Abstract:
A proportional pressure control valve includes a valve box ( 10 ) having a pump (P), user (A) and reservoir (T) connections. Control piston ( 18 ) is guided in a longitudinally displaceably inside the valve box ( 10 ) for optionally connecting the pump connection (P) to the user connection (A) and the user connection (A) to the reservoir connection (T). A fluid-carrying connection is established between the pump connection (P) and a pilot chamber ( 20 ) of a pilot valve ( 22 ). The pilot valve ( 22 ) is controlled by a magnet system, especially a proportional magnet system ( 28 ). The proportional pressure control valve, for the fluid-carrying connection to the pilot chamber ( 20 ), has a bore ( 27 ) extending axially inside the wall of the valve box ( 10 ) and from a radial bore ( 9 ) of the housing ( 10 ) forming the pump connection (P).

Description:
FIELD OF THE INVENTION 
     The invention relates to a proportional pressure control valve comprising a valve housing having at least three fluid-conducting connections, particularly in the form of a pump connection, a user connection, and a tank connection. A control piston is guided to be able to move lengthwise within the valve housing for selective connection of the pump connection to the user connection and of the user connection to the tank connection. A fluid-conducting connection is provided between the pump connection and a pilot chamber of a pilot valve. The pilot valve is controllable by a magnet system, in particular a proportional magnet system. 
     BACKGROUND OF THE INVENTION 
     For applications in which large volumetric flows are controlled, pilot-controlled pressure control valves are preferably used instead of directly controlled valves. A high volumetric flow means both large opening cross sections of the valves for large strokes and large flow forces which counteract the magnetic force of the magnet system to be actuated as a disturbance variable. To resolve these problems, the magnet system would have to be dimensioned to be correspondingly large for directly controlled valves. 
     For applications of this type, valves are known in the prior art which have hydraulic piloting, see DE 103 25 178 A1. This known solution is characterized, compared to other proposed solutions which are prior art and which are disclosed by U.S. Pat. No. 6,286,535 B1, in that the valve is able to set a pressure value of 0 bar on the user connection when the magnet system is not actuated. For the valves disclosed in that U.S. patent, this ability is not possible because, according to its construction, the control piston is returned to its end position by a clamped compression spring when the magnet system has not been actuated. Due to this mechanical configuration, these valves still have a pressure level which corresponds to the force of the clamped spring when there is no electrical control signal of the magnet system present. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide an improved proportional pressure control valve which can be set, according to DE 103 25 178 A1, with the user connection at a residual pressure of 0 bar having a simpler and more compact construction. 
     According to the invention, this object is basically achieved by a proportional pressure control valve having the fluid-conducting connection to the pilot chamber integrated essentially completely into the valve housing by a bore. The bore extends in the axial direction, is formed in a housing wall and emerges from a radial bore of the valve housing forming the pump connection. In the latter known solution, to form the fluid-conducting connection, the control piston is provided with an inner connecting channel which, before discharging into the pilot chamber, has an orifice to which a flow diffusor is connected downstream and a protective screen is connected upstream. For the control piston this yields not only a comparatively complex construction, but also a considerable installation length, as a result of which in turn a corresponding installation length of the valve housing is dictated. The valve according to the invention is, in contrast, characterized by the desired compact and simplified construction. 
     In another advantageous configuration, according to the invention the user connection can be formed by the coaxial, end-side opening of the valve housing. This configuration yields the especially advantageous possibility of further reducing the installation length, because, offset in the longitudinal direction of the valve housing, on the valve housing only two connections through which flow takes place radially need be formed by radial bores, specifically the pump connection and the tank connection. The control piston need then has a correspondingly smaller number of peripheral control edges, allowing simplification and a reduction in the required installation length. 
     Advantageously, the control piston can have, as a movable boundary of the pilot chamber, a closed, planar piston surface which lies in one radial plane. 
     Advantageously, a valve body of the pilot valve, which body is located stationary in the valve housing, forms a further, stationary boundary of the pilot chamber and the end section of the fluid-conducting connection to the pilot chamber, which section is remote from the pump connection. 
     In these exemplary embodiments, the end section of the fluid-conducting connection contains a radial channel which extends between an inner coaxial bore of the valve body and an annular gap. Between the peripheral surface of the valve body and the valve housing, the annular gap forms a filtration gap into which the end of the radial bore of the valve housing discharges. This design likewise contributes to a compact structure because the installation of the protective filter for the pilot fluid does not necessitate any additional axial installation length. 
     Since, as mentioned, a valve system is devised in which it can be ensured that on the user connection a pressure value of 0 bar is set without the magnet system actuated, the invention is especially well suited for use in hydraulically actuated clutches, for whose operational reliability it is essential that when the clutch is released. The clutch packs or disk packs which are engaged are reliably separated from one another. The subject matter of the invention is therefore also the use of the valve according to the invention for hydraulically actuatable clutches. 
     Other objects, advantages and salient features of the present invention will become apparent from the following detailed description, which, taken in conjunction with the annexed drawings, discloses preferred embodiments of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Referring to the drawings which form a part of this disclosure: 
         FIG. 1  is a front elevational view, partially in section, of a proportional pressure control valve according to the prior art; 
         FIGS. 2 to 4  are front elevational views partially in section of the proportional pressure control valve according to a first exemplary embodiment of the invention in different operating or actuating positions; 
         FIG. 5  is a front elevational view in section of a proportional pressure control valve according to a second exemplary embodiment of the invention, drawn on a somewhat smaller scale compared to  FIGS. 2 to 4 ; 
         FIG. 6  is a partial front elevational view in section of only the region designated in  FIG. 5  within the dot-dash circle, enlarged compared to  FIG. 5 ; 
         FIG. 7  is a simplified schematic diagram of a proportional pressure control valve according to the invention for use in a multiple-disk clutch; and 
         FIG. 8  is a graph illustrating the progression of a clutch play process for a clutch valve arrangement according to the hydraulic arrangement from  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a proportional pressure control valve of the prior art according to DE 103 25 178 A1. The valve, designed as a screw-in cartridge, has a valve housing  10  which can be screwed into a machine part (not detailed), for example, in the form of a valve block  3 , via a screw-in section  12 . For the sealed connection to the valve block  3 , the valve housing  10  has gaskets  14  on the outer peripheral side seated in the corresponding receivers. The valve housing  10 , viewed in the direction of  FIG. 1 , from top to bottom has radial bores  5  for a tank connection T, radial bores  7  for a user connection A, and radial bores  9  for a pump connection P for a hydraulic pump  16  (cf.  FIG. 7 ). Within the valve housing  10 , a control piston  18  is movably guided lengthwise for selective connection of the pump connection P to the user connection A and of the user connection A to the tank connection T. 
     To establish a fluid-conducting connection between the pump connection P and a pilot chamber  20  of a pilot valve  22 , the control piston  18  is provided with a connecting channel  24  which is coaxial to the longitudinal axis  26 . Connecting channel  24  is offset in its end section at the bottom in  FIG. 1  leading to a radial bore  9  of the pump connection P and is connected in its upper end section to the pilot chamber  20  via an outlet system  15 . The outlet system  15  contains an orifice to which, in the fluid flow direction, a protective screen is connected upstream and a diffusor is connected downstream. The diffuser is used preferentially to deflect the directed oil jet flowing out of the orifice so that it does not directly strike the movable closing part  40  of the pilot valve  22 . 
     The pilot valve  22  has a stationary valve body  42  in which an inner, coaxial bore  11  is open, on the one hand, toward the pilot chamber  20  and, on the other hand, on the opening edge it has a seat  13  for the movable closing part  40  of the pilot valve  22 . Valve  22  can be actuated via a magnet system  28 , in particular in the form of a proportional magnet system. If this magnet system is energized, its actuating plunger  32  is moved downward in  FIG. 1 , as a result of which the closing part  40  is pressed against the valve seat  13  via a spring arrangement  17  with a closing force dependent on the intensity with which the magnet system  28  is energized to close the pilot valve  22 . 
     If the proportional magnet system  28  remains deenergized, hydraulic medium (oil) can flow from the user connection A to the tank connection T. In this valve state, the pilot valve  22  is open, and the control piston  18  is moved onto its upper stroke stop against the lower side of the valve body  42 . In this operating position, the oil flows from the pump connection P through the control piston  18  to the pilot chamber  20  and from there via the opened pilot valve  22  to a distributor chamber  19  from which it drains via channels  58  to the tank connection T. This volumetric flow can be defined as a pilot oil flow or leakage. 
     When current is supplied to the magnet system  28 , the closing part  40  presses on the valve seat  13  and, in so doing, interrupts the volumetric flow. The pilot chamber  20  is thus filled with the hydraulic medium, as a result of which the pressure in this chamber rises. This rising pressure acts on the upper face side of the control piston  18  and moves it in the direction of the lower stroke stop  70  against the compressing compression spring  64 . The pressure in the pilot chamber  20  then corresponds to the adjusted pressure. 
     When the closing pressure of the closing part  40  on the seat  13  of the valve body  42  closes the pilot valve  22  by energizing the magnet system  28 , the pressure in the pilot chamber  22  rises to a pressure value at which the control piston  18  is moved downward in the figure against the main piston spring  64  until a position is reached in which the user connection A is connected to the pump connection P. When the controlled pressure is reached, the control piston  18  is moved such that the connection between the pump connection P and the user connection A is throttled. The control piston  18  is moved into a position in which the two force levels are in equilibrium with one another, and in this way it defines an opening window between the pump connection P and the user connection A. Therefore, a pressure is established on the user connection A, which is in a direct relationship to the electrical control signal of the magnet system  28 . 
       FIGS. 2 to 4  illustrate a first exemplary embodiment of the proportional pressure control valve according to the invention. Parts which correspond to those of the valve of  FIG. 1  are marked with the same reference numbers as in  FIG. 1 . The plunger of the magnet system  28 , which plunger is not shown, acts via a pilot spring  21  on the closing part  40  of the pilot valve  22 , which part is formed by a ball. As in the known solution according to  FIG. 1 , the closing part  40  interacts with a valve seat  13  located on the opening edge of an inner coaxial bore  11  of a stationary valve body  42 . The bottom of the valve body  42  which faces away from the valve seat  13  forms the stationary boundary of the pilot chamber  20  and the upper stroke stop of the control piston  18 , whose upper planar piston surface forms the movable boundary of the pilot chamber  20 . The interior of the coaxial inner bore  11  of the valve body  42  is fluid-connected via a damping orifice  23  to the pilot chamber  20 . This orifice  23  forms the end part of the fluid-conducting connection between the pump connection P and pilot chamber  20 . The main part of the fluid-conducting connection is formed by an axial bore  27  in the wall of the valve housing  10  and having its origin on a radial bore  9  of the pump connection P. From here the axial bore  27  leads to the outer periphery of the stationary valve body  42  where the axial bore  27  undergoes transition into an annular gap  29 . The gap  29  forms a filtration gap between the end of the axial bore  27  and a radial channel  31  which leads in the valve body  42  via a control oil orifice  33  to the inner coaxial bore  11 , whence the fluid connection via the damping orifice  23  to the pilot chamber  20  is completed. 
       FIG. 2  shows an operating state in which the magnet system  28  is not energized, the pilot valve  22  conversely is not closed, and thus a fluid pressure does not build up in the pilot chamber  20  because the fluid which has been supplied via fluid-conducting connection  27 ,  29 ,  31 ,  33  can drain via the distributor chamber  19  to the tank side. Accordingly, the control piston  18  is under the influence of the spring  64  in the upper end position where it adjoins the stroke stop, i.e., the bottom of the valve body  42 . Since in the valve according to the invention only the tank connection T and the pump connection P are formed by radial bores  5  and  9  respectively, while the user connection A is formed by the coaxial, end-side opening  35  of the housing  10 , in the operating position from  FIG. 2  the user connection A and the tank connection T are connected to one another. Specifically, the control piston  18  then has an interior open to the opening  35  of the valve housing  10 . Fluid in the interior of control piston  18  can emerge via passages  37  in the wall of the piston  18  to the tank connection T. 
       FIGS. 3 and 4  show operating states depending on the energizing of the magnet system  28 .  FIG. 3  shows the operating state in which the closing part  40  is pressed onto the valve seat  13  by energizing the magnet system  28  via the spring  21  so that in the pilot chamber  20  a pressure is built up which has moved the control piston  18  onto its lower stroke stop  70 . As is apparent, in this piston position the pump connection P and the user connection A are connected to one another. Also apparent from  FIG. 3 , is that large opening cross sections between the interior of the control piston  18  and the radial bores  9  are formed so that in an application to actuate a clutch cylinder, filling is prompt. 
     When a fill pressure of the consumer is reached, on the user connection A, for example, of the clutch cylinder, and when there is a force which acts in this way on the piston  18 , the piston is pushed upward  FIG. 4 , until the connection from the pump connection P to the user connection A is throttled or completely blocked. As likewise shown in  FIG. 4 , the user connection A and the tank connection T can be connected to one another, with a piston position being established in which the piston is in force equilibrium. The illustrated valve construction is characterized by high dynamics and low pressure loss, as a result of which, when used for clutch actuation, rapid filling with oil and rapid evacuation of the clutch are ensured. The invention is therefore also especially well suited for these applications because in the deenergized state of the magnet system  28  the user connection A is completely relieved. 
     A second, modified exemplary embodiment of the valve according to the invention is shown in  FIGS. 5 and 6 . In the example of  FIGS. 2 to 4 , the valve is subject to a certain leakage because in almost any operating state a control oil flow drains permanently to the tank. While the control oil orifice  33  keeps this leakage to a low value, it is still useful to reduce leakage losses. In the exemplary embodiment from  FIGS. 5 and 6 , for this purpose the piloting is configured such that, instead of a seat valve with spring-loaded closing part, a directly controlled pressure regulator is integrated into the piloting. The fluid-conducting connection, as in the above described exemplary embodiment, in the starting part is made by the axial bore  27  extending in the wall of the valve housing  10  and leading to the inner coaxial bore  11  in the valve body  42  via the peripheral annular gap  29  of the stationary valve body  42  and via a radial channel  31  located in it. A valve piston  38  is guided in inner bore  11  to be able to move lengthwise and is held nonpositively on the plunger  32  of the magnet system  28  via a reset spring  39 , and, when the magnet system  28  is energized, can be moved downward in  FIGS. 5-6 . The valve piston  38  has a bore  41  which is open to the pilot chamber  20  and peripheral control edges  43 ,  44  which are connected to that bore  41  so that, depending on the axial position of the valve piston  38 , the radial channel  31  and thus the fluid-conducting connection to the pump connection P are connected to the pilot chamber  20  or are blocked. In the position in which the radial channel  31  is blocked, the pilot chamber  20  is opened to the distributor chamber  19  and thus to the tank via the axial piston bore  41  and the control edge  44 . There is no direct connection from the pump connection P to the tank connection T in any operating state. The valve then works without additional losses due to the draining pilot oil. The leakage is therefore reduced to the valve spool leakage, which occurs on the annular gaps of the peripheral surfaces of the two pistons. 
     The proportional pressure control valve according to the invention is one which is advantageous especially for clutch applications. In these applications, the main demands are for high dynamics and low pressure losses in order to be able to ensure a rapid process of filling with oil and a rapid evacuation of the clutch. These demands are easily accomplished with this valve configuration. Moreover, the valve according to the invention can be completely relieved; i.e., when the electrical control signal on the magnet system  28  is taken away, the controlled pressure on the user connection A is brought to the pressure value of 0 bar. In conventionally pilot-operated pressure valves, this main stage (control piston) is returned with a clamped compression spring to its end position so that, when there is no electrical control signal on the magnet system, the known valves always have a pressure level that corresponds to the force of the clamped spring, then leading to problems in the decoupling of hydraulically operating clutches. 
     To illustrate this, the use of the proportional pressure control valve according to the invention is detailed with reference to  FIGS. 7 and 8  for a hydraulically operating clutch. According to the representation in  FIG. 7  the proportional pressure control valve is connected between the clutch parts  72 ,  74 ,  76  and the hydraulic pump  16 . 
     Clutches are used, among other things, to connect two shafts, for example the shafts of heavy machinery to transmission shafts. In this hydraulic clutch, a cylinder chamber  72  is connected to the pressure line or the pressure connection P of the hydraulic pump  16  by actuating the proportional pressure control valve according to the invention. In so doing, the spring-loaded piston  74  compresses a clutch disk pack which is not detailed. By switching over the proportional pressure control valve, the cylinder chamber  72  is then evacuated, and the compression spring arrangement  76  according to  FIG. 7  pushes the piston  74  back into its initial position. In so doing, the remaining hydraulic medium is pushed out in the direction toward the tank T via the user connection A. 
       FIG. 8  shows the progression of a clutch play. First, the clutch must be quickly filled with oil (hydraulic medium). This filling takes place in the time interval t 1  to t 2 , with the piston  74  beginning to compress the clutch disk pack. This process is accompanied by a brief, very high volumetric flow. Afterwards, this state is maintained in the time interval from t 2  to t 3  and is slowly “ramped up” in the interval t 3  to t 4  by the pressure being slowly raised linearly by the proportional pressure control valve according to the invention. The force from the heavy machinery is then uniformly transmitted to the transmission line. At time t 5 , by returning the electrical control signal on the magnet system  28 , the pressure in the clutch is removed so that the compressed disk pack, under additional action of the compression spring arrangement  76 , can push the piston  74  back into its original position again. This operation to remove pressure is easily possible since as already shown the pressure value on the connection A has the value 0 in this operating position. 
     While various embodiments have 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 appended claims.