METHOD AND DEVICE FOR MEASURING THE MECHANICAL STRENGTH OF A COMPRESSED GAS ACCUMULATOR FOR A VEHICLE

Description

[0001] The invention relates to the field of vehicles, such as for example motor vehicles, trucks, buses, trains, airplanes, motorcycles or even boats. The invention relates more particularly to a method for measuring the mechanical strength of a pressurized gas storage tank for a vehicle. The invention also relates to a device for measuring the mechanical strength of a pressurized gas storage tank for a vehicle.

[0002] A pressurized gas storage tank for a vehicle is typically composed of an internal envelope called a liner, which serves as a seal against the gas contained in the tank. The liner has at least one opening, which is topped by a nozzle. The liner and the nozzle are surrounded by a reinforcing structure, generally made by winding strips of composite material based on a thermosetting polymer, for example based on epoxy or polyurethane resin, filled with glass and / or carbon fibers. Thus, the "plastic" type liner includes at least one opening for filling and emptying the tank. It is manufactured by injection or rotational molding or by extrusion-blow molding of a thermoplastic or thermosetting polymer material (abbreviated as "thermodur") such as, for example, polyethylene, polyamide, polyphthalamide, polyurethane, silicone. Such a tank is called type IV.Alternatively, the tank is simply made of a thermoplastic composite shell without a liner. Such a tank is called type V.

[0003] Such pressurized gas storage tanks for vehicles are subjected to mechanical resistance tests. These tests consist of subjecting said tanks to pressures, P int ., of the order of 1.5 times the nominal pressure, P n . This nominal pressure, P n , is generally of the order of 350 to 700 bar depending on the use of the pressurized gas storage tanks for vehicles.

[0004] When testing the mechanical strength of pressurized gas storage tanks for vehicles, the pressurization of the tanks is carried out using a liquid, generally water. The tanks to be tested are filled with the liquid and the pressure exerted, P int ., is increased to 1.5 times the nominal pressure, P n . A measurement of the deformation of the tank is carried out once the test pressure, P int ., is reached or after a certain period of time during which the tank is maintained at the test pressure, P int . Such mechanical strength tests correspond in particular to measurements of elastic and permanent expansions, as described in the European standard EC79. Examples of mechanical strength tests are provided in JP S57 154032 A and DE 10 2018 201494 A1.The test according to JP S57 154032 A comprises a step of introducing a bladder-shaped member into a tank, a step of filling the member with water and a step of pressurizing the water, in order to exert pressure on the walls of the tank.

[0005] At the end of the mechanical resistance tests, the tanks are emptied of the test liquid and must be dried, particularly for their use for the storage of pressurized gas. The tank drying operation is relatively long and complex because the drying must be complete, which significantly lengthens the production cycle times. In addition, pressurized gas storage tanks for vehicles sometimes include a polyamide "liner", which is a water-sensitive polymer due to its ability to absorb water, thus modifying the properties of the polyamide.

[0006] The invention aims in particular to overcome these drawbacks of the prior art.

[0007] More specifically, an objective of the invention, in at least one of its embodiments, is to implement a method for measuring the mechanical resistance of a storage tank for pressurized gas for a vehicle which has shorter cycle times than existing methods.

[0008] Another objective of the invention, in at least one of its embodiments, is to provide a device for measuring the mechanical resistance of a storage tank for pressurized gas for a vehicle.

[0009] According to a particular embodiment, the invention relates to a method for measuring the mechanical resistance of a storage tank for pressurized gas for a vehicle.

[0010] According to the invention, such a method is set forth in claim 1.

[0011] The general principle of the invention is based on the use of an expandable element inserted into the pressurized gas storage tank for vehicles during the mechanical strength test. This expandable element is filled with liquid during the test and allows the pressurized gas storage tank for vehicles to be pressurized while avoiding direct contact between the liquid and the inner walls of the pressurized gas storage tank for vehicles.

[0012] Thus, the invention is based on a completely new and inventive approach to implementing a method for measuring the mechanical strength of a pressurized gas storage tank for a vehicle that does not require a long drying step of the tested tank after carrying out the test and makes it possible to avoid possible degradation of the liner constituting the interior of the tank. Indeed, when the expandable element is removed from the pressurized gas storage tank for a vehicle after the test, the interior walls are still dry. Furthermore, the method according to the invention makes it possible to avoid the use of a drying device and thus reduces the cost of producing and testing a pressurized gas storage tank for a vehicle.

[0013] The expandable element is impermeable to liquid. The term impermeable to liquid means that during the test the liquid does not come into contact with the inner walls of the pressurized gas storage tank for vehicles by diffusion through the expandable element. The expandable element is, for example, a large-surface sheet capable of covering the inner walls of the pressurized gas storage tank for vehicles under the effect of the weight of the liquid.

[0014] An evacuation of the gas contained in the expandable element and, if necessary, of the gas included in the tank is provided during the step of filling the expandable element with the liquid. This evacuation is carried out with a gas evacuation means. This gas is, for example, air or a tracer gas. A tracer gas advantageously makes it possible to combine the mechanical resistance test with a leak test of the pressurized gas storage tank for vehicles. Indeed, if, for example, a volume of tracer gas is enclosed between the expandable element and the internal wall of the tank, pressurizing the expandable element causes this volume of tracer gas to be pressurized. Then, in the event of a leak, it is possible to detect the tracer gas outside the pressurized gas storage tank for vehicles.In addition, since the volume of tracer gas carried at high pressure is reduced compared to existing leak testing processes, the energy released in the event of a tank rupture is reduced, which simplifies the sizing of safety devices. This results in significant savings in cycle time, investments and consumables specific to leak testing.

[0015] The step of connecting the expandable element is preferably carried out before the step of introducing the expandable element into the pressure storage tank through the at least one opening.

[0016] The step of measuring a possible deformation of the pressurized gas storage tank for vehicles is, for example, a dimensional measurement such as measuring the diameter and length of the tank. This dimensional measurement can be carried out using a camera, a 3D scanner, a distance measurement using a laser or a probe of the LVDT (Linear Variable Differential Transformer) type, by contact with a comparator-type system. According to another example, the measurement of a possible deformation of the pressurized gas storage tank for vehicles is a volumetric measurement corresponding to the measurement of the quantity of liquid added during the pressure increase. If the measurement of a possible deformation of the pressurized gas storage tank for vehicles is a dimensional measurement, it must make it possible to calculate a volumetric expansion.This step of measuring possible deformation of the pressurized gas storage tank for vehicles aims to determine that the volumetric expansion is maintained within a tolerance range. Said tolerance range is such that a tank must not deform by more than 10% of the average deformation of all the tanks in the same production batch.

[0017] Advantageously, the method for measuring the mechanical resistance of a pressurized gas storage tank for a vehicle is such that the expandable element is a bladder.

[0018] Thus, a bladder-type expandable element allows easier insertion of the expandable element into the vehicle pressurized gas storage tank.

[0019] The method for measuring the mechanical strength of a pressurized gas storage tank for a vehicle is such that it comprises a step of stretching the expandable element in the length direction.

[0020] Thus, stretching the expandable element lengthwise allows for easier insertion of the latter into the tank via the opening, called the first opening, more particularly when the expandable element is a bladder whose outer diameter is larger than the inner diameter of the opening of the tank, called the first opening, through which it is inserted. Such a step makes it possible to reduce the outer diameter of the bladder by stretching lengthwise. In addition, stretching the expandable element lengthwise makes it possible to standardize the stresses applied to the expandable element when it is pressurized. Therefore, the pressure, P int ., applied to all of the inner walls of the pressurized gas storage tank for vehicles is standardized, which contributes to making the mechanical strength measurement method more reliable and improving its reproducibility.

[0021] This lengthwise stretching step is carried out before, during or after the insertion of the expandable element into the pressurized gas storage tank for a vehicle, thus making it possible to bring the expandable element into contact more quickly with all of the interior walls of the pressurized gas storage tank for a vehicle, and in particular the bottom of the tank. Thus, in the case of an expandable element in the form of a bladder having an outside diameter smaller than the inside diameter of the opening of the tank through which it is inserted, this step makes it possible to reduce the duration of the test. The first stretching means allowing the stretching of the expandable element is, for example, a pressure differential between the inside and the outside of the bladder.

[0022] The method for measuring the mechanical resistance of a pressurized gas storage tank for a vehicle is such that it comprises a step of assembling a first coupling means to the expandable element.

[0023] Thus, this step of assembling a first coupling means to the expandable element makes it possible to obtain good sealing of the assembly obtained and to maintain the expandable element during the step of filling the latter with the liquid. The coupling element also makes it possible to connect the internal volume of the expandable element to a device for pressurizing by the fluid.

[0024] The method for measuring the mechanical resistance of a pressurized gas storage tank for a vehicle is such that the step of stretching the expandable element is carried out by at least one translational movement of a first stretching means relative to the first coupling means.

[0025] Thus, a step of stretching the expandable element carried out by at least one translational movement of a first stretching means relative to the first coupling means makes it possible to use the first coupling means in counter-support of the first stretching means.

[0026] The first stretching means for stretching the expandable element may be a weight inserted into the expandable element such as a ball or the simple weight of a portion of the liquid used to perform the mechanical strength test. The first stretching means for stretching the expandable element may also be a rod or a bar which is introduced into the opening of the pressurized gas storage tank for vehicles following the expandable element. Alternatively, the first stretching means for stretching the expandable element may also be respectively a rod provided with a means for gripping the expandable element or a magnetized rod for example which is introduced into the pressurized gas storage tank for vehicles through a second opening located relative to the tank opposite the opening, called the first opening, through which the expandable element is introduced.In the case of a magnetic rod, this is used in addition to a metal ball having ferromagnetic properties, the magnetic rod and the metal ball being located on either side of the expandable element.

[0027] According to a preferred implementation of the preceding embodiment of the invention, the method for measuring the mechanical resistance of a storage tank for pressurized gas for a vehicle is such that the first stretching means is a pipe for filling the expandable element with liquid.

[0028] Thus, the use of a filling line as the first stretching means makes it possible to reduce the number of operations linked to the process of measuring the mechanical resistance of a pressurized gas storage tank for a vehicle. A single means is used for stretching the expandable element and filling it with liquid.

[0029] According to a preferred implementation of the preceding embodiment of the invention, the method for measuring the mechanical resistance of a storage tank for pressurized gas for a vehicle is such that the filling pipe of the expandable element with the liquid has an outside diameter less than the inside diameter of the at least one opening, called the first opening.

[0030] Thus such a pipe can be introduced into the tank through at least one opening, called the first opening, this allowing easier filling with liquid. Advantageously, this pipe is used to empty the liquid contained in the expandable element.

[0031] According to a preferred implementation of the invention, the method for measuring the mechanical resistance of a storage tank for pressurized gas for a vehicle is such that the filling pipe of the liquid-expandable element passes through the first coupling means.

[0032] According to an advantageous implementation of the invention, the method for measuring the mechanical resistance of a storage tank for pressurized gas for a vehicle is such that the liquid is selected from the group of liquids consisting of water or a water-based solution, preferably the liquid is tap water, more preferably the liquid is filtered and softened tap water.

[0033] Thus, the use of liquid selected from water or water-based solutions allows the use of a liquid with a high density and readily available. Advantageously, the water contains additional solvents such as alcohol in order to obtain an azeotrope having a lower evaporation temperature than water. The use of filtered and softened tap water makes it possible to avoid the accumulation of limescale in the expandable element and / or the hydraulic circuit to which the tank is connected for the purposes of the mechanical strength test.

[0034] According to an advantageous implementation of the invention, the method for measuring the mechanical strength of a pressurized gas storage tank for a vehicle is such that the expandable element is based on an elastomer more particularly selected from the group of Butadiene-Acrylonitrile rubber (NBR), Hydrogenated Butadiene Acrylonitrile (HNBR), Carboxylated Nitrile (XNBR), Ethylene-Propylene-Diene rubber (EPDM), Polysiloxane-Vinyl-Methyl Silicone (VMQ), Fluorinated rubber (FKM), Perfluorinated rubber (FFKM), Chloroprene (CR), Polyacrylate (ACM), Ethylene-acrylate (AEM) and natural rubber. Preferably, the elastomer has a significant stretching capacity, for example a stretching capacity of approximately 400%.The material constituting the expandable element advantageously has a low coefficient of friction with the material of the internal wall of the pressurized gas storage tank so as to be able to slide freely during its expansion without creating too much local stretching, which could lead to rupture of the expandable element. Advantageously, the coefficient of friction is reduced by applying a specific product to the external surface of the expandable element, said product leaving no moisture and having a tendency to evaporate very quickly.

[0035] Advantageously, the internal geometry of the pressurized gas storage tank for vehicles is free of sharp angles in order to avoid locally excessive stretching of the expandable element, which could lead to its rupture.

[0036] According to an advantageous implementation of the invention, the method for measuring the mechanical resistance of a storage tank for pressurized gas for a vehicle is such that the coupling means is secured to the opening, called the first opening, of said tank by threading.

[0037] This way, the recoil force exerted by the liquid pressure during the test is better absorbed.

[0038] According to an advantageous implementation of the invention, the method for measuring the mechanical resistance of a storage tank for pressurized gas for a vehicle is such that the gas contained in said tank is evacuated during the filling of the expandable element, said gas being air for example.

[0039] This minimizes residual gas pockets and better controls the geometry of the expandable element after expansion.

[0040] The gas may be freely discharged through the opening of the vehicle pressurized gas storage tank or may be discharged through vents provided for this purpose in the coupling means, if the latter is secured to the tank opening. Finally, the gas may also be discharged through a second opening if the tank has two openings.

[0041] According to an advantageous implementation of the invention, the method for measuring the mechanical resistance of a storage tank for pressurized gas for a vehicle is such that it comprises, before the step of filling the expandable element with liquid, a step of pre-filling the expandable element with liquid.

[0042] During pre-filling, the lower part of the expandable element inflates to come into contact with the inner wall of the tank, forcing air out of the tank. Pre-filling thus prevents air bubbles from becoming trapped between the expandable element and the tank, which could distort the process for measuring the mechanical strength of the tank. This also helps to prevent damage to the expandable element when implementing the process for measuring the mechanical strength of a pressurized gas storage tank for a vehicle.

[0043] According to an advantageous implementation of the invention, the method for measuring the mechanical resistance of a storage tank for pressurized gas for a vehicle is such that it comprises, before the step of filling the expandable element with liquid, a step of inflating the expandable element.

[0044] This inflation step allows for uniform stretching of the expandable element to ensure uniform contact between the expandable element and the inner wall of the tank, thereby preventing wrinkles from forming on the surface of the expandable element. This improves the reliability and reproducibility of the method for measuring the mechanical strength of a pressurized gas storage tank for a vehicle. This also helps to prevent damage to the expandable element when implementing the method for measuring the mechanical strength of a pressurized gas storage tank for a vehicle.

[0045] The invention also relates to a device for measuring the mechanical resistance of a storage tank for pressurized gas for a vehicle, said device being capable of implementing the method according to the invention.

[0046] According to an embodiment in accordance with the invention, the device for measuring the mechanical resistance of a storage tank for pressurized gas for a vehicle is stated according to claim 9.

[0047] The expandable element is capable of receiving liquid even if it is only partially inserted into the pressurized gas storage tank for vehicles. This is the case when the weight of the liquid allows the expandable element to be inserted into the tank.

[0048] According to an advantageous embodiment, the device for measuring the mechanical resistance of a storage tank for pressurized gas for a vehicle is such that the expandable element is a bladder.

[0049] According to an advantageous embodiment, the device for measuring the mechanical resistance of a storage tank for pressurized gas for a vehicle is such that the first stretching means is a rod.

[0050] According to an advantageous embodiment, the device for measuring the mechanical resistance of a storage tank for pressurized gas for a vehicle is such that the rod is the liquid pipe, preferably a cane.

[0051] According to an advantageous embodiment, the device for measuring the mechanical resistance of a storage tank for pressurized gas for a vehicle is such that it comprises a pump capable of evacuating the liquid contained in the expandable element.

[0052] According to an advantageous embodiment, the device for measuring the mechanical resistance of a storage tank for pressurized gas for a vehicle is such that the expandable element comprises a zone for receiving the first coupling means.

[0053] Thus, a receiving area of the first coupling means on the expandable element allows for better assembly between the first coupling element and the expandable element. This area can be produced in the case of a bladder materialized by the presence of projections on the outer wall of the bladder in an area of smaller diameter.

[0054] According to an advantageous embodiment, the device for measuring the mechanical resistance of a storage tank for pressurized gas for a vehicle is such that it comprises means for introducing a gas into the expandable element and / or the tank. Preferably, the means for introducing a gas correspond to the means for evacuating gas contained in the expandable element and / or the tank.

[0055] Other characteristics and advantages of the invention will appear more clearly on reading the following description of a preferred embodiment, given as a simple illustrative and non-limiting example, and the appended drawings, among which: there figure 1 illustrates the steps of providing a pressurized gas storage tank for a vehicle comprising at least one opening for introducing an expandable element into the pressurized gas storage tank for a vehicle through the at least one opening and connecting the expandable element to a liquid conduit; figure 2 illustrates an embodiment of a first coupling means allowing the connection of the expandable element and the liquid conduit to the at least one opening of the storage tank for pressurized gas for a vehicle; figure 3 illustrates the step of introducing the expandable element into the storage tank for pressurized gas for a vehicle through the at least one opening; figure 4 describes the end of the step of introducing the expandable element into the storage tank for pressurized gas for a vehicle through at least one opening; figure 5 illustrates the step of pre-filling the expandable element within the reservoir with a liquid; the figure 6 illustrates the step of inflating the expandable element within the tank; figure 7 illustrates the step of filling the expandable element within the reservoir with liquid; and the figure 8 illustrates the end of the filling stage and the start of pressurization, P int ., of all the interior walls of the tank by means of the liquid-filled expandable element.

[0056] We present, in relation to the figure 1 , a method of implementing the steps of providing a pressurized gas storage tank for a vehicle 1 comprising at least one opening 10 and connecting the expandable element 2 to a liquid pipe 3 according to the invention. The opening 10 is surmounted by a metal end piece making it possible to connect the tank 1 to the filling and / or emptying circuit of the tank (not shown). The pressurized gas storage tank for a vehicle 1 subjected to the mechanical resistance test comprises at least one opening 10, called the first opening, through which the expandable element 2, which is a bladder 20 made of elastomeric material, will be introduced. The tank comprises a second opening 11 located opposite the opening 10 through which the expandable element 2 will be introduced. The second opening 11 is surmounted by a metal end piece making it possible to connect the tank 1 to the filling and / or emptying circuit of the tank (not shown).This second opening 11 is left open. The bladder 20 made of elastomeric material is connected to a liquid pipe 3. The liquid pipe 3 is in the form of a rod 30. The bladder 20 is assembled to a first coupling means 4 in a sealed manner. The liquid pipe 3 passes through the first coupling means 4. This liquid pipe 3 may protrude outside the bladder 20 by a distance equivalent to the internal length of the tank 1, for example more than 2 m. For shorter tanks, it will protrude less.The length of this liquid pipe 3 inside the bladder 2 in the case of a rigid cane is less than the length of the tank to be tested, preferably the length of this liquid pipe 3 inside the rigid bladder 2 is close to the length of the tank to be tested, so as to stretch the expandable element 2 up to a distance from the opposite part of the tank 1, opposite part with respect to the opening 10, called the first opening, equivalent to approximately the internal radius of the tank 1. In this way the expandable element 2 can stretch in a more or less uniform manner in all directions.

[0057] There figure 2 illustrates an embodiment of the first coupling means 4. The first coupling means 4 comprises a main body 41 which is hollow so that it can be traversed over its entire length by the liquid conduit 3. The main body 41 can further accommodate an end portion of the expandable element 2, open, so that it is positioned in the main body 41 and around the liquid conduit 3.

[0058] The first coupling means 4 is configured to be able to be fixed, here by screwing, in a sealed manner in the at least one opening 10 of the pressurized gas storage tank for vehicle 1. For this purpose, the first coupling means 4 comprises at least one annular seal 42 making it possible to ensure the sealing of the connection between the main body 41 and the pressurized gas storage tank for vehicle 1. The first coupling means 4 is further configured to ensure a tight and sealed fixing of the end part of the expandable element 2 in the main body 41. This sealing is here ensured by other annular seals 42.

[0059] The first coupling means 4 comprises a filling member 43 which is attached in a sealed manner partly inside the main body 41, the sealing being achieved here using an additional annular seal 42. The filling member 43 comprises an air passage 44 making it possible, alternately, to inject air into the expandable element 2 and to empty the expandable element 2 of the air it contains. The filling member 43 comprises a pressure reducer (not shown) configured to regulate the air pressure in the expandable element during its filling and emptying.

[0060] There figure 3 illustrates a method of implementing the step of introducing the expandable element 2 into the pressurized gas storage tank for a vehicle 1 through at least one opening 10. Before implementing this step of introducing the expandable element 2, which is a bladder 20 made of elastomeric material, said bladder is stretched lengthwise by moving a first stretching means 5. The step of stretching the expandable element 2 is carried out by at least one translational movement of a first stretching means 5 relative to the first coupling means 4. This movement is represented by the arrow in broken lines. This stretching step makes it possible to reduce the section of the expandable element 2 and thus makes it easier to introduce the bladder 20 into the tank 1 through the opening 10, called the first opening. The first stretching means is advantageously constituted by the liquid pipe 3 in the form of a rod 30.During this step, the second opening 11 is left open.

[0061] There figure 4 illustrates the end of the step of introducing the expandable element 2 into the pressurized gas storage tank for vehicle 1 through the at least one opening 10. It can be seen that the movement of the first stretching means 5 is complete, said first stretching means 5 comprising the liquid pipe 3 in the form of a rod 30. At the end of the step of introducing the expandable element 2 into the pressurized gas storage tank for vehicle 1, the first coupling means 4 is positioned on the at least one opening 10, called the first opening. The first coupling means 4 comprises a closing means 40 capable of being inserted into the at least one opening 10, called the first opening. The first coupling means 4 can thus, for example, be screwed into the opening 10 to be secured to the tank and thus not move back under the pressure force during the mechanical strength test.The expandable element 2 which is a bladder 20 made of elastomeric material is still free of liquid. The second opening 11 which was open is then closed using a second closing means 110. To control the positioning of the expandable element 2 in the reservoir 1, the movement of the first stretching means 5 is carried out until it comes into abutment against the second closing means 110, so that the first stretching means 5 and the expandable element 2 are in abutment against the second closing means 110.

[0062] There figure 5 illustrates the step of pre-filling the expandable element 2 within the pressurized gas storage tank for vehicle 1 with a liquid 6. The filling of the expandable element 2 which is a bladder 20 made of elastomeric material is carried out via the liquid pipe 3 which is in the form of a rod 30, said liquid pipe 3 having served as a first stretching means 5 of the expandable element 2. The liquid pipe 3 passes through the first coupling means 4. The first coupling means 4 comprises a closing means 40 inserted into the at least one opening 10, called the first opening. During this pre-filling step, the expandable element 2 is filled with liquid to approximately 10% of the internal volume of the tank 1 by means of the liquid pipe 3. As shown in the figure 5 , the length of the liquid pipe 3 allows the liquid to be introduced into the expandable element in the lower part thereof. From then on, the lower part of the expandable element 2 expands to come into contact with the internal wall of the tank 1 by expelling the air from the tank through the air passage 44 of the filling member 43, the movement of this air being represented by the arrows in broken lines. The pre-filling thus makes it possible to prevent air bubbles from becoming trapped between the expandable element 2 and the internal wall of the tank 1, which could distort the method for measuring the mechanical strength of the tank. The dotted arrows indicate the inlet of liquid 6 into the bladder 20. The liquid used is selected from the group of liquids consisting of water or water-based solution, preferably the liquid is tap water, more preferably the liquid is filtered and softened tap water.The second opening 11 is closed using the second closing means 110.

[0063] There figure 6 illustrates the step of inflating the expandable element 2 within the pressurized gas storage tank for a vehicle 1. Air is introduced into the expandable element 2 through the air duct 44 provided in the filling member 43 until an air pressure of approximately 5 bar is reached inside the expandable element. The liquid introduced into the bladder 20 in the previous step remains at the bottom thereof. This inflation step makes it possible to achieve a uniform stretching of the expandable element in order to ensure uniform contact between the expandable element and the internal wall of the tank 1, thereby preventing folds from forming on the surface of the expandable element 2.

[0064] There figure 7 illustrates the step of filling the expandable element 2 within the pressurized gas storage tank for vehicle 1. Liquid is introduced into the expandable element via the liquid line 3. During this filling, the pressure reducer allows the evacuation of the air contained in the expandable element 2, expelled by the liquid at higher pressure than the air, via the air duct 44 provided in the filling member 43. The air is kept under pressure by the pressure reducer during its evacuation so as not to break the uniform contact between the expandable element 2 and the internal wall of the tank 1, established in the previous step, during filling.

[0065] There figure 8illustrates the end of the filling step and the start of pressurization, P int ., of all the internal walls of the pressurized gas storage tank for vehicle 1 by means of the expandable element 2 filled with liquid 6. The expandable element 2 in the form of a bladder 20 fills the entire internal volume of the tank by being “glued” or pressed against the internal walls of the latter under the effect of the pressure exerted by the liquid 6. To this end, the filling member 43 is removed from the first coupling means 4 and replaced by a so-called “high pressure” sub-adapter making it possible to fill the expandable element 2 with the liquid at a high pressure. The tank is closed at its openings 10, 11. The opening 10, called the first opening, is closed using the coupling means 4 via the closing means 40. The second opening 11 is closed using the second closing means 110.The liquid line 3 is left inside the tank 1 and is left connected to the liquid circuit so as to apply a pressure on the inner walls of the tank 1 which is equal to 1.5 times the working pressure or nominal pressure. The tank 1 is subjected to said pressure for a time which can range from at least one second to in certain cases 10 minutes.

[0066] The measurement of a possible deformation of the pressurized gas storage tank for vehicles can be a dimensional measurement such as measuring the diameter and length of the tank. This dimensional measurement can be carried out using a camera, a 3D scanner, a distance measurement using a laser or a probe of the LVDT type (Linear Variable Differential Transformer), by contact with a comparator type system. The measurement of a possible deformation of the pressurized gas storage tank for vehicles can also be a volumetric measurement corresponding to the measurement of the quantity of liquid added during the pressure increase.

[0067] The tank 1 is then emptied of the liquid 6 contained in the expandable element 2. This emptying operation can be carried out via the liquid pipe 3 using a pump. The expandable element 2 is then removed from the pressurized gas storage tank for vehicles 1 through the at least one opening 10. Advantageously, the expandable element 2 is first subjected to greater suction so as to press it against the liquid pipe 3.

[0068] Ideally, the device used to implement the method for measuring the mechanical strength of a pressurized gas storage tank for a vehicle 1 is oriented vertically so that gravity helps to uniformly stretch the expandable element 2, preferably the bladder 20 under the weight of the liquid 6. Preferably, the internal geometry of the tank 1 has gentle shapes and curvatures in order to avoid locally greater stretching of the expandable element, preferably the bladder 20, which would risk tearing it. For example, if the test is carried out on a tank comprising two openings 10, 11, the second opening 11 is plugged so as to prevent the expandable element 2, preferably the bladder 20, from being pinched in an abrupt geometry, or from coming out through the second opening 11 and bursting.Advantageously, the second closing means 110 is used as the second jaw of a vice consisting of this second closing means and as the first jaw the rod 30 having also served as the first stretching means 5 of the expandable element 2, said vice clamping the expandable element 2 and making it possible to secure the stretching of the expandable element 2, preferably of the bladder, in this critical zone.

Claims

1. A method for measuring mechanical strength of a pressurized gas storage tank for a vehicle (1), said method comprising at least the following steps: • Providing a pressurized gas storage tank for a vehicle (1) having at least one opening (10); • Assembling a first coupling means (4) to an expandable element (2); • Stretching the expandable element (2) in the lengthwise direction by at least one translational movement of a first stretching means (5) with respect to the first coupling means (4); • Introducing the expandable element (2) into the pressurized gas storage tank for a vehicle (1) via the at least one opening (10); • Connecting the expandable element (2) to a pipe (3) for a liquid (6); • Filling the expandable element (2) with liquid (6); • Exerting a pressure, Pint., on all the interior walls of the pressurized gas storage tank for a vehicle (1) by means of the expandable element (2) filled with liquid (6); • Measuring a possible deformation of the pressurized gas storage tank for a vehicle (1); • Emptying the liquid (6) contained in the expandable element (2); • Removing the expandable element (2) from the pressurized gas storage tank for a vehicle (1) via the at least one opening (10).

2. The method for measuring mechanical strength of a pressurized gas storage tank for a vehicle (1) according to claim 1, wherein the expandable element (2) is a bladder (20).

3. The method for measuring mechanical strength of a pressurized gas storage tank for a vehicle (1) according to any one of the preceding claims, wherein the first stretching means (5) is a filling pipe (3) for filling the expandable element (2) with the liquid (6).

4. The method for measuring mechanical strength of a pressurized gas storage tank for a vehicle according to claim 3, wherein the filling pipe (3) for filling the expandable element (2) with the liquid (6) has an outside diameter smaller than the inside diameter of the at least one opening (10).

5. The method for measuring mechanical strength of a pressurized gas storage tank for a vehicle (1) according to any one of the preceding claims, wherein the liquid (6) is selected from the group of liquids consisting of water or water-based solution, preferentially the liquid (6) is mains water.

6. The method for measuring mechanical strength of a pressurized gas storage tank for a vehicle according to any one of the preceding claims, wherein the expandable element (2) is based on a material selected from the group consisting of acrylonitrile-butadiene rubber (NBR), hydrogenated acrylonitrile-butadiene rubber (HNBR), carboxylated nitrile (XNBR), ethylenepropylene-diene rubber (EPDM), vinyl-methyl polysiloxane silicone (VMQ), fluorinated rubber (FKM), perfluorinated rubber (FFKM), chloroprene (CR), polyacrylate (ACM), acrylate-ethylene (AEM) and natural rubber.

7. The method for measuring mechanical strength of a pressurized gas storage tank for a vehicle according to any one of the preceding claims, wherein it comprises, before the step consisting of filling the expandable element (2) with liquid (6), a step of pre-filling the expandable element (2) with liquid (6).

8. The method for measuring mechanical strength of a pressurized gas storage tank for a vehicle according to any one of the preceding claims, wherein it comprises, before the step consisting of filling the expandable element (2) with liquid (6), a step of inflating the expandable element (2).

9. A device for measuring mechanical strength of a pressurized gas storage tank for a vehicle (1), said device comprising: • an expandable element (2) able to be inserted into the pressurized gas storage tank for a vehicle (1), said expandable element (2) being able to contain a liquid (6) once inserted into said tank (1); • a first coupling means (4) able to be assembled with the expandable element (2); • a first stretching means (5) of the expandable element (2) able to be connected to the first coupling means (4) and able to stretch the expandable element (2) in the lengthwise direction by at least one translational movement of the first stretching means (5) with respect to the first coupling means (4); • a liquid (6) pipe (3) able to be connected to the first coupling means (4); • means for discharging the gas contained in the expandable element (2) and / or the tank (1).

10. The device for measuring mechanical strength of a pressurized gas storage tank for a vehicle (1) according to claim 9, wherein the expandable element (2) is a bladder (20).

11. The device for measuring mechanical strength of a pressurized gas storage tank for a vehicle (1) according to any one of claims 9 to 10, wherein the first stretching means (5) is a rod.

12. The device for measuring mechanical strength of a pressurized gas storage tank for a vehicle according to claim 11, wherein the rod is the liquid pipe (3).

13. The device for measuring mechanical strength of a pressurized gas storage tank for a vehicle according to any one of claims 9 to 12, wherein it comprises a pump able to discharge the liquid (6) contained in the expandable element (2).

14. The device for measuring mechanical strength of a pressurized gas storage tank for a vehicle according to any one of claims 9 to 13, wherein the expandable element (2) comprises a zone for receiving the first coupling means (4).