Patent Publication Number: US-9404483-B2

Title: Hydraulic control arrangement

Description:
This application is a 35 U.S.C. §371 National Stage Application of PCT/EP2010/007883, filed on Dec. 22, 2010, which claims the benefit of priority to Serial No. DE 10 2010 009 705.5, filed on Mar. 1, 2010 in Germany, the disclosures of which are incorporated herein by reference in their entirety. 
     BACKGROUND 
     The disclosure relates to a hydraulic control arrangement for supplying pressure medium to two consumer groups. 
     To supply pressure medium to hydraulic consumers of mobile working appliances, such as, for example, excavators, tractors or dredger loaders, LS (load sensing) or throttle systems are often employed. In what are known as LS systems, the pump pressure is regulated as a function of the maximum load pressure of the consumers. So that the pressure medium volume flow to each consumer can be set independently of the load pressure, in what are known as LS control blocks each of the consumers is assigned an adjustable metering orifice and a pressure balance which keep the pressure medium volume flow constant independently of the load pressure. In what are known as LUDV systems, a subgroup of the LS systems, the pressure balance is acted upon in the closing direction by the maximum load pressure of all the consumers and in the opening direction by the pressure downstream of the metering orifice. In the event of undersaturation, in these LUDV systems the available volume flow is apportioned proportionally in the ratio of the opened metering orifice cross sections. 
     In LS systems, the pump delivery flow is therefore adapted to the respective requirements. In contrast to this, in a load pressure-dependent throttle system the pump always conveys the maximum possible or constant delivery rate. In this case, the pump may be designed as a fixed displacement or variable displacement pump. In these throttle controls, what are known as open-center control blocks are used, such as are described, for example, in data sheets RD 64 266 or RD 64 122 of Bosch Rexroth AG. These throttle control blocks have a multiplicity of directional valve elements which, in their basic position, route the pump volume flow via a bypass duct back to the tank with a low pressure loss. When a valve slide of a valve element is being adjusted, the connection to the assigned consumer is opened continuously while the pressure medium volume flow in the bypass duct is throttled, so that the pump pressure rises to the load pressure of the consumer. 
     When a plurality of consumers are activated via a throttle control block of this type, the volume flow to the individual consumers is apportioned as a function of the respective load pressure, the pressure medium preferably flowing to the consumer having the lowest load pressure. When a plurality of consumers are activated, in this case a pump pressure is set which corresponds approximately to the maximum load pressure of the consumers plus a predetermined pressure difference. The pump pressure therefore has to be throttled back correspondingly to actuate the consumer with the lowest load, and therefore considerable throttle losses arise. 
     As already mentioned, mobile working appliances, for example dredger loaders, are designed with control blocks of this type. A dredger loader has, for example, at its front a loading shovel and at its rear dredger equipment, so that the dredger loader combines the functions of a wheeled loader and those of a dredger. The front-side attachments and rear-side attachments are usually activated in each case via a control block, while for reasons of cost a throttle control block is often used for the dredger function and makes it possible at lower outlay to activate the attachment with relative sensitivity, but has the throttle losses mentioned. 
     A further problem is that the rear-side hydraulic consumers and the front-side hydraulic consumers are often operated at a different load pressure level, so that, in the case of a common pump, setting to the maximum load pressure is carried out and the load pressures to the other consumers have to be throttled back considerably. 
     DE 43 22 127 B4 discloses a hydraulic control engine with two control blocks, of which one is designed as an LS control block and a further control block is designed as a throttle control block with an open-center directional valve. Both the LS control block and the throttle control block are supplied with pressure medium from a common variable displacement pump which is activated as a function of the maximum load pressure of both control blocks, so that the pump pressure always lies above the maximum load pressure of the system by a predetermined pressure difference. In a basic position of the directional valve of the throttle control block, an LS control line branching off from a pump line carrying the pump pressure is relieved toward the tank via the open center of the directional valve, so that, by the directional valve being adjusted, the control oil volume flow is throttled and the control pressure communicated to the variable displacement pump rises correspondingly. The maximum control pressure at the throttle control block is limited via a pressure-limiting valve. 
     This solution basically has the same disadvantages as those explained above. When different consumer groups having a different load pressure level are activated, the variable displacement pump has to be regulated in terms of the maximum load pressure, and this high load pressure has to be throttled back at the control block having the lower load pressure level, the throttle losses being considerable. 
     By contrast, the object on which the disclosure is based is to provide a hydraulic control arrangement, by means of which two consumer groups with a different load level can be activated, along with reduced losses. 
     SUMMARY 
     This object is achieved by means of a hydraulic control arrangement having the features of the disclosure. 
     Advantageous developments of the disclosure are the subject matter of the subclaims. 
     According to the disclosure, the hydraulic control arrangement has a variable displacement pump, adjustable as a function of a load pressure or control pressure, for supplying pressure medium to two consumer groups to which a control block is assigned in each case, the control pressure picked off in one of the control blocks being limited by a pressure-limiting valve. According to the disclosure, a pressure-limiting valve, assigned to the other control block, is provided for limiting the control pressure level to a pressure different from the first pressure-limiting valve. 
     By the pressure-limiting valves being suitably set, the control pressure which prevails in the respective control block and may correspond to the maximum load pressure of the consumers activated by the control block can be limited to different levels, so that throttle losses in the control block having a lower control pressure level are limited. On account of this lower control pressure level, the losses are reduced considerably, as compared with the conventional solution, since only a limited control oil volume flow flows via the control block, this also being accompanied by an improvement in response behavior and controllability, particularly during mechanical actuation. By means of the control arrangement according to the disclosure, therefore, there is virtually a decoupling of the maximum control pressures in the two control blocks, this being without example in the prior art. 
     In a preferred exemplary embodiment of the disclosure, the control blocks are designed either identically or differently, basically throttle control blocks, LUDV control blocks or LS control blocks being capable of being used. 
     When a throttle control block is used, this is preferably designed in an open-center type of construction, and in the basic position the control line being connected to the tank in bypass. 
     In an exemplary embodiment of the disclosure, the control blocks are connected in series with their control lines, the load pressure in the control block adjacent to the variable displacement pump in the flow direction being limited to a higher value than the load pressure of the other control block. 
     In such a solution, the control lines are preferably connected to one another via a non-return valve which opens in the direction towards the downstream control block. 
     In an alternative solution, the control lines of the control blocks are connected in parallel. 
     In this case, it may be advantageous if the control line in a control block designed as a throttle control block is picked off via a flow-regulating valve from an inflow line carrying the pump pressure. 
     Advantageously, the control block having a lower control pressure level is designed as a throttle control block, and the control block having the higher control pressure level is designed as an LUDV or LS control block, there being provided downstream of said flow-regulating valve an LS switching valve which is acted upon in the closing direction by the control pressure in the other control block having the higher control pressure level and in the opening direction by the control pressure in the throttle block. By means of a design of this type, the control oil volume flow through the throttle block is switched off when the other, primary control block (LUDV, LS) operates at a higher control pressure level. 
     According to the disclosure, it is preferable if all the outflow lines issue in a tank line having a pressurizing valve, so that outflow to the tank takes place only at a pressure which lies above the tank pressure. 
     In a preferred exemplary embodiment of the disclosure, the control block having the higher control pressure level supplies a steering system via a priority valve. 
     In such a variant, it is preferable if the flow-regulating valve for limiting the control oil volume flow is arranged downstream of this priority valve. 
     The variable displacement pump is preferably activated as a function of the higher of the load/control pressures in the steering system, in the primary control block (higher control pressure level) or in the secondary control block (lower control pressure level). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred exemplary embodiments of the disclosure are explained in more detail below by means of diagrammatic drawings in which: 
         FIG. 1  shows a circuit diagram of a control arrangement of a dredger loader with two throttle control blocks; 
         FIG. 2  shows a circuit diagram of a variable displacement pump for a control arrangement according to  FIG. 1 ; 
         FIG. 3  shows an enlarged partial illustration of a directional valve section of a control block from  FIG. 1 ; 
         FIG. 4  shows a hydraulic control arrangement for supplying pressure medium to a dredger loader with an LUDV control block and a throttle control block, and 
         FIG. 5  shows a partial illustration of the LUDV control block from  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a circuit diagram of a hydraulic control arrangement of a dredger loader which has a dredger appliance on the rear-side and a loading shovel on the front-side. To activate these items of equipment, the control arrangement is designed with two control blocks  2 ,  4 , the latter being assigned to the rear-side dredger appliance and the control block  2  being assigned to the front-side loading shovel. A steering system  6  of the dredger loader is also supplied with pressure medium via this control block  2 . The control arrangement has, furthermore, a variable displacement pump  10 , illustrated merely diagrammatically in  FIG. 1 , which is set as a function of the maximum load pressure of the activated consumers such that the pump pressure lies above this maximum load pressure by the amount of a predetermined pressure difference. 
     The basic set-up of a variable displacement pump  10  of this type is known per se from DE 199 30 618 A1 and is explained by means of  FIG. 2 . The variable displacement pump  10  can be designed, for example, as an axial piston pump which sucks in pressure medium from a tank  11  and conveys it into a pump line  12 . A swash plate  13 , indicated in  FIG. 2  by a double arrow, can be pivoted by the interaction of two actuating cylinders  14 ,  15 . The two actuating cylinders are differential cylinders which have a piston  16 ,  17  and in each case a piston rod  18  by means of which they engage on the swash plate  13 . In each case only the piston rod-remote pressure space of the actuating cylinders  14 ,  15  is acted upon by the pressure. The piston surface of the piston  17  of the actuating cylinder  15  is smaller than the piston surface of the piston  16  of the other actuating cylinder. Extension of the piston rod  18  of the actuating cylinder  14  causes a reduction and extension of the piston rod  18  of the actuating cylinder  15  an increase in the pivot angle of the swash plate and consequently in the delivery volume of the variable displacement pump  10 . In addition to the pressure in the actuating cylinder  15 , a spring  19  exerts upon the swash plate  13  a force in the direction of an increase in the pivot angle. 
     The pressure space in the actuating cylinder  15  is constantly connected to the inflow line  12 . The inflow and outflow of pressure medium to and from the pressure space of the actuating cylinder  14  is controlled by a pump-regulating unit  25  which is built onto the variable displacement pump  10  and which has a connection LS to which a load communication line  26  is connected. The pump-regulating unit  25  has an LS pump-regulating valve  27  and a pressure-regulating valve  28  which is set at a pressure lying above the load pressures usually occurring. The pressure-regulating valve  28  has a first connection which can be connected to the tank  11  via a relief line  29 . A second connection of the pressure-regulating valve  28  lies on the pump line  12 . A third connection, which can be connected to the first or to the second connection, is connected to the pressure space of the actuating cylinder  14 . One connection of the LS pump-regulating valve  27  lies on the relief line  29  and a second connection lies on the inflow line  12 . A third connection of the pump-regulating valve  27  can be connected to its first or second connection and is connected permanently to the first connection of the pressure-regulating valve  28 . A slide of the pressure-regulating valve  28  is acted upon by a compression spring  30  with the effect of increasing the pivot angle and by the inflow pressure with the effect of reducing the pivot angle of the variable displacement pump  10 . A slide of the LS pump-regulating valve  27  is acted upon with the effect of increasing the pivot angle of the variable displacement pump  10  by a compression spring and by the pressure prevailing in the load communication line  26  and with the effect of reducing the pivot angle by the inflow pressure. A force equilibrium prevails at the slide of the pump-regulating valve  27  when a difference corresponding to the force of the spring  31  is present between the inflow pressure and the pressure in the load communication line  26 . This difference usually lies between 10 and 20 bar. Equilibrium prevails at the valve  28  when the inflow pressure generates a force which corresponds to the force of the spring  30 . Usually, in the case of an equilibrium, the inflow pressure lies in the region of 350 bar. 
     The two control blocks  2 ,  4  are designed in each case as throttle control blocks. A lifting cylinder  32  and a shovel cylinder  34  of the front-side loading shovel are actuated, in addition to the steering system  6 , via the control block  2 . The front-side equipment with two parallel-connected pivoting cylinders  36 , with a boom cylinder  38 , with a dipper arm cylinder  40  and with a dipper cylinder  42  is activated via the further control block  4 . 
     The control block  2  designed as a throttle control block is composed essentially of an input section  44  and of two essentially identically constructed direction valve sections  46 ,  48  and of an output section  50 . Provided on this control block  2  are a tank connection T, a pressure connection P connected to the pump line  12 , a load communication connection DLS carrying the load pressure of the steering system  6 , an LS connection connected to the load communication line  26 , a working connection D connected to the steering system  6 , two working connections LA 1 , LB 1  connected to the lifting cylinder  32 , two working connections LA 2 , LB 2  connected to the shovel cylinders  34  and a further LS connection. 
     The tank connection T is connected to the tank  11  via a tank duct  52 . Provided in the tank line  52  is a pressurizing valve  54  which opens the pressure medium connection to the tank  11  when the pressure prevailing in the tank line  52  is higher than the equivalent of a closing spring of the pressurizing valve  54 . 
     The control block  4  which is assigned to the rear-side dredger appliance has four directional valve sections  56 ,  58 ,  60 ,  62 , the set-up of which corresponds to the directional valve sections  46 ,  48  of the control block  2 . Furthermore, the control block  4  is designed with an input section  64  and an output section  66 . The input section  64  has formed on it a pressure connection P connected to the pump line  12 , a further LS connection connected to the LS connection of the control block  2  and a tank connection T connected to the tank duct  52 . 
     The two control blocks  2 ,  4  are thus connected in parallel in terms of the supply of pressure medium via the pump line  12 , whereas they are connected in series via the two connections LS-LS in terms of a control line carrying the load pressure or a corresponding pressure. This is made even clearer by means of the following depictions. 
       FIG. 3  shows an enlarged illustration of the input section  44  and of the directional valve section  46 . As already mentioned, the pump line  12  issues in the pressure connection P of the input section  54  and is connected at the input of a priority valve  68 . The latter is prestressed via a spring and via the load pressure prevailing at the steering system  6  and is picked off by the connection DLS into a basic position in which the pump line  12  is connected via a steering duct  70  to the working connection D to which the steering system  6  is connected. The pressure in the steering duct  70  acts in the opposite direction on a slide of the priority valve  68 , so that, with rising pressure in this steering duct  70 , the priority valve is displaced into a position in which a pressure medium connection to an inflow duct  72  is opened. In the event that the steering system  6  requires no pressure medium, the priority valve  68  is adjusted by the pressure in the steering duct  70  such that the pressure medium connection to the steering duct  70  is closed completely, so that the pressure medium flows via the priority valve  68  into the inflow duct  72 . 
     A control line  74  branches off from the inflow duct  72  and has provided in it a flow-regulating valve  76 , via which a control oil volume flow is branched off from the inflow duct  72 . The pressure downstream of the flow-regulating valve  76  is limited to a predetermined control pressure level via a pressure-limiting valve  78 . The output of the pressure-limiting valve  78  issues in an outflow duct  72  which is connected to the tank connection T of the input section  44  and is therefore connected to the tank line  52 . 
     The pressure downstream of the flow-regulating valve  76  is communicated to the input of a shuttle valve  80 . The other input connection of the latter is acted upon by the pressure at the connection DLS, so that the higher of these pressures is communicated via the LS connection in the LS line  26  and the variable displacement pump  10  is adjusted as a function of this pressure. 
     The directional valve section  46  has an open-center directional valve  82  which, as illustrated, can be adjusted by hand or else hydraulically or electrohydraulically. The basic set-up of the directional valve  82  is described in the initially mentioned data sheets RD 64 266 or RD 64 122, and therefore reference is made for details toward the relevant statements and only the structural elements essential for understanding the disclosure are explained here. 
     The OC directional valve  82  has a pressure connection P connected to the inflow duct  72 , a tank connection T connected to the outflow duct  84 , a control connection D connected to the control line  74 , two output connections A, B which are connected to the working connections LA 1 , LB 1 , and also a control output D′ which issues in a further portion of the control line  74  which passes through both control blocks  2 ,  4  according to  FIG. 1 . For the sake of clarity, separate reference symbols have not been given to the individual portions of the control line  74  upstream and downstream of the individual valves. 
     In the spring-prestressed basic position illustrated, the connections P, T, A, B of the OC directional valve  82  are shut off, however, the control oil connections D, D′ are connected to one another, so that the control oil can flow essentially pressurelessly through the directional valve  82 . The two working connections A, B of the OC directional valve  82  are connected to the working connections LA 1 , LB 1  via working ducts  86 ,  88 . These working ducts  86 ,  88  act as a forward flow line or return flow line, depending on the adjustment of the OC directional valve  82 . 
     Provided in each case in each of the working ducts  86 ,  88  is a combined aftersuction/pressure limiting valve  90 ,  92 , via which, on the one hand, the pressure in the working lines  88 ,  86  is limited and, on the other hand, in the event of a pulling load, pressure medium can be aftersucked from the tank  11  into the enlarging pressure space. 
     When the directional the valve  82  is adjusted in one of the two directions illustrated in  FIG. 3 , this control oil connection is closed and the control oil volume flow is correspondingly throttled, the pressure medium connection from the pressure connection P to one of the working connections A, B is opened and the outflow from the reducing pressure space is correspondingly opened to the tank connection T of the OC directional valve  82  via the other of the two working connections A, B. An OC directional valve  82  of this type allows highly accurate activation of the connected hydraulic consumers, the set-up being very simple, although the disadvantage is that the control oil volume flow has to be throttled so that the respective hydraulic consumer can be activated. 
     The other directional valve sections  56 ,  58 ,  60 ,  62  of the control blocks  2 ,  4  have the same set-up as the directional valve section  46  described by means of  FIG. 3 , and therefore further explanations are unnecessary. 
     According to  FIG. 1 , the control line  74  is connected to the LS connection of the input section  64  of the control block  4 , so that this control line  74  is also continued in the control block  4 . In the output section  66  of the control block  4 , a deflection  94  is provided, via which the control line  74  is connected to an outflow line  96  which is common to all the sections  64 ,  56 ,  58 ,  60 ,  62  and which is connected to the tank line  52  via the tank connection T of the input section  64 . The pump line  12  is connected to the pressure connection P of the input section  64  and issues in an inflow line  98  common to all the sections of the control block  4 . Arranged within the input section  64 , in the control line  74 , is a non-return valve  100  which permits a control oil flow to the directional valve sections  56 ,  58 ,  60 ,  62  and shuts off said flow in the opposite direction. The non-return valve  100  permits a control oil flow to the control block  4  when the control pressure/load pressure in the region of the control block  2  is higher than in the control block  4 . 
     The pressure downstream of the non-return valve  100  is limited via a further pressure-limiting valve  102  to a pressure level which lies below the pressure level limited via the pressure-limiting valve  78 . In the illustrated basic position of the OC directional valves  82  of the directional valve sections  46 ,  48 ,  56 ,  58 ,  60 ,  62 , the control oil flows through all the OC directional valves  82  virtually pressurelessly to the tank  11  in bypass. 
     By the pressure level being limited via the pressure-limiting valve  102  in the input section  64 , the control oil volume flow is limited via the bypass edges of the directional valves  82  of the control block  4  and therefore the throttle losses are reduced. That is to say, via the two pressure-limiting valves  78 ,  102 , the load pressure level of each control block  2 ,  4  is limited to a level which is optimal in terms of minimizing the control oil throttle losses, the pressure level in the control block  4  lying below that of the control block  2 . 
     The control/load pressure which is set in the control line  74 , depending on the activation of the consumers  32 ,  34 ,  36 ,  38 ,  40 ,  42 , is then compared with the load pressure of the steering system  6  and in each case the higher load pressure in the load communication line  26  is communicated, so that the pump pressure is then regulated above this maximum load pressure by the amount of the predetermined pressure difference. 
     The OC directional valves  82  used in the exemplary embodiment according to  FIG. 1  make it possible at minimal outlay to activate the individual hydraulic consumers with very high sensitivity, although, as before, there are throttle losses. In order to minimize these even further, instead of one of or the throttle control blocks  2 ,  4 , another control block, for example an LUDV control block, may also be used. An exemplary embodiment of this type is explained by means of  FIG. 4 . 
     In this exemplary embodiment, activation of the hydraulic consumers of the dredger appliance likewise takes place again via a throttle control block  4  which differs merely in the set-up of the input section  64  from the exemplary embodiment according to  FIG. 1 , and therefore only the differences are explained below. The control block assigned to the loading shovel is designed as an LUDV control block  2 ′ with an input section  104  and two identically constructed LUDV sections  106 ,  108  and also a closing plate  110 . The variable displacement pump  10  has the same set-up as in the exemplary embodiment described above. 
     The set-up of the LUDV control block  2 ′ is explained by means of  FIG. 5 . The steering system  6  is supplied in the same way as in the exemplary embodiment described above via a priority valve  68  which is acted upon with the effect of supplying pressure medium to the steering system  6  by the steering load pressure prevailing at the connection DLS and with the effect of supplying pressure medium to the LUDV sections  106 ,  108  by the pressure downstream of the priority valve  68 , that is to say by the pressure in the steering duct  70 . As in the exemplary embodiment described above, a second output connection of the priority valve  68  has connected to it the inflow duct  72 , via which the pressure medium flows to the LUDV sections  106 ,  108 . 
     The LUDV section  106  has a set-up, as described in the initially mentioned DE 199 30 618 A1 or in data sheet RD 64 122 of Bosch Rexroth AG. An LUDV section  106  of this type has a continuously adjustable LUDV directional valve  112  which has a velocity part, formed by a metering orifice  114 , and a direction part  116 , via which the pressure medium flow direction to and from the assigned consumer, here the lifting cylinder  32 , is determined. 
     A pressure connection P of the directional valve  112  is connected to the inflow duct  72 . An outflow connection T is in pressure medium connection with the outflow duct  84  connected to the tank connection T, two output connections A, B are connected to the two working connections LA 1 , LB 1  via the working ducts  86 ,  88 , a pressure balance connection C is connected to the input of an LUDV pressure balance  118  which is acted upon in the closing direction by the pressure in a load communication line  120  and in the direction of an increase in a throttle cross section by the pressure at the pressure balance connection C, that is to say by the pressure downstream of the metering orifice  114 . With the LUDV pressure balance opened completely, the pressure downstream of the metering orifice  114  in the load communication line  120  is communicated. 
     Via this LUDV pressure balance  118 , the pressure drop across the metering orifice  114  is kept constant independently of the load pressure and the maximum load pressure prevailing at the input of the LUDV pressure balance  118  is throttled back to the individual load pressure. The pressure medium throttled back to the individual load pressure then flows from the output of the pressure balance  118  via a connection P′ of the LUDV directional valve  112  and the direction part  116  and the corresponding working duct  86 ,  88  into the enlarging pressure space of the lifting cylinder  32  and flows out from the reducing pressure space via the corresponding working line  88 ,  86 , the direction part  116  and the outflow duct  84  to the tank  11 . As in the exemplary embodiment described above, in each case a combined after suction/pressure-limiting valve  90 ,  92  is arranged in the working ducts  86 ,  88 . 
     The load communication line  120  is connected to the LS connection of the input section  104  and is connected via a further non-return valve  122  to the connection DLS carrying the steering load pressure. In the event that the load pressure of the steering system  6  is higher than the load pressure in the load communication line  120 , the non-return valve  122  opens, so that the steering load pressure is then communicated in the LS line  26 . With the non-return valve  122  closed, the pressure in the load communication line  120  also prevails on the LS line  26 . The pressure in the load communication line  120  is again limited via a pressure-limiting valve  78  to a pressure level which lies above the pressure level of the throttle control block  4 . In the exemplary embodiment according to  FIG. 4 , in parallel with the pressure-limiting valve  78 , a small flow-regulating valve  124  is provided, via which a continuous control oil volume flow to the outflow duct  84  is made possible. 
     As in the exemplary embodiment described above, the supply of pressure medium to the throttle control block  4  takes place via the pump line  12  which is connected to the connection P of the input section  64 . The load pressure in the LS line  26  also prevails at the connection LS of the input section  64 . The outflow connection T of the input section  64  is in pressure medium connection with the tank duct  52 . 
     Within the throttle control block  4 , an inflow line  98  for supplying pressure medium to the directional valve sections  56 ,  58 ,  60 ,  62  is connected to the pressure connection P. The outflow connection T lies on the outflow line  96  which is connected via the deflection  94  of the output section  64  to the control line  74  passing through the control block  4 . Said control line can be connected to the inflow line  98  via a switching valve  124  and a flow-regulating valve  126 . 
     As in the exemplary embodiment described above, the control oil volume flow in the control line  74  can be set via the flow-regulating valve  126 . The switching valve  124  is acted upon the closing position by the load pressure in the LS line  26  and in the opening direction by the pressure in the control line  74  and the force of a comparatively weak spring. 
     Supply of control oil to the control line  74  accordingly takes place only when the load pressure is higher by the amount of the pressure equivalent of this spring than the control pressure in the control line  74  which is set when the cross sections of the respective OC directional valves  82  are throttled. 
     According to  FIG. 4 , the control line  74  can be connected to the LS line  26  via a non-return valve  128 , this non-return valve  128  opening in the direction of the LS line  26  when the pressure in the control line  74  is higher than the load pressure in the LS line  26 . That is to say, in this case, the higher control pressure in the throttle control block  4  is communicated to the pump-regulating unit  25  in the LS line  26  and the pump is adjusted according to this higher control pressure. 
     As in the exemplary embodiment described above, the pressure in the control line  74  is limited by the pressure-limiting valve  102  to a lower pressure level than in the LUDV control block  2 ′. The exemplary embodiment according to  FIG. 4  otherwise corresponds to the exemplary embodiment according to  FIG. 1 , and therefore further explanations are unnecessary. 
     A hydraulic control arrangement for supplying pressure medium to two consumer groups via a common variable displacement pump is disclosed. According to the disclosure, the pressure level of a control block assigned to one consumer group is set at a pressure level other than that of a further control block assigned to the other consumer group.