Housing for a drive unit

Abstract

A housing 150 for an electric drive unit (EDU) 100. The housing defines: an interior volume 162 for one or more drive unit components of the EDU, a sump 152 defining a sump compartment 164 below the i

Description

TECHNICAL FIELD The present disclosure relates to a housing for a drive unit Aspects of the invention relate to a housing for a drive unit, a drive unit, a vehicle, and a method of producing a sump of a housing for a drive unit BACKGROUND For vehicle powertrains comprising a drive unit (e.g., an electric drive unit (EDU)), it is known to provide a housing which contains the moving components of the drive unit (e.g., prime movers, bearings, gears, shafts, etc.). It is also known to provide a fluid recirculation system which directs fluid through the housing in order to lubricate and cool the drive components. The housing may include a sump at a lower end for containing the fluid which is circulated through the housing. The size and shape of the sump will influence the performance of the fluid recirculation system. For example, a deeper and narrower sump can be less prone to changes in the level of fluid within the sump based on orientation of the vehicle, and thus less likely to have interruption of fluid pick-up from the sump. However, the size and shape of the sump will also have an impact on the size and shape of the housing, which have an effect on packaging of the drive unit in the vehicle. 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 housing for a drive unit, a drive unit, a vehicle, and a method of producing a sump of a housing for a drive unit as claimed in the appended claims. According to an aspect of the present invention there is provided a housing for a drive unit (e.g., an electric drive unit (EDU)). The housing defines an interior volume for one or more drive unit components of the drive unit, a sump defining a sump compartment below the interior volume, and a sump outlet forming part of a flow path between the sump compartment and the interior volume for providing a lubricant from the sump compartment to the one or more drive unit components. The sump compartment comprises a first sump chamber and a second sump chamber which is partially offset from the first sump chamber in a lateral direction. The first sump chamber and the second sump chamber are open to each other. According to an aspect of the present invention there is provided a housing for a drive unit (e.g., an electric drive unit (EDU)). The housing defines an interior volume for one or more drive unit components of the drive unit, a sump defining a sump compartment below the interior volume, and a sump outlet forming part of a flow path between the sump compartment and the interior volume for providing a lubricant from the sump compartment to the one or more drive unit components. The sump compartment comprises a first sump chamber and a second sump chamber which is contiguous with and partially offset from the first sump chamber in a lateral direction. In other words, the housing has a vertical axis which extends from the sump at a lower end of the housing to an upper end of the housing opposite to the sump, and the second sump chamber is partially offset from the first sump chamber in a direction which is transverse (e.g., perpendicular) to the vertical axis. The term “lateral direction” is used herein to refer to a direction which extends along a horizontal plane of the drive unit. For example, when the housing is mounted to a vehicle in use, the lateral direction may be a longitudinal direction between front and rear ends of the vehicle, or a transverse direction between left and right sides of the vehicle. The sump compartment may comprise a planar base surface and the lateral direction may be parallel to the planar base surface. In this way, there is no step between the base surface of the first sump chamber and the base surface of the second sump chamber, so that lubricant can flow freely between the first and second sump chambers. The housing may define a rotational axis for one or more output shafts of the drive unit. The housing may define a first end having a first opening for receiving a first shaft, a second end having a second opening for receiving a second shaft, and a rotational axis or central axis which extends from the first opening to the second opening. The central axis can be considered to extend along a horizontal plane of the drive unit. The lateral direction in which the second sump chamber is offset in relation to the first sump chamber may be any direction parallel with the horizonal plane defined by the central axis. Optionally, the lateral direction is transverse (e.g., perpendicular) to the rotational axis. The lateral direction may be perpendicular to both the vertical axis and the rotational axis of the housing. In this manner, when the drive unit is installed in a vehicle such that the rotational axis is parallel to the front and rear axes of the vehicle (i.e. in a side-to-side direction of the vehicle), the lateral direction in which the second sump chamber is offset in relation to the first sump chamber will extend in the longitudinal direction of the vehicle. This can be beneficial in minimising lubricant surge and / or reduced lubricant supply under vehicle acceleration or deceleration. In this context, it will be understood that the term “contiguous with” means that the first and second sump chambers are open to each other so that lubricant or other fluid can freely flow between the first and second sump chambers. This includes both configurations in which the first and second sump chambers meet at shoulder surfaces arranged parallel to the lateral direction, or configurations in which there is a transition zone between the first and second sump chambers (e.g., sloping shoulders arranged at an angle to the lateral direction). In this context, it will be understood that the term “partially offset” means that each sump chamber has a cross-sectional area with an intersecting portion which overlaps with the cross-sectional area of the other sump chamber, and an offset portion which does not overlap with the cross-sectional area of the other sump chamber. It will be understood that packaging constraints may change along a length of the sump (e.g., to accommodate mounts for the housing, interior volumes for drive unit components, to provide increased ground clearance for off-road applications etc.). By having a sump with contiguous first and second sump chambers which are partially offset in the lateral direction, different packaging constraints can be taken into consideration whilst maintaining a sump area and / or depth along a length of the sump (e.g., as opposed to just moving a single side wall of the sump or raising part of the floor of the sump, either or which would result in a reduced sump area). For example, this sump arrangement may be particularly beneficial for accommodating clearance for a mount for the housing near the second sump chamber. Such a sump design may also provide improved rigidity of the housing in relation to a conventional sump arrangement. For example, it will be understood that by partially offsetting the second sump chamber from the first sump chamber in the lateral direction, a first shoulder surface is formed in a first side of the sump and a second shoulder surface is formed in a second side of the sump, the first and second shoulders surfaces facing different directions. Such shoulders may increase rigidity in comparison to straight / flat sides. In addition, the size of the housing and any structural features such as supporting ribs may be increased in the extra space formed on one side of the sump by offsetting the second sump chamber, which may further improve rigidity. Such shoulders may also inhibit lubricant surge within the sump (e.g., under acceleration / deceleration) by acting as baffles along the first and second sides of the sump. Furthermore, such a sump shape may be manufactured by inserting and then removing casting cores from opposite sides (i.e., a first casting core for the first sump chamber and a second casting core for the second sump chamber). This may be easier than manufacturing other more complex sump shapes. 2 Optionally, the sump compartment comprises first and second sides, wherein the first side of the sump comprises a first shoulder surface between the first and second sump chambers and the second side of the sump comprises a second shoulder surface between the first and second sump chambers. Such shoulders may increase rigidity in comparison to straight / flat sides. Such shoulders may also inhibit lubricant surge within the sump (e.g., under acceleration / deceleration) by acting as baffles along the first and second sides of the sump. One or both of the first and second shoulders may extend at an angle to the lateral direction such that the transition between the first and second chambers is gradual. Optionally, the first and second shoulder surfaces extend parallel to the lateral direction and face opposite directions. Such a sump compartment may be easier to manufacture than more complex shapes in which the shoulders are not parallel to the lateral direction. For example, such a sump compartment may be manufactured by abutting two flat and partially offset core faces against each other during a casting process. The provision of parallel shoulders can also act as internal baffles within the sump compartment to help reduce lubricant surge due to vehicle orientation changes. Optionally, the first sump chamber has a different cross-sectional shape to the second sump chamber in the lateral direction. In other words, the first and second sump chambers do not just have the same shape partially offset in the lateral direction, but instead have a different shape to each other. This may facilitate optimal shaping of the sump compartment in different regions of the housing. For example, partial offsetting of the second sumpchamber may allowa non-overlapping portion of the second sump chamber to be increased in height. Optionally, the cross-sectional shape of the first sump chamber is substantially symmetrical. Such a substantially symmetrical shape may be beneficial for output of lubricant from the first sump chamber. For example, the cross-sectional shape of the first sump chamber may be split into two sides of substantially the same area, which may reduce the likelihood of lubricant pooling on one particular side of the first sump chamber. Optionally, the cross-sectional shape of the first sump chamber is substantially trapezoidal. A trapezoidal cross-sectional shape (e.g., with an upper edge, a lower edge and sides which taper inwards towards the lower edge) may be particularly beneficial as the tapered sides may allow the housing to taper towards a base of the first sump chamber. This may be beneficial for improving ground clearance, and may ensure suitable pooling of lubricant in the narrower lower end of the first sump chamber to increase reliability of lubricant pick-up. Optionally, the sump outlet comprises a mounting arrangement configured to mount a lubricant pick-up pipe in the first sump chamber. Such a lubricant pick-up pipe facilitates recirculation of lubricant. In addition, where the pick-up pipe is mounted in the first sump chamber which is substantially symmetrical (e.g. trapezoidal), this may reduce the likelihood of lubricant pooling in areas away from the pick-up pipe (e.g. when on a hill). Optionally, the mounting arrangement is configured to align the lubricant pick-up pipe with a centre of the first sump chamber in the lateral direction. Aligning the lubricant pick-up pipe with a centre of the first sump chamber in the lateral direction may facilitate improved lubricant pick-up in range of operating conditions (e.g., during acceleration / deceleration, or when positioned on a hill). Optionally, the interior volume comprises a curved portion having a curved periphery, wherein the second sump chamber is located underneath the curved portion, and wherein an upper surface of the second sump chamber is curved to correspond to the curved periphery of the curved portion. The curved portion may be a motor volume for receiving an electric motor of the drive unit. Having an upper surface of the second sump chamber being curved to correspond to the 3 curved periphery of the curved portion may facilitate increased volume of the second sump chamber by increasing height of the second sump chamber away from centre of the curved portion. In addition, such an arrangement may reduce mass of the housing in comparison to arrangements where the upper surface of the second sump chamber is flat (i.e., so that the upper surface does not track the curved periphery of the curved portion). Optionally, the curved portion is substantially cylindrical, and the second sump chamber comprises a second sump chamber axis which is offset from a central axis of the curved portion in the lateral direction. In other words, the upper surface of the second sump chamber curves further around one side of curved portion than the other side, which may facilitate increased area of the chamber. Optionally, the first and / or second sump chamber comprises a base surface, an upper surface, and first and second sides, wherein the first and second sides flare outwards in the lateral direction from the base surface to the upper surface. In other words, the first and / or second sump chamber has a greater volume at an upper end of the chamber than at a lower end of the chamber. This may help to facilitate pooling of lubricant in the base of the chamber, and thus more reliable pickup of lubricant via the sump outlet. In addition, this may facilitate tapering of exterior sides of the housing towards the lower end of the housing, which may be useful for improving ground clearance (e g., where the drive unit is to be used in an offroad application). The sump compartment may be provided with lubricant from any suitable source. For example, from an external pump. The housing may comprise at least one sump inlet to allow lubricant contained within the interior volume to be transferred into the sump compartment. The at least one sump inlet may comprise first and second sump inlets each in fluid communication with a different region of the interior volume. Optionally, the interior volume comprises a transmission volume for receiving a transmission of the drive unit and a motor volume for receiving an electric motor of the drive unit, wherein the first sump chamber comprises a first sump inlet to allow lubricant contained within the transmission volume to be transferred into the first sump chamber, and wherein the second sump chamber comprises a second sump inlet to allow lubricant contained within the motor volume to be transferred into the second sump chamber. In other words, the sump acts as a common reservoir for lubricant to be transferred (e.g., drained) into from both the transmission volume and the motor volume. This allows a common sump outlet (e.g., lubricant pick-up pipe) to be used for the flow path (e.g., instead of separate sumps / sump outlets for the transmission volume and motor volume). In other embodiments, the sump comprises a single sump inlet to allow lubricant contained within the interior volume to be transferred into the sump compartment. Alternatively, the sump may comprise three or more sump inlets to allow lubricant contained within at least three different regions of the interior volume to be transferred into the sump compartment. Optionally, the housing comprises a dividing wall between the motor volume and the transmission volume, wherein the dividing wall comprises an aperture proximal to a lower end of the dividing wall to allow lubricant to be transferred from the motor volume to the transmission volume. Such a dividing wall keeps the motor and transmission components separate. However, by having an aperture proximal to a lower end of the dividing wall, lubricant can be transferred (e.g. drained) from the motor volume to the transmission volume to avoid capture of lubricant on either side of the dividing wall. According to a further aspect of the present invention there is provided a drive unit comprising a housing as disclosed herein. Such a drive unit benefits from the advantages of the housing outlined above. In some embodiments, the drive unit is an electric drive unit (EDU). In other embodiments, the drive unit is of any other suitable kind (e.g., the housing may house a prime mover such as an internal combustion engine, an electric motor, and / or transmission components such as gears). According to a further aspect of the present invention there is provided a vehicle comprising a drive unit (e.g., an EDU) as disclosed herein. Such a vehicle benefits from the advantages of the housing outlined above. According to a further aspect of the present invention there is provided a method of producing a sump of a housing for a drive unit (e.g., an EDU). The method comprises: a) locating a first core for a first sump chamber of the sump in a casting mould; b) locating a second core for a second sump chamber of the sump in the casting mould so that the second core is in abutment with the first core and partially offset from the first core in a lateral direction; c) introducing molten material into the casting mould; and d) solidifying the molten material to form the first and second sump chambers, whereby the first and second sump chambers are contiguous and partially offset in the lateral direction. Such a method may be used to produce a sump with different sump chambers which are partially offset from each other. This may be beneficial for taking into consideration different packaging constraints whilst maintaining a sump area along a length of the sump. This may also provide improved rigidity of the housing. For example, it will be understood that when the first core is partially offset from the second core, a shoulder at the end of the first core is exposed and a shoulder at the end of the second core is exposed. When the housing is then cast, this results in a first shoulder surface being formed in the first side of the sump and a second shoulder surface being formed in the second side of the sump, the first and second shoulders surfaces facing different directions. Such shoulders in the sump may increase rigidity in comparison to straight / flat sides. Such shoulders in the sump may also act as baffles to inhibit lubricant surge within the sump. Furthermore, such a casting method may allow easier manufacturing of this type of housing / sump than alternatives (such as machining from a block of material). Optionally, the first core has a different cross-sectional shape to the second core in the lateral direction. In other words, the first and second sump cores do not just have the same shape partially offset in the lateral direction, but instead have a different shape to each other. As a consequence, the first and second sump chambers will have different cross-sections. This may facilitate optimal shaping of the sump compartment in different regions of the housing. Optionally, the cross-sectional shape of the first core is substantially symmetrical. Such a substantially symmetrical core shape will produce a substantially symmetrical first sump chamber, which may be beneficial for output of lubricant from the first sump chamber. For example, the cross-sectional shape of the first sump chamber may be split into two sides of substantially the same area, which may reduce the likelihood of lubricant pooling on one particular side of the first sump chamber. Optionally, the cross-sectional shape of the first core is substantially trapezoidal. Atrapezoidal cross-sectional shape (e.g., with an upper edge, a lower edge and sides which taper inwards towards the lower edge) may be particularly beneficial as the tapered sides may allow the housing to taper towards a base of the first sump chamber. This may be beneficial for improving ground clearance, and may ensure suitable pooling of lubricant in the narrower lower end of the first sump chamber to increase reliability of lubricant pick-up. Optionally, the method further comprises prior to step c), locating a third core for an interior volume of the housing in the casting mould, wherein the third core comprises a curved periphery, and wherein the second core comprises a surface 5 which is arranged proximal to the curved periphery of the third core in the casting mould and which is curved to correspond to the curved periphery of the third core. Having a surface of the second core which is arranged proximal to the curved periphery of the third core and which is curved to correspond to the curved periphery may facilitate increased volume of the second sump chamber formed using the second core, by increasing height of the second core away from centre of the third core. In addition, such an arrangement may reduce the area between the second and third core in comparison to arrangements where the proximal surface of the second core is flat, which may reduce the casting mass of the housing. Optionally, the third core is substantially cylindrical, wherein the second core comprises a second core axis, wherein the second and third cores are positioned within the casting mould so that the second core axis is offset from a central axis of the third core in the lateral direction. In other words, the proximal surface of the second core curves further around one side of the third core than the other side, which may facilitate increased sizing of the second core and thus the second sump chamber. Optionally, the first core and / or second core comprises a base surface, an upper surface, and first and second sides, wherein the first and second sides flare outwards in the lateral direction from the base surface to the upper surface. In other words, the first and / or second core defines a greater volume at an upper end of the core than at a lower end of the core. This may help to facilitate pooling of lubricant in the base of the first and second chambers cast with the cores, and thus more reliable pick-up of lubricant. In addition, this may facilitate tapering of exterior sides of the cast housing towards the lower end of the housing, which may be useful for improving ground clearance (e.g., where the drive unit is to be used in an off-road application). 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 an embodiment of the invention; Figure 2 schematically shows functional units and a control system of the vehicle; Figure 3 shows a controller for use in the vehicle of Figure 2; Figure 4 shows a schematic cross-sectional view of an Electric Drive Unit (EDU) assembly of the vehicle of Figures 1 and 2; Figure 5 shows an underside view of the EDU assembly of Figure 4; Figure 6 shows an enlarged underside view of the EDU assembly of Figures 4 and 5; Figure 7 shows an enlarged side cross-sectional view of the EDU assembly of Figures 4 and 5; Figure 8 shows a schematic plan view of a sump of the EDU assembly of Figures 4 to 7; Figure 9 shows a perspective cross-sectional view of a housing of the EDU assembly of Figures 4 to 7, taken along plane A-A illustrated in Figure 7; Figure 10 shows a perspective cross-sectional view of a housing of the EDU assembly of Figures 4 to 7, taken along plane B-B illustrated in Figure 7; Figure 11 shows an enlarged perspective cross-sectional view of a first sump chamber of the housing of Figures 9 and 10; Figure 12 shows an enlarged perspective cross-sectional view of a second sump chamber of the housing of Figures 9 and 10; Figure 13 shows a flowchart of a method of producing a sump of a housing for a drive unit, according to an embodiment; Figure 14 shows a schematic plan view of a casting apparatus for performing the method of Figure 13; and Figure 15 shows a schematic side cross-sectional view of the casting apparatus of Figure 14. DETAILED DESCRIPTION Figures 1 and 2 show an example of an electric vehicle (EV) 10. The electric vehicle 10 comprises a battery or battery pack 40. The battery 40 may be recharged from an external electrical source. The electric vehicle 10 comprises a pair of front wheels 12 at a front axle 28 and a pair of rear wheels 14 at a rear axle 38. The vehicle has at least one electric drive unit (EDU) by which one or more of the wheels are driven. In the illustrated embodiment, the vehicle comprises two electric drive units, each associated with one of the pairs of wheels. In other embodiments, the vehicle may have a dedicated EDU for each of the front wheels 12 and / or a dedicated EDU for each of the rear wheels 14. In the illustrated embodiment, the front wheels 12 are driven by a first electric drive unit (EDU) 20. The first EDU 20 comprises a first motor 22, a front transmission 24 and power electronics 26. The rear wheels 14 are driven by a second electrical drive unit (EDU) 30. The second EDU 30 comprises a second motor 32, a rear transmission 34 and power electronics 36. The first EDU 20 and the second EDU 30 each receive a DC supply from battery 40. The first EDU 20 can be called a first propulsion unit and the second EDU 30 can be called a second propulsion unit. As used herein, the term “transmission” may refer to a device with a plurality of gears through which torque can be transmitted from the drive unit to one or more of the wheels. For example, this may refer to a differential, transaxle, and / or a gearbox. The electric vehicle 10 has a control system with a controller 50 which controls operation of the first EDU 20 and the second EDU 30. In operation, the controller 50 controls the power output of each of the EDUs 20, 30 to supply torque to the wheels 12, 14. Power electronics 26 comprise an inverter which converts the DC supply from battery 40 to an AC supply to drive the first motor 22. The first motor 22 drives the front transmission 24 which, in turn, drives the front axle 28 to apply torque to the front wheels 12. Power electronics 36 comprise an inverter which converts the DC supply from battery 40 to an AC supply to drive the second motor 32. The second motor 32 drives the rear transmission 34 which, in turn, drives the rear axle 38 to apply torque to the rear wheels 14. One or both of the front and rear axles 28, 38 may be a continuous shaft extending through their respective EDU, or a pair of half shafts which extend from their respective EDU. Figure 3 schematically shows the control system. The control system comprises one controller 50, although it will be appreciated that this is merely illustrative. The controller 50 comprises at least one processor 56 which may be any type of processor for executing instructions to control the operation of the system. The processor 56 is electrically connected to other components of the controller via one or more buses 57. Processor-executable instructions 48 may be provided using any data storage device or computer-readable media, such as memory 58. The processor-executable instructions 48 comprise instructions for implementing the functionality of the described methods. The storage / memory 58 is of any suitable type such as non-volatile memory, a magnetic or optical storage device. The processor 56 is configured to access the memory 58 and execute the stored instructions 48. Memory 58, or a separate memory / storage stores data 60 used by the processor 56. Data 60 may comprise data which defines a plurality of operating points of the first motor 22. Instructions 48 may comprise rules for selecting between plurality of operating points of the first motor 22. The controller 50 comprises an input interface 54. The input interface 54 is configured to receive one or more input signals 53 (e.g., a demand for acceleration or a demand for speed). The controller 50 comprises an output interface 55. The output interface 55 is configured to output outputs, such as the control signal 51 to control the first motor 22 (sent to power electronics 26) and the control signal 52 to control the second motor 32 (sent to power electronics 36). The controller 50 is configured to use one or more of the input signals 53 and stored data 60, to generate output signals 51, 52. Optionally, the controller 50 may operate the vehicle in the following ways: (i) Rear-wheel drive (RWD). Torque is only supplied to the rear wheels 14 by operating the second motor 32 to drive the rear wheels 14. The front wheels 12 are not driven by the first motor 22; (ii) All-wheel drive (AWD). Torque is supplied to the rear wheels 14 and to the front wheels 12 by operating the second motor 32 to drive the rear wheels 14 and operating the first motor 22 to drive the front wheels 12; (Hi) Front-wheel drive (FWD). Torque is only supplied to the front wheels 12 by operating the first motor 22 to drive the front wheels 12. The rear wheels 14 are not driven by the second motor 32. In some vehicles, the controller 50 may only operate according to options (i) and (ii), and may not operate according to option (iii). In other embodiments, the electric vehicle may include only one EDU 20, 30. For example, the second EDU 30 may be omitted in embodiments where the electric vehicle is a “front-wheel drive” vehicle, or the first EDU 20 may be omitted in embodiments where the electric vehicle is a “rear-wheel drive” vehicle. In further embodiments, one or more of the wheels may be driven individually by a dedicated EDU. For example, the front wheels 12 may each be connected to one of a pair of front EDUs. In a further example, the rear wheels 14 may be connected to a plurality of rear EDUs, and / or the front wheels 12 may be connected to a plurality of front EDUs. Referring now to Figures 4 and 5, an EDU assembly is indicated at 100. The EDU assembly 100 includes a motor 102 (shown schematically in Figure 4), a transmission 112 (shown schematically in Figure 4), and a housing 150 for the motor 102 and the transmission 112. It will be understood that the EDU assembly 100 illustrated in Figures 4 and 5 could be, or form part of, the first EDU 20 and / or the second EDU 30 illustrated schematically in Figure 2, along with the additional power electronics 26, 36 described above (not illustrated in the EDU assembly 100 of Figures 4 and 5). The motor 102 may be an induction motor (IM). An induction motor can also be called an induction machine, as it is capable of operating as a motor and as a generator. Alternatively, the motor 102 may be a permanent magnet (PM) synchronous motor. In either case, the motor 102 includes a rotor 104 and a stator 106 with electrical windings 108. The motor 102 is operated by suppling an AC supply to the stator windings 108 which causes movement of the rotor 104 about a rotational axis R. IM and PM motors are known and will therefore not be described in more detail. In some embodiments, the motor 102 is of a different kind, such as a DC motor, a universal motor, or a non-electrical motor such as a hydraulic motor. The rotor 104 is coupled to a motor output shaft 110. In other words, the rotor 104 and output shaft 110 are configured for co-rotation about the rotational axis R. In this way, as the rotor 104 is rotated by the AC supply to the stator windings 108, the output shaft 110 is also rotated. The output shaft 110 is supported for rotation relative to the housing 150 by an output shaft bearing arrangement 116 which, in this embodiment, includes a first bearing 116A (shown schematically in Figure 4) on a first side of the output shaft 110 and a second bearing 116B (shown schematically in Figure 4) on a second side of the output shaft 110. The first and second bearings 116A, 116B may be ball bearings, roller bearings or any other suitable bearing. The transmission 112 is responsible for transmitting power from the output shaft 110 of the motor 102 to the front or rear wheels 12, 14 of the electric vehicle 10. Optionally, the transmission 112 includes a differential 118 (shown schematically 8 in Figure 4) which allows half shafts (not shown in Figure 4 or 5) of the respective axle 28, 38 to be rotated at different speeds while receiving power from the motor 102. In some embodiments, the transmission 112 may comprise a gearbox between the output shaft 110 of the motor 102 and the differential 118. The differential 118 may be of any suitable configuration. The differential 118 may include one or more components which are supported for rotation relative to the housing 150 by a differential bearing arrangement (not shown) including one or more bearings. Although not illustrated in Figures 4 and 5, the half shafts of the respective axle 28, 38 may be coupled to the differential 118 via any suitable means (e.g., by engaging external splines on the half shafts with internal splines on a component of the differential 118). The half shafts may be supported for rotation relative to the housing by one or more half shaft bearings 130, which may be ball bearings, roller bearings or any other suitable bearing. The illustrated EDU assembly 100 includes a lubricant recirculation system 200, which supplies lubricant to one or more rotating components of the EDU (e.g., motor 110, bearings 116A, 116B, 130, and / or the differential 118 outlined above). The lubricant, such as oil, may both lubricate and cool those rotating components. The lubricant recirculation system 200 includes a sump 152 and a lubricant pump 202 which supplies lubricant along a flow path between the sump 152 and the interior of the housing 150. The flow path is at least in part defined by one or more conduits. The lubricant which is supplied into the housing 150 is then drained into the sump 152 at a lower end of the housing 150. A lubricant pick-up pipe 154 is provided adjacent to or in the sump 152. The lubricant pick-up pipe 154 has a lubricant inlet aperture 156 through which lubricant may be drawn into the pick-up pipe 154 by means of the lubricant pump 202. In this way, lubricant is recirculated by the lubricant pump 202 through the housing 150. The lubricant recirculation system 200 may also include a lubricant filter 204. In the illustrated embodiment, the lubricant filter 204 is located along the flow path downstream of the lubricant pump 202. In the illustrated embodiment, the housing 150 has a first portion 150A which houses the motor 102, and a second portion 150B which houses the transmission 112. In the illustrated embodiment, the first and second housing portions 150A, 150B are discrete components which are coupled together (e.g., via a bolting arrangement). The housing 150 may also include a cover 150C (shown schematically in Figure 4) which closes an end of the first housing portion 150A opposite to the second housing portion 150B. The cover 150C may be a discrete component which is coupled to the first housing portion 150A (e.g. via a bolting arrangement), or may instead be integrally formed with the first housing portion 150A. In alternative embodiments, any other suitable housing configuration may be used. The housing 150 may have one or more mounting features 132 for mounting the EDU assembly 100 to a sub-frame of the electric vehicle 10 and / or for reacting torsional forces generated by the EDU assembly. The illustrated EDU assembly 100 also includes seal assemblies 300 at opposite ends of the housing 150, for sealing against the half shafts of the respective axle 28, 38. Such seal assemblies 300 provide a sealed system inside the housing 150 and thereby inhibit ingress of contaminants (e.g., dirt,, debris, water, etc.) inside the housing 150. Referring now to Figures 4 to 12, the housing 150 and sump 152 will be described in more detail. In the illustrated embodiment, the housing 150 defines an interior volume 162 for one or more drive unit components of the EDU assembly 100. In particular, the interior volume 162 includes a transmission volume 162A for receiving the transmission 112 of the EDU assembly 100 and a motor volume 162Bfor receiving the electric motor 102 of the EDU. As mentioned above, the housing 150 also has a sump 152 which defines a sump compartment 164 below the interior volume 162. One or more sump inlets 170A, 170B are provided in the housing 150 to allow lubricant contained within the interior volume 162 to be transferred (e.g., drained) into the sump compartment 164. The housing 150 also defines a sump outlet 168 forming part of a flow path between the sump compartment 164 and the interior volume 162 for providing a lubricant from the sump 152 to the one or more drive unit components via the lubricant recirculation system 200. In the illustrated embodiment, the sump compartment 164 has a first sump chamber 164A and a second sump chamber 164B which is contiguous with and partially offset from the first sump chamber 164A in a lateral direction L. In other words, the housing 150 has a vertical axis V (illustrated on Figure 4) which extends from the sump 152 at a lower end 157 of the housing 150 to an upper end 158 of the housing 150 opposite to the sump 152, and the second sump chamber 164B is partially offset from the first sump chamber 164A in a direction which is transverse (e.g., perpendicular) to the vertical axis V. The term “lateral direction” is used herein to refer to a direction which extends along a horizontal plane of the EDU assembly 100. For example, when the housing 150 is mounted in the vehicle 10 in use, the lateral direction L may be a longitudinal direction between front and rear ends of the vehicle 10, or a transverse direction between left and right sides of the vehicle 10. The sump compartment 164 may comprise a substantially planar base surface 182 and the lateral direction L may be parallel to the substantially planar base surface 182. In this way, there is no step between the base surface 182A of the first sump chamber 164A and the base surface 182B of the second sump chamber 164B, so that lubricant can flow freely between the first and second sump chambers 164A, 164B. In this context, the term “substantially planar” will be understood to mean that there are no steps in the base surface 182, but the base may not be exactly planar due to draft angles of casting cores used to produce the sump 152. In the illustrated embodiment, the housing 150 defines a first end 160A having a first opening for receiving a first shaft (not shown), a second end 160B having a second opening for receiving a second shaft (not shown), and a central axis C which extends from the first opening to the second opening. In this embodiment, the central axis C is coaxial with the rotational axis R described above. The central axis C can be considered to extend along a horizontal plane of the EDU. The lateral direction L in which the second sump chamber 164B is offset in relation to the first sump chamber 164A is in a direction parallel with the horizonal plane defined by the central axis C. In particular, the lateral direction L is perpendicular to both the vertical axis V and the central axis C of the housing 150. In this context, it will be understood that the term “partially offset” means that each sump chamber 164A, 164B has a cross-sectional area with an intersecting portion 165A, 165B which overlaps with the cross-sectional area of the other sump chamber 164A, 164B, and an offset portion 166A, 166B which does not overlap with the cross-sectional area of the other sump chamber 164A, 164B. For example, such intersecting portions 165A, 165B are shown by the dashed box on Figure 8. Similarly, such offset portions 166A, 166B are shown on either side of the dashed box on Figure 8. As best illustrated in Figure 8, the first sump chamber 164A has a first sump chamber axis Si which defines a central axis of the first sump chamber 164A. Similarly, the second sump chamber 164B has a second sump chamber axis S2 which defines a central axis of the second sump chamber 164B. The first and second sump chamber axes Si, S2 are parallel but offset from each other in the lateral direction L. By having a sump 152 with contiguous first and second sump chambers 164A, 164B which are partially offset in the lateral direction L, different packaging constraints can be taken into consideration whilst maintaining a sump area along a length of the sump 152 (e.g., as opposed to just moving a single side wall of the sump 152, which would result in a reduced sump area). For example, as best illustrated in Figure 10, the partial off-setting of the second sump chamber 164B provides increased clearance for an EDU mount 132 on a lower half of the housing 150. This allows the EDU mount 132 to be 10 positioned higher up the housing 150 and / or for an angled surface 184 to be formed on the housing behind the second sump chamber 164B in the lateral direction, which may improve ground clearance of the vehicle (e.g., for off-road applications). As best illustrated in Figures 8, 11 and 12, the sump compartment 164 has a first side 174 and a second side 178. The first side 174 of the sump compartment 164 has a first shoulder surface 176 between the first and second sump chambers 164A, 164B. Similarly, the second side 178 of the sump compartment 164 has a second shoulder surface 181 between the first and second sump chambers 164A, 164B. Such shoulder surfaces 176, 181 may increase rigidity in comparison to straight / flat sides. Such shoulder surfaces 176, 181 may also inhibit lubricant surge within the sump 152 (e.g., under acceleration / deceleration) by acting as baffles along the first and second sides 174, 178 of the sump compartment 164. In the illustrated embodiment, the first and second shoulder surfaces 176, 181 extend parallel to the lateral direction Land face opposite directions. In alternative embodiment, the first and / or second shoulder surfaces may be angled relative to the lateral direction L. As best illustrated in Figures 9 to 12, the first sump chamber 164A has a different cross-sectional shape to the second sump chamber 164B in the lateral direction. In other words, the first and second sump chambers 164A, 164B do not just have the same shape partially offset in the lateral direction, but instead have a different shape to each other. This may facilitate optimal shaping of the sump compartment 164 in different regions of the housing 150. In the illustrated embodiment, the cross-sectional shape of the first sump chamber 164A is substantially symmetrical. In this context, the term “substantially symmetrical” means that the cross-sectional shape of the first sump chamber 164A may be split into two sides of approximately the same area and shape, but the two sides may not be exactly identical. For example, as illustrated in Figure 11, the second side 178A is flat whereas the first side 174A has a slight curve to accommodate a fastening feature of the housing 150, but both sides of the first sump chamber 164A are approximately equal in size and shape. In the illustrated embodiment, the cross-sectional shape of the first sump chamber is substantially trapezoidal (e.g., having an upper surface 180A, a lower surface 182A and sides 174A, 178A which taper inwards towards the lower surface 182A). As best illustrated in Figures 10 and 12, the motor volume 162B of the interior volume 162 has a curved periphery 183, and the second sump chamber 164B is located underneath the motor volume 162B. The upper surface 180B of the second sump chamber 164B is curved to correspond to the curved periphery 183 of the motor volume 162B. In the illustrated embodiment, the motor volume 162B is substantially cylindrical and defines a central axis which, in this embodiment, is coaxial with the central axis C of the housing 150 and the rotational axis R of the motor 102 described above. The second sump chamber axis S2 is offset from the central axis of the motor volume 162B curved portion in the lateral direction L. In other words, the upper surface 180B of the second sump chamber 164B curves further around one side of the motor volume 162B than the other side. In particular, the second side 178B of the second sump chamber 164B extends to a greater height than the first side 174B. Although the first and second sump chambers 164A, 164B have different cross-sectional shapes outlined above, both have a base surface 182A, 182B, an upper surface 180A, 180B, and first and second sides 174A, 174B, 178A, 178B. In both the first and second sump chambers 164A, 164B, the firstand second sides 174A, 174B, 178A, 178B flare outwards in the lateral direction L from the base surface 182A, 182B to the upper surface 180A, 180B. In other words, the first and second sump chambers both have a greater volume at an upper end of the chamber 164A, 164B than at a lower end of the 11 chamber 164A, 164B. This may help to facilitate pooling of lubricant in the base of the chamber 164A, 164B, and thus more reliable pick-up of lubricant via the sump outlet 168. In addition, this may facilitate tapering of exterior sides of the housing 150 towards the lower end 157 of the housing 150 (e.g., the angled surface 184 shown in figure 10). This may be useful for improving ground clearance (e.g., where the EDU 100 is to be used in an off-road application). As best illustrated in Figure 7, the first sump chamber 164A has a first sump inlet 170A to allow lubricant contained within the transmission volume 162Ato be transferred into the first sump chamber 170A. Similarly, the second sump chamber 164B has a second sump inlet 1706 to allow lubricant contained within the motor volume 1626 to be transferred into the second sump chamber 164B. In other words, the sump 152 acts as a common reservoir for lubricant to be transferred (e.g., drained) into from both the transmission volume 162A and the motor volume 1628. This allows a common sump outlet 168 to be used instead of separate sumps / sump outlets for the transmission volume 162A and motor volume 1628. In other embodiments, the sump 152 has a single sump inlet to allow lubricant contained within the interior volume 162 to be transferred into the sump compartment 164. For example, lubricant may be transferred from the motor volume 162B to the transmission volume 162A and then from the transmission volume 162A to the sump 152. In the illustrated embodiment, the housing 150 has a dividing wall 163 between the motor volume 162B and the transmission volume 162A. In the illustrated embodiment, the dividing wall 163 has an aperture 185 proximal to a lower end of the dividing wall 163 to allow lubricant to be transferred from the motor volume 162B to the transmission volume 162A (e.g., to avoid capture of lubricant on either side of the dividing wall 163). The aperture 185 may be particularly beneficial when the EDU assembly 100 is not flat (e.g., when the vehicle 10 is positioned on a hill) so that any lubricant which is not able to drain from the motor volume 162B through the second sump inlet 170B into the second sump chamber 164B can instead pass through the aperture 185 into the transmission volume 162A and then into the first sump chamber 164A via the first sump inlet 170A. As best illustrated in Figure 7, the sump outlet 168 has a mounting arrangement 172 configured to mount the lubricant pick-up pipe 154 in the first sump chamber 164A. In particular, the mounting arrangement 172 is configured to align the lubricant pick-up pipe 154 with a centre of the first sump chamber 164A (i.e., with the first sump chamber axis Si), as illustrated schematically by the dashed lines on Figure 6. This may facilitate improved lubricant pick-up in range of operating conditions (e.g., during acceleration / deceleration, or when positioned on a hill). A method of producing the sump 152 of the housing 150 is illustrated as a flow chart in Figure 13. An apparatus for performing the method is illustrated schematically in Figures 14 and 15. The method of producing the sump 152 of the housing 150 involves the following steps: a) locating a first core 188 for a first sump chamber 164A of the sump 152 in a casting mould 187; b) locating a second core 189 for a second sump chamber 164B of the sump 152 in the casting mould 187 so that the second core 189 is in abutment with the first core 188 and partially offset from the first core 188 in a lateral direction L (as illustrated in Figure 14); c) introducing molten material into the casting mould 187; and d) solidifying the molten material to form the first and second sump chambers 164A, 164B, whereby the first and second sump chambers 164A, 164B are contiguous and partially offset in the lateral direction L. Such a method may be used to produce the sump 152 described in detail above. Such a casting method may also be easier than other alternatives (such as machining from a block of material). The first core 188 may have a different cross-sectional shape to the second core 189 in the lateral direction L For example, the first core 188 may have the same cross-sectional shape as the first sump chamber 164A outlined in Figure 11, and the second core 189 may have the same cross-sectional shape as the second sump chamber 164B outlined in Figure 12. The method of producing the sump 152 may also include, prior to step c), locating a third core 190 in the casting mould 187 (e.g., for the motor volume 162B described above), and / or locating a fourth core 191 in the casting mould 187 (e.g., for the transmission volume 162A described above). The third core 190 may have a curved periphery 192 (e.g., the third core 190 may be substantially cylindrical) and the second core 189 may have a surface 193 which is arranged proximal to the curved periphery 192 of the third core 190 in the casting mould 187 and which is curved to correspond to the curved periphery 192 of the third core 190. The second core 189 may have a second core axis, and the second and third cores 189, 190 may be positioned within the casting mould 187 so that the second core axis is offset from a central axis of the third core 190 in the lateral direction L. In other words, the proximal surface 193 of the second core 189 may curve further around one side of the third core 190 than the other side. The first core 188 and / or second core 189 may each have a base surface 194, an upper surface 195, and first and second sides 196, 197. The first and second sides 196, 197 flare outwards in the lateral direction L from the base surface 194 to the upper surface 195. In other words, the first and / or second core 188, 189 may define a greater volume at an upper end of the core than at a lower end of the core. 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 housing for an electric drive unit, wherein the housing defines:an interior volume for one or more drive unit components of the EDU, a sump defining a sump compartment below the interior volume, and a sump outlet forming part of a flow path between the sump compartment and the interior volume for providing a lubricant from the sump to the one or more drive unit components,wherein the sump compartment comprises a first sump chamber and a second sump chamber which is contiguous with and partially offset from the first sump chamber in a lateral direction.

2. The housing of claim 1, wherein the sump compartment comprises first and second sides, wherein the first side of the sump comprises a first shoulder surface between the first and second sump chambers and the second side of the sump comprises a second shoulder surface between the first and second sump chambers.

3. The housing of claim 2, wherein the first and second shoulder surfaces extend parallel to the lateral direction and face opposite directions.

4. The housing of any preceding claim, wherein the first sump chamber has a different cross-sectional shape to the second sump chamber in the lateral direction.

5. The housing of any preceding claim, wherein the cross-sectional shape ofthe first sump chamber is substantially symmetrical, optionally substantially trapezoidal.

6. The housing of claim any preceding claim, wherein the sump outlet comprises a mounting arrangement configured to mount a lubricant pick-up pipe in the first sump chamber; optionally, wherein the mounting arrangement is configured to align the lubricant pick-up pipe with a centre ofthe first sump chamber.

7. The housing of any preceding claim, wherein the interior volume comprises a curved portion having a curved periphery, wherein the second sump chamber is located underneath the curved portion, and wherein an upper surface of the second sump chamber is curved to correspond to the curved periphery of the curved portion.

8. The housing of claim 7, wherein the curved portion is substantially cylindrical, and wherein the second sump chamber comprises a second sump chamber axis which is offset from a central axis of the curved portion in the lateral direction.

9. The housing of any preceding claim, wherein the first and / or second sump chamber comprises a base surface, an upper surface, and first and second sides, wherein the first and second sides flare outwards in the lateral direction from the base surface to the upper surface.

10. The housing of any preceding claim, wherein the interior volume comprises a transmission volume for receiving a transmission ofthe EDU and a motor volume for receiving an electric motor ofthe EDU, wherein the first sump chamber comprises a first sump inlet to allow lubricant contained within the transmission volume to be transferred into the first sump chamber, and wherein the second sump chamber comprises a second sump inlet to allow lubricant contained within the motor volume to be transferred into the second sump chamber.

11. An electric drive unit comprising the housing of any preceding claim.

12. A vehicle comprising the EDU of claim 11.

13. A method of producing a sump of a housing for an electric drive unit, the method comprising:locating a first core for a first sump chamber of the sump in a casting mould;locating a second core for a second sump chamber of the sump in the casting mould so that the second core is in abutment with the first core and partially offset from the first core in a lateral direction;introducing molten material into the casting mould; andsolidifying the molten material to form the first and second sump chambers, whereby the first and second sump chambers are contiguous and partially offset in the lateral direction.

14. The method of claim 13, wherein the first core has a different cross-sectional shape to the second core in the lateral direction.

15. The method of claim 13 or 14, further comprising:prior to introducing molten material into the casting mould, locating a third core for an interior volume of the housing in the casting mould, wherein the third core comprises a curved periphery, and wherein the second core comprises a surface which is arranged proximal to the curved periphery of the third core in the casting mould and which is curved to correspond to the curved periphery of the third core.

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