Fluid tank

Abstract

The invention relates to a fluid tank for vehicles, comprising an inner container for a fluid, in particular liquefied gas, and a housing surrounding the inner container, wherein a volume is provided between the inner container and the housing in which an insulating vacuum can be produced, in particular a high vacuum with a pressure in the range of 10-3 to 10-8 mbar or a fine vacuum in the range of 1 to 10-3 mbar, and wherein, in order to maintain a produced insulating vacuum, the fluid tank is provided with at least one of its own vacuum pumps installed on the fluid tank, in particular a turbomolecular vacuum pump, and a connection for the vacuum pump and / or has a connection for an external vacuum pump device.

Description

[0001] The invention relates to a fluid tank for vehicles, comprising an inner container for a fluid, in particular a liquefied gas, and a housing surrounding the inner container. A volume is present between the inner container and the housing in which an insulating vacuum can be created. The insulating vacuum can be, for example, a high vacuum with a pressure in the range of 10 -3 to 10 -8 mbar or a fine vacuum in the range of 1 to 10 -3 mbar.

[0002] Due to the climate impact and limited availability of fossil fuels, alternative fuels are becoming increasingly important. Alternative fuels, particularly liquefied petroleum gas such as liquid hydrogen, can be used, among other things, to power all types of vehicles (cars, trucks, agricultural vehicles such as tractors, construction machinery such as excavators, ships, aircraft). Even if they are not used to power vehicles, it may be necessary to transport alternative fuels in liquid or gaseous form – generally as a fluid – by vehicle. In both cases, fluid tanks are used, which must meet specific requirements depending on the fluid in question.

[0003] Some fluids, especially liquefied gases, require cooling, sometimes requiring extremely high cooling to temperatures well below -200°C. Due to the large temperature difference between the fluid and the environment, effective thermal insulation is crucial to minimize heat transfer into the cooled fluid. The poorer the thermal insulation, the greater the boil-off problem—problems caused by losses of liquefied gas due to the conversion of part of the cooled liquid into the gaseous phase.

[0004] A well-known method for thermally insulating containers for liquefied gases is to provide an insulating vacuum surrounding the respective container. The vacuum in the volume between the container and a surrounding casing reduces heat transfer by convection. Heat transfer by thermal radiation can be minimized by additional measures, for example, by wrapping the container with a thermal insulation material, such as multilayer insulation (MLI), also known as superinsulation.

[0005] In practice, it is unavoidable that the insulation vacuum deteriorates over time. For example, an insulation vacuum of approximately 10 -5 < mbar is desired, which is a high vacuum according to the common definition. In other applications, an insulation vacuum of approximately 10 -2 < mbar may be desired, which is a fine vacuum according to the common definition. The deterioration of the insulation vacuum observed in practice, i.e., an increase in pressure in the volume between the inner container and the housing, can have various causes. For example, permeation through the walls of the surrounding housing and the inner container can contribute to the pressure increase in the insulation vacuum.Desorption can also play a significant role, for example, from the inner housing wall, from the outer layers of any multilayer insulation, or from cables and cable bushings traversing the insulation vacuum, provided they are made of appropriate materials. Cable bushings of any kind can also be a source of permeation. Most of the effects mentioned above are often summarized under the term "outgassing."

[0006] Especially in mobile applications, i.e. when fluid tanks have to be transported, it is difficult to control a deterioration of the insulation vacuum, which increases the heat input into the fluid, consequently promoting the conversion of the liquid phase into the gaseous phase, thus increasing the loss rate and thus overall reducing the efficiency of the alternative energy source in question.

[0007] US 2015 / 028039 A1 discloses a fluid tank for vehicles according to the preamble of claim 1.

[0008] The object of the invention is therefore to further reduce the heat input into the inner container of a fluid tank of the type mentioned above.

[0009] This problem is solved by the features of the independent claims.

[0010] In a fluid tank according to the invention, it is accordingly provided that, in order to maintain an insulation vacuum created, the fluid tank is provided with at least one separate vacuum pump installed on the fluid tank and a connection for this vacuum pump.

[0011] The invention provides a way to actively maintain the insulation vacuum on the fluid tank by evacuating the volume between the inner container and the housing. With a dedicated vacuum pump installed on the fluid tank, this can be done more effectively while the vehicle in question is moving on land, in water, or in the air.

[0012] The invention eliminates the need to rely exclusively on passive measures intended to counteract a deterioration of the insulation vacuum, such as thermal insulation of the inner container, or on measures to reduce outgassing.

[0013] The connection is preferably a flange connection, i.e. a connection that has a flange which is connected to a flange of the vacuum pump.

[0014] The vacuum pump can also be used to initially create the isolation vacuum or to restore the isolation vacuum, e.g. after intentional or unintentional venting of the volume.

[0015] Known fluid tanks usually already have a connection that is used during manufacture of the fluid tank and therefore during the initial evacuation to create the isolation vacuum and is then closed, for example, by means of a gate valve. A designated connection for an external vacuum pumping device can be provided in addition to such a connection used only during manufacture. This makes it possible to make the fluid tank compatible with one or more specific external vacuum pumping devices that are not compatible with the connection intended for manufacture. This can be the case, for example, due to a lack of standardization or due to different standards for the manufacture of the fluid tank on the one hand and the operation of the fluid tank on the other.

[0016] This makes it possible, for example, to create a vehicle fleet and a service network that are compatible with each other, whereby each vehicle in the fleet can visit any service station in the network to improve the insulation vacuum in the fluid tank and, if necessary, refuel with new fluid.

[0017] The fluid tank may additionally have a connection for an external vacuum pump device.

[0018] Preferably, an additionally provided connection for an external vacuum pumping device is provided with a closure device which is designed such that the connection can be repeatedly opened and closed in order to be able to carry out repeated pumping processes with the connection being closed in between.

[0019] According to some refinements of the invention, the dedicated vacuum pump can have at least one suction port and be connected directly to the outside of the housing via the suction port. This allows the dedicated vacuum pump to be installed directly on the fluid tank. A particularly good suction effect can be achieved in this way.

[0020] The separate vacuum pump installed on the fluid tank is installed on the fluid tank in such a way that, when the fluid tank is arranged correctly on the vehicle and the vehicle is used as intended, the effects of vehicle acceleration on moving parts of the vacuum pump are avoided or minimized. A moving part of a vacuum pump, in particular a turbomolecular vacuum pump, is, for example, a rotor that rotates about an axis of rotation during operation. According to the invention, the vacuum pump is installed on the fluid tank in such a way that the rotor, i.e. its axis of rotation, is oriented perpendicular to the direction of travel of the vehicle when the fluid tank is arranged correctly on the vehicle and the vehicle is used as intended. In this case, no gyroscopic forces act on the rotor when the vehicle corners.

[0021] In some embodiments, the rotor, which rotates about the rotational axis during pumping operation of the vacuum pump, can be rotatably supported by at least two bearings spaced apart along the rotational axis, and each bearing can be a rolling bearing, in particular a ball bearing. Unlike vacuum pumps, in which one or each bearing for the rotor is a magnetic bearing, rolling bearings ensure a particularly rigid mounting of the rotor, which is particularly advantageous for pumping operation on a moving vehicle.

[0022] Furthermore, in some embodiments, it can be provided that the dedicated vacuum pump installed on the fluid tank has a suction capacity of less than 15 l / s and is designed in particular as a turbomolecular vacuum pump.

[0023] Since a relatively long time is generally available to maintain the created insulation vacuum, meaning that a relatively high suction capacity of the vacuum pump is not essential for the application according to the invention, at least in most cases, it is sufficient to use a vacuum pump with a comparatively low suction capacity. Such vacuum pumps are characterized by their relatively low weight, thus only insignificantly increasing the overall weight of the vehicle. In practice, for example, turbomolecular vacuum pumps are known that have a suction capacity of approximately 10 l / s (for nitrogen) with a weight of less than 2 kg.

[0024] According to some embodiments of the invention, the connection for the dedicated vacuum pump or for the external vacuum pump device can be arranged in a central region of a housing side, away from any bends or angles in the housing. This allows comparatively large cross-sections to be achieved in the area of a suction opening of the vacuum pump, so that the effective suction capacity, which depends in particular on the suction capacity of the vacuum pump and the respective conductance, is at least substantially the same everywhere.

[0025] Furthermore, the connection for the internal vacuum pump or for the external vacuum pumping device can be arranged at a location where comparatively high outgassing is expected. This can be the case, for example, in the area of open edges of any multilayer insulation.

[0026] According to further possible embodiments of the invention, the inner container can be surrounded by thermal insulation. As already mentioned, such thermal insulation can be multilayer insulation. Such thermal insulation, also referred to as superinsulation, is generally known and can consist of a plurality of individual layers, for example, metal-coated plastic films. The individual layers can be closed or perforated.

[0027] According to some possible embodiments, in a multilayer insulation intended as thermal insulation for the inner container, at least one of the outer layers can be perforated and at least one of the inner layers can be closed. It has been found that with such a multilayer insulation design, an effect can occur whereby particles can be pumped out of the outer, perforated layer(s), whereas particles can be trapped and thus bound in the area of the inner layer(s).

[0028] The fluid tank can be provided with a control device designed to control or regulate the operation of the vacuum pump according to a fixed, predetermined program or as a function of one or more parameters, in particular measured values. For this purpose, the fluid tank can be provided with one or more measuring devices, e.g. a pressure sensor and / or a temperature sensor. Alternatively or additionally, the fluid tank, in particular a control device of the fluid tank, can be designed to receive and evaluate signals from measuring devices. Furthermore, alternatively or additionally, the fluid tank, in particular a control device of the fluid tank, can be designed to receive or evaluate one or more signals that represent a measure of the boil-off rate of the fluid.

[0029] The invention also relates to a vehicle with at least one fluid tank according to the invention. As already mentioned above, the vehicle can be a car, a truck, a vehicle used in agriculture such as a tractor or combine harvester, a construction machine such as an excavator, a ship, or an aircraft.

[0030] In particular, it can be provided that the vehicle has a drive for moving the vehicle, and the fluid contained in the inner container of the fluid tank serves as fuel for the drive. However, this is not mandatory. The fluid tank can also serve merely to transport the fluid by means of the vehicle, without the fluid being used for the operation of the vehicle. Alternatively, the fluid can be used not for the drive but for another purpose for the operation of the vehicle.

[0031] According to the invention, the vehicle is provided with its own vacuum pump installed on the fluid tank in such a way that, when the fluid tank is arranged as intended on the vehicle and when the vehicle is used as intended, a rotor of the vacuum pump, ie its axis of rotation, is oriented perpendicular to the direction of travel of the vehicle.

[0032] As already mentioned elsewhere, this prevents the rotor from being influenced by vehicle acceleration. In particular, it prevents gyroscopic forces from acting on the rotor when the vehicle is cornering.

[0033] A service station with at least one vacuum pumping device for vehicles according to the invention can be stationary and, for example, part of a service network comprising a plurality of such service stations that can be accessed by the vehicles as needed to perform a pumping process on the fluid tank of a respective vehicle using a vacuum pumping device belonging to the respective service station to improve the insulation vacuum. A service station can also be designed as a filling station and thus serve to fill the inner container of the fluid tank with the respective fluid, for example, liquid hydrogen.

[0034] Alternatively, it is possible for the service station to be mobile and, for example, to form part of a tanker truck, so that when refueling a vehicle, for example with liquefied gas - or shortly before or shortly after a refueling process - a pumping process can be carried out using the vacuum pump device in order to improve the insulation vacuum of the fluid tank. Regardless of whether the mobile service station belongs to a tanker truck or not, the mobile service station can be part of a service network comprising many individual mobile stations, each of which comprises, for example, a service vehicle with one or more vacuum pump devices. With such a fleet, for example, private or non-private companies can be specifically targeted that maintain a fleet of many vehicles, each of which has one or more fluid tanks according to the invention.

[0035] The - stationary or mobile - vacuum pump device can have a suction head which is connected to a base part of the service station via a flexible connection, wherein the suction head is designed as a vacuum pump or has a vacuum pump, or wherein the suction head is connected to a vacuum pump of the service station via the flexible connection.

[0036] In a system having one or more vehicles, each as disclosed herein, and having one or more service stations, it may be provided that each vacuum pumping device of a respective service station is compatible with each connection of a respective fluid tank of a respective vehicle provided for an external vacuum pumping device.

[0037] The invention also relates to a method for maintaining an insulation vacuum of a fluid tank according to the invention on a vehicle. In the method, the insulation vacuum is maintained by a pumping process. The pumping process can take place permanently or temporarily, in particular according to a closed-loop control. Regardless of whether the pumping process takes place permanently or temporarily, the pumping process can take place only when the vehicle is stationary, during any movement of the vehicle, or only during one or more specific movement states of the vehicle.

[0038] To carry out the pumping process, the vehicle or the fluid tank can be provided with a control device which is designed to control or regulate the operation of the vacuum pump according to a fixed program or depending on one or more parameters, in particular measured values.

[0039] If the vehicle is an aircraft, for example, it can be provided that no pumping process takes place during a take-off or landing procedure, but the vacuum pump is only active when the aircraft is in normal flight operation, for example at a specified flight altitude.

[0040] A temporary pumping process can comprise a number of individual pumping events occurring at regular or irregular intervals. The intervals can be fixed, for example. Alternatively, pumping events can be triggered within the framework of a closed-loop control system.

[0041] For example, it can be provided that an environmental parameter is used for a temporary pumping process, for example the outside temperature, whereby the number of pumping processes per unit of time increases with the outside temperature, ie at a higher outside temperature the vacuum pump is active more frequently than at a lower outside temperature.

[0042] Preferably, the pumping process is carried out using a vacuum pump installed on the fluid tank. Alternatively, it is also possible to carry out the pumping process using an external vacuum pumping device.

[0043] To implement a controlled pumping process, a measure of the quality of the insulation vacuum can be determined, and a pumping process can be started whenever the quality of the insulation vacuum falls below a predetermined level. A pumping process can therefore comprise a plurality of individual pumping processes occurring at intervals.

[0044] A measure of the quality of the insulation vacuum can be determined in different ways.

[0045] For example, the pressure in the volume can be measured and used as a measure of the quality of the insulation vacuum.

[0046] Alternatively or additionally, a boil-off rate of the fluid can be measured and used as a measure of the quality of the insulation vacuum.

[0047] Alternatively or additionally, it may be provided that an operating parameter of the fluid tank is used as a measure of the quality of the insulation vacuum. This operating parameter may, for example, be the performance of a device for cooling the fluid in the inner container.

[0048] Alternatively or additionally, an environmental parameter can be used as a measure of the quality of the insulation vacuum. This environmental parameter could, for example, be an expected or measured increase in the outside temperature.

[0049] For the dedicated vacuum pump installed on the fluid tank and / or for the vacuum pumping device of a service station as disclosed herein, an additional pre-pump may be provided which generates a pre-vacuum that may be required for the vacuum pump or the vacuum pumping device, as is generally known in vacuum technology.

[0050] The invention is described below by way of example with reference to the drawings. They show: Fig. 1 schematically shows a vehicle provided with a fluid tank according to the invention, and Fig. 2 shows a non-claimed example of a vehicle with a fluid tank at a service station comprising a refueling device and a vacuum pumping device.

[0051] Fig. 1 1 schematically shows the use of a fluid tank 11 according to the invention on a land vehicle 13, such as a car or a truck. As already mentioned elsewhere, other vehicles can also be equipped with one or more fluid tanks 11 according to the invention, for example, aircraft or ships.

[0052] The fluid tank 11 comprises an inner container 15 and a housing 19 surrounding it. When the fluid tank 11 is filled, a fluid, for example a liquefied gas such as liquid hydrogen 17, is located in its inner container 15, which serves as fuel for a vehicle engine 35 with which the vehicle 13 is driven.

[0053] A cooling device (not shown) keeps the liquefied gas 17 within the container 15 at a low temperature of, for example, -240°C. To prevent heating by radiation, the inner container 15 is surrounded by thermal insulation in the form of multilayer insulation (MLI) 33. Heat input by convection is minimized by maintaining an insulating vacuum in the volume 21 between the inner container 15 and the surrounding housing 19, which is already created during the production of the fluid tank 11. The insulating vacuum is, for example, a high vacuum in the range from 10 -3 < to 10 -8 < mbar or a fine vacuum in the range from 1 to 10 -3 < mbar.

[0054] As explained in the introduction, the insulation vacuum in volume 21 deteriorates over time, which, due to the large temperature difference between the cooled liquid gas 17 on the one hand and the environment on the other, results in an increased heat input into the liquid gas 17 with the disadvantages already explained.

[0055] In order to maintain the insulation vacuum within the volume 21 during operation of the vehicle 13, the fluid tank 11 is provided with its own vacuum pump 23, for example, a turbomolecular vacuum pump. For this purpose, the housing 19 has a connection flange 25 for the vacuum pump 23 in a central region of one side of the housing. In this way, the vacuum pump 23 is directly connected with its suction opening 31 to the opening of the housing 19 defined by the connection flange 25.

[0056] The vacuum pump 23 includes, among other things—shown purely schematically here—a rotor 51 for one or more turbomolecular pump stages and one or more Holweck pump stages. The design and operation of vacuum pumps of this type are known, so they need not be discussed in detail here. The vacuum pump 23 is installed such that the rotor 51 is oriented vertically and thus perpendicular to the direction of travel of the vehicle 13.

[0057] For the rotary mounting of the rotor 51, which rotates about an axis of rotation 53 shown here in dashed lines during pumping operation, two bearings 55 are provided which are spaced apart from one another along the axis of rotation 53 and are shown here purely schematically, each of which is a ball bearing, thus realizing a comparatively rigid mounting for the rotor 51.

[0058] In the illustrated embodiment, the fluid tank 11 is additionally provided with a further connecting flange 27 on one of the other housing sides, which makes it possible to evacuate the volume 21 between the inner container 15 and the housing 19 by means of an external vacuum pump device, which will be explained below in connection with Fig. 2 is entered into.

[0059] As already mentioned in the introduction, the insulation vacuum in volume 21 can be maintained by continuous operation of the vacuum pump 23 or by regulating the operation of the vacuum pump 23. Within the scope of such a control, it can be provided, for example, to measure the pressure within volume 21 using a pressure sensor (not shown) and to initiate a pumping process by activating the vacuum pump 23 when the measured pressure exceeds a predetermined value.

[0060] Alternatively, the control of the operation of the vacuum pump 23 could be based on a measurement of the so-called boil-off rate, which represents a measure of the evaporation of the liquid gas 17 within the container 15, i.e. the conversion from the liquid phase 17a into the gaseous phase 17b, and can thus be used as a measure of the quality of the insulation vacuum in the volume 21.

[0061] It has been determined that a pressure increase within volume 21 occurs more slowly than previously if, after an initial pumping operation to create the insulation vacuum, at least one further pumping operation occurs after a certain period of time. Continuous operation of the vacuum pump 23 is therefore not intended in all cases. Rather, such temporary operation of the vacuum pump 23 may suffice. Alternatively, in other applications, it may be intended to operate the vacuum pump 23 continuously.

[0062] Controlling the operation of the vacuum pump 23 may also depend on other conditions, for example, the movement behavior of the vehicle 13. For example, it may be provided that the vacuum pump 23 is controlled such that pumping operations only occur when the vehicle 13 is stationary or moving at a constant speed. In this way, influences of accelerations of the vehicle 13 on moving parts of the vacuum pump 23, in particular on its rotor 51, can be avoided.

[0063] In Fig. 1Not shown are lines running within the volume 21, which lead, for example, from outside the housing 19 to the inner container 15 or to feedthroughs formed on the inner container 15, or to devices arranged within the volume 21 but outside the inner container 15. As mentioned in the introductory section, such lines and feedthroughs can, for example, act as sources of outgassing, leading to an increase in pressure in the volume 21 and thus to a deterioration of the insulation vacuum. Taking this circumstance into account, the arrangement of the connecting flange 25 for the internal vacuum pump 23 or the connecting flange 27 for an external vacuum pump device can be such that the suction opening of the vacuum pump 23 or the external vacuum pump device is located at a point where a comparatively high degree of outgassing is to be expected.

[0064] As in Fig. 1As shown, the connection flange 25 for the dedicated vacuum pump 23 can be arranged in an area opposite a connection point 49 at which the individual layers of the multilayer insulation 33 are brought together and connected to one another.

[0065] A further optimization can be achieved by - as already mentioned in the introductory section - not only using closed or perforated layers for the multilayer insulation 33, but one or more inner layers located closer to the inner container 15 are closed and one or more outer layers are perforated.

[0066] The inner container 15 is further provided with a connection 47 (not shown here) for filling with the liquid gas 17.

[0067] Fig. 2shows a vehicle 13 with an unused fluid tank 11 at a stationary service station 37. For simplicity, the fluid tank 11 is shown here without thermal insulation, e.g., in the form of multilayer insulation for the inner container 15. However, such thermal insulation is also provided in this embodiment.

[0068] The fluid tank 11 has in the example of Fig. 2 does not have its own vacuum pump 23 and is therefore not provided with a corresponding connection flange. Instead, a connection flange 27 is provided for an external vacuum pump device 29. This comprises a suction hose 41 with a suction head 39 at the free end, which includes a vacuum pump 40, for example, a turbomolecular pump.

[0069] The flexible connection formed by the suction hose 41 between the suction head 39, which is designed as a vacuum pump in this way, and a base 43 of the service station 37 makes it possible to connect the vacuum pump 40 directly to the connection flange 27 of the fluid tank 11 of the vehicle 13 standing at the service station 37 in order to evacuate the volume 21.

[0070] The vehicle 13's stay at the service station 37 can also be used to refuel the vehicle 13, i.e., to fill the inner container 15 with liquefied gas 17, e.g., liquid hydrogen. A refueling device 45 of the service station 37 serves this purpose; its outlet end can be connected to a refueling connection 47 of the fluid tank 11. List of reference symbols

[0071] 11Fluid tank 13Vehicle 15Inner container 17Fluid 17aLiquid phase 17bGaseous phase 19Housing 21Volume 23Independent vacuum pump 25Connection for independent vacuum pump 27Connection for external vacuum pump device 29External vacuum pump device 31Suction opening 33Thermal insulation, MLI (Multilayer Insulation) 35Vehicle drive, engine 37Service station 39Suction head 40Suction head vacuum pump 41Flexible connection, suction hose 43Base 45Refueling device 47Connection for refueling device 49Connection point 51Rotor 53Rotation axis 55Bearing

Claims

1. A fluid tank (11) for vehicles (13), said fluid tank (11) comprising an inner container (15) for a fluid (17), in particular a liquefied gas, and a housing (19) surrounding the inner container (15), wherein a volume (21) is present between the inner container (15) and the housing (19), in which volume (21) an insulation vacuum can be produced, in particular a high vacuum with a pressure in the range from 10-3 to 10-8 mbar or a fine vacuum in the range from 1 to 10-3 mbar, and wherein, to maintain a produced insulation vacuum, the fluid tank (11) is provided with at least one separate vacuum pump (23), in particular a turbomolecular vacuum pump, installed at the fluid tank (11) and with a connection (25) for the vacuum pump (23), characterized in that the separate vacuum pump (23) installed at the fluid tank (11) is installed at the fluid tank (11) such that, with an intended arrangement of the fluid tank (11) at the vehicle (13) and on an intended use of the vehicle (13), a rotor (51) of the vacuum pump (23) rotating about an axis of rotation (53) during the pump operation is oriented with its axis of rotation (53) perpendicular to the direction of travel of the vehicle (13).

2. A fluid tank (11) according to claim 1, wherein the separate vacuum pump (23) has at least one suction opening (31) and is connected directly to an outer side of the housing (19) with the suction opening (31).

3. A fluid tank (11) according to claim 1 or 2, wherein the fluid tank (11) furthermore comprises a connection (27) for an external vacuum pump device (29).

4. A fluid tank (11) according to any one of the preceding claims, wherein the vacuum pump (23) comprises the rotor (51) rotating about the axis of rotation (53) during the pump operation, wherein the rotor (51) is rotatably supported by at least two bearings (55) spaced apart from one another along the axis of rotation (53), and wherein each bearing (55) is a rolling element bearing, in particular a ball bearing.

5. A fluid tank (11) according to any one of the preceding claims, wherein the separate vacuum pump (23) installed at the fluid tank (11) has a pumping speed of less than 15 l / s.

6. A fluid tank (11) according to any one of the preceding claims, wherein the connection (25, 27) for the separate vacuum pump (23) or for the external vacuum pump device (29) is arranged in a central region of a housing side, said central region being remote from curvatures or bends of the housing (19).

7. A fluid tank (11) according to any one of the preceding claims, wherein the inner container (15) is surrounded by a thermal insulation (33), in particular a multilayer insulation, in particular wherein at least one of the outer layers of the multilayer insulation is perforated and at least one of the inner layers of the multilayer insulation is closed.

8. A vehicle (13) comprising at least one fluid tank (11) according to any one of the preceding claims, in particular wherein the vehicle (13) has a drive (35) for moving the vehicle (13) and the fluid (17) contained in the inner container (15) of the fluid tank (11) serves as fuel for the drive (35).

9. A method of maintaining an insulation vacuum of a fluid tank (11) according to any one of the claims 1 to 7 at a vehicle (13), in which the insulation vacuum is maintained by a pumping process, wherein the pumping process takes place permanently or temporarily, in particular in accordance with an open-loop control, and / or wherein the pumping process only takes place when the vehicle (13) is stationary or only in one or more specific movement states of the vehicle (13).

10. A method according to claim 9, wherein the pumping process comprises a plurality of individual pumping processes taking place at regular or irregular intervals; and / or wherein the pumping process is carried out with a vacuum pump (23) installed at the fluid tank (11).

11. A method according to claim 9 or 10, wherein, in order to carry out a controlled pumping process, a measure of the quality of the insulation vacuum is determined and a pumping process is started in each case when the quality of the insulation vacuum falls below a predefined measure.

12. A method according to claim 11, wherein the pressure in the volume (21) is measured and is used as a measure of the quality of the insulation vacuum, and / or wherein a boil-off rate of the fluid (17) is measured and is used as a measure of the quality of the insulation vacuum, and / or wherein an operating parameter of the fluid tank (11) is used as a measure of the quality of the insulation vacuum, in particular the output of a device for cooling the fluid (17) in the inner container (15), and / or wherein an environmental parameter is used as a measure of the quality of the insulation vacuum, in particular an expected or measured increase in the outside temperature.

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