Oil sump

Abstract

An oil sump (100 Fig. 5) has a first shell 130 that in use forms a base of the oil sump, a second shell 120 that forms a roof of the oil sump, and a mesh 129 with an outer rim 129b, for filtering oil being drawn from the oil sump by a pump (200 Fig. 5). The first shell can include a first contacting part 135 for engaging with a first face of the outer rim of the mesh and the second shell can include a second contacting part 125 for engaging with a second face of the outer rim of the mesh, the shells engaging to clamp the mesh. Alternatively, the first shell can include a tray having an open upper face 132a for receiving the mesh and an opening in the base 132b for receiving oil, with the opening covered by the mesh. The tray can include a retaining rib 136 or protrusions which are of an internal diameter smaller than an external diameter of the mesh. The arrangement provides clamping of the mesh between the upper and lower shells of the sump and avoids over-moulding and does not require any additional fixings or adhesives.

Description

TECHNICAL FIELD The present disclosure relates to an oil sump. Aspects of the invention relate to an oil sump, a vehicle comprising an oil sump, and a method of assembling an oil sump. BACKGROUND An electric vehicle is provided with one or more electric drive units which receive electrical energy from a vehicle battery and generate torque for propelling the vehicle using an electric motor. The electric drive unit may be oil lubricated, with the oil being pumped into the electric drive unit from an oil sump provided below the electric drive unit, into which oil pools under gravity from the electric drive unit. Overtime, it is possible that debris may find its way into the recirculating oil. To address this problem, a mesh may be fitted into the oil sump during assembly and will accumulate debris over the life of the unit, filtering it out before the oil is pumped back into the electric drive unit. However, since the mesh is a distinct part from the shell of the oil sump, fixing it in place is not straightforward. It is important that the mesh be securely held in position to protect the internals of the oil sump. It is desirable that this be achieved without additional mechanical fixings (such as screws or clips) and without adhesives (which may not function effectively while immersed in oil). While over-moulding of the mesh could be an option, this would add significantly to the complexity of the tooling required to form the various parts of the oil sump. 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 an oil sump, a vehicle comprising an oil sump, and a method of assembling an oil sump as claimed in the appended claims. According to an aspect of the invention, there is provided an oil sump, comprising: a first shell, to form a base of the oil sump; a second shell, to form a roof of the oil sump; and a mesh for filtering oil being drawn from the oil sump by a pump, the mesh having an outer rim; wherein the first shell comprises a first contacting part for engaging with a first face of the outer rim of the mesh, and the second shell comprises a second contacting part for engaging with a second face of the outer rim of the mesh; and wherein when the first shell and the second shell are engaged with each other, the outer rim of the mesh is clamped between the first contacting part and the second contacting part. In this way, it is possible to provide an oil sump geometry designed which provides a clamping mechanism for the mesh between the upper and lower shells of the sump. The two shells may then be welded or otherwise fixed together around their perimeter while the mesh remains securely clamped between the shells. This technique avoids any requirement for over-moulding, and does not require any additional fixings or adhesives. The first contacting part and the second contacting part may be annular. The annuluses may have different diameters. For example, the first contacting part and the second contacting part may contact the outer rim of the mesh at different radial positions. As a result, when the first and second contacting parts press towards each other and contact the mesh, the mesh deflects, providing an improves seal between the first contacting part, the mesh, and the second contacting part. The first shell may comprise a tray having an open upper face for receiving the mesh, and having an opening in the base thereof for receiving oil, wherein the opening is covered, in use, by the mesh. The first contacting part may comprise a continuous raised ridge on the base of the tray extending around the opening in the base. The walls of the tray may serve to constrain the location of the mesh prior to it being secured by compression between the first and second contacting parts. The tray may comprise an internal rib or protrusions on a wall thereof for retaining the mesh within the tray. The rib or protrusions may have an internal diameter smaller than an external diameter of the mesh. As a result, the mesh may be retained generally in place even if the first shell is moved around or inverted, which is beneficial during assembly of the sump when the lower shell may need to be manipulated (for example turned upside down) before the second shell is secured to it (at which point the first and second contacting parts will prevent or inhibit movement of the mesh). The second shell may comprise a conduit for bearing oil to the pump, wherein the conduit terminates at the second contacting part. In this way, no additional parts are required to define the second contacting part - it can be an integral part of the upper shell, and in particular of the conduit. According to another aspect of the invention, there is provided an oil sump, comprising: a first shell, to form a base of the oil sump; a second shell, to form a roof of the oil sump; and a mesh for filtering oil being drawn from the oil sump by a pump, the mesh having an outer rim; wherein the first shell comprises a tray having an open upper face for receiving the mesh, and having an opening in the base thereof for receiving oil, wherein the opening is covered, in use, by the mesh; and wherein the tray comprises an internal rib or protrusions on a wall thereof for retaining the mesh within the tray, the rib or protrusions having an internal diameter smaller than an external diameter of the mesh. In this way, the mesh can be easily retained (in the tray) during assembly. In particular, once the mesh is pressed into the lower shell (past the internal rib or protrusions), this geometry provides a temporary retention feature before the upper shell is clamped down and welded on. According to another aspect, there is provided a vehicle comprising an electric drive unit and an oil sump according to any preceding claim, wherein the pump is configured to pump oil from the oil sump through the mesh and to the electric drive unit. According to another aspect, there is provided a method of assembling the oil sump described above, comprising: urging the mesh past the rib to be received into the tray; inverting the first shell; and welding the first shell and the second shell together while inverted. 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 schematic representation of a vehicle formed having an electric drive unit to be lubricated with oil from a sump; Figure 2 shows a schematic 3D view of an oil sump; Figure 3 shows a schematic plan view of an upper shell of the oil sump of Figure 2; Figure 4 shows the schematic view of Figure 3 with a pump attached; Figure 5 shows the oil sump in situ beneath an electric drive unit; Figure 6 shows a cross-sectional schematic view through a portion of the oil sump including a mesh and tray retention feature; Figure 7 shows a schematic view of the pickup pipe, mesh and the tray features of Figure 6; Figure 8 shows a schematic view of the components of Figure 7, along with an upper portion of the oil sump, with the oil flow direction depicted; and Figure 9 shows a schematic view of the pickup pipe and upper portion of the oil sump with a lid removed and the lower shell removed. DETAILED DESCRIPTION An oil sump, a vehicle comprising an oil sump, and a method of assembling an oil sump in accordance with embodiments of the present invention are described herein with reference to the accompanying figures 1 to 9. With reference to Figure 1, there is illustrated a simplified top view of a vehicle 1. The vehicle 1 is an electric vehicle having an electric drive unit (EDU) 10 which receives electrical energy from a battery 20 and generates torque which is delivered via a powertrain to the wheels of the vehicle 1. The electric drive unit 10 comprises a motor for generating torque, power electronics (fordrawing electrical power from the vehicle battery 20 and delivering it to the motor as an AC voltage), and a transmission including a gearbox for delivering the torque to the wheels at the most appropriate gear ratio. The electric drive unit 10 uses oil to lubricate certain moving parts of the motor and transmission. This oil is pumped into the appropriate part of the main housing of the electric drive unit 10, and in use moves under gravity to the bottom of the housing of the electric drive unit 10 to pool in a sump (described subsequently), from which it can be pumped back into the main housing of the electric drive unit 10. Shown in Figures 2, 3 and 4 is an oil sump 100, suitable for being positioned at the base of (immediately beneath) the electric drive unit 10. Figure 2 shows the exterior of the oil sump 100. The oil sump 100 can be seen from Figure 2 to comprise an upper shell 120 and a lower shell 130. These are welded togetherto form a chamber 101 for holding oil. The electric drive unit 10 is positioned in use above the upper shell 120. Figure 3 shows a plan view of the upper shell 120. The upper shell 130 can be seen to comprise a plurality of openings 122. These align with openings in the base of the EDU 10 not visible), and receive oil from the EDU 10, entering the openings 122 under gravity. Oil in the chamber 101 is drawn up a pickup-pipe 126 which has one end close to a base of the chamber 101 (proximate the lower shell 130) and another end which terminates at a connector 126a. As shown in Figure 4, a pump 200 is connected to the connector 126a, and is connected also to a connector 124c, which leads to a high-pressure conduit 124b integrated into the upper shell 120. A pipe 124a is a continuation of the high-pressure conduit 124b and extends upwardly from the upper shell 120, towards and into the main body of the electric drive unit 10, where it is delivered to parts of the electric drive unit 10 to be lubricated. Figure 5 shows the electric drive unit 10, the sump 100 and the pump 200 in an assembled state. It can be seen that the electric drive unit 10 is disposed immediately above the sump 100. Oil moves from the electric drive unit 10 into the sump 100 via the openings 122 under gravity (at low pressure), and from the sump 100 into the electric drive unit 10 via the pump 200 and the high-pressure conduit and pipe 124b, 124a under high pressure, as generated by the pump 200. In this way, the oil is recirculated through the electric drive unit 10. A breather pipe 128 extends upwardly from the upper shell 120, and provides an opening between the chamber within the sump 100 and atmospheric pressure, to reduce air lock forming in the sump 100. Referring to Figure 6, a portion of the lower shell 130 is shown. This forms the base of the oil sump 100, including a floor 102. The upper shell 120 (which forms the roof of the oil sump 100, as well as providing other internal features to be described subsequently) is not visible in Figure 6, and the oil sump 100 is in a disassembled state. The first shell 130 comprises a tray 132 having an open upper face 132a for receiving a mesh 129, and having an opening 132b in a base 133 thereof for receiving oil. The opening 132b is covered, in use, by the mesh 129. The mesh 129 serves to filter oil being drawn from the oil sump by the pump 200. The tray 132 is spaced away from the floor 102 of the oil sump by a support 103. As a result, oil is able to flow into the space provided between the tray 132 and the floor 102. The mesh 129 has a perforated central portion 129a and an unperforated outer rim 129b. The perforated central portion 129a serves a filtering function by permitting the passage of liquid oil but not solid debris, while the outer rim 129b rests on the base 133 of the tray 132, around the periphery of the opening 132b. The base 133 comprises a first annular contacting part 135 for engaging with a first face of the outer rim 129b of the mesh 129. More specifically, the outer rim 129b of the mesh 129 rests, in use, on the first annular contacting part 135. In this implementation, the first annular contacting part 135 comprises a continuous raised ridge on the base 133 of the tray 132 extending around the opening 132b in the base 133. The tray 132 comprises an internal rib 136 on a wall 138 thereof for retaining the mesh 129 within the tray 132. The wall 138 is perpendicular to the base 133 of the tray 132, and has a cylindrical shape. The rib 136 has an internal diameter smaller than an external diameter of the (outer rim 129b of the) mesh 129. While in the Figures a single continuous rib is provided, one or more protrusions could be provided instead. As a result, once the mesh 129 has been placed in the tray 132 and urged past the rib 136 (or protrusions), it cannot exit the tray 132 even if the entire assembly is inverted. It will be appreciated that it is possible to urge the mesh 129 past the rib 136 because the mesh 129 is able to deform slightly to move past the rib 136 when sufficient pressure is applied due to its thinness and flexible nature. Referring to Figure 7, the same portion of the lower shell 130 of Figure 6 is shown, but in this case with internal structures of the upper shell 120 being present, and the lower shell 130 and upper shell 120 being in an assembled state. The space between the lower shell 130 and the upper shell 120 defines the chamber 101 for holding the oil. The upper shell 120 comprises the pickup pipe 126 forming a conduit for bearing oil to the pump 200. The upper shell 120 comprises a second annular contacting 125 part for engaging with a second face (opposite to the first face) of the outer rim 129b of the mesh 129. When the lower shell and the upper shell are engaged with each other (that is, when the lower and upper shells of the sump are assembled together), the outer rim 129b of the mesh 129 is clamped between the first annular contacting part 135 and the second annular contacting part 125. The first annular contacting part 135 and the second annular contacting part 125 contact the outer rim 129b of the mesh 129 at different radial positions with respect to a longitudinal axis of the mesh 129. As a result of the different radial positions of the two contacting parts, when the mesh 129 is clamped between the first and second and second contacting parts this causes the mesh 129 (and most particularly the outer rim 129b) to deform and deflect from its natural (unstressed and unclamped) position, which tends to take up any imperfections in the mesh outer rim 129b and / or the contacting parts 125,135, resulting in a better seal. In the Figures, the first annular contacting part 135 is inward (has a smaller diameter) than the second annular contacting part 125, but in other implementations this arrangement could be reversed. Figures 8 and 9 show the internal features of the upper shell which define the pickup pipe, and how those interact with the internal features of the lower shell 130. In particular, Figure 8 shows the assembly including the lower shell 130, the upper shell 120, with a secondary cover 170 provided over the main part of the upper shell 120. Part of the pickup pipe 124 is defined between a channel 185 formed in the upper shell 120 and the underside 172 of the secondary cover 170. Figure 9 shows only the upper shell 120 structures, with the secondary cover 170 removed and the lower shell 130 absent, to provide a clearer view of the upper shell features. Considering Figures 7 to 9, it will be appreciated that the upper shell defines (in part) the conduit (pick up pipe) 126 for bearing the oil to the pump 200. The pick-up pipe 126 can be seen to extend from a pick-up mouth 127 near the base of the chamber 101 (the opening in the base of the tray 132, which is covered, in use, by the mesh), to an outlet, which may either be the connection 24, or an upstream part of the conduit 126 in fluid communication with the connection 24. Directional arrow A shows a flow path from the main body of the chamber 101 and into the mouth 127, then along the pipe 126 and out of the sump 100 (towards and to the electric drive unit 10). It can be seen that the pipe 126 turns through 90° as it approaches the roof of the upper shell 120, then extends parallel with the roof of the upper shell 120 and the base of the lower shell 130 towards the outlet and pump 200. The opening (at or near the mouth of the pickup pipe) has a first diameter and the outlet has a second diameter. The first diameter is larger than the second diameter. More specifically, the conduit comprises a transition portion 198 having sides which slope inwards from the mouth to reduce the diameter of the conduit towards the second diameter. The second diameter may be reached relatively close to the mouth of the pickup pipe (compared with the distance to the outlet), and then the conduit may continue with substantially the second diameter until the outlet. The mesh 129 is provided within or at the mouth 127 to inhibit debris I solids from being drawn into the pick-up pipe 126 and carried to the pump 200. Such solids could damage the pump, or reduce its pumping efficiency and / or pressure. The mesh is shaped to extend into (and to be at least partially recessed into) the mouth 127 and the transition portion 198 of the conduit. That is, both the transition portion of the conduit and the mesh have a frustoconical shape. The sides of the frustoconical shape of the mesh extend parallel with the sloping sides of the transition portion into the conduit. The upper shell 120 can be seen to comprise a generally cylindrical wall 190 which includes a first annular part of the conduit 192 which extends into the tray 132, terminating in the second annular contacting part which clamps against the mesh 129. The transition portion 198 of the conduit extends inwardly from the generally cylindrical wall (towards a common central axis), defining one or more cavities 187a, 187b between the cylindrical wall 190 and the sloping sides of the transition portion 198. That is, to save weight and materials and simplify the manufacturing process a void is formed between the generally cylindrical wall 190 which extends with constant cross section from the main body of the second shell 130 to provide rigidity (important because these walls 190 provide the clamping force to the mesh 129), and the walls of the pickup pipe as they follow the narrowing cross-section 198. These cavities (the void) extend around most or all of the circumference of the conduit. To one side of the conduit at least one of the cavities is open to the conduit downstream of the transition portion. This is the side of the conduit in the direction of flow of To assemble the oil sump, the first (lower) shell is provided, and the mesh is urged past the rib to be received into the tray. The first shell is then inverted, which provides improved access to joins between the first and second shells which are to be welded in a subsequent stage. The rib prevents the mesh from falling out of the tray in the first shell while it moves into and adopts the inverted position. The second shell is then placed against the first shell, resulting in the mesh becoming clamped between the first and second contacting parts. The first shell and the second shell are then welded together while inverted. The oil sump may then be returned to its upright position for further assembly steps, such as attachment of the pump and integration with the electric drive unit 10. From the above description, it shall be appreciated that the geometry of the internal feature of the upper and lower shells of the sump 100 provides a clamping mechanism between the upper shell 120 and lower shell 130 of the sump 100. The two shells 120,130 are then welded together around the perimeter thereof. The mesh 129 also needs to be retained during assembly. To achieve this, once the mesh is pressed into the (tray 132 of the) lower shell 130, the geometry provides a temporary retention feature (rib 136) which retains the mesh 129 in place until the upper shell 120 is clamped down and welded on (whereupon the mesh is clamped by the first and second contacting parts). The start of the pickup pipe (from the mouth 127) widens to act like a funnel, smoothing the turbulent flow of oil around the entrance of the pick-up pipe 126. Since it would be undesirable to introduce additional sliders to the tooling used to form the upper shell 120, the proposed geometry achieves the flared design with just an upper and lower tool. While this does create a cavity in the pipe, oil flow analysis indicates that this does not have a significant negative effect on the oil flow. While in the Figures the first and second contacting parts are annular, in other examples the contacting parts may not be annular, but of a different shape. For example, the contacting parts may be oval, square, rectangular or any other shape. However, an annular contacting part, paired with a circular pickup mouth and circular, conical orfrustoconical mesh can be expected to provide better fluid flow qualities as oil is drawn into the pickup pipe. 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. An oil sump, comprising:a first shell, to form a base of the oil sump;a second shell, to form a roof of the oil sump; anda mesh for filtering oil being drawn from the oil sump by a pump, the mesh having an outer rim;wherein the first shell comprises a first contacting part for engaging with a first face of the outer rim of the mesh, and the second shell comprises a second contacting part for engaging with a second face of the outer rim of the mesh; andwherein when the first shell and the second shell are engaged with each other, the outer rim of the mesh is clamped between the first contacting part and the second contacting part.

2. The oil sump according to claim 1, wherein the first contacting part and the second contacting part are annular.

3. The oil sump according to claim 1, wherein the first contacting part and the second contacting part contact the outer rim of the mesh at different radial positions.

4. The oil sump according to any preceding claim, wherein the first shell comprises a tray having an open upper face for receiving the mesh, and having an opening in the base thereof for receiving oil, wherein the opening is covered, in use, by the mesh.

5. The oil sump according to claim 4, wherein the first contacting part comprises a continuous raised ridge on the base of the tray extending around the opening in the base.

6. The oil sump according to claim 4 or claim 5, wherein the tray comprises an internal rib or protrusions on a wall thereof for retaining the mesh within the tray.

7. The oil sump according to claim 6, wherein the rib or protrusions have an internal diameter smaller than an external diameter of the mesh.

8. The oil sump according to any preceding claim, wherein the second shell comprises a conduit for bearing oil to the pump, wherein the conduit terminates at the second contacting part.

9. An oil sump, comprising:a first shell, to form a base of the oil sump;a second shell, to form a roof of the oil sump; anda mesh for filtering oil being drawn from the oil sump by a pump, the mesh having an outer rim;wherein the first shell comprises a tray having an open upper face for receiving the mesh, and having an opening in the base thereof for receiving oil, wherein the opening is covered, in use, by the mesh; andwherein the tray comprises an internal rib or protrusions on a wall thereof for retaining the mesh within the tray, the rib or protrusions having an internal diameter smaller than an external diameter of the mesh.

10. A vehicle comprising an electric drive unit and an oil sump according to any preceding claim, wherein5 the pump is configured to pump oil from the oil sump through the mesh and to the electric drive unit.

11. A method of assembling the oil sump of claim 9, comprising:urging the mesh past the rib to be received into the tray;inverting the first shell; and10 welding the first shell and the second shell together while inverted.

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