Stator assembly

Abstract

Aspects of the present invention relate to a stator assembly comprising a stator core with a plurality of slots. The stator assembly also comprises windings formed of conductor elements which form coils arranged in the slots. The coils are connectable to an alternating current supply in multiple electrical phases, and each slot contains conductor elements in the same phase. The number of slots per pole per electrical phase is a non- integer number. The conductor elements comprise hairpin conductor elements each having two parallel conductor sides, a bent end which connects the parallel conductor sides, and a welded end at which the conductor sides are welded to conductor sides of other conductor elements to form the coils. The conductor elements further comprise at least one joining portion which connects two parallel conductor sides and which extends across the bent ends and / or welded ends of the hairpin conductor elements.

Description

[0001] STATOR ASSEMBLY

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to a stator assembly for a multi-pole electric machine. Aspects of the invention relate to a stator assembly, to a multi-pole electric machine, to a vehicle, and to a method.

[0004] BACKGROUND

[0005] A known multi-pole electric machine includes a rotor and a stator assembly. The stator assembly has a stator core which defines a plurality of slots, and a plurality of windings formed of conductor elements which are configured to form coils arranged in the slots. The coils are connected in multiple electrical phases. The current in each electrical phase may have an identical waveform (e.g., consisting of one or more sinusoidal components) with the base harmonics of the waveforms of the multiple electrical phases being out of phase. For example, in a three-phase system, the base harmonics of the waveforms are 120 electrical degrees out of phase. These currents in the phase coils result in a rotating magnetic excitation field in the stator assembly moving circumferentially around the stator core. Poles on the rotor are attracted to poles of the rotating magnetic excitation field in the stator assembly. In this way, the rotating magnetic excitation field causes the rotor to rotate about a central stator axis.

[0006] The number of slots per pole per electrical phase is typically an integer number. For example, a common electric machine for vehicle traction motors includes 48 slots, 8 poles and three electrical phases. It is known to provide the conductor elements in such an electric machine as hairpin conductor elements which are arranged in a wave pattern. In such a configuration, each hairpin conductor element comprises two parallel conductor sides, a bent end which connects the parallel conductor sides, and a welded end at which the conductor sides are welded to conductor sides of other conductor elements to form the coils. This may provide benefits such as higher power density and enhanced thermal performance, in comparison to other types of conductor elements.

[0007] It is an aim of the present invention to address one or more of the disadvantages associated with the prior art.

[0008] SUMMARY OF THE INVENTION

[0009] Aspects and embodiments of the invention provide a stator assembly, an electric machine, and a vehicle as claimed in the appended claims.

[0010] According to an aspect of the present disclosure, there is provided a stator assembly for a multi-pole electric machine. The stator assembly comprises a stator core comprising a first end, a second end, and a plurality of slots which extend from the first end to the second end. The stator assembly also comprises a plurality of windings formed of conductor elements which are configured to form coils arranged in the slots, wherein the coils are connected in multiple electrical phases, and wherein each slot contains conductor elements in the same phase. The number of slots per pole per electrical phase is a non-integer number. The conductor elements comprise hairpin conductor elements which are arranged in a wave pattern.It will be understood that having the number of slots per pole per electrical phase as a non-integer number (otherwise known as a “fractional slot winding”) reduces torque ripple in the associated electric machine. Such a reduction in torque ripple may lead to reduced vibration and noise, increased efficiency, and lower mechanical stresses.

[0011] It will also be understood that having hairpin conductor elements arranged in a wave pattern provides benefits such as higher power density and enhanced thermal performance.

[0012] The phrase “the coils are connectable to an alternating current supply in multiple electrical phases” means that there are multiple sets of coils, which are connectable to multiple electrical phases that are shifted by a given number of electrical degrees. The current in each electrical phase may have an identical waveform (e.g., consisting of one or more sinusoidal components) and the base harmonics of the waveforms of the multiple electrical phases are a given number of electrical degrees out of phase. For example, in a three-phase system, the base harmonics of the waveforms are 120 electrical degrees out of phase. In a two-phase system, the base harmonics of the waveforms would be 180 electrical degrees out of phase.

[0013] According to a further aspect of the present disclosure, there is provided a stator assembly for a multi-pole electric machine. The stator assembly comprises a stator core comprising a first end, a second end, and a plurality of slots which extend from the first end to the second end. The stator core also comprises a plurality of windings formed of conductor elements which are configured to form coils arranged in the slots, wherein the coils are connectable to an alternating current supply in multiple electrical phases, and wherein each slot contains conductor elements in the same phase. The number of slots per pole per electrical phase is a noninteger number. The conductor elements comprise hairpin conductor elements which are arranged in a wave pattern. Each hairpin conductor element comprises two parallel conductor sides, a bent end which connects the parallel conductor sides, and a welded end at which the conductor sides are welded to conductor sides of other conductor elements to form the coils. The conductor elements further comprise at least one joining portion which connects two parallel conductor sides and which extends across the bent ends and / or welded ends of the hairpin conductor elements.

[0014] It will be understood that having the number of slots per pole per electrical phase as a non-integer number (otherwise known as a “fractional slot winding”) reduces torque ripple in the associated electric machine. Such a reduction in torque ripple may lead to reduced vibration and noise, increased efficiency, and lower mechanical stresses.

[0015] It will also be understood that having hairpin conductor elements arranged in a wave pattern provides benefits such as higher power density and enhanced thermal performance.

[0016] Where the number of slots per pole and per electrical phase is a non-integer number, it may not be possible to follow the wave pattern of the hairpin conductor elements around the entire circumference of the stator core. For example, in regions of the stator core where there is an extra slot for a given electrical phase, it may be difficult to follow the wave pattern. However, the joining portions which extend over the bent or welded ends of the hairpin conductors can act as bridges between the hairpin conductors in such areas, so that a continuouscoil can be formed. In this way, the dual benefits of reduced torque ripple can be provided in addition to those advantages associated with hairpin conductor elements.

[0017] In this context the term “extend across the bent ends or welded ends” is intended to mean positioned axially outboard of the bent ends or welded ends relative to a central stator axis of the stator assembly, and passing circumferentially over at least some of those bent ends or welded ends. Put another way, the at least one joining portion extends over the bent ends and / or welded ends of the hairpin conductor elements.

[0018] In this context the term “conductor element” is intended to mean any discrete length of conductive material, whether it is bent or straight. Where conductor elements are welded to other conductor elements to form a continuous coil, the conductor elements can still be considered as separate discrete elements.

[0019] The at least one joining portion may extend across slots containing conductor elements of multiple electrical phases.

[0020] The at least one joining portion may span a larger number of slots than the hairpin conductor elements.

[0021] Optionally, the at least one joining portion comprises a bent joining portion which is defined by a jumping conductor element comprising at least one conductor side, a bent end which extends from the at least one conductor side and which forms at least part of the bent joining portion, and a welded end at which the at least one conductor side is welded to a conductor side of at least one other conductor element to form the coils. Such a bent joining portion may reduce the amount of welding required to form the joining portion compared to alternative configurations (e.g., additional discrete joining conductors).

[0022] Optionally, the jumping conductor element comprises two parallel conductor sides and the bent joining portion connects the two parallel conductor sides. In this way, the jumping conductor may be installed in the respective slots in a similar way to the hairpin conductor elements, but with a different configuration of the bent end.

[0023] In alternative embodiments, the bent joining portion is bent from only one conductor side and is welded to another conductor element (e.g., to a bent joining portion of another jumping conductor, or to a conductor side of a hairpin conductor).

[0024] Optionally, the bent joining portion extends over the bent ends of the hairpin conductor elements. In other words, at the end where the hairpin conductors are bent, the joining portions may also be bent. In this way, welding at this end of the stator core may be reduced or avoided, which may simplify manufacturing.

[0025] Optionally, at least one of the joining portions comprises a welded joining portion comprising a discrete joining conductor which is welded between two separate conductor sides. Such a welded joining portion may act as a bridge between standard hairpin conductor sides in areas where the wave pattern cannot be followed.In some embodiments, the discrete conductor is welded between conductor sides of two of the hairpin conductors. In other embodiments, the discrete conductor is welded between other conductor elements (e.g., between a conductor element defining only a single conductor side.

[0026] Optionally, the welded joining portion extends over the welded ends of the hairpin conductor elements. In other words, at the end where the hairpin conductors are welded, the joining portions may also be welded. This may simplify manufacturing.

[0027] Optionally, each joining portion comprises a flat section which is positioned axially outboard of the bent ends and / or welded ends of the hairpin conductor elements. Such a flat section allows a reduced height (i.e. axial projection) of the joining portion in comparison to alternatives (e.g., having a triangular shape).

[0028] Optionally, each joining portion tapers outwards in width from the respective parallel conductor sides to the flat section. Such a bent joining portion may be useful for providing a “returning jump”, which may be needed in portions of the stator core where there is an additional slot for the given electrical phase.

[0029] Optionally, each joining portion tapers inwards in width from the respective parallel conductor sides to the flat section. Such a bent joining portion may be useful for providing an “over jump”, which may be needed in portions of the stator core where there is a reduced number of slots for the given electrical phase.

[0030] Optionally, the coils are connected in three electrical phases.

[0031] Optionally, the stator assembly is for an 8-pole electric machine.

[0032] Optionally, the stator core comprises 54 slots. A common electric machine for vehicle traction motors has 8 poles, three electrical phases and 48 slots. In this case, the number of slots per pole and per electrical phase is an integer. In order to modify the 48-slot design to provide a non-integer number of slots per pole and per electrical phase, two slots can be added per electrical phase, which results in the stator core having 54 slots.

[0033] Optionally, the stator core comprises 42 slots. A common electric machine for vehicle traction motors has 8 poles, three electrical phases and 48 slots. In this case, the number of slots per pole and per electrical phase is an integer. In order to modify the 48-slot design to provide a non-integer number of slots per pole and per electrical phase, two slots can be removed per electrical phase, which results in the stator core having 42 slots.

[0034] Optionally, the stator core comprises 60 slots. A common electric machine for vehicle traction motors has 8 poles, three electrical phases and 48 slots. In this case, the number of slots per pole and per electrical phase is an integer. In order to modify the 48-slot design to provide a non-integer number of slots per pole and per electrical phase, four slots can be added per electrical phase, which results in the stator core having 60 slots.

[0035] Optionally, the stator core comprises 66 slots. A common electric machine for vehicle traction motors has 8 poles, three electrical phases and 48 slots. In this case, the number of slots per pole and per electrical phaseis an integer. In order to modify the 48-slot design to provide a non-integer number of slots per pole and per electrical phase, six slots can be added per electrical phase, which results in the stator core having 60 slots.

[0036] Optionally, the stator core comprises 36 slots. A common electric machine for vehicle traction motors has 8 poles, three electrical phases and 48 slots. In this case, the number of slots per pole and per electrical phase is an integer. In order to modify the 48-slot design to provide a non-integer number of slots per pole and per electrical phase, four slots can be removed per electrical phase, which results in the stator core having 36 slots.

[0037] Optionally, the stator assembly is for a 4-pole electric machine.

[0038] Optionally, the stator core comprises 30 slots. A known electric machine has 4 poles, three electrical phases and 24 slots. In this case, the number of slots per pole and per electrical phase is an integer. In orderto modify the 24-slot design to provide a non-integer number of slots per pole and per electrical phase, two slots can be added per electrical phase, which results in the stator core having 30 slots.

[0039] Optionally, the stator core comprises 36 slots. A known electric machine has 4 poles, three electrical phases and 24 slots. In this case, the number of slots per pole and per electrical phase is an integer. In orderto modify the 24-slot design to provide a non-integer number of slots per pole and per electrical phase, four slots can be added per electrical phase, which results in the stator core having 30 slots.

[0040] Optionally, the stator core comprises 42 slots. A known electric machine has 4 poles, three electrical phases and 24 slots. In this case, the number of slots per pole and per electrical phase is an integer. In orderto modify the 24-slot design to provide a non-integer number of slots per pole and per electrical phase, six slots can be added per electrical phase, which results in the stator core having 30 slots.

[0041] Optionally, the stator assembly is for a 10-pole electric machine.

[0042] Optionally, the stator core comprises 66 slots. A known electric machine has 10 poles, three electrical phases and 60 slots. In this case, the number of slots per pole and per electrical phase is an integer. In orderto modify the 60-slot design to provide a non-integer number of slots per pole and per electrical phase, two slots can be added per electrical phase, which results in the stator core having 66 slots.

[0043] Optionally, the stator core comprises 72 slots. A known electric machine has 10 poles, three electrical phases and 60 slots. In this case, the number of slots per pole and per electrical phase is an integer. In orderto modify the 60-slot design to provide a non-integer number of slots per pole and per electrical phase, four slots can be added per electrical phase, which results in the stator core having 72 slots.

[0044] Optionally, the stator core comprises 78 slots. A known electric machine has 10 poles, three electrical phases and 60 slots. In this case, the number of slots per pole and per electrical phase is an integer. In orderto modify the 60-slot design to provide a non-integer number of slots per pole and per electrical phase, six slots can be added per electrical phase, which results in the stator core having 78 slots. A known electric machine has 10poles, three electrical phases and 90 slots. In this case, the number of slots per pole and per electrical phase is an integer. In order to modify the 90-slot design to provide a non-integer number of slots per pole and per electrical phase, four slots can be removed per electrical phase, which results in the stator core having 78 slots.

[0045] Optionally, the stator core comprises 84 slots. A known electric machine has 10 poles, three electrical phases and 60 slots. In this case, the number of slots per pole and per electrical phase is an integer. In orderto modify the 60-slot design to provide a non-integer number of slots per pole and per electrical phase, eight slots can be added per electrical phase, which results in the stator core having 84 slots. A known electric machine has 10 poles, three electrical phases and 90 slots. In this case, the number of slots per pole and per electrical phase is an integer. In orderto modify the 90-slot design to provide a non-integer number of slots per pole and per electrical phase, two slots can be removed per electrical phase, which results in the stator core having 84 slots.

[0046] Optionally, each slot is configured to receive six conductor elements. Such a configuration allows the stator assembly to provide increased torque to a rotor of an electric machine compared to arrangements with less conductor elements per slot.

[0047] Optionally, each slot is configured to receive four conductor elements. Such a configuration provides a more compact arrangement than those with more conductor elements per slot.

[0048] According to a further aspect of the present disclosure there is provided a multi-pole electric machine comprising a stator assembly as disclosed herein, and a rotor. Such an electric machine benefits from the advantages of the stator assembly outlined above.

[0049] Optionally, the multi-pole electric machine is an 8-pole electric machine.

[0050] Optionally, the multi-pole electric machine is a 4-pole electric machine.

[0051] Optionally, the multi-pole electric machine is a 10-pole electric machine.

[0052] According to a further aspect of the present disclosure there is provided a vehicle comprising an electric machine as disclosed herein. Such a vehicle benefits from the advantages of the electric machine and stator assembly outlined above.

[0053] Optionally, the electric machine is a vehicle traction motor for driving wheels of the vehicle.

[0054] According to a further aspect of the present disclosure there is provided a method of manufacturing a stator for a multi-pole electric machine. The method comprises:

[0055] a) manufacturing a stator core comprising a first end, a second end, and a plurality of slots which extend from the first end to the second end; andb) providing a plurality of windings formed of conductor elements which form coils arranged in the slots, and connecting the coils in multiple electrical phases, wherein each slot contains conductor elements in the same phase and wherein the number of slots per pole per electrical phase is a non-integer number; and wherein the conductor elements comprise hairpin conductor elements which each have two parallel conductor sides and a bent end which connects the parallel conductor sides, and wherein step b) comprises:

[0056] b1) inserting the two parallel conductor sides in the respective slots, bending free ends of the conductor sides and then welding to the free ends of conductor sides of other hairpin conductor elements to form the coils;

[0057] wherein the conductor elements further comprise at least one joining portion which connects two parallel conductor sides, and wherein step b) further comprises:

[0058] b2) providing the at least one joining portion over the bent ends and / orwelded ends of the hairpin conductor elements.

[0059] According to a further aspect of the present disclosure there is provided a method of manufacturing a stator for a multi-pole electric machine, the method comprising:

[0060] taking a baseline stator design comprising a stator core comprising: a plurality of slots; a plurality of windings formed of conductor elements which are configured to form coils arranged in the slots, wherein the coils are connectable to an alternating current supply in multiple electrical phases, and wherein each slot contains conductor elements in the same phase; wherein the number of slots per pole and per electrical phase is an integer number;

[0061] determining a modified stator core by adding X slots to, or removing X slots from, the baseline stator design, wherein X is an integer multiple of the number of electrical phases, so that the number of slots per pole and per electrical phase is a non-integer number;

[0062] determining a modified winding design which includes conductor elements in the added slots, wherein the conductor elements of the modified winding design comprise hairpin conductor elements which are arranged in a wave pattern, wherein each hairpin conductor element comprises two parallel conductor sides, a bent end which connects the parallel conductor sides, and a welded end at which the conductor sides are welded to conductor sides of other conductor elements to form the coils;

[0063] wherein the conductor elements of the modified winding design further comprise at least one joining portion which connect two parallel conductor sides and which extend over the bent ends and / or welded ends of the hairpin conductor elements;

[0064] wherein the method further comprises producing a stator assembly having the modified stator core and the modified winding design.

[0065] It will be understood that by modifying the stator core to add or remove slots from the baseline design so that the number of slots per pole and per electrical phase is a non-integer number (otherwise known as a “fractional slot winding”) reduces torque ripple in the associated electric machine. Such a reduction in torque ripple may lead to reduced vibration and noise, increased efficiency, and lower mechanical stresses.

[0066] It will also be understood that determining a modified winding design which includes hairpin conductor elements arranged in a wave pattern provides benefits such as higher power density and enhanced thermal performance.Where the number of slots per pole and per electrical phase is a non-integer number, it may not be possible to follow the wave pattern of the hairpin conductor elements around the entire circumference of the stator core. For example, in regions of the stator core where there is an extra slot for a given electrical phase, it may be difficult to follow the wave pattern. However, by determining a modified winding design which includes joining portions which extend over the bent or welded ends of the hairpin conductors, these joining portions can act as bridges between the hairpin conductors in such areas, so that a continuous coil can be formed. In this way, the dual benefits of reduced torque ripple can be provided in addition to those advantages associated with hairpin conductor elements.

[0067] In this context the term “extend over the bent ends or welded ends” is intended to mean positioned axially outboard of the bent ends or welded ends relative to a central stator axis of the stator assembly, and passing circumferentially over at least some of those bent ends or welded ends.

[0068] In this context the term “conductor element” is intended to mean any discrete length of conductive material, whether it is bent or straight. Where conductor elements are welded to other conductor elements to form a continuous coil, the conductor elements can still be considered as separate discrete elements.

[0069] According to a further aspect of the present disclosure there is provided a stator assembly for a multi-pole electric machine, the stator assembly comprising:

[0070] a stator core comprising a first end, a second end, and a plurality of slots which extend from the first end to the second end and which are distributed around an axis of the stator core; and

[0071] a plurality of windings formed of conductor elements in the slots which are configured to form coils, wherein the coils are connectable to an alternating current supply in multiple electrical phases to define a predetermined number of magnetic poles for each phase around said axis and wherein each slot contains a predetermined number of said conductor elements of the same phase;

[0072] wherein the angular position and strength of the magnetic poles defined by the coils is asymmetrical about said axis, whereby harmonic resonance of the machine in use is reduced.

[0073] Optionally, the predetermined number of said conductor elements in each slot is not the same in every slot whereby the strength of the magnetic field at the different poles are not identical.

[0074] Optionally, the number of slots per pole per electrical phase is a non-integer number.

[0075] Optionally, the stator assembly comprises eight poles and is adapted for three phase electrical supply, wherein the 12thharmonic of the machine due to the alternating current supply is reduced.

[0076] Optionally, the slots in which the current-carrying conductor elements are disposed are distributed unevenly around the axis of the stator.

[0077] Optionally, the slots are evenly distributed around the axis and some of the slots are empty or contain fewer conductor elements than most of the slots which are filled with conductor elements.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 anyway 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.

[0078] BRIEF DESCRIPTION OF THE DRAWINGS

[0079] One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0080] Figure 1 shows a vehicle according to an embodiment;

[0081] Figure 2 shows a schematic longitudinal cross-sectional view of an electric machine comprising a stator assembly according to an embodiment;

[0082] Figure 3 shows a transverse cross-sectional view of the electrical machine of Figure 2;

[0083] Figure 4 shows an enlarged view of one of the slots of the stator assembly of Figures 1 and 2;

[0084] Figure 5 shows a perspective view of hairpin conductor elements of the kind used in the stator assembly of Figures 1 to 3;

[0085] Figure 6A shows a schematic sectional view of the hairpin conductor element of Figure 5 during insertion to the respective slots;

[0086] Figure 6B shows the hairpin conductor element of Figure 6A after insertion into the respective slots, and with the conductor sides bent for welding to adjacent hairpin conductor elements;

[0087] Figure 7 shows a transverse cross-sectional view of a stator assembly according to an embodiment;

[0088] Figure 8 shows one layer of one phase of a winding diagram of the stator assembly of Figure 7, the layer including two conductor elements in the respective slots;

[0089] Figure 8A shows one phase of a winding diagram of the stator assembly of Figure 7;

[0090] Figure 8B shows the winding path of one coil of one layer of the winding diagram of Figure 8A;

[0091] Figure 8C shows the transverse cross-sectional view of Figure 7 with the winding path of Figure 8B overlaid;

[0092] Figure 9 shows a jumping conductor element for use in the stator assembly of Figures 7 and 8;

[0093] Figure 10A shows partial jumping conductor elements for use in the stator assembly of Figures 7 and 8;

[0094] Figure 10B shows a discrete joining conductor for use in the stator assembly of Figures 7 and 8;Figure 11 shows part of a winding diagram of a stator assembly according to an embodiment;

[0095] Figure 12 shows a jumping conductor element for use in the stator assembly of Figure 11 ;

[0096] Figure 13A shows partial jumping conductor elements for use in the stator assembly of Figure 11 ;

[0097] Figure 13B shows a discrete joining conductor for use in the stator assembly of Figure 11 ;

[0098] Figure 14 shows a transverse cross-sectional view of a stator assembly according to an embodiment;

[0099] Figure 15 shows one layer of one phase of a winding diagram of the stator assembly of Figure 14, the layer including two conductor elements in the respective slots;

[0100] Figure 15A shows a winding diagram of the stator assembly of Figure 14;

[0101] Figure 16 shows an enlarged view of three of the slots of the stator assembly of Figures 14 and 15;

[0102] Figure 17 shows a transverse cross-sectional view of a stator assembly according to an embodiment;

[0103] Figure 18 shows one layer of one phase of a winding diagram of the stator assembly of Figure 17, the layer including two conductor elements in the respective slots;

[0104] Figure 18A shows a winding diagram of the stator assembly of Figure 17;

[0105] Figure 19 shows an enlarged view of three of the slots of the stator assembly of Figures 17 to 18A;

[0106] Figure 20 shows a transverse cross-sectional view of a stator assembly according to an embodiment;

[0107] Figure 21 shows one layer of one phase of a winding diagram of the stator assembly of Figure 20, the layer including two conductor elements in the respective slots;

[0108] Figure 21 A shows a winding diagram of the stator assembly of Figure 20;

[0109] Figure 22 shows a table of finite element simulation results of the torque spectrums of peak torque of the stator assemblies of Figures 3 to 21 ;

[0110] Figure 23 shows a table of possible fractional slot winding topologies for an 8-pole electric machine;

[0111] Figure 24 shows a table of possible fractional slot winding topologies for a 4-pole electric machine;

[0112] Figure 25 shows a table of possible fractional slot winding topologies for a 10-pole electric machine;

[0113] Figure 26 shows a flow chart of a method of manufacturing a stator assembly for a multi-pole electrical machine according to an embodiment; and

[0114] Figure 27 shows a flow chart of a further method of manufacturing a stator assembly for a multi-pole electrical machine according to an embodiment.DETAILED DESCRIPTION

[0115] Examples of the present disclosure relate to a stator assembly. In particular, examples of the present invention relate to a stator assembly of 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. Nonlimiting examples will now be described with reference to accompanying Figures 1 to 8, where the figures illustrate a stator assembly 10, an electric machine 100, an electric drive unit (EDU) 206 and a vehicle 200. Figure 1 illustrates a vehicle 200 having a first electric machine 100-1 which is 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 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, i.e., a single vehicle traction motor which is 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 Figures 2 and 3, described below.

[0116] As illustrated schematically on Figure 1 , the electric machine(s) 100 may be part of an electric drive unit (EDU) 206. 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 206-1 for driving front wheels of the vehicle 200, and the second electric machine 100-2 is part of a second EDU 206-2 fordriving rear wheels of the vehicle 200.

[0117] Referring to Figures 2 and 3, 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 end 18 of the stator core 12 to a second end 20 of the stator core 12.

[0118] The stator core 12 has a plurality of winding slots or “slots” 22 extending radially to support electrical conductor elements 38 which are connected to define electrical stator windings 30 (as described in more detail below). A plurality of stator teeth 24 are provided between the slots 22. In other words, the stator teeth 24 are interspersed between the slots 22 in a circumferential direction about the stator core 12. Both the plurality of 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.

[0119] The electric machine 100 also includes a rotor 102 which drives a shaft 104. The rotor 102 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 102 provides a surface concentric with a circumference of the cylindrical inner channel 14,such that as the rotor 102 rotates within the cylindrical inner channel 14 of the stator core 12, a consistent air gap 26 is maintained between the rotor 102 and the stator core 12.

[0120] As mentioned above, the windings 30 are formed of conductor elements 38 which are configured to form coils 40 arranged in the slots 22. The coils 40 are connected in multiple electrical phases 32, 34, 36. In the illustrated stator assembly 10, each slot 22 contains conductor elements 38 in the same electrical phase 32, 34, 36. For example, Figure 3 illustrates slots in which the conductor elements 38 are connected to a first electrical phase 32, slots in which the conductor elements 38 are connected to a second electrical phase 34, and slots in which the conductor elements 38 are connected to a third electrical phase 36.

[0121] The conductor elements 38 are arranged and connected so that, coils 40 of each electrical phase 32, 34, 36 form poles 60, where the electrical phases are shifted by 120 electrical degrees. The poles of the rotating magnetic field, generated by the stator currents which flow in the windings 30, attract poles 106, which are the result of the excitation of the rotor 102 and stator assembly 10, on the rotor 102. The current in each electrical phase 32, 34, 36 may have an identical waveform (e.g., consisting of one or more sinusoidal components), and the base harmonics of the waveform of the three electrical phases 32, 34, 36 are 120 electrical degrees out of phase. These currents in the phase coils result in a rotating magnetic excitation field in the stator assembly 10 moving circumferentially around the stator core 12. The number of poles of this rotating magnetic excitation field is identical to the number of poles 60 defined by the phase coils, which is also equivalent to the number of poles 106 on the rotor 102. The poles 106 of the rotor 102 are the result of excitations of the stator windings 30 and rotor excitation, which can be produced by magnets and / or current. The poles 106 on the rotor 102 are attracted to the poles of the rotating magnetic excitation field in the stator assembly 10. In this way, the rotating magnetic excitation field causes the rotor 102 to rotate about the central stator axis 16. In the illustrated configuration, the electric machine 100 has 8 poles (i.e., 8 fixed poles 106 on the rotor 102, and a corresponding 8 poles 60 generated in the windings 30 of the stator assembly 10). In other configurations, the number of poles 60, 106 may differ (e.g., 4-pole or 10-pole configurations may be used). However, it will be understood that in each configuration, the number of poles 60 generated in the windings 30 of the stator assembly 10 and the number of poles 106 on the rotor 102 will be equal.

[0122] The functioning of electric machines 100 and electric drive units (EDUs) 206 is known, and so will not be described here in more detail.

[0123] Figure 4 illustrates one of the slots 22 of the stator assembly 10 in more detail. The slot 22 has a plurality of receiving spaces 37 for the conductor elements 38. In the illustrated configuration, there are six receiving spaces and six respective conductor elements 38 located in the receiving spaces 37. In other configurations, there may be other numbers of receiving spaces 37 and conductor elements 38 per slot 22 (e.g., 2, 4, 8, 10). As is known in the art, the conductor elements 38 are coated with an insulating layer (not shown). The insulating layer is typically applied to the conductor elements 38 before locating in the receiving spaces 37, although it may be possible to apply the insulating layer and / or add to the insulating layer after the conductor elements 38 are arranged in the received spaces 37. It will be understood that the insulating layers fill the portions of the receiving spaces 37 which are not occupied by the conductive portions of the conductor elements 38.Figures 5 to 6B illustrate the kind of conductor elements 38 used in the stator assembly 10 in more detail.. Each hairpin conductor element 38A has two parallel conductor sides 44 which are located in the respective slots 22. The conductor sides 44 extend through the respective slots 22 parallel to the central stator axis 16 (i.e., from the first end 18 to the second end 20 of the stator core 12). Each hairpin conductor element 38A also has a bent end 46 which connects the parallel conductor sides 44, and a welded end 48 at which the conductor sides 44 are welded to conductor sides 44 of other conductor elements 38A to form the coils 40. The bent ends 46 are positioned to the first side 18 of the stator core 12, and the welded ends 48 are positioned to the second side of the stator core 12.

[0124] In the illustrated configuration, the conductor elements 38 are hairpin conductor elements 38A which are arranged in a wave pattern 42. In particular, the parallel conductor sides 44 of each hairpin conductor element 38A are located in different positions in their respective slots 22. For example, in Figure 5, the right-hand conductor side 44 is located in an upper position in the slot 22, whereas the left-hand conductor side 44 is located in a lower position in the slot 22. In this way, when the hairpin conductor elements 38A are welded to adjacent hairpin conductor elements 38A to form a continuous coil 40, the coil 40 alternates between the upper and lower positions in the slots 22. Such a configuration defines the wave pattern 42.

[0125] The coils 40 define electrical paths for passing electrical current up and down through the stator core. However, in the hairpin winding configuration the coils 40 are not formed of loops of wire as in a traditional wire wound electrical winding, but instead have the wave pattern 42 described above.

[0126] It will be appreciated that, although Figure 5 shows a configuration with slots 22 sized to receive two hairpin conductor elements 38A per slot, the slots may have any suitable size. In particular, the slots 22 in the configuration of Figure 3 are configured to receive six hairpin conductor elements 38A. In such configurations, it will be appreciated that the pattern illustrated in Figure 5 may be “stacked” in layers to fill the slots 22. During manufacturing, the parallel conductor sides 44 are inserted into the respective slots 22, as illustrated by the arrow on Figure 6A. After the conductor sides 44 are located in the respective slots 22, the conductor sides 44 are bent (e.g., as illustrated by the arrows on Figure 6B) to form the welded end 48 for connection to conductor sides 44 of other conductor elements 38B.

[0127] After bending and welding, the hairpin conductor elements 38A are coated with a non-conductive material to electrically isolate the coils from each other. There are various known methods for such coating, and so this will not be described in more detail.

[0128] Such a configuration of hairpin conductor elements 38A arranged in a wave pattern 42 is known to provide benefits such as higher power density and enhanced thermal performance, in comparison to other winding techniques.

[0129] The stator assembly 10 illustrated in Figure 3 has 48 slots, three electrical phases 32, 34, 36 and 8 poles 60. Such a configuration of the stator assembly 10 can be manufactured with standard hairpin technology without application of special processes which increase the complexity of manufacturability, and has therefore been widely used in electric machines for vehicle traction motors. Therefore, this configuration will be hereinafter referred to as the “48-slot baseline” stator assembly 10.Although the 48-slot baseline stator assembly 10 can be manufactured with standard hairpin technology, this configuration results in “torque ripple” in the associated electric machine 100. For example, Figure 22 illustrates finite element simulation results of the 48-slot baseline stator assembly 10, with peak torque values calculated with identical current values (hereafter the “nominal current value”) at an identical magnet temperature (hereafter the “nominal magnet temperature”). These simulation results show that there is a substantial torque harmonic component at the 12thharmonic (i.e., over 10% of the peak average base torque calculated for the 48-slot machine for an electrical cycle). The effects of this torque ripple may lead to unwanted noise, vibration, reduced efficiency and higher mechanical stresses on the electric machine 100.

[0130] Figures 3, 7 to 8C, 11 , 14 to 15A, 17 to 18A, and 20 to 21A illustrate different configurations of the stator assembly 10. Each of the stator assemblies 10 illustrated in Figures 7 to 8C, 11 , 14 to 15A, 17 to 18A, and 20 to 21 A could be used in the electric machine 100 of Figures 2 and 3. Common features between the different stator assemblies 10 are given the same reference numerals, and only differences from the previously described stator assemblies 10 will be discussed in detail.

[0131] Figures 7 to 8C illustrate a stator assembly 10 in which the number of slots 22 per pole 60 per electrical phase 32, 34, 36 is a non-integer number. In other words,

[0132] Number of slots

[0133] - - - - - - - - - - — - - - — - - = Non integer Number Number of poles x Number of Electrical Phases

[0134] Such a configuration is known as a “fractional slot winding topology”, which reduces the torque ripple in the associated electric machine 100 compared to configurations in which the number of slots per pole per electrical phase is an integer number, known as a “non-fractional slot winding topology” (e.g., as in the 48-slot baseline stator configuration of Figure 3).

[0135] In the configuration of Figures 7 to 8C, there are 54 slots, eight poles and three electrical phases. In other words:

[0136]

[0137] Figure 22 illustrates finite element simulation results of the configuration of Figures 7 to 8C, with peak torque values calculated with nominal current values at the nominal magnet temperature. These simulation results show that there is a substantial reduction in torque ripple compared to the 48-slot baseline stator assembly 10. For example, compared to the torque peak of 10.5% of the peak average base torque calculated for the 48-slot machine for an electrical cycle at the 12thharmonic for the 48-slot baseline design, the torque peak at the 12thharmonic for the configuration of Figures 7 to 8C is only 0.4% of the peak average base torque calculated for the 48-slot baseline for an electrical cycle. Further, in the configuration of Figures 7 to 8C, the reduction in torque peak at the 12thharmonic is achieved without any loss of peak average torque.

[0138] In other configurations, the stator assembly 10 may have a fractional slot winding topology with a different number of slots. For example, Figure 23 illustrates possible fractional slot winding topologies for an 8-pole stator assembly, and shows how these can be derived from the 48-slot baseline stator assembly 10 by either adding or removing slots. Similarly, Figure 24 illustrates possible fractional slot winding topologies for a 4-polestator assembly and shows how these can be derived from a 24-slot baseline stator assembly or a 36-slot baseline stator assembly by either adding or removing slots. Similarly, Figure 25 illustrates possible fractional slot winding topologies for a 10-pole stator assembly and shows how these can be derived from a 60-slot baseline stator assembly or a 90-slot baseline stator assembly by either adding or removing slots. In Figures 23 to 25, the three electrical phases are indicated as A, B, C respectively, and the + / - indicate the reference directions of the conductors in the respective slots.

[0139] In all of the configurations outlined in Figures 23 to 25, the number of slots added or removed compared to the respective baseline configuration is an integer multiple of the number of electrical phases. However, configurations in which the number of slots added to or removed from the baseline configuration is not an integer multiple of the number of electrical phases may also be useful.

[0140] Referring again to Figures 7 to 8C, the additional slots 22 added to the stator core 12 mean that it is no longer possible for all of the conductor elements 38 to be hairpin conductor elements 38A which follow the same wave pattern. Therefore, in this configuration, the conductor elements 38 include at least one joining portion 50 which connects two parallel conductor sides 44 and which extends across the bent ends 46 and / or welded ends 48 of the hairpin conductor elements 38A. In other words, the joining portion 50 extends over the bent ends 46 and / or welded ends 48 of the hairpin conductor elements 38A. Put another way, the at least one joining portion 50 is positioned axially outboard of the bent ends 46 and / or welded ends 48 of the hairpin conductor elements 38A relative to the central stator axis 16.

[0141] In the configuration of Figure 7, each slot 22 contains six conductor elements 38. The conductor elements 38 are connected in layers, each layer including two conductor elements 38 per slot. In other words, the number of layers is three. In other configurations where the number of conductor elements 38 per slot 22 is greater or less than six (e.g., four or eight), the number of layers varies accordingly. Figure 8 illustrates a wiring diagram for one of such layers and one phase of a 54-slot configuration. It will be understood that, because the wiring diagram of Figure 8 illustrates a circular arrangement of slots in linear form, the leftmost slots are repeated on the right hand side of the diagram and vice versa. For example, in Figure 8 the slots numbered “1”, “2”, and “3” are replicated on both sides of the diagram.

[0142] Figure 8A illustrates a wiring diagram of the full phase of the windings 30 of the stator assembly 10 of Figure 7 (i.e., including all three layers). The slots are numbered from “1” to “54”. For space saving purposes, slots “10”, “20, “30”, “40”, “50” and “54” are labelled in full, with the intermediate values being labelled with the last digit only (e.g., in Figure 8A slots “21” to “29” are the slots which are labelled as “1” to “9” between the slots labelled “20” and “30”). It will be understood that, because the winding diagram of Figure 8A illustrates a circular arrangement of slots in linear form, the leftmost slots are repeated on the right hand side of the diagram and vice versa. For example, Figure 8A shows an arrangement in which slots “51”, “52”, “53”, “54” and “1” are repeated on both sides of the diagram.

[0143] In Figure 8A, the positions of the six conductor elements 38 in each slot are labelled from “a” to “f” (for example, corresponding to the positions illustrated in Figure 4, with “a” being the radially innermost position, and “f” being the radially outermost position).In the phase illustrated in Figure 8A, there are two coils which run respectively from Start 1 to End 1 and from “Start 2” to “End 2”. The conductor elements which make up the coils alternate between two different positions in each layer. This is illustrated by the change between dotted and dashed lines along the coils. For example, in the top layer of Figure 8A, the conductor elements which are located in slot position “e” are indicated by dashed lines, whereas the conductor elements which are located in slot position “f” are indicated by solid lines. Such an alternating configuration may be referred to as a wave pattern.

[0144] in Figure 8A, jumps between the layers are indicated by the connections labelled A to D. For example, the conductor element which terminates at “A” in the upper layer is connected to the conductor element which terminates at “A” in the middle layer. Similarly, the conductor element which terminates at “B” in the upper layer is connected to the conductor element which terminates at “B” in the middle layer. Similarly, the conductor element which terminates at “C” in the middle layer is connected to the conductor element which terminates at “C” in the lower layer. Similarly, the conductor element which terminates at “D” in the middle layer is connected to the conductor element which terminates at “D” in the lower layer.

[0145] The numbers next to the ends of the coils indicate the next slots which the coils will pass through. For example, the number “6” on the right hand side of the upper layer of Figure 8A indicates that the coils which have conductor elements in positions “e” and “f” at slot number “53” will then run through slot number “6”. Such a path is illustrated on the left hand side of the upper layer of Figure 8A. Similarly, the number “7” on the right hand side of the upper layer of Figure 8A indicates that the coils which have conductor elements in positions “e” and “f” at slot number “54” will then run through slot number “7”. Such a path is also on the left hand side of the upper layer of Figure 8A. Referring now to Figure 8B, a single coil 40 or “winding path” of the upper layer of the winding diagram of Figure 8A is illustrated. The other coil 40 of this layer is omitted for simplicity. A joining portion 50 is provided to perform a “returning jump” which extends in the opposite direction to the wave pattern 42 of the hairpin conductor elements. For example, starting from the left-hand side of Figure 8B, the wave pattern 42 moves rightwards until it is interrupted by the joining portion 50, which “jumps” backwards in the opposite direction (e.g., from slot 28 to slot 19).

[0146] Figure 8C shows the coil 40 of Figure 8B overlaid on the transverse cross-sectional view of the stator assembly 10 of Figure 7. In Figure 8C, the slot numbers which the coil 40 passes through are labelled with the same numbering as shown in Figure 8B (e.g., slot numbers, 6, 7, 13, 14, 19, 20, 21 , 22, 26, 27, 28, 33, 34, 40, 41 , 47, 48, 53, 54). In Figure 8C, the bent ends of the conductor elements are shown radially inside the stator core 12 and the welded ends of the conductor elements are shown radially outside the stator core 12 for illustrative purposes. However, it will be understood that in practice, the bent and welded ends would be provided at opposite axial ends 18, 20 of the stator core 12.

[0147] It will be understood that the coils 40 illustrated in Figures 8A to 8C correspond to a different phase to the layer illustrated in Figure 8. As such, the joining portions 50 are provided between different slot numbers in Figures 8A to 8C compared to the joining portions 50 of Figure 8.

[0148] In the layer illustrated in Figure 8, two joining portions 50 are required to perform a “returning jump” which extends in the opposite direction to the wave pattern 42 of the hairpin conductor elements 38A. It can be seen from Figure 8 that each joining portion 50 extends across slots 22 of multiple electrical phases 32, 34, 36. Insome embodiments, the joining portions 50 may span a larger number of slots than the hairpin conductor elements 38A. For example, in Figure 8, the joining portions 50 span 8 slots (i.e. jump over 8 slots) whereas the standard hairpin conductor elements 38A span 5 or 6 slots.

[0149] In Figure 8, the solid lines indicate bent ends 46 of the conductor elements 38, whereas the dashed lines indicate welded ends 48 of the conductor elements 38. In the illustrated configuration, the joining portion 50 which passes over the bent ends 46 of the hairpin conductor elements 38A is a bent joining portion 50A which is defined by a jumping conductor element 38B. Such a jumping conductor element 38B is illustrated in Figure 9. The jumping conductor element 38B has two conductor sides 44 (similar to the hairpin conductor elements 38A), and a bent end 46 which extends from the conductor sides 44 and which forms the bent joining portion 50A. The jumping conductor element 38B also has a welded end 48 at which the conductor sides 44 are welded to conductor sides 44 of other conductor elements 38 (e.g., hairpin conductor elements 38A) to form the coils 40.

[0150] The conductor sides 44 of the jumping conductor elements 38B may be inserted into the respective slots 22 and then bent at the welded end 48 in a similar way to the hairpin conductor elements 38A (as described above with reference to Figures 6A and 6B). In other words, the jumping conductor elements 38B of the kind illustrated in Figure 9 may be installed in the respective slots 22 in a similar way to the hairpin conductor elements 38A, but with a different configuration of the bent end 46. Alternatively, one of the conductor sides 44 may be inserted into the respective slot, and then the jumping conductor element 38B may be bent to form the bent joining portion 50A before inserting the second conductor side 44 into the respective slot 22.

[0151] In alternative arrangements, the bent joining portion 50A is bent from only one conductor side 44 and is welded to another conductor element 38 to form the complete joining portion 50A. Such a configuration is illustrated in Figure 10A, in which “half jumping conductor elements 38C each have a single conductor side 44 and a bent joining portion 50A which is welded to the bent joining portion 50A of the other half jumping conductor element 38C to form the overall joining portion 50.

[0152] In the illustrated configuration, the joining portion 50 which passes over the welded ends 48 of the hairpin conductor elements 38A is a welded joining portion 50B. The welded joining portion 50B may include a discrete joining conductor 54 which is welded between two separate conductor sides 44 (e.g., of the hairpin conductor elements 38A and / or jumping conductor elements 38B). Such a welded joining portion 50B may act as a bridge between conductor sides 44 of standard hairpin conductor elements 38A in areas where the wave pattern cannot be followed.

[0153] An example of such a discrete joining conductor 54 is illustrated in Figure 10B. In this configuration, the discrete joining conductor 54 is a straight piece of conductive material which is welded between conductor sides 44 of two of the hairpin conductor elements 38A. To facilitate this, the conductor sides 44 which the discrete joining conductor 54 is welded to may be adapted (e.g., lengthened) in order to connect to the discrete joining conductor 54 axially outboard of the welded ends 48 of the hairpin conductor elements 38A. In other words, the hairpin conductor elements 38A which are connected by the discrete joining conductor 54 may be bent similarly to the configuration shown in Figure 6B, but with the conductor side 44 that is welded to the discretejoining conductor 54 being slightly longer to facilitate positioning of the discrete joining conductor 54 over the welded ends of the hairpin conductor elements 38A.

[0154] In alternative arrangements, the discrete joining conductor 54 may have any other suitable shape or configuration. For example, the discrete joining conductor 54 may have one or more legs which are bent from the straight portion of the discrete joining conductor 54 for overlapping with and welding to conductor sides 44 of the hairpin conductor elements 38A.

[0155] It will be understood that, because the joining portion 50 which extends over the bent ends 46 of the hairpin conductor elements 38A is a bent joining portion 50A, and the joining portion 50 which extends over the welded ends 48 of the hairpin conductor elements 38A is a welded joining portion 50B, all welding may be performed at the second end 20 of the stator core 12, which may simplify manufacturing. However, in alternative arrangements there may be a bent joining portion 50A over the welded ends 48 of the hairpin conductor elements 38A and / or a welded joining portion 50B over the bent ends 46 of the hairpin conductor elements 38A.

[0156] The joining portions 50, 50A, 50B of Figures 8 to 10B may each have a flat section 56 which is positioned axially outboard of the bent ends 46 and / or welded ends 48 of the hairpin conductor elements 38B. For example, such a flat section 56 is illustrated as an approximately horizontal (i.e., cross-page) section in Figures 8 to 10B. It will be understood that the flat section 56 may extend in an axis which is approximately perpendicular to the axes of the respective conductor sides 44 (i.e., perpendicular to the central stator axis 16). This contrasts with the bent end 46 of the traditional hairpin conductor elements illustrated in Figures 6A and 6B, which does not have such a flat section and instead has two sections which extend in axes which are acute angles to the axes of the respective conductor sides 44.

[0157] Such a flat section 56 allows a reduced height (i.e. axial projection) of the joining portion 50, 50A, 50B in comparison to alternatives (e.g., non-flat sections which project further in an axial direction from the end of the windings). For example, the increased axial projection resulting from the joining portion 50, 50A, 50B may be limited to the thickness of the jumping conductor element 38B or discrete joining conductor 54, which is axially outboard of the respective bent and welded ends.

[0158] In the configuration of Figures 8 to 10B, each joining portion 50, 50A, 50B tapers outwards in width from the respective parallel conductor sides 44 to the flat section 56. In this context, the term “width” refers to a dimension of the joining portion 50, 50A, 50B in a plane which is perpendicular to the central stator axis 16 (i.e., in a direction corresponding to the cross-page direction in Figure 9). In other words, the joining portion 50, 50A, 50B includes side sections 59 which flare outwards and connect the flat section 56 to the parallel conductor sides 44, as best illustrated in Figure 9. This shape may be useful for providing the “returning jump” described above.

[0159] Referring now to Figure 11 , a portion of a wiring diagram for a 42-slot, 8-pole 3-phase stator assembly is illustrated. In this configuration, the baseline 48-slot stator assembly has been modified to remove six slots (i.e., two slots per electrical phase 32, 34, 36). Such a configuration means that it is no longer possible for all of the conductor elements 38 to be hairpin conductor elements 38A which follow the same wave pattern. Therefore, in this configuration, the conductor elements 38 include at least one joining portion 50 which isrequired to perform an overjump which jumps over regions of the stator core 12 where slots 22 have been removed.

[0160] The ’’overjump” joining portion 50 differs in shape from the “returning jump” joining portion 50 of Figures 8 to 10B, but is otherwise similar in function. For example, both “overjump” and “returning jump” joining portions 50 connect two parallel conductor sides 44 and extend across (i.e. over) the bent ends 46 and / or welded ends 48 of the hairpin conductor elements 38A (i.e., axially outboard of the bent ends 46 and / or welded ends 48 of the hairpin conductor elements 38A relative to the central stator axis 16). In addition, both “over jump” and “returning jump” joining portions 50 extend across slots 22 of multiple electrical phases 32, 34, 36. In addition, “overjump” joining portions 50 may also span a greater number of slots 22 than the standard hairpin conductor elements 38A. For example, in Figure 11 , the joining portions 50 span 14 slots (i.e. jump over 14 slots) whereas the standard hairpin conductor elements 38A span 4 or 5 slots.

[0161] In the configuration of Figure 11 , the joining portion 50 which passes over the bent ends 46 of the hairpin conductor elements 38A is a bent joining portion 50A which is defined by a jumping conductor element 38B. Such a jumping conductor element 38B is illustrated in Figure 12. The jumping conductor element 38B has two conductor sides 44 (similar to the hairpin conductor elements 38A), and a bent end 46 which extends from the conductor sides 44 and which forms the bent joining portion 50A. The jumping conductor element 38B also has a welded end 48 at which the conductor sides 44 are welded to conductor sides 44 of other conductor elements 38 (e.g., hairpin conductor elements 38A) to form the coils 40.

[0162] The conductor sides 44 of the jumping conductor elements 38B may be inserted into the respective slots 22 and then bent at the welded end 48 in a similar way to the hairpin conductor elements 38A (as described above with reference to Figures 6A and 6B). In other words, the jumping conductor elements 38B of the kind illustrated in Figure 12 may be installed in the respective slots 22 in a similar way to the hairpin conductor elements 38A, but with a different configuration of the bent end 46. Alternatively, one of the conductor sides 44 may be inserted into the respective slot, and then the jumping conductor element 38B may be bent to form the bent joining portion 50A before inserting the second conductor side 44 into the respective slot 22.

[0163] In alternative arrangements, the bent joining portion 50A is bent from only one conductor side 44 and is welded to another conductor element 38C to form the complete joining portion 50. Such a configuration is illustrated in Figure 13A, in which “half jumping conductor elements 38C each have a single conductor side 44 and a bent joining portion 50A which is welded to the bent joining portion 50A of the other half jumping conductor element 38C to form the overall joining portion 50.

[0164] In the configuration of Figure 11 , the joining portion 50 which passes over the welded ends 48 of the hairpin conductor elements 38A is a welded joining portion 50B. The welded joining portion 50B may include a discrete joining conductor 54 which is welded between two separate conductor sides 44 (e.g., of the hairpin conductor elements 38A and / or jumping conductor elements 38B). Such a welded joining portion 50B may act as a bridge between conductor sides 44 of standard hairpin conductor elements 38B in areas where the wave pattern cannot be followed.

[0165] An example of such a discrete joining conductor 54 is illustrated in Figure 13B. In this configuration, the discrete joining conductor 54 is a straight piece of conductive material which is welded between conductor sides 44 oftwo of the hairpin conductor elements 38A. To facilitate this, the conductor sides 44 which the discrete joining conductor 54 is welded to may be adapted (e.g., lengthened) in order to connect to the discrete joining conductor 54 axially outboard of the welded ends 48 of the hairpin conductor elements 38A. In other words, the hairpin conductor elements 38A which are connected by the discrete joining conductor 54 may be bent similarly to the configuration shown in Figure 6B, but with the conductor side 44 that is welded to the discrete joining conductor 54 being slightly longer to facilitate positioning of the discrete joining conductor 54 over the welded ends of the hairpin conductor elements 38A.

[0166] It will be understood that the discrete joining conductor 54 of Figure 13B is similar to the discrete joining conductor 54 of Figures 10B, apart from differences in length of the conductive material due to the different shape of the “overjump” compared to the “returning jump”.

[0167] In alternative arrangements, the discrete joining conductor 54 may have any other suitable shape or configuration. For example, the discrete joining conductor 54 may have one or more legs which are bent from the straight portion of the discrete joining conductor 54 for overlapping with and welding to conductor sides 44 of the hairpin conductor elements 38A.

[0168] The joining portions 50, 50A, 50B of Figures 11 to 13B may each have a flat section 56 which is positioned axially outboard of the bent ends 46 and / or welded ends 48 of the hairpin conductor elements 38B. For example, such a flat section 56 is illustrated as an approximately horizontal (i.e. cross-page) section in Figures 11 to 13B. It will be understood that the flat section 56 may extend in an axis which is approximately perpendicular to the axes of the respective conductor sides 44 (i.e., perpendicular to the central stator axis 16). This contrasts with the bent end 46 of the traditional hairpin conductor elements illustrated in Figures 6A and 6B, which does not have such a flat section and instead has two sections which extend in axes which are acute angles to the axes of the respective conductor sides 44.

[0169] Such a flat section 56 allows a reduced height (i.e. axial projection) of the joining portion 50, 50A, 50B in comparison to alternatives (e.g., having a triangular shape). For example, the increased axial projection resulting from the joining portion 50, 50A, 50B may be limited to the width of the jumping conductor element 38B or discrete joining conductor 54.

[0170] In the configuration of Figures 11 to 13B, each joining portion 50, 50A, 50B tapers inwards in width from the respective parallel conductor sides 44 to the flat section 56. In this context, the term “width” refers to a dimension of the joining portion 50, 50A, 50B in a plane which is perpendicular to the central stator axis 16 (i.e., in a direction corresponding to the cross-page direction in Figure 12). In other words, the joining portion 50, 50A, 50B includes side sections 59 which flare inwards and connect the flat section 56 to the parallel conductor sides 44, as best illustrated in Figure 12. This shape may be useful for providing the “overjump” described above.

[0171] Referring now to Figures 14 to 16, a modification of the stator assembly 10 of Figures 7 and 8 is illustrated. In this configuration, the stator assembly 10 also has 54 slots, 8 poles, and three electrical phases 32, 34, 36 (although other configurations such as those outlined in Figures 23 to 25 could be modified in a similar way).In the configuration of Figures 14 to 16, the joining portions 50 and associated conductor elements 38 are omitted, so that some of the slots are partly-empty slots 22B in which at least one of the receiving spaces 37 does not contain a conductor element 38. In particular, there are twelve partly-empty slots 22B. In other configurations, there may be other numbers of partly-empty slots (e.g., double the number of slots added to or removed from the baseline configuration). In configurations where the number of slots added to or removed from the baseline configuration is an integer multiple of the number of electrical phases 32, 34, 36, the number of partly-empty slots 22B may be double the integer multiple of the number of electrical phases 32, 34, 36. It will be understood that the omission of the joining portions 50 and associated empty receiving spaces leads to a slight decrease in torque density of the stator assembly 10. For example, Figure 22 illustrates finite element simulation results of the configuration of Figures 14 to 16, with peak torque values calculated for nominal peak current at nominal magnet temperature. These simulation results show that for the stator assembly 10 of Figures 14 to 16 the peak average torque calculated for an electrical cycle is 95.9% of the average peak torque of the 48-slot baseline stator assembly 10. This compares to 102.3% of the average peak torque of the 48-slot baseline for the stator assembly 10 of Figures 7 and 8. However, the configuration of Figures 14 to 16 may be manufactured more easily because all of the conductor elements 38 can be provided as standard hairpin conductor elements 38A (as described above with reference to Figures 5 to 6B) with an equal coil pitch (i.e., an equal number of slots spanned by each hairpin conductor element 38A).

[0172] In addition, the overall torque performance of the configuration of Figures 14 to 16 still provides an improvement over the 48-slot baseline stator assembly 10 of Figure 3. In particular, the simulation results of Figure 22 show that there is a substantial reduction in torque ripple compared to the 48-slot baseline stator assembly 10. For example, comparing the amplitude of torque ripple harmonics expressed as the percentage of the average peak toque of the 48-slot baseline, the amplitude of the 12th torque harmonic of the 48-slot baseline design is 10.5% compared to the configuration of Figures 14 to 16 in which the amplitude of the same harmonic component is 1 .7%. This may lead to a noticeable reduction in vibration, noise, mechanical stresses etc. on the electric machine 100, which may compensate for any loss in average peak torque.

[0173] In the configuration of Figure 15, a single layer of a single phase of the 54-slot configuration is illustrated (in a similar way to the single layer illustrated in Figure 8, described above).

[0174] Figure 15A illustrates a full wiring diagram of the windings 30 of the stator assembly 10 of Figure 14 (i.e., including all three layers). The numbering of the slots in Figure 15A is the same as that described above for Figure 8A. In Figure 15A, slots “52”, “53”, “54”, “1” and “2” are repeated on both the left and right sides of the winding diagram. In this diagram, the positions of the six conductor elements 38 in each slot are labelled from “a” to “f”, in a similar manner to as described above with reference to Figure 8A.

[0175] In each phase illustrated in Figure 15A, there are two coils which run respectively from “SfX 1” to “EfX 1” and from “SfX 2” to “EfX 2”, where “X” indicates the phase number. As in Figure 8A, the conductor elements which make up the coils alternate between two different positions in each layer. This is illustrated by the change between dotted and dashed lines along the coils. For example, in the middle layer of Figure 15A, the conductor elements which are located in slot position “c” are indicated by dashed lines, whereas the conductor elementswhich are located in slot position d are indicated by solid lines. Such an alternating configuration may be referred to as a wave pattern.

[0176] In Figure 15A, jumps between the layers are indicated by the connections labelled A to Y. For example, the conductor element which terminates at “A” in the upper layer is connected to the conductor element which terminates at “A” in the middle layer, and so on.

[0177] In Figure 15A, parts of the paths which are connected in serial are denoted by “JfX Y” where “X” indicates the phase number and “Y” indicates the path number. For example, the conductor element which terminates at “ Jf 1 1 ” in the bottom layer is connected in series with the other conductor element which terminates at “Jf1 1 ” in the bottom layer, and so on.

[0178] The numbers next to the ends of the coils indicate the next slots which the coils will pass through, as described above with reference to Figure 8A.

[0179] Figure 16 illustrates some of the partly-empty slots 22B of Figures 14 and 15 in more detail. In the partly-empty slots 22B, conductor elements 38 are located in some of the receiving spaces 37 and no conductor elements 38 are located in others of the receiving spaces 37. This contrasts with a “full” slot 22 in which all of the receiving spaces 37 are filled with conductor elements 38. In the illustrated configuration, the partly-empty slots 22B are half empty. In other words, half of the receiving spaces 37 in the half empty slots contain conductor elements 38, and the other half of the receiving spaces 37 do not contain conductor elements 38. In the illustrated configuration, the partly-empty slots 22B are spaced apart from each other by at least one “full” slot 22 in which all of the receiving spaces are filled with conductor elements 38. In other configurations, some of the partly-empty slots 22B may be provided adjacent each other.

[0180] In the arrangement of Figure 16, the partly-empty slots 22B have spacers 62 in the receiving spaces 37 which do not contain conductor elements 38. Such spacers 62 inhibit movement of the conductor elements 38 in those slots 22B (and thus reduces likelihood of any associated issues such as wear / breakage of the welding at the welded ends 48 of the coils 40).

[0181] Each of the spacers 62 can be any element which fits within the respective receiving space 37 (i.e., having a similar cross-sectional size / shape to the conductor elements 38). The spacers 62 are not connected to the conductor elements 38 to form the coils 40. For example, the spacers 62 may be plastic shims / bars or any other suitable spacers. The spacers 62 may be non-conductive (e.g., formed of non-conductive material, or coated with a non-conductive material).

[0182] In alternative configurations, the spacers 62 are omitted.

[0183] Referring again to Figure 14, the partly-empty slots 22B are arranged in a regular pattern which is distributed around a circumference of the stator core 12. In particular, the partly-empty slots 22B are provided in groups (i.e., pairs spaced apart by a full slot 22, as illustrated in Figure 16), and the groups are evenly distributed about the circumference of the stator core 12. In other embodiments, the partly-empty slots 22B may be provided in a different regular pattern (e.g., the partly-empty slots 22B may be evenly distributed about a circumference of the stator core 12), or in an irregular pattern.Referring now to Figures 17 to 19, a modification of the stator assembly 10 of Figures 14 to 16 is illustrated. In this configuration, the stator assembly 10 also has 54 slots, 8 poles, and three electrical phases (although other configurations such as those outlined in Figures 23 to 25 could be modified in a similar way).

[0184] In the configuration of Figures 17 to 19, the conductor elements 38 in some of the partly-empty slots 22B of Figures 14 to 16 are shifted so that some of the slots are empty slots 22C which do not contain any conductor elements 38. In particular, there are six empty slots 22C. In other configurations, there may be other numbers of empty slots 22C (e.g., the same number of slots which are added to or removed from the baseline configuration). In configurations where the number of slots added to or removed from the baseline configuration is an integer multiple of the number of electrical phases 32, 34, 36, the number of empty slots 22C may be the integer multiple of the number of electrical phases 32, 34, 36.

[0185] Figure 22 illustrates finite element simulation results of the configuration of Figures 17 to 19, with peak torque values calculated for nominal peak current at nominal magnet temperature. These simulation results show that the torque performance of the stator assembly 10 of Figures 17 to 19 is similar to that of the previous configuration of Figures 14 to 16. In other words, while there is a slight reduction in torque peak at the fundamental frequency compared to the baseline design, the overall performance is improved by a considerable reduction in the torque peak at the 12thharmonic. In other words, the reduction in torque ripple may compensate for any loss in average peak torque.

[0186] It will be understood that, because of the addition of empty slots 22C, some of the hairpin conductor elements 38A will have a different coil pitch to others. In other words, hairpin conductor elements 38A which span an empty slot 22C have a coil pitch which is greater than hairpin conductor elements 38A which do not span an empty slot 22C. This means that two different types of hairpin conductor elements 38A have to be used to manufacture the stator assembly 10 of Figures 17 to 19. However, the benefits of this configuration compared to the partly-empty slots 22B of Figures 14 to 16 is that no spacers 62 are required in the empty receiving spaces 37.

[0187] In the configuration of Figure 18, a single layer of a single phase of the 54-slot configuration is illustrated (in a similar way to the single layer illustrated in Figures 8 and 15, described above).

[0188] Figure 18A illustrates a full wiring diagram of the windings 30 of the stator assembly 10 of Figure 17 (i.e., including all three layers). The numbering of the slots in Figure 18A is the same as that described above for Figure 8A. In Figure 15A, slots “52”, “53”, “54”, “1” and “2” are repeated on both the left and right sides of the winding diagram. In this diagram, the positions of the six conductor elements 38 in each slot are labelled from “a” to “f”, in a similar manner to that described above with reference to Figure 8A.

[0189] In each phase illustrated in Figure 18A, there are two coils which run respectively from “SfX 1” to “EfX 1” and from “SfX 2” to “EfX 2”, where “X” indicates the phase number. As in Figure 8A, the conductor elements which make up the coils alternate between two different positions in each layer. This is illustrated by the change between dotted and dashed lines along the coils. For example, in the lower layer of Figure 18A, the conductor elements which are located in slot position “a” are indicated by dashed lines, whereas the conductor elements which are located in slot position “c” are indicated by solid lines. Such an alternating configuration may be referred to as a wave pattern.in Figure 18A, jumps between the layers are indicated by the connections labelled A to Y. For example, the conductor element which terminates at “A” in the upper layer is connected to the conductor element which terminates at “A” in the middle layer, and so on.

[0190] In Figure 18A, parts of the paths which are connected in serial are denoted by “JfX Y” where “X” indicates the phase number and “Y” indicates the path number. For example, the conductor element which terminates at “ Jf 1 1 ” in the bottom layer is connected in series with the other conductor element which terminates at “ Jf1 1 ” in the bottom layer, and so on.

[0191] The numbers next to the ends of the coils indicate the next slots which the coils will pass through, as described above with reference to Figure 8A.

[0192] In the illustrated configuration, the empty slots 22C are spaced apart from each other by at least one slot 22 which contains conductor elements (e.g., a “full” slot 22, in which each of the receiving spaces contains a conductor element). In other configurations, some of the empty slots 22C may be provided adjacent each other.

[0193] Referring again to Figure 17, the empty slots 22C are evenly distributed around a circumference of the stator core 12. In other embodiments, the empty slots 22C may be unevenly distributed about a circumference of the stator core 12 (e.g., in an irregular pattern).

[0194] Referring now to Figures 20 and 21 , a modification of the stator assembly 10 of Figures 17 to 19 is illustrated. In this configuration, the stator assembly 10 has 51 slots, 8 poles, and three electrical phases (although other configurations such as those outlined in Figures 23 to 25 could be modified in a similar way).

[0195] In the configuration of Figures 20 to 21 , half of the empty slots 22C of the Figure 17 arrangement are omitted. In other words, three of the empty slots 22C have been removed so that there are only three remaining empty slots 22C. It will be noted that the number of empty slots 22C is still an integer multiple of the number of electrical phases 32, 34, 36.

[0196] Figure 22 illustrates finite element simulation results of the configuration of Figures 20 to 21 , with peak torque values calculated for nominal peak current at nominal magnet temperature. These simulation results show that the torque performance of the stator assembly 10 of Figures 20 to 21 is similar to that of the previous configurations of Figures 14 to 19. In other words, while there is a slight reduction in average peak torque calculated for an electrical cycle compared to the baseline design, the overall performance is improved by a considerable reduction in the torque peak at the 12thharmonic. In other words, the reduction in torque ripple may compensate for any loss in average peak torque.

[0197] It will be understood that, because there are fewer empty slots 22C compared to the stator assembly 10 of Figures 17 to 19, a more compact stator assembly 10 can be provided without any reduction in peak torque. In the configuration of Figure 21 , a single layer of a single phase of the 54-slot configuration is illustrated (in a similar way to the single layer illustrated in Figures 8, 15 and 18, described above).Figure 21A illustrates a full wiring diagram of the windings 30 of the stator assembly 10 of Figure 20 (i.e., including all three layers). The numbering of the slots in Figure 21 A is the same as that described above for Figure 8A, however, the number of slots is different. In particular, there are 51 slots rather than 54 slots as in Figure 8A. In Figure 21 A, slots “50”, “51”, “1”, “2” are repeated on both the left and right sides of the winding diagram.

[0198] In the diagram of Figure 21 A, the positions of the six conductor elements 38 in each slot are labelled from “a” to “f”, in a similar manner to as described above with reference to Figure 8A.

[0199] In each phase illustrated in Figure 21 A, there are two coils which run respectively from “SfX 1” to “EfX 1” and from “SfX 2” to “EfX 2”, where “X” indicates the phase number. As in Figure 8A, the conductor elements which make up the coils alternate between two different positions in each layer. This is illustrated by the change between dotted and dashed lines along the coils. For example, in the upper layer of Figure 21 A, the conductor elements which are located in slot position “e” are indicated by dashed lines, whereas the conductor elements which are located in slot position “f” are indicated by solid lines. Such an alternating configuration may be referred to as a wave pattern.

[0200] In Figure 21A, jumps between the layers are indicated by the connections labelled A to Y. For example, the conductor element which terminates at “A” in the upper layer is connected to the conductor element which terminates at “A” in the middle layer, and so on.

[0201] In Figure 21A, parts of the paths which are connected in serial are denoted by “JfX Y” where “X” indicates the phase number and “Y” indicates the path number. For example, the conductor element which terminates at “ Jf 1 1 ” in the bottom layer is connected in series with the other conductor element which terminates at “Jf1 1 ” in the bottom layer, and so on.

[0202] The numbers next to the ends of the coils indicate the next slots which the coils will pass through, as described above with reference to Figure 8A.

[0203] In the illustrated configuration, the empty slots 22C are spaced apart from each other by at least one slot 22 which contains conductor elements (i.e., a “full” slot 22, in which each of the receiving spaces contains a conductor element). In other configurations, some of the empty slots 22C may be provided adjacent each other.

[0204] Referring again to Figure 20, the empty slots 22C are evenly distributed around a circumference of the stator core 12. In other embodiments, the empty slots 22C may be unevenly distributed about a circumference of the stator core 12 (e.g., in an irregular pattern).

[0205] In some embodiments, at least one of the empty slots 22C is filled with material which is not connected to the alternating current supply. For example, at least one of the empty slots 22C may be defined by an enlarged stator tooth 24 which has a greater circumferential dimension than the rest of the stator teeth. Put another way, at least one of the empty slots 22C may be filled in with material of the stator core 10 to define an enlarged stator tooth 24 which has a circumferential dimension which is equal to the sum of the circumferential dimensions of a single slot 22 and two standard stator teeth 24. Although such an enlarged stator tooth 24does not define an empty space, it can be considered as an empty slot 22C for the purposes of this application.

[0206] The stator assemblies 10 of Figures 7 to 21 described above can be classified as one of three different fractional slot winding configurations: 1) full slots 22 with extra joining portions 50 (Figures 7 to 13B); 2) partly-empty slots 22B (Figures 14 to 16); or 3) fully-empty slots 22C (Figures 17 to 21). However, in other embodiments some of these fractional slot winding configurations may be combined in the same stator assembly 10. For example, a stator assembly 10 may have a fractional slot winding configuration including some full slots with extra joining portions and / or some partly-empty slots 22B and / or some fully-empty slots 22C, in any suitable combination.

[0207] Although the different stator assemblies of Figures 3 to 21 have been described above in an iterative manner (i.e., starting from the 48-slot baseline stator assembly of Figure 3; modifying to the 54-slot “full slot” stator assemblies 10 of Figures 7 to 13B; further modifying to the 54-slot “partly-empty” stator assembly 10 of Figures 14 to 16; further modifying to the 54-slot “fully-empty” stator assembly 10 of Figures 17 to 19; and further modifying to the 51-slot “fully-empty” stator assembly 10 of Figures 20 and 21) it will be understood that it would be possible to produce any of the described stator assemblies 10 without having to go through such an iterative process. For example, it would be possible to modify the 48-slot baseline design of Figure 3 to provide the 51-slot stator assembly of Figures 20 and 21 simply by adding three empty slots, without considering any of the intervening configurations.

[0208] A method of manufacturing a stator assembly for a multi-pole electric machine is illustrated in Figure 26 as a flow chart. The method includes the following steps:

[0209] a) taking a baseline stator design comprising a stator core comprising: a plurality of slots; a plurality of windings formed of conductor elements which are configured to form coils arranged in the slots, wherein the coils are connected in multiple electrical phases, and wherein each slot contains conductor elements in the same phase; wherein the number of slots per pole and per electrical phase is an integer number;

[0210] b) determining a modified stator core by adding X slots to, or removing X slots from, the baseline stator design, wherein X is an integer multiple of the number of electrical phases, so that the number of slots per pole and per electrical phase is a non-integer number;

[0211] c) determining a modified winding design; and

[0212] d) producing a stator assembly having the modified stator core and the modified winding design.

[0213] In some embodiments, step c) involves determining a modified winding design which includes conductor elements in the added slots. For example, such a method may be used to produce any of the stator assemblies 10 of Figures 7 to 16 described above.

[0214] In some embodiments, the conductor elements of the modified winding design comprise hairpin conductor elements which are arranged in a wave pattern, wherein each hairpin conductor element comprises two parallel conductor sides, a bent end which connects the parallel conductor sides, and a welded end at which the conductor sides are welded to conductor sides of other conductor elements to form the coils. For example, such a method may be used to produce any of the stator assemblies 10 of Figures 7 to 21 described above.In some embodiments, the conductor elements of the modified winding design further comprise at least one joining portion which connects two parallel conductor sides and which extends over the bent ends and / or welded ends of the hairpin conductor elements. For example, such a method may be used to produce any of the stator assemblies 10 of Figures 7 to 11 described above.

[0215] In some embodiments, the modified winding design of step c) includes some partly-empty slots in which at least one of the receiving spaces does not contain a conductor element, wherein the number of partly-empty slots is 2X. For example, such a method may be used to produce the stator assembly 10 of Figures 14 to 16. In some embodiments, the method further comprises step c1) (between steps c) and d)) of determining a further modified winding design by shifting conductor elements from the partly-empty slots of the modified winding design into other partly-empty slots of the modified winding design, so that half of the partly-empty slots of the modified winding design are converted to full slots in the further modified design, and half of the partly-empty slots of the modified winding design are converted to empty slots in the further modified design. For example, such a method may be used to produce either of the stator assemblies 10 of Figures 17 to 21. A method of manufacturing a stator assembly for a multi-pole electric machine is illustrated in Figure 27 as a flow chart. The method includes the following steps:

[0216] a) manufacturing a stator core comprising a first end, a second end, and a plurality of slots which extend from the first end to the second end; and

[0217] b) providing a plurality of windings formed of conductor elements which form coils arranged in the slots, and connecting the coils in multiple electrical phases, wherein each slot contains conductor elements in the same phase and wherein the number of slots per pole per electrical phase is a non-integer number; and

[0218] wherein the conductor elements comprise hairpin conductor elements which each have two parallel conductor sides and a bent end which connects the parallel conductor sides, and wherein step b) comprises:

[0219] b1) inserting the two parallel conductor sides in the respective slots, bending free ends of the conductor sides and then welding to the free ends of conductor sides of other hairpin conductor elements to form the coils.

[0220] Such a method may be used to produce any of the stator assemblies 10 of Figures 7 to 21 described above.

[0221] In some embodiments, the conductor elements further comprise at least one joining portion which connects two parallel conductor sides, and wherein step b) further comprises: b2) providing the at least one joining portion over the bent ends and / or welded ends of the hairpin conductor elements. Such a method may be used to produce either of the stator assemblies 10 of Figures 7 to 11.

[0222] 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.

[0223] The following text may be used in the figures in lieu of the associated numerals to aid understanding:

[0224]

[0225]

Claims

CLAIMS1. A stator assembly for a multi-pole electric machine, the stator assembly comprising:a stator core comprising a first end, a second end, and a plurality of slots which extend from the first end to the second end;a plurality of windings formed of conductor elements which are configured to form coils arranged in the slots, wherein the coils are connectable to an alternating current supply in multiple electrical phases, and wherein each slot contains conductor elements in the same phase;wherein the number of slots per pole of the multi-pole electric machine per electrical phase is a noninteger number; andwherein the conductor elements comprise hairpin conductor elements which are arranged in a wave pattern, wherein each hairpin conductor element comprises two parallel conductor sides, a bent end which connects the parallel conductor sides, and a welded end at which the conductor sides are welded to conductor sides of other conductor elements to form the coils;wherein the conductor elements further comprise at least one joining portion which connects two parallel conductor sides and which extends across the bent ends and / or welded ends of the hairpin conductor elements.

2. The stator assembly of claim 1 , wherein the at least one joining portion comprises a bent joining portion which is defined by a jumping conductor element comprising at least one conductor side, a bent end which extends from the at least one conductor side and which forms at least part of the bent joining portion, and a welded end at which the at least one conductor side is welded to a conductor side of at least one other conductor element to form the coils.

3. The stator assembly of claim 2, wherein the jumping conductor element comprises two parallel conductor sides and the bent joining portion connects the two parallel conductor sides.

4. The stator assembly of claim 1 , 2 or 3, wherein at least one of the joining portions comprises a welded joining portion comprising a discrete joining conductor which is welded between two separate conductor sides.

5. The stator assembly of any preceding claim, wherein each joining portion comprises a flat section which is positioned axially outboard of the bent ends and / or welded ends of the hairpin conductor elements.

6. The stator assembly of claim 5, wherein each joining portion tapers outwards in width from the respective parallel conductor sides to the flat section.

7. The stator assembly of claim 5, wherein each joining portion tapers inwards in width from the respective parallel conductor sides to the flat section.

8. The stator assembly of any preceding claim, wherein the stator assembly is for an 8-pole electric machine, wherein the coils are connected in three electrical phases.

9. The stator assembly of claim 8, wherein the stator core comprises 54 slots.

10. The stator assembly of claim 8, wherein the stator core comprises 42 slots.11 . The stator assembly of any preceding claim, wherein each slot is configured to receive six conductor elements.

12. The stator assembly of any of claims 1 to 10, wherein each slot is configured to receive four conductor elements.

13. A multi-pole electric machine comprising the stator assembly of any preceding claim, and a rotor.

14. A vehicle comprising the electric machine of claim 13; optionally, wherein the electric machine is a vehicle traction motor for driving wheels of the vehicle.

15. A method of manufacturing a stator assembly for a multi-pole electric machine, the method comprising:a) manufacturing a stator core comprising a first end, a second end, and a plurality of slots which extend from the first end to the second end; andb) providing a plurality of windings formed of conductor elements which form coils arranged in the slots, and connecting the coils in multiple electrical phases, wherein each slot contains conductor elements in the same phase and wherein the number of slots per pole per electrical phase is a non-integer number; and wherein the conductor elements comprise hairpin conductor elements which each have two parallel conductor sides and a bent end which connects the parallel conductor sides, and wherein step b) comprises:b1) inserting the two parallel conductor sides in the respective slots, bending free ends of the conductor sides and then welding to the free ends of conductor sides of other hairpin conductor elements to form the coils;wherein the conductor elements further comprise at least one joining portion which connects two parallel conductor sides, and wherein step b) further comprises:b2) providing the at least one joining portion over the bent ends and / orwelded ends of the hairpin conductor elements.

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