GB2638761A - Stator assembly - Google Patents

Abstract

A stator assembly 10 for an electrical machine, the stator assembly comprising a stator core 12 defined by a stator lamination stack 44 formed of a plurality of stator materials; and a bolting arrangement 46 configured to provide a clamping force to the stator lamination stack. The bolting arrangement comprises a bolt 48 which extends through a bolt passageway 54 in the stator lamination stack where the bolt is formed of a bolt material having substantially the same co-efficient of thermal expansion as the stator lamination stack. The bolt material may differ from the stator materials. The stator lamination stack may comprise metallic layers interspersed between layers of non-metallic bonding material, and the bolt material may be substantially the same co-efficient of thermal expansion as the combined co-efficient of thermal expansion of the metallic layers and non-metallic bonding layers forming the stator lamination stack. The bolt material may be a metallic material with a co-efficient of thermal expansion which may be greater than the co-efficient of thermal expansion of the metallic layers of the stack. The metallic layers may comprise ferrous material and the bolt material may comprise aluminium or aluminium alloy. The ferrous material may comprise electrical steel material. A cross-section of the bolt passageway may be greater than a cross-section of the bolt along its entire length, such that a clearance is defined therebetween.

Description

STATOR ASSEMBLY

TECHNICAL FIELD

The present disclosure relates to a stator assembly. Aspects of the invention relate to a stator assembly, to an electrical machine, to an electric drive unit, to a vehicle, and to a method of manufacturing a stator assembly.

BACKGROUND

It is known to provide a stator core defined by a stator lamination stack formed of a plurality of layers which are stacked one atop the other. It is also known to provide a bolting arrangement which is configured to provide a clamping force to the stator lamination stack to inhibit delamination (i.e., separation of layers) in the stack (e.g., during manufacturing).

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, an electrical machine, an electric drive unit, a vehicle, and a method of manufacturing a stator assembly as claimed in the appended claims.

According to an aspect of the present disclosure there is provided an assembly comprising a body defined by a lamination stack formed of a plurality of body materials. The assembly also comprises a bolting arrangement configured to provide a clamping force to the lamination stack. The bolting arrangement comprises a bolt which extends through a bolt passageway in the lamination stack. The bolt is formed of a bolt material having substantially the same co-efficient of thermal expansion as the lamination stack.

Having a bolting arrangement configured to provide a clamping force to the lamination stack inhibits delamination (i.e., separation of layers) in the stack (e.g., during manufacturing). It will be understood that the bolt may extend the entire length of the bolt passageway, in order to facilitate a clamping force which acts on opposing ends of the lamination stack. Further, because the bolt material has substantially the same or the same co-efficient of thermal expansion as the lamination stack, this will inhibit variations in the clamping force provided by the bolting arrangement during temperature changes (e.g., during manufacturing and/or use of the assembly).

A further aspect of the present disclosure provides a stator assembly for an electrical machine. The stator assembly comprises a stator core defined by a stator lamination stack formed of a plurality of stator materials.

The stator assembly also comprises a bolting arrangement configured to provide a clamping force to the stator lamination stack. The bolting arrangement comprises a bolt which extends through a bolt passageway in the stator lamination stack. The bolt is formed of a bolt material having substantially the same co-efficient of thermal expansion as the stator lamination stack.

Having a bolting arrangement configured to provide a clamping force to the stator lamination stack inhibits delamination (i.e., separation of layers) in the stack (e.g., during manufacturing). It will be understood that the bolt may extend the entire length of the bolt passageway, in order to facilitate a clamping force which acts on opposing ends of the stator lamination stack. Further, because the bolt material has substantially the same or the same co-efficient of thermal expansion as the stator lamination stack, this will inhibit variations in the clamping force provided by the bolting arrangement during temperature changes (e.g., during manufacturing and/or use of the stator assembly).

Optionally, the bolt material differs from the plurality of stator materials. It will be understood that because the stator lamination stack is formed of a plurality of stator materials, which may each have a different co-efficient of thermal expansion, the stator lamination stack as a whole may have a different co-efficient of thermal expansion to any of the individual stator materials which form the stator lamination stack. Therefore, by having a bolt material which is different to the plurality of stator materials, the co-efficient of thermal expansion of the bolt can be matched to the overall co-efficient of thermal expansion of the stator lamination stack.

Optionally, the stator lamination stack comprises metallic layers interspersed between layers of non-metallic bonding material. Such metallic layers interspersed between layers of bonding material provides a simple means of constructing the stator lamination stack.

Optionally, the bolt material has substantially the same co-efficient of thermal expansion as the combined coefficient of thermal expansion of the metallic layers and non-metallic bonding layers forming the stator lamination stack. By matching the bolt material to the combined co-efficient of thermal expansion, variations in the clamping force during temperature changes can be inhibited.

Optionally, the bolt material is a metallic material with a co-efficient of thermal expansion which is greater than the co-efficient of thermal expansion of the metallic layers of the stator lamination stack. It will be understood that the bonding material may have a greater co-efficient of thermal expansion than the metallic layers, which may lead to increased expansion of the overall stator lamination stack. Therefore, having a bolt material with a greater co-efficient of thermal expansion than the metallic layers of the stator lamination stack allows matching with the overall thermal expansion of the stator lamination stack.

Optionally, the metallic layers comprise ferrous material and the bolt material comprises aluminium or aluminium alloy. Aluminium and aluminium alloys may match the co-efficient of thermal expansion of a combination of ferrous (e.g., steel) and non-metallic bonding layers.

Optionally, the ferrous material comprises electrical steel material. Such a material in combination with layers of non-metallic bonding material, has been found to match the co-efficient of thermal expansion of an aluminium or aluminium alloy bolt.

Optionally, a cross-section of the bolt passageway is greater than a cross-section of the bolt along its entire length, such that a clearance is defined therebetween. In this way, the clearance defines a space for the bolt to expand more than the portion of the bolt passageway defined by the metallic layers.

Optionally, the non-metallic bonding material comprises epoxy material. Such a material is suitable for bonding metallic layers in a stator lamination stack. In addition, in embodiments where the metallic layers are formed of a ferrous material (e.g. steel), and the bolt material comprises aluminium or aluminium alloy, this type of bonding material may provide the stator lamination stack with an overall co-efficient of thermal expansion which is substantially the same as aluminium or aluminium alloy.

Optionally, the metallic layers form at least 90% of the thickness of the stator lamination stack, and the nonmetallic bonding layers form the remainder of the thickness of the stator lamination stack. For example, in one embodiment the metallic layers form around 95% of the thickness of the stator lamination stack, and the non-metallic bonding layers form the remaining 5% of the thickness of the stator lamination stack 44. Such a configuration provides a stator lamination stack with a co-efficient of thermal expansion which is approximately the same as a co-efficient of thermal expansion of an aluminium bolt.

Optionally, the bolt acts between a cooling manifold provided at a first end of the stator lamination stack, and a second end of the stator lamination stack, to urge the cooling manifold towards the first end of the stator lamination stack. In other words, a first end of the bolt (e.g., a threaded end of the bolt) engages the cooling manifold (e.g., in a female thread of the cooling manifold) to urge it towards the first end of the stator lamination stack, while a second end of the bolt (e.g., a bolt head) acts on the second end of the stator lamination stack. This provides the clamping force. In embodiments where the cooling manifold provides the female thread, this may reduce the component count (e.g., in comparison to embodiments where a separate nut is required to act on the first end of the stator lamination stack).

It will be understood that, in embodiments where the bolting arrangement is configured to compress a seal between the cooling manifold and the first end of the stator lamination stack, having a bolt material with substantially the same co-efficient of thermal expansion as the stator lamination stack inhibits variation of the compression force on the seal with changes in temperature. This may improve seal performance over a wider range of temperatures.

Optionally, the bolting arrangement comprises a plurality of bolts distributed circumferentially about the stator core. Such a plurality of bolts facilitates an increased clamping force, as well as an even distribution of force about the stator lamination stack. This further inhibits de-lamination of the stator lamination stack.

Optionally, the bolting arrangement comprises at least three bolts, optionally at least four bolts, optionally at least five bolts, optionally at least six bolts.

Optionally, each bolt is formed of a bolt material having substantially the same co-efficient of thermal expansion as the stator lamination stack.

A further aspect of the present disclosure provides an electrical machine comprising a stator assembly as disclosed herein. Such an electrical machine benefits from the advantages of the stator assembly outlined above.

A further aspect of the present disclosure provides an electric drive unit (EDU) comprising an electrical machine as disclosed herein. Such an electric drive unit benefits from the advantages of the stator assembly outlined above.

A further aspect of the present disclosure provides a vehicle comprising an electrical machine as disclosed herein and/or an electric drive unit as disclosed herein. Such a vehicle benefits from the advantages of the stator assembly outlined above.

A further aspect of the present disclosure provides a method of manufacturing a stator assembly. The method comprises: providing a stator core defined by a stator lamination stack formed of a plurality of stator materials, the stator lamination stack having a coefficient of thermal expansion; determining a bolt material having substantially the same coefficient of thermal expansion as the stator lamination stack; providing a bolt in the determined bolt material; inserting the bolt through a bolt passageway in the stator lamination stack; and engaging a thread of the bolt with a complementary female thread in a receiving component to provide a clamping force to the stator lamination stack.

Such a method inhibits delamination (i.e., separation of layers) in the stator lamination stack (e.g., during manufacturing), by providing a clamping force to the stack. Further, by having the step of providing a bolt in a bolt material which has substantially the same co-efficient of thermal expansion as the stator lamination stack, such a method will inhibit variations in the clamping force during temperature changes (e.g., during manufacturing and/or use of the stator assembly).

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 longitudinal cross-sectional view of an electrical machine comprising a stator assembly according to an embodiment; Figure 2 shows an enlarged view of the electrical machine of Figure 1, corresponding to the dashed box area highlighted on Figure 1; Figure 3 shows a transverse cross-sectional view of the electrical machine of Figures 1 and 2; Figure 4 shows an enlarged longitudinal cross-sectional view of the electrical machine of Figures 1 to 3, corresponding to the dashed box area highlighted on Figure 2; Figure 5 shows a longitudinal cross-sectional view of a portion of a stator assembly for an electrical machine, according to an embodiment; Figures 6A and 6B show enlarged views of first and second ends of the stator assembly of Figure 5; Figure 7 shows a perspective view of the second end of the stator assembly of Figures 5 to 6B; Figure 8 shows a transverse cross-sectional view of the stator assembly of Figures 5 to 7, taken along plane A-A of Figure 6A; Figure 9 shows a vehicle according to an embodiment; Figure 10 shows a flow chart of a method of manufacturing a stator assembly according to an embodiment; Figure 11 shows a flow chart of a method of assembling a stator assembly according to an embodiment; Figure 12 shows a flow chart of a method of cooling a bolt provided in a bolt passageway through a stator lamination stack according to an embodiment; and Figure 13 shows a flow chart of a method of coupling a cooling manifold 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 in an electric machine. 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 9, where the figures illustrate a stator assembly 10, an electric machine 100, an electric drive unit (EDU) 160 and a vehicle 200.

Referring to Figures 1 to 4, the stator assembly 10 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 end 18 of the stator core 12 to a second end 20 of the stator core 12.

The stator core 12 has a plurality of winding slots 22 extending radially to support electrical stator windings 150. For simplicity, the electrical stator windings 150 are illustrated in Figure 3 in only one winding slot 22. A plurality of stator teeth 24 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 end 18 to the second end 20 of the stator core 12.

The stator assembly 10 is intended for use in an electric machine 100, as illustrated in cross sectional view in Figures 1 and 3, where the electric machine 100 includes the stator assembly 10 and 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 electrical machine 100 may have forty-eight winding slots 22 and eight rotor poles. Other combinations of winding slot numbers and rotor pole numbers are useful.

As shown in Figures 1 and 3, the electrical machine 100 has a housing 102 surrounding the stator assembly 10. In some embodiments the housing 102 is a cylindrical housing (as illustrated in Figure 3), 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 end 18 of the stator core 12. In particular, the cooling passageways 28 extend from the first end 18 to the second end 20 of the stator core 12. The cooling passageways 28 are distributed about a circumference of the stator core 12.

The electrical machine 100 has a first cooling manifold 30A which at least partly covers the first end 18 of the stator core 12. The first cooling manifold 30A defines a first chamber 32A in fluid communication with the 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 1, 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 electrical machine 100 also has a second cooling manifold 30B which at least partly covers the second end 20 of the stator core 12. The second cooling manifold 30B defines a second chamber 32B in fluid communication with the cooling passageways 28 and 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 cooling passageways 28 to the second chamber 32B and then out of the manifold outlet 34B.

In the arrangement of Figure 1, 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 Figures 1 and 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.

The electrical machine 100 of Figure 1 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).

In the illustrated arrangement, the stator core 12 is defined by a stator lamination stack 44. In other words, the stator core 12 is formed of a plurality of layers 44A, 44B (as illustrated most clearly in Figure 4). The layers 44A, 44B are stacked one atop the other to form the stator lamination stack 44, which extends from the first end 18 of the stator core 12 to the second end 20 of the stator core 12. The layers 44A, 44B 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 with a plastic material to provide sealing such that coolant is prevented, or resisted, from passing between the laminations (i.e. layers 44A, 44B) 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 stator assembly 10 includes a bolting arrangement 46 which is configured to provide a clamping force to the stator lamination stack 44. This inhibits delamination (i.e., separation of layers 44A, 44B) in the stack 44 (e.g., during manufacturing). The bolting arrangement 46 includes a bolt 48 having a shaft 50 which extends through a bolt passageway 54 in the stator lamination stack 44. In particular, the illustrated bolt 48 extends the entire length of the bolt passageway 54 in order to facilitate a clamping force which acts on opposing ends 18, of the stator lamination stack 44.

The bolting arrangement 46 also includes a receiving component 56 which, in the arrangement of Figure 1, is provided at the first end 18 of the stator lamination stack 44. The receiving component 56 has a female thread 57 for receiving a threaded end 51 of the shaft 50 of the bolt 48 (i.e., an end of the shaft 50 opposite to a bolt head 52 of the bolt 48). In this way, the receiving component 56 pushes against the first end 18 of the stator lamination stack 44 and the bolt head 52 pushes against the second end 20 of the stator lamination stack 44, which provides a clamping force therebetween. The receiving component 56 may be a nut (e.g., as illustrated in Figure 1) or may be part of the first or second cooling manifold 30A, 30B (as described below with reference to Figures 5 to 8).

In the illustrated arrangement, the bolting arrangement 46 includes a plurality of bolts 48 distributed circumferentially about the stator core 12. In particular, there are six bolts 48, but other numbers of bolts 48 may be used (e.g., one, two, three, four, five, or greater than six bolts 48). Each bolt 48 may have its own receiving component 56 (e.g., a nut as illustrated in Figure 1) or there may be a common receiving component 56 for all the bolts 48 (e.g., a cooling manifold, as described below with reference to Figures 5 to 8). The description below refers to a single bolt 48 for simplicity; however, it will be understood that each of the plurality of bolts 48 is of the same configuration and thus has the features described below.

As illustrated in Figure 4, the stator lamination stack 44 is formed of a plurality of stator materials. In other words, the layers 44A, 44B of the stator lamination stack 44 are made of different materials.

The bolt 48 is formed of a bolt material having substantially the same co-efficient of thermal expansion as the stator lamination stack 44. This inhibits variations in the clamping force provided by the bolting arrangement 46 during temperature changes (e.g., during manufacturing and/or use of the stator assembly 10). In this context, the phrase "substantially the same co-efficient of thermal expansion" will be understood to mean that the bolt 48 and stator lamination stack 44 expand or contract by approximately the same amount (e.g., in a longitudinal direction) when subjected to similar changes in temperature. For example, the amount by which the bolt expands or contracts is within a small percentage of the amount by which the stator lamination stack expands or contracts (e.g., within 20%, within 10%, within 5%).

It will be understood that because the stator lamination stack 44 is formed of a plurality of stator materials, which may each have a different co-efficient of thermal expansion, the stator lamination stack 44 as a whole may have a different co-efficient of thermal expansion to any of the individual stator materials which form the stator lamination stack 44. Therefore, the bolt material may differ from the plurality of stator materials, so that the co-efficient of thermal expansion of the bolt 48 can be matched to the overall co-efficient of thermal expansion of the stator lamination stack 44.

In the illustrated arrangement, the stator lamination stack 44 includes metallic layers 44A interspersed between layers of non-metallic bonding material 44B. The bolt material has substantially the same co-efficient of thermal expansion as the combined co-efficient of thermal expansion of the metallic layers 44A and non-metallic bonding layers 44B forming the stator lamination stack 44.

It will be understood that the layers of bonding material 44B may have a greater co-efficient of thermal expansion than the metallic layers 44A, which may lead to increased expansion of the overall stator lamination stack 44. Therefore, the bolt material may be a metallic material with a co-efficient of thermal expansion which is greater than the co-efficient of thermal expansion of the metallic layers 44A of the stator lamination stack 44, in order to facilitate matching with the overall thermal expansion of the stator lamination stack 44.

In the illustrated arrangement, a cross-section of the bolt passageway 54 is greater than a cross-section of the bolt 48 along an entire length of the shaft 50, such that a clearance is defined therebetween. In this way, the bolt 48 is permitted to expand in a radial direction by more than the metallic layers 44A of the stator lamination stack 44, whilst allowing overall thermal expansion (i.e., in a longitudinal direction parallel to the central stator axis 16) to be matched. In other words, the clearance defines a space for the bolt 48 to expand more than the portion of the bolt passageway 54 defined by the metallic layers 44A.

In some embodiments, the metallic layers 44A of the stator lamination stack 44 comprise ferrous material (e.g., electrical steel material). In some embodiments, the bolt material comprises aluminium or aluminium alloy. In some embodiments, the non-metallic bonding material comprises an epoxy material. For example, the metallic layers 44A may be of electrical steel material, the bolt material may be of aluminium alloy material and the non-metallic bonding material may be of epoxy material. This combination of materials provides matching of thermal expansion between the bolt 48 and the stator lamination stack 44.

In some embodiments, the metallic layers 44A form at least 90% of the thickness of the stator lamination stack 44, and the non-metallic bonding layers 44B form the remainder of the thickness of the stator lamination stack 44. For example, in one embodiment the metallic layers 44A form around 95% of the thickness of the stator lamination stack 44, and the non-metallic bonding layers 44B form the remaining 5% of the thickness of the stator lamination stack 44. It will be understood that the layers illustrated schematically in Figure 4 are not shown to scale.

The metallic layers 44A may be of any suitable thickness (e.g., as defined by commonly available gauges of sheet metal material).

It will be understood that in bolting arrangements 46 with a plurality of bolts 48, each bolt 48 may be of the same bolt material (i.e., a bolt material having substantially the same co-efficient of thermal expansion as the stator lamination stack 44).

In other stator assemblies 10, the bolt 48 may be made of a bolt material having a different co-efficient of thermal expansion to the stator lamination stack 44 (e.g., in arrangements where the stator assembly 10 is not likely to experience substantial changes in temperature during manufacturing or use).

A method of manufacturing a stator assembly 10 is illustrated in Figure 10 as a flow chart. The method includes the following steps: a) providing a stator core 12 defined by a stator lamination stack 44 formed of a plurality of stator materials 44A, 44B, the stator lamination stack 44 having a coefficient of thermal expansion; b) determining a bolt material having substantially the same coefficient of thermal expansion as the stator lamination stack; c) providing a bolt 48 in the determined bolt material; d) inserting the bolt 48 through a bolt passageway 54 in the stator lamination stack 44; and e) engaging a thread of the bolt 48 with a complementary female thread 57 in a receiving component 56 to provide a clamping force to the stator lamination stack 44.

Still referring to Figures 1 to 4, the stator assembly 10 includes a bolt insulation arrangement 58 which electrically insulates the bolt 48 from the stator lamination stack 44. This inhibits formation of a current loop through the bolt 48, which could be detrimental to performance of the electrical machine 100.

The bolt insulation arrangement 58 includes an annular space 60 between the bolt 48 and a wall 55 of the bolt passageway 54. In other words, a clearance is defined between the shaft 50 of the bolt 48 and the wall 55 of the bolt passageway 54. This prevents direct contact between the bolt 48 and the wall 55 of the bolt passageway 54, which provides electrical insulation.

As illustrated in Figure 2, the bolt insulation arrangement 58 includes an insulation sleeve 62 which at least partly surrounds the shaft 50 of the bolt 48. The insulation sleeve 62 is a circumferential insulation portion which is formed of electrically insulating material. This acts as an electrically insulating barrier between the shaft 50 of the bolt 48 and the wall 55 of the bolt passageway 54. In addition, the insulation sleeve 62 may also act as a locating formation which aligns the shaft 50 within the bolt passageway 54, e.g., so that other portions of the shaft 50 not covered by the insulation sleeve 62 are surrounded by an annular space 60 between the shaft 50 and the wall 55 of the bolt passageway 54.

In the illustrated arrangement, the insulation sleeve 62 extends only partly along the length of the shaft 50 (e.g., from an end of the shaft 50 proximal to the bolt head 52 to a position partway along the length of the shaft 50). This may facilitate improved cooling of other portions of the shaft 50 (e.g., by passing a flow of cooling fluid along a bolt cooling space between the shaft 50 and the wall 55 of the bolt passageway 54, as described in detail below).

In some arrangements, the bolt insulation arrangement 58 includes a plurality of insulation sleeves 62 which are spaced apart along a length of the shaft 50. This may facilitate improved alignment of the shaft 50 along a length of the bolt passageway 54 (e.g., in comparison to a single insulation sleeve 62 provided at one end of the shaft 50). This arrangement also allows cooling of the shaft 50 between the insulation portions.

In alternative arrangements, the insulation sleeve 62 extends over substantially all of the length of the bolt passageway 54. In such embodiments, if cooling of the shaft 50 is required, the insulation sleeve 62 may be made of an electrically insulating but thermally conducting material, e.g., a ceramic material such as aluminium nitride or boron nitride.

In some arrangements, the insulation sleeve 62 has an electrical insulation resistance of at least 1 megaohms (e.g., at least 10 megaohms or at least 100 megaohms). This provides suitable electrical insulation between the shaft 50 of the bolt 48 and the wall 55 of the bolt passageway 54. It will be understood, however, that the voltages that may be conducted along the bolt 48 are low in comparison to other applications (e.g., electrical cables) and so the appropriate electrical insulation resistance may be lower than this in some embodiments.

In some arrangements, the insulation sleeve 62 is formed of polyether ether ketone material (e.g., material sold under the brand name Victrex®). This provides good electrical insulation. In addition, such a polyether ether ketone material may have other advantages such as high temperature resistance, chemical resistance, mechanical strength, dimensional stability and low friction. In alternative embodiments, the insulation sleeve 62 is made of any suitable insulation material which has suitable compressive strength at an operating temperature in the range of 70 to 120 °C.

In some arrangements, the insulation sleeve 62 has a radial thickness of at least 0.1 mm (e.g., at least 0.2 mm, at least 0.3 mm, at least 0.4 mm, at least 0.5 mm or at least 0.6 mm). Such a radial thickness may provide an electrical insulation resistance of at least 1 megaohms (e.g., at least 10 megohms or at least 100 megaohms), for example when made of polyether ether ketone material. In addition, or alternatively, such a radial thickness may provide suitable annular spacing between other parts of the shaft 50 not covered by the insulation sleeve 62 and the wall 55 of the bolt passageway 54. In this context, the term "radial thickness" means a thickness of the insulation sleeve 62 in a direction transverse to a longitudinal axis of the shaft 50 of the bolt 48 (i.e., in a direction transverse to the central stator axis 16).

In some arrangements, the insulation sleeve 62 is shrink-fitted to the shaft 50 of the bolt 48. This ensures a tight fit of the insulation sleeve 62 against the shaft 50, which inhibits unwanted movements of the insulation sleeve 62 relative to the shaft 50.

As illustrated in Figure 2, the bolt insulation arrangement 58 also includes an insulation washer 64 provided between the bolt head 52 of the bolt 48 and the second end 20 of the stator lamination stack 44. Such an insulation washer 64 (e.g., a washer formed of an electrically insulating material) provides electrical insulation between the bolt head 52 and the end of the stator lamination stack 44.

In some arrangements, the insulation washer 64 has an electrical insulation resistance of at least 1 megaohms (e.g., at least 10 megaohms or at least 100 megaohms). Such an electrical insulation resistance provides suitable electrical insulation between the bolt head 52 and the second end 20 of the stator lamination stack 44. It will be understood, however, that the voltages that may be conducted along the bolt 48 are low in comparison to other applications (e.g., electrical cables) and so the appropriate electrical insulation resistance may be lower than this in some embodiments.

In some arrangements, the insulation washer 64 is formed of formed of polyether ether ketone material (e.g., material sold under the brand name Victrex®). Using such a polyether ether ketone material provides good electrical insulation. In addition, such a polyether ether ketone material may have other advantages such as high temperature resistance, chemical resistance, mechanical strength, dimensional stability and low friction. In alternative embodiments, the insulation washer 64 is made of any suitable insulation material which has suitable compressive strength at an operating temperature in the range of 70 to 120 °C.

In some arrangements, the insulation washer 64 has an axial thickness of at least 0.1 mm (e.g., at least 0.2 mm, at least 0.3 mm, at least 0.4 mm, at least 0.5 mm or at least 0.6 mm). Such an axial thickness may provide an electrical insulation resistance of at least 1 megaohms (e.g., at least 10 megohms or at least 100 megaohms), for example when made of polyether ether ketone material. In this context, the term "axial thickness" means a thickness of the insulation washer 64 in a direction parallel to a central axis of the insulation washer 64 (e.g., in a direction parallel to the longitudinal axis of the shaft 50 of the bolt 48).

Although the illustrated arrangement shows the insulation washer 64 and insulation sleeve 62 as separate components, in alternative arrangements the insulation washer 64 and insulation sleeve 62 may be joined together and/or integrally formed. In this way, the insulation washer 64 defines a flange at an end of the insulation sleeve 62. In such arrangements, the insulation washer 64 and insulation sleeve 62 can each be considered a part of a single insulation covering. For example, a single insulation covering defining the insulation sleeve 62 and insulation washer 64 may be over-moulded onto a base material of the bolt 48.

In some arrangements, the bolt insulation arrangement 58 electrically insulates the threaded end 51 of the shaft 50 (i.e., an end distal the bolt head 52) and/or the receiving component 56 from the first end 18 of the stator lamination stack 44. For example, the receiving component 56 may be formed of an electrically insulating material, such as polyether ether ketone material. Alternatively, or additionally, an insulation washer (e.g., of the same kind as the insulation washer 64 described above) may be provided between the receiving component 56 and the first end 18 of the stator lamination stack 44. Alternatively, or additionally, an insulation sleeve (e.g., similar to the insulation sleeve 62 described above) may be provided between the thread of the shaft 50 and the female thread 57 of the receiving component 56. In other embodiments, such as the illustrated embodiment, the bolt insulation arrangement 58 does not electrically insulate the threaded end 51 of the shaft or the receiving component 56 from the first end 18 of the stator lamination stack 44.

It will be understood that in bolting arrangements 46 with a plurality of bolts 48, each bolt 48 may have a bolt insulation arrangement 58 of the kind described above. This inhibits formation of a current loop through adjacent bolts, which could be detrimental to performance of an electrical machine 100 including the stator assembly 10.

In other stator assemblies 10, the bolt insulation arrangement 58 may be omitted (e.g., in arrangements where electrical performance is less important than other factors such as compactness or manufacturing cost).

A method of assembling a stator assembly 10 is illustrated in Figure 11 as a flow chart. The method includes the following steps: a) providing a stator core 12 defined by a stator lamination stack 44; b) providing a bolt 48 having a shaft 50; c) inserting the bolt 48 through a bolt passageway 54 in the stator lamination stack 44 such that the bolt is electrically insulated from the stator lamination stack 44; and d) engaging a thread of the bolt 48 with a female thread 57 in a receiving component 56 to provide a clamping force to the stator lamination stack 44.

In some embodiments, step b) comprises applying an insulation sleeve 62 to the shaft, so that the insulation sleeve 62 at least partially surrounds the shaft 50.

In some embodiments, step b) comprises over-moulding an insulation sleeve 62 and insulation washer 64 onto a base material of the bolt 48.

In some embodiments, step b) comprises passing the shaft 50 of the bolt 48 through an aperture of the insulation sleeve 62, and shrink-fitting the insulation sleeve 62 onto the shaft 50.

Still referring to Figures 1 to 4, the stator assembly 10 is configured so that a bolt cooling space 66 is provided between the shaft 50 of the bolt 48 and the wall 55 of the bolt passageway 54, for receiving a flow of cooling fluid therethrough. For example, the block arrows on Figure 2 schematically illustrate a flow path of cooling fluid through the bolt cooling space 66. This allows a temperature of the bolt 48 to be controlled.

It will be understood that the cooling fluid recirculation system 120 described above will supply cooling fluid to the bolt cooling space 66 as well as the cooling passageways 28 during use (e.g., using the common first and second cooling manifolds 30A, 30B, also described above).

In the illustrated arrangement, the bolt cooling space 66 completely surrounds the shaft 50 of the bolt 48 for at least a portion of the length of the shaft 50. In other words, for at least a portion of the length of the shaft 50, cooling fluid can be passed around an entire circumference of the shaft 50. For example, the bolt cooling space 66 completely surrounds the shaft 50 of the bolt 48 for at least the portion of the shaft 50 not covered by insulation sleeve 62 described above.

As illustrated in Figure 3, the bolt cooling space 66 includes a radially extending notch 68 in the wall 55 of the bolt passageway 54. This provides a larger bolt cooling space 66 for a given diameter of the bolt passageway 54 and thus allows a greater flow of cooling fluid along the bolt passageway 54, which increases the amount of heat which can be removed from the bolt 48.

In the illustrated arrangement, the radially extending notch 68 provides an outlet 67 through which cooling fluid can exit the bolt passageway 54 at the second end 20 of the stator lamination stack 44 (which is otherwise covered by the insulation washer 64 and/or bolt head 52 described above).

In the illustrated arrangement, the radially extending notch 68 is present over substantially all of the length of the bolt passageway 54. In other arrangements, the radially extending notch 68 is present over only part of the length of the bolt passageway 54 (e.g., at one or both ends of the bolt passageway 54 to permit inflow and/or outflow of cooling fluid around the bolt head 52 of the bolt 48 and/or washer 64 and/or receiving component 56 provided at the respective end of the bolt passageway 54).

As illustrated in Figure 3, the radially extending notch 68 has a substantially triangular cross-section. This facilitates an increased volume of the bolt cooling space 66 proximal to the shaft 50 (i.e., at a wider end of the triangular cross-section), whilst reducing the amount of material removed from the stator lamination stack 44 further away from the shaft 50 (i.e., at a narrower end of the triangular cross-section). The triangular shaped cross-section may also facilitate maintaining a clearance between the bolt passageway 54 and other cooling passageways 28 through the stator lamination stack 44, which are diagonally offset from the bolt passageway 54 (e.g., as illustrated in the further arrangement of Figure 8, which shows a similarly shaped bolt passageway 54).

In the illustrated arrangement, the wall 55 of the bolt passageway 54 defines a multi-lobed cross-sectional shape in which the wall 55 bulges outwards at multiple different points or "lobes" 70, 72, 74. In particular, the wall 55 defines a tri-lobed cross-sectional shape having a first lobe 70, second lobe 72 and third lobe 74. Such a multi-lobed shape allows an increased area of the bolt cooling space 66 at the multiple lobes 70, 72, 74 (i.e., to facilitate an increased flow of cooling fluid along the shaft 50 and thereby increase cooling performance).

It will be understood that, because the multi-lobed cross-sectional shape includes portions between the multiple lobes 70, 72, 74 where the clearance between the wall 55 and the shaft 50 of the bolt 48 is smaller, this may facilitate better location of the shaft 50 in a particular position compared to arrangements where the wall 55 has a larger circular cross-sectional shape.

In the illustrated arrangement, the first lobe 70 is defined by the radially extending notch 68 in the wall 55 of the bolt passageway 54. While the radially extending notch 68 has a substantially triangular cross-section, the second and third lobes 72, 74 are substantially rounded. In addition, the radially extending notch 68 extends further from the shaft 50 of the bolt 48 than the second and third lobes 72, 74. In other arrangements, the lobes 70, 72, 74 may be of the same size and/or shape (e.g., all rounded like the illustrated second and third lobes 72, 74, or all triangular like the illustrated first lobe 70).

In some arrangements, the stator assembly 10 has one or more locating formations 62, 76 configured to align the shaft 50 of the bolt 48 inside the bolt passageway 54. Such locating formations 62, 76 help to maintain a correct position of the shaft 50 within the bolt passageway 54, so that a suitable cooling space 66 is provided around the shaft 50. In the illustrated arrangement, the insulation sleeve 62 described above ads as a locating formation by engaging the wall 55 of the bolt passageway 54 at one or more positions along the length of the bolt passageway 54. In addition, the portions of the wall 55 of the bolt passageway 54 located between the different lobes 70, 72, 74 act as locating formations 76. In other words, the insulation sleeve 62 abuts against these locating formations 76 to align the shaft 50 inside the bolt passageway 54.

In alternative arrangements, the locating formations may include any other suitable type of radial projection from the shaft 50 and/or wall 55.

In the illustrated arrangement, the bolt passageway 54 has a constant cross-sectional shape along its length. In other words, the bolt cooling space 66 has a constant cross-sectional shape along a length of the stator lamination stack 44. This allows identical layers 44A, 44B of material to be used to build up the stator lamination stack 44, which simplifies manufacturing. For example, where the layers 44A, 44B of the stator lamination stack are formed of stamped sheet material, having a constant cross-section along the length allows a single stamp to be used to form each layer 44A, 44B.

In alternative arrangements, the bolt passageway 54 has a varying cross-sectional shape along its length. For example, the radially extending notch 68 may be machined into one end of the bolt passageway 54 as described above, and/or the second and third lobes 72. 74 may be omitted at areas of the shaft 50 covered by the insulation sleeve 62 (e.g., to facilitate better alignment of the shaft 50 within the bolt passageway 54).

As discussed above, the stator core 12 has a plurality of cooling passageways 28 distributed about a circumference of the stator core 12. The bolt cooling space 66 is separated circumferentially from the cooling passageways 28. In the illustrated arrangement, the bolt cooling space 66 has a radial dimension which at least partly overlaps with a radial dimension of the cooling passageways 28. In other words, the inner and outer edges of the cooling passageways are prescribed by inner and outer circumferences 78, 80 and the bolt cooling space 66 at least partly overlaps with the space defined between the inner and outer circumferences 78, 80 (e.g., as illustrated in the further arrangement of Figure 8, which shows a similarly shaped bolt passageway 54). Put another way, the bolt cooling space 66 is located between a first radial distance range with respect to the central stator axis 16, and the cooling passageways 28 are located between a second radial distance range with respect to the central stator axis 16, and the first radial distance range at least partly overlaps with the second radial distance range. This configuration allows a common cooling manifold to be used for input of cooling fluid to the bolt cooling space 66 and the cooling passageways 28. For example, the first chamber 32A defined by the first cooling manifold 30A described above may input cooling fluid to the bolt cooling space 66 and the cooling passageways 28. Similarly, cooling fluid may be expelled from both the bolt cooling space 66 and the cooling passageways 28 into the second chamber 32B defined by the second cooling manifold 30B described above.

It will be understood that in bolting arrangements 46 with a plurality of bolts 48, a bolt cooling space 66 may be provided between the shaft 50 of each bolt 48 and the wall 55 of the respective bolt passageway 54.

In other stator assemblies 10, the bolt cooling space 66 may be omitted (e.g in arrangements where the bolt 48 is not likely to require cooling during use).

A method of cooling a bolt 48 provided in a bolt passageway 54 through a stator lamination stack 44 is illustrated in Figure 12 as a flow chart. The method includes the following steps: a) providing a bolt cooling space 66 between a shaft 50 of the bolt 48 and a wall 55 of the bolt passageway 54; and b) passing cooling fluid through the bolt cooling space 66.

Referring now to Figures 5 to 8, an alternative stator assembly 10 suitable for use in an electrical machine 100 of the kind described above is shown. The stator assembly 10 of Figures 5 to 8 has many common features with the stator assembly 10 of Figures 1 to 4, and so the same reference numerals will be used below.

It will be understood that, although not described in detail, the stator assembly 10 of Figures 5 to 8 has a similar bolting arrangement 46 to that described above (e.g. including a similar bolt insulation arrangement 58, bolt passageway 54 / bolt cooling space 66 configuration, and matched thermal expansion of the bolt 48 and stator lamination stack 44).

In the arrangement of Figures 5 to 8, a first seal 40A is located between the first end 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 seal 40A is an annular seal. The first seal 40A is located in a first annular recess 42A in the first cooling manifold 30A, which locates the first seal 40A in the correct position. Similarly, a second seal 40B is located between the second end 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 seal 4013 is an annular seal. The second seal 40B is located in a second annular recess 42B in the second cooling manifold 308, which locates the second seal 40B in the correct position.

In the arrangement of Figures 5 to 8, a third seal 40C is provided at an opposite side of the second cooling manifold 30B to the second seal 40B. The third seal 40C is configured to form a seal between the second cooling manifold 30B and the housing 102 and/or an outboard component located between the second cooling manifold 30B and the housing 102. The third seal 40C is located in a third annular recess 42C in the second cooling manifold 30B, which locates the third seal 40C in the correct position.

The first, second and third seals 40A, 40B, 44 may be formed of a polymeric material; for example, an elastomeric material such as a fluorosilicone material.

Similar to the previous arrangement of Figures 1 to 4, the schematic arrows on Figures 5 to 6B show a flow of cooling fluid through the manifold inlet 34A of the first cooling manifold 30A (e.g., after passing through the first opening 104 in the housing, described above), into the first cooling manifold 30A, along the cooling passageways 28, and into the second cooling manifold 30B. However, it will be understood that the flow of cooling fluid could be reversed. In other words, cooling fluid could instead flow into the second cooling manifold 30B, along the cooling passageways 28, into the first cooling manifold 30A and then out a manifold outlet (corresponding to the manifold inlet 34A of the illustrated arrangement) of the first cooling manifold 30A (e.g., and then out through the first opening 104 in the housing, described above).

In the arrangement of Figures 5 to 8, the bolting arrangement 46 is configured to urge the first cooling manifold 30A towards the first end 18 of the stator core 12 and thereby compress the first seal 40A therebetween. This facilitates a strong compression force on the first seal 40A, which allows a pressure of cooling fluid inside the first chamber 32A to be increased without leakage. Such an increased pressure may facilitate increased throughput of cooling fluid through the cooling passageways 28, and thus improved cooling performance.

Such a bolting arrangement 46 may be particularly beneficial in arrangements where the first cooling manifold 30A and cooling passageways 28 are part of an upstream portion of the cooling fluid recirculation circuit 122, since the cooling fluid may have to pass through the first cooling manifold 30A and cooling passageways 28 at a higher pressure in order to provide sufficient pressure at downstream portions of the cooling fluid recirculation circuit 122.

As described above, the bolting arrangement 46 includes a bolt 48. The bolt 48 extends along an axis aligned substantially parallel to the central stator axis 16. In this way, a force provided by tensioning of the bolt 48 acts in a direction parallel to the central stator axis 16 (i.e., transverse to the first end 18 of the stator core 12) which facilitates compression of the first seal 40A.

As described above, the bolting arrangement 46 is configured to provide a clamping force to the stator core 12. In particular, the bolt 48 extends through the bolt passageway 54 in the stator core 12 and acts between the second end 20 of the stator core 12 and the first cooling manifold 30A to urge the first cooling manifold 30A towards the first end 18 of the stator core 12. In other words, the bolting arrangement 46 provides dual functions of clamping the stator lamination stack 44 to inhibit delamination of the stack 44 (e.g., during manufacturing), and compression of the first seal 40A to facilitate increased pressure inside the first chamber 32A.

In the illustrated arrangement, the first cooling manifold 30A defines a female thread 57 which is engaged by the threaded end 51 of the bolt 48 to urge the first cooling manifold 30A towards the first end 18 of the stator core 12. This removes the need for an additional nut (e.g., the nut 56 illustrated in Figures 1 to 4 can be omitted), which reduces the component count of the stator assembly 10.

In the illustrated arrangement, the female thread 57 is provided in a through-hole 82 of the first cooling manifold 30A. This may be easier to provide than alternatives, such as a blind hole. The stator assembly 10 may also include a sealant provided between the threaded end 51 of the bolt 48 and the female thread 57. The sealant may comprises a curable polymer, PTFE tape, an acrylic resin such as methacrylate ester acrylic, or any other suitable sealant. Such a sealant inhibits leakage of cooling fluid through the threads of the bolt 48 and through-hole 82. This facilitates increased pressure of cooling fluid inside the first chamber 32A defined by the first cooling manifold 32A.

In alternative arrangements, a female threaded hole is provided within the stator core 12, and the bolt 48 is passed through the first cooling manifold 30A to engage the female thread in the stator core 12 and thereby compress the first seal 40A. For example, the female threaded hole may be machined into the stator core 12 after the stator core 12 has been formed (e.g., by building up layers of the stator lamination stack 44).

In some arrangements, the bolting arrangement 46 is configured to provide a clamping force of at least 500 N (e.g., at least 600 N, at least 700 N, at least 800 N, at least 900 N, at least 1000 N, at least 1100 N, at least 1200 N, at least 1300 N, at least 1400 N, at least 1500 N or at least 1600 N) to urge the first cooling manifold 30A towards the first end 18 of the stator core 12. Such a clamping force (i.e., tensioning) facilitates a strong compression force on the first seal 40A, which allows a high pressure of cooling fluid to be maintained inside the first chamber 32A. For example, such a clamping force may facilitate a pressure of at least 100 kPa (e.g., 17 at least 150 kPa, at least 200 kPa, at least 250 kPa or at least 300 kPa) inside the first chamber 32A without leakage.

It will be understood that the illustrated arrangement provides such a clamping force in a direction parallel to the central stator axis 16, rather than transverse to the central stator axis 16, so that the clamping force is transferred to the first seal 40A.

Although only a single bolt 48 is illustrated in the portions of the stator assembly 10 shown in Figures 5 to 8, it will be understood that the bolting arrangement 46 may include a plurality of bolts 48 distributed circumferentially about the stator core 12 and first cooling manifold 30A. For example, there may be six bolts 48 as in the arrangement of Figures 1 to 4. Alternatively, there may be one, two, three, four, five or greater than six bolts 48.

In embodiments where the bolting arrangement 46 includes a plurality of bolts 48, it will be understood that each bolt 48 engages the first cooling manifold 30A. In this way, the first cooling manifold 30A acts as a common receiving component for all of the bolts 48 (e.g., as opposed to the arrangement of Figures 1 to 4, in which each bolt 48 has a dedicated nut 56). In addition, the plurality of bolts 48 facilitate increased clamping force, and a more even distribution of force about the first seal 40A, which improves seal performance.

In some embodiments, each bolt 48 is tightened to achieve a bolt stretch value of at least 0.1mm (e.g., at least 0.15mm, e.g. at least 0.2mm). For example, each bolt 48 may be tightened to an initial bolt torque (e.g., approximately 0.5 Nm) and then turned a specified angle to achieve the required bolt stretch. For example, where the bolt 48 has a pitch of 0.8mm, a bolt stretch value of 0.2mm may be achieved with a quarter turn (i.e., 90 degrees). Other initial bolt torque values, bolt stretch values and angles may be used in alternative embodiments. Such a bolt stretch value facilitates a strong compression force on the first seal 40A, which allows a high pressure of cooling fluid to be maintained inside the first chamber 32A. For example, such a bolting torque may facilitate a pressure of at least at least 100 kPa (e.g., at least 150 kPa, at least 200 kPa, at least 250 kPa or at least 300 kPa) inside the first chamber 32A without leakage.

It will be understood that the stator assembly 10 of Figures 5 to 8 may replace the stator assembly 10 in the electrical machine 100 and electric drive unit 160 of Figures 1 to 4. In such a configuration, it will be understood that the cooling fluid recirculation circuit 122 may be connected to the first cooling manifold 30A to pass cooling fluid through the stator assembly 10 in a similar way to that described above.

A method of coupling a cooling manifold 30A to a stator core 12 is illustrated in Figure 13 as a flow chart. The method includes the following steps: a) providing a stator core 12 comprising a first end 18 and a plurality of cooling passageways 28 which extend in a longitudinal direction through the stator core 12 away from the first end 18; b) providing a cooling manifold 30A which at least partly covers the first end 18 of the stator core 12, wherein the cooling manifold 30A defines a chamber 32A in fluid communication with the cooling passageways 28 and a manifold inlet 34A for connecting the chamber 32A to a cooling fluid source; c) locating a seal 40A between the stator core 12 and the cooling manifold 30A to seal an edge 38A of the chamber 32A; and d) fastening the cooling manifold 30A to the stator core 12 via a bolting arrangement 46 which is configured to urge the cooling manifold 30A towards the first end 18 of the stator core 12 and thereby compress the seal 40A therebetween.

The electrical machine 100 described above with reference to Figures 1 to 8 may provide the function of a motor and/or generator for operation in a vehicle 200. For example, Figure 9 illustrates a vehicle 200 having a first electric machine 100-1 for driving one or more front wheels of the vehicle 200 and a second electric machine 100-2 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, arranged or configured to drive one of one or more front wheels of the vehicle 200 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 1.

As illustrated schematically on Figure 9, the electrical machine 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 electrical machine 100. In the vehicle 200 of Figure 9, the first electric machine 100-1 is part of a first EDU 160-1 for driving 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.

The functioning of electrical machines 100 and electric drive units (EDUs) 160 is known, and so will not be described here in more detail.

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 (15)

1. CLAIMS1. A stator assembly for an electrical machine, the stator assembly comprising: a stator core defined by a stator lamination stack formed of a plurality of stator materials; and a bolting arrangement configured to provide a clamping force to the stator lamination stack, wherein the bolting arrangement comprises a bolt which extends through a bolt passageway in the stator lamination stack; wherein the bolt is formed of a bolt material having substantially the same co-efficient of thermal expansion as the stator lamination stack.
2. The stator assembly of claim 1, wherein the bolt material differs from the plurality of stator materials.
3. 3. The stator assembly of claim 2, wherein the stator lamination stack comprises metallic layers interspersed between layers of non-metallic bonding material, and the bolt material has substantially the same co-efficient of thermal expansion as the combined co-efficient of thermal expansion of the metallic layers and non-metallic bonding layers forming the stator lamination stack.
4. 4. The stator assembly of claim 3, wherein the bolt material is a metallic material with a co-efficient of thermal expansion which is greater than the co-efficient of thermal expansion of the metallic layers of the stator lamination stack.
5. 5. The stator assembly of claim 4, wherein the metallic layers comprise ferrous material and wherein the bolt material comprises aluminium or aluminium alloy.
6. 6. The stator assembly of claim 5, wherein the ferrous material comprises electrical steel material.
7. 7. The stator assembly of any of claims 4 to 6, wherein a cross-section of the bolt passageway is greater than a cross-section of the bolt along its entire length, such that a clearance is defined therebetween.
8. 8. The stator assembly of any of claims 3 to 7, wherein the non-metallic bonding material comprises epoxy material.
9. 9. The stator assembly of any of claims 3 to 8, wherein the metallic layers form at least 90% of the thickness of the stator lamination stack, and the non-metallic bonding layers form the remainder of the thickness of the stator lamination stack.
10. 10. The stator assembly of any preceding claim, wherein the bolt acts between a cooling manifold provided at a first end of the stator lamination stack, and a second end of the stator lamination stack, to urge the cooling manifold towards the first end of the stator lamination stack.
11. 11. The stator assembly of any preceding claim, wherein the bolting arrangement comprises a plurality of bolts distributed circumferentially about the stator core, wherein each bolt is formed of a bolt material having substantially the same co-efficient of thermal expansion as the stator lamination stack; optionally, wherein the bolting arrangement comprises at least three bolts, optionally at least four bolts, optionally at least five bolts, optionally at least six bolts.
12. 12. An electrical machine comprising the stator assembly of any preceding claim.
13. 13. An electric drive unit comprising the electrical machine of claim 12.
14. 14. A vehicle comprising the electrical machine of claim 12 and/or the electric drive unit of claim 13.
15. 15. A method of manufacturing a stator assembly comprising: providing a stator core defined by a stator lamination stack formed of a plurality of stator materials, the stator lamination stack having a coefficient of thermal expansion; determining a bolt material having substantially the same coefficient of thermal expansion as the stator lamination stack; providing a bolt in the determined bolt material; inserting the bolt through a bolt passageway in the stator lamination stack; and engaging a thread of the bolt with a complementary female thread in a receiving component to provide a clamping force to the stator lamination stack.