Remote release device for a pressure vessel and assembly with a pressurized gas storage tank and such a remote release device

Abstract

Remote release device (14), comprising a housing (20), a piezoelectric element (26), a piston (22) which is received in the housing (20), and a preloading device (24), wherein the piston (22) is adjustable between a starting position in which the preloading device (24) is held in a preloaded state and an actuating position in which it is acted upon by the preloading device (24) against the piezoelectric element (26), wherein the piston (22) is held in the starting position by means of a temperature-sensitive locking mechanism, and wherein a heat-sensitive adhesive is provided in the area between the piston (22) and the housing (20).

Description

[0001] The invention relates to a remote release device for a pressure vessel and to an assembly comprising a compressed gas reservoir and such a remote release device.

[0002] The compressed gas storage system can be used in a vehicle to store a pressurized gas used to provide energy, particularly to power the vehicle. The compressed gas can be hydrogen, for example.

[0003] The compressed gas storage tank is typically equipped with a pressure relief valve that opens under predetermined ambient conditions to allow the contents of the compressed gas storage tank to flow out in a controlled manner. Thermally activated pressure relief valves are known to be activated when temperatures reach those encountered during a vehicle fire. If the pressure relief valve does not open during a vehicle fire, the compressed gas tank could burst uncontrollably.

[0004] Various pressure relief valves are known from the prior art. In a simple embodiment, the pressure relief valve can be designed similarly to a fuse, in which a sealing element melts at high temperatures, allowing the compressed gas to flow out of the compressed gas container.

[0005] More recent designs increasingly utilize electrically operated pressure relief valves. These have the advantage that they can be triggered by one or more remote release devices located at various points on the compressed gas storage tank or at other locations in the vehicle. This increases operational reliability because the pressure relief valve opens not only when the temperature there exceeds a specified limit, but also when a limit temperature is exceeded at other locations "monitored" by a remote release device.

[0006] The object of the invention is to provide a remote release device which is characterized by a simple structure and a high functional reliability.

[0007] To achieve this object, the invention provides a remote release device comprising a housing, a piezoelectric element, a piston accommodated in the housing, and a preloading device. The piston is adjustable between an initial position, in which the preloading device is held in a preloaded state, and an actuating position, in which it is urged against the piezoelectric element by the preloading device. The piston is held in the initial position by means of a temperature-sensitive locking mechanism. The invention is based on the fundamental idea of ​​using dimensional changes during temperature changes to release the piston, so that as soon as a structurally predetermined threshold is exceeded, it is urged against the piezoelectric element under the action of the preloading device, where it generates a voltage signal that is used to trigger the pressure relief valve.

[0008] According to one embodiment of the invention, the locking mechanism is formed by a press fit within the housing, wherein the press fit is dimensioned such that the holding force generated by it becomes smaller than the force generated by the preloading device when a limit temperature is exceeded. This embodiment is based on the fundamental idea of ​​using the thermal expansion of the housing and the piston as a triggering or release mechanism. In the initial state, the piston is mechanically firmly fixed in the housing so that the preloading device cannot relax. If, due to thermal expansion, the clamping force holding the piston in the initial position is no longer sufficient, the piston is released so that it strikes the piezo element.This generates a voltage that can either be used as a signal to open the pressure relief valve, or the voltage pulse can be used directly to open the pressure relief valve. The particular advantage of the mechanical design is that no aging or settling processes affect the clamping force that holds the piston in its initial position. Furthermore, the design effort is minimal.

[0009] According to one embodiment of the invention, the thermal expansion coefficients of the housing and the piston differ by less than 10%, in particular, the housing and the piston are made of the same material. This embodiment is based on the effect that, in a disc and a tightly enclosing ring, the inner diameter of the ring increases more rapidly during thermal expansion than the outer diameter of the disc. For example, steel can be used for the piston and the housing, so that despite an identical thermal expansion coefficient, the interference fit initially becomes a transition fit and finally a clearance fit as the temperature rises.If the speed at which the transition from an interference fit to a clearance fit is to occur with increasing temperatures is to be increased, materials with different thermal expansion coefficients can also be used for the material of the housing and the piston, with the thermal expansion coefficient of the housing being greater than the thermal expansion coefficient of the piston, in particular more than 10% greater.

[0010] According to a preferred embodiment of the invention, the receiving space has a clamping section with a first diameter and a release section with a second diameter that is larger than the first diameter, wherein the piezo element is located on the side of the release section and the piston, in the starting position, is located in the clamping section near the transition to the release section. The advantage of this configuration is that the piston, as soon as it has left its starting position, reliably impacts the piezo element, even if the housing in regions lying between the starting position of the piston and the piezo element is at a lower temperature than where the piston is in the starting position.

[0011] According to one embodiment, the locking mechanism is formed by a press fit between the piston and a retaining element, which is held in a recess in the piston by means of a press fit. This design has the advantage that only the recess and the part of the retaining element accommodated in the recess require precise machining.

[0012] The locking mechanism can also be formed by a tension element acting between the housing and the piston, wherein the thermal expansion coefficient of the housing is greater than the thermal expansion coefficient of the tension element. The advantage of this embodiment is that a positive connection can be used to hold the piston in the initial position. The piston is only released when the difference between the thermal expansion of the housing and the thermal expansion of the tension element is so great that the tension element is destroyed.

[0013] The tension element can be a rod equipped with a predetermined breaking point. This allows for precise adjustment of the breaking load at which the tension element releases the piston.

[0014] The locking mechanism can also be formed by a retaining element that surrounds the piston and has a thermal expansion coefficient that is lower than the thermal expansion coefficient of the piston, with the retaining element resting against a contact shoulder in the housing. This embodiment also uses a positive locking mechanism to reliably hold the piston in its initial position as long as the limit temperature has not yet been reached.

[0015] The holding element can be designed as a closed ring with a predetermined breaking point so that the breaking force can also be precisely adjusted.

[0016] Preferably, the piezo element is arranged on the side of the piston facing away from the preloading element, so that the piston directly impacts the piezo element when the press fit is released to such an extent that the preloading device moves the piston out of the starting position.

[0017] The piezo element is preferably housed in the housing so that it is protected from external influences and the remote release device remains functional over operating periods of several decades.

[0018] The housing may have a cylindrical receiving space in which the preloading device and the piston are arranged. Such a cylindrical receiving space can be manufactured particularly easily, especially if the cylindrical receiving space has a circular cross-section.

[0019] A heat-sensitive adhesive can be provided in the area between the piston and the housing to increase the clamping effect of the press fit.

[0020] The preloading device can, in principle, be any mechanism capable of applying a sufficiently high force to the piston against the piezo element once it is released, so that the element generates the desired voltage pulse. A magnetic preload, a compressed gas cushion, or similar is conceivable. A mechanical compression spring made of spring steel is particularly preferred, as this provides a substantially unchanged high preload force over a very long period of time.

[0021] To achieve the above-mentioned object, the invention also provides an assembly comprising a compressed gas reservoir, an electrically operated pressure relief valve mounted on the compressed gas reservoir, and a remote release device, as explained above. A particular advantage of this assembly is that the remote release device can be mounted at a distance from the pressure relief valve at locations either on the compressed gas reservoir or, for example, in a vehicle, that are suitable for detecting high temperatures that are critical for the safe operation of the compressed gas reservoir.Another particular advantage compared to the triggering of a conventional, thermally activated pressure relief device, which is in direct contact with the pressure vessel via a pressurized gas line, is that an electrical line is insensitive to an unintentional release of the gaseous fuel when exposed to direct external mechanical loads, which can occur, for example, in a vehicle accident.

[0022] The invention is described below with reference to an embodiment illustrated in the accompanying drawings, in which: - Fig. 1 schematically shows an assembly with a compressed gas reservoir, a pressure relief valve and three remote release devices; - Fig. 2 in a schematic section one of the components used in the assembly of Fig. 1 used remote triggering devices according to a first embodiment; - Fig. 3 shows a schematic section of a remote release device according to a second embodiment; - Fig. 4 shows a schematic section through a remote release device according to a third embodiment; - Fig. 5 the remote release device of Fig. 5 in the triggered state; - Fig. 6 shows a schematic section of a remote release device according to a fourth embodiment; - Fig. 7 in a plan view of the remote release device of Fig. 6 used holding element, - Fig. 8 shows a schematic section of the remote release device of Fig. 6 in the triggered state; and - Fig. 9 in a plan view the holding element of the remote release device of Fig. 8.

[0023] In Fig. 1 shows a compressed gas storage device 10 designed to store a gas under high pressure. The gas can be used to provide propulsion energy for a motor vehicle, for example, to directly operate an internal combustion engine or a fuel cell used to generate electrical energy. The gas stored in the compressed gas storage device 10 can be, for example, hydrogen.

[0024] The gas stored in the compressed gas reservoir can be at a pressure of several hundred bar. To reliably prevent the compressed gas reservoir 10 from being destroyed uncontrollably in the event of a vehicle fire, a pressure relief valve 12 is attached to the compressed gas reservoir 10. When ambient temperatures exceed a predetermined limit, this valve opens a pressure relief opening through which the compressed gas contained in the compressed gas reservoir 10 can escape in a controlled manner. The compressed gas reservoir 10 is then depressurized, so there are no consequences if its structure becomes weakened or fundamentally damaged due to further rising temperatures.

[0025] The pressure relief valve 12 is, in particular, an electrically triggered pressure relief valve. Various designs are known for this. One example is a pyrotechnic charge that is electrically ignited when needed. The pressurized gas generated after the pyrotechnic charge is ignited then opens the pressure relief opening, e.g., by destroying a membrane or moving a valve element from a closed position to an open position.

[0026] Several remote release devices 14 are arranged on the compressed gas storage device 10 and are connected to the pressure relief valve 12 via a line 16.

[0027] The remote release devices 14 can generally be considered sensors arranged at suitable locations on the compressed gas storage device 10 to monitor whether excessively high temperatures are present, i.e., temperatures above a predetermined limit. The limit is particularly selected to be below the temperatures at which structural weakening or damage to the compressed gas storage device 10 occurs.

[0028] In the embodiment shown, a remote release device 14 is arranged at each of the two ends of the compressed gas storage device 10 and one is arranged approximately centrally between the ends on the outer circumference.

[0029] In addition to the remote release devices 14 shown, further remote release devices can also be provided separately from the compressed gas storage device 10.

[0030] The cable 16 is, in particular, an electrical cable designed with such strength that it is not damaged by the stresses occurring in the event of a vehicle accident.

[0031] If the temperature at one of the remote release devices 14 exceeds a predetermined limit, an electrical signal is sent via line 16, which causes the pressure relief valve 12 to be activated, i.e., opened. This releases the gas contained in the compressed gas reservoir 10 into the environment in a controlled manner.

[0032] In Fig. 2 shows one of the remote release devices 14 in section.

[0033] The remote release device 14 has a housing 20, which in this case has an elongated, cylindrical interior. The housing 20 has, in particular, a circular cross-section.

[0034] A piston 22 is arranged inside the housing 20, dividing the interior of the housing 20 into two sections. A preloading device 24 is arranged on one side of the piston 22 (above in the illustrated embodiment). A piezo element 26 is arranged on the opposite side.

[0035] In the embodiment shown, the pretensioning device 24 is a compression spring made of spring steel.

[0036] In Fig. 2, the piston 22 is shown in an initial position in which it is fixed within the housing 20 by means of a temperature-sensitive locking mechanism.

[0037] In the embodiment shown, the temperature-sensitive locking mechanism is formed by a press fit. The press fit is symbolized here by the reference symbol P. The press fit is created by the fact that, at normal operating temperatures of the assembly formed by the compressed gas reservoir 10 and the remote release device 14, i.e., in the range of, for example, -40 to +80 degrees Celsius, the outer diameter D of the piston 22 is so much larger than the inner diameter d of the housing 20 that the piston 22 is elastically clamped within the housing 20. The clamping forces or holding forces generated in this way are greater than the force exerted by the pretensioning device 24 on the side of the piston 22 facing away from the piezo element 26, which forces the piston 22 toward the piezo element 26.

[0038] Steel is particularly suitable as a material for the housing 20 and the piston 22.

[0039] When the temperature in the environment of the remote release device 14 increases, the inner diameter d of the housing 20 increases due to thermal expansion. At the same time, the outer diameter D of the piston 22 increases. Assuming that the thermal expansion coefficient of the housing material is similar to the thermal expansion coefficient of the piston 22 material, however, the inner diameter d of the housing 20 increases more than the outer diameter D of the piston 22. As a result, the holding forces provided by the press fit P decrease with increasing temperature until finally the forces generated by the pretensioning device 24 are greater than the holding forces that hold the piston 22 in the initial position of Fig. 2. From this moment on, the piston 22 is urged against the piezo element 26 by the preloading device 24.

[0040] When the piston 22 impacts the piezo element 26, an electrical voltage is generated therein, which is passed via the line 16 to the pressure relief valve 12.

[0041] As in Fig. 2, the inner diameter of the housing 20 is not constant over the entire axial length of the interior. On the side of the piston 22 facing away from the pretensioning device 24, the inner diameter (here designated by the reference symbol F) is larger than in the region in which the piston 22 is clamped in the initial position. This ensures that the piston 22, as soon as it is released, can no longer be slowed down by friction effects on its way to the piezo element 26, but rather impacts the piezo element 26 unhindered under the action of the pretensioning device 24. According to the different diameters, the receiving space inside the housing 20 in the region with the diameter d is referred to as the clamping section, while in the region with the inner diameter F it is regarded as the release section.

[0042] The selected oversize of the piston 22 relative to the inner diameter d of the clamping section of the housing 20 is selected such that the clamping force of the press fit P is greater than the force of the preloading device 24 up to the desired limit temperature.

[0043] The release of the piston 22 can also be influenced by using different materials for the housing 20 and the piston 22, namely a material for the housing 20 that has a noticeably higher coefficient of thermal expansion than the material of the piston 22. As a result, the inner diameter d of the housing 20 increases at a greater rate than the outer diameter D of the piston 22 when the temperature increases.

[0044] In Fig. Figure 3 shows a second embodiment. The same reference numerals are used for components and features known from the first embodiment, and reference is made to the above explanations.

[0045] In the third embodiment, the temperature-sensitive locking mechanism is also formed by a press fit. In contrast to the embodiment of the remote release device of Fig. 2, the press fit is formed here between the piston 22 and a holding element 30 which is firmly attached to the housing 20.

[0046] The holding element 30 is designed here as a rod which is held in a receptacle 32 in the piston 22 by means of a press fit, so that the holding force is greater than the effect of the pretensioning device 24.

[0047] The piston 22 itself is accommodated with play inside the housing 20.

[0048] In principle, the same material can be used for the retaining element 30 and the piston 22, since the dimensions of the recesses increase more than the diameter of the retaining element 30 with a temperature increase. Nevertheless, a material whose expansion coefficient is higher than the expansion coefficient of the retaining element 30 can be used for the piston 22.

[0049] If a design-specified limit temperature is exceeded, the interference fit develops into a transition fit, so that the piston 22 is released and is urged against the piezo element 26 under the action of the preloading device 24.

[0050] In Fig. Figure 4 shows a third embodiment of the remote release device. The same reference numerals are used for the components and features known from the previous embodiments, and reference is made to the above explanations.

[0051] In the third embodiment, the temperature-sensitive locking mechanism is formed by a tension element 40, one end of which is fixedly attached to the housing 20 and the other end of which is fixedly attached to the piston 22. The piston 22, in turn, rests against a shoulder 42 in the housing.

[0052] The tension element 40 is designed here as a rod with a predetermined breaking point 44.

[0053] The material of the housing 20 is selected relative to the material of the tension element 40 such that the thermal expansion coefficient of the housing 20 is higher than the thermal expansion coefficient of the tension element 40. Therefore, when the remote release device is heated, the distance between the shoulder 42 and the upper portion of the housing 20 to which the tension element 40 is attached increases more than the length of the tension element 40 increases.

[0054] In the initial state, the piston 22 rests against the shoulder 42 with little or no play. When the remote release device 14 is heated, the end to which the tension element 40 is attached moves away from the piston 22, so that increasingly strong tensile forces are exerted on the tension element 40. At a certain point, the predetermined breaking point 44 gives way, so that the pretensioning device 24 can force the piston 22 against the piezo element 26 (see Fig. 5).

[0055] In Fig. A fourth embodiment is shown in Figure 6. The same reference numerals are used for components and features known from the previous embodiments, and reference is made to the above explanations.

[0056] In the fourth embodiment, the temperature-sensitive locking mechanism is formed by a holding element 60 which rests against a bearing shoulder 62 in the housing 20.

[0057] The holding element 60 is formed by a ring closed in the circumferential direction (see Fig. 7), which is provided with a predetermined breaking point 64.

[0058] In the illustrated embodiment, the retaining element 60 is received in a circumferential groove 66 of the piston 22. For this purpose, the piston can be designed in two parts to enable the assembly of the retaining element 60. It is also possible for the piston 22 to be designed in a stepped manner, wherein the diameter in Fig. 6 lower section of the piston 22 then corresponds to the inner diameter of the holding element 60.

[0059] In this embodiment, a material is used for the piston 22 whose thermal expansion coefficient is higher than the thermal expansion coefficient of the material from which the holding element 60 is made.

[0060] In the initial state, the holding element 60 supports the piston 22 against the action of the pretensioning device 24. When the remote release device 14 is heated, the piston 22 expands to such an extent that the holding element 60 is destroyed (see Fig. 9), so that it can no longer hold the piston 22 in its initial position. This is then forced against the piezo element 26 by the action of the pretensioning device 24 (see Fig. 8).

Claims

[1] Remote release device (14), with a housing (20), a piezo element (26), a piston (22) which is accommodated in the housing (20), and a pretensioning device (24), wherein the piston (22) is adjustable between an initial position in which the pretensioning device (24) is held in a pretensioned state, and an actuating position in which it is acted upon by the pretensioning device (24) against the piezo element (26), wherein the piston (22) is held in the initial position by means of a temperature-sensitive locking mechanism. [2] Remote release device (14) according to claim 1, characterized by that the locking mechanism is formed by a press fit (P) within the housing, wherein the press fit (P) is dimensioned such that the holding force generated by it becomes smaller than the force generated by the pretensioning device (24) when a limit temperature is exceeded. [3] Remote release device (14) according to claim 2, characterized bythat the thermal expansion coefficient of the housing and the piston differ from each other by less than 10%, in particular wherein the housing (20) and the piston (22) are made of the same material. [4] Remote release device (14) according to claim 2, characterized by that the thermal expansion coefficient of the housing (20) is greater than the thermal expansion coefficient of the piston (22), in particular more than 10% greater. [5] Remote release device (14) according to one of claims 2 to 4, characterized by in that the receiving space has a clamping section with a first diameter (d) and a release section with a second diameter (F) which is larger than the first diameter (d), wherein the piezo element (26) is located on the side of the release section and the piston (22) is located in the starting position in the clamping section near the transition to the release section. [6] Remote release device (14) according to claim 1, characterized by that the locking mechanism is formed by a press fit between the piston (22) and a holding element (30) which is held in a recess (32) in the piston (22) by means of the press fit. [7] Remote release device according to claim 1, characterized by that the locking mechanism is formed by a tension element (40) which acts between the housing (20) and the piston (22), wherein the thermal expansion coefficient of the housing (20) is greater than the thermal expansion coefficient of the tension element (40). [8] Remote release device according to claim 7, characterized by that the tension element (40) is a rod with a predetermined breaking point (44). [9] Remote release device according to claim 1, characterized byin that the locking mechanism is formed by a holding element (60) which surrounds the piston (22) and has a thermal expansion coefficient which is smaller than the thermal expansion coefficient of the piston (22), wherein the holding element (60) bears against a bearing shoulder (62) in the housing (20). [10] Remote release device according to claim 9, characterized by that the holding element (60) is a closed ring which has a predetermined breaking point (64). [11] Remote release device (14) according to one of the preceding claims, characterized by that the piezo element (26) is arranged on the side of the piston (22) facing away from the pretensioning device (24). [12] Remote release device (14) according to one of the preceding claims, characterized by that the piezo element (26) is accommodated in the housing (20). [13] Remote release device (14) according to one of the preceding claims, characterized bythat the housing (20) has a cylindrical receiving space in which the pretensioning device (24) and the piston (22) are arranged. [14] Remote release device (14) according to claim 12, characterized by that the cylindrical receiving space has a circular cross-section. [15] Remote release device (14) according to one of the preceding claims, characterized by that a heat-sensitive adhesive is provided in the area between the piston (22) and the housing (20). [16] Assembly comprising a compressed gas accumulator (10), an electrically operated pressure relief valve (12) mounted on the compressed gas accumulator (10), and a remote release device (14) according to any one of the preceding claims.

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