Abstract:
A valve, especially a pressure control valve, includes a housing ( 10 ) with a pump connection (P), an appliance connection (A) and a tank connection (T). A piston ( 16 ) controlled by a magnet armature ( 26 ) is guided inside the housing ( 10 ) of the valve. The vavle is provided with a hydraulic damping device ( 34 ) having a damping chamber ( 36 ) in fluid communication with appliance connection (A) through a throttle ( 38 ). The pump connection (P) or the tank connection (T) is selectively joined to the appliance connection (A) via a connecting line ( 40 ) according to the position of the piston ( 16 ). This valve improves upon known control valves so that the control valve remains stable in terms of behavior, especially with regard to permanent oscilliations.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a valve, a pressure control valve in particular, with a valve housing having pump, appliance and tank connections. A valve piston can be driven by a magnetic inductor for guided movement within the valve housing. 
     BACKGROUND OF THE INVENTION 
     Conventional proportional pressure control valves are used, among other things, as control valves for oil-hydraulic systems to deliver a more or less constant output pressure with variable input pressure. The output pressure to be controlled is assigned by the current signal delivered by suitable triggering electronics and acting on an actuating magnet. The actuating magnet may be designed as a pressure sealed oil bath magnet with a long service life. 
     Proportional pressure control valves serving this purpose may be directly controlled piston valves of a three-way design, that is, with pressure protection on the output side. They are employed, among other things, in oil-hydraulic systems to control couplings, in shift transmissions for exerting a specific pressure buildup and pressure reduction effect, for remote pressure adjustment, for control of pressure variation over time and for pilot control of hydraulic valves and logic elements. 
     Conventional proportional pressure control valves employed for these purposes are characterized by poor stability, especially in the case of low-viscosity fluid media. They begin to vibrate, something especially harmful if the conventional valves are to perform special functions, for example, in motor vehicle power steering systems, areas relating to safety engineering, or the like. Generally, susceptibility to disturbances has been found to occur in the natural frequency range of the valve. The instabilities arising may result in functional failure of a valve and the relevant parts of its system. 
     SUMMARY OF THE INVENTION 
     Objects of the present invention are to provide improved valves with more stable behavior, in particular with respect to steady-state vibrations, so that the valve is also well suited for special appliances. 
     The valve according to the present invention is provided with a hydraulic damping device having a damping chamber connected by a throttle to the connection of the appliance to convey fluid. Optionally, the pump connection or tank connection communicates with the appliance connection. In the event of displacement of the valve piston toward the choke as a result of the magnetic force of a switching magnet, the fluid stored in the damping chamber is displaced toward the appliance connection by the throttle. The displacement volume flow generates local pressure buildup by the throttle. A force directed against the deflecting force of the valve piston onto the effective pressure surface adjoining the flow restriction point may be determined. Thus, a damping effect may be exerted on the entire valve piston. As the valve piston travels back in the opposite direction, this volume of fluid must flow back away from the appliance connection into the damping space, now increasing, again by of the throttle as defined. This flow also results in damping of the vibrations which occur. 
     In a preferred embodiment of the valve of the present invention, the throttle is in the form of a ring disk which impedes the flow of fluid between damping space and appliance connection by a flow restriction point. In one embodiment of the valve of the present invention, the flow restriction point may be in the form of a through opening inside the ring disk. Preferably, however, in an alternative embodiment, the flow restriction point is at least in part in the form of an annular passage formed between the ring disk and parts of the valve housing surrounding the ring disk. The latter solution improves damping results and can be applied cost effectively during manufacture. 
     In addition, the annular passage can discharge into a connecting duct of the ring disk communicating with to the damping space to conduct fluid. The ring disk can be flange-connected to the valve housing at various points, the annular passage being interrupted at the connection points, just as it is by frontal mounting of the annular passage in the interior of the valve housing. A simple yet functionally reliable connection of the throttle to the remaining portion of the valve housing is obtained in this manner. 
     In another especially preferred embodiment of the present invention, the connecting line extends at least in part parallel to the direction of advance of the valve piston inside the valve housing. This piston optionally makes connection with the tank or with the pump connection. As a result of the connecting line, the functional component proper of the valve is separated from the damping component, and, as a result, the functional reliability of the valve design is increased. 
     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: 
     FIG. 1 is a top view, partly in section, of a conventional proportional pressure control valve; 
     FIG. 2 is a top view, partly in section, of a valve according to the present invention; 
     FIG. 3 is a front elevational view of the throttle of the valve of FIG. 2; and 
     FIG. 4 is a side elevational view of the throttle of FIG.  3 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     For better understanding of the valve of the invention, a conventional proportional pressure control valve is described in detail with reference to FIG.  1 . 
     The conventional valve shown in FIG. 1 includes a valve housing  10  in the form of a screw-insertion cartridge, also designated as a cartridge valve. The conventional valve is screwed or threaded into a valve receptacle  12  with its fluid connections P, T, and A, by way of external threading  11 . A is the appliance connection. P is the pump connection. T is the tank connection. The main or valve piston  16  extends longitudinally inside the valve housing  10 , and is suitably hardened and ground. A magnet system  20 , for electric actuation of the piston, includes a circuit box  22  and a controllable magneto inductor  26  introduced into a magnetic coil  24 . The magneto inductor  26  is connected to the valve piston  16  by a tappet-like actuating element  28 . The front end of element  28  rests on a resetting or pressure spring  32 , specifically, in the area of the appliance connection A. The other free end of the pressure spring  32  is in contact with a frontal inner recess in valve housing  10 . 
     In the initial position, in which no current flows and the magneto inductor  26  has not been actuated, the valve is closed on the input side by the pump connection P. Also, on the output side, connection A communicates with the tank connection T to conduct fluid. For this purpose the valve piston  16  has on its external circumference, at a prescribed distance, an annular recess  54 . If a current signal is now applied to the magnet system  20  by the circuit box  22 , the magneto inductor  26  presses against the valve piston  16  with a force corresponding to the level of the control current. As a result, the control piston  16  is forced downward against the reset spring  32  and the fluid or oil flows from the pump connection P to the appliance connection A. If a consumer appliance device, such as a hydraulic cylinder or the like, is connected to the appliance connection A, a pressure builds up at the connection A which acts on the end surface of the control piston and generates a force opposite the magnetic force of the magnet system  20  to force the valve or control piston upward again. As a result, the inflow of the pump connection P to the appliance connection A is reduced until the pressure of the magnetic force applied to the appliance connection, and thus, the pressure value assigned by the current signal are again equal. If the consumer device requires no more pressurized fluid, for example, because the hydraulic cylinder has reached its throw limit, the valve piston  16  moves upward again and seals the pump connection P. If the output pressure drops, as a result of relief of pressure on the consumer device, below the prescribed pressure value, the magneto inductor  26  presses the valve piston  16  back downward and the control process may begin again. The maximum output pressure which may be reached, also designated as pressure stage, is established by the magnetic force. 
     One possible method of output pressure protection at the directly controlled piston valve from appliance connection A to tank connection T is executed as follows. If the pressure at the appliance connection A increases beyond the prescribed pressure, the valve piston is displaced upward with the magneto inductor  26  until the connection of appliance connection A to the tank connection T is opened. The pressure on the appliance connection A is consequently limited. In the event of interruption of the control current, the valve piston  16  is moved upward by the pressure on connection A and the reset spring  32 . As a result, the appliance connection A is again connected to the tank connection T and the pressure on the appliance connection A drops to the tank pressure level. 
     The proportional pressure control valve used for this purpose is characterized by poor stability, in particular when low-viscosity media are employed. In theory, harmful vibrations of the valve around the area of the valve seat  14  are possible. 
     To counteract this harmful vibrational behavior, as is to be seen in FIGS. 2 to  4 , the valve of the present invention has a hydraulic damping device  34 . To the extent that the conventional valve elements described above are also used in the valve of the present invention, such valve elements are identified by the same reference number. The same description also applies to such valve elements in the disclosed embodiment of the present invention as well. Such elements are explained only to the extent that the embodiment of the present invention differs from that of the conventional valve previously described. 
     The damping device  34  is provided with a damping space  36  communicating with the appliance connection A by a throttle  38  so as to conduct fluid, and being filled with fluid. Optionally, the pump connection P or the tank connection tank connection T communicates with the appliance connection A through a connecting line  40 , as a function of the position of the valve piston  16 . In the switching position illustrated in FIG. 2, the pump connection P is separated from the appliance connection A. However, pump connection P communicates at least to some extent with the tank connection T by way of the valve piston  16 . 
     The throttle  38  is in the form of a ring disk  42 , as is shown in greater detail in FIGS. 3 and 4. The ring disk  42  impedes flow of fluid in both fluid directions between damping space  36  and appliance connection A by a throttle point  44 . The throttle point  44  results from the ring disk  42  having a clearance of about 55 to 70 μm relative to the intake opening  46  in the valve housing  10 . The ring disk  42  is otherwise sealed off from the appliance connection A. The throttle point could also be in the form of a through opening  47 , preferably in the center of the of the ring disk  42 . For production engineering reasons alone, manufacture of the mounting between ring disk  42  and intake opening  46  of the valve body  10  is simpler to accomplish and so more cost effective. 
     As seen especially from FIGS. 3 and 4, the ring disk  42  has on its inner side facing the damping space  36  a grooved connecting channel  48 . The connecting channel  48  may be produced cost effectively, if, in manufacture of the ring disk  42 , a through opening later forming the semicircular ring channel as connecting channel  48  is made before tapping of the turned component involved. The connecting channel  48  discharges outward on both sides of the ring disk  42 . For the purpose of use of the valve illustrated in FIG. 2, recesses  50  are made in the external circumference on the valve housing  10 , to be received in a suitable valve recess  12  (not shown). The recesses receive sealing means, especially sealing rings, to ensure sealing of the interior of the valve from the environment. 
     The ring disk  42  is hinge-connected or connected at various points  49  to the valve housing  10 . The fluid-conducting annular gap is interrupted at the hinge connecting points  49 , and by frontal mounting of the ring disk  42  on the interior of the valve housing  10  in the form of the intake opening  46 . For the purpose of reliable hinge connection and dependable retention of the ring disk  42  inside the valve housing  10 , hinge connecting points are provided at angles of 90°. At this point, the intake opening  46  narrows at various locations and the cylindrical valve receptacle  52 , which faces the appliance connection or consumer connection A on the free end of the valve, is correspondingly narrowed at these locations. Up to the four points of application, however, flow of fluid between the appliance connection A and the damping space  36  is not impeded. Since the ring disk  42  rests frontally against the valve housing, subsequent flow of fluid into the damping space  36  takes place through the connecting channel  48 , which both discharges into the damping space  36  and is connected so as to conduct fluid by way of its frontal surfaces to the throttling ring gap. 
     As is also to be seen from FIG. 2, the connecting line  40  is mounted to extend in part parallel to the direction of travel of the valve piston  16  inside the valve housing  10 . The piston optionally communicates with the tank connection T or the pump connection P. The connecting line  40  extending parallel to the direction of displacement of the valve piston  16  inside the valve housing discharges at one of its free ends into the appliance connection A. At its other free end, line  40  discharges into a tie line  56  which discharges into the annular recess  54  in every displacement position of the valve piston  16 . The tie line  56  is sealed off from the outside by a sealing ball  58 . Like the pump connection P, the tank connection T is mounted transversely to the longitudinal direction of the valve piston  16 . A pressure equalization line  60  discharges at one end into tank connection T. The other free end of pressure equalization line  60  discharges into a pressure space  62  penetrated by the actuating component  28  of the magneto inductor  26 . In this area, magneto inductor  26  comes to rest against the valve piston  16 . 
     The tank connection T and the pump connection P are separated from each other for fluid conduction or communication by a central valve piston component  64  having the annular recess  54 . Depending on the state of the system, and thus depending on the displaced position of the valve piston  16  and of the central valve piston component  64 , a fluid conducting connection or fluid communication is established between the appliance connection A and the tank connection T or between the appliance connection A and the pump connection P. Covering of the annular recess  54  with the pertinent connection P or T is effected for the fluid-conducting connection in question. Connections P and T otherwise discharge into a ringshaped narrowing  66  inside the valve piston  16 . These connections are separated by the central valve piston component  64 . 
     Other piston components  68  each have conventional sealing means to seal the pertinent narrowing  66  in both directions. For the sake of better understanding of the valve of the present invention, this valve will now be discussed in greater detail on the basis of the function of the valve. 
     When the valve or control piston  16  is displaced in the positive, X, direction, that is, toward the ring disk  42 , by the magnetic force of the magnetic system  20 , the volume of fluid present inside the damping space  36  is forced from this point in the direction of the appliance connection A, through the throttle  38  in the form of an annular gap  38  between valve housing  10  and ring disk  42 . This flow volume displaced through the ring gap generates a local pressure buildup. A damping force on the effective pressure surface of the piston  16  may be detected. A force directed against the displacing force of the valve piston  16  then exerts a damping effect over the entire axis of the valve. On any return of the valve piston  16  in the opposite, negative, X direction, this volume of fluid must now flow back again into the now expanding damping space  36  through the ring gap defined as throttle  38 . This flow again exerts an inhibiting effect on the valve piston  16 . On the basis of this inhibiting effect produced by the throttle  38 , a pressure control valve marked by high stability toward steady-state vibrations is thus developed at low cost by simple and cost-effective production engineering means, since inhibition of valve piston movement is created by the throttle  38  and the damping space  36 . Since instability conditions associated with the valve may be counteracted in this way, breakdowns during operation are prevented. 
     The damping space  36  is a component of a central channel extending along the longitudinal axis of the valve housing  10 . The damping space  36  is bounded on one of its sides by one piston component  68  and on the other side by the throttle  38 . Both the throttle  38  and the damping space  36  are adjacent to the appliance connection A on the free, frontal, end of the valve housing  10 . In addition, the free end of the connecting line  40 , which extends parallel to the central channel, discharges into the open at the frontal termination or end of the valve housing  10 . 
     An especially compact structure is thus achieved for the valve, one which performs its function with only one throttle point. In addition, the damping is equalized directly as a result of the effect exerted on the frontal, free, end of the lower piston component  68 . The damping space  36  is additionally characterized by the fact that this space, except for the throttle  38 , is more or less closed, in particular by way of the sealing device of piston components  68  in the direction of the narrowing  66  toward the pump connection P. 
     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.