Vehicle sump

Abstract

A sump 20 for an electric drive unit of a vehicle. The sump comprises a housing 28 that encloses an internal volume for collecting fluid, such as a coolant or lubricant. The housing comprises at least

Description

TECHNICAL FIELD The present disclosure relates to a vehicle sump, and in particular to a sump for an electric drive unit of a vehicle. Aspects of the invention relate to a sump, to an electric drive unit, to a vehicle assembly and to a vehicle. BACKGROUND Some vehicles, such as electric vehicles (EVs) or hybrid vehicles, include an electric drive unit (EDU) that defines at least part of a powertrain of the vehicle. An EDU may include a sump for collecting fluid and to act as a reservoir from which such fluid can be recirculated through the EDU. The fluid collected by the sump may be, for example, coolant draining from an electric motor of the EDU, or lubricating oil draining from a transmission of the EDU, among others. The sump of an EDU may be in the general form of an enclosed housing having inlet and outlet channels for receiving and discharging fluid. A pump may draw fluid through the sump outlet(s), for example via a pickup tube that extends into the sump, and recirculate the fluid through the EDU. Fluid extracted from the sump may be replaced by corresponding fluid draining through the inlet(s) of the sump, but at times air may also flow into the sump due to its lower viscosity relative to oil. Undesirably, such air may then be picked up by the pump and pumped through the EDU. 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 sump, an electric drive unit, a vehicle assembly and a vehicle as claimed in the appended claims. According to an aspect of the present invention, there is provided a sump for a vehicle, the sump comprising a housing that encloses an internal volume for collecting fluid. The housing comprises: at least one inlet through which fluid flows into the internal volume, in use; at least one outlet through which fluid is drawn from the internal volume, in use; and a vent configured to allow air to flow into and out from the internal volume, in use. According to an aspect of the present invention, there is provided a sump for an electric drive unit of a vehicle. The sump comprises a housing that encloses an internal volume for collecting fluid, for example coolant or lubricating fluid, the fluid being in liquid form and optionally being an oil, in which case the sump may also be referred to as an ‘oil pan’. The housing comprises: at least one inlet through which fluid flows into the internal volume, in use; at least one outlet through which fluid is drawn from the internal volume, in use; and a vent configured for fluid connection to a housing volume of the electricdrive unit. The vent allows airto flow between the internal volume and the housing volume, in use. The inlet may comprise an inlet channel, and may define a drain. The outlet may comprise an outlet channel. The vent provides a route for air to flow in and out of the internal volume of the sump. This may help to avoid an airlock from forming within the sump, for example, which could lead to air being drawn through the outlet instead of the collected fluid. The vent may therefore help to reduce the extent to which air is drawn from the sump and pumped through an electric drive unit with which the sump is used. The vent may also contribute to equalising pressure between the internal volume of the sump and the housing volume. The sump may comprise a ventilation channel that comprises the vent. The vent may be defined by an open end of the ventilation channel, for example, or by the channel as a whole. A ventilation channel may enhance control over the point at which air enters and leaves the housing, for example. A ventilation channel may also facilitate connection of the vent to the housing volume. The ventilation channel may protrude outwardly from the housing, and optionally may protrude from a top of the housing. Such an arrangement may space the vent from the internal volume of the sump, and may reduce a risk of collected fluid flowing through the vent. The ventilation channel may be generally tubular. The ventilation channel may be open-ended. The vent may be positioned further from a bottom tray of the sumpthan the inlet and / or the outlet. For example, a lower end of the vent may be further from the bottom tray than an upper end of the inlet and / or an upper end of the outlet. This arrangement may help to promote airflow through the vent and may reduce the risk of collected fluid flowing through the vent. According to another aspect of the invention, there is provided an electric drive unit comprising the sump of the above aspect, and a housing or body enclosing a housing volume. The vent of the sump is fluidly connected to the housing volume. The vent allows air to flow between the internal volume of the sump and the housing volume, in use. The housing or body may comprise, or form part of, a main housing of the electric drive unit, for example. In some embodiments, the sump may be assembled with, mounted on, or supported by or relative to, the housing or body. In either of the above aspects, the housing volume may be a transmission volume, for example. In some embodiments, the housing volume is a link shaft volume. The housing volume may be a main volume, or part of a main volume, of the electric drive unit. The housing volume may comprise, or form part of, a cavity of the electric drive unit. The cavity may be a cavity of a transmission of the electric drive unit. The vent of the sump may be connected to the cavity or other housing volume, for example directly connected. By connecting to a housing volume, the vent of the sump may conveniently exploit existing ventilation within the electric drive unit. In this respect, the housing volume may be ventilated. Connecting the vent to the housing volume may also establish a closed loop for the fluid and so contain the fluid within the electric drive unit. In embodiments in which the sump comprises a ventilation channel, the ventilation channel may engage the housing or body. The ventilation channel may be received within a socket of the housing or body, for example. A fluid seal may be created between the ventilation channel and the housing or body. Such embodiments may beneficially constrain the fluid to a closed loop and so contain the fluid within the electric drive unit. The electric drive unit may comprise a pump connected to the outlet of the sump. The pump may beneficially draw fluid from the sump, through the outlet, to recirculate the fluid through the electric drive unit. Another aspect of the invention provides a vehicle assembly comprising the sump or the electric drive unit of either of the above aspects, and an assembly vent that is spaced from the sump and in fluid communication with the housing volume. The assembly vent may be protected and so may help to avoid ingress of water, dirt or other contaminants into the housing volume and, in turn, the sump. Another aspect of the invention provides a vehicle comprising the sump, the electric drive unit, or the vehicle assembly of any of the above aspects. Within the scope of this application, it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and / or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and / or features of any embodiment can be combined in anyway and / or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and / or incorporate any feature of any other claim although not originally claimed in that manner. BRIEF DESCRIPTION OF THE DRAWINGS One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a vehicle including an electric drive unit; Figure 2 shows a portion of the electric drive unit of Figure 1 including a sump; Figure 3 shows the sump of Figure 2 in isolation; and Figure 4 shows a detail view of a portion of the sump of Figure 2. DETAILED DESCRIPTION A sump and an electric drive unit (EDU) in accordance with embodiments of the present invention are described herein with reference to the accompanying Figures. As shown in Figure 1, the sump and the EDU are installed in a vehicle in the disclosed embodiment. In this example the sump is used to collect oil that is used both for lubrication and as a coolant, and so may also be referred to as an ‘oil pan’. More specifically, Figure 1 illustrates, in simplified and schematic form, a vehicle 10 including an EDU 12 according to an embodiment of the present invention. The EDU 12 defines a powertrain for the vehicle 10. In this respect, the EDU 12 includes power electronics and an electric motor configured to produce propulsive power for moving the vehicle 10, and a transmission 14 for applying a gear ratio to the output of the motor. The power electronics, motor and transmission 14 are contained within a main housing 15 of the EDU 12, hereafter referred to as the EDU housing 15, which may be formed as a single-piece casting for example. Figure 1 shows a link shaft 16 extending from the transmission 14, through which torque is output from the EDU 12 to drive wheels 18 of the vehicle 10. Figure 1 also shows a sump 20 positioned beneath the transmission 14 and the link shaft 16. The sump 20 is assembled with, and so forms part of, the EDU 12 in this embodiment, and Figure 2 shows the portion of the EDU 12 that includes the sump 20 in more detail. This shows that the sump 20 is positioned directly beneath a generally tubular and hollow link shaft housing 22 that contains an end portion of the link shaft 16 that connects to a transmission 14. The link shaft housing 22 is integral with, and so forms part of, the EDU housing 15 in this example. Figure 2 also shows that the EDU housing 15 includes a transmission cavity 24 that accommodates the transmission 14 and that provides for one or more air-filled housing volumes around the transmission. The housing volumes may provide for movement of fluids within the EDU 12, for example air flow for ventilation and flows of lubricating oil. The hollow interior of the link shaft housing 22 defines a link shaft chamber 26, through which the link shaft 16 extends centrally so that a generally annular volume of air is formed around the link shaft 16. The link shaft chamber 26 defines a housing volume of the EDU 12. More specifically, the link shaft chamber 26 forms part of the transmission cavity of the EDU 12, in that the chamber 26 is fluidly connected to one or more other airfilled volumes around the transmission 14, and so may be regarded as a sub-volume of the transmission cavity 24, In this respect, a lower portion of the transmission cavity 24 defining another such air-filled volume is visible in Figure 2 beneath the transmission 14, to the right of the sump 20. It follows that the transmission cavity may also be regarded as a housing volume of the EDU 12. The link shaft chamber 26 is also fluidly connected to a duct 23 that leads to a protected vent 25 (shown in Figure 1) that is spaced from the EDU 12 within the vehicle 10, in a sheltered position with a low risk of water or dirt ingress. The protected vent 25 forms part of a vehicle assembly that also includes the EDU 12. The protected vent 25 is configured to allow air to flow into and out of the duct 23 and, in turn, the link shaft chamber 26, while resisting ingress of water and other contaminants. The link shaft chamber 26 and, in turn, the transmission cavity 24, are therefore ventilated, for example for thermal management and pressure equalising purposes. The link shaft chamber 26 therefore also serves as a ventilation passage for the transmission cavity 24 and optionally other air channels within the EDU 12, providing ventilation for those channels and the associated components of the EDU 12. The sump 20 is shown in more detail in Figures 3 and 4, and so the following description refers to Figures 2 to 4 collectively. The sump 20 comprises a hollow, box-like sump housing 28, which encloses an internal volume 30 for collecting fluid, specifically oil that is used for lubricating the transmission 14 and as a coolant for the electric motor. A dashed line in Figure 2 shows the level of the oil 31 in the internal volume 30, although this is purely illustrative. The internal volume 30 is substantially enclosed by the sump housing 28, with access to the internal volume 30 being possible only through a set of discrete openings and channels formed in the sump housing 28, as shall become clearer from the description that follows. So, for example, the sump housing 28 includes an upper wall 32 that closes the top of the sump 20, unlike traditional open-topped engine sumps. In general terms, the sump housing 28 is shaped to fit against and attach to the exterior of the EDU housing 15. More specifically, the sump housing 28 is shaped to fit into a space bounded at the top by an underside of the link shaft housing 22, and at the side by a lower portion of the EDU housing 15 extending downwardly from the link shaft housing 22 and enclosing the lower portion of the transmission cavity 24. The sump housing 28 is formed as an assembly of two parts in this example, those parts including a main housing 34 and a bottom tray 36. The bottom tray 36 and main housing 34 are moulded components in this example. The bottom tray 36 is fixed to a lower end of the main housing 34 to form the sump housing 28 and to enclose the internal volume 30 of the sump 20. The bottom tray 36 is a shallow tray having a generally flat bottom wall and short side walls, and so the main housing 34 accounts for the majority of the internal volume 30. Figure 3 shows a set of bolt-receiving apertures 38 used to secure the main housing 34 to the bottom tray 36, although other fixing methods may be used in different embodiments. More generally, it is also possible to form the sump housing 28 in different ways. Figure 4 shows that the bottom tray 36 includes short side walls surmounted by a lip 40 that extends around a perimeter of the bottom tray 36. A horizontal upper surface of the lip 40 is shaped to accommodate a sealing member and to receive a lower end of the main housing 34, to create a sealed interface between the bottom tray 36 and the main housing 34 and therefore seal the internal volume 30 of the sump 20. In use, the sump 20 is oriented such that the bottom tray 36 is at the bottom of the sump housing 28, with an underside of the bottom tray 36 being generally parallel to a floor of the vehicle 10 and hence also to a surface on which the vehicle 10 travels. The sump 20 also includes a laterally-extending end portion 42 of reduced height that is shown to the right in the Figures, the end portion 42 extending beneath the EDU housing 15. Effectively, the end portion 42 is created by shaping the main housing 34 to become a shallow lid for the bottom tray 36 in that region of the sump housing 28. An upper surface of the end portion 42 of the sump 20 includes a generally oblong aperture defining a first drain opening 44. The first drain opening 44 aligns with and engages an opening in a lower wall of the EDU housing 15, to enable oil that has passed through the transmission 14 to drain into the sump 20 from the transmission cavity 24 of the EDU housing 15. A sealing member 46 is provided around the first drain opening 44 to create a fluid seal at the interface between the first drain opening 44 and the opening in the EDU housing 15. At an opposite end of the sump 20 to the end portion 42, a second drain opening 48 is defined by a generally square opening formed in the upper wall 32 of the main housing 34 of the sump 20. The second drain opening 48 is positioned to collect coolant oil draining from the electric motor of the EDC 12, which oil is used for cooling the electric motor, and so the second drain opening 48 acts as a coolant drain. As best seen in Figure 3, the sump housing 28 includes a recess that, as shown in Figure 2, defines a pump pocket 50 of the sump 20 that accommodates a pump 52 on the outside of the sump housing 28. Figure 3 also shows that the sump housing 28 includes four outwardly-extending tubular protrusions. These protrusions include two protrusions extending into the pump pocket 50 from a side wall of the main housing 34 along generally horizontal axes to define horizontal tubes, and two protrusions extending upwardly from the upper wall 32 of the main housing 34 of the sump 20 along generally vertical axes to define vertical tubes. The horizontal tubes are arranged at different heights on the sump housing 28. The lower of the horizontal tubes defines a pump inlet channel 54 that is connected to an inlet port of a pump 52. On the interior of the sump 20, a pickup tube (not shown) is connected to the pump inlet channel 54 and extends down to the bottom tray 36 and therefore below the level of oil held in the internal volume 30. The pump 52 can therefore draw fluid from the internal volume 30 of the sump 20 through the pump inlet channel 54. The pump inlet channel 54 therefore represents an outlet of the sump 20. The pickup tube may be formed as part of the sump housing 28, or may be a separate tube that is connected to the pump inlet channel 54. The level of the oil 31 inside the sump 20 is typically above the level of the pump inlet channel 54, enabling the pump 52 to draw oil from the sump 20. The uppermost horizontal tube is connected to the closest one of the vertical tubes extending from the top of the sump housing 28 by suitable ducting inside the sump housing 28, to form a continuous passage that passes through the sump 20 and turns through a right angle, the passage defining a pump outlet channel 56. The pump outlet channel 56 therefore has a horizontal portion 56a corresponding to the horizontal tube extending into the pump pocket 50, and a vertical portion 56b corresponding to the vertical tube. An outlet port of the pump 52 is connected to the horizontal portion 56a of the pump outlet channel 56, and the vertical portion 56b of the pump outlet channel 56 is connected to a fluid circuit that conveys oil to the transmission 14. Accordingly, in operation the pump 52 displaces oil in the sump into and through the pump outlet channel 56 to recirculate the oil through the transmission 14. The second vertical tube on the top of the sump housing 28 defines a ventilation channel 60, which is positioned on a tall part of the housing 28 adjacent to the end portion 42, and therefore near to the first drain opening 44 and at an opposite end of the sump 20 to the second drain opening 48. The ventilation channel 60 represents a vent or breather of the sump 20. The ventilation channel 60 is in the form of a generally straight tube that protrudes upwardly and outwardly from the upper wall 32 of the sump housing 28, and that opens at its lower end directly into the internal volume 30 of the sump 20, through the upper wall 32. A lower edge of the ventilation channel 60 is rounded for enhanced fluid dynamics between the ventilation channel 60 and the internal volume 30. As best seen in Figure 4, a short, generally annular wall defining a skirt 61 projects downwardly from the lower end of the ventilation channel 60, into the internal volume 30, the skirt 61 serving to guard against splashing of oil into the ventilation channel 60. The ventilation channel 60 acts as a breather to ventilate the internal volume 30 of the sump 20, by allowing air to flow into and out of the internal volume 30. This helps to equalise pressure between the internal volume 30 and the exterior of the sump 20 as fluid is pumped from the internal volume 30, and reduces the extent to which air is pulled into the sump 20 and the EDU 12. In this respect, when the pump 52 draws oil from the internal volume 30 of the sump 20, the displaced volume of oil is ideally replaced by a corresponding volume of fluid to avoid a creating pressure differential between the internal volume 30 of the sump 20 and the surroundings, to reduce the demands placed on the pump 52. Ideally, the oil extracted from the internal volume 30 is replaced by oil flowing into the sump 20 through the drain openings 44, 48. However, air may also be pulled through the drain openings 44, 48, due to its lower viscosity and corresponding higher flow rate relative to the oil. This airflow through the drain openings 44, 48 may impede the flow of oil into the sump 20. There is also a risk of air becoming trapped within the internal volume 30 of the sump 20, creating an airlock, depending on the level of the oil 31 in the sump 20 and the orientation of the sump 20. This risk may be exacerbated by the fact that the internal volume 30 of the sump 20 is not a regular, cuboidal shape, but instead has an irregular shape due to the packaging constraints imposed by the EDU housing 15, the pump 52 and other components of the vehicle 10, some details of which have been omitted for the sake of clarity. This irregular shape creates potential for one or more sub-volumes within the sump 20 to fill with air that then becomes isolated by surrounding oil, if the oil reaches a certain level and / or if the sump 20 is at a particular orientation. Such trapped air reduces the space available for oil within the sump 20 and constrains the flow of oil between the drain openings 44, 48 and the pickup tube. This potentially leads to the level of the fluid 31 inside the sump 20 around the pump inlet channel 54 moving partially or fully below the pump inlet channel 54, so that the pump 52 picks up air instead of, or in addition to, oil and so pumps that air into the EDU 12, thus reducing the flow rate of oil through the associated systems of the EDU 12. The vent defined by the ventilation channel 60 mitigates this by providing an additional, dedicated flow route for air to enter and leave the sump 20 during pumping, providing for exchange of air between the sump 20 and its surroundings and thereby helping to balance pressure for the sump 20. In particular, air that is pulled into the sump 20 through one of the drain openings 44, 48 can escape through the ventilation channel 60, instead of being picked up by the pump 52. The vent 60 may allow air within the internal volume 30 to be released and so avoid an airlock, and conversely may provide a more effective flow route for air into the sump 20 if, for example, oil is temporarily being pumped out at a higher rate than it is returning through the drain openings 44, 48. This has an overall effect of reducing the quantity of air that is pulled into the sump 20 and the EDU 12. The ventilation channel 60 is positioned at the top of the sump 20, which reduces the risk of the vent 60 being blocked by oil. The positioning of the ventilation channel 60 may be particularly effective for ventilating the internal volume 30 when the vehicle 10 and the sump 20 are oriented generally horizontally, which may be when the risk of an airlock developing is highest. In this respect, the first and second drain openings 44, 48 may be able to act as vents, at least to some extent, when the sump 20 is articulated away from a horizontal orientation. For example, the sump 20 may support an articulation angle of up to 25°. In this example, the ventilation channel 60 of the sump 20 is fluidly connected directly to the link shaft chamber 26, therefore creating a fluid connection between the internal volume 30 of the sump 20 and the protected vent 25 of the vehicle 10. In this way, the ventilation channel 60 of the sump 20 exploits the existing ventilation arrangements within the EDU 12. Making use of the existing ventilation arrangement of the EDU 12 also takes advantage of the protection offered by the protected vent 25, thereby mitigating the risk of water ingress into the sump 20. More specifically, the ventilation channel 60 extends into and engages a socket 62 formed in the underside of the link shaft housing 22. The socket 62, in turn, opens into the link shaft chamber 26. The ventilation channel 60 and the socket 62 therefore define a male-female interface between the sump 20 and the EDU housing 15. In this way, the vent 60 of the sump 20 is configured for fluid connection to a housing volume of the EDU 12, namely the link shaft chamber 26 in this example. The ventilation channel 60 has an end portion 64 of reduced diameter, such that a shoulder 66 is defined at an interface between the end portion 64 and the remainder of the ventilation channel 60. An O-ring 68 is positioned on the end portion 64 of the ventilation channel 60 and in abutment with the shoulder 66. The interior of the socket 62 is shaped to define a narrowed upper portion 70, with a diameter corresponding to that of the end portion 64 of the ventilation channel 60, and a wider lower portion 72. When the ventilation channel 60 is inserted into the socket 62, a tip end of the end portion 64 of the ventilation channel 60 is received in the upper portion 70 of the socket 62, while some of the end portion 64 remains in the lower portion 72 of the socket 62. The O-ring 68 locates in the area of overlap between the end portion 64 of the ventilation channel 60 and the lower portion 72 of the socket 62, and bears against the respective cylindrical surfaces of the end portion 64 of the ventilation channel 60 and the lower portion 72 of the socket 62, to form a sealing interface that provides a fluid seal. By sealing the interface between the ventilation channel 60 and the EDU housing 15, the risk of ingress of water into the sump 20 is reduced, as only air that has entered through the protected vent 25 of the vehicle 10 can reach the sump 20. Conversely, the seal between the ventilation channel 60 and the EDU housing 15 also ensures that all oil is contained with the EDU 12, noting that the sump 20 is part of the EDU 12. Accordingly, the sump 20 and the EDU 12 are configured to constrain oil to one or more closed loops. It is noted that an interface between the ventilation channel 60 and the EDU housing 15 may be sealed in other ways in alternative embodiments. Similar sealing interfaces involving O-rings are also provided for the other tubular protrusions of the sump 20, namely the pump inlet channel 54 and the horizontal and vertical portions of the pump outlet channel 56. Conveniently, O-rings used at each interface may be similar. 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. For example, a vent of a sump may connect to a different housing volume, and so not necessarily a link shaft chamber as in the above example. Alternatively, a sump vent may not connect to another housing or body, and may instead vent directly to the surrounding space around the sump. A vent may not be in the form of a 5 channel as in the above example, but could, for example, be a simple opening formed in the sump housing. A ventilation channel could also extend into the housing instead of outwardly from the housing as in the above example. In the above example, the sump is fabricated as a moulded component in which the various channels, including 10 the ventilation channel, are formed integrally with the sump housing. In other embodiments, a ventilation channel and / or other channels may be formed as a separate piece that is connected to a main housing of a sump.

Claims

1. A sump for an electric drive unit of a vehicle, the sump comprising a housing that encloses an internal volume for collecting fluid, the housing comprising:at least one inlet through which fluid flows into the internal volume, in use;at least one outlet through which fluid is drawn from the internal volume, in use; anda vent configured for fluid connection to a housing volume of the electric drive unit, wherein the vent allows air to flow between the internal volume and the housing volume, in use.

2. The sump of claim 1, comprising a ventilation channel that comprises the vent.

3. The sump of claim 2, wherein the ventilation channel protrudes outwardly from the housing.4, The sump of any preceding claim, wherein the vent is positioned further from a bottom tray of thesump than the inlet and / or the outlet.

5. An electric drive unit comprising the sump of any preceding claim, and a housing or body enclosing a housing volume, the vent of the sump being fluidly connected to the housing volume, wherein the vent allows air to flow between the internal volume of the sump and the housing volume, in use.

6. An electric drive unit according to claim 5, wherein the housing volume comprises, or forms part of, a cavity of the electric drive unit, and wherein the vent of the sump is connected to the cavity.

7. An electric drive unit according to claim 6, wherein the cavity is a cavity of a transmission of the electric drive unit.

8. An electric drive unit according to any of claims 5 to 7, wherein the housing volume is a link shaft volume.

9. An electric drive unit according to any of claims 5 to 8, wherein the housing volume is ventilated.

10. An electric drive unit according to any of claims 5 to 9 when dependent on claim 2, wherein theventilation channel engages the housing or body.

11. An electric drive unit according to claim 10, wherein the ventilation channel is received within a socket of the housing or body.

12. An electric drive unit according to any of claims 5 to 11, comprising a pump connected to the outlet of the sump.

13. A vehicle assembly comprising the sump of any of claims 1 to 4, or the electric drive unit of any of claims 5 to 12, and an assembly vent that is spaced from the sump and in fluid communication with the housing volume.5 14. A vehicle comprising the sump of any of claims 1 to 4, the electric drive unit of any of claims 5 to 12,or the vehicle assembly of claim 13.12

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