Stator design in electric traction motors

Abstract

A vehicle drive train (200, figure 2) having a front traction electric motor (202, figure 2) with a first stator, and a rear traction electric motor (204, figure 2) with a second stator. One of the mo

Description

TECHNICAL FIELD The present disclosure relates to stator design in electric traction motors of a vehicle drive train. Aspects of the invention relate to a vehicle drive train, to a vehicle, and to a method of manufacturing laminations for use in stators of electric motors. BACKGROUND Electric vehicles often use induction motors to provide traction. Induction motors comprise a rotor and a stator. The rotor typically comprises a rotor cage comprising a plurality of aluminium rotor bars that surround a shaft. In use, current is applied to the stator which creates a rotating magnetic field. This induces current in the rotor which induces a magnetic field therein. The magnetic fields of the stator and rotor interact to turn the rotor and the shaft. This torque can be used to propel the vehicle. Electric vehicles often also use permanent magnet motors to provide additional traction. A permanent magnet motor also comprises a stator and a rotor and is similar to an induction motor except that rather than a power source being used to induce an electromagnetic field in the rotor, the rotor of a permanent magnet motor includes a permanent magnet (e.g., rare earth magnet). In use, the permanent magnet in the rotor is repelled by a rotating magnetic field generated in windings of the stator, which causes the rotor to rotate and torque to be produced, which is used to propel the vehicle. SUMMARY OF THE INVENTION Some electric vehicle designs traditionally use two electric motors; a 4-pole induction motor (which might otherwise be referred to as a 4-pole induction machine) acting as a front electric traction motor, and an 8-pole permanent magnet machine acting as a rear electric traction motor. There are various advantages to such designs, in that the rear permanent magnet motor can be used to provide the majority of the traction, while the front induction motor can be used for improved steering. Furthermore, each motor can be optimised for maximum torque individually. Both induction motors and permanent magnet motors have a stator. It has been realised in the disclosure herein, that vehicle manufacturing processes can be simplified if both the front and rear motors comprise stator laminations with the same geometry. For example, the stators for the front and rear motors may have eight poles / pole pairs. This simplifies the manufacturing process and reduces costs because the same manufacturing tools, and the same stator components can be used for both the front induction motor and the rear permanent magnet motor. In particular, the laminations of the stators of both motors can be stamped using a common stamp, or, if the laminations are cut out with a laser, the same programme (corresponding to a particular laser path) can be used to cut out the stator laminations for both the permanent magnet motor and the induction motor. The disclosure herein thus describes a vehicle drive train comprising front and rear traction electric motors which both use stators with the same geometry, such that the stators for the front and rear traction electric motors can be manufactured using the same manufacturing tools. Aspects and embodiments of the invention provide a vehicle drive train, a vehicle, and a method of manufacturing laminations for electric motors as claimed in the appended claims. According to an aspect of the present invention there is provided a vehicle drive train comprising: a front traction electric motor comprising a first stator; and a rear traction electric motor comprising a second stator; wherein one of the front traction electric motor and the rear traction electric motor is a permanent magnet motor and the other is an induction motor, and wherein the first stator and second stator comprise laminations having the same geometry. This results in a simplerand more efficient manufacturing process with reduced costs, as the same apparatus (e.g. stamping die) can be used to make stator laminations for both the induction motor and the permanent magnet motor. Accordingly, there is an increased commonality of parts between the front and rear electric traction motors. If a laser is used to cut out the stator laminations, the laser can follow the same path when cutting the stator laminations for the induction motor and the permanent magnet motor, meaning the laser does not need to be switched to a different path or programme when switching between cutting laminations for the induction motor and cutting laminations for the permanent magnet motor. The first stator and second stator may both be eight-pole stators. The front traction electric motor may be the induction motor, and the rear traction electric motor may be the permanent magnet motor. The rear permanent magnet motor can be used to provide the majority of the traction, while the front induction motor can be used for additional traction and / or improved steering. The front traction electric motor may be a permanent magnet motor, and the rear traction electric motor may be an induction motor. The induction motor may further comprise a rotor; wherein the rotor comprises a lamination comprising: a central slot for receiving a rotor shaft of the rotor; and a plurality of apertures arranged circumferentially around the central slot, wherein each aperture is shaped substantially as a truncated circular sector. Each aperture may comprise an outer circumferential edge and an inner edge, whereby the radial distance between the outer circumferential edge and the inner edge is greater at a first position towards the end of the inner edge compared to a second position towards the middle of the inner edge. This shape forms a lip on the inner edge, which helps act to redistribute interference stresses around the apertures. In this way, the apertures can be larger, and thus more mass can be taken from the laminations, reducing their weight and that of the full induction motor. This leads to a more efficient induction motor and can compensate for any reduction in torque resulting from changing a 4-pole induction motor to an 8-pole motor, as in some embodiments herein. The vehicle drive train may comprise a second front traction electric motor comprising a third stator, wherein the first, second and / or third stator comprise laminations having the same geometry. The vehicle drive train may comprise a second rear traction electric motor comprising a fourth stator, wherein the first, second, and / or fourth stator comprise laminations have the same geometry. The vehicle drive train may comprise a second front traction electric motor comprising a third stator and a second rear traction electric motor comprising a fourth stator, wherein the first, second, third and / or fourth stator comprise laminations have the same geometry. For example, the vehicle drive train may comprise two front traction electric motors, each comprising a stator with stator laminations, and one rear traction electric motor comprising a stator with stator laminations, wherein the stator laminations of the front and rear traction electric motors have the same geometry. The front traction electric motors may be induction motors and the rear traction electric motor may be a permanent magnet motor. Alternatively, the front traction electric motors may be permanent magnet motors and the rear traction electric motor may be an induction motor. Alternatively, the vehicle drive train may comprise one front traction electric motor comprising a stator with stator laminations and two rear traction electric motors, each comprising a stator with stator laminations, wherein the stator laminations of the front and rear traction electric motors have the same geometry. The front traction electric motor may be a permanent magnet motor and the rear traction electric motors may be induction motors. Alternatively, the front traction electric motor may be an induction motor and the rear traction electric motors may be permanent magnetic motors. Alternatively, the vehicle drive train may comprise two front traction electric motors, each comprising a stator with stator laminations, and two rear traction electric motors, each comprising a stator with stator laminations, wherein the stator laminations of the front and rear electric motors have the same geometry. The front traction electric motors may be permanent magnet motors and the rear traction electric motors may be induction motors. Alternatively, the front traction electric motors may be induction motors and the rear traction electric motors may be permanent magnet motors. The front traction electric motors may be induction motors and the rear traction electric motors may be permanent magnet motors. The front traction electric motors may be permanent magnet motors and the rear traction electric motors may be induction motors. According to a further aspect of the present invention, there is provided a vehicle comprising the vehicle drive train described herein. According to yet a further aspect of the present invention, there is provided a method of manufacturing a first lamination for a first stator of a first electric motor of a vehicle and a second lamination for a second stator of a second electric motor of the vehicle, wherein one of the first and second electric motor is a permanent magnet, and the other is an induction motor; the method comprising: stamping or cutting the first lamination for the first electric motor; and stamping or cutting the second lamination for the second electric motor; such that the laminations for the first and second electric motor have the same geometry. The first and second electric motor stator may be eight-pole stators. The first electric motor may be a front traction induction motor, and the second electric motor may be a rear traction permanent magnet motor. The first electric motor may be a front traction permanent magnet motor, and the second electric motor may be a rear traction induction motor. Within the scope of this application, it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and / or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and / or features of any embodiment can be combined in any way and / or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and / or incorporate any feature of any other claim although not originally claimed in that manner. BRIEF DESCRIPTION OF THE DRAWINGS One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a schematic face-on representation of an induction motor comprising a rotor and a stator in accordance with an embodiment of the invention; Figure 2 shows a schematic representation of a vehicle drive train in accordance with an embodiment of the invention; Figure 3 shows a schematic representation of a rotor of an induction motor; Figure 4 shows a schematic representation of a modified rotor lamination in accordance with an embodiment of the invention; Figure 5 shows a schematic representation of a vehicle comprising a front traction electric motor and a rear traction electric motor in accordance with an embodiment of the invention; and, Figure 6 shows a method of manufacturing a lamination for a stator of a first electric motor of a vehicle and a lamination for a stator of a second electric motor of the vehicle in accordance with an embodiment of the invention. DETAILED DESCRIPTION Embodiments herein relate to a vehicle drive train comprising an induction motor and a permanent magnet motor as a front and rear electric traction motor, wherein the stator of the induction motor and the stator of the permanent magnet motor comprise laminations having the same geometry. This simplifies the manufacturing process and enables the same components to be used to make the stator of the induction motor and the stator of the permanent magnet motor. Other embodiments relate to a vehicle comprising such a vehicle drive train, and a method of manufacturing a lamination of the stator of the induction motor and a lamination of the stator of the permanent magnet motor. The skilled person will be familiar with induction motors. An induction motor is an electric motor comprising a stator and a rotor. In use, electromagnetic induction from the magnetic field of windings in the stator produces an electric current in the rotor, which in turn produces a magnetic field in the rotor. Interaction between the magnetic fields of the stator and rotor produce torque (causing the rotate and the rotor to rotate). The rotor comprises a shaft, a plurality of rotor bars, and end rings. A plurality of rotor laminations are placed along the rotor shaft (in the manner of a stack of discs). The stator comprises a plurality of stator laminations with apertures (also referred to as stator slots) forming winding slots for copper wire. The stator slots (apertures) are cut or stamped out from the material the lamination is formed of (e.g. metal sheet, typically steel). The stator laminations are typically made of flat pieces of metal. The stator laminations may for example be made of steel, such as silicon steel or electrical steel. The stator laminations may for example be bonded, welded, or stacked together. The rotor is positioned inside the stator. An example section view of an induction motor 100 is shown in Figure 1. The hole for the rotor shaft 102 is shown in the centre and a rotor lamination 104 is shown to be surrounding the hole for the rotor shaft 102. Around the rotor lamination 104 is a stator lamination 106 comprising a series of winding slots 108. Windings or coils 110, typically formed of copper wire, conductors or a strip of copper, may be positioned in the winding slots, for example wound around pieces of stator lamination (e.g., projections) in between the apertures. The stator lamination 106 is shown to comprise cooling ducts 112 which take heat away from a stator core and conductors. The cooling ducts 112 may or may not be present in the stator lamination 106. The pole of a stator refers to the number of magnetic poles in the magnetic field of the stator. The number of poles may correspond to the number of winding slots 108 or a multiple of the number of winding slots. For example, a lamination for an eight-pole stator may comprise eight winding slots 108 or a multiple of eight apertures (16, 24 etc.). In other examples, the number of poles does not correspond to the number of winding slots or a multiple of the number of winding slots, such as in fractional slot machines. Whilst the stator lamination 106 shown in Figure 1 comprises forty-eight winding slots, the stator laminations 106 of the present disclosure may comprise any number of winding slots. The number of winding slots will be an even number. For example, the stator laminations may comprise two, four, six, eight, ten, twelve, or n winding slots. The stator lamination 106 shown in Figure 1 is annular (ring-shaped). Whilst the stator lamination 106 is typically circular with winding slots for copper coils 110, other shapes may be used, such as octagonal, or other multi-sided shapes approximating a circle. The stator lamination 106 has a circular slot at the centre to receive the rotor. The striped markings on the rotor shaft 102, rotor lamination 104, and stator lamination 108 are merely illustrative markings provided to distinguish between the different features shown. The skilled person will additionally be familiar with permanent magnet motors. A permanent magnet motor also comprises a stator and a rotor and is similar to an induction motor except that rather than a power source being used to induce an electromagnetic field in the rotor, the rotor of a permanent magnet motor includes a permanent magnet (e.g., rare earth magnet). In use, the interaction of the stator with the magnetic field of the rotor forces the rotor to rotate in the case of a motoring action (e.g., when the vehicle is in motion). In the case of a generating action (e.g., in a regenerative mode), the interaction of the stator with the magnetic field of a revolving rotor generates energy in the stator winding. Whilst the permanent magnet motor is not shown herein, the stator laminations used in the permanent magnet motor may correspond, at least geometrically, to the stator lamination used in the induction motor and shown in Figure 1. The stator laminations used in the permanent magnet motor may also be made of the same material as the stator laminations used in the induction motor. Turning now to other embodiments, a vehicle drive train is a group of components that provide power to wheels of a vehicle or receive power from wheels when regenerative braking is carried out. A vehicle drive train may comprise a front traction electric motor and a rear traction electric motor, which are used to propel the vehicle. The front traction electric motor provides power to the front wheels and the rear traction electric motor provides power to the rear wheels. In one arrangement, the front traction electric motor is an induction motor, and the rear traction electric motor is a permanent magnet motor. This arrangement minimises drag losses without a mechanical disconnect. The permanent magnet motor typically provides more power than the induction motor, and the induction motor acts as a booster machine to provide tractive force as and when required. In another arrangement, the front traction electric motor is a permanent magnet motor, and the rear traction electric motor is an induction motor. As noted above, in current systems, very often a first type of stator is used for the permanent magnet motor and a second type of stator, comprising laminations with different geometry to the first type of stator, is used for the induction motor. The permanent magnet motor may for example use an eight-pole stator (i.e., a plurality of laminations with eight winding slots), and the induction motor may use a four-pole stator (i.e., a plurality of laminations with four winding slots). Traditionally, these may have been optimised individually. Figure 2 shows an example vehicle drive train 200. The vehicle drive train 200 is shown to comprise a front traction electric motor 202 and a rear traction electric motor 204. One of the front traction electric motor (202) and the rear traction electric motor (204) is a permanent magnet motor and the other is an induction motor. The front traction electric motor comprises a first stator and the rear traction electric motor comprises a second stator. The first stator and the second stator comprise laminations having the same (e.g. a common) geometry. Induction motors and permanent magnet motors were described above and the detail therein applies equally to the embodiment of Figure 2. Whilst the front traction motor 202 is shown adjacent to the front axle 206 and the rear traction motor 204 is shown adjacent to the rear axle 208, it will be appreciated that the front and rear traction motors 202, 204 may be positioned at other locations in the vehicle drive train. Furthermore, although two traction motors are illustrated in Figure 2, it will be appreciated that this is merely an example, and that more than two traction motors are equally possible. For example, there may be a traction motor associated with each wheel. In such embodiments, each traction motor may comprise a stator and all of the stators may have the same geometry. Thus, a vehicle drive train 200 is provided which comprises a permanent magnet motor and an induction motor, wherein the stator laminations used for the permanent magnet motor have the same geometry as the stator laminations 106 used for the induction motor 100. The geometry may for example refer to the overall shape and / or size of the respective laminations. For example, the radial width, thickness, or any other size or shape property of the laminations. It may refer to the geometry of features on the respective laminations, such as the number, size, position and / or shape properties of apertures, or any other features of the laminations. In some embodiments, the stator laminations of the permanent magnet motor may be the same as (e.g. indistinguishable from) the stator laminations of the induction motor. For example, in some embodiments, the stator laminations in the permanent magnet motor may have the same number of winding slots as the stator laminations 106 in the induction motor. The stator laminations in the permanent magnet motor may have the same number of poles as the stator laminations 106 in the induction motor. The stator laminations in the permanent magnet motor may for example be made using the same manufacturing process that is used to make the stator laminations 106 in the induction motor 100. The stator laminations used in the permanent magnet motor may for example be made using the same stamping die used to make the stator laminations 106 used in the induction motor 100. If the stator laminations are made using laser cutting, the same programme may be used to make the stator laminations of the permanent magnet motor and the stator laminations 106 of the induction motor 100. As an example, the vehicle drive train may have an 8-pole induction motor at the front and an 8-pole permanent magnet motor at the rear. As described above, both the 8-pole induction motor and the 8-pole permanent magnet motor have stator laminations with the same geometry e.g. with a common design. Using stator lamination with the same geometry for both the stator of the permanent magnet motor and the stator of the induction motor simplifies the manufacturing process and reduces the number of components required to make stators for both the permanent magnet motor and the induction motor. Stator laminations for the permanent magnet motor and the induction motor can therefore be made more easily and efficiently. Thus, in embodiments herein, a stator optimised fora permanent magnet motor may be used in an induction motor. A stator optimised for an induction motor may be used in a permanent magnet motor. This may effectively serve as a boundary condition in subsequent design of the permanent magnet and / or induction motors. Using a stator with laminations 106 optimised fora permanent magnetic motor in an induction motor 100 may result in less torque being generated compared to a stator with laminations optimised for an induction motor being used in the induction motor. For example, when an eight-pole induction motor is used as a front electric traction motor (to match an eight-pole stator design of a rear permanent magnet motor), there can be a reduction in torque compared to the torque generated using a four-pole induction motor as a front electric traction motor. In such examples, the design of the rotor of the induction motor can be adjusted to compensate. An example of a rotor lamination design that increases torque is illustrated in Figures 3 and 4. Briefly, Figure 3 shows an example rotor 300 of an induction motor. The rotor 300 comprises a shaft 302, a plurality of rotor bars 304, end rings 306 and a plurality of laminations (not shown) placed along the rotor shaft 302. As noted above, rotor laminations are made from flat pieces of metal such as steel and are stacked along the rotor shaft The rotor bars 304 and the end rings 306 form a rotor cage. Each rotor lamination may have a plurality of slots for receiving a rotor bar. When the lamination is arranged in a lamination stack, the slots of each of the individual lamination may be aligned along the stack, thus forming a cylindrical hole projecting through the lamination stack in which to receive a respective rotor bar 304. During manufacture of the rotor cage, molten metal, for example molten aluminium, is poured into the rotor after the circular laminations are stacked. The molten metal thus fills the aligned slots and then solidifies to form the rotor bars 304. Accordingly, the cross-sectional shape of the rotor bar 304 corresponds to the shape of the slots in the circular lamination. The rotor bars 304 are connected at both ends of the stack by end rings 306, thus forming a short circuit and a cage-like structure. Fig. 4 shows a lamination 400 for a rotor 300 of an induction motor according to some embodiments herein. Aspects of this lamination design can, for example, increase torque. As an example, if, as described above, the same geometric design is used for the stator of the induction motor as the permanent magnet motor, the design in Figure 4 can be used to compensate for any resulting loss of torque in the induction motor. The lamination 400 can be used with a rotor such as the rotor 300 of Fig. 3. In this embodiment, the lamination 400 has a central slot 402 for receiving a rotor shaft of the rotor. The rotor lamination 400 further comprises a plurality of slots 404 for receiving a plurality of rotor bars. The shapes of the slots in Fig. 4 are merely an example shape and other shapes can equally be used. The rotor lamination 400 further comprises a plurality of apertures 406 arranged circumferentially around the central slot 402. The apertures 406 are holes cut into the lamination 400 and may be produced in a manufacturing process that for example involves stamping a sheet of metal to create the laminations 400 using a mechanical stamping tool or cutting a sheet of metal with a blade or laser. The stamping or cutting may create the shape of the overall laminations and the apertures. The apertures reduce the weight of the lamination. Each aperture 406 may be shaped substantially as a truncated circular sector with an outer circumferential edge 406a and an inner edge 406b, the inner edge 406b being of a shape whereby the radial distance between the outer circumferential edge and the inner edge 406b is greater at a first position 406c towards the end of the inner edge compared to a second position 406d towards the middle of the inner edge 406b. The apertures 406 may be substantially shaped as truncated circular segments, e.g. circular segments with the apex (or point) cut away. In this sense, “substantially” is used to indicate the approximate overall shape of the apertures 406, subject to the shape deviations described herein. The apertures 406 may have an inner edge 406b that is shaped so that the radial aperture width 406c towards the edge of the aperture 406, is greater than the radial aperture width towards the centre of the inner edge 406b, at point 406d. As such, the inner edge 406b is deformed so as to project inwardly into the aperture 406, effectively creating a ‘lip’ on the inner edge 406b (e.g. compared to a purely circumferentially shaped inner edge). The inner edge is thus shaped to form a lip that extends inwardly into the aperture 406. The inner edge 406b of each aperture 406 may be curved inwardly into the aperture 406 with a degree of curvature greaterthan a circle concentric with the central slot and having a circumference that partially overlaps the inner edge. In other words, with a degree of curvature greaterthan that of “true” truncated circular segment. It has been found through empirical methods that apertures 406 shaped in this way, with curved inner edges that form a “lip”, are good for redistribution of the forces on the rotor lamination 400 when in use. As such, the shape of the inner edges 406b of the apertures 406 allows i) for the apertures 406 to be placed closer to the central hole 402 for the rotor shaft and ii) for the apertures 406 to be larger, leading to a lighter, more efficient rotor 300 overall. It is generally harder to remove mass closer to the rotor shaft than further away from it, due to interference stresses being higher closer to the shaft. The aperture design herein thus compensates for the increased interference stresses. These factors can serve to increase the torque of the induction motor. The plurality of apertures 406 may be arranged circumferentially around the central slot 402, forming a radial spoke 408 between each pair of adjacent apertures 406. The width of the spokes 408 may for example be i) constant with radius (e.g. the sides 410 and 412 of adjacent apertures 406 can be parallel to one another), or ii) decrease with increasing radius. The apertures 406 may further have rounded or curved corners, which reduces the stresses at said corners, compared to if they were angular. Turning now to other embodiments, Figure 5 shows a passenger vehicle 500 according to some embodiments herein. Figure 5 shows the vehicle 500 comprising a front traction electric motor 502 and a rear traction electric motor 504, wherein one of the front traction electric motor 502, and the rear traction electric motor 504 is a permanent magnet motor and the other is an induction motor. The front traction electric motor 502 and a rear traction electric motor 504 may be comprised in a vehicle drive train 200, as described above with respect to Figure 2. Whilst Figure 5 shows squares representing the front and rear electric motors 502, 504 situated in particular positions in the vehicle 500, these motors 502, 504 may be situated in any part of the front or rear of the passenger vehicle 500 respectively. Furthermore, there may be more than one induction motor and / or permanent magnet motor in the vehicle. The vehicle drive train described herein may further comprise a second front traction electric motor also comprising a stator, and / or a second rear traction electric motor comprising a stator. The second front traction electric motor may be a permanent magnet motor or an induction motor. The second rear traction electric motor may be a permanent magnet motor or an induction motor. The stator of the first and / or second front traction motor, and / or the first and / or second rear traction motor comprise laminations with the same geometry. Figure 6 shows a method 600 according to an embodiment of the present invention. The method 600 is a method of manufacturing a lamination fora stator of a first electric motor of a vehicle (i.e., a first lamination for a first stator), and a lamination for a stator of a second electric motor of the vehicle (i.e. a second lamination for a second stator). One of the first and second electric motor is a permanent magnet motor, and the other is an induction motor. The method comprises stamping or cutting, at Step 602, the first lamination for the first electric motor; and stamping or cutting, at Step 604, the second lamination for the second electric motor, such that the laminations for the first and second electric motor have the same (e.g. a common) geometry. Stamping may for example refer to stamping sheets of metal (e.g., steel) with a stamp or stamping die to stamp or cut out stator laminations. Cutting may for example refer to cutting out stator laminations with a laser or blade. As described above, the geometry of the stator laminations may for example refer to the shape and size of the laminations. This may for example include the number of winding slots, which may correspond to the number of poles of the stator. The terms first and second electric motor and first and second electric traction motor have been used interchangeably. It will be appreciated that various changes and modifications can be made to the present invention without departing from the scope of the present application.

Claims

1. A vehicle drive train comprising:a front traction electric motor comprising a first stator;and a rear traction electric motor comprising a second stator;wherein one of the front traction electric motor and the rear traction electric motor is a permanent magnet motor and the other is an induction motor; and, wherein the first stator and second stator comprise laminations having the same geometry.

2. The vehicle drive train of claim 1 wherein the first stator and second stator are both eight-pole stators.

3. The vehicle drive train of claim 1 or 2, wherein the front traction electric motor is the induction motor,and the rear traction electric motor is the permanent magnet motor.

4. The vehicle drive train of claim 1 or 2, wherein the front traction electric motor is a permanent magnet motor, and the rear traction electric motor is an induction motor.

5. The vehicle drive train of claim 3 or 4, wherein the induction motor further comprises a rotor; wherein the rotor comprises a rotor lamination comprising:a central slot for receiving a rotor shaft of the rotor; anda plurality of apertures arranged circumferentially around the central slot, wherein each aperture is shaped substantially as a truncated circular sector.

6. The vehicle drive train of claim 5, wherein each aperture comprises:an outer circumferential edge; and,an inner edge,the inner edge having a lip extending inwardly into the aperture, the lip being of a shape whereby the radial distance between the outer circumferential edge and the inner edge is greater at a first position towards the end of the inner edge compared to a second position towards the middle of the inner edge.

7. The vehicle drive train of any preceding claim, further comprising a second front traction electric motor comprising a third stator, wherein the first, second and / or third stator comprise laminations having the same geometry.

8. The vehicle drive train of any preceding claim, further comprising a second rear traction electric motor comprising a fourth stator, wherein the first, second, and / or fourth stator comprise laminations have the same geometry.

9. The vehicle drive train of claim 7 or 8, wherein the front traction electric motors are induction motors; and the rear traction electric motors are permanent magnet motors.

10. The vehicle drive train of claim 7 or 8, wherein the front traction electric motors are permanent magnet motors, and the rear traction electric motors are induction motors.

11. A vehicle comprising the vehicle drive train of any of claims 1 to 10.

12. A method of manufacturing a first lamination for a first stator of a first electric motor of a vehicle and a second lamination fora second stator of a second electric motor of the vehicle, wherein one of the first and second electric motor is a permanent magnet motor, and the other is an induction motor; the method comprising:stamping or cutting the first lamination for the first electric motor; andstamping or cutting the second lamination for the second electric motor;such that the laminations for the first and second electric motor have the same geometry.

13. The method of claim 12, wherein the first and second electric motor stator are eight-pole stators.

14. The method of claim 12 or 13, wherein the first electric motor is a front traction induction motor, and the second electric motor is a rear traction permanent magnet motor.

15. The method of any of claims 12 to 14, wherein the first electric motor is a front traction permanent magnet motor, and the second electric motor is a rear traction induction motor.13

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