WO2015025017A1

WO2015025017A1 - Vent apparatus for a battery casing

Info

Publication number: WO2015025017A1
Application number: PCT/EP2014/067857
Authority: WO
Inventors: David White; Naima ISSA; Christopher LYNESS
Original assignee: Jaguar Land Rover Limited
Priority date: 2013-08-21
Filing date: 2014-08-21
Publication date: 2015-02-26
Also published as: GB201314988D0; GB2517468A

Abstract

The present invention relates to a vent apparatus for a battery casing containing one or more battery cells. The apparatus comprises a first portion adapted for mounting in an opening formed in the battery casing, the first portion comprising a vent aperture formed there through. A rupture diaphragm is mounted on the first portion so as to close the vent aperture. The rupture diaphragm has first and second major faces and comprises an inner portion and an outer portion, the outer portion disposed around the periphery of the inner portion, a rupture line being defined at the boundary between the inner and outer portions, wherein the rupture diaphragm is configured so as to rupture at least partially along the rupture line when a fluid pressure exerted on the first major face is exceeded by a fluid pressure exerted on the second major face by a first threshold value. A second portion for applies a clamping force to the outer portion of the rupture diaphragm so as to hermetically seal the vent aperture. Other aspects of the invention relate to a rupture diaphragm and a vehicle.

Description

VENT APPARATUS FOR A BATTERY CASING

TECHNICAL FIELD The present invention relates to a vent apparatus for a battery. In one aspect the invention relates to a vent apparatus for the battery casing of a vehicle battery, such as a high voltage battery for a hybrid electric vehicle (HEV) or a battery electric vehicle (BEV). Other aspects of the invention relate to a rupture diaphragm, a battery and a vehicle.

BACKGROUND

Hybrid vehicles typically comprise a combustion engine, e.g. a compression-ignition or spark-ignition combustion engine, and an electrical machine in the form of a motor/generator, each of which are operable to provide traction power to a drive shaft of the vehicle. Such hybrid vehicles also comprise a high voltage battery from which current may be drawn to power the electrical machine to propel the vehicle when it operates in a hybrid electric (HEV) mode or a fully electric (EV only) mode. The high voltage batteries used in the type of hybrid or electric vehicles described above may be nickel metal hydride or lithium ion batteries and typically comprise a plurality of battery cells which are connected together and mounted in a battery casing. The battery casing may be provided with a socket to allow connection of an electrical cable thereto so as to allow a direct current provided by the battery cells to be provided to an inverter where it is converted into an alternating current for powering the electrical machine. The battery casing may also comprise means for monitoring the state of charge of the battery cells and/or providing diagnostic signals relating to the operating conditions of the battery to a vehicle control unit via a closed area network (CAN).

Additionally, the battery casing must also be adapted so as to protect against the ingress of water whilst simultaneously being able to accommodate changes in atmospheric pressure which may be experienced when the vehicle is driven at altitudes above sea level or which may be caused by the changes in the ambient temperature such as when the vehicle is operated in hot or cold climates. Furthermore, for hybrid or electric vehicles which are designed to travel Off-road' across rough, uneven terrain and through water, the battery may be subjected to pressure changes due to being partially or wholly submerged in water during wading, i.e. 'quenched'.

During the lifetime of a battery of the kind described above, it is possible that one or more of the cells in the battery casing may develop a defect, e.g. due to overcharging or over-heating of the cell. Defective battery cells may emit large volumes of hot gas and/or liquid in a short space of time which could lead to a rapid increase in the pressure inside the battery casing, impairing the performance of the battery and potentially causing damage to the battery casing.

It is an aim of the present invention to provide a vent apparatus for a battery casing which substantially overcomes or mitigates at least some of the problems described above. SUMMARY OF THE INVENTION

In one aspect, the present invention provides a vent apparatus for a battery casing containing one or more battery cells, the apparatus comprising:

a first portion adapted for mounting in an opening formed in the battery casing, the first portion comprising a vent aperture formed therethrough;

a rupture diaphragm mounted on the first portion so as to close the vent aperture, the rupture diaphragm having first and second major faces and comprising an inner portion and an outer portion, the outer portion disposed around the periphery of the inner portion, a rupture line being defined at the boundary between the inner and outer portions, wherein the rupture diaphragm is configured so as to rupture at least partially along the rupture line when a fluid pressure exerted on the first major face is exceeded by a fluid pressure exerted on the second major face by a first threshold value; and

a second portion for applying a clamping force to the outer portion of the rupture diaphragm so as to hermetically seal the vent aperture.

Thus, embodiments of the present invention provide an apparatus which can mitigate the risk of overpressurisation of a battery casing in the event of a fault with one or more of the battery cells. In the event of a build-up of fluid pressure within a casing of a battery, the rupture diaphragm will rupture along the rupture line allowing fluid from inside a battery casing to which the apparatus is installed to be vented through the vent aperture. Advantageously, the threshold pressure difference value which causes a rupture is a property which is inherent to the rupture diaphragm itself. Accordingly, no further element, such as a pin or blade, is required to cause the rupture diaphragm to rupture, which simplifies construction of the apparatus. Rather, all that is required is for the outer portion of the rupture diaphragm to be clamped in place. Furthermore, the presence of a predetermined rupture line ensures that, when the threshold pressure difference value is exceeded, the rupture diaphragm will rupture in a predictable way which allows for the unobstructed flow of fluid through the vent aperture. Moreover, in the event that the rupture diaphragm is ruptured inadvertently when there is not a battery fault, it can readily be replaced by removing the vent apparatus from the casing and replacing it with a new apparatus, i.e. replacement is simplified by virtue of the fact that the rupture diaphragm is not attached directly to the battery casing, for example by means of an adhesive or otherwise. In one embodiment, the clamping force is applied by attachment of the second portion to the first portion.

The second portion may comprise one or more retaining members for engaging with the outer portion of the rupture diaphragm.

The second portion may be push-fitted to the first portion, the one or more retaining members being sized so as to apply a clamping force having a predetermined magnitude to the outer portion of the rupture diaphragm when so push-fitted. In some embodiments, the vent apparatus can be assembled quickly and simply, since no further fixings (i.e. screws, nuts and bolts, etc.) or adhesives are required to seal the rupture diaphragm around the vent aperture. Furthermore, it is possible for the vent apparatus to be assembled prior to being installed in a battery casing, which can facilitate manufacture of the battery. The first portion may comprise a seal member, the seal member being disposed around the periphery of the vent aperture and being shaped such that the outer portion of the rupture diaphragm overlies the seal member along its length.

The second portion may be a cover portion which defines an enclosure around the rupture diaphragm. Thus, the cover portion may therefore serve to protect the rupture diaphragm from objects, such as stones, which may impact the battery casing when a vehicle to which the battery is driven, particularly in an off-road environment. Furthermore, the cover portion can serve to prevent a user from pressing on the unsupported inner portion of the rupture diaphragm.

The cover portion may comprise a cover plate which is arranged substantially co- planar with and spaced apart from the rupture diaphragm. The cover plate may comprise one or more apertures formed at the periphery thereof. The apertures may be sized so as to reduce the likelihood of debris, such as sand or gravel, from collecting in the space between the rupture diaphragm and the cover plate. Furthermore, with the apertures disposed at the periphery of the cover plate, the unsupported inner portion of the rupture diaphragm remains substantially touch- proof, and protected from impact with objects, such as stones, etc, whilst providing a pathway for fluid which is vented in the event that the rupture diaphragm ruptures. In one embodiment, the apertures disposed toward the bottom of the cover plate, when installed in a battery casing on a vehicle, are larger to further facilitate any debris exiting the space between the rupture diaphragm and the cover plate.

The vent apparatus may comprise a breather port for placing the cavity of the battery casing in fluid communication with an environment outside of the battery casing. Such an arrangement is advantageous in that both the vent aperture and the breather port can be installed in a single opening formed in the wall of a battery casing thereby reducing the number of openings in the battery casing. This is beneficial because manufacturing costs are reduced. Moreover, reducing the number of openings in the battery casing reduces the likelihood of ingress/egress of fluid into/out of the casing other than via the breather port.

The breather port may be defined at least in part by a bore formed through the first portion disposed adjacent to the vent aperture.

The first portion may comprise a flange, the vent aperture being formed in the flange, wherein the rupture diaphragm and the second portion are disposed on one side of the flange and a seal member is disposed on the opposite side of the flange for forming a hermetic seal with a surface of the battery casing adjacent to the opening in the battery casing when the vent apparatus is installed therein. Optionally, the first threshold value is approximately 1 .0 bar. The rupture diaphragm may be configured so as to resist rupturing along the rupture line when a fluid pressure exerted on the first major face is exceeded by a fluid pressure exerted on the second major face by less than a second threshold value, the second threshold value being less than the first threshold value.

Optionally, the second threshold value is approximately 0.3 bar.

The rupture diaphragm may be configured so as to resist rupturing along the rupture line when a fluid pressure exerted on the second major face is exceeded by a fluid pressure exerted on the first major face by less than a third threshold value, the third threshold value being greater than the second threshold value.

Optionally, the third threshold value is approximately 1 .0 bar. The rupture diaphragm may be formed as a unitary member.

The rupture line may be substantially circular.

The rupture diaphragm may be substantially disc shaped and the outer portion may be an annular portion.

The rupture line may be defined by a V-shaped profile formed in the first major face. The V-shaped profile may define an obtuse angle. The inner portion may be a domed portion having a convex profile on the first major face.

The rupture diaphragm may be formed from a polymer material, optionally Polybutylene Terephthalte (PBT). Alternatively, the rupture diaphragm may be formed from a ceramic material.

The material from which the rupture diaphragm is formed may be selected to have a melting temperature, for example 150 degrees Celsius, which will reduce the likelihood of the apertures in the cover plate from becoming blocked. In this way, following a rupture of the rupture diaphragm, the venting of hot fluid in excess of the melting temperature of the rupture diaphragm will, conveniently, cause any residual parts of the rupture diaphragm to melt, preventing them from blocking the apertures in the cover portion.

In a further aspect, the present invention provides a rupture diaphragm for a battery casing, the rupture diaphragm having first and second major faces, and comprising first and second portions, a rupture line being defined at the boundary between said first and second portions;

wherein the rupture diaphragm is configured so as to rupture at least partially along the rupture line when a fluid pressure exerted on the first major face is exceeded by a fluid pressure exerted on the second major face by a first threshold value.

Thus, by virtue of a pre-defined rupture line, embodiments of the present invention provide a rupture diaphragm which ruptures in predictable way when the first threshold pressure difference is exceeded. Furthermore, the threshold pressure difference is a characteristic which is inherent to the rupture diaphragm meaning that no other elements are required to cause the diaphragm to rupture, which allows for a simplified construction. Optionally, the first threshold value is approximately 1 .0 bar

The rupture diaphragm may be configured so as to resist rupturing along the rupture line when a fluid pressure exerted on the first major face is exceeded by a fluid pressure exerted on the second major face by less than a second threshold value, the second threshold value being less than the first threshold value.

Optionally, the second threshold value is approximately 0.3 bar

Optionally, the third threshold value is approximately 1 .0 bar.

The rupture diaphragm may be formed as a unitary member. The first portion may be disposed around the periphery of the second portion.

The rupture line may be substantially circular. The rupture diaphragm may be substantially disc shaped and the first portion is an annular portion.

The rupture line may be defined by a V-shaped profile formed in the first major face. The V-shaped profile may define an obtuse angle.

The second portion may be a domed portion having a convex profile on the first major face.

In another aspect, the present invention provides a vent apparatus for a battery casing containing one or more battery cells, the apparatus comprising:

a body portion adapted for mounting in an opening formed in a battery casing, the body portion comprising a vent aperture formed therethrough;

a rupture diaphragm as described in the preceding paragraphs mounted on the body portion so as to close the vent aperture; and

a second portion arranged so as to apply a clamping force to the first portion of the rupture diaphragm so as to hermetically seal the vent aperture.

In another aspect, the present invention provides an apparatus for a battery casing containing one or more battery cells, the apparatus comprising:

a body portion adapted for mounting in an opening formed in the battery casing, the body portion comprising a vent aperture formed therethrough;

a rupture diaphragm mounted on the body portion so as to close the vent aperture, the rupture diaphragm being configured so as to rupture when a fluid pressure exerted on a first major face thereof is exceeded by a fluid pressure exerted on a second major face thereof by a first threshold value; and

a cover portion releasably attachable to the body portion, the cover portion comprising a cover plate arranged to protect at least the portion of the rupture diaphragm which overlies the vent aperture and at least one aperture spaced laterally from said portion of the rupture diaphragm when so attached.

In another aspect, the present invention provides a battery comprising a battery casing accommodating one or more battery cells and a vent apparatus or a rupture diaphragm as described in the preceding paragraphs.

In a further aspect, the present invention provides a vehicle comprising a battery, a vent apparatus or a rupture diaphragm as described in the preceding paragraphs.

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. Features described in connection with one embodiment are applicable to all embodiments, unless such features are incompatible.

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 is an exploded perspective view of a vent apparatus for a battery casing according to an embodiment of the present invention;

Figure 2 is a reverse perspective view of the vent apparatus shown in Figure

1 ;

Figure 3 is a cross-sectional view of a rupture diaphragm of the vent apparatus shown in Figure 1 viewed along the line A-A;

Figure 4 is a perspective view of the vent apparatus of Figures 1 and 2 when in an assembled state;

Figure 5 is a cross-sectional view of the vent apparatus shown in Figure 4;

Figure 6 is a rear plan view of the vent apparatus shown in Figure 4;

Figure 7 is a perspective view of a battery casing for a hybrid electric vehicle comprising the vent apparatus shown in Figure 4; and

Figure 8 is a perspective cross-sectional view through a side of the battery casing and vent apparatus shown in Figure 7. DETAILED DESCRIPTION

Referring to Figures 1 to 3, the vent apparatus 1 comprises a base portion 2, a body portion 3, a rupture diaphragm 4 (also known as a burst member or burst disc) and a cover portion 5.

The base portion 2 comprises a substantially planar base 7 having an opening 9 formed therethrough. A side wall 1 1 of the base portion 2 is disposed around the perimeter of the base 7 and projects substantially perpendicularly therefrom. A plurality of latch members 13 extend from the top of the side wall 1 1 , opposite the planar base 7, at respective spaced apart locations therealong. Each latch member 13 comprises a snap-fit tab which terminates in a hook 15.

The body portion 3 generally comprises a flange 17, a throat 19 and a breather port 21 . The throat 19 defines a pressure relief vent aperture 23 having an elongate cross-section. The flange 17 projects substantially perpendicularly from one end of the throat 19 and comprises a generally circular portion 17a, which is co-axial with the vent aperture 23, and an extension portion 17b, which projects laterally from the circular portion 17a. The flange 17 has first and second major surfaces 16a, 16b.

The circular portion 17a of the flange 17 comprises an annular groove 18 on the first major surface 16a, which encircles the vent aperture 23. A sealing member 25, in the form of a gasket or O-ring, is disposed within the annular groove 18. A plurality of locating bosses 27 are disposed at respective spaced apart locations around the outer circumference of the annular groove 18. A latch member 14 extends perpendicularly from the first major surface 16a of the flange 17 and is disposed at the boundary between the circular portion 17a and the extension portion 17b. The latch member 14 on the body portion 3 is of substantially the same construction as the latch members 13 of the base portion 2 having a hook 15 disposed at one end thereof.

The breather port 21 comprises a hollow tubular member 29 which projects from the first major surface 16a of the extension portion 17b of the flange 17. The tubular member 29 comprises an axial through bore 30 which extends through the flange 17 so as to create an opening 31 in the second major surface 16b. An annular rib 32 is provided on around the outer circumference of the tubular member 29, approximately half way along its length in the axial direction. The rupture diaphragm 4 has a generally disc-shaped form having first and second major faces 41 , 42 and comprises a first, outer annular portion 43 and a second, inner domed portion 44. A rupture line 45 is defined by the boundary between the outer annular portion 43 and the inner domed portion 44. In the present embodiment, the rupture diaphragm is made from a polymer material such as Polybutylene Terephthalte (PBT). In other embodiments, the rupture diaphragm may be formed from a ceramic material. The outer diameter of the outer annular portion 43 is sized such that it substantially matches that of the sealing member 25. A plurality of locating tabs 46 project radially outward from the outer circumference of the outer annular portion 43 at respective spaced apart locations.

As best illustrated in Figure 3, the second major face 42 of the rupture diaphragm 4 is substantially planar. Conversely, on the first major surface 41 of the rupture diaphragm 4, the inner domed portion 44 defines a convex dome, the thickness of which decreases toward the rupture line 45. The inner circumference of the outer annular portion 43 comprises a bevelled edge such that the rupture line 45 is defined at the bottom of the resulting 'V-shaped' profile at the boundary between the respective portions 43, 44.

The cover portion 5 generally comprises a planar cover plate 51 having an approximately circular shape. A side wall 52 extends perpendicularly from an outer edge of the cover plate 51 . The cover plate 51 has first and second major surfaces 51 a, 51 b. A plurality of apertures 53 are formed at respective spaced apart locations around the outer periphery of the cover plate 51. Each aperture 53 is formed at the intersection between the outer edge of the cover plate 51 and the side wall 52 and has the form of an elongate slot which extends across both the cover plate 51 and the adjacent portion of the side wall 52. Each aperture 53 defines a lip 54 in the side wall 52.

A plurality of retaining members 55 extend from the second major surface 51 b of the cover plate 51 . The retaining members 55 are arranged in a circle which has a diameter substantially the same as that of the annular groove 18 on the body portion 3. Each retaining member 55 generally comprises a tab having an arc-shaped cross- section with a first end coupled to the second major surface 51 b of the cover plate 51 and a second, free end. Assembly of the vent apparatus will now be described with reference to Figures 4, 5 and 6.

Firstly, the rupture diaphragm 4 is positioned on the body portion 3. The locating tabs 46 on the rupture diaphragm 4 co-operate with the locating bosses 27 on the flange 17, so as to facilitate alignment of the rupture diaphragm 4, such that the outer annular portion 43 of the rupture diaphragm 4 rests upon the sealing member 25 around the entire circumference thereof. The body portion 3 is inserted into the base portion 2 such that the flange 17 of the body portion 3 seats against the planar base 7 of the base portion 2. The throat 19 of the body portion 3 projects through the opening 9 in the base portion 2. The outer edge of the flange 17 of the body portion 3 and the side wall 1 1 of the base portion 2 have complimentary shapes so as to be a close fit with one another.

Next, the cover portion 5 is attached to the body portion 3 and the base portion 2 by means of each of the respective hooks 15 of the latch members 13, 14 being received in a corresponding one of the apertures 53 formed in the cover portion 5. In more detail, the side wall 52 of the cover portion 5 is sized so as to receive the latch members 13 of the base portion 2 within it. When the cover portion 4 is push-fitted to the base and body portions 2, 3 each of the respective latch members 13, 14 are deflected inwardly by the side wall 52 of the cover portion 5. When the hook 15 of each latch member 13, 14 is aligned with a respective one of the apertures 53 in the cover portion 5, the latch member 13, 14 will spring back such that the hook 15 engages with the lip 54 of the respective aperture 53. Accordingly, the cover portion 5 is coupled to both the base portion 2 and the body portion 3.

Attachment of the cover portion 5 to the base and body portions 2, 3 causes engagement of the retaining members 55 on the second major face 51 b of the cover portion 5 with the rupture diaphragm 4. More specifically, each lip 54 of the respective apertures 53 is dimensioned such that, when the cover portion 5 is attached to the base and body portions 2, 3, the free ends of the respective retaining members 55 are in abutment with the outer annular portion 43 of the rupture diaphragm 4. The pressing force applied by the retaining members 55 acts to compress the outer annular portion 43 of the rupture diaphragm 4 against the sealing member 25, forming a hermetic seal therebetween. The vent apparatus 1 is adapted so as to be installed in an opening formed in the wall of a battery casing as will now be described in more detail. Referring to Figures 7 and 8, a battery casing 60 for a high voltage "traction" battery, such as a Lithium- ion battery, comprises first and second parts 61 , 62 which can be coupled together to define a cavity 63 for accommodating one or more battery cells (not shown) therein.

The first and second parts 61 , 62 of the battery casing 60 are fixed together by means of a plurality of bolts 64 which pass through holes formed in respective flanges of the first and second parts 61 , 62. When joined together in this way, the cavity 63 is sealed such that fluid communication with the outside atmosphere is permitted only via the vent apparatus 1 as will be explained in more detail later.

The vent apparatus 1 is installed in an opening 66 formed in a wall 61 a of the first part 61 of the battery casing 60. A seal member 65 (best shown in Figure 6) is disposed on the second major face 16b of the flange 17 of the body portion 3. The seal member 65 is arranged so as to encircle both the throat 19 and the bore 30 of the breather port 21 where it opens on the extension portion 17b of the flange 17.

The opening 66 in the first part 61 of the battery casing 60 is sized so as to receive the throat 19 of the body portion 3. The vent apparatus 1 may be secured to the battery casing 60 by suitable attachment means. For example, in the presently described embodiment, the throat 19 of the body portion 3 comprises fixing parts 20 on the outer surface thereof. Once inserted through the opening 66 in the battery casing 60, a correspondingly shaped fixing part (not shown), e.g. comprising a U- shaped channel having a cross-section which co-operates with the outer profile of the fixing parts 20, may be slid over each of the fixing parts 20 on the throat 19 thereby locking the vent apparatus 1 in place with respect to the battery casing 60.

The fixing parts 20 are arranged such that, when the vent apparatus 1 is locked in place, the seal member 65 is compressed against the outer surface of the first part 61 of the battery casing 60. In this configuration, the vent apparatus 1 is sealed against the surface of the battery casing 60. As shown in Figure 6, a pair of parallel supporting ribs 22 extend between the bore 30 of the breather port 21 and the adjacent outer surface of the throat 19. The supporting ribs 22 ensure that, when the vent apparatus 1 is compressed against the seal member 65, the opening of the bore 30 is kept spaced apart from the adjacent wall of the battery casing 60. Accordingly, the battery cavity 63 is maintained in fluid communication with the external atmosphere via the breather port 21 .

The first and second parts 61 , 62 of the battery casing 60 are provided with a seal therebetween, to prevent the flow of fluid therepast. Accordingly, once the battery casing 60 has been assembled, the only means by which fluid can enter or leave the battery casing 60 under normal operating conditions is via the breather port 21 of the vent apparatus 1 . As explained previously, the battery casing 60 houses a plurality of battery cells (not shown), such as lithium-ion cells, which are coupled electrically so as to provide a rechargeable power source for a hybrid powertrain of the vehicle via an electric machine, such as a crank-integrated motor/generator (CIMG). Typically, in a hybrid vehicle, the battery casing 60 will be mounted low down in the vehicle. This is because the battery is a relatively heavy component and it is advantageous to keep the centre of gravity of the vehicle as low as possible during regular on-road use, to improve handling characteristics, i.e. to minimise body roll, etc. Hybrid vehicles which are designed to go off-road, e.g. 4x4 hybrid vehicles, will typically be required to be able to drive through a body of water up to a prescribed wading depth without there being a detrimental effect on the operation of the vehicle. During a so-called wading event, the level of the water through which the vehicle is travelling may rise above the level at which the battery casing 60 is mounted such that the battery is submerged. In order to prevent water from entering the battery casing 60 via the breather port 21 , a breather tube (not shown) may be affixed to the tubular member 29 of the breather port 21 . For example, a first end of a plastic tube may be push- fitted over the tubular member 29. The annular rib 32 helps to secure the breather tube in place. A second end of the breather tube may be positioned higher up on the vehicle, above the level of a maximum wading line, which corresponds to the maximum permissible depth of water through which the vehicle can safely wade.

During use, the cells of the battery will become hot due to repeated charging and discharging. Accordingly, the air in the cavity 63 of the battery casing 60 which surrounds the cells will heat up and expand. The breather port 21 is therefore provided so as allow for the expansion of the air in the cavity 63 by venting air to the outside atmosphere thereby preventing undesirably high pressure building up in the battery casing 60. Conversely, in the case that the vehicle is driven through a body of water during a wading event, the battery casing 60 may be submerged in cold water causing it to be rapidly quenched. The rapid cooling of the battery may result in a negative pressure differential between the cavity 63 in the battery casing 60 and the outside atmosphere. Again, this pressure difference can be equalised by virtue of the breather port 21 , which allows air from the atmosphere to be drawn into the battery casing 60.

The bore 30 of the breather port 21 is sized such that it provides sufficient flow of air therethrough to equalise the pressure in the battery casing 60 under a range of operating conditions of the vehicle. In particular, the breather port 21 is adapted so as to be able to equalise the pressure difference caused when the vehicle battery is quenched by submersion in water at a temperature of zero degrees Celsius. Furthermore, the breather port 21 must be able to equalise pressure differences which may result from the vehicle being driven in different conditions, such as at different altitudes and in hot and cold climates. The above described conditions may be considered to be "normal" operating conditions which the battery may be subjected to during the lifetime of the vehicle. However, in addition to the "normal" conditions outlined above, the battery may also experience a "fault" condition, such as might occur in the event of a malfunction of one or more of the battery cells. For example, a fault may occur in one or more of the battery cells due to overcharging or overheating of the cell/s. Under such circumstances, it is possible that hot gas will be emitted from the faulty cell/s in the battery casing. For example, in the case of a lithium-ion battery, reaction products such as CO, C0₂, H₂, and small chain organic materials may be emitted. The quantity and rate of the gas emitted may depend on the number of cells affected and may be in the region of 150 litres per second. Additionally, the temperature of the gas may be in the region of 800 degrees Celsius. Under such circumstances, the breather port 21 does not have sufficient capacity to allow the gas to be vented before excessive pressure has built up within the cavity 63 of the battery casing 60. By excessive pressure, it is meant that the fluid pressure in the cavity 63 builds to a level at which damage may be caused to other components of the battery and/or the battery casing 60. To mitigate the effects of such a pressure increase, the rupture diaphragm 4 of the vent apparatus 1 is constructed such that, when the pressure inside the cavity 63 increases to the point at which the pressure difference on opposite sides of the rupture diaphragm 4 (i.e. the difference between the fluid pressure exerted on the second major face 42 of the rupture diaphragm 4 by the gas in the battery cavity 63 compared to the pressure exerted on the first major face 41 of the rupture diaphragm 4 by the ambient atmosphere) exceeds a threshold value, it will rupture along the rupture line 45. When the rupture diaphragm 4 ruptures, the pressurised gas in the battery cavity 63 can flow out of the battery casing 60 through the throat 19 of the body portion 3 and out through the apertures 53 in the cover portion 5. Thus, rapid venting of gas in the cavity 63 can be achieved when the rupture diaphragm 4 ruptures compared to the amount of gas which could be vented via the breather port 21 alone.

The threshold pressure difference which causes the rupture diaphragm 4 to rupture is determined by the construction of the rupture diaphragm 4. In particular, the thickness of the rupture diaphragm 4 in the region of the rupture line 45 and the angle of the 'V formed between the outer edge of the inner domed portion 44 and the inner edge of the outer annular portion 43 may be selected, together with the material from which the rupture diaphragm 4 is constructed, so as to determine the threshold pressure difference. In the presently described embodiment, the pressure difference at which the rupture diaphragm 4 must rupture to ensure excessive pressure does not build up inside the battery casing 63 is 1 bar, and the typical pressure difference which will cause a rupture is between 0.5 and 1 .0 bar at a temperature of 20 degrees Celsius. That is, if the fluid pressure in the cavity 63 of the battery casing 60 (i.e. the pressure exerted on the second major face 42 of the rupture diaphragm 4) is 1 bar or more greater than the atmospheric pressure outside the battery casing 60 (i.e. the pressure exerted on the first major face 41 of the rupture diaphragm 4), the rupture diaphragm 4 will rupture along the rupture line 45. The rupture diaphragm 4 may rupture along the entire length of the rupture line 45 such that the inner domed portion 44 is completely separated from the outer annular portion 43. However, it will be appreciated by those skilled in the art that, providing the rupture diaphragm 4 ruptures sufficiently such that the inner domed portion 44 is displaced relative to the outer annular portion 43 so as to create an opening through which fluid in the battery cavity 63 can be expelled, the rupture diaphragm 4 may only partially rupture along the rupture line 45. The extent of the rupture will likely depend on the magnitude of the pressure difference on the opposite sides of the rupture diaphragm 4 and/or the rate at which the fluid pressure in the battery cavity 63 builds up due to the gas emitted by faulty cells. In addition to the specified threshold value above which the rupture diaphragm 4 is designed to rupture, there is also a minimum pressure difference which the rupture diaphragm 4 is designed to be able to withstand without rupturing. In the presently described embodiment, the minimum threshold pressure difference is 0.3 bar. This ensures that the rupture diaphragm 4 is not ruptured by only moderate pressure increases in the battery casing 60 which could otherwise be equalised over a suitable period of time by means of the breather port 21 .

Moreover, the structure of the rupture diaphragm 4 is such that the threshold pressure difference value which causes it to rupture along the rupture line 45 is asymmetric with respect to the direction of the pressure difference across the major faces 41 , 42 of the rupture diaphragm 4, i.e. the pressure difference required for the rupture diaphragm 4 to rupture when the pressure in the cavity 63 of the battery casing 60 is greater than the ambient atmosphere is different from the pressure difference required to rupture the rupture diaphragm 4 when the pressure of the atmosphere outside the battery casing 60 is greater than it is within the cavity 63. In other words, the pressure difference required to make the rupture diaphragm 4 burst outwards (toward the cover portion 5) is less than the pressure difference required to make the rupture diaphragm 4 burst inwards (into the cavity 63 of the battery casing 60). This is advantageous because the primary purpose of the rupture diaphragm 4 is to provide additional venting capacity for expelling gas from inside the battery casing 60 in the event of a faulty battery cell. However, when the battery is operating under normal conditions, the rupture diaphragm 4 is required to provide an air-tight seal such that there is no air or water ingress/egress past the rupture diaphragm 4 into the battery casing 60.

As explained above, in the case of a hybrid vehicle which is designed to go Off-road' the battery casing 60 may be submerged during a wading event. In this situation, water will flow in through the apertures 53 in the cover portion 5 and cause an increased fluid pressure to act on the first major face 41 of the rupture diaphragm 4. If the battery is operating under normal conditions, the air pressure within the casing 60 will be equal to atmospheric pressure by virtue of the breather port 21 . Thus, the pressure on the first major face 41 of the rupture diaphragm 4 will be greater than that on the second major face 42 creating a pressure difference between the respective major faces 41 , 42 of the rupture diaphragm 4. In this situation, it is undesirable for the rupture diaphragm 4 to rupture since this would lead to water flooding into the battery casing 60 which may impair operation of the battery. Accordingly, the rupture diaphragm 4 is arranged such that it can withstand a minimum pressure difference of 1 bar in the reverse direction, i.e. when the pressure in the cavity 63 is 1 bar or more lower than the pressure outside the battery casing 60.

In the presently described embodiment, the V-shaped profile which defines the rupture line 45 is arranged such that, when the pressure on the second major face 42 is greater than that on the first major face 41 , the 'V shape opens which acts to concentrate the force at the thinnest part of the rupture diaphragm 4 so as to promote rupturing. Conversely, when the pressure on the first major face 41 is greater, the force on the rupture diaphragm 4 acts to close the 'V shape, which means that a greater pressure difference is required before a rupture is formed. Accordingly, the rupture diaphragm 4 can withstand a higher pressure difference when the pressure on the first major surface 41 is greater. Thus, the rupture diaphragm 4 is adapted so as to provide sufficient resistance to rupture by the application of external pressure, such as during submersion of the battery casing 60 in water, whilst simultaneously ensuring that any build-up of pressure inside the casing 60 due to faulty cells can be vented safely. The configuration of the vent apparatus 1 described above has a number of further advantages. Firstly, the cover portion 5 advantageously protects the rupture diaphragm 4 from being inadvertently punctured by objects, such as stones, which may be flicked up and impact the battery casing 60 when the vehicle is being driven. Similarly, the risk of a user rupturing the rupture diaphragm 4 by pressing on it is mitigated by the fact that the rupture diaphragm 4 is only accessible via the apertures 53 in the cover portion 5, which are disposed around the periphery of the cover plate 51 . Accordingly, it is not readily possible for a user to press on the unsupported portion of the rupture diaphragm 4 which extends over the opening of the throat 19 in the body portion 3.

Moreover, the vent apparatus 1 described above is advantageously easy to assemble by virtue of the cover portion 5 being a push fit on the latch members 13, 14 of the base and body portions 2, 3. In particular, the rupture diaphragm 4 is held in place between the retaining members 55 of the cover portion 5 and the seal member 25 on the body portion 3 without the need for any form of adhesive or additional fixing means. Furthermore, the threshold pressure difference values at which the rupture diaphragm 4 will rupture are inherent to the structure of the rupture diaphragm 4 such that the rupture diaphragm 4 is not required to contact another element, such as a spike or other piercing member to cause it to rupture.

Additionally, the configuration of the vent apparatus 1 is advantageous by virtue of the fact that the cover portion 5 substantially surrounds the rupture diaphragm 4. Thus, in the event that there is a build-up of pressure in the cavity 63 of the battery casing 60 which causes the rupture diaphragm 4 to rupture, the cover portion 5 can facilitate the dissipation of energy as fluid is expelled through the vent aperture 23, i.e. the kinetic energy of fluid expelled from the battery cavity 63 may be expended dislodging the cover portion 5 such that the likelihood of damage to other components of the vehicle which are disposed adjacent to the battery casing 60 will be minimised.

A further advantage of the above-described configuration is that a breather port 21 and a vent aperture 23 can be provided in the same assembly, such that they can both be installed in a single opening formed in the wall of the battery casing 60. Reducing the number of openings in the battery casing 60 is beneficial because manufacturing costs are reduced. Moreover, reducing the number of openings in the battery casing 60 reduces the likelihood of ingress/egress of fluid into/out of the casing 60 other than via the breather port 21 .

The apertures 53 in the cover portion 5 may be sized so as to reduce the likelihood of debris, such as sand or gravel, from collecting in the space between the rupture diaphragm 4 and the cover plate 51 in the assembled vent apparatus 1 . In one embodiment, the apertures disposed toward the bottom of the cover plate 51 , when installed in a battery casing on a vehicle, may be larger to further facilitate any debris exiting the space between the rupture diaphragm 4 and the cover plate 51.

In one embodiment, the material from which the rupture diaphragm 4 is formed may be selected to have a melting temperature, for example 150 degrees Celsius, which will reduce the likelihood of the apertures 53 in the cover plate 51 from becoming blocked. In this way, following a rupture of the rupture diaphragm 4, the venting of hot fluid in excess of the melting temperature of the rupture diaphragm 4 will, conveniently, cause any residual parts of the rupture diaphragm 4 to melt, preventing them from blocking the apertures 53 in the cover portion 51. In the above-described embodiment, the rupture diaphragm 4 is disc-shaped having a first, outer annular portion 43 which is disposed around the periphery of a second, inner domed portion 44, such that the rupture line 45 is circular. However, it will be appreciated by those skilled in the art that alternative configurations of rupture diaphragm may be useful. For example, the rupture line 45 may be polygonal. Alternatively or in addition, the rupture line 45 may not define a 'closed loop'. In this case the second portion of the rupture diaphragm may comprise a flap, a part of which remains attached to the first portion when ruptured. Alternatively, the rupture diaphragm may comprise first and second portions which are disposed adjacent to one another with the rupture line arranged therebetween.

In the above-described embodiment, the vent apparatus 1 comprises the base portion 2, body portion 3 and cover portion 5, and is arranged such that the rupture diaphragm 4 is clamped between two portions, namely, the body and cover portions 3, 5, with the latch members 13 on the base portion 2 serving to fix the cover portion 5 in place with respect to the body portion 3. It will be appreciated by the person skilled in the art that the base portion 2 could be formed integrally with the body portion 3 such that the vent apparatus 1 comprises just a first, integrated base and body portion and a second, cover portion.

It will be appreciated by the person skilled in the art that alternative means for securing the cover portion to the body portion 3 may be employed in place of the retaining members 14, 15. For example, the cover portion 5 may be attached by threaded fixing means, such as a screw or a bolt, in order to bias the cover portion 5 against the body portion 3 so as to clamp the rupture diaphragm 4 in place.

Further aspects of the present invention are set out in the following numbered paragraphs; 1 . A vent apparatus for a battery casing containing one or more battery cells, the apparatus comprising:

2. A vent apparatus according to paragraph 1 , wherein the clamping force is applied by attachment of the second portion to the first portion.

3. A vent apparatus according to paragraph 2, wherein the second portion comprises one or more retaining members for engaging with the outer portion of the rupture diaphragm. 4. A vent apparatus according to paragraph 3, wherein the second portion is push-fitted to the first portion, the one or more retaining members being sized so as to apply a clamping force having a predetermined magnitude to the outer portion of the rupture diaphragm when so push-fitted. 5. A vent apparatus according to paragraph 1 , wherein the first portion comprising a seal member, the seal member being disposed around the periphery of the vent aperture and being shaped such that the outer portion of the rupture diaphragm overlies the seal member along its length. 6. A vent apparatus according to paragraph 1 , wherein the second portion is a cover portion which defines an enclosure around the rupture diaphragm.

7. A vent apparatus according to paragraph 6, wherein the cover portion comprises a cover plate which is arranged substantially co-planar with and spaced apart from the rupture diaphragm.

8. A vent apparatus according to claim 7, wherein the cover plate comprises one or more apertures formed at the periphery thereof. 9. A vent apparatus according to paragraph 1 , comprising a breather port for placing the cavity of the battery casing in fluid communication with an environment outside of the battery casing. 10. A vent apparatus according to paragraph 9, wherein the breather port is defined at least in part by a bore formed through the first portion disposed adjacent to the vent aperture.

1 1 . A vent apparatus according to paragraph 1 , wherein the first portion comprises a flange, the vent aperture being formed in the flange, wherein the rupture diaphragm and the second portion are disposed on one side of the flange and a seal member is disposed on the opposite side of the flange for forming a hermetic seal with a surface of the battery casing adjacent to the opening in the battery casing when the vent apparatus is installed therein.

12. A vent apparatus according to paragraph 1 , wherein the first threshold value is approximately 1 .0 bar.

13. A vent apparatus according to paragraph 1 , wherein the rupture diaphragm is configured so as to resist rupturing along the rupture line when a fluid pressure exerted on the first major face is exceeded by a fluid pressure exerted on the second major face by less than a second threshold value, the second threshold value being less than the first threshold value.

14. A vent apparatus according to paragraph 13, wherein the second threshold value is approximately 0.3 bar. 15. A vent apparatus according to paragraph 13, wherein the rupture diaphragm is configured so as to resist rupturing along the rupture line when a fluid pressure exerted on the second major face is exceeded by a fluid pressure exerted on the first major face by less than a third threshold value, the third threshold value being greater than the second threshold value.

16. A vent apparatus according to paragraph 15, wherein the third threshold value is approximately 1 .0 bar.

17. A vent apparatus according to paragraph 1 , wherein the rupture diaphragm is formed as a unitary member. 18. A vent apparatus according to paragraph 1 , wherein the rupture line is substantially circular.

19. A vent apparatus according to paragraph 1 , wherein the rupture diaphragm is substantially disc shaped and the outer portion is an annular portion.

20. A vent apparatus according to paragraph 1 , wherein the rupture line is defined by a V-shaped profile formed in the first major face. 21 . A vent apparatus according to paragraph 20, wherein the V-shaped profile defines an obtuse angle.

22. A vent apparatus according to paragraph 1 , wherein the inner portion is a domed portion having a convex profile on the first major face.

23. A vent apparatus according to paragraph 1 , wherein the rupture diaphragm is formed from a polymer material.

24. A vent apparatus according to paragraph 23, wherein the polymer material is Polybutylene Terephthalte (PBT).

25. A rupture diaphragm for a battery casing, the rupture diaphragm having first and second major faces, and comprising first and second portions, a rupture line being defined at the boundary between said first and second portions;

wherein the rupture diaphragm is configured so as to rupture at least partially along the rupture line when a fluid pressure exerted on the first major face is exceeded by a fluid pressure exerted on the second major face by a first threshold value. 26. A rupture diaphragm according to paragraph 25, wherein the first threshold value is approximately 1 .0 bar

27. A rupture diaphragm according to paragraph 25, wherein the rupture diaphragm is configured so as to resist rupturing along the rupture line when a fluid pressure exerted on the first major face is exceeded by a fluid pressure exerted on the second major face by less than a second threshold value, the second threshold value being less than the first threshold value. 28. A rupture diaphragm according to paragraph 27, wherein the second threshold value is approximately 0.3 bar 29. A rupture diaphragm according to paragraph 27, wherein the rupture diaphragm is configured so as to resist rupturing along the rupture line when a fluid pressure exerted on the second major face is exceeded by a fluid pressure exerted on the first major face by less than a third threshold value, the third threshold value being greater than the second threshold value.

30. A rupture diaphragm according to paragraph 29, wherein the third threshold value is approximately 1 .0 bar.

31 . A rupture diaphragm according to paragraph 25, wherein the rupture diaphragm is formed as a unitary member.

32. A rupture diaphragm according to paragraph 25, wherein the first portion is disposed around the periphery of the second portion. 33. A rupture diaphragm according to paragraph 25, wherein the rupture line is substantially circular.

34. A rupture diaphragm according to paragraph 25, wherein the rupture diaphragm is substantially disc shaped and the first portion is an annular portion.

35. A rupture diaphragm according to paragraph 25, wherein the rupture line is defined by a V-shaped profile formed in the first major face.

36. A rupture diaphragm according to paragraph 35, wherein the V-shaped profile defines an obtuse angle.

37. A rupture diaphragm according to paragraph 25, wherein the second portion is a domed portion having a convex profile on the first major face. 38. A rupture diaphragm according to paragraph 25, wherein the rupture diaphragm is formed from a polymer material. 39. A rupture diaphragm according to paragraph 38, wherein the polymer material is Polybutylene Terephthalte (PBT).

40. A vent apparatus for a battery casing containing one or more battery cells, the apparatus comprising:

a rupture diaphragm according paragraph 25 mounted on the body portion so as to close the vent aperture; and

a further portion arranged so as to apply a clamping force to the first portion of the rupture diaphragm so as to hermetically seal the vent aperture.

41 . A battery comprising a battery casing accommodating one or more battery cells and a vent apparatus according to paragraph 1 .

42. A battery comprising a battery casing accommodating one or more battery cells and a rupture diaphragm according to paragraph 25.

43. A vehicle comprising a battery according to claim 41 .

44. A vehicle comprising a vent apparatus according to paragraph 1 .

45. A vehicle comprising a rupture diaphragm according to paragraph 25.

Claims

1 . A vent apparatus for a battery casing containing one or more battery cells, the apparatus comprising:

2. A vent apparatus according to claim 1 , wherein the clamping force is applied by attachment of the second portion to the first portion.

3. A vent apparatus according to claim 2, wherein the second portion comprises one or more retaining members for engaging with the outer portion of the rupture diaphragm.

4. A vent apparatus according to claim 3, wherein the second portion is push- fitted to the first portion, the one or more retaining members being sized so as to apply a clamping force having a predetermined magnitude to the outer portion of the rupture diaphragm when so push-fitted.

5. A vent apparatus according to any one of the preceding claims, wherein the first portion comprising a seal member, the seal member being disposed around the periphery of the vent aperture and being shaped such that the outer portion of the rupture diaphragm overlies the seal member along its length.

6. A vent apparatus according to any one of the preceding claims, wherein the second portion is a cover portion which defines an enclosure around the rupture diaphragm.

7. A vent apparatus according to claim 6, wherein the cover portion comprises a cover plate which is arranged substantially co-planar with and spaced apart from the rupture diaphragm.

8. A vent apparatus according to claim 7, wherein the cover plate comprises one or more apertures formed at the periphery thereof.

9. A vent apparatus according to any one of the preceding claims, comprising a breather port for placing the cavity of the battery casing in fluid communication with an environment outside of the battery casing.

10. A vent apparatus according to claim 9, wherein the breather port is defined at least in part by a bore formed through the first portion disposed adjacent to the vent aperture.

1 1 . A vent apparatus according to any one of the preceding claims, wherein the first portion comprises a flange, the vent aperture being formed in the flange, wherein the rupture diaphragm and the second portion are disposed on one side of the flange and a seal member is disposed on the opposite side of the flange for forming a hermetic seal with a surface of the battery casing adjacent to the opening in the battery casing when the vent apparatus is installed therein.

12. A vent apparatus according to any one of the preceding claims, wherein the first threshold value is approximately 1 .0 bar.

13. A vent apparatus according to any one of the preceding claims, wherein the rupture diaphragm is configured so as to resist rupturing along the rupture line when a fluid pressure exerted on the first major face is exceeded by a fluid pressure exerted on the second major face by less than a second threshold value, the second threshold value being less than the first threshold value.

14. A vent apparatus according to claim 13, wherein the second threshold value is approximately 0.3 bar.

15. A vent apparatus according to claim 13 or claim 14, wherein the rupture diaphragm is configured so as to resist rupturing along the rupture line when a fluid pressure exerted on the second major face is exceeded by a fluid pressure exerted on the first major face by less than a third threshold value, the third threshold value being greater than the second threshold value.

16. A vent apparatus according to claim 15, wherein the third threshold value is approximately 1 .0 bar.

17. A vent apparatus according to any one of the preceding claims, wherein the rupture diaphragm is formed as a unitary member.

18. A vent apparatus according to any one of the preceding claims, wherein the rupture line is substantially circular.

19. A vent apparatus according to any one of the preceding claims, wherein the rupture diaphragm is substantially disc shaped and the outer portion is an annular portion.

20. A vent apparatus according to any one of the preceding claims, wherein the rupture line is defined by a V-shaped profile formed in the first major face.

21 . A vent apparatus according to claim 20, wherein the V-shaped profile defines an obtuse angle.

22. A vent apparatus according to any one of the preceding claims, wherein the inner portion is a domed portion having a convex profile on the first major face.

23. A vent apparatus according to any one of the preceding claims, wherein the rupture diaphragm is formed from a polymer material.

24. A vent apparatus according to claim 23, wherein the polymer material is Polybutylene Terephthalte (PBT).

26. A rupture diaphragm according to claim 25, wherein the first threshold value is approximately 1 .0 bar

27. A rupture diaphragm according to claim 25 or claim 26, wherein the rupture diaphragm is configured so as to resist rupturing along the rupture line when a fluid pressure exerted on the first major face is exceeded by a fluid pressure exerted on the second major face by less than a second threshold value, the second threshold value being less than the first threshold value.

28. A rupture diaphragm according to claim 27, wherein the second threshold value is approximately 0.3 bar

29. A rupture diaphragm according to claim 27 or claim 28, wherein the rupture diaphragm is configured so as to resist rupturing along the rupture line when a fluid pressure exerted on the second major face is exceeded by a fluid pressure exerted on the first major face by less than a third threshold value, the third threshold value being greater than the second threshold value.

30. A rupture diaphragm according to claim 29, wherein the third threshold value is approximately 1 .0 bar.

31 . A rupture diaphragm according to any one of claims 25 to 30, wherein the rupture diaphragm is formed as a unitary member.

32. A rupture diaphragm according to any one of claims 25 to 31 , wherein the first portion is disposed around the periphery of the second portion.

33. A rupture diaphragm according to any one of claims 25 to 32, wherein the rupture line is substantially circular.

34. A rupture diaphragm according to any one of claims 25 to 33, wherein the rupture diaphragm is substantially disc shaped and the first portion is an annular portion.

35. A rupture diaphragm according to any one of claims 25 to 34, wherein the rupture line is defined by a V-shaped profile formed in the first major face.

36. A rupture diaphragm according to claim 35, wherein the V-shaped profile defines an obtuse angle.

37. A rupture diaphragm according to any one of claims 25 to 36, wherein the second portion is a domed portion having a convex profile on the first major face.

38. A rupture diaphragm according to any one of claims 25 to 37, wherein the rupture diaphragm is formed from a polymer material.

39. A rupture diaphragm according to claim 38, wherein the polymer material is Polybutylene Terephthalte (PBT).

a rupture diaphragm according to any one of claims 25 to 39 mounted on the body portion so as to close the vent aperture; and

41 . An apparatus for a battery casing containing one or more battery cells, the apparatus comprising:

42. A battery comprising a battery casing accommodating one or more battery cells and a vent apparatus according to any one of claims 1 to 24 or claim 40 or claim 41 , or a rupture diaphragm according to any one of claims 25 to 39.

43. A vehicle comprising a battery according to claim 42, a vent apparatus according to any one of claims 1 to 24 or claim 40 or claim 41 , or a rupture diaphragm according to any one of claims 25 to 39.

44. A rupture diaphragm, a vent apparatus, a battery or a vehicle substantially hereinbefore described with reference to the accompanying drawings.