Abstract:
A storage device for a liquid medium has a housing having an interior provided with at least one partitioning element dividing the interior into a first chamber for receiving the liquid medium and into a second chamber filled at least partially with a gas under pressure. The gas keeps the liquid medium in the first chamber under pressure. The at least one partitioning element is formed at least partially of an expandable bellows fastened pressure-tightly to a lid of the housing.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a storage device for a liquid medium that is received in a receiving chamber of a housing and separated by at least one partitioning element from a chamber filled at least partially with a gas that is under pressure and keeps the liquid medium in the receiving chamber under pressure. 
     2. Description of the Related Art 
     In the automotive field, piston and membrane storage devices are used which have two separate variable volume chambers separated from one another by a piston or a membrane or diaphragm. The storage device serves as a reservoir for a liquid medium, usually oil, contained in a first one of the chambers and maintained under pressure by a gas located in the second chamber. The storage devices can be adapted by variation of their size and the preload pressure of the gas to different requirements and conditions of use. Depending on the temperature and the pressure range, the piston as well as the membrane are prone to leak, i.e., the gas escapes from the gas chamber via the piston seal or by diffusion via the membrane. Particularly membrane storage devices are very susceptible to diffusion. By providing multi-layer membranes, diffusion can be reduced; however, it cannot be completely prevented. Accordingly, over the service life of the storage device the gas pressure in both systems will decrease gradually; this leads to a limitation of the usable pressure range and a reduction of the available storage volume. Large temperature differences in operation, combined with large piston or membrane movements, increase gas loss. In addition, the membrane is susceptible to tearing in the case of large deformations at low temperatures. Conventional gases are, for example, nitrogen (N 2 ) or carbon tetrafluoride (CF 4 ) as well as a mixture of these gases. The gas to be used is selected depending on the range of temperature of the respective application as well as the permissible diffusion, i.e., the permissible gas loss over the service life of the device. The materials of the piston seal and of the membrane must be matched to the media employed in the device. Otherwise, depending on the medium, swelling of the seal or gasket or failure of the membrane can be the result. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to configure the storage device of the aforementioned kind such that a reliable operation over the service life of the storage device is ensured. 
     In accordance with the present invention, this is achieved in that the partitioning element is formed at least partially by an expandable bellows. 
     In the storage device according to the invention, the receiving chamber for the liquid medium and the chamber for the gas are separated from one another by an expandable bellows. The volume change of this bellows is realized by a geometric change of the bellows folds. The connecting locations of the bellows can be simply welded in a pressure-tight way to other components. The bellows itself is reliably seal-tight so that the gas can neither escape through the bellows nor through sealing locations. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  shows a section of the storage device according to the present invention at maximum system pressure. 
         FIG. 2  shows the storage device according to  FIG. 1  at minimum system pressure. 
         FIG. 3  shows a second embodiment of the storage device according to the present invention in a representation corresponding to FIG.  1 . 
         FIG. 4  shows the second embodiment of the storage device according to the present invention in a representation corresponding to FIG.  2 . 
         FIG. 5  shows a third embodiment of the storage device according to the present invention in a representation corresponding to FIG.  1 . 
         FIG. 6  shows the third embodiment of the storage device according to the present invention in a representation corresponding to FIG.  2 . 
         FIG. 7  shows a fourth embodiment of the storage device according to the present invention in a representation corresponding to FIG.  1 . 
         FIG. 8  shows the fourth embodiment of the storage device according to the present invention in a representation corresponding to FIG.  2 . 
         FIG. 9  shows a fifth embodiment of the storage device according to the present invention in a representation corresponding to FIG.  1 . 
         FIG. 10  shows the fifth embodiment of the storage device according to the present invention in a representation corresponding to FIG.  2 . 
         FIG. 11  shows a sixth embodiment of the storage device according to the present invention in a representation corresponding to FIG.  1 . 
         FIG. 12  shows the sixth embodiment of the storage device according to the present invention in a representation corresponding to FIG.  2 . 
         FIG. 13  shows a seventh embodiment of the storage device according to the present invention in a representation corresponding to FIG.  1 . 
         FIG. 14  shows the seventh embodiment of the storage device according to the present invention in a representation corresponding to FIG.  2 . 
         FIG. 15  is a section of an eighth embodiment of the storage device according to the present invention. 
         FIG. 16  shows partially in an end view and partially in section a control device for transmissions of motor vehicles with the storage device according to FIG.  15 . 
         FIG. 17  shows an exploded view of an embodiment of the storage device according to the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The storage device to be described in the following serves as a reservoir for a liquid medium, usually oil, and is used in the automotive industry. For example, such storage devices can be used in electronic-hydraulic control device for transmissions of motor vehicles; this will be explained in more detail in an exemplary fashion in connection with FIG.  16 . With these control devices, the gutters and gears of the transmission can be selected in an automatically controlled manual transmission (direct shift gearbox). 
     In the embodiment according to FIG.  1  and  FIG. 2 , the storage device has a cup-shaped housing  1  with a cylindrical housing jacket  2  and a housing bottom  3 . At least one opening  4  is provided as a pressure connector in the housing bottom  3  by which the interior of the housing is in communication with a hydraulic system. A lid  5  is attached to the end face of the housing jacket  2  which has at least one filling opening  6  for a pressure medium, preferably gas. The filling opening  6  is closed by means of a closure member  7  in a pressure-tight way. The filling opening  6  can be closed, for example, by welding. Also, it is possible to provide the filling opening with a check valve which ensures a pressure-tight closure. 
     The filling opening  6  opens into a chamber  8  delimited by a portion of the lid  5  and the partitioning element comprising bellows  9  and bottom part  10 . The lateral bellows  9  forms the sidewall of the chamber  8  and is connected with a first end in a pressure-tight way to the inner side of the lid  5 . The bottom part  10  is also connected in a pressure-tight way to the other end of the bellows  9 . The bellows  9  is advantageously made of stainless steel. 
     The disk-shaped lid  5  is connected along its edge in a pressure-tight way to the housing jacket  2 , for example, by welding or gluing. 
     The housing jacket  2  surrounds the bellows  9  at a distance. In this way, the medium supplied to the housing  1 , for example, oil or another liquid, can flow into the space defined between the housing jacket  2 , the bellows  9 , and the housing lid  5 , which space is the housing chamber  11 . The medium contained in the housing chamber  11  is subjected to a system pressure p s  while the gas contained in the chamber  8  is under the gas pressure p g . The bellows  9  is seal-tight so that the gas enclosed by it cannot escape into the housing chamber  11 . For filling the chamber  8 , any suitable gas can be used, in particular, nitrogen or carbon tetrafluoride. 
       FIG. 1  shows the situation in which the medium contained in the housing chamber  11  is subjected to maximum system pressure p max . This has the result that the bellows element  9 ,  10  is compressed by elastic deformation of the bellows  9  until the pressure p g  of the gas contained in the chamber  8  corresponds to the maximum pressure p max  of the medium contained in the housing chamber  11 . The pressure p g  of the gas in the chamber  8  is determined as follows. 
       p   g   =p   system −stroke of bellows×spring rate of the bellows  9 . 
       FIG. 2  shows the situation with minimum system pressure. The bellows  9  is expanded by the pressure p g  of the gas contained in the chamber  8 . In the illustrated example, the bellows  9  is expanded to such an extent that the bottom part  10  rests against the housing bottom  3 . The pressure p g  of the gas in the chamber  8  corresponds to the minimum pressure p min  of the gas. The volume V g  of the gas in the chamber  8  corresponds to the maximum volume V max . 
     The bottom part  10  closes the opening  4  when the bellows  9  is in its maximum expansion position so that no medium of the hydraulic system can reach the housing chamber  11 . This has the result that the pressure p D  of the medium present in the area between the bellows  9  and the housing jacket  2  corresponds to the pressure p g  of the gas in the chamber  8 . 
     The bellows element  9 ,  10  is comprised of steel, preferably stainless steel, and can therefore be used within a very large range of temperatures of use. It is possible to use this bellows storage device in aeronautics and aerospace industries where very great temperature fluctuations are encountered. The filling gas can be any suitable gas because it cannot diffuse from the chamber  8  into the chamber  11  through the bellows  9 . In this way, gas loss does not occur and the least expensive available gas can be used. The hydraulic medium, which reaches via the opening  4  the housing chamber  11 , can be almost any liquid because the bellows  9  made of stainless steel is insensitive with regard to most liquids and to corrosion. If needed, the housing  1  and the lid  5  can also be made of stainless steel. 
     The bellows element  9 ,  10 , depending on its configuration and geometry, can be filled up to a certain differential pressure between the inner and outer side. When a higher preload pressure of the gas is required in the bellows element  9 ,  10 , a corresponding counterpressure can be provided by the system (inner chamber  11  of the housing) so as to maintain a differential pressure below the permissible limit. For this purpose, the inner chamber  11  is filled with so much oil that no air is present in the housing chamber  11  and the bellows  9  with the bottom part  10  just closes off the openings  4  in a seal-tight way. Subsequently, the filling pressure of the bellows storage device  9 ,  10  can be increased almost to any desired level because the pressure on the exterior of the bellows  9  increases without causing deformation of the bellows as a result of the medium present in the housing chamber  11 , which medium that is to be considered incompressible; in this way the bellows cannot be damaged. 
     In order to prevent damage of the bellows after gas has been filled into the chamber  8  when the pressure in the hydraulic system drops below the gas preload pressure, the counterpressure is maintained at the preload pressure level by closing the bore  4  on the oil supply side. This can be achieved by the bellows  9  itself or by the bottom part  10  which at maximum bellows stroke rests against the housing bottom  3  of the housing  1  and closes off the opening  4 . With a corresponding configuration of the opening  4  on the inner side of the housing  1 , seal-tightness of this closure can be ensured. When during operation the pressure in the housing chamber  11  increases past the adjusted preload pressure in the chamber  8 , the bottom part  10  of the bellows  9  is pushed back and, in this way, the opening  4  is released. The storage device can then fulfill its function. The gas volume in the chamber  8  can be reduced by means of the closure member  7  or by means of an incompressible medium that is not miscible with the filling gas, for example, oil. In this way, the pressure/filling volume characteristic line of the bellows storage device can be adjusted to the maximum permissible bellows stroke. 
     In the embodiment according to  FIGS. 3 and 4 , in the chamber  8  of the bellows element  9 ,  10  not only a gas but also an incompressible medium  13  in the form of liquid, for example, oil, is present. The gas  12  and the medium  13  do not mix with one another. 
     In comparison to the preceding embodiment, the gas volume is reduced by use of the liquid  13 . By means of the liquid  13 , the pressure/filling volume characteristic line can be adjusted with respect to its gradient. In comparison to filling the chamber  8  with gas only (FIGS.  1  and  2 ), the pressure/filling volume characteristic line becomes steeper, when the incompressible medium  13  is used in the chamber  8 . By means of the mixing ratio of gas  12  and liquid  13  the pressure increase can thus be optimally adjusted via the stroke. 
     The storage device according to  FIGS. 3 and 4  is otherwise embodied in the same way as the preceding embodiment.  FIG. 3  shows the situation in which the system pressure in the housing chamber  11  corresponds to maximum pressure p max . Correspondingly, the deformation of the bellows  9  has caused the bottom part  10  to be retracted to such an extent that it is spaced from the housing bottom  3 . 
       FIG. 4  shows the situation where the system pressure p min  is at minimum. The bellows  9  has correspondingly expanded to such an extent that the bottom part  10  rests against the inner side of the housing bottom  3  and closes off the opening  4 . The volume of the gas contained in the chamber  3  is V max  in this case, while the volume of the liquid  13  has remained unchanged. The gas volume V in the chamber  8  is V min  for maximum system pressure. This results in the following equation.
   p   min   /p   max   =V   max   /V   min . 
     FIG.  5  and  FIG. 6  show a storage device with the bellows element  9 ,  10  in whose chamber  8  the gas  12  is located. Similar to the embodiment according to FIG.  3  and  FIG. 4 , the gas volume is reduced in comparison to the embodiment according to FIG.  1  and FIG.  2 . In contrast to the embodiment according to FIG.  3  and  FIG. 4 , the volume reduction of the gas  12  is realized by a solid body  14  which is fastened on the inner side of the lid  5 . It has at least one through opening  15  which connects the filling opening with the chamber  8 . The solid body  14  is a filling member whose size depends on the desired volume reduction of the gas  12 . The bellows  9  surrounds the solid body  14  at a spacing. 
     Otherwise, the storage device according to FIG.  5  and  FIG. 6  is identical to the embodiment according to FIG.  1  and FIG.  2 . In the illustration according to  FIG. 5 , maximum system pressure p max  is present In the housing chamber  11 . The bottom part  10  in this way is spaced from the housing bottom  3 . The bellows element  9 ,  10  is configured such that the bottom part  10  has a spacing from the solid body  14  at maximum system pressure. 
       FIG. 6  shows the conditions when the system pressure is at minimum (p min ). As in the preceding embodiments, the bottom part  10  of the bellows storage device rests against the inner side of the housing bottom  3  and closes off the opening  4  in the housing bottom  3 . 
     By selecting a proper size of the solid body  14 , the pressure/filling volume characteristic line of the bellows storage device can be optimally adjusted. 
     FIG.  7  and  FIG. 8  show a bellows storage device which is basically of the same configuration as the embodiment according to FIG.  1  and FIG.  2 . The difference resides only in the special shape of the housing  1  and of the bottom part  10  of the bellows element  9 ,  10 . The housing bottom  3  is spherical and has centrally an opening  4  which connects the housing chamber  11  with the hydraulic system. The opening  4  is provided in the projection  16  of the housing bottom  3  which projects inwardly and outwardly. 
     The bottom part  10  of the bellows element  9 ,  10  has centrally a cylindrical projection  17  which extends in the direction toward the projection  16  of the housing  1  and has a plane bottom part  18 . The bellows  9  is fastened on the edge of the bottom part  10 , as in the preceding embodiments. Within the bellows element  9 ,  10 , the gas  10  is provided which completely fills the chamber  8 . 
       FIG. 7  shows the conditions for maximum system pressure p max . The bottom part  18  of the bottom part  10  has a spacing from the housing projection  16 . The gas  12  has minimum volume V min  . 
       FIG. 8  shows the conditions for minimal system pressure p min . As a result of the minimum system pressure, which is smaller than the gas pressure in the chamber  8 , the bellows  9  is expanded until the bottom part  18  of the bottom part  10  rests against the plane end face  19  of the part of the projection  16  projecting into the housing chamber  11  and closes off the opening  4 . The gas  12  in the chamber  8  has thus maximum volume V max . 
     The embodiment according to FIG.  9  and  FIG. 10  corresponds substantially to the embodiment of FIG.  7  and FIG.  8 . In the chamber  8  of the bellows element  9 ,  10 , in accordance with the embodiment of FIG.  3  and  FIG. 4 , an incompressible medium  13 , for example, oil, is provided in addition to the gas  12 . The incompressible medium  13  reduces the gas volume in the bellows element  9 ,  10 , as has been explained in connection with FIG.  3  and FIG.  4 . 
       FIG. 9  shows the position of the bellows  9  when the system pressure in the housing chamber  10  is at maximum. In this case, the bellows  9  is compressed to such an extent that the inner pressure in the chamber  8  corresponds to that of the externally acting system pressure. The bottom part  18  has a spacing from the housing projection  16  so that the housing chamber  10  is connected with the hydraulic system by means of the opening  4 . 
       FIG. 10  shows the situation where the pressure in the housing chamber  10  is at minimum. The bottom part  18  rests against the plane end face  19  of the projection  16  and closes off the opening  4 . As in the preceding embodiments, the housing jacket  2  surrounds the bellows  9  at a spacing so that the medium contained in the housing chamber  11  can flow into the area between the housing jacket  2  and the bellows  9 . 
     The embodiment according to  FIGS. 11 and 12  corresponds essentially to the embodiment according to FIG.  7  and FIG.  8 . The only difference is that in the chamber  8  of the bellows element  9 ,  10 , in accordance with the embodiment of FIG.  5  and  FIG. 6 , a solid body  14  is provided in addition to the gas  12 . Depending on the size of the solid body  14 , the gas volume in the chamber  8  is different. The body  14  is identical to the embodiment according to FIG.  5  and FIG.  6  and also connected to the lid  5 . 
       FIG. 11  shows the situation in which the system pressure in the housing chamber  11  is at maximum (p max ) so that the bottom part  18  is spaced from the projection  16  of the housing  1 . 
       FIG. 12  shows the situation in which the system pressure in the housing chamber  11  is at minimum (p min ). The bellows  9  is expanded to such an extent that the bottom part  18  rests against the end face  19  of the projection  16  and closes off the opening  4 . 
     FIG.  13  and  FIG. 14  show the bellows storage device mounted in a control device for automatically controlled manual transmissions of vehicles. The control device will be explained in more detail in connection with FIG.  16 . It has a housing  1  with a receptacle  20  for the bellows element  9 ,  10 . A pressure bore  21  opens into the receptacle  20  via which the medium is supplied at system pressure to the receptacle  20 . The gas  12  is contained in the bellows element  9 ,  10 . At the end opposite the bottom part  10 , the bellows element  9 ,  10  is provided with a plate-shaped fasting part  22  which closes off the chamber  8  of the bellows storage device and with which it rests against the closure  23  of the receptacle  20 . The closure  23  is inserted in a sealed fashion into the receptacle  20  and closes off the receptacle  20  tightly. 
     According to  FIG. 13 , the system pressure p min  is minimal so that the bellows  9  has expanded to such an extent that the bottom part  10  of the bellows element  9 ,  10  rests against the wall  24  of the receptacle  20  neighboring the pressure bore  21 . The bellows  9  is arranged such in the receptacle  20  that the medium supplied via the pressure bore  21  can reach the space defined between the bore wall, the bellows  9 , and the closure  23 . 
     When the system pressure is at maximum (p max —FIG.  14 ), the bellows element  9 ,  10  is compressed until the pressure of the gas  12  in the chamber  8  corresponds to the maximum system pressure p max . 
     The bellows storage device according to  FIGS. 13 and 14  can be provided corresponding to the embodiments of FIG.  3  and  FIG. 4  as well as FIG.  5  and  FIG. 6  with an incompressible medium  13  or with a solid body  14  in addition to the gas  12  in order to adjust the pressure/filling volume characteristic line to the respective application. 
       FIGS. 15 and 16  show a bellows storage device which is mounted in an electronic-hydraulic control device for automatically controlled manual transmissions of motor vehicles. The control device can be used generally for transmissions, for example, also for twin-clutch transmissions. The control device has a magnetic housing  25  in which solenoids are arranged (not illustrated). The solenoid housing  25  rests with flange  26  against a transmission housing (not illustrated) and is attached thereto in a seal-tight way. By means of the solenoids arranged in the solenoid housing  25  one or several clutches can be actuated and gears and gutters of the transmission can be selected. The control device with hydraulic housing  27  projects through a mounting opening of the transmission housing; the housing  27  is connected in a seal-tight way to the magnet housing  25  arranged externally on the transmission housing. A cover  28  is placed onto the solenoid housing  25  and covers electronic components arranged underneath. 
     The hydraulic medium which is controlled by the solenoids arranged in the solenoid housing  25  is conveyed by means of a pump arranged on the underside of a motor  29 . The pump is positioned within the transmission housing while the motor  29  projects to the exterior. Most of the motor  29  is located outside of the transmission housing. A line  30  is connected to the pump and the hydraulic medium is taken in via this line, as is known in the art. The hydraulic medium is advantageously transmission fluid which is present in the transmission housing. 
     The hydraulic housing  27  has a lateral projection  31  which is positioned within the transmission housing. The pump is connected to its underside and the motor  29  to its top side. The pressure medium which is conveyed by the pump flows via at least one line (not illustrated) to the solenoids in the hydraulic housing  27 . The bellows element  9 ,  10  is integrated into the control device. It is arranged in a receptacle  32  of the solenoid housing  25 . A pressure bore  33  for supplying the pressure medium opens into the receptacle  32 . The bellows  9  is fastened to the housing bottom  34  of the receptacle  32 . Depending on the pressure of the hydraulic medium within the receptacle  32 , the bellows  9  is compressed to a greater or lesser extent. 
     The hydraulic housing  27  has a receptacle  35  for an actuating device  36  that acts as a gear selector for selecting the gutters and the gears of the transmission. The actuating device  36  has a U-shaped control element  37  positioned in the receptacle  35  which can be moved by means of actuating elements (not illustrated) transversely to the plane of the drawing. These actuating elements can be piston-cylinder units having piston rods engaging the legs of the control element  37 . Between the legs of the control element  37  a spherical end of a two-arm switching lever  38  is positioned which is supported on a shaft  39  penetrating the receptacle  35  perpendicularly to the switching lever  38  and supported with its two ends in the hydraulic housing  27 . The shaft  39  extends parallel to the longitudinal axis of the control element  37 . 
     The end of the switching lever  38  projecting downwardly from the receptacle  35  supports a coupling member  40  with which the switching lever  38  can be coupled to switching fingers  41  which are seated fixedly on switching shafts  42  of the transmission extending parallel to one another.  FIG. 16  shows only one of the switching shafts  42 . 
     The switching lever  38  is positioned on the shaft  39  and is axially slidable by means of a bushing  43 . For moving it, two adjusting members (not illustrated) are provided which engage the right and left end faces of the control element  37  (FIG.  16 ); the adjusting members are preferably pressure-loaded pistons. Depending on the load of these adjusting members, the control element  37  and also the switching lever  38  are moved on the shaft  39  in the desired direction. Since the coupling member  40  of the switching lever  38  engages the selected switching finger  4 O of the corresponding switching shaft  42 , the switching shaft  42  is also moved in the desired direction. 
     First, the U-shaped control element  37  is pivoted about the shaft  39  so that the coupling member  40  engages the corresponding coupling receptacle  44  of the switching finger  41  of the corresponding switching shaft  42 . By pivoting the switching lever  38  about the shaft  39 , the switching shaft  42  designated for a certain gutter of the transmission is coupled by means of the coupling member  40  with the switching lever  38 . As soon as the gutter of the transmission has been selected, the control element  37  is moved by the adjusting members (not illustrated) so that by movement of the selected switching shaft  42  the gear available in selected gutter is selected. 
     In order to detect the required pivot path of the switching lever  38  when selecting the gutter and the required displacement stroke of the switching lever  38  for selecting the desired gear, the shaft  39  has correlated therewith at least one sensor  45 , preferably a PLCD sensor (permanent magnet linear displacement sensor) which is arranged in the hydraulic housing  27 . 
     Since the bellows element  9 ,  10  is arranged within the control device, a compact configuration is provided. 
       FIG. 15  shows the bellows element  9 ,  10  in the receptacle  32 . It is filled with hydraulic medium at the respective system pressure.  FIG. 15  shows the situation where the hydraulic medium in the receptacle  32  is at maximum system pressure p max . When the system pressure drops to minimum system pressure p min , the bellows element  9 ,  10  expands to such an extent that the bottom part  10  closes off the bore  33 . 
     The bellows element  9 ,  10  according to FIG.  15  and  FIG. 16  can be configured in the same way as described in the preceding embodiments. In particular, the bellows storage device can contain not only the gas  12  but also the incompressible medium  13  or the solid body  14 . 
       FIG. 17  shows an exploded view of a bellows storage device with bellows  9  which is closed off at one end by the bottom part  10  and with the other end is fastened in a pressure-tight way to the lid  5 . The chamber is delimited by the lid  5 , the bellows  9 , and the bottom part  10 . The chamber contains the gas, optionally together with the incompressible medium  13  and the solid body  14 . This bellows storage device is inserted as a pre-mounted unit into the housing  1 . The housing comprises the housing bottom  3  with the projection  16  in which the opening  4  is provided with which the pressure medium can reach the interior  11  of the housing  1 . The end face  46  of the jacket  2  of the housing  1  is connected pressure-tightly to the lid  5  which preferably has the same contour as the housing jacket  2 . 
     While specific embodiments of the invention have been shown and described in detail to illustrate the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.