WO2010069473A1

WO2010069473A1 - Hydraulic control arrangement having lowering brake valves

Info

Publication number: WO2010069473A1
Application number: PCT/EP2009/008649
Authority: WO
Inventors: Matthieu Desbois-Renaudin; Wolfgang Kauss; Edwin Heemskerk; Thomas Weickert
Original assignee: Robert Bosch Gmbh
Priority date: 2008-12-19
Filing date: 2009-12-04
Publication date: 2010-06-24
Also published as: DE102008064137A1

Abstract

The invention relates to a hydraulic controls arrangement for supplying pressure medium to at least one consumer, having an electrically or electrohydraulically adjustable valve device, by means of which a flow line to the consumer can be connected to a pump (22), and a return line from the consumer can be connected to a tank (24). A lowering brake valve (72,74) is disposed in the return line and, according to the invention, is associated with a secondary pressure limiting valve (100,102), the output thereof being connected to the tank.

Description

description

HYDRAULIC CONTROL ARRANGEMENT WITH VALVE BRAKE VALVES

The invention relates to a hydraulic control arrangement for supplying pressure medium to at least one consumer according to the preamble of patent claim 1.

Such a control arrangement is known for example from US 5,138,838 A. In this control arrangement, a consumer, for example a differential cylinder, is supplied with pressure medium via a valve device, which is provided by a pump. In the flow to and in the return from the consumer, each a continuously adjustable directional control valve is arranged. The directional control valves are biased in their neutral position in a blocking position and can be adjusted via pressure reducing valves in each case in one direction in which the pump with the associated pressure chamber and in another direction, in each of which the associated pressure chamber is connected to the tank. In this known control arrangement can be operated by a suitable control of the two-way valves, the consumer with a so-called regeneration circuit. In this case, for example, during the extension of a cylinder, the decreasing annular space is connected via the associated directional control valve to the pressure medium inlet to the enlarging pressure chamber, so that the cylinder is extended in rapid traverse. A disadvantage of the regeneration / differential circuit is that due to the clamping of the consumer (effective effective area corresponds to the piston rod area at the same pressures in the annulus and in the cylinder chamber) the consumer can not be operated with the maximum power.

If such a control arrangement is used for example in a mobile work equipment, such as a backhoe loader, a mini and compact excavator or a telehandler, the retrievable grave performance in the regeneration mode due to the clamping of the consumer is relatively low. The regeneration mode is accordingly preferably used when lowering the equipment of the mobile implement. To operate the load with high performance, for example, when digging or lifting a load is then switched to the normal function, in the the increasing pressure chamber with the pump and the decreasing pressure chamber is connected to the tank.

In order to avoid the formation of cavitations in the pressure medium flow when pulling load, a lowering brake valve can be provided in the return from the consumer, as described in DE 196 08 801 C2 or from the data sheet VPSO-SEC-42; 04.52.12-X-99-Z of the company OiI Control, a subsidiary of the applicant is known.

Such a lowering brake valve consists in principle of a continuously adjustable directional control valve, which is biased by a spring in a non-return position in which a flow of pressure medium to the consumer is possible. This valve is acted upon in an opening direction (without check function) by the respective pressure in the flow, so that cavitations in the flow can be avoided in pulling load. In the spring-biased home position a leakage-free support of the consumer or the load acting on the load is enabled. In the known solutions, the lowering brake valve also acts as a secondary pressure limiting valve, via which the pressure in the sequence can be limited to a maximum pressure.

In such a solution, the lowering brake function and the secondary pressure limiting function are thus integrated into the lowering brake valve. This has the advantage of a very compact design.

In certain conditions, for example when driving in a cylinder without load, a comparatively high pressure level can be set in the return, since the pressure limiting valve integrated in the lowering brake valve is designed and adjusted with regard to the return pressure occurring when the load is pulled. Furthermore, the lowering brake valve described in the aforementioned prior art has a comparatively complex structure.

In contrast, the present invention seeks to provide a hydraulic control arrangement with low device complexity. This object is achieved by a hydraulic control arrangement with the features of claim 1.

According to the invention, the hydraulic control arrangement for pressure medium supply at least one consumer has an electric or electro-hydraulically adjustable valve device, via which a flow to the consumer with a pump and a return from the consumer with a tank is connected, wherein in each return a Senkbremsventil is arranged, the pressure in the Supply is acted upon in its open position. In the solution according to the invention, a secondary pressure limiting valve is provided parallel to the lowering brake valve, via which the pressure in the return to a predetermined maximum pressure can be limited. For this separate secondary pressure relief valve, a comparatively simple valve can be selected, so that the device-technical effort for the realization of the hydraulic control arrangement relative to the solution described above is minimal. According to the invention, the outlet of the pressure-limiting valve is connected to a tank connection. In the solution described above, the connection to the tank is dependent on a corresponding setting of the valve device in the secondary pressure limiting function, so that, even with a secondary pressure limitation, throttling of the pressure medium volume flow occurs via the valve device the lowering brake valve can come to pressure peaks.

Such a control arrangement is particularly simple if the counter-sunk lowering valve is controlled by the pressure in the flow.

In a solution according to the invention, the valve device in the respective sequence downstream of the lowering brake valve has a continuously adjustable directional control valve with two switching positions, one of which is an open neutral position, wherein the secondary pressure limiting valve is also connected in parallel to this directional control valve.

In this embodiment may be opened in the neutral position of the directional control valve, a pressure medium connection to the tank. According to a preferred embodiment of the invention, a respective Senkbremsventil and a directional control valve with parallel-connected secondary pressure relief valve are arranged in the flow and in the return, wherein the flow-side lowering brake valve is acted upon by the pressure in the return in the direction of its open position.

In one variant, the pressure in the flow or in the return between the lowering brake valve and the directional control valve is tapped.

The lowering brake valve can have a non-return function, in which a pressure medium flow from the consumer is possible and from which the lowering brake valve is adjustable in the direction of an open position.

In one embodiment of the invention, the two-way valves can be adjusted via a control unit in a regeneration position, in which both the flow and the return are connected to the pump.

The secondary pressure limiting valve connected in parallel can be made comparatively small if the pressure in the supply can be set as a function of the maximum pressure set on the secondary pressure limiting valve. This variant makes it possible to set the pressure in the flow so that in normal operating conditions the pressure in the return line is below the maximum pressure set on the pressure relief valve. By using such simply constructed pressure relief valves, the investment costs for the hydraulic control arrangement can be further reduced.

The change in the flow pressure as a function of the maximum pressure of the secondary pressure limiting valve can be effected, for example, via a pressure sensor, by way of which the pump pressure is detected. The case resulting control signal is compared via a controller with the maximum pressure of the secondary pressure limiting valve and in the case in which this maximum pressure is less than the pressure detected by the pressure sensor, via a control signal generator generates a control signal for adjusting the aforementioned directional control valve or the pump, so that the Pressure in the flow is lowered below the maximum pressure. According to the invention it is preferred if a valve body of the lowering brake valve is biased by a spring into a closed position, the spring chamber is relieved to the atmosphere.

In the case of the hydraulic control arrangement, an electrically or electrohydraulically adjustable pump is preferably carried out, it being possible to regulate the pump pressure via a control loop with a pump regulator.

Other advantageous developments of the invention are the subject of further subclaims.

In the following, a preferred embodiment of the invention is explained in more detail with reference to schematic drawings. Show it:

Figure 1 is a circuit diagram of a control arrangement according to the invention for supplying pressure medium to multiple consumers;

Figure 2 is a detail view of a consumer associated directional valve section of the control arrangement in a neutral position and

Figure 3 is a diagram illustrating the control of the flow pressure.

FIG. 1 shows a hydraulic control arrangement 1 for the pressure medium supply of two consumers 2, 4 of a mobile working device, for example an excavator, a backhoe loader, a mini and compact excavator or a telehandler. This is a so-called EFM system (electronic flow management), in which the actuation of the pressure medium volume flow and the pressure fluid flow direction determining valve elements is carried out electrically or electro-hydraulically depending on, stored in a control unit 6, characteristic fields. The input of the desired values takes place via a joystick 8, which is actuated by the operator, to control the equipment (eg boom, bucket) of the implement in terms of speed and position.

In the illustrated embodiment, the two consumers 2, 4 are each designed as a differential cylinder with a bottom-side pressure chamber 10 and 12 and a piston rod-side annulus 14 and 16, respectively. These pressure chambers 10, 14; 12, 16 can each be connected via a directional control valve section 18, 20 with a variable displacement pump 22 or a tank 24 to the cylinder on or extend. The variable displacement pump 22 is pressure-controlled via a pump regulator 26, via which, after reaching the predetermined pressure, the delivery flow of the pump is adjusted so that the pressure in the system remains constant independently of the delivery flow. With a pressure medium volume flow change virtually no pressure change should be connected.

The variable displacement pump 22 is acted upon by a setting cylinder 30 by a spring-loaded return cylinder 28 in the direction of the maximum pressure medium volume flow (pivot angle maximum) and in the direction of reducing the pressure medium volume flow. The pressure chamber of the actuating cylinder 30, which acts in the direction of reducing the pressure medium volume flow, can be acted upon either by the pump pressure or by the tank pressure via a pump control valve 32 designed with three connections. The pump control valve 32 is acted upon in the direction of a connection of the pressure chamber of the actuating cylinder 30 with the tank 24 via a control spring and the pressure downstream of a nozzle 34 which is arranged in a control line 36, via which the pressure in a connected to the pressure port of the variable displacement pump 22 Pump line 38 is tapped. This pressure also acts in the direction of a connection of the pressure chamber of the adjusting cylinder 30 with the pump pressure on the pump control valve 32. The downstream of the nozzle 34 located region of the control line 36 is connected via a pressure relief valve 40 to the tank 24. This pressure relief valve 40 is energized electrically via a signal line connected to the control unit 6. In its illustrated, spring-biased home position, the pressure relief valve 40 shuts off the pilot oil connection to the tank 24.

The pump controller 26 is adjusted so that an adjustment of the swivel angle is possible only from a stand-by pressure of 20 bar. In the spring-biased basic position of the pump control valve 32, the pressure chamber of the actuating cylinder 30 is connected via two further nozzles 42, 44 with a leading to the tank 24 tank control line 46. When controlling the pressure relief valve 40 of the downstream of the nozzle 34 located part of the control line 36 is connected via the pressure relief valve 40 to the tank control line 46 so that the pump control valve 32 is shifted in the illustration of Figure 1 by the pump pressure to the right and the pressure medium connection of the pressure chamber of Adjusting cylinder 30 is opened to the control line 36. The control oil can then flow via the pump control valve 32 and the nozzle 44 to the actuating cylinder 30, so that the swivel angle is reduced by the pressure build-up in the pressure chamber of the actuating cylinder 30 until the set via the control unit 6 pump pressure. Further explanations on the operation of the pump controller 26 are unnecessary, since the basic structure of such pressure regulator is described for example in the data sheet RD 92 703 Bosch Rexroth AG. Instead of a pressure regulator, other controllers, such as electro-proportional swivel angle controller (EP or EK) can be used. Such regulators are described in the data sheet RE 92 708 of the Bosch Rexroth AG, so that reference can be made to these statements with regard to further details.

The pressure in the pump line 38 is detected by a pressure sensor 48 and reported via a signal line to the control unit 6.

The suction connection of the variable displacement pump 22 is connected to the tank 24 via a suction line 50 and a filter. The pumped by the variable displacement pump 22 pressure fluid flows through the pump line 38 and the two-way valve sections 18, 20, whose structure will be explained below with reference to Figure 2, to the consumers 2, 4. The pressure fluid flows on the return side of the consumers 2, 4 on the associated Directional control valve sections 18, 20 and a tank line 52 from the tank 24, wherein in the end portion of the tank line 52, a further filter is provided which is bypassed via a pressure relief valve and which opens when the filter is added and thus the pressure loss across the filter. The temperature of the pressure medium received in the tank 24 is detected by a temperature sensor 54 and reported to the control unit 6 via a signal line. In order to prevent overheating of the pressure medium, a purge valve 57 is provided between the tank line 52 and the pump line 38. This purge valve 57 also has a pressure limiting function, so that the pressure in the pump line 38 can be limited to a maximum pressure. When the purge valve 57 is open, the pressure medium used to actuate the consumers, in particular in the regeneration circuit, can be exchanged for "fresh" pressure medium from the tank 24. The control of the flushing valve 57 is also carried out electrically in response to a signal of the control unit 6.

Figure 2 shows the basic structure of the two-way valve sections 18, 20, wherein the directional control valve segment 18 is shown as an example and the variable displacement pump 22 and the tank 24 are shown in simplified form.

According to FIG. 2, the directional valve section 18 has two pressure ports P, which are each connected to the pump line 38 via a supply line 56, 58. Two tank connections T of the directional valve section 18 are connected to the tank line 52 via discharge lines 60, 62. Each connection pair P, T of the directional control valve section 18 is associated with a working port A and B, which is connected via a flow line 64 and a return line 66 to the pressure chamber 10 and the annular space 14 of the consumer 2. In the pressure medium flow path between the terminals P, T and the associated working ports A, B, a continuously adjustable 3-way valve 68, 70 with two switching positions and three terminals and a lowering brake valve 72 and 74 are respectively arranged. Each directional control valve 68,70 is biased via a control spring in its neutral position shown, in which the drain line 60, 62 is in fluid communication with a connecting channel 76, 78, which extends in each case to the adjacent lowering brake valve 72, 74.

The adjustment of the directional control valve 68, 70 is in each case via a pilot valve 81, 83 with a proportional solenoid 80, 82, which can be supplied with current via signal lines from the central control unit 6, by adjusting the pilot valves 81, 83, for example of pressure reducing valves, the directional control valves 68, 70 independently to move in the direction of a position in which the pressure medium connection of the supply lines 56, 58 are opened to the connection channels 78 and 76, respectively. Accordingly, the two-way valves 68, 70 with their open to the tank 24 neutral position an extremely simple structure, wherein the adjustment - in contrast to the prior art described above - only a pilot valve and a proportional solenoid 80, 82 is required, while in the known Solutions with closed center position, two expensive proportional solenoids and two pilot valves must be used. In principle, the directional control valves 68, 70 can also be controlled directly via the proportional solenoids.

The two Senkbremsventile 72, 74 are each biased by a biasing spring 84, 86 in a check position in which a flow of pressure medium to the respective pressure chamber 10, 14 is possible and is shut off in the opposite direction, so that the load is supported leak-free. The displacement of the lowering brake valve 72, 74, which is designed as a 2-way valve, takes place via the pressure in the respective other connecting channel 76, 78, which is tapped "crosswise" via control lines 92, 94. That is, when the hydraulic cylinder 2 is extended (without pulling load) the pressure medium on the biased into its neutral position lowering brake valve 72 to the increasing pressure chamber 10 and from the decreasing annular space 14 via the in its open position by the pressure in the flow (connecting channel 76) adjusted in its open position lowering brake valve to the tank 24 from is indicated, the spring chambers of the lowering brake valves 72, 74 and the two-way valves 68, 70 via a respective discharge line 95, 97 connected to the drain lines 60 and 62 respectively.

For each of the lowering brake valves 72, 74, a secondary pressure limiting valve 100, 102 is connected in parallel. In this case, branches from the flow line 64 and the return line 66 from a pressure limiting channel 96 and 98, which is guided to the input of the respective secondary pressure relief valve 100, 102. This is biased in the usual way via adjustable pressure limiting spring 104, 106 in an open position and can bring about the pressure in the pressure limiting channel 96 and 98 in its open position to limit the pressure in this area to a maximum pressure, by setting the pressure relief spring 104, 106 predetermined is. The outlet connection of the pressure-limiting valve 100 or 102 is connected in each case via a pressure-limiting outlet 108, 110 to the respective drain line 62 or 60.

As already stated, the two pressure relief valves 100, 102 can be designed with a comparatively small nominal diameter and a very simple construction, since they open practically only in the load case in which the maximum pressure is exceeded in the respective return. In all other cases where the pressure is below this maximum pressure, the return flow of the pressure medium via the lowering brake valve, which must be designed accordingly.

By these two simple pressure relief valves 100, 102 of the device engineering effort compared to the prior art can be significantly reduced.

In the neutral positions of the two-way valves 68, 70 illustrated in FIGS. 1 and 2, the two pressure chambers of each consumer 2, 4 are connected to the tank 24. The load F acting on the load 2 is supported leak-free by the lowering brake valve 72, 74 designed as a seat valve. In this case, the load F can be designed as a pulling or pushing load. The secondary pressure limiting valves 100, 102 ensure that a maximum pressure in the lines 64, 66 can not be exceeded.

For a better understanding of the invention, some load cases are explained.

It is first assumed that on the cylinder 2, a pulling load F attacks and that this is to be extended as shown in Figure 3 (movement to the right). This extension should be at maximum speed (rapid traverse). For this purpose, the two directional valves 68, 70 are adjusted in the direction of the position shown in Figure 3, in which a regeneration takes place. That is, the consumer 2 is controlled via a differential circuit, in which both the annular space 14 and the soil-side pressure chamber 10 are connected to the pump 22. For this purpose, the directional control valves via the two proportional magnets 80, 82 from the neutral position (FIG. 2) shifted to the left, so that both pressure ports P of the directional control valve section 18 with the connecting channels 76, 78 are connected. The pressure medium is conveyed by the pump 22 via the pressure port P, the directional control valve 68, the connecting line 76, the bypass passage 96, the check valve 100 and the supply line 64 into the enlarging bottom-side pressure chamber 10. The pressure medium displaced out of the annular space 14 flows via the return line 66 and the counterbalancing valve 74, which is completely opened by the pressure in the connecting channel 76, the connecting channel 78 and the directional control valve 70 to the inlet line 56 and from there into the pump line 38, so that the pressure medium volume flow passing through the consumer is added to the funded by the pump 22 pressure medium flow.

In the bottom-side pressure chamber 10 while a pressure is applied, depending on the slider setting between the maximum pump pressure (for example, 250 bar) and 0 bar (slide in neutral position). Assuming that the pressure in the annular space 14 is about 250 bar (slide of the directional control valve 70 completely, pump set to 250 bar) and that the pulling load corresponds to a pressure of 50 bar, then a pressure should be set in the bottom pressure chamber 10 , which is the difference of the pressure in the annulus 14 minus the load divided by the area ratio of the differential cylinder (for example 2), so that at 250 bar in the annulus 14 and a load of 50 bar, a pressure of about 100 bar in the pressure chamber 10 results.

When the load is pressing, the function is corresponding, wherein the pressure in the flow-side supply line 64 is limited by the pressure limiting function of the lowering brake valve 72.

During regeneration, the consumer is moved at maximum speed, but the force applied by the consumer is comparatively low, since the effective effective area of the consumer corresponds to the piston rod area. To retrieve the maximum power of the load 2, the control arrangement of regeneration is switched to the normal operation shown in Figure 4 by the directional control valve 70 is adjusted in the direction of its Ne.utralposition so that the pressure medium from the annular space 14 via the return line 66, the controlled lowering brake valve 74, the connecting channel 78 and the directional control valve 70 and the drain line 60 to the tank 24th flows out. In pulling load (Figure 4) cavitations in the region of the supply line 64 are reliably prevented by the lowering brake valve 74, as this prevents the clamping of the consumer 2 uncontrolled, too fast extension of the load 2 due to the pulling load. The maximum pressure in the return line 66 is limited by the secondary pressure limiting valve 102. The pressure in the pressure medium flow is in turn determined by the opening cross section set by the slide of the directional control valve 68 and is thus between 0 bar and the maximum pump pressure (for example 250 bar).

When the load is under load and when the cylinder 2 extends (FIG. 4), a pressure in the bottom-side pressure chamber 10, which lies between the load pressure and the maximum pump pressure, arises as a function of the slide position of the directional valve 68 and the control of the variable-displacement pump 22 ). The counter-sunk lowering valve 74 is completely opened by the pressure in the inlet (tapped via the pilot line 94), so that the pressure medium can flow out of the annular space 14 to the tank 24. In this load case, no regeneration operation is provided and cavitations are not to be feared.

When the cylinder and pulling or pushing load, the directional control valve section 18 is switched to the position shown in Figure 5, in which the directional control valve 68 aufsteuert the pressure medium connection to the tank 24 and via the directional control valve 70 pressure medium from the pump 22 is conveyed into the annular space 14. The pressure in the inlet to the annular space 14 then depends on the load, the opening cross section of the directional control valve 70 and the set pump pressure. The pressure medium is conveyed via the bypass passage 98 and the opening nonreturn valve 102 and via the return line 66 into the annular space 14 and flows out of the decreasing pressure chamber 10 via the feed line 64 and the lowering brake valve 72 opened by the pressure in the inlet (connecting channel 78) as well as adjusted in the direction of its neutral position valve 68 and the drain line 62 to the tank 24 from. The pressure level in the process is limited by the secondary pressure limiting valve 100. Depending on the direction of the load, the pressure level in the inlet is between the maximum pump pressure and 0 bar (pushing load, minimum retraction speed). Based on Figure 3, a control concept is explained, which ensures the function of the system according to the invention, even at high pressure medium flow rates.

As explained above, the secondary pressure relief valves 100, 102 are relatively simple in design with a small nominal diameter. In order to prevent these from responding to a relatively large pressure medium volume flow in the flow and corresponding increase in pressure in the return, this high pressure medium flow is inventively limited.

FIG. 3 shows the left-hand part of the circuit according to FIG. 2 with the directional control valve 68, the secondary-pressure limiting valve 100, the variable-displacement pump 22 with a pump regulator 112 for setting the pump pivoting angle. The basically identical area with the directional control valve 74 and the associated secondary pressure limiting valve 102 and the lowering brake valves 72, 74 are omitted for the sake of simplicity.

In this solution, a pressure transducer 114 is provided in the pump line 38 (or the supply line 58), the signal of which is evaluated by a microprocessor 116 of the control unit 6. The signal of the pressure transducer 114 is compared via a signal line 118 via a comparator 120 with a signal corresponding to the set at the associated secondary pressure relief valve 100 maximum pressure signal. If the pressure in the pump line 38 is greater than this maximum pressure, a set volume flow is calculated, in which the adjusting pressure in the pump line 38 is less than the maximum pressure set at the secondary pressure relief valve 100, 102. From this target pressure or desired pressure medium volume flow, an adjustment signal for the associated directional control valve 68, 70 is then determined via the directional control valve characteristic 126. The signal is delivered via a signal amplifier 127 and a signal line 128 to the directional control valve 68 in order to adjust the flow cross-section thereof so that the predetermined target pressure or desired pressure medium volume flow is established. In this way, the proper functioning of the respectively effective secondary pressure limiting valve 100, 102 is ensured. In the above-described embodiment, the flow-side directional control valves 68, 70 are adjusted - in principle it is also possible to adjust the pivot angle of the pump in order to reduce the system pressure acting on the respective secondary pressure relief valve 100, 102 system pressure.

Disclosed is a hydraulic control arrangement for supplying pressure medium at least one consumer with an electrically or electro-hydraulically adjustable valve device, via which a flow to the consumer with a pump and a return from the consumer with a tank is connectable. In return, a lowering brake valve is arranged, which according to the invention is associated with a secondary pressure limiting valve whose output is connected to the tank.

Claims

claims

1. Hydraulic control arrangement for supplying pressure medium at least one consumer (2, 4), with an electrically or electrohydraulically continuously adjustable valve means (18, 20) via which a flow to the consumer (2, 4) with a pump (22) and a return from Consumer (2, 4) with a tank (24) is connectable, wherein in the return a lowering brake valve (72, 74) is arranged, which is acted upon by the pressure in the flow in its open position and a Sekundärdruckbegren- zungsventil (100, 102) for Pressure limitation of the pressure in the return line is connected in parallel and that when a maximum pressure is exceeded, a pressure medium connection to the tank (24) opens.

2. Control arrangement according to claim 1, wherein the valve means (18, 20) in the respective sequence downstream of the lowering brake valve (72, 74) arranged, continuously adjustable directional control valve (68, 70) with two switching positions, of which an open neutral position, wherein the secondary pressure limiting valve (100, 102) is also connected in parallel to the directional control valve (68, 70).

3. Control arrangement according to claim 1 or 2, wherein in the neutral position of a directional control valve (68, 70) a pressure medium connection to the tank (24) is open.

4. Control arrangement according to one of the preceding claims, wherein in the flow and in the return in each case a lowering brake valve (72, 74) and a directional control valve (68, 70) with parallel-connected secondary pressure relief valve (100, 102) is arranged, wherein the flow-side secondary pressure limiting valve (100, 102) is acted upon by the pressure in the return in the direction of its open position.

5. Control arrangement according to claim 4, wherein the pressure in the flow or in the return between the lowering brake valve (72, 74) and the directional control valve (68, 70) is tapped.

6. Control arrangement according to one of the preceding claims, wherein the lowering brake valve (72, 74) has a non-return position in which a pressure medium Flow to the consumer is possible and is adjustable from this direction in the direction of an open position.

7. Control arrangement according to one of the preceding claims, with a control unit (6) via which both directional control valves (68, 70) are simultaneously adjustable to a position in which both consumer pressure chambers (10, 14, 12, 16) with the pump (22 ) are connected.

8. Control arrangement according to one of the preceding claims, wherein via a control unit (6), a pressure or a pressure medium flow in the flow in response to the secondary pressure limiting valve (100, 102) set maximum pressure is adjustable.

9. Control arrangement according to claim 8, comprising a pressure sensor (114) for detecting the pump pressure and a comparison member (120) for comparing a signal corresponding to the pump pressure with the secondary pressure limiting valve (100, 102) set maximum pressure signal and with a control signal generator (127 , 128) for adjusting the directional valve (68, 70) or the pump (22) such that the pressure in the flow is less than the maximum pressure.

10. Control arrangement according to one of the preceding claims, wherein a valve body of the lowering brake valve (72, 74) via a spring (84, 86) is biased in a closed position, the spring chamber is relieved to the atmosphere.

11. Control arrangement according to one of the preceding claims, wherein the pump (22) is electrically or electro-hydraulically adjustable and the pump pressure via a control loop with a pump regulator (112) is adjustable.