Thermally activated safety valve

Abstract

Thermally actuated safety valve (10) for a pressurized gas container (8) for storing gas under high pressure, with an elongated actuating element (13) made of a shape-memory material which has a first length at a first temperature and a second length at a second higher temperature, and which interacts at least indirectly with a valve bolt (15) movable in a valve body (11), which closes a blow-off opening (12, 12a) for the gas in the valve body in its first position and opens it in its second position, wherein the valve bolt (15) is biased in its first position against the release element (13) in its first length or an intermediate element (18) connected thereto by spring force and / or the pressure force of the gas, wherein the release element (13) in its second length releases the valve bolt (15), the valve body (11) is cylindrical in design, and the blow-off opening (12, 12a) runs parallel to the central axis of the cylindrical valve body, at least in the area where it interacts with the valve bolt (15), wherein the valve bolt (15) is designed to move radially from its first position outwards to its second position in a radial channel (14) in the valve body (11).

Description

[0001] The invention relates to a thermally triggered safety valve for a compressed gas container.

[0002] Thermally triggered safety valves are well known in the art for compressed gas cylinders. They are often referred to as TPRDs (Thermal Activated Pressure Release Devices). They can be used in any type of compressed gas cylinder, particularly in those used to store gases as fuel in vehicles. Their purpose is to empty the compressed gas cylinder, particularly if, for example, a fire breaks out in the event of a vehicle accident, before the heat from the fire causes it to become so high internal pressure that it explodes. Designs with bursting bodies that hold a plug in a vent are well known in the art.If the bursting device, such as a liquid-filled glass ampoule, becomes heated due to strong expansion of the liquid, the plug is released, allowing the pressurized gas container to empty. Alternatives to this include fusible plugs, which essentially consist of a hollow screw with a fusible link sealed at the opening. If the temperature rises, the fusible link softens and is forced out through the hole by the internal pressure of the gas acting on the screw. The gas can then escape.

[0003] These designs, particularly when using bursting bodies, can be subject to vibrations or impacts, which can even lead to the destruction of the bursting body. In this case, the safety valve would be triggered inadvertently. This also represents a significant disadvantage.

[0004] From the generic US 2012 / 0 011 843 A1, a valve is also known in the area of ​​a compressed gas container, which can be controlled by an elongated wire-like element made of a shape memory alloy. For this purpose, the wire made of the shape memory alloy is connected to a fixed point, for example at the other end of the compressed gas container, via a lever element designed to actuate the valve device. If the length of the wire made of the shape memory alloy changes from a first length at a first temperature to a second length at a higher temperature, then corresponding tensile forces are applied to the lever, or the lever, previously preloaded by the wire against a spring, is released. It then changes to its other position and can open and / or close the valve accordingly, depending on the initial situation.

[0005] The disadvantage of this design is that the elongated element made of shape memory material is located inside the compressed gas reservoir. This makes the design extremely complex with regard to possible maintenance, repair, or replacement of the shape memory alloy material.

[0006] From US 2016 / 0 131 274 A1, a temperature-activated valve is known which is provided with a trigger which causes the actuation of the valve. The trigger comprises a temperature-responsive trigger part having a plurality of individual trigger segments connected in series with one another. The individual trigger segments comprise a plurality of temperature-responsive trigger segments. Each of the temperature-responsive trigger segments independently contains a composite material, the composite material comprising: (a) a component comprising a shape-changing material configured to assume a shape change in response to the absorption of thermal energy by the temperature-responsive trigger segment, and (b) a component comprising a relatively inelastic material having a modulus of elasticity greater than the modulus of elasticity of the component comprising the shape-changing material.

[0007] Further prior art is disclosed in the documents US 5 788 212 A, US 2012 / 0 199 764 A1, JP 2005- 147 385 A and US 2013 / 0 167 377 A1.

[0008] The object of the present invention is to provide a thermally triggered safety valve which can be implemented extremely simply and efficiently and which requires little effort, particularly with regard to maintenance.

[0009] According to the invention, this object is achieved by a safety valve having the features of claim 1. Advantageous embodiments and further developments of the thermally triggered safety valve according to the invention emerge from the dependent claims.

[0010] The thermally triggered safety valve according to the invention is intended for a compressed gas container for storing gas under high pressure, in particular for a hydrogen storage device in which hydrogen is stored at a nominal pressure of 700 bar or more. Similar to the prior art design, the thermally triggered safety valve according to the invention uses an elongated trigger element made of a shape memory material, which has a first length at a first temperature and a second length at a second, higher temperature. The trigger element interacts at least indirectly with a valve bolt movable in a valve body, which closes a blow-off opening for the gas in the valve body in a first position and opens it in a second position.The valve pin is preloaded in its first position against the release element in its first length or a connected intermediate element by spring force and / or the pressure of the gas. In its second length, the release element releases the valve pin directly or via the intermediate element.

[0011] In the safety valve according to the invention, the trigger element secures the valve pin, which in particular directly forms a sealing surface within the safety valve, in its first position. This closes the safety valve and prevents the gas from escaping. Spring forces, but in particular the force of the pressurized gas itself, press the valve pin against the trigger element or an intermediate element connected to the trigger element. This ensures a secure and reliable position of the valve pin. Even in the event of impacts, vibrations, or the like, it cannot move from this position, which securely and reliably closes the valve.Only after the length of the release element has been changed due to a temperature increase, i.e., the release element has become correspondingly longer or shorter, is the valve pin released. It can either use the space freed up by the additional length of the release element for its own movement, or the release element and / or the intermediate element connected to it are moved from the position blocking the valve pin by shortening the release element. The valve pin can then move at least far enough to release the vent opening; in particular, it is moved into this new open position of the safety valve by the pressure of the gas.

[0012] According to a further very advantageous embodiment of the thermally triggered safety valve according to the invention, it can now be further provided that the trigger element and the valve pin are not connected to each other. Eliminating such a connection between the trigger element, or any intermediate element connected to it, and the valve pin is a decisive advantage. This prevents any forces introduced via the trigger element from leading to false triggering, as a direct connection is eliminated.

[0013] The valve body of the thermally triggered safety valve is cylindrical. The trigger element can then preferably be arranged in a ring-shaped or spiral shape around or within the valve body. In particular, the blow-off opening runs parallel to the central axis of the cylindrical valve body, at least in the region in which it interacts with the valve pin, wherein the valve pin is designed such that it moves radially outward from its first position to its second position in a radial channel in the valve body. Such a radial movement of the valve pin is particularly simple and efficient, as it can be very easily controlled with an elongated trigger element made of shape memory material. For example, the radial channel of the valve pin intersects an annular groove or a spiral channel in the valve body in which the trigger element is arranged.At the first length of the trigger element, the passage of the radial channel is blocked accordingly and the valve pin is preloaded against the trigger element or an intermediate element connected to it. If the length of the trigger element changes, the radial channel is at least partially opened, for example by an intermediate element being pulled out of the area of ​​the radial channel because the trigger element shortens, or because the trigger element lengthens accordingly and thus moves to a larger radius and thus enables a radial movement of the valve pin at least by a certain amount. The blow-off opening is then opened and the gas can flow out accordingly after the trigger element has reached the second temperature and thus the second length.

[0014] According to an advantageous development, the shape memory material can be in the form of a metallic alloy. Such metallic alloys, known as shape memory materials or shape memory alloys, are generally known in the art. In German-speaking countries, they are also frequently referred to as memory metals. Typically, the corresponding metals are alloys based on nickel and titanium, for example the very well-known material generally referred to as Nitinol. The addition of copper is also conceivable. There are also copper-zinc or copper-zinc-aluminum alloys, copper-aluminum-nickel alloys, or iron alloys, for example iron-nickel-aluminum or iron-manganese-silicon. Materials such as zinc, gold, and copper are also conceivable in principle, but some are comparatively expensive.

[0015] According to an alternative embodiment, instead of the typically very robust metallic shape memory alloys, a shape memory material based on plastic can be used. Thermoplastic polyurethane is particularly suitable for this purpose.

[0016] Furthermore, it can be provided that the shape memory material is a shape memory material with a one-way memory effect. Such a one-way memory effect is typically much easier to achieve than a two-way memory effect, in which the shape memory material returns to its original shape below the limit temperature. This is neither desired nor necessary with the design designed here. Rather, it is sufficient if, above a certain limit temperature, the shape of the trigger element changes so that the valve pin is released. If the temperature drops, the shape does not have to change back, since the compressed gas container is typically empty at this point anyway. This is desirable for safety reasons anyway.A one-way memory effect in the material for the trigger body in the safety valve according to the invention is therefore not only completely sufficient, but even advantageous, so that the trigger body can be realized accordingly easily.

[0017] As already mentioned, a safety valve according to the invention with the described trigger body made of shape memory material enables very safe and reliable use and ensures secure closure of the safety valve as long as it is not intended to trigger, but is potentially exposed to vibrations and shocks. Such use with vibrations, shocks, and relatively large temperature changes occurs particularly in motor vehicles. The particularly preferred use of the safety valve according to the invention therefore lies in its use in a compressed gas container for storing gaseous fuel in a vehicle. Gaseous fuel in a vehicle can be, for example, compressed natural gas or hydrogen, which is supplied to an internal combustion engine.In particular, in the particularly preferred use of the compressed gas container for storing hydrogen, this hydrogen can also be converted into electrical drive power in a fuel cell, so that in this case the vehicle is designed as a so-called fuel cell vehicle.

[0018] Further advantageous embodiments of the safety valve according to the invention, its use and / or the manufacturing method for its triggering element emerge from the remaining dependent subclaims and become clear from the exemplary embodiment which is illustrated in more detail below with reference to the figures.

[0019] Showing: Fig. 1 a schematically illustrated vehicle with a compressed gas tank; Fig. 2 a schematic diagram of a thermally triggered safety valve; Fig. 3 a representation of the safety valve according to Fig. 2 in two different states; and Fig. 4 an alternative design of the safety valve.

[0020] In the presentation of the Fig. 1 shows a schematically indicated vehicle 1 which, in the illustrated embodiment, is to be supplied with electrical drive power via a fuel cell 2. The electrical power generated by the fuel cell is processed via power electronics 3 and fed to an indicated traction motor 4 of the vehicle 1. The fuel cell 2 can be constructed in a conventional manner as a stack of individual cells, a so-called fuel cell stack or fuel cell stack 2. This fuel cell stack 2 comprises an anode region and a cathode region in the area of ​​each of the individual cells. A common cathode chamber 5 and a common anode chamber 6 are indicated by way of example. Air is supplied to the cathode chamber 5 as an oxygen supplier via an air conveying device 7. Hydrogen is supplied to the anode chamber 6 as fuel, which is stored in a compressed gas reservoir 8 in the vehicle 1.The hydrogen is fed to the fuel cell 2 directly or via further valve devices, processing devices and the like via a valve 9, which is typically connected to the compressed gas storage 8 and is screwed directly to the compressed gas storage. For the present invention, the functionality of the fuel cell 2 or of the fuel cell system is of secondary importance, so that this structure is only shown very rudimentarily and is not described in more detail below. In the area of ​​the valve 9 and / or at the other end of the compressed gas storage 8, it is customary to provide a valve as shown in the illustration. Fig. 1, a safety valve 10 not visible, which is typically designed as a thermally activated safety valve 10, is provided. It is often referred to by the abbreviation TPRD, which stands for Thermal Activated Pressure Release Device. The functionality of the thermally activated safety valve(s) 10 used here is illustrated by way of example in the following figures.

[0021] Fig. Figure 2 shows a schematic diagram of a possible design of the safety valve 10 according to the invention in a three-dimensional representation. This shows a valve body 11 having a central vent opening 12. A trigger element 13 made of a shape-memory material extends around the valve body 10, preferably in a groove in the valve body 10 (not visible here).

[0022] In the basic sectional view of the Fig. 3, two different lengths of the shape memory material can be seen. In the illustration of the Fig. Figure 3a shows a section through the valve body 11 at the level of the trigger element 13 made of shape memory material. A valve pin 15 is arranged in a channel 14, which runs radially to a central axis of the cylindrical valve body 11. This pin is movable in the radial channel 14 perpendicular to the plane of the drawing.

[0023] It closes the blow-off opening 12 (not visible here) and is pressed radially outwards against the material of the trigger element 13 by the pressure of the gas stored in the compressed gas reservoir 8. The trigger element 13 made of the shape memory material has a ring-shaped structure and in the Fig. 3a, a first length. If the temperature in the area of ​​the thermally triggered safety valve 10 increases, the shape memory material of the triggering element 13 assumes a second, in the embodiment shown here, longer length. This is shown in the illustration of Fig. 3b. The ring 13 thus moves radially outwards away from the valve body 11. This frees up an additional path by which the valve pin 15 can move from its Fig. 3a shown first position. In the illustration of the Fig. 3b shows this second position of the valve pin 15, in which it has already moved outwards a certain distance, as far as the material of the trigger element 13 allows in its second length. This movement is sufficient to open the blow-off opening 12, which in the illustration of Fig. 3b, to be released accordingly. The gas can then escape from the compressed gas reservoir through the vent opening 12 and is ideally guided into the area of ​​a discharge pipe, a so-called venting tube, which discharges the gas, for example, into a non-critical area underneath the vehicle. The design with the trigger element 13 made of shape memory material creates a very simple and reliable design in which the valve bolt 15, which is prestressed in its first length by the pressure of the gas against the shape memory material of the trigger element 13, is then released by a sufficient distance when the temperature rises and the shape memory material of the trigger element 13 assumes its second length. In this case, the vent opening 12 is then opened by the valve bolt 15 and the gas can escape in the desired manner.

[0024] In the presentation of the Fig. 4 shows another alternative embodiment of the structure. The structure, also referred to here as valve body 11, has a round cross-section and can be, for example, a separate valve body of the thermally triggered safety valve 10 or the so-called boss of the compressed gas reservoir 8, i.e. its metallic end piece, which is intended to accommodate the valve device or its functional elements. In the illustration of Fig. 4, the blow-off opening 12 can be seen again, which is sealed by a tip 16 of the piston-shaped valve pin 15 against a region of the blow-off opening 12, designated 12a, which is connected to the environment. The central in the illustration of the Fig. The area designated 12 in FIG. 4 is connected to the interior of the compressed gas container 8, while the area designated 12a is connected to the environment. The tip 16, which may have additional sealing elements, blocks the passage of the gas as long as the valve pin 15 is in the position shown in FIG. Fig. 4. It is pressed by the pressure of the gas and, in the exemplary embodiment shown here, by a spring 17, against a locking pin as an intermediate element 18, which holds the valve bolt 15 in the position shown here within the radial channel 14. The locking pin 18 is connected as an intermediate element to the actual trigger element 13, in this case a wire made of a shape memory alloy, for example a nickel-titanium wire. The wire runs through a channel 19 into the outer region of the valve body 11 and is then formed in a groove designated 20, one or more times circumferentially around the valve body 11, before being secured with a fastening bolt 21.A comparatively large amount of wire of the trigger element 13 can be arranged between the locking pin 18 and the fastening bolt 21, preferably by enclosing the trigger element several times around the valve body 11. A change in the length of the trigger element from a first length to a second length, which accompanies a change in temperature, can be mechanically "amplified" by a correspondingly long wire, so that a relatively small effect in the shape memory alloy is sufficient to move the locking pin connected to it by a relatively large distance and with a relatively large force.

[0025] In the Fig. 4, the wire of the trigger element 13 is shortened accordingly, whereby the locking pin 18 is released from the position shown in Fig.4 and is pulled out of the radial channel 14 in the circumferential direction with its part projecting into the radial channel 14. The valve pin 15 is then released accordingly and can be moved radially outwards by the pressure of the gas, and here supported by the force of the spring 16, whereby the tip 16 of the valve pin 15 opens the passage opening between the part of the blow-off opening designated 12 and the part of the blow-off opening designated 12a. These movements, with the trigger element 13 shortening, are indicated by the arrows. The gas can then flow out of the interior of the compressed gas container into the area connected to the part 12a of the blow-off opening, for example into the surroundings of the vehicle 1 or in particular into a venting tube which directs the gas into the surroundings.As a result, the desired effect of the safety valve 10 is always achieved when the temperature of the shape memory material of the trigger element 13 rises above the specified value. If this is not the case, the design is correspondingly safe and reliable, since the preload of the valve pin 15 relative to the locking pin 18 ensures a secure engagement, which is typically not triggered even in the event of shocks and vibrations, since in this case the locking pin would have to be moved against the forces exerted against it by the wire of the trigger element 13, which is not the case in force situations typically occurring in vehicles 1.

Claims

[1] Thermally triggered safety valve (10) for a compressed gas container (8) for storing gas under high pressure, with an elongated trigger element (13) made of a shape memory material, which has a first length at a first temperature and a second length at a second higher temperature, and which cooperates at least indirectly with a valve bolt (15) movable in a valve body (11), which closes a blow-off opening (12, 12a) for the gas in the valve body in its first position and releases it in its second position, wherein the valve bolt (15) is prestressed by spring force and / or the pressure force of the gas in its first position against the trigger element (13) in its first length or an intermediate element (18) connected thereto, wherein the trigger element (13) in its second length releases the valve bolt (15), the valve body (11) is cylindrical, and the blow-off opening (12, 12a) extends parallel to the central axis of the cylindrical valve body at least in the region in which it interacts with the valve pin (15), wherein the valve pin (15) is designed such that it moves radially outwards from its first position to its second position in a radial channel (14) in the valve body (11). [2] Thermally triggered safety valve (10) according to claim 1, characterized by that the trigger element (13) and the valve pin (15) are not connected to each other. [3] Thermally triggered safety valve (10) according to claim 1 or 2, characterized by that the trigger element (13) is formed or runs in a ring-shaped or spiral shape. [4] Thermally triggered safety valve (10) according to one of claims 1 to 3, characterized bythat the trigger element (13) is arranged in an annular groove around the valve body (11) which intersects the radial channel (14) for the valve pin (15). [5] Thermally triggered safety valve (10) according to one of claims 1 to 3, characterized by that the trigger element (13) is arranged in an at least partially spiral-shaped channel (19) in the valve body (11), which intersects the radial channel (14) for the valve pin (15). [6] Thermally triggered safety valve (10) according to one of claims 1 to 5, characterized by in that the trigger element (13) cooperates with, and is in particular connected to, an intermediate element (18), which is movable in particular in the circumferential direction and which, in a first position, holds the valve pin (15) in its first position and releases it in a second position, the position of the intermediate element (18) changing depending on the length of the trigger element (13). [7] Thermally triggered safety valve (10) according to one of claims 1 to 6, characterized by that the shape memory material is based on a metallic alloy. [8] Thermally triggered safety valve (10) according to one of claims 1 to 6, characterized by that the shape memory material is based on a plastic, in particular a thermoplastic polyurethane.

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