Stator assembly

Abstract

A stator assembly 10 for an electrical machine of a vehicle traction motor, the stator assembly comprises: a stator core 12 comprising an axial end surface 18; a cover 30A which covers the axial end s

Description

TECHNICAL FIELD The present disclosure relates to a stator assembly for an electrical machine of a vehicle traction motor. Aspects of the invention relate to a stator assembly, to a cooling manifold, to a stator core, to an electric machine, to a vehicle, and to a method. BACKGROUND It is known to provide an electrical machine with a stator core having a plurality of cooling passageways which extend in a longitudinal direction through the stator core. In such an electrical machine, there may be a cooling manifold which defines a chamber in fluid communication with the cooling passageways. In this way, a flow of cooling fluid can be input to the chamber and then through the cooling passageways to remove heat from the stator core. 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 assembly, a cooling manifold, a stator core, an electric machine, and a vehicle as claimed in the appended claims. According to an aspect of the present disclosure, there is provided a stator assembly. The stator assembly comprises: a stator core, and a cover which at least partly covers the stator core. The stator assembly also comprises an interlocking arrangement configured to secure the cover to the stator core. Such an interlocking arrangement provides a means of securing a cover to a stator core (e.g., to an axial end surface of the stator core) without the need for additional fasteners (e.g., by pushing and twisting the cover and stator core relative to each other, or by snap-fitting resilient clips etc.). Further, it will be understood that because a stator core generally remains static within a housing of an electric machine (in contrast to the rotating rotor), use of an interlocking arrangement may provide a suitably robust connection between the cover and the stator core. The stator assembly may be for an electrical machine of a vehicle traction motor. Optionally, the stator core comprises an axial end surface, and the cover at least partly covers the axial end surface of the stator core. Optionally, the stator core comprises a plurality of cooling passageways which extend in a longitudinal direction through the stator core away from the axial end surface. Optionally, the cover is a cooling manifold which defines at least one cooling channel in fluid communication with the plurality of cooling passageways. Such an arrangement allows the stator core to be cooled by passing a flow of cooling fluid through the cooling manifold and cooling passageways. Optionally, the at least one cooling channel comprises a chamber in fluid communication with the cooling passageways. Optionally, the cooling manifold further comprises a manifold inlet or manifold outlet for connecting the chamber to a cooling fluid circuit. Optionally, the stator assembly comprises a seal positioned between the stator core and the cover, such that the seal is compressed therebetween by the interlocking arrangement. By compressing the seal with the interlocking arrangement, a contact pressure between the seal and the stator core and cover can be increased, which improves seal performance. For example, this may be useful when the cover is a cooling manifold which defines a chamber, whereby the seal is configured to seal an edge of the chamber. Optionally, the interlocking arrangement comprises a bayonet arrangement. Such a bayonet arrangement provides a simple means of securing a cover a stator core (e.g, by pushing and twisting the cover and stator core relative to each other). Further, once connected such a bayonet arrangement may be able to withstand greater axial separation forces than alternatives, such as snap-fit arrangements. Optionally, the bayonet arrangement is configured to withstand an axial separation force of at least 2kN, optionally at least 3kN, optionally at least 4kN, optionally at least 5kN. This provides a robust connection between the cover and the stator core. For example, this may be useful when the cover is a cooling manifold as the bayonet arrangement may be able to withstand a high pressure of cooling fluid inside within the cooling manifold, and / or a resilient force of a seal compressed between the stator core and the cover. Optionally, the cover is formed of metallic material. Optionally, the cover is formed of steel or aluminium alloy material. This provides a robust cover. Further, the cover side of the bayonet arrangement being formed of metallic material helps to provide a robust connection between the cover and the stator core. Optionally, the bayonet arrangement comprises at least one bayonet connector on the cover and at least one bayonet receiver on the stator core. Such a combination of bayonet connector(s) and bayonet receiver® provides a simple bayonet arrangement. Further, because the bayonet connector® (e.g., projecting part® of the bayonet arrangement) are on the cover and the bayonet receiver® (e.g, recessed portion® of the bayonet arrangement) are on the stator core, the stator core can be produced via normal manufacturing techniques (e.g, as a stator lamination stack). As used herein, the terms “bayonet arrangement”, “bayonet fitting”, and “bayonet mount” are used interchangeably to refer to a fastening or attachment mechanism in which an interlocking arrangement is formed between two components by pushing the respective components axially towards each other, and then rotating the respective components relative to each other to inhibit relative axial movement between the respective components in at least one axial direction. In some embodiments, a biasing force is also present to maintain the interlocking arrangement and resist relative rotation (e.g, by increasing friction between interlocking portions of the bayonet arrangement. For example, such a biasing force may be provided by compression of a seal positioned between the respective components, and / or pressurised fluid acting between the respective components and / or a spring and / or any other suitable biasing arrangement. In some embodiments, an additional locking component may be used to inhibit relative rotation between the respective components (e.g, a pin or grub screw). Optionally, the bayonet arrangement comprises a plurality of bayonet connectors on the cover and corresponding plurality of bayonet receivers on the stator core. Having a plurality of bayonet connectors and bayonet receivers may provide a more robust connection between the cover and the stator core. Optionally, the plurality of bayonet connectors and bayonet receivers are distributed circumferentially about the stator core and the cover. The bayonet connectors and bayonet receivers may be evenly distributed circumferentially. Optionally, the bayonet arrangement comprises at least three, optionally at least four, optionally at least five, optionally at least six bayonet connectors and a corresponding number of bayonet receivers. In some embodiments, the bayonet arrangement comprises at least one bayonet connector on the stator core and at least one bayonet receiver on the cover. In some embodiments, the bayonet arrangement comprises at least one bayonet connector on the stator core, at least one bayonet connector on the cover, at least one bayonet receiver on the stator core, and at least one bayonet receiver on the cover. In some embodiments, the bayonet arrangement comprises at least one bayonet receiver on the stator core, and at least one bayonet receiver on the cover. In such embodiments, the bayonet arrangement may further comprise an intermediate component. The intermediate component may comprise at least one bayonet connector for connecting to the at least one bayonet receiver of the stator core, and at least one bayonet connector for connecting to the at least one bayonet receiver of the cover. Optionally, the bayonet arrangement is configured so that the cover is pushed axially towards the axial end surface of the stator core to insert the or each bayonet connector into the corresponding bayonet receiver, and then twisted about a central axis of the cover and / or stator core to form an interlocking arrangement between the or each bayonet connector and the corresponding bayonet receiver and thereby inhibit axial movement of the cover relative to the stator core. Optionally, the cover is twisted about the central axis of the cover in an anti-clockwise direction with respect to the axial end surface of the stator core to form the interlocking arrangement. Optionally, the stator core is at least partly defined by a stator lamination stack, and wherein the profile of the at least one bayonet receiver is formed by stacking layers of stator laminates together in an axial direction towards the axial end surface of the stator core. This provides a simple means of manufacturing the bayonet receiver. The stator laminates may have different profiles. The stator laminates may have the same or similar profiles. In such embodiments, at least some of the stator laminates may be arranged in the stack at different rotational orientations about a central axis in order to define the profile of the at least one bayonet receiver. The stator core may be entirely defined by a stator lamination stack. Optionally, the stator lamination stack comprises at least one layer having a first profile which does not define any bayonet receiver features, at least one layer having a second profile which defines a portion of an axial recess and a portion of a circumferential recess of the bayonet receiver, and at least one layer having a third profile which defines a further portion of the axial recess and a step for an abutment surface of the bayonet receiver. This provides a simple means of providing a suitable bayonet receiver. Alternatively, the at least one bayonet receiver may be machined into the stator core (e g., into a stator lamination stack of identical layers, or into a forged / cast stator core). Optionally, the at least one bayonet receiver comprises an axial recess which extends axially inboard from the axial end surface of the stator core, a circumferential recess which extends circumferentially from an axially inboard end of the axial recess, and an abutment surface positioned axially between the circumferential recess and the axial end surface of the stator core. Optionally, the at least one bayonet connector comprises an axial projection which extends from the cover and a transverse projection which extends from a free end of the axial projection. In this way, the axial projection of the at least one bayonet connector can be pushed along the axial recess of the at least one bayonet receiver (e.g., by pushing the cover towards the stator core), the corresponding components can then be rotated so that the transverse projection of the at least one bayonet connector moves along the circumferential recess of the at least one bayonet receiver, so that the transverse projection engages the abutment surface to inhibit axial separation of the cover and stator core. Optionally, the axial and circumferential recesses comprise grooves in an outer radial surface of the stator core. This may be easier to manufacture than alternatives (e.g., internal bores within the stator core). Optionally, the grooves have a radially inner edge at a first radial dimension, and a radially outer edge at a second radial dimension, and wherein the stator core has a third radial dimension between the abutment surface and the axial end surface of the stator core, wherein the third radial dimension is between the first and second radial dimensions. In this way, the axial projection of the bayonet connector can extend over the abutment surface while remaining flush with an outer radial surface of the stator core. Optionally, the interlocking arrangement comprises a snap-fit arrangement. Such a snap-fit arrangement allows the cover to be secured to the stator core simply by pushing the cover towards the axial end surface of the stator core. Optionally, the snap-fit arrangement comprises at least one resilient clip on the cover and at least one clip recess on the stator core, for receiving the at least one resilient clip. Optionally, the snap-fit arrangement comprises a plurality of resilient clips on the cover and a corresponding plurality of clip recesses on the stator core for receiving the resilient clips. Having a plurality of resilient clips and a corresponding plurality of clip recesses provides a more robust connection than a single clip / recess. Optionally, the plurality of clip recesses are distributed circumferentially about the stator core. The plurality of clip recesses may be evenly distributed circumferentially. Optionally, the snap-fit arrangement comprises a plurality of resilient clips on the cover and an annular clip recess on the stator core for receiving the resilient clips. Such an annular clip recess allows the cover to be pushed to form the snap-fit engagement in any angular orientation (i.e., without the need to align the resilient clip(s) with corresponding clip recess(es) first. Optionally, the plurality of resilient clips are distributed circumferentially about the cover. The plurality of resilient clips may be evenly distributed circumferentially. Optionally, the snap-fit arrangement comprises at least three, optionally at least four, optionally at least five, optionally at least six resilient clips on the cover. Optionally, the cover is formed of plastic material. This may facilitate integrally forming the resilient clips with the cover (e.g., in contrast with covers made from more rigid materials, such as metal). Alternatively, the resilient clips may be formed of plastic material and the cover itself may be formed of a different material. Optionally, the stator core is at least partly defined by a stator lamination stack, and wherein the profile of the at least one clip recess for receiving the resilient clips is formed by stacking layers of stator laminates together in an axial direction towards the axial end surface of the stator core. This provides a simple means of manufacturing the at least one recess. The stator laminates may have different profiles. The stator laminates may have the same or similar profiles. In such embodiments, at least some of the stator laminates may be arranged in the stack at different rotational orientations about a central axis in order to define the profile of the at least one clip recess for receiving the resilient clips. The stator core may be entirely defined by a stator lamination stack. Optionally, the stator lamination stack comprises at least one layer having a first profile which does not define any clip recess features, and at least one layer having a second profile which defines the at least one clip recess. This provides a simple means of manufacturing the at least one clip recess. Alternatively, the at least one clip recess may be machined into the stator core (e.g., into a stator lamination stack of identical layers, or into a forged / cast stator core). Optionally, the at least one clip recess for the at least one clip comprises at least one groove in an outer radial surface of the stator core. This may be simpler to manufacture than alternatives (such as an internal bore in the stator core). In some embodiments, the axial end surface is a first axial end surface, the cover is a first cooling manifold secured to the first axial end surface of the stator core by a bayonet arrangement as disclosed herein, and the stator assembly further comprises a second cooling manifold secured to a second axial end surface of the stator core by a snap-fit arrangement as disclosed herein. A further aspect of the present disclosure provides a cooling manifold for coupling to a stator core. The cooling manifold defines at least one cooling channel which is open at an axial end of the cooling manifold for fluid communication with an axial end surface of the stator core. The cooling manifold further comprises at least one bayonet connector configured to form an interlocking arrangement with a corresponding bayonet receiver of the stator core to secure the cooling manifold to said stator core. Such a cooling manifold may be secured easily to a stator core by engaging the at least one bayonet connector of the cooling manifold with the corresponding bayonet receiver of the stator core. Optionally, the at least one cooling channel comprises a chamber which is open at the axial end of the cover for fluid communication with the axial end surface of the stator core. Optionally, the cooling manifold further comprises a manifold inlet or manifold outlet for connecting the chamber to a cooling fluid circuit. Optionally, the chamber is open at the axial end of the cover for transfer of cooling fluid from the chamber to one or more cooling passageways positioned adjacent to the cover when assembled. The cooling manifold may be for coupling to a stator core of a stator assembly for an electrical machine of a vehicle traction motor. A further aspect of the present disclosure provides a cooling manifold for coupling to a stator core. The cooling manifold defines at least one cooling channel which is open at an axial end of the cooling manifold for fluid communication with an axial end surface of the stator core. The cooling manifold further comprises at least one resilient clip configured to form an interlocking arrangement with a corresponding recess of the stator core to secure the cooling manifold to said stator core. Such a cooling manifold may be secured easily to a stator core by engaging the at least one resilient clip of the cooling manifold with the corresponding recess in the stator core. Optionally, the at least one cooling channel comprises a chamber which is open at the axial end of the cover for fluid communication with the axial end surface of the stator core. Optionally, the cooling manifold further comprises a manifold inlet or manifold outlet for connecting the chamber to a cooling fluid circuit. Optionally, the chamber is open at the axial end of the cover for transfer of cooling fluid from the chamber to one or more cooling passageways positioned adjacent to the cover when assembled. The cooling manifold may be for coupling to a stator core of a stator assembly for an electrical machine of a vehicle traction motor. A further aspect of the present disclosure provides a stator core. The stator core comprises an axial end surface, and at least one bayonet receiver configured to form an interlocking arrangement with a corresponding bayonet connector of a cooling manifold to secure said cooling manifold to the stator core over the axial end surface. Such a stator core may facilitate easy connection with a cooling manifold by receiving at least one bayonet connector of the cooling manifold in the at least one bayonet receiver. The stator core may be for an electrical machine of a vehicle traction motor. Optionally, the stator core comprises a plurality of cooling passageways which extend in a longitudinal direction through the stator core away from the axial end surface. A further aspect of the present disclosure provides a stator core. The stator core comprises an axial end surface, and at least one recess configured to form an interlocking arrangement with a corresponding resilient clip of a cooling manifold to secure said cooling manifold to the stator core over the axial end surface. Such a stator core may facilitate easy connection with a cooling manifold by receiving at least one resilient clip of the cooling manifold in the at least one recess. The stator core may be for an electrical machine of a vehicle traction motor. Optionally, the stator core comprises a plurality of cooling passageways which extend in a longitudinal direction through the stator core away from the axial end surface. A further aspect of the present disclosure provides an electric machine comprising a stator assembly as disclosed herein. Such an electric machine benefits from the advantages of the stator assembly outlined above. The electric machine may be for driving one or more wheels of a vehicle. Optionally, the electric machine further comprises a housing having an axial end surface, wherein the stator assembly is positioned inside the housing with a first side of the cover facing the axial end surface of the stator core and a second side of the cover facing the axial end surface of the housing, and wherein the electric machine further comprises at least one further component positioned axially between the second side of the cover and the axial end surface of the housing. It will be understood that, in such an arrangement, because there is at least one further component positioned axially between the second side of the cover and the axial end surface of the housing (e.g., one or more busbars or other electrical components), the cover may not be easily clamped between the stator core and the housing. Therefore, having the cover secured to the stator core by an interlocking arrangement provides a secure connection between the cover and the stator core without having to modify the design or positioning of the at least one further component. A further aspect of the present disclosure provides a vehicle comprising an electric machine as disclosed herein. The electric machine may be arranged to drive one or more wheels of the vehicle. Such a vehicle benefits from the advantages of the stator assembly outlined above. A further aspect of the present disclosure provides a method of coupling a cover to a stator core (e.g., of an electric machine for a vehicle traction motor). The method comprises: a) providing a stator core comprising an axial end surface; b) positioning a cover against the axial end surface of the stator core; and c) securing the cover to the stator core using an interlocking arrangement; optionally, wherein the interlocking arrangement is a bayonet arrangement which is engaged by pushing the cover axially towards the axial end surface of the stator core and then twisting the cover about a central axis of the cover and / or stator core; or wherein the interlocking arrangement is a snap-fit arrangement which is engaged by pushing the cover axially towards the axial end surface of the stator core. Such a method provides a simple means of securing a cover to an end of a stator core (e.g., by pushing and twisting the cover and stator core relative to each other). Further, it will be understood that because a stator core generally remains static within a housing of an electric machine (in contrast to the rotating rotor), use of an interlocking arrangement may provide a robust connection between the cover and the stator core. 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 vehicle according to an embodiment; Figure 2 shows a longitudinal cross-sectional view of an electric machine comprising a stator assembly according to an embodiment; Figure 3 shows a stator core and first cover of the stator assembly of Figure 2 in a disconnected state; Figure 4 shows the stator core and first cover of Figure 3 in a partially connected state; Figure 5 shows the stator core and first cover of Figures 3 and 4 in a secured state; Figure 6 shows a perspective view of a portion of a bayonet arrangement of the stator assembly of Figures 2 to 5; Figure 7 shows a cross-sectional view of the portion of the bayonet arrangement of Figure 6; Figure 8 shows a cross-sectional view of the first cover of the stator assembly of Figures 2 to 7; Figure 9 shows a side view of the stator core of the stator assembly of Figures 2 to 7; Figure 10 shows a cross-sectional view of the stator core of Figure 9 taken along plane A-A; Figure 11 shows a cross-sectional view of the stator core of Figure 9 taken along plane B-B; Figure 12 shows a cross-sectional view of the stator core of Figure 9 taken along plane C-C; Figure 13 shows the stator core and a second cover of the stator assembly of Figures 2 to 12 in a disconnected state; Figure 14 shows the stator core and second cover of Figure 13 in a secured state; Figure 15 shows a perspective view of a portion of a snap-fit arrangement of the stator assembly of Figures 2 to 14; Figure 16 shows a cross-sectional view of a portion of the snap-fit arrangement of Figure 15; Figure 17 shows a side view of the stator assembly of Figures 2 to 16 with both the first and second covers secured to the stator core; and Figure 18 shows a flow chart of a method of coupling a cover to a stator core according to an embodiment. DETAILED DESCRIPTION Examples of the present disclosure relate to a stator assembly. In particular, examples of the present invention relate to a stator assembly for an electric machine of a vehicle traction motor. Such an electric machine may be of a synchronous type or asynchronous type, for example a permanent magnet synchronous motor. Non-limiting examples will now be described with reference to accompanying Figures 1 to 18, where the figures illustrate a stator assembly 10, a stator core 12, a cover 30A, 30B, an electric machine 100, an electric drive unit (EDU) 160 and a vehicle 200. Figure 1 illustrates a vehicle 200 having a first electric machine 100-1 which is part of a vehicle traction motor for driving one or more front wheels of the vehicle 200. The vehicle 200 also has a second electric machine 100-2 which is part of a vehicle traction motor for driving one or more rear wheels of the vehicle 200. In other embodiments the vehicle 200 may comprise only a single electric machine 100, which is part of a vehicle traction motor, arranged or configured to drive one or more front wheels of the vehicle 200 and / or one or more rear wheels of the vehicle 200. At a vehicle axle, the electric machine 100 may be arranged to drive both wheels, either directly or through other transmission components. In other arrangements, there may be more than one electric machine 100 arranged to provide torque to a vehicle axle, for example, to provide torque vectoring functionality for the vehicle 200. Other arrangements may have one electric machine 100 arranged or configured to drive each wheel of the vehicle 200. The electric machine 100 comprised in the vehicle 200 may have a stator assembly 10 as described herein. For example, the electric machine 100 comprised in the vehicle 200 may be the electrical machine of Figure 2, described below. As illustrated schematically on Figure 1, the electric machine(s) 100 may be part of an electric drive unit (EDU) 160. For example, the EDU may include transmission components, lubrication and cooling components, and / or power electronics, in addition to the electric machine 100. In the vehicle 200 of Figure 1, the first electric machine 100-1 is part of a first EDU 160-1 fordriving front wheels of the vehicle 200, and the second electric machine 100-2 is part of a second EDU 160-2 for driving rear wheels of the vehicle 200. Referring to Figure 2, the electric machine 100 of the vehicle 200 is illustrated. The electric machine includes a stator assembly 10 which has an annular stator core 12. The stator core 12 has a cylindrical inner channel 14, which defines a central stator axis 16. The cylindrical inner channel 14 extends in a direction parallel to the central stator axis 16 from a first axial end surface 18 of the stator core 12 to a second axial end surface 20 of the stator core 12. The stator core 12 has a plurality of winding slots 22 extending radially to support electrical stator windings (not shown). A plurality of stator teeth 24 (shown on Figures 10 to 12) are provided between the winding slots 22. In other words, the stator teeth 24 are interspersed between the winding slots 22 in a circumferential direction about the stator core 12. Both the plurality of winding slots 22 and the plurality of stator teeth 24 extend from the first axial end surface 18 to the second axial end surface 20 of the stator core 12. The electric machine 100 also includes a rotor 112. The rotor 112 is configured to fit within the cylindrical inner channel 14 of the stator core 12 with a small air gap 26 therebetween. The outside surface of the rotor 112 provides a surface concentric with a circumference of the cylindrical inner channel 14, such that as the rotor 112 rotates within the cylindrical inner channel 14 of the stator core 12, a consistent air gap 26 is maintained between the rotor 112 and the stator core 12. The electric machine 100 may have forty-eight winding slots 22 and eight rotor poles. Other combinations of winding slot numbers and rotor pole numbers are also possible. As shown in Figure 2, the electric machine 100 has a housing 102 surrounding the stator assembly 10. In some embodiments the housing 102 is a cylindrical housing, though it will be understood that the stator core 12 may have a non-circular cross section, in particular where the outer form of the stator core 12 is oblate or has projections thereon, such that the housing 102 may be non-circular. The stator core 12 has a plurality of cooling passageways 28 which extend in a longitudinal direction (i.e., in a direction parallel to the central stator axis 16) through the stator core 12 away from the first axial end surface 18 of the stator core 12. In particular, the cooling passageways 28 extend from the first axial end surface 18 to the second axial end surface 20 of the stator core 12. The cooling passageways 28 are distributed about a circumference of the stator core 12. The electric machine 100 has a first cover 30A which at least partly covers the first axial end surface 18 of the stator core 12. In the illustrated embodiment, the first cover 30A is a first cooling manifold. The first cooling manifold 30A defines at least one cooling channel 32A in fluid communication with the plurality of cooling passageways 28. In the illustrated embodiment, the at least one cooling channel 32A is a first chamber 32A in fluid communication with the plurality of cooling passageways 28. The first cooling manifold 30A also defines a manifold inlet 34A for connecting the first chamber 32A to a cooling fluid source. In this way, cooling fluid may pass through the manifold inlet 34A, into the first chamber 32A and then through the cooling passageways 28. In the arrangement of Figure 2, the manifold inlet 34A is defined by a radially outer edge of the first cooling manifold 30A, which is open to the housing 102 so that cooling fluid can enter the first chamber 32A through a first opening 104 in the housing 102. In other words, a radially outer edge 36A of the first chamber 32A is defined by the housing 102. The electric machine 100 also has a second cover 30A which at least partly covers the second axial end surface 20 of the stator core 12. In the illustrated embodiment, the second cover 30B is a second cooling manifold. The second cooling manifold 30B defines at least one cooling channel 32B in fluid communication with the plurality of cooling passageways 28. In the illustrated embodiment, the at least one cooling channel 32B is a second chamber 32B in fluid communication with the plurality of cooling passageways 28. The second cooling manifold 30B also defines a manifold outlet 34B for expelling cooling fluid from the second chamber 32B. In this way, cooling fluid may pass through the manifold inlet 34A into the first chamber 32A of the first cooling manifold 30A, through the plurality of cooling passageways 28 to the second chamber 32B and then out of the manifold outlet 34B. In the arrangement of Figure 2, the manifold outlet 34B is defined by a radially outer edge of the second cooling manifold 30B, which is open to the housing 102 so that cooling fluid can be expelled from the second chamber 32B through a second opening 106 in the housing 102. In other words, a radially outer edge 36B of the second chamber 32B is defined by the housing 102. It will be understood that, although the schematic arrows on Figure 2 show a flow of cooling fluid through the first opening 104 in the housing, through the first cooling manifold 30A, along the cooling passageways 28, into the second cooling manifold 30B and then out of the second opening 106 in the housing 102, the flow of cooling fluid could be reversed. In other words, cooling fluid could instead flow through the second opening 106 in the housing 102, through the second cooling manifold 30B, along the cooling passageways 28, into the first cooling manifold 30A and then out of the first opening 104 in the housing 102. In such a configuration, the manifold inlet 34A of the first cooling manifold 30A would instead be a manifold outlet, and similarly the manifold outlet 34B of the second cooling manifold 30B would instead be a manifold inlet. In the illustrated arrangement, the first and second cooling manifolds 30A, 30B are annular. In this way, the first and second chambers 32A, 32B are also annular. The first and second cooling manifolds 30A, 30B can be considered as part of the stator assembly 10, along with the stator core 12. In the illustrated embodiment, the housing 102 of the electric machine 100 has a first axial end surface 102A and a second axial end surface 102B. The stator assembly 10 is positioned inside the housing 102 so that a first side of the first cooling manifold 30A faces the first axial end surface 18 of the stator core 12 and a second side of the first cooling manifold faces the first axial end surface 102Aofthe housing 102. Similarly, a first side of the second cooling manifold 30B faces the second axial end surface 20 of the stator core 12, and a second side of the second cooling manifold 30B faces the second axial end surface 102B of the housing 102. In the illustrated embodiment, the second side of the second cooling manifold 30B is provided adjacent to the second axial end surface 102B of the housing 102. On the contrary, although the second side of the first cooling manifold 30A faces the first axial end surface 102A of the housing 102, the first cooling manifold 30A is not provided adjacent to the first axial end surface 102A of the housing 102. In other words, the first cooling manifold 30A is spaced apart from the first axial end surface 102A of the housing 102 in an axial direction. In addition, at least one further component 114 of the electric machine 100 is positioned axially between the second side of the first cooling manifold 30A and the first axial end surface 102A of the housing 102 (as illustrated schematically on Figure 2). It will be understood that, in such an arrangement, because there is at least one further component 114 (e.g., one or more busbars or other electrical components) positioned axially between the first cooling manifold 30A and the first axial end surface 102A of the housing 102, the first cooling manifold 30A may not be easily clamped between the first axial end surface 18 of the stator core 12 and the housing 102. Therefore, the first cooling manifold 30A may be secured to the stator core 12 by an interlocking arrangement (e.g., as described in detail below with reference to Figures 3 to 12) to provide a secure connection between the stator core 12 and first cooling manifold 30A, without having to modify the design or positioning of the at least one further component 114. The electric machine 100 of Figure 2 also has a cooling fluid recirculation system 120 which is configured to supply cooling fluid to the manifold inlet 34A of the first cooling manifold 30A in a cooling fluid recirculation circuit 122 (i.e., via the first opening 104 in the housing 102). As will be described in more detail below, the stator core 12 is defined by a stator lamination stack 44. In other words, the stator ewe 12 is formed of a plurality of layers. The layers are stacked one atop the other to form the stator lamination stack 44, which extends from the first axial end surface 18 of the stator core 12 to the second axial end surface 20 of the stator core 12. The layers may be stamped from sheet material (e.g., sheet metal), or formed via any other suitable process. In this way, a stator core 12 having a complex cross-sectional shape can be formed. In some arrangements the cooling passageways 28 are coated on their inner surfaces, for example with a plastic material, to provide sealing such that coolant is prevented, or resisted, from passing between the laminations (i.e. layers 44A, 44B, 44C) of the stator lamination stack 44 under the temperatures and pressures described herein. There are different methods for producing this arrangement. The plastic may be applied to the inner surface of the cooling passageway 28 by flowing the thermoplastic through the cooling passageway 28, or by inserting a formed thermoplastic tube into the cooling passageway 28 and optionally applying pressure to the tube to blow mould the tube to the shape of the cooling passageway 28. The thermoplastic may have a complex cross-sectional shape either internally and / or externally. The external surface of the thermoplastic tube may have a simple rounded shape and the inner surface of the cooling passageway 28 may be similarly rounded. Once the plastic coating is in place the thickness of the coating of the inner surface of the cooling passageways 28 is in the region of 0.5mm, but other thicknesses are useful. The thermal conductivity of the plastic material is in the range 1 to 40 watts / mK. The functioning of electrical machines 100 and electric drive units (EDUs) 160 is known, and so will not be described here in more detail. In the arrangement of Figure 2, a first axial seal 40A is located between the first axial end surface 18 of the stator core 12 and the first cooling manifold 30A to seal a radially inner edge 38A of the first chamber 32A. In particular, the first axial seal 40A is an annular seal. The first axial seal 40A is located in a first annular recess 42A in the first cooling manifold 30A, which locates the first axial seal 40A in the correct position. Similarly, a second axial seal 40B is located between the second axial end surface 20 of the stator core 12 and the second cooling manifold 30B to seal a radially inner edge 38B of the second chamber 32B. In particular, the second axial seal 40B is an annular seal. The second axial seal 40B is located in a second 9 annular recess 42B in the second cooling manifold 30B, which locates the second axial seal 40B in the correct position. Similarly, a third axial seal 40C is provided at an opposite side of the second cooling manifold 30B to the second axial seal 40B. The third axial seal 40C is configured to form a seal between the second cooling manifold 30B and the second axial end surface 102B of the housing 102. The third axial seal 40C is located in a third annular recess 42C in the second cooling manifold 30B, which locates the third axial seal 40C in the correct position. In the arrangement of Figure 2, a radial seal 41 is located between the radially outer edge 36A of the first cooling manifold 30A and a radial inner surface of the housing 102. In particular, the radial seal 41 is an annular seal (e.g., an O-ring). The radial seal 41 is located in a fourth annular recess 43 in the radially outer edge 36A of the first cooling manifold 30A, which locates the radial seal 41 in the correct position. In this context, the term “axial seal” will be understood to mean a seal which is configured to have compression applied to axial ends of the seal’s cross-section. Conversely, the term “radial seal” will be understood to mean a seal which is configured to have compression applied to the inner and outer radial surfaces of the seal. Often, axial seals have a cross-section which is elongate in the axial direction, although this is not always the case. Referring now to Figures 3 to 17, the stator assembly 10 of the electric machine 100 of Figure 2 is described in more detail. As mentioned above, the stator assembly 10 includes the stator core 12 and a first cover 30A which, in this embodiment, is a first cooling manifold 30A which covers the first axial end surface 18 of the stator core 12. The stator assembly 10 also includes a first interlocking arrangement 50 which is configured to secure the first cooling manifold 30A to the stator core 12. Such an interlocking arrangement 50 provides a simple means of securing without the need for additional fasteners. Further, it will be understood that because the stator core 12 generally remains static within the housing 102 (in contrast to the rotating rotor 112), use of an interlocking arrangement 50 may provide a suitably robust connection between the first cooling manifold 30A and the stator core 12. In the illustrated embodiment, the first axial seal 40A, which is positioned between the stator core 12 and the first cooling manifold 30A, is compressed therebetween by the first interlocking arrangement 50. By compressing the first axial seal 40A with the first interlocking arrangement 50, a contact pressure between the first axial seal 40A and the stator core 12 and first cooling manifold 30A can be increased, which improves seal performance. In other words, the pressure of cooling fluid inside the first chamber 32A can be increased. As best illustrated in Figures 3 to 12, the first interlocking arrangement 50 is a bayonet arrangement. Such a bayonet arrangement 50 provides a simple means of securing the first cooling manifold 30A to the stator core 12 (e.g., by pushing and twisting the first cooling manifold 30A and stator core 12 relative to each other). Further, once connected such a bayonet arrangement 50 may be able to withstand greater axial separation forces than alternatives, such as snap-fit arrangements. In some embodiments, the bayonet arrangement 50 is configured to withstand an axial separation force of at least 2kN (e.g., at least 3kN, at least 4kN, or at least 5kN). This provides a robust connection which may be able to withstand a high pressure of cooling fluid inside within the first cooling manifold 30A, and / or a high resilient force of the first axial seal 40A compressed between the stator core 12 and the first cooling manifold 30A. It will be understood that such an axial separation force may be achieved by forming the stator core 12 and first cooling manifold 30A from particular materials (e.g., metallic materials such as steel or aluminium alloy material). It will be understood that such an axial separation force may also be achieved by selecting an appropriate number of bayonet connectors and bayonet receivers (described below), and or by sizing and shaping the bayonet connectors and bayonet receivers to withstand such an axial separation force. As best illustrated in Figures 3 to 7, the bayonet arrangement 50 includes at least one bayonet connector 52 on the first cooling manifold 30A and at least one bayonet receiver 54 on the stator core 12. In particular, the bayonet arrangement 50 has a plurality of bayonet connectors 52 on the first cooling manifold 30A and corresponding plurality of bayonet receivers 54 on the stator core 12. In the illustrated embodiment, the plurality of bayonet connectors 52 and bayonet receivers 54 are distributed circumferentially about the stator core 12 and the first cooling manifold 30A. In the illustrated embodiment, the bayonet arrangement 50 includes six bayonet connectors 52 and six bayonet receivers 54. However, in other embodiments there may be a different number of bayonet connectors 52 and bayonet receivers 54 (e.g., one, two, three, four, five, or greater than six). As will be described in more detail below, because the bayonet receivers 54 (e.g., recessed portions of the bayonet arrangement 50) are on the stator core 12, the stator core 12 can be produced via normal manufacturing techniques (e.g., as a stator lamination stack 44). However, in alternative embodiments, the bayonet arrangement 50 includes at least one bayonet connector 52 on the stator core and at least one bayonet receiver 54 on the first cooling manifold 30A. For example, the bayonet connectors 52 and bayonet receivers 54 may be reversed. Alternatively, there may be at least one bayonet connector 52 on the stator core 12, at least one bayonet connector 52 on the first cooling manifold 30A, at least one bayonet receiver 54 on the stator core 12, and at least one bayonet receiver 54 on the first cooling manifold 30A. In other words, both the cooling manifold 30Aand stator core 12 may have a bayonet receiver 54 which is engaged by a bayonet connector 52 of the other component, and bayonet connector 52 which is engaged by a bayonet receiver 54 of the other component. In some embodiments, the bayonet arrangement 50 includes at least one bayonet receiver 54 on the stator core 12, and at least one bayonet receiver 54 on the first cooling manifold 30A. In such embodiments, the bayonet arrangement 50 may further include an intermediate component (not shown). In such embodiments, the intermediate component may include at least one bayonet connector 52 for connecting to the at least one bayonet receiver 54 of the stator core 12, and at least one bayonet connector 52 for connecting to the at least one bayonet receiver 54 of the first cooling manifold 30A. It will be understood that, regardless of the particular construction of the bayonet arrangement 50, the bayonet arrangement 50 may be configured so that the first cooling manifold 30A is pushed axially towards the first axial end surface 18 of the stator core 12 to insert the bayonet connectors 52 into the corresponding bayonet receivers 54. This is illustrated in the transition of the first cooling manifold 30A between Figures 3 and 4. The first cooling manifold 30A may then be twisted about a central axis of the first cooling manifold 30A (i.e., an axis which is coaxial with the central axis 16 of the stator core 12) to form an interlocking arrangement between the bayonet connectors 52 and the corresponding bayonet receivers 54. This is illustrated in the transition of the first cooling manifold 30A between Figures 4 and 5. It will be understood that once the first cooling manifold 30A has been pushed and twisted about the central axis 16, the interlocking arrangement between the bayonet connectors 52 and bayonet receivers 54 inhibits axial movement of the first cooling manifold 30A relative to the stator core 12. In other words, this interlocking arrangement allows the bayonet arrangement 50 to withstand an axial separation force (e.g., caused by resilient compression of the first axial seal 40A and / or a pressure of cooling fluid inside the first chamber 32A). In the illustrated embodiment, the first cooling manifold 30A is twisted about the central axis 16 in an anti-clockwise direction with respect to the first axial end surface 18 of the stator core 12 to form the interlocking engagement. In alternative embodiments, the first cooling manifold 30A is twisted about the central axis 16 in the opposite direction to form the interlocking engagement. It will be understood that the stator core 12 and first cooling manifold 30A are static components within the housing 102 of the electric machine 100. In other words, they are not susceptible to relative rotation as part of normal use of the electric machine 100 (in comparison to the rotor 112, or other “rotating” components of the electric machine 100). In any case, movement of the bayonet arrangement 50 from the state illustrated in Figure 5 to the state illustrated in Figure 4 (e.g., via rotation about the central axis 16 in a clockwise direction with respect to the first axial end surface 18 of the stator core 12) is inhibited by friction between the corresponding bayonet connectors 52 and bayonet receivers 54. This friction is increased by the biasing force caused by compression of the first axial seal 40A between the stator core 12 and the first cooling manifold 30A, which acts to urge the first cooling manifold 30A and stator core 12 away from each other. During use, a further biasing force in the form of pressurised cooling fluid inside the first chamber 32A of the first cooling manifold 30A also acts to urge the first cooling manifold 30A and stator core 12 away from each other. This further increases the friction between the bayonet connectors 52 and bayonet receivers 54 to inhibit relative rotation between the stator core 12 and the first cooling manifold 30A. In some embodiments, the bayonet connectors 52 and bayonet receivers 54 are configured so that a further interlocking arrangement is formed therebetween to inhibit relative rotation of the stator core 12 and first cooling manifold 30A (e.g., in addition to friction). In such embodiments, the first cooling manifold 30A maybe pushed in a first axial direction towards the first axial end surface 18 of the stator core 12, twisted about the central axis of the first cooling manifold 30A to form the interlocking arrangement which inhibits axial separation, and then pushed in a second axial direction opposite to the first axial direction to form the further interlocking engagement which inhibits rotation. Pushing in the second axial direction may be achieved by a biasing force (e.g., caused by compression of the first axial seal 40A, pressurised cooling fluid inside the first chamber 32A, and / or a spring or other biasing element), to keep the further interlocking engagement in an engaged state. In some embodiments, after the bayonet connectors 52 and bayonet receivers 54 have formed an interlocking arrangement (as illustrated in Figure 5) an additional locking component may be used to inhibit relative rotation between the stator core 12 and the first cooling manifold 30A (e.g., a pin or grub screw, for example, passing radially through a bayonet connector 52 and an adjacent portion of the stator core 12). As best illustrated in Figures 6 and 7, each of the bayonet receivers 54 has an axial recess 56 which extends axially inboard from the first axial end surface 18 of the stator core 12, a circumferential recess 58 which extends circumferentially from an axially inboard end 60 of the axial recess 56, and an abutment surface 62 positioned axially between the circumferential recess 58 and the first axial end surface 18 of the stator core 12. Each bayonet connector 52 has an axial projection 64 which projects from the first cooling manifold 30A and a transverse projection 66 which extends from a free end 68 of the axial projection 64. In this way, the axial projections 64 of the bayonet connectors 52 can be pushed along the axial recesses 56 of the bayonet receivers 54 (e.g., by pushing the first cooling manifold 30A towards the stator core 12). The corresponding components can then be rotated so that the transverse projections 66 of the bayonet connectors 52 move along the circumferential recesses 58 of the bayonet receivers 54, so that the transverse projections 66 engage the abutment surfaces 62 to inhibit axial separation of the first cooling manifold 30A and the stator core 12. In the illustrated embodiment, the axial recesses 56 and circumferential recesses 58 are grooves in an outer radial surface 70 of the stator core 12. In alternative embodiments, the axial recesses 56 and / or circumferential recesses 58 are internal bores within the stator core 12. As best illustrated in Figure 7, the axial recesses 56 and circumferential recesses 58 have a radially inner edge 72 at a first radial dimension, and a radially outer edge 74 at a second radial dimension. The stator core 12 has a third radial dimension between the abutment surfaces 62 and the first axial end surface 18 of the stator core 12, which is between the first and second radial dimensions. In this way, the axial projections 64 of the bayonet connectors 52 can extend over the abutment surfaces 62 while remaining flush with the outer radial surface 70 of the stator core 12. Put another way, there is an intermediate step 76 between each abutment surface 62 and the first axial end surface 18 of the stator core 12. The intermediate step 76 does not extend radially to the outer radial surface 70 of the stator core 12. As mentioned briefly above, the stator core 12 is defined by a stator lamination stack 44. In the illustrated embodiment, the profile of the bayonet receivers 54 is formed by stacking layers of stator laminates 44A, 44B, 44C (See Figures 10, 11 and 12) together in an axial direction towards the first axial end surface 18 of the stator core 12. This provides a simple means of manufacturing the bayonet receivers 54. In the illustrated embodiment, the stator laminates 44A, 44B, 44C have different profiles. In particular, the stator lamination stack 44 has at least one layer 44A having a first profile which does not define any bayonet receiver features (as illustrated in Figure 10). The stator lamination stack 44 also has at least one layer 44B having a second profile which defines a portion of the axial recesses 56 and a portion of the circumferential recesses 58 of the bayonet receivers 54 (as illustrated in Figure 11). The stator lamination stack 44 also has at least one layer 44C having a third profile which defines a further portion of the axial recesses 56 of the bayonet receivers 54 and the intermediate step 76 (as illustrated in Figure 12). In other embodiments, the stator laminates may have the same or similar profiles. In such embodiments, at least some of the stator laminates may be arranged in the stack 44 at different rotational orientations about the central axis 16 of the stator core 12 in order to define the profile of the bayonet receivers 54. Alternatively, the bayonet receivers 54 may be machined into the stator core 12 (e.g., into a stator lamination stack 44 of identical layers, or into a forged / cast stator core 12). As best illustrated in Figures 13 to 16, the stator assembly 10 also includes a second interlocking arrangement 80 which is configured to secure the second cooling manifold 30B to the stator core 12. Such an interlocking arrangement 80 provides a means of securing without the need for additional fasteners. Further, as outlined above, because the stator core 12 generally remains static within the housing 102 (in contrast to the rotating rotor 12 112), use of an interlocking arrangement 80 may provide a suitably robust connection between the second cooling manifold 30B and the stator core 12. In the illustrated embodiment, the second axial seal 40B, which is positioned between the stator core 12 and the second cooling manifold 30B, is compressed therebetween by the second interlocking arrangement 80. By compressing the second axial seal 40B with the second interlocking arrangement 80, a contact pressure between the second axial seal 40B and the stator core 12 and second cooling manifold 30B can be increased, which improves seal performance. In other words, the pressure of cooling fluid inside the second chamber 32B can be increased. It will be understood that, the second axial seal 40B may be further, or alternatively, compressed due to the second cooling manifold 30B being clamped between the second axial end surface 102B of the housing 102, and the second axial end surface 20 of the stator core 12. As best illustrated in Figures 13 to 16, the second interlocking arrangement 80 is a snap-fit arrangement. Such a snap-fit arrangement 80 allows the second cooling manifold 30B to be secured to the stator core 12 simply by pushing the second cooling manifold 30B towards the second axial end surface 20 of the stator core 12 (as illustrated in the transition between Figures 13 and 14). In the illustrated embodiment, the snap-fit arrangement 80 includes at least one resilient clip 82 on the second cooling manifold 30B and at least one clip recess 84 on the stator core 12, for receiving the at least one resilient clip 82. In particular, the snap-fit arrangement 80 has a plurality of resilient clips 82 on the second cooling manifold 30B and a corresponding plurality of clip recesses 84 on the stator core 12 for receiving the resilient clips 82. In the illustrated embodiment, the plurality of resilient clips 82 are distributed circumferentially about the second cooling manifold 30B and the plurality of clip recesses 84 are distributed circumferentially about the stator core 12. In the illustrated embodiment, the snap-fit arrangement 80 includes six resilient clips 82 and six clip recesses 84. However, in other embodiments there may be a different number of resilient clips 82 and clip recesses 84 (e.g., one, two, three, four, five, or greater than six). In the illustrated embodiment, the clip recesses 84 are of the same construction as the circumferential recesses 58 of the bayonet receivers 54 described above. In other words, the clip recesses 84 are recessed portions of the stator core 12 which are axially spaced apart from the second axial end surface 20 of the stator core 20 by an intermediate step 76. In this embodiment, the clip recesses 84 are grooves in the outer radial surface 70 of the stator core 12. In the illustrated embodiment, the clip recesses 84 are formed using the same stator laminates 44A, 44B, 44C as the bayonet receivers 54. It will be understood that this results in redundant axial recesses in the second axial end surface 20 of the stator core 12 as these are not needed for the snap-fit arrangement 80. However, by using the same stator laminates 44A, 44B, 44C, this reduces the number of stamps that are required to form the stator lamination stack 44 (i.e., only three stamps are needed to produce both the bayonet receivers 54 and the clip recesses 84), which may lead to manufacturing cost savings. In addition, this may allow a common stator core 12 which can be coupled to covers using both bayonet arrangements 50 or snap-fit arrangements 80 at either end. In some embodiments, the clip recesses 84 may have a different construction to the bayonet receivers 54. For example, the axial recess 56 may be omitted at the second axial end surface 20 of the stator core 12. In such embodiments, the stator lamination stack 44 may include at least one layer 44A having a first profile which does not define any clip recess features, and at least one layer 44B having a second profile which defines the at least one clip recess 84. In some embodiments, the stator laminates may have the same or similar profiles. In such embodiments, at least some of the stator laminates may be arranged in the stack 44 at different rotational orientations about the central axis 16 of the stator core 12 in order to define the profile of the clip recesses 84. Alternatively, the clip recesses 84 may be machined into the stator core 12 (e.g., into a stator lamination stack 44 of identical layers, or into a forged / cast stator core 12). In some embodiments, the number of clip recesses 84 is less than the number of resilient clips 82, so that each clip recess 84 receives more than one resilient clip 82. For example, the snap-fit arrangement 80 may include a plurality of resilient clips 82 on the second cooling manifold 30B and a single annular clip recess 84 on the stator core 12 for receiving the resilient clips 82. Such an annular clip recess allows the second cooling manifold 13 30B to be pushed to form the snap-fit engagement 80 in any angular orientation (i.e., without the need to align the resilient clips 82 with corresponding clip recesses 84 first). In such embodiments, the second cooling manifold 30B and resilient clips 82 may have the same configuration as in the illustrated embodiment. As best illustrated in Figures 15 and 16, each resilient clip 82 has an axial projection 86 (similar to the axial projection 64 of the bayonet connectors 52 described above) and a transverse projection 88 (similar to the transverse projection 66 of the bayonet connectors 52 described above) which extends from a free end 90 of the axial projection 86. In this way, once the resilient clips 82 are pushed over the intermediate steps 76, the transverse projections 88 sit inside the clip recesses 84 and engage the abutment surface 62 to form an interlocking arrangement which inhibits axial separation of the second cooling manifold 30B and the stator core 12. It will be understood that, in order for the transverse projections 88 of the resilient clips 82 to pass over the intermediate step 76, the axial projections 86 have to flex radially outwards. To facilitate this flexing, each axial projection 86 is connected at its fixed end 92 to a radial leg 94 of the resilient clip 82. The radial leg 94 extends transverse to the axial projection 86 (e.g., perpendicular). In addition, to ease pushing the transverse projections 88 over the intermediate steps 76 during flexing of the resilient clips 82, each transverse projection 88 has a tapered leading edge 89. In this embodiment the tapered leading edge 89 is flat, but in other embodiments the tapered leading edge 89 may be curved. In some embodiments, the second cooling manifold 30B is formed of plastic material. This may facilitate integrally forming the resilient clips 82 with the second cooling manifold 30B (e.g., in contrast with cooling manifolds 30B made from more rigid materials, such as metal). Alternatively, the resilient clips 82 may be formed of plastic material and the main body of the second cooling manifold 30B may be formed of a different material. It will be understood that, because the clip recesses 84 are of the same configuration as the bayonet receivers 54, and the resilient clips 82 have similar axial and transverse projections 86, 88 in the illustrated embodiment, the second cooling manifold 30B could be coupled to the stator core 12 by pushing and twisting (i.e., as a bayonet arrangement) rather than by flexing the resilient clips 82 to pass over the intermediate steps 76. It will also be understood that, because of the plastic material and / or flexibility of the resilient clips 82, the snap fit arrangement 80 between the second cooling manifold 30B and the stator core 12 (whether pushed to form the snap-fit, or twisted in a bayonet fashion) may not be able to withstand the same axial separation force as the bayonet arrangement 50 between the first cooling manifold 30A and the stator core 12. However, when assembled inside the housing 102, the second cooling manifold 30B is clamped between the second axial end surface 102B of the housing 102 and the second axial end surface 20 of the stator core 12 (as illustrated in Figure 2), which further inhibits axial separation. Therefore, the snap-fit arrangement 80 may be used during assembly to ensure correct positioning of the second cooling manifold 30B relative to the stator core 12 and / or keep the stator assembly 10 as a fixed unit. In such an assembly stage, there would be no pressure of cooling fluid acting to separate the second cooling manifold 30B and the stator core 12, and thus the snap-fit arrangement 80 may be of sufficient strength. In alternative embodiments, the second cooling manifold 30B may be spaced from the second axial end surface 102B of the housing 102. In such embodiments, a bayonet arrangement 50 of the kind described above may be used instead of the snap-fit arrangement 80. In alternative embodiments, the first cooling manifold 30A may be clamped between the first axial end surface 102A of the housing 102 and the stator core 12 (e.g., the at least one further component 114 maybe omitted). In such embodiments, a snap-fit arrangement 80 of the kind described above may be used instead of the bayonet arrangement 50. In alternative embodiments, other types of interlocking arrangement may be used to couple the first cooling manifold 30A and / or second cooling manifold 30B to the stator core 12. It will be understood that although the interlocking arrangements 50, 80 described above are for securing first and second cooling manifolds 30A, 30B to the stator core 12 (as best illustrated in Figure 17), similar interlocking arrangements 50,80 may be used to connect other types of components to the stator core 12. For example, in some embodiments the component(s) coupled to the stator core 12 by the interlocking arrangement 50,80 may include: a wire harness for electrical windings; power electronics; other types of cooling components; lubrication or bearing components; transmission components; housing components; or any other electric machine component. Such components may be considered as a cover which at least partly covers a portion of the stator core 12 (e.g., one of the axial end surfaces 18, 20), regardless of any other functionality that the components perform. A method of coupling a cover 30A, 30B to a stator core 12 is illustrated in Figure 18 as a flow chart. The method includes the following steps: a) providing a stator core 12 comprising an axial end surface 18, 20; 5 b) positioning a cover 30A, 30B against the axial end surface 18, 20 of the stator core 12; and c) securing the cover 30A, 30B to the stator core 12 using an interlocking arrangement 50,80. In some embodiments, the interlocking arrangement is a bayonet arrangement 50 which is engaged by pushing the cover 30A axially towards the axial end surface 18 of the stator core 12 and then twisting the cover 30A about a central axis 16 of the cover 30A and / or stator core 12. I n some embodiments, the interlocking arrangement is a snap-fit arrangement 80 which is engaged by pushing the cover 30B axially towards the axial end 10 surface 20 of the stator core 12. 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. It should also be noted that whilst the appended claims set out particular combinations of features described above, the scope of the present disclosure is not limited to the particular combinations hereafter claimed, but instead extends to encompass any combination of features herein disclosed.

Claims

1. A stator assembly for an electrical machine of a vehicle traction motor, the stator assembly comprising:a stator core comprising an axial end surface;a cover which at least partly covers the axial end surface of the stator core; and an interlocking arrangement configured to secure the cover to the stator core.

2. The stator assembly of claim 1, wherein the stator core comprises a plurality of cooling passageways which extend in a longitudinal direction through the stator core away from the axial end surface, and wherein the cover is a cooling manifold which defines at least one cooling channel in fluid communication with the plurality of cooling passageways.

3. The stator assembly of claim 1 or 2, wherein the stator assembly comprises a seal positioned between the stator core and the cover,such that the seal is compressed therebetween by the interlocking arrangement.

4. The stator assembly of any preceding claim, wherein the interlocking arrangement comprises a bayonet arrangement.

5. The stator assembly of claim 4, wherein the bayonet arrangement is configured to withstand an axial separation force of at least 2kN,optionally at least 3kN, optionally at least 4kN, optionally at least 5kN.

6. The stator assembly of claim 4 or 5, wherein the cover is formed of metallic material, optionally steel or aluminium alloy material.

7. The stator assembly of any of claims 4 to 6, wherein the bayonet arrangement comprises at least one bayonet connector on the coverand at least one bayonet receiver on the stator core; optionally, wherein the bayonet arrangement comprises a plurality of bayonet connectors on the cover and corresponding plurality of bayonet receivers on the stator core; optionally, wherein the plurality of bayonet connectors and bayonet receivers are distributed circumferentially about the stator core and the cover; and / or optionally, wherein the bayonet arrangement comprises at least three, optionally at least four, optionally at least five, optionally at least six bayonet connectors and a corresponding number of bayonet receivers.

8. The stator assembly of claim 7, wherein the stator core is at least partly defined by a stator lamination stack, and wherein the profile of the at least one bayonet receiver is formed by stacking layers of stator laminates together in an axial direction towards the axial end surface of the stator core.

9. The stator assembly of claim 7 or 8, wherein the at least one bayonet receiver comprises an axial recess which extends axially inboardfrom the axial end surface of the stator core, a circumferential recess which extends circumferentially from an axially inboard end of the axial recess, and an abutment surface positioned axially between the circumferential recess and the axial end surface of the stator core; and wherein the at least one bayonet connector comprises an axial projection which extends from the cover and a transverse projection which extends from a free end of the axial projection.

10. The stator assembly of any of claims 1 to 3, wherein the interlocking arrangement comprises a snap-fit arrangement; optionally, whereinthe snap-fit arrangement comprises at least one resilient clip on the cover and at least one clip recess on the stator core, for receiving the at least one resilient clip.

11. A cooling manifold for coupling to a stator core of a stator assembly for an electrical machine of a vehicle traction motor, wherein the cooling manifold defines at least one cooling channel which is open at an axial end of the cooling manifold for fluid communication with an axial end surface of the stator core, andwherein the cooling manifold comprises at least one bayonet connector configured to form an interlocking arrangement with a corresponding bayonet receiver of the stator core to secure the cooling manifold to said stator core.1612. A stator core for an electrical machine of a vehicle traction motor, the stator core comprising: an axial end surface, andat least one bayonet receiver configured to form an interlocking arrangement with a corresponding bayonet connector of a cooling 5 manifold to secure said cooling manifold to the stator core over the axial end surface.

13. An electric machine for driving one or more wheels of a vehicle, the electric machine comprising the stator assembly of any of claims 1 to 10, a cooling manifold as claimed in claim 11 and / or a stator core as claimed in claim 12.10 14. The electric machine of claim 13, further comprising a housing having an axial end surface, wherein the stator assembly is positionedinside the housing with a first side of the cover facing the axial end surface of the stator core and a second side of the cover facing the axial end surface of the housing, and wherein the electric machine further comprises at least one further component positioned axially between the second side of the cover and the axial end surface of the housing.15 15. A vehicle comprising the electric machine of claim 13 or 14.

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