Fuel system

Abstract

A tank system comprises a cryogenic container for storing a liquefied gas, wherein the cryogenic container has at least a double-walled shell enclosing a storage space for the liquefied gas, a first electrical contact element and a separate second electrical contact element arranged in the storage space, and an electrical conductor electrically connected to the contact elements, wherein the electrical conductor is designed as a coaxial conductor and comprises at least one inner conductor made of steel, an insulating sheath made of an electrically insulating material surrounding the at least one inner conductor, and a shield made of steel braid surrounding the insulating sheath. The inner conductor projects beyond the insulating sheath at a first end of the coaxial conductor in the direction of travel, the projecting section being welded to the first contact element.The shield is routed away from the insulating sheath at the first end of the coaxial cable, either transversely or obliquely to the direction of travel, with the routed section being welded to the second contact element.

Description

The invention relates to a tank system comprising a cryogenic container for storing a liquefied gas, wherein the cryogenic container has an at least double-walled casing which encloses a storage space for the liquefied gas, a first electrical contact element and a separate second electrical contact element which are arranged in the storage space, and an at least two-core electrical line which is electrically connected to the contact elements.Such tank systems are used, for example, to carry fuels such as hydrogen or natural gas to motor vehicles. Cryogenic vessels are designed to keep liquefied gases at a particularly low temperature level for a relatively long period of time, so that a comparatively large amount of gas can be stored at relatively low pressure. This is generally achieved by a heat-insulating design of the casing, in particular by a double-wall structure with vacuum. In principle, the sleeve can also have a triple-wall structure or another multiple-wall structure. If necessary, an active cooling of the cryocontainer can also take place. Modern cryogenic vessels are capable of holding liquid hydrogen at a temperature of -253°C or less for a period of several days.Electrical devices such as fill level sensors, temperature sensors and the like are generally to be arranged in cryocontainers. In practice, however, it is demanding to provide reliable electrical connections within the storage space. Plug connections have the problem that many plastics used in conventional plugs are not suitable for the conditions in cryocontainers. Soldered connections are generally associated with unfavourable material pairings. In particular, the different thermal expansion coefficients of the solder and of the base material can lead to problems in the event of repeated marked temperature changes. In the case of screw and clamping connections, undesired changes in the transition resistance can occur as a result of repeated cooling processes.It is an object of the invention to make the transmission of signals and / or supply energy in the storage space more reliable by means of an electrical line in a tank system of the aforementioned type.The solution is achieved by a tank system having the features of claim 1.The invention provides that the electrical line is designed as a coaxial line and comprises at least one inner conductor made of steel, an insulating jacket which envelopes the at least one inner conductor and is made of an electrically insulating material, and a shield made of steel braid which envelopes the insulating jacket, wherein the inner conductor protrudes beyond the insulating jacket in the line direction at a first end of the coaxial line and the protruding section of the inner conductor is welded to the first contact element, and wherein the shield is led away from the insulating jacket at the first end of the coaxial line transversely or obliquely to the line direction and the led-away section of the shield is welded to the second contact element.The two contact points are insulated from one another by the insulating jacket of the coaxial line which is present in any case, so that the provision of an additional plastic insulator such as, for example, a plug body made of polymer is superfluous. This not only saves manufacturing costs, but also avoids the problems of susceptibility of current plug components to the extreme conditions in cryogenic tanks. By embodying the inner conductor and the shield as steel components, welded connections are made possible which avoid the problems of pairings of different materials and of two-part connections and, as a result of the material-bonding nature, make possible a particularly reliable transmission of electrical signals and / or energy in cryocontainers.It is preferably provided that the first contact element and the inner conductor are manufactured from the same material and / or that the second contact element and the shield are manufactured from the same material. The components welded to one another thus have identical coefficients of thermal expansion and the electrical connection is not weakened even in the event of frequent and marked temperature changes.The inner conductor, the shield, the first contact element and / or the second contact element are preferably manufactured from stainless steel. Electrical conductors made of stainless steel can also be used reliably in particularly corrosive environments.The inner conductor, the shield, the first contact element and / or the second contact element are preferably manufactured from austenitic stainless steel, in particular from chromium-nickel steel, in order to ensure sufficient durability in a hydrogen environment.The insulating jacket can be made of a plastic, preferably of a fluoroplastic, particularly preferably of polytetrafluoroethylene (PTFE). Fluoroplastics have considerable stability and corrosion resistance, so that they exhibit a reliable and durable insulating effect even in areas that are particularly material-consuming, such as liquid hydrogen tanks.Between the protruding portion of the inner conductor and the first contact element, a tungsten-inert gas welded joint or a resistance welded joint may be formed. Alternatively or additionally, a tungsten-inert gas welded connection or a resistance welded connection can be formed between the led-away section of the shield and the second contact element. Such welded connections have proven to be particularly reliable.According to one embodiment of the invention, a fill level sensor with a cylinder capacitor is arranged in the storage space, wherein the cylinder capacitor comprises an inner cylinder made of steel forming the first contact element and an outer cylinder made of steel forming the second contact element, or vice versa. Capacitive fill level sensors are capable of reliably detecting the fill quantity in cryocontainers. Since the cylinders of the capacitor are made of steel, the inner conductor and the shield of the coaxial line can be welded directly to them.The coaxial line may be clamped to the outer cylinder by means of a steel clamp in order to provide strain relief. An additional effect is improved contacting if the shield of the coaxial line is exposed, as is preferred, at least as far as the steel clamp and is accordingly pressed flat against the outer cylinder.A further embodiment of the invention provides that a coaxial plug connector having a central connecting pin and an outer connecting sleeve is arranged at the first end of the coaxial line, wherein the central connecting pin forms the first contact element and the outer connecting sleeve forms the second contact element. Thus, the coaxial line can be easily and quickly connected to a terminal or another line by plugging. The coaxial plug connector can be designed as a coaxial plug or as a coaxial socket.The central connecting pin can extend in the region of the welded connection next to the inner conductor. That is, the central terminal pin may be welded flat to the inner conductor.Alternatively, it can be provided that the central connection pin has a cavity and the inner conductor is accommodated in the cavity.According to a special embodiment of the invention, the led-away section of the shield is welded to the outer connection sleeve in the twisted state. For this purpose, the outer connection sleeve can be provided with a recess through which the twisted steel braid is guided to the rear sleeve base.Alternatively, the led-away section of the shield can be clamped between the outer connection sleeve and a clamping sleeve, preferably in a fanned-out state.According to a special embodiment of the invention, the cryocontainer is designed for fastening to the supporting frame of a motor vehicle. In the case of mobile tank systems for vehicles, such as fuel cell vehicles, for example, a configuration according to the invention has proven to be particularly advantageous.The invention also relates to a method for producing a tank system, in particular a tank system as described above, having the steps: (i) providing a cryogenic container which has an at least double-walled casing which encloses a storage space for a liquefied gas, (ii) arranging a first electrical contact element and a separate second electrical contact element in the storage space, (iii) providing an electrical line which is designed as a coaxial line and comprises at least one inner conductor made of steel, an insulating jacket which envelopes the at least one inner conductor and is made of an electrically insulating material and a shield made of steel braid which envelopes the insulating jacket, (iv) welding a section of the inner conductor which protrudes beyond the insulating jacket in the line direction at a first end of the coaxial line to the first contact element, (v) welding a section of the shield, which is directed away from the insulating jacket transversely or obliquely to the line direction at the first end of the coaxial line, to the second contact element.In a method according to the invention, no plug body, screw clamp or the like having an insulator made of polymer has to be provided, because the insulating jacket of the coaxial line itself provides the insulating effect.Preferably, steps (iv) and (v) are carried out by means of inert tungsten gas welding or by means of resistance welding. This has proven to be particularly favorable.Further developments of the invention can also be taken from the dependent claims, the description and the accompanying drawings.The invention will be described below by way of example with reference to the drawings. FIG. 1 is a schematic illustration of a tank system according to the invention. FIG. 2 shows a coaxial line of the tank system according to FIG. 1 in a perspective partial view. FIG. 3 shows a fill level sensor of the tank system according to FIG. 1 with a connected coaxial line in a perspective partial view. FIG. 4 shows an arrangement of coaxial line and coaxial plug connector of a tank system according to the invention. FIG. 5 shows an alternatively configured arrangement of coaxial line and coaxial plug connector of a tank system according to the invention. FIG. 6 shows a part of a further alternatively configured coaxial plug connector of a tank system according to the invention.The tank system 11 shown in simplified form in FIG. 1 is designed as a fuel tank system for a commercial vehicle and comprises a cryogenic container 13 for storing liquid hydrogen. In order to provide sufficient thermal insulation, the cryogenic container 13 has a double-walled evacuated envelope 15, preferably made of stainless steel, which encloses a storage space 17 for the liquefied hydrogen.The tank system 11 also comprises a fill level sensor 18 arranged in the storage space 17, to which an electrical line 21 for transmitting the sensor signals to an electronic evaluation unit, not shown, is connected. For this purpose, the electrical line 21 can be led to the outside by means of a line feedthrough.The line 21 shown individually in FIG. 2 is designed as a coaxial line 31 and comprises an inner conductor 33 made of steel, an insulating jacket 35 which envelopes the inner conductor 33 and is made of an electrically insulating material, and a shield 37 made of steel braid which envelopes the insulating jacket 35. The insulating jacket 35 is preferably made of a fluoroplastic such as polytetrafluoroethylene (PTFE), but could in principle also be made of another plastic. An insulating outer sheath could also be provided, which is not shown in FIG. 2, however.As shown, a section 45 of the inner conductor 33 at the end of the coaxial line 31 protrudes beyond the insulating jacket 35 in the line direction 38. Furthermore, a section 47 of the shield 37 at the relevant end of the coaxial line 31 is led away from the insulating jacket 35 transversely or obliquely to the line direction 38, for example by bending in a twisted state.The fill level sensor 18 is shown in more detail in FIG. 3. It is designed for capacitive fill quantity detection and comprises a cylinder capacitor 40 with an inner cylinder 41 and an outer cylinder 43. Both the inner cylinder 41 and the outer cylinder 43 are made of hydrogen-compatible stainless steel, preferably of the same stainless steel from which the inner conductor 33 and the shield 37 of the coaxial line 31 are made.The protruding portion 45 of the inner conductor 33 is welded flat to the inner cylinder 41, whereas the lead-away portion 47 of the shield 37 is welded flat to the outer cylinder 43. The coaxial line 31 is thus electrically connected to the fill level sensor 18, wherein the inner cylinder 41 forms a first contact element 51 and the outer cylinder 43 forms a second contact element 52. The electrical separation of the two contact elements 51, 52 takes place by the insulating jacket 35 of the coaxial line 31 and by the surrounding medium.For strain relief, the coaxial line 31 is clamped to the outer cylinder 43 by means of a steel clamp 55. Since the coaxial line 31 is designed without an insulating outer jacket, the shield 37 is pressed flat against the outer cylinder 43 by the steel clamp 55. Thus, the clamping improves the electrical contact. In principle, in the embodiment of FIG. 3, the coaxial line 31 could have an insulating outer jacket. However, it is preferred that such an outer jacket is interrupted in the region of the steel clamp 55 or only begins after the steel clamp 55 with respect to a line direction pointing away from the cylinder condenser 40.In a tank system 11 according to the invention, the coaxial line 31 can be electrically connected not only to a sensor, but also to another electrical device which has two contact elements 51, 52. By way of example, FIG. 4 shows a coaxial line 31, at the end of which a coaxial plug connector 57 having a central connection pin 58 and an outer connection sleeve 59 is arranged. Both the central connecting pin 58 and the outer connecting sleeve 59 are made of high-grade steel suitable for hydrogen.The central terminal pin 58 has a cavity 61 in which the protruding portion 45 of the inner conductor 33 is accommodated. The section 45 of the inner conductor 33 received in the cavity 61 is furthermore welded to the connection pin 58. The led-away portion 47 of the shield 37 is led out of the outer connection sleeve 59 in the twisted state through a recess 63 of the latter and welded to a rear portion 66 of the outer connection sleeve 59 to form a welded connection 65. Thus, in the embodiment of FIG. 4, the central terminal pin 58 forms the first contact element 51, while the outer terminal sleeve 59 forms the second contact element 52. In the embodiment of FIG. 4, the coaxial line 31 has an insulating outer jacket 64.FIG. 5 shows an alternative embodiment of a coaxial line 31 with a coaxial plug connector 67 on the end side. As in the embodiment of Figure 4, the coaxial connector 67 includes a central terminal pin 58 and an outer terminal sleeve 59 both made of hydrogen-compatible stainless steel. The protruding section 45 of the inner conductor 33 is also received here in the cavity 61 of the central connecting pin 58 and welded thereto. The section 47 of the screen 37 guided away is, however, not twisted, but rather fanned out and clamped between the outer connection sleeve 59 and a clamping sleeve 68 enclosing the latter. In addition, the clamped shield 37 is welded to the outer fitting sleeve 59 and to the collet 68.The central connecting pin 69 can also be designed without a hollow space as shown in FIG. 6 and welded flat to the inner conductor 33.The tank system 11 according to the invention (FIG. 1 ) can be designed in the manner of a module, so that it can be used as a fuel tank in different commercial vehicles.During the production of the tank system 11, the cryogenic container 13 including the assembled fill level sensor 18 and the coaxial line 31 is first provided. The coaxial line 31 is prepared at one end in such a way that the inner conductor 33 projects beyond the insulating jacket 35 in the line direction 38 and the shield 37 is led away from the insulating jacket 35 transversely or obliquely to the line direction. The section 45 of the inner conductor 33 protruding beyond the insulating jacket 35 is then welded to the first contact element 51 by means of a welding device. By way of example, a resistance welding device 70 is shown in FIGS. 4 and 6. Likewise, the section 47 of the shield 37 guided away from the insulating jacket 35 transversely or obliquely to the line direction 38 is welded to the second contact element 52 by means of the resistance welding device 70. In principle, welding can also be carried out using a tungsten inert gas welding device or another welding device.The invention provides a reliable electrical interface for use in cryogenic containers 13 that avoids susceptible polymers, two-part connections, and adverse material pairings.List of reference numbers:11 Tank system 13 Cryogenic container 15 Casing 17 Storage space 18 Fill level sensor 21 Electrical line 31 Coaxial line 33 Inner conductor 35 Insulating casing 37 Screen 40 Cylinder capacitor 41 Inner cylinder 43 Outer cylinder 45 Protruding section 47 Guided-away section 51 First contact element 52 Second contact element 55 Steel clip 57 Coaxial plug connector 58 Central connection pin 59 Outer connection sleeve 61 Cavity 63 Recess 65 Welded connection 64 Outer casing 66 Rear section 67 Coaxial plug connector 68 Clamping sleeve 69 Connection pin 70 Resistance welding device

Claims

Tank system (11) having a cryogenic container (13) for storing a liquefied gas, wherein the cryogenic container (13) has an at least double-walled casing (15) which encloses a storage space (17) for the liquefied gas, a first electrical contact element (51) and a separate second electrical contact element (52) which are arranged in the storage space (17), and an at least two-core electrical line (21) which is electrically connected to the contact elements (51, 52), wherein the electrical line (21) is designed as a coaxial line (31) and comprises at least one inner conductor (33) made of steel, an insulating casing (35) which envelopes the at least one inner conductor (33) and is made of an electrically insulating material, and a shield (37) made of steel braid which envelopes the insulating casing (35), wherein the inner conductor (33) protrudes beyond the insulating jacket (35) at a first end of the coaxial line (31) in the line direction (38) and the protruding section (45) of the inner conductor (33) is welded to the first contact element (51), and wherein the shield (37) at the first end of the coaxial line (31) is guided away from the insulating jacket (35) transversely or obliquely to the line direction (38) and the guided-away section (47) of the shield (37) is welded to the second contact element (52).The tank system according to claim 1, wherein the first contact element (51) and the inner conductor (33) are made of the same material and / or wherein the second contact element (52) and the shield (37) are made of the same material.Tank system according to claim 1 or 2, wherein the inner conductor (33), the shield (37), the first contact element (51) and / or the second contact element (52) are made of stainless steel.Tank system according to one of the preceding claims, wherein the insulating jacket (35) is manufactured from a plastic, preferably from a fluoroplastic, particularly preferably from polytetrafluoroethylene (PTFE).The tank system according to any one of the preceding claims, wherein a tungsten-inert gas welded joint or a resistance welded joint (65) is formed between the protruding portion (45) of the inner conductor (33) and the first contact element (51), and / or wherein a tungsten-inert gas welded joint or a resistance welded joint (65) is formed between the led-away portion (47) of the shield (37) and the second contact element (52).Tank system according to one of the preceding claims, wherein a fill level sensor (18) with a cylinder capacitor (40) is arranged in the storage space (17), wherein the cylinder capacitor (40) comprises an inner cylinder (41) made of steel forming the first contact element (51) and an outer cylinder (43) made of steel forming the second contact element (52), or vice versa.The tank system according to claim 6, wherein the coaxial pipe (31) is clamped to the outer cylinder (43) by means of a steel clamp (55).Tank system according to one of the preceding claims, wherein a coaxial plug connector (57, 67) having a central connecting pin (58, 69) and an outer connecting sleeve (59) is arranged at the first end of the coaxial line (31), wherein the central connecting pin (58, 69) forms the first contact element (51) and the outer connecting sleeve (59) forms the second contact element (52).Tank system according to claim 8, wherein the central connection pin (69) runs in the region of the welded connection (65) next to the inner conductor (33).The tank system of claim 8, wherein the central terminal pin (58) has a cavity (61), and the inner conductor (33) is received in the cavity (61).The tank system according to any one of claims 8 to 10, wherein the lead-away portion (47) of the shield (37) is welded to the outer connection sleeve (59) in a twisted state.The tank system of any of claims 8 to 10, wherein the lead away portion (47) of the shield (37) is clamped between the outer fitting sleeve (59) and a collet (68).Tank system according to one of the preceding claims, wherein the cryocontainers (13) are designed for fastening to the supporting frame of a motor vehicle.Method for producing a tank system (11), in particular a tank system (11) according to one of the preceding claims, having the steps: (i) providing a cryogenic container (13) which has an at least double-walled casing (15) which encloses a storage space (17) for a liquefied gas, (ii) arranging a first electrical contact element (51) and a separate second electrical contact element (52) in the storage space (17), (iii) providing an electrical line (21) which is designed as a coaxial line (31) and comprises at least one inner conductor (33) made of steel, an insulating jacket (35) which envelopes the at least one inner conductor (33) and made of an electrically insulating material, and a shield (37) made of steel braid which envelopes the insulating jacket (35), (iv) welding a section of the inner conductor (33) protruding beyond the insulating jacket (35) at a first end of the coaxial line (31) in the line direction (38) to the first contact element, and (v) welding a section (47) of the shield (37), which section is guided away from the insulating jacket (35) at the first end of the coaxial line (31) transversely or obliquely to the line direction (38), to the second contact element (52).The method of claim 14, wherein steps (iv) and (v) are performed by tungsten inert gas welding or by resistance welding.

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