of rotation. The machine may comprise a stator (310, fig 2) with a hub having a similar arrangement of windings with a peripheral portion and side portions. The circumferential width of the side portions may decrease with decreasing radial distance from the axis of rotation. The side portions may extend from the peripheral portion along one or more sides of the rotor or stator. The hub may be a non‐magnetic material. The thicknesses of the side portions may vary in the axial and radial directions. The windings may further comprise end portions 218 arranged to extend inwardly or outwardly from the side portions in an axial direction. The rotor or stator may comprise segments with an outer convex surface and inwardly radially extending side walls extending towards the axis of rotation. The machine may have multiple phases and be enclosed in a housing used for a vehicle.

Description

Winding for Electrical Machine

Field of the Invention

The invention generally relates to rotors and stators for electrical machines. Background As the need to move away from the use of fossil fuels increases, the use of electric motors has substantially increased. For example, many motor vehicles are now hybrid vehicles or are fully electric. Similarly, prototype fully electric aeroplanes are in development. Accordingly, there is a need for electric motors to provide significant power while being light and compact.

One approach to reduce the weight of an electric machine is to replace the magnetic core of the rotor (made of a material such as iron) with a lighter, non-magnetic material. While this may significantly reduce the weight of the motor, the iron core contributes significantly to magnetic coupling between the rotor and the stator of the electric motor. As such, its removal significantly reduces the power output of the electric motor.

In order to increase the magnetic coupling between the rotor and the stator of the electric motor, often the electric motor is made larger in size. However, as there is a desire for electric motors to be more compact, such a solution is unsuitable.

The present inventors have identified an improved approach for significantly increasing the magnetic coupling between the rotor and stator of an electrical machine. Accordingly, the electric machine can be made smaller in size while achieving the same level of power output.

Summary of the Invention

Aspects of the invention are set out in the accompanying claims.

In a first aspect there is provided a rotor for an electrical machine. The rotor comprises a rotor hub, and one or more windings attached to the rotor hub, wherein each of the one or more windings comprises: a peripheral portion extending in an axial direction of the rotor, and one or more side portions, wherein the one or more side portions extend radially inward from the peripheral portion towards an axis of rotation of the rotor.

The rotor windings may, for example, be conductors in the form of bars of conductive material, such as copper or gold. Alternatively, the rotor windings may comprise bars of conductive material wrapped in coils of conductive material. The rotor windings may be multiple windings or may take the form of a single winding with multiple portions connected together. Furthermore, the rotor may be an internal rotor, where the rotor is closer to the axis of rotation than the stator of the electrical machine, or the rotor may be an external rotor, where the rotor is further from the axis of rotation than the stator of the electrical machine.

In the rotor according to this aspect, the rotor windings are longer than comparable similarly-sized rotors as the rotor windings of this aspect have a radial length as well as an axial length. Accordingly, the greater length of the rotor windings allows for a larger interaction surface between the windings of the rotor and the windings of a stator compared to similar sized rotors. As such, the magnetic coupling between the rotor and the stator is increased. Therefore, greater power can be generated than comparable motors of a similar size. Furthermore, the electric motor can be made smaller, if desired, without loss of power.

In a second aspect there is provided a stator for an electrical machine. The stator comprises: a stator hub, and one or more windings attached to the stator hub, wherein each of the one or more windings comprises: a peripheral portion extending in an axial direction of the stator, and one or more side portions, wherein the one or more side portions extend radially inward from the peripheral portion towards an axis of rotation of the stator.

The stator windings may, for example, be conductors in the form of bars of conductive material, such as copper or gold. Alternatively, the stator windings may comprise bars of conductive material wrapped in coils of conductive material. The stator windings may be multiple windings or may take the form of a single winding with multiple portions connected together. The stator may comprise additional electronic components to facilitate the provision of a driving voltage to the windings of the stator using known techniques. Furthermore, the rotor may be an internal rotor, where the rotor is closer to the axis of rotation than the stator of the electrical machine, or the rotor may be an external rotor, where the rotor is further from the axis of rotation than the stator of the electrical machine.

In the stator according to this aspect, the stator windings are longer than comparable stators as the stator windings of this aspect have a radial length as well as an axial length. Accordingly, the greater length of the stator windings allows for a larger interaction surface between the windings of the stator and the windings of a rotor. As such, the magnetic coupling between the stator and the rotor is increased. Therefore, greater power can be generated than comparable motors of a similar size. Furthermore, the electric motor can be made smaller, if desired, without loss of power.

Advantageously, a circumferential width of the one or more side portions of the rotor or stator decreases with decreasing radial distance from the axis of rotation. The term circumferential width is intended to refer to the distance measured circumferentially of the width of a segment at a given radius from the axis of rotation of the rotor. In other words, the circumferential width of the one or more side portions is larger at a first radial position than at a second radial position, where the first radial position is further from the axis of rotation than the second radial position.

The circumferential width of the windings decreases towards the axis of rotation in this way as the available space for the side portions of the windings decreases towards the axis of rotation.

Accordingly, the windings can be readily fitted to the rotor or stator.

In some aspects, the one or more side portions extend from the peripheral portion along one or more sides of the rotor or stator. In other words, where the rotor or stator is an internal rotor or stator (closer to the axis of rotation than the corresponding stator or rotor respectively), the windings extend along a body or scaffolding of the rotor or stator towards the axis of rotation.

In contrast, if the rotor or stator is an external rotor or stator (further from the axis of rotation than the corresponding stator or rotor respectively), the windings do not extend along the windings of the rotor or stator to which the windings belong. Instead, the windings extend along one or more sides of the corresponding stator or rotor respectively such that the windings extend along a body or chassis of the stator or rotor respectively towards the axis of rotation.

In some aspects, the rotor hub or stator hub is formed of a non-magnetic material. As such, the weight of the rotor or stator is significantly reduced while minimising the loss in magnetic coupling between the rotor and the stator.

Advantageously, an axial thickness of the one or more side portions in an axial direction of the rotor or stator increases with decreasing radial distance from the axis of rotation. In other words, the side portions may be thought of as being tapered with increasing radial distance from the axis of rotation. Accordingly, the overall quantity of the windings is increased and as such the level of magnetic coupling between the rotor and stator is increased. Furthermore, in aspects where a circumferential width of the one or more side portions decreases with decreasing radial distance from the axis of rotation, the increasing axial thickness compensates for the decrease in axial length.

As such, the overall quantity of copper can be maintained as compared to a rotor or stator without side portions but with a larger axial length. As such, the magnetic coupling between the rotor and the stator is improved.

Advantageously in this aspect, the axial thickness of the one or more side portions may increase uniformly with decreasing radial distance from the axis of rotation. This provides a compromise between maximising the quantity of the windings, while minimising the weight of the rotor or stator. Furthermore, a uniform increase in thickness provides manufacturing simplicity.

In some aspects, the axial thickness of the one or more side portions increases inwardly towards an axial centre of the rotor or stator with decreasing radial distance from the axis of rotation. In other words, the axial position of an outermost surface of the windings is constant, while the axial position of an innermost surface of the windings becomes closer to the axial centre of the rotor or stator with decreasing radial position. As such, for an internal rotor or stator, the magnetic coupling between the rotor and stator can be increased without increasing the axial width of the electrical machine.

Advantageously, the one or more windings further comprise one or more end portions, wherein the one or more end portions are arranged to extend inwardly from the one or more side portions in an axial direction towards and axial centre of the rotor or stator. In such aspects, the one or more end portions may connect a plurality of windings to one another and may be located at an end of the side portions closest to the axis of rotation.

Accordingly, as the end windings connecting windings to one another are located close to the axis of rotation, their length in a circumferential direction is small relative to comparable approaches where the end windings are located close to the peripheral portion of the windings. The end windings of the rotor or stator do not magnetically interact with the corresponding stator or rotor windings respectively. As such, reducing the length of the end windings in this way reduces the overall resistance of the machine, therefore increasing the torque produced by the electrical machine.

In some aspects, the axial thickness of the one or more side portions of the one or more windings increases outwardly away from an axial centre of the rotor or stator with decreasing radial distance from the axis of rotation. In other words, the axial position of an innermost surface of the windings is constant, while the axial position of an outermost surface of the windings becomes further from the axial centre of the rotor or stator with decreasing radial position. As such, for an external rotor or stator, the magnetic coupling between the rotor and stator can be increased.

Advantageously, the one or more windings further comprise one or more end portions, wherein the one or more end portions are arranged to extend outwardly from the one or more side portions in an axial direction away from an axial centre of the rotor or stator. An axial centre of the rotor or stator is the centre of the rotor or stator in a direction extending along the axis of rotation of the rotor or stator. In such aspects, the one or more end portions may connect a plurality of windings to one another and may be located at an end of the side portions closest to the axis of rotation.

Accordingly, as the end windings connecting windings to one another are located close to the axis of rotation, their length in a circumferential direction is small as compared to approaches where the end windings are located close to the peripheral portion of the windings. The end windings of the rotor or stator do not magnetically interact with the corresponding stator or rotor windings respectively. As such, reducing the length of the end windings in this way reduces the overall resistance of the machine, therefore increasing the torque produced by the electrical machine.

According to a third aspect there is provided an electrical machine. The electrical machine comprises a rotor as described above and a stator as described above, wherein the peripheral portion of the windings of the rotor are located closer to an axis of rotation of the electrical machine than the peripheral portion of the windings of the stator.

According to a fourth aspect there is provided an electrical machine. The electrical machine comprises a rotor as described above and a stator as described above, wherein the peripheral portion of the windings of the rotor are located further from an axis of rotation of the electrical machine than the peripheral portion of the windings of the stator.

In some aspects, the electrical machine further comprises a housing encasing the rotor and the stator. As such, the risk of damage to the electrical machine during use or transport is reduced. In some aspects, the electrical machine is a three-phase electric motor or a multiple three-phase electric motor for a vehicle. A three-phase electric motor provides a three-phase driving signal to the windings of the stator to create a rotating magnetic field. A multiple three-phase electric motor provides multiple different three-phase driving signals to the windings of the stator to create a rotating magnetic field.

According to fifth aspect there is provided a rotor for an electrical machine, the rotor comprising a plurality of segments arranged in use to rotate together about an axis of rotation of the electrical machine, each segment being in the form of an outer convex surface and inwardly radially extending side walls extending from the outer convex surface towards the axis of rotation of the machine, the outer convex surface and inwardly extending side walls defining an inner volume to each segment and wherein one or more side walls of each segment has a thickness increasing towards the axis of rotation of the machine.

In the rotor according to this aspect, the rotor segments are longer than comparable similarly-sized rotors as the rotor segments of this aspect have a radial length as well as an axial length. Accordingly, the greater length of the rotor segments allows for a larger interaction surface between the rotor and the stator compared to similar sized rotors. As such, the magnetic coupling between the rotor and the stator is increased. Therefore, greater power can be generated than comparable motors of a similar size. Furthermore, the electric motor can be made smaller, if desired, without loss of power.

In some aspects, a thickness of the side walls increases per unit reduction in radius, measured from the axis of rotation of the rotor, wherein the thickness of the side walls is measured along a circumferential line at a radius from the axis about which the rotor rotates. As such, the magnetic coupling between the rotor and stator can be increased without increasing the axial length of the electrical machine.

Advantageously, a portion of the side walls most distal to the convex surface further comprise an axially extending portion extending in a direction parallel to the axis of rotation of the machine. As the axially extending portions are located at a portion of the side walls most distal to the convex surface, their length is reduced such that the overall resistance of the machine is reduced, therefore increasing the torque produced by the electrical machine.

In some aspects, the inner volume contains non-magnetic material. As such, the weight of the rotor is significantly reduced while minimising the loss in magnetic coupling between the rotor and the stator.

According to a sixth aspect there is provided a stator for an electrical machine, the stator comprising a plurality of segments arranged in use to rotate together about an axis of rotation of the electrical machine, each segment being in the form of an outer convex surface and inwardly radially extending side walls extending from the outer convex surface towards the axis of rotation of the machine, the outer convex surface and inwardly extending side walls defining an inner volume to each segment and wherein one or more side walls of each segment has a thickness increasing towards the axis of rotation of the rotor.

In the stator according to this aspect, the stator segments are longer than comparable similarly-sized stators as the stator segments of this aspect have a radial length as well as an axial length. Accordingly, the greater length of the stator segments allows for a larger interaction surface between the stator and the rotor compared to similar sized stators. As such, the magnetic coupling between the stator and the rotor is increased. Therefore, greater power can be generated than comparable motors of a similar size. Furthermore, the electric motor can be made smaller, if desired, without loss of power.

In some aspects a thickness of the side walls increases per unit reduction in radius, measured from the axis of rotation of the stator, wherein the thickness of the side walls is measured along a circumferential line at a radius from the axis about which the stator rotates. As such, the magnetic coupling between the stator and rotor can be increased without increasing the axial length of the electrical machine.

Advantageously, a portion of the side walls most distal to the convex surface further comprise an axially extending portion extending in a direction parallel to the axis of rotation of the stator. As the axially extending portions are located at a portion of the side walls most distal to the convex surface, their length is reduced such that the overall resistance of the machine is reduced, therefore increasing the torque produced by the electrical machine.

In some aspects, the inner volume contains non-magnetic material. As such, the weight of the stator is significantly reduced while minimising the loss in magnetic coupling between the rotor and the stator.

Brief Description of the Drawings

Embodiments of the invention will now be described, by way of example only, with reference to the following figures.

In accordance with one (or more) embodiments of the present invention the Figures show the following: Figure la depicts a rotor of an electrical machine from a side angle view. Figure lb depicts a stator of an electrical machine from a side angle view Figure 2 depicts a cross-section of rotor of an electrical machine.

Figure 3 depicts a cross-section of a rotor and stator of an electrical machine.

Any reference to prior art documents in this specification is not to be considered an admission that such prior art is widely known or forms part of the common general knowledge in the field. As used in this specification, the words "comprises", "comprising", and similar words, are not to be interpreted in an exclusive or exhaustive sense. In other words, they are intended to mean "including, but not limited to". The invention is further described with reference to the following examples. It will be appreciated that the invention as claimed is not intended to be limited in any way by these examples. It will also be recognised that the invention covers not only individual embodiments but also combination of the embodiments described herein.

The various embodiments described herein are presented only to assist in understanding and teaching the claimed features. These embodiments are provided as a representative sample of embodiments only, and are not exhaustive and/or exclusive. It is to be understood that advantages, embodiments, examples, functions, features, structures, and/or other aspects described herein are not to be considered limitations on the scope of the invention as defined by the claims or limitations on equivalents to the claims, and that other embodiments may be utilised and modifications may be made without departing from the spirit and scope of the claimed invention. Various embodiments of the invention may suitably comprise, consist of, or consist essentially of, appropriate combinations of the disclosed elements, components, features, parts, steps, means, etc, other than those specifically described herein. In addition, this disclosure may include other inventions not presently claimed, but which may be claimed in future.

Detailed Description

Figure la shows a rotor 110 according to an example teaching of the disclosure. The rotor 110 includes a plurality of windings 112. In the example of Figure la, the windings are conductors in the form of bars of conductive material (for example copper or gold). However, the rotor windings 112 may comprise bars of conductive material wrapped in coils of conductive material. While the example of Figure la includes multiple windings, the rotor 110 may instead take the form of a single winding with multiple portions connected together.

The rotor 110 may include a rotor hub (not shown) on which the windings 112 are mounted. The rotor hub may be a solid rotor core formed of a magnetic material such as iron. Alternatively, the solid rotor core may be formed of a non-magnetic material (for example a plastic material). Instead of a solid rotor core, the rotor hub may instead be a scaffolding on which the rotor windings 114 are mounted, such that the rotor is a core-less rotor, otherwise known as an air-core rotor. Replacing the solid magnetic rotor core with a non-magnetic material or with an air core significantly reduces the weight of the rotor. However, doing so reduces the magnetic coupling between the rotor 110 and a corresponding stator.

The rotor windings 112 each include a peripheral portion 114. The peripheral portion 114 is located at an outermost circumferential surface of the rotor and extends in an axial direction of the rotor. The windings 112 also include side portions 116. The side portions 116 extend radially inward from the peripheral portion 114 towards an axis of rotation of the rotor 110.

The side portions 116 increase the overall length of the windings 112 as compared to a conventional rotor including only the peripheral portions 114. As such, the magnetic coupling between the rotor 110 and a stator is increased relative to conventional rotors of similar axial length as the interaction surface between the rotor 110 and stator is increased.

As shown in Figure la, the circumferential width of the side portions 116 decreases with decreasing radial distance from the axis of rotation. That is, the circumferential width of the side portions 116 is larger at a first radial position than at a second radial position, where the first radial position is further from the axis of rotation than the second radial position. This allows the side portions 116 to be fitted along the side of the rotor 110, as the available space for the side portions 116 decreases closer to the axis of rotation. Accordingly, the side portions 116 are similar in appearance to a sector of a circle.

Figure lb shows a stator 120 according to an example teaching of the disclosure. The stator 120 is similar in appearance to the rotor 110 and contains windings 122 which may be similar to rotor windings 112. In particular the stator windings 122 of Figure lb are conductors in the form of bars of conductive material (for example copper or gold). However, the stator windings 122 may comprise bars of conductive material wrapped in coils of conductive material. While the example of Figure lb includes multiple windings, the stator 120 may instead take the form of a single winding with multiple portions connected together.

The stator windings 122 each include a peripheral portion 124 and side portions 124. The side portions 126 extend radially inward from the peripheral portion 124 towards an axis of rotation of the stator 120. The stator 120 may include a stator hub (not shown) on which the stator windings 122 are mounted. For example, the stator windings 122 may be mounted to the stator hub at the periphery portion 124. In this example, the side portions 126 are not directly mounted on the stator hub but are mounted via the periphery portion 124, such that the side portions 126 extend away from the stator hub.

The circumferential width of the side portions 126 decreases with decreasing radial distance from the axis of rotation for the same reasons as those set out in respect of the rotor 110 in relation to Figure la above. The periphery portions 124 of the stator windings 122 are arranged to magnetically interface with the periphery portions 114 of the rotor windings 112 in the presence of a driving voltage provided to the stator windings 112 in a conventional manner. In addition, the side portions 126 of the stator windings 122 are also arranged to magnetically interface with the side portions 116 of the rotor windings 112 in the presence of a driving voltage provided to the stator windings 122.

The rotor 110 and stator 120 shown in Figures la and 2b respectively are arranged such that the rotor 110 can be located internally closer to the axis of rotation of the electrical machine than the stator 120. That is, the stator 120 is external to the rotor 110. However, the techniques of the above example teaching of the disclosure can be equally applied to an external rotor and internal stator.

That is, a stator that is closer to the axis of rotation than a corresponding rotor may be provided with side portions similar to the side portions 116 with which the rotor 110 of Figure la is provided. Similarly, a rotor that is further form the axis of rotation than a corresponding stator may be provided with side portions similar to the side portions 126 with which the stator 120 of Figure lb is provided.

Figure 2 shows a cross-section of a rotor 200 according to an example teaching of the disclosure, where the axis of rotation of the rotor 200 is shown by the dashed horizontal line. The rotor 200 includes rotor windings 212 similar to rotor windings 112 of the rotor of Figure la. The rotor windings 212 include a peripheral portion 214 and side portions 216. The rotor also includes a rotor hub 220. The rotor hub 220 shown in Figure 2 is a solid rotor core, however the rotor hub could instead be a scaffolding on which the rotor windings 212 are mounted. The side portions 216 of the rotor windings 212 extend along the side of the rotor 200 towards the axis of rotation of the rotor. In the example of Figure 2, the side portions 216 increase in axial thickness closer to the axis of rotation of the rotor 200. In other words, the axial thickness of the side portions 216 is larger at a first radial position than at a second radial position, where the first radial position is further from the axis of rotation than the second radial position.

This increase in axial thickness increases the magnetic coupling between the rotor 200 and a stator as the overall quantity of the windings 212 increases. Furthermore, the increase in axial thickness with decreasing radius compensates for the decrease in circumferential thickness explained above in relation to Figure la. In this way, the decrease in circumferential thickness does not lead to an overall reduction in the quantity of the winding 212. Figure 2 depicts a uniform increase in axial thickness with decreasing radius provides a compromise between maximising the quantity of the windings, while minimising the weight of the rotor 200. Furthermore, a uniform increase in thickness provides manufacturing simplicity. However, it is possible to utilise a non-uniform increase in the axial thickness of the side portions 216.

Rotor winding 212 may also include end portions 218. End portions 218 extend inwardly from the side portions 216 in an axial direction towards an axial centre of the rotor 200 and are located closer to the axis of rotation than the peripheral portion 214. The side portions 216 are connected to the peripheral portion 214 at a first end of the side portion 216, and the end portions 218 are connected to the side portions 216 at a second end of the side portions 216 opposite the first end. In other words, the end portions 218 are located at an end of the side portions 216 closest to the axis of rotation.

The end portions 218 may electrically connect a plurality of windings 212 together. That is, the end portions may include a joining section (not shown) that extends in a circumferential direction between end portions 218 of different windings. As the end portions 218 are located close to the axis of rotation, the length of the joining section of the end portions 218 may be comparatively smaller than if the end portions 218 were located at a similar radius to the peripheral portion 214.

The end windings 218 do not magnetically interact with windings of a stator and as such do not contribute to the magnetic coupling between the rotor 200 and a stator. As such, the end windings 218 increase the resistance of the machine. However, as the end portions 218 shown in Figure 2 are comparatively shorter in length, the overall resistance in the rotor 200 is comparatively low and as such the torque produced by the electrical machine as a whole is greater.

Figure 3 shows a cross-section of an electrical machine 300 including the rotor 200 of Figure 2 and a stator 310, where the axis of rotation of the electrical machine 300 is shown by the dashed horizontal line. The stator 310 includes stator windings 312. The stator windings 312 include a peripheral portion 314 and side portions 316. The stator 310 may also include a stator hub (not shown) to which the stator windings 312 are mounted in a similar manner to that described in relation to Figure lb above. The peripheral portion 314 is arranged to magnetically interface with the peripheral portion 214 of the rotor 200 in the presence of a driving voltage provided to the stator windings 312.

The side portions 316 of the stator windings 312 extend along the side of the rotor 200 towards the axis of rotation. In the example of Figure 3, the side portions 316 increase in axial thickness closer to the axis of rotation. In other words, the axial thickness of the side portions 316 is larger at a first radial position than at a second radial position, where the first radial position is further from the axis of rotation than the second radial position.

This increase in axial thickness increases the magnetic coupling between the stator 310 and the rotor 200 as the overall quantity of the windings 312 increases. Furthermore, the increase in axial thickness with decreasing radius compensates for the decrease in circumferential thickness explained above in relation to Figure lb. In this way, the decrease in circumferential thickness does not lead to an overall reduction in the quantity of the winding 312. Figure 3 depicts a uniform increase in axial thickness with decreasing radius provides a compromise between maximising the quantity of the windings, while minimising the weight of the stator 310. Furthermore, a uniform increase in thickness provided manufacturing simplicity. However, it is possible to utilise a nonuniform increase in the axial thickness of the side portions 316.

Stator winding 312 may also include end portions 318. End portions 318 extend outwardly from the side portions 316 in an axial direction away from an axial centre of the stator 310 and are located closer to the axis of rotation than the peripheral portion 314. The side portions 316 are connected to the peripheral portion 314 at a first end of the side portion 316, and the end portions 318 are connected to the side portions 316 at a second end of the side portions 316 opposite the first end. In other words, the end portions 318 are located at an end of the side portions 316 closest to the axis of rotation.

The end portions 318 electrically connect a plurality of stator windings 312 together in a similar manner in which the rotor end portions 218 electrically connect a plurality of rotor windings 212. As such, end portions 318 may include a joining section (not shown) that extends in a circumferential direction between end portions 318 of different windings. As the end portions 318 are located close to the axis of rotation, the length of the joining section of the end portions 318 may be comparatively smaller than if the end portions 318 were located at a similar radius to the peripheral portion 314. The end windings 318 do not magnetically interact with windings of the rotor 200 and as such do not contribute to the magnetic coupling between the stator 310 and the rotor 200. As such, the end windings 318 increase the resistance of the machine 300. However, as the end portions 318 shown in Figure 3 are comparatively shorter in length, the overall resistance in the stator 310 is reduced and as such the torque produced by the electrical machine 300 as a whole is greater.

The example electric machine 300 of Figure 3 increases the magnetic coupling between the rotor and the stator 310 through the side portions 216, 316 by about 50% or more depending on the diameter of the rotor hub. As such, any removal of a magnetic core of the rotor 200 may be at least partially compensated for by this increase in magnetic coupling. Consequently, the electric machine 300 can be kept small in size, for example so as to be suitable for use in a vehicle such as a car, bike or aeroplane.

In Figure 3, the rotor 200 is shown as being closer to the axis of rotation and closer to an axial centre of the electrical machine 300 than the stator 310. However, the example of Figure 3 can be readily adapted such that the stator 300 is closer to the axis of rotation and closer to an axial centre of the electrical machine 300 than the rotor 200, as explained above in relation to Figures la-lb. The electrical machine 300 of Figure 3 may additionally include a housing (not shown) in which the rotor and stator 310 are located. The housing may protect the electrical machine 300 from damage during use or transport. Furthermore, the electrical machine may be a three-phase electric motor. In such examples, a driving voltage with three phases is provided to the windings to create a rotating magnetic field with which the rotor windings 212 magnetically couple. The electric machine may be a multiple three-phase electric motor for a vehicle, where multiple three-phase driving voltages are supplied to the stator windings 312.

Furthermore, while the above examples have been described primarily in relation to electric motors, the techniques are equally applicable to other types of electrical machine, such as a generator. In such examples, the rotor might include a series of permanent magnets while the stator includes windings similar to those shown in Figures lb and 3 (however other implementations are possible).

As such, from one perspective there has been described a rotor or stator for an electrical machine, the rotor or stator comprising a rotor or stator hub, and one or more windings attached to the rotor or stator hub, wherein each of the one or more windings comprises: a peripheral portion extending in an axial direction of the rotor or stator, and one or more side portions, wherein the one or more side portions extend radially inward from the peripheral portion towards an axis of rotation of the rotor or stator.

Claims

Claims 1. A rotor for an electrical machine, the rotor comprising: a rotor hub, and one or more windings attached to the rotor hub, wherein each of the one or more windings comprises: a peripheral portion extending in an axial direction of the rotor, and one or more side portions, wherein the one or more side portions extend radially inward from the peripheral portion towards an axis of rotation of the rotor.
2. A stator for an electrical machine, the stator comprising: a stator hub, and one or more windings attached to the stator hub, wherein each of the one or more windings comprises: a peripheral portion extending in an axial direction of the stator, and one or more side portions, wherein the one or more side portions extend radially inward from the peripheral portion towards an axis of rotation of the stator.
3. The rotor or stator according to claim 1 or claim 2, wherein a circumferential width of the one or more side portions decreases with decreasing radial distance from the axis of rotation.
4. The rotor or stator according to any of claims 1-3, wherein the one or more side portions extend from the peripheral portion along one or more sides of the rotor or stator.
5. The rotor or stator according to any of claims 1-4, wherein the rotor hub or stator hub is formed of a non-magnetic material.
6. The rotor or stator according to any of claims 1-5, wherein an axial thickness of the one or more side portions in an axial direction of the rotor or stator increases with decreasing radial distance from the axis of rotation.
7. The rotor or stator according to claim 6, wherein the axial thickness of the one or more side portions increases uniformly with decreasing radial distance from the axis of rotation.
8. The rotor or stator according to claim 6 or claim 7, wherein the axial thickness of the one or more side portions increases inwardly towards an axial centre of the rotor or stator with decreasing radial distance from the axis of rotation.
9. The rotor or stator according to any of claims 1-8, wherein the one or more windings further comprise: one or more end portions, wherein the one or more end portions are arranged to extend inwardly from the one or more side portions in an axial direction towards and axial centre of the rotor or stator.
10. The rotor or stator according to claim 6 or claim 7, wherein the axial thickness of the one or more side portions of the one or more windings increases outwardly away from an axial centre of the rotor or stator with decreasing radial distance from the axis of rotation.
11. The rotor or stator according to any of claims 1-7 and 10, wherein the one or more windings further comprise: one or more end portions, wherein the one or more end portions are arranged to extend outwardly from the one or more side portions in an axial direction away from an axial centre of the rotor or stator.
12. An electrical machine comprising: a rotor according to any of claims 1-9, and a stator according to claims 1-7, 10, and 11, wherein the peripheral portion of the windings of the rotor are located closer to an axis of rotation of the electrical machine than the peripheral portion of the windings of the stator.
13. An electrical machine comprising: a rotor according to claim 1-7, 10 and 11, and a stator according to claim 1-9, wherein the peripheral portion of the windings of the rotor are located further from an axis of rotation of the electrical machine than the peripheral portion of the windings of the stator.
14. The electrical machine according to claim 12 or claim 13, further comprising a housing encasing the rotor and the stator.
15. The electrical machine according to any of claims 12-14, wherein the electrical machine is a three-phase electric motor or a multiple three-phase electric motor for a vehicle.
16. A rotor for an electrical machine, the rotor comprising a plurality of segments arranged in use to rotate together about an axis of rotation of the electrical machine, each segment being in the form of an outer convex surface and inwardly radially extending side walls extending from the outer convex surface towards the axis of rotation of the machine, the outer convex surface and inwardly extending side walls defining an inner volume to each segment and wherein one or more side walls of each segment has a thickness increasing towards the axis of rotation of the machine.
17. The rotor according to claim 16, wherein a thickness of the side walls increases per unit reduction in radius, measured from the axis of rotation of the rotor, wherein the thickness of the side walls is measured along a circumferential line at a radius from the axis about which the rotor rotates.
18. The rotor according to claim 16 or claim 17, wherein a portion of the side walls most distal to the convex surface further comprise an axially extending portion extending in a direction parallel to the axis of rotation of the machine.
19. The rotor according to any of claims 16-18, wherein the inner volume contains non-magnetic material.
20. A stator for an electrical machine, the stator comprising a plurality of segments arranged in use to rotate together about an axis of rotation of the electrical machine, each segment being in the form of an outer convex surface and inwardly radially extending side walls extending from the outer convex surface towards the axis of rotation of the machine, the outer convex surface and inwardly extending side walls defining an inner volume to each segment and wherein one or more side walls of each segment has a thickness increasing towards the axis of rotation of the rotor.
21. The stator according to claim 20, wherein a thickness of the side walls increases per unit reduction in radius, measured from the axis of rotation of the stator, wherein the thickness of the side walls is measured along a circumferential line at a radius from the axis about which the stator rotates.
22. The stator according to claim 20 or claim 21, wherein a portion of the side walls most distal to the convex surface further comprise an axially extending portion extending in a direction parallel to the axis of rotation of the stator
23. The rotor according to any of claims 20-22, wherein the inner volume contains non-magnetic material.