GB2594695A

GB2594695A - Burst disc housing and cover

Info

Publication number: GB2594695A
Application number: GB2003916.0A
Authority: GB
Inventors: P White Mark; Alexander Newnham Ian
Original assignee: Cummins Inc
Current assignee: Cummins Inc
Priority date: 2020-03-18
Filing date: 2020-03-18
Publication date: 2021-11-10
Also published as: CN215834665U; GB202003916D0

Abstract

A pressure operated vent for a battery pack comprises a rigid disc housing 12 having an inner seal 20 and an outer seal 46. The housing is arranged to be fixed to the inside of the battery pack outer wall. The outer seal is arranged to be compressed between the inside surface of the battery pack wall and the disc housing to form a gas-tight seal. The vent also comprises a frangible disc arranged to rupture when a pressure differential between an inner side and an outer side exceeds a pre-determined threshold. The disc is mounted over the inner seal of the disc housing to compress the inner seal and thereby effect a gas-tight seal. The disc housing defines an aperture 54 adjacent the disc forming a passage for vent gases when the disc ruptures. The inner and/or outer seal may be located in a recess in the disc housing surface to prevent excessive compression of the seal, for example the inner seal 20 may be located in an annular groove (24, Fig 7A). A cover 42 may stand clear of the outer wall of the battery pack such that there is a gap for the escape of gases.

Description

Burst Disc Housing And Cover This invention relates to a burst disc for a battery pack.

The highly reactive chemistry of a battery, such as a lithium battery, is carefully managed by design and control features within the individual cells, and in the collection of interconnected individual cells, or battery modules, that comprises a typical battery pack. Under extreme abuse conditions, it is possible for damaged or malfunctioning components, short circuits, or other events to start a thermal runaway process that develops a rapidly rising gas pressure, leading to an explosive release of that pressure from a cell, or pack, though uncontrolled rupture of the housing.

To achieve the required power output of an application, individual battery cells are combined into a single, turnkey energy pack such as those used in electric vehicles. If an individual cell within a pack is compromised and overheats, or causes a fire, it can then cause a similar reaction in adjacent cells.

To optimize safety, lithium battery manufacturers typically provide protective design and control features as well as last resort venting mechanisms for each cell, as well as for battery packs. Traditional pressure relief techniques used in legacy battery designs, such as crimped seals or seams in the battery can that will open to relieve pressure, are significantly less reliable with next generation low mass / high energy lithium chemistry cells and battery packs.

This has left battery manufacturers searching to provide more reliable, stable pressure relief technology at the low pressures demanded for low mass battery and battery pack products.

One of the most popular pressure relief devices for lower-pressure applications such as lithium batteries is the rupture or burst disk; Also known as a pressure safety disk or burst diaphragm. Burst discs are incorporated into battery packs in case a pressure threshold is breached within the pack. This could be caused by damaged or overcharged cells venting gas and catching fire within the pack.

A burst disc allows controlled venting of gas from a battery pack, preventing destruction of the pack, which could be dangerous to the surrounding environment.

In a first aspect, the invention provides a pressure operated vent for a battery pack, comprising, a generally rigid disc housing having an inner and an outer seal and arranged to be fixed to the inside surface of the battery pack outer wall, a frangible disc arranged to rupture when a pressure differential between an inner and an outer side exceeds a pre-determined threshold, the disc being mounted over the inner seal to compress the inner seal and thereby effect a gas-tight seal between the disc and the housing, and the outer seal being arranged to be compressed between the inside surface of the battery pack wall and the disc housing when the disc housing is fixed, to effect a gas-tight seal between the disc housing and the wall, the disc housing defining an aperture adjacent the disc which forms a passage for vent gases when the disc ruptures.

Preferably, the inner and/or outer seal is located in a recess in the disc housing surface so that the clamped distance between the disc housing and the respective other clamping surface is controlled to a predetermined amount in the vicinity of the seal, so that the seal is not, in use, excessively compressed.

Typically, the aperture is defined by a surrounding volume of material that is large relative to the rest of the housing, so that the housing is stiff and remains sufficiently undistorted from mounting clamp forces to provide a stable and flat sealing surface of the seals. The ratio of depth to width of this material may be of the order of 1:10.

Advantageously, the vent has a generally planar cover mountable in generally axial alignment with the disc and aperture and arranged to be mounted near the outer surface of the battery pack outer wall so as to extend entirely across the end of the aperture but to leave a peripheral gap between the outer periphery of the cover and the outer wall of the pack, which gap is in fluid communication with the aperture.

Preferably, the cover is mountable to the disc housing, through the pack outer wall via a plurality of peripherally located fixing bolts or screws, whereby the bolts or screws form obstructions to gas flow and cause gas exiting the peripheral gap to be separated into a plurality of gas flows. This may be achieved by causing, gas exiting the aperture to impact an inner surface of the cover, so that it is caused to change direction by about 90 degrees and to be deflected generally radially outward to exit the cover through the peripheral gap.

Preferably, the peripheral gap is dimensioned to be smaller than typical road debris or other anticipated debris that might be present around the vent.

The peripheral edge of the cover may be directed inwardly such that in use it is closer to the pack outer wall than the bulk of the cover.

Embodiments of the invention will now be described by way of example, with reference to the drawings in which:-Figure 1A is a perspective view of a battery pack; Figure 1B is a perspective view of a battery pack showing a burst disc mounted to a battery pack outer wall.

Figure 2 is an exploded view of a burst disc assembly; Figure 3A is a detailed view of an assembled burst disc; Figure 3B is a detailed view of Figure 3A; Figure 4 is a view of the outer cover of a burst disc showing gas flow directions; Figure 5 is a diametric section through the burst disc showing airflow channels; Figure 6 is a diametric section through a burst disc showing gas flow; Figure 7A is a perspective view of the inner face of a burst disc housing; and Figure 7B is a perspective view of an outer face of a burst disc housing.

With reference to Figures 1A and 1B, a battery pack 2 has outer walls 4A,4B,4C typically formed from extruded aluminium sections which are welded together to form a rectangular outer frame which in the assembled pack, forms the vertical side walls. The battery pack also has a top cover 6 and a bottom cover (not shown). In a preferred embodiment, the top and bottom covers are made from a lightweight but strong material such as carbon fibre.

Inside the frame 4 and between the top and bottom covers, a plurality of battery modules are located. The battery pack is typically braced with a plurality of cross members (not shown) which are fixed to the long side walls 4B and run parallel with the short side walls 4A and 4C. The cross members are typically fixed to the top and bottom covers and in Figure 1A, fixing locations Bare shown, which are the pipoint at which the cover mounts to the cross-members and which are also strong points for lifting and/or mounting of the battery pack in its final location, such as a road vehicle.

The assembled battery pack with its outer walls and top and bottom covers generally forms a gas tight enclosure and thus the enclosure is provided with one or more burst disc 8, which is designed to provide a mechanical pressure relief operation. A burst disc 8 is shown in Figure 1B located in the rear wall 40 of the battery pack 2. It is designed to burst, or rupture, at a known pressure differential between the pressure inside the battery pack and the ambient pressure. Once the disc has burst, controlled venting of gases occurs from inside the battery pack to the external environment. This controlled venting therefore prevents failure of other parts of the battery pack housing when excess interior pressure is experienced, for example, during a battery module fault.

With reference to Figure 2, the burst disc has several components which are assembled to one of the outer walls of the battery pack (typically one of the extruded aluminium side walls such as the rear wall 40) during battery pack manufacture. The burst disc is a separate module which potentially could be replaced during a repair operation. As will be seen, potentially only the disc itself need be replaced.

With reference to Figure 2, a burst disc assembly has a frangible disc 10 which is designed to rupture once a predetermined pressure threshold across the disc, has been exceeded. The burst disc is clamped to a burst disc housing 12 using a plurality of threaded bolts 14. The bolts 14 pass through apertures 16 formed in the periphery of the disc (generally located on a notional circumferential ring; Although other arrangements are possible) and screwed into threaded bosses 18 which protrude from the burst disc housing.

A seal typically formed from a material such as silicone foam (so that it is compressible to take up any machining tolerances or marks) is located between the burst disc 10 and a disc sealing face 22 formed on the inner face of the disc housing 12. With reference to Figure 7A, it will be seen that the sealing face 22 has a recessed annular groove 24 into which the seal 20 fits and that there is a circumferential raised portion 26 towards the outer edge of the sealing face 22 and also an inner annular raised surface 28. The inner annular raised surface 28 surrounds a vent aperture 30 through which over-pressure gases may be vented, in the direction marked by arrow A. The raised rings 28 and 26 define the outer limits of the annular groove 24 and allow the burst disc 10 to be clamped to the housing 12 with reasonably high torque but without excessively compressing the silicone foam gasket/seal 20. Thus, the rings 26 and 28 effectively form stand-offs against which the clamping force provided by the bolts 14 can be reacted, via the burst disc.

The assembly of burst disc and burst disc housing 10 and 12 may then be clamped to a battery pack outer wall 40. This is typically achieved using bolts 40 which pass for outside the pack, through a burst disc cover 42 through aligned apertures in the wall 40 and into threaded bosses 44 formed in the disc housing 12. A further seal (also typically formed from silicone foam) 46 is placed between the disc housing 12 and the inner face of the battery pack outer wall. With reference to Figure 7B, the disc housing 12 also has an annular raised portion 48 around the vent aperture 30. This raised portion 48 and raised rings 50 around the threaded entries into the bosses 44, provide similar distance standoffs to the rings 26 and 28 on the other face of the housing, so as to avoid over compressing the seal 46.

Finally, on the interior parts of the burst disc, sealing washers are provided under the heads of the bolts 14, to ensure a good seal between the bolts and the burst disc.

Thus, it will be appreciated that this assembly provides a gas tight seal with a venting aperture 30 which aligns with a corresponding aperture 54 in the wall 40; this venting aperture being closed off by the burst disc 10. Thus, when the disc 10 ruptures, gas may flow from the inside of the battery pack through the burst disc 10, through the aperture 30, out of the aperture 54 and (as will be described in more detail below) impact the inner face of the burst disc cover 42 and exit into the atmosphere from there.

Figures 4, 5 and 6 show the detailed gas flow and diffusion arrangements which help to reduce the velocity and adjust the direction of vent gases. As noted above, the burst disc cover 42 is mounted through the wall 4C into the burst disc housing 12, using bolts 40 (with spring washers 50 under the bolt heads into bosses 44 formed in the housing 12).

Once the burst disc 10 has ruptured, gases are free to flow generally in the direction of arrow A through the aperture 30 in the housing 12, and the aperture 54 in the battery pack outer wall. With particular reference to Figure 6, these gases quickly impact the inner face of the burst disc cover 42 and are deflected radially outwardly by this surface from a higher pressure region in the centre, towards the lower pressure external atmospheric pressure at the circumferential edges of the burst disc cover 42.

The cover 42 has standoff bosses 62 formed on the inner surface around the fixing points and with apertures for the bolts 40 to pass through. These standoffs cause the burst disc cover 42 to stand clear of the outer surface of the wall 4C thus providing a peripheral gap which allows gas flow. Thus, as the gases vent generally in the direction of arrow A and impact the inner surface of the cover 42, the gases change direction approximately through ninety degrees to exit in a direction B around the periphery of the burst disc cover. With particular reference to Figure 4, it will be seen that this provides good radial diffusion and, given that there is typically a greater surface area, velocity reduction of the vent gases.

This arrangement also provides good protection for the burst disc and the burst disc apertures 30 and 54, from obstruction, for example, from road debris or snow and hail stones. The whole arrangement provides protection to at least IP67 / 6k9k standards so that it is dust tight and water tight down to lm. The peripheral gap prevents particles greater than 2.5mm from entering and thus the maximum space between the disc and the pack outer wall is typically 2.5mm, and is more typically around 1.8mm. In this respect it will be noted that the disc is optionally radiused to curve towards the outer surface of the battery pack wall, at its outer edges 66, to further prevent ingress of debris into the exit apertures for the burst disc assembly. Thus the burst disc cover prevents damage to, or blocking of, the fragile burst disc depending on where the battery pack is mounted on the vehicle. This damage could be from road debris, along with gravel, rocks, snow, and also hailstones if mounted on the top of the vehicle It will be noted that the burst disc housing 12 has a deep portion 70 which forms a long throat to the aperture 30. This has two main functions. Firstly, this long throat means that fragments of the burst disc when the disc ruptures, do not damage the outer wall of the battery pack 40 as they are generally contained in the replaceable burst disc housing 12. It will be noted that at rupture, high velocity fragments of the burst disc tend to cause damage to the apertures. However, optionally, but in this case, the vent aperture 30 has a smaller diameter than the aperture 54 in the outer wall and the depth of the throat means that damage from fragments is isolated from the outer battery pack wall and will occur only to the throat area 30 and the inner surface of the cover 42. These are both easily replaceable items. Furthermore, the large amount of material used to form the throat area, both in terms of annular thickness D and height H (see Figure 5) means that the disc housing 12 is a stiff structure. An exemplary ratio for D:H would be around 10:1. Typically the material will be a cast and machined metal such as aluminium, and more particularly an aluminium-magnesium-silicon alloy such as aluminium 6082-T6. With M4 fixing bolts torqued to 2Nm for the burst disk mounting and 4Nm to mount the assembly to the pack outer wall, distortion is reduced to acceptable levels.

This type of arrangement means that the assembly resists distortion during fixing and thus provides a flat mounting surface both for the burst disc and also for the seal against the battery pack wall.

Claims

SClaims 1. A pressure operated vent for a battery pack, comprising a generally rigid disc housing having an inner and an outer seal and arranged to be fixed to the inside surface of the battery pack outer wall, a frangible disc arranged to rupture when a pressure differential between an inner and an outer side exceeds a pre-determined threshold, the disc being mounted over the inner seal to compress the inner seal and thereby effect a gas-tight seal between the disc and the housing, and the outer seal being arranged to be compressed between the inside surface of the battery pack wall and the disc housing when the disc housing is fixed, to effect a gas-tight seal between the disc housing and the wall, the disc housing defining an aperture adjacent the disc which forms a passage for vent gases when the disc ruptures.
2. A vent as claimed in claim 1, wherein the inner and/or outer seal is located in a recess in the disc housing surface so that the clamped distance between the disc housing and the respective other clamping surface is controlled to a predetermined amount in the vicinity of the seal, so that the seal is not, in use, excessively compressed.
3. A vent as claimed in claim 1 or claim 2, wherein the aperture is defined by a surrounding volume of material that is large relative to the rest of the housing, so that the housing is stiff and remains sufficiently undistorted from mounting clamp forces to provide a stable and flat sealing surface of the seals.
4. A vent as claimed in any preceding claim, having a generally planar cover mountable in generally axial alignment with the disc and aperture and arranged to be mounted near the outer surface of the battery pack outer wall so as to extend entirely across the end of the aperture but to leave a peripheral gap between the outer periphery of the cover and the outer wall of the pack, which gap is in fluid communication with the aperture.
5. A vent as claimed in claim 4, which is mountable to the disc housing, through the pack outer wall via a plurality of peripherally located fixing bolts or screws, whereby the bolts or screws form obstructions to gas flow and cause gas exiting the peripheral gap to be separated into a plurality of gas flows.
6. A vent as claimed in claim 4 or claim 5, wherein in use, gas exiting the aperture impacts an inner surface of the cover, is caused to change direction by about 90 degrees be deflected generally radially outward to exit the cover through the peripheral gap.
7. A vent as claimed in any of claims 4 to 6, wherein the peripheral gap is dimensioned to be smaller than typical road debris or other anticipated debris that might be present around the vent.
8. A vent as claimed in any of claims 4 to 7, wherein the peripheral edge of the cover is directed inwardly such that in use it is closer to the pack outer wall than the bulk of the cover.
9. A vent as claimed in claim 7 or claim 8, wherein the peripheral gap is less than 2.5mm.