Baffle for a gear system

Abstract

A radial baffle 21 in an electric vehicle gear system, mounted stationary relative to a gear 5 with a fluid flow outlet directed toward the edge of the gear, such that when the system is in use fluid

Description

TECHNICAL FIELD The present disclosure relates to a baffle for a gear system and a differential. Aspects of the invention relate to a radial baffle, a radial baffle system, an electric vehicle gear system, an electric vehicle differential, and to an electric vehicle. BACKGROUND It is known to provide shields and housings around rotating vehicle components which have lubricant or coolant supplied to them. These shields and housings may help to keep fluids in the vicinity of the rotating components and may also be used to control or prevent the flow of fluid to other components. It is also known to provide fluid supply networks to supply lubricants or coolants to intended places within a vehicle drivetrain. These networks sometimes supply fluid to the general vicinity of the rotating component. 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 radial baffle, a radial baffle system, an electric vehicle differential and an electric vehicle, some of which are as claimed in the appended claims. According to an aspect of the present invention there is provided a radial baffle fora vehicle gear system which has a rotatable gear, the radial baffle comprising a fluid flow surface with a flow outlet end, wherein the fluid flow surface faces, e.g., in a direction towards, a circumferential periphery of the rotatable gear, in use. The radial baffle may comprise a fixing portion for fixing the radial baffle to the structure such that the fluid flow surface faces, e.g., in a direction towards, a circumferential periphery of the rotatable gear, in use. The fixing portion and fluid flow surface may be configured such that, when in use in the electric vehicle gear system, fluid flowing from the outlet end of the flow surface is directed towards the rotatable gear. Another aspect of the invention provides a radial baffle for an electric vehicle gear system where the electric vehicle gear system comprises a rotatable gear and a structure which is stationary relative to the rotatable gear, the radial baffle comprising: a fluid flow surface with a flow outlet end; and a fixing portion for fixing the radial baffle to the structure such that the fluid flow surface faces, e.g., in a direction towards, a circumferential periphery of the rotatable gear, in use; wherein the fixing portion and fluid flow surface are configured such that, when in use in the electric vehicle gear system, fluid flowing from the outlet end of the flow surface is directed towards the rotatable gear. Advantageously, when the radial gear baffle is in situ next to the rotating gear, air flow generated by the rotating gear, as well as fluid flung from the rotating gear, may be guided by the fluid flow surface and directed to back onto the rotating gear. The rotatable gear may be a helical gear. A radius of curvature of the fluid flow surface may change with position along the fluid flow surface. The fluid flow surface may have a substantially planar portion leading to the flow outlet end. The fluid flow surface may have a lower curvature portion starting with the flow inlet end and a higher curvature portion between the lower curvature portion and the planar portion or the flow outlet end. Advantageously, fluid flow may be received on the fluid flow surface after leaving the rotatable gear and then directed back, onto the rotatable gear, in use. The radial baffle may comprise a sidewall extending from either side of the fluid flow surface in a direction which is towards the rotatable gear, in use. The radial baffle may provide a fluid flow conduit. The radial baffle may comprise a base wall connecting the sidewalls together. The radial baffle may provide an enclosed fluid flow conduit. Advantageously, fluid may be retained proximal to the rotatable gear for re-entry onto to gear. A cross-sectional area of the fluid flow conduit may be smaller at the flow outlet end of the fluid flow surface than at the fluid flow inlet end of the fluid flow surface. Advantageously, a lot of fluid may enter the fluid flow conduit due to the larger cross-sectional area at the flow inlet end. A cross-sectional area of the fluid flow conduit may be smallest at the flow outlet end of the fluid flow surface. Advantageously, fluid may be focussed onto the rotatable gear. The fixing portion and fluid flow surface may be configured such that, when in use in the electric vehicle gear system, fluid flow is directed from the fluid flow surface with a principal flow direction which converges with a tangent, closest to the flow outlet end, of a reference circle which is representative of an outer diameter of the rotatable gear. It will be understood that the principal flow direction may refer to the main flow direction, or the flow direction along which the majority of fluid flow rate occurs. The reference circle may be a reference circle which passes through the tip of each radial tooth of the gear or which defines a radial extent of the gear. Advantageously, the convergence between the principal flow direction and the rotatable gear may mean that any fluid present in the fluid flowing along the fluid flow surface is moved onto the circumferential periphery of the rotatable gear to offer more lubrication and / or cooling. The fluid flow surface may have a flow inlet end. The fixing portion and fluid flow surface may be configured such that, when in use in the electric vehicle gear system, a principal flow direction entering the fluid flow surface at the flow inlet end converges with a tangent, closest to the flow inlet end, of a reference circle which is representative of an outer diameter of the rotatable gear. Advantageously, fluid may be directed back to the rotatable gear, in use. The base wall may provide a secondary fluid flow surface, i.e., along an outer surface thereof. The second fluid flow surface may face, e.g., in a direction towards, the rotatable gear, in use. The secondary fluid flow surface may comprise a flow inlet end and a concave section which is concaved facing the rotatable gear, in use. The concave section may comprise an end corresponding to the flow outlet end. Advantageously, fluid may be directed back, to the rotatable gear, in use. The secondary fluid flow surface may comprise an end corresponding to the flow inlet end. The concave section may be an accumulation section. The accumulation section may comprise an end corresponding to the flow outlet end. With distance along the accumulation section in a direction from the end corresponding to flow inlet end to the end corresponding to the flow outlet end, a distance may increase between the secondary fluid flow surface and the reference circle or the central axis of the rotatable gear to a maximum distance, and then the distance may decrease between the secondary fluid flow surface and the central axis orthe reference circle of the rotatable gear, when the radial baffle is in use in the electric vehicle gear system. Advantageously, the shape of the secondary fluid flow surface in the concave or accumulation section may allow a steeper gradient at the end corresponding to the flow outlet end, to direct fluid more directly to the desired location on the rotatable gear. The secondary fluid flow surface may comprise a converging section which comprises an end corresponding to the flow inlet end of the fluid flow surface. A distance between the secondary fluid flow surface and the central axis or the reference circle of the rotatable gear may decrease with distance along the converging section from the end corresponding to the flow inlet end. Advantageously, more fluid may be guided into the area between the secondary fluid flow surface and the rotatable gear. The secondary fluid flow surface may comprise a parallel section between the converging section and the concave section. A distance between the secondary fluid flow surface and the central axis or the reference circle of the rotatable gear may be constant over the parallel section, when the radial baffle is in use in the electric vehicle gear system. The parallel section may otherwise be referred to as a concentric section. The concentric section may have a radius of curvature which is concentric with the reference circle of the rotatable gear. Advantageously, laminar flow may be established over the parallel section, creating less drag on the rotatable gear. The rotatable gear may be a first rotatable gear which is meshed with a second rotatable gear. The radial baffle may be for an electric vehicle system where the electric vehicle system has a first rotatable gear meshed with a second rotatable gear. The fixing portion may be for fixing the radial gear baffle to the structure such that the fluid flow surface faces, e.g., in a direction towards, the circumferential periphery of the first rotatable gear. The fixing portion and fluid flow surface may be configured such that, when in use in the electric vehicle gear system, fluid flowing from the outlet end of the flow surface is directed towards a meshed location, for example to a location in the vicinity, between the first rotatable gear and the second rotatable gear. Advantageously, any air and liquid being guided by the flow surface may be directed to a location where the gears are meshed together. This may be beneficial in that the liquid is recirculated to the meshed location. Furthermore, this may be especially beneficial when there is a liquid nozzle directing liquid to the meshed location, because the radial gear baffle may shield the flow of liquid from air flow generated by the rotating gear as well as any liquid flung from the rotating gear, which would otherwise disrupt the flow of liquid. Furthermore, directing any air and liquid to the meshed location like this may act to entrain liquid flowing from the liquid nozzle, to reinforce liquid flow to the meshed location. The first rotatable gear may be a helical gear. The second rotatable gear may be a helical gear. When the radial baffle is in use in the electric vehicle gear system, a distance between the fluid flow surface and a central axis of the, or the first, rotatable gear may change with position along the fluid flow surface. Advantageously, the fluid flow surface may be shaped to provide improved flow characteristics to the fluid to direct the fluid to a desired location on the rotatable gear. The fluid flow surface may comprise a flow inlet end. When the radial baffle is in use in the electric vehicle gear system, a distance between the flow inlet end and a central axis of the, or the first, rotatable gear may be greater than a distance between the flow outlet end and the central axis of the, or the first, rotatable gear. Advantageously the fluid leaving the outlet end may be closer to a target location and so be more accurate, and have less of an effect on other lubricant flow. Another aspect of the invention provides an electric vehicle gear system comprising: a rotatable gear; a structure which is stationary relative to the rotatable gear; the aforementioned radial baffle; wherein the fluid flow surface of the radial baffle faces, e.g., in a direction towards, a circumferential periphery of the rotatable gear; and wherein the fixing portion and fluid flow surface are configured such that, when in use, fluid flowing from the outlet end of the flow surface is directed towards the rotatable gear. The rotatable gear may be the rotatable gear comprised in the electric vehicle system that the aforementioned radial baffle is for. The rotatable gear may be a first rotatable gear, and the electric vehicle system may comprise a second rotatable gear meshed with the first rotatable gear. The first rotatable gear may be the first rotatable gear comprised in the electric vehicle system that the aforementioned radial baffle is for. The second rotatable gear may be the second rotatable gear comprised in the electric vehicle system that the aforementioned radial baffle is for. Another aspect of the invention provides a radial baffle system for an electric vehicle gear system, where the electric vehicle gear system comprises a first rotatable gear which is meshed with a second rotatable gear, and where the electric vehicle gear system comprises a structure which is stationary relative to the first and second rotatable gears, the radial baffle system comprising: a first radial baffle which is one of, or which has features of one of, the aforementioned radial baffles, the fluid flow surface of the first radial baffle facing, e.g., in a direction towards, a circumferential periphery of the first rotatable gear, in use; a second radial baffle which is one of, or which has features of one of, the aforementioned radial baffles, the fluid flow surface of the second radial baffle facing, e.g., in a direction towards, a circumferential periphery of the second rotatable gear, in use; wherein the fixing portion and fluid flow surface of each first and second radial baffle are configured such that, when in use in the electric vehicle gear system, fluid flowing from the outlet end of the flow surface of each radial baffle is directed towards a meshed location between the first and second rotatable gear. The first radial baffle may be bigger than the second radial baffle. The aforementioned advantages may be realised for two rotatable gears which are meshed together. The first radial baffle and the second radial baffle may be configured, when the radial baffle system is in use in the electric vehicle gear system, such that an unobstructed passage is provided therebetween fora flow of lubricant to pass through. The unobstructed passage may be along a tangent to the first and second rotatable gears at a meshed location. The first radial baffle and the second radial baffle may be a unitary component. The passage may be an aperture through the unitary component. Advantageously, lubricant may still be provided to the meshed location despite the presence of the radial baffles. The radial baffle system may comprise a lubricant supply outlet or lubricant nozzle configured to provide a flow of lubricant to the meshed location between the first and second rotatable gears. Another aspect of the invention provides an electric vehicle gear system comprising: a first rotatable gear; a second rotatable gear meshed with the first rotatable gear; the aforementioned radial baffle system; wherein the fluid flow surface of the first radial baffle faces, e.g., in a direction towards, a circumferential periphery of the first rotatable gear, the fluid flow surface of the second radial baffle faces, e.g., in a direction towards, a circumferential periphery of the second rotatable gear; and wherein the fixing portion and fluid flow surface of each radial baffle are configured such that, when in use, fluid flowing from the outlet end of each fluid flow surface is directed towards a meshed location between the first and second rotatable gears. The first rotatable gear may be the first rotatable gear comprised in the electric vehicle system that the aforementioned radial baffle system is for. The second rotatable gear may be the second rotatable gear comprised in the electric vehicle system that the aforementioned radial baffle system is for. The electric gear vehicle system may comprise a lubricant supply outlet or a lubricant nozzle configured to supply a flow of lubricant to the meshed location between the firstand second rotatable gears. Advantageously, this may lubricate and cool the gears at the meshed location. The first rotatable gear may be a ring gear of a differential of an electric vehicle. The second rotatable gear may be a pinion gear which transfers rotational power from an electric motor to the ring gear, in use. The electric motor may provide motive power to the electric vehicle. Advantageously, wear caused by high speed rotation of such gears may be reduced by the baffle. Another aspect of the invention provides an electric vehicle differential comprising the aforementioned electric vehicle system. The first rotatable gear may be a ring gear of a differential of an electric vehicle. The second rotatable gear may be a pinion gear which transfers rotational power from an electric motor to the ring gear, in use. The differential may comprise an axial shield located on an axial side of a ring gear of the differential. A radial extent of the axial shield, relative to a central axis of the ring gear, may be at least equal to an outer radius of the ring gear. The axial shield may be unitary with the, or the first, radial baffle. The axial shield may be unitary with any of the aforementioned radial baffles. Any of the aforementioned radial baffles may comprise a plastic material, for example a moulded plastic material, for example an injection moulded plastic component. Any of the aforementioned radial baffles may comprise a fibre reinforced plastic (FRP). Any of the aforementioned radial baffles may comprise metal, for example stamped or pressed metal sheet. Advantageously, the baffles may be lightweight and easily installed. Another aspect of the invention provides an electric vehicle comprising any one of the aforementioned radial baffles, any one of the aforementioned electric vehicle gear systems, any one of the aforementioned radial baffle systems, or the aforementioned electric vehicle differential. Another aspect of the invention provides an electric vehicle differential comprising an axial shield and a ring gear, the axial shield located on an axial side of the ring gear. A radial extent of the axial shield, relative to a central axis of the ring gear, may be at least equal to an outer radius of the ring gear. Another aspect of the invention provides an electric vehicle differential comprising an axial shield and a ring gear, the axial shield located on an axial side of the ring gear, a radial extent of the axial shield, relative to a central axis of the ring gear, being at least equal to an outer radius of the ring gear. It will be appreciated that the ring gear has the usual meaning, namely the gear of the differential which is first gear in the differential to receive motive power from a drive unit, for example an electric traction motor, an internal combustion engine or a hybrid power unit, in use. Advantageously, windage and lubricant spray leaving the ring gear in an axial direction, in use, may be intercepted by the axial shield. This may be beneficial in that the sprayed lubricant can be redirected for use. This may also be beneficial in that other components can be protected from windage and spray, such as flow of lubricant from a nearby lubricant supply outlet or lubricant nozzle. The differential may be a four-pin bevel gear differential comprising a plurality of differential gears. The plurality of differential gears may be four differential bevel gears. The differential gears may alternatively be referred to as side gears. The electric vehicle differential may comprise a differential gear casing attached to the ring gear such that the differential gear casing extends from a side of the ring gear and rotates with the ring gear, in use. The electric vehicle differential may comprise a plurality of differential gears rotatably mounted inside of the differential gear casing. The axial shield may be located on a side of the ring gear which the differential gear casing extends from. Advantageously, lubricant may be provided to the differential gears without being affected by windage and / or lubricant spray in an axial direction, from the ring gear. The electric vehicle differential may comprise two axle gears. Each axle gear may be for rotationally mounting to an end of a respective axle. Each axle gear may be meshed with each of the plurality of differential gears. The electric vehicle differential may comprise a lubricant supply outlet or a lubricant nozzle arranged to provide a flow of lubricant to the plurality of differential gears, in use. The axial shield may be located, along an axial direction of the ring gear, between the ring gear and the lubricant supply outlet or lubricant nozzle. Advantageously flow of lubricant from the lubricant supply outlet may be protected from windage and / or lubricant spray, in an axial direction, from the ring gear. The axial shield may be mounted to the differential gear casing. Advantageously, the differential gear casing may have more design versatility than any of the gears, and so mounting the axial shield to the differential gear casing may simplify design, manufacture and assembly of the electric vehicle differential. The axial shield may be mounted to the ring gear. Advantageously, the axial shield may be configurable such that any lubricant caught by the axial shield is directed back to the ring gear. An outer periphery of the axial shield may be circular. The axial shield may be substantially annular in shape. The axial shield may be mounted to a structure which is stationary relative to the ring gear when the ring gear is rotating. Advantageously, the structure may have more design versatility than any of the gears, and so mounting the axial shield to the structure may simplify design, manufacture and assembly of the electric vehicle differential. The electric vehicle differential may comprise a housing. The axial shield may be mounted to the housing. Advantageously, the differential housing may have more design versatility than any of the gears, and so mounting the axial shield to the structure may simplify design, manufacture and assembly of the electric vehicle differential. The axial shield may be spaced from the ring gear. Advantageously, lubricant sprayed from the rotating ring gear may be captured by the axial shield and directed to a required location, for example back to the ring gear. The electric vehicle differential may comprise an annular channel. A first sidewall of the annular channel may be provided by the axial shield. A second sidewall of the annular channel may be provided be the ring gear. The annular channel may have a radially outward facing base wall for lubricant to flow along. Advantageously, lubricant which is flung from the ring gear may be caught by the axial shield and may flow along the annular channel to a desired location. The ring gear may be a helical gear. The axial shield may be especially beneficial for a helical gear, because helical gears generate more axial windage than some non-helical gears. The electric vehicle differential may comprise a helical pinion gear which is meshed with the helical ring gear, and which is configured to drive the helical ring gear. The electric vehicle differential may comprise a radial baffle. The radial baffle may be any of the aforementioned radial baffles. The radial baffle may comprise a fluid flow surface with a flow outlet end. The radial baffle may comprise a fixing portion for fixing the radial baffle to a or the structure which is stationary relative to the rotating ring gear, in use, such that the fluid flow surface faces, e.g., in a direction towards, a circumferential periphery of the ring gear. The fixing portion and fluid flow surface may be arranged such that, when in use, fluid flowing from the outlet end of the flow surface is directed towards the ring gear. Advantageously, when the radial baffle is in situ next to the ring gear, air flow generated by the rotating ring gear, as well as lubricant flung from the rotating ring gear, may be guided by the fluid flow surface and directed to back onto the ring gear. The fixing portion and fluid flow surface may be arranged such that, when in use, fluid flowing from the outlet end of the flow surface is directed towards a meshed location between the helical ring gear and the helical pinion gear. Advantageously, any air and lubricant being guided by the flow surface may be directed to a location where the gears are meshed together. This may be beneficial in that the lubricant is recirculated to the meshed location. Furthermore, this may be especially beneficial when there is a lubricant supply outlet directing lubricant to the meshed location, because the radial baffle may shield the flow of lubricant from air flow generated by the rotating gear as well as any lubricant flung from the rotating gear, which would otherwise disrupt the flow of lubricant. Furthermore, directing any air and lubricant to the meshed location like this may act to entrain lubricant flowing from the lubricant supply outlet, to reinforce lubricant flow to the meshed location. The ring gear may be the aforementioned rotatable gear, or the aforementioned first rotatable gear. The electric vehicle differential may comprise a radial baffle system. The radial baffle system may be any of the aforementioned radial baffle systems. The radial baffle system may comprise a first radial baffle. The first radial baffle may be any of the aforementioned radial baffles. The first radial baffle may comprise a fluid flow surface with a flow outlet end, and a fixing portion for fixing the first radial baffle to a or the structure which is stationary relative to the rotating ring gear, in use, the fluid flow surface of the first radial baffle facing, e.g., in a direction towards, a circumferential periphery of the ring gear. The radial baffle system may comprise a second radial baffle. The second radial baffle may be any of the aforementioned radial baffles. The second radial baffle may comprise a fluid flow surface with a flow outlet end, and a fixing portion for fixing the second radial baffle to a or the structure which is stationary relative to the rotating pinion gear, in use, the fluid flow surface of the second radial baffle facing, e.g., in a direction towards, a circumferential periphery of the pinion gear. The fixing portion and fluid flow surface of each first and second radial baffle may be arranged such that, when in use, fluid flowing from the outlet end of the flow surface of each radial baffle is directed towards a meshed location between the ring gear and the pinion gear. The pinion gear may be the aforementioned second rotatable gear. The electric vehicle differential may comprise a lubricant supply outlet or lubricant nozzle configured to provide a flow of lubricant to the meshed location between the ring gear and the pinion gear. Advantageously, a lubricant supply outlet may be arranged to direct lubricant to the meshed location, past the radial baffle. The radial baffle may protect the flow of lubricant from windage, and direct air flow such that the flow of lubricant is reinforced. The or each radial baffle may be integral with the axial shield. Advantageously, windage and spray may be shielded using a single component. Another aspect of the invention provides an electric vehicle comprising the aforementioned electric vehicle differential. The axial shield or radial baffle / s may comprise a plastic material, for example a moulded plastic material, for example an injection moulded plastic component. The axial shield or radial baffle / s may comprise a fibre reinforced plastic (FRP). The axial shield or radial baffle / s may comprise metal, for example stamped metal sheet. 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 radial baffle according to an embodiment of the invention; Figure 2 shows a radial baffle system according to another embodiment of the invention; Figure 3 shows another view of the radial baffle system of Figure 2; Figure 4 shows another view of the radial baffle system of Figure 2; Figure 5 shows a section view of the radial baffle system of Figure 2; Figure 6 shows an electric vehicle differential according to another embodiment of the invention; Figure 7 shows another view of the electric vehicle differential of Figure 6; and Figure 8 shows an electric vehicle in accordance with another embodiment of the invention. DETAILED DESCRIPTION A radial baffle 1 in accordance with an embodiment of the present invention is described herein with reference to the accompanying Figure 1. A radial baffle system 2 in accordance with an embodiment of the present invention is shown in Figures 2 to 5. An electric vehicle differential 3 in accordance with an embodiment of the present invention is shown in Figures 6 and 7. The electric vehicle differential 3, and in some examples the radial baffle and radial baffle system 2, are for use in an electric vehicle 4, an example of which is shown in Figure 8. Referring firstly to Figure 1 the radial baffle 1 is shown. The radial baffle 1 of this example has the shape of a conduit, as best shown in Figures 4 and 5. The radial baffle 1 has a sidewall 17 extending from either side of the fluid flow surface 11. The sidewalls 17 extend in a direction towards the first rotatable gear 5. The radial baffle 1 has a base wall 18 connecting the sidewalls 17 together. In this way, the fluid flow surface 11, sidewalls 17 and base wall 18 provide an enclosed fluid flow conduit. As can be seen in Figure 1, a cross-sectional area of the fluid flow conduit is smallest at the flow outlet end 11 of the fluid flow surface. The radial baffle 1 has a fluid flow surface 11 which faces in a direction towards a circumferential periphery of a first rotatable gear 5. That is, the fluid flow surface faces a direction towards radially outwardly facing teeth of the first rotatable gear 5. In this example the first rotatable gear 5 is a helical gear and the fluid flow surface 11 faces in a direction towards the helical gear teeth. The radial baffle 1 has a fixing portion (not shown) for fixing the radial baffle 1 to a structure (not shown) which is stationary relative to the first rotatable gear 5 when the first rotatable gear 5 is rotating, in use. The fluid flow surface 11 has a fluid flow inlet end 12 and a fluid flow outlet end 13. The fixing portion and fluid flow surface 11 are configured such that, when in use in an electric vehicle gear system, fluid flowing from the outlet end 13 of the flow surface 11 is directed towards the first rotatable gear 5. It will be appreciated that fluid flowing from the outlet end 13 of the fluid flow surface 11 has a principal flow direction, indicated by an arrow 14 in Figure 1, the term ‘principal flow direction’ being associated with reference numeral 14 henceforth. It will be appreciated that the principal flow direction 14 defines a main flow direction, or a direction of the majority of fluid flow. When in use in the electric vehicle gear system, fluid flow is directed from the fluid flow surface 11 with the principal flow direction 14 converging with a tangent 51, closest to the flow outlet end 13, of a reference circle (not shown in the figures) which is representative of an outer diameter of the first rotatable gear 5. It will be appreciated that the reference circle is an artificial, or non-physical, reference circle which passes through a tip of each radial tooth of the gear. In other words the reference circle defines a radial extent of the first rotatable gear 5. This configuration means that, when the radial gear baffle 1 is in situ next to the first rotatable gear 5, air flow generated by the first rotatable gear 5 when rotating, in use, as well as fluid flung from the rotation of the first rotatable gear 5, may be guided by the fluid flow surface 11 and directed to back onto the rotating first rotatable gear 5. In this example, a radius of curvature of the fluid flow surface 11 changes with position along the fluid flow surface 11. In this example, the fluid flow surface 11 has a substantially planar portion leading to the flow outlet end 13. The fluid flow surface 11 has a lower curvature portion starting with the flow inlet end 12 and a higher curvature portion between the lower curvature portion and the planar portion. Accordingly, in this example a distance between the fluid flow surface 11 and a central axis, or the reference circle, of the first rotatable gear 5 changes with position along the fluid flow surface 11. This may enable the fluid flow surface 11 to be shaped to provide desirable fluid flow characteristics of the air and lubricant flowing along it to guide the lubricant towards the first rotatable gear 5. The base wall 18 provides a secondary fluid flow surface 181 along an outside surface thereof. That is, the secondary fluid flow surface 181 is provided on an outside surface of the fluid flow conduit. This is because some fluid will flow along this secondary fluid flow surface 181, in use. The secondary fluid flow surface 181 of this example has two sections: a parallel section; and a concave section. The concave section may also be referred to as an accumulation section, and comprises an end corresponding to the flow outlet end 13. The concave section is concaved facing the first rotatable gear 5 such that, with distance along the concave section of the secondary fluid flow surface 181from an end corresponding to the flow inlet end 12, a distance between the secondary fluid flow surface 181 and the reference circle of the first rotatable gear 5 first increases and then decreases, up until the end corresponding to the flow outlet end 13 . The shape of the secondary fluid flow surface 181 in the concave or accumulation section may thereby allow a steeper gradient at the end corresponding to the flow outlet end, to direct fluid more directly to the desired location on the first rotatable gear 5. That is, the shape of the concave section provides the convergence between a principal flow direction at the end corresponding to the flow outlet end 13, and the tangent of the reference circle of the first rotatable gear 5 closest to the flow outlet end 13. The parallel section of the secondary fluid flow surface 181 comprises an inlet end of the secondary fluid flow surface 181 and joins this inlet end and the concave section together. The parallel section may also be referred to as a concentric section. The parallel section is substantially parallel to the reference circle of the first rotatable gear, such that the surface is curved to follow a shape of a part of the reference circle. In other words, the parallel section has a radius or curvature which is concentric with the reference circle of the first rotatable gear 5. The parallel section is spaced from the gear teeth of the first rotatable gear 5. The radial baffle 1 of the example of Figure 1 has other outer surfaces. In this example, the fixing portion is attached to a side surface of one or both sidewalls 17 of the radial baffle 1, but this could instead be attached to the outer wall which has the fluid flow surface 11. The radial baffle 1 may be made using any suitable material and process, for example being moulded with a plastic material, a fibre reinforced plastic material, or being formed using pressed or stamped sheet metal. It will be appreciated that this example of Figure 1 is purely illustrative, and the radial baffle 1 may in other examples be provided by a single sheet shaped to provide the fluid flow surface 11 with no sidewalls 17 or base wall 18. In this example the radial baffle 1 is located adjacent the first rotatable gear 5 which is meshed with a second rotatable gear 6. In this example the first rotatable gear 5 has a greater diameter than the second rotatable gear6. The fixing portion and the fluid flow surface 11 of the radial baffle 1 are arranged such that the principal flow direction 14 of fluid leaving the flow outlet end 13 is to the meshed location between the first and second rotatable gears 5, 6. In this way air and lubricant which is flowing along the fluid flow surface 11 is directed to the meshed location. The fluid may be directed to the vicinity of the meshed location or directly to the meshed location. Also in this example, a flow of lubricant 7, which may also be referred to as a lubricant jet, is shown schematically. It will be appreciated that the schematic shown in the Figures is purely indicative of a direction of a flow of lubricant, and does not represent a physical structure. It will be also appreciated that whilst this is referred to as lubricant, this could also be a coolant. The flow of lubricant 7 is provided by a lubricant supply outlet (not shown), which in this example is a lubricant nozzle (not shown). The flow of lubricant is directed to the meshed location between the gears, either directly to the meshed location or to the vicinity of the meshed location. The radial baffle 1 has a shape and is mounted to the or another stationary structure such that the flow of lubricant 7 is not interrupted or obstructed by the radial baffle 1. When the first and second rotatable gears 5, 6 are rotated air and / or lubricant leaving the first radial gear 5 with a radial component of velocity, enters the fluid flow conduit of the radial baffle 1. The fluid is guided by the fluid flow surface 11. The fluid exits the fluid flow surface 11 from the flow outlet end 13 and travels to the meshed location between the first and second rotatable gears 5, 6. This fluid flow may entrain lubricant flow 7 from the lubricant nozzle. It will be appreciated that entrainment of fluid means that momentum of fluid flow may cause lubricant flow 7 to follow the same fluid flow path. Lubricant and air may also travel along the secondary fluid flow surface 181, being guided along the parallel section and the concave section, to the meshed location. The radial baffle 1 may therefore help to lubricate and / or cool the gears for any number of the following reasons: • the radial baffle 1 helps to prevent air and lubricant, which leaves the gear with a radial component of velocity, from interrupting the flow of lubricant 7 from the lubricant nozzle, due to a shielding effect of the base wall 18; • The flow of air and lubricant which travels inside of the fluid flow conduit and leaves from the outlet end 13 of the fluid flow surface 11 reinforces the flow of lubricant 7 from the lubricant nozzle, by entraining the flow of lubricant 7; and • The radial baffle 1 recirculates lubricant which is flung from the first rotatable gear 5 to the meshed location between the first and second rotatable gears 5, 6. The first rotatable gear 5 of this example is a ring gear of an electric vehicle differential, and the second rotatable gear 6 is a pinion gear that drives the ring gear. The pinion gear is either mounted directly to an electric motor, which provides motive power to the electric vehicle, or is a part of a drive train from the electric motor to the ring gear. Referring now to Figures 2 to 5, an example of a radial baffle system 2 is shown. The radial baffle system 2 has a first radial baffle 21 and a second radial baffle 21 ’. The first radial baffle 21 is similar to the radial baffle 1 described with reference to Figure 1, and similar features are denoted with the same reference numerals with a preceding ‘2’. The second radial baffle 21’ is similar to the first radial baffle 21 but is smaller by an amount roughly corresponding to the relative size of the second rotatable gear 6 to the first rotatable gear 5. Aside from the difference in size, the second radial baffle 21’ has the same features as the first radial baffle 21, and these same features are denoted with the same reference numerals with a succeeding prime (‘). For clarity in the Figures, most reference numerals associated with the second radial baffle 21’ are omitted from Figure 3 and shown in Figure 2, and most reference numerals associated with the first radial baffle 21 are omitted from Figure 2 and shown in Figure 3. The second radial baffle 21’ is orientated in an opposite direction to the first radial baffle 21, and so the inlet end 212’ of the second radial baffle 21 ’ faces an opposite direction to the angular velocity of the second rotatable gear 6 similarly to the inlet end 212 of the first radial baffle 21 facing an opposite direction to the angular velocity of the first rotatable gear 5. In the depicted example the first and second radial baffles 21,21’ are joined together at or proximal the outlet ends 213, 213’, such that they are a single component. A lubricant channel (not shown) is provided between the first and second radial baffles 21,21’ to allow the flow of lubricant 7 to reach the meshed location between the first and second rotatable gears 5, 6. By joining the first and second radial baffles 21,21’ together assembly of the radial baffle system into the gear system may be easier because fewer fixing portions may be required and / or it may remove the requirement that the radial baffles 21, 21’ are precisely aligned relative to one another. However, in another example the first and second radial baffles may be separate components and a gap may be provided therebetween, to allow the flow of lubricant 7 to pass the radial baffles and reach the meshed location. In this case, fixing portions are provided on each radial baffle. The operation of the radial baffle system is now described with reference to the first radial baffle 21 and second radial baffle 21’ shown in Figures 2 to 5, but it will be appreciated that a radial baffle system where the first and second radial baffles are separate will work in substantially the same way. Each radial baffle 21,21’ of the radial baffle system 2 works in substantially the same way as the radial baffle 1 of Figure 1. That is, air and lubricant flung from the first rotatable gear 5 enters the fluid flow conduit of the first radial baffle 21 at the inlet end 212 and flows over the fluid flow surface 211 of the first radial baffle 21, starting from the inlet end 212. The air and lubricant are directed towards the meshed location by the fluid flow surface 211. Some air and lubricant is also guided by the secondary fluid flow surface 181 of the first radial baffle 21 to the meshed location. At the same time, air and lubricant flung from the second rotatable gear 6 enter the fluid flow conduit of the second radial baffle 21 ’ at the inlet end 212’ and are directed along the fluid flow surface 211’ of the second baffle 21 ’. Air and lubricant are directed by the fluid flow surface 211’ of the second radial baffle 21’ to the meshed location. Some air and lubricant is also guided by the secondary fluid flow surface 181 of the second radial baffle 21’ to the meshed location. Advantageously, this flow of air and lubricant from both radial baffles 21, 21’ reinforces the flow of lubricant 7 from the lubricant nozzle, and recirculates lubricant back to the gears 5, 6. The radial baffle system 2 is also beneficial in that the flow of lubricant 7 is shielded from air and lubricant being flung from both of the rotatable gears 5, 6, unlike the when just one radial baffle is provided. In these examples, the first and second rotatable gears 5, 6 are a part of a gear system of an electric vehicle. For example, the first rotatable gear may be a ring gear of an electric vehicle differential, and the second rotatable gear may be a pinion gear attached to, or driven by, an electric motor which provided motive power to the vehicle. Also in these examples, the radial baffles 1, 21, 21’ are made from a plastic material, and may be made by injection moulding, for example. However, they may be made from any suitable material, such as metal or fibre reinforced plastic, and manufactured in any suitable way. Referring now to Figures 6 and 7, there is shown an electric vehicle differential 3 according to another embodiment of the invention. As is usual in vehicle differentials, the electric vehicle differential 3 has a ring gear 31, which is driven by the electric motor (not shown), the electric motor providing motive power to the electric vehicle. The ring gear 3 is a helical ring gear. The ring gear 3 is omitted from Figure 7 for clarity. In this example the differential 3 is a four-pin bevel gear differential comprising a plurality of differential gears 32a, 32b, 32c, 32d, which may otherwise be referred to as side gears. There are four differential gears 32a, 32b, 32c, 32d, each one being bevelled. There is a first pin 33a with a first differential gear 32a mounted at one end and a second differential gear 32b mounted at the other end. There is a second pin 33b with a third differential gear 32c mounted at one end and a fourth differential gear 32d mounted at the other end. The first and second pins 33a, 33b are arranged perpendicular to one another, and the first pin 33a passes through a hole in the centre of the second pin 33b. In this way, the first and second differential gears 32a, 32b are able to rotate with the first pin 33a and the third and fourth differential gears 32c, 32d are able to rotate with the second pin 33b. The first and second pins 33a, 33b are rotatably mounted inside of a differential gear casing 34. The differential gear casing 34 is fixedly mounted to the ring gear 31. In this way, rotation of the ring gear 31 causes rotation of the differential gear casing 34 and so whole body rotation of the differential gears 32a-32d about a central axis of the ring gear 31. In this example the differential gear casing 34 has four apertures 35 through sides thereof. The electric vehicle differential 3 has two axle gears 36, only one of which is shown in Figure 7. Each axle gear 36 is rotationally mounting to an end of a respective wheel axle 37. Each axle gear 36 is bevelled. A wheel W (as shown in Figure 8) of the vehicle is located at another end of each axle 37. The axle gears 36 are located either side of the differential gears 32a-32d, and are meshed with each differential gear32a-32d. Therefore, the electric vehicle differential delivers rotational power from the electric motor to the wheels W of the vehicle in the usual way. That is: the ring gear 31 is rotated by the electric motor; this, in turn, rotates the differential gear casing 34 which moves the differential gears 32a-32d about a central axis of the ring gear 31; when the wheels W at the ends of the axles 37 rotate at the same speed as one another, rotational power is transferred to the two axle gears 36 without the differential gears 32a-32d rotating about their own axes; if the wheels rotate at different speeds to one another, for example due to cornering, the differential gears 32a-32b rotate about their own axes to transfer different amounts of rotation to the two axle gears 36. In other differentials, for example those driven by an internal combustion engine, the ring gear might instead be a bevel gear which is driven by a drive shaft, but the operation will be similar or the same. The electric vehicle differential has an associated lubricant supply outlet 38 which, in this example, is a lubricant nozzle 38, and which is configured to deliver a flow of lubricant 39 to a side of the differential gear casing 34. The flow of lubricant 39 is delivered in a direction perpendicular to the rotational axis of the differential gear casing 34, and is arranged such that the flow of lubricant 39 passes through each aperture 35 in the differential gear casing 34 when the aperture 35 passes through the flow of lubricant 39. In this way, the inside of the differential gear casing 34 is lubricated and / or cooled. The electric vehicle differential 3 has an axial shield 310 located on an axial side of a ring gear 31. In this example a radial extent of the axial shield 310, relative to a central axis of the ring gear 31, is equal to an outer radius of the ring gear 31. In other examples, the radial extent of the axial shield 310, relative to a central axis of the ring gear 31, may be greater than an outer radius of the ring gear 31. The axial shield 310 is located, along an axial direction of the ring gear 31, between the ring gear 31 and the lubricant nozzle 38. This means that air and lubricant spray leaving the ring gear 31 in an axial direction, in use, may be intercepted by the axial shield 310. This may be beneficial in that the flow of lubricant 39 is protected from the air and lubricant spray. In this example an outer periphery of the axial shield 310 is circular and the axial shield 310 is substantially annular in shape. The axial shield 310 is spaced from the ring gear 31. An annular channel is provided by the axial shield 310 because a first sidewall of the annular channel is provided by the axial shield 310, a second sidewall of the annular channel is provided be the ring gear 31 and there is a radially outward facing base wall joining the first sidewall to the second sidewall. This may be advantageous in that lubricant can be captured in the annular channel. In this example the axial shield 310 is mounted to the ring gear 31 such that the axial shield 310 rotates with the ring gear 31. The axial shield 310 may be a separate component from the ring gear 31, for example a moulded plastic component, which is attached to the ring gear 31 using fasteners. It is envisaged that the axial shield could instead be integral with the ring gear 310 and / or may be made from metal or a fibre reinforced plastic. It will be appreciated that the axial shield 310 may instead be mounted to the differential gear casing or to a structure which is stationary relative to the ring gear when the ring gear is rotating. For example, the axial shield 310 may be mounted to a housing of the electric vehicle differential. In use, when the ring gear 31 is rotating, the helical gear teeth create axial windage which generates an axial airflow and spray of lubricant with an axial component. Without the axial shield 310 this air and lubricant flow might interrupt the flow of lubricant 39 from the lubricant nozzle 39. Therefore, the axial shield 310 protects the flow of lubricant 39 to the differential gear casing 34. The axial shield 310 may provide a secondary advantage in that lubricant can flow around the annular channel and either be sprayed in a direction with negligible axial component, or to drip from the annular channel to a convenient location. In another embodiment, a pinion gear, which is meshed with the ring gear to drive the ring gear, also has an axial shield. This axial shield has a radius equal to or greater than a radial extent of the pinion gear. The operation and advantages are the same for this axial shield of the pinion gear as the axial shield of the ring gear. In another embodiment, the electric vehicle differential has the axial shield, or both axial shields, and the radial baffle 1 of Figure 1, or the radial baffle system 2 of Figures 2 to 5. It is envisaged that the radial baffle or radial baffle system is separate to the axial shield / s, because the axial shield / s will rotate with the respective gear. However, if the axial shield / s is / are mounted to the housing, the axial shield / s may be attached to, or even unitary with, the or both radial baffle / s. Referring to Figure 8 there is shown an electric vehicle 4 comprising any of the radial baffle, the radial baffle system, the gear system or the electric vehicle differential. It will be appreciated that various changes and modifications can be made to the present invention without departing from the scope of the present application.

Claims

1. A radial baffle for an electric vehicle gear system where the electric vehicle gear system comprises a rotatable gear and a structure which is stationary relative to the rotatable gear, the radial baffle comprising:a fluid flow surface with a flow outlet end; anda fixing portion for fixing the radial baffle to the structure such that the fluid flow surface faces in a direction towards a circumferential periphery of the rotatable gear, in use;wherein the fixing portion and fluid flow surface are arranged such that, when in use in the electric vehicle gear system, fluid flowing from the outlet end of the flow surface is directed towards the rotatable gear.

2. A radial baffle according to claim 1, comprising a sidewall extending from either side of the fluid flow surface in a direction which is towards the rotatable gear, in use, the radial baffle providing a fluid flow conduit.

3. A radial baffle according to claim 2, comprising a base wall connecting the sidewalls together.

4. A radial baffle according to claim 3, wherein a cross-sectional area of the fluid flow conduit is smallestat the flow outlet end of the fluid flow surface.

5. A radial baffle according to any preceding claim, wherein the fixing portion and fluid flow surface are configured such that, when in use in the electric vehicle gear system, fluid flow is directed from the fluid flow surface with a principal flow direction which converges with a tangent, closest to the flow outlet end, of a reference circle which is representative of an outer diameter of the rotatable gear.

6. A radial baffle according to any preceding claim, wherein the radial baffle is for an electric vehicle system where the electric vehicle system has a first rotatable gear meshed with a second rotatable gear, and wherein the fixing portion is for fixing the radial gear baffle to the structure such that the fluid flow surface faces in a direction towards the circumferential periphery of the first rotatable gear, and the fixing portion and fluid flow surface are configured such that, when in use in the electric vehicle gear system, fluid flowing from the outlet end of the flow surface is directed towards a meshed location between the first rotatable gear and the second rotatable gear.

7. A radial baffle according to any preceding claim, wherein the fluid flow surface comprises a flow inlet end, and wherein, when the radial baffle is in use in the electric vehicle gear system, a distance between the flow inlet end and a central axis of the, or the first, rotatable gear is greater than a distance between the flow outlet end and the central axis of the, or the first, rotatable gear.

8. An electric vehicle gear system comprising:a rotatable gear;a structure which is stationary relative to the rotatable gear;a radial baffle according to any preceding claim;wherein the fluid flow surface of the radial baffle faces in a direction towards a circumferential periphery of the rotatable gear; andwherein the fixing portion and fluid flow surface are configured such that, when in use, fluid flowing from the outlet end of the flow surface is directed towards the rotatable gear.

9. A radial baffle system for an electric vehicle gear system, where the electric vehicle gear system comprises a first rotatable gear which is meshed with a second rotatable gear, and where the electric vehicle gear system comprises a structure which is stationary relative to the first and second rotatable gears, the radial baffle system comprising:a first radial baffle which is a radial baffle according to any of claims 1 to 8, the fluid flow surface of the first radial baffle facing in a direction towards a circumferential periphery of the first rotatable gear, in use;a second radial baffle which is a radial baffle according to any of claims 1 to 8, the fluid flow surface of the second radial baffle facing in a direction towards a circumferential periphery of the second rotatable gear, in use;wherein the fixing portion and fluid flow surface of each first and second radial baffle are arranged such that, when in use in the electric vehicle gear system, fluid flowing from the outlet end of the flow surface of each radial baffle is directed towards a meshed location between the first and second rotatable gear.

10. A radial baffle system according to claim 9, wherein the first radial baffle and the second radial baffle are configured, when the radial baffle system is in use in the electric vehicle gear system, such that an unobstructed passage is provided therebetween for a flow of lubricant to pass through.

11. A radial baffle system according 10, comprising a lubricant supply outlet configured to provide a flow of lubricant to the meshed location between the first and second rotatable gears.

12. An electric vehicle gear system comprising:a first rotatable gear;a second rotatable gear meshed with the first rotatable gear;a radial baffle system according to either of claims 9 or 10;wherein the fluid flow surface of the first radial baffle faces in a direction towards a circumferential periphery of the first rotatable gear, the fluid flow surface of the second radial baffle faces in a direction towards a circumferential periphery of the second rotatable gear; andwherein the fixing portion and fluid flow surface of each radial baffle are arranged such that, when in use, fluid flowing from the outlet end of each fluid flow surface is directed towards a meshed location between the first and second rotatable gears.13, An electric vehicle gear system according to claim 12, comprising a lubricant supply outlet configured to supply a flow of lubricant to the meshed location between the first and second rotatable gears.

14. An electric vehicle differential comprising an electric vehicle system according to either of claim 12 5 or 13, wherein the first rotatable gear is a ring gear of a differential of an electric vehicle and thesecond rotatable gear is a pinion gear which transfers rotational power from an electric motor to the ring gear, in use.

15. An electric vehicle comprising a radial baffle according to any of claims 1 to 8, an electric vehicle 10 gear system according to claim 9, a radial baffle system according to claim 10 or 11, an electricvehicle gear system according to claim 12 or 13, or an electric vehicle differential according to claim 14.21

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