Abstract:
A hydraulic control assembly, in particular for controlling hydraulic consumers of a mobile machine, includes a load reporting line ( 26 ) that can be subjected to the highest load pressure of a plurality of hydraulic consumers, triggered simultaneously each via a respective main control valve ( 38, 57 ), and that is connectable by an end portion ( 26   a ) to a pump regulator ( 25 ). A pressure limiting valve ( 50 ) limits the control pressure in the end portion ( 26   a ) of the load reporting line ( 26 ). The pressure limiting valve ( 50 ) is adjustable as a function of the magnitude of a pilot control signal serving to trigger a main control valve ( 38, 57 ).

Description:
CROSS-REFERENCE 
     The invention described and claimed hereinbelow is also described in PCT/EP2007/003280, filed on Apr. 13, 2007 and DE 10 2006 018 706.7, filed on Apr. 21, 2006. This German Patent Application, whose subject matter is incorporated here by reference, provides the basis for a claim of priority of invention under 35 U.S.C. 119(a)-(d). 
     BACKGROUND OF THE INVENTION 
     The invention relates to a hydraulic control assembly, which is used in particular for controlling hydraulic consumers in mobile machines. 
     One such hydraulic control assembly is known for instance from European Patent Disclosure EP 0 566 449 A1. This is a hydraulic control assembly on the load-sensing principle, in which an adjusting pump is set, as a function of the highest load pressure of the hydraulic consumers actuated, such that the pump pressure is above the highest load pressure by a defined pressure difference. The pressure medium flows to the hydraulic consumers via adjustable metering apertures, which are located between an inflow line leading away from the adjusting pump and the hydraulic consumers and are typically integrated with a main control valve serving to control the direction of a hydraulic consumer. By means of the pressure balances downstream of the metering apertures, it is attained that at an adequate quantity of pressure medium furnished by the adjusting pump, a defined pressure difference across the metering apertures exists, regardless of the load pressures of the hydraulic consumers, so that the quantity of pressure medium flowing to a hydraulic consumer is now dependent only on the opening cross section of the respective metering aperture. If a mobile machine is opened wider, then a higher quantity of pressure medium must flow across it in order to generate the defined pressure difference. The adjusting pump is adjusted in each case such that it furnishes the required quantity of pressure medium. This is accordingly also called demand flow regulation. For that purpose, the adjusting pump has a pump regulator, which can be subjected via a load reporting line to the highest load pressure of the simultaneously triggered hydraulic consumers. For limiting the pump pressure, a fixedly set pressure limiting valve is connected to the end portion, connected to the pump regulator, of the load reporting line, and this pressure limiting valve, in cooperation with a throttle restriction that decouples the end portion from the remainder of the load reporting line, limits the pressure reported to the pump regulator and thus also limits the pump pressure. 
     The pressure balances downstream of the metering apertures are urged in the opening direction by the pressure downstream of the respective metering aperture and in the closing direction by a control pressure prevailing in a rear control chamber; this pressure typically corresponds to the highest load pressure of all the hydraulic consumers supplied by the same hydraulic pump. If, when a plurality of hydraulic consumers are actuated simultaneously, the metering apertures are opened so widely that the quantity of pressure medium furnished by the hydraulic pump, which has been displaced as far as the stop is less than the total quantity of pressure medium supplied], then the quantities of pressure medium flowing to the individual hydraulic consumers are reduced in proportion, regardless of the load pressure at the various hydraulic consumers. This is accordingly called control with load-independent flow distribution (LIFD control). Since in LIFD control the highest load pressure is also sensed, and as a result of the variation in the quantity of pressure medium pumped, the hydraulic pump generates an inflow pressure that is above the highest load pressure by a defined pressure difference, LIFD control is a special case of load-sensing control (LS control). 
     When there is a plurality of hydraulic consumers, to which pressure medium flows via a respective metering aperture with an upstream pressure balance that is urged in the closing direction only by the pressure upstream of the metering aperture and is urged in the opening direction, via an individual load reporting line, only by the load pressure of the respective hydraulic consumer and by a compression spring, load-independent flow distribution is not obtained. In that case, only LS control and LS consumers are involved. Such control is known for instance from German Patent DE 37 09 504 C2. When a plurality of hydraulic consumers are actuated simultaneously and there is an inadequate quantity of pressure medium furnished by the adjusting pump, initially only the quantity of pressure medium flowing to the hydraulic consumer with the highest load pressure is reduced. When it stops, the quantity of pressure medium flowing to the consumer having the second-highest load pressure then decreases, and so forth. 
     In the hydraulic control assembly of German Patent DE 37 09 504 C2, an end portion, leading to the pressure balance is connected via a throttle restriction to the remainder of the individual load reporting line of a hydraulic consumer and to a pressure limiting valve. The latter is adjustable as a function of the magnitude of a pilot control signal serving to trigger the main control valve associated with the hydraulic consumer. The pressure balance now acts like a pilot-controlled pressure reduction valve, whose setting is variable by the pilot control signal, and which closes when a defined pressure is reached at its outlet. The pressure at which the pressure balance closes, and which prevails at a hydraulic consumer whose pressure balance is triggered accordingly on the closing side, can thus be limited individually for the consumer and varied via the pilot control signal. 
     In German Patent Disclosure DE 198 31 595 A1, an LIFD control is shown in which once again the pressure is limited individually for a hydraulic consumer. This requires that the rear control chamber of an LIFD pressure balance be constructively disconnected from the load reporting line. Also, a multi-way valve is necessary, as a function of whose switching position the rear control chamber communicates with the load reporting line or is subjected to pump pressure. The multi-way valve is switched as a function of the load pressure. No provision is made for varying the switching pressure during operation. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to refine a hydraulic control assembly having the characteristics of the preamble to claim  1  further in such a way that with pilot control signals for the main control valves, pressure control is possible for a plurality of hydraulic consumers as well in a simple and economical way. 
     This goal is attained, in a hydraulic control assembly claim  1 , in accordance with the invention in that in accordance with the body of claim  1 , the pressure limiting valve is adjustable as a function of the magnitude of a pilot control signal serving to trigger a main control valve. Thus according to the invention, the pressure limiting valve, with which the pressure reported to the pump regulator can be limited, is adjustable. The invention is based on the thought that mobile machines exist, in which upon a pressure control of one hydraulic consumer, it is only rarely that a further hydraulic consumer can be actuated. In particular, according to the invention, pressure control of one hydraulic consumer is possible even in an LIFD control assembly, by very simple means and without changes in the individual pressure balances associated with the metering apertures. 
     If the pressure limiting valve is adjustable as a function of the magnitude of a plurality of pilot control signals, then if a plurality of pilot control signals are present, it is advantageously adjusted as a function of the strongest pilot control signal. The assumption then is that the pressure set at the pressure limiting valve is higher, the stronger the pilot control signal, 
     In an embodiment, according to which the pressure limiting valve is adjustable as a function of a pilot control signal only up to a set value that is below the maximum set value, it is possible for the machine operator to individually predetermine the maximum consumer pressure that can be set with a pilot control signal, depending on the type of machine or the type of work to be handled. 
     Advantageously, the pressure control can be switched off by means of a further embodiment. In that case, demand flow control is obtained, with a limitation of the load pressure to a high value. 
     The pressure limiting valve is hydraulically adjustable and has an adjusting piston adjacent to a pressure chamber that communicates with the control line. Fundamentally, the pressure limiting valve may also be of a kind that is electrically or electrohydraulically adjustable. Especially if the main control valve is actuated electrically, such an adjustability of the pressure limiting valve can be favorable. Conversely, in the event of hydraulic actuation of the main control valve, the use of a purely hydraulically adjustable pressure limiting valve appears more advantageous. 
     If the main control valve is hydraulically actuatable, then a pilot control pressure is typically generated with the aid of an adjustable pressure reduction valve, which has a pressure connection, at which a largely constant supply pressure prevails, preferably at a level of 30 to 35 bar; a tank connection; and a regulating connection, at which the pilot control pressure is regulated. The pressure limiting valve can then be adjusted in a simple way to its maximum set value, if there is an arbitrarily actuatable multi-way valve, as a function of whose switching position the pressure chamber of the pressure limiting valve can be subjected to the pilot control pressure or to the supply pressure. 
     With the multi-way valve, it is possible in alternation to connect either a line in which the supply pressure prevails or a line in which the pilot control pressure prevails with the pressure chamber of the pressure limiting valve. The multi-way valve can be embodied more simply, however, if a check valve opening toward the pressure chamber is located between the pilot control line and the pressure chamber at the pressure limiting valve. This check valve prevents the high supply pressure from reaching the pilot control line as well and affecting the triggering of the main control valve. 
     With check valves that are located in a further embodiment, the highest hydraulic pilot control signal can be selected in a simple manner and fed into the pressure chamber of the pressure limiting valve. 
     To limit pressure control via a pilot control signal to a pressure value that is below the maximum set value of the pressure limiting valve, there is a second pressure limiting valve. Naturally, this pressure limiting valve should not be operative in every case whenever an adjustment of the first pressure limiting valve to the maximum set value by subjecting the pressure chamber to the supply pressure is desired. For that mode of operation, the multi-way valve is advantageously employed, by way of which valve the supply pressure is switched through to the pressure chamber. 
     The pressure relief of the pressure chamber at the pressure limiting valve is expediently effected via a flow valve, which can be implemented by a simple nozzle but is preferably a flow regulating valve. 
     Several exemplary embodiments of a hydraulic control assembly according to the invention are shown in the drawings. The invention will now be described in further detail in terms of these exemplary embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a first exemplary embodiment, operating by the LIFD principle, with the pressure limiting valve that is connected to an end portion of the load reporting line and is hydraulically adjustable as a function of a hydraulic pilot control signal; 
         FIG. 2  shows a second exemplary embodiment, operating on the LS principle, with the pressure limiting valve that is connected to the end portion of the load reporting line and is hydraulically adjustable as a function of a hydraulic pilot control signal; and 
         FIG. 3  shows the arrangement, which can be used for both exemplary embodiments, of pilot control valves for actuating the main control valves and for adjusting the pressure limiting valve. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the two hydraulic control assemblies shown, an adjusting pump  10 , such as an axial piston pump on the principle of an oblique disk principle, is used as the pressure medium source; it aspirates pressure medium from a tank  11  and feeds it into an inflow line  12 , and whose oblique disk  13 , represented by a double arrow, can be pivoted in cooperation with two adjusting cylinders  14  and  15 . Both adjusting cylinders are differential cylinders, which have a respective piston  16  and  17  and each have one piston rod  18 , with which they engage the oblique disk  13 . Only the pressure chamber of the adjusting cylinders that is remote from the piston rod is acted upon by the pressure. The piston face of the piston  17  of the adjusting cylinder  15  is smaller than the piston face of the piston  16  of the other adjusting cylinder  14 . An extension of the piston rod  18  of the adjusting cylinder  14  causes a decrease, and an extension of the piston rod  18  of the adjusting cylinder  15  causes an increase, in the pivot angle of the oblique disk and hence in the stroke volume of the adjusting pump  10 . In addition to the pressure in the adjusting cylinder  15 , a compression spring  19  exerts a force on the oblique disk in the direction of increasing the pivot angle. 
     The pressure chamber of the adjusting cylinder  15  communicates constantly with the inflow line  12 . Thus the same pressure prevails in this pressure chamber as in the inflow line. The inflow and outflow of pressure medium to and from the pressure chamber of the adjusting cylinder  14  is controlled by a pump regulating unit  25 , which is mounted on the adjusting pump  10  and has an outer connection LS, to which an end portion  26   a  of a load reporting line  26  is connected, and which essentially includes two 3/2-way proportional multi-way valves, of which one is an LS pump regulating valve  27  and the other is a pressure regulating valve  28  that is set to a pressure that is above the load pressures that typically occur. The pressure regulating valve  28  has a first connection, which can be made to communicate with the tank  11  via a relief line  29 . A second connection of the pressure regulating valve  28  communicates with the inflow line  12 . The third connection, which can be made to communicate with the first or the second connection, communicates with the pressure chamber of the adjusting cylinder  14 . A first connection of the LS pump regulating valve communicates with the relief line  29 ; a second connection communicates with the inflow line  12 . The third connection of the valve  27  can be made to communicate with the first or second connection of this valve and communicates constantly with the first connection of the valve  28 . A slide, not shown in detail, of the valve  28  is urged by a compression spring  30  in the direction of increasing the pivot angle and by the inflow pressure in the direction of decreasing the pivot angle of the pump  10 . A slide, not shown in detail, of the LS pump regulating valve  27 , finally, is urged in the direction of increasing the pivot angle of the pump  10  by a compression spring  31  and by the pressure prevailing in the end portion  26   a  of the load reporting line  26 , and it is urged in the direction of decreasing the pivot angle by the inflow pressure. A force equilibrium prevails at the slide of the valve  27  when a difference that is equivalent to the force of the spring  31  exists between the inflow pressure and the pressure in the end portion  26   a  of the load reporting line  26 . Typically, the difference is between  10  bar and  20  bar. Equilibrium prevails at the slide of the valve  28  when the inflow pressure generates a force that is equivalent to the force of the spring  30 . Typically, in an equilibrium, the inflow pressure is in the range of  350  bar. 
     The exemplary embodiment of  FIG. 1  is given the characteristic as an LIFD control assembly by the type of control block  35  that is present, which contains LIFD multi-way valve sections. In  FIG. 1 , two sections are shown as an example, which are constructed fully identically. It is understood that further sections may also be present. 
     The control block  35  has an inflow connection P, a tank connection T, a load reporting connection LS, and various consumer connections A and B. An inflow conduit  36 , as part of the inflow line  12 , begins at the inflow connection P, and a tank conduit  37  of the control block begins at the tank connection T. In the control block, two LIFD multi-way valves  38  with a closed center are embodied, with which two hydraulic consumers, for instance two differential cylinders, can be controlled. The multi-way valves  38  are hydraulically actuatable. In them, a speed control part and a direction control part are embodied, separately from one another, at the same control slide. If a multi-way valve  38  has been moved out of its center position to one of its two lateral work positions, pressure medium arriving from the inflow conduit  36  flows from an inflow chamber  39  via a metering aperture  40  into a first intermediate chamber  41 , and from there via the opening cross section of a pressure balance  42  into a second intermediate chamber  43 , and then, via the directional part of the multi-way valve, into a consumer chamber  44  or  45 . From there, pressure medium reaches the consumer connection A or B. The regulating piston of the pressure balances  42  is urged in the opening direction by the pressure in the intermediate chamber  41 , that is, by the pressure downstream of the metering aperture  40 , and in the closing direction by the pressure in a load reporting conduit that extends as part of the load reporting line in the control block. The regulating piston of the pressure balances  42  is embodied such that, when the pressure balance is fully open, it establishes a fluidic communication between the intermediate chamber  41  and the load reporting conduit. This is the case when the respective hydraulic consumer is actuated by itself, or in the event of a simultaneous actuation of a plurality of hydraulic consumers, the particular consumer with which the pressure balance is associated has the highest load pressure. 
     The outer connections P, T and LS of the control block  35  are located in an inlet section  48 , through which the conduits  36 ,  37  and the load reporting line  26  extend to the multi-way valve sections. Inside the inlet section, the end portion  26   a  of the load reporting line  26  is hydraulically decoupled from the remaining portions of the load reporting line by a nozzle  54 . Upon a flow of pressure medium through the nozzle  54 , a pressure difference occurs at the nozzle, so that the pressure becomes less in the end portion  26   a  of the load reporting line  26  than the other parts of that line. Inside the inlet section, a pressure limiting valve  50  is moreover connected by its inlet connection  51  to the end portion  26   a  of the load reporting line  26  and by its outlet connection  52  to the tank conduit  37 . By means of the valve  50  and the nozzle  54 , the pressure that can be built up in the end portion  26   a  of the load reporting line is limitable. Upstream of the nozzle  54 , a small flow regulating valve  57 , located in the inlet section  48 , connects the load reporting line  26  and the tank conduit  37  to one another. 
     The exemplary embodiment of  FIG. 2  is given the characteristic as an LS control assembly by the type of control block  55  present, which is composed of LS multi-way valve disks, and by how the control block of  FIG. 1  has an inflow connection P, an outflow connection T, and a load reporting connection LS. In  FIG. 2 , two multi-way valve disks  56  are shown as examples. It is understood that further disks may also be present. 
     Each multi-way valve disk  56  serves as a housing for one multi-way valve  57 , which is hydraulically actuatable. Both multi-way valve disks  56  are completely identical to one another and contain the same components and conduits. Each multi-way valve  57  includes a control slide  58 , which is axially displaceable in a valve bore, not shown in detail, and which solely by the action of two centering springs  59  assumes a middle neutral position. In that position, a consumer conduit  60 , which leads to a consumer connection B, a consumer conduit  61 , which leads to a consumer connection A, and the inflow conduit  36  and the outflow conduit  37  are all disconnected from one another. 
     The control slide  58  of a multi-way valve is displaced out of its neutral position in one direction by subjection to the pressure of a control pressure chamber  62  and in the other direction by subjection to the pressure of a control pressure chamber  63 . Depending on the displacement position, either the consumer conduit  60  or the consumer conduit  61  communicates with the inflow conduit  36 , and the respective other consumer conduit communicates with the outflow conduit  37 . Upon a displacement out of the neutral position, the control slide opens a metering aperture between an inflow inlet at the multi-way valve and a consumer conduit, whose opening cross section determines the quantity of pressure medium that flows to the hydraulic consumer. 
     Specifically, the pressure difference across the metering aperture is kept constant, so that the quantity of pressure medium flowing via the metering aperture is dependent solely on the opening cross section. For that purpose, in the part of the inflow conduit  36  leading to the inflow inlet of the multi-way valve, there is a pressure balance  65 , which is urged in the closing direction by the pressure upstream of the metering aperture and in the opening direction by the pressure downstream of the metering aperture and by a compression spring  66 . The pressure drop across the metering aperture is equivalent to the force of the compression spring  66  and is set to a value of between 10 bar and 20 bar. 
     The pressure downstream of the metering aperture is equivalent to the load pressure of the respective hydraulic consumer. This pressure moreover prevails at an inlet to a shuttle valve  67  as well, and the other inlet of the shuttle valve  67  of one multi-way valve disk communicates with the outlet of the shuttle valve  67  of the other multi-way valve disk. The other inlet of the shuttle valve  67  of the last multi-way valve disk communicates with the outlet conduit  37  via an end plate  68 . From the outlet of the shuttle valve  67  of the first multi-way valve disk, a conduit leads to the load reporting connection LS of that disk. At this connection LS, the highest load pressure of the hydraulic consumers that are actuatable with the two multi-way valves prevails. The pressure in the inflow conduit  36  is above the highest load pressure by a predetermined pressure difference, for instance of 15 bar. The pressure equivalent to the force of the compression spring  66  of a pressure balance  65  can likewise be 15 bar, so that regardless of whether one hydraulic consumer is now generating the highest load pressure or not, the pressure drop across the metering aperture of the respective multi-way valve is the same. 
     In the exemplary embodiment of  FIG. 2 , just as in the exemplary embodiment of  FIG. 1 , the end portion  26   a  of the load reporting line  26  is hydraulically decoupled from the remaining parts of the load reporting line by a nozzle  54 . At the end portion  26   a , or in other words upstream of the nozzle  54 , a pressure limiting valve  50  is connected by its inlet connection  51  to the load reporting line  26  and by its outlet connection  52  to the tank conduit  37 . Upstream of the nozzle  54 , a small flow regulating valve  53  connects the load reporting conduit  46  and the tank conduit  37  to one another again. 
     In both exemplary embodiments, the pressure limiting valve  50  is hydraulically adjustable and for that purpose has an adjusting piston  73 , which borders on a pressure chamber  74  and is movable a distance predetermined by the spacing of two stops from one another and by its length. A regulating spring  75  of the pressure limiting valve  50  is minimally prestressed when the adjusting piston is in contact against one stop and is maximally prestressed when the adjusting piston is in contact against the other stop. The pressure at which the pressure limiting valve  50  responds can accordingly be set between a minimal and a maximal value. The way in which the pressure limiting valve  50  is adjustable will be described in further detail in conjunction with  FIG. 3 . 
     There, two hydraulic pilot control devices  78  can be seen, which both operate in a generally known manner on the basis of directly controlled pressure reduction valves  79 , of which one is shown symbolically in each pilot control device. Each pilot control device has a total of four pilot control valves  79  and correspondingly four control outlets  80 . In addition, each pilot control device has one tank connection T and one pressure connection P, and at the latter, a largely constant supply pressure prevails, at a level of between 30 and 35 bar. Via a pilot control level  81 , which can be pivoted in four directions out of a center position in which tank pressure prevails at all the control outlets  80 , the pilot control valves  79  can be adjusted. Depending on the lever deflection, they dictate a defined pilot control pressure at the corresponding control outlet  80 . From the control outlets  80 , pilot control lines  82  lead to the control pressure chambers  62  and  63  of the multi-way valves  38  ( FIG. 1) and 57  ( FIG. 2 ). After a small pivot angle of a lever  81 , the pilot control pressure jumps to an initial value and then rises continuously with the pivot angle. At a defined pivot angle, the pilot control pressure then jumps to the supply pressure. 
     One branch line  83  originates at each pilot control line  82 , and a nozzle  84  and in succession with it a check valve, blocking toward the pilot control line, are located in the branch line. Downstream of the check valves  85 , all the branch lines  83  discharge into one common control line  86 , which leads to the pressure chamber  74  of the pressure limiting valve  50 . Thus all the pilot control lines  82  communicate, parallel to one another, each via a respective nozzle  84  and a check valve  85 , with the pressure chamber  74  of the pressure limiting valve  50 . The control line  86  is moreover connected to a first connection of a 3/2-way valve  87 , from which a second connection communicates with the line leading to the supply pressure and a third connection communicates with the inlet to a second pressure limiting valve  88 . In a position of repose, which the multi-way valve  87  assumes under the influence of a compression spring  89 , the control line  86  communicates with the pressure limiting valve  88 . The second connection is blocked. With the aid of an electromagnet  90 , the multi-way valve  87  can be put in a switching position in which the control line  86  communicates with the second connection, and the third connection is blocked. The electromagnet  90  communicates via an electric line with an electric switch, accommodated in the one pilot control lever  81 , and this switch can be actuated via a push button  91 . Thus the electromagnet  90  can be triggered and switched off via the push button  91 . The pressure limiting valve  88  is manually adjustable. In the position of repose of the multi-way valve  87 , it serves together with the nozzles  84  to make it possible to limit the pressure in the control line  86  to a value that is lower than the maximum pilot control pressure that can be dictated by a pressure reduction valve  79 . Via a flow regulating valve  92 , the control line  86  can be relieved to the tank  11 . 
     For the discussion of the mode of operation of the control assembly, let the following assumptions be made: 
     The supply pressure for the pilot control devices is 30 bar. With the pressure reduction valves  79 , pilot control pressures of up to 24 bar can be dictated proportionally, and the adjustment of the respective main control valves  38  and  57  begins at 5 bar, and their full stroke is attained at 25 bar. Given a pressure of up to 5 bar prevailing in the control line, and because of an initial prestressing of the spring  75 , the pressure limiting valve  50  limits the pressure in the end portion  26   a  of the load reporting line to 50 bar. The set value of the pressure limiting valve  50  rises linearly with the pressure in the control line  86  and reaches a maximum value of 250 bar at a pressure of 25 bar in the control line. The pressure limiting valve  88  is set 20 bar. The pump Δp, that is, the difference between the pressure in the end portion  26   a  of the load reporting line and the pressure in the inflow line  12 , is 20 bar. 
     Thus in the position of repose, shown, of the multi-way valve  87 , the following mode of operation is obtained: 
     When a pilot control lever is deflected and a pressure reduction valve  79  is adjusted, a pilot control pressure builds up in a pilot control line  82 . Up to a pilot control pressure of 5 bar, nothing initially happens. After that, the motion of the control slide of the triggered main control valve begins. After a slight initial stroke, the corresponding metering aperture is opened wider and wider. The pressure in the control line  86  and thus the pressure prevailing in the pressure chamber  74  of the pressure limiting valve  50  is slightly less than the pilot control pressure, namely by the pressure difference that is generated by the quantity of pressure medium, flowing via the flow regulator  92 , at a nozzle  82 . The pressure difference may for example be 0.5 bar. Thus the pressure in the end portion  26   a  of the load reporting line, up to a pilot control pressure of 5.5 bar, is limited to 50 bar, and with increasing pilot control pressure, it rises. For instance, if the pilot control pressure is 15 bar, then the pressure in the control line  86  is 14.5 bar, and the pressure in the end portion  26   a  of the load reporting line is limited to 145 bar. 
     If the load pressure of the triggered hydraulic consumer is less than or equal to 145 bar, then the pressure limitation in the end portion  26   a  has no effect. The load pressure prevails there. The adjusting pump  10  pumps a sufficient quantity of pressure medium that the pressure in the inflow line  12  is 20 bar above the reported load pressure. The hydraulic consumer is moved at a speed that is determined by the opening cross section of the metering aperture. 
     If the load pressure is greater than 145 bar, then at the adjusting pump  10  a pressure of 145 bar is reported, since now the pressure limiting valve  50  does not permit the pressure in the end portion  26   a  to become any higher. The pressure in the inflow line is then 165 bar. If the load pressure is less than 165 bar, then with the pressure balance open, a quantity of pressure medium flows to the hydraulic consumer, largely unthrottled, via the metering aperture; this quantity is determined by the opening cross section of the metering aperture and by the difference between the inflow pressure, at the level of 165 bar, and the load pressure. Thus both in LIFD control as in  FIG. 1  and in LS control as in  FIG. 2 , a finely graduated actuation of the hydraulic consumer is possible without throttling losses at a pressure balance. 
     If the load pressure is higher than 165 bar, then a delivery of pressure medium to the hydraulic consumer is possible only after further deflection of the pilot control valve. However, if the load pressure is greater than 220 bar, then the pilot control lever must be deflected so far that the pressure in the control line  86  becomes 20 bar. The pressure limiting valve  88  then responds. Despite any further lever deflection, the pressure in the control line  86  remains at 20 bar, and thus the pressure in the end portion  26   a  remains at 200 bar and thus the inflow pressure remains at 220 bar. This pressure of 220 bar prevails in the consumer, so that a corresponding force can be exerted. 
     If a hydraulic consumer with a load pressure of up to 250 bar is to be controlled solely by the degree of opening of the metering aperture and by way of the full stroke of a main control valve, then the button  91  on a pilot control lever is pressed and hence the multi-way valve is reversed. The supply pressure of 30 bar now prevails in the control line  86 . The check valves  85  assure that the pilot control pressure predetermined by the pilot control device prevails in the respective pilot control line. The pressure limiting valve  50  is set to its highest value of 250 bar. The pressure in the end portion  26   a  of the load reporting line is now equal to the load pressure, up to a load pressure of 250 bar. The pressure in the inflow line  12  is 20 bar higher than the load pressure. Thus a load of up to 250 bar can be moved, at a speed determined solely by the opening cross section of the associated metering aperture. Up to a load pressure of 270 bar, because of the reduced pressure difference across the metering aperture, a slowed motion is possible. At a load pressure over 270 bar, the load can no longer be moved. 
     In the exemplary embodiment of  FIG. 3 , each pilot control line  82  is connected to the control line  86  via a nozzle  84  and a check valve  85 . Thus for each of the hydraulic consumers that are controllable via the two pilot control devices  78  and for each direction of motion, a pressure control is possible. Upon a simultaneous actuation of a plurality of hydraulic consumers, the check valves  85  assure that the highest pilot control pressure prevails in the control line  86 , and that the pilot control pressures in the pilot control lines  82  do not affect one another. 
     Naturally for individual consumers or for one motion direction, the possibility of pressure control can also be dispensed with. In that case, there is no branch line  83  between the corresponding pilot control line  82  and the control line  86 . In the final analysis, there may also be a branch line only between a single pilot control line  82  and the control line  86 .