Electric traction motor shaft assembly

Abstract

A component (e.g. a bearing 30, gear, clutch, brake, sensor) mounted on a shaft 28 with a retaining ring 32 expandable in a radial direction (e.g. a circlip) to restrict axial movement of the componen

Description

TECHNICAL FIELD The present disclosure relates to an electric traction motor shaft assembly for a vehicle. Aspects of the invention relate to a shaft assembly, to an electric traction motor, to a vehicle and to a method. BACKGROUND It is known to provide an electric traction motor with a shaft assembly, which includes a shaft, one or more components mounted thereon, and a retaining means for axially retaining the one or more components on the shaft. In some applications, the shaft is required to have a large diameter and / or rotate at high rotational speed (i.e. have a high RPM). Such high-speed and / or large diameter shafts may generate centrifugal forces that can impair the ability of such retaining means to function effectively. It is an aim of the present invention to address one or more of the disadvantages associated with the prior art. SUMMARY OF THE INVENTION Aspects and embodiments of the invention provide a shaft assembly, an electric traction motor, a vehicle, and a method as claimed in the appended claims. According to an aspect of the invention, there is provided a shaft assembly for a vehicle, the shaft assembly comprising: a shaft defining a longitudinal axis; a component mounted on the shaft; a retaining ring mounted on the shaft adjacent to the component to restrict axial movement of the component along the shaft, wherein the retaining ring is expandable in a radial direction; and a ring retention element mounted on the shaft adjacent to the retaining ring, the ring retention element being configured to restrict radial movement of the retaining ring away from the shaft. Optionally, the shaft assembly is an electric traction motor shaft assembly for a vehicle. Optionally, the ring retention element comprises a retention surface extending over at least part of an outer radial surface of the retaining ring to restrict radial movement of the retaining ring away from the shaft. Advantageously, the ring retention element can restrict or prevent a radially outward movement of the retaining ring relative to the shaft due to expansion under centrifugal forces. In this way, the retaining ring is radially secured, so as to restrict axial movement of the component, thereby facilitating proper functioning of components on the shaft and contributing to the overall stability of the shaft assembly. The provision of the ring retention element is particularly advantageous in shaft assemblies having a shaft rotating at a high RPM and / or having a shaft with a large diameter (e.g. an electric traction motor shaft assembly). Such high-speed and / or large diameter shafts generate centrifugal forces that can typically cause the retaining ring to move radially outward, leaving components on the shaft with limited axial support. In this way, the ring retention element assists in maintaining the radial position of the retaining ring, ensuring its continued functionality even in applications that include high-speed and / or large diameter shafts. As used herein, the term “retaining ring” refers to an axial retention device that defines a generally circular shape and extends around all or part of the circumference of the shaft. Such a ring is expandable in a radial direction for installation on and removal from the shaft. The circular shape may include an opening therein to assist with installing and removing the retaining ring. Alternatively, the retaining ring may be formed from multiple segments which are joined together during installation to form a partial or complete annulus, and / or may comprise a helical body forming a complete annulus. Example retaining rings include, but are not limited to: circlips, snap rings, and spiral retaining rings. Although it is known to provide some shaft assemblies with a self-locking retaining ring, such retaining rings can be complex to manufacture and / or assemble correctly. The inventors have also found that the centrifugal forces exerted on such retaining rings in certain applications can overcome the self-locking mechanism, leading to radial expansion of the retaining ring and axial movement of the component held by the ring. Optionally, the retention surface extends over only a portion of the axial length of the outer radial surface of the retaining ring. Advantageously, the ring retention element restricts radial movement of the retaining ring without contacting the component. It is the retaining ring that restricts axial movement of the component (e.g. by abutting the component), whereas the ring retention element only restricts radial movement of the retaining ring without abutting the component. In this way, additional load is not applied to the ring retention element (e.g. from providing axial support to the component), reducing the likelihood of the ring retention element becoming overloaded and components being ineffectively retained. This can also prevent additional load being applied to the component by the ring retention element. The retaining ring may abut an axial surface of the component on the shaft. The ring retention element may be axially spaced apart from an axial surface of a component on the shaft. By spacing the ring retention element from the component in the axial direction, the ring retention element can be more easily positioned correctly in the axial direction without the need to closely control axial dimension tolerances of the ring and / or the ring retention element. Optionally, the retention surface abuts against the outer radial surface of the retaining ring. Advantageously, there is no space in the radial direction between the retention surface and the retaining ring for the retaining ring to move into. As such, radial retention of the retaining ring is improved. Alternatively, a radial clearance may be present between the retention surface and the outer radial surface. For example, in embodiments in which the retaining ring is in a groove around the outer surface of the shaft, a radial clearance of less than the depth of the groove may be present between the retention surface and the outer radial surface, preventing the retaining ring fully lifting from the groove. Optionally, the ring retention element is dimensioned to form an interference fit with the shaft. Advantageously, the ring retention element is effectively secured on the shaft, reducing axial movement thereof and ensuring maintained radial retention of the retaining ring. 2 Optionally, the ring retention element abuts against an axial end of the retaining ring. Advantageously, the ring retention element provides support to the retaining ring in an axial and a radial direction, reducing the risk, that the retaining ring will move from its position. Moreover, the arrangement improves ease and accuracy of manufacture of the shaft assembly, as the ring retention element can be mounted on the shaft until the element abuts against the retaining ring. In this way, the ring retention element will be in the preferred position once it abuts the ring. Optionally, the retention surface extends around substantially the whole circumference of the retaining ring. Advantageously, the radial retention provided by the ring retention element is improved, resulting in a more robustly located retaining ring. In other embodiments, the retention surface may extend around only a portion of the circumference of the retaining ring. In such embodiments, the retention surface may be provided by a continuous surface or by a series of discontinuous retention surfaces. Optionally, the shaft and the ring retention element are formed from materials having substantially the same coefficient of thermal expansion. Advantageously, the ring retention element and the shaft will respond similarly to fluctuations in temperature, preventing the ring retention element from becoming detached from the shaft if one part were to expand where another does not. In this way, the ring retention element is effectively fixed relative to the shaft, providing effective radial retention to the retaining ring, irrespective of temperature fluctuations. The shaft and the ring retention element may be formed from the same material. Optionally, the ring retention element is formed of metallic material, optionally steel or aluminium alloy material. This provides a robust ring retention element that effectively retains the retaining ring. Optionally, the ring retention element comprises a circumferential groove on an outer radial surface thereof for receiving a removal tool. Advantageously, the groove can assist in removing the ring retention element from the shaft, by receiving a removal tool therein. This improves ease of access / removal of the retention element or other parts on the shaft for maintenance or replacement. The groove provides a surface feature by which the removal tool may grip the ring retention element. Alternative surface features include one or more protrusions or recesses in the outer radial surface of the ring retention element. Optionally, the retaining ring is positioned axially between the component and the ring retention element. Advantageously, the retaining ring can provide effective axial support to the component on one axial side, while being radially supported by the ring retention element on the other axial side, improving the stability of the shaft assembly. Alternatively, the ring retention element may be located between the component and the retaining ring. In such embodiments, the retaining ring may restrict axial movement of the component along the shaft indirectly via the ring retention element. Optionally, the retaining ring is received in a circumferential groove on the shaft. Optionally, the retaining ring is secured by friction and / or by a projection on the shaft. Advantageously, the shaft provides for retention of the retaining ring in an axial direction, improving the stability of the shaft assembly. Optionally, the retaining ring is a snap ring, a circlip or a spiral retaining ring. Advantageously, such retaining rings are simple to install, have a compact design and can provide reliable axial retention. Optionally, the component is a bearing. Advantageously, a bearing can provide effective support to other components mounted on the shaft. As such, effectively restricting axial movement of the bearing ensures the shaft assembly operates as intended. Optionally, the electric traction motor shaft assembly comprises a further component axially spaced from the component, and comprising a further retaining ring mounted on the shaft adjacent to the further component to restrict axial movement of the further component along the shaft, and a further ring retention element mounted on the shaft adjacent to the further retaining ring, the further ring retention element having a retention surface extending over at least part of an outer radial surface of the further retaining ring to restrict radial movement of the further retaining ring away from the shaft. Advantageously, multiple components can be supported on the shaft. Furthermore, the shaft is effectively balanced. A further aspect of the present disclosure provides an electric traction motor for a vehicle, the electric traction motor comprising the electric traction motor shaft assembly described herein. Such a motor benefits from the advantages of the shaft assembly outlined above. A further aspect of the present disclosure provides a vehicle comprising the electric traction motor described herein. Such a vehicle benefits from the advantages of the shaft assembly outlined above. A further aspect of the present disclosure provides a method of manufacturing a shaft assembly for an electric traction motor for a vehicle, the method comprising: providing a shaft defining a longitudinal axis; mounting a component on the shaft; mounting a retaining ring on the shaft adjacent to the component to restrict axial movement of the component along the shaft; and mounting a ring retention element on the shaft adjacent to the retaining ring, the ring retention element having a retention surface extending over at least part of an outer radial surface of the retaining ring to restrict radial movement of the retaining ring away from the shaft. Such a method benefits from the advantages of the shaft assembly outlined above. Optionally, the shaft assembly is an electric traction motor shaft assembly for a vehicle. Optionally, the shaft assembly is an electric traction motor shaft assembly as described herein. Optionally, the step of mounting the ring retention element on the shaft comprises forming an interference fit between the ring retention element and the shaft. Advantageously, this provides for a secure and stable connection between the ring retention element and the shaft, with reduced risk of loosening, facilitating effective retention by the ring retention element. Optionally, the ring retention element is mounted on the shaft using a hydraulic press. Advantageously, a hydraulic press can allow for effective and reliable fitting of components, particularly when dealing with tight interference fits. Optionally, the step of mounting the ring retention element on the shaft comprises axially moving the ring retention element on the shaft until the ring retention element abuts an axial surface of the retaining ring. 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. BRIEF DESCRIPTION OF THE DRAWINGS One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a vehicle; Figure 2 shows a schematic longitudinal cross-sectional view of an electric traction motor comprising a shaft assembly according to an embodiment; Figure 3 shows a transverse cross-sectional view of the electric traction motor of Figure 2; Figure 4 shows a side view of a shaft assembly according to an embodiment; Figure 5 shows a longitudinal perspective cross-sectional view of the shaft assembly of Figure 4; Figure 6A shows an enlarged view of the region X in the longitudinal cross-sectional view of Figure 5; Figure 6B shows an enlarged view of the region Y in the longitudinal cross-sectional view of Figure 5; Figure 7 shows a perspective view of a ring retention element according to an embodiment; Figure 8 shows a perspective cross-sectional view of the ring retention element of Figure 7 adjacent to a retaining ring; Figure 9 shows a perspective view of a ring retention element according to an embodiment; Figure 10 shows a perspective cross-sectional view of the ring retention element of Figure 9 with a retaining ring; Figure 11 shows a method of manufacturing a shaft assembly. DETAILED DESCRIPTION Examples of the present disclosure relate to a shaft assembly. In particular, examples of the present invention relate to an electric traction motor shaft assembly for a vehicle. Such an electric traction motor may be of a synchronous type or asynchronous type, for example a permanent magnet synchronous motor. Non-limiting examples will now be described with reference to accompanying Figures 1 to 11, where the figures illustrate a an electric traction motor 100 having a shaft assembly 10, a stator core 12, a rotor 112, and an electric drive unit (EDU) 160, a vehicle 200 and a method. Figure 1 illustrates a vehicle 200 having a first electric traction motor 100-1 for driving one or more front wheels of the vehicle 200. The vehicle 200 also has a second electric traction motor 100-2 fordriving one or more rear wheels of the vehicle 200. In other embodiments, the vehicle 200 may comprise only a single electric 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 traction motor 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 traction motor 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 traction motor 100 arranged or configured to drive each wheel of the vehicle 200. The electric traction motor 100 comprised in the vehicle 200 may have an electric traction motor shaft assembly 10 as described herein. For example, the electric traction motor 100 comprised in the vehicle 200 may be the electric traction motor of Figure 2, described below. As illustrated schematically on Figure 1, the electric traction motor(s) 100 may be part of an electric drive unit (EDU) 160. For example, the EDU may include transmission components, lubrication and cooling components, and / or power electronics, in addition to the electric traction motor 100. In the vehicle 200 of Figure 1, the first electric traction motor 100-1 is part of a first EDU 160-1 for driving front wheels of the vehicle 200, and the second electric traction motor 100-2 is part of a second EDU 160-2 fordriving rear wheels of the vehicle 200. Referring to Figures 2 and 3, the electric traction motor 100 of the vehicle 200 is illustrated. The electric traction motor 100 includes a stator assembly which has an annular stator core 12. The stator core 12 has a cylindrical inner channel 14, which defines a central stator axis 16 and which extends in a direction parallel to the central stator axis 16 from a first axial end surface 18 of the stator core 12 to a second axial end surface 20 of the stator core 12. The stator core 12 has a plurality of winding slots 22, each extending radially to support electrical stator windings 150 running the length of the stator core. For simplicity, the electrical stator windings 150 are illustrated in Figure 3 in only one winding slot 22. A plurality of stator teeth 24 are provided between the winding slots 22. In other words, the stator teeth 24 are interspersed between the winding slots 22 in a circumferential direction about the stator core 12. Both the plurality of winding slots 22 and the plurality of stator teeth 24 extend from the first axial end surface 18 to the second axial end surface 20 of the stator core 12. In the illustrated arrangement, the stator core 12 is defined by a stator lamination stack 44. In other words, the stator core 12 is formed of a plurality of layers. The layers are stacked one atop the other to form the stator lamination stack 44, which extends from the first axial end surface 18 of the stator core 12 to the second axial end surface 20 of the stator core 12. The layers may be stamped from sheet material (e.g., sheet metal), or formed via any other suitable process. In this way, a stator core 12 having a complex cross-sectional shape can be formed. The electric traction motor 100 also includes a rotor 112. The rotor 112 is configured to fit within the cylindrical inner channel 14 of the stator core 12 with a small air gap 26 therebetween. The outside surface of the rotor 112 provides a surface concentric with a circumference of the cylindrical inner channel 14, such that as the rotor 112 rotates within the cylindrical inner channel 14 of the stator core 12, a consistent air gap 26 is maintained between the rotor 112 and the stator core 12. As shown in Figures 2 and 3, the electric traction motor 100 has a housing 102 surrounding the stator assembly 10 and at least part of the rotor 112. In some embodiments the housing 102 is a cylindrical housing, though it will be understood that the stator core 12 may have a non-circular cross section, in particular where the outer form of the stator core 12 is oblate or has projections thereon, such that the housing 102 may be non-circular. The rotor 112 may include or be otherwise connected to a shaft assembly 10. As will be discussed in more detail below, components of the shaft assembly 10 may be rotatable about an axis of rotation that is coaxial with the central stator axis 16. Although not shown, it will be understood that the shaft assembly 10 may be coupled to one or more output components, including the wheels of the vehicle 200, a gearbox (e.g. a reduction gearbox), a transmission, a differential, a brake system, or the like. The electric traction motor 100 may have forty-eight winding slots 22 and eight rotor poles. Other combinations of winding slot numbers and rotor pole numbers may be utilised. The functioning of electric traction motors 100 and electric drive units (EDUs) 160 is known, and so will not be described here in more detail. Referring now to Figures 4, 5, 6A and 6E3, the shaft assembly 10 will be described in more detail. The shaft assembly 10 described is an electric traction motor shaft assembly 10. However, it will be appreciated that the shaft assembly 10 may be utilised in any suitable arrangement, e.g. the shaft assembly 10 may be a shaft assembly for a vehicle (e.g. a transmission input shaft assembly). The shaft assembly 10 includes a shaft 28 that defines a longitudinal axis L. The shaft 28 is rotatable about the longitudinal axis L. The longitudinal axis L of the shaft 28 is coaxial with the central stator axis 16. The shaft 28 may be a rotor shaft of the rotor 112 of Figures 2 and 3. At least one component 30A, 30B is mounted on the shaft 28. In the figures, the component 30 is a bearing. It will be appreciated that the component may be any part, for example, the component may be a gear, a collar, a clutch, a brake component (e.g. a disc brake), a sensor or the like. Other transmission and drivetrain components may be utilised. A plurality of components 30 may be mounted on the shaft 28. In the illustrated arrangement, two bearings 30A, 30B are mounted on the shaft 28. The bearings 30A, 30B are arranged so as 7 to be axially spaced apart from one another (i.e, spaced apart on the shaft in a direction parallel to the longitudinal axis L). It will be appreciated that the plurality of components 30 may be different from each other, e.g. the bearings 30A, 30B may be of a different type or size, or the plurality of components 30 may be different components. In alternative arrangements, only one component 30 may be provided. A retaining ring 32 is mounted on the shaft 28. The retaining ring 32 is configured to restrict axial movement of the component 30A, 30B along the shaft 28. The retaining ring 32 is positioned on the shaft 28 adjacent to a respective component 30A, 30B. In the illustrated arrangement, the retaining ring 32 abuts against an axial surface of the respective component 30A, 30B so as to prevent axial movement of the component 30A, 30B (e.g. the retaining ring 32 blocks the component 30A, 30B from moving axially). In alternative arrangements, the retaining ring 32 may be axially spaced apart from the component 30A, 30B. In such an arrangement, the component 30A, 30B may be axially moveable along the shaft 28 until an axial surface of the component 30A, 30B abuts against a first axial surface 32B of the retaining ring 32. In this case, slight movement of the component 30A, 30B may be acceptable. In the illustrated arrangement, one retaining ring 32 is provided adjacent to one component 30A, and another retaining ring 32 is provided adjacent to another component 30B. The retaining rings 32 may be substantially the same as one another, although may include different dimensions (e.g. depending on the diameter of the shaft 28 in the different locations and the size of the component 30A, 30B). As used herein, the term “retaining ring” refers to an axial retention device that defines a generally circular or part-circular shape and extends around all or part of the circumference of the shaft 28. Such a ring 32 is expandable in a radial direction (e.g. for installation on and removal from the shaft 28). The circular shape may include an opening therein to assist with installing and removing the retaining ring 32. Alternatively, the retaining ring 32 may be formed from multiple segments which are joined together during installation to form a partial or complete annulus, and / or may comprise a helical body forming a complete annulus. Example retaining rings include, but are not limited to: circlips, snap rings, and spiral retaining rings. The or each retaining ring 32 may be formed from any suitable material, for example, the retaining ring 32 may be formed from a metallic material, e.g. steel or aluminium alloy material. The retaining ring 32 may be formed from spring steel. The retaining ring 32 is mounted on the shaft 28 in such a way so as to restrict axial movement of the retaining ring 32 along the shaft 28 (e.g. in response to movement of the component 30A, 30B). In the figures (e.g. see Figures 6A and 6B), a retaining groove 34 is provided on an outer surface of the shaft 28. The retaining groove 34 is provided as a circumferential groove extending about the shaft 28. The retaining groove 34 is configured to receive the retaining ring 32. The retaining groove 34 is configured to restrict axial movement of the retaining ring 32 along the shaft 28. The retaining groove 34 is dimensioned such that a portion of the retaining ring 32 projects radially outwardly from the groove 34 when located therein (e.g. so as to provide the abutment surface 32B for preventing axial movement of the component 30A, 30B). In other arrangements, other means of restricting axial movement of the retaining ring 32 may be implemented. For example, the retaining ring 32 may be secured to the shaft 28 by friction (e.g. the retaining ring 32 may be dimensioned to form an interference fit with the shaft 28). The retaining ring 32 may additionally or alternatively be prevented from moving axially on the shaft 28 via a projection on the shaft 28 against which the retaining ring 32 may abut. It will be appreciated that any suitable means may be implemented to restrict axial movement of the retaining ring 32 along the shaft 28. It will be appreciated that the retaining ring 32 may be exposed to a large centrifugal force (e.g. from the rotation of the shaft 28) which may cause the retaining ring 32 to expand radially outward (e.g. away from the groove 34) and may cause the retaining ring 32 to become disconnected from the shaft 28 and cease to provide effective axial support to the component 30A, 30B. The centrifugal force increases as a function of the radius of the circular path and the square of the angular velocity. Consequently, the centrifugal force can be large in shaft assemblies 10 having a shaft 28 rotating quickly (e.g. at a high RPM) and / or having a shaft 28 with a large diameter (e.g. an electric traction motor shaft assembly 10). In this way, the issue of retaining rings 32 expanding radially outward is particularly relevant in rotor shafts 28 of an electric traction motor 100 of a vehicle 200 which have large diameters and rotate at high speeds. If sufficiently large, the centrifugal force could cause the retaining ring 32 to radially expand by a sufficient extent to lift the retaining ring 32 away from the shaft 28 and out of the groove 34. Example shafts of electric traction motors may rotate at maximum speeds of at least 8000 RPM, for example in the range of 8000 RPM to 14,000 RPM. Such shafts may have a diameter of at least 25 mm, for example in the range of 25 mm to 70 mm. Reducing the likelihood that the retaining ring 32 is dislodged and / or disconnected from the shaft 28 is important in maintaining the axial position of a component 30A, 30B on the shaft 28, facilitating proper functioning of components 30A, 30B on the shaft 28 and contributing to the overall stability of the shaft assembly 10. In order to compensate for the increased risk of radial expansion of the retaining ring, the shaft assembly 10 includes a ring retention element 36. The ring retention element 36 is mounted on the shaft 28 adjacent to the retaining ring 32. The ring retention element 36 is configured to restrict radial expansion and / or radial movement of the retaining ring 32 away from the shaft 28. In the figures, two ring retention elements 36A, 36B are provided (e.g. one per retaining ring 32). It will be appreciated that any number of ring retention elements 36A, 36B may be provided. Referring now to Figures 7 to 10 in conjunction with Figures 4 to 6B, the ring retention element 36A, 36B will be discussed in detail. The ring retention element 36A of Figures 7 and 8 is substantially the same as the ring retention element 36B of Figures 9 and 10. As will be discussed below, the primary difference between the ring retention elements 36A, 36B is that the ring retention element 36A defines a lesser axial length than the ring retention element 36B. The difference in axial length may be due to space constraints in different areas of the shaft assembly 10. It will be appreciated that the ring retention elements 36A, 36B may have the same axial length in alternative arrangements. The ring retention element 36A, 36B includes a retention surface 38 that extends over or overlies at least part of an outer radial surface 32A of the retaining ring 32. The retention surface 38 restricts radial movement or expansion of the retaining ring 32 away from the shaft 28. The retention surface 38 acts as a radial barrier to the retaining ring 32, blocking movement of the retaining ring 32 in a radially outward direction. The ring retention element 36A, 36B can reduce or prevent a radially outward movement of the retaining ring 32 relative to the shaft 28, maintaining the function of the retaining ring 32 in reducing axial movement of the component 3uA, 30B. This facilitates effective functioning of components on the shaft 28, reducing the need fordowntime and maintenance. In the figures, the ring retention element 36A, 36B includes an annular body 40 that is mounted on the shaft 28. The annular body 40 of the ring retention element 36A defines a lesser axial length than the annular body 40 of the ring retention element 36B. The ring retention elements 36A, 36B may have the same axial length in alternative arrangements and / or the annular body 40 of the ring retention element 36A may define a greater axial length than the annular body 40 of the ring retention element 36B. It will be appreciated that the axial length of the annular body 40 of a respective ring retention element 36A, 36B may be influenced by numerous factors, including space constraints along the shaft 28. The retention surface 38 is defined by a projection or shoulder that extends from the annular body 40 (e.g. in a generally axial direction over the retaining ring 32). In the illustrated arrangement, the retention surface 38 is a continuation of an outer radial surface of the annular body 40. The retention surface 38 may be defined as an upper edge of a recess provided in an axial end face of the annular body 40. The recess is configured for receiving part of the retaining ring 32. The retention surface 38 may be integrally formed with the annular body 40. Alternatively, the retention surface 38 may be secured to the annular body 40. In such an arrangement, the retention surface 38 may be defined by one or more pins that are secured to an axial surface of the annular body 40 and arranged to overlay the outer radial surface 32A of the retaining ring 32. In some arrangements, the ring retention element 36A, 36B may be only partially annular, or define a different shape. In the illustrated arrangement, the retention surface 38 abuts against the outer radial surface 32A of the retaining ring 32 so as to prevent radially outward movement of the ring 32 (e.g. the retention surface 38 blocks the retaining ring 32 in the event the retaining ring 32 moves in a radially outward direction). In alternative arrangements, the ring retention element 36A, 36B may be configured such that the retention surface 38 is radially spaced apart from the retaining ring 32 to define a radial clearance therebetween. In such an arrangement, the retaining ring 32 may move or expand in a radially outward direction until the retaining ring 32 (e.g. the outer radial surface 32A thereof) abuts against the retention surface 38. This may be preferable where slight expansion of the retaining ring 32 is acceptable. In arrangements in which the retaining ring 32 is in a groove 34 around the outer surface of the shaft 28, a radial clearance of less than the depth of the groove 34 may be present between the retention surface 38 and the outer radial surface 32A of the retaining ring 32, preventing the retaining ring 32 fully lifting from the groove 34. The retention surface 38 may extend over only a portion of the axial length of the outer radial surface 32A in some arrangements. In such an arrangement, the axial extent of the retention surface 38 and / or the axial position of the ring retention element 36A, 36B relative to the retaining ring 32 results in a portion of the axial length of the outer radial surface 32A not locating beneath the retention surface 38. The retention surface 38 does not contact or abut the component 30A, 30B. The retention surface 38 extends over only part of the outer radial surface 32A of the retention surface 38 such that there is an axial clearance between the retention surface 38 and the component 30A, 30B that the ring 32 is axially retaining. In this way, only the retaining ring 32 is intended to restrict axial movement of the component 30A, 30B (e.g. by abutting against the component 10 3uA, 30B). This prevents additional load being applied to the ring retention element 36A, 36B (e.g. from providing axial support to the component 30A, 30B as well as radial support to the ring 32), reducing the likelihood that the ring retention element 36A, 36B is axially displaced or, in some cases, becomes overloaded. In the arrangement shown in the figures, the first axial surface 32B of the retaining ring 32 abuts the component 30A, 30B. The retention surface 38 (or the ring retention element 36A, 36B) is axially spaced apart from the component 30A, 30B. The ring retention element 36A, 36B may be arranged to abut against an axial end of the retaining ring 32, e.g. against a second axial surface 32C of the retaining ring 32. In the figures, the annular body 40 includes an abutment surface 42 that contacts the second axial surface 32C of the retaining ring 32. This arrangement improves ease and accuracy of manufacture of the shaft assembly 10, as the ring retention element 36A, 36B can be mounted on the shaft 28 and moved axially thereover until abutting against the retaining ring 32. In this way, the ring retention element 36A, 36B will be in the preferred position once the annular body 40 abuts the retaining ring 32. It will be appreciated that the ring retention element 36A, 36B may be arranged on the shaft 28 so as to be axially spaced apart from the retaining ring 32 in alternative arrangements. As is best seen in Figures 8 and 10, the retaining ring 32 may nest within the respective ring retention element 36A, 36B, abutting against both radial and axial surfaces of the ring retention element 36A, 36B. In this way, the ring retention element 36A, 36B provides support to the respective retaining ring 32 in an axial and a radial direction, reducing the risk that the retaining ring 32 will move from its position. The retaining ring 32 may be positioned on the shaft 28 so as to locate axially between a respective component 30A, 30B and the ring retention element 36A, 36B. In the illustrated arrangement, the first axial surface 32B of the retaining ring 32 abuts against a component 30A, 30B and the second axial surface 32C of the retaining ring 32 abuts against the ring retention element 36A, 36B (e.g. the abutment surface 42 of the annular body 40). In this way, the retaining ring 32 is effectively “sandwiched” between the component 30A, 30B and the ring retention element 36A, 36B. Such an arrangement provides a compact shaft assembly 10 and provides effective retention to both the component 30A, 30B and the retaining ring 32. Alternatively, the ring retention element 36A, 36B may be located between the component 30A, 30B and the retaining ring 32. In such embodiments, the retaining ring 32 may restrict axial movement of the component 30A, 30B along the shaft indirectly via the ring retention element 36A, 36B. In a further alternative arrangement, the component 30A, 30B may be located axially between the retaining ring 32 and the ring retention element 36A, 36B. In such an arrangement, the retention surface 38 may be defined by a projection that extends (e.g. from the annular body 40) in an axial direction over an outer radial surface of the component 30A, 30B and over the outer radial surface 32A of the retaining ring 32. The retention surface 38 may extend around the whole circumference of the retaining ring 32. This arrangement provides for improved retention of the retaining ring 32, resulting in a more robustly located retaining ring 32. In alternative embodiments, the retention surface 38 may extend around only a portion of the circumference of the retaining ring 32. In such embodiments, the retention surface may be provided by a continuous surface or by a series of discontinuous retention surfaces. The ring retention element 36A, 36B may be mounted on the shaft 28 in such a way so as to restrict axial movement of the ring retention element 36A, 36B along the shaft 28. The ring retention element 36A, 36B is configured to be effectively secured on the shaft 28, so as to reduce or prevent axial movement thereof and ensuring maintained radial retention of the retaining ring 32. The ring retention element 36A, 36B may be dimensioned to form an interference fit with the shaft 28. Put another way, the inner diameter of the annular body 40 may be less than the outer diameter of the shaft 28 such that the ring retention element 36A, 36B is secured to the shaft 28 by friction between the annular body 40 and the shaft 28. Other means of restricting axial movement of the retaining ring 32 may be implemented. For example, the ring retention element 36A, 36B may be received in a groove in the outer surface of the shaft 28, or may abut against a projection thereon. It will be appreciated that any suitable means may be implemented to restrict axial movement of the ring retention element 36A, 36B along the shaft 28. The ring retention element 36A, 36B includes a circumferential groove 44 on an outer radial surface thereof. In the figures, the groove 44 extends circumferentially about the outer surface of the annular body 40. The groove 44 is configured to receive a removal tool. The groove 44 provides a surface feature by which the removal tool may grip the ring retention element 36A, 36B. Alternative surface features include one or more protrusions or recesses in the outer radial surface of the ring retention element 36A, 36B. The shaft 28 and the ring retention element 36A, 36B may be formed from materials having substantially the same coefficient of thermal expansion. As used herein, the term “coefficient of thermal expansion” refers to the relative change in size or volume of a material in response to a change in temperature, i.e. the extent of expansion or contraction in response to a temperature change. Forming the shaft 28 and the ring retention element 36A, 36B from materials having the same or similar coefficients of thermal expansion results in the ring retention element 36A, 36B and the shaft 28 responding similarly to fluctuations in temperature. This prevents the ring retention element 36A, 36B from becoming detached from the shaft 28 if one part were to expand where another does not. In this way, the ring retention element 36A, 36B is effectively fixed relative to the shaft 28, providing effective radial retention to the retaining ring 32, irrespective of temperature fluctuations. The ring retention element 36A, 36B may be formed of metallic material, optionally steel or aluminium alloy material. This provides a robust ring retention element 36A, 36B that effectively retains the retaining ring 32. The shaft 28 and the ring retention element 36A, 36B may be formed from the same material in some arrangements. A method of manufacturing a shaft assembly 10 for an electric traction motor 100 fora vehicle 200 is illustrated in Figure 11 as a flow chart. The method includes the following steps: a) providing a shaft 28 defining a longitudinal axis L; b) mounting a component 30A, 30B on the shaft 28; c) mounting a retaining ring 32 on the shaft 28 adjacent to the component 30A, 30B to restrict axial movement of the component 30A, 30B along the shaft 28; and d) mounting a ring retention element 36A, 36B on the shaft 28 adjacent to the retaining ring 32, the ring retention element 36A, 36B having a retention surface 38 extending over at least part of an outer radial surface 32A of the retaining ring 32 to restrict radial movement of the retaining ring 32 away from the shaft 28. In some embodiments, step (d) may include forming an interference fit between the ring retention element 5 36A, 36B and the shaft 28. The ring retention element 36A, 36B may be mounted on the shaft 28 using a hydraulic press. This can allow for effective and reliable fitting. The retention element may be heated prior to installation on the shaft whereby its internal radius is thermally expanded. Step (d) may include axially moving the ring retention element 36A, 36B along the shaft 28 (e.g. in an axial direction) until the ring retention element 36A, 36B abuts against the second axial surface 32C of the retaining 10 ring 32. 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 15 features herein disclosed.

Claims

1. An electric traction motor shaft assembly for a vehicle, the shaft assembly comprising:a shaft defining a longitudinal axis;a component mounted on the shaft;a retaining ring mounted on the shaft adjacent to the component to restrict axial movement of the component along the shaft, wherein the retaining ring is expandable in a radial direction; anda ring retention element mounted on the shaft adjacent to the retaining ring, the ring retention element having a retention surface extending over at least part of an outer radial surface of the retaining ring to restrict radial movement of the retaining ring away from the shaft.

2. The electric traction motor shaft assembly according to claim 1, wherein the retention surface extends over only a portion of the axial length of the outer radial surface of the retaining ring.

3. The electric traction motor shaft assembly according to claim 1 or claim 2, wherein the retention surface abuts against the outer radial surface of the retaining ring.

4. The electric traction motor shaft assembly according to any preceding claim, wherein the ring retention element is dimensioned to form an interference fit with the shaft.

5. The electric traction motor shaft assembly according to any preceding claim, wherein the ring retention element abuts against an axial end of the retaining ring.

6. The electric traction motor shaft assembly according to any preceding clam, wherein the retention surface extends around substantially the whole circumference of the retaining ring.

7. The electric traction motor shaft assembly according to any preceding clam, wherein the shaft and the ring retention element are formed from materials having substantially the same coefficient of thermal expansion.

8. The electric traction motor shaft assembly according to any preceding clam, wherein the ring retention element comprises a circumferential groove on an outer radial surface thereof for receiving a removal tool.

9. The electric traction motor shaft assembly according to any preceding clam, wherein the retaining ring is positioned axially between the component and the ring retention element.

10. The electric traction motor shaft assembly according to any preceding clam, wherein the retaining ring is received in a circumferential groove on the shaft.

11. The electric traction motor shaft assembly according to any preceding clam, comprising a further component mounted on the shaft axially spaced from the component, and comprising a further retaining ring mounted on the shaft adjacent to the further component to restrict axial movement of the further componentalong the shaft, and a further ring retention element mounted on the shaft adjacent to the further retaining ring, the further ring retention element having a retention surface extending over at least part of an outer radial surface of the further retaining ring to restrict radial movement of the further retaining ring away from the shaft.

12. An electric traction motor for a vehicle, the electric traction motor comprising the electric traction motor shaft assembly according to any preceding claim.

13. A vehicle comprising the electric traction motor of claim 12.

14. A method of manufacturing a shaft assembly for an electric traction motor for a vehicle, the method comprising:providing a shaft defining a longitudinal axis;mounting a component on the shaft;mounting a retaining ring on the shaft adjacent to the component to restrict axial movement of the component along the shaft; andmounting a ring retention element on the shaft adjacent to the retaining ring, the ring retention element having a retention surface extending over at least part of an outer radial surface of the retaining ring to restrict radial movement of the retaining ring away from the shaft.

15. The method of claim 14, wherein the step of mounting the ring retention element on the shaft comprises forming an interference fit between the ring retention element and the shaft.16

Images