Abstract:
A valve ( 18 ), for a valve assembly ( 10 ) for regulating the pressure of a fluid guided in a hydraulic system for supplying pressure to at least one hydraulic consumer ( 12   a,    12   b ), includes a pilot control stage ( 48 ) and a main control stage ( 38 ) for at least partially clearing or blocking a fluid path from a supply connection (P) to an outflow connection (T). A relief stage ( 54 ) for pressure relief of a fluid chamber is arranged between the pilot control stage ( 48 ) and the main control stage ( 38 ). The relief stage ( 54 ) compares the existing load pressure at load terminal (LS) dedicated to the hydraulic consumer ( 12   a,    12   b ) with the outflow pressure at the outflow connection (T), clearing the pressure relief if both pressures are approximately the same. The relief stage ( 54 ) can be directly connected to the load connection (LS) and can be charged with load pressure.

Description:
FIELD OF THE INVENTION 
     The invention relates to a valve for a valve assembly for regulating the pressure of a fluid conducted in a hydraulic system for supplying pressure to at least one hydraulic consumer. The valve comprises a pilot control stage and a main control stage for the at least partial clearing or blocking of a fluid path from a supply connection to an outflow connection. A relief stage for releasing the pressure of a fluid chamber is disposed between the pilot control stage and the main control stage. The relief stage compares the load pressure present on a load connection associated with the at least one hydraulic consumer with the outflow pressure at the outflow connection and clears the pressure relief when both pressures are close to one another or equal. 
     BACKGROUND OF THE INVENTION 
     Such a valve is known, for example from WO 2011/045063 A1, and is used to adapt the transported fluid current and the supply pressure to the requirement of the at least one hydraulic consumer. The load pressure, in the case of several hydraulic consumers the highest load pressure, is reported back to the valve via a hydraulic load sensing system and is taken into consideration during the regulation of the pressure in such a manner that given a load pressure close to or equal to the outflow pressure, a pressureless circulation, is adjusted via the relief stage. In as far as supply pressure is required by the hydraulic consumer and the load pressure rises in a corresponding manner, the relief stage is closed again and the pilot control stage and the main control stage assume their particular control position. In this manner the power loss in the hydraulic system can be reduced for supplying pressure to the at least one hydraulic consumer. 
     SUMMARY OF THE INVENTION 
     The present invention addresses the problem of simplifying the construction of the valve and making the valve accessible for other functions. 
     This problem is basically solved by a valve where a relief stage can be directly connected to a load connection and loaded with loading pressure. The transfer of the loading pressure to the relief stage as well as the pressure relief, are integrated in the valve. The fluid chamber can be realized with a few pressure connections and fluid connections that can be constructed in a simple manner. The valve advantageously comprises a valve housing with at least one connection line from the load connection to the relief stage and constructed in the housing, preferably as a bore. The load pressure present on the load connection can be guided directly, i.e., without passing through or flowing through other fluid chambers, to the relief stage via the connection line. Delays or influences possibly associated with other fluid chambers during the operation of the valve of the invention are avoided. 
     An especially compact construction of the valve is achieved if at least one of the stages comprises a valve piston that is shiftably disposed in a particular piston chamber in the valve housing and is preferably pre-tensioned. The piston chamber associated with the relief stage is loaded on the one end by the load pressure, which is typically present in a load sensing line, and on the other end by the outflow pressure. The relief stage can be constructed as a slide valve or a seat valve. The valve piston and/or the valve element are disposed and pre-tensioned in such a manner that a fluid outflow can be cleared from the fluid chamber to its pressure relief at no or only a low load pressure. 
     Advantageously, the pump pressure can be transmitted via the main control stage, preferably via a passage bore formed in the appropriate valve piston, to the fluid chamber. The fluid chamber is connected in a fluid-conducting manner to the pressure relief controllable by the relief stage. The relief stage assumes a position that clears the pressure relief of the fluid chamber or a blocking position according to the ratio between the two pressures, the load pressure and the outflow pressure, present on the relief stage. 
     The fluid chamber can be subdivided into a first partial chamber associated with the pilot control stage and a second partial chamber associated with the main control stage. A throttle is preferably disposed between both partial chambers. A throttle disposed between the second partial chamber and the first partial chamber of the fluid chamber can therefore serve as a damping member for the relief stage. In a preferred embodiment of the invention, the relief stage controls a connection from the fluid chamber, in particular from the second partial chamber, to a relief line associated with the outflow connection. 
     Advantageously, the pilot control stage and/or the main control stage can be loaded with loading pressure. A connection line from the pilot control stage to the relief line is especially preferably provided in a fluid-conducting manner. A pressure relief of a corresponding piston chamber of the pilot control stage can take place via the connection line. This connection line can extend from the second piston chamber to the relief line in the valve housing. 
     If another connection line is provided from the fluid chamber, in particular from the first partial chamber, to the load connection, another throttle is preferably arranged in the other connection line. A desired pressure change between the fluid chamber and the load connection can be adjusted by the other throttle. Fluid, such as hydraulic oil, can flow off at the load connection via the other connection line from the main control stage to the load connection so that the valve in accordance with the invention can regulate a corresponding load pressure given a connection of the load connection to a hydraulic consumer. In this preferred embodiment of the invention, the relief stage clears a load sensing line to the load tap in at least one hydraulic consumer. 
     Instead of an integrated construction of pilot control stage, main control stage and relief stage, a decentralized individual disposition of the cited stages to a valve in accordance with the invention is also possible. The relief stage can be disposed, for example, in a parallel disposition to the pilot control stage and the main control stage between a pump and a container for fluid. The relief stage can be directly pre-controlled. However, the relief stage can also be constructed as an electrically actuatable 2/2-way valve that can be controlled, for example, by a control- and/or regulating device processing the signals of a pressure sensor. 
     The invention furthermore comprises a valve assembly for regulating the pressure of a fluid conducted in a hydraulic system for supplying pressure to at least one hydraulic consumer, with at least one valve in accordance with the invention. 
     The previously cited features and the ones cited below can be realized in accordance with the invention individually or in any combinations with each other. 
     Other objects, advantages and salient features of the present invention will become apparent from the following detailed description, which, taken in conjunction with the drawings, discloses a preferred embodiment of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Referring to the drawings that form a part of this disclosure and schematic and not to scale: 
         FIG. 1  is a side view in section of a valve for regulating the pressure of a fluid, with the valve located in a hydraulic system for supplying pressure to two hydraulic consumers, according to an exemplary embodiment of the invention; 
         FIG. 2 a -2 d    are side views in section of the valve of  FIG. 1  in different switching positions; and 
         FIG. 3  is an enlarged, partial side view in section of the valve of a section of  FIG. 2   b.    
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a valve assembly  10  with a closed hydraulic circuit for supplying two hydraulic consumers  12   a ,  12   b  with fluid. Fluid is transported by a pump  14  constructed as a constant pump from a reservoir  16  to the hydraulic consumers  12   a ,  12   b  that are each constructed as a hydro-motor with two possible directions of flow. The hydraulic circuit including the pump  14  and the hydraulic consumers  12   a ,  12   b  is closed by a valve  18  in accordance with the invention. The hydraulic consumers  12   a ,  12   b  are regulated by electrically actuatable 4/3-way valves  20   a ,  20   b , respectively. The load pressure present on the particular hydraulic consumer  12   a ,  12   b  is reported to a load sensing (LS) line  26   a ,  26   b  by a changeover valve  22   a ,  22   b . This valve control is preceded by a 2/2-way valve  24   a ,  24   b  with a pressure-limiting function in the open switching position. 
     To operate the hydraulic consumers  12   a ,  12   b  at a programmable speed, the volume flow of the fluid transported by the pump  14  is regulated by the valve  18 . This combination of a constant pump with the valve  18  for pressure regulation is an economical alternative to an adjusting pump. A nonreturn valve  28   a ,  28   b  is connected into the hydraulic circuit in the load sensing lines  26   a ,  26   b , provided for tapping off the load in the particular hydraulic consumer  12   a ,  12   b , in front of each changeover valve  22   a ,  22   b . Each nonreturn valve has the same opening pressure and opens in the direction of the valve  18 , more precisely in the direction of its load-sensing connection LS. This parallel connection of the load sensing lines  26   a ,  26  regarding the valve  18  allows a comparison of the two load pressures on the hydraulic consumers  12   a ,  12   b . The greater of the two load pressures is considered for the pressure regulating on the valve  18 . 
     The valve  18  is connected or can be connected by its load connection LS to the load sensing lines  26   a ,  26   b . The valve  18  is connected or can be connected by its supply connection P to the supply line  29  supplied with pressure by the pump  14  and extending to the hydraulic consumers  12   a ,  12   b , as well as by its outflow connection T to a reservoir  16  that can be a pressure agent container or a tank. The valve  18  is an independent unit that can be manipulated and can be inserted as needed into the valve assembly  10 . 
     The design of the valve  18  can be gathered from the  FIGS. 2 a -2 d    that show the valve  18  in section with a cartridge-like valve housing  30  designed as a screw-in valve. A first piston chamber  32 , a fluid chamber  34 , which is subdivided into a first partial chamber  35   b  and a second partial chamber  35   a  and a second piston chamber  36  are constructed in the valve housing  30  coaxially to the axis of rotation R. A main control stage or piston  38  is constructed in the first piston chamber  32  by valve pistons that can shift in the particular piston chamber  32 ,  36  parallel to the axis of rotation R. A pilot control stage or piston  48  is constructed in the second piston chamber  36 . The particular valve pistons  38 ,  38  are pre-tensioned by a first spring element  40  and a second spring element  50 , respectively. 
     A third piston chamber  52  constructed in the valve housing  30  is parallel to the fluid chamber  34  and connected to it, more precisely to the second partial chamber  35   a , by a connection  60 . A valve piston of the relief stage  54  is shiftably disposed in the third piston chamber  52  and pre-tensioned by a third spring element  56 . The third piston chamber  52  is connected by a connection line  61  to the load connection LS and by a relief line  62  to the outflow connection T, so that the load pressure and the outflow pressure are present on the relief stage  54 . The relief stage  54  compares the load pressure to the outflow pressure and opens, as soon as the load pressure on the load connection LS is close to or equal to the outflow pressure on the outflow connection T, a bypass for relieving the pressure of the fluid chamber  34 . 
     In the exemplary embodiment shown, the bypass is realized by a connection  60  between the fluid chamber  34  and the relief line  62  extending to the outflow connection T. The connection  60  can be cleared by the valve piston of the relief stage  54 , as is shown in the  FIGS. 2 b  and 2 c   ), or closed, as shown in the  FIGS. 2 a  and 2 d   . In the clearing position of the valve piston of the relief stage  54 , an annular groove  58  formed in the valve piston is disposed in the crossing area between the third piston chamber  52  directed parallel to the axis of rotation R and the connection  60  extending transversely to the third piston chamber  52  and to the axis of rotation R. In the open position, cf.  FIG. 3 , fluid can flow off from the fluid chamber  34  via the connection  60  past the annular groove  58  of the valve piston of the relief stage  54  via the relief line  62  to the outflow connection T. 
     In the view of  FIG. 2 a   , the valve piston associated with the pilot control stage  48  and loaded by the second spring element  50  rests on a valve seat formed on the appropriate end of the fluid chamber  54  or of the first partial chamber  35   b . The valve piston associated with the main control stage  38  and loaded by the first spring element  40  is disposed in the valve housing  30  in such a manner that a fluid path  40  is blocked by the supply connection P via radial passage openings  42  formed in a section of the valve housing  30 . The load pressure present on the load connection LS exceeds the outflow pressure or tank pressure present on the outflow connection T so that the third spring element  56  loading the valve piston of the relief stage  54  is compressed and the bypass to the pressure relief, here the connection  60 , is blocked, in other words, closed. 
     As soon as the load pressure drops and approaches the outflow pressure, the valve piston moves into the position shown in the  FIGS. 2 b  and 2 c   , clearing the connection  60 . A fluid path from a supply connection P or pump connection to the outflow connection T or tank connection is cleared corresponding to the pressure drop in the fluid chamber  34  accompanying the pressure relief. While the fluid path in  FIG. 2 b    is only partially cleared, the valve piston of the main control stage  38  is located in the view of  FIG. 2 c    in its position that maximally clears the fluid path and rests on a valve seat formed on the valve housing  30 . Fluid can also flow from this fluid chamber to the outflow connection T via another connection  60 ′ constructed as a bore and that extends from the second piston chamber  36  to the relief line  62  in the valve housing  60 . 
     The fluid pressure on the fluid chamber  34  present on the pump side on the main control stage  38  can be transferred between the main control stage  38  and the pilot control stage  48  via a passage bore  44  constructed centrally, that is, along the radial axis R, in the valve piston of the main control stage  38 . As soon as the load pressure rises again and exceeds the outflow, the relief stage  54  and in a corresponding manner the connection  60  from the fluid chamber  34  to the outflow connection T is closed and the pilot control stage  48  is opened by the rising fluid pressure in the fluid chamber  34 , as shown in  FIG. 2 d   . In the following step, the valve position or switching position in  FIG. 2 a   , the blocking of the fluid path from the supply connection P to the outflow connection T is adjusted again. 
     As  FIG. 3  in particular shows, another connection line  64  extends from the load connection LS to the fluid chamber  34 , more precisely to the first partial chamber  35   b . A pressure stage is set in the other connection line  64  by another throttle  66 . The valve  18  offers as another function, in other words, the option of an outflow of fluid such as hydraulic oil via the other connection line  64 . Upon the connection of a hydraulic consumer  12   a ,  12   b  on the corresponding load connection LS, the valve  18  regulates the corresponding load pressure, which can be reduced as required by the relief stage  54 . 
     While one embodiment has been chosen to illustrate the invention, it will be understood by those skilled in the art that various changes and modifications can be made therein without departing from the scope of the invention as defined in the claims.