Abstract:
A hydraulic pilot control unit includes at least one pressure control valve that can be controlled by means of an actuating device. The pressure control valve includes a control piston connected to a stem by means of a neck. The stem has a resilient operative connection to the actuating device. The neck is fastened to the stem. Thus, the mass of the control piston, which tends to oscillate, is reduced compared to the prior art.

Description:
This application is a 35 U.S.C. §371 National Stage Application of PCT/EP2010/007886, filed on Dec. 22, 2010 which claims the benefit of priority to Serial No. DE 10 2010 006 196.4, filed on Jan. 29, 2010 in Germany, the disclosures of which are incorporated herein by reference in their entirety. 
     The present disclosure relates to a hydraulic pilot control unit as described herein. 
     BACKGROUND 
     Such hydraulic pilot control units having pressure-regulating valves serve, in particular, for pressurizing and therefore adjusting valve spools of valves or main stages, which are subjected to relatively high pressure forces. For this purpose the pilot control units comprise joysticks or handles, which serve for adjusting the respective control pistons of the pressure-regulating valves. 
     DE 196 22 948 A1 shows a pressure-regulating valve of such a hydraulic pilot control unit. Here (according to  FIG. 1 ) a control pressure present acting on the connection P is transmitted wholly or partially to a working connection A, when a control piston is displaced in an opening direction by a tappet. 
     One disadvantage to such hydraulic pilot control units is that oscillations can be induced in the control piston here by pressure acting on various surfaces and by various springs. This is exacerbated by the fact that the control piston is composed of iron and thereby has a relatively large mass. Furthermore, the inducement of oscillations is exacerbated in that the control piston has a relatively long neck, via which a main portion of the control piston is connected to the tappet. 
     DE 103 24 051 A1 shows a pressure-reducing valve, the control piston of which, embodied as a stepped piston, is relatively heavily damped. For this purpose a damping passage is provided with a damping pin. This increases the stability of the feedback loop, but at the same time also presents disadvantages, such as a slower response speed, for example. 
     A further possible way of increasing the stability is to reduce the gain of the feedback loop in accordance with FR 2 857 705 B1. 
     In the light of this, the object of the disclosure is to create a hydraulic pilot control unit having at least one pressure-regulating valve, in which the stability of the feedback loop is increased through a directly acting parameter. 
     This object is achieved by a hydraulic pilot control unit having the features described herein. 
     SUMMARY 
     The hydraulic pilot control unit according to the disclosure has at least one pressure-regulating valve, which can be controlled by way of an actuating device and which comprises a control piston connected to a tappet by way of a neck. Here the tappet is operatively connected to the actuating device. According to the disclosure the neck is fixed to the tappet. This serves to reduce the mass of the control piston susceptible to oscillations, as compared to the state of the art. A directly acting parameter of the feedback loop of the pressure regulating valve is therefore modified in such a way that the inducement of oscillations in the control piston is reduced. This also serves, for example, to reduce the noise generated by the hydraulic pilot control unit according to the disclosure. 
     Further advantageous developments of the disclosure are described herein. 
     In an especially preferred development each control piston is composed substantially of aluminum or plastic. This further reduces its mass and hence the inducement of oscillations, compared to steel. 
     In an especially preferred development each tappet and the associated control piston can be displaced by the actuating device in an opening direction of the control piston. In this case a shear-elastic connection is provided between each neck and the associated control piston. 
     The shear-elastic connection is preferably formed by a regulating spring and by a head, fixed to an end portion of the neck and inserted into a recess arranged on a first end portion of the control piston. The regulating spring here is supported against the tappet and biases the control piston in an opening direction. The head is received in the recess in opposition to the force of the regulating spring, so that it is displaceable in an opening direction. This allows for the possibility of a jump in pressure on a working connection of the associated pressure-regulating valve during a first part of an adjustment travel of the operating unit or the tappet. 
     It is especially preferred if each head can be brought into bearing contact with an end face of the recess when the associated tappet is displaced in an opening direction. Beyond a predefined differential between a regulating spring force and pressure forces acting in opposition, this affords a direct or unsprung displacement of the control piston in an opening direction, resulting in a jump in pressure on the working connection. 
     In an especially preferred development each pressure-regulating valve has a return spring, which is supported against a housing of the pilot control unit or of the associated pressure-regulating valve, and which biases the tappet in a closing direction. A force acting in a closing direction of the pressure-regulating valve is thereby generated in opposition to a manual force acting on the operating control element, in order to close the pressure-regulating valve again after an actuation. 
     It is preferred if each recess is defined in a closing direction by a return bearing surface, with which the associated head can be brought into bearing contact. The return spring, by way of the tappet, the neck, the head and the return bearing surface, can thereby draw the control piston in the closing direction. 
     To facilitate assembly and the connection of the tappet to the control piston, each first end portion of the control piston may comprise a lateral passage, through which the head can be inserted into the recess. 
     In a preferred development the control piston is a stepped piston, which has a first ring surface acting in an opening direction and a second ring surface acting in a closing direction, both of which surfaces are subjected to the pressure of a working connection of the pressure-regulating valve. Here the first ring surface is smaller than the second ring surface. A pressure force acting on the control piston in a closing direction is thereby generated. 
     In a practically relevant exemplary embodiment of the pilot control unit according to the disclosure four pressure-regulating valves are provided, two pressure-regulating valves in each case being connected by way of their associated working connections to a valve spool of a consumer or a main stage. 
     It is preferred if each pressure-regulating valve has a control pressure chamber and a tank pressure chamber and a working pressure chamber arranged between them, multiple control pressure chambers being connected to a common control pressure connection of the pilot control unit and multiple tank pressure chambers being connected to a common tank connection of the pilot control unit. 
     For pressure balancing it is preferred if each control piston comprises a longitudinal bore, a chamber arranged between the housing and a second end portion of the control piston remote from the respective tappet being connected to the tank pressure chamber by way of the longitudinal bore and by way of the passage. 
     In a practically relevant exemplary embodiment the actuating device has a joystick. If the hydraulic pilot control unit according to the disclosure is arranged in an excavator, excavator-loader, telescoping loader, wheeled loader, compact loader or crane, the noise reduction achieved through the reduction in oscillations is particularly advantageous for a driver or operator. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An exemplary embodiment of the disclosure is described in detail below with reference to the figures, of which: 
         FIG. 1  shows a substantial detail of an exemplary embodiment of a hydraulic pilot control unit according to the disclosure in lateral section, a pressure-regulating valve according to the state of the art and a pressure-regulating valve according to the disclosure being shown combined; 
         FIG. 2   a  shows an enlarged detail of the exemplary embodiment according to the disclosure in  FIG. 1  in a further lateral section; and 
         FIG. 2   b  shows a detail enlargement of the shear-elastic connection in  FIG. 2   a.    
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a substantial detail of an exemplary embodiment of a hydraulic pilot control unit according to the disclosure in lateral section. Four pilot control valves embodied as pressure-regulating valves, of which only two pressure-regulating valves  2   a ,  2   b  are represented in  FIG. 1 , are arranged in a housing  1 . The pressure-regulating valves  2   a ,  2   b  are actuated by a rocking actuation plate  4 , which can be inclined about a horizontally running first rocker axis  6   a  ( FIG. 1 ), and in relation to the housing  1  by way of a second rocker axis  6   b , arranged perpendicularly to the drawing plane. This is done by way of a joystick fixed to the actuation plate  4  above the latter, only a relatively small part  8  of which joystick is shown in  FIG. 1 . Fitted to this part  8  is a handle, which serves for inclining the actuation plate  4  about the two rocker axes  6 . 
     The two pressure-regulating valves  2   a ,  2   b  are shown in their respective neutral positions, in which a respective control piston  10   a ,  10   b  is arranged in an upper closed position in the housing  1 , so that a respective working pressure chamber  12   a ,  12   b  and thereby a working connection (not shown) associated with each of these is not supplied with control pressure. For this purpose a hydraulic fluid connection, running from the central control pressure connection P of the pilot control unit according to the disclosure via the control pressure chambers  14   a ,  14   b  assigned to the respective pressure-regulating valves  2   a ,  2   b , to the respective working pressure chambers  12   a ,  12   b , is shut off by the control piston  10   a ,  10   b.    
     In the neutral position shown the working pressure chamber  12   a ,  12   b  is connected by control grooves (not shown) of the control piston  10   a ,  10   b  to a respective tank pressure chamber  16   a ,  16   b  and is therefore relieved of pressure. The tank pressure chambers  16   a ,  16   b  are connected to a tank (not shown) by way of a common tank connection (not shown) of the pilot control unit. The tank pressure chambers  16   a ,  16   b  are furthermore isolated from the control pressure chambers  14   a ,  14   b  and thereby from the control pressure connection P by a screw plug or a plug  18 . 
     Each control piston  10   a ,  10   b  is connected by a shear-elastic connection  20   a ,  20   b  and by a neck  22   a ,  22   b  to a tappet  24   a ,  24   b . The tappet  24   a ,  24   b  is biased upwards into the neutral position by a return spring  26   a ,  26   b  and a ring  27   a ,  27   b  (in  FIG. 1 ). For this purpose the return spring  26   a ,  26   b  is supported against a radial flange of the housing  1 . The control piston  10   a ,  10   b  is thereby also drawn into its neutral position against a (in  FIG. 1 ) downwardly directed force of a regulating spring  28   a ,  28   b.    
     In the case of the pressure-regulating valve  2   b  according to the disclosure represented on the right in  FIG. 1  the piston is drawn into the neutral position by the neck  22   a , which is fixed to the tappet  24   a  and attached to the end portion of which, facing the control piston  10   a , is a head  30   a  formed by a radial extension. The head  30   a  grips behind a return bearing surface  32   a  of an adjacent first end portion  33   a  of the control piston  10   a.    
       FIG. 2   a  shows an enlarged detail of the pressure-regulating valve  2   a  according to the disclosure in a further lateral section, which is set at 90 degrees to the section in  FIG. 1 . Here the tappet  24   a  with the neck  22   a  and with the head  30   a  is again shown in its neutral position. A sleeve-shaped tappet guide  34   a , fixed to the housing, is provided for guiding a (in  FIG. 2   a ) downwardly directed movement of the tappet  24   a.    
     Also shown is the ring  27   a , by way of which the tappet  24   a  is biased (in  FIG. 2   a ) upwards in the closing direction by the return spring  26   a  (not shown in  FIG. 2   a ). 
     Arranged concentrically inside the ring  27   a  is a washer  36   a , on which the regulating spring  28   a  is supported against the tappet  24   a  and in so doing biases the control piston  10   a  in an opening direction. An end-face concentric recess  38   a , the diameter of which is approximately equal to that of the head  30   a , is inserted on the first end portion  33   a  of the control piston  10   a . The recess  38   a  radially is more tightly stepped at an end face of the first end portion  33   a , so that a return bearing surface  32   a  is formed. In the neutral position shown the head  30   a  bears against the return bearing surface  32   a.    
     On its side situated opposite the return bearing surface  32   a  the recess  38   a  has an end face  40   a , a predefined interval being provided between the head  30   a  and the end face  40   a . This interval serves to define a length of travel of the tappet  24   a  in an opening direction of the pressure-regulating valve  2   a , over which—apart from pressure forces—only a force of the regulating spring  28  is operative. In the event of a further opening movement of the tappet  24   a , the head  30   a  comes into bearing contact with the end face  40   a  and then assists the (in the figures) downwardly directed opening movement of the control piston  10   a . A jump in pressure at the respective working pressure chamber  12   a  and at the associated working pressure connection is thereby possible at the end of the control range of the hydraulic pilot control unit according to the disclosure. 
     As the joystick (not shown) pivots back about the second rocker axis  6   b  (cf.  FIG. 1 ) from an assumed inclination to the right, for the reasons described above the tappet  24   a  moves (in the figures) upwards, the head  30   a  coming into bearing contact with the return bearing surface  32   a  and in so doing carrying the control piston  10   a  with it over the return bearing surface  32   a.    
     The control piston  10   a  is a stepped piston having two ring surfaces  42   a ,  44   a  (cf.  FIG. 2 ) subjected to the pressure of the working pressure chamber  12   a , the second ring surface  44   a  acting in the closing direction of the control piston  10   a  being larger than the first ring surface  42   a  acting in the opening direction. 
     The first control edge assigned to the first ring surface  42   a  controls the hydraulic fluid connection from the control pressure chamber  14   a  to the working pressure chamber  12   a , whilst the second control edge assigned to the second ring surface  44   a  controls the hydraulic fluid connection from the working pressure chamber  12   a  to the tank pressure chamber  16   a . Here a (comparatively small) cross section between the working pressure chamber  12   a  and the tank pressure chamber  16   a  is opened also in the neutral position. 
       FIG. 1  shows a sealing plug  46   a , which is screwed in the housing  1  and which together with a second end portion  48   a  of the control piston  10   a  defines a chamber  50   a.    
       FIG. 2   a  shows that the chamber  50   a  is connected by way of a longitudinal bore  52   a  to the recess  38   a.    
       FIG. 2   b  shows a detail enlargement of the shear-elastic connection  20   a  in a sectional view according to  FIG. 2   a . Here a radial passage  54   a  is provided laterally on the first end portion  33   a  of the control piston  10   a . The chamber  50   a  is thereby connected to the tank pressure chamber  16   a  by way of the longitudinal bore  52   a , the recess  38   a  and the lateral passage  54   a  (cf.  FIG. 1 ) and is therefore relieved. 
       FIG. 2   a  shows the passage  54   a , which is formed partly in the return bearing surface  32   a  and partly in the area of the recess  38   a . When assembling or putting the tappet  24   a  together with the control piston  10   a , the passage  54   a  allows the head  30   a  to be pushed radially into the recess  38   a.    
       FIG. 1  provides an illustration through a comparison of the exemplary embodiment of the pressure-regulating valve  2   a  represented on the right (in the figure) with an example of a pressure-regulating valve  2   b  according to the state of the art represented on the left (in the figure). The neck  22   b  and the head  30   b , which according to the state of the art are fixed to the control piston  10   b , are according to the disclosure separated therefrom and are associated with the tappet  24   a . The volume and hence the mass of the tappet  10   a  according to the disclosure are thereby significantly reduced compared to the tappet  10   b . Tests have confirmed that this reduction in the mass leads to a distinctly reduced inducement of oscillations of the control piston  10   a  and thereby of the hydraulic pilot control unit according to the disclosure. 
     It has further emerged from tests that a hydraulic pilot control unit, in which the necks of its pressure-regulating valves are not fixed to the tappet in accordance with the disclosure, but the necks of which are fixed to the respective control piston as in the state of the art, likewise exhibits a good oscillation damping if the control pistons are produced from a lighter material. Such materials include, in particular, aluminum and plastic. 
     The disclosure discloses a hydraulic pilot control unit, which comprises at least one pressure-regulating valve, which can be controlled by way of an actuating device and which in turn comprises a control piston connected to a tappet by way of a neck. Here the tappet has a resilient operative connection to the actuating device. According to the disclosure the neck is fixed to the tappet. This serves to reduce the mass of the control piston susceptible to oscillations, in comparison with the state of the art.