Anti-propagation exhaust device for aircraft lithium-ion batteries

An assembly for supplying power to an aircraft is disclosed having at least one battery housed in a respective housing, each housing comprising a wall in which a through-opening is arranged, and an exhaust device including a discharge duct connecting each housing opening to a common discharge port, a valve mounted on each opening. Each valve includes a membrane arranged so as to seal the opening closed and having a surface of pressure application towards the inside of the housing and a surface of pressure application towards the outside of the housing. The surface of pressure application towards the outside of the housing is larger than the surface of pressure application towards the inside of the housing, so that the membrane bursts at a bursting pressure inside the housing that is lower than a bursting pressure reached outside the housing.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a National Phase of International Application Number PCT/FR2021/051398 filed Jul. 27, 2021, which designated the U.S. and claims priority benefits from French Application Number FR20 08293 filed Aug. 5, 2020, the entire contents of each of which are hereby incorporated by reference.

TECHNICAL FIELD

This disclosure relates to an exhaust device for aircraft batteries, in particular in the event of thermal runaway of one or more batteries.

PRIOR ART

Currently, aircraft which carry passengers do not have lithium batteries, but Ni-Cad batteries which are not subject to the risk of thermal runaway. For an aircraft to be able to carry lithium batteries, it must comply with DO311A certification, which involves setting up a discharge system between each battery and the outside of the aircraft so that, in the event of thermal runaway of a battery, the generated gases are discharged outside the aircraft. This discharge system must comply with pressure and high-temperature resistance constraints.

However, if the aircraft carries several batteries, for reasons of size, weight, and design difficulties it is not desirable to provide one discharge device per battery on board the aircraft. In addition, to obtain certification, it is necessary to provide a discharge device with high reliability.

SUMMARY

In view of the above, one object of the invention is to provide a device for discharging the gases generated in the event of thermal runaway of a battery on board an aircraft, which is shared by several batteries, with no risk of thermal runaway contamination between batteries.

Another object of the invention is to provide a device having high reliability.

To this end, the invention proposes an exhaust device for at least one battery housed in at least one housing and mounted in an aircraft, each housing comprising a wall in which is arranged a through-opening, the device comprising:a discharge duct connecting the opening of each housing to a common discharge port leading to outside the aircraft,a check valve mounted on the opening of each housing,
wherein each check valve comprises a membrane mounted on the wall of each housing in which the through-opening is arranged, so as to seal closed said opening, each membrane having a surface of pressure application towards the inside of the housing and a surface of pressure application towards the outside of the housing,
and wherein the surface of pressure application towards the outside of the housing is larger than the surface of pressure application towards the inside of the housing, so that the membrane bursts at an internal bursting pressure value reached inside the housing that is lower than an external bursting pressure value reached outside the housing.

In some embodiments, the surface of pressure application of each membrane towards the inside is less than or equal to one third of the surface of pressure application towards the outside of the housing.

In some embodiments, each membrane is located outside the housing and the surface of pressure application of the membrane towards the outside is equal to the internal cross-section of the discharge duct.

In some embodiments, the device may further comprise a membrane support in contact with a main face of the membrane oriented towards the inside of the housing, and shaped to reduce the surface of pressure application towards the inside of the housing.

In some embodiments, each membrane support comprises a set of bars extending parallel to the membrane and transversely to each other.

In some embodiments, each membrane support is formed of a grid or a cross.

In some embodiments, each valve comprises an endpiece for connection to the discharge duct, the endpiece being attached to the wall of the housing in which the through-opening is arranged, and the membrane being interposed between the endpiece and the wall.

In some embodiments, each valve comprises an endpiece for connection to the discharge duct, the endpiece comprising a first portion suitable for insertion into the through-opening and a second portion forming a peripheral shoulder suitable for resting against an edge of the through-opening, the membrane being housed inside the endpiece which rests against the peripheral shoulder.

In some embodiments, each membrane is formed of silicone.

In some embodiments, the device may further comprise a sensor arranged on each membrane and suitable for detecting an open or closed state of each membrane.

In some embodiments, the device connects between one and six housings to the common discharge port.

In some embodiments, the device further comprises a pressure relief valve mounted on the common discharge port and suitable for closing off this port as long as the pressure in the discharge duct is lower than a threshold pressure value that is less than the external bursting pressure of the membranes, and to allow fluid communication to the outside of the aircraft when the pressure in the discharge duct reaches said threshold pressure.

In this case, a method implemented by such a device comprises, in the event of an increase in pressure in a battery housing,the bursting of the membrane of said battery housing when the pressure therein reaches the internal bursting pressure value inside the housing, and the escape of gas contained in the battery housing into the discharge duct, andthe opening up of the common discharge port by the pressure relief valve when the pressure in the discharge duct reaches the threshold pressure value which is less than the external bursting pressure of the other housings, to allow the discharge of gases to outside the aircraft.

According to another object, an assembly for supplying power to an aircraft is described comprising a plurality of batteries mounted in an aircraft, the batteries being housed in a plurality of housings, each housing comprising a wall in which a through-opening is arranged, the assembly further comprising an exhaust device for the batteries according to the above description.

In some embodiments, the batteries (2) are lithium batteries.

The device described herein allows connecting a set of batteries, in particular lithium batteries, to a single discharge port that leads to outside the aircraft, with no moving parts. To achieve this, the valve mounted on each battery housing allows gases generated during a potential thermal runaway of a battery to escape to the discharge port, since the membrane of the valve yields to the pressure applied by these gases, without the membranes of the valves of the other batteries yielding under this pressure. The risk of thermal runaway contagion between batteries is therefore eliminated.

The device also offers advantages in the case of a single battery, since the membrane, which seals the battery housing, makes it possible to form a fluidtight barrier which eliminates the need to use a temporary plugging device to prevent the entry of objects or liquids into the battery housing, in particular in the event of assembly or maintenance.

In the case where a membrane further comprises a sensor which allows detecting a rupture of the membrane, this sensor can provide an additional indication to a battery management device in order to know the state of the battery or batteries contained in the housing closed off by the membrane.

DESCRIPTION OF EMBODIMENTS

Reference is now made toFIG.1, which shows an example of an assembly for supplying power to an aircraft, comprising a plurality of batteries2mounted in an aircraft3, and an exhaust device1for the batteries. The batteries may be lithium batteries, in particular batteries of the LFP or NMC type. In addition, the batteries may have a cylindrical, prismatic, or pouch cell format (i.e. in a bag or case). The aircraft in which the batteries2and the exhaust device1are mounted may be for example an airplane for civil or commercial applications, a helicopter, a flying taxi type of autonomous vehicle, a space shuttle, or any other aircraft, in particular intended for passenger transport applications.

Each battery2is housed in a housing suitable for containing the flames and gases generated in the event of thermal runaway of the battery. For example, each battery housing20may be formed of aluminum. In one embodiment, each battery2is housed in a respective housing. Alternatively, a housing may house several batteries, for example two batteries.

As described in more detail below, the exhaust device1makes it possible to connect a plurality of battery housings20, and therefore a plurality of batteries, to a common discharge port30arranged in a wall of the aircraft and leading to outside the aircraft. In some embodiments, the exhaust device makes it possible to connect at least one housing20for batteries2to the discharge port30, and preferably between 1 and 6 housings. In the case where each housing houses one battery, the device thus makes it possible to connect between 1 and 6 batteries to the discharge port30.

Each housing20comprises a wall21in which is arranged a through-opening22. The exhaust device1comprises, for each housing20, a discharge duct10connecting the through-opening22of the housing20to the discharge port30. The discharge ducts therefore comprise a portion specific to each battery housing20and a portion common to all of the battery housings, and all of the discharge ducts are in communication with one another so that gases can freely circulate in all the discharge ducts. The exhaust device further comprises a valve11for each battery housing20, carried at the housing end of each discharge duct10and mounted on the through-opening22of the housing.

Referring toFIGS.2ato2c, the valve11comprises a membrane12, mounted on the wall21of the housing so as to seal closed the through-opening22of the housing. The membrane is made of a fluidtight material that is non-flammable. For example, the membrane may be made of silicone. Alternatively, it may also be formed of a metal strip. In addition to the function described below, the fact that the membrane seals the through-opening makes it possible to ensure that the housing is fluidtight. As a result, the fluidtightness of the housing is guaranteed, including during assembly or maintenance operations, eliminating the need for a temporary plugging device.

The valve11may also comprise a connection endpiece, suitable for receiving one end of a discharge duct, so as to connect the through-opening22of the housing with the duct10.

The valve is adapted so that the membrane12is able to withstand an external pressure PE on the discharge duct side, meaning outside the housing that is greater than the internal pressure PI inside the housing of the battery. In particular, each valve is adapted so that the membrane12yields at an internal pressure PI within the battery housing20that is equal to a determined pressure P1, without yielding when this pressure P1is reached, or even exceeded, by the pressure PE in the discharge duct. Preferably, each valve is adapted so that the membrane12has an internal bursting pressure PIBthat is less than or equal to half, or even a third, of the external bursting pressure PEB.

Each membrane12has a surface of pressure application towards the outside of the housing S→Eand a surface of pressure application towards the inside of the housing S→I. In the following, the surface of pressure application is the portion of the section of the membrane, which is less than or equal to the total surface of the membrane, on which is exerted a force resulting from a gas pressure according to the equation F=P.S. The surface of pressure application may be formed by several separate regions of the membrane section. Alternatively, it may be formed by a single region, which has a surface area less than or equal to the surface area of the membrane.

For example, the surface of pressure application of a main face of the membrane may correspond to the surface of the membrane that is free to deform under pressure. In an example in which the membrane is on the outside of the housing so as to cover the through-opening of the housing, the surface of pressure application towards the inside S→Iof the housing may correspond to the cross-section of the through-opening.

Depending on the geometry of the exhaust device1on either side of the membrane, the surfaces of pressure application towards the inside S→Iand towards the outside S→Eof the membrane may therefore be different.

In order for the membrane12to be able to withstand, on the discharge duct side, a pressure greater than the pressure PIBexerted inside the housing at which it yields, the geometry of the membrane12is adapted so that the surface of pressure application towards the outside of the housing S→Eis larger than the surface of pressure application S→Itowards the inside of the housing. In this manner, at identical pressure on either side of the membrane, the force exerted by gases on the membrane12is greater towards the outside than towards the inside, which causes the membrane to rupture at an internal bursting pressure PIBreached inside the housing20that is less than a bursting pressure PEBin the discharge duct10. In some embodiments, the section of pressure application towards the inside S→Iis less than or equal to half or even a third of the section of pressure application towards the outside S→E, to allow a sufficient difference in pressure between the pressures that can be withstood on either side of the membrane.

In some embodiments, the membrane12may be located outside the housing20, and cover the through-opening22so as to close off this opening. With reference toFIG.2a, in this embodiment, the surface of pressure application S→Itowards the inside of the housing may correspond to the cross-section of the through-opening20of the housing. On the other hand, the surface of pressure application S→Etowards the outside of the housing corresponds to the internal cross-section of the discharge duct10, this cross-section advantageously being greater than the cross-section of the through-opening, and preferably at least twice the cross-section of the through-opening.

In the example shown inFIGS.2aand4, this embodiment can be obtained by pinching the membrane12between the connection endpiece of the valve and the wall21of the housing. The connection endpiece13is suitable for attachment to the wall of the housing in which the through-opening is arranged, for example by means of a mounting plate130. The connection endpiece can then be attached to the housing, for example by screwing or by bolting the mounting plate to the wall21of the housing. The membrane12is then interposed between the wall of the housing and the end of the connection endpiece formed by the mounting plate130, so as to close off the opening in a sealed manner, without any need to add an additional gasket.

In other embodiments, the membrane12may be an element integrated into the connection endpiece of the valve.

According to an exemplary embodiment shown inFIGS.2band2c, the connection endpiece13comprises a main body139comprising a portion131suitable for insertion into the through-opening22of the housing20, and an adjacent portion132of greater diameter, forming a peripheral shoulder suitable for resting against an edge of the through-opening22. In this case, the connection endpiece13can be fixed rigidly to the wall of the housing by bolting the peripheral shoulder to the wall of the housing, or in the case where the portion131inserted into the through-opening projects beyond the wall of the housing, by tightening a nut133around the projecting portion. A gasket134may be provided between the peripheral edge of the connection endpiece and the wall of the housing. The membrane12may itself be held in place in the connection endpiece, resting on the peripheral shoulder, by another clamping nut135.

In the example shown inFIG.2b, the peripheral shoulder of the connection endpiece13is located inside the housing20, and the membrane12is therefore also inside the housing. Alternatively, the reverse configuration could be adopted and the membrane12would then be outside the housing.

In addition, to further reduce a membrane's surface of pressure application towards the inside relative to the surface of pressure application towards the outside, each valve may comprise a membrane support14located on the side of the membrane located inside the housing. The membrane support14is preferably in contact with the main face of the membrane oriented towards the inside of the housing. The membrane support14is shaped to reduce the surface of pressure application towards the inside of the housing by reducing the surface of the membrane that is free to deform inward.

The membrane support14may be formed of one or more bars extending parallel to the membrane and transversely to each other. For example, the membrane support may be formed of a cross or a grid extending in a plane parallel to the plane of the membrane and in contact with the membrane. The membrane support therefore makes it possible to reduce the membrane's surface of pressure application towards the inside and to increase the difference between the internal bursting pressure PI and the external bursting pressure PE of the membrane.

In the example ofFIG.2b, a membrane support is shown, this nut being a grid formed as one piece with the nut holding the membrane in place in the connection endpiece.

In one embodiment, the membrane support14may be formed integrally with the wall21of the housing in which the through-opening22is made. This is the case in the example shown inFIG.3. Alternatively, the membrane support14may be a separate part attached to the wall of the housing or to one of the components of the valve11. For example, in the embodiment shown inFIG.2b, the support is formed integrally with the clamping nut135keeping the membrane12integral with the body139of the endpiece for connection to the discharge duct.

In some embodiments, a sensor (not shown) may be arranged on the membrane, suitable for detecting a closed or open (burst) state of the membrane. The sensor may be, for example but not limited thereto, of the strain gauge type, break wire type, etc. In addition, the sensor may then be connected to a device for managing the battery or batteries (or BMS, acronym for Battery Management System) that are contained in each housing, so that the battery management device can have access to additional information about the state of the membrane.

Referring toFIG.1andFIG.4, the device further comprises a pressure relief valve40mounted on the discharge port common to all the battery housings, or, if not mounted directly on the discharge port, it is arranged on a common portion of the set of discharge ducts.

The pressure relief valve is suitable for closing off the discharge port as long as the pressure inside the discharge ducts is below a threshold pressure PS, and for opening up this port, for example by bursting, when the pressure reaches or exceeds the threshold pressure.

Advantageously, the threshold pressure PSis less than the external bursting pressure PEBof the membranes of the valves mounted on the housings. In addition, the threshold pressure is advantageously less than or equal to the internal bursting pressure PIBof these membranes, so that in the event of thermal runaway of a battery, the corresponding membrane of the housing bursts, and consequently the pressure relief valve also opens up the discharge port. For example, the threshold pressure PS may be equal to pressure PIB.

Thus,FIG.4shows some kinematics allowed by the exhaust device1presented above in the event of thermal runaway of a battery. During a first step S1, a battery undergoes thermal runaway, causing the generation of gas and an increase in pressure in the battery housing, until the internal bursting pressure PIBof the membrane is reached, for example two bars.

During a second step S2, the membrane of the housing bursts, which causes the gases to spread through all of the discharge ducts of the exhaust device and an increase in pressure in these ducts.

During a third step S3, the pressure in the discharge ducts reaches the threshold pressure PS where the pressure relief valve40opens up the discharge port30. This threshold pressure is lower than the external pressure PEBat which the membranes of the other housings20give way. Consequently, the discharge port30is opened up to allow discharging the gases without contaminating the other batteries with thermal runaway.

During a final step S4, the gases are discharged to outside the aircraft and the pressure in the discharge ducts decreases, without having reached the external bursting pressure PEBof the other membranes, and therefore the risk of thermal runaway is eliminated.

LIST OF REFERENCE SYMBOLS

1: exhaust device,10: discharge duct,11: valve,12: membrane13: connection endpiece,130: mounting plate,131: portion that can be inserted into the opening in the housing,132: portion forming a shoulder,133: nut,134: gasket,135: membrane clamping nut,139: main body of the endpiece,14: membrane support,2: battery,20: battery housing,21: housing wall,22: opening in the wall21,3: aircraft,30: discharge port,40: pressure relief valve,S→E: membrane surface of pressure application towards the outside of the housing,S→I: membrane surface of pressure application towards the inside of the housing.