Abstract:
A valve includes a housing, in which a first valve body is accommodated so that it is moveable in a direction of a longitudinal axis, a first valve seat configured to be closed by the first valve body and arranged on the housing, a first fluid flow path extending from a first connection via the first valve seat to a second connection, a second valve seat closeable by a moveable second valve body, the second valve body formed separately from the first valve body, a second fluid flow path extending from the first connection via a bypass duct in the first valve body, onwards via the second valve seat to the second connection, so that pressure at the first connection is limited upwardly by the first and the second valve body in that hydraulic fluid is led to the second connection via the first fluid flow path.

Description:
[0001]    This application claims priority under 35 U.S.C. §119 to patent application no. DE 10 2014 219 740.6, filed on Sep. 30, 2014 in Germany, the disclosure of which is incorporated herein by reference in its entirety. 
         [0002]    The disclosure relates to a valve as described herein. 
       BACKGROUND 
       [0003]    The data sheet RE 64602, discloses a valve. The valve is a pilot-operated pressure relief valve with feed function, which is designed as a built-in valve. The valve has a housing, which is also referred to as a bushing. A first valve body, which is also referred to as a piston, is accommodated in the housing so that it is moveable relative to a longitudinal axis. A first valve seat, which can be closed by the first valve body, is arranged on the housing. A first fluid flow path extends from a first connection via the first valve seat to a second connection. A pilot control is furthermore provided, which comprises a second valve seat, which can be closed by a moveable second valve body. The second valve body is formed separately from the first valve body. A second fluid flow path extends from the first connection via a bypass duct in the first valve body, onwards via the second valve seat to the second connection. The pressure at the first connection is limited upwardly by the first and the second valve body in that hydraulic fluid is led to the second connection via the first fluid flow path. The valve is therefore a pressure relief valve, which limits the pressure at the first connection. 
         [0004]    The first connection is arranged end face-on to the first valve body, relative to the longitudinal axis, the second connection being arranged circumferentially to the first valve body, relative to the longitudinal axis. 
         [0005]    The data sheet RD 18318-22, moreover discloses a pressure relief valve in which the first connection is arranged circumferentially to the first valve body, relative to the longitudinal axis, the second connection being arranged end-face on to the first valve body, relative to the longitudinal axis. This valve has no pilot control. 
       SUMMARY 
       [0006]    The object of the disclosure is to transfer the connection assignment of the latter valve to the first aforementioned valve. 
         [0007]    This object is achieved in that the first connection is arranged circumferentially to the first valve body, relative to the longitudinal axis, the second connection being arranged end face-on to the first valve body, relative to the longitudinal axis, a first orifice of the bypass duct being arranged circumferentially to the first valve body, relative to the longitudinal axis. The proposed arrangement of the first orifice allows hydraulic fluid, which flows from the circumferentially arranged first connection according to the disclosure, to pass into the bypass duct. The pilot control thereby functions even with the modified connection assignment. 
         [0008]    The first and the second fluid flow path are each open in at least one operating state of the valve, but may possibly be closed in other operating states. The valve is preferably designed as a built-in valve, the housing being the bushing of the built-in valve. It is also feasible, however, for the housing to form an integral part of a larger assembly, for example an axial-piston machine. The second fluid flow path preferably bypasses the first valve seat via the bypass duct. The bypass duct preferably forms a restrictor or an orifice plate in the second fluid flow path. The first orifice of the bypass duct is preferably connected to the first connection in any position of the first valve body. A second orifice, which is arranged at the other end of the bypass duct relative to the first orifice, preferably faces in the direction of the longitudinal axis, being arranged on the side of the first valve body remote from the first valve seat. 
         [0009]    The second valve body is preferably moveable in the direction of the longitudinal axis, the closing directions of the first and the second valve body being opposed to one another. This results in an especially compact valve. 
         [0010]    The second valve seat is preferably arranged on the first valve body. This results in an especially compact valve. 
         [0011]    The second valve body preferably passes through the first valve body at the second valve seat, the second valve body, at least when it bears on the second valve seat, protruding beyond the first valve body. The protruding portion may serve to keep the second valve body in an opened position when the first valve body is in the opened position. For this purpose a stop, which can come into contact with the protruding portion, is preferably provided on the housing. 
         [0012]    The pressure at the first connection preferably loads the first valve body in its closing direction, at least when the second valve seat is closed, and loads the second valve body in its opening direction. As a result, the movement of the first valve body can be controlled by the second valve body. The pressure at the first connection at the same time immediately lifts the second valve body off from the second valve seat. The flow resistance of the bypass duct is preferably at least 5 times greater than the flow resistance of the opened second valve seat. 
         [0013]    The pressure at the second connection preferably loads the first valve body in its opening direction. This affords a feed function in which hydraulic fluid flows from the second working connection to the first working connection, when the pressure at the second working connection is higher than the pressure at the first working connection. This operating state may occur, for example, when the valve according to the disclosure is connected via the first working connection to a hydraulic cylinder, on which a tractive load is acting. The feed function serves to prevent a vacuum being produced in the cylinder by the tractive load. 
         [0014]    A biased first spring preferably loads the first valve body in its closing direction. This ensures that the first valve seat is closed when the valve is in the unpressurized state. 
         [0015]    A biased second spring preferably loads the second valve body in its closing direction, the bias of the second spring preferably being adjustable. The bias of the second spring determines the pressure at the first working connection at which the valve responds, so that the first fluid flow path is opened for pressure relief purposes. 
         [0016]    The second spring is preferably held between the first and the second valve body. This results in an especially compact valve. 
         [0017]    A spring plate, on which the second spring bears, is preferably arranged at the end of the second valve body remote from the second valve seat. This results in an especially compact valve, allowing the first valve body, in particular, to be of small design. 
         [0018]    The features described above and those yet to be explained below may obviously be used not only in the particular combination specified but also in other combinations or in isolation without departing from the scope of the present disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The disclosure is explained in more detail below with reference to the drawings attached, of which: 
           [0020]      FIG. 1  shows a rough, diagrammatic sectional representation of a valve according to a first embodiment of the disclosure; 
           [0021]      FIG. 2  shows a rough, diagrammatic sectional representation of a valve according to a second embodiment of the disclosure; and 
           [0022]      FIG. 3  shows a rough, diagrammatic sectional representation of a valve according to a third embodiment of the disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]      FIG. 1  shows a rough, diagrammatic sectional representation of a valve  10  according to a first embodiment of the disclosure. The valve  10  has a housing  12 , in which a first valve body  30  is accommodated so that it can move in the direction of a longitudinal axis  11 . Here it is guided with very little clearance in a piston bore  22 , which is circular cylindrical relative to the longitudinal axis  11 . A first valve seat  33 , which is of a circular conical shape relative to the longitudinal axis  11 , is assigned to the first valve body  30 . The first valve body  30  is formed in the manner of a stepped piston, allowing it to close the first valve seat  33  tightly with its smaller end face  40 . 
         [0024]    The second connection  15  is arranged end face-on to the first valve body  30 , relative to the longitudinal axis. The second connection  15  is formed by a bore, which is circular cylindrical relative to the longitudinal axis  11  and which opens into the first valve seat  33 . The pressure at the second connection  15  accordingly acts on the smaller end face  40  of the first valve body  30 . 
         [0025]    The first connection  14  is formed by a circular cylindrical bore, the central axis of which intersects the longitudinal axis  11  at right angles. The first connection  14  is arranged circumferentially to the first valve body  30 , relative to the longitudinal axis  11 . The first connection  14  opens into a groove  20  in the housing  12 , which runs annularly around the first valve body  30  and is arranged in the area of the annular surface  41  of the first valve body. The groove  20  ensures that hydraulic fluid is distributed evenly over the entire exposed cross section on the first valve seat  33 . The pressure at the first connection  14  acts directly on the annular surface  41  of the first valve body  30 . 
         [0026]    The first connection  14  is connected by way of a bypass duct  35  in the first valve body  30  to a control chamber  21 , which is defined by the housing  12  and the first valve body  30 . Here the hydraulic fluid can pass from the first connection  14  into the control chamber  21  solely via the bypass duct  35 . The bypass duct  35  has a first orifice, which according to the disclosure is arranged circumferentially on the first valve body  30 , relative to the longitudinal axis  11 , so that it is situated directly opposite the first connection  14  in any position of the first valve body  30 . At the opposite end the bypass duct  35  has a second orifice  37   a , which opens into the control chamber  21 . The second orifice  37   a  faces in the direction of the longitudinal axis  11 , being arranged on the side of the first valve body  30  remote from the first valve seat  33 . A restrictor  36 , at which a fall in pressure occurs when the hydraulic fluid flows along the second fluid flow path  17 , is arranged in the bypass duct between the first and the second orifice  37 ;  37   a . While ever the second fluid flow path  17  is closed, the pressure in the control chamber  21  is equal to the pressure at the first connection  14 . This pressure therefore acts both on the annular surface  41  and on the larger end face  42  of the first valve body  30 , so that the latter is effectively pressed against the first valve seat  33 . It does not matter here that the larger end face  42  is not flat, owing to the presence of the stop  39 . 
         [0027]    A second valve seat  53 , which takes the form of an edge running annularly around the longitudinal axis  11 , is also formed in the housing. A second valve body  50 , which has a circular conical sealing face, relative to the longitudinal axis  11 , serving to seal the second valve seat  53 , is assigned to the second valve seat  53 . The closing direction  31  of the first valve body  30  and the closing direction  51  of the second valve body  50  are identically oriented, that is to say downwards in  FIG. 1 . The second fluid flow path  17  runs from the first connection  14  via the bypass duct  35 , onwards via the control chamber  21 , via the second valve seat  50 , via the connecting duct  19  in the housing  12  to the second connection  15 . The first fluid flow path  16  runs from the first connection  14  via the first valve seat  33  to the second connection  15 . 
         [0028]    The first valve body  30  is pressed against the first valve seat  33  by the biased first spring  34 . The second valve body  50  is pressed against the second valve seat  53  by the biased second spring  54 . The first and the second spring  34 ;  54  are preferably helical springs. When the valve  10  is in the unpressurized state, both fluid flow paths  16 ;  17  are accordingly closed. If the pressure at the first connection  14  now rises, the first valve body  30  is pressed against the first valve seat  33 , as explained above. The second valve body  50  is loaded in opposition to the biasing force of the second spring  54 . As soon as the pressure at the first connection  14  is great enough, the second valve body  50  lifts off from the second valve seat  53 . A fluid flow consequently flows along the second fluid flow path  17  from the first working connection  14  to the second working connection  15 . This causes a fall in pressure at the restrictor  36  in the bypass duct  35 . A smaller pressure thereby acts on the larger end face  42  of the first valve body  30  than on its annular surface  41 . The corresponding pressure and surface ratios are designed so that, in effect, a force results which lifts the first valve body  30  off from the first valve seat  33 , so that the first fluid flow path  16  is opened. 
         [0029]    Eventually the stop  39  on the first valve body  30  impinges on the sidewall of the control chamber  21 , at the same time impinging on a protruding portion  57  of the second valve body  50 , so that the latter is kept in the opened position. 
         [0030]    If the pressure at the first connection  14  now falls, the corresponding pressure on the first valve body  30  eventually no longer suffices to overcome the biasing force of the first and the second spring  34 ;  54 . As a result, the first and the second valve body  30 ;  50  move towards their valves seats  33 ;  53 , the second valve seat  53  closing first, so that the second fluid flow path  17  is interrupted. As a result, the fall in pressure at the restrictor  36  ceases, so that the pressure at the first working connection  14  acts both on the annular surface  41  and on the larger end face  42  on the first valve body  30 . The first valve body  30  is thereby pressed against the first valve seat  33 , so that the first fluid flow path  16  is closed. The valve  10  is then back in the initial position described above. 
         [0031]      FIG. 2  shows a rough, diagrammatic sectional representation of a valve  10 ′ according to a second embodiment of the disclosure. The second embodiment is of identical design to the first embodiment, except for the differences described below, so that reference is made to the embodiment in  FIG. 1  regarding this. Here the same or corresponding parts in  FIGS. 1 and 2  are identified by the same reference numerals. 
         [0032]    The second valve seat  53  is arranged in the first valve body  30 . The second valve body  50  is moveably accommodated in a bore  43  of the first valve body  30 . The bore  43  at the same time replaces the connecting duct (no.  19  in  FIG. 1 ) by establishing a fluid exchange connection between the second valve seat  53  and the second connection  15 . The second fluid flow path  17  runs from the first connection  14 , via the bypass duct  35 , onwards via the control chamber  21 , via the second valve seat  53 , via the bore  43  to the second connection  15 . 
         [0033]    An annular, circumferential step  56 , which if desired may be formed by a separate retaining ring, is provided on the inner circumferential face of the bore  43 . The second spring  54  is fitted under pre-tension between the step  56  and the second valve body  50 , so that the second valve body  50  is pressed in the direction of the second valve seat  53 . The closing direction  31  of the first valve body  30  is opposed to the closing direction  51  of the second valve body  50 , both closing directions  31 ;  51  running parallel to the longitudinal axis  11 . 
         [0034]    The second valve body  50  passes through the first valve body  30  at the second valve seat  53 . The second valve body  50 , at least when it bears on the second valve seat  53 , protrudes beyond the first valve body  30 . The corresponding protruding portion  57  comes into contact with a stop  18  on the housing  12 , so that the second valve body  50 , as in the first embodiment, is kept in the opened position when the first valve body  30  is in the opened position. 
         [0035]    The modified arrangement of the second valve seat  53  and the second valve body  50  reduces the space required compared to the first embodiment. This does not result in any modifications compared to the first embodiment in terms of the operating principle of the valve  10 ′. 
         [0036]      FIG. 3  shows a rough, diagrammatic sectional representation of a valve  10 ″ according to a third embodiment of the disclosure. The third embodiment is of identical design to the second embodiment, except for the differences described below, so that reference is made to the embodiment in  FIGS. 1 and 2  regarding this. Here the same or corresponding parts in  FIGS. 1 ,  2  and  3  are identified by the same reference numerals. 
         [0037]    The second spring  54  encloses the protruding portion  57  of the second valve body  50 . A spring plate  55  is arranged at the outer end of the protruding portion  57 . The second spring  54  is fitted between the spring plate  55  and the first valve body  30  under pre-tension. A portion of the second spring  54  may conceivably be accommodated in a countersink (not shown) in the first valve body  30 , in order that the maximum travel of the second valve body  50  may be selected irrespective of the overall space required for the second spring  54 . 
         [0038]    In the third embodiment, too, the protruding portion  57  of the second valve body  50  impinges on the step  18  on the housing  12 , in order to keep the second valve body  50  in an opened position when the first valve body  30  is in the opened position. 
         [0039]    The chosen distance between the second valve seat  53  and the upper end of the first valve body  30  in  FIG. 3  is greater than in the second embodiment. There the second valve body  50  is guided with a significant clearance in a portion  43   a  of the bore  43 . This chosen clearance is large enough to allow a sufficient quantity of hydraulic fluid to flow along the second fluid flow path  17 . The large length of the portion  43   a  ensures that the second valve body  50  is oriented substantially parallel to the longitudinal axis  11 , so that the second valve seat  53  can be reliably closed. 
       LIST OF REFERENCE NUMERALS 
       [0000]    
       
           10  valve (first embodiment) 
           10 ′ valve (second embodiment) 
           10 ″ valve (third embodiment) 
           11  longitudinal axis 
           12  housing 
           14  first connection 
           15  second connection 
           16  first fluid flow path 
           17  second fluid flow path 
           18  stop (for protruding portion) 
           19  connecting duct 
           20  annular groove 
           21  control chamber 
           22  piston bore 
           30  first valve body 
           31  closing direction of the first valve body 
           32  opening direction of the first valve body 
           33  first valve seat 
           34  first spring 
           35  bypass duct 
           36  restrictor 
           37  first orifice of the bypass duct 
           37   a  second orifice of the bypass duct 
           38  outer circumferential surface of the first valve body 
           39  stop (for the protruding portion) 
           40  smaller end face 
           41  annular surface 
           42  larger end face 
           43  bore 
           43   a  portion of the bore 
           50  second valve body 
           51  closing direction of the second valve body 
           52  opening direction of the second valve body 
           53  second valve seat 
           54  second spring 
           55  spring plate 
           56  step 
           57  protruding portion