GB2499111A

GB2499111A - A hydraulic control arrangement

Info

Publication number: GB2499111A
Application number: GB201301410A
Authority: GB
Inventors: Vincenzo Domenico Bollero
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2012-02-01
Filing date: 2013-01-25
Publication date: 2013-08-07
Anticipated expiration: 2033-01-25
Also published as: JP2013160382A; CN103291673A; GB2499111B; DE102012001874A1; CN103291673B; GB201301410D0

Abstract

A hydraulic control arrangement, which serves to supply pressure medium to at least two hydraulic consumers via a common pump 4, is provided. The pump 4 has an integral pump regulator. The control arrangement has at least two variable metering orifices 8a, 8b; 108a, 108b of which a first is disposed between a feed line 6; 106, which goes out from the pump 4, and the first consumer, and a second is disposed between the feed line 6; 106 and the second consumer. Furthermore, at least two pressure balances 12a, 12b; 112a, 112b are provided, of which the first is connected in series after the first metering orifice 8a; 108a and the second is connected in series after the second metering orifice 8b; 108b. A respective regulating piston of the pressure balances 12a, 12b; 112a, 112b can be acted upon, on a front side, by the pressure after the respective metering orifice 8a, 8b; 108a, 108b, in the opening direction, and by a highest load pressure of the consumers that is present in a rear control chamber, or by a pressure that is derived therefrom, in the closing direction, according to the principle of load-independent flow distribution (LIFD), via a common load indicating line 14, 18; 114, 118. The common load indicating line 14, 18; 114, 118 can be acted upon by pump pressure - instead of being acted upon by the highest load pressure of the consumers - via a safety valve 2; 102; 202, or emergency stop valve.

Description

Hydraulic control arrangement

Description

5 The invention relates to a control arrangement, by means of which at least two hydraulic consumers are supplied with pressure medium, and which has the features from the preamble of Claim 1.

Known from the prior art are hydraulic control arrangements that operate 10 according to the load-sensing principle, in which a variable-displacement pump is set in dependence on the highest load pressure of at least two actuated hydraulic consumers, respectively, such that the pump pressure is greater, by a defined pressure difference, than the highest load pressure. The pressure medium flows to the hydraulic consumers via variable metering 15 orifices, of which a first is disposed between a pump line, or feed line, which goes out from the variable-displacement pump, and a first hydraulic consumer, and the second is disposed between the feed line and the second hydraulic consumer. Owing to the pressure balances connected in series after the metering orifices, when a sufficient quantity of pressure medium has 20 been delivered, irrespective of the load pressures of the hydraulic consumers, there is a defined pressure difference across the metering orifices, such that the quantity of pressure medium flowing to a hydraulic consumer then depends merely on the aperture cross-section of the respective metering orifice. If a metering orifice is opened further, a greater quantity of pressure 25 medium must flow through it in order to produce the defined pressure difference.

The variable-displacement pump is adjusted in each case, such that it delivers the required quantity of pressure medium. The term demand flow 30 regulation is therefore also used.

l

The pressure balances connected in series after the metering orifices are acted upon, in the opening direction, by the pressure after the respective metering orifice and, in the closing direction, by a control pressure that is present in a rear control chamber and that usually corresponds to the highest 5 load pressure of all hydraulic consumers supplied by the same hydraulic pump. If, in the case of simultaneous actuation of a plurality of hydraulic consumers, the metering orifices are opened so widely that the quantity of pressure medium delivered by the hydraulic pump, when adjusted to the stop position, is less than the quantity of pressure medium required in total, the

10 quantities of pressure medium flowing to the individual hydraulic consumers are reduced proportionally, irrespective of the respective load pressure of the hydraulic consumers. The term control with load-independent flow distribution (LIFD control) is therefore used. Hydraulic consumers operated in such a manner are referred to in short as LIFD consumers. Since, in the

15 case of an LIFD control, the highest load pressure is also sensed and a feed pressure that is greater, by a defined pressure difference, than the highest load pressure is generated by the pressure-medium source, an LIFD control is a special case of a load-sensing control (LS control).

2 0 An LIFD control arrangement for a plurality of consumers of a mobile machine, which are supplied jointly by a pump having load-independent flow distribution, is disclosed in each of the publications DE 196 46 427 B4 and DE 10 2010 009 705 A1.

25 A disadvantage of such hydraulic LIFD control arrangements is that no emergency switch-off is provided. This is disadvantageous, in particular, if the LIFD control arrangement is used to operate a consumer of a telehandler (e.g. fork-lift truck, wheeled loader, mobile crane or working platform), by means of which persons could be lifted and crushed.

30

2

In contrast thereto, the invention is based on the object of for creating a hydraulic control arrangement providing increased safety for persons.

This object is achieved by a hydraulic control arrangement having the 5 features of Claim 1.

The hydraulic control arrangement according to the invention serves to supply pressure medium to at least two hydraulic consumers via a pump, which has a pump regulator, having at least two variable metering orifices, of 10 which a first is disposed between a feed line, which goes out from the pump, and the first consumer, and a second is disposed between the feed line and the second consumer. Furthermore, at least two pressure balances are provided, of which the first is connected in series after the first metering orifice and the second is connected in series after the second metering 15 orifice. A respective regulating piston of the pressure balances can be acted upon, on a front side, by the pressure after the respective metering orifice, in the opening direction, and by a highest load pressure of the consumers that is present in a rear control chamber, or by a pressure that is derived therefrom, in the closing direction, according to the LIFD principle, via a 20 common load indicating line. The common load indicating line can be acted upon by a higher pressure, via a safety valve, or emergency stop valve, instead of being acted upon by the highest load pressure of the consumers, and for this purpose is supplied with control oil directly from the pressure port of the pump. According to the invention, therefore, all directly connected 25 pressure balances are closed by means of a switch-over of the one safety valve, and all consumers assigned to the pressure balances are stopped (emergency stop).

In the case of a particularly preferred application, the hydraulic control 30 arrangement and the consumers supplied by it are disposed on a telehandler (e.g. fork-lift truck, wheeled loader, mobile crane or working platform).

3

Further advantageous designs of the invention are described in the dependent claims.

5 Preferably, the common load indicating line has a consuming-side portion, or a pump-side load indicating line, and a pressure-balance-side portion, or a pressure-balance-side load indicating line. Provided between the two line portions there is a non-return valve that closes from the pressure-balance-side load indicating line to the pump-side load indicating line. Therefore, in 10 the case of an emergency-stop switching operation of the control arrangement according to the invention, the pump pressure, or a pressure that is greater than pressure indicated to the pump, can build up rapidly in the pressure-balance-side load indicating line and close the pressure balances, while the pump-side load indicating line is not acted upon, or not affected, by 15 said pressure.

Also, in the case of a failure of an actuator of the safety valve (for example, in the case of an electric power failure in the case of an electromagnetic actuator), it is particularly safe if the pressure-balance-side load indicating 2 0 line is connected to the feed line via the safety valve when the latter is in its basic position, which is biased by a spring, and the emergency stop is thus initiated in the absence of electric current.

In the case of a preferred development of the control arrangement according 25 to the invention, pressure medium is supplied by the pump to a further consumer, prioritised for safety reasons, for example a hydraulic steering system. For this purpose, the control arrangement has a variable, prioritised metering orifice, disposed between the feed line and the prioritised consumer, and has a prioritised pressure balance that, with the metering orifice, 30 constitutes a flow regulator. Hydraulic steering systems are usually realized as so-called LS consumers, in which the pressure balance is acted upon in

4

the opening direction by the pressure downstream from the metering orifice and a spring, and is acted upon in the closing direction by the pressure upstream from the metering orifice.

5 It is particularly preferred in this case if a priority valve, realized as a continuously variable 3/3-way valve, is disposed in the feed line. The prioritised consumer is connected to a prioritised output port of the priority valve, via a prioritised portion of the feed line. The other consumers are connected to the priority valve at a further output port of the priority valve (via 10 another portion of the feed line). Via a prioritising load indicating line, the priority valve can be acted upon by control pressure, in such a way that the prioritised consumer is supplied in preference.

The prioritising load indicating line can be connected to the pump-side load 15 indicating line via a non-return valve, whose opening direction is aligned from the prioritising load indicating line to the pump-side load indicating line.

In the case of a particularly preferred development, individual pressure balances or all pressure balances are continuously variable 3/3-way valves. 20 When in a basic position that is biased in the closing direction by a respective spring, they shut off a respective flow line, via which the assigned consumer is connected to the assigned metering orifice.

In the case of a first variant of the pump, the latter is a variable-displacement 25 pump, the delivery volume of which c3n be set, via the pump regulator, in dependence on the highest load pressure of all consumers. As a result, the energy consumption of the pump is minimized.

In the case of a second variant of the pump, the latter is a constant-30 displacement pump, an input pressure balance being connected to the feed line supplied by the constant-displacement pump, in the bypass to a return

5

line, as a pump regulator, the valve body of which input pressure balance is acted upon, in the closing direction, by the highest load pressure of all consumers and a spring and, in the opening direction, is acted upon by the pump pressure. As a result, the resource requirement of the pump in respect 5 of equipment is minimized.

In the case of a first variant of a safety valve, the latter is a 4/2 switching valve which, when in the basic position, or emergency stop position, biased by the spring, connects the pump-side load indicating line to the pump 10 regulator and, when in a switching position, or in normal operation, connects the pressure-balance-side load indicating line to the pump regulator.

In the case of a second variant of the safety valve, the latter is a 4/2 switching valve that, when in the basic position, or emergency stop position, 15 biased by the spring, connects the pump-side load indicating line to a return line, via a throttle, and, when in a switching position, or in normal operation, connects the pressure-balance-side load indicating line to the return line, via the throttle.

20 Three differing exemplary embodiments of the invention are described in detail in the following with reference to the figures.

In the figures

Figure 1 shows a circuit diagram of a first exemplary embodiment of a 25 hydraulic control arrangement according to the invention,

Figure 2a shows a circuit diagram of a second exemplary embodiment of a hydraulic control arrangement according to the invention, and Figure 2b shows a safety valve according to a third exemplary embodiment of a hydraulic control arrangement according to the invention.

6

The hydraulic control arrangement according to Figure 1 has a valve arrangement 1 and a safety valve 2. Connected to a pump port P of the valve arrangement 1 there is a load-sensing, regulated variable-displacement pump 4, which, via a feed line 6, supplies various hydraulic consumers of a 5 telehandler that are not shown in greater detail. For this purpose, the valve arrangement 1 has four pairs of working ports A1, B1 - A4, B4, which can be supplied with pressure medium or shut off via respective 7/3-way valves 8a -8d. The 7/3-way valves 8a - 8d realize metering orifices, pressure balances 12a -12d being disposed in respective flow lines 10a - 10d. These pressure 10 balances are realized as 3/3-way valves, and provide for a load-independent flow distribution (LIFD control) between the four hydraulic consumers. For this purpose, the pressure balances 12a -12d are disposed downstream from the metering orifices 8a - 8d, and are acted upon in a closing direction via a common pressure-balance-side load indicating line 14. Likewise acting in the 15 closing direction is a respective spring of the pressure balances 12a - 12d. Opposing that, in the opening direction, a pressure acts on each of the pressure balances 12a - 12d, which pressure is tapped, between the metering orifice of the respective 7/3-way valve 8a - 8d and the respective pressure balance 12a - 12d, at the respective flow line 10a - 10d. The 2 0 pressure balance that is assigned to the hydraulic consumer of highest load pressure makes up an additional control edge and indicates the highest load pressure into the load indicating line 14.

The pressure-balance-side load indicating line 14 is connected, via a nozzle 25 and a non-return valve 16, to a pump-side load indicating line 18. Prevailing in the latter is the highest load pressure of all hydraulic consumers supplied simultaneously via the valve arrangement 1, and of further hydraulic consumers supplied with pressure medium by the pump. Between the nonreturn valve 16 and the nozzle, a pressure limiting valve and a flow regulating 30 valve, a parallel to each other, are connected to the load indicating line. The

7

outputs of the two valves are connected to a return line of the valve arrangements, which return line leads to a tank connection piece.

Besides the above-mentioned consumers, a further hydraulic consumer is 5 connected, as a prioritised consumer, to the valve arrangement 1 and, in the case of the first exemplary embodiment, is constituted by a hydraulic steering system, not shown in greater detail. For this purpose, the valve arrangement 1 has a prioritised consumer port S, which is connected, via a priority valve 22 and via a prioritised feed line 20, to the common feed line 6. The 10 prioritised feed line 20 thus branches off from the feed line 6, via the priority valve 22. The priority valve 22 is therefore connected on the input side to the common feed line 6 and, on the output side, branches, on the one hand, into the prioritised feed line 20 and, on the other hand, into the feed line 6 of the other consumers. The load pressure of the steering system that is present at 15 a load indicating port XS of the valve arrangement 1 serves to control the priority valve 22. The load pressure of the steering system is indicated to the priority valve 22 via a prioritising load indicating line 26, the load indicating line being connected to the feed line 20 via a nozzle and being decoupled from the feed line 20 in respect of pressure via this nozzle. The load 20 indicating line 26 is connected to the pump-side load indicating line 18 via a non-return valve 24, the non-return valve 24 opening from the prioritising load indicating line 26 to the pump-side load indicating line 18, and therefore indirectly also to the pressure-balance-side load indicating line 14. In this case, an increase in pressure at the load indicating port XS acts upon a valve 2 5 body of the priority valve 22 in such a way that an increasing proportion of the pressure medium delivered by the variable-displacement pump 4 is conveyed into the prioritised feed line 20 and therefore to the steering system. By means of this function, it is ensured that the steering system is always supplied with sufficient pressure medium via the variable-displacement pump 30 4, even if the load pressure of the other consumers is lower than the load pressure of the steering system.

8

According to the invention, the safety valve 2 of the first exemplary embodiment is realized as a 4/2-way valve. It has a basic position 0, shown in Figure 1, that is biased by a spring 28, and has a switching position a that 5 can be switched by an electromagnet 30. In the basic position 0, the emergency stop of the other consumers, i.e. all consumers other than the steering system, according to the invention, is effected. For this purpose, the pump pressure is transferred into the pressure-balance-side load indicating line 14 via a first control line 32, the safety valve 2 and via a second control 10 line 34.

As a result, the pressure balances 12a - 12d of the subordinate consumers are closed, such that the flow lines 10a - 10d are shut off and the consumers are stopped. A throttle 36 is disposed in the first control line 32. 15 Furthermore, in the basic position 0, the consumer-side load indicating line 18 is connected, via a control line 40, to a the pump regulator, not shown in greater detail, of the variable-displacement pump 4. Consequently, according to the load-sensing principle - known from the prior art - the variable-displacement pump 4 can be regulated in dependence on the steering 20 system.

When the first exemplary embodiment of the control arrangement according to the invention is in normal operation, the safety valve 2 is switched to the switching position a. In this switching position, the control line 40 is 25 connected simultaneously to the load indicating line 18 and to the second control line 34. As a result, the pressure prevailing in the consumer-side load indicating line 18 is transferred to the pump regulator via the non-return valve 16, the pressure-balance-side load indicating line 14, a port LS1, the second control line 34, the safety valve 2 and the control line 40. Consequently, 30 according to the load-sensing principle, the variable-displacement pump 4 can be regulated in dependence on the consumer of highest load, including

9

the steering system, the pressure balances 12a to 12d also being acted upon by the load pressure of the steering system, insofar as the steering-system pressure is the highest load pressure.

5 The hydraulic control arrangement according to Figure 2 has a valve arrangement 101 and a safety valve 102. Connected to a pump port P of the valve arrangement 101 is the variable-displacement pump 4 according to Figure 1, which supplies five differing hydraulic consumers, not shown in greater detail, via a feed line 106. For this purpose, the valve arrangement 10 101 has five pairs of consumer ports A1, B1 - A5, B5. Some consumer ports A1, A2, B2, A3, B3, A4, B4 are connected to a return line 146 via respective infeed valves 144a, 144b, 144c, 144d.

The working ports A1, B1 - A5, B5 can be alternately supplied with pressure 15 medium or shut off via respective 6/3-way valves 108a - 108e. Pressure balances 112a - 112e are disposed in respective flow lines 110a - 110e. The pressure balances 112a - 112e are acted upon in a closing direction via a common pressure-balance-side load indicating line 114. Likewise acting in the closing direction is a respective spring of the pressure balances 112a -20 112e. Again, the pressure balance that is assigned to the hydraulic consumer of highest load pressure makes up an additional control edge and indicates the highest load pressure into the load indicating line 114.

The pressure-balance-side load indicating line 114 is connected, via a non-25 return valve 116, to a pump-side load indicating line 118. Prevailing in the latter is the highest load pressure of all consumers supplied by the valve arrangement 101.

A prioritised steering system can be supplied via a prioritised consumer port 30 S of the valve arrangement 101. The port S is connected to the common flow line 106 via a priority valve 122 and via a prioritised flow line 120. The load

10

pressure of the steering system that is present at a prioritising load indicating port XS of the valve arrangement 101 serves to control the priority valve 122. The load pressure of the steering system is indicated to the priority valve 122 via a prioritising load indicating line 126. The prioritising load indicating line 5 126 is connected to the consumer-side load indicating line 118 via a nonreturn valve 124, the non-return valve 124 opening from the prioritising load indicating line 126 to the pump-side load indicating line 118, and therefore indirectly also to the pressure-balance-side load indicating line 114. The load indicating line 126 is connected to the feed line 120 via a nozzle a filter and is 10 decoupled from the feed line 120 in respect of pressure via the nozzle. The control oil for controlling the priority valve 122 is thus taken from the prioritising feed line, as in the case of the exemplary embodiment according to Figure 1.

15 The safety valve 102 of the second exemplary embodiment is realized as a 4/2-way valve. It has a basic position 0, shown in Figure 2a, that is biased by a spring 128, and has a switching position a that can be switched by an electromagnet 130. In the basic position 0, the emergency stop of the other consumers, i.e. all consumers other than the steering, according to the 20 invention, is effected. For this purpose, the pump pressure is transferred out of the feed line 106 'and into the pressure-balance-side load indicating line 114 via a first control line 132, which has a throttle 136, and via the safety valve 102 and via a second control line 134. As a result, the pressure balances 112a -112e of the subordinate consumers are closed, such that the 25 flow lines 110a - 110e are shut off and the consumers are stopped. Furthermore, in the basic position 0, the pump-side load indicating line 118 is connected, via a port LS, the safety valve 102 and via a control line 140, to the port MLS of the valve arrangement and, via the latter, to the pump regulator, not shown in greater detail, of the variable-displacement pump 4.

30

11

When the second exemplary embodiment of the control arrangement according to the invention is in normal operation, the safety valve 102 is switched to the switching position a. In this case, the first control line 132 is disconnected from the pump-side load indicating line 118 via the safety valve 5 102, such that the pump pressure present in the first control line 132 is not transferred into the pump-side load indicating line 118. Furthermore, the second control line 134 is connected to the control line 140. As a result, the pressure prevailing in the consumer-side load indicating line 118 is transferred to the pump regulator via the non-return valve 116, the pressure-10 balance-side load indicating line 114, the second control'line 134, the safety valve 102 and the control line 140.

In the case of the third exemplary embodiment, which contains only a small modification as compared with the exemplary embodiment according to 15 Figure 2b, and of which only the safety valve 202 that contains the modification and that replaces the safety valve 102 according to Figure 2a is represented. This safety valve is likewise realized as a 4/2-way valve. It has a basic position 0, shown in Figure 2b, that is biased by a spring 228, and has a switching position a that can be switched by an electromagnet 230. In 2 0 the basic position 0, the emergency stop of the other consumers, i.e. all consumers other than the steering system, according to the invention, is effected. Also provided is a non-return valve 238, by means of which, in normal operation, transfer of the pump pressure of the feed line 106 into the load indicating lines 118, 114 is prevented.

25

In variation from the three exemplary embodiments previously described, the variable-displacement pump 4 shown only in Figure 1 can be replaced by a constant-displacement pump. Then, according to the load-sensing principle, an input pressure balance 42, shown in Figure 1, which is controlled by the 30 pump pressure and by the pressure present in the pump-side load indicating line 18; 118, is required as a pump regulator on the flow line 6; 106.

12

There is disclosed a hydraulic control arrangement, which serves to supply pressure medium to at least two hydraulic consumers via a common pump. The pump has a pump regulator. The control arrangement has at least two 5 variable metering orifices, of which a first is disposed between a feed line, which goes out from the pump, and the first consumer, and a second is disposed between the feed line and the second consumer. Furthermore, at least two pressure balances are provided, of which the first is connected in series after the first metering orifice and the second is connected in series 10 after the second metering orifice. A respective regulating piston of the pressure balances can be acted upon, on a front side, by the pressure after the respective metering orifice, in the opening direction, and by a highest load pressure of the consumers that is present in a rear control chamber, or by a pressure that is derived therefrom, in the closing direction, according to the 15 principle of load-independent flow distribution (LIFD), via a common load indicating line. The common load indicating line can be acted upon by a higher pressure, via a safety valve, or emergency stop valve - instead of being acted upon by the highest load pressure of the consumers - and for this purpose is supplied with control oil from the pressure port of the pump. 2 0 Therefore, all directly connected pressure balances are closed by means of a switch-over of the one safety valve, and all consumers assigned to the pressure balances are stopped.

13

Claims

1. Hydraulic control arrangement for supplying pressure medium to at least two hydraulic consumers, having a pump (4), which has a pump 5 regulator, having at least two variable metering orifices (8a, 8b; 108a,

108b), of which a first is disposed between a feed line (6; 106), which goes out from the pump (4), and the first consumer, and a second is disposed between the feed line and the second consumer, and having at least two pressure balances (12a, 12b; 112a, 112b), of which the 10 first is connected in series after the first metering orifice (8a; 108a) and the second is connected in series after the second metering orifice (8b; 108b), and whose respective regulating piston can be acted upon by the pressure after the respective metering orifice (8a, 8b; 108a, 108b), in the opening direction, and by a highest load pressure of the. 15 consumers, in the closing direction, via a common load indicating line

(14, 18; 114, 118), characterized in that the common load indicating line (14, 18; 114, 118) can be acted upon by pump pressure, via a safety valve (2; 102; 202).

20

2. Hydraulic control arrangement according to any one of the preceding claims, the common load indicating line having a pump-side load indicating line (18; 118) and a pressure-balance-side load indicating line (14; 114), and a non-return valve (16; 116) that closes from the pressure-balance-side load indicating line (18; 118) to the pump-side 25 load indicating line (14; 114) being disposed therebetween.

3. Hydraulic control arrangement according to Claim 2, the pressure-balance-side load indicating line (14; 114) being connected to the feed line (6; 106) via the safety valve (2; 102; 202) when the latter is in its 30 basic position (0), which is biased by a spring (28; 128; 228).

14

Hydraulic control arrangement according to Claim 2 or 3, a further, prioritised consumer being able to be supplied by the pump (4), having a variable, prioritised metering orifice, disposed between the feed line (6; 106) and the prioritised consumer, and having a prioritised pressure balance, which is assigned to the prioritised metering orifice.

Control arrangement according to Claim 4, a priority valve (22; 122), realized as a continuously variable 3/3-way valve, being disposed in the feed line (6; 106), and the prioritised consumer being able to be supplied via the priority valve (22; 122) and via a prioritised feed line (20; 120), and the other consumers being able to be supplied via the priority valve (22; 122), and the preferred supply to the prioritised consumer being able to be produced as a result of the priority valve (22; 122) being acted upon by control pressure, via a prioritising load indicating line (26; 126) from the prioritised consumer.

Control arrangement according to any one of the preceding claims, at least one of the pressure balances (12a, 12b, 12c, 12d; 112a, 112b, 112c, 112d, 112e) having a continuously variable 3/3-way valve that, when in a basic position that is biased in the closing direction by a respective spring, shuts off a respective flow line (10a, 10b, 10c, 10d; 110a, 110b, 110c, 110d, 110e), via which the respective consumer is connected to the respective metering orifice (8a, 8b, 8c, 8d; 108a, 108b, 108c, 108d, 108e).

Control arrangement according to any one of the preceding claims, the pump being a variable-displacement pump (4), whose delivery volume can be set via a load-sensing regulating valve that, to increase the delivery rate, can be acted upon by the highest load pressure of all hydraulic consumers and a spring and, to reduce the delivery rate, can be acted upon by pump pressure.

8. Control arrangement according to any one of Claims 1 to 6, the pump being a constant-displacement pump, and there being connected between the feed line and a return line an input pressure balance (42)

5 whose valve body is acted upon, in the closing direction, by the highest load pressure of all hydraulic consumers and a spring and, in the opening direction, is acted upon by the pump pressure.

9. Control arrangement at least according to any one preceding claim, the 10 safety valve (2) being a 4/2 switching valve by means of which, when it is in the basic position (0), biased by the spring (28), the pump-side load indicating line (18) is connected to the pump regulator, and the pressure-balance-side load indicating line (14) being connected to the pump regulator by means of the safety valve (2) when it is in a is switching position (a).

10. Control arrangement at least according to any one preceding claim, the safety valve (102; 202) being a 4/2 switching valve by means of which, when it is in the basic position (0), biased by the spring (128; 228), the

20 pump-side load indicating line (118) is connected to a return line (146)

via a choke (148), and the pressure-balance-side load indicating line (114) being connected to the return line (146), via the choke (148), by means of the safety valve (102; 202) when it is in a switching position (a).

16