Abstract:
A tank for cryogenic liquids, which is intended for installation in motor vehicles and which consists of an outer container and of an inner container suspended in the latter in tension or compression struts. In order to take the contrasting requirements in motor vehicles into account in an optimum way, between the outer container and inner container abutments and supporting faces are additionally provided, which can be spaced apart from one another when the vehicle is at a standstill and can be brought to bear when the vehicle is driving. The abutments inside the outer container Co.-operate with supporting faces on the inner container and can be displaced by means of an actuator.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The invention relates to tanks for cryogenic liquids, said tanks being intended for installation in motor vehicles and which consists of an outer container and of an inner container suspended in the latter, the suspension being formed by spatially arranged tension or compression struts of low thermal conductivity which compensate for displacements of the inner container due to thermal expansion differences.  
         [0002]     A cryotank for rockets is known from U.S. Pat. No. 4,481,778. The bands serving for suspension surround short struts which are articulated on connectors with play on both sides. In the event of the high acceleration occurring in the longitudinal direction during starting, the struts are laid against the connectors. Owing to its application in rocket technology, however, this design does not afford either sufficient cold insulation (the struts are highly effective heat bridges) or sufficient freedom of movement for the inner container.  
         [0003]     DE-A-101 28 516 discloses a generic tank for cryogenic liquids, which is intended for use in motor vehicles, with spatially arranged tension or compression struts which engage on a tube mounted centrally in the inner container. These struts are again very strong and thermally conductive components, but cannot withstand more pronounced shocks, let alone collisions.  
         [0004]     Further, GB 2 025 029 discloses a storage container for liquid gases, the inner container of which is centered in the outer container by means of the repulsion of permanent magnets.  
         [0005]     None of these designs can satisfy the special requirements arising in the event of use in motor vehicles. These are, on the one hand, that the heat insulation is to be particularly good, in order to minimize evaporation (the vehicle must be ready to drive even after being at a standstill for a week and it must be possible to walk around in the garage with a cigarette); and, on the other hand, the support of the inner container must withstand movements and accelerations in all directions, not only those in the event of a collision, but also those constantly occurring due to unevennesses of the road. The object of the invention is to take into account these contrasting requirements in an optimum way.  
       SUMMARY OF THE INVENTION  
       [0006]     The object is achieved, according to the invention, in that, between the outer container and the inner container, restraints, in particular abutments and supporting faces, are additionally provided, which can be spaced apart from one another when the vehicle is at a standstill and can be brought to bear when the vehicle is driving. The invention is based on the recognition, on the one hand, that especially good heat insulation during driving is not necessary, because fuel is in any case extracted continuously, preferably in vapor form, from the tank, and that, on the other hand, a firm support during standstill is not required.  
         [0007]     The restraints or abutments and supporting faces do not need to be poor conductors of heat and do not need any special heat insulation since they form heat bridges only during operation. The thus increased evaporation of the cryogenic liquid is even conducive to the extraction of fuel. Owing to the restraints, the spatially arranged tension or compression struts serving for the permanent suspension of the inner container have to support the inner container only with the vehicle at a standstill and can consequently be dimensioned with especially small cross-sections for maximum heat insulation, because no dynamic loads of any kind occur during standstill.  
         [0008]     In a practical embodiment, supporting faces are formed on the inner container and the abutments co-operating with said supporting faces are arranged inside the outer container and can be displaced by means of an actuator. The actuator therefore does not need to be accommodated in the sensitive vacuum zone between the outer and the inner container and is accessible from outside. In particular and preferably, the actuator is an electromagnet mounted on the outer container and the abutment is covered by a sealing diaphragm.  
         [0009]     In a preferred basic embodiment, the supporting faces are formed on a tubular perforation of the inner container and the abutments co-operating with said supporting faces are formed by/on a hollow body which is arranged inside the outer container and passes through the tubular perforation of the inner container and the form of which can be varied by a variation of the internal pressure, and the hollow body and the supporting faces are centrically symmetrical. The tubular perforation of the inner container and the hollow body passing through the inner container make it possible, as compared with engagement on the periphery of the inner container, to have a symmetrical and virtually thermocentric support and engagement of the abutments. When the spatially arranged tension or compression struts serving for the permanent suspension of the inner container also engage on this hollow body, the advantages mentioned are also beneficial to these struts. Actuation by internal pressure (or, in the case of an appropriate reversal, by under pressure) allows uncomplicated actuation without sealing-off problems.  
         [0010]     For this purpose, various embodiments in terms of detail are possible. The hollow body may be connected with its two ends to the outer container by means of, fastenings and the spatially arranged tension or compression struts of the suspension of the inner container also engage on said outer container. This makes it possible to secure the inner container at two mutually opposite points of the hollow body, without direct connection to the outer container, and allows a thermocentric and kinematically optimum suspension of the inner container.  
         [0011]     A specialist simple design is obtained when the outer container is deformable in a diaphragm-like manner in the surroundings of the connection point to the hollow body and when the casing of the hollow body is designed at least partially as a bellows. As a result, no movable connections of any kind are necessary on the inside, apart from the compression or tension struts, and the atmospheric pressure acting on the outer container from outside exerts a restoring force on the pressure-loaded bellows (an under pressure or vacuum of course prevails between the two containers). Moreover, the firm connection between the bellows and the outer container increases the load-bearing capacity.  
         [0012]     In another embodiment, the hollow body is surrounded by centrically symmetrical bellows-like structures which are expandable by means of internal pressure and which can be laid by the internal pressure against the inner container wall surrounding the hollow body. The bellows-like structures provide a large-area and elastic bearing surface which can absorb considerable shocks and thus effectively protects the inner container.  
         [0013]     In a development of the idea of the invention, according to the invention, in generic tanks, inside the outer container and on the outside of the inner container, restraints are additionally provided, which are ineffective when the vehicle is at a standstill and can be coupled when the vehicle is driving, so that a displacement of the inner container and outer container in relation to one another is prevented. This measure can be employed alternatively to or in addition to the abutments. It prevents a displacement in the direction parallel to the container walls, whereas the abutments prevent displacements in the direction transverse to the container walls; however, this is only when said measure is activated during driving. There is no connection when the vehicle is at a standstill.  
         [0014]     In a practical embodiment, the restraints are formed, on the one hand, from a first molding with a defined contour and, on the other hand, from a second molding with a negative contour matching the latter, one of the two moldings being capable of being brought into positive engagement with the other molding. In particular, one molding is a tenon projecting from the wall of one container into the interspace between the outer container and the inner container, and the other molding is a ring projecting from the wall of the other tank and matching the tenon, one of the two moldings being displaceable in the direction of the other molding.  
         [0015]     Thus, one of the moldings is mounted on the inside of the outer container and the other on the outside of the inner container, in which case, depending on the form of the tank and other considerations, it is selectable which of the moldings is displaceable and which is fixed and which has the positive and which the negative contour.  
         [0016]     There are various possibilities for displacing one molding or the other. Either the displaceable molding is arranged on a shoe deformable in a bimetal-like manner, in which case this shoe is preferably mounted on the inside of the outer container and may be equipped with resistance heating. Or the displaceable molding is a permanent magnet which can be repelled by means of a separately excited magnet mounted on the outer wall of the outer container. Owing to the repulsion, said permanent magnet is brought into engagement with the other molding, without the wall needing to be perforated. For this purpose, a third molding may also be firmly mounted on the other container wall in each case. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     The invention is described and explained below with reference to figures in which:  
         [0018]      FIG. 1 : illustrates a tank according to the invention in a first embodiment, diagrammatically in cross section, with the detail A extracted,  
         [0019]      FIG. 2 : illustrates the same as  FIG. 1 , in a second embodiment,  
         [0020]      FIG. 3 : illustrates a variant of  FIG. 2 ,  
         [0021]      FIG. 4 : illustrates the same as  FIG. 1 , in a third embodiment,  
         [0022]      FIG. 5 : illustrates a detail B in  FIG. 1 , in a first embodiment,  
         [0023]     a) in a released position,  
         [0024]     b) in a restrained position,  
         [0025]      FIG. 6 : illustrates a detail B in  FIG. 1 , in a second embodiment,  
         [0026]     a) in the released position,  
         [0027]     b) in the restrained position.  
     
    
     DETAILED DESCRIPTION  
       [0028]     In  FIG. 1 , the outer container is designated by  1  and the inner container received approximately equidistantly in the latter is designated by  2 . The outer container  1 , the longitudinal direction of which may be thought of as being normal to the image plane, consists of a cylindrical lower part  3 , of an elongate dome-like upper part  4  and of a transition part  5  which appears to be straight in the image plane. Between the inner container  2  and the outer container  1 , there is an interspace  6 , which contains highly effective heat insulation, for example a multilayer vacuum insulation. A tubular perforation can be seen in the inner container  2 , and a further perforation could also be provided in front of or behind the image plane. A hollow body  8 , designed here as a carrying tube, runs, concentrically to the tubular perforation  7 , between fastenings  9 ,  10  on the two mutually opposite sides of the outer container  1 , approximately level with the transition part  5 . The inner container is suspended on this hollow body  8  by means of spatially arranged tension or compression struts  11 . These are arranged in such a way that displacements of the inner container  2  with respect to the outer container  1  caused by thermal expansion differences are compensated for and/or absorbed. In order to protect the inner container  2  against displacements with respect to the outer container  1  in the direction of extent of the container wall, restraints  16  may additionally also be provided.  
         [0029]     In the embodiment of  FIG. 1 , the fastening parts  9 ,  10  of the outer container  1  have formed in them abutments  13  which project inward on both sides and which can be displaced inward on the hollow body  8  by means of an actuator  14 , for example an electromagnet. For this purpose, either said abutments pass through the fastenings  9 ,  10 , so that the electromagnet  14  can engage directly, or the abutments  13  are themselves permanent magnets which, when the outer electromagnets  14  are activated, are repelled and are thus pressed inward. In the form of instance, a sealing diaphragm  15  is required. The latter must be gastight, so that the vacuum in the interspace  6  and inside the perforation  7  is maintained. The abutments  13  co-operate on both sides with supporting faces  12  which are formed as conical faces on the two outlet edges of the perforation  7 .  
         [0030]     In  FIG. 1 , the abutments do not bear against the supporting faces  12 . The inner container is connected to the outer container  1  only by means of the tension or compression struts  11 . This position corresponds to the standstill of the motor vehicle, during which normally no vibrations of any kind occur. The tension or compression struts  11  can thus be designed to be very lightweight and with a very small cross section, so that they form only minimal heat bridges. In the extracted detail A, the abutment  13  bears against the supporting face  12 , with the sealing diaphragm  15  being interposed. In this case, the inner container  2  is firmly connected, free of play, to the outer container  1 , the inner container is thus secured in the outer container  1  and the tension or compression struts are not subjected to load.  
         [0031]     In  FIG. 2 , identical components bear the reference symbols of the preceding figure. This embodiment differs in that a hollow body  18  is provided, which is extendable in its longitudinal direction and on which the abutments  23  are formed. Said hollow body is again connected to the inner container  2  by means of the tension or compression struts  11 . The supporting faces  22  are annular conical faces, this time with an inwardly open cone, because the abutments  23  lie within the supporting faces  22 . Said abutments are brought to bear in that, by means of a line  24 , pressure medium is supplied to or discharged from the pressure space  25  formed inside the hollow body  18 . In the event of an increase in pressure, the abutments  23  are shifted or displaced until they touch the supporting faces  22 .  
         [0032]     In the variant of  FIG. 3 , the hollow body  28  is designed in a very special way. It is designed, on both sides between the abutment  33  and a shoulder  30  for the engagement of the tension or compression struts, as a bellows  29  which changes its length in the event of a change in the internal pressure. In this case, there may be provision for the walls of the outer container  1  to yield outwardly in a diaphragm-like manner in the straight transition part  5 , this being indicated by broken lines. When pressure is applied through the line  24 , the two bellows  29  are lengthened and, on each side, bring the abutment  33  to bear against the supporting faces  22 , this being illustrated likewise by broken lines. The inner container is consequently secured in the outer container.  
         [0033]     The variant of  FIG. 4  differs from the preceding variants in that the hollow body  38 , which is fastened in the outer container  1  at  9  and  10  and which can again be connected to a pressure source by a line  24 , is connected via passages  39  to bellows-like structures  40  consisting of an elastic material. Four individual bellows-like structures  40  of this type can be seen in the figure, and the tension or compression struts  11  can engage between two of these in each case. Said structures could, however, also be provided elsewhere, that is to say outside the tubular perforations  7 , as is applicable to all the variants described. The material properties of the bellows-like structures  40  are selected such that they expand to the desired extent both in the radial and in the axial direction. As a result, with their abutments  43  formed on the respective outer bellows-like structure, they can co-operate with the supporting faces designed as in the version of  FIG. 2 . They may, however, also widen in the radial direction, so that all the bellows-like structures  40  butt against the wall of the tubular perforation  7 .  
         [0034]      FIG. 5  shows a restraint  16  additionally provided. Of the entire container, only a piece of the wall  50  of the outer container and a piece of the wall  51  of the inner container can be seen. A first molding  52  is fastened to the latter wall and a third molding  56  is fastened to the wall  50  of the outer container. Moreover, a second molding is provided, which can be moved in the normal direction to the walls  50 ,  51 . The contour  54  of the first molding  52  and of the third molding  56  corresponds to the negative contour  55  of the second molding  53 . When the first and third moldings  52 ,  56  are tenons of circular cross section, the second molding is a circular ring. It is designed as a permanent magnet. A separately excited magnet  57  is provided outside the wall  50  of the outer container. Depending on the polarity of the current supplied, said magnet either attracts the second molding  53 , which is in the position shown in  FIG. 5   a , or repels it, see  FIG. 5   b . In this position, the second molding  3  connects the first molding  52  and the third molding  56  positively. In this position, the walls  50 ,  51  cannot be displaced in parallel relative to one another.  
         [0035]     In the variant of  FIG. 6 , the second molding  52  is mounted as before, but the second molding  63  is mounted on a bimetallic shoe  64 . The bimetallic shoe  64  is firmly connected on one side to the wall  50  of the outer container. In the position of  FIG. 6   a , the bimetallic shoe  64  is flat and the second molding  63  does not co-operate with the first molding  52 ; a displacement of one of the two walls is possible per se. If, then, a specific temperature change occurs, as may also take place due to resistance heating installed in the bimetallic shoe  64 , the shoe curves up and brings the second molding  63  into the position  63 ′ in which it positively surrounds the first molding  52 .  
         [0036]     The restraints described again follow the teaching according to the invention. With the vehicle at a standstill, they do not touch one another, and, when the vehicle is in operation, they prevent a relative movement of the walls  50 ,  51  of the inner container and outer container in the direction of their extent. In the embodiment of  FIG. 6 , the restraint may additionally also exert a force acting normally to the walls  50 ,  51 .