EP4627698A1

EP4627698A1 - Stator core

Info

Publication number: EP4627698A1
Application number: EP23817960.0A
Authority: EP
Inventors: Matthew CROUCH; Fasil MUHAMMED; Jose MALUMBRES RUIZ; Istvan Kiraly
Original assignee: Jaguar Land Rover Ltd
Current assignee: Jaguar Land Rover Ltd
Priority date: 2022-12-02
Filing date: 2023-11-27
Publication date: 2025-10-08
Also published as: WO2024115374A1; GB2625065A; GB2625065B; GB202218123D0

Abstract

Aspects of the present invention relate to a stator core (1) for a stator (3) of an electric machine (5). The stator core (1) has a central stator axis (X1). A plurality of winding slots (15) are formed in the stator core (1). Each of the plurality of winding slots (15) is configured to receive a winding (17) and a slot liner (39), the winding slots (15) each having a length extending along a respective central slot axis (SY). The respective central slot axes (SY) extend radially from, and orthogonal to, the central stator axis (X1). The winding slots (15) each comprise a first slot sidewall (51) and a second slot sidewall (53), the first and second slot sidewalls (51, 53) being disposed on respective first and second sides of the central slot axis (SY) of the winding slot (15). The first slot sidewall (51) extends at least substantially parallel to the central slot axis (SY) of the winding slot. The second slot sidewall (53) comprises or consists of a first region (53A) and a second region (53B). The first region (53A) is offset from the second region (53B) in a direction perpendicular to the central slot axis (SY) of the winding slot (15) to form a slot expansion region (45) for accommodating at least a portion of an overlap (40) of the slot liner (39). The first region (53A) extends at least substantially parallel to the central slot axis (SY) of the winding slot (15). Aspects of the present invention also relate to a stator (3), an electric machine (5) and a vehicle (V).

Description

STATOR CORE

TECHNICAL FIELD

The present disclosure relates to a stator core. The stator core is suitable for use in a stator of an electric machine. Aspects of the invention relate to a stator core, a stator, an electric machine and a vehicle.

BACKGROUND

It is known to use one or more electric machine in a vehicle. Such electric machines may operate as motors or as generators. Electric machines may operate as traction motors for propelling a vehicle such as an automobile, van, truck, motorcycle, boat, or aeroplane. Electric machines may be used in place of, or in addition to, an internal combustion engine.

Such electric machines comprise a stator and a rotor, separated by an air gap, for example as part of a permanent magnet synchronous motor. The stator is a stationary element of the electric machine which may comprise a plurality of slots within which electrical stator windings are located. The rotor is a rotating element of the electric machine allowing a transfer of electrical energy input into the motorto a mechanical output, such as the rotation of a driveshaft of the vehicle.

The vehicle may, for example, comprise a battery electric vehicle (BEV), a plug-in hybrid electric vehicle (PHEV) or a hybrid electric vehicle (HEV) where the electric machine is a traction motor for the vehicle. It is desirable to have the lightest possible traction motor with optimised energy conversion from an electrical energy input to a mechanical energy output whilst maintaining the integrity of the traction motor.

A stator core 101 for a stator 103 of an electric machine is shown in Figure 1 . The stator core 101 comprises a plurality of winding slots 115 for stator windings 118. A slot liner 139 is provided in each winding slot 115 in order to electrically insulate the stator windings 118 from the stator core 101. The slot liner 139 is formed from a sheet member arranged such that the first and second ends are arranged in a face-to-face arrangement to form an overlap 140. The overlap 140 in this arrangement is smallerthan the width of the winding slot 115. This configuration may be suitable for a low-voltage electric machine. In the arrangement shown in Figure 2, the width of the coils has been reduced in the winding slot 115 to allow the first and second ends of the sheet memberto form an overlap extending in a radial direction. This arrangement is suitable for a high-voltage electric machine, for example having an operating voltage of 800 volts or higher. However, the reduced thickness of the coils may reduce the power density of the electric machine.

It is an aim of the present invention to address one or more of the disadvantages associated with the prior art.

SUMMARY OF THE INVENTION

Aspects and embodiments of the invention provide a stator core, a stator, an electric machine and a vehicle as claimed in the appended claims

According to an aspect of the present invention there is provided a stator core for a stator of an electric machine, the stator core comprising: a central stator axis; a plurality of winding slots in the stator core, each of the plurality of winding slots being configured to receive a winding and a slot liner, the winding slots each having a length extending along a respective central slot axis, each of the respective central slot axes extending radially from, and orthogonal to, the central stator axis; and wherein the winding slots each comprise: a first slot sidewall and a second slot sidewall, the first and second slot sidewalls being disposed on respective first and second sides of the central slot axis of the winding slot; the first slot sidewall extending at least substantially parallel to the central slot axis of the winding slot; and wherein the second slot sidewall comprises or consists of a first region and a second region, the first region being offset from the second region in a direction perpendicular to the central slot axis of the winding slot to form a slot expansion region for accommodating at least a portion of an overlap of the slot liner, the first region extending at least substantially parallel to the central slot axis of the winding slot.

The slot liner is provided in a stator to electrically insulate stator windings provided in the winding slot from the stator core. The slot liner may comprise one or more sheet members of an electrically insulating material. At least in certain embodiments, the slot liner comprises or consists of a single sheet member of the electrically insulating material. The sheet member may, for example, be folded into a loop which extends around an interior of the winding slot. The ends of the sheet member are disposed in an overlapping arrangement to form the overlap. The overlap is typically in the form of a lap joint in which the ends of the sheet member are disposed in a face-to-face arrangement. The overlap should be of sufficient width to provide effective electrical insulation. The resulting overlap may have a thickness which is two or more times the thickness of the sheet member of electrically insulating material. The overlap results in a localised section of the slot liner have a greaterthickness. The slot expansion region formed in the second slot sidewall is configured to accommodate at least a portion of the resulting overlap. The winding slots each comprise a central slot axis extending radially from the central stator axis. The winding slots may be asymmetric about their respective central slot axes. The slot expansion region formed by the offset between the first and second regions of the second slot sidewall preserves material in the stator core. The offset between the first and second regions of the second slot sidewall may be greater than or equal to the thickness of the slot liner. At least in certain embodiments, this may provide improved electromagnetic and/or structural properties of the stator core.

The first slot sidewall may be formed without a slot expansion region. The first slot sidewall may be substantially planar.

The first region is configured to accommodate the overlap of the slot liner. The first region forms the slot expansion region which, in the assembled stator, has sufficient volume to receive the overlap of the slot liner. The first region may form a section of the stator slot having sufficient width (in a circumferential direction) to accommodate the windings plus the overlapping region of the slot liner. In an assembled stator, the first region may be spaced apart from the windings by a circumferential distance which is greater than or equal to twice the thickness of the slot liner. The first region may be formed in a radially inboard position or a radially outboard position along a length of the stator slot. At least in certain embodiments, the second region does not have sufficient width (in a circumferential direction) to receive the overlap of the slot liner. The second region forms a section of the stator slot having insufficient width to accommodate the windings plus the overlapping region of the slot liner. The second region may form a section of the stator slot which is not capable of accommodating the overlap of the slot liner. In an assembled stator, the second region may be spaced apart from the windings by a circumferential distance which is less than twice the thickness of the slot liner, for example substantially equal to the thickness of the slot liner. The second region may form a section of the stator slot having sufficient width (in a circumferential direction) to accommodate only the windings plus a single (non-overlapping) layer of the slot liner on each side of the windings. At least in certain embodiments, the second region helps to preserve material in the stator core. The second region may be formed in a radially inboard position or a radially outboard position along a length of the stator slot.

The first region may be formed in one of a radially inboard position and a radially outboard position along a length of the stator slot. The second region may be formed in the other one of the radially inboard position and the radially outboard position along a length of the stator slot.

The first region of the second slot sidewall may be substantially planar. Alternatively, or in addition, the second region of the second slot sidewall may be substantially planar.

The first region of the second slot sidewall may extend at least substantially parallel to the central slot axis of the winding slot. Alternatively, or in addition, the second region of the second slot sidewall may extend at least substantially parallel to the central slot axis of the winding slot.

The second region of the second slot sidewall may extend at least substantially parallel to the central slot axis of the winding slot. The first and second regions of the second slot sidewall may be disposed respective first and second planes. The first and second planes may extend at least substantially parallel to each other.

The second slot sidewall may comprise a step between the first and second regions. The step may comprise an interruption or discontinuity in the second slot sidewall. For example, the step may extend substantially perpendicular to the central slot axis. Alternatively, the step may comprise a tapered section or an inclined section. For example, the step may be inclined at an acute angle to the central slot axis.

The first region is offset from the second region by a distance substantially equal to the thickness of the slot liner.

According to an aspect of the present invention there is provided a stator core for an electric machine, the stator core comprising: a central stator axis; a plurality of winding slots in the stator core, each of the plurality of winding slots being configured to receive a winding and a slot liner, the winding slots each having a length extending along a respective central slot axis, each of the respective central slot axes extending radially from, and orthogonal to, the central stator axis; and wherein the winding slots each comprise: a first slot sidewall and a second slot sidewall, the first and second slot sidewalls being disposed on respective first and second sides of the central slot axis of the winding slot; the first slot sidewall extending at least substantially parallel to the central slot axis of the winding slot; and wherein the second slot sidewall comprises or consists of a first region, the first region being inclined at an acute angle to the central slot axis of the winding slot to form a slot expansion region arranged to accommodate at least a portion of an overlap of the slot liner.

The first region of the second slot sidewall may be substantially planar.

The second slot sidewall may optionally comprise a second region. The second region may extend at least substantially parallel to the central slot axis of the winding slot. The second region may be disposed adjacent to the slot expansion region. The second region of the second slot sidewall may be substantially planar.

The first region is configured to accommodate the overlap of the slot liner. The first region forms the slot expansion region which, in the assembled stator, has sufficient volume to receive the overlap of the slot liner. The first region forms a section of the stator slot having sufficient width (in a circumferential direction) to accommodate the windings plus the overlapping region of the slot liner. In an assembled stator, the first region may be spaced apart from the windings by a circumferential distance which is greater than or equal to twice the thickness of the slot liner. The first region may be formed in a radially inboard position or a radially outboard position along a length of the stator slot.

At least in certain embodiments, the second region does not have sufficient width (in a circumferential direction) to receive the overlap of the slot liner. The second region forms a section of the stator slot having insufficient slot width to accommodate the windings plus the overlapping region of the slot liner. The second region may form a section of the stator slot which is not capable of accommodating the overlap of the slot liner. In an assembled stator, the second region may be spaced apart from the windings by a circumferential distance which is less than twice the thickness of the slot liner, for example substantially equal to the thickness of the slot liner. The second region may form a section of the stator slot having sufficient width (in a circumferential direction) to accommodate only the windings plus a single (non-overlapping) layer of the slot liner on each side of the windings. At least in certain embodiments, the second region helps to preserve material in the stator core. The second region may be formed in a radially inboard position or a radially outboard position along a length of the stator slot. The plurality of winding slots may each have a winding slot opening directed towards the central stator axis. The stator core may comprise opposing first and second projections formed on first and second sides of each winding slot opening.

The first and second projections may have respective first and second surfaces oriented into an interior of the winding slot. The first and second surfaces may be asymmetric about the central slot axis. One of the first and second surfaces may be offset relative to the other one of the first and second surfaces to form a slot expansion region. The first and second surfaces may be offset from each other in a radial direction. The first surface may be disposed at a first radial distance from the central stator axis; and the second surface may be disposed at a second radial distance from the central stator axis. The first radial distance may be greater than the second radial distance. The first surface may be offset in a radial direction relative to the second surface to form the slot expansion region.

The first surface may be offset from the second surface by a distance substantially equally to the thickness of the slot liner.

The first surface may be inclined at a the width of the winding slot 15 (in a direction perpendicular to the central slot axis SY1) increases in a radially outwards direction, to the central slot axis of the winding slot. The second surface may be inclined at a second angle to the central slot axis of the winding slot. The first and second angles may be substantially equal to each other. The first and second angles may be acute angles.

According to an aspect of the present invention there is provided a stator core for an electric machine, the stator core comprising: a central stator axis; a plurality of winding slots in the stator core, each of the plurality of winding slots being configured to receive a winding and a slot liner, the winding slots each having a length extending along a respective central slot axis, each of the respective central slot axes extending radially from, and orthogonal to, the central stator axis; and wherein the winding slots each comprise a first slot sidewall and a second slot sidewall, the first and second slot sidewalls being disposed on respective first and second sides of the central slot axis of the winding slot; and a winding slot opening; wherein the stator core comprises opposing first and second projections formed on first and second sides of each said winding slot opening, the first and second projections having respective first and second surfaces oriented into the winding slot, wherein the first surface is offset from the second surface in a radial direction to form a slot expansion region arranged to provide relief for accommodating at least a portion of an overlap of the slot liner.

The first surface may be inclined at a first angle to the central slot axis of the winding slot, and the second surface may be inclined at a second angle to the central slot axis of the winding slot. The first and second angles may be substantially equal to each other. In a variant, the first and second angles may be different from each other. The first and second angles may be acute angles. The first and second angles may be less than or equal to 90°.

According to a further aspect of the present invention there is provided a stator comprising a stator core as described herein. The stator may comprise a plurality of the slot liners. One of the slot liners is provided in each of the plurality of stator winding slots. The slot liner in each stator winding slot may be formed from one or more sheet members. At least in certain embodiments, the slot liner may consist of a single sheet member. The one or more sheet members may be folded to form a loop having an overlap. The overlap may be aligned with the slot expansion region formed in each stator winding slot.

The stator may comprise a stator winding. The slot liner may be provided in each winding slot between the stator winding and the stator core.

The slot liner has been described herein as comprising or consisting of a single sheet member of the electrically insulating material. In certain embodiments, the slot liner may comprise more than one sheet member of the electrically insulating material. For example, the slot liner may comprise at least first and second sheet members of an electrically insulating material. The overlap may be formed by overlapping ends of the first and second sheet members, for example. This configuration of slot liner may be used in combination with any of the stator cores described herein.

According to a further aspect of the present invention there is provided an electric machine comprising a stator as described herein.

According to a further aspect of the present invention there is provided a vehicle comprising an electric machine as described herein.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 shows a winding slot having a slot liner with an overlap restricted by a width of the winding slot; and

Figure 2 shows an arrangement in which the winding coils have a reduced width to accommodate an overlap of the ends of the slot liner. Figure 3 shows a vehicle comprising an electric machine having a stator core in accordance with an embodiment of the invention;

Figure 4 shows a transverse section through the electric machine shown in Figure 3;

Figure 5 shows a longitudinal section through the electric machine shown in Figure 3;

Figure 6 shows an asymmetric arrangement of a winding slot in the stator core according to an embodiment of the present invention;

Figure 7 shows an asymmetric arrangement of a winding slot in the stator core according to a further embodiment of the present invention;

Figure 8 shows an asymmetric arrangement of a winding slot in the stator core according to a still further embodiment of the present invention; and

Figure 9 shows an asymmetric arrangement of a winding slot in the stator core according to a yet further embodiment of the present invention.

DETAILED DESCRIPTION

A stator core 1 in accordance with embodiments of the present invention will now be described with reference to Figures 3 to 9. The stator core 1 is suitable for a stator 3 of an electric machine 5.

As shown schematically in Figure 3, the electric machine 5 is configured to be used in an electric drive unit EDU1 of a vehicle V. The vehicle V is a road vehicle having a plurality of wheels W-n. The electric machine 5 is configured, in use, to generate torque to drive one or more of the wheels W-n. The electric machine 5 may be referred to as a traction motor or a drive motor. The vehicle V comprises one or more traction battery BTT1 for storing electrical energy. The vehicle V may be a battery electric vehicle (BEV), a hybrid electric vehicle (HEV) or a plug-in hybrid electric vehicle (PHEV). The electric drive unit EDU1 comprises one or more controller 7 and at least one inverter 9 for converting direct current (DC) supplied from the traction battery BTT1 to alternating current (AC) for supply to the electric machine 5. The electric machine 5 is a three-phase machine in the present embodiment. In use, the electric machine 5 generates a torque which is output to an axle of the vehicle V to drive one or more of the wheels W-n. One or more of the electric machines 5 may be used in the vehicle V. The vehicle V in the present embodiment is a passenger vehicle, such as an automobile. The electric machine 5 may be used in other types of vehicles, such as a utility vehicle or a sports utility vehicle.

A transverse section through the electric machine 5 is shown in Figure 4; and a longitudinal section through the electric machine 5 is shown in Figure 5. The stator core 1 is configured to form a plurality of magnetic poles which, in use, are selectively energized to cause a rotor 1 1 to rotate about a rotational axis X. The stator core 1 has a central stator axis X1 which is coincident with the rotational axis X. The stator core 1 is composed of a plurality of steel laminations, typically electrical steel. The stator core 1 comprises a radially inner portion STIN and a radially outer portion STOUT, as shown in Figure 5. The radially outer portion STOUT may be referred to as a back-iron region of the stator core 1. The stator core 1 comprises an inner surface 13 in the form of a right circular cylinder; and an outer surface 14 in the form of a right circular cylinder. A gap (not shown) is maintained between the inner surface 13 of the stator core 1 and the rotor 11. The outer surface 14 of the stator core 1 is not necessarily a right circular cylinder and other shapes are contemplated.

The stator core 1 comprises a plurality of winding slots 15. The winding slots 15 are formed in the radially inner portion STIN of the stator core 1 . The winding slots 15 are configured to receive a stator winding 17 (shown schematically in Figure 4) made up of wound coils 18 (shown in Figure 6). The winding slots 15 extend in a longitudinal direction substantially parallel to the central stator axis X1 along a length of the stator core 1 . The winding slots 15 each have a central slot axis SY (shown in Figure 6) extending in a radial direction substantially perpendicular to the central stator axis X1 . Adjacent slot axes SY are offset from each other by an angular spacing (pitch) which is substantially uniform around the stator core 1 . The winding slots 15 each comprise: a slot opening 19 open to the inner surface 13 of the stator core 1 ; and a slot end wall 20 disposed in a radially outer position.

The stator core 1 comprises a plurality of stator teeth 21. The stator teeth 21 are formed between the winding slots 15 and project radially inwardly from the radially outer portion STOUT of the stator core 1. Each of the plurality of stator teeth 21 comprises a central tooth axis TY (shown in Figure 6) extending in a radial direction substantially perpendicular to the central stator axis X1 . The stator teeth 21 are at least substantially symmetrical about the respective tooth axis TY. The stator teeth 21 are formed integrally with the stator core 1 and each have a radially inner end 21 A and a radially outer end 21 B. A first lateral projection 23 and a second lateral projection 25 are formed on the radially inner end 21 B of each stator tooth 21. The first and second lateral projections 23, 25 extend in first and second circumferential directions which are opposite to each other. The first and second lateral projections 23, 25 have respective first and second surfaces 27, 29 disposed on a radially outer side thereof and oriented into the winding slots 15. In the present embodiment, the first and second surfaces 27, 29 are inclined at respective first and second acute angles p1 , p2 to the central tooth axis TY. The first and second angles p1 , p2 substantially equal to each other in the present embodiment. In a variant, the first and second angles pi , p2 may be different from each other. The first and second angles p1 , p2 are acute angles. In a variant, the first and second surfaces 27, 29 may extend substantially perpendicular to the central tooth axis TY. The radially inner end 21A of each stator tooth 21 has a part-cylindrical inner surface 30. The plurality of part-cylindrical inner surfaces 30 collectively form the inner surface 13 of the stator core 1 .

The winding slots 15 are configured to receive the coils 18 to form the stator winding 17. In the present embodiment, the coils 18 comprise a hairpin-type flat coil which is inserted into winding slots 15. Other types of coil are also contemplated. The coils 18 form a plurality of layers in each winding slot 15. The coils 18 are disposed along the central slot axis SY of each winding slot 15. In the present embodiment, the coils 18 are arranged in six (6) layers (labelled 37A to 37F) formed in a radial direction of the stator core 1 . The coils 18 are formed from an electrically conductive material, such as copper, having an electrically insulating coating to electrically isolate each layer 37A to 37F of the stator winding 17. There may be more than or less than six (6) layers 37A to 37F. A slot liner 39 is provided in each of the winding slots 15. The slot liner 39 forms a loop extending around an internal perimeter of the winding slots 15. The slot liner 39 is composed of a sheet member 41 of an electrically insulating material, such as Nomex (RTM). The sheet member 41 may have a thickness in the range 0.1 mm to 0.2mm, preferably in the range 0.15mm to 0.2mm. In the present embodiment, the sheet member 41 has a thickness of approximately 0.17mm. The present invention is not limited to a particular thickness of the sheet member 41 . The slot liner 39 is provided in each winding slot 15 to form an electrical insulating layer between the coils 18 and the stator core 1. The slot liner 39 extends in a longitudinal direction along the length of the stator 3. In the present embodiment, the slot liner 39 consists of a single sheet member 41 of the electrically insulating material. The sheet member 41 is folded to form a loop which extends around an outside of the layers 37A to 37F.

The slot liner 39 comprises an overlap 40 where first and second end regions 41 A, 41 B of the sheet member 41 are arranged in a face-to-face arrangement. The overlap 40 is in the form of a lap joint formed by the first and second end regions 41 A, 41 B. The first and second end regions 41 A, 41 B are located alongside each other to form the overlap 40 and may optionally be fastened to each other, for example using an adhesive. The overlap 40 has an overlap distance OD which is sufficient to ensure that the coils 18 remain electrically isolated. The overlap distance OD may, for example, be larger in high-voltage systems than in low-voltage systems as there may be a greater possibility of electrical arcing from the coils 18 to the stator core 1. The overlap 40 may comprise a radial overlap portion (extending in a radial direction at least substantially parallel to the central slot axis SY1); and/or a circumferential overlap portion (extending in a circumferential direction at least substantially perpendicular to the slot central slot axis SY1). The overlap distance OD may comprise a radial overlap distance OD(R) (as shown in Figure 6) and/or a circumferential overlap distance OD(C) (as shown in Figure 7). The overlap distance OD is the sum of the radial overlap distance OD(R) and the circumferential overlap distance OD(C) (i.e., OD=OD(R)+OD(C)). One of the radial overlap distance OD(R) and the circumferential overlap distance OD(C) may be zero (0) in certain embodiments. The winding slots 15 in the stator core 1 are configured to accommodate the overlap 40 of the slot liner 39. In particular, each of the winding slots 15 comprises a slot expansion region 45 to accommodate the overlap 40. Different embodiments of the slot expansion region 45 will now be described by way of example.

A stator core 1 comprising a plurality of winding slots 15 each having a slot expansion region 45 in accordance with an embodiment of the present invention is shown in Figure 6. The winding slots 15 in the stator core 1 all have like configurations. A first one of the winding slots 15 is shown in Figure 6. The stator core 1 will be described with reference to one of the winding slots 15. Each of the winding slots 15 in the stator core 1 have like configurations.

The winding slots 15 each comprise a first slot sidewall 51 and a second slot sidewall 53. The first and second slot sidewalls 51 , 53 are disposed on respective first and second sides of the central slot axis SY1 The first slot sidewall 51 extends at least substantially parallel to the central slot axis SY1 . The first slot sidewall 51 is at least substantially planar. The second slot sidewall 53 comprises a first region 53A and a second region 53B. The first region 53A is a radially outer region of the second slot sidewall 53; and the second region 53B is a radially inner region of the second slot sidewall 53. In the present embodiment, the first region 53A is at least substantially planar; and the second region 53B is at least substantially planar. The first and second regions 53A, 53B are configured to accommodate the desired overlap 40 of the slot liner 39. In particular, the relative positions and dimensions of the first and second regions 53A, 53B accommodate the desired overlap 40 of the slot liner 39. The first region 53A is configured to accommodate the overlap 40 of the slot liner. The first region 53A forms the slot expansion region 45 which has sufficient width (in a circumferential direction) to receive the windings 18 and the overlap 40 of the slot liner 39. The first region 53A may be spaced apart from the windings 18 by a circumferential distance which is greater than or equal to twice the thickness of the slot liner 39. The second region 53B is formed to preserve material in the stator core 1 . The second region 53B constrains or limits a width of the winding slot 15 such that the overlap 40 of the slot liner 39 cannot be accommodated between the second slot sidewall 53 and the windings 18. The second region 53B defines a section of the winding slot 15 having sufficient width only to accommodate the windings 18 plus a single (non-overlapping) layer of the slot liner 39 on each side of the windings 18. The second region 53B may be spaced apart from the windings 18 by a circumferential distance which is less than or equal to twice the thickness of the slot liner 39. The second region 53B may be spaced apart from the windings 18 by a circumferential distance which is substantially equal to the thickness of the slot liner 39.

As described herein, the first and second regions 53A, 53B are offset from each other to accommodate the overlap 40 formed by the first and second end regions 41 A, 41 B of the sheet member 41. The first region 53A extends in a first plane extending at least substantially parallel to the central slot axis SY1. The second region 53B extends in a second plane extending at least substantially parallel to the central slot axis SY1 . The first and second planes extend at least substantially parallel to each other.

The second slot sidewall 53 comprises a circumferential offset AZ between the first region 53A and the second region 53B. The circumferential offset AZ occurs in a direction Z substantially perpendicular to the central slot axis SY1. The first region 53A is spaced apart from the central slot axis SY1 by a first distance Z1 ; and the second region 53B is spaced apart from the central slot axis SY1 by a second distance Z2. The first distance Z1 is greater than the second distance Z2. In the present embodiment, the first slot sidewall 51 is spaced apart from the central slot axis SY1 by the second distance Z2. The magnitude of the circumferential offset AZ corresponds to the difference between the first and second distances Z1 , Z2 (i.e., Z1-Z2= AZ). The circumferential offset AZ forms the slot expansion region 45 in the winding slot 15 to accommodate the overlap 40 of the slot liner 39. The slot expansion region 45 is coincident with the first region 53A of the second slot sidewall 53. As shown in Figure 6, the slot expansion region 45 is formed in a radially outer portion of the winding slot 15. In a variant, the first distance Z1 may be less than the second distance Z2. In this arrangement, the slot expansion region 45 may be formed in a radially inner portion of the winding slot 15.

The formation of the slot expansion region 45 in the winding slot 15 may help to reduce or to avoid localised forces being applied to the slot liner 39 by the stator winding 17. The size of the circumferential offset AZ is determined in dependence on the thickness of the sheet member 41 used to form the slot liner 39. The sheet member41 has a thickness of approximately 0.17mm in the present embodiment. The circumferential offset AZ is approximately 0.2mm to accommodate the additional layer of the sheet member 41 in the region of the overlap

40. The circumferential offset AZ is greater than or equal to the thickness of the sheet member 41. The circumferential offset AZ in the present embodiment is slightly larger than the thickness of the sheet member

41 , for example by a distance corresponding to a manufacturing tolerance. The circumferential offset AZ may be greater than 0.2mm, for example 0.25mm, 0.3mm or 0.4mm. Alternatively, the circumferential offset AZ may be less than 0.2mm, for example 0.15mm or 0.1 mm. In the present embodiment, the first region 53A of the second sidewall 53 extends at least substantially parallel to the central slot axis SY1 ; and the second region 53B of the second sidewall 53 extends at least substantially parallel to the central slot axis SY1 . The circumferential offset AZ is formed by a step 55 in the second sidewall 53 between the first region 53A and the second region 53B. The step 55 in the present embodiment comprises an inclined region 57, for example inclined a first acute angle to the central slot axis SY1. The step 55 may optionally comprise one or more rounded corners. The one or more rounded corners may help to reduce the localised forces applied to the sheet member 41 forming the slot liner 39.

As shown in Figure 6, the first end region 41 A of the sheet member 41 is located adjacent to the coils 18. The first end region 41 A extends alongside at least some of the layers 37A to 37F of the coils 18. An edge of the first end region 41 A of the sheet member is disposed proximal to or at the slot end wall 20. The first end region 41 A does not overlap the slot end wall 20 in the present embodiment. This arrangement is advantageous since it avoids forming a fold in the first end region 41 A of the sheet member 41. The second end region 41 B of the sheet member 41 is disposed between the first end region 41 A and the second sidewall 53 of the winding slot 15. In this arrangement, the whole of the overlap 40 is formed alongside the second sidewall 53 of the winding slot 15. In particular, the whole of the overlap 40 is formed alongside the first region 53A of the second sidewall 53. The step 55 between the first and second regions 53A, 53B creates the circumferential offset AZ which forms the slot expansion region 45. The step 55 forms a slot extending along the length of the stator core 1. The step 55 is formed in the second sidewall 53 at a first slot distance SD1 measured from the slot end wall 20 in a direction parallel to the central slot axis SY1. The first slot distance SD1 is greater than or equal to the overlap distance OD(R), i.e., SD1 >=OD(R). The slot expansion region 45 is formed along the second sidewall 53 for at least the first slot distance SD1 (measured from the slot end wall 20). The slot expansion region 45 has a radial extent substantially equal to the first slot distance SD1 . It will be appreciated that the winding slot 15 is asymmetric about the central slot axis SY1 , i.e. does not have a line of reflection symmetry along the central slot axis SY1.

In the assembled stator 3, the first and second end regions 41 A, 41 B of the sheet member 41 are arranged to form the overlap 40. The overlap 40 is disposed in the slot expansion region 45 formed by offsetting the first region 53A of the second sidewall 53 relative to the second region 53B of the second sidewall 53 in a direction perpendicular to the central slot axis SY1.

In a variant shown in Figure 7, the slot expansion region 45 is again formed by offsetting the first region 53A relative to the second region 53B by the circumferential offset AZ. However, the slot expansion region 45 also comprises extending the winding slot 15 in a radial direction by a radial offset AY. In the present embodiment, the radial offset AY is substantially equal to the circumferential offset AZ. The slot expansion region 45 comprises a radial portion formed by forming the slot end wall 20 to create a radial gap between the radially outer layer 37A of the winding 18 and the slot end wall 20. The slot end wall 20 is offset from the previous embodiment by the radial offset AY. Thus, the slot expansion zone 45 is formed in the second sidewall 53 and at the radially outer portion of the winding slot 15. The winding slots 15 in the stator core 1 all have like configurations. A first one of the winding slots 15 is shown in Figure 7. The first sidewall 51 is substantially planar and extends substantially parallel to the central slot axis SY1 . The formation of the slot expansion region 45 in the second sidewall 53 of the slot winding 15 is unchanged from the previous embodiment. The first and second region 53A, 53B each extend at least substantially parallel to the central slot axis SY1 . The circumferential offset AZ is formed by the step 55 between the first and second regions 53A, 53B. The step 55 may optionally comprise an inclined region 57 and/or one or more rounded corners. However, the radial location of the step 55 is modified in this arrangement to reduce the radial extent of the slot expansion region 45 (compared to the previous embodiment).

As shown in Figure 7, the first end region 41 A of the sheet member 41 is located adjacent to the coils 18. The first end region 41 A extends at least partway across a top of the radially outer layer 37A. The edge of the first end region 41A of the sheet member 41 terminates proximal to or at the first sidewall 51 without extending alongside the first sidewall 51. The first end region 41 A extends alongside the second sidewall 53 and the slot end wall 20. The second end region 41 B of the sheet member 41 is disposed between the first end region 41 A and the second sidewall 53 of the winding slot 15. In this arrangement, the overlap 40 comprises a circumferential overlap formed between the radially outer layer 37A and the slot end wall 20; and a radial overlap formed alongside the second sidewall 53 of the winding slot 15. The total overlap distance OD is equal to the sum of a circumferential overlap distance OD(C) and a radial overlap distance OD(R) (i.e., OD=OD(C)+OD(R)). The step 55 between the first and second regions 53A, 53B creates the circumferential offset AZ which forms a portion of the slot expansion region 45. The remainder of the overlap distance OD is created by the increased length of the winding slot 15. The step 55 is formed in the second sidewall 53 at a second slot distance SD2 measured from the slot end wall 20. The second slot distance SD2 is less than the overlap distance OD, i.e., SD2<OD. The second slot distance SD2 is greater than or equal to the radial overlap distance OD(R), i.e., SD2>=OD(R). The slot expansion region 45 is formed by extending the winding slot 15 in a radial direction by a radial offset AY (compared to the previous embodiment); and along the second sidewall 53 for the second slot distance SD2 (measured from the slot end wall 20). In the present embodiment, the radial offset AY is at least substantially equal to the circumferential offset AZ. The slot expansion region 45 has a radial extent substantially equal to the first slot distance SD1. It will be appreciated that the winding slot 15 is asymmetric about the central slot axis SY1 , i.e., the winding slot 15 does not have a line of reflection symmetry along the central slot axis SY1 .

In the assembled stator 3, the first and second end regions 41 A, 41 B of the sheet member 41 are arranged to form the overlap 40. The slot expansion region 45 comprises a circumferential portion formed by offsetting the first region 53A of the second sidewall 53 relative to the second region 53B of the second sidewall 53 in a direction perpendicular to the central slot axis SY1 ; and a radial portion formed by offsetting the slot end wall 20 in a radial direction (along the central slot axis SY1) to increase a radial gap (clearance) between the radially outer layer 37A of the winding 18 and the slot end wall 20.

In a further variant shown in Figure 8, the slot expansion region 45 is at least partially formed by inclining the second sidewall 53 at a first acute angle a1 relative to the central slot axis SY1. The winding slots 15 in the stator core 1 all have like configurations. A first one of the winding slots 15 is shown in Figure 8.

The first and second sidewalls 51 , 53 are not parallel in this arrangement. Rather, the second sidewall 53 tapers outwardly away from the central slot axis SY1 towards an outside of the stator core 1 . The slot expansion region 45 may optionally also comprise extending the winding slot 15 in a radial direction by a radial offset AY. The radial offset AY may, for example, be substantially equal to the circumferential offset AZ. The slot expansion region 45 comprises a radial portion formed by forming the slot end wall 20 to create a radial gap between the radially outer layer 37A of the winding 18 and the slot end wall 20. The winding slot 15 is asymmetric about the central slot axis SY1.

In the arrangement illustrated in Figure 8, the first sidewall 51 is substantially planar and extends substantially parallel to the central slot axis SY1 . At least a portion of the second sidewall 53 is substantially planar and is oriented at the first acute angle a1 to the central slot axis SY1. In the present embodiment, the whole of the second sidewall 53 is substantially planar and is oriented at the first acute angle a1 to the central slot axis SY1 . The resulting winding slot 15 has a continuous taper. The taper angle corresponds to the first acute angle a1 with respect to the central slot axis SY1. The width of the winding slot 15 (in a direction perpendicular to the central slot axis SY1) increases in a radially outwards direction. This arrangement does not require the formation of the step 55 in the second sidewall 53. The width of the winding slot 15 is largest in a radially outer position, thereby forming the slot expansion region 45 to accommodate the overlap 40 of the slot liner 39.

The second slot sidewall 53 comprises a first region 53A and a second region 53B. The first region 53A is configured to accommodate the overlap 40 of the slot liner. The first region 53A forms the slot expansion region 45 which has sufficient width (in a circumferential direction) to receive the windings 18 and the overlap 40 of the slot liner 39. The first region 53A may be spaced apart from the windings 18 by a circumferential distance which is greater than or equal to twice the thickness of the slot liner 39. The second region 53B is formed to preserve material in the stator core 1 . The second region 53B constrains or limits a width of the winding slot 15 such that the overlap 40 of the slot liner 39 cannot be accommodated between the second slot sidewall 53 and the windings 18. The second region 53B defines a section of the winding slot 15 having sufficient width only to accommodate the windings 18 plus a single (non-overlapping) layer of the slot liner 39 on each side of the windings 18. The second region 53B may be spaced apart from the windings 18 by a circumferential distance which is less than or equal to twice the thickness of the slot liner 39. The second region 53B may be spaced apart from the windings 18 by a circumferential distance which is substantially equal to the thickness of the slot liner 39.

The first region 53A is a radially outer region of the second slot sidewall 53; and the second region 53B is a radially inner region of the second slot sidewall 53. In the present embodiment, the second slot sidewall 53 is substantially planar and the first and second regions 53A, 53B are at least substantially aligned with each other. The first region 53A is configured to accommodate the desired overlap 40 of the slot liner 39. In particular, the first region 53A is configured to form the slot expansion region 45 to accommodate the desired overlap 40 of the slot liner 39. In the assembled stator 3, the first region 53A is spaced apart from the windings 18 in a circumferential direction to form the slot expansion region 45. The first region 53A is configured such that, in the assembled stator 3, the spacing between the first region 53A and the windings 18 is greater than or equal to the thickness of the overlap 40 of the slot liner 39. The overlap 40 of the slot liner 39 extends at least partway along the length of the first region 53A.The second region 53B is configured such that, in the assembled stator 3, the spacing between the second region 53B and the windings 18 is less than the thickness of the overlap 40 of the slot liner 39. The overlap 40 of the slot liner 39 does not extend alongside the second region 53B of the second sidewall 53. The first end region 41 A extends at least partway across a top of the radially outer layer 37A. The first end region 41 A terminates proximal to or at the first sidewall 51 without extending alongside the first sidewall 51 . The first end region 41A extends alongside the second sidewall 53 and the slot end wall 20. The second end region 41 B of the sheet member 41 is disposed between the first end region 41 A and the second sidewall 53 of the winding slot 15. In this arrangement, the overlap 40 comprises a circumferential overlap OD(C) formed between the radially outer layer 37A and the slot end wall 20; and a radial overlap OD(R) formed alongside the second sidewall 53 of the winding slot 15. The total overlap distance OD is equal to the sum of a circumferential overlap distance OD(C) and a radial overlap distance OD(R) (i.e., OD=OD(C)+OD(R)).

The second sidewall 53 is inclined at the first acute angle a1 to form the slot expansion region 45. The first acute angle a1 is defined such that the slot expansion region 45 has sufficient width (in a direction perpendicular to the central slot axis SY1) to accommodate the overlap 40 formed by the first and second end regions 41 A, 41 B of the sheet member 41 . At a radial position substantially coincident with the distal end of the second end region 41 B of the sheet member 41 forming the slot liner 37, the second sidewall 53 is spaced apart from the apart from the central slot axis SY1 by a first distance Z1 ; and the first slot sidewall 51 is spaced apart from the central slot axis SY1 by a second distance Z2. The difference between the first and second distances Z1 , Z2 may, for example, correspond to the magnitude of the circumferential offset AZ outlined above (i.e. Z1-Z2=AZ). The circumferential offset AZ may, for example, be substantially equal to or greater than the thickness of the sheet member 41.

In the assembled stator 3, the first and second end regions 41 A, 41 B of the sheet member 41 are arranged to form the overlap 40. The slot expansion region 45 comprises a circumferential portion formed by inclining the second sidewall 53 at the first acute angle a1 relative to the central slot axis SY1 ; and a radial portion formed by offsetting the slot end wall 20 in a radial direction by a radial offset AY (along the central slot axis SY1) to increase a radial gap (clearance) between the radially outer layer 37A of the winding 18 and the slot end wall 20. In the present embodiment, the radial offset AY is at least substantially equal to the circumferential offset AZ. The radial offset AY may, for example, be substantially equal to or greater than the thickness of the sheet member 41.

In a variant of the above example, the second sidewall 53 may comprise first and second regions 53A, 53B. One of the first and second regions 53A, 53B may be oriented substantially parallel to the central slot axis SY1 ; and the other one of the first and second regions 53A, 53B may be tapered at the first acute angle a1 relative to the central slot axis SY1 . For example, the first region 53A disposed in a radially outer position of the winding slot 15 may be oriented substantially parallel to the central slot axis SY1 . The second region 53B disposed in a radially inner position of the winding slot 15 may be oriented at the first acute angle a1 relative to the central slot axis SY1. The width of the winding slot 15 (in a direction perpendicular to the central slot axis SY1) is at least substantially uniform in the first region 53A. The width of the winding slot 15 is largest in the radially outer position coincident with the first region 53A. In this arrangement, the slot expansion region 45 which accommodates the overlap 40 of the slot liner 39 is formed by the first region 53A. The width of the winding slot 15 (in a direction perpendicular to the central slot axis SY1) increases in a radially outwards direction in the second region 53B. The first region 53A is configured such that, in the assembled stator 3, the spacing between the first region 53A and the windings 18 is greater than or equal to the thickness of the overlap 40 of the slot liner 39. The overlap 40 of the slot liner 39 extends at least partway along the length of the first region 53A. In the second region 53B, the width of the winding slot 15 (in a direction perpendicular to the central slot axis SY1) increases in a radially outwards direction. The taper angle of the second region 53B corresponds to the first acute angle a1 with respect to the central slot axis SY1 . The second region 53B is configured such that, in the assembled stator 3, the spacing between the second region 53B and the windings 18 is less than the thickness of the overlap 40 of the slot liner 39. The overlap 40 of the slot liner 39 does not extend alongside the second region 53B of the second sidewall 53.

In the assembled stator 3, the first and second end regions 41 A, 41 B of the sheet member 41 are arranged to form the overlap 40. The slot expansion region 45 comprises a circumferential portion formed by the first region 53A of the second sidewall which is offset from the slot central slot axis SY1 by the circumferential offset AZ formed by inclining the second region 53B of the second sidewall 53 at the first acute angle a1 relative to the central slot axis SY1. The slot expansion region 45 may optionally also comprise a radial portion formed by offsetting the slot end wall 20 in a radial direction (along the central slot axis SY1) to increase a radial gap (clearance) between the radially outer layer 37A of the winding 18 and the slot end wall 20.

It will be understood that the slot expansion region 45 may be formed in a radially inner position of the stator core 1. In a further variant illustrated in Figure 9, at least a portion of the slot expansion region 45 may be accommodated, at least in part, by features of the first and second lateral projections 23, 25 formed on the stator teeth 21. As outlined herein, the first and second lateral projections 23, 25 have respective first and second surfaces 27, 29 oriented into the winding slots 15. In the present embodiment, the first and second surfaces 27, 29 extend substantially perpendicular to the central tooth axis TY. The first and second surfaces 27, 29 are offset from each other in a radial direction by a radial offset AY. By offsetting the first and second surfaces 27, 29 in a radial direction, at least a portion of the slot expansion region 45 is formed at a radially inner position of the winding slot 15. It will be understood that this could be combined with the other features described herein to extend the slot expansion region 45 in a radial direction. The resulting slot expansion region 45 would include radial and circumferential expansions configured to accommodate an overlap 40 having a larger overlap distance OD.

It will be appreciated that various changes and modifications can be made to the present invention without departing from the scope of the present application.

Claims

1. A stator core for a stator of an electric machine, the stator core comprising: a central stator axis; a plurality of winding slots in the stator core, each of the plurality of winding slots being configured to receive a winding and a slot liner, the winding slots each having a length extending along a respective central slot axis, each of the respective central slot axes extending radially from, and orthogonal to, the central stator axis; and wherein the winding slots each comprise: a first slot sidewall and a second slot sidewall, the first and second slot sidewalls being disposed on respective first and second sides of the central slot axis of the winding slot; the first slot sidewall extending at least substantially parallel to the central slot axis of the winding slot; and wherein the second slot sidewall comprises or consists of a first region and a second region, the first region being offset from the second region in a direction perpendicular to the central slot axis of the winding slot to form a slot expansion region for accommodating at least a portion of an overlap of the slot liner, the first region extending at least substantially parallel to the central slot axis of the winding slot.

2. A stator core according to claim 1 , wherein the second region of the second slot sidewall extends at least substantially parallel to the central slot axis of the winding slot.

3. A stator core according to claim 1 or claim 2, wherein the second slot sidewall comprises a step between the first and second regions.

4. A stator core according to any one of claims 1 , 2 or 3, wherein the second region of the second slot sidewall is substantially planar.

5. A stator core according to any one of the preceding claims, wherein the first region is offset from the second region by a distance substantially equal to the thickness of the slot liner.

6. A stator core for an electric machine, the stator core comprising: a central stator axis; a plurality of winding slots in the stator core, each of the plurality of winding slots being configured to receive a winding and a slot liner, the winding slots each having a length extending along a respective central slot axis, each of the respective central slot axes extending radially from, and orthogonal to, the central stator axis; and wherein the winding slots each comprise: a first slot sidewall and a second slot sidewall, the first and second slot sidewalls being disposed on respective first and second sides of the central slot axis of the winding slot; the first slot sidewall extending at least substantially parallel to the central slot axis of the winding slot; and wherein the second slot sidewall comprises or consists of a first region, the first region being inclined at an acute angle to the central slot axis of the winding slot to form a slot expansion region arranged to accommodate at least a portion of an overlap of the slot liner.

7. A stator core according to claim 6, wherein the second slot sidewall comprises a second region, the second region extending at least substantially parallel to the central slot axis of the winding slot and being disposed adjacent to the slot expansion region.

8. A stator core according to any one of the preceding claims, wherein each of the plurality of winding slots have a winding slot opening directed towards the central stator axis; the stator core comprising opposing first and second projections formed on first and second sides of each winding slot opening.

9. A stator core according to claim 8, wherein the first and second projections have respective first and second surfaces oriented into an interior of the winding slot, wherein the first surface is offset in a radial direction relative to the second surface to form the slot expansion region.

10. A stator core according to claim 9, wherein the first surface is offset from the second surface by a distance substantially equally to the thickness of the slot liner.

11. A stator core according to claim 9, wherein the first surface is inclined at a first angle to the central slot axis of the winding slot, and the second surface is inclined at a second angle to the central slot axis of the winding slot; the first and second angles being substantially equal acute angles.

12. A stator core for an electric machine, the stator core comprising: a central stator axis; a plurality of winding slots in the stator core, each of the plurality of winding slots being configured to receive a winding and a slot liner, the winding slots each having a length extending along a respective central slot axis, each of the respective central slot axes extending radially from, and orthogonal to, the central stator axis; and wherein the winding slots each comprise a first slot sidewall and a second slot sidewall, the first and second slot sidewalls being disposed on respective first and second sides of the central slot axis of the winding slot; and a winding slot opening; wherein the stator core comprises opposing first and second projections formed on first and second sides of each said winding slot opening, the first and second projections having respective first and second surfaces oriented into the winding slot, wherein the first surface is offset from the second surface in a radial direction to form a slot expansion region arranged to provide relief for accommodating at least a portion of an overlap of the slot liner.

13 A stator core according to claim 12, wherein the first surface is offset from the second surface by a distance substantially equally to the thickness of the slot liner.

14. A stator core according to claim 12 or claim 13, wherein the first surface is inclined at a first angle to the central slot axis of the winding slot, and the second surface is inclined at a second angle to the central slot axis of the winding slot; the first and second angles being substantially equal acute angles.

15 A stator comprising a stator core as claimed in any one of the preceding claims.

16. A stator as claimed in claim 15 comprising a slot linerdisposed in each of the plurality of stator winding slots, the slot liner in each stator winding slot being formed from a sheet member, the sheet member being folded to form a loop having an overlap, wherein the overlap is aligned with the slot expansion region formed in each stator winding slot.

17. An electric machine comprising a stator as claimed in claim 15 or claim 16.

18. A vehicle comprising an electric machine as claimed in claim 17.