Multi-function degassing valve device for electric vehicle battery

Abstract

The invention relates to a valve device (2) configured to retain and selectively release a gaseous mixture contained in an inside volume of a chamber, the valve device comprising a base (3) and a piston (4) movably mounted with respect to the base between a closed rest position and an open position, the base comprising a sleeve (31) and an annular rim (32), wherein the piston, in the closed rest position, is pushed against a valve seat (8) by a spring, the piston comprising a breakable membrane (6) closing in normal time a central passage of the piston delimited radially by the piston, the base comprising a shoulder on which a purge tool (9) configured to push the piston back towards the open position can rest, the valve device comprising passages (11, 12) that communicate the inside volume with an outside space in the open position of the piston.

Description

DESCRIPTION TITLE OF THE INVENTION: Multi-function degassing valve device for electric vehicle battery The present invention relates to a multifunctional degassing valve device for an electric vehicle battery and a battery pack comprising such a valve device. [0 The battery of an electric vehicle comprises electrochemical cells grouped together in a unit called in the trade a 'battery pack'. The electrochemical cells are contained in an enclosure also called in the trade 'casing' or 'housing'. Unit cells can be prismatic, cylindrical, or pouch-shaped ('pouch' is used in industry jargon). Unit cells can be optionally organized into groups or subsets. The most common traction batteries in electric vehicles are lithium-ion batteries. There are several types of these, including NMC (Nickel Manganese Cobalt), LFP (Lithium Iron Phosphate / LifePo4), and others. Each electrochemical cell contains chemical elements hermetically sealed within a cell envelope. In addition, the entire electrochemical cell assembly is hermetically sealed within the battery pack envelope.

[0008] It cannot be excluded that one (or more) lithium-ion battery cell(s) may be subject, under certain circumstances, to excessive heating which causes an internal release of gas and an increase in the pressure inside the cell envelope. Each electrochemical cell therefore has, in order to avoid any risk of explosion, a gas discharge device also called a safety valve. When the safety valve opens, gases present inside the cell envelope escape. This phenomenon is called "degassing" of the cell. If one or more electrochemical cells vent, the vent gases are released into the general interior volume of the battery pack, increasing the pressure. Therefore, a relief valve must also be provided on one wall of the enclosure to prevent excessive pressure build-up and the risk of sudden rupture of the enclosure.

[0010] It also turns out that in the long term, gas leaks can occur from inside the cells into the general volume inside the envelope box.

[0011] The presence of these gases inside the battery pack must be taken into account in cases of maintenance intervention which lead to disassembling the battery pack, for example to change a defective battery cell or a relay, or to prepare a second life for the battery pack (outside the vehicle).

[0012] When it becomes necessary to disassemble the battery pack, there is a need to be able to purge the gases inside the front box to carry out the actual disassembly, so that operators can work safely.

[0013] The inventors sought a solution that could combine the function of the safety relief valve and the specific purge function. [For this purpose, a valve device (2) is provided configured to retain and selectively release a gas mixture contained in an interior volume of a hermetic enclosure, the valve device comprising a base (3) and a piston (4) mounted movably along a valve axis (A) relative to the base between a closed rest position and an open position, the base comprising a sleeve and an annular rim, the base being hermetically mounted on a wall of the hermetic enclosure, in which the piston, in the closed rest position, is pushed against a valve seat by an elastic element (5), in which the piston comprises a ring delimiting an interior radial space of the piston, characterized in that the piston comprises a breakable membrane (6) normally closing a central passage of the piston delimited radially by the ring,the breakable membrane having a breaking strength up to a first breaking strength threshold in response to a pressure difference across its faces, the base comprising a shoulder, facing the interior volume, relative to which a purge tool configured to push the piston back to the open position can rest or be anchored, the valve device comprising purge passages communicating, in the open position of the piston, the interior volume with a space outside the hermetic enclosure.,

[0015] Thanks to these provisions, it is possible, by means of the proposed single valve device, on the one hand to selectively cause a controlled purge of the gases present in the interior volume of the hermetic enclosure, and on the other hand to provide passive protection against internal overpressure via the rupture of a breakable membrane.

[0016] It is noted that the breakable membrane is cleverly mounted on a mobile piston, unlike known conventional configurations where the breakable membrane is installed stationary relative to the wall of the envelope to be protected.

[0017] Advantageously, the purge procedure by pushing back the piston does not involve the breakable membrane, which remains intact and can operate later if necessary. Advantageously, it is sufficient to push the piston inwards, i.e. towards the interior volume of the hermetic enclosure, to free a purge passage between the interior and the exterior, without involving the breakable membrane. [C The breakable membrane acts as a safety valve, i.e. a relief device in the event of overpressure. When the breakable membrane tears and opens, this is a non-reversible phenomenon; it does not close again. Once open, the breakable membrane releases a passage of significant cross-section to allow gas to escape at a high flow rate, in response to a sudden increase in internal pressure within the sealed enclosure.

[0020] The function described in the previous paragraph should not be confused with a pressure equalization valve (also called a 'breathing valve') which may also be present on the casing box. The breathing valve reacts to slow drifts in pressure differential but its passage section (i.e. leakage) is not sufficient to react correctly to rapid overpressure. In this document, the qualifiers 'inside' and 'outside', when associated with a qualifier 'radial' or an adverb 'radially', are to be interpreted geometrically in relation to the main axis of valve A. Otherwise, the qualifiers 'inside' and 'outside' relate respectively to the inside of the hermetic enclosure or to the outside of the hermetic enclosure. [0 In this document, the qualifiers 'front' and 'rear' are to be interpreted for the valve device in relation to a point of view located outside the sealed enclosure, namely 'front' is located towards the outside and 'rear' is located towards the inside

[0023] According to one embodiment, the purge passages comprise first passages passing through the socket of the base and communicating the interior volume with an interior radial space of the socket. Thus, the path taken by the gases during the purge procedure arrives radially on the outside of the piston upstream of the valve seat and can exit through a front area of ​​the piston as soon as the piston is lifted from the valve seat.

[0025] According to one embodiment, the base and the piston preferably have shapes generally of revolution around the valve axis and the elastic element is formed as a helical spring. The piston and the base are thus easy to manufacture by turning. The helical spring, e.g. metal, is an inexpensive component and forms a very reliable elastic element. In one embodiment, the breakable membrane is a disc made of synthetic polymer material, fixed along its peripheral edge to the piston ring, on the radially inner side. Such an element is simple to manufacture, and its circular edge can be sandwiched between two elements to obtain a robust fixing. According to one embodiment, the breakable membrane has a constant overall thickness of between 0.1 mm and 1 mm and at least one weakening groove. The trigger threshold can thus be well controlled. According to an exemplary embodiment, this threshold can in practice be between 1 bar and 3 bars. According to one embodiment, the purge passages comprise second radial passages passing through the piston ring and communicating an outer radial space of the piston with an inner radial space of the piston, on a front side of the breakable membrane along the valve axis. Thus, the path taken by the purged gases first passes through the first radial passages and then in a row in the second radial passages promoted here to reach the center of the piston on the outer side of the membrane and escape to the atmosphere. [0 According to one embodiment, the second radial passages are opposite the first radial passages when the piston is in the open position, away from the seat. This minimizes the pressure losses in the path taken by the purged gases.

[0030] According to one embodiment, the valve seat (8) is a shoulder of the sleeve, on which a collar protruding from the piston ring radially outwards is supported.

[0031] The sealing of this arrangement is particularly efficient, there is a flat annular surface in the direction of the force of the elastic element, which firmly pushes the piston against the valve seat. According to one embodiment, the central passage of the piston has a diameter noted D1 and the hole in the wall has a diameter noted D3, said diameters being such that D3 / D1 < 1.4 and preferably D3 / D1 < 1.3. [0 According to one embodiment, the central passage of the piston has a diameter noted D1 and the base has an overall diameter noted D4, said diameters being such that D4 / D1 < 1.6 and preferably D4 / D1 < 1.5. It is noted that the device is particularly compact in the radial direction, it does not occupy much more space than the central passage provided for a discharge and safety evacuation of an internal overpressure. Thus the valve device can be installed on a low-height section of the box. The valve device occupies a small volume and does not weaken the casing box much in view of the moderate diameter hole that it requires.

[0035] In one embodiment, the piston and base are made of aluminum alloy or plastic with high mechanical properties. This contributes to the lightness of the solution. The present invention also relates to a valve system comprising a valve device as defined above and a gas purge and recovery tool (9) configured to selectively push the piston against the elastic element and thus move the piston towards the open position.

[0037] According to one embodiment, the gas purge and recovery tool comprises a positioning handle and at least one actuating handle. This allows intuitive positioning by an operator of the purge tool on the valve device. Advantageously, the positioning handle is located in the valve axis. According to one embodiment, the gas purging and recovery tool comprises a gas collection cover and a suction line. Thus, the purged gases are not allowed to escape to the atmosphere, but are channeled to a suction and recovery system. The present invention also relates to a battery pack comprising a plurality of electrochemical electric battery cells, and a valve device as defined previously, in which the hermetic enclosure is formed as an envelope box enclosing the electrochemical cells. The present invention also relates to an electric or hybrid vehicle, comprising at least one valve device as defined previously. The invention will be further detailed by the description of non-limiting embodiments, and on the basis of the appended figures illustrating variants of the invention, in which: - [Fig.1] illustrates a side view of an electric vehicle in which the present invention is implemented; - [Fig.2] represents a schematic sectional view of an example of a battery pack according to a first embodiment, with only a few cells represented; - [Fig.3] illustrates an axial sectional view of a first example of a valve device according to the present invention, with the closed position on the left and the open position on the right; - [Fig.4] represents a view of the valve device of figure 3 in perspective and in exploded mode; - [Fig.5] illustrates an axial sectional view of the valve device with an example of a gas purge and recovery tool; - [Fig.6] illustrates a sectional and perspective view of the valve device with the associated gas purge and recovery tool, in the closed position; - [Fig.7] illustrates a sectional and perspective view of the valve device with the associated gas purge and recovery tool, in the open position; - [Fig.8] illustrates a perspective view of an example of a gas purging and recovery tool; - [Fig.9] illustrates a second example of a valve device according to the present invention; - [Fig.10] illustrates a third example of a valve device according to the present invention, with the closed position on the left and the open position on the right; - [Fig.11] illustrates a front view of the piston, seen from the rear according to the third example of valve arrangement. In the various figures, the same references designate identical or similar elements. For reasons of clarity of the presentation, some elements are not necessarily shown to scale. It should be noted that the chemical elements contained inside the battery cells have not been shown in the figures.

[0043] With reference to Figures 1 and 2, a battery pack 1 used in an electric vehicle is now described. The battery pack comprises electrochemical cells. For example, electrochemical cells are based on Lithium-Ion type electrochemistry. However, it should be noted that the presentation can be applied to any electrochemical variant of electrochemical cells for traction batteries of electric vehicles. Regarding the amount of energy stored in the battery pack, we are talking in practice about a significant amount of energy, several tens of kWh. A 100% electric vehicle battery has an energy storage capacity typically between 40 kWh and 100 kWh, depending on the target range, weight and consumption of the vehicle. The number of electrochemical cells can range from 20 to 200, without excluding a larger number. Battery pack 1 is installed in the floor area of ​​the vehicle 7 shown here. The vehicle can be of any type, whether passenger car or commercial vehicle, e.g., sedan, station wagon, SUV, minivan, van, truck. Off-road vehicles, e.g., recreational vehicles, are also considered. Watercraft are also not excluded.

[0047] A battery management computer 74 is provided (this computer is called in the jargon of the profession BMS from the English Battery Management System), in charge of monitoring the operation of the battery to periodically calculate its state of charge, to isolate if necessary the battery pack from the rest of the high voltage electrical network of the vehicle, to monitor the temperature of the cells or cell modules and to cooperate with a cooling system in order to maintain the cells in an optimal temperature range. The battery pack 1 comprises an envelope housing enclosing the electrochemical cells C. The envelope housing forms a hermetic envelope EH. The envelope housing comprises a valve device 2 configured to retain and selectively release a pressurized gas mixture contained in an interior volume V1 of the envelope housing. The envelope housing comprises a base plate 71 (e.g. cooled) and an upper casing 72 as known per se and therefore not described in detail here. Turning to Figures 3 to 8, an example of a valve device 2 according to a first embodiment is discussed. The valve device 2 is received in a round hole 47 of diameter D3 in the wall 14 of the box. According to one example, the valve device 2 is positioned on the edge of the box as illustrated in Figure 1. Other positions are of course possible with any orientation. According to one option, a deflector or a duct is provided to channel the hot gas flows that can exit the interior volume V1 through the valve device 2 to the ground. [0 The valve device 2 comprises a base 3 and a piston 4 mounted movably along a valve axis A relative to the base, the piston being returned to a rest position by an elastic element 5 discussed later. Base The base 3 has a generally revolutionary shape around the valve axis A. The base comprises a sleeve 31 with an internal diameter D2 and an external diameter D30 and an annular rim 32 arranged at one end of the sleeve, here on the external side relative to the internal volume of the airtight enclosure.

[0057] The annular rim 32 has a radial dimension larger than the outer diameter of the sleeve. The annular rim 32 forms a bearing surface and bears externally on the rim of the hole 47. Base 3 is made of aluminum or rigid plastic polymer, HDPE or other for example. The sleeve 31 comprises a housing 18 in an internal radial position in which the helical spring 5 is housed. The radial depth of said housing is slightly greater than the thickness of the metal wire which constitutes the helical spring. The length in the axial direction of the housing 18 makes it possible to house the helical spring without constraint or with a slight prestress as well as the collar 45 of the piston which will be seen below. The outer diameter of the sleeve D30 is slightly smaller than the diameter D3 of the hole 47. Radial passages 11 are provided, passing through the sleeve. In the example illustrated, these are radial axis holes distributed regularly around the circumference of the sleeve 31. These passages 11 are called here first radial passages. The number of passages can be any, for example 4, 6, 8 or more. The first radial passages 11 connect the interior volume V1 with an interior radial space 81 of the sleeve. The annular rim 32 comprises a docking face 36 on the wall. The annular rim 32 comprises a shoulder 15, facing the interior volume V1, relative to which a purging tool 9 can rest or be anchored, which will be discussed later.

[0062] The sleeve 31 comprises a valve seat 8. More precisely, the valve seat 8 is arranged on the inner side of the sleeve 31, it is a flat annular shoulder facing the inner volume V1. [0 The piston is pushed against the valve seat 8 by a helical spring 5. It should be noted that any elastic element tending to urge the piston 4 towards the outside EXT so that it comes to bear on the valve seat 8 may be suitable within the framework of the present invention. The base has an overall diameter marked D4. D4 can be chosen for example between 2 cm and 5 cm. According to an exemplary embodiment illustrated in Figure 3, the base comprises an elastic clipping tab marked 16 which locks behind the wall 14 when the base is inserted into the hole 47 from the outside. Furthermore, a sealing gasket 17 is provided interposed between the docking face 36 and the outer side 14a of the wall 14. This provides an example of a simple, hermetic mounting of the base in the hole 47 of the wall of the hermetic box. The base has an axial length L2 taken along the axis A. Piston with membrane e generally form of revolution around the valve axis A. The piston 4 can be made of aluminum or rigid plastic polymer, HDPE or other for example. The piston 4 comprises a generally cylindrical ring 41. The ring 41 delimits an internal radial space 10 of the piston. The central passage of the piston has a diameter denoted D1. D1 can be chosen for example between 1 cm and 4 cm.

[0070] The central passage of the piston being of diameter D1 and the hole in the wall being of diameter noted D3, said diameters are such that the ratio D3 / D1 is less than 1.4 and preferably the ratio D3 / D1 is less than 1.3. This characterizes the radial compactness of the solution promoted here.

[0071] Similarly, the base having an overall diameter D4, the diameters are such that the ratio D4 / D1 is less than 1.6 and preferably the ratio D4 / D1 is less than 1.5.

[0072] A collar 45 is provided which extends from the ring radially outwards. Said collar comprises a bearing surface 48, which presses flat on the valve seat 8. The ring 41 is of revolution around a valve axis A. The ring 41 comprises a radially inner annular groove 19 which receives the peripheral edge 62 of the membrane. The piston 4 has an axial length L1 taken along the axis A. The axial length L1 is slightly smaller than the axial length L2 of the base 3. According to a particular characteristic, the axial length L1 of the piston is at least equal to 40% of the internal diameter D2 of the sleeve 31 of the base, so as to ensure positive guidance and good quality sliding of the piston and so as to prevent any jamming and / or skewing.

[0077] Second radial passages 12 are provided passing through the tubular ring 41 of the piston and communicating an outer radial space of the piston with the inner radial space 10 of the piston, in front of the breakable membrane, that is to say on the axially outer side relative to the breakable membrane. The piston comprises a breakable membrane 6 which normally closes a central passage of the piston delimited radially by the tubular ring 41.

[0079] The breakable membrane 6 has a breaking strength up to a first breaking strength threshold in response to a pressure difference across its faces (i.e. a higher pressure on one face than on the other).

[0080] The breakable membrane 6 can be made of various plastic materials with a certain flexibility such as neoprene, Teflon™, but more generally any synthetic polymer such as polyamide, polyester, polyethylene. A membrane made of rubber or polyurethane is also possible. A membrane in the form of a thin metal sheet or a metal / plastic composite sheet may also be suitable.

[0081] The breakable membrane is a disc made of synthetic polymer material, fixed along its peripheral edge 62 to the piston ring, on the radially inner side, for example in an inner annular groove 19. The breakable membrane 6 has a constant general thickness of between 0.1 mm and 2 mm, preferably between 0.2 mm and 1 mm depending on the material chosen. As seen in Figure 4, the breakable membrane 6 has at least one weakening groove marked 61. The breakable membrane 6 is designed to be able to tear when the pressure inside the internal volume V1 becomes substantially higher than the external pressure. The pressure differential which causes the membrane to rupture can be chosen between 0.5 bar and 3 bar, and preferably between 1 bar and 2 bar.

[0085] Once the breakable membrane 6 has been broken, it allows gas to pass as needed over a passage section which can extend as far as the area delimited inside the tubular ring of the piston. After rupture, the membrane is deconstructed as illustrated by the example shown in Figure 3A at reference 60. When a force is exerted on the piston 4 directed towards the inside of the airtight box, represented by the arrow marked P in figure 3B, the piston is moved to the left in figure 3, and the helical spring 5 is compressed. In this position, the collar 45 and its bearing surface 48 are distant from the valve seat 8 and a gas flow can follow a path represented by dotted lines and marked F1. The purge path F1 passes, from the interior volume V1, through the first radial passages 11 then through the second radial passages 12 and ends up exiting in the central zone 10 of the piston. [0 Gas can thus be sucked from the inside of the airtight enclosure to the outside, if necessary using a tool which will now be described. Bleeding tool provides for the use of a gas purge and recovery tool 9, shown alone in Figure 8. The tool 9 includes a gas collection cover 91. In the actual use configuration (i.e. coupled purge tool), the cover 91 covers the area of ​​the valve device 2 as shown in Figure 5.

[0091] A sealing O-ring marked 85 is provided which rests on the front face 37 of the annular rim 32 of the base. This prevents a leak between the annular rim 32 and the gas collection cover 91.

[0092] The tool 9 comprises a system for locking the coupled position by means of three locking fingers 96. Each locking finger 96 comprises a ball 86 forced radially inwards by a spring. In the actual use configuration, the balls 86 are wedged behind the shoulder 15 already mentioned provided on the annular rim 32 of the base.

[0093] In alternative embodiments, any other locking system may be used, for example a bayonet movement system, screwing, a removable hook system, etc. The tool 9 comprises an internal channel 29 and a suction line 28, allowing the inner area of ​​the cover to be fluidically connected with a suction device 26 and a collection container 24.

[0095] The tool 9 comprises a pusher 90 which has a rim of diameter similar to that of the piston which is adapted to push the piston against the helical spring 5. The pusher 90 comprises a hub pierced with orifices 88, the hub and the rim preferably being formed as a single piece. The pusher 90 is connected to an actuating rod 92, movable along the axis by a handle actuating system, seen below. The tool 9 comprises a positioning handle 97, mounted on legs 95 fixed to the cover 91. Once the cover 91 is installed around the flange-forming edge 32 of the base, the positioning handle 97 is then located in the axis of the valve device A; this allows a logical and intuitive positioning from the user's point of view.

[0097] The tool 9 comprises two actuating handles 98, 99. Thanks to the toggle-type joint 87, it is sufficient to squeeze one handle 98 towards the other 99, to activate the purge, because in fact this causes the actuating rod 92 to move towards the inside of the valve device (i.e. to the left in the figures). It follows that the actuating rod 92 moves the pusher 90 which in turn pushes the piston 4 of the valve device, which opens the passage path (respective paths F1, F2, F3 according to each of the three exemplary embodiments). The knee joint 87 comprises two articulation joints X1, X2, connected by a short connecting rod 82, which allows the axis X3 to always be in line with the general valve axis A and to push well in the axis. The arm 100 extending the handle 98 is articulated on the actuating rod 92 by means of an articulation of axis X3.

[0100] The arm 101 extending the handle 99 is fixedly mounted relative to the cover 91. Any other means for pushing the piston 4 against the spring 5 can be used within the framework of the present invention.

[0102] A seal 84 is provided at the passage of the rod 92 through the cover 91, the location of axial sliding. The purge path of the gas F1 passes through the first radial passages 11, the second radial passages 12, the internal space of the piston 10, the orifices 88 of the pusher, the internal channel of the cover 29 and the connecting pipe 28. In Figure 9, a second exemplary embodiment is shown. Anything not described again here is considered similar or identical to what was previously described for the first exemplary embodiment.

[0105] In this second example, the second passages in the form of radial orifices are replaced by external axial grooves 67 provided on the outside of the piston ring. The external axial grooves 67 are made between the collar and the front edge 49 of the piston.

[0106] The path taken by the gases in the purge configuration is represented by the dotted arrow marked F2.

[0107] The purge path F2 passes, from the interior volume V1, through the first radial passages 11 then through the external axial grooves 67 and exits through the peripheral zone of the piston. [1 In Figure 9, a variant is illustrated concerning the positioning and holding of the breakable membrane 6. The piston 4 comprises an annular shoulder 44, facing backwards, on which the breakable membrane 6 rests. A ring 43 is then installed to hold the membrane against the annular shoulder 44. The ring 43 can be screwed, clipped, or fixed by structural gluing. Any other means of mounting and holding the breakable membrane can be used within the framework of the present invention.

[0109] In Figures 10 and 11, a third exemplary embodiment is shown. Anything not described again here is considered similar or identical to what was previously described for the first exemplary embodiment. In this third example, not only are the second passages in the form of radial orifices replaced by external axial grooves 67 provided on the outside of the piston ring, but also the first passages in the form of radial orifices are replaced by external axial grooves 64. The external axial grooves 64 are made between the rear edge 42 of the piston and the collar 45. To complete, additional grooves are provided in the collar 45, a groove 65 in the radial direction arranged at the interface with the spring (so that the spring, even when compressed, does not prevent the gas from passing) and a groove 66 in the axial direction to allow the gas to pass outside the collar 45. The path taken by the gases in the purge configuration is represented by the dotted arrow marked F3. The purge path F3 passes, from the interior volume V1, through the external axial grooves 64, then through the radial grooves 65, then through the axial groove 66 on the collar, then the external axial grooves 67 and exits through the peripheral zone of the piston. As illustrated in Figure 11, the groove arrangements as described above are 4 in number in the example presented, regularly distributed around the circumference of the piston, but of course the groove arrangements could be more numerous around the circumference. The total passage section can be adjusted according to the time required for the purging operation. We note that in this third embodiment, the gas passes through gaps between the piston and the sleeve, without passing through the central zone of the piston. In this third embodiment, the base 3 and the piston 4 can be manufactured by molding without having to perform a rework to drill the radial holes. In Figure 10, there is also illustrated an alternative mounting of the sleeve 31, here made in two parts, to facilitate the mounting of the flanged piston inside the sleeve. A rear closing ring 63 is provided, fixed by screws 68 to the cylindrical main body of the sleeve. Furthermore, the mounting of the socket in the hole 47 of the wall 14 may use a retaining ring 69 which makes it possible to sandwich the wall 14 between said retaining ring 69 and the docking face 36 of the annular rim 32. It is noted that during the purging operation, it may be provided that a breathing valve (of the type described in the introduction) allows fresh air to enter from the outside, in order to facilitate the drawing and extraction of the gases present in the airtight box at the start of the purging, and to avoid having to create too strong a depression to suck.

[0120] It is noted that the breakable membrane 6 is designed to withstand the depression caused by the suction system 28, without tearing.

Claims

CLAIMS 1. Valve device (2) configured to retain and selectively release a gas mixture contained in an interior volume (V1) of a hermetic enclosure (EH), the valve device comprising a base (3) and a piston (4) mounted movably along a valve axis (A) relative to the base between a closed rest position and an open position, the base comprising a sleeve (31) and an annular rim (32), the base being hermetically mounted in a hole (47) of a wall (14) of the hermetic enclosure, in which the piston, in the closed rest position, is pushed against a valve seat (8) by an elastic element (5), in which the piston comprises a ring (41) delimiting an interior radial space of the piston, characterized in that the piston comprises a breakable membrane (6) normally closing a central passage of the piston delimited radially by the ring,the breakable membrane having a breaking strength up to a first breaking strength threshold in response to a pressure difference at its faces, the base comprising a shoulder (15), facing the interior volume, relative to which a purge tool (9) configured to push the piston back to the open position can bear, the valve device comprising purge passages (11, 12, 64, 65, 66, 67) communicating, in the open position of the piston, the interior volume (V1) with a space outside (EXT) of the hermetic enclosure., 2. Valve device according to claim 1, in which the passages comprise first radial passages (11) passing through the socket of the base and communicating the interior volume (V1) with an interior radial space (81) of the socket.

3. Valve device according to any one of claims 1 to 2, wherein the base and the piston preferably have shapes generally of revolution around the valve axis (A) and the elastic element (5) is formed as a helical spring.

4. Valve device according to any one of claims 1 to 3, in which the breakable membrane (6) is a disc made of synthetic polymer material, fixed along its peripheral edge (62) to the piston ring, on the radially inner side.

5. Valve device according to any one of claims 1 to 4, in which the purge passages comprise second radial passages (12) passing through the ring of the piston and communicating an outer radial space of the piston with an inner radial space of the piston (10), on a front side of the breakable membrane.

6. Valve device according to any one of claims 1 to 5, in which the valve seat (8) is a shoulder of the sleeve (31), on which a collar (45) projects radially outwards from the piston ring is supported.

7. Valve device according to any one of claims 1 to 6, in which the central passage of the piston has a diameter denoted D1 and the hole in the wall has a diameter denoted D3, said diameters being such that D3 / D1 < 1.4, preferably D3 / D1 < 1.

3.

8. A valve system comprising a valve device according to any one of claims 1 to 7, and a gas purge and recovery tool (9) configured to selectively push the piston (4) against the elastic element (5) and thereby move the piston to the open position.

9. A valve system according to claim 8, wherein the gas purge and recovery tool (9) comprises a positioning handle (97) and at least one actuating handle (98,99).

10. A valve system according to claim 8 or claim 9, wherein the gas purge and recovery tool (9) comprises a gas collection cover (91) and a suction line (28).

11. Battery pack comprising a plurality of electrochemical cells (C) of an electric battery, and a valve device according to any one of claims 1 to 7, in which the hermetic enclosure (EH) is formed as an envelope box enclosing the electrochemical cells.

12. Electric or hybrid vehicle, comprising at least one battery pack according to claim 11.

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