A gear assembly

Abstract

A gear assembly comprising a shaft 12 and a gear 14 selectively engaged with the shaft. A transfer member 16 is mounted on the shaft and is axially moveable between a connected position in which the t

Description

TECHNICAL FIELD The present disclosure relates to a gear assembly and to a vehicle. BACKGROUND Gear assemblies are crucial components in automotive vehicles, facilitating the transfer of power between the engine and vehicle wheels at various speeds and torques. The performance and efficiency of a gear assembly in a vehicle significantly impacts the overall drivability, fuel economy and reliability of a vehicle. Traditional designs often face challenges related to bulkiness, complexity and the smoothness of gear engagement and disengagement, which can affect the driving experience and durability of a vehicle transmission system. While various attempts to improve performance and efficiency of gear assemblies have been proposed, particularly in view of developments in electric vehicles, achieving a balance between compactness and optimal gear engagement remains a challenge in automotive design. As such, there is a need for a gear assembly that offers a more compact design without compromising on operation and durability. 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 gear assembly, a vehicle and a method of gear selection. According to an aspect of the invention, there is provided a gear assembly for a vehicle, the gear assembly comprising: a shaft having a longitudinal axis; a gear configured to selectively engage with the shaft to transfer a motive force between the gear and the shaft when engaged; a transfer member mounted on the shaft so as to be rotationally coupled therewith, the transfer member axially moveable between a connected position, in which the transfer member is engaged with the gear so as to transfer motive force between the gear and the shaft, and a disconnected position, in which the transfer member is disengaged from the gear; an actuation member coupled to the transfer member, wherein the actuation member is configured to move the transfer member between the connected position and the disconnected position; and a piston moveable relative to the shaft in a first axial direction and a second axial direction, the piston coupled to the actuation member such that the actuation member is moveable in first and second axial directions therewith. The piston may be arranged to extend circumferentially about the shaft. The gear assembly may further comprise a locking arrangement configured to couple the actuation member and the transfer member. The locking arrangement may be configured such that the transfer member is axially moveable towards the disconnected position upon movement of the piston in the second axial direction. Advantageously, the gear assembly is compact and reliable. The circumferentially arranged piston provides for an effective means of moving the transfer member, while making use of limited space in the vehicle (e.g. compared with a piston that is arranged axially relative to the shaft rather than circumferentially about the shaft), allowing for a more tightly packed assembly. Moreover, while the piston and actuation member provide a smooth means of moving the transfer member into a connected position (e.g. by "pushing" the transfer member into engagement), the locking arrangement provides smooth, effective movement of the transfer member into a disconnected position (e.g. by "pulling" the transfer member out of engagement), allowing for both positive engagement and disengagement of the transfer member and the gear. The gear assembly as set forth has enhanced efficiency and improved reliability. Wear between components can be reduced (e.g. compared with systems not having a means of positively disengaging the transfer member and the gear), reducing maintenance requirements and improving the lifespan of assembly components, whilst also providing a compact and spaceefficient gear assembly. Optionally, the locking arrangement comprises an interlocking arrangement. Such an interlocking arrangement provides a simple means of securing two components (e.g., by pushing and twisting the components relative to each other). Further, once connected such an interlocking arrangement may be able to withstand greater axial separation forces than alternatives, such as snap-fit arrangements. Inhibiting axial separation of the transfer member and the actuation member facilitates the axial movement of the transfer member with the actuation member, particularly in the second axial direction (i.e. toward the disconnected position), as simply moving the piston in the second axial direction will not positively move the transfer member out of the connected position. In this way, disconnection of the gear and the shaft can be effectively achieved. Optionally, the interlocking arrangement comprises a connector on the transfer member and a receiver on the actuation member. Such a combination of the connector and receiver provides a simple interlocking arrangement. In some arrangements, the interlocking arrangement comprises a connector on the actuation member and a receiver on the transfer member. In some arrangements, the interlocking arrangement comprises at least one connector on the transfer member, at least one connector on the actuation member, at least one receiver on the transfer member, and at least one receiver on the actuation member. Optionally, the interlocking arrangement is configured so that transfer member is pushed axially towards a first end of the actuation member to insert the connector into the receiver, and then twisted about a central axis of the actuation member and / or transfer member to form an interlocking engagement between the connector and the receiver and thereby inhibit axial movement of the transfer member relative to the actuation member (i.e. such that the transfer member will move with the actuation member in the first axial direction or the second axial direction in response to movement of the piston). Optionally, the connector and the receiver each comprise one or more interlocking protrusions. Having interlocking protrusions may provide a more robust connection between the actuation member and the transfer member. Optionally, the connector and the receiver each comprise a plurality of interlocking protrusions. Optionally, the receiver comprises one or more axial recesses positioned adjacent an interlocking protrusion of the receiver, the or each axial recess extending axially inboard from a first end of the actuation member, wherein the receiver further comprises a circumferential recess which extends circumferentially from an axially inboard end of the axial recess, and wherein the or each protrusion of the connector is configured to be received in a respective axial recess of the receiver and in the circumferential recess. The protrusions of the interlocking connector can be pushed along the axial recess of the interlocking receiver (e.g. by pushing the transfer member towards the actuation member), the corresponding components can then be rotated so that the protrusions of the connector moves along the circumferential recess to locate axially behind a protrusion of the interlocking receiver to inhibit axial separation of the transfer member and the actuation member. This provides a simple means of connecting the transfer member with the actuation member. In arrangements in which the receiver and the connector each comprise a plurality of interlocking protrusions, the receiver may comprise a plurality of axial recesses, each recess defined between adjacent protrusions of the receiver. Each protrusion of the plurality of protrusions of the connector may be configured to be received in a respective axial recess of the receiver and in the circumferential recess. Optionally, the interlocking arrangement comprises a securing element configured to restrict circumferential movement of the connector relative to the receiver. Advantageously, such an arrangement prevents any disconnection of the connector and the receiver, maintaining a robust fit. Optionally, the securing element is provided as first and second abutment surfaces of one of the one or more interlocking protrusions of the connector, the abutment surfaces configured to abut opposing circumferential ends of a respective one of the one or more interlocking protrusions of the receiver. This provides a simple means of utilising the features of the interlocking arrangement that restrict axial movement to also restrict circumferential movement, providing for a simple and compact means of restricting such movement. Optionally, the first and second abutment surfaces each comprise a projection on the respective one of the one or more interlocking protrusions of the connector at or proximal to opposing circumferential ends thereof; optionally, wherein the projection is defined by a bent or folded region of the respective one of the one or more interlocking protrusions. This is a simple means of manufacturing an abutment surface, without requiring additional parts. Optionally, the connector is an annular locking element mounted on the transfer member. Advantageously, providing the interlocking connector as a separate component to the transfer member avoids the need for any protrusions to be machined in the transfer member. In this way, the transfer member can be produced via normal manufacturing techniques. Optionally, the annular locking element is configured to abut a shoulder on an outer radial surface of the transfer member upon movement of the piston in the second axial direction, such that the transfer member is axially moveable toward the disconnected position upon movement of the annular locking element with the piston in the second axial direction. This provides a simple and compact means of moving the transfer member out of engagement with the gear in response to the piston moving in the second axial direction. The annular locking element may be axially moveable relative to the transfer member. Optionally, the annular locking element is dimensioned to form an interference fit with the outer radial surface of the transfer member. This provides a simple means of pulling the transfer member out of engagement with the gear, without requiring additional parts to be included on the transfer member (e.g. without requiring a shoulder). The locking ring may be axially fixed relative to the transfer member, such that the transfer member moves axially with the locking ring. Optionally, the annular locking element comprises an annular body and a plurality of protrusions extending in a radially outward direction from the annular body. Optionally, the annular locking element defines a closed loop in cross section. Advantageously, such an arrangement provides for a more secure fit to the surface of the transfer member than other, open loop substantially annular locking elements, e.g. a circlip. Optionally, the actuation member comprises a first surface extending over at least part of an outer radial surface of the transfer member, wherein the receiver is provided on the first surface, and wherein the annular locking element is mounted on the transfer member so as to locate radially between the first surface of the actuation member and the transfer member. This provides a compact locking arrangement that does not occupy significant axial space in the vehicle. Optionally, the receiver may be machined into the actuation member (e.g. into the first surface of the actuation member). Optionally, the actuation member comprises an actuation surface configured to engage with an axial surface of the transfer member upon a movement of the piston in the first axial direction, such that the transfer member is moveable toward the connected position upon movement of the actuation member with the piston in the first axial direction. In this way, the transfer member can be effectively pushed into engagement with the gear. This is a simple and effective means of engaging. Optionally, the gear assembly further comprises an axial thrust bearing interposed between the actuation surface of the actuation member and the axial surface of the transfer member. Advantageously, the actuation member engages with the transfer member via the thrust bearing. The bearing allows for smooth engagement between the actuation member and the transfer member, which may be rotating at different speeds, facilitating effective transfer of axial motion to the transfer member and a smooth engagement between the transfer member and gear. As such, wear between parts is reduced. Optionally, the piston extends around the whole circumference of the shaft. Advantageously, the axial force provided by the piston is more evenly distributed, reducing wear of components and improving the smoothness of the movement of the actuation member and the transfer member into and out of engagement with the gear. In some arrangements, the piston is an annular piston that is coaxial with the shaft (e.g. the piston is arranged concentrically about the shaft). Optionally, the piston is pneumatically actuated. Utilising air to actuate the piston provides for a smooth, gentle actuation of the piston that can be effectively controlled. Moreover, many vehicles are manufactured with a compressed air system, facilitating the retrofitting of the vehicle in pre-existing vehicles. Optionally, the assembly further comprises a piston housing configured to house the piston, wherein the piston housing comprises a first inlet port configured to introduce a fluid to drive the piston in the first axial direction, and a second inlet port configured to introduce a fluid to drive the piston in the second axial direction. In some arrangements, the piston is a bidirectional piston. Providing multiple inlet ports provides a more precise control over the direction and speed of movement of the piston compared with other means of enabling bidirectional control (e.g. using a spring). Optionally, the actuation member is received in a groove on an outer surface of the piston. The actuation member is effectively secured to the piston, facilitating effective movement of the actuation member with the piston, and reducing delay between movement of the piston and movement of the transfer member. Optionally, the gear assembly further comprises a retaining ring mounted on the piston adjacent to the actuation member to restrict axial movement of the actuation member relative to the piston; optionally, wherein the retaining ring is a circlip. This provides effective axial retention of the actuation member relative to the piston. Optionally, the transfer member is a dog clutch component having a plurality of axially extending teeth configured to selectively engage with corresponding teeth of the gear. This provides for an effective engagement between the gear and the shaft. Optionally, the gear is mounted on the shaft via a roller bearing; optionally, wherein the roller bearing is a needle roller bearing. This makes effective use of axial space within the vehicle. The needle roller bearing effectively supports the load from the gear without occupying significant space in the vehicle. Optionally, the gear assembly further comprises one or more of the following features: a second gear axially spaced apart from the gear, the second gear configured to selectively engage with the shaft to transfer a motive force between the second gear and the shaft when engaged; a second transfer member mounted on the shaft so as to be rotationally coupled therewith, the second transfer member axially moveable between a connected position, in which the second transfer member is engaged with the second gear so as to transfer the motive force between the second gear and the shaft, and a disconnected position, in which the second transfer member is disengaged from the second gear; a second actuation member coupled to the second transfer member, wherein the second actuation member is configured to move the second transfer member between the connected position and the disconnected position; a second piston moveable relative to the shaft in the first axial direction and the second axial direction, the second piston coupled to the second actuation member such that the second actuation member is moveable in first and second axial directions therewith, wherein the second piston is arranged to extend circumferentially about the shaft; and a second locking arrangement configured to couple the second actuation member and the second transfer member, the second locking arrangement configured such that the second transfer member is axially moveable towards the disconnected position upon a movement of the second piston in the first axial direction. Optionally, one or more of the second transfer member, second actuation member, second piston and second locking arrangement are arranged substantially symmetrically relative to one or more of the transfer member, actuation member, piston and locking arrangement about a plane of symmetry extending radially between the first and second piston. In this way, a single shaft can engage with either gears, making use of limited axial space in the vehicle. The symmetrical arrangement improves the balance and stability of the shaft. Optionally, the second transfer member, second actuation member, second piston and second locking arrangement are substantially the same as the transfer member, actuation member, piston and locking arrangement. Optionally, the assembly further comprises a fluid supply system for supplying fluid to move the pistons, and a control system configured to control the supply of fluid to the pistons, wherein the control system is configured to control the fluid supply system such that the second transfer member is in the disconnected position when the transfer member is in the connected position, and such that the transfer member is in the disconnected position when the second transfer member is in the connected position. This prevents both gears from ever being engaged at the same time, which may cause damage to the vehicle. According to an aspect of the invention, there is provided a gearbox comprising a gearbox housing and the gear assembly as described herein, wherein the gear assembly is at least partially housed within the gearbox housing. The gearbox benefits from the advantages of the gear assembly outlined above. According to an aspect of the invention, there is provided a vehicle comprising the gear assembly according to any preceding claim. The vehicle benefits from the advantages of the gear assembly outlined above. 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 is a cross-sectional view of a gear assembly according to an embodiment; Figure 2 is an exploded view of components of the gear assembly of Figure 1; Figure 3 is a cross-sectional view of the gear assembly of Figure 1 during installation; Figure 4 is a cross-sectional view of the gear assembly of Figure 4 upon installation; Figure 5 is an isometric detailed / partial view of the section X of Figure 4; Figure 6 is a means of lubricating the gear assembly according to an embodiment; Figure 7 is a gear assembly according to an embodiment; Figure 8 is a schematic of a vehicle according to an embodiment; and Figure 9 is a flow chart of a method of gear selection according to an embodiment. DETAILED DESCRIPTION Referring to Figure 1, a gear assembly 10 is illustrated. The gear assembly 10 is configured for use in a vehicle 1000, for example in a transmission system of a vehicle 1000. The gear assembly 10 includes a shaft 12 having a longitudinal axis L. The shaft 12 is rotatable about the longitudinal axis L. The gear assembly 10 includes a gear 14 configured to selectively engage with the shaft 12 to transfer a motive force between the gear 14 and the shaft 12 when engaged. The shaft 12 may be an input shaft or main shaft that receives a motive force from a prime mover of the vehicle 1000 (e.g. by the engine or power source) and that transfers said force to the gear 14 when engaged. In alternative arrangements, the shaft 12 may be an output shaft or secondary shaft that receives motive force from the gear 14 (e.g. that is coupled with the main shaft) when engaged, and that transfers said motive force to one or more wheels of the vehicle 1000. The shaft 12 may be an intermediate shaft or layshaft that transfers motive force between a main shaft and an output shaft. A transfer member 16 is mounted on the shaft 12 so as to be rotationally coupled therewith. The transfer member 16 is axially moveable between a connected position, in which the transfer member 16 is engaged with the gear 14 so as to transfer the motive force between the gear 14 and the shaft 12, and a disconnected position, in which the transfer member 16 is disengaged from the gear 14. In Figure 1, the transfer member 16 is in the disconnected position. The transfer member 16 may be positioned so as to be axially adjacent the gear 14 on the shaft 12. The gear assembly 10 includes an actuation member 18 coupled to the transfer member 16. The actuation member 18 is configured to move the transfer member 16 between the connected position and the disconnected position. In the figures, the actuation member 18 is positioned so as to be axially adjacent the transfer member 16 on the shaft 12. In the illustrated arrangement, the transfer member 16 is located between the gear 14 and the actuation member 18. A piston 20 is provided that is moveable relative to the shaft 12 in a first axial direction and a second axial direction. That is, the piston 20 is actuated in both directions of movement. In the figures, the first axial direction is toward the gear 14 (e.g. to the left in Figure 1), and the second axial direction is opposite, away from the gear 14 (e.g. to the right in Figure 1). The piston 20 is coupled to the actuation member 18 such that the actuation member 18 is moveable in first and second axial directions with the piston 20. The piston 20 is arranged to extend circumferentially about the shaft 12. In some arrangements, the piston 20 extends partially about the circumference of the shaft 12. Alternatively, the piston 20 may extend around the entire circumference of the shaft 12. The piston 20 is a concentric piston 20 having a central axis that is coaxial with the longitudinal axis L of the shaft 12. The piston 20 may be a substantially annular piston that is coaxial with the shaft 12. The circumferentially extending piston 20 provides for an effective means of moving the transfer member 16 while making use of limited space in a vehicle (e.g. compared with a piston that is arranged axially relative to the shaft). This allows for a more compact gear assembly. A piston 20 that extends completely around the circumference of the shaft 12 can promote a more evenly distributed force being applied to the actuation member 18 and thus to the transfer member 16. The piston 20 may be supported in the assembly (e.g. in a gearbox) such that the piston 20 does not rotate with the shaft 12. In one arrangement, the piston 20 may be secured to a housing (not shown), e.g. a gearbox housing, that houses components of the gear assembly 10. The transfer member 16 is moveable toward the connected position upon movement of the actuation member 18 with the piston 20 in the first axial direction. The transfer member 16 can be effectively pushed into engagement with the gear 14 by movement of the actuation member 18 with the piston 20 in the first axial direction. In the illustrated embodiment, the actuation member 18 includes an actuation surface 18a configured to engage with a surface 16c of the transfer member 16 upon movement of the piston 20 in the first axial direction. The surfaces 16c, 18a of the transfer member and actuation member 18 may be axial surfaces. The surfaces 16c, 18a may be substantially planar. The arrangement of the surfaces may result in a compact arrangement in which motive force is transferred in a generally axial direction. A bearing arrangement is provided between the actuation member 18 and the transfer member 16. The bearing arrangement allows for smooth engagement between the actuation member 18 and the transfer member 16, which may be rotating at different speeds, facilitating effective transfer of axial motion to the transfer member 16 and a smooth engagement between the transfer member 16 and gear 14. As such, wear between parts is reduced. In the illustrated arrangement, an axial thrust bearing 28 is located between the actuation member 18 and the transfer member 16. The axial thrust bearing 28 may be interposed between the actuation surface 18a of the actuation member 18 and the axial surface 16c of the transfer member 16. In the figures, the actuation surface 18a can abut against a first axial surface of the bearing 28 and the surface 16c of the transfer member 16 abuts against an opposing, second axial surface of the bearing 28. The piston 20 and actuation member 18 provide for a smooth means of moving the transfer member 16 into the connected position, e.g. by moving in the first axial direction and "pushing" the transfer member 16 toward and into engagement with the gear 14. Movement of the piston 20 and actuation member 18 in the second axial direction may not positively pull the transfer member 16 out of engagement from the gear 14. For this reason, the assembly 10 includes a locking arrangement 32 configured to couple the actuation member 18 and the transfer member 16. The locking arrangement 32 is configured such that the transfer member 16 is axially moveable towards the disconnected position upon movement of the piston 20 in the second axial direction. Put another way, when the piston 20 and the actuation member 18 move in the second axial direction, the locking arrangement 32 promotes a positive disengagement of the transfer member 16 from the gear 14 to the disconnected position. The locking arrangement 32 advantageously provides smooth, effective movement of the transfer member 16 into the disconnected position, for example by "pulling" the transfer member 16 out of engagement with the gear 14. In this way, the gear assembly 10 allows for both 10 positive engagement and disengagement of the transfer member 16 and the gear 14. The gear assembly 10 has enhanced efficiency and improved reliability. Wear between components can be reduced (e.g. compared with systems not having a means of positively disengaging the transfer member 16 and the gear 14), reducing maintenance requirements and improving the lifespan of assembly components, whilst also providing a compact and space-efficient gear assembly 10. The gear 14 may be mounted on the shaft 12 via a bearing arrangement. In the figures, the gear 14 is mounted on the shaft 12 via a roller bearing 30. The roller bearing 30 may be a needle roller bearing. Mounting the gear 14 to the shaft 12 makes effective use of axial space within the vehicle 1000, for example within a gearbox (e.g. the gear 14 is not mounted axially adjacent to the shaft 12). The bearing arrangement allows the gear 14 to rotate relative to the shaft 12. A needle roller bearing 30 can effectively support a load from the gear 14 without occupying significant space. In the illustrated arrangement, the transfer member 16 is mounted on the shaft 12 via a splined arrangement, facilitating a transmission of torque between the shaft 12 the transfer member 16, while permitting axial movement of the transfer member 16 along the shaft. It will be appreciated that any suitable means of mounting the transfer member 16 to the shaft may be utilised. In the figures, the shaft 12 includes a series of splines 12a. The transfer member 16 may include a series of internal splines 16a (see Figure 2) that correspond with the splines 12a of the shaft 12. In this way, the transfer member 16 is moveable to the connected position by axial movement of the transfer member 16 along the splines 12a. In the figures, the transfer member 16 is a dog clutch component having a plurality of teeth 16b configured to selectively engage with corresponding teeth 14a of the gear 14. The teeth 16b extend in a generally axial direction from the transfer member 16. The teeth 14a extend in a generally axial direction from the gear 14. Axial movement of the transfer member 16 along the splines 12a toward the gear 14 can move the axially extending teeth 16b into engagement with the gear teeth 14a, moving the transfer member 16 into the connected position. It will be appreciated that the transfer member 16 may be in any suitable form to selectively transfer torque between the gear 14 and the shaft 12. The actuation member 18 may be received in a groove 20a on a surface of the piston 20. The groove 20a may be in the outer surface of the piston 20. The groove 20a allows the actuation member 18 to move with the piston 20 in both the first and second axial directions. The actuation member 18 may be attached to the piston in alternative arrangements, e.g. via a bolt arrangement, a threaded arrangement, or by dimensioning the actuation member 18 to form an interference fit with the outer surface of the piston 20. Alternatively, the actuation member 18 and the piston 20 may be integrally formed. It will be appreciated that the piston 20 and the actuation member 18 may be formed in any way so as to facilitate effective movement of the actuation member 18 in response to axial movement of the piston in either axial direction (i.e. in the first and second axial directions). A retaining ring 22 may be mounted on the piston adjacent to the actuation member 18 to restrict axial movement of the actuation member 18 relative to the piston 20. The retaining ring 22 may be a circlip or the like. In the figures, the piston 20 is positioned so as to be axially adjacent the actuation member 18. In this way, the actuation member 18 may locate axially between the transfer member 16 and the piston 20. A piston housing 24 is provided to house the piston 20 in the illustrated embodiment. The piston housing 24 may be secured to a gearbox housing to support the piston 20 relative to the shaft 12. The piston 20 may be secured in the housing 24, e.g. via various seals, circlips, O-rings and the like to ensure effective functioning of the piston 20. The piston housing 24 includes a first inlet port 24a configured to introduce a fluid to drive the piston 20 in the first axial direction and a second inlet port 24b configured to introduce a fluid to drive the piston 20 in the second axial direction. The ports 24a, 24b provide for a simple means of inducing bidirectional movement in the piston 20 and allow for more precise control over the direction and speed of movement of the piston 20 compared with other means of facilitating bidirectional control (e.g. via a single port and a spring arrangement or the like). The ports 24a, 24b are axially spaced apart from one another so as to facilitate the introduction of fluid to different regions of the housing 24 and to different axial sides of the piston 20. In alternative arrangements, a valve arrangement may be provided to split the fluid supply and facilitate flow of fluid to the required side of the piston 20 in the housing 24. In the figures, a fluid supply system 26 is provided to supply fluid to the piston 20, e.g. into the housing 24 via the ports 24a, 24b. A control system 50 is provided that is configured to control the supply of the fluid to the housing 24. The control system 50 may instruct the fluid supply system 26 on which inlet port 24a, 24b to use, and / or on the amount (e.g. volume) of fluid to supply and / or on the pressure of fluid to supply. In the figures, the dashed lines between the control system 50 and fluid supply system 26 represent signals sent by the controller 50 (e.g. electrical signals). The dashed lines between the fluid supply system 26 and the piston housing 24 represent fluid flow. An example of operating the fluid supply system 26 will now be discussed. When it is desired to engage the gear 14 (e.g. to transfer motive force between the shaft 12 and the gear 14), the control system 50 is configured to instruct the fluid supply system 26 to supply fluid to the first inlet port 24a so as to move the piston 20 in the first axial direction and subsequently move the transfer member 16 into the connected position. Once the transfer member 16 is in the connected position, the control system 50 is configured to instruct the fluid supply system 26 to reduce the pressure of the fluid supplied to the first inlet port 24a. The reduced pressure can hold the piston 20 in position, but since the transfer member 16 is engaged with the gear 14, there is no requirement to continue applying a force to move the piston 20. When it is desired to disengage the gear (e.g. to cease transferring motive force between the shaft 12 and the gear 14), the control system is configured to instruct the fluid supply system 26 to stop or reduce the fluid supplied to the first inlet port 24a and to supply fluid to the second inlet port 24b so as to move the piston 20 in the second axial direction. The control system 50 may include one or more sensors to determine pressure and / or flow rate of fluid supplied to the piston housing 24. The control system 50 may include one or more sensors to determine the position of the transfer member 16. For example, the control system 50 may include position sensors on the transfer member 16 and / or rotational speed sensors on the transfer member 16 and / or shaft 12. The piston 20 may be hydraulically or pneumatically actuated. It may be advantageous for the piston 20 to be pneumatically actuated, e.g. for the fluid to be compressed air. Utilising air to actuate the piston 20 provides for a smooth, gentle actuation of the piston 20 that can be effectively controlled. Many vehicles are manufactured with a compressed air system, allowing for the retrofitting of the assembly 10 in pre-existing vehicles without requiring to completely reconfigure the fluid supply system 26 (e.g. by adding a new air supply system to the vehicle). The locking arrangement 32 will now be described in more detail with reference to Figures 1 to 5. The locking arrangement 32 includes or may be an interlocking arrangement 32. Such an interlocking arrangement 32 provides a simple means of securing two components (e.g., by pushing and twisting the components relative to each other). Further, once connected such an interlocking arrangement 32 may be able to withstand greater axial separation forces than alternatives, such as snap-fit arrangements. Inhibiting axial separation of the transfer member 16 and the actuation member 18 facilitates the axial movement of the transfer member 16 with the actuation member 18, particularly in the second axial direction (i.e. toward the disconnected position). In this way, disconnection of the gear 14 and the shaft 12 can be effectively achieved. As best illustrated in Figures 2 to 5, the interlocking arrangement 32 includes a connector 34 on the transfer member 16 and a receiver 36 on the actuation member 18. Such a combination of the connector 34 and receiver 36 provides a simple interlocking arrangement 32. In alternative arrangements, the interlocking arrangement 32 includes a connector 34 on the actuation member 18 and a receiver 36 on the transfer member 16. For example, the connector 34 and receiver 36 may be reversed. In other arrangements, the interlocking arrangement 32 includes at least one connector 34 on the transfer member 16, at least one connector 34 on the actuation member 18, at least one receiver 36 on the transfer member 16, and at least one receiver 36 on the actuation member 18. In other words, both the transfer member 16 and the actuation member 18 may have a receiver 36 which is engaged by a connector 34 of the other component, and a connector 34 which engages a receiver 36 of the other component. In some arrangements, the interlocking arrangement 32 includes at least one receiver 36 on the transfer member 16, and at least one receiver 36 on the actuation member 18. In such arrangements, the interlocking arrangement 32 may further include an intermediate component 13 (not shown). In such an arrangement, the intermediate component may include at least one connector 34 for connecting to the at least one receiver 36 of the transfer member 16, and at least one connector 34 for connecting to the at least one receiver 36 of the actuation member 18. It will be understood that, regardless of the particular construction of the interlocking arrangement 32, the arrangement 32 may be configured so that the transfer member 16 is pushed axially towards an axial surface of the actuation member 18 to insert the connector 34 into the corresponding receiver 36, as shown in Figure 3. The transfer member 16 may then be twisted about a central axis L of the actuation member 18 and / or the transfer member 16 (i.e., an axis which is coaxial with the longitudinal axis L of the shaft 12) to form an interlocking engagement between the connector 34 and the corresponding receiver 36, as shown in Figure 4. It will be understood that once the transfer member 16 has been pushed and twisted about the central axis L, the interlocking engagement between the connectors 34 and receivers 36 inhibits axial movement of the transfer member 16 relative to the actuation member 18. In other words, this interlocking engagement allows the transfer member 16 to axially move with the actuation member 18 when the actuation member 18 moves in the first or second axial direction with the piston 20. The connector 34 and the receiver 36 each include one or more interlocking protrusions 38, 40. In the figures, the connector 34 and the receiver 36 each include a plurality of protrusions 38, 40 that are distributed circumferentially about the transfer member 16 and the actuation member 18. In the illustrated arrangement, ten protrusions 38, 40 are provided on each of the connector 34 and receiver 36. In other arrangements, a different number of protrusions 38, 40 may be provided. The connector 34 and receiver 36 may have a corresponding number of interlocking protrusions 38, 40 or may have a different number of interlocking protrusions. In the figures, the protrusions 38 extend radially outwardly from the transfer member 16. The protrusions 40 extend radially inwardly from the actuation member 18. The receiver 36 includes one or more axial recesses 42 positioned adjacent an interlocking protrusion 40 of the receiver 36. The or each axial recess 42 extends axially inboard from a first axial end of the actuation member 18. The receiver 36 further includes a circumferential recess 44 which extends circumferentially from an axially inboard end 42b of the axial recess 42. The or each protrusion 38 of the connector 34 is configured to be received in a respective axial recess 42 of the receiver 36 and in the circumferential recess 44. The arrangement of recesses 42, 44 allows the protrusions 38 of the connector 34 to be pushed along a respective axial recess 42 of the receiver 36 (e.g. by axially moving the transfer member 16 towards the actuation member 18). The connector 34 can then be rotated relative to the receiver 36 so that the or each protrusion 38 of the connector 34 moves along the circumferential recess 44 to locate axially beneath a protrusion 40 of the interlocking receiver 36 to inhibit axial separation of the connector 34 and the receiver 36 and thus the transfer member 16 and the actuation member 18. This provides a simple means of interlocking the transfer member 16 and the actuation member 18, facilitating movement of the transfer member 16 with the actuation member 18 and the piston 20. In the illustrated arrangement, the receiver 36 has a plurality of axial recesses 42. Each axial recess 42 is defined between adjacent protrusions 40 of the receiver 36. Each protrusion 38 of the connector 34 may be configured to be received in a respective axial recess 42 of the receiver 36 and in the circumferential recess 44. In this way, the number of axial recesses 42 may correspond to the number of protrusions 38 of the connector 34. This may not be the case in other arrangements. In the figures, the receiver 36 includes ten axial recesses 42. The circumferential recess 44 may extend circumferentially about the actuation member 18. The circumferential recess 44 may define a closed loop that circumferentially connects adjacent axial recesses 42. As can be best seen in Figure 5, the interlocking arrangement 32 may include a securing element 46. The securing element 46 is configured to restrict circumferential movement of the connector 34 relative to the receiver 36. Restricting such movement reduces the risk of the connector 34 and receiver 36 becoming disconnected during use, ensuring a robust connection and maintaining effective functioning of the assembly 10. The securing element 46 may provided as first and second abutment surfaces 48a, 48b on one or more of the interlocking protrusions 38 of the connector 34. The abutment surfaces 48a, 48b are configured to abut opposing circumferential ends of a respective interlocking protrusion 40 of the receiver 36. The abutment surfaces 48a, 48b may define a thickness in the axial direction that is greater than the axial width of the circumferential recess 44, thereby preventing the connector 34 from rotating within the recess 44. In the figures, the first and second abutment surfaces 48a, 48b include a projection on the respective interlocking protrusion 38 of the connector 34. The projection is defined as a region of increased axial thickness. The projection is provided at or proximal to opposing circumferential ends of the respective protrusion 48. The projection(s) of the figures are defined by a bent or folded region of the respective interlocking protrusion 38 of the connector 34. The bent or folded region is provided at or proximal to opposing circumferential ends of the respective protrusion 38. The connector 34 may include at least one protrusion 38a that defines a larger circumferential length than at least one protrusion 40 of the receiver 36. The receiver 36 may include at least one axial recess 42a that defines a circumferential length that is greater than or equal to the larger circumferential protrusion 38 so as to allow the longer protrusion 38a to be received therein. Once the connector 34 has been twisted relative to the receiver 36 so as to be axially retained, opposing circumferential ends of the at least one protrusion 38a of the connector 34 may extend beyond opposing circumferential ends of the at least one protrusion 40 of the receiver 36, as is shown in Figure 4. The opposing circumferential ends of the at least one protrusion 38 of the connector 34 may then be formed into first and second abutment surfaces 48a, 48b. In the figures, the opposing circumferential ends of the at least one protrusion 38 are bent or folded over (e.g. using a tool or by hand) so as to define respective abutment surfaces 48a, 48b that prevent circumferential movement of the connector 34 (see Figure 5). Alternatives are envisaged in which a pin or other suitable projection is provided at or toward the opposing circumferential ends of the at least one protrusion 38 of the connector 34 so as to serve as the abutment surfaces 48a, 48b. In the illustrated arrangement, the connector 34 includes two protrusions 38a that define a greater circumferential length than the protrusions 40 of the receiver 36. As can be seen in Figure 4, the remaining protrusions 38 of the connector 34 define the same circumferential length of the protrusions 40 of the receiver 36. The receiver 36 includes two axial recesses 42a that have a circumferential length corresponding to that of the longer protrusion 38a. The two protrusions 38a and, by extension, the two recesses 42a are provided on opposing circumferential sides of the connector 34 and receiver 36, respectively, in the figures, e.g. the two protrusions 38a and corresponding recesses 42a may be diametrically opposed. In other arrangements, protrusions 38a and corresponding recesses 42a may be provided in any location on the connector 34. In some arrangements, the connector 34 may be integrally formed with the transfer member 16, e.g. the protrusions 38 may be machined on an outer surface of the transfer member 16. Alternatively, the connector 34 may be provided as a separate component to the transfer member 16. This avoids the need for any protrusions 38 of the connector to be machined in the transfer member 16, allowing the transfer member 16 to be produced via normal manufacturing techniques. In the figures, the connector 34 is an annular locking element 34 that is mounted on the transfer member 16. The annular locking element 34 includes an annular body 34a with one or more connector protrusions 38 extending in a radially outward direction therefrom. As can best be seen in Figure 1, the actuation member 18 includes a radial surface 18b. The radial surface 18b extends from the actuation surface 18a. The radial surface 18b extends over at least a part of an outer radial surface of the transfer member 16. The radial surface 18b may be seen as a radially inner surface of the actuation member 18. The receiver 36 is located on the radial surface 18b. The connector 34 (e.g. the annular locking element 34) is provided on the outer radial surface of the transfer member 16. In this way, the locking element 34 (e.g. the annular locking element 34) locates radially between or is radially interposed between the radial surface 18b of the actuation member 18 and the radially outer surface of the transfer member 16. Such an arrangement is a compact means of securing the components, without occupying significant axial space. Alternative arrangements of the interlocking arrangement 32 are envisaged, for example in which the connector 34 and receiver 36 are axially arranged. In some arrangements, the receiver 36 is machined into the radial surface 18b of the actuation member 18. Alternatively, the receiver 36 may be provided as a separate component that is provided on the radially inner surface 18b of the actuation member 18. The annular locking element 34 may be part-annular or may define a complete annulus. In the figures, the annular locking element 34 defines a closed loop in cross-section. Forming the annular locking element 34 as a complete annulus provides a more secure fit between the transfer member 16 and actuation member 18 compared with other, open loop locking elements, e.g. a circlip. The annular locking element 34 may be configured to be axially moveable relative to the transfer member 16. For example, the annular locking element 34 may be mounted on the transfer member 16 and connected to the actuation member 18 (e.g. via the locking arrangement 32) such that movement of the actuation member 18 with the piston 20 causes movement of the annular locking element 34 over the surface of the transfer member 16. In some arrangements, the annular locking element 34 may be slidable over the outer surface of the transfer member 16. As is best seen in Figure 1, the transfer member 16 may include a shoulder 16d on an outer radial surface of the transfer member 16. The shoulder 16d may be defined as a generally radially outward projection from an outer radial surface of the transfer member 16. The annular locking element 34 may be configured to abut the shoulder 16d upon movement of the actuation member 18 with the piston 20 in the second axial direction. The abutment of the locking element 34 against the shoulder 16d can cause the transfer member 16 to be axially moveable toward the disconnected position upon movement of the annular locking element 34 with the actuation member 18 and piston 20 in the second axial direction. Put another way, contact between the locking element and a region of the transfer member 16 (e.g. the shoulder 16d) alongside continued axial movement of the locking element 34 with the piston 20 can effectively pull the transfer member 16 in the second axial direction, away from or out of engagement with the gear 14 and toward the disconnected position. In this way, the transfer member 16 is positively moveable (e.g. pushed) into the connected configuration upon movement of the piston 20 in the first axial direction, via contact between axial surfaces of the actuation member 18 and the transfer member 16 (e.g. via the bearing 28). The transfer member 16 is also positively moveable (e.g. pulled) into the disconnected configuration upon movement of the piston 20 in the second axial direction, via contact between the annular locking element 34 and a region of the transfer member 16 (e.g. the shoulder 16d), and the continued movement of the annular locking element 34 with the actuation member 18. The annular locking element 34 may be positioned relative the transfer member 16 so as to be axially spaced apart from the shoulder 16d, for example when the transfer member 16 is in the connected position. The locking element 34 may be retained in a position axially spaced apart from the shoulder 16d when the transfer member 16 is in the connected position. This may reduce wear between the locking element 34 and the shoulder 16d, e.g. prevent the locking element 34 from continuously rubbing against the shoulder 16d when the transfer member 16 is engaged. In such an arrangement, the piston 20 and actuation member 18 may be configured to move the locking element 34 away from the shoulder 16d when moving the transfer member 16 into engagement with the gear 14. The locking element 34 may then be retained in a location axially spaced apart from the shoulder 16d by the continued pressure from the piston 20. The annular locking element 34 may be configured to move the transfer member 16 toward the disconnected position via other means in alternative arrangements. For example, the transfer member 16 may include a groove, a cammed arrangement or any formation engageable by the annular locking element 34 upon movement of the locking element 34 relative to the transfer member 16. In some arrangements, the annular locking element 34 may be axially fixed relative to the transfer member 16. For example, the annular locking element 34 may be dimensioned to form an interference fit with the outer radial surface of the transfer member 16. In this way, the transfer member 16 is axially moveable with the locking element 34, and any additional formations or abutment surfaces are not required on the surface of the transfer member 16. As noted above, in some arrangements, the annular locking element 34 and / or the interlocking connector 34 may be integrally formed with the transfer member 16. The transfer member 16 may be machined to include the interlocking protrusions 38 of the connector 34 and thus may be directly connected to the actuation member 18 and be moveable therewith. A brief overview of an example method of engaging and disengaging the gear 14 with the gear assembly 10 will now be discussed with reference to Figure 1. Initially, the transfer member 16 may be in the disconnected position (e.g. as shown in Figure 1), such that no motive force is transferred between the shaft 12 and the gear 14. When it is desired to transfer motive force between the shaft 12 and the gear 14, the control system 50 may instruct the fluid supply system 26 to supply fluid to the first inlet port 24a of the piston housing 24. In response, the piston 20 may move in the first axial direction (e.g. toward the gear 14 in Figure 1). Consequently, the actuation member 18 will move in the first axial direction with the piston 20, and will effectively push against the axial surface 16c of the transfer member 16. The bearing 28 may account for differences of rotational speed of the actuation member 18 and transfer member 16 (e.g. to reduce wear between components and allow for a smooth engagement). The transfer member 16 will be pushed along the spline arrangement of the shaft 12 toward the gear 14, until the teeth 16b of the transfer member 16 engage with the teeth 14a of the gear 14. In this way, the 18 motive force is transferred from the gear 14 to the shaft 12, via the transfer member 16 that is mounted to the shaft 12. At this point, the control system 50 may instruct the fluid supply system 26 to reduce the pressure of the fluid supplied to the first inlet port 24a (e.g. to a "holding" pressure) so as to hold the piston 20 in position without continuing to move the piston 20. When it is desired to cease transfer of motive force between the shaft 12 and the gear 14, the control system 50 may instruct the fluid supply system to supply fluid to the second inlet port 24b (e.g. and cease supplying fluid to the first port 24a). The piston 20 may subsequently move in the second axial direction (e.g. away from the gear 14 in Figure 1). The actuation member 18 will then move in the second axial direction with the piston 20. The locking arrangement 32 will then force the transfer member 16 to move with the actuation member 18 away from the gear 14. In the illustrated arrangement, axial movement of the actuation member 18 in the second axial direction causes the annular locking element 34 to slide over the outer surface of the transfer member 16 until the locking element 34 abuts against the shoulder 16d. This abutment causes the transfer member 16 to be forcefully pulled in the second axial direction along the splines 12a of the shaft 12 away from the gear 14, until the transfer member 16 is disengaged therefrom. Referring to Figure 6, a means of lubricating the gear assembly 10 is indicated. In the figure, the shaft 12 includes a first passageway 52 extending longitudinally therethrough and a second passageway 54 extending radially therethrough between the first passageway 52 and an outer radial surface of the shaft 12. The first passageway 52 may be in fluid communication with a lubricant supply system (not shown), e.g. an oil supply system, in order for a lubricant to be supplied to the first passageway 52 and the second passageway 54. The second passageway 54 may formed by an annular groove in the shaft 12. The annular groove may extend through the splines 12a on the shaft such that a lubricant can lubricate the splines 12a. The transfer member 16 may include one or more radially extending passageways 56, 58. The one or more radially extending passageways 56, 58 are configured to extend through a region of the transfer member 16 toward the bearing 28. The one or more radially extending passageways 56, 58 are configured to be in fluid communication with a lubricant supply system (not shown), such that lubricant can flow through the one or more passageways 56, 58 toward the bearing 28 so as to lubricate the bearing 28. The one or more radially extending passageways 56, 58 are arranged to align with the second passageway 54 of the shaft 12. In this way, the first and second passageways 52, 54 of the shaft 12 and the one or more passageways 56, 58 of the transfer member 16 can form a lubricant flow path through the shaft 12, through the splines 12a, through the transfer member 16 and toward the bearing 28. In the figures, the transfer member 16 includes two radially extending passageways 56, 58 that are longitudinally spaced apart from one another. The first of the passageways 56 may be positioned to align with the second passageway 54 of the shaft 12 when the transfer member is in the disconnected position. The second of the passageways 58 may be positioned to align with the second passageway 54 of the shaft 12 when the transfer member is in the connected position. In this way, a flow path for lubricant is provided irrespective of the position of the transfer member 16, providing effective lubrication to the bearing 28 during operation of the gear assembly 10. In the figure, the transfer member 16 is in the disconnected position, and the fluid flow path is indicated by the arrows through the first of the passageways 56 of the transfer member 16. Although not shown in this figure, it will be understood from Figure 1 that the lubricant may pass through the bearing 28 and move toward the locking arrangement 32 (e.g. via the centrifugal force generated by the rotating components) to provide lubrication thereto. Referring now to Figure 7, an alternative embodiment of the gear assembly is indicated generally at 100. The gear assembly 100 is similar to the gear assembly 10 of Figures 1 to 6, and so only the differences will be discussed in detail. The vehicle gear assembly 100 may include any or all of the features of the assembly 10 of Figure 1, but may further include a second gear 140 axially spaced apart from the gear 14, the second gear 140 configured to selectively engage with the shaft 12 to transfer rotational movement between the second gear 140 and the shaft 12 when engaged. The gear assembly 100 may also include a second transfer member 160 mounted on the shaft 12 so as to be rotationally coupled therewith. The second transfer member 160 may be axially moveable between a connected position in which the second transfer member 160 is engaged with the second gear 140 so as to transfer the motive force between the second gear 140 and the shaft 12, and a disconnected position, in which the second transfer member 160 is disengaged from the second gear 140. The assembly 100 may include a second actuation member 180 coupled to the second transfer member 160. The second actuation member 180 is configured to move the second transfer member 160 between the connected position and the disconnected position. A second piston 200 may be provided that is moveable relative to the shaft 12 in the first axial direction and the second axial direction. The second piston 200 is coupled to the second actuation member 180 such that the second actuation member 180 is moveable in first and second axial directions therewith. The second piston 200 may be arranged to extend circumferentially about the shaft 12. A second locking arrangement 320 configured to couple the second actuation member 180 and the second transfer member 160 is provided. The second locking arrangement 320 is configured such that the second transfer member 160 is axially moveable towards the disconnected position upon a movement of the second piston 200 in the first axial direction. In the figure, the second transfer member 160, second actuation member 180, second piston 200 and second locking arrangement 320 are arranged substantially symmetrically relative to the transfer member 16, actuation member 18, piston 20 and locking arrangement 32 about a plane of symmetry X extending radially between the first and second piston 20, 200. It should 20 be understood that the term "substantially symmetrical" refers to the components being arranged similarly relative to each other on opposing longitudinal ends of the shaft 12. The components may not be spaced apart in exactly the same way, or be exactly the same size (e.g. the gears 14, 140 may be differently sized), but a similar arrangement of the components may be provided on the shaft 12. In alternative arrangements, the components may not be arranged symmetrically on the shaft. The double gear arrangement of Figure 7 facilitates a single shaft 12 being engageable with either gear 14, 140, making use of limited axial space in the vehicle 1000 (e.g. in a gearbox) to select between two different gears. The substantially symmetrical arrangement improves the balance and stability of the shaft 12. The second transfer member 160, second actuation member 180, second piston 200 and second locking arrangement 320 may be substantially the same as the transfer member 16, actuation member 18, piston 20 and locking arrangement 32 as described in relation to Figures 1 to 6. For example, the second locking arrangement 320 may include a connector 340 on the second transfer member 160 and a receiver on the second actuation member 180. The assembly 100 of Figure 7 may include any of the features discussed in relation to Figures 1 to 6. For example, as shown in the figures, a second thrust bearing 280 may be interposed between the second transfer member 160 and the second actuation member 180. A second roller bearing 300 may be provided between the second gear 140 and the shaft 12. A second splined arrangement may be provided to facilitate axial movement of the second transfer member 160 relative to the shaft 12. A second piston housing 240 may be provided to house the second piston 200. The second piston housing 240 may include first and second inlet ports 240a, 240b to control the movement of the second piston 200. In the illustrated arrangement, the second piston housing 240 and first piston housing 24 are integrally formed, so as to share a central wall that separates the two pistons 20, 200. The central wall may define the plane of symmetry between the components at opposing ends of the shaft 12. The second locking arrangement 320 may be substantially the same as that described herein. The lubrication supply arrangement described in relation to Figure 6 may be provided to both ends of the shaft 12, i.e. through both transfer members 16, 160 and to both bearings 28, 280. It will be understood that any features described in relation to Figures 1 to 6 may be introduced into the assembly 100 of Figure 7, to both or either arrangement of components at opposing ends of the shaft 12. In Figure 7, the assembly 100 includes a single fluid supply system 26 and control system 50 to supply fluid to various positions of the respective piston housings 24, 240. In alternative arrangements, multiple fluid supply systems may be provided (e.g. one for each port). The control system 50 may be configured to control the supply of fluid to the pistons 20, 200. The control system 50 is configured to control the supply of fluid provided by the system 26. The control system 50 may instruct the supply of fluid to move the first piston 20 in the first axial direction when it is desired that motive force is transferred between the gear 14 and the shaft 12. The control system 50 may instruct the supply of fluid to move the second piston 200 in the second axial direction when it is desired that motive force is transferred between the second gear 140 and the shaft 12. The control system 50 may be configured to control the fluid supply system 26 such that the second transfer member 160 is in the disconnected position when the transfer member 16 is in the connected position, and such that the transfer member 16 is in the disconnected position when the second transfer member 160 is in the connected position. In this way, both gears 14, 140 are never engaged at the same time, avoiding damage to the vehicle 1000. In an example arrangement, the control system 50 may be configured to instruct the fluid supply system 26 to introduce fluid into the second inlet port 240b of the second piston housing 240 at the same time as instructing the supply system 26 to introduce fluid into the first inlet port 24a of the first piston housing 24. In this way, the second transfer member 160 is moved toward and / or held in the disconnected position (e.g. the second piston 200 is moved in the first axial direction away from the second gear 140), when the transfer member 16 is moved toward and / or held in the connected position (e.g. the first piston 20 is moved in the first axial direction toward the first gear 14). Similarly, the control system 50 may be configured to instruct the fluid supply system 26 to introduce fluid into the second inlet port 24b of the piston housing 24 at the same time as instructing the system 26 to introduce fluid into the first inlet port 240a of the second piston housing 240. In this way, the transfer member 16 is moved toward and / or held in the disconnected position (e.g. the piston 20 is moved in the second axial direction away from the gear 14), when the second transfer member 160 is moved toward and / or held in the connected position (e.g. the piston 200 is moved in the second axial direction toward the second gear 140). The control system 50 is thus configured to prevent a scenario in which both gears 14, 140 are engaged by the respective transfer members 16, 160 at the same time. A vehicle 1000 is indicated schematically in Figure 8. As can be seen, the vehicle 1000 includes the gear assembly 10, 100 of any of Figures 1 to 7. The respective gear assembly may be provided in a gearbox housing 60. It will be understood that the gear assembly may not be entirely contained in the housing 60 in some arrangements. For example, the shaft 12 may extend beyond the housing 60 (e.g. to connect to one or more wheels or a prime mover of the vehicle 1000). It will be appreciated that the components other than the shaft 12 may be completely located in the housing 60. The gear assembly 10, 100 may be coupled with one or more wheels of the vehicle 1000. The vehicle 1000 may be an automotive vehicle, e.g. a car. The gear assembly 10, 100 may be coupled with an internal combustion engine of the vehicle 1000. In some arrangements, the vehicle is a heavy goods vehicle (HGV). The vehicle may be an electric vehicle or a hybrid vehicle. In such an arrangement, the gear assembly 10, 100 may be coupled with an electric drive unit of the vehicle. A method of gear selection and deselection in a vehicle 1000 is illustrated in Figure 9. The method includes the following steps: a) providing a gear assembly as has been described; b) introducing fluid to the piston so as to move the piston in the first axial direction, thereby moving the actuation member and the transfer member in the first axial direction such that the transfer member engages with the gear and motive force is transferred between the shaft and the gear; and / or c) introducing fluid to the piston so as to move the piston in the second axial direction, thereby moving the actuation member and transfer member in the second axial direction such that the transfer member is disengaged from the gear and motive force is not transferred between the shaft and the gear. Step (b) may include supplying a fluid to a first location of a piston housing so as to move the piston in the first axial direction. Step (c) may include supplying a fluid to a second location of a piston housing so as to move the piston in the second axial direction. The locking element may be an interlocking arrangement, e.g. the annular locking element as described. It will be appreciated that various changes and modifications can be made to the present invention without departing from the scope of the present application. It should also be noted that whilst the appended claims set out particular combinations of features described above, the scope of the present disclosure is not limited to the particular combinations hereafter claimed, but instead extends to encompass any combination of features herein disclosed.

Claims

1. A gear assembly for a vehicle, the gear assembly comprising:a shaft having a longitudinal axis;a gear configured to selectively engage with the shaft to transfer a motive force between the gear and the shaft when engaged;a transfer member mounted on the shaft so as to be rotationally coupled therewith, the transfer member axially moveable between a connected position, in which the transfer member is engaged with the gear so as to transfer motive force between the gear and the shaft, and a disconnected position, in which the transfer member is disengaged from the gear;an actuation member coupled to the transfer member, wherein the actuation member is configured to move the transfer member between the connected position and the disconnected position;a piston moveable relative to the shaft in a first axial direction and a second axial direction, the piston coupled to the actuation member such that the actuation member is moveable in first and second axial directions therewith, wherein the piston is arranged to extend circumferentially about the shaft; anda locking arrangement configured to couple the actuation member and the transfer member, the locking arrangement configured such that the transfer member is axially moveable towards the disconnected position upon movement of the piston in the second axial direction.

2. The gear assembly according to claim 1, wherein the locking arrangement comprises an interlocking arrangement.

3. The gear assembly according to claim 2, wherein the interlocking arrangement comprises a connector on the transfer member and a receiver on the actuation member.

4. The gear assembly according to claim 3, wherein the connector and the receiver each comprise one or more interlocking protrusions.

5. The gear assembly according to claim 4, wherein the receiver comprises one or more axial recesses positioned adjacent an interlocking protrusion of the receiver, the or each axial recess extending axially inboard from a first end of the actuation member, wherein the receiver further comprises a circumferential recess which extends circumferentially from an axially inboard end of the axial recess, and wherein the or each protrusion of the connector is configured to be received in a respective axial recess of the receiver and in the circumferential recess.

6. The gear assembly according to claim 4 or claim 5, wherein the interlocking arrangement comprises a securing element configured to restrict circumferential movement of the connector relative to the receiver.

7. The gear assembly according to claim 6, wherein the securing element is provided as first and second abutment surfaces of one of the one or more interlocking protrusions of the connector, the abutment surfaces configured to abut opposing circumferential ends of a respective one of the one or more interlocking protrusions of the receiver.

8. The gear assembly according to claim 7, wherein the first and second abutment surfaces each comprise a projection on the respective one of the one or more interlocking protrusions of the connector at or proximal to opposing circumferential ends thereof; optionally, wherein the projection is defined by a bent or folded region of the respective one of the one or more interlocking protrusions.

9. The gear assembly according to any of claims 3 to 8, wherein the connector is an annular locking element mounted on the transfer member.

10. The gear assembly according to claim 9, wherein the annular locking element is configured to abut a shoulder on an outer radial surface of the transfer member upon movement of the piston in the second axial direction, such that the transfer member is axially moveable toward the disconnected position upon movement of the annular locking element with the piston in the second axial direction.

11. The gear assembly according to claim 9, wherein the annular locking element is dimensioned to form an interference fit with an outer radial surface of the transfer member.

12. The gear assembly according to any of claims 9 to 11, wherein the annular locking element comprises an annular body and a plurality of protrusions extending in a radially outward direction from the annular body.

13. The gear assembly according to any of claims 9 to 12, wherein the annular locking element defines a closed loop in cross section.

14. The gear assembly according to any of claim 9 to 13, wherein the actuation member comprises a first surface extending over at least part of an outer radial surface of the transfer member, wherein the receiver is provided on the first surface, and wherein the annular locking element is mounted on the transfer member so as to locate radially between the first surface of the actuation member and the transfer member.2515. The gear assembly according to any preceding claim, wherein the actuation member comprises an actuation surface configured to engage with an axial surface of the transfer member upon a movement of the piston in the first axial direction, such that the transfer member is moveable toward the connected position upon movement of the actuation member with the piston in the first axial direction.

16. The gear assembly according to claim 15, further comprising an axial thrust bearing interposed between the actuation surface of the actuation member and the axial surface of the transfer member.

17. The gear assembly according to any preceding claim, wherein the piston extends around the whole circumference of the shaft.

18. The gear assembly according to any preceding claim, wherein the piston is pneumatically actuated.

19. The gear assembly according to any preceding claim, further comprising a piston housing configured to house the piston, wherein the piston housing comprises a first inlet port configured to introduce a fluid to drive the piston in the first axial direction, and a second inlet port configured to introduce a fluid to drive the piston in the second axial direction.

20. The gear assembly according to any preceding claim, wherein the actuation member is received in a groove on an outer surface of the piston.

21. The gear assembly according to any preceding claim, wherein the transfer member is a dog clutch component having a plurality of axially extending teeth configured to selectively engage with corresponding teeth of the gear.

22. The gear assembly according to any preceding claim, wherein the gear is mounted on the shaft via a roller bearing; optionally, wherein the roller bearing is a needle roller bearing.

23. The gear assembly according to any preceding claim, further comprising:a second gear axially spaced apart from the gear, the second gear configured to selectively engage with the shaft to transfer a motive force between the second gear and the shaft when engaged;a second transfer member mounted on the shaft so as to be rotationally coupled therewith, the second transfer member axially moveable between a connected position, in which the second transfer member is engaged with the second gear so as to transfer the motive force 26between the second gear and the shaft, and a disconnected position, in which the second transfer member is disengaged from the second gear;a second actuation member coupled to the second transfer member, wherein the second actuation member is configured to move the second transfer member between the connected position and the disconnected position;a second piston moveable relative to the shaft in the first axial direction and the second axial direction, the second piston coupled to the second actuation member such that the second actuation member is moveable in first and second axial directions therewith, wherein the second piston is arranged to extend circumferentially about the shaft; anda second locking arrangement configured to couple the second actuation member and the second transfer member, the second locking arrangement configured such that the second transfer member is axially moveable towards the disconnected position upon a movement of the second piston in the first axial direction;wherein the second transfer member, second actuation member, second piston and second locking arrangement are arranged substantially symmetrically relative to the transfer member, actuation member, piston and locking arrangement about a plane of symmetry extending radially between the first and second piston.

24. The gear assembly according to claim 23, further comprising a fluid supply system for supplying fluid to move the pistons, and a control system configured to control the supply of fluid to the pistons, wherein the control system is configured to control the fluid supply system such that the second transfer member is in the disconnected position when the transfer member is in the connected position, and such that the transfer member is in the disconnected position when the second transfer member is in the connected position.

25. A vehicle comprising the gear assembly according to any preceding claim.

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