Abstract:
A pressure reducing valve includes main and pilot valves. The pilot valve is configured to regulate a pilot pressure, and includes pilot, drain, and first control-oil ports, a first opening cross section between the first control-oil and pilot ports, a second opening cross section between the pilot and drain ports; and a pilot part. The pilot part is configured to keep the pilot pressure at least substantially constant and control the first and second opening cross sections to be open during a pressure control operation. The main valve is fluidically connected to the pilot port and includes a second control-oil port, an outlet port, a third opening cross section between the second control-oil port and the outlet port, and a control part configured to control the third opening cross section based on the pilot pressure.

Description:
[0001]    This application claims priority under 35 U.S.C. §119 to patent application no. DE 10 2014 205 041.3, filed on Mar. 19, 2014 in Germany, the disclosure of which is incorporated herein by reference in its entirety. 
         [0002]    The disclosure relates to a pressure reducing valve, especially a piloted pressure reducing valve. 
       BACKGROUND 
       [0003]    A pressure reducing valve keeps an output pressure (secondary pressure) constant in the case of a variable inlet pressure (primary pressure). 
         [0004]    Such a pressure reducing valve is disclosed in printed document DE 35 37 336 A1. This has a switching valve as a main stage and a control valve as a pilot stage. By means of the control valve, the secondary pressure is controlled up to a specified pressure limit. If the secondary pressure exceeds the pressure limit, then a spool of the switching valve is operated in such a way that a control-oil port is connected directly to an output port and the connection is no longer carried out via the control valve. A disadvantage in the case of this solution is that the entire pressure reducing valve is prone to vibrations. During the control process in the pilot stage, two restrictors of the control valve are opened in turn. Especially the opening and closing of that restrictor which controls the opening cross section between the control-oil port and the output port leads to a vibration excitation of a spool of the control valve of the main stage. 
         [0005]    Further pressure reducing valves are disclosed in printed document DE 195 26 601 B4 and in printed document DE 37 39 824 C2. 
       SUMMARY 
       [0006]    In contrast to this, the disclosure is based on the object of creating a pressure reducing valve, the tendency of which towards vibrations is comparatively low or is avoided. 
         [0007]    This object is achieved by means of a pressure reducing valve according to the detailed description, the drawings, and the claims. 
         [0008]    According to the disclosure, provision is made for a pressure reducing valve, especially a 3-way pressure reducing valve, which has a main valve (main stage) and a pilot valve (pilot stage). The main valve has a control part (control spool) which, in dependence upon a pilot pressure which is controlled via a pilot valve, controls an opening cross section between a control-oil port and an output port. For keeping the pilot pressure constant, the pilot valve has a pilot part or two interacting pilot parts. As a result, during a pressure control operation of the pilot valve the adjusted pilot pressure can be kept constant. According to the disclosure, by means of the pilot part, or the pilot parts, a first opening cross section between a further control-oil port or the control-oil port and a pilot port, which is fluidically connected to the main valve, can be controlled. In addition, a second opening cross section can be controlled by means of the pilot part, or the pilot parts, between the pilot port and a drainage port (tank port). Furthermore, both opening cross sections can be opened during the pressure control operation. 
         [0009]    This solution has the advantage that by the opening of both opening cross sections during the pressure control operation vibrations are significantly reduced or even avoided since the opening cross sections are not opened and closed in turn. 
         [0010]    In the case of the pilot valve outside of the pressure control operation, especially in the de-activated state of the pilot valve, at least one opening cross section is advantageously closed. This advantageously leads to there being no control oil loss outside of the pressure control operation. 
         [0011]    In a further embodiment of the disclosure, the pilot pressure can be applied to the control part of the main valve via the pilot port. 
         [0012]    The main valve can have a control-oil port, an output port and a tank port. By means of the control part, preferably either the control-oil port is connected to the output port or the output port is connected to the tank port. 
         [0013]    The control part is preferably acted upon via a first end face by a force of a spring and the pressure medium of the output port, and via a second end face by the pressure medium of the pilot port of the pilot valve. If the pilot valve is in the “de-activated” state, then the control part can be displaced into an initial position via the force of the spring. 
         [0014]    The control-oil ports of the pilot valve and of the main valve can be fluidically connected. Alternatively, it is conceivable to isolate both control-oil ports from each other, as a result of which the pilot valve can be supplied with control oil independently of the main valve. 
         [0015]    In a further embodiment of the disclosure, the control part of the main valve, in a center control position in which the forces acting upon the end faces of the control part are neutralized, can isolate the output port from the pressure port and the tank port. 
         [0016]    By the force of the spring and the pressure medium of the output port, the control part of the main valve can be acted upon in the direction of first control positions. In these, starting from the center control position, the control part meters an opening cross section between the output port and the tank port via a first restrictor or via a first metering edge. In opposition to the spring force, the control part can be acted upon by the pressure medium of the pilot port of the pilot valve and therefore by the pilot pressure in the direction of second control positions. In these, starting from the center control position, the control part meters an opening cross section between the output port and the pressure port via a second restrictor or second metering edge. Therefore, a secondary pressure can be kept constant in a simple manner by means of the main valve. 
         [0017]    The end faces of the control part can have an identical size. 
         [0018]    The control part is preferably designed as a control spool. This can be designed with displacement capability in a slide bore and can have a first metering land. This together with control-oil port which opens into the slide bore can then form a first restrictor. Furthermore, the control spool can have a second metering land which together with the tank port which opens into the slide bore forms a second restrictor. 
         [0019]    The output port can also open into the slide bore and be formed between the tank port and the pressure port. If the control spool has a recess (annular recess) which is delimited by the metering lands, then via this the pressure port can be fluidically connected to the output port and the output port can be fluidically connected to the tank port. 
         [0020]    The metering lands are provided between the end faces of the control spool, for example. 
         [0021]    In the pilot valve, the interacting pilot parts can be formed from a first and second pilot part. Therefore, the pilot valve has two pilot parts. The first pilot part can be designed as a pilot spool with a radial land via which the second opening cross section can be controlled. By means of the pilot spool, a seating valve body can be operated as the second pilot part via which the first opening cross section can be controlled. This leads to an exceptionally simple design with regard to equipment engineering in order on the one hand to open both opening cross sections during the pressure control operation and to close one of the opening cross sections outside of the pressure reducing valve. 
         [0022]    For adjusting the pilot pressure, the pilot spool can be simply acted upon by a force of an actuator in the direction of the seating valve body. With a displacement of the pilot spool in this direction, the second opening cross section is preferably made smaller and the first opening cross section made larger. In the opposite direction, the pilot spool, especially via the seating valve body, can be acted upon by a primary pressure or by the control oil. If no actuator force is applied to the pilot spool or if the pressure force acting upon the seating valve body (second pilot part) via the control oil is greater than the actuator force, then the first opening cross section can be closed, for example outside to the control operation, if the actuator is “de-activated”. 
         [0023]    The radial land of the pilot spool can also be designed as a seating valve body. In an initial position of the pilot spool, this seating valve body can make contact with a valve seat and close the second opening cross section. In this case, the second opening cross section is preferably opened. 
         [0024]    The pilot spool can have a functional face (end face) pointing away from the second pilot part, via which the pilot spool can be acted upon by the actuator force. Via a further functional face, which points towards the second pilot part, it can act on this in order to displace this. 
         [0025]    With regard to equipment engineering, the seating valve body of the second pilot valve can be simply designed as a ball valve body. This, as already explained previously, can be acted upon by the control oil (primary pressure) in opposition to the actuator force. After a determined displacement distance of the pilot spool in a direction away from the seating valve body, the seating valve body makes contact with the valve seat and closes the first opening cross section. 
         [0026]    As the actuator, provision is preferably made for a solenoid, especially a proportional solenoid, via which the actuator force can be adjusted. 
         [0027]    In the de-energized or “de-activated” state of the actuator, the second opening cross section can preferably be closed, as a result of which the radial land, as a seating valve body, makes contact with its valve seat in this initial position. This can be achieved by the seating valve body being acted upon a force of a spring. If, however, the forces acting upon the second pilot part exceed the spring force, then the first opening cross section is closed by means of the second pilot part and the second opening cross section is open. 
         [0028]    After a determined energizing of the actuator, especially in the case of a maximum energizing, the seating valve body of the first pilot part makes contact with its valve seat and closes the second opening cross section, whereas the first opening cross section is opened. Therefore, one of the opening cross sections can be closed in a respective end position of the pilot spool. This furthermore leads to control oil being minimized or completely eliminated as a result of the flow-optimized end positions if it is not required and constitutes a loss capacity. 
         [0029]    The pilot spool can be acted upon by a force of a spring of the solenoid in the direction of the second pilot part, as already explained previously. An increasing energization of the solenoid can lead to an increase of the actuator force and in the case of a decreasing energization of the solenoid the actuator force can be reduced. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0030]    In the following text, a preferred embodiment of the disclosure is explained in more detail with reference to drawings. In the drawings: 
           [0031]      FIG. 1  shows in a schematic longitudinal section a pressure reducing valve according to the disclosure according to an exemplary embodiment and 
           [0032]      FIG. 2  shows a pressure-current characteristic line of the pressure reducing valve from  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0033]    Shown according to  FIG. 1  is a pressure reducing valve  1 . In this case, it is a piloted 3-way pressure reducing valve. This is used for example in power shift transmissions of private motor vehicles, lorries, buses, construction machines or tractors. It is also suitable for a large number of other hydraulic applications, for example for actuating comparatively large directional valves, power brakes, fan drives, hydraulic pumps or hydraulic motors. The pressure reducing valve has a low susceptibility to vibrations and has low control oil losses. It can be used for high pressures and high volumetric flows of pressure medium. 
         [0034]    The pressure reducing valve  1  has a main stage  2  and a pilot stage  4 . The main stage  2  has a main valve  6 . Via a control part in the form of a control spool  8 , a pressure medium connection between the control-oil port P and an output port A and between the output port A and a tank port T can be controlled. In control positions, the output port A is connected in turn in this case either to the control-oil port P or to the tank port T, or all the ports P, A and T are isolated from each other. The ports P, A and T open in each case into a spool bore  10  (slide bore), as seen in series in the axial direction. 
         [0035]    The control spool  8  is radially recessed in the middle and as a result of this has an annular groove  12 . As a result of this, a first radial land  14  (metering land) and a second radial land  16  (metering land) are formed. Provision is made on the first radial land  14  for a metering edge  18  which together with the control-oil port P which opens into the spool bore  10  forms a first restrictor. The second radial land  16  has a metering edge  20  which together with the tank port T which opens into the spool bore  10  forms a second restrictor. In the center control position shown in  FIG. 1 , the output port A is isolated both from the control-oil port P and from the output port A. Via a first end face  21 , the control spool  8  is acted upon by a force of a spring  22  in the direction of a metered control of an opening cross section between the output port A and the tank port T. In addition, the control spool  8  is acted upon in this direction by a pressure medium of the output port A which is tapped off from the output port A via a control passage  24  and is fed to a spring chamber  26  which is delimited by the end face  21 . The end face  28  of the control spool  8  which points away from the end face  21  can be acted upon by the pressure medium of a pilot port  30  of a pilot valve  32  of the pilot stage  4 . Therefore, a pilot pressure can act upon the control spool  8  via the end face  28  in opposition to the force of the spring  22  and in opposition to the pressure medium from the output port A. With a displacement of the control spool in this direction, starting from the control position shown in  FIG. 1 , an opening cross section between the control-oil port P and the output port A is metered. 
         [0036]    The pilot valve  32  also has a control-oil port  34 . This is connected via a connecting flow path  36  to the control-oil port P. In the connecting flow path  36 , provision can additionally be made for a hydraulic pump  38 . Furthermore, the pilot valve  32  has a drain port  40  which is connected to a tank  42 . The pilot valve  32  has two interacting parts  44  and  46 . The pilot part  44  is a pilot spool  44  with a radial land  48 . This serves as a seating valve body  48 , especially as a poppet-type seating valve. A valve seat  50  is associated with this. If the radial land  48  is in contact with the valve seat  50 , then the pilot port  30  is blocked towards the drain port  40 . The pilot spool  44  has a section  52  which extends away from the radial land  48  and from the pilot part  46 . Via this section, the pilot spool  44  can be acted upon by a force of an actuator in the form of a proportional solenoid  54 . This has a spring  56  via which the pilot spool  44  and therefore the radial land  48  is acted upon by a spring force in the direction of the valve seat  50 . For this purpose, the spring  56  acts upon an armature  58  of the proportional solenoid  54  which in turn butts against an end face of the pilot spool  44 . The armature  58  is encompassed by a coil arrangement  60 . If this is energized, then the armature  58  is acted upon by a magnetic force in the direction of the force of the spring  56 . With increasing energization of the coil arrangement  60 , the actuator force acting upon the pilot spool  44  therefore increases. 
         [0037]    Extending from the radial land  48  in the opposite direction to the spool section  52  is a further spool section  62 . This can butt by its end face against the second pilot part  46  which is designed in the form of a ball valve body. A valve seat is also associated with the ball valve body  46 . If the ball valve body  46  is in contact with the valve seat, then a pressure medium connection between the control-oil port  34  and the pilot port  30  is closed. If the pilot spool  44  butts against the ball valve body  46  and is moved in a direction away from the proportional solenoid  54 , then the ball valve body  46  is removed from its valve seat. 
         [0038]    According to  FIG. 1 , the pilot parts  44 ,  46  are shown during the pressure control operation. In this, both the radial land  48  and the ball valve body  46  are lifted from their valve seat. 
         [0039]    Therefore, both the pressure medium connection between the control-oil port  38  and the pilot port  30  and the pressure medium connection between the pilot port  30  and the drain port  40  are open, as a result of which vibration excitations of the pilot valve  32  and of the main valve  6  are reduced or avoided. By means of the pilot valve  32 , a pilot pressure which is applied to the end face  28  of the control spool  8  can be kept constant. The pilot pressure is adjusted in this case by the energizing of the proportional solenoid  54 . 
         [0040]    In the de-energized state of the proportional solenoid  54 , the pilot part  44  is displaced by the force of the spring  56  away from the proportional solenoid  54  if the forces acting upon the pilot part  46  in opposition to the spring force are greater. In this case, the radial land  48  makes contact with the valve seat  50 . If the forces acting upon the pilot part  46  in the de-energized state of the proportional solenoid  54  in opposition to the spring force exceed the spring force, then the pilot valve  46  is displaced onto its valve seat and closes the corresponding opening cross section. Therefore, no control oil can flow from the control-oil port  34  to the drain port  40  outside of the pressure control operation since one of the opening cross sections is closed. This further leads to the control oil losses of the pilot valve  32 , and therefore of the entire pressure reducing valve  1 , being exceptionally low. 
         [0041]    The pilot port  30  of the pilot valve  32  is connected according to  FIG. 1  to a pressure chamber  64  of the spool bore  10  which is delimited by the end face  28  of the control spool  8 . 
         [0042]    According to  FIG. 1 , the main valve  6  is arranged coaxially to the pilot valve  32 . 
         [0043]    According to  FIG. 2 , a current-output pressure characteristic line of the pressure reducing valve  1  is shown. If the proportional solenoid  54  from  FIG. 1  is engaged and energized, then the output pressure p A  in the output port A of the main valve  6  increases only from a current I 1  onwards—see characteristic line  66  in  FIG. 2 . This results from the force of the spring  22  having to be overcome so that the control spool  8  can be displaced into its control positions by means of the pilot pressure. The adjusted output pressure p A  is approximately proportional to the current I of the proportional solenoid  54  from the current I 1  onwards. If the energizing of the proportional solenoid is decreased, then the output pressure p A  is proportional to the current I corresponding to a characteristic line  68 —see FIG.  2 —which results on account of a hysteresis. From a current I 2  onwards, with a decrease of said current, the output pressure p A  is zero, wherein I 2  is less than I 1 . 
         [0044]    Disclosed is a pressure reducing valve with a main valve and a pilot valve. This, in dependence upon a pilot pressure which is regulated via the pilot valve, adjusts an opening cross section between a control-oil port and an output port and between the output port and a tank port. The pilot valve keeps the adjusted pilot pressure constant during the pressure control operation. The pilot valve has at least one pilot part, by means of which a first opening cross section between a control-oil port and a pilot port which is fluidically connected to the main valve can be controlled. Furthermore, by means of the at least one pilot part a second opening cross section between the pilot port and a drain port can be controlled. During a pressure control operation for regulating the pilot pressure, both opening cross sections are opened. 
       List Of Designations 
       [0000]    
       
           1  Pressure reducing valve 
           2  Main stage 
           4  Pilot stage 
           6  Main valve 
           8  Control spool 
         P Control-oil port 
         A Output port 
         T Tank port 
           10  Spool bore 
           12  Annular groove 
           14  Radial land 
           16  Radial land 
           18  Metering edge 
           20  Metering edge 
           21  End face 
           22  Spring 
           24  Control passage 
           26  Spring chamber 
           28  End face 
           30  Pilot port 
           32  Pilot valve 
           34  Control-oil port 
           36  Connecting flow path 
           38  Hydraulic pump 
           40  Drain port 
           42  Tank 
           44  Pilot part 
           46  Pilot part 
           48  Radial land 
           50  Valve seat 
           52  Spool section 
           54  Proportional solenoid 
           56  Spring 
           58  Armature 
           60  Coil arrangement 
           62  Spool section 
           64  Pressure chamber 
           66  Characteristic line 
           68  Characteristic line