Abstract:
The invention relates to distributing valve for load-independent control of a hydraulic consumer with regard to direction and speed. Similar distributing valves known per se have a control valve ( 30 ) which can be axially displaced in a slide bore hole ( 11 ) of a valve housing ( 10 ). In a neutral position, said control valve ( 30 ) blocks off two consumer chambers ( 13, 15 ) from a feed chamber ( 14 ) and selectably connects one of the two consumer chambers ( 13, 15 ) to a feed chamber ( 14 ) and the other consumer chamber ( 15, 13 ) to a return chamber in two operating positions. In addition, two brake pistons ( 51, 52 ) are arranged in two opposite lying receiving areas ( 33, 34 ) of the control valve ( 30 ). Both pistons can be pressurized in the direction of an enlargement of the opening section of a flow path leading from one consumer chamber ( 13, 15 ) to a return chamber ( 12, 16 ) via the respective receiving area, said pistons being pressurized in the other consumer chamber ( 15, 13 ) in a direction opposite to that of a spring ( 53 ) placed in a spring chamber ( 12 ). According to the invention, a slide longitudinal bore hole ( 36 ) which can be connected to a load indicator channel ( 22 ) extends from one pressure chamber ( 58 ) on one brake piston ( 51, 52 ) to the other pressure chamber ( 58 ) on the other brake piston ( 51, 52 ), and can be connected, upon displacement of the control valve ( 30 ) from the neutral position, to one consumer chamber ( 13 ) or another consumer chamber ( 15 ) depending on the direction of displacement.

Description:
FIELD AND BACKGROUND OF THE INVENTION 
     The invention is based on a directional control valve which is suitable for the load-independent control of the direction and speed of a hydraulic load. 
     A directional control valve is disclosed by German Offenlegungsschrift 23 42 498. It has a control slide which is axially displaceable in a slide bore in a valve housing and, in a neutral position, shuts off two load chambers on the slide bore from a feed chamber and, in two operating positions on either side of the neutral position, selectively connects one of the two load chambers to a feed chamber and connects the respectively other load chamber to a return chamber. In each of two accommodation chambers, which are located opposite each other and are made in the control slide from the opposite ends thereof, there is arranged a brake piston, which opens a flow path between a load chamber and a return chamber in each case only to such an extent that the hydraulic load can no longer lead the amount of fluid flowing toward it, that is to say that no lack of filling is produced in the flow line between said hydraulic load and the other load chamber. For this purpose, the brake piston is acted on by a spring with the effect of reducing the opening cross section of the flow path, and is acted on by the pressure in the other load chamber with the effect of enlarging the opening cross section. For the application of pressure, the control slide has a longitudinal slide bore, which can be connected via a transverse bore to the other load chamber and which opens into a pressure chamber between the bottom of an accommodation chamber and the brake piston located in this accommodation chamber. The longitudinal bore runs eccentrically in the control slide. In order to apply pressure to the other brake piston, there is a further longitudinal slide bore running eccentrically in the control slide, and a further transverse bore. 
     In the directional control valve disclosed by German Offenlegungsschrift 23 42 498, two feed chambers run around the slide bore at a distance from each other. The control slide has two annular grooves which are spaced apart axially from each other and of which each is respectively used to connect one of the two feed chambers to a load chamber. In the piston collar between the two annular grooves, the control slide has two further, narrower annular grooves which are separated from each other by a narrow web. One longitudinal slide bore is connected to the one narrow annular groove by a first transverse bore, and the other longitudinal slide bore is connected to the other narrow annular groove by a second transverse bore. A load indicator channel, which in the neutral position of the control slide is covered by the narrow web between the two narrow annular grooves, opens into the slide bore. Depending on the direction in which the control slide is moved from the neutral position, the load indicator channel is opened toward one or the other annular groove, and hence the load pressure prevailing in the respective load chamber is indicated in the load indicator channel. 
     While the directional control valve according to German Offenlegungsschrift 23 42 498 has two feed chambers, and a load indicator channel opens into the slide bore between these two feed chambers, the brochure 9129 8557-02 (GB) from Voac Hydraulics AB discloses a directional control valve, designated K170LS, in which, in a slide bore, a return chamber, a load chamber, a single feed chamber, another load chamber and a further return chamber follow one another, and a load indicator channel opens into the slide bore laterally at a point, that is to say, as viewed from a load chamber, on the other side of the adjacent return chamber. Using such an arrangement, it is possible for the directional control valve to be shorter in the axial direction of the control slide than that from German Offenlegungsschrift 23 42 498. In the directional control valve according to the above-mentioned brochure, a longitudinal bore which is closed on both sides runs centrally through the control slide, and three transverse bores or transverse bore stars lead from said longitudinal bore to the outside of the control slide. In the neutral position of the control slide, a first transverse bore star is located at a short distance from a load chamber, between the latter and the feed chamber. The second transverse bore star is located at a short distance from the other load chamber, between the latter and the feed chamber. Finally, a third transverse bore opens into an annular groove on the outside of the control slide and, in the neutral position of the control slide, is located symmetrically in relation to the mouth of the load indicator channel and, in every position of the control slide, connects the longitudinal slide bore to the load indicator channel. 
     SUMMARY OF THE INVENTION 
     The invention is based on the object of further developing a directional control valve of the precharacterizing clause of claim  1 , that is to say a directional control valve having brake pistons in the control slide, in such a way that it is of more simple construction and is cheaper to produce. 
     According to the invention, this object is achieved in the case of such a directional control valve having the features of the precharacterizing clause of claim  1  by the fact that a single longitudinal slide bore extends from the one pressure chamber in one brake piston to the other pressure chamber in the other brake piston, and by the fact that if the control slide is displaced from the neutral position, the longitudinal slide bore can be connected either to one load chamber or to the other load chamber, depending on the direction of displacement. As a result of the presence of only one longitudinal slide bore, which leads to both pressure chambers in both brake pistons, the control slide is simplified and its production is made cheaper. The invention is based on the surprising finding that the control of a hydraulic load is not influenced if, in addition to the brake piston which controls the opening cross section of the flow path between the one load chamber and a return chamber and is acted on by the pressure in the other load chamber, the other brake piston is also subjected to the pressure in the other load chamber. Although the other brake piston is lifted from the bottom of the accommodation bore, the other return chamber remains closed by the control slide in relation to the other load chamber. 
     In a directional control valve according to the invention, too, at one point to the side of all the working chambers, the load indicator channel is open toward the slide bore, with the effect of producing a short axial design. In order to make such an arrangement of the load indicator channel possible, one brake piston is provided with a longitudinal load indicator bore which is open with respect to the pressure chamber in front of one end of this brake piston and is closed with respect to the spring chamber in front of the other end of this brake piston, and via which the longitudinal slide bore is connected to the opening of the load indicator channel into the slide bore. 
     The connection between the longitudinal load indicator bore in one brake piston and the load indicator channel is expediently produced via a transverse bore in the brake piston and via a transverse bore in [lacuna] sleeve surrounding the brake piston and belonging to the control slide. 
     An axial and/or a peripheral offset between the two transverse bores is advantageously compensated for by an annular groove which is located between the brake piston and the sleeve of the control slide, preferably on the outside of the brake piston. 
     If two brake pistons are accommodated in the control slide, it is usual for these two brake pistons to be formed in the same way or at least very similarly, with the effect of a low diversity of parts. Each brake piston has an annular groove which is located in the flow path between the load chamber and the return chamber and on each side of which there is a piston collar. In a directional control valve according to the invention, in which one brake piston has a longitudinal load indicator bore, the piston collar on the side of the spring chamber can now reach a considerable length, in order to be able to produce the connection between the longitudinal load indicator bore and the load indicator channel. The other brake piston is also not made to be exactly the same length, at its piston collar on the side of the spring chamber, as the brake piston having the longitudinal load indicator bore. This avoids unnecessary lengthening of the control slide. 
     The spring chamber behind the brake piston having the longitudinal load indicator bore can be relieved to a return chamber via a channel running inside the brake piston. In principle, this is also possible in the other brake piston. 
     An exemplary embodiment of a directional control valve according to the invention is illustrated in the drawings. The invention will now be explained in more detail with reference to the two figures of these drawings, in which: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a simplified illustration of a section through the exemplary embodiment, the section passing through the axis of the control slide; and 
     FIG. 2 shows a circuit diagram of the exemplary embodiment. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     According to FIG. 1, a valve housing  10  has extending through it a slide bore  11 , which has a continuously constant diameter and around which various mutually spaced working chambers  12 ,  13 ,  14 ,  15  and  16  and control chambers  17 ,  18  and  19  run. The working chambers  12  and  16  which are the furthest removed from each other are return chambers, from each of which there originates a return channel  20 , each of which is indicated by an arrow. The two return channels are led together in a generally known way outside the valve housing and can be connected to a tank. Located centrally between the two return chambers  12  and  16  is the feed chamber  14 , to which pressure medium can be fed by a hydraulic pump via a pressure channel  21 , which is likewise indicated in FIG. 1 by an arrow. Between the return chamber  12  and the feed chamber  14  there is a first load chamber  13  and between the return chamber  16  and the feed chamber  14  there is a second load chamber  15 . Each load chamber can be connected via a load channel to a connection of a hydraulic load (not specifically illustrated). 
     The three control chambers  17 ,  18  and  19  are located to the side of the return chamber  12 . The central control chamber  18  is designated as load indicator chamber here, and can be connected via a load indicator channel  22  to a control chamber in a load-sensing controller of a variable displacement pump or to a control chamber of a pressure compensator arranged in the bypass of a constant delivery pump, via which compensator some of the amount of pressure medium supplied by the constant delivery pump is fed back to the tank. The two control chambers  17  and  19  are each connected to a pressure limiting valve (not specifically illustrated). 
     A control slide  30  is axially movably guided in the slide bore  11  of the valve housing  10 . Said control slide has a circumferential annular groove  31 , which is relatively deep in the radial direction and is broader in the axial direction than the feed chamber  14 , and which, in the neutral position of the control slide  30 , shown in FIG. 1, is located in a central position in relation to the feed chamber  14 . Fine control grooves  32 , which are distributed over the circumference of the control slide  30 , run axially toward both sides from the annular groove  31  and, in the neutral position of the control slide  30 , in each case end at a short distance in front of the load chamber  13  and  15 , respectively. 
     From each end of the control slide  30 , an accommodation chamber  33  and  34 , respectively, is made in the form of a blind bore in said control slide  30 . The two bottoms  35  of the two accommodation chambers  33  and  34  are at a distance from each other which approximately corresponds to the clear distance, that is to say the distance of the axial boundary walls on the feed chamber side, of the load chambers  13  and  15  from each other. A longitudinal slide bore  36  goes through the control slide  30  from bottom  35  to bottom  35 . Just before a bottom  35  in each case, a transverse bore  37  opens into the longitudinal slide bore  36 , said bore originating from the outside of the control slide  30  in the region between two fine control grooves  32 . In the neutral position of said control slide  30 , both transverse bores  37  are closed by the wall of the slide bore  11 . 
     At a distance from the bottom  35 , two mutually diametrically opposite first radial bores  38  pass through the sleeve of the control slide  30 , between the accommodation chamber  33  or  34  and the outside, and, in the neutral position of the control slide  11 , are covered by material of the valve housing  10  which is located axially between the respective load chamber and the respective return chamber. At a greater distance from the bottom  35 , two mutually diametrically opposite second radial bores  39  pass through the sleeve; their diameter is smaller than the diameter of the radial bores  38  and they open on the outside into a flat annular groove  40  in the control slide  30 , said annular groove  40  extending in the axial direction to the outside from the radial bores  39  and ensuring that, if the control slide is displaced from the neutral position in one direction, the radial bores  39  are always open toward the return chamber  12  or  16 . The annular groove  40  on the return chamber  12  is axially longer than the other annular groove  40  and, in the neutral position of the control slide, produces a connection between the control chamber  17  and the return chamber  12 . At a distance from this longer annular groove  40 , a further annular groove  41  is machined into the control slide  30  and, in the neutral position of the control slide, bridges all three control chambers  17 ,  18  and  19 . The piston section  42  between the annular grooves  40  and  41  is accordingly axially shorter than the control chamber  17 . In the neutral position of the control slide  30 , there is therefore an open connection between the return chamber  12  and the three control chambers  17 ,  18  and  19 , in which, in the neutral position of the control slide  30 , the pressure present is accordingly the low pressure which prevails in the return channel  20 . 
     There is a brake piston  51  in the accommodation chamber  33  of the control slide  30 , and there is a brake piston  52  in the accommodation chamber  34 . The two brake pistons are axially displaceable within the respective accommodation chamber, and are loaded in the direction of the bottom  35  of the respective accommodation chamber by a helical compression spring  53 , which is supported on a closure screw  54  which closes the respective accommodation chamber. Each brake piston has, between two piston sections  55  and  56 , an annular groove  57  via which the first radial bores  38  can be connected to the second radial bores  39  of the control slide  30 . The distance of the annular groove  57  from that end of a brake piston which faces the bottom  35  of an accommodation chamber is identical in both brake pistons. The piston section  55  seals off a pressure chamber  58  between the bottom  35  of an accommodation chamber and the respective brake piston from the annular groove  57 . The longitudinal slide bore  36  opens into both pressure chambers  58 . The brake pistons  51  and  52  can therefore be acted on by the pressure prevailing in the longitudinal slide bore  36 , counter to the helical compression spring  53 . A spiral depression, or one or more depressions which run radially, in the ends of the brake pistons ensure that the pressure can act on a brake piston even if the latter is pressed by the helical compression spring  53  against the bottom  35  of an accommodation chamber. 
     The brake piston  52  is shorter than the brake piston  51 . Accordingly, the accommodation chamber  34  is also shorter than the accommodation chamber  33 . The brake piston  51  is longer than the brake piston  52  because it is used to produce a connection between the longitudinal slide bore  36  and the annular groove  41  running around the slide on the outside. For this purpose, it has at its center an axially extending blind bore  65 , which is open at its end facing the bottom  35  of the accommodation chamber  30  and reaches as far as the piston section  56 . This section  56  of the brake piston  51  is longer than the section  56  of the other brake piston  52 , which necessitates the greater length of the brake piston  51 . On the outside, a flat annular groove  66  runs around the piston section  56  and, in the rest position shown of the brake piston  51 , in which the latter is supported on the bottom  35  of the accommodation chamber  33 , is already located axially outside the second radial bores  39  of the control slide  30 , that is to say cannot be connected to the return chamber  12  by the radial bores  39 . A connection between the annular groove  66  and the blind bore  65  is produced by an oblique bore  67 . On the other side, in any position of the brake piston  51 , a connection is produced, via an oblique bore  68  in the control slide  30 , between the annular groove  66  in said brake piston  51  and the annular groove  41  running around the control slide  30  on the outside. Thus, in any position of the brake piston  51 , the longitudinal slide bore  36  is connected to the annular groove  41  via one pressure chamber  58 , the blind bore  65 , the oblique bore  67 , the annular groove  66  and the oblique bore  68 . The annular groove  66  on the brake piston  51  compensates for any axial and peripheral offset between the oblique bores  67  and  68 . 
     Between a spring chamber  72 , in which there is a helical compression spring  53 , and a return chamber  12  or  16 , compensation for the volume of pressure medium contained in a spring chamber can take place via bores in the respective brake piston  51  or  52 . For this purpose, the brake piston  52  has an axial blind bore  73  which is open toward the spring chamber  72 , and a number of radial bores  74 , which originate from said blind bore  73 , run in the piston section  56 , open on the outside into a narrow annular groove  76  and, in any position of the brake piston  52 , are open toward the second radial bores  39  of the control slide  30 . Captured in the blind bore  73  is a ball  75  which, together with a seat (not specifically designated) in the blind bore  73 , forms a nonreturn valve, which opens from the return chamber  16  toward the spring chamber  72 . Thus, in the event of an enlargement of the spring chamber  72 , that is to say in the event of a movement of the brake piston in the direction of the bottom  35  of the accommodation chamber  34 , pressure medium can flow rapidly out of the return chamber  16  into the spring chamber  72 . A flow of pressure medium from the spring chamber  72  to the return chamber  16  is possible, bypassing the nonreturn valve, via a restrictor (not specifically designated). Said restrictor may be formed, for example, by a notch in the seat for the ball  75 . The movement of the brake piston  52  in the direction of the closure screw  54  is therefore damped. 
     The same is also true for a movement of the brake piston  51  in the direction of the corresponding closure screw  54 . In order to connect the spring chamber  72  to the return chamber  12 , the brake piston  51  has the same short axial and central blind bore  73  as the brake piston  52 , and a radial bore  74  which, just before the annular groove  57 , opens on the outside into a narrow annular groove  76  on the brake piston and on the inside ends in front of the blind bore  65 . An oblique bore  77  runs between the bores  73  and  74 . Once again, a ball  75  is captured in the bore  73  and is part of a nonreturn valve, which opens toward the spring chamber  72 . A restrictor is once more formed by a notch in the seat of the nonreturn valve. 
     Each of the two control chambers  17  and  19  is connected to a pressure limiting valve (not specifically illustrated). The two pressure limiting valves limit the pressure in these control chambers and, for this purpose, can be set to different maximum pressures. 
     The control slide  30  is centered in the neutral position with the aid of two springs  80 , and can be displaced hydraulically in one direction or the other. 
     In the circuit diagram according to FIG. 2, the usual letter designations A, B, P and T are also indicated for the working chambers  12 ,  13 ,  14 ,  15  and  16 . The designation LS is also used for the control chamber  18 . Finally, the control chambers  17  and  19  also bear the designation LSB and LSA, respectively. The nonreturn valve in the connection between a return chamber  12  or  16  and a spring chamber  72  bears the reference number  80 , the parallel-connected restrictor bears the reference number  81 . Inserted between the load indicator channel  22  and the respective main flow path in an operating position of the control slide  30  is a restrictor, which is provided with the reference number  67 , that is to say is formed by the corresponding transverse bore in the brake piston  51 . 
     In the shown neutral position of the control slide  30 , all the working chambers are shut off from one another. The transverse bores  37 , the longitudinal slide bore  36 , the pressure chambers  58 , the blind bore  65 , the oblique bore  67 , the annular groove  66 , the transverse bore  68  and the three control chambers  17 ,  18  and  19  are relieved of pressure toward the return chamber  12 . The brake pistons  51  and  52  are pressed by the compression springs  53  against the bottom  35  of the respective accommodation chamber  33  and  34 . Let it now be assumed that the control slide is displaced to the left in the view of FIG.  1 . As a result, a metering orifice is opened between the feed chamber  14  and the load chamber  13 , its opening cross section depending on the extent of the displacement of the control slide  30 . One transverse bore  37  of the control slide  30  is also opened to the load chamber  13 . While the load pressure of the respective hydraulic load is present in the load chamber  13 , the pressure which prevails in the feed chamber  14  is the pump pressure, which, in the case of load-sensing control systems, within which the valve shown is used, is higher, by a specific difference of the order of 15 to 20 bar, than the load pressure of the driven hydraulic load or higher than the maximum load pressure of a plurality of hydraulic loads driven in parallel. Via the opened transverse bore  37  and the longitudinal slide bore  36 , the load pressure prevailing in the load chamber  13  is also present in the pressure chambers  58 , and presses the brake pistons against the closure screws  54 . As a result, the brake piston  52  opens the connection between the load chamber  15  and the return chamber  16 , the pressure medium flowing out of the load chamber  15 , through the first radial bores  38  of the control slide  30 , the annular groove  57  of the brake piston  52  and the second radial bores  39  of the control slide  30  to the return chamber  16 . The movement of the brake piston  51  has no influence on the connection between the working chambers nor on the connection of the control chambers to one another. The load pressure is passed via the blind bore  65 , the transverse bore  67  and the annular groove  66  of the brake piston  51 , and, via the transverse bore  68  and the annular groove  41  in the control slide  30 , to the control chamber  18  which, because of the displacement of the control slide  30 , is separated by its piston section  42  from the control chamber  17  and from the return chamber  12 , and is only still connected to the control chamber  19 . From the control chamber  18 , the load pressure can be indicated, via the load indicator channel  22 , to the control valve of a variable displacement pump or to the pressure compensator connected in the bypass of a constant delivery pump. 
     The force of the compression springs  53  on the brake pistons  51  and  52  corresponds to a pressure of, for example, 5 bar in the pressure chambers  58 . As soon as the pressure in the load chamber  13  falls below this value, because of any lead of the hydraulic load, the brake piston  52  moves in the direction toward the bottom  35  of its accommodation chamber  34  and reduces the opening cross section between the second radial bores  39  of the control slide  30  and its annular groove  57 . In the process, it reduces the cross section to such an extent that in the load chamber  13  and therefore in the pressure chamber  58  a pressure is set which maintains equilibrium with the force of the spring  53 . The pressure is therefore approximately 5 bar. 
     If the control slide  30  is displaced to the right from the neutral position, the load chamber  15  is connected to the feed chamber  14 , and the load chamber  13  is connected via the brake piston  51  to the return chamber  12 . The brake piston  51  then ensures that a minimum pressure is maintained in the load chamber  15 . In addition, the other transverse bore  37  is then open toward the load chamber  15 , so that the load pressure of the hydraulic load which is prevailing in said load chamber  15  can continue into the control chamber  18 . The latter is then connected to the control chamber  17 , both control chambers  17  and  18  being shut off from the return chamber  12  by the piston section  42 .