Abstract:
A valve device includes a housing ( 2 ) and a valve piston ( 4 ) axially displaceable in a piston bore ( 3 ) of housing ( 2 ). First and second load connections (A, B) can alternately be connected to a pressure connection (P) and to tank connections (T 1 , T 2 ) by moving the piston from an idle position by first and second solenoids ( 5, 6 ). First and second pilot control chambers ( 7, 9 ) pressurize first and second piston back sides ( 8, 10 ) of the valve piston ( 4 ). The pressure in the pilot control chambers ( 7, 9 ) is controlled by first and second pilot control pistons ( 12, 13 ) movable by the solenoids ( 5, 7 ). The pilot control chambers ( 7, 9 ) are connected via a connection ( 11 ) to the pressure connection (P). The pilot control pistons ( 12, 13 ) open or close connections ( 14 ) between the pilot control chambers ( 7, 9 ) and the tank connections (T 1 , T 2 ).

Description:
FIELD OF THE INVENTION 
     The invention relates to a valve device comprising a valve housing and a valve piston arranged to be able to move axially in a piston bore of the valve housing. Via the valve piston, a first load connection and a second load connection can be alternately connected to a pressure connection and to a tank connection. The valve piston can be moved out of a centered, preferably middle rest position, for connecting the first load connection to a pressure connection and the second load connection to the tank connection in one direction and for reversed fluidic communication of the connections in an opposite direction. 
     BACKGROUND OF THE INVENTION 
     Generic valve devices are readily available on the market in a plurality of embodiments, for example, as multiport valves. In conjunction with an electromagnetic actuation, they are an important component of the proportional valve technology. This technology is essentially characterized in that an electrical input signal as voltage is converted into an electrical current with an electronic amplifier of the corresponding voltage level. 
     A proportional solenoid as an switching magnet generates the output quantities force or path proportionally to this electrical current. These quantities are used as the input signal for the valve device or the hydraulic valve and, proportionally thereto, signify a specific volumetric flow or a specific pressure. For the respective actuated load and for a working element that has been actuated with it on a machine, in addition to influencing the direction of movement, this arrangement leads to the possibility of continuously influencing the speed and force. At the same time, according to a corresponding time characteristic, for example, change of the volumetric flow over time, acceleration or deceleration can be continuously influenced. Depending on the function being emphasized, that is, the path function, the flow function, and/or the pressure function, proportional hydraulics are used in directional valves, flow control valves, or so-called pressure valves. 
     The technical advantages of proportional valve technology include controlled actuation transitions, continuous control of the setpoints, and the reduction of the hydraulic apparatus for certain control tasks. Furthermore, with proportional valves, prompt and exact sequences of motion are possible with simultaneously improved accuracy of the control processes. 
     In practice, the known valve device solutions also leave much to be desired in the field of proportional valve technology for many control tasks, as can arise in double-acting hydraulic working cylinders in which the triggering takes place for positioning tasks while avoiding mechanical coupling elements, especially with respect to the operational reliability of the overall system as well as prompt reaction. 
     DE 43 19 162 A1 discloses a generic valve device with two opposing solenoids connected to a valve housing, with fluid connection sites mounted in the valve housing in the form of at least one pump connection P, at least two user connections A, B, and at least two tank connections T 1  and T 2 . A valve piston has radial projections that can each be assigned to one fluid connection site A, B, T 1 , T 2  at a time in the valve housing and fluid-conducting paths between the projections. In a neutral position block, the path to the respective assignable user connection A, B is blocked or cleared in part or in full. With the cleared user connections A, B cleared, the respective pressure connection P is completely blocked by the assignable projection. The known solution relates to a hydraulic valve that can be used for actuating a hydraulic actuator in a roll stabilization system of a motor vehicle. 
     DE 600 16 510 T2 describes a piloted directional valve with position determination. A housing has a number of connections and a housing bore in which each connection discharges. A valve piston is movably guided to be able to move axially in the bore to change the flow paths between the connections. Complex controls control the valve piston, with the controls comprising a piston on each side of the valve piston and one or two pilot valves for setting the valve piston by controlling the pilot fluid acting on the piston. A magnet is attached to one side of the valve piston such that it can be moved in synchronous operation with the valve piston. The magnet is arranged such that it borders at least one side of the valve piston. By a magnetic sensor, the magnetic force of the magnet can be detected over the entire displacement path of the valve piston. 
     DE 102 24 739 A1 discloses a valve device in which a first pilot chamber pressurizes a first back side of the valve piston and a second pilot chamber pressurizes a second piston back side. The pressure in the pilot chambers can be controlled by a first and second pilot pistons that can be moved by a first and a second electromagnet, respectively. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide an improved valve device that is mechanically simple in structure and still enables reliable operation even under difficult operating conditions. 
     This object is basically achieved according to the invention by a valve device having first and second pilot chambers connected to the pressure connection via a fluid-conducting connection and pilot pistons that clear or block one fluid-conducting connection at a time between the pilot chambers and the tank connection. Due to the continuous fluid-conducting connection between the pressure connection and the first and second pilot chambers, the pressure medium in the pilot chambers can be used directly as a control. According to the position setting of the pertinent pilot piston, the fluid-conducting connection is specified between the pertinent pilot chamber and the tank connection, and thus, the pressure in the pilot chamber, which setting is effected by the pertinent electromagnet. With a simple construction, an overall system is formed characterized by operational reliability and prompt reaction. 
     Any deleterious effect on the valve piston caused by forces of friction or flow can be compensated without control effort by an intensified outflow of the pressure medium from the pertinent pilot chamber. As a result, the valve piston continues to move in the direction of the desired position. 
     If the electrical current for the first electromagnet is lowered or turned off, the pilot piston moves, preferably, additionally prompted by an energy storage mechanism, in the direction of a blocking position of the fluid-conducting connection between the first pilot chamber and the tank connection. The pressure that builds up again in the first pilot chamber shifts the valve piston again in the direction of its rest position. 
     The valve piston can also be axially displaced in the opposite direction in the same described manner as described when the second electromagnet is energized. In this way, the second load connection can be connected to the pressure connection and the first load connection to the tank connection. 
     Continuously, a fluid-conducting connection is between the pressure connection and the first and second pilot chambers. The pressure medium in the pilot chambers can act directly on the respective back side of the valve piston. It may also be advisable to provide mechanical coupling elements between the respective pilot chamber and the pertinent back side of the valve piston. 
     To enable a compact construction of the valve device, the respective fluid-conducting connection can be arranged between the pressure connection and the pilot chambers in the valve piston itself or in the valve housing. In an arrangement of the pertinent fluid-conducting connection, an off-center longitudinal bore in the valve piston is recommended. In the valve housing, the fluid-conducting connection can alternatively be made in a longitudinal bore with radial distance to a longitudinal axis of the valve housing. On the respective ends or end regions of the longitudinal bore, branch ducts can be routed to the pertinent two pilot chambers. A fluid-conducting connection is then produced that transfers a continuous pressure of the pressure medium out of the pressure connection to the pilot chambers. 
     In the valve piston, preferably, a continuous fluid-conducting connection is routed from the pilot chambers to the tank connection. The pertinent fluid-conducting connection is controlled by one pilot piston at a time on the opposite ends or back sides of the assignable valve piston. Preferably, a seat valve is formed using one end of each pilot piston, which end is formed as a cone or tip. 
     The fluid-conducting connections have a small diameter that is overall suited to enabling the required positioning rates of the valve piston, triggered by the pressure difference in the two pilot chambers. 
     The valve piston is held in a neutral position by an energy storage mechanism acting with the same compressive force in addition to the same compressive force of the pressure medium in the pilot chambers on both back sides of the piston. In order not to tap the supply pressure directly from the pressure connection, the pressure connection and thus the fluid-conducting connections from the pressure connection to the pilot chambers can advantageously be connected at the same time by one load connection that represents the load side of the load via a shuttle valve. This arrangement permits operating the valve arrangements with the pressure medium pump turned off, solely by the load pressure on the consumer. When the pressure medium pump is turned on again, the shuttle valve blocks, and the pressure on the pressure connection is transferred directly from the pump to the two pilot chambers. 
     To route the available pressure that is the highest at the time either from the pressure connection or the two load connections in the load circuit to the pilot chambers as a pilot pressure, all three pertinent connections, specifically the pressure connection, first load connection, and second load connection, can be connected via one nonreturn valve at a time to a collecting line to the fluid-conducting connection to the pilot chambers. 
     To center the valve piston in a neutral middle rest position in the piston bore and to return the valve piston when it is deflected, in addition one energy storage mechanism at a time or especially one compression spring can be inserted into each pilot chamber. The spring can shorten the switching time for resetting the piston. Likewise, each pilot piston can be acted upon using an energy storage mechanism, preferably designed as a compression spring, for purposes of closing the fluid-conducting connection from the pertinent pilot chamber to the pertinent tank connection. Advantageously, each armature of an electromagnet can be acted on with a compression spring for purposes of moving the valve piston into a neutral position. 
     A symmetrical embodiment of the valve device, that is easy to fabricate, is produced by selecting a middle position of the pressure connection of the pressure medium pump with reference to the longitudinal axis of the valve housing. To both sides of the pressure connection, the first and second load connections and first and second tank connections are connected to the pressure connection with respectively preferably the same distance. 
     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 that form a part of this disclosure: 
         FIG. 1  is a schematic, side elevational view in section, not to scale, of a valve device according to a first exemplary embodiment of the invention; 
         FIG. 2  is an enlarged, partial side elevational view in section of detail II in  FIG. 1 ; 
         FIG. 3  is a schematic, side elevational view in section, not to scale, of a valve device according to a second exemplary embodiment of the invention. 
         FIG. 4  is a schematic, side elevational view in section, not to scale, of a valve device according to a third exemplary embodiment of the invention; and 
         FIG. 5  is a schematic, side elevational view in section, not to scale, of a valve device according to a fourth exemplary embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1 , in a schematic longitudinal section that is not to scale, shows a valve device  1  for controlling pressure media, such as hydraulic oil, to a load (not shown). The valve device  1  has a valve housing  2  made essentially cylindrical. A through bore, designed as a piston bore  3  or cylinder for a valve piston  4 , is made in the valve housing  2 . For indirect actuation of the valve piston  4 , on both sides of the valve housing  2 , first and second electromagnets  5 ,  6  are separably mounted in one centering bore in the valve housing  2  in a manner that is not shown. The electromagnets  5 ,  6  are designed as proportional solenoids. In the valve housing  2 , fluid connection sites are made in the form of at least one pump or pressure connection P, two load connections A, B, and two tank connections T 1 , T 2 . The valve piston  4  is guided to be able to move lengthwise in the valve housing  2  and has projections  31 ,  32  that are radial on the outer peripheral side. The respective radial outer periphery of the respective projection is chosen such that it can slide sealingly on the inner peripheral side of the piston bore  3 . 
     In the exemplary embodiments of  FIGS. 1 to 5 , the two middle projections  31  are assigned to the load connections A, B, and the two projections  32  located axially on the ends of the valve piston  4  are assigned to the tank connections T 1  and T 2 . Between the projections  31 ,  32 , the valve piston  4  is reduced in diameter so that fluid-conducting paths are formed between the interior of the valve housing and the respectively reduced outside diameter of the valve piston  4 . 
     On its two opposite sides or axial ends, the valve housing  2  has one first pilot chamber  7  and one second pilot chamber  9  at a time whose respective volume can be changed by the pilot piston  36 ,  37 . The respective pilot chambers  7 ,  9  are connected to conduct fluid to the respective bores  33 ,  34  that are routed or extend axially from a first back side  8  and a second back side  10 , respectively, of the valve piston  4 . 
     The two pilot chambers  7 ,  9  are furthermore exposed to the control pressure or pump pressure with the pressure connection P via a fluid-conducting connection  11  made as a longitudinal bore in the valve piston  4 . The fluid-conducting connection  11  in the valve piston  4  is continued to the pilot chambers  7 ,  9  in the valve piston  4  in an off-center bore  33 ,  34  of reduced diameter. The reduced-diameter bores are each made in a valve seat piece  35 ,  36  as shown in  FIGS. 1 ,  2 ,  4 , and  5 . The valve seat pieces  35 ,  36  are sealingly fitted in the valve piston  4  in a respective widening of the bores. They can come to rest in the region of the tank connections T 1 , T 2  in the rest positions of the valve piston  4 . 
     One pilot piston  12 ,  13  at a time can be axially moved by the first and second electromagnets  5 ,  6  and comes to rest in a drain line  17 ,  18  located radially, each next to the bores  33 ,  34 , in the valve seat pieces  35 ,  36  or the openings  15 ,  16  of the drain lines with a piston tip  37 ,  38 . The drain lines  17 ,  18  in the valve seat pieces  35 ,  36  form fluid-conducting connections  14  from the pilot chambers  7 ,  9  to the respective tank connections T 1 , T 2  for purposes of draining pressure medium  19 . One compression spring  22 ,  23  at a time forms an energy storage mechanism  20 ,  21  for pressurizing the respective pilot piston  12 ,  13 . The compression springs  22 ,  23  thus cause sealed pressing of the piston tips  37 ,  38  onto the openings  15 ,  16  and, moreover, a spring centering of the valve piston  4  under the influence of the equalizing compression forces of the compression springs  22 ,  23  in a rest position of the valve piston  4 . The compression springs  22 ,  23  are supported on a housing  39 ,  40  of each electromagnet  5 ,  6  and on a stop collar  41 ,  42  of the respective pilot piston  12 ,  13 . 
     As  FIG. 4  furthermore shows, one spring  28 ,  29  at a time in each pilot chamber  7 ,  9  can be arranged loosely centered on its cylindrical inner peripheral surfaces. The springs  28 ,  29  in the pilot chambers  7 ,  9  are cylindrical compression springs, as are the other springs of the valve device  1 . Those springs  28 ,  29  also have a considerably larger diameter than the compression springs  22 ,  23  that act on the respective pilot piston  12 ,  13  so that they radially encompass these compression springs  22 ,  23  and the respective pilot piston  12 ,  13 . The springs  28 ,  29  in the pilot chambers  7 ,  9  are supported on a diameter offset  43  of the pilot chambers  7 ,  9 , which offset is adjacent to the respective electromagnet  5 ,  6  that is assigned to the pilot piston  12 ,  13 . 
     On their other ends, the springs  28 ,  29  are each supported on a cylindrical sleeve  45  provided with a collar  44 , with the cylindrical sleeve  45  extending through the springs  28 ,  29  with its outer peripheral surface. The respective collar  44  of a sleeve  45  strikes one face side  46  of a projection  32 , which side faces the respective electromagnet  5 ,  6 , on the valve piston  4  and strikes a pilot chamber bottom  47  formed by the valve housing  2 . In this way, in the valve device  1  shown in  FIG. 4 , the valve piston  4  is moved axially into an exactly reproducible rest position. This valve piston is centered with the compression springs  22 ,  23  and  28 ,  29  and the respective pressure in the pilot chambers  7 ,  9 . The respective collar  44  of the sleeve  45  can be moved axially within certain limits that are defined by a face surface  48  of a screw-in nipple  49  of the respective housing  39 ,  40  of the electromagnets  5 ,  6 . The respective sleeve  45  has radial through holes  50  for pressure medium  19 . As  FIG. 5  shows, in the region of each electromagnet, further compression springs  55  can additionally cause centering of the valve piston  4  in its neutral position. The compression spring  55  in  FIG. 5  is supported on one end of each armature  54  of the electromagnets  5 ,  6 , which end is opposite the respective pilot piston  12 ,  13 , and a pole core  56 . 
     As the version of the valve device  1  in  FIG. 3  shows, the fluid-conducting connection  11  between the pressure connection P and the pilot chambers  7 ,  9 , which connection is designed as a bypass line that is continuously exposed to system or pump pressure, can also be implemented via a longitudinal bore  51  and branch ducts  52  that are routed by the bore perpendicular to the respective pilot chambers  7 ,  9  with corresponding filler plugs  53  in the valve housing  2 . The longitudinal bore  51  lies radially spaced from the longitudinal axis  30  of the valve housing  2 . 
     The operation of the valve device  1  according to the invention is detailed below using the exemplary embodiment in  FIG. 1  and the detail II in  FIG. 2 . If the valve device  1  is in its neutral position, which position is shown in all the figures, the coil windings of the electromagnets  5 ,  6  are not energized. The valve piston  4  is kept in the middle position via compression springs (pole tube springs)  55  and/or via the two compression springs  22 ,  23  and the pilot piston  12 ,  13  that they act upon. The piston tips  37 ,  38  of the pilot pistons  12 ,  13  close the openings  15 ,  16  of the drain lines  17 ,  18 . The pilot chambers  7 ,  9  are exposed to the pump pressure, the load connections A, B can be pressurized, and the tank connections T 1 , T 2  are unpressurized. This valve position would then correspond to the unextended middle position of a hydraulic working cylinder as a connected load, by way of example. 
     If the first electromagnet  5  is supplied with an electrical current, the first pilot piston  12  and its piston tip  37  move in the direction of the first electromagnet  5 . In this way, the opening  15  is cleared, and pilot fluid can flow from the first pilot chamber  7  to the tank connection T 1 . The pressure in the second pilot chamber  9  conversely remains at the pump pressure level so that the valve piston  4  is moved in the direction toward the first electromagnet  5  by the pressure imbalance that is established in the pilot chambers  7 ,  9 . In this way, fluid-conducting connections in the valve housing  2  between the pressure connection P and the load connection A, as well as between the load connection B and the tank connection T 2 , are cleared. Any deleterious effects on the valve piston  4  caused by forces of friction and flow are equalized by virtue of the fact that the flow of pressure medium  19  or pilot fluid increases. As a result, the pressure in the first pilot chamber  8  then continues to drop and the imbalance of forces in the axial direction of the valve piston  4  increases to the left in the viewing direction of the drawings. If the power to the first electromagnet  5  is lowered or even cut off, the valve piston  4  returns to its initial position under the action of the springs  28 . The same sequence of events takes place in the reverse order when the second electromagnet  6  is energized. 
     As  FIG. 3  shows, the supply pressure for the two pilot chambers  7 ,  9  can be tapped not only from the pressure connection P, but also via a coupling of the load connections A, B and the pressure connection P, with the interposition of a shuttle valve  24  either by the pressure connection P or one of the load connections A, B, before the pressure medium is supplied to the pilot chambers  7 ,  9 . Due to this design measure, the valve device  1  can be operated even with the pressure medium pump turned off. 
     As  FIG. 4  shows advantageously, tapping the highest available pressure medium pressure can be accomplished by connecting the indicated connections P, A, B in parallel via one nonreturn valve  25 ,  26 ,  27  at a time, each of which opens respectively in the direction of the pilot chambers  7 ,  9  between the connections and the fluid-conducting connection  11 . This piloted valve device  1  then does not require path sensors for the valve piston  4  or any analysis or control electronics. The valve device  1  thus has a simple structure and low fault susceptibility. When the current supply of the electromagnets  5 ,  6  is interrupted, the valve piston  4  automatically returns to its spring-centered middle initial 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.