A pressure relief device for a vehicle

Abstract

Aspects of the present invention relate to a pressure relief device (10) for a battery unit assembly and a vehicle comprising the pressure relief device. The pressure relief device (10) comprises a body (12) having an opening (14) for the release of gas from the battery unit assembly and a cap (38) for covering the opening. One of the body (12) and the cap (38) comprises a spring clip (66) and the other of the body (12) and the cap (38) comprises an engagement portion (68). The clip (66) is configured to grip the engagement portion (68) so that the cap (38) covers the opening (14) until a pressure threshold within the battery unit assembly is reached, whereby the clip (66) is configured to deform to release the engagement portion (68) so that the opening (14) is uncovered by the cap (38).

Description

[0001] A PRESSURE RELIEF DEVICE FOR A VEHICLE

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to a pressure relief device for a battery unit assembly. Aspects of the invention relate to a pressure relief device, a battery unit assembly and a vehicle comprising the pressure relief device.

[0004] BACKGROUND

[0005] It is known to use traction batteries within vehicles, such batteries may be used within hybrid vehicles and electric vehicles. Typically, a traction battery is made up of a plurality of battery cells. The battery is enclosed within a housing of a battery unit assembly. The housing protects the battery from ingress of water and debris.

[0006] Over the life span of a battery, one or more of the battery cells may fail and experience thermal runaway. When a battery cell fails in this way, the battery cell rapidly releases large volumes of hot gases which causes the pressure within the battery unit assembly to rise rapidly. Therefore, there is a need to provide a weak point on the housing of the battery unit assembly through which gases can exit rapidly and in a controlled way in the event of a battery cell failure. The weak point allows for the emergency release of gases from the battery unit assembly. The rapid release of gases reduces the risk of further damage to the battery occurring.

[0007] It is known to provide a vent as the weak point for the rapid release of gas from a battery unit assembly. It is an aim of the present invention to improve the speed of and the control of releasing gas from a battery unit assembly in an emergency.

[0008] SUMMARY OF THE INVENTION

[0009] Aspects and embodiments of the invention provide a pressure relief device for a battery unit assembly, a battery unit assembly and a vehicle as claimed in the appended claims.

[0010] According to an aspect to the invention, there is provided a pressure relief device comprising: a body having an opening; and a cap for covering the opening; wherein one of the body and the cap comprises a deformable clip and the other of the body and the cap comprises an engagement portion; and wherein the clip is configured to grip the engagement portion so that the cap covers the opening until a pressure threshold is reached, whereby the clip is configured to deform to release the engagement portion so that the opening is uncovered by the cap.

[0011] The pressure relief device enables an opening to be quickly uncovered when a pressure threshold is reached because once the engagement portion is released, the opening is entirely uncovered by the cap. This is advantageous as the pressure relief device may be used on an enclosure to allow a rapid reduction of pressure within the enclosure in, for example, an emergency.

[0012] In certain embodiments, the deformable clip may be a spring clip. According to an aspect to the invention, there is provided a pressure relief device for a battery unit assembly. The device comprising: a body having an opening for the release of gas from the battery unit assembly; and a cap for covering the opening; wherein one of the body and the cap comprises a spring clip and the other of the body and the cap comprises an engagement portion; and wherein the clip is configured to grip the engagement portion so that the cap covers the opening until a pressure threshold within the battery unit assembly is reached, whereby the clip is configured to deform to release the engagement portion so that the opening is uncovered by the cap.

[0013] The pressure relief device enables gas to be released quickly from a battery unit assembly. The quick release of gas from such an assembly may be required in an emergency, such as, if a battery cell within the battery assembly unit fails and experiences thermal runaway. In normal operating conditions at pressures below the pressure threshold, the cap covers the opening so that gas does not pass through the opening. As pressure increases within the battery unit assembly, the force on the cap caused by the pressure increases. If the pressure threshold is reached, the force on the cap is sufficient that clip releases the engagement portion so that the cap no longer covers the opening allowing emergence release of gas from the battery unit assembly. Once the engagement portion is released, the opening is entirely uncovered by the cap which allows the release of gas from the battery unit assembly to occur quickly. The spring clip may be tuned to release the engagement portion at a desired pressure threshold.

[0014] In embodiments of either the above-described aspects of the invention, one or more of the following may apply.

[0015] The clip may comprise a first leg and a second leg configured to grip the engagement portion therebetween and wherein the clip comprises a bridge connecting the first leg and the second leg. This configuration of the clip may be simple to tune to a particular pressure threshold and may also improve the ease of releasing the clip from the engagement portion as the legs of the clip merely need to move apart from one another. Advantage of this claim is not that strong but the claim is included so the features can be built on separately in other dependent claims.

[0016] Optionally, each leg may comprise a first portion and a second portion, the first portion extending between the bridge and the second portion, wherein the second portion extends at an angle to the first portion and the second portion is configured to grip the engagement portion. The two portions of each leg may improve each of tuning the clip to release the engagement portion at a particular pressure threshold because the clip can be tuned by changing the angle between the first and second leg portions, and / or relative lengths of the first and second leg portions.

[0017] The second portion of each leg may extends at an obtuse angle a (i.e. less than 180 degrees and greater than 90 degrees) of relative to the respective first portion. The clip may comprise a flange extending from either side of the bridge, wherein the clip is attached to the cap or the body via the flange. The flanges may improve the ease of connecting the clip to the device and may allow clip to bend independently of its attachment to the device.

[0018] The engagement portion may comprise a first side facing the first leg and an opposing second side facing the second leg, the first side and the second side each defining a contact region for the clip to grip; and wherein the width of the engagement portion decreases from the contact region in a direction towards the bridge of the clip. The width being the distance from the first side to the second side o the engagement portion. This shape of the engagement portion may improve the ease of releasing clip from the engagement portion because once the clip has moved passed the contact regions, the engagement portion will not interfere further with the clip due to the narrowing width.

[0019] The width of the engagement portion may be greatest between the contact regions of the first and second sides. The width of the engagement portion may decreases on either side of the contact region.

[0020] Optionally, the first side may comprise a first upper surface and a first lower surface and wherein the contact region of the first side is defined by a corner at which the first upper and lower surfaces meet; and wherein the second side comprises a second upper surface and a second lower surface and wherein the contact region of the second side is defined by a corner at which the second upper and lower surfaces meet. The corners provides a single point of contact between the clip and the engagement portion thereby improving ease of tuning clip to release the engagement portion at the pressure threshold.

[0021] The width of the engagement portion may taper continuously from the contact regions to an end of the engagement portion which faces towards the bridge of the clip. The continuous taper may ensure that there are no features on the surface of the engagement portion that could interfere with the clip being released from the engagement portion once it has passed the widest portion. As such, release of the clip from the engagement portion may be improved.

[0022] In certain embodiments, the device may comprise a seal for fluidly sealing the opening, wherein the body comprises a groove surrounding the opening for receiving the cap and the seal is positioned within the groove between the cap and the body. Positioning the seal between the cap and the body in this way may provide an improved seal between the cap and the body because the seal is compressed by the clip gripping the engagement portion when the cap covers the opening.

[0023] Optionally, the body may comprise a drainage channel fluidly connected to the groove, the drainage channel being configured to drain liquid from the groove in a direction away from the opening. The pressure relief device may be used in vehicles that are designed for wading and the battery unit assembly is positioned below a maximum wading depth of the vehicle. Therefore, during a wading event the device may be underwater and after the wading event water may be present in the groove. The drainage channel allows water to be drained from the groove thereby reduce the risk of water ingress into the battery unit assembly. In certain embodiments, the cap may comprise the spring clip and the body may comprise the engagement portion.

[0024] The body comprises a plurality of spokes to support the engagement portion within the opening. Using spokes to support the engagement portion within the opening reduces the amount of the opening that is occluded by the spokes thereby improving the speed at which gas can be ejected through the opening. Positioning the engagement portion within the opening enables the force from pressure in the battery unit assembly to act on all sides of the clip with may improve release of the engagement portion at the pressure threshold.

[0025] In certain embodiments, the body comprises the spring clip and the cap may comprises the engagement portion. The body comprises a plurality of spokes to support the spring clip within the opening.

[0026] Optionally, the cap may comprise a recess positioned adjacent to the bridge of the clip to accommodate deformation of the clip during use. The recess allows to move towards the cap as the clip deforms during use. As such, the cap does not restrict the movement of the clip.

[0027] The clip and the engagement portion may be positioned at the centre of the opening. This positioning of the clip and engagement portion may improve the uniformity of ferees on either side of the clip and the engagement portion. This may in turn improve the reliability of the cap opening at the pressure threshold.

[0028] In certain embodiments, the device may comprise a metal grid extending across the opening, wherein the metal grip comprises a least one sprung finger at a periphery of the grid. When the device is used with a battery unit assembly, the metal grid contacts the body of the assembly within which the battery is located. The purpose of the metal grid is to reduce the chance of unwanted electromagnetic emissions affecting the battery. The sprung fingers improve the electrical connection of the grid with the body of the assembly unit, ensuring the grid performs as intended.

[0029] In certain embodiments, the cap to be gas impermeable. That is, the cap may be formed from a gas impermeable material.

[0030] In certain embodiments, the body to be gas impermeable. That is, the body may be formed from a gas impermeable material.

[0031] According to another aspect of the invention, there is provided a battery unit assembly comprising the abovedescribed pressure relief device.

[0032] According to another aspect of the invention, there is provided a vehicle comprising the above-described pressure relief device.

[0033] 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.

[0034] BRIEF DESCRIPTION OF THE DRAWINGS

[0035] One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0036] Figure 1 shows a schematic representation of a pressure relief device viewed from above in accordance with an embodiment of the invention;

[0037] Figure 2 schematically shows a schematic representation of the pressure relief device of Figure 1 viewed from beneath;

[0038] Figure 3 schematically shows a sectional view of the pressure relief device of Figure 1 ;

[0039] Figure 4 schematically shows a side view of the pressure relief device of Figure 1 ;

[0040] Figure 5 schematically shows a cross-sectional view of the pressure relief device of Figure 1 attached to a battery unit assembly;

[0041] Figure 6 schematically shows a perspective view clip of the pressure relief device of Figure 1 ;

[0042] Figure 7 schematically shows a side view clip of the pressure relief device of Figure 1 ; and

[0043] Figure 8 shows a vehicle in accordance with an embodiment of the invention.

[0044] DETAILED DESCRIPTION

[0045] Figures 1 to 5 show a pressure relief device 10 according to an embodiment of the invention. The pressure relief device 10 is for a battery unit assembly 200. The battery unit assembly 200 may comprise housing 210. The housing 210 may define a cavity 220 for enclosing a battery (not shown), such as a traction battery. The battery may comprise a plurality of battery cells. The housing 210 may be sealed to prevent or reduce ingress of liquid, such as water, into the housing 210.

[0046] The pressure relief device 10 may be attached to the battery unit assembly 200 to provide a controlled point of failure on the battery unit assembly 200. The pressure relief device 10 allows the quick release of gas from the battery unit assembly 200 which may be required in an emergency, such as, if a battery cell fails and experiences thermal runaway.

[0047] The battery unit assembly 200 may be for use in a vehicle 2000. In a vehicle 2000, the battery unit assembly 200 may be for mounting under a floor of the vehicle 2000. Figure 8 shows a vehicle 2000 which comprises the pressure relief device 10 according to an embodiment of the invention.

[0048] The pressure relief device 10 comprises a body 12 having an opening 14 for the release of gas from the battery unit assembly 200. The housing 210 of the battery unit assembly 200 may comprise a corresponding aperture 230 so that gas in the cavity 220 of the battery unit assembly 200 can be released. As shown in Figure 5, when the pressure relief device 10 is attached to the battery unit assembly 200, the opening 14 of in the body 12 of the pressure relief device 10 is aligned with the aperture 230 in the housing 210 of the battery unit assembly 200. The opening 14 and the aperture 230 may be substantially the same size and shape. In the embodiment shown in the Figures, the opening 14 through the body 12 and the aperture 230 in the battery unit assembly 200 are circular.

[0049] As shown in Figures 3 and 5, the opening 14 may extend through the body 12 of the pressure relief device 10. The opening 14 may extend from an upper side 16 of the body 12 to an opposing lower side 18 of the body 12. The lower side 18 of the body 12 is the side which contacts or faces towards the battery unit assembly 200 when the pressure relief device 10 is attached to the battery unit assembly 200. The upper side 16 of the body 12 is the side which faces away from the battery unit assembly 200 when the pressure relief device 10 is attached to the battery unit assembly 200 as shown in Figure 5. The opening 14 may be defined by an internal wall 18 of the body 12. The internal wall 18 may extend from the upper side 16 to the lower side 18 of the body 12. The internal wall 18 may be substantially perpendicular to the lower side 18 and / or the upper side 16 of the body 12.

[0050] The pressure relief device 10 may be attached to the housing 210 of the battery unit assembly 200 by any suitable means. As shown in the non-limiting embodiment in the Figures, the body 12 of the pressure relief device 10 may comprise a plurality of through holes 20 for receiving fasteners. The housing 210 may comprise a corresponding plurality of through holes (not shown). As such, the pressure relief device 10 may be attached to the battery unit assembly 200 by a plurality of fasteners (not shown).

[0051] As shown in Figures 1 and 2, the body 12 of the pressure relief device 10 may be substantially rectangular. The body 12 is bounded by an external wall 22 which demarcates the rectangular shape of the body 12. The body 12 may comprise a through hole 20 for a fastener at each of the four corners of the body 12. However, the invention is not limited to the geometry shown in the Figures.

[0052] The body 12 of the pressure relief device 10 may be sealed against the housing 210 of the battery unit assembly 200 prevent or reduce ingress of liquid, such as water, into the battery unit assembly 200. As shown in the in Figures 3 and 5, the pressure relief device 10 may comprise a gasket 24 disposed between the body 12 of the pressure relief device 10 and the housing 210 of the battery unit assembly 200. The gasket 24 may be arranged to extend around the opening 14 in the body 12 of the pressure relief device 10 and the aperture 230 in the housing 210 of the battery unit assembly 200. The gasket 24 may be concentric with both the aperture 230 and the opening 14. The gasket 24 may be compressed between the body 12 of the pressure relief device 10 and the housing 210 of the battery unit assembly 200 when the pressure relief device 10 is attached to the assembly thereby preventing liquid passing between the body 12 of the pressure relief device 10 and the housing 210 of the battery unit assembly 200.

[0053] As shown in the embodiment in the Figures, the lower side 18 of the body 12 of the pressure relief device 10 may comprise a lower groove 26 for receiving the gasket 24. The lower groove 26 is positioned radially outwards of the opening 14 in the body 12 of the pressure relief device 10 where the radial position is relative to a centre of the opening 14. As shown in Figure 3, the gasket 24 may extend out ofthe lower groove 26 such that when the pressure relief device 10 is attached to the battery unit assembly 200, by fasteners for example, the gasket 24 is compressed.

[0054] The pressure relief device 10 may comprise metal grid 28 configured to extend across the opening 14. The metal grid 28 may comprise outer and inner concentric rings 30, 32 connected by a plurality of spokes 34. As shown in Figure 2, the outer and inner rings 30, 32 may be connected by eight spokes 34 that extend from the inner ring 32 to the outer ring 30. However, a different number of spokes 34 may be used. The outer ring 30 may have substantially the same diameter as the opening 14 in the body 12 of the pressure relief device 10. The housing 210 of the battery unit assembly 200 may comprise aluminium or another suitable metal to shield The battery within the battery unit assembly 200 from electromagnetic emissions. The metal grid 28 may provide similar shielding across the opening 14 in the body 12 ofthe pressure relief device 10 and the aperture 230 in the housing 210 of the battery unit assembly 200. The metal grid 28 may comprise aluminium or stainless steel. To ensure that the metal grid 28 contacts the housing 210 of the battery unit assembly 200 when the pressure relief device 10 is attached to the battery unit assembly 200, the metal grid 28 may comprise a least one sprung finger 34. The sprung finger 36 is positioned at a periphery of the grid 28 to ensure that the grid 28 contacts the housing 210 of the battery unit assembly 200. As shown in Figures 3 and 5, the sprung finger 36 extends from one of the spokes 34 of the grid 28 in a direction away from the body 12 of the pressure relief device 10. The sprung finger 36 may contact the housing 210 and be compressed when the pressure relief valve is attached to the battery unit assembly 200. Spokes of grid 28 line up with spokes in body 12.

[0055] The device comprises a cap 38 for covering the opening 14 in the body 12 of the pressure relief device 10. Figures 1 to 5 show the cap 38 in a closed position covering the opening 14. As shown in the embodiment in the Figures, the cap 38 may be substantially circular in shape.

[0056] When the cap 38 covers the opening 14, the cap 38 may seal the opening 14 to prevent fluid entering or exiting the battery enclosure via the opening 14. The pressure relief device 10 may therefore comprise a seal 40 for fluidly sealing the cap 38 to the body 12. The body 12 may comprise a upper groove 42 for receiving the seal 40. In the embodiment shown in the Figures, the upper groove 42 is formed in the upper side 16 of the body 12 of the pressure relief device 10. The upper groove 42 may surround the opening 14 in the body 12. The upper groove 42 may be positioned radially outwards of the opening 14 in the body 12 of the pressure relief device 10 where the radial position is relative to a centre of the opening 14. As shown in Figures 3 and 5, the seal 40 may be positioned within the upper groove 42 between the cap 38 and the body 12 such that the seal 40 is radially inwards of the cap 38.

[0057] As shown the Figures, the cap 38 may comprise a rim 44. When the cap 38 is in the closed position covering the opening 14, the rim 44 may be configured to extend into the upper groove 42. As shown in the embodiment in the Figures, the cap 38 may comprise a covering portion 46 sized to cover the opening 14. The rim 44 may extend from the covering portion 46 in order to be received in the upper groove 42. The rim 44 may extend from the covering portion 46 of the cap 38 at an angle greater than or equal to 90 degrees and less than 180 degrees. The upper groove 42 may be defined by an inner surface 48 and an outer surface 50 which extend into the body 12 from the upper side 16. The inner surface 48 is radially inwards of the outer surface 50 relative the centre of the opening 14. A connecting surface 52 may extend radially from the inner surface 48 to the outer surface 50. As shown in Figures 3 and 5, the inner surface 48 may comprise a first section 54 and a second section 56. The first section 54 of the inner surface 48 may extend from the upper side 16 of the body 12 to the second section 56 of the inner surface 48. The second section 56 may extend from the first section 54 of the inner surface 48 to the connecting surface 52. The second section 56 of the inner surface 48 may be at an obtuse angle (i.e. an angle between 90 degrees and 180 degrees) relative to the first section 54 of the inner surface 48. The obtuse angle is an interior angle of the upper groove 42 (i.e. the obtuse angle is within the upper groove 42). As shown in the Figures, the seal 40 may be configured to be disposed at the junction between the first and second sections 54, 56 of the inner surface 48. As shown in Figures 3 and 5, the rim 44 of the cap 38 may be substantially parallel to the second section 56 of the inner surface 48 when the cap 38 is in the closed position. As such, the orientation of the first and second sections 54, 56 of the inner surface 48 in combination with the rim 44 of the cap 38 help hold the seal 40 in place. As shown in the non-limiting embodiment in the Figures, the first section 54 of the inner surface 48 may be sustainably parallel with the outer surface 50. The first section 54 of the inner surface 48 and the outer surface 50 may be substantially parallel with the internal wall 18 of the body 12 which defines the opening 14.

[0058] During use of the pressure relief device 10 in a vehicle 2000, water may accumulate in the upper groove 42 of the pressure relief device 10. This may occur when the pressure relief device 10 is positioned below the maximum wading depth of the vehicle 2000. The pressure relief device 10 may comprise at least one drainage channel 58 to allow water to be drained from the upper groove 42. The drainage channel 58 may be configured to drain liquid from the upper groove 42 in a direction away from the opening 14. The drainage channel 58 is shown in Figures 2, 3 and 4 but are omitted in Figure 5. As shown in the embodiment in the Figures, the body 12 may comprise the drainage channel 58. The drainage channel 58 may extend from the upper groove 42 to the external wall 22 of the body 12. The drainage channel 58 may comprise an inlet 60 through the outer surface 50 of the upper groove 42. The drainage channel 58 may extend through the body 12 to an outlet 62 in the external wall 22 as shown in Figures 3 and 4. On the external wall 22, the outlet 62 may be positioned towards or at the lower side 18 of the body 12. In the embodiment shown in the Figures, the pressure relief device 10 has drainage channels 58 on opposing edges 64 of the device 10, where the edges of the device 10 are defined by the external wall 22. As shown in Figures 2, 3 and 4, the device may comprise two drainage channels 58 on two opposing edges 64 of the rectangular body 12 of the device.

[0059] One of the body 12 of the pressure relief device 10 and the cap 38 comprises a spring clip 66. The other of the body 12 and the cap 38 comprises an engagement portion 68. As shown in the Figures, the clip 66 and the engagement portion 68 may be positioned at the centre of the opening 14 of the body 12 of the pressure relief device 10. As shown in the embodiment in the Figures, the cap 38 may comprise the spring clip 66 and the body 12 may comprise the engagement portion 68. However, the skilled person will appreciate that the invention in not limited to this arrangement. In alternative embodiments, the body 12 may comprise the spring clip 66 and the cap 38 may comprise the engagement portion 68. The clip 66 and the engagement portion 68 may be positioned off-centre in the opening 14 of the body 12 of the pressure relief device 10.

[0060] The clip 66 is configured to grip the engagement portion 68 so that the cap 38 covers the opening 14. That is, the engagement of the clip 66 and the engagement portion 68 holds the cap 38 in the closed position covering the opening 14. The seal 40 may be compressed between the cap 38 and the body 12 of the pressure relief device 10 by the clip 66 gripping the engagement portion 68.

[0061] The clip 66 is configured to grip the engagement portion 68 so that the cap 38 covers the opening 14 until a pressure threshold within the battery unit assembly 200 is reached. When the pressure threshold is reached, the clip 66 is configured to deform to release the engagement portion 68 so that the opening 14 is uncovered by the cap 38. Once the engagement portion 68 is released, the opening 14 may be entirely uncovered by the cap 38 which allows the release of gas from the battery unit assembly 200 to occur quickly. The pressure relief device 10 may be attached to the battery unit assembly 200 to provide a controlled point of failure on the battery unit assembly 200. The clip 66 may be tuned to release the engagement portion 68 at a desired pressure threshold. The pressure threshold may be greater than the water entry pressure of the device 10. That is, at the pressure threshold when the clip 66 deforms, the force on the cap 38 from the pressure within the battery unit assembly is greater than the force required to compress the seal between the cap 38 and the body 12 of the device 10. Therefore, at pressures below the pressure threshold, the clip 66 grips the engagement portion 68 with force sufficient to compress seal and provide a water tight seal between the body and the cap.

[0062] As shown in the Figures, the clip 66 may comprise a first leg 70 and a second leg 72 configured to grip the engagement portion 68 therebetween. The clip 66 may comprise a bridge 74 connecting the first leg 70 to the second leg 72. The first and second legs 70, 72 may be connected to opposing ends of the bridge 74. Figures 6 and 7 show the clip 66 without the other features of the pressure relief device 10. As shown in the embodiment in the Figures, the clip 66 may by symmetrical about a plane A positioned equidistant between the first and second legs 70, 72.

[0063] Each leg 70, 72 of the clip 66 may comprise a first portion 76 and a second portion 78. The first portion 76 may extend from the bridge 74 to the second portion 78. The first portion 76 of each leg may extend from the bridge 74 at an obtuse angle 0, where the angle 0 is an interior angle of the clip 66. That is, with reference to Figure 7, the angle 0 between the bridge 74 and first portion 76 of the first leg 70 is measured in a clockwise direction from the bridge 74 to the first portion 76 whereas the angle between the bridge 74 and the first portion 76 of the second leg 72 is measured in an anti-clockwise direction from the bridge 74 to the first portion 76. During use when the pressure in the battery unit assembly 200 exceeds the pressure threshold, the clip 66 may flex or deform at the junctions between the first portion 76 of each leg and the bridge 74 so that the clip 66 releases the engagement portion 68.

[0064] The second portion 78 of each leg may extend from the first portion 76 at an angle a. The angle a may be the same for the first and second legs 70, 72. The second portion 78 may be configured to grip the engagement portion 68. Therefore, the angle a between the first and second portions 76, 78 of the second leg 72 may be an obtuse angle a (i.e. less than 180 degrees and greater than 90 degrees), where the is an interior angle of the clip 66. That is, with reference to Figure 7, the angle a between the first and second portions 76, 78 of the first leg 70 is measured in a clockwise direction from the first portion 76 to the second portion 78 whereas the angle a between the first and second portions 76, 78 of the second leg 72 is measured in an anti-clockwise direction from the first portion 76 to the second portion 78. During use when the pressure in the battery unit assembly 200 exceeds the pressure threshold, the clip 66 may flex or deform at the junctions between the first and second portions 76, 78 of each leg 70, 72 so that the clip 66 releases the engagement portion 68.

[0065] The second portion 78 of each leg 70, 72 may comprise a curved section 80 priorto the end 82 of the respective leg 70, 72. The curved section 80 may direct the end 82 of the leg 70, 72 away from the engagement portion 68 when the cap 38 covers the opening 14 to reduce the risk of the end 82 of the leg 70, 72 catching on the engagement portion 68 when the clip 66 releases the engagement portion 68 at pressures above the pressure threshold.

[0066] The bridge 74 may comprise a plurality of sections. The bridge 74 may be symmetrical about the plane A positioned equidistantly between the two legs of the clip 66. As shown in Figures 6 and 7, the bridge 74 may comprise a central section 84 from which two outer sections 86, 88 extend. One outer section 86 may extend from the central section 84 of the bridge 74 to the first leg 70 and the other outer section 88 extends from the opposite side of the central section 84 to the second leg 72. Each of the outer sections 86, 88 may extend away from the central section 84 of the bridge 74 and towards the cap 38. During use when the pressure in the battery unit assembly 200 exceeds the pressure threshold, the clip 66 may flex or deform at the junctions between of the central section 84 and the two outer sections 86, 88 of the bridge 74.

[0067] The clip 66 may comprise a flange 90 extending from either side of the bridge 74. The clip 66 may be attached to the cap 38 or the housing 210 via the flange. As shown in the Figures, each flange 90 may comprise a plurality of apertures 92 for securely attaching the clip 66 to the cap 38. The clip 66 may be attached to the cap 38 by, for example, welding. As shown in the embodiment in the Figures, the two flanges 90 may be attached on either side of the central section of the bridge 74. The flanges 90 and the central section of the bridge 74 may reside in the same plane. As shown in Figures 3 and 5, the cap 38 may comprise a recess 94 positioned adjacent to the bridge 74 of the clip 66 to accommodate deformation of the clip 66 during use. The flanges 90 may be connected to the cap 38 on either side of the recess 94 so that there is space between the cap 38 and the bridge 74 of the clip 66.

[0068] The engagement portion 68 is shown in Figures 2, 3 and 5. As shown in the Figures, the engagement portion 68 may comprise a first side 94 configured to face the first leg 70 of the clip 66 and an opposing second side 96 configured to face the second leg 72 of the clip 66. Therefore, when the cap 38 covers the opening 14, the first and second legs 70, 72 of the clip 66 grip the first side 94 and the second side 96 of the engagement position 68, respectively, to hold the cap 38 in place. The engagement portion 68 is gripped between the first and second legs 70, 72 of the clip 66. The first side 94 and the second side 96 of the engagement portion 68 may each define a contact region 98 for the clip 66. Each contact region 98 may provide a single point for the respective leg 70, 72 of the clip 66 to minimise direct contact between the clip 66 and the engagement portion 68. As shown in the embodiment in the Figures, the first side 94 of the engagement portion 68 may comprise a first upper surface 99 and a first lower surface 97. The contact region 98 of the first side 94 may be defined by a corner at which the first upper and lower surfaces 99, 97 meet. In the same manner, the second side 96 may comprise a second upper surface 95 and a second lower surface 93. The contact region 98 of the second side 96 may be defined by a corner at which the second upper and lower surfaces 95, 93 meet.

[0069] The engagement portion 68 may be symmetrical about a plane equidistant from the first and second surfaces. As such, the contact region 98 of the first side 94 of the engagement portion 68 may be at the same height as the contact region 98 on the second side 96 of the engagement portion 68 relative to the lower and upper sides 16, 18 of the body 12.

[0070] The width of the engagement portion 68 may taper from the contact regions 98 to one or both ends of the engagement portion 68. The width of the engagement portion 68 is the distance between the first and second sides 94, 96 of the engagement portion 68 in a direction perpendicular to the plane equidistant between the first and second sides 94, 96 of the engagement portion 68. As shown in Figures 3 and 5, with maximum width of the engagement portion 68 may be smaller than the length of the bridge 74 of the clip 66.

[0071] The width ofthe engagement portion 68 may taper from the contact regions 98 to an end 91 ofthe engagement portion 68 which faces towards the bridge 74 of the clip 66 (i.e. the end 91 of the engagement member which is closest to the bridge 74 of the clip 66 when the cap 38 is in the closed position covering the opening 14) which may improve the release of the clip 66 from the engagement portion 68. The width of the engagement portion 68 may taper continuously from the contact regions 98 to the end 91 of the engagement portion 68. The continuous taper may ensure that there are no features on the surface of the engagement portion 68 that could interfere with the clip 66 being released from the engagement portion 68 once it has passed the contact portions 98. The angle of the taper from the contact regions 98 to the end 91 of the engagement portion 68 may vary. The width of the engagement portion 68 may taper from the contact regions 98 to an end 89 of the engagement portion 68 which faces away the bridge 74 of the clip 66 (i.e. the end of the engagement member which is furthest from the bridge 74 ofthe clip 66 when the cap 38 is in the closed position covering the opening 14) which may minimise the amount of contact between the clip 66 and the engagement portion 68. The width of the engagement portion 68 may therefore be greatest between the contact regions 98 ofthe first and second sides 94, 96.

[0072] The engagement portion 68 is positioned within the opening 14 of the body 12. The body 12 may comprise a plurality of spokes 87 to support the engagement portion 68 within the opening 14. The spokes 87 may have substantially the same height as the depth on the opening 14. That is, the spokes 87 may have substantially the same height as the internal wall 18 of the body 12. Supporting the engagement portion 68 using a plurality of spokes 87 may provide uniform support for the engagement portion 68 whilst minimising the area of the opening 14 that needs to be obscured to support the engagement portion 68. In the non-limiting embodiment shown in the Figures, the engagement portion 68 is supported by eight spokes 87. As described above, the grid 28 may also comprise a plurality of spokes 34 extending between the inner and the outer rings 30, 32. The spokes 64 of the grid 28 may be configured to align with the spokes 87 of the body 12. One or more of the spokes 34 of the grid 28 may comprise a clip 85 to connect the grid to the spokes 87 of the body 12. In the embodiment shown in the Figures, four of the spokes 34 of the grid comprise a clip 85 to connect the grid to the spokes 87 of the body 12. The body 12 and the grid 28 may comprise the same number and angular distribution of spokes 34, 87. The spokes 87 of the body 12 and the spokes 34 of the grid 28 may also be the same width as each other. As shown in Figure 2, the diameter of the inner ring 32 of the grid 28 may be such that the radial extent of the clip 66 and the engagement portion 68 is smaller than the diameter of the inner ring 32.

[0073] Figures 1 to 5 show the cap 38 of the pressure relief device 10 in the closed position covering the opening 14. As shown in Figures 3 and 5, in the closed position the clip 66 grips the engagement portion 68. In particular, the second sections of the first and second legs 70, 72 grip the contact regions 98 on the first and second sides 94, 96 of the engagement portion 68. This allows the cap 38 to be held in place covering the opening 14. The force by which the clip 66 grips the engagement portion 68 compresses the seal 40 between the cap 38 and the body 12 of the pressure relief device 10 thereby sealing the opening 14. During use of the pressure relief device 10 with the battery unit assembly 200, the pressure in the battery unit assembly 200 may increase if, for example, a battery cell fails and experiences thermal runaway. In such an event, gases released by the failure would ideally be released rapidly from the battery unit assembly 200. The pressure relief device 10 enables this to be done. As pressure increases within the battery unit assembly 200, the force on the cap 38 caused by the pressure increases. When the pressure in the battery unit assembly 200 increases above a pressure threshold, the force on the cap 38 is sufficient to cause the clip 66 to deform and release the engagement portion 68. The clip 66 deforms by the distance between the second sections of the first and second legs 70, 72 increasing. This deformation may be caused by the clip 66 flexing at the junction between the first and second portions 76, 78 of the legs, the junctions between the bridge 74 and each leg 70, 72, and junctions between the sections 84, 86, 88 of the bridge 74. As the clip 66 deforms, the outer sections of the bridge 74 may move into the recess 94 in the cap 38. As the distance between the second sections 78 of the first and second legs 70, 72 increases each of the legs 70, 72 of the clip 66 slide past the contact regions 98. Since the clip 66 and engagement portion 68 are positioned in the centre of the opening 14, the first and second legs 70, 72 may slide past the contact regions 98 at substantially the same time. The clip 66 releases the engagement portion 68 once the curved sections 80 of the legs 70, 72 have moved past the contact regions 98. The taper of the engagement portion 68 towards the end 91 of the engagement portion 68 which faces the bridge 74 of the clip 66 and the curved section 80 of the legs 70, 72 may help ensure that the release of the engagement portion 68 is not hindered or slowed once the ends 82 of the clip 66 have moved passed the contact regions 98. Once the engagement portion 68 is released, the cap 38 is separate from the body 12 of the pressure relief device 10 and the opening 14 is uncovered. Using spokes 87 to support the engagement portion 68 minimises the area of the opening 14 that is obscured thereby helping improve the rapid release of gas through the opening 14 of the pressure relief device 10. Similarly, using spokes 34 minimises the area of the opening 14 that is obscured to shield the battery within the battery unit assembly 200 from electromagnetic emissions. The clip 66 may be tuned to release the engagement portion 68 at a desired pressure threshold. The shape of the legs and the bridge 74 may be tuned to the desired pressure threshold. For example, the lengths and angles between the sections 76, 78 of the legs 70, 72 and the bridge 74 portions may be tuned to the desired pressure threshold. Additionally, the thickness of the material from which the clip 66 is formed may be adjusted forthe desired pressure threshold. Additionally or alternatively, the shape and width of the engagement portion 68 may also be tuned to release the engagement portion 68 at a desired pressure threshold.

[0074] Until the pressure threshold is reached, the pressure relief device 10 may not provide any ventilation of the battery unit assembly 200. When the cap 38 is in the closed position, the opening 14 may be fluidly sealed. As such, the device does not comprise, and does not need to comprise, an air premeable membrane for ventilation of the battery unit assembly 200. This may be advantageous when the pressure relief device 10 is positioned below the maximum wading depth of a vehicle 2000. The absence of an air premeable membrane may reduce the risk of water entering the battery unit assembly 200 through the pressure relief device 10. Additionally, the absence of an air premeable membrane may allow for a faster release of gases from the battery unit assembly 200 via the pressure relief device 10.

[0075] The pressure relief device 10 may be made from any suitable material. The body 12 and the cap 38 may be made from gas impermeable materials. Non-limiting examples include polymers, such as polyphenylene ether, and glass fibre. The seal 40 and the gasket 24 may comprise rubber. The clip 66 is a spring clip 66 as such the clip 66 is flexible. The clip 66 may comprise metal.

[0076] 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.

[0077] In a modification to the above-described embodiment, the body 12 of the pressure relief device 10 may comprise the clip 66 and the cap 38 may comprise the engagement portion 68. In such an embodiment, the clip 66 may be attached to the spokes of the body 12. The bridge 74 of the clip 66 may be positioned near the lower side 18 of the body 12 and the legs of the clip 66 may extend towards the upper side 16 of the body 12. That is, the clip 66 may be rotated by 180 degrees relative to the arrangement in the embodiment shown in the Figures. Similarly, the engagement portion 68 may be attached to the cap 38. The engagement portion 68 may also be rotated by 180 degrees relative to the arrangement in the embodiment shown in the Figures.

[0078] In the above-described embodiment, the clip 66 is a spring clip. However, in alternative embodiments, the clip may comprise any deformable clip. The deformable clip may deform when the pressure threshold in the battery unit assembly is reached and release the engagement portion.

Claims

CLAIMS1 . A pressure relief device for a battery unit assembly, the device comprising: a body having an opening for the release of gas from the battery unit assembly; and a cap for covering the opening; wherein one of the body and the cap comprises a spring clip and the other of the body and the cap comprises an engagement portion; and wherein the clip is configured to grip the engagement portion so that the cap covers the opening until a pressure threshold within the battery unit assembly is reached, whereby the clip is configured to deform to release the engagement portion so that the opening is uncovered by the cap.

2. A device according to claim 1 , wherein the clip comprises a first leg and a second leg configured to grip the engagement portion therebetween and wherein the clip comprises a bridge connecting the first leg and the second leg.

3. A device according to claim 2, wherein each leg comprises a first portion and a second portion, the first portion extending between the bridge and the second portion, wherein the second portion extends at an angle to the first portion and the second portion is configured to grip the engagement portion.

4. A device according to claim 2 or 3, wherein the clip comprises a flange extending from either side of the bridge, wherein the clip is attached to the cap or the body via the flange.

5. A device according to any one of claims 2 to 4, wherein the engagement portion comprises a first side facing the first leg and an opposing second side facing the second leg, the first side and the second side each defining a contact region for the clip to grip; and wherein the width of the engagement portion decreases from the contact region in a direction towards the bridge of the clip.

6. A device according to claim 5, wherein the first side comprises a first upper surface and a first lower surface and wherein the contact region of the first side is defined by a corner at which the first upper and lower surfaces meet; and wherein the second side comprises a second upper surface and a second lower surface and wherein the contact region of the second side is defined by a corner at which the second upper and lower surfaces meet.

7. A device according to claim 5 or 6, wherein the width of the engagement portion tapers continuously from the contact regions to an end of the engagement portion which faces towards the bridge of the clip.

8. A device according to any one of the preceding claims, comprising a seal for fluidly sealing the opening, wherein the body comprises a groove surrounding the opening for receiving the cap and the seal is positioned within the groove between the cap and the body.

9. A device according to claim 8, wherein the body comprises a drainage channel fluidly connected to the groove, the drainage channel being configured to drain liquid from the groove in a direction away from the opening.

10. A device according to any one of the preceding claims, wherein the cap comprises the spring clip and the body comprises the engagement portion.

11. A device according to claim 10, wherein the body comprises a plurality of spokes to support the engagement portion within the opening.

12. A device according to claim 10 or 11 , wherein the cap comprises a recess positioned adjacent to the bridge of the clip to accommodate deformation of the clip during use.

13. A device according to any one of the preceding claims, wherein the clip and the engagement portion are positioned at the centre of the opening.

14. A device according to any one of the preceding claims, comprising a metal grid extending across the opening, wherein the metal grip comprises a least one sprung finger at a periphery of the grid.

15. A vehicle comprising the device according to any one of the preceding claims.

Images