A gear shroud

Abstract

A gear shroud 200 for protecting a gear 108, the gear shroud comprising: a spigot 206 received in a fluid dispensing orifice 118; a shroud body having a first wall 202 for impeding flow of fluid towards the gear from the orifice; and a connecting member 210 fixedly connecting the spigot to the shroud body.

Description

TECHNICAL FIELD The present disclosure relates to a gear shroud and particularly a transmission unit for a vehicle that incorporates the gear shroud. Aspects of the invention relate to a gear shroud, to a drive unit housing, and to a vehicle. BACKGROUND It is known to provide a gear shroud to protect a gear from a surrounding environment. The environment may contain debris or liquid, which may damage the gear or cause drag on the gear. Further, units with several moving parts may have a lubrication system for applying lubricant to the moving components such as bearings and gears. An outlet for the lubrication system may be directed toward a gear, meaning that fluid may be projected toward the gear, resulting in aeration of the fluid and drag on the gear. It may also be difficult to assemble a spigot and / or a restrictor in the lubrication system outlet adjacent a gear or gear shroud. 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 transmission unit, a gear shroud, a vehicle drive unit, and a vehicle as claimed in the appended claims According to one aspect of the present invention a transmission unit comprises: a transmission housing having a housing wall that defines an internal volume of the transmission housing; a gear rotatable about a gear axis; a passage in the housing wall to deliver liquid lubricant to the internal volume and terminating in an orifice; and a shroud within the internal volume, wherein the shroud comprises a first wall for impeding a flow of lubricant towards the gear from the orifice and a spigot depending from said first wall and received in the orifice, the spigot including a conduit directing lubricant flow from the orifice into the internal volume. The shroud may be connected to the housing wall by the spigot and / or the shroud may be connected to the housing wall around said orifice by at least one boss receiving a fastener connected to said housing wall. According to an aspect of the present invention there is provided a gear shroud for protecting a gear, the gear shroud comprising: a spigot arranged to be received in a fluid dispensing orifice; a shroud body; and a connecting member configured to fixedly connect the spigot to the shroud body. The shroud body may comprise a first wall for impeding a flow of fluid towards the gear from the fluid dispensing orifice In some cases, fluid such as oil may be arranged to leave an orifice and may leave the orifice on a trajectory that means the oil has a high chance of contacting a moving part such as a gear. Where a fluid contacts a gear, it may cause drag on the gear and the gear may aerate the fluid such that the fluid properties become undesirable. In the case of oil, aeration may result in less effective cooling of components. Further, in cases where an orifice is arranged adjacent to a moving component that may be shrouded, it may be difficult to assemble a spigot in the orifice and an adjacent shroud. The present inventors have therefore realised that, by coupling the spigot to the shroud body, assembly may be simplified. Further, the spigot may act as a structural support for the gear shroud, improving the coupling of the gear shroud to adjacent components. Generally, the spigot may function to receive fluid from the orifice and to allow fluid to flow therethrough to leave the orifice. In order to maintain sufficient upstream fluid pressure, the fluid restrictor may be arranged in fluid communication with the spigot. The fluid restrictor may therefore restrict the flow of fluid leaving the orifice via the spigot. The gear shroud may further comprise a flow restrictor fluidly coupled to the spigot for restricting the flow of fluid through the orifice. By coupling a fluid restrictor within the spigot, the part count of the assembly may be reduced, allowing the gear shroud to be assembled more simply. Further, the restrictor may be held in place more resiliently. The flow restrictor may be arranged inside the spigot. In this way, known spigots and restrictors may be used. The spigot may extend away from the first wall such that the spigot is arranged to be received in an orifice directed toward the first wall. Drag on a gear and aeration of fluid may be particularly severe where an orifice may be arranged to direct fluid toward a gear, and so a gear shroud may have particular benefit in this situation. The connecting member may comprise a deflection wall arranged to impede an upward flow of the fluid. In some cases, fluid may contact a gear shroud and be deflected such that the fluid is sprayed across a wide area. The spraying may lead to aeration of the fluid. The deflection surface may reduce the deflection of fluid across a wide area and may thereby reduce the aeration of the fluid. The deflection surface may therefore improve the properties of the fluid. In particular, fluid may be deflected upwardly in some cases. The term “upwardly” is intended to mean a direction opposite to the direction of gravity, when the gear shroud is installed about the intended gear. In particular, a gear shroud may be used to shroud a gear from a pool of fluid in which the gear would otherwise sit. The “upward” direction of a gear shroud may therefore be identified as the direction an open surface of a volume defined by the gear shroud faces. The deflection wall may be curved about an axis extending from the spigot to the shroud body. A curved wall portion arranged about an axis may provide a compact means for reducing the spread and aeration of fluid passing through the spigot. The connecting member may comprise: a conduit extending from the spigot to the first wall, and an opening in the conduit arranged to allow the fluid to flow therethrough out of the conduit. The opening may be a hole at the end of the conduit, and in this way the conduit may carry the fluid directly from the orifice to a collection point, avoiding the fluid contacting the gear. The deflection wall may form at least a portion of the conduit. The opening may extend along the length of the conduit, such that the conduit may be U-shaped or C-shaped in cross section. By providing an opening the length of the conduit, the direction and spread of the fluid flow may be controlled, and the fluid may flow out of the passage at a sufficient rate to avoid a build-up in the orifice. The conduit may extend from the spigot to a fluid collection volume such as an oil sump. The conduit may run along the first wall in order to guide fluid from the orifice to the fluid collection volume. This may reduce dispersal of the fluid and thereby may reduce aeration of the fluid. The spigot may comprise a flange arranged to limit an insertion depth of the spigot into the fluid dispensing orifice. By providing a flange, the gear shroud may be more resiliently located. The fixing of the gear shroud to an adjacent component may therefore be more reliable. The gear shroud may further comprise a fixing member extending from the first wall on the same side of the first wall as the spigot, the fixing member being arranged to support the gear shroud structurally by engagement with an adjacent body. The fixing member, which may be a boss for receiving a bolt, may be used to fix the gear shroud in place. By arranging the fixing member and the spigot on the same side of the first wall, the gear shroud may be installed by insertion of the spigot into the office followed by fixing of the fixing member such as by bolting the gear shroud to an adjacent housing portion. The spigot may be located in the orifice more easily than the fixing members may be located adjacent corresponding fixing location on the housing portion, also referred to as a shroud connector, and so the overall assembly process may be improved. The shroud body may further comprise a second wall extending from the first wall such that the first and second walls define a volume for receiving a gear. By providing a second wall, the gear may be better isolated from the fluid, further reducing drag on the gear. The second wall may extend in a substantially horizontal direction from the first wall. According to a further aspect of the invention, there is provided a drive unit housing comprising: a housing wall defining an interior volume; a fluid passageway, the fluid passageway terminating in the fluid dispensing orifice; and the gear shroud of the first-mentioned aspect; wherein the spigot is received in the orifice. The drive unit housing may further comprise a shroud connector arranged to fix the gear shroud relative to the housing wall. The shroud connector may be a part of the housing arranged to couple to a or the connector of the gear shroud. The shroud connector may therefore hold the gear shroud resiliently in place. The housing wall may be formed of a first housing section and a second housing section, the shroud connector may be arranged on the first housing section, and the gear shroud may be arranged between the first housing section and the second housing section. The gear shroud may comprise a second wall extending from the first wall such that the first and second walls define a volume for receiving a gear. The second wall may be arranged to engage the second housing section such that the first wall, the second wall, and an inner surface of the second housing section define a volume for receiving a gear. By arranging the gear shroud between two housing sections, the gear shroud may be coupled to the first housing section, leaving the gear receiving volume open to allow easier installation of the gear within the shroud, before engagement with the second housing section. According to a still further aspect of the invention, there is provided a drive unit comprising: the drive unit housing of the further aspect, and a gear rotatable arranged within the interior volume, wherein the gear is arranged between the first wall of the gear shroud and the second housing section. By arranging the gear on an opposite side of the gear shroud from the connector to the gear shroud, the gear may be more easily coupled to the housing, after connection of the gear shroud. According to a yet still further aspect of the invention, there is provided a vehicle comprising the gear shroud of the first-mentioned aspect, and / or the drive unit housing of the further aspect, and / or the drive unit of the yet still further aspect. According to a yet still further aspect of the invention, there is provided a transmission unit comprising a transmission housing having a housing wall that defines an internal volume of the transmission housing, a gear rotatable about a gear axis, a passage in the housing wall to deliver liquid lubricant to the internal volume and terminating in an orifice; and a shroud within the internal volume. The shroud comprises a first wall for impeding a flow of lubricant towards the gear from the orifice and a spigot depending from said first wall and received in the orifice, the spigot including a conduit directing lubricant flow from the orifice into the internal volume. Optionally the shroud is connected to the housing wall by the spigot. Optionally the shroud is connected to the housing wall around said orifice by at least one boss receiving a fastener connected to said housing wall. Optionally the spigot is connected to the first wall by a connecting member defining said conduit. Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and / or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and / or features of any embodiment can be combined in any way and / or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and / or incorporate any feature of any other claim although not originally claimed in that manner. BRIEF DESCRIPTION OF THE DRAWINGS One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a vehicle in accordance with the invention; Figure 2 shows an electric drive unit in accordance with the invention; Figure 3 shows a cross sectional view of a known electric drive unit; Figure 4 shows a cross sectional view of an electric drive unit; Figure 5 shows a cross sectional view of an electric drive unit in accordance with the invention; Figure 6 shows the gear shroud of Figure 5; Figure 7 shows a further gear shroud in accordance with the invention; Figure 8 shows an side view of the further gear shroud of Figure 7; Figure 9 shows a detail view of the further gear shroud of Figure 7; Figure 10 shows a detail view of a yet further gear shroud in accordance with the invention; Figure 11 shows a still further gear shroud in accordance with the invention; and Figure 12 shows a yet still further gear shroud in accordance with the invention. DETAILED DESCRIPTION Figure 1 shows a vehicle 10 to provide context for this invention. The vehicle 10 may be a fully electric vehicle having only an electric machine for propulsion and no internal combustion engine or may be a hybrid vehicle having both an electric machine and an internal combustion engine arranged to propel the vehicle. The vehicle 10 may be a plug-in hybrid electric vehicle (PHEV) or a mild hybrid electric vehicle (MHEV). The vehicle 10 has at least one vehicle drive unit 100 containing a power source such as an electric machine or an internal combustion engine and one or more drivetrain components such as a gear or a differential arranged to transfer torque from the power source to the wheels of the vehicle. The vehicle drive unit 100 may be an electric drive unit (EDU) that contains an electric machine and one or more drivetrain components. Figure 2 shows an electric drive unit 100. The drive unit 100 contains an electric machine for propelling the vehicle. The electric machine has a stator 102 and a rotor 104, the stator being arranged to receive electrical power from a battery or generator and to impart a magnetic field to the rotor 104 to power the vehicle. The rotor 104 is coupled to a rotor shaft 106 which is arranged to transfer torque to downstream components of the electric drive unit. The rotor shaft 106 has a geared end portion 107 that is arranged to engage with and to transfer torque to a differential gear 108. The differential gear 108 is arranged to rotate and to transfer torque to the wheels of the vehicle. The vehicle drive unit 100 also has a lubricant jet 110 that is arranged to project lubricant, such as oil, onto the geared portion 107 of the rotor shaft 106 and the differential gear 108 at the point at which the two gears mesh. The electric drive unit 100 may generally be considered as a two-part unit having a power source portion 100a and a transmission portion 100b. The power source portion 100a contains the electric machine and the rotor shaft, whereas the transmission portion 100b contains the differential gear, the geared portion of the rotor shaft 107 and other transmission components including stub axle shafts (not shown) for transferring drive to the wheels. The transmission portion 100b may also be referred to as a transmission unit 100b. The vehicle drive unit 100 is formed of a two-part housing. The two-part housing comprises a first part 112 and a second part 114. The first part 112 substantially contains the power source and the second part 114 substantially contains the transmission component. The two-part housings 112, 114 are bolted together at an interface. Figure 3 shows a detailed view of a known vehicle drive unit 100 (not necessarily the same drive unit shown in Figure 2). The vehicle drive unit 100 has a lubrication channel 116 terminating in a lubricant dispensing orifice 118. The drive unit 100 has a bung B arranged in the orifice 118, the bung B being arranged to restrict a flow of fluid through the orifice 118. By restricting the flow of fluid through the orifice 118, the pressure in the fluid passage 116 may be controlled and the distribution of the fluid, which may be a lubricant, to other parts of the drive unit 100 may be better managed. However, a consequence of the fluid restriction is that the bung B may expel a high-velocity jet of fluid, which may directly impinge upon the differential gear 108. Due to the movement of the differential gear 108, the fluid may be dispersed widely and also aerated while generating drag on the gear, causing the vehicle drive unit to operate less efficiently. Further, the drive unit 100 has a fluid collecting volume F. The fluid collecting volume F is at a lower portion of the vehicle drive unit 100 when installed in a vehicle and in normal operation and orientation. The volume F may be an oil sump or may be fluidically coupled to an oil sump. As the differential gear 108 may intersect the fluid collecting volume F, the collected fluid may cause drag on the differential gear 108 and may also be aerated by the gear 108. Figure 4 shows a drive unit 100 with a gear shroud 150 arranged to prevent a fluid jet from the bung B contacting the differential gear 108. The gear shroud generally is arranged between the bung B and the differential gear 108 such that the fluid jet may impact the gear shroud 150, as opposed to the differential gear 108. The gear shroud 150 may also shield the differential gear 108 from the fluid F in the fluid collecting volume, in order to reduce drag on the gear. However, the assembly of the bung B and the gear shroud 150 in close proximity may be difficult and affixing the gear shroud 150 to an adjacent portion of the drive unit 100 may also require a high level of care and precision. Figure 5 shows a detailed view of a cross-section of a vehicle drive unit 100 according to the invention. The vehicle drive unit has a differential gear 108 and a fluid channel 116 substantially similar to those previously described and a gear shroud 200 for protecting the differential gear 108. It will be understood that the gear shroud 200 may be manufactured separately from the rest of the vehicle drive unit 100 and that a similar gear shroud may be arranged adjacent to a range of different moving parts such as a rotor or other gear and that the application shown herein is merely an example of an application of the gear shroud 200. The gear shroud 200 has a first wall 202 arranged between the fluid dispensing orifice 118 and the differential gear 108. The purpose of the first wall 202 is to prevent fluid that is ejected from the orifice 118 from directly contacting the differential gear 108 by providing a resilient barrier. The gear shroud 200 also comprises a second wall 204 which, together with the first wall 202 defines a volume for receiving the differential gear 108. The second wall 204 comprises a seal 205 extending from the second wall. The seal 205 is arranged to engage a wall of the drive unit housing 112 in order to substantially seal the volume in which the differential gear 108 is arranged and to isolate the gear receiving volume from the fluid collecting volume F. The housing portion 112 may also comprise a recess 113 arranged to receive the seal 205 in order to improve the resilience of the seal formed between the second wall 204 and the housing 112. Deflection of the second wall 204 may also be reduced by engagement with the recess 113. Together, the first wall 202 and the second wall 204 form a gear shroud body. Extending from the gear shroud body is a spigot 206, which is received in the fluid dispensing orifice 118. The spigot 206 may comprise an O-ring and may be arranged to form a substantially fluid tight outer seal with the orifice 118 such that the fluid through the orifice passes through the spigot 206 as opposed to around the spigot 206. The spigot 206 may be coupled to the gear shroud body by any means, which may be one or more solid members or a deflection wall or conduit. Preferably, the spigot 206 may be coupled to the gear shroud body rigidly such that the spigot 206, when engaged with the orifice, may support the gear shroud body during assembly and the gear shroud body may hold the spigot 206 in place during use. In the arrangement shown in Figure 5, the spigot 206 is coupled to the first wall 202 of the gear shroud 200 via a deflection wall 210. The deflection wall 210 may be curved about an axis along which fluid is projected from the orifice 118, such that the deflection wall 210 constrains the fluid and is arranged between the first wall 202 and the orifice 118. In this way, the deflection wall 210 may reduce dispersal and consequent aeration of the fluid, such that the fluid is channelled into the fluid collecting volume F with improved properties. The gear shroud 200 also has a fluid restrictor 208, which is arranged to limit a flow rate of the fluid through the orifice 118. To this end, the fluid restrictor 208 may have an annular surface arranged to prevent passage of the fluid and a fluid channel that has a smaller cross section than the orifice 118. In this way, the pressure and flow rate of the fluid through the orifice 118 may be controlled. The gear shroud 200 also has a flange 211 coupled to the spigot 206. The flange 211 is arranged to abut a periphery of the orifice 118 in order to prevent over-insertion of the spigot 206 into the orifice and thereby also provides more resilient locating of the gear shroud 200 during assembly. Figure 6 shows an end view of the gear shroud 200 from an alternative perspective. In Figure 6, a cut out 212 is visible. The purpose of the cut out 212 is that, during a stationary state of the vehicle drive unit, where the differential gear is not rotating, the vehicle drive unit may be filled with oil to a pre-determined, required level. This may ensure that there is adequate lubrication fluid in the system to lubricate all parts appropriately. The cut out 212 allows oil in the fluid containing volume F to flow into the volume in which the gear is received, such that there is a substantially consistent fluid meniscus level across the vehicle drive unit. When the vehicle drive unit is started and the differential gear rotates, movement of the gear expels fluid from the internal volume of the gear shroud 200, such that the gear shroud 200 becomes substantially empty of fluid and that drag on the gear in a steady state working mode is reduced. Figure 7 shows an alternative gear shroud 300. The alternative gear shroud 300 has a first wall 302, a second wall 304, a seal 305 extending from the second wall 304, a spigot 306, flange 311 and deflection wall 310 which are substantially similar to the corresponding features of the gear shroud 200 described in conjunction with Figures 5 and 6. The gear shroud 300 also has a cut out 312 for the same purpose as the cut out 212 of the gear shroud 200. It will be understood that the cut outs 212, 312 are an optional feature and may be present or absent in any embodiment without affecting any other features of the gear shroud. The gear shroud 300 of Figure 7 further comprises connecting portions, which may be referred to as fixing members, 314a, 314b. The fixing portions 314a, 314b are bosses arranged to receive bolts or machine screws therethrough for fixing the gear shroud to an adjacent portion of the housing of the vehicle drive unit. However, it will be understood that any fixing members, such as barbed plugs or engaging lips may be used for fixing the gear shroud in place. Figure 8 shows a side view of the gear shroud 300 and it can be seen that the gear shroud 300 may have strengthening ridges or ribs 316 extending between the fixing members 314a, 314b and the first wall 302. This may improve the resilience of the gear shroud 302. Figure 9 shows a further view of the gear shroud 300. In particular, the view in Figure 9 shows an opening 318 within the deflecting wall 310. It can be seen that the deflecting wall 310 forms a substantially C-shaped barrier between the spigot 306 and the first wall 302 ofthe gear shroud 300. The gear shroud 300 also has an opening 318 extending along the length ofthe deflecting wall 310 between the spigot 306 and the first wall 302. The deflecting wall 310 may extend about at least 180 degrees around the axis a between the orifice 118 and the first wall 302, optionally at least 270 degrees. In this way, fluid from the orifice 118 may be appropriately directed toward the fluid containing volume F. Figure 10 shows an alternative gear shroud 400. The gear shroud 400 may be substantially similar to the above-described gear shrouds. In particular, the gear shroud may have a first wall 402, a second wall 404, a seal (not shown), a cut out (not shown), fixing means, of which only one fixing means 414b is shown. The gear shroud 400 also has a spigot 406 which may be substantially similar to previously described spigots and may be received in the same orifice. However, the spigot may have a substantially complete conduit 410 extending between the spigot 406 and the first wall 402. The spigot 406 may also have no restrictor arranged within the spigot 406. In this case, the conduit may be an effectively T-shaped junction such that an opening 418 is formed as a hole in the wall of the conduit 410 extending downwardly to direct fluid directly into the fluid receiving volume F. The gear shroud 400 may also have a restrictor 408, which may be arranged at the opening 418, such that fluid passes through the orifice and into the conduit 410 at the same pressure that it is in the fluid passage and the restrictor 408 may be arranged downstream of the conduit. In this arrangement, fluid may be directed into the fluid receiving volume F more directly, reducing aeration of the fluid. A further alternative gear shroud 500 is shown in Figure 11. The gear shroud 500 has a first wall 502, a second wall (not shown), connecting portions 514a, 514b and a spigot 506, a restrictor 508 and flange 511 substantially similar to those described with reference to the above-described embodiments. The gear shroud 500 has a conduit 510 extending from the spigot 506 substantially along the first wall 502 to an opening 518. In this case, the opening 518 may be below a fluid level of the fluid containing volume F, such that fluid may be directly received in the fluid containing volume, reducing dispersal of the fluid and consequent aeration of the fluid further. The connecting portions 514a, 514b may pass through the conduit 510 in order to simplify manufacture of the gear shroud 500. Figure 12 shows a further conduit 600, the conduit having a first wall 602, a second wall (not shown), a seal (not shown), a spigot 606, a restrictor 608, a flange 611 and fixing means 614a, 614b substantially similar to those described above and may further comprise a conduit 610 that is formed as a tube extending along the first wall 602 from the spigot 606 to an opening 618. The tube 610 may be arranged to circumvent the fixing 614b, such that the fixing may be unaffected by the conduit 610 and the conduit may therefore provide fluid to the fluid containing volume f directly via the opening 618. 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 gear shroud for protecting a gear, the gear shroud comprising:a spigot arranged to be received in a fluid dispensing orifice;a shroud body comprising a first wall for impeding a flow of fluid towards the gear from the fluid dispensing orifice;anda connecting member configured to fixedly connect the spigot to the shroud body.

2. A gear shroud according to claim 1, further comprising a flow restrictor fluidly coupled to the spigot for restricting the flow of fluid through the orifice.

3. A gear shroud according to claim 2, wherein the flow restrictor is arranged inside the spigot.

4. A gear shroud according to any preceding claim, wherein the spigot extends away from the first wallsuch that the spigot is arranged to be received in an orifice directed toward the first wall.

5. A gear shroud according to any preceding claim, wherein the connecting member comprises a deflection wall arranged to impede an upward flow of the fluid.

6. A gear shroud according to claim 5, wherein the deflection wall is curved about an axis extending from the spigot to the shroud body.

7. A gear shroud according to any preceding claim, wherein the connecting member comprises: a conduit extending from the spigot to the first wall, andan opening in the conduit arranged to allow the fluid to flow therethrough out of the conduit.

8. A gear shroud according to any preceding claim, wherein the spigot comprises a flange arranged to limit an insertion depth of the spigot into the fluid dispensing orifice.

9. A gear shroud according to any preceding claim, further comprising a fixing member extending from the first wall on the same side of the first wall as the spigot, the fixing member being arranged to support the gear shroud structurally by engagement with an adjacent body.

10. A gear shroud according to any preceding claim, wherein the shroud body further comprises a second wall extending from the first wall such that the first and second walls define a volume for receiving a gear.

11. A drive unit housing comprising:a housing wall defining an interior volume;a fluid passageway, the fluid passageway terminating in the fluid dispensing orifice; andthe gear shroud of any preceding claim;wherein the spigot is received in the orifice.

12. A drive unit housing according to claim 11, the electric drive unit further comprising a shroud connector arranged to fix the gear shroud relative to the housing wall.

13. A drive unit housing according to claim 12, wherein the housing wall is formed of a first housing section and a second housing section,wherein the shroud connector is arranged on the first housing section, andwherein the gear shroud is arranged between the first housing section and the second housing section.

14. A drive unit comprising:the drive unit housing of claim 13, anda gear rotatable arranged within the interior volume,wherein the gear is arranged between the first wall of the gear shroud and the second housing section.

15. A vehicle comprising:the gear shroud of any one of claims 1 to 10, orthe drive unit housing of claim 11, 12 or 13, orthe drive unit of claim 14.12

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