Abstract:
The invention is based on an apparatus ( 10 ) for regulating the pressure in a hydraulic circuit that comprises an electrically triggerable pressure-control valve ( 12 ), a receptacle device ( 14 ) in which the pressure-control valve ( 12 ) is installed, and means ( 54, 64 ) for damping pressure pulsations. In order to save space, simplify the manufacture of the receptacle device ( 14 ), and save additional holding elements, it is proposed according to the invention that the means ( 54, 64 ) for damping pressure pulsations be designed as integral components of the pressure-control valve ( 12 ).

Description:
BACKGROUND OF THE INVENTION 
     The invention is based on an apparatus for regulating the pressure in a hydraulic circuit. Apparatuses of this type are used in automatic gearboxes of motor vehicles in particular, to trigger gear changes via control of the pressure level, for example. 
     For this, known apparatuses comprise an electrically triggerable pressure-control valve, like the one made known previously in DE 197 33 660 A, for example. This pressure-control valve comprises a solenoid part constructed in conventional fashion having coil, coil core, flux concentrating element and armature, and a hydraulic part having mechanical linkage with the solenoid part. In the hydraulic part, a shutoff element able to be acted upon by the armature controls the flow of hydraulic fluid between inlet passages, working passages, and return passages. 
     This known pressure-control valve can be installed with its hydraulic part in a receptacle device—a “hydraulic control block”—in which recesses are provided that direct hydraulic fluid and are matched to the corresponding passages of the pressure-control valve. Appropriate devices are provided to dampen pressure pulsations, which can occur during operation of the pressure-control valve in the recess matched to the working passage. These devices are attached in the receptacle device as separate components. 
     The separate arrangement of the damping devices described is disadvantageous, because it makes a large number of holding elements necessary, takes up a relatively large space, generates additional work, and is costly to install. 
     SUMMARY OF THE INVENTION 
     In contrast, an apparatus according to the invention for controlling the pressure in a hydraulic circuit has the advantage that the means for damping pressure pulsations are an integral component of the pressure-control valve. This saves space, simplies the manufacture of the receptacle device, and makes separate holding elements superfluous, without making assembly of the pressure-control valve itself more difficult. The pressure pulsations are damped by means of the invention directly at the site of origin, which greatly improves the damping effect. Due to the damping, the pressure/flow characteristic of a pressure-control valve can be kept within narrow tolerances under nearly all operating conditions. Additionally, the prevention of pressure pulsations has a positive effect on the wearing behavior of the pressure-control valve, so that its service life is extended. 
     The devices can be integrally molded on one of the sealing elements of the pressure-control valve particularly easily, so that the total number of components to be obstructed remains unchanged. The devices, together with the housing of the pressure-control valve, enclose a damping chamber having a variable volume. Its damping behavior can be varied by means of vents to the recess of the receptacle device matched to the return passage of the pressure-control valve in accordance with the specific case of application. This vent can also be designed in advantageous fashion as throttling point. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     Exemplary embodiments of the invention are presented in the drawing and explained in greater detail in the following description. 
     FIGS. 1 and 2 are sectional diagrams of a longitudinal section of two different exemplary embodiments of an apparatus according to the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Each of the apparatuses for controlling the pressure in a hydraulic circuit labelled in FIGS. 1 and 2 with the position number  10  comprises an electronically triggerable pressure-control valve  12  and a receptacle device  14  in which this pressure-control valve  12  with its hydraulic part  18  is installed. In addition to its hydraulic part  18 , the pressure-control valve  12  also comprises a solenoid part  16 . Comprising this solenoid part  16 , an electrically triggerable, hollow-cylindrical coil  20 , a moveably guided armature  22 , and a flux concentrating element  24  surrounding the coil on its circumference are shown in sections. 
     The armature  22  comprises a section  22   a  projecting into the interior of the coil  20 , a collar  22   b  adjoining this and spanning the front side of the coil  20 , and a neck  22   c  in axial extension of this collar  22   b . A through hole  26  extends through the center of the armature  22 , into which a pushrod  28  is pressed in the region of the neck  22   c . This pushrod  28  penetrates a guide  30  provided in the hydraulic part  18  and designed in the shape of an eyelet and actuates a shutoff element  32  with its end, the outer diameter of which is tapered. The shutoff element  32  is designed in the shape of a ball and bears against the pushrod  28  as a result of hydraulically-induced forces of flow and pressure. The shutoff element  32  serves to control a first valve seat  34  formed in the hydraulic part  18 , the inner diameter of which is greater than the outer diameter of the pushrod  28 . An annular orifice therefore exists between pushrod  28  and valve seat  34 , through which hydraulic fluid can flow when the valve seat  34  is opened. 
     A second valve seat  36  of the hydraulic part  18  is formed on a perforated plate  38  that is injected, facing the solenoid part  16 , into the hydraulic part  18 . This perforated plate  38  is controlled by the front end of the neck  22   c  and lies in alignment with the first valve seat  34 . In the non-energized starting position of the armature  22  shown, the first valve seat  34  is open and the second valve seat  36  is closed. In addition, the armature  22  is moved into the starting position shown by a return device, e.g., in the form of a spring (not shown). Current is not supplied to the coil  20 . 
     The hydraulic part  18  is firmly connected to the solenoid part  16  of the pressure-control valve  12 . This solenoid part  16  is manufactured using injection molding technology, preferably using plastic, and comprises an injected holding element  40 . The latter is designed in the shape of a sleeve, and its diameter is offset repeatedly. A non-extrusion-coated part of the holding element  40  projects over the hydraulic part  18  and firmly encloses the flux concentrating element  24  of the solenoid part  16 . A second guide  42  for the armature  22  is located at the smallest diameter of the holding element  40  lying inside the hydraulic part  18 . At the same time, this guide  42  forms an end stop for limiting the up-and-down motion of the armature  22 . 
     A continuous, longitudinal recess  44  extending in the direction of its longitudinal axis is provided at the hydraulic part  18  for directing hydraulic fluid, into which two transverse passages  46 ,  48 , one extending over the top of the other, empty at right angles. The first transverse passage  46  facing the solenoid part  16  is designed in the fashion of a blind hole and forms the return passage R of the pressure-control valve  12 , while the transverse passage  48  opposite to the solenoid part  16  penetrates the hydraulic part  18  and acts as the working passage A. The front end of the longitudinal recess  44  forms an inlet passage  50 —labelled “P”—for the hydraulic part  18 . The latter empties into the working passage A when the valve seat  34  is open, while the hydraulic passage between the working passage A and the return passage R is interrupted. Using an electrically triggered coil  20 , these relationships are reversed accordingly, that is, a hydraulic connection exists between the return passage R and the working passage A, while the inlet passage P is blocked. 
     Recesses  46 ′,  48 ′,  50 ′ of the receptacle device  14  are matched to the passages  46 ,  48 ,  50  of the pressure-control valve  12 . Sealing elements  52  and  54  are provided on the circumference of the hydraulic part  18  for the mutual sealing of these recesses  46 ′,  48 ′,  50 ′. The first sealing element  52  separating the inlet passage P from the working passage A is a conventional O-ring that is held on a filter cage  56 . The annular filter cage  46  manufactured out of plastic that is resistant to hydraulic fluid is slid onto the end section of the hydraulic part  18  and comprises a filter fabric that covers the opening cross section of the working passage A. This filters contaminants out of the hydraulic fluid flowing out of the working passage A to a hydraulic consuming device (not shown). 
     The second sealing element  54  serving to separate the working pasage A from the return passage R is composed, according to the invention, of an O-ring cross section  58  having sealing function and an integrally molded diaphragm  60  having a thickened end  62 . The sealing element  54  is also produced out of elastic material resistant to hydraulic fluid having good impermeability properties, so that the diaphragm  60  can be stretched using its thickened end  62  between the filter cage  56  and a shoulder of the hydraulic part  18  on the housing side. An annular pressure chamber  64  closed off from the surroundings is thereby produced between the diaphragm  60  and the housing of the hydraulic part  18 . The interior space of this pressure chamber  64  is filled with air. 
     In the installed stated of the pressure-control valve  12  shown, the diaphragm  60  is located in the recess  48 ′ of the receptacle device  14  matched to the working passage A. Due to its malleability and, therefore, the variability of the volume of the pressure chamber  64  enclosed by it, the latter is capable of damping pressure pulsations that can occur in the working passage  48  and the connected recess  48 ′. Using the sealing element  54  designed according to the invention, therefore, a hydraulic capacity is created in the working passage A without appreciably changing the space required therefore, the number of individual parts or the installation expenditure required. An increase in the stiffness of the diaphragm  60  could be realized, if necessary, by means of a spring element (not shown) that can be located in the interior space of the pressure chamber  64 . By varying the spring elements used, a damping characteristic adapted to the specific case of application could be achieved. 
     The second exemplary embodiment according to FIG. 1 differs from the first exemplary embodiment by the fact that the pressure chamber  60 —the volume of which can be changed—is connected to the recess  46 ′ of the receptacle device  14  matched to the return passage R of the pressure-control valve  12  via a vent  66 . As a further actuating variable on the damping characteristic, the vent  66  can be designed as damping throttle. It would also be feasible to provide a plurality of such vents  66  or to divide the pressure chamber  64  into multiple sections. 
     Further-reaching changes or additions to the exemplary embodiments are possible, of course, without deviating from the basic idea of the invention. A 3/2 directional-control proportioning valve is preferably used as the pressure-control valve  12 , the armature  22  of which can be moved into any intermediate position by the solenoid part  16 . Operating positions can also be described in which both valve seats  34  and  36  are open simultaneously.