Abstract:
A valve, in particular, a proportional pressure relief valve, includes an electrically controlled solenoid system ( 10 ) for the control of an operating part ( 12, 12   a ). The operating part cooperates with a valve element ( 26 ) extending longitudinally inside a valve housing ( 24 ) to release a fluid transport connection path between a fluid inlet ( 32 ) and a fluid outlet ( 34 ) in its open position and to block the through path in its closed position. An energy store, preferably in the form of a compression spring ( 58 ), is arranged between the operating part ( 12, 12   a ) and valve element ( 26 ) in a free gap between the two and tends to hold the valve element ( 26 ) in the direction of its closed position. The operating piece ( 12   a ) is embodied as a guide piston having a longitudinal guide for the valve element ( 26 ).

Description:
FIELD OF THE INVENTION 
     The invention relates to a valve, in particular a proportional pressure relief valve, having an electrically triggerable solenoid system for triggering an actuating part to interact with a valve element guided to be longitudinally displaceable in the valve housing. In one of its open positions, the valve element clears a fluid-carrying connecting path between a fluid inlet and outlet. In its blocked position, the valve element blocks this path. Between the actuating part and the valve element, an energy storage device, preferably in the form of at least one compression spring, seeks to keep or biases the valve element in the direction of its closed position. 
     BACKGROUND OF THE INVENTION 
     In fluid systems the pressure relief valve is designed to limit the system pressure to a certain predetermined pressure level. When this predetermined value is reached, the pressure relief valve responds and routes the excess volumetric flow, that is to say, the difference flow between the pump flow and consumer flow, from the fluid system toward the tank side. In addition to the pilot-controlled pressure relief valves which will not be explained in greater detail. Directly controlled pressure relief valves, viewed dynamically, act as a spring-mass system executing vibrations when set into motion. These vibrations also act on the prevailing fluid pressure and must be balanced appropriately by damping. In this connection, the impulse forces of the fluid flow are used to virtually balance the increase of the spring force in operation of the valve. 
     To obtain good pressure setting and a flat Δp-Q characteristic (pressure increases as small as possible with increasing volumetric flow) over the entire pressure range, the entire pressure range can be divided into pressure increments. The maximally adjustable pressure is determined from the maximum magnetic force (force at the rated current of the solenoid system) and the area of the valve seat active for pressure (circular area of the seat diameter) according to the following formula: 
     
       
         
           
             
               p 
               max 
             
             = 
             
               
                 
                   F 
                   
                     Magnet 
                     , 
                     max 
                   
                 
                 
                   A 
                   seat 
                 
               
               = 
               
                 
                   
                     F 
                     
                       Magnet 
                       , 
                       max 
                     
                   
                   · 
                   4 
                 
                 
                   
                     D 
                     seat 
                     2 
                   
                   · 
                   B 
                 
               
             
           
         
       
     
     In a plurality of embodiments of these valves, providing an electrically triggerable solenoid system with an actuating coil to trigger the valve element is known in the prior art. 
     In one known solution available on the market, the valve element in the form of a closing part with a tapering closing cone is directly tied to the rod-shaped actuating part of the solenoid system. In operation of the valve, this arrangement can lead to instabilities due to the mass inertia of the armature in the form of an actuating part. The resulting friction between the actuating part and the valve closing element also leads to increased hysteresis in valve operation. 
     In the prior art it has already been proposed, to stop this unstable behavior, that the solenoid system be decoupled from the actual valve unit by an energy storage device in the form of a compression spring supported on the end sides on the interior of the valve housing and on the valve element itself to avoid instabilities. Based on dimensional tolerances alone, in particular for increasing fluid volumetric flows, angular displacements between the axis of the closing cone and the actual direction of travel of the valve closing element occur. The closing cone then may not be able to exactly block or could even damage the edge of the valve seat assigned to it in the housing, with the result that the valve then can no longer effect a leak-proof seal. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide an improved valve ensuring stable control behavior and leak-proof operation, with simultaneously low production and maintenance costs. 
     This object is basically achieved by a valve where the actuating part is made in the manner of a guide piston having a longitudinal guide for the valve element. The solenoid system is for the most part decoupled from the valve element in terms of mass inertia so that instabilities in operation of the valve do not occur. In addition, the longitudinal guide results in the valve element with the closing part preferably interacting and moving in the seat execution with a valve seat in the valve housing always with axial precision into its intended closed position. The angular displacements occurring in the prior art and causing leaks in the region of the valve seat are then reliably prevented. Due to the decoupling via the energy storage device, preferably in the form of at least one compression spring, the valve according to the invention fundamentally works in a force-controlled manner. If in operation the described dynamic effects occur, they are balanced by the energy storage device in the form of the compression spring. In this way, the valve element with its closing part is therefore influenced by the mass inertia of the armature undertaking triggering to a much smaller degree than in the known described solutions. 
     The valve according to the invention requires few components and is reliable over a longer period of use so that production and maintenance costs can be kept correspondingly low. 
     The valve according to the invention is used as a proportional pressure relief valve in the seat execution and in direct triggering, preferably for small fluid volumetric flows up to approximately 10 l/min. The valve can also and preferably be used in pilot control tasks, for example, to build pilot-controlled pressure relief or pressure control systems. 
     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 a preferred embodiment of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Referring to the drawings which form a part of this disclosure and which are schematic and not to scale: 
       The valve according to the invention will be detailed below using one embodiment as shown in the drawings. The figures are schematic and not to scale. 
         FIG. 1  is a front elevational view partially in section of a valve in the form of a proportional pressure relief valve according to the prior art; 
         FIG. 2  is a front elevational view partially in section of a valve according to an exemplary embodiment of the invention; and 
         FIG. 3  is a hydraulic graphic symbol for the valve according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The known, directly controlled proportional pressure relief valve in the seat execution as shown in  FIG. 1  is provided with an electrically triggerable or actuatable solenoid system  10 . These solenoid systems for triggering valves are sufficiently known in the prior art (DE 44 16 279 A1). By an actuating coil (not shown) of the solenoid system  10 , an armature in the form of a rod-shaped actuating part  12  can be triggered in the manner of a piston part. In the illustrated embodiment the solenoid system  10  is made as a compressing magnet. In the energized state it moves the actuating part  12  viewed in the direction of  FIG. 1  from left to right. In the de-energized state the actuating part  12  is reset again via an energy storage device configuration as described below. 
     The housing  14  of the solenoid system  10  is designed as a screw-in cartridge. Along the longitudinal axis  16  of the valve, housing  14  has a center hole  18  through which the rod-shaped actuating part  12  extends. This center hole  18  at its free end discharges or opens into a widening space  20  with an internal thread  22  into which a correspondingly made valve housing  24  with its outside thread can be screwed. Within the valve housing  24  along the longitudinal axis  16 , a valve element  26  is guided to be longitudinally displaceable and has a closing cone  28  and an adjacent valve closing element  30 . 
     In its illustrated position the valve element  26  closes the possible fluid path between a fluid inlet  32  and a fluid outlet  34 . The fluid inlet  32  is located on the face side on the free end of the valve housing  24  and extends coaxially to the longitudinal axis  16  of the valve. The fluid outlet  34  conversely is designed as a transverse hole extending through the valve housing wall with its axis  36  perpendicular to the longitudinal axis  16 . To leave its blocking position, the valve element  26 , viewed in the direction of  FIG. 1 , must be moved to the left in one of its open positions in which the fluid path is then cleared. In this connection the closing cone  28  is raised off an annular contact surface  38  as the valve seat of a valve insert  40 . This valve insert  40  encompasses the fluid inlet  32  of the valve and can be inserted, in particular screwed, into the free end of the remaining valve housing  24  with a capacity to be adjusted lengthwise to the longitudinal axis  16  and to the possible direction of travel of the closing cone  28  by an external thread  42 . 
     This longitudinal adjustment of the valve insert  40  allows precision positioning for the valve seat  38  and thus precision matching. This adjustment refers to the insertion behavior when the valve cone  28  is being closed on the valve seat  38 . The plug-like valve insert  40  on the outer peripheral side has a gasket  44  in a groove recess. Further annular sealing systems  46  are located on the outer peripheral side on the solenoid system housing  14  and on the free end of the valve housing  24  to make the overall valve system as a screw-in valve. 
     As is furthermore to be seen from  FIG. 1 , another actuating part  12   a  is connected to the rod-shaped actuating part  12  as a second piston part. On its side facing the rod-shaped actuating part  12 , actuating part  12   a  has a cylindrical contact flange  48  with a cross section widened in diameter and, in the illustrated graphic representation, is supported on the adjacent wall surface  50  of the housing  14  of the solenoid system  10 . On its side opposite the actuating part  12 , the contact flange  48  is connected to a guide part  52  having a screw-in section (not shown) along which an adjusting nut  54  can be adjusted. To implement this adjustment, the valve housing  24  has a widening recess  56  with a round cross section. Between the actuating part  12   a  and the valve element  26 , an energy storage device in the form of a compression spring  58  is provided. This compression spring  58  with its spring force seeks to keep or biases the valve element  26  to its closed position shown in the figure. 
     The valve element  26  also has a contact surface  60  widening in diameter but smaller in diameter than the adjacent contact surface  62  of the actuating part  12   a . Between the contact surfaces  60 ,  62  the compression spring  58  extends with its two ends facing away from one another. As seen in  FIG. 1 , between the sides of the actuating part  12   a  and valve element  26  facing one another adjacently, there are no structural components except for the edge boundary formed by the inside periphery  64  of the valve housing  24 . A cavity  66  is formed between the facing sides of the actuating part  12   a  and valve element  26 . 
     To be able to achieve reliable lifting of the closing cone  26  off the valve seat  38  when fluid enters via the fluid inlet  32 , this lifting motion is supported by another energy storage device in the form of another compression spring  68 . Spring  68  has a much smaller spring stiffness than compression spring  58 . Furthermore, the spring force behavior of compression spring  58  and compression spring  68  can be analogously adjusted via the adjusting nut  54  before the valve is started. To avoid obstacles in operation, the rod-like actuating part  12  is made only in loose contact with the facing end side of the other cylindrical actuating part  12   a  and is not connected integrally to it. To ensure uniform fluid intake via the inlet site  32 , the inflow cross section viewed in the direction of  FIG. 1  tapers from right to left. Cavity  66  in the longitudinal direction parallel to the longitudinal axis  16  of the valve is dimensioned such that in any case the most closely adjacent sides of the actuating part  12   a  and valve element  26  cannot abut one another, but are actively kept apart by the compression spring  58  even if it assumes a very widely compressed position. 
     With the pressure relief valve according to the invention, pressure values can be stipulated via direct triggering. When they are exceeded at the fluid inlet  32  against the magnet force of the solenoid system  10  and against the force of the compression spring  58 , the closing cone  28 , supported by the other compression spring  68 , is raised off the valve seat  38  and clears the fluid path from the fluid inlet  32  to the fluid outlet  34  (tank side). In the reverse direction of force, when the pressure is dropping on the fluid inlet side  32 , the valve can be closed again via the closing cone  28 . 
     With the known solution, except for the compression spring  58 , essentially massless decoupling from the solenoid system  10  relative to the actual valve system with the valve element  26  is achieved. The mass inertia of the armature in the form of the actuating parts  12 ,  12   a  is then actively reduced via the interposed energy storage device (compression spring  58 ). Due to the dimensional tolerances of the compression spring, especially when the volumetric flows are rising, angular displacements can occur between the closing cone  28  and the longitudinal axis  16  of the actual valve body. This structure results in the previously described problems. Especially, the closing cone  28  can damage the edge of the valve seat  38  such that the valve no longer effects a leak-proof seal, clearly adversely affecting serviceability of the valve. 
     The valve solution according to the invention as shown in  FIG. 2  avoids this problem with the structural features described individually below. To avoid repetition, the same components as in  FIG. 1  of the prior art are reproduced with the same reference symbols. The statements made previously then also apply to the exemplary embodiment according to the invention as shown in  FIG. 2 . 
     The actuating part  12   a  is designed as a guide piston  70  having a longitudinal guide for the valve element  26 . For this purpose, the guide piston  70  first has an outside guide  72  displaceable along the inside periphery or surface  64  of the valve housing  24  and has an inside guide or surface  74  in which parts of the valve element  26  are guided and engage. The inside guide  74  is formed from a center hole or bore in the guide piston  70  extending along the longitudinal axis  16  of the valve housing  24 . The parts of the valve element  26  to be guided are formed from a guide journal or pin  76  which, as shown in  FIG. 2 , engages the center hole. The outside guide  72  is made short in the axial direction to keep friction values low. The shoulder-shaped outside guide  72  is located in the lower half of the guide piston  70  facing the compression spring  58 . 
     The axial length of the center hole is selected to be greater than the length of the cylindrical guide journal  76 . The guide journal  76  is provided in the direction to the closing cone  28  with a stop shoulder  78  limiting the travelling path of the end  80  of the guide piston  70  which is free on the face side for this purpose. The energy storage device in the form of a compression spring  58  extends between the outside guide  72  of the guide piston  70  and the contact surface  60  of the valve element  26 . Analogous to  FIG. 1 , in  FIG. 2  the valve is shown in its closed position. In the direction of its open position, the travel path of the valve element  26  viewed in the direction of  FIG. 2  is bordered to the top by the contact shoulder  78 . To be able to equalize the pressure, the guide piston  70  is penetrated by a transverse hole  82  connecting the interior of the center hole to the widening space  20 . This widening space  20  in the valve housing  24  has a connecting hole  84  extending obliquely down and used as a leak drain. In the embodiment shown in  FIG. 2 , the valve housing  24  on the outer peripheral side extends over the housing  14  of the solenoid system  10 . To keep the mass of the guide piston  70  moved low, the piston in the region of the contact surface toward the rod-shaped actuating part  12  of the solenoid system  10  has an annular recess  86 . The guide piston  70  is kept very slender and has one shoulder-shaped widening on its outer peripheral surface solely to produce the outside guide  72 . 
     According to the invention, via the compression spring  58  massless decoupling from the solenoid system  10  relative to the actual valve system with the valve element  26  is achieved. The mass inertia of the armature in the form of the actuating parts  12 ,  12   a  is actively reduced via the interposed energy storage device (compression spring  58 ). Instabilities of the system, as can occur, for example, due to the large fluctuations of pressure or volume and by pulsations on the fluid inlet  32 , can be effectively controlled to ensure operating reliability of the pressure relief valve in a wide range. 
     In the illustrated embodiment shown in  FIG. 2 , both contraction of the spring  58  via the inner guide and movement of the complete spring assembly in the valve body are possible. The decoupling spring  58  is made very stiff. As a result, the valve works fundamentally force-controlled. Moreover, the indicated guidance results in the valve element  26  with its closing part  28  always traveling with axial precision into its intended closing position. The angular displacements occurring in the prior art with leaks due to damage to the valve seat  38  are then reliably avoided. 
     The valve according to the invention works very reliably and operates with few components, helping to reduce production costs. The valve can be used for a long time to reduce maintenance costs. The proportional pressure relief valve can generally be used as a pressure relief valve for small volumetric flows (up to 10 l/min). The valve is also preferably used in pilot control tasks, for example, to build pilot-controlled pressure relief or pressure control systems. 
     While one embodiment has been chosen to illustrate the invention, it will be understood by those skilled in the art that various changes and modifications can be made therein without departing from the scope of the invention as defined in the appended claims.