EP2320094A2 - Valve assembly - Google Patents

Abstract

The valve building group has two load-side connections (A,B), a pumping connection (P) and tank connection (T) with four control edges (C1-C4) hydraulically controlled over a control port. Two pilot valves (Y1,Y2) are provided for controlling the control ports (c1-c4) of each control edge.

Description

The present invention relates to a valve assembly for the - in particular load-independent - control of at least one consumer such as a hydraulic cylinder, a hydraulic motor or the like. Applications for such a valve assembly are particularly in the field of agricultural machinery with hydraulically driven or adjustable units or construction equipment.

Out EP 0 473 030 A1 Such a valve assembly is known, which has two hydraulically controlled control edges between two consumer-side connections, a pump and a tank connection, which connect the pump connection and the tank connection with each of the consumer-side connections. The control edges between the pressure port and the consumer-side ports are arbitrarily controllable. When one of them is opened, high pressure passes through a check valve to a first one of the consumer-side ports. The control edge between the second consumer-side terminal and the tank terminal has a control input which is connected to the output of the first control edge, so that when opening the first control edge at the Output occurring high pressure causes the second control edge also to open. Thus, when via the first control edge and the first consumer-side connection hydraulic oil flows to a first chamber of a double-acting consumer, hydraulic oil flow from a second chamber of the consumer via the second consumer-side terminal and the second control edge to the tank.

In order to maintain a high pressure at the consumer-side outputs, which fixes the consumer in a set position, even when the pump is inactive, two check valves are provided between the first and second control edge and the two consumer-side ports. Since the entire influx of hydraulic oil to the load must pass through one of the two check valves, the pressure drop that occurs thereby adversely affects the efficiency of a hydraulic machine using the known valve group.

The known valve assembly can be used for load pressure independent supply of a consumer by the load flowing to the load load at the input of one of the check valves and fed via a load pressure signaling line a compensator on the pump side connection of the valve assembly and optionally a regulator of the pump. In order to reliably shut off the compensator in an idle state or to keep the pump switched off, the pressure on the load pressure signaling line must be reliably equal to the tank pressure despite possible high pressures in other parts of the valve assembly. To ensure this, the first and second control edges controlling the flow of the pressurized fluid between the pump port and the consumer-side ports are each combined as a main control edge in a directional control valve with an auxiliary control edge, the auxiliary control edge of each directional control valve in the locked state of the main control edge over the load pressure signaling line Leakage oil return connects to the tank. The main control edges of the directional control valves must be generously dimensioned to allow the entire flow of oil between pump and consumer to pass with a slight pressure drop. The integration of the auxiliary control edges in these directional control valves increases their space requirements even further.

An object of the invention is to provide a valve assembly for driving at least one consumer, in which internal pressure losses are minimized and thus enables operation of the consumer with high efficiency.

The object is achieved by providing a valve assembly with two consumer-side terminals, a pump and a tank connection and four each hydraulically controlled via a control terminal control edges, of which a first pump port and the first consumer-side port, the second pump port and the second consumer-side connection, the third the first consumer-side connection and the tank connection and the fourth the second consumer side Connection and the tank connection connects, a first and a second pilot valve for driving the control terminals of each two of the control edges are provided. By thus eliminating the conventional control of the third and fourth control edges by the prevailing at the output of the first and second control edge pressure, no check valves are required to maintain a pressure difference between a consumer-side terminal and the control terminal of the third or fourth control edge. With the elimination of the check valves also eliminates the associated pressure drop, which improves the efficiency of the consumer. By controlling each pilot valve not only one, but two control edges, and the required to operate the pilot valves throughput of hydraulic fluid and consequently associated with the operation of the pilot valves power loss can be kept small.

There are several ways to assign the control edges to the pilot valves. According to a first simple embodiment, the control ports of the first and fourth control edges are connected in parallel with an output of the first pilot valve and the control ports of the second and third control edges are connected in parallel with an output of the second pilot valve to simultaneously open the first and fourth control edges, and so on To drive a double-acting consumer in a first direction, or to open the second and third control edge and drive the consumer in the opposite direction.

According to a second, further developed embodiment, a float position of the consumer, in which it is movable under a force acting on it from the outside, can be realized by respectively assigning a first and a second switching valve to the first and second control edges the first or control edge selectively connects to the first and second pilot valve or to the tank connection. Thus, via the first control valve, depending on the position of the associated first switching valve, the inflow of hydraulic fluid to a consumer or the outflow from this consumer at the first consumer-side connection can be controlled. Coordinated actuation of both pilot valves allows the consumer to be driven in two opposite directions.

The switching valves may be changeover valves or directional control valves. If the switching valves are designed as directional control valves, in particular the first directional control valve can selectively connect to one of the control terminals of its two associated control edges, in particular the first and third control edge, while the second directional control valve, the second pilot valve with either one of the control terminals of its two associated control edges, in particular the second and fourth control edge connects. Thus, for example, a pressure output by the first pilot valve can be forwarded via the first directional control valve, on the one hand, to the third control edge in order to prevent hydraulic fluid from flowing away from the first control valve allow consumer-side connection to the tank connection, and at the same time enable the second directional control valve in a position in which it passes a present at the output of the second pilot valve pressure to the control input of the second control edge, so as to an inflow of hydraulic fluid to the consumer via the second consumer-side connection enable.

A required for switching the first and second switching valve output pressure of the pilot valves is preferably lower than the output pressure required to open the control edges. Thus, by coordinately increasing the pressure at the outlet of both pilot valves, the two switching valves can first be switched. A switching of the switching valves at open control edges is thereby excluded.

Preferably, the two switching valves each have a second control input to which one of its outputs is returned, so that the pressure prevailing at the output counteracts the pressure applied to the first control input pressure. This recirculated at the second control input pressure can secure the switching valve in the position which it assumes even in a depressurized state, despite a pressure applied to the first control input, so that at the same time pressurizing both switching valves that do not change their switching position.

The pilot valves are preferably designed as proportional pressure reducing valves.

In order to enable load-independent control of a connected consumer, an individual pressure compensator controlled by the pressure prevailing at one of the consumer-side connections is preferably inserted between the pump connection and the first and second control edges.

By means of a pilot-operated check valve between a control input of the individual pressure balance and each consumer-side connection, the highest pressure applied to the consumer-side connections can be forwarded to the individual pressure balance, without thereby changing the pressure present at the other consumer-side connection. When the pump is turned off, the check valves prevent a flow of pressurized fluid from one consumer-side port to the other via the load pressure signaling line and thus an unwilling yielding of the consumer under an external load. Unlocking one of the check valve makes it possible to transmit a decreasing pressure correctly from a consumer-side port to the individual pressure compensator.

In order to control the unlocking of the pilot-operated check valves, it is expedient to use one output signal each of one of the pilot valves.

As already mentioned, an uncontrolled pressure increase at the control connection of the individual pressure compensator must be prevented at standstill in order to control the pump or pilot valves incorrectly to avoid. To ensure this, the unlockable check valves are advantageously arranged to connect the control port of the individual pressure compensator with the tank connection in the locked state. Since the pilot-operated check valves only have to cope with a small fraction of the throughput that runs over the first to fourth control edges, these pilot-operated check valves can be dimensioned small, and correspondingly little space requires the implementation of a connection of the control terminal of the individual pressure compensator with the tank connection via the unlockable check valves.

A check valve integrated in the individual pressure compensator makes it possible, in the event of a failure of the pump, to avoid a sudden drop in pressure at the connections on the consumer side and thus an uncontrolled movement of the load under load.

Subject of the invention is also a tractor with a valve assembly of the type described above, to which a hydraulically adjustable or driven unit such as a plow or a mower can be connected.

Fig. 1

ein Hydraulikdiagramm einer Ventilan- ordnung gemäß einer ersten Ausgestal- tung der Erfindung;

Fig. 2

einen schematischen Schnitt durch eines der in Fig. 1 gezeigten Ventile;

Fig. 3

ein Hydraulikdiagramm einer Ventilan- ordnung gemäß einer zweiten Ausgestal- tung der Erfindung; und

Fig. 4

ein Hydraulikdiagramm gemäß einer drit- ten Ausgestaltung der Erfindung.

Further features and advantages of the invention will become apparent from the following description of embodiments with reference to the accompanying figures. Show it:

Fig. 1

a hydraulic diagram of a valve assembly according to a first embodiment of the invention;

Fig. 2

a schematic section through one of in Fig. 1 shown valves;

Fig. 3

a hydraulic diagram of a valve assembly according to a second embodiment of the invention; and

Fig. 4

a hydraulic diagram according to a third embodiment of the invention.

Fig. 1 shows a hydraulic diagram of a valve assembly according to a first embodiment of the invention, which may be attached to the front or rear of a tractor, for example, as consumer a control cylinder or a hydraulic motor of a replaceable front or rear aggregate such as a sweeping broom, a snow blade, a plow to connect a multi-part mower or the like. The valve assembly shown in the figure is connected to four lines shown in the lower part of the figure as parallel lines, namely a coming from a pump not shown here high pressure line P, leading to a tank unpressurised line T, a control pressure line Px and a load pressure signaling line LS , Several copies of the valve assembly can be connected in parallel to the four lines P, T. Px, LS, possibly to several consumers of a connected unit to supply or drive the unit in several degrees of freedom or control.

A branch P1 originating from the high-pressure line P extends via an individual pressure compensator C5 controlled by the pressure present on the load pressure signaling line LS to two hydraulically piloted directional valves C1 and C2 reset by a spring. Two consumer-side ports A, B are connected to outputs of the two-way valves C1, C2. The directional control valves are designed in seat construction and arranged so that their valve body is pressed in each case by an overpressure on the consumer-side connection against its seat. The directional control valves C1, C2 are therefore absolutely tight against a high pressure at one of the consumer-side ports, which may occur when an external load acts on a connected consumer, e.g. to a hydraulic cylinder that holds a plow connected to the tractor for road or shunting in a raised position from the ground or presses it against the ground to keep the ploughshare at a desired depth when plowing.

Two further directional control valves C3, C4 connect the consumer-side ports A, B with the unpressurized line T.

The directional valves C1 to C4 are in Fig. 1 all shown closed. By opening the directional control valves C1 and C4, a chamber of a double-acting consumer connected to the connection point A, B can be supplied with hydraulic fluid at the connection A. while from a second chamber of the consumer, the corresponding amount flows through the port B. If, on the other hand, the directional control valves C2, C3 are open, hydraulic fluid flows via the connection B to the consumer, and via the connection A, it flows back to the tank. The passage area of the directional control valves C1 to C4 is a continuous function of a control pressure applied to a control port c1 to c4 of each directional control valve.

Two proportional pressure reducing valves Y1, Y2 serve as pilot valves for generating this control pressure. The pressure reducing valves Y1, Y2 are connected to the control pressure line Px and the unpressurized line T and each have a controlled connection y1, y2, the pressure of which is continuously adjustable electrically between the pressures of the lines Px and T. The pressure reducing valve Y1 controls the pressure on a pilot line 1 connecting control ports c1, c4 of the valves C1, and C4; the pressure reducing valve Y2 controls in an analogous manner via a pilot control line 2, the valves C2 and C3.

Unlockable check valves R1, R2 each have a control port r1 and r2, respectively, connected to the pilot control line 1 and 2, an inlet connected to the fuel-side port A and B, and two outlets connected to the unpressurized line T or via line branches LS1 and LS2 and a shuttle valve W1 are connected to the load pressure signaling line LS.

A second change-over valve W2 inserted in the load-pressure signaling line LS allows either the pressure shown in the figure at the control port c5 of the individual pressure compensator C5 or that connected to the lines P, T, Px, LS shown in parallel in FIG Switch valve assembly for controlling an external pump supplying the line P.

In the in Fig. 1 the check valves R1, R2 are shown in a rest position, in which their respective two outlets are connected to each other. As a result, the load pressure signaling line LS is securely held without pressure. Consequently, the individual pressure compensator C5 locks and the external pump is switched off. Any leaks over which hydraulic fluid could flow into the load pressure sensing line LS can not result in an increase in pressure.

When one of the two pressure reducing valves, for example Y1, is opened, the pressure on the pilot control line 1 increases, and the directional control valves C1, C4 open in proportion to this pressure. The output pressure of the pressure compensator C5 is therefore at the port A, while via the port B pressurized fluid can flow to the tank. At the same time, the high pressure on the pilot control line 1 leads to switching of the directional control valve R1 into a position in which it connects the connection A to the branch LS1 and at the same time interrupts the connection of the branch LS1 to the unpressurized line T. The load pressure signaling line LS thus carries the pressure prevailing at port A. The pressure compensator C5 regulates in a conventional manner that through them from the pump to the port A running fluid flow such that there is a constant pressure difference between the output of the pressure compensator C5 and its connected to the load pressure signaling line LS control input. This pressure difference is substantially equal to the pressure drop at the control edge of the directional control valve C1, and there is a direct linear relationship between the opening cross section at the control edge of the directional control valve C1 and the volume flow supplied to the consumer via the connection A.

If due to a malfunction of the pump, the pressure on the high-pressure line P drops or an external force acting on the consumer causes the pressure at the consumer-side terminal A is higher than that on the line P, then an integrated check valve 3 causes a blocking of the individual pressure compensator C5. In these cases, therefore, there is no downward movement of the consumer, but this remains in the position once reached.

Fig. 2 shows a schematic section through the pilot-operated check valve R1 or R2 according to a preferred embodiment. In a housing 10, a hole is formed with multi-stepped diameter. In a large part of this hole, on the right side of the Fig. 2 , a movable piston 11 is housed. A rear side 12 of the piston 11 is exposed to the pressure of the control pressure line Px; a front side 13 of the piston defines a chamber 14 connected to the non-pressurized line T. An insert 15 screwed into the bore of the housing 10 has a recess 16 of the piston front side 13 engaging projection 17. The projection 17 centers a coil spring 18 which drives the piston 11 against the control pressure acting on its rear side 12 to the right.

The insert 15 comprises an axial bore 19 and at least three radial bores 20, 21, 22 intersecting the axial bore 19. The bore 20 opens into the chamber 14, the bore 21 is connected to one of the branches LS1 or LS2 of the load pressure signaling line LS, and the bore 22 with one of the consumer-side terminals A and B in the bore 19, a mandrel 23 is axially displaceable. In the in Fig. 2 shown position is a narrow tip 24 of the mandrel in a bore 20, 21 connecting portion of the axial bore 19, so that the load pressure signaling line LS is connected to the chamber 14 and is held at tank pressure. A spring 25 and optionally on the consumer side port A and B prevailing overpressure hold a ball 26 against a valve seat 27 between the holes 21, 22 pressed. The ball 26 and the valve seat 27 thus form a check valve capable of maintaining a high pressure at port A or B, even when the load pressure sensing line LS and with it the bore 21 is depressurized.

Under the influence of a positive control pressure on the back 12 of the piston 11, this moves in the figure to the left, taking the mandrel 23 with it. A foot portion 28 of the mandrel 23, whose cross section corresponds exactly to the bore 19, moves while in the bores 20, 21 connecting portion of the axial bore 19 and blocks it. Thus, the connection between the load pressure signaling line LS and the unpressurized chamber 14 is interrupted. Subsequently, the tip 24 abuts against the ball 26 and lifts it from the valve seat 27. Thus, the check valve is unlocked, and the load pressure signaling line LS assumes the prevailing at the consumer side port A or B pressure. By firstly blocking the connection to the chamber 14 before releasing the check valve, uncontrolled outflow of pressurized fluid from the user-side port A or B to the tank via the directional control valve R1 or R2 is precluded.

As can be seen, the cross-section of the piston 11 is many times greater than the diameter of the ball 26, so that a relatively low control pressure on the piston rear side 12 is sufficient to release the ball 26 from its seat 27, even if this by a high Pressure on the device-side connection against the seat 27 is pressed.

Fig. 3 shows a valve assembly according to a second embodiment of the invention. The lines P, T, Px, Ls, the valves C1 to C4, Y1, Y2 and R1, R2 and the individual pressure compensator C5 are the same as in Fig. 1 and will not be explained again. A major difference between the design of the Fig. 3 and those of Fig. 1 are additional directional valves V1, V2. In an in Fig. 3 shown idle state, the directional control valve V1 connects the controlled port y1 of the pressure reducing valve Y1 with control terminals c3, v2 of the directional control valves C3 and V2 and the control terminals c1, r1 of the directional control valves C1, R1 with the unpressurized line T. By a high pressure applied to its control terminal v1, the directional control valve V1 is switchable to a position in which it Control terminals c1, r1 with the pressure reducing valve Y1 and the control terminals c3, v2 with the non-pressurized line T connects. In an analogous manner connects the directional control valve V2 in the pressureless state, the controlled connection y2 of the pressure reducing valve Y2 with the control terminals c4, v1 of the valves C4, V1 and the control terminals c2, r2 of the valves C2, R2 with the unpressurized line T, whereas it concerns a concern high pressure at the control port v2 the pressure reducing valve Y2 with the control terminals c2, r2 and the non-pressurized line T with the control terminals c4, v1 connects.

If both pressure-reducing valves Y1, Y2 are closed, the directional control valves C1 to C4 are also blocked. When the pressure reducing valve Y1 is opened and the pressure at its controlled port y1 rises, this first leads to the opening of C3 so that pressurized fluid can flow away from the consumer via the consumer side port A and to switch from V2 to its high pressure state. Now, if the pressure reducing valve Y2 is opened, this leads to the opening of C2, so that high pressure appears on the consumer side port B. At the same time R2 switches, so that this high pressure spreads to the load pressure signaling line LS and controls the operation of the individual pressure compensator C5. Thus flows a load-independent regulated pressure fluid flow over port B to the consumer, and a complementary current returns from the consumer via port A to the tank.

If the pressure reducing valves Y1, Y2 are opened in the reverse order, high pressure appears at port A, port B communicates with the unpressurized line T, and the consumer is driven in the opposite direction.

The Fig. 3 shows two control inputs to the directional valves V1, V2, an input v1 and v2, which, as mentioned above, is connected to an output of the respective other directional valve V2 or V1, and an input v1 'or v2', via which Output pressure of each directional valve V1, V2 is returned to it itself. When both pressure reducing valves Y1, Y2 are simultaneously opened, the influences of the pressures at these two control ports v1 and v1 'and v2 and v2' cancel each other, and the directional valves V1, V2 remain in the in Fig. 3 shown rest position. As a result, while valves C3, C4 open, valves C1, C2 remain closed. In this state floats a connected to the terminals A, B consumer; ie, it can yield to an externally applied force, such as the weight of the plow held in the raised position, while sucking hydraulic fluid from the tank via one of the ports A, B, while hydraulic fluid is returned to the tank via the other port. The floating position makes it possible, in particular, to use aggregates, such as a broom or a snow plow, to passively follow the contour of the vehicle floor.

Alternatively to the above-considered possibility, with the valve assembly of the Fig. 3 To operate a double-acting consumer, which is connected to both consumer-side terminals A, B, there is the ability to independently control two single-acting consumers when the required to switch the directional control valve V1 and V2 control pressure is lower than that for opening the directional valves C1 to C4 required. Thus, for example, the control pressure required for switching over the directional control valves V1, V2 can amount to approximately 3 bar, while the directional control valves C1 to C4 only start to open at a control pressure of 5 bar or above and are completely open at a control pressure of approximately 20 bar. In order to drive in a single-acting consumer at port A, it is necessary to open the directional control valve C3, while the directional control valves C1, C2, C4 remain closed. When the pressure reducing valve Y1 is opened while Y2 remains closed, the directional control valve V2 switches as soon as the pressure at the controlled connection of the directional control valve Y1 exceeds 3 bar. Since Y2 is closed, however, this does not affect the directional valves C2 and C4. C3 opens as soon as the pressure at the controlled connection of Y1 exceeds 5 bar. Meanwhile, the control port of C1 is depressurized through V1 so that C1 remains closed.

To extend the load on port A, it must be possible to open C1 while keeping C2 to C4 closed. This is achieved by first applying a pressure of Y2 to the controlled port y2 of Y2 eg 4bar is set. This causes the directional control valve V1 to switch but is not yet enough to open C4. V1 now connects the controlled port y1 to c1 so that opening Y1 opens C1.

The fact that a consumer can be controlled at port B in exactly the same way is due to the symmetry of the valve assembly without detailed explanations.

Fig. 4 shows a third embodiment of the valve assembly, which differs from that of Fig. 1 by the addition of two hydraulically controlled shuttle valves F1, F2 different. The shuttle valves F1, F2 are respectively connected upstream of the control ports c1, c2 of the directional control valves C1 and C2, controlled by the pressure reducing valve Y2 either with the controlled port y1 of Y1 or with the unpressurized line T or c2 controlled by Y1 with y2 or to connect with the non-pressurized line T. The shuttle valves F1, F2 serve as the directional valves V1, V2 of Fig. 3 to allow opening of both the flow control valves C3, C4 controlling the drain, while at the same time keeping closed the directional control valves C1, C2 controlling the inlet to the consumer, thus bringing about a floating state of the consumer.

For example, if the controlled port y2 is depressurized, the shuttle valve F1 controlled via this port connects the control port c1 to y1. When the pressure reducing valve Y1 is opened while Y2 is closed, it rises as in the embodiment of Fig. 1 the pressure at the control terminals c1 and c4, and a double-acting consumer connected to the terminals A, B are driven in a first direction. When Y2 opens while Y1 remains closed, the directional control valves C2, C3 open, and the consumer is driven in the opposite direction. However, if both pressure reducing valves Y1, Y2 open simultaneously, then the two shuttle valves F1, F2 switch before the pressure at the control ports of the directional control valves C1, C2 is high enough to open them. As a result, the control terminals c1, c2 are connected to the unpressurized line T, and C1, C2 remain closed, while C3 and C4 open as soon as the pressure applied to their control terminals c3, c4 sufficient pressure.

reference numeral

1

pilot line

2

pilot line

3

check valve

10

casing

11

piston

12

back

13

front

14

chamber

15

commitment

16

recess

17

head Start

18

coil spring

19

axial bore

20

radial bore

21

radial bore

22

radial bore

23

mandrel

24

top

25

feather

26

Bullet

27

valve seat

28

foot section

A

consumer-side connection

B

Consumer connection

C1-C4

way valve

C5

Individual pressure balance

C1-c5

Control connection of Ci

F1, F2

shuttle valve

P

High-pressure line

px

Control pressure line

R1, R2

unlockable check valve

r1, r2

Control connection of R1 or R2

V1, V2

way valve

v1, v2

Control connection of V1 or V2

W1, W2

shuttle valve

Y1, Y2

Proportional pressure reducer valve

y1, y2

controlled connection of Y1 or Y2

Claims (15)

Valve assembly for controlling at least one consumer, having two consumer-side connections (A, B), a pump connection and a tank connection (P, T), with four control edges (C1-C4) which are hydraulically controlled via a respective control connection, of which a first one (FIG. C1) the pump connection (P) and the first consumer-side connection (A), the second (C2) the pump connection and the second consumer-side connection (B), the third (C3) the first consumer-side connection (A) and the tank connection (T) and the fourth (C4) connects the second consumer-side port (B) and the tank port (T), characterized by a first pilot valve (Y1) and a second pilot valve (Y2) for driving the control ports (c1-c4) of each two of the control edges (C1-C4). Valve assembly according to claim 1, characterized in that the control terminals (c1, c4) of a pair of the control edges, in particular the first and fourth control edge (C1; C4), in parallel with an output (y1) of the first pilot valve (Y1) and the control terminals (Y1) c2, c3) of another pair of the control edges, in particular the second and third control edges (C2, C3), connected in parallel with an output (y2) of the second pilot valve (Y2). Valve assembly according to claim 1, characterized in that the first and the second control edge (C1, C2) in each case a first or second switching valve (F1, F2, V1, V2) is associated, wherein the first switching valve (F1, V1) a control terminal (c1) connects the first control edge (C1) optionally to the first pilot valve (Y1) or to the tank connection (T) and the second switching valve (F2, V2) connects a control connection (c2) of the second control edge (C2) optionally to the second Pilot valve (Y2) or with the tank connection (T) connects. Valve assembly according to claim 3, characterized in that the first switching valve is a first directional valve (V1), which the first pilot valve (Y1) optionally with one of the control terminals (c1, c3) of its two associated control edges, in particular the first and third control edge ( C1, C3), and in that the second switching valve is a second directional control valve (V2) which selectively connects the second pilot valve (Y2) to one of the control connections (c2, c4) of its two associated control edges, in particular the second and fourth control edges (Y2). C2, C4), connects. Valve assembly according to claim 3 or 4, characterized in that the first switching valve (F1, V1) connected to the second pilot valve (Y2) first control input (v1) and the second switching valve (F2, V2) with the first pilot valve (Y1) connected first control input (v1). Valve assembly according to claim 5, characterized in that a required for switching the first and second switching valve (V1, V2, F1, F2) output pressure of the pilot valves (Y1, Y2) is lower than the opening pressure of the control edges (C1-C4) required , Valve assembly according to claim 6, characterized in that both pilot valves (Y1, Y2) are simultaneously actuated. Valve assembly according to claim 7, characterized in that at the first and second switching valve (V1, V2), an output to a second control input (v1 ', v2') is returned, so that the pressure prevailing at the output of the first control input (v1, v2) counteracts applied pressure. Valve assembly according to one of the preceding claims, characterized in that the pilot valves (Y1, Y2) are proportional pressure reducing valves. Valve assembly according to one of the preceding claims, characterized in that a by the prevailing at one of the consumer-side ports pressure controlled individual pressure compensator (C5) between the pump port (P) and the first and second control edge (C1, C2) is inserted. Valve assembly according to claim 10, characterized in that a pilot-operated check valve (R1, R2) between a control input of the individual pressure compensator (C5) and each consumer-side terminal (A, B) is provided. Valve assembly according to claim 11, characterized in that the pilot-operated check valves (R1, R2) via each one of the pilot valves (Y1, Y2) are unlocked. Valve assembly according to claim 11 or 12, characterized in that the pilot-operated check valves (R1, R2) are arranged to connect in the locked state, the control port of the individual pressure compensator (C5) with the tank port (T). Valve assembly according to one of the preceding claims, characterized in that a check valve (3) in the individual pressure compensator (C5) is integrated. Tractor with a valve assembly according to one of the preceding claims, characterized in that on the valve assembly, a hydraulically adjustable or driven unit, in particular a plow or a mower, can be connected.

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