EP2013487A1

EP2013487A1 - Hydraulic control arrangement

Info

Publication number: EP2013487A1
Application number: EP07724220A
Authority: EP
Inventors: Wolfgang Kauss
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2006-04-21
Filing date: 2007-04-13
Publication date: 2009-01-14
Anticipated expiration: 2027-04-13
Also published as: JP2009534596A; DE102006018706A1; US8281583B2; WO2007121873A1; EP2013487B1; US20090094972A1; JP5174804B2

Abstract

The invention relates to a hydraulic control arrangement that is used particularly for controlling hydraulic consumers of a mobile machine tool. Said hydraulic control arrangement comprises a load signaling line to which the maximum load pressure of several hydraulic consumers that are simultaneously triggered via one respective main control valve can be applied, and a final section of which can be connected to a pump regulator. The hydraulic control arrangement further comprises a pressure relief valve which allows the control pressure to be limited in the final section of the load signaling line. In order to be able to easily and inexpensively control the pressure also for several hydraulic consumers, the pressure relief valve can be displaced in accordance with the level of a pilot signal that is used for triggering a main control valve.

Description

description

Hydraulic control arrangement

The invention relates to a hydraulic control arrangement, which is used in particular for controlling hydraulic consumers on mobile machines and having the features of the preamble of claim 1.

Such a hydraulic control arrangement is known, for example, from EP 0 566 449 A1. This is a hydraulic control arrangement according to the load-sensing principle, in which a variable displacement pump is set in each case depending on the highest load pressure of the actuated hydraulic consumers so that the pump pressure is above the highest load pressure by a certain pressure difference. The hydraulic consumers, the pressure medium flows through adjustable metering orifices, which are arranged between an outgoing from the variable flow pump and the hydraulic consumers and are usually integrated in a also the direction control of a hydraulic consumer serving main control valve. By the metering orifices downstream pressure compensators is achieved that at a sufficiently supplied by the variable pressure fluid independent of the load pressures of the hydraulic consumers a certain pressure difference across the metering orifices, so that the inflowing hydraulic pressure consumer fluid quantity depends only on the opening cross section of the respective metering orifice. If a metering orifice is opened further, more pressure medium must flow over it in order to generate the specific pressure difference. The variable displacement pump is adjusted in such a way that it supplies the required amount of pressure medium. Therefore, one speaks of a demand flow control. For this purpose, the variable displacement pump has a pump regulator which can be acted upon by a load-sensing line with the highest load pressure of the simultaneously actuated hydraulic consumers. To limit the pump pressure, a fixed pressure setting is applied to the end section of the load signaling line connected to the pump regulator. connected limit valve, which limits the reported pressure to the pump controller and thus also the pump pressure in conjunction with a decoupling the end portion of the remaining load sensing line throttle.

The pressure compensators connected downstream of the metering orifices are acted upon in the opening direction by the pressure downstream of the respective metering orifice and in the closing direction by a control pressure prevailing in a rearward control chamber, which usually corresponds to the highest load pressure of all the hydraulic consumers supplied by the same hydraulic pump. If, during a simultaneous actuation of several hydraulic consumers, the metering orifices are opened so far that the pressure medium supplied by the stoppered hydraulic pump is less than the total required pressure medium, the quantities of pressure medium flowing to the individual hydraulic consumers will be independent of the respective load pressure the hydraulic consumer see reduced proportionally. This is why one speaks of one

Control with load-independent flow distribution (LUDV control). Because the highest load pressure is sensed in a LUDV control and the intake pump generates a supply pressure that exceeds the highest load pressure by a certain pressure difference over the highest load pressure, a LUDV control is a special case of a load-sensing or load - sensing control (LS control).

For several hydraulic consumers to which pressure medium flows in each case via a metering orifice with upstream pressure compensator, which is acted upon in the closing direction only by the pressure before the metering orifice and in the opening direction via an individual Lastmeldeleitung only from the load pressure of the respective hydraulic consumer and a compression spring, you get no load independent flow distribution. One has a mere LS control and LS consumer. Such a control is known for example from DE 37 09 504 C2. In the case of a simultaneous actuation of a plurality of hydraulic consumers and a quantity of pressure medium insufficiently supplied by the variable-displacement pump, only the pressure medium quantity flowing to the last-highest hydraulic consumer is initially detected here. duced. At its stoppage then reduces the consumer with the second highest load pressure inflowing pressure medium quantity, etc.

In the hydraulic control arrangement according to DE 37 09 504 C2 leading to the pressure compensator end portion is connected via a throttle with the other individual load reporting line of a hydraulic load and connected to a pressure relief valve. This is adjustable in dependence on the amount of a control of the hydraulic control consumer associated main control valve serving pilot signal. The pressure compensator now acts as a pilot-operated pressure reducing valve whose setting can be changed by the pilot control signal and which closes when a certain pressure is reached at its outlet. The pressure at which the pressure compensator closes and which is present at a hydraulic consumer, whose pressure compensator is correspondingly controlled on the closing side, can thus be limited individually for the consumer and changed via the precontrol signal.

In DE 198 31 595 A1 a LUDV control is shown in which also individually for a hydraulic consumer, the pressure is limited. It is necessary that the rear control chamber of a LUDV pressure compensator is structurally separated from the load-sensing line. And it is a directional valve necessary, depending on the switching position of the rear control chamber is connected to the load-sensing line or is acted upon by pump pressure. The directional valve is switched depending on the load pressure. A change in the switching pressure during operation is not provided.

The invention has for its object to develop a hydraulic control arrangement with the features of the preamble of claim 1 so that with pilot signals for the main control valves in a simple and cost-effective manner, a pressure control for several hydraulic consumers is possible. The desired aim is achieved in a hydraulic control arrangement with the features of the preamble of claim 1 according to the invention in that according to the characterizing part of patent claim 1, the pressure limiting valve in dependence on the height of a control of a main control valve serving pilot signal is adjustable. According to the invention, therefore, the pressure limiting valve is adjustable, with which the pressure reported to the pump regulator can be limited. The invention is based on the idea that there are mobile machines on which in a pressure control of a hydraulic consumer is rarely still another hydraulic consumer to operate. In particular, according to the invention, a pressure control of a hydraulic consumer is also possible in a LUDV control arrangement with very simple means and without changes to the individual pressure compensators associated with the metering orifices.

Advantageous embodiments of a hydraulic control arrangement according to the invention can be found in the dependent claims.

If the pressure relief valve is adjustable in dependence on the height of a plurality of pilot signals, it is advantageously adjusted when queuing several pilot signals in response to the largest pilot signal. It is assumed that the higher the pre-control signal, the higher the pressure set at the pressure relief valve.

In an embodiment according to claim 3, according to which the pressure relief valve is adjustable in response to a pilot control signal only up to a set value, which is below the maximum set value, it is possible for the machine operator, the adjustable with a pilot signal maximum consumer pressure depending on the type the machine or the type of work to be done individually. Advantageously, can be turned off by a design according to claim 4, the pressure control. It then has a demand flow control with a limitation of the load pressure to a high value.

According to claim 5, the pressure relief valve is hydraulically adjustable and has an adjacent to a pressure chamber connected to the control chamber actuating piston. In principle, the pressure relief valve may also be one which is electrically or electro-hydraulically adjustable. In particular, if the main control valve is electrically actuated, such an adjustability of the pressure relief valve may be favorable. In a hydraulic actuation of the main control valve, however, the use of a purely hydraulically adjustable pressure limiting valve appears more advantageous.

If the main control valve can be actuated hydraulically, then a pilot pressure is usually generated with the aid of an adjustable pressure reducing valve, which has a pressure connection, at which a substantially constant supply pressure is preferably present at a height of 30 to 35 bar, a tank connection and a control connection the pilot pressure is adjusted. The pressure limiting valve can now be easily adjusted to its maximum setting value if, according to claim 6, an arbitrarily actuable directional control valve is provided, depending on the switching position of the pressure chamber of the pressure relief valve with the pilot pressure or the supply pressure can be acted upon.

It is possible, with the directional control valve alternately either a line in which the supply pressure is present, or a line in which the pilot pressure is present to connect with the pressure chamber of the pressure relief valve. However, the directional control valve can be of simpler construction if, according to claim 7, a check valve opening to the pressure chamber is located between the pilot control line and the pressure chamber on the pressure limiting valve. This prevents the high supply pressure from entering the pilot control line and influencing the control of the main control valve. With check valves, which are arranged according to claim 8, can be easily select the highest hydraulic pilot signal and einsteuem in the pressure chamber of the pressure relief valve.

In order to limit a pressure control via a pilot control signal to a below the maximum set value of the pressure relief valve pressure value, according to claim a second pressure relief valve is present. Of course, this should not be effective in any case when an adjustment of the first pressure relief valve to the maximum setting value is desired by acting on the pressure chamber with the supply pressure. For this operation, according to claim 1 1 advantageously the directional control valve is used, via which the supply pressure is switched through into the pressure chamber.

The pressure relief of the pressure chamber on the pressure relief valve is conveniently done via a flow control valve, which can be realized by a simple nozzle, but preferably a flow control valve is.

Several embodiments of a hydraulic control arrangement according to the invention are shown in the drawing. On the basis of these embodiments, the invention will now be explained in more detail.

1 shows a first, working according to the LUDV principle embodiment with the connected to an end portion of the load-sensing line, in response to a hydraulic pilot signal hydraulically adjustable pressure relief valve,

FIG. 2 shows a second embodiment, operating according to the LS principle, with the connection element connected to an end section of the load-signaling line, speed of a hydraulic pilot signal hydraulically adjustable pressure relief valve and

Figure 3 shows the usable for both embodiments arrangement of pilot control valves for actuating the main control valves and for adjusting the pressure relief valve.

In the two hydraulic control arrangements shown, a variable displacement pump 10, for example an axial piston pump according to the swashplate principle, is used as the pressure medium source, which draws in pressure medium from a tank 11 and discharges it into a supply line 12 and its swash plate 13 indicated by a double arrow in the interaction of two actuating cylinders 14 and 15 can be pivoted. Both actuating cylinders are differential cylinders, which have a piston 16 or 17 and in each case a piston rod 18, with which they engage the swash plate 13. By pressure is applied only the Kolbenstangenabseitige pressure chamber of the actuating cylinder. The piston surface of the piston 17 of the adjusting cylinder 15 is smaller than the piston surface of the piston 16 of the other actuating cylinder 14. An 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 swivel angle of the swash plate and thus the Hubvolumens the variable displacement 10. In addition to the pressure in the adjusting cylinder 15 exerts a compression spring 19 on the swash plate a force in the direction of increasing the pivot angle.

The pressure chamber of the actuating cylinder 15 is permanently connected to the supply line 12. In this pressure chamber so there is always the same pressure as in the supply line. The inflow and outflow of pressure fluid to and from the pressure chamber of the actuating cylinder 14 is controlled by a pump control unit 25 which is constructed on the variable displacement pump 10 having an outer terminal LS, to which an end portion 26a of a load reporting line 26 is connected, and the two substantially 3/2-way proportional valves comprises, one of which is a LS-pump control valve 27 and the other a pressure control valve 28, the is set to a pressure above the usually occurring load pressures. The pressure control valve 28 has a first port which is connectable via a discharge line 29 to the tank 11. A second connection of the pressure regulating valve 28 is located on the supply line 12. The third connection, which can be connected to the first or the second connection, is connected to the pressure chamber of the adjusting cylinder 14. A first connection of the LS pump control valve 27 is located on the discharge line 29, a second connection on the supply line 12. The third connection of the valve 27 can be connected to its first or second connection and permanently connected to the first connection of the valve 28. A non-illustrated slide of the valve 28 is acted upon by a compression spring 30 in the sense of increasing the pivot angle and the inlet pressure in the sense of a reduction of the pivot angle of the pump 10. Finally, a slide (not shown in detail) of the LS pump control valve 27 is acted upon by a pressure spring 31 and by the pressure prevailing in the end section 26a of the load signaling line 26 and in the sense of reducing the pivoting angle by the inlet pressure. At the slide of the valve 27, there is a balance of forces when there is a difference between the inlet pressure and the pressure in the end portion 26a of the load-sensing line 26, which corresponds to the force of the spring 31. Usually the difference is between 10 bar and 20 bar. Balance prevails on the spool of the valve 28 when the supply pressure produces a force corresponding to the force of the spring 30. Usually, the equilibrium of the inlet pressure in the range of 350 bar.

The characteristic as LUDV control arrangement receives the embodiment of Figure 1 by the type of existing control block 35 containing LUDV- Wegeventilsektionen. In Figure 1, two sections are shown by way of example, which are constructed completely the same. Of course, there may be more sections.

The control block 35 has an inlet connection P, a tank connection T, a load-signaling connection LS and various consumer connections A and B. At the inlet port P begins as part of the inlet line 12, an inlet channel 36 and the tank port T a tank channel 37 of the control block. In the control block two LUDV directional control valves 38 are formed with a closed center, with which two hydraulic consumers, for example two differential cylinders are controllable. The directional valves 38 are hydraulically actuated. In them, a speed control part and a direction control part are formed separately from each other on the same spool. When a directional control valve 38 has been brought from its center position into one of its two lateral working positions, pressure medium coming from inlet channel 36 flows from an inlet chamber 39 via a metering orifice 40 into a first intermediate chamber 41, from there via the opening cross section of a pressure compensator 42 into a second From there, pressure fluid to the consumer port A or B. The control piston of the pressure compensators 42 is in the opening direction of the pressure in the intermediate chamber 41, ie from the pressure to the metering orifice 40 and in Closing direction acted upon by the pressure in a load-signaling channel running as part of the load-signaling line in the control block. The control piston of the pressure compensators 42 is designed so that, when the pressure compensator is completely open, it establishes a fluidic connection between the intermediate chamber 41 and the load-signaling channel. This is the case when the respective hydraulic consumer is operated alone or when a simultaneous actuation of several hydraulic consumers that consumer, which is associated with the pressure balance, has the highest load pressure.

The outer terminals P, T and LS of the control block 35 are located at an input section 48, through which pass the channels 36, 37 and the Lastmeldeleitung 26 to the directional control valve sections. Within the input section, the end portion 26a of the load-sensing line 26 is hydraulically decoupled from its remaining parts by a nozzle 54. With a pressure medium flow through the nozzle 54, a pressure difference occurs at this, so that the pressure in the end portion 26a of the load reporting line 26 is lower than in the other parts thereof. Within the input section is also a pressure relief valve 50 with its input terminal 51 to the end portion 26 a of the load reporting line 26 and its output port 52 connected to the tank channel 37. By the valve 50 and the nozzle 54 of the build-up in the end portion 26a of the load reporting line pressure can be limited. Upstream of the nozzle 54, a small flow control valve 53 located in the inlet section 48 connects the load detection channel 26 and the tank channel 37.

The characteristic as LS control arrangement receives the embodiment of Figure 2 by the type of existing control block 55, which is composed of LS directional control valves and how the control block of Figure 1 a supply port P, a drain port T and a load reporting connection LS having. In FIG. 2, two directional valve disks 56 are shown by way of example. Of course, more discs may be present.

Each directional valve disc 56 serves as a housing for a directional control valve 57, which is hydraulically actuated. Both directional valve discs 56 are completely identical to each other and contain the same components and channels. To each directional control valve 57 includes a spool 58 which is axially displaceable in a valve bore unspecified and occupies a middle neutral position under the mere effect of two centering springs 59. In this position, a consumer channel 60, which leads to a consumer connection B, a consumer channel 61, which leads to a consumer connection A, the inlet channel 36 and the outlet channel 37 are separated from each other.

By pressurizing a control pressure chamber 62, the spool 58 of a directional control valve is displaced out of the neutral position in one direction and by pressurizing a control pressure space 63 in the other direction. Depending on the direction of displacement, either the consumer channel 60 or the consumer channel 61 is connected to the inlet channel 36 and the respective other consumer channel to the outlet channel 37. In a shift from the neutral position of the spool opens a metering orifice between an inlet inlet to the directional control valve and a consumer channel whose opening cross-section determines the amount of pressure medium flowing to the hydraulic consumer. Namely, the pressure difference across the metering orifice is kept constant, so that the amount of pressure medium flowing through the metering orifice depends solely on the opening cross section. For this purpose, a pressure compensator 65 is arranged in the leading to the inlet inlet of the directional control valve part part 36, which is acted upon in the closing direction by the pressure before the metering orifice and in the opening direction of the pressure to the metering orifice and by a compression spring 66. The pressure drop across the metering orifice is equivalent to the force of the compression spring 66 and set to a value between 10 bar and 20 bar.

The pressure after the metering orifice corresponds to the load pressure of the respective hydraulic consumer. This pressure is also applied to an input of a shuttle valve 67, wherein the other input of the shuttle valve 67 of a directional control valve disc is connected to the output of the shuttle valve 67 of the other directional control valve disc. The other input of the shuttle valve 67 of the latter directional valve disc is connected via an end plate 68 to the drain channel 37. From the output of the shuttle valve 67 of the former directional control valve disc, a channel leads to the load reporting LS of this disc. At this connection LS, the highest load pressure of the hydraulic consumers operable with the two directional valves is applied. The pressure in the inlet channel 36 is a predetermined pressure difference of z. B. 15 bar above the highest load pressure. The pressure equivalent to the force of the compression spring 66 of a pressure compensator 65 may also be 15 bar, so that regardless of whether a hydraulic load generates the highest load pressure or not, the pressure drop across the metering orifice of the respective directional control valve is the same.

In the embodiment of Figure 2, as in the embodiment of Figure 1, the end portion 26a of the load-sensing line 26 is hydraulically decoupled from the other parts by a nozzle 54. At the end portion 26a, ie downstream of the nozzle 54, a pressure limiting valve 50 is connected with its input terminal 51 to the load-signaling line 26 and with its output terminal 52 to the tank channel 37. Upstream of the nozzle 54 In turn, a small flow control valve 53 connects the load reporting channel 46 and the tank channel 37.

The pressure relief valve 50 according to both embodiments is hydraulically adjustable and has an actuating piston 73, which adjoins a pressure chamber 74 and a by the distance between two stops from each other and its length predetermined distance is movable. A control spring 75 of the pressure relief valve 50 is minimally biased when the actuator piston is applied to a stop, and maximum biased when the actuator piston rests against the other stop. The pressure at which the pressure limiting valve 50 responds can therefore be set between a minimum and a maximum value. The way in which the pressure limiting valve 50 is adjustable can be seen in more detail from FIG.

There are two hydraulic pilot control devices 78 can be seen, both of which work in a well-known manner on the basis of directly controlled pressure reducing valves 79, one of which is shown symbolically in each pilot unit. Each pilot unit has a total of four pilot valves 79 and correspondingly four control outputs 80. In addition, each pilot unit has a tank port T and a pressure port P, at which a substantially constant supply pressure is present at a level between 30 and 35 bar. Via a pilot control lever 81, which can be deflected from a central position in which there is tank pressure at all control outputs 80, the pilot valves 79 can be adjusted. Depending on the lever deflection, they regulate a specific pilot pressure at the corresponding control output 80. From the control outputs 80 lead pilot lines 82 to the control pressure chambers 62 and 63 of the directional control valves 38 (Figure 1) and 57 (Figure 2). In this case, the pilot pressure jumps after a small pivot angle of a lever 81 to an initial value and then increases continuously with the swivel angle. At a certain tilt angle, the pilot pressure then jumps to the supply pressure. From each pilot line 82 is a branch line 83 from, in which a nozzle 84 and a blocking the pilot line back check valve 85 are in succession. Downstream of the check valves 85 all branch lines 83 open into a common control line 86 which leads to the pressure chamber 74 of the pressure-limiting valve 50. All pilot control lines 82 are thus connected in parallel to each other via a respective nozzle 84 and a check valve 85 with the pressure chamber 74 of the pressure relief valve 50.

The control line 86 is also connected to a first port of a 3/2 directional control valve 87, of which a second port is connected to the line carrying the supply pressure and of which a third port is connected to the input of a second pressure limiting valve 88. In a rest position, which occupies the directional control valve 87 under the action of a compression spring 89, the control line 86 is connected to the pressure relief valve 88. The second connection is blocked. The directional control valve 87 can be brought by means of an electromagnet 90 in a switching position in which the control line 86 is connected to the second terminal and the third terminal is shut off. The electromagnet 90 is connected via an electrical line to an electrical switch accommodated in the one pilot control lever 81, which can be actuated by a pushbutton 91. About the push button 91 so the solenoid 90 can be controlled and turned off. The pressure relief valve 88 is manually adjustable. It serves together with the nozzles 84 to be able to limit the pressure in the control line 86 in the rest position of the directional control valve 87 to a value which is lower than the maximum controllable by a pressure reducing valve 79 pilot pressure. Via a flow control valve 92, the control line 86 can be relieved to the tank 11.

For the consideration of the mode of operation of the control arrangement, the following assumptions are made: The supply pressure for the pilot control devices is 30 bar. With the pressure reducing valves 79 pilot pressures up to 25 bar can be adjusted proportionally, the adjustment of the main control valves 38 and 57 starts at 5 bar and whose full stroke is achieved at 25 bar. The pressure relief valve 50 limits at a pending in the control line pressure up to 5 bar because of an initial bias of the spring 75, the pressure in the end portion 26a of the load sensing line to 50 bar. The set value of the pressure relief valve 50 increases 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 relief valve 88 is set to 20 bar. The pump Δpalso the difference between the pressure in the end portion 26a of the load reporting line and the pressure in the feed line 12 is 20 bar.

This results in the rest position of the directional control valve 87 shown below

Functionality:

When a pilot control lever is deflected and a pressure reducing valve 79 is displaced, a pilot pressure builds up in a pilot line 82. Up to a pre-control pressure of 5 bar, nothing works at first. Thereafter, the movement of the spool of the controlled main control valve begins. After a small initial stroke, the corresponding metering orifice is opened more and more. The pressure in the control line 86 and thus the pressure present in the pressure chamber 74 of the pressure limiting valve 50 is slightly smaller than the pilot pressure, namely the pressure difference which generates the amount of pressure medium flowing through the flow regulator 92 at a nozzle 84. The pressure difference may be, for example, 0.5 bar. Thus, the pressure in the end portion 26a of the load-sensing line is limited to 50 bar to a pilot pressure of 5.5 bar and increases with increasing pilot pressure. If the pilot pressure is, for example, 15 bar, then the pressure in the control line 86 is 14.5 bar and the pressure in the end section 26a of the load reporting line is limited to 145 bar.

If the load pressure of the controlled hydraulic consumer is less than or equal to 145 bar, then the pressure limit in the end section 26a is irrelevant. It is there the load pressure. The variable displacement pump 10 delivers so much pressure medium quantity that the pressure in the supply line 12 is 20 bar above the reported load pressure is. The hydraulic consumer is moved at a speed which is determined by the opening cross-section of the metering orifice.

If the load pressure is greater than 145 bar, a pressure of 145 bar is reported to the variable displacement pump 10, because now the pressure limiting valve 50 does not allow the pressure in the end section 26a to become higher. The pressure in the supply line is then 165 bar. If the load pressure is less than 165 bar, an open pressure compensator flows largely unrestricted to the hydraulic consumer via the metering orifice, which results from the opening cross section of the metering orifice and the difference between the inlet pressure of 165 bar and the load pressure , It is thus possible both in a LUDV control of Figure 1 and in a LS control of Figure 2, a sensitive operation of the hydraulic load without throttling losses at a'Druckwaage possible.

If the load pressure is higher than 165 bar, a pressure medium supply to the hydraulic consumer is only possible after further deflection of the pilot control lever. 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. Then the pressure limiting valve 88 responds. Despite further lever deflection, the pressure in the control line 86 remains at 20 bar, so that the pressure in the end portion 26a at 200 bar and thus the inlet pressure at 220 bar. This pressure of 220 bar is in the consumer, so that a corresponding force can be exercised.

If a hydraulic load with a load pressure up to 250 bar is to be controlled solely by the degree of opening of the metering orifice and the full stroke of a main control valve, the button 91 is pressed on a pilot control lever and thus the directional control valve is switched. Now the supply pressure of 30 bar is in the control line 86. The check valves 85 ensure that the pre-control pressure predetermined by the pilot control device prevails in the respective pilot control line. The pressure relief valve 50 is on set its highest value of 250 bar. The pressure in the end portion 26a of the load-sensing line is now equal to the load pressure up to a load pressure of 250 bar. The pressure in the feed line 12 is 20 bar higher than the load pressure. Thus, a load up to 250 bar can be moved with a speed determined solely by the opening cross section 5. Of the associated metering orifice. Up to a load pressure of 270 bar, a slower movement is possible because of the reduced pressure difference across the metering orifice. With a load pressure of more than 270 bar, the load can no longer be moved.

In the embodiment according to FIG. 3, each pilot control line 82 is connected to the control line 86 via a nozzle 84 and a check valve 85. It is therefore possible for each of the two pilot control devices 78 controllable hydraulic consumers and for each direction of pressure control. In the case of a simultaneous actuation of a plurality of hydraulic consumers, the non-return valves 85 ensure that the highest pilot pressure is present in the control line 86 and that the pilot control pressures in the pilot control lines are present

82 do not influence each other.

Of course, for individual consumers or for a direction of movement, 0 can also be dispensed with the possibility of pressure control. Then, between the corresponding pilot control line 82 and the control line 86 is not a branch line

83 available. Finally, a branch line may also be present only between a single pilot control line 82 and the control line 86

Claims

claims

1. Hydraulic control arrangement, in particular for controlling hydraulic consumers of a mobile work machine, with a Lastmeldelei- device (26) which can be acted upon with the highest load pressure of several simultaneously via a respective main control valve (38, 57) controlled hydraulic consumer and an end portion (26 a ) is connectable to a pump regulator (25), and with a pressure limiting valve (50), with which the control pressure in the end portion (26 a) of the load reporting line (26) can be limited, characterized in that the pressure relief valve (50) in dependence on the height of a the control of a main control valve (38, 57) serving pilot signal is adjustable.

2. Hydraulic control arrangement according to claim 1, characterized in that the pressure relief valve (50) is adjustable in dependence on the height of a plurality of pilot signals and that when queuing several pilot signals, the pressure relief valve (50) in response to the largest pilot signal is adjustable.

3. Hydraulic control arrangement according to claim 1 or 2, characterized in that the pressure limiting valve (50) is adjustable in response to a pilot signal only to a set value, which is below the maximum setting value.

4. Hydraulic control arrangement according to claim 1, 2 or 3, characterized in that the pressure limiting valve (50) is independent of the currently pending pilot control signal for the main control valve (38, 57) adjustable to its maximum set value.

5. Hydraulic control arrangement according to one of the preceding claims, characterized in that the pressure limiting valve (50) is hydraulically adjustable and one connected to a with a control line (86). Compression chamber (74) adjacent actuating piston (73).

6. A hydraulic control arrangement according to claim 5, characterized in that the pilot signal is a pilot pressure, which is generated by an adjustable pilot valve (79) from a supply pressure and in a pilot line (82) of a main control valve (38, 57) is present and in Abhän - Actuation of the switching position of an arbitrarily operable directional control valve (87), the pressure chamber (74) of the pressure relief valve (50) with the pilot pressure or the supply pressure can be acted upon.

7. Hydraulic control arrangement according to claim 6, characterized marked, that the pilot control line (82) is connected via a blocking valve to her (85) with the pressure chamber (74) on the pressure relief valve (50).

8. A hydraulic control arrangement according to one of claims 5 to 7, characterized in that a plurality of controllable pressure can be acted upon pilot control lines (82) to one or more main control valves (38, 57) lead and that a plurality of pilot control lines (82) parallel to each other via a check valve ( 85) are connected to the pressure chamber (74) on the pressure limiting valve (50).

9. A hydraulic control arrangement according to one of claims 6 to 8, characterized in that a second pressure relief valve (88) is present, with which the pressure in the pressure chamber (74) of the first pressure relief valve (50) can be limited, which is set to a limit pressure, which is below the maximum pilot pressure, and which is effectively switchable when the pressure chamber (74) of the first pressure limiting valve (50) can be acted upon by a pilot pressure.

10. A hydraulic control arrangement according to claim 9, characterized in that the second pressure relief valve (88) is manually adjustable.

11. A hydraulic control arrangement according to one of claims 6 to 10, characterized in that the directional control valve (87) has a first switching position, in which the second pressure relief valve (88) to the pressure chamber (74) of the first pressure relief valve (50) is connected and the pressure chamber (74) is separated from the supply pressure, and has a second switching position in which the second pressure relief valve (88) from the pressure chamber (74) of the first pressure limiting valve (50) is separated and the pressure chamber (74) can be acted upon by supply pressure.

12. A hydraulic control arrangement according to claim 11, characterized in that the first switching position is the rest position of the directional control valve (87).

13. A hydraulic control arrangement according to one of claims 5 to 12, characterized in that to the control line (86), a flow control valve (92) is connected, via the pressure reduction to the pressure fluid from the control line (86) to a reservoir (T) can be drained.

14. A hydraulic control arrangement according to claim 13, characterized in that the flow control valve (92) is a flow control valve.