Hydraulic system of an agricultural or construction vehicle

Abstract

Hydraulic system (1) of a vehicle usable in agriculture or construction for supplying pressure medium to at least one consumer (7) assigned to a working hydraulic circuit (6), which consumer is controllable via at least one switching valve (5), and to a hydrostatic steering system which is arranged within a hydraulic steering circuit (13) and has a steering valve (14), wherein pressure medium can be conveyed both into the steering circuit (13) and into the working hydraulic circuit (6) via a primary pump (3) designed as a variable displacement pump, characterized by a control device (23) via which a feed pump (18) can be switched on to supply the steering circuit when the volume flow of the primary pump (3) reaches a saturation state, wherein the hydraulic system (1) is designed as a load-sensing system, wherein a delivery volume of the primary pump (3) is dependent on a load pressure (p LS) of the hydraulic consumers of the working hydraulic circuit (6) and the hydraulic steering system, wherein a pump line (19) of the feed pump (18) is connectable via a first pressure compensator (20) to a main line (12) leading to the steering valve (14), wherein the first pressure compensator (20) is actuated via a differential pressure between a supply pressure of the steering valve (14) and a load pressure determined via a hydraulic load signal line (30, 31) on the steering valve (14).

Description

[0001] The invention relates to a hydraulic system of a vehicle usable in agriculture or construction for supplying pressure medium to at least one consumer assigned to a working hydraulic circuit, which consumer can be controlled via at least one switching valve, and to a hydrostatic steering system which is arranged within a hydraulic steering circuit and has a steering valve, wherein pressure medium can be conveyed both into the steering circuit and into the working hydraulic circuit via a primary pump designed as a variable displacement pump.

[0002] In the past, a corresponding hydraulic system in an agricultural or construction vehicle, which includes both working hydraulics and steering hydraulics, was usually designed as an open-center system. A fixed-displacement pump always delivers a constant flow rate at its maximum power consumption, even when none of the hydraulic consumers is being supplied with hydraulic power. The result is high power loss and correspondingly significant heating of the pressure medium. Therefore, closed-center systems with variable-displacement hydraulic pumps are now mostly used, delivering only the flow rate required.

[0003] Components of the working hydraulics can include, for example, a rear and, if applicable, a front power lift, a hydrostatic drive, or attachments that are supplied with pressure fluid from the vehicle via remote connections. It is important to ensure that the vehicle's hydrostatic steering system is always supplied with sufficient flow and pressure to ensure that the vehicle can operate with functional steering in all driving situations.

[0004] A hydraulic system of the type specified in the preamble of patent claim 1 is known from DE 3 513 452 A1. In this system, a central control pump delivers a pressure medium flow into two line sections of a main line, one of which leads to a steering hydraulic circuit and the other to a working hydraulic circuit referred to as the secondary consumer hydraulic circuit. Within the line branch leading to the working hydraulic circuit, a steering safety valve is arranged, which can open or block the pressure medium supply to the working hydraulic circuit. Furthermore, the hydraulic circuit, designed as a closed-center system, has a so-called load-sensing system, which consists of load signal lines connected to the steering hydraulic circuit and the working hydraulic circuit, and a pressure compensator assigned to the control pump.

[0005] DE 35 13 967 C2 also discloses a safety device for priority hydraulic consumers, in particular for the power steering of agricultural tractors and implements. The hydraulic circuit comprising the safety device includes a main pump, an auxiliary pump and a pressure compensator. The pressure compensator opens the valve assigned to the auxiliary pump towards the tank, so that the auxiliary pump is switched to pressureless circulation. If the pressure supplied by the main pump is no longer sufficiently high because the secondary consumers are drawing too much working fluid, or if a leak occurs in the secondary system, the pressure drop in the pump's pressure line switches the pressure compensator and the outlet to the tank is blocked, so that the primary consumer is now supplied by the auxiliary pump.

[0006] Further devices for supplying pressure medium to a primary main consumer circuit and a secondary consumer circuit are known from DE 41 08 915 C2 and EP 2 672 125 B1.

[0007] It is an object of the present invention to provide means within the hydraulic circuit by means of which safe operation of the hydrostatic steering can be ensured under all working and driving conditions of the vehicle used in agriculture or construction, namely even when a large amount of pressure medium has to be made available to the working hydraulics, which may possibly exceed the maximum delivery rate supplied by the primary pump.

[0008] This object is achieved by the characterizing features of the preamble of claim 1. Advantageous embodiments are set forth in the dependent claims, each of which, taken individually or in combination, may constitute an aspect of the invention.

[0009] According to this, the hydraulic system should have a control device via which a feed pump can be connected to the hydraulic steering circuit. Such a connection of the feed pump to the steering circuit is established when the volume flow of the primary pump reaches a saturation state due to a large volume flow pumped into the working hydraulics, in which case the control device additionally separates the steering circuit from the working hydraulics circuit. A saturation state is a state of the hydraulic system in which the volume flow required by the working hydraulics circuit and the steering circuit is greater than the maximum deliverable volume flow of the adjustable primary pump.

[0010] Prioritizing the steering circuit ensures optimal steerability in all driving conditions. The additional flow delivered by the feed pump, which is fed into the steering circuit via the control unit, also ensures that the variable displacement pump now supplies the working hydraulic circuit exclusively, allowing the individual adjustment functions to be performed without delay and at the desired speed. Since the feed pump only delivers pressure fluid to the steering circuit when the primary pump is saturated, losses that would otherwise lead to overheating of the hydraulic system at unfavorable operating points can be minimized.

[0011] In contrast, according to DE 3 513 452 A1, both the steering circuit and the secondary consumer hydraulic circuit are supplied with pressure fluid exclusively via the variable-displacement pump. The electrically or hydraulically actuated steering safety valve is designed to prevent further oil loss in the event of an impending oil shortage, caused, for example, by a leak in the secondary consumer hydraulic circuit, by shutting off all secondary consumers. This is a safety circuit designed to ensure the operational reliability of the steering circuit under all conditions. However, shutting off all secondary consumers results in the temporary interruption of the functions of the vehicle's lifting devices or the hydraulic drive systems of an attached implement on a vehicle used for agricultural or construction purposes.Therefore, such a control system may be suitable as a safety circuit that only becomes active in the event of a sudden loss of pressure due to a leak in the hydraulic system. However, if the flow rate required by the hydraulic steering circuit and the working hydraulic circuit is greater than the maximum flow rate that can be delivered by the variable-displacement pump, the working hydraulics should never be interrupted.

[0012] In a further embodiment of the invention, the feed pump is designed as a fixed displacement pump. During normal operation of the hydraulic system, in which the primary pump is not saturated, this fixed displacement pump delivers a speed-dependent volume flow into the tank via the control device, whereby the pressure and thus the power consumption of the fixed displacement pump are only low. If, on the other hand, the control device determines that the required volume flow of the steering hydraulics and the working hydraulics is greater than the maximum deliverable volume flow of the variable displacement pump, so that the variable displacement pump is saturated, the path running from the pressure line of the primary pump to the steering hydraulic circuit is blocked by means of the control device and the steering hydraulic circuit is connected to the fixed displacement pump. The fixed displacement pump then supplies the steering circuit exclusively.

[0013] According to the invention, the hydraulic system is designed as a load-sensing system, wherein a delivery volume of the variable displacement pump is determined as a function of a load pressure p LS the hydraulic consumer of the working hydraulic circuit and the hydraulic steering. In this case, the saturation of the primary pump is detected by a differential pressure between a pump pressure p prevailing in a pressure line p and a load pressure p LS in a signal line falls below a certain threshold. The load pressure is determined at the steering valve and at least one switching valve of the working hydraulic circuit and transmitted as a load-sensing signal via the signal line to an adjustment device of the primary pump, so that the swivel angle of a primary pump designed as an axial piston pump can be changed accordingly.

[0014] The control device also includes a first pressure compensator. In this case, a pressure line of the feed pump can be connected via the first pressure compensator to a main line leading to the steering valve or to a tank line. The first pressure compensator is actuated by a differential pressure between a supply pressure of the steering valve and a load pressure determined via a hydraulic load signal line at the steering valve.

[0015] The first pressure compensator can be designed as a 3 / 2-way valve such that the pump line is connected to a tank line leading to the tank in a first switching position of the first pressure compensator and to the main line in its second switching position. In the first switching position of the first pressure compensator, the pressure medium delivered by the feed pump is thus fed to the tank. In addition, an oil cooler can be arranged within the pump line of the feed pump or within the tank line downstream of the first pressure compensator, so that the volume flow delivered by the fixed displacement pump is fed continuously or in phases to this cooling device so that the overall pressure medium temperature can be limited. In the second switching position of the first pressure compensator, designed as a 3 / 2-way valve, the fixed displacement pump feeds a volume flow into the steering circuit, which ensures the function of the steering hydraulics.

[0016] A connecting line branches off from the pressure line of the primary pump, in which a second pressure compensator is located. A section of this connecting line, located on the outlet side of the second pressure compensator, is connected to the main line leading to the steering valve. Thus, a hydraulic connection between the pressure line of the primary pump and the main line leading from the first pressure compensator to the steering valve can be established or blocked by means of the second pressure compensator.

[0017] In this context, the second pressure compensator is actuated by a differential pressure between a pump pressure of the primary pump and a load pressure, with the load pressure actuation being assisted by a compression spring. If the differential pressure between the pump pressure and the load pressure falls below a certain threshold, this indicates saturation of the variable displacement pump, and the second pressure compensator separates the steering hydraulic circuit from the pressure line of the primary pump, so that the primary pump only supplies the working hydraulic circuit. As a result, the differential pressure between the load pressure and the supply pressure of the steering hydraulics drops, so that the first pressure compensator is moved by the load pressure and a compression spring acting in the same direction into a position in which the feed pump is connected to the main line.

[0018] Consequently, if the primary pump is saturated, a sufficient pressure supply to the steering hydraulic circuit is ensured. Since the primary pump in this case supplies exclusively the working hydraulic circuit, all functions of the working hydraulics can be maintained. Preferably, the second pressure compensator should be designed as a 2 / 2-way valve that opens the connecting line in a first switching position and closes it in a second switching position. A corresponding control spool of this 2 / 2-way valve is actuated at one end by the pump pressure p supplied by the primary pump. p and on its other end face by the load pressure p LS and additionally acted upon by the compression spring.

[0019] Furthermore, it is provided that a hydraulic load signal line has a power branch leading to the second pressure compensator, in which an orifice and a pressure relief valve are arranged. This line branch can be connected via a shuttle valve either to at least one switching valve of the working hydraulics or to the steering valve of the steering hydraulic circuit. Furthermore, a branching signal line leads from this line branch, in an area between the shuttle valve and the orifice, to an adjustment device of the primary pump. Downstream of the orifice, a control line is connected to the line branch, which, as already explained, actuates the second pressure compensator together with the compression spring. The pressure relief valve is also connected to the line branch in this area.

[0020] As already explained, the saturation of the variable displacement pump should be detected by the second pressure compensator, where in this case the differential pressure between the pump pressure p p and the load pressure p LS falls below a certain threshold. The second pressure compensator then separates the steering hydraulic circuit from the working hydraulic circuit supplied by the primary pump, and then connects the steering hydraulic circuit to the feed pump via the first pressure compensator.

[0021] If, on the other hand, the pressure in the primary pump is cut off when the maximum load pressure in the hydraulic system is exceeded because the limit system pressure would otherwise be exceeded with increasing working resistance, the overall result would be that the differential pressure between the load pressure and the pressure in the connecting line would also collapse. This would lead to the previously explained separation of the steering hydraulic circuit from the primary pump and the working hydraulic circuit and the feeding of pressure medium into the steering hydraulic circuit via the feed pump. However, it would be disadvantageous to switch on the feed pump in this case, as this would impair the hydraulic efficiency of the hydraulic system. The previously explained combination of the orifice and the pressure relief valve can be used to detect the pressure cut-off load case, although in this case the second pressure compensator does not separate the primary pump from the steering.

[0022] At a maximum load pressure, which causes pressure cutoff, the pressure relief valve opens, thus relieving the control pressure on the spring side of the second pressure compensator. This ensures that the second pressure compensator remains in its open position, thus keeping the steering hydraulic system connected to the primary pump. Furthermore, the orifice plate ensures that the pressure drop caused by the pressure relief valve does not lead to a corresponding pressure drop in the signal line connected to the primary pump's adjustment device, but rather that the maximum load pressure continues to be reported to the signal line.

[0023] Furthermore, a first check valve is to be arranged in the pressure line between the feed pump and a connection of a connecting line, which blocks the flow of pressure medium towards the first pressure compensator. Furthermore, a control line that supplies the first pressure compensator with the supply pressure is to be connected to a connecting line, with a second check valve being arranged between this connection and a second pressure compensator, which blocks the flow of pressure medium towards the second pressure compensator. The first check valve prevents this pressure medium from being directed towards the first pressure compensator during the normal operating state of the hydraulic system, in which the primary pump also supplies the steering hydraulic circuit with a volume flow.The second check valve is in its blocking position when the feed pump supplies pressure medium into the steering hydraulic circuit and prevents this pressure medium from flowing towards the second pressure compensator.

[0024] The invention is not limited to the specified combination of features of independent claim 1 with the dependent claims. Furthermore, possibilities arise for combining individual features, provided they emerge from the claims, the advantages related to the claims, the following description of the exemplary embodiment, or at least from the drawings. The reference of the claims to the drawings by the corresponding use of reference symbols is not intended to limit the scope of protection of the claims.

[0025] For further explanation of the invention, reference is made to the drawing, which shows a simplified embodiment. Shown are: Fig. 1 a hydraulic diagram of a hydraulic system according to the invention, which is provided for a vehicle which can be used in agriculture or construction and which, as a closed-center system, has a working hydraulic system and a steering hydraulic system, wherein a control device is in a position in which a primary pump supplies both a working hydraulic system and a steering hydraulic system with pressure medium and Fig. 2 the hydraulic system from the Fig. 1, wherein the control device is in a position in which the primary pump supplies the working hydraulics and a feed pump supplies the steering hydraulics with pressure medium.

[0026] In the Fig. 1 and Fig. 2, 1 designates a hydraulic system that is intended, for example, for an agricultural tractor or an agricultural system vehicle. This hydraulic system 1 is designed as a closed-center system in which pressure medium is pumped from a tank 2 via a primary pump 3, which is preferably designed as an axial piston unit according to the bent-axis principle, into a pressure line 4. A schematically illustrated switching valve 5 of a working hydraulic circuit 6 is connected to this pressure line 4. This switching valve 5 can, for example, be designed as an electromagnetically actuated 4 / 4-way valve and serves to actuate a double-acting hydraulic cylinder 7, which can, for example, be part of a lifting device of a front or rear power lift of the tractor. For this purpose, the switching valve 5 is connected on the output side to the lifting cylinder 7 via working lines 8 and 9.

[0027] In addition, a connecting line 10 branches off from the pressure line 4, in which a second pressure compensator 11 is arranged. This second pressure compensator 11 is designed as a 2 / 2-way valve and is located in the illustration according to the Fig. 1 in its flow position. The pressure medium delivered by the primary pump 3 is thus conveyed via this connecting line 10 into a main line 12, which leads to a steering valve 14 arranged in a hydraulic steering circuit 13. This steering valve 14 is actuated via a steering wheel (not shown in detail) of the vehicle, so that the pressure medium is selectively supplied to one of the two pressure chambers of a steering cylinder 17 via working lines 15 and 16.

[0028] Furthermore, the hydraulic system 1 has a feed pump 18, which pumps pressure medium from the tank 2 via a pump line 19, which is connected to a first pressure compensator 20. This first pressure compensator 20 is designed as a 3 / 2-way valve and, in a first switching position, connects the pump line 19 to the tank 2 via a tank line 21 and an oil cooler 22. Alternatively, the oil cooler 22 can also be arranged within the pump line 19. The first pressure compensator 20 and the second pressure compensator 11 together form a control device 23 according to the invention.

[0029] The hydraulic system 1 has a load-sensing system, which has a signal line 25 connected to an actuating device 24 of the primary pump 3. This actuating device 24 can include an adjusting cylinder (not shown in detail), an additional pressure compensator, and a pressure regulator. The load-sensing system ensures that the primary pump 3 only supplies the switching valve 5 and the steering valve 14 with an appropriate amount of pressure fluid when the corresponding hydraulic power is required. Consequently, this system regulates the flow rate and pressure according to demand. The load pressure in the signal line 25 increases when the operator of the agricultural vehicle calls up one of its hydraulic functions.

[0030] As can be seen from the Fig. 1 and Fig. 2, the signal line 25 is connected to a line branch 26, which is connected on the one hand to a pressure relief valve 27 and on the other hand to a shuttle valve 28. From the shuttle valve 28, a first load signal line 29 leads to the switching valve 5 and a second load signal line 30 to the steering valve 14. The second load signal line 30 has a branch 31, which is connected as a control line to the front of the first pressure compensator 20, wherein this pressurization of the first pressure compensator 20 is supported by a compression spring 32. At its opposite front, the first pressure compensator 20 is pressurized with the pressure of the connecting line 10 via a control line 33. Within the main line 12, between the second pressure compensator 11 and the inlet of the connecting line 10, a check valve 34 is arranged, which prevents a flow of the pressure medium from the connecting line 10 in the direction of the second pressure compensator 11.Another check valve 35 blocks the flow of pressure medium from the main line towards the second pressure compensator 11.

[0031] The second pressure compensator 11 is subjected to a pressure from line branch 26 at a first end face via a control line 36 and a compression spring 37, while a pressure from the connecting line 10 acts on an opposite end face of the first pressure compensator 11 via a control line 38. The control line 36 is connected to the line branch 26 of the signal line 25 between the pressure relief valve 27 and an orifice 39.

[0032] In the Fig. 1 shows normal operation of the hydraulic system 1, in which the volume flow requirement of the primary pump 3 is lower than its maximum output volume flow. In this case, the primary pump 3 supplies the hydraulic steering circuit 13 and the working hydraulic circuit 6. The pressure compensators 11 and 20 are in their Fig. 1. The first pressure compensator 20 directs the volume flow of the feed pump 18 via the oil cooler 22 into the tank 2. As a result, the pressure and thus the power consumption of the feed pump 18 are low. The hydraulic steering circuit 13 is supplied with pressure medium by means of the primary pump 3, which, via the pressure line 4, pumps pressure medium both into the working hydraulic circuit 6 and the open second pressure compensator 11, i.e., via the connecting line 10 and the main line 12 into the hydraulic steering circuit 13.

[0033] If the volume flow required by the hydraulic steering circuit 13 and the working hydraulic circuit 6 is greater than the maximum output volume flow of the primary pump 3, saturation of the primary pump 3 occurs. In this case, the second pressure compensator 11 is controlled by the load pressure in such a way that it shuts off the connecting line 10, so that the entire volume flow of the primary pump 3 is available to the switching valve 5 and thus to the working hydraulic circuit 6. In this case, the second pressure compensator 11 is actuated via branch 31 of the second load signal line 30 in such a way that it establishes a flow position from the pump line 19 to the main line 12.

[0034] Accordingly, the hydraulic steering circuit 13 is supplied by the feed pump 18, so that the feed pump 18 supports the primary pump 3 in this load case. The saturation of the primary pump 3 is detected by the second pressure compensator 11 when the differential pressure between the pressure line 4, i.e., the pump pressure, and the load pressure in the line branch 26 of the signal line 25, falls below a certain threshold. If this threshold is exceeded, the second pressure compensator 11, as already explained, disconnects the hydraulic steering circuit 13 from the working hydraulic circuit 6.

[0035] If the hydraulic steering circuit 13 is no longer supplied by the primary pump 3, the differential pressure between the supply pressure of the hydraulic steering circuit 13, i.e. the pressure in the connecting line 10, and the load pressure, i.e. the pressure in the branch 31 of the second load signal line 30, also falls. This leads to the displacement of the first pressure compensator 20 into its position in which it connects the pump line 19 to the main line 12.

[0036] The throttle 38 and the pressure relief valve 27 prevent the feed pump 18 from being switched on in the event of a pressure cutoff. In this case, the primary pump 3 should continue to supply the hydraulic steering circuit 13 with pressure fluid, since the primary pump 3 can deliver a sufficient volume flow and switching on the feed pump 18 would result in excessive losses. Since the differential pressure between the load pressure and the steering pressure also collapses at maximum load pressure and the resulting pressure cutoff of the primary pump 3, this load case must be detected by the control device 23.

[0037] The combination of orifice 39 and pressure relief valve 27 detects the pressure cut-off load case, so that the second pressure compensator 11 does not isolate the primary pump 3 from the hydraulic steering circuit 13. At the maximum load pressure, the pressure relief valve 27 opens and relieves the pressure in the control line 36, i.e., on the front side of the second pressure compensator 11, on which the compression spring 32 also acts. As a result, the second pressure compensator 11 remains in its open position, so that the hydraulic steering circuit 13 is connected to the primary pump 3. The orifice 39 ensures that the pressure drop caused in the line branch 26 by the pressure relief valve 27 is not transmitted to the signal line 25, thus relieving the pressure there, because otherwise the load signal pressure in the signal line 25 would be negatively affected, which would lead to an undesired adjustment of the primary pump 3 via the actuating device 24. Reference symbol 1 hydraulic system 2 tanks 3 Primary pump 4 pressure line 5 switching valve 6 Working hydraulic circuit 7 double-acting hydraulic cylinders 8 Work management 9 Work management 10 connecting line 11 second pressure compensator 12 Main line 13 hydraulic steering circuit 14 Steering valve 15 Work management 16 Work management 17 steering cylinders 18 Feed pump 19 Pump line 20 first pressure balance 21 Tank line 22 oil coolers 23 Control device 24 Actuating device 25 Signal line 26 line branch 27 Pressure relief valve 28 shuttle valve 29 first load signal line 30 second load signal line 31 branch of 30 32 compression spring 33 Control line 34 Check valve 35 Check valve 36 Control line 37 compression spring 38 Control line 39 aperture

Claims

[1] Hydraulic system (1) of a vehicle used in agriculture or construction for supplying pressure medium to at least one consumer (7) assigned to a working hydraulic circuit (6), which consumer is controllable via at least one switching valve (5), and to a hydrostatic steering system arranged within a hydraulic steering circuit (13) and having a steering valve (14), wherein pressure medium can be conveyed both into the steering circuit (13) and into the working hydraulic circuit (6) via a primary pump (3) designed as a variable displacement pump, characterized by a control device (23) via which a feed pump (18) can be switched on to supply the steering circuit when the volume flow of the primary pump (3) reaches a saturation state, wherein the hydraulic system (1) is designed as a load-sensing system, wherein a delivery volume of the primary pump (3) is dependent on a load pressure (p LS) of the hydraulic consumers of the working hydraulic circuit (6) and the hydraulic steering system, wherein a pump line (19) of the feed pump (18) is connectable via a first pressure compensator (20) to a main line (12) leading to the steering valve (14), wherein the first pressure compensator (20) is actuated via a differential pressure between a supply pressure of the steering valve (14) and a load pressure determined via a hydraulic load signal line (30, 31) on the steering valve (14). [2] Hydraulic system according to claim 1, characterized by that the feed pump (18) can be connected to the hydraulic steering circuit (13) via the control device and the steering circuit (13) can be shut off from the working hydraulic circuit (6). [3] Hydraulic system according to claim 1, characterized by that the feed pump (18) is designed as a constant pump. [4] Hydraulic system according to claim 1, characterized bythat the first pressure compensator (20) is designed as a 3 / 2-way valve which connects the pump line (19) in a first switching position to a tank line (21) leading to the tank (2) and in a second switching position to the main line (12). [5] Hydraulic system according to claim 4, characterized by that an oil cooler (22) is arranged in the pump line (19) or the tank line (21). [6] Hydraulic system according to claim 1, characterized by that a pressure line (4) of the primary pump (3) is connected to the main line (12) via a connecting line (10), wherein a second pressure compensator (11) is arranged in the connecting line (10), via which a hydraulic connection between the pressure line (4) and the main line (12) can be established or shut off. [7] Hydraulic system according to claim 6, characterized bythat the second pressure compensator (11) is actuated via a differential pressure between a pump pressure of the primary pump (3) and a load pressure, wherein the load pressure actuation is supported by a compression spring (37). [8] Hydraulic system according to claim 7, characterized by that the second pressure compensator (11) is designed as a 2 / 2-way valve which opens the connecting line (10) in a first switching position and blocks it in a second switching position. [9] Hydraulic system according to claim 7, characterized by that a signal line (25) has a line branch (26) leading to the second pressure compensator (11), in which an orifice plate (39) and a pressure relief valve (27) are arranged. [10] Hydraulic system according to claim 1, characterized bythat a first check valve (34) is arranged in the main line (12) between the feed pump (18) and a connection of a connecting line (10), which blocks a pressure medium flow in the direction of the first pressure compensator (20). [11] Hydraulic system according to claim 1, characterized by that a control line (33) applying the supply pressure to the first pressure compensator (20) is connected to a connecting line (10). [12] Hydraulic system according to claim 11, characterized by that between this connection and a second pressure compensator (11) a second check valve (35) is arranged, which blocks a pressure medium flow in the direction of the second pressure compensator.

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