ENERGY STORAGE VENTING DEVICE

A venting device 9a to 9c for a battery 6a including a burst disc 13; a fluid flow path including first and second outlet ducts 14, 15; a flexible coupling 16 around a junction between the first and second outlet ducts; and a piston seal 17 between one of the outlet ducts and the flexible coupling. The piston seal 17 and the flexible coupling 16 provide an expansion cavity 22 for gases exiting the burst disc. The flexible coupling 16 includes an elastomeric tube 20 arranged to expand as the device reacts to a shock wave and returns to normal dimensions.

RELATED APPLICATION

This application incorporates by reference and claims priority to India patent application IN 202311017467, filed Mar. 15, 2023.

FIELD OF TECHNOLOGY

This invention relates to a venting device for an energy storage system such as a battery or system of batteries. The invention further relates to an energy storage system including such a venting device, and to a vehicle including such a venting device and/or energy storage system, such as an aircraft.

BACKGROUND

An aircraft conventionally includes an electrical system arranged to energize various devices on the aircraft, such as flight instruments, navigation aids, cabin heating and lighting. An aircraft's electrical system typically includes one or more batteries arranged to store electrical energy. Previously, lead-acid or Nickel-Cadmium batteries were employed, but there has recently been a move towards Lithium ion batteries, which are rechargeable and dependable. A typical aircraft battery installation comprises groups of cells contained in one or more enclosures or modules.

A problem which may be encountered with aircraft batteries is that, if the battery deteriorates, hot gases can be emitted which must be evacuated to the environment outside of the aircraft. To this end, a venting system is provided between the, or each, battery pack and a vent on the exterior surface of the vehicle.

It has been proposed to utilize a burst disc (also known as a rupture disc) as a pressure relief safety valve. The burst disc is arranged to rupture when the pressure inside a battery module increases beyond a predetermined threshold. It has been found that the hot and high pressure exhaust flow from a ruptured disc has a Mach number which is close to 1, i.e. close to the speed of sound. This can cause a shock wave to be generated in the venting system. Such shock waves can change the properties of the fluid flow in the venting system, causing abrupt changes in temperature, pressure and density. Furthermore, in order to withstand this excess pressure, the venting system is typically made to be very strong and relatively heavy, which is detrimental from the point of view of fuel consumption for the aircraft.

It has been proposed to use a combination of a burst disc with a bellows-type expansion joint downstream of the burst disc. The expansion joint is arranged to absorb the shock wave from the flow emerging from the burst disc. However, it has been found that the corrugated interior surface of the bellows has the capability to cause complicated shock patterns having very strong areas of compression, resulting in increased turbulence, excessive vibration, noise and flow related losses due to the high speed flow over a wavy surface.

SUMMARY OF THE TECHNOLOGY

The invention may be embodied as a venting device for an energy storage system, comprising: a burst disc; a fluid flow path including first and second outlet ducts; a flexible coupling around a junction between the outlet ducts; and a piston seal between an outlet duct and the flexible coupling. The provision of a flexible coupling allows for shock waves to be absorbed or dampened. The flexible coupling is located external to the outlet ducts and so the flexible coupling has low impact on the linearity of the fluid flow emerging from the burst disc.

The piston seal and the flexible coupling may be arranged to provide an expansion cavity for gases exiting the burst disc. Shock waves produced by the gases interact with the flexible coupling by means of the expansion cavity.

Part of the flexible coupling and the piston seal may be capable of relative sliding movement. Such sliding movement assists the venting device in absorbing shock waves.

The flexible coupling may include first and second rigid structural members associated with the respective outlet ducts and a flexible sleeve between the rigid structural members. The rigid structural members provide strength and rigidity to the flexible coupling whilst the flexible sleeve accommodates the movement required to absorb the shock waves.

The flexible sleeve may comprise a tube of elastomeric material. Alternatively, the flexible sleeve may comprise a bellows duct. Each of these types of sleeve is capable of returning the flexible coupling to its original position after it has absorbed a shock wave.

One of the structural members may be arranged to be capable of sliding movement with respect to the outlet ducts.

The piston seal may be attached to the first outlet duct and is arranged to make sliding contact with the second structural member.

The outlet ducts may be arranged along a common axis, with the flexible coupling being arranged coaxially around the ducts.

The energy storage system may include a housing having an outlet to the burst disc.

The invention may be embodied to provide an energy storage system comprising at least one battery in a housing and a venting device constructed according to the first aspect of the invention. Preferably, a plurality of batteries is provided in a plurality of housings, with each housing being associated with a venting device constructed according to the first aspect of the invention.

The invention may be embodied to provide a vehicle including such an energy storage system.

A venting system may be provided comprising at least one duct between the, or each, venting device and an exterior surface of the vehicle. The vehicle may take the form of an aircraft.

DETAILED DESCRIPTION

With reference toFIG.1, an aircraft in the form of a typical transonic commercial passenger airplane1. The aircraft1comprises a fuselage2, wings3, main engines4and a tail5. The aircraft1further contains within it an energy storage system. The energy storage system comprises a plurality of battery packs, two of which6a,6bare shown in broken lines inFIG.1. Each battery pack6a,6bcomprises a housing containing at least one battery or cell, for example a lithium-ion battery. The batteries are arranged to provide electrical power to devices on the aircraft through electrical conductors (not shown) running between the battery packs6a,6band the electrical devices.

In the event of deterioration of one or more of the batteries, a venting system7is provided for the removal of gases. The general layout of an example venting system7is shown inFIG.2. The venting system7is arranged to fluidly connect the energy storage system to the ambient environment via an exit port8in the outer skin of the aircraft.

With reference toFIG.2, the energy storage system comprises a plurality of battery packs6a-6c, including the two packs6a,6bshown inFIG.1. Of course, any number of battery packs6could be provided. Each battery pack6a-6cis fluidly connected to the venting system7via a venting device9a-9c, which will be described in more detail later in this specification. The respective outlets10a-10cof each venting device are connected to respective exhaust ducts, e.g., pipes11ato11c. The exhaust ducts11ato11care fluidly connected to a main line12that is also connected to the exit port8arranged through the outer skin of the aircraft1. Thus, any gasses emitted by one or more of the batteries can be vented to the atmosphere through the system of ducts11ato11cand12.

Deterioration of a battery can also result in the generation of excess pressure, which can propagate through the venting system7. In order to prevent such propagation, each battery pack6a-6cis associated with a venting device9a-9cconstructed according to the invention, an example of which is shown inFIG.3.

The venting device9amay include: a burst disc13; a first outlet duct14immediately downstream of the burst disc; a second outlet duct15, coaxial with and downstream of the first duct14; a flexible coupling16arranged around the junction of the ducts14,15; and a piston seal17arranged between one of the ducts (in this case duct15) and the flexible coupling16. In this embodiment, the flexible coupling16comprises a structural members18,19arranged around, and coaxial with, the first and second outlet ducts14,15; and a flexible sleeve arranged as a bridge between the two structural members18,19. The flexible coupling16is arranged to form a flexible outer envelope around the junction between the first and second outlet ducts14,15.

The first structural member18comprises a metallic flange in the form of a collar, with a neck part18aarranged to fit around the outer circumference of the first outlet duct14, and a shoulder part18bthat extends radially outwardly. The shoulder part18bis attached by means of fasteners21a,21bto a first end portion of the flexible sleeve.

The flexible sleeve comprises a tube20of an elastomeric fabric. The fabric may be formed from a fluoro-elastomer, which is a fluorocarbon-based synthetic rubber. Fluoro-elastomers are typically hard-wearing and resistant to chemicals, heat and abrasion. The other end portion of the elastomeric tube20is attached by fasteners21c,21dto the second structural member19. The provision of a simple fastening system facilitates assembly of the venting device, and also disassembly in case of replacement or repair of the flexible coupling16.

The second structural member19comprises a metallic flange having a neck part19aarranged to fit around the outer circumference of the second outlet duct15, a shoulder part19bthat extends radially outwardly, a sleeve part19cthat extends along an axis coaxial with the axis of the outlet ducts14,15, and a rim part19dthat extends radially outwardly. The rim19dis the part that that the second end portion of the elastomeric tube20is attached to.

The piston seal17includes an elastomer ring arranged around the outer circumference of the first outlet duct14, at the end portion remote from the burst disc13. The piston seal17may be attached directly to the outer surface of the outlet duct14or may, as is shown inFIG.3, be held by a flange-like holder that is fastened or bonded to the end of the outlet duct14. The piston seal17is arranged to make intimate contact with the inner surface of the sleeve part19cof the second structural member19. There is an expansion cavity22defined by the end face of the seal17, an end portion of the inner surface of the sleeve part19cand the shoulder part19bof the second structural member, the function of which will be discussed below.

A burst disc is a device that is calibrated to rupture when the pressure exerted on it exceeds a predetermined threshold. In this embodiment, the burst disc13is arranged to form part of a face of one of the battery pack housings6a, such as covering an opening in the housing. The mechanical resistance of the burst disc13is lower than the mechanical resistance of the other faces of the battery pack6ato ensure that the burst disc will rupture before any other part of the battery pack housing. Thus, the burst disc13provides an outlet for gases when the pressure of those gases inside the battery pack6aexceeds the predetermined threshold.

When the burst disc13ruptures, the outgoing gas flow may be hot and at high pressure, leading to a shock wave being produced. The flexible coupling16is arranged to absorb or dampen any shock waves. The shock wave expands into the expansion cavity22and causes a pressure thrust against the shoulder19bof the second structural member19. The second structural member19is arranged to be able to slide over the second outlet duct15, and the elastomeric tube20stretches to accommodate this movement. The relative movement of the second structural member19and the outlet duct15means that the piston seal slides along the inner surface of the sleeve part19bof the second structural member19as the apparatus absorbs a shock wave. When the shock wave has been absorbed, the second structural member19moves back to its original position under a restoring force exerted on it by the elastomeric tube20.

Only a small portion of the gaseous flow exiting the burst disc13is pushed into the expansion cavity22by the shock wave. A majority of the flow is smooth and unperturbed, and so the fluid flow exiting the venting device9aexhibits a smaller amount of turbulence than was achievable hitherto. Hence, the flow of fluid in the venting system7is relatively low in turbulence. This means that the ducts11ato11c,12of the venting system7can be made lighter in weight than was possible hitherto.

The flexible coupling16and the seal17may also advantageously absorb vibration of the venting device9aduring use, which can reduce strain on the venting system7. The flexible coupling16can also absorb thermal expansion and contraction that would be experienced by the venting device9aduring flight. As the fluid exiting the burst disc does not come into contact with the elastomeric tube20, it does not need to be as resistant to high temperatures and corrosive chemicals as in prior devices where the fluid flow is arranged to flow along a flexible sleeve.

An alternative venting device is shown inFIG.4. In this embodiment, there is a burst disc13and outlet ducts14,15downstream of the burst disc. A flexible coupling25is arranged around the junction between the ducts14,15. A piston seal17is arranged between the first outlet duct14and the flexible coupling25as before. However, in this embodiment, the flexible sleeve of the flexible coupling takes the form of a bellows duct23. The bellows duct23is a tube that is corrugated along its length, with a plurality of circumferential ridges. The bellows duct23could be made of metal, an elastomer or a hard-wearing fabric.

The flexible coupling25includes two rigid structural members24,19arranged around the respective outlet ducts14,15. The end portions of the bellows duct23are connected to respective ones of the structural members24,19. The second structural member19is the same as that shown inFIG.3, with a neck part19aarranged to fit around the outer circumference of the second outlet duct15, a shoulder part19bthat extends radially outwardly, a sleeve part19cthat extends along an axis coaxial with the axis of the outlet ducts14,15, and a rim part19dthat extends radially outwardly. The rim part19dis attached to an end of the bellows duct23.

The structural member24is arranged around the first outlet duct14, in a similar way to the structural member18ofFIG.3. However, the structural member24has a more convoluted shape, with a neck part24aarranged to fit around the outer circumference of the first outlet duct14, a shoulder part24bthat extends radially outwardly, a sleeve24cthat extends back around the neck part24a, and a rim part24dthat extends radially outwardly. The rim part24dis attached to the other end of the bellows duct23. The structural member24is rigid and able to accommodate strain forces experienced by the venting device in use. The folded shape of the structural member is able to accommodate a longer flexible sleeve than the apparatus ofFIG.3.

The venting device ofFIG.4operates in a similar way to that ofFIG.3. The hot, high-pressure gas emerging from the burst disc13expands into an expansion cavity22defined by the end face of the seal17, an end portion of the inner surface of the sleeve part19cand the shoulder part19bof the second structural member. The pressure wave caused by the emerging gas flow causes a pressure thrust against the shoulder19bof the second structural member19. The second structural member19is arranged to be able to slide over the second outlet duct15, and the bellows duct23expands to accommodate this movement. The relative movement of the second structural member19and the outlet duct15means that the piston seal17slides along the inner surface of the sleeve part19bof the second structural member19as the apparatus absorbs the shock wave. When the shock wave has been dampened or absorbed, the bellows duct23retracts and returns the second structural member19to its original position.

Variations may be made without departing from the scope of the invention. For example, the invention is applicable to other forms of vehicle other than an aircraft seals, such as O-rings, may be employed between components of the venting device of the present invention to prevent leakage of gases into the aircraft or vehicle.

A low-friction coating may be provided between the second structural member19and the second outlet duct15to facilitate relative sliding movement between them as the device reacts to a shock wave and returns to its original position.

The elastomeric sleeve20need not be formed from a fluoro-elastomer: silicon rubber, neoprene or other rubbers may be employed. The elastomeric sleeve20and/or the bellows duct23may be formed as a composite and may include reinforcing fibers, such as carbon fiber or glass fiber.

The internal shape of the flexible sleeve (whether in the form of an elastomeric sleeve20or a bellows duct23) may be circular, oval, square or rectangular, in dependence on the shape of the outlet duct15and the ducts or pipes of the remainder of the venting system7. The end portions of the flexible sleeve may be bonded onto, cured with, or over-molded on the structural members18,19,24. Alternatively, a combination of joining methods may be employed to increase the security of the connection.

One end portion of the flexible sleeve may be fastened or bonded to a wall of the battery pack6a, such that the sleeve surrounds the burst disc13. In this variant, the battery pack itself forms one of the rigid structural members.

The burst disc13may take the form of a pressure relief valve or other safety valve. The burst disc may be circular, oval or a panel (i.e. rectangular) or have any other suitable geometry. The burst disc is preferably unidirectional but may be bi-directional. The burst disc may be single use, such that it needs to be replaced once activated, or multi-use. The burst disc may have a single bursting membrane or may have multiple membranes.

The structural members18,19,24, may have simple or convoluted shapes. They are shown simply in these drawings as simple, straight-sided components having right-angle joints between the parts of each member. However, they may be made of any suitable shape and configuration having slopes, curves and bends in accordance with the requirements of the venting system and the available space in the aircraft or other vehicle.

The venting device according to the invention is shown as being employed immediately adjacent or close to each battery pack of the electronic storage system. Such venting devices may be employed at other locations in the venting system—for example, close to the exit port near the skin of the aircraft. The venting devices9a,9b,9cemployed in a venting system may all be of the type shown inFIG.3or may all be of the type shown inFIG.4. Alternatively, a combination of types of venting device may be utilized.