Patent Publication Number: US-6712091-B2

Title: Control device for a hydraulic control motor

Description:
FIELD OF THE INVENTION 
     The invention relates to a control device. 
     BACKGROUND INFORMATION 
     U.S. Pat. No. 3,714,868 describes a control device that operates on the closed-center principle. 
     It is an object of the present invention to provide a control device configured to operate on the open-center principle and which substantially avoids leakages. The control device may be constructed in a simple manner, may operate reliably and may be produced without a high outlay in manufacturing terms. 
     SUMMARY 
     The above and other beneficial objects of the present invention are achieved by providing a control device as described herein. 
     In accordance with the present invention, quantity-independent functioning may be ensured. The control device according to the present invention may be used for various applications and may easily be adapted to changed requirements. It may be used, for example, for a hydraulic control motor, e.g., when the activation of the latter functions on the open-center principle. 
     Example embodiments of the present invention are described herein. However, the present invention is not restricted to the feature combinations described herein but include further appropriate possibilities for the combination of features. 
     The present invention may allow a modular construction of the, e.g., electrohydraulic control device, so that a large number of parts may be used many times, which may provide considerable advantages with regard to the outlay in terms of manufacturing and assembly terms. By virtue of the simple construction, standard seals may be used, which do not place stringent requirements on the components in terms of tolerances and surface quality. In addition, the use of special materials may be dispensed with, which may be advantageous with regard to heat treatment and surface treatment. At the same time, high flexibility for various applications is preserved. Particularly reliable functioning may be ensured in that no moveable parts are mounted one in the other. When the control device according to the present invention is used for a hydraulic control motor, the latter may be activated on the open-center or closed-center principle. 
     A control device according to the present invention for a hydraulic control motor has at least one valve which is controlled actively by an actuating force and which has a first piston with stepped diameters, which is mounted axially moveably in a housing and is loaded by a spring and which forms a first pressure space with an, e.g., disk-shaped element having a throttle point. Furthermore, such a control device has at least one passive valve which is operatively connected to the actively controlled valve and which has a second piston with stepped diameters, which is mounted axially moveably in the housing and is loaded by a spring and which forms with the housing a second pressure space. These two pressure spaces are operatively connected via a line, so that the actively controlled valve co-controls the passive valve. The actively controlled valve has an adjustable throttle point which may be regulated actively by a throttle needle. The actuating force which regulates the throttle point may be applied mechanically, electrically, electromagnetically, hydraulically, pneumatically, etc. The pistons have special sealing elements which, in addition to performing their sealing function, also have bearing properties. They may be produced from resistant and low-wear materials, such as, for example, Teflon. Integrated in the piston of the actively controlled valve is at least one bore which serves for the feed of pressure medium into a pressure space which is connected to the passive valve by a line. 
     An exemplary embodiment of the present invention is described below, in principle, with reference to the FIGURE. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The FIGURE illustrates a control device according to the present invention which controls a hydraulic control motor. 
    
    
     DETAILED DESCRIPTION 
     A pressure medium conveyed out of a tank  2  by a pump  1  flows through an inflow bore  3  into a housing  4  having a plurality of bores  5 , 6 , 7 , 8  which are connected via lines  9 , 10 . A piston  12  loaded by a spring  11  is mounted axially moveably in the bore  5 . The piston  12  has a stepped outside diameter. A sealing element  13  in the piston  12  separates the bore  5  into two pressure spaces  14 ,  15 . The sealing element  13  also serves at the same time for the low-friction guidance of the piston  12 . The spring  11  is supported on a disk-shaped element  16  connected firmly to the housing  4 . The disk-shaped element  16  has a throttle point  17  which co-operates with a throttle needle  18  axially displaceable by an actuating force and thus allows a change in volume flow. 
     The pressure medium flowing through the throttle point  17  flows through a further pressure space  24  and via a line  23  back to the tank. If, for example, the volume flow in the inflow bore  3  is to be reduced or interrupted, the throttle needle  18  is pushed into the throttle point  17 . The pressure medium then has to flow through a bore  19  arranged in the piston  12 . Due to the smaller throughflow cross-section of the throttle points  17 , there is a pressure build-up in the pressure space  14 . Beyond a defined pressure in the pressure space  14 , a force equilibrium occurs between the pressure forces acting on end faces  20  and  21 . The spring  11  has the task of pushing the piston  12 , in the neutral position, against the housing  4  so that, due to the throttling of the volume flow of the pressure medium in an annular gap  22 , a predetermined pressure difference may arise, which, when a throttle effect occurs at the throttle point  17 , brings about, on the end face  21  of the piston  12 , a pressure force which overcomes the friction of the sealing element  13 . When the force equilibrium is reached, the piston  12  moves in the direction of the inflow bore  3  due to the force of the spring  11 . The annular gap  22  located between the housing  4  and the end face  20  is thereby narrowed. As a result, the pressure of the pressure medium of the inflow bore  3  rises. The actuating force on the throttle needle  18  corresponds in amount to the pressure of the pressure medium in the pressure space  14 , which, in turn, corresponds to the pressure of the pressure medium in the inflow bore  3 . This gives rise to proportionality between the actuating force acting on the throttle needle  18  and the pressure of the pressure medium which is established in the inflow bore  3 . A further piston  27  pressure-loaded by a spring  26  is located in the bore  6  in the housing  4 . The spring  26  is supported on a disk-shaped element  28 . 
     If the pressure medium is to be led to a pressure space  40  of a hydraulic control motor  41  via a line  39 , then a throttle needle  29  may close a throttle point  30 , with the result that an annular gap  31  is closed. The pressure medium flows through a bore  32  into a pressure space  33  and from there further on, via a line  34 , into a pressure space  35  which is formed by a piston  36 , axially displaceable in the bore  7 , and the housing  4 . The piston  36  pressure-loaded by a spring  37  closes an annular gap  38 . A piston  42  of the hydraulic control motor  41  is displaced and the pressure medium is led further on from a second pressure space  43  via a line  44  to the line  10  in the housing  4 . The pressure medium may flow off to the tank  2  via an open annular gap  45  which occurs between the housing  4  and a piston  46  axially displaceable in the bore  8  and loaded by a spring  47 . 
     A pressure space  50 , which is formed by the housing  4  and the piston  46  pressure-loaded by a spring  47 , is operatively connected to the pressure space  14  via a line  25 . 
     An actively controlled valve  48  thus at the same time also controls a passive valve  49 . A bore  52  may be provided, in addition, in the piston  46  of the passive valve  49 , in order to return the pressure medium into the pressure space  14 . 
     REFERENCE SYMBOLS 
       1 . Pump 
       2 . Tank 
       3 . Inflow bore 
       4 . Housing 
       5 . Bore 
       6 . Bore 
       7 . Bore 
       8 . Bore 
       9 . Line 
       10 . Line 
       11 . Spring 
       12 . Piston 
       13 . Sealing element 
       14 . Pressure space 
       15 . Pressure space 
       16 . Disk-shaped element 
       17 . Throttle point 
       18 . Throttle needle 
       19 . Bore 
       20 . End face 
       21 . End face 
       21 . End face 
       22 . Annular gap 
       23 . Line 
       24 . Pressure space 
       25 . Line 
       26 . Spring 
       27 . Piston 
       28 . Disk-shaped element 
       29 . Throttle needle 
       30 . Throttle point 
       31 . Annular gap 
       32 . Bore 
       33 . Pressure space 
       34 . Line 
       35 . Pressure space 
       36 . Piston 
       37 . Spring 
       38 . Annular gap 
       39 . Line 
       40 . Pressure space 
       41 . Hydraulic control motor 
       42 . Piston 
       43 . Pressure space 
       44 . Line 
       45 . Annular gap 
       46 . Piston 
       47 . Spring 
       48 . Valve 
       49 . Valve 
       50 . Pressure space 
       51 . Sealing element 
       52 . Bore