A transmission fluid device

Abstract

A transmission fluid device for an electric vehicle drive unit, the device comprising a housing portion (20, see fig.4), a fluid chamber (50), a fluid inlet (22, see fig.2), main fluid outlet (24) and

Description

TECHNICAL FIELD The present disclosure relates to a transmission fluid device. Aspects of the invention relate to a transmission fluid device, to an electric drive unit of a vehicle, a vehicle, and to a method of assembling a transmission fluid device. BACKGROUND It is known to provide transmission fluid devices in vehicles. Such transmission fluid devices may convey or move transmission fluid to a part of a vehicle, for example to-and-from a vehicle sub-system. In order to ensure fluid tightness of the device during its use the device may be assembled in a manner that requires use of a relatively high force (for example equal to or greater than 100 N) to insert one component of the device into another component. Assembly may be done manually on an assembly line, as such repeated insertion of the component at the relatively high force may be time consuming or requiring the usage of specialist tooling to insert the component. It is an aim of the present invention to address one or more of the disadvantages associated with the prior art. SUMMARY OF THE INVENTION Aspects and embodiments of the invention provide a transmission fluid device, an electric drive unit of a vehicle, a vehicle, and a method of assembling a transmission fluid device as claimed in the appended claims. According to an aspect of the present invention there is provided a transmission fluid device for an electric drive unit of a vehicle, the transmission fluid device comprising: a housing portion defining a fluid chamber having a fluid inlet, a main fluid outlet, and a bypass fluid outlet; and a bypass valve for controlling fluid flow between the fluid inlet, the main fluid outlet, and the bypass fluid outlet, wherein the bypass valve comprises: a valve body at least partially located within the fluid chamber to form a clearance gap between an inner wall of the fluid chamber and an outer wall of the valve body, wherein the valve body comprises a circumferential channel that is fluidly connected to the fluid chamber by the clearance gap, and an annular seal disposed within the circumferential channel, the annular seal comprising an annular body, an elastically deformable circumferential lip extending around the annular body, and an annular channel defined between the annular body and the circumferential lip, wherein the annular channel is oriented to be fluidly connected to the fluid chamber via the clearance gap such that a fluid passing through the clearance gap from the fluid chamber hydraulically urges the circumferential lip against the inner wall of the fluid chamber. The lip seal enables easier insertion of the bypass valve into the bypass valve seat as compared to an O-ring. This arrangement is particularly advantageous during assembly of the transmission fluid device as a reduced force is required to insert the valve body into the housing than if an O-ring were used. An O-ring, as will be apparent, does not have a flexible lip which is able to elastically deform as the body is entered into the housing. The bypass valve outer surface may be any surface on the outside of the bypass valve, such as on the bypass valve body or housing. The outer surface may be a portion of the bypass valve body or housing adjacent to the annular seal on the ‘dry’ side such that the portion is not fluidly connected to the fluid chamber due to the fluid interface formed by the annular seal. According to another aspect of the present invention, there is provided a device, the device comprising: a housing portion defining a fluid chamber having a fluid inlet, a main fluid outlet, and a bypass fluid outlet; and a bypass valve for controlling fluid flow between the fluid inlet, the main fluid outlet, and the bypass fluid outlet, wherein the bypass valve comprises: a valve body at least partially located within the fluid chamber to form a clearance gap between an inner wall of the fluid chamber and an outer wall of the valve body, wherein the valve body comprises a circumferential channel that is fluidly connected to the fluid chamber by the clearance gap, and an annular seal disposed within the circumferential channel, the annular seal comprising an annular body, an elastically deformable circumferential lip extending around the annular body, and an annular channel defined between the annular body and the circumferential lip, wherein the annular channel is oriented to be fluidly connected to the fluid chamber via the clearance gap such that a fluid passing through the clearance gap from the fluid chamber hydraulically urges the circumferential lip against the inner wall of the fluid chamber. The device has at least the same advantages of the previous aspect. Additionally, or optionally, according to either previous aspect, there may be provided additional / optional features as will be described below. Optionally, the bypass valve has at least one inlet, the inlet is fluidly connected to the main outlet in the first position; the inlet is fluidly connected to the bypass outlet in the second position. The bypass valve therefore allows fluid to be selectively conveyed from an inlet to a main or bypass outlet. Optionally, the bypass valve further comprises a valve member disposed within the fluid chamber and movable between a first position, in which the bypass fluid outlet is closed and the fluid chamber is fluidly connected to the main fluid outlet, and a second position, in which the main fluid outlet is closed and the fluid chamber is fluidly connected to the bypass fluid outlet. The bypass valve therefore allows fluid to be selectively conveyed from an inlet to a main or bypass fluid outlet. Optionally, the cross-section of the annular channel is substantially C-shaped or U-shaped. As the crosssection of the annular channel may be U-shaped or C-shaped the annular channel is open on one side to enable fluid to enter into the annular channel more easily. Optionally, the annular body has a first cross-sectional thickness and the circumferential lip has a second cross-sectional thickness; and wherein the second cross-sectional thickness is smaller than the first cross-sectional thickness. The relatively thinner circumferential lip enables the lip to flex relative to the body. Optionally, the annular channel is biased to a radially open position. Biasing the channel and therefore circumferential lip to a radially open position means that the channel may be open across the whole interface in use prior to hydraulic force acting upon the valve. Optionally, the annular seal has an annular spring biased to bias the annular channel to the open position. Such an arrangement helps to keep the channel open after installation. Optionally, the annular spring is configured to fit in the annular channel. Such an arrangement helps to keep the channel open after installation. Optionally, the annular spring has an annular spring channel. The annular spring channel enables fluid to enter the spring and hydraulically force the spring apart. Optionally, the cross-section of the annular spring channel is substantially C-shaped or U-shaped. Such an arrangement means that the spring can have an open cross-section along its length enabling a greater volume of fluid to enter the spring and annular channel more easily. Optionally, the annular seal comprises a second circumferential lip extending around the annular body; the second circumferential lip being axially spaced from the first circumferential lip. Providing an additional circumferential lip means that there may be additional leak prevention. According to a further aspect of the present invention, there is provided an electric drive unit of a vehicle comprising the transmission fluid device according to any embodiment of either of the prior aspects. The electric drive unit having at least the advantages of the embodiment that it comprises. Optionally, the electric drive unit further comprises a pump and a radiator; the pump and radiator being fluidly connected to at least one of the main and bypass fluid outlets. Provision of a pump and radiator may enable the cooling of fluid that is used by the electric drive unit. According to a yet further aspect of the present invention there is provided a vehicle comprising the transmission fluid device or the electric drive unit. The vehicle having at least the advantages of the embodiment that it comprises. According to an even further aspect of the present invention there is provided a method of assembling a transmission fluid device for an electric drive unit of a vehicle, the transmission fluid device comprising: a housing portion defining a fluid chamber having a fluid inlet, a main fluid outlet, and a bypass fluid outlet; and a bypass valve for controlling fluid flow between the fluid inlet, the main fluid outlet, and the bypass fluid outlet, the method comprising the steps of: positioning an annular seal within a circumferential channel of a valve body of the bypass valve, the annular seal comprising an annular body, an elastically deformable circumferential lip extending around the annular body, and an annular channel defined between the annular body and the circumferential lip; and inserting the valve body of the bypass valve at least partially into the fluid chamber to define a clearance gap between an inner wall of the fluid chamber and an outer wall of the valve body, the circumferential channel being fluidly connected to the fluid chamber by the clearance gap, wherein the annular channel is oriented to be in fluid communication with the fluid chamber via the clearance gap such that a fluid passing through the clearance gap from the fluid chamber hydraulically urges the circumferential lip against the inner wall of the fluid chamber. The lip seal enables easier insertion of the bypass valve into the bypass valve seat. This arrangement is particularly advantageous during assembly of the transmission fluid device as a reduced force is required to insert the valve body into the housing than if an O-ring were used. An O-ring, as will be apparent, does not have a flexible lip which is able to elastically deform as the body is entered into the housing. Optionally, the step of inserting the bypass valve body into the housing portion further comprises: elastically deforming the circumferential lip radially away from the annular body as the valve body is inserted into the housing portion. By elastically deforming the circumferential lip radially away from the annular body the lip may be less likely to become pinched during insertion of the bypass valve body into the fluid chamber. The method may comprise any further feature or step as described in any other aspect of the present invention. 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 with an electric drive unit in accordance with an embodiment of the invention; Figure 2 shows a schematic representation of an electric drive unit in accordance with an embodiment of the invention; Figure 3 shows an isometric view of the transmission fluid device with a housing portion removed; Figure 4 shows an cross-sectional view through the transmission fluid device; Figure 5 shows a close up view of the cross-section of Figure 4; Figure 6 shows another close up view of the cross-section of Figures 4 and 5 with a fluid passing through a clearance gap; Figure 7 shows an annular seal in accordance with an embodiment of the invention; Figure 8 shows a cross-sectional view of the annular seal of Figure 7 normal to plane A; Figure 9 shows another embodiment of the annular seal of Figure 7 seen in cross-section, the cross-section being seen normal to plane A; and Figure 10 shows a flowchart comprising method steps in accordance with an embodiment of the invention. DETAILED DESCRIPTION A vehicle 1 in accordance with an embodiment of the present invention is described herein with reference to the accompanying Figure 1. As shown in Figure 1, the vehicle 1 is having a subsystem 2, the subsystem 2 having a transmission fluid device 10. The vehicle 1 depicted is of the 4x4 or SUV type, however the vehicle 1 may be a car, a van, a light goods vehicle, or other such vehicle. A sub-system 10 of the vehicle 1 is shown schematically in Figure 2. The sub-system 2 comprises the transmission fluid device 10 that is connected or connectable to an electric drive unit 18 (also referred to herein as: an EDU 18, or prime mover 18a, or electric traction motor 18b). The subsystem 2 may also comprise the electric drive unit 18. The subsystem may additionally comprise one or both of a pump 12 and a radiator 16. The vehicle 1 has a powertrain. The powertrain comprises a propulsion system comprising at least one prime mover 18a. The prime mover(s) 18a are selectively operable for the purpose of providing drive torque for accelerating the vehicle 1. In alternative configurations with two prime movers 18a, the first prime mover 18a may provide drive to a front axle and the second prime mover 18a may provide drive to a rear axle, or vice versa. In such an embodiment both prime movers 18a may be supplied with electrical energy from electrical storage means. The prime mover 18a is an electric traction motor 18b. Where a plurality of prime movers are provided, there may be a plurality of electric traction motors 18b. The vehicle 1 may be a fully electric vehicle 1 having only an EDU 18 as a power source for propulsion and no internal combustion engine or may be a hybrid vehicle having both an EDU 18 and an internal combustion engine arranged to propel the vehicle 1. The EDU 18 is powered by a battery which may be a traction battery or a battery module. The vehicle 1 may be a plug-in hybrid electric vehicle (PHEV) or a mild hybrid electric vehicle (MHEV). It shall be appreciated that in alternative embodiments, the vehicle 1 may be 5 a hydrogen electric vehicle (HEV) and hence the EDU 18 may be powered by a hydrogen fuel cell arrangement comprising one or more hydrogen fuel cells. It shall be appreciated that the following description directed to a battery powered electric vehicle may also apply to a hydrogen electric vehicle. The at least one prime mover 18a comprises an electric traction motor 18b. An electric motor is arranged to convert electrical energy into kinetic energy in the form of mechanical torque and may also be arranged to convert kinetic energy into electrical energy. The electric traction motor 18b may be an alternating current induction motor or a permanent magnet motor, or another type of suitable electric machine. The electric traction motor 18b may form part of an electric drive unit 18 (EDU). The terms “electric traction motor”, “prime mover” and “electric drive unit” may be used interchangeably throughout the present application. The transmission fluid device 10 shown in Figure 2 has a bypass valve 14 and a housing portion 20. The subsystem 2 may also comprise a pump 12 and a radiator 16. The transmission fluid device 10 is configured to selectively bypass the radiator 16 and supply fluid directly to the EDU 18 and / or transmission components of the vehicle 1. This is advantageous on startup of the vehicle where the fluid, such as coolant or transmission fluid will be cold and thus in a more viscous state than when at an intended operating temperature. The fluid may be less viscous as its temperature increases. To heat the fluid up quickly from an ambient temperature (e.g. 10°C) it is directed to the moving components of the EDU 18 and / or transmission components. In order to prevent unwanted cooling during the start-up and initial running of the vehicle 1 the bypass valve 14 bypasses a main fluid pathway 30 which directs fluid to the radiator 16 (connected to the bypass valve 14 via a main fluid outlet 24 in housing portion 20) and instead directs flow of fluid along the bypass fluid pathway 32 (connected to the bypass valve 14 via a bypass fluid outlet 26 in housing portion 20). The fluid then passes directly to the EDU 18 through the bypass fluid pathway 32. Once the fluid has reached a sufficient working temperature the bypass valve 14 closes the bypass fluid outlet 26 and opens the main fluid outlet 24 enabling fluid to flow to the EDU 18 via the radiator 16. In such an operational configuration the radiator 16 enables the fluid to be cooled as it passes along the main fluid pathway 30. The fluid temperature may be measured by a temperature sensor located on the fluid circuit shown in Figure 2. The temperature sensor may be any temperature sensor known in the art configured to measure fluid temperature. The temperature sensor may be located at the bypass valve inlet 22. The transmission fluid device 10 is shown in more detail in Figures 3-9. The transmission fluid device 10 comprises the housing portion 20 and the bypass valve 14. The housing portion 20 defines a fluid chamber 50 that is connected to the fluid inlet 22, main fluid outlet 24 and bypass fluid outlet 26. As will be appreciated, the housing portion 20 may be part of a larger housing, such as an EDU housing or a transmission housing. The larger housing is not shown for reasons of clarity. The bypass valve 14 has a valve body 40 and a bypass valve member 42. The valve body 40 is partially received within the fluid chamber 50. The bypass valve member 42 is shown in Figure 4 and may be a rotary member 42 with a channel 44 located in the bypass valve member 42. The channel 44 is configured to selectively connect the fluid inlet 22 to one of the main fluid outlet 24 and the bypass fluid outlet 26. In alternative configurations, the valve body 40 may comprise a gate or gates which selectively open and close the outlets 24, 26. Alternatively, the bypass valve 14 may have an alternative configuration suitable for controlling fluid flow between the fluid inlet 22, main fluid outlet 24 and bypass fluid outlet 26. The bypass valve 14 may be operated by means known in the art, for example the bypass valve 14 and the valve member 42 may be electro-mechanically operated, for example by means of a solenoid. Alternatively, the valve member 42 may be driven by hydraulic or pneumatic means. The bypass valve 14 also comprises an annular seal 60, shown in Figure 7 and in cross-section in Figure 8. The annular seal 60 comprises an annular body 62, a circumferential lip 64 and an annular channel 66. The annular channel 66 is defined between the annular body 62 and the circumferential lip 64. The circumferential lip 64 is elastically deformable and extends around the annular body 62 as shown in Figure 7. In use, the annular seal 60 is located on the valve body 40 as shown in Figure 3. The annular seal 60 is configured to prevent fluid from passing out of the fluid chamber 50 as will be described in more detail below. The transmission fluid device 10 is shown in more detail in Figures 4-6. Figure 4-6 shows a cross-sectional view of the transmission fluid device 10. Figure 4 shows the annular seal 60 and its arrangement between the housing portion 20 and the bypass valve body 40. This arrangement is shown in more detail in Figure 5 and 6. The valve body 40 is located partially within the fluid chamber 50 between an inner wall 52 of the fluid chamber on the housing portion 20. A clearance gap 70 is formed between an outer wall 46 of the valve body 40 and the inner wall 52 as shown in Figure 5 when the valve body 40 is inserted into the housing portion 20. The clearance gap 70 is fluidly connected to the fluid chamber 50, as a result fluid may pass out of the fluid chamber 50 via the clearance gap 70 for example by capillary action. In order to prevent fluid loss out of the transmission fluid device 10 via the clearance gap 70, the annular seal 60 is located between the bypass valve body 40 and housing portion 50. The annular seal 60 is located in a circumferential channel 48 of the valve body 40. As can be seen in Figure 5, the annular body 62 of annular seal 60 abuts against the circumferential channel 48 in use. The circumferential lip 64 in use abuts the inner wall 52. As can be seen in Figures 5 and 6, the annular seal 60 is orientated in the transmission fluid device 10 such that the annular channel 66 is oriented to be fluidly connected to the clearance gap 70. In the example of Figures 5 and 6, the annular channel 66 faces the clearance gap 70. As shown in Figure 6, when the fluid f (indicated by the dot-dash line f) passes along the clearance gap 70 from the fluid chamber 50, the fluid enters the annular channel 66. The fluid, under pressure P, hydraulically urges (or forces) the circumferential lip 64 into the inner wall 52 and away from the annular body 62. This has the effect of forcing the annular channel 66 into a ‘more open’ position to try and increase the volume of the annular channel 66. As a result the circumferential lip 64 is forced into engagement with the inner wall 52. This has the effect of increasing the efficacy of the seal when the transmission fluid device 10 is being used and fluid is present in the annular channel 66. The fluid pressure P may be 1.1 MPa to 15 MPa, or 2 MPa to 12 MPa, or 5 MPa to 10 MPa. The annular seal 60 is shown in more detail in Figures 7 and 8. The annular seal 60 is shown in Figure 7 by itself without the other components of the transmission fluid device 10 for reasons of clarity. As can be seen in Figure 7, the annular seal 60 is rotationally symmetrical. However, it is envisioned that the annular seal 60 may take different shapes as known in the art, for example, oval, ellipsoid, square, rectangular, etc. In the embodiment of Figures 7 and 8 the annular seal 60 is unitary and may be made by means known in the art, for example injection moulding or another moulding process. The annular seal 60 may be made from a polymer, either a thermoset or a thermoplastic. For example, the annular seal 60 may be made from any one of: silicone, rubber, ethylene propylene diene monomer (‘EDPM’), natural rubber, synthetic rubber, neoprene, nitrile, polyvinyl chloride, or any other material known in the art suitable for use as a seal. A cross-section of the annular seal 60 is shown in Figure 8. The cross-section is viewed as normal to plane A shown in Figure 7. As can be seen in Figure 8, the annular seal 60 has an annular body 62 with a first thickness t1 and a circumferential lip 64 of a second thickness t2. Thickness t1 is greater than t2. Thickness t2 is smaller than t1. This configuration enables the circumferential lip 64 to flex to a greater degree than the annular body 62. Figure 9 shows another embodiment of a seal 160. The seal 160 is identical to the seal 60 other than it comprises an annular spring 162 located within the annular channel 66. The annular spring 162 is configured to open the channel 66. The annular spring 162 is configured to fit within the annular channel 66 as shown in Figure 9. The annular spring 162 may have an annular spring channel 164. The annular spring channel 164 may be arranged in the annular channel 66 such that the annular spring channel 164 is orientated to be fluidly connected to the clearance gap 70. The annular spring 162 may therefore be U-shaped or C-shaped as shown in the example of Figure 9. In alternative configurations of the seal 60, 160, the seal 60,160 may comprise a second circumferential lip 64 extending from the annular body 62. In such an arrangement increased sealing may be achieved as if any fluid passes around the first circumferential lip 64 it will engage a second annular channel causing the second circumferential lip to engage the inner wall 52. Figure 10 illustrates a flowchart 200 comprising method steps according to an embodiment of the invention. The method 200 is a method of assembling a transmission fluid device 10 of a vehicle 1, such as the vehicle 1 illustrated in Figure 1. In particular, the method 200 is a method of assembling a transmission fluid device 10 for an electric drive unit 18 of a vehicle 1. The method of assembling the transmission fluid device 10 of the present embodiment of the invention is particularly advantageous during assembly of the transmission fluid device as a reduced force is required to insert the valve body into the housing than if an O-ring were used. An O-ring, as will be apparent, does not have a flexible lip which is able to elastically deform as the body is entered into the housing. The method at step 210 comprises providing a housing portion 20 defining a fluid chamber 50 having a fluid inlet 22, a main fluid outlet 24, and a bypass fluid outlet 26; and a bypass valve 14 for controlling fluid flow between the fluid inlet 22, the main fluid outlet 24, and the bypass fluid outlet 26. After step 210, the method further comprising the step of positioning 220 an annular seal 60 within a circumferential channel 48 of a valve body 42 of the bypass valve 14. The annular seal 60 comprising an annular body 62, an elastically deformable circumferential lip 64 extending around the annular body 64, and an annular channel 66 defined between the annular body 62 and the circumferential lip 64. Subsequently, at step 230, the method 200 comprises inserting the valve body 40 of the bypass valve 14 at least partially into the fluid chamber 50 to define a clearance gap 70 between an inner wall 52 of the fluid chamber and an outer wall 46 of the valve body. The circumferential channel 48 being fluidly connected to the fluid chamber 50 by the clearance gap 70. The annular channel 66 is oriented to be in fluid communication with the fluid chamber 50 via the clearance gap 70 such that a fluid passing through the clearance gap 70 from the fluid chamber hydraulically urges the circumferential lip 64 against the inner wall 52 of the fluid chamber 50. As will be apparent, the transmission fluid device 10 utilised in method 200 may be any previously described transmission fluid device 10. Optionally, the step 220 of inserting the bypass valve body 40 into the housing portion 20 may further comprise elastically deforming the circumferential lip 64 radially away from the annular body 62 as the valve body 40 is inserted into the housing portion 20. Optionally the step 220 of inserting the bypass valve body 40 into the housing portion 20 may require a force of 10 N to 70 N, or 20 N to 60 N, or 40 N or 50 N, or any range, subrange, individual value or combination thereof. 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. No.           Feature A Plane f Fluid P Pressure 1 Vehicle 2 Subsystem 10 Transmission Fluid Device 12 Pump 14 Bypass Valve 16 Radiator 18 Electric Drive Unit 18a Prime Mover 5 18b Electric Traction Motor 20 Housing Portion 22 Fluid Inlet 24 Main Fluid Outlet 26 Bypass Fluid Outlet 10 30 Main Fluid Pathway 32 Bypass Fluid Pathway 40 Valve Body 42 Valve Member 44 Member Channel 15 46 Outer Wall 48 Circumferential Channel 50 Fluid Chamber 52 Inner Wall 60,160 Annular Seal 20 62 Annular Body 64 Circumferential Lip 66 Annular Channel 70 Clearance Gap 162 Annular Spring 25 164 Annular Spring Channel 200 Flowchart 210 Method Step 220 Method Step 230 Method Step 30

Claims

1. A transmission fluid device for an electric drive unit of a vehicle, the transmission fluid devicecomprising:a housing portion defining a fluid chamber having a fluid inlet, a main fluid outlet, and a bypass fluid outlet; anda bypass valve for controlling fluid flow between the fluid inlet, the main fluid outlet, and the bypass fluid outlet;wherein the bypass valve comprises:a valve body at least partially located within the fluid chamber to form a clearance gap between an inner wall of the fluid chamber and an outer wall of the valve body, wherein the valve body comprises a circumferential channel that is fluidly connected to the fluid chamber by the clearance gap, andan annular seal disposed within the circumferential channel, the annular seal comprising an annular body, an elastically deformable circumferential lip extending around the annular body, and an annular channel defined between the annular body and the circumferential lip,wherein the annular channel is oriented to be fluidly connected to the fluid chamber via the clearance gap such that a fluid passing through the clearance gap from the fluid chamber hydraulically urges the circumferential lip against the inner wall of the fluid chamber.

2. The transmission fluid device of claim 1, wherein the cross-section of the annular channel issubstantially C-shaped or U-shaped.

3. The transmission fluid device of claim 1 or 2, wherein the annular body has a first cross-sectional thickness (t1) and the circumferential lip has a second cross-sectional thickness (t2); and wherein the second cross-sectional thickness is smaller than the first cross-sectional thickness.

4. The transmission fluid device of any preceding claim, wherein the annular channel is biasedto a radially open position.

5. The transmission fluid device of claim 4, wherein the annular seal has an annular springbiased to bias the annular channel to the open position.

6. The transmission fluid device of claim 5, wherein the annular spring is configured to fit in theannular channel.

7. The transmission fluid device of claim 5 or 6, wherein the annular spring has an annularspring channel.

8. The transmission fluid device of claim 7, wherein the cross-section of the annular springchannel is substantially C-shaped or U-shaped.

9. The transmission fluid device of any preceding claim, wherein the annular seal comprises asecond circumferential lip extending around the annular body; the second circumferential lip being axially spaced from the first circumferential lip.

10. An electric drive unit of a vehicle comprising the transmission fluid device according to anypreceding claim.

11. The electric drive unit of claim 10, wherein the electric drive unit further comprises a pumpand a radiator; the pump and the radiator being fluidly connected to at least one of the main and the bypass fluid outlets.

12. A vehicle comprising the transmission fluid device of any of claims 1 to 9 or the electric driveunit of claim 10 or 11.

13. A method of assembling a transmission fluid device for an electric drive unit of a vehicle, thetransmission fluid device comprising:a housing portion defining a fluid chamber having a fluid inlet, a main fluid outlet, and a bypass fluid outlet; anda bypass valve for controlling fluid flow between the fluid inlet, the main fluid outlet, and the bypass fluid outlet,the method comprising the steps of:positioning an annular seal within a circumferential channel of a valve body of the bypass valve, the annular seal comprising an annular body, an elastically deformable circumferential lip extending around the annular body, and an annular channel defined between the annular body and the circumferential lip; andinserting the valve body of the bypass valve at least partially into the fluid chamber to define a clearance gap between an inner wall of the fluid chamber and an outer wall of the valve body, the circumferential channel being fluidly connected to the fluid chamber by the clearance gap,wherein the annular channel is oriented to be in fluid communication with the fluid chamber via the clearance gap such that a fluid passing through the clearance gap from the fluid chamber hydraulically urges the circumferential lip against the inner wall of the fluid chamber.

14. The method of claim 13, wherein the step of inserting the bypass valve body into the housing portion further comprises: elastically deforming the circumferential lip radially away from the annular body as the valve body is inserted into the housing portion.s

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