DE102015116761A1 - Hydraulic constant pressure system of a mobile work machine - Google Patents

Abstract

The invention relates to a hydraulic constant pressure system (1) for a mobile work machine which has at least two constant pressure levels (P 1; P N) with different pressure levels (P 1; P 2; P 3) from which at least one consumer drive (VA) is supplied with pressure medium. wherein a pump module (PUM) driven by a drive motor (AM), in particular an internal combustion engine, is provided which supplies the pressure medium to the at least two constant pressure levels (PH; PM; PN), wherein the constant pressure levels (PH; PM; PN) are each a supply line (LH; LM; LN), which are in communication with a pressure medium storage module (DM), wherein a valve device (VE) is provided for controlling each consumer drive (VA). The valve device (VE) of each consumer drive (VA) has a control valve (10) by means of which the direction of movement and the speed of movement of the consumer drive (VA) is controllable, wherein the control valve (10) to a supply line (11) for supplying pressure medium from to the supply lines (LH; LM; LN), to a discharge line (12) for discharging pressure medium into the supply lines (LH; LM; LN) and to consumer lines (13,14) connecting the control valve (10) to the consumer drive Connect (VA). A first selector valve (AV1) is provided which controls the connection of the feed line (11) of the control valve (10) to the supply lines (LH; LM; LN). A second selector valve (AV2) is provided which controls the connection of the drain line (12) of the control valve (10) to the supply lines (LH; LM; LN).

Description

The invention relates to a hydraulic constant pressure system for a mobile work machine, which has at least two constant pressure levels with different pressure levels from which at least one consumer drive is supplied with pressure medium, wherein one of a drive motor, in particular an internal combustion engine, driven pump module is provided, the at least two constant pressure levels supplied with pressure medium, wherein the constant pressure levels each have a supply line, which are in communication with a pressure medium storage module, wherein a valve device is provided for controlling each consumer drive.

Mobile machines, such as excavators, place high demands on the dynamic behavior of the consumer drives and at the same time on the energy efficiency of the hydraulic drive system.

Known hydraulic drive systems, for example a load-sensing drive system, of mobile working machines always call the power currently required by the consumer drives from the drive motor, as a rule an internal combustion engine. In addition, the storage and recovery of energy in a load-sensing drive system is complex. This has the consequence that in a load-sensing drive system, the drive motor must be constantly operated at a high speed in order to respond briefly to fluctuating power requirements of the consumer drives can. However, this means that the possible efficiency of the drive motor is reduced by about 25%. With load-sensing drive systems, there are already approaches to recover potential or kinetic energy from the movement of the consumer drives of the mobile working machine and to store them in a pressure medium store. However, due to the very fluctuating system pressure in load-sensing drive systems, use of the energy recovered and stored in a fluid reservoir is often inefficient.

Known hydraulic drive systems, for example a load-sensing drive system, thus have the following disadvantages.

All components of the hydraulic drive system from the drive motor to the consumer drives must be designed for maximum performance. During operation of the mobile working machine, the components of the hydraulic drive system operate in a part of the operating range that is inefficient for efficiency in large parts of the operating points. If an energy recovery takes place with a negative load on a consumer drive, this recovered energy can often only be inefficiently fed back into the drive system due to the variable system pressure in the load-sensing drive system.

It is already known to use a hydraulic constant pressure system with different pressure levels as a hydraulic drive system in mobile machines. Such a constant pressure system has at least two constant pressure levels with different pressure levels, from which at least one consumer drive of the drive system is supplied with pressure medium. A pump module, which is driven by a drive motor, for example an internal combustion engine, supplies the at least two constant pressure levels with pressure medium. The at least two constant pressure levels each have a supply line which is in communication with a pressure medium storage module.

In such a constant pressure system, which has at least two constant pressure levels with different pressure levels, the drive motor driving the pump module can be operated constantly in an energetically favorable and thus efficient operating point. The driven by the drive motor pump module is used to charge the accumulator module with pressure medium. When operating a consumer drive, the adaptation of the load pressure of the consumer to the accumulator pressure or the different storage pressures of the accumulator module by means of a corresponding valve device. In a generic constant pressure system is an essential feature of the constant operation of the drive motor in certain operating points. Either the accumulator module is loaded or the drive motor runs in a stand-by mode, for example, in the lower idle. Thus, since the drive motor can be operated in a stand-by mode at low speed, for example in the lower idle, when the accumulator module is loaded and operated to charge the pressure medium accumulator module in an energy-efficient and therefore efficient operating point, the drive motor will operate with one high efficiency. In addition, it is possible to provide a downsizing of the drive motor, since the corner power of the consumer drives is provided by the pressure medium storage module. In addition, the pressure medium storage module enables energy recovery.

Compared to a load-sensing drive system, a hydraulic constant pressure system with different pressure levels has the following advantages.

The drive motor and pump module can be designed for medium power. The drive motor and the pump module can be operated constantly in energetically favorable and therefore efficient operating points. In the case of a negative load on a consumer drive, energy can be returned to the pressure medium storage module and thus an energy recovery takes place. This energy is directly available again for the supply of consumer drives.

This results in an improvement in energy efficiency through energy recovery and better operating points of the drive motor and the pump module. The accumulator module makes it possible to provide higher performance in the short term.

A hydraulic constant pressure system with at least two different pressure levels thus has an improved overall efficiency of the hydraulic drive system compared to a load-sensing system.

In known constant pressure systems, the valve means, by means of which the adaptation of the load pressure of the consumer to the accumulator pressure or the various accumulator pressures of the accumulator module takes place, i. by means of which, depending on the load pressure of the consumer, the consumer is connected to the constant pressure system with the appropriate constant pressure level, designed as a digital circuit of valves.

This also for the reason that as linear drives, such as hydraulic cylinders, trained consumer drives are not variable, so that with a digital circuit of valves, the system pressure of the constant pressure system, i. the appropriate constant pressure level is adapted to the load pressure of the consumer.

Such a digital circuit of valves as a valve device has a plurality of electrically actuated switching valves, by means of which the inlet side and the outlet side of the consumer in dependence on the load pressure of the consumer to the supply lines of the constant pressure system can be connected. Here, a switching valve for the inlet side and another switching valve for the discharge side of the consumer is required at each consumer drive for each constant pressure level of the constant pressure system. Each switching valve has a blocking position and a flow position. In a constant pressure system with, for example, three different constant pressure levels, three switching valves for the inlet side and three switching valves for the outlet side are thus required at each consumer drive. In order to reduce the number of switching valves, it is already known, instead of electrically actuated switching valves, which are at the input or at the output respectively with only one supply line and thus a constant pressure level in conjunction to provide electrically actuated changeover valves, each at the input side Select pressure from two constant pressure levels and forward it to the inlet side of the consumer, or communicate with two constant pressure levels on the outlet side and connect the outlet side of the consumer to the corresponding constant pressure level. In a constant pressure system with, for example, three different constant pressure levels, a first changeover valve may be provided on the inlet side of a consumer drive, which selects the pressure in the first and second constant pressure levels on the input side and forwards the selected pressure to a first input of a second changeover valve at a second input is connected to the third constant pressure level and forwards the selected pressure to the inlet side of the consumer drive. On the discharge side of a consumer drive, a first changeover valve may be provided, which is connected on the input side to the discharge side of the consumer drive and is connected on the output side to the third constant pressure level and the first input of a second changeover valve, which is connected on the output side to the second and the first constant pressure level. In a constant pressure system with, for example, three different constant pressure levels, two changeover valves for the inlet side and two changeover valves for the outlet side are thus required at each consumer drive.

For controlling the switching valves or the switching valves, an electronic control device is provided which detects the current load pressure at each consumer by means of pressure sensors. Due to the large number of switching valves or changeover valves and the required pressure sensors on each consumer, such a digital circuit of valves as a valve device has a high number of components and thus a high construction cost. In addition, with a changing load pressure of the consumer during a movement of the consumer, which requires a connection of the consumer to another constant pressure level, switching transitions occur between the switching valves or the changeover valves.

The present invention has for its object to provide a constant pressure system of the type mentioned are available, which has a simple structure with low construction costs for the valve means for controlling the respective consumer drives.

This object is achieved in that the valve device each consumer drive has a control valve by means of which the direction of movement and the movement speed of the consumer drive is controllable, wherein the control valve to a supply line for supplying pressure medium from the supply lines to a drain line for the discharge of pressure medium in the supply lines and connected to consumer lines connecting the control valve to the consumer drive, wherein a first selector valve is provided which controls the connection of the feed line of the control valve with the supply lines, and a second selector valve is provided which communicates the connection of the drain line of the control valve with controls the supply lines. In the control valve device according to the invention, the control valve is used to specify the direction of movement and the speed of movement of the consumer drive and thus to control. The first selector valve serves to connect the supply line of the control valve to the supply line of the constant pressure level with the appropriate pressure level. Accordingly, the second selector valve serves to connect the drain line of the control valve to the supply line of the constant pressure level with the appropriate pressure level. Such a valve device, which has a control valve for each consumer drive, and in each case a selection valve for the supply line and the drain line of the control valve, has a simple construction with low construction costs compared to a digital circuit of valves of the prior art.

According to an advantageous embodiment of the invention, the first selection valve is designed as a supply pressure compensator, which is controlled by the pressure drop at an inlet-side measuring throttle of the control valve. With such a hydraulic, controlled by the pressure drop at an inlet side throttle of the control valve inlet pressure compensator, with the supply line of the control valve is connected to the supply line of the constant pressure level with the appropriate pressure level, there are special advantages, since the first selection valve for the supply line of the control valve purely operates hydraulically, so that no pressure sensors for detecting the load pressure of the consumer and no electronic control device for actuating the first selector valve are required. As a result, the construction cost of the valve device is further reduced.

The inlet pressure compensator is connected in accordance with an advantageous embodiment of the invention by means of branch lines to the supply lines of all constant pressure levels, wherein the inlet pressure compensator has a shut-off position in which the connections of the supply lines to the supply line are shut off, and one of the number of constant pressure levels corresponding number of control positions, wherein a first control position, the supply line is connected to the supply line of the lowest constant pressure level and in each further control position, the supply line is additionally connected to the supply line of the next higher constant pressure level. The inlet pressure compensator is thus connected on the input side to all constant pressure levels and connected on the output side to the supply line of the control valve. The inlet pressure compensator can thus be supplied with pressure medium by all constant pressure levels. With such a supply pressure compensator, it is possible in a simple manner to connect the supply line of the control valve with the constant pressure level with the appropriate constant pressure level.

Particular advantages arise when, according to a development of the invention, except for the branch line which connects the inlet pressure compensator with the highest constant pressure level, in all other branch lines in each case one in the direction of Zulaufdruckwaage opening check valve, in particular check valve is arranged. With such check valves is prevented in a simple manner that in the other control position of the supply pressure compensator, in which the inlet pressure compensator on the input side is connected to at least two supply lines of the constant pressure levels, pressure medium can flow from a constant pressure level with a higher pressure level in a constant pressure level with a lower pressure level ,

The inlet pressure compensator is advantageously acted upon by the pressure prevailing in the direction of the shut-off position upstream of the inlet-side measuring throttle of the control valve and in the direction of the control positions by the pressure prevailing downstream of the inlet-side measuring throttle of the control valve. As a result, it is achieved in a simple manner that the inlet pressure compensator is controlled by the pressure drop at the inlet-side measuring throttle of the control valve.

According to an advantageous development of the invention, the control valve detects the pressure downstream of the inlet-side measuring throttle of the control valve and reports the pressure downstream of the inlet-side measuring throttle to the inlet pressure compensator during an actuation. Upon actuation of the control valve can thus be detected in a simple manner, the pressure downstream of the upstream measuring throttle of the control valve and forwarded to the Zulaufdruckwage to their actuation.

Advantageously, the supply pressure compensator is acted upon by a default force in the direction of the control positions. The default force ensures that a defined Δp is applied via the inlet-side measuring throttle of the control valve.

The default force can be specified by a spring device according to an embodiment of the invention.

According to an advantageous embodiment of the invention, the supply line of the control valve is connected by means of a connecting line to a tank line of the constant pressure system, wherein in the connecting line in the direction of the inlet line opening check valve, in particular check valve, is arranged. With such a connecting line pressure medium from the tank line of the constant pressure system can be sucked into the supply line of the control valve in a simple manner.

According to an advantageous embodiment of the invention, the second selection valve is designed as a discharge pressure balance, which is controlled by the pressure drop at a downstream measuring throttle of the control valve. With such a hydraulic, controlled by the pressure drop at a downstream measuring throttle of the control valve discharge pressure compensator, with the drain line of the control valve is connected to the supply line of the constant pressure level with the appropriate pressure level, there are special advantages, since the second selector valve for the drain line of the control valve purely operates hydraulically, so that no pressure sensors for detecting the load pressure of the consumer and no electronic control device for actuating the second selector valve are required. As a result, the construction cost of the valve device is further reduced.

The discharge pressure compensator is connected according to an advantageous embodiment of the invention by means of branch lines to a tank line of the constant pressure system and up to the constant pressure level with the highest pressure level to the supply lines of all other constant pressure levels, wherein the discharge pressure compensator has a connection position in which the drain line to the tank line and the supply lines is connected, and having a number of constant pressure levels corresponding number of control positions, wherein in a first control position, the connection of the drain line to the connected Konstantdruckniveaus opened and the connection of the drain line to the tank line is shut off and in each additional control position in addition to the connection of the drain line the supply line of the next higher constant pressure level is shut off. The discharge pressure compensator is thus connected on the output side to the tank line and to the constant pressure level with the highest pressure level to all other constant pressure levels and connected on the input side to the drain line of the control valve. The discharge pressure compensator can thus feed pressure medium back into the tank line as well as the connected constant pressure levels. With such a discharge pressure balance, it is easily possible to connect the drain line of the control valve with the tank line or the constant pressure level with the appropriate constant pressure level.

Particular advantages arise when, according to a development of the invention, except for the branch line connecting the discharge pressure compensator with the tank line, in all other branch lines in each case one in the direction of the discharge pressure balance blocking check valve, in particular check valve is arranged. With such check valves is prevented in a simple manner that in the connection position and in those control position of the discharge pressure balance in which the discharge pressure compensator is connected at the output side with at least two supply lines of the constant pressure levels, pressure medium from a constant pressure level with a higher pressure level in a constant pressure level with a lower Can discharge pressure level.

The discharge pressure compensator is advantageously acted upon by the pressure prevailing upstream of the outlet-side measuring throttle of the control valve in the direction of the control positions and by the pressure prevailing downstream of the outlet-side measuring throttle of the control valve in the direction of the connecting position. As a result, it is achieved in a simple manner that the discharge pressure balance is controlled by the pressure drop at the outlet-side measuring throttle of the control valve.

According to an advantageous development of the invention, the control valve detects the pressure upstream of the outlet-side measuring throttle of the control valve and reports the pressure upstream of the outlet-side measuring throttle to the discharge pressure balance further. Upon actuation of the control valve can thus be detected in a simple manner, the pressure upstream of the outlet-side measuring throttle of the control valve and forwarded to the Ablaufdruckwage to their actuation.

Advantageously, the discharge pressure balance is acted upon by a default force in the direction of the connection position. The default force ensures that a defined Ap is applied via the outlet side throttle of the control valve.

The default force can be specified by a spring device according to an embodiment of the invention.

According to an advantageous embodiment of the invention, the drain line of the control valve connected by means of a connecting line to the supply line of the highest constant pressure level, wherein in the connecting line in the direction of a drain line blocking check valve, in particular check valve, is arranged. With such a connecting line pressure medium from the drain line of the control valve can be fed back into the supply line of the highest constant pressure level in a simple manner.

According to an advantageous embodiment of the invention, the discharge pressure compensator is provided with a locking device which locks the discharge pressure compensator in the first control position in a locking position and prevents actuation of the discharge pressure compensator in the connecting position. By locking the discharge pressure compensator in the first control position it is achieved that at least the pressure of the lowest constant pressure level is present in the discharge line. The pressure in the supply line is thereby increased and increased accordingly. With such a locking device for the discharge pressure balance thus a pressure upshift on the supply line can be achieved with the throttling losses can be reduced in the supply of the consumer drive with the pressure from one of the constant pressure levels in unfavorable operating points.

The locking device is formed according to an advantageous embodiment of the invention of a engageable with the discharge pressure compensator latching device. With a locking device, the drain pressure scale can be blocked in the first control position with low construction costs and prevents the discharge pressure compensator occupies the connection position.

The locking device can be actuated hydraulically or electrically between a locking position and a release position.

If the locking device is hydraulically actuated, there are particular advantages when a switching valve is provided by means of which in a first switching position, a control surface of the locking device to the tank line for actuating the locking device in the release position is relieved and in a second switching position with the control surface of the locking device a pressure source for actuating the locking device in the locking position is connectable. With such a switching valve, the locking device can be hydraulically operated in a simple manner between the locking position and the release position.

The pressure source is expediently formed by one of the constant pressure levels and the switching valve is connected by means of a connecting line to one of the supply lines. By the pressure from one of the constant pressure levels, which is passed by means of the switching valve to a control surface of the latching device, the latching device can be actuated in a simple manner.

The switching valve may be electrically operated. With particular advantage, the switching valve is actuated by a spring and the pressure in the supply line in the direction of the first switching position and by the pressure in the discharge line in the direction of the second switching position.

Conveniently, the switching valve is actuated by the pressure selected by means of the inlet pressure compensator and thus by the currently selected constant pressure level in the direction of the second switching position.

The switching valve is thus actuated hydraulically. From the switching valve thus the current pressure difference on the inlet pressure compensator can be detected and the locking device of the discharge pressure compensator are actuated in the locking position when the current pressure difference exceeds the value defined by the spring.

According to an advantageous development of the invention, an additional valve device is provided by means of which the default force at the inlet pressure compensator and / or the default force at the outlet pressure compensator is variable. With such an additional valve device can thus be achieved by changing the default force on the inlet pressure compensator and / or the default force on the discharge pressure balance a Δp control. With such a Δp control is prevented in a simple manner that in the case of a positive load on the consumer drive a Δp on the outlet side of the consumer drive and in the case of a negative load on the consumer drive a Δp on the inlet side of the consumer drive is adjusted. As a result, the losses of the constant pressure system according to the invention can be further reduced.

According to an advantageous embodiment of the invention, the additional valve device has a first control position in which the inlet pressure balance and the discharge pressure balance are active, a second control position in which the supply pressure balance is active and the discharge pressure balance is switched off, and a third control position in which the discharge pressure balance active and the inlet pressure compensator is switched off. In the first control position, in which the inlet pressure compensator and the outlet pressure compensator are active, it is achieved that a Δp is set both in the inlet side and in the outlet side of the consumer drive. As a result, a clamping of the consumer drive is achieved and achieved an improved dynamic behavior of the load drive during load changes. In the second control position If the supply pressure compensator is active and the discharge pressure compensator is switched off, it is prevented by switching off the discharge pressure compensator that, in the case of a positive load on the consumer drive, a Δp is adjusted on the discharge side of the consumer drive. In the third control position, the discharge pressure balance is active and the supply pressure compensator is switched off, so that it is prevented by switching off the supply pressure compensator that in the case of a negative load on the consumer drive a Δp is adjusted at the inlet side of the consumer drive.

The additional valve device generates this in the first control position on the inlet pressure compensator and the discharge pressure equal to a default force, increased in the second control position, the default force on the discharge pressure balance and reduced in the third control position, the default force on the inlet pressure compensator. By increasing the default force on the discharge pressure compensator, the discharge pressure compensator can be switched off in the second control position in a simple manner. By reducing the default force on the inlet pressure compensator, the inlet pressure compensator in the third control position can be switched off in a simple manner.

Advantageously, the additional valve device is actuated at a positive load on the consumer drive in the second switching position and actuated at a negative load on the consumer drive in the third switching position. In this way it is easily prevented that in the case of a positive load on the consumer drive a Δp on the outlet side of the consumer drive and in the case of a negative load on the consumer drive a Δp is adjusted at the inlet side of the consumer drive.

The default force on the supply pressure compensator is generated according to an advantageous embodiment of the invention by a pending on a control surface pressure signal and generates the default force at the discharge pressure balance of a pending on a control surface pressure signal.

The additional valve device connects advantageously in the first control position to the control surface of the inlet pressure compensator guided control line and guided to the control surface of the discharge pressure control line with a pilot line in which a default pressure is present, connects in the second control position, the control line of the supply pressure compensator with the pilot line and the Control line of the discharge pressure balance with one of the supply lines, and connects in the third control position, the control line of the inlet pressure compensator to the tank line and the control line of the discharge pressure balance with the pilot line connects. The preselected pressure in the pilot control line forms a Δp setpoint. In the first control position is thus in the control position of the supply pressure compensator and in the control position of the discharge pressure balance each of the default pressure, so that the supply pressure compensator and the discharge pressure balance are active and adjust a Δp. In the second control position is achieved by the admission of the control position of the supply pressure from the default pressure that the supply pressure compensator is active, and achieved by the action of the control position of the discharge pressure balance with one of the supply lines that the default force is increased at the discharge pressure balance to turn off the discharge pressure compensator , In the third switching position is achieved by the application of the control position of the discharge pressure balance of the default pressure that the discharge pressure balance is active, and achieved by relieving the control position of the Zulaufdruckwaage to the tank line, that the default force is reduced at the Zulaufdruckwaage to turn off the Zulaufdruckwaage.

Appropriately, in this case, the default pressure is lower than the lowest constant pressure level.

Preferably, the first control position of the additional valve device is designed as a spring-biased neutral position of the additional valve device.

The additional valve device is advantageously acted upon by the pressure prevailing in the direction of the second control position as a function of the pressure upstream of the inlet-side measuring throttle of the control valve and in the direction of the third control position as a function of the pressure prevailing upstream of the outlet-side measuring throttle of the control valve. As a result, a positive load or a negative load on the consumer drive can be detected in a simple manner to control the inlet and outlet pressure compensator accordingly. Due to the spring-biased neutral position of the additional valve device, in which the supply pressure compensator and the discharge pressure compensator are active, it is achieved that at low load pressures of the consumer drive in the inlet side and in the discharge side of the consumer drive a Δp is adjusted, whereby the clamping of the consumer drive and the dynamic behavior can be improved during load changes.

According to an advantageous embodiment of the invention, a limit load control device is provided, by means of which the default pressure in the pilot line can be reduced. With such a limit load control is made possible in a simple manner to lower the default pressure and thus the value of .DELTA.p for the Zulaufdruckwaage and the discharge pressure balance to the pressure medium flow to the consumer drives corresponding to the opening cross sections of the metering throttles on the spools lower, if over a longer period of the consumer drives more power is called, as can be supplied by the pump module.

Further advantages and details of the invention will be explained in more detail with reference to the embodiments illustrated in the schematic figures. This shows

1 an inventive constant pressure system in a schematic representation,

2 a first embodiment of a valve device according to the invention,

3 a further education 2 .

4 A second embodiment of a valve device according to the invention,

5 A first embodiment of a pump module of a constant pressure system according to the invention,

6 A second embodiment of a pump module of a constant pressure system according to the invention,

7 A third embodiment of a pump module of a constant pressure system according to the invention,

8th A fourth embodiment of a pump module of a constant pressure system according to the invention,

9 A fifth embodiment of a pump module of a constant pressure system according to the invention,

10 A first embodiment of a pressure medium storage module of a constant pressure system according to the invention,

11 a second embodiment of a pressure medium storage module of a constant pressure system according to the invention,

12 A third embodiment of a pressure medium storage module of a constant pressure system according to the invention,

13 the circuit diagram of a first embodiment of a constant pressure system according to the invention,

14 the circuit diagram of a second embodiment of a constant pressure system according to the invention,

15 a diagram with the throttle losses of the constant pressure system according to the invention and

16 a diagram with the throttle losses of the constant pressure system according to the invention with a locking device for the discharge pressure balance.

In the 1 is a hydraulic constant pressure system according to the invention 1 trained drive system for a mobile machine, such as an excavator, shown in a schematic representation.

In the illustrated embodiment, the constant pressure system 1 three constant pressure levels PH, PM, PN, each with different pressure levels on.

The constant pressure level PM is formed as a middle pressure level with a pressure P2 and has a supply line LM. The constant pressure level PH is designed as a high pressure level with a pressure P1 and has a supply line LH. The constant pressure level PN is designed as a low pressure level with a pressure P3 and has a supply line LN.

The constant pressure system 1 further comprises a biased tank line TL, which is guided to a container and is under a tank bias TV.

In the constant pressure system according to the invention 1 For the pressure P1 of the high pressure level PH, the pressure P2 of the mean pressure level PM, the pressure P3 of the low pressure level PN, and the pressure T in the prestressed tank line TL, the following applies: P1>P2>P3> T

The pressure P1 of the constant pressure system according to the invention 1 For example, 350 bar, the pressure P2, for example, 250 bar and the pressure P3, for example, 150 bar.

The constant pressure system according to the invention 1 has a pump module PUM, which is driven by a drive motor AM, for example an internal combustion engine, and supplies the pressure levels PH, PM, PN with pressure medium.

The constant pressure system according to the invention 1 also has a pressure medium storage module DM, which is connected to the supply lines LH, LM, LN of the pressure levels PH, PM, PN. The accumulator module DM is further connected to the tank line TL.

The constant pressure system according to the invention 1 has at least one consumer drive VA of the drive system, for example, a hydraulic cylinder or hydraulic motor. The consumer drive VA is connected by means of a valve device VE to the supply lines LH, LM, LN and the tank line TL. The valve device VE of each consumer drive VA consists of a control module SM and a selection module AM.

The control module SM of the valve device VE has - as in the 2 to 4 is shown in more detail - a control valve 10 on, by means of which the direction of movement and the speed of movement of the consumer drive VA can be specified. The control valve 10 is to a supply line 11 for supplying pressure medium from the supply lines LH, LM, LN, to a drain line 12 for discharging pressure medium into the supply lines LH, LM, LN, the tank line TL and to consumer lines 13 . 14 connected to the control valve 10 connect to the consumer drive VA. To protect the consumer drive VA against overpressure and lack of filling are combined pressure relief and Nachsaugeventile 35 . 36 intended. The pressure limiting and re-suction valves 35 is in a connection line 37 arranged by the consumer line 13 led to the tank line TL. Accordingly, the pressure relief and Nachsaugeventile 36 in a connection line 38 arranged by the consumer line 14 led to the tank line TL

In the illustrated embodiment, the consumer drive VA is a double-acting hydraulic cylinder 15 designed as a differential cylinder with a piston side 15a and a piston rod side 15b is trained.

The control valve 10 has a neutral position 10a on, in which the connections of the supply line 11 and the drain line 12 with the consumer lines 13 . 14 is locked. In a first control position 10b of the control valve 10 is the supply line 11 with the consumer line 13 and the drain line 12 with the consumer line 14 connected. In a second control position 10c of the control valve 10 is the supply line 11 with the consumer line 14 and the drain line 12 with the consumer line 13 connected. The control valve 10 is designed as a throttling in intermediate positions proportional valve. In the control positions 10b . 10c forms the opening cross section of the control valve 10 from the supply line 11 to the consumer management 13 respectively. 14 an inlet-side measuring throttle MZ. According forms in the control positions 10b . 10c the opening cross section of the control valve 10 from the consumer line 14 respectively. 13 to the drain line 12 an outlet-side measuring throttle MA. The control valve 10 is with a load pressure tap 16 provided with the in the control positions 10b . 10c the pressure downstream of the inlet-side measuring throttle MZ in a load pressure line 17 can be reported. The control valve 10 is with another load pressure tap 18 provided with the in the control positions 10b . 10c the pressure upstream of the outlet-side measuring throttle MA in a load pressure line 19 can be reported.

The control valve 10 is by means of springs 20a . 20b in the neutral position 10a actuated. To operate the control valve 10 in the direction of the first control position 10b is an actuator 21a provided and for actuating the control valve 10 in the direction of the second control position 10c an actuator 21b ,

The selection module AM of the valve device VE has - as in the 2 to 4 is shown in more detail - a first selection valve AV1, which is the connection of the supply line 11 of the control valve 10 with the supply lines LH, LM, LN controls, and a second selection valve AV2, which connects the drain line 12 of the control valve 10 with the supply lines LM, LN and the tank line TL controls. The first selector valve AV1 and the second selector valve AV2 serve to the control valve 10 at the inlet side 11 and on the drain side 12 to provide the appropriate pressure level PH, PM, PN. The second selection valve AV2 is also used for energy recovery with negative loads on the consumer drive VA.

The first selection valve AV1 is designed as a supply pressure compensator ZDW, which depends on the pressure drop across the inlet-side measuring throttle MZ of the control valve 10 is controlled.

The Zulaufdruckwaage ZDW is by branch lines 25 . 26 . 27 to the supply lines LH, LM, LN all constant pressure levels PH, PM, PN connected. The branch line 25 In this case, it is guided by an inlet of the inlet pressure compensator ZDW to the supply line LN of the lowest constant pressure level PN. The branch line 26 is guided by a further input of the inlet pressure compensator ZDW to the supply line LM of the mean constant pressure level PM. The branch line 27 In this case, it is guided by a further input of the inlet pressure compensator ZDW to the supply line LH of the highest constant pressure level PH. The Zulaufdruckwaage ZDW has a shut-off AS, in which the connections of the supply lines 25 . 26 . 27 to the supply line 11 shut off. The inlet pressure compensator ZDW furthermore has a number of control positions ST1, ST2, ST3 corresponding to the number of constant pressure levels, the supply line being in a first control position ST1 11 only with the supply line LN of the lowest constant pressure level PN is connected and in each additional control position ST2, ST3 the supply line 11 is additionally connected to the supply line LM or LH of each next higher constant pressure level PM or PN. In the first control position ST1 this is the supply line 11 with the branch line 25 connected and the connection of the supply line 11 with the branch lines 26 . 27 shut off, so that the supply line 11 only connected to the lowest constant pressure level PN. In the second control position ST2 this is the supply line 11 with the branch line 25 and the branch line 26 connected and the connection of the supply line 11 with the branch line 27 shut off, so that the supply line 11 is connected to the lowest constant pressure level PN and the mean constant pressure level PM. In the third control position ST3 this is the supply line 11 with all branch line 25 . 26 and 27 connected so that the supply line 11 is connected to the lowest constant pressure level PN, the mean constant pressure level PM and the highest constant pressure level PH.

Except for the branch line 27 , which connects the inlet pressure compensator ZDW with the highest constant pressure level PH, is in all other branch lines 25 . 26 one in each direction towards the inlet pressure compensator 11 opening check valve 28 . 29 , For example, a check valve arranged.

The inlet pressure compensator ZDW is of the upstream of the upstream measuring throttle MZ of the control valve 10 applied pressure in the direction of the shut-off AS. For this purpose, one of the feed line to a corresponding control surface of the inlet pressure compensator ZDW 11 branching control line 30 guided. The inlet pressure compensator ZDW is of the downstream of the inlet-side measuring throttle MZ of the control valve 10 applied pressure in the direction of the control positions ST1, ST2, ST3. To a corresponding control surface of the inlet pressure compensator ZDW this is the load pressure line 17 guided.

From the control valve 10 becomes on actuation in the direction of the control positions 10b . 10c by means of the load pressure tap 16 the pressure downstream of the upstream measuring throttle MZ of the control valve 10 recorded and forwarded to the inlet pressure compensator ZDW.

The inlet pressure compensator ZDW is acted on by a default force in the direction of the control positions ST1, SDT2, ST3. In the 2 and 3 is the default force of a spring device 31 generated and given.

The supply line 11 of the control valve 10 is in the 2 and 3 by means of a connecting line 32 with a tank line TL of the constant pressure system 1 connected. In the connection line 32 is one towards the inlet pipe 11 opening check valve 33 , For example, a check valve arranged.

The second selection valve AV2 is designed as a discharge pressure compensator ADW, which is dependent on the pressure drop at the outlet-side measuring throttle MA of the control valve 10 is controlled.

The pressure compensator ADW is by means of branch pipes 40 . 41 . 42 to the tank line TL of the constant pressure system 1 and to the constant pressure level PH with the highest pressure level to the supply lines LM, LN all other constant pressure levels PM, PN connected. The branch line 40 For this purpose, it is guided by an outlet of the discharge pressure compensator ADW to the tank line TL. The branch line 41 For this purpose, it is guided by a further outlet of the discharge pressure compensator ADW to the supply line LN of the lowest constant pressure level PN. The branch line 42 For this purpose, it is guided by a further outlet of the discharge pressure compensator ADW to the supply line LM of the mean constant pressure level PM. The pressure compensator ADW has a connection position VS, in which the drain line 12 is connected to the tank line TL and the supply lines LM, LN. In the connection position VS this is the drain line 12 with all branch lines 40 . 41 . 42 connected so that the drain line 12 with the tank line TL, with the lowest constant pressure level PN and the mean constant pressure level PM is connected. The discharge pressure compensator ADW furthermore has a number of control positions ST1, ST2, ST3 corresponding to the number of constant pressure levels, wherein in a first control position ST1 the connection of the discharge line 12 to the connected constant pressure levels PN, PM opened and the connection of the drain line 12 is shut off to the tank line TL and in each additional control position ST2 or ST3 additionally the connection of the drain line 12 is shut off to the supply line LN or LM of the next higher constant pressure level PN or PM. In the first control position ST1, this is the drain line 12 with the branch lines 41 . 42 connected and the connection of the drain line 12 with the branch line 40 shut off, leaving the drain pipe 12 only connected to the lowest constant pressure level PN and the mean constant pressure level PM. In the second control position ST2 is the drain line 11 with the branch line 42 connected and the connection of the drain line 12 with the branch lines 40 . 41 shut off, leaving the drain pipe 12 only connected to the mean constant pressure level PM. In the third control position ST3 are the connections of the drain line 12 with all branch line 40 . 41 and 42 shut off.

Except for the branch line 40 , which connects the discharge pressure compensator ADW with the tank line TL, is in all other branch lines 41 . 42 in each case one in the direction of the outlet pressure compensator ADW blocking blocking valve 43 . 44 , For example, check valve arranged.

The outlet pressure compensator ADW is of the upstream of the downstream measuring throttle MA of the control valve 10 applied pressure in the direction of the control positions ST1, ST2, ST3. To a corresponding control surface of the discharge pressure compensator ADW this is the load pressure line 19 guided. The discharge pressure compensator ADW is of the downstream of the outlet side measuring throttle MA of the control valve 10 applied pressure in the direction of the connection position VS acted upon. For this purpose, to a corresponding control surface of the discharge pressure balance ADW one of the drain line 12 branching control line 45 guided.

From the control valve 10 becomes on actuation in the direction of the control positions 10b . 10c by means of the load pressure tap 18 the pressure upstream of the downstream measuring throttle MA of the control valve 10 recorded and forwarded to the pressure compensator ADW.

The pressure compensator ADW is acted upon by a default force in the direction of the connection position VS. In the 2 and 3 is the default force of a spring device 46 generated and given.

The drain line 12 of the control valve 10 is in the 2 and 3 by means of a connecting line 47 is connected to the supply line LH of the highest constant pressure level PH. In the connection line 47 is one towards the drain line 12 blocking check valve 47 , For example, a check valve arranged.

The selection module AM formed by the first selector valve AV1 and the second selector valve AV2 has the function of that of the control valve 10 formed control module SM on the supply line 11 and at the drain line 12 to provide the pressure level of appropriate constant pressure level PH, PM, PN. For this purpose, the inlet pressure compensator ZDW is informed of the pressure upstream and the pressure downstream of the inlet-side measuring throttle MZ. For this purpose, the outlet pressure compensator ADW is informed of the pressure upstream and the pressure downstream of the outlet-side measuring throttle MA. The in the 2 and 3 from the spring device 31 . 46 generated default force ensures that always a defined Δp on the measuring throttles MZ, MA of the control valve 10 is applied.

The inlet pressure compensator ZDW in the inlet side of the consumer drive VA operates as follows. Will the control valve 10 starting from the neutral position 10a in the direction of the tax position 10b respectively. 10c actuated, the pressure difference at the inlet-side measuring throttle MZ drops and the inlet pressure compensator ZDW located in the shut-off position AS is acted on in the first control position ST1, in which the inlet pressure compensator initially connects the supply line 11 to the supply line LN of the lowest constant pressure level PN opens. If the pressure P3 of the lowest constant pressure level PN is not sufficient to establish the Δp via the inlet-side measuring throttles MZ, the inlet pressure compensator ZDW is acted upon in the second control position ST2, in which the inlet pressure compensator ZDW additionally connects the supply line 11 to the supply line LM of the mean constant pressure level PM opens. If the pressure P2 of the mean constant pressure level PM is not sufficient to produce the Δp via the inlet-side measuring throttles MZ, the inlet pressure compensator ZDW is acted upon in the third control position ST3, in which the inlet pressure compensator ZDW additionally connects the supply line 11 to the supply line LH of the highest constant pressure level PH opens. The check valves 28 . 29 prevent in this case that in the control positions ST2, ST3 pressure medium can flow from the higher constant pressure level to a lower constant pressure level.

The pressure compensator ADW in the discharge side of the consumer drive VA is used for energy recovery and ensures that in the drain line 12 a pressure is present which is lower by the Δp than the load pressure of the consumer drive VA upstream of the outlet-side throttle device MA. Pressure medium in the drain line 12 is then automatically fed into the supply line LM, LN with the next lower pressure level or discharged into the tank line TL. The check valves 43 . 44 prevent a short circuit between the supply lines LM, LN with different pressure levels PM, PN.

In the 3 a development is shown, in which the pressure compensator ADW with a locking device 50 is provided, which blocks the discharge pressure compensator ADW in the first control position ST1 in a locking position and prevents further actuation of the discharge pressure compensator ADW in the connection position VS. In a locking position of the locking device 50 Thus, the discharge pressure compensator ADW can be limited in the control positions ST1, ST2, ST3 and further actuation of the discharge pressure compensator ADW can be prevented in the connection position VS.

The locking device 50 is as a mechanical locking device 51 trained with that the drain pressure balance ADW can be brought into operative connection.

In the in the 3 illustrated embodiment is the locking device 51 hydraulically actuated between a locking position and a release position.

For actuating the locking device 51 is a switching valve 52 provided by means of the in a first switching position 52a a control surface 53 the locking device 51 to the tank line TL is relieved and in a second switching position 52b the control surface 53 the locking device 51 can be connected to a pressure source.

The pressure source is formed by one of the constant pressure levels PH, PM, PN and the switching valve 52 by means of a connecting line 54 is connected to one of the supply lines LH, LM, LN. In the illustrated embodiment, the constant pressure level PN is used as the pressure source and is the connection line 54 connected to the supply line LN.

In the first switching position 52a the switching valve 52 this is the locking device 51 operated in the release position in which the discharge pressure compensator ADW is blocked in the first control position ST1. In the second switching position 52a the switching valve 52 becomes the locking device 51 operated in the locked position in which the pressure compensator ADW can no longer take the connection position VS.

The switching valve 52 is from a spring 55 and the pressure in the supply line 11 in the direction of the first switching position 52a and the pressure in the drain line 12 and the selected pressure of the inlet pressure compensator ZDW in the direction of the second switching position 52b actuated. At one in the direction of the first switching position 52a acting control surface of the switching valve 52 this is one with the supply line 11 related control line 56 guided. At one in the direction of the second switching position 52b acting control surface of the switching valve 52 this is one with the drain line 12 related control line 57a guided and to a second control surface, which is also in the direction of the second switching position 52b acts, a control line 57b guided, in which the selected pressure of the supply pressure compensator ZDW is pending. The switching valve 52 thus recognizes by means of the pressures in the control lines 56 . 57a . 57b the current pressure difference across the inlet pressure compensator ZDW and switches when exceeding a predetermined limit, the bias of the spring 55 corresponds to the locking device 51 in the locking position.

In the locking position limits the locking device 51 the discharge pressure compensator ADW on the control position ST1, ST2, ST3 and prevents further actuation of the discharge pressure compensator ADW in the connection position VS, so that in the drain line 12 always at least the pressure of the lowest constant pressure level PN is set. In the control position 10b of the control valve 10 This can be the pressure P3 on the piston rod side 15b of the hydraulic cylinder 15 be switched. As a result, the load pressure on the piston side 15a of the hydraulic cylinder 15 according to the area ratio of the hydraulic cylinder 15 elevated. At an area ratio of the hydraulic cylinder 15 from the piston side 15a to piston rod side 15b from 2: 1, the load pressure on the piston side can thus be raised by P3 · 0.5.

With the locking device 51 can thus be achieved in the locked position, a pressure upshift on the consumer drive VA to reduce in unfavorable operating points, the throttle losses in the supply of the consumer drive VA from one of the constant pressure levels LN, LM, LH.

In the 4 is shown a development in which instead of the spring device 31 . 46 for the inlet pressure compensator ZDW and the outlet pressure compensator ADW, which specifies a fixed Δp as the default force, the control module SM with an additional valve device 60 is provided, by means of which the default force at the inlet pressure compensator ZDW and the default force at the discharge pressure compensator ADW is variable.

The additional valve device 60 has a first control position 60a on, in which the inlet pressure compensator ZDW and the outlet pressure compensator ADW are active, a second control position 60b on, in which the supply pressure compensator ZDW is active and the pressure compensator ADW is switched off, and a third control position 60c on, in which the pressure compensator ADW is active and the supply pressure compensator ZDW is switched off.

The additional valve device 60 generated in the first control position 60a at the inlet pressure compensator ZDW and at the outlet pressure compensator ADW an equally large default force, so that the inlet pressure compensator ZDW and the discharge pressure compensator ADW are active. In the second control position 60b the default force on the discharge pressure compensator ADW is increased in order to switch off the discharge pressure compensator ADW. In the third control position 60c the default force is reduced at the inlet pressure compensator ZDW to turn off the supply pressure compensator ZDW.

The additional valve device 60 is at a positive load on the consumer drive VA in the second switching position 60b operated and at a negative load on the consumer drive VA in the third switching position 60c actuated.

The first control position 60a is as a neutral position of the additional valve device 60 educated. The additional valve device 60 is by means of springs 61 . 62 operated in the neutral position formed as a middle position. The additional valve device 60 is dependent on the downstream of the inlet-side measuring throttle MZ of the control valve 10 Pending load pressure in the direction of the second control position 60b applied. To a corresponding control surface of the additional valve device 60 this is the load pressure line 17 guided. The additional valve device 60 is in function of the upstream of the downstream measuring throttle MA of the control valve 10 Pending load pressure in the direction of the third control position 60c applied. To a corresponding control surface of the additional valve device 60 this is the load pressure line 19 guided.

In the in the 4 illustrated embodiment, the default force at the Zulaufdruckwaage ZDW from one to a control surface 65 pending pressure signal generated and the default force on the discharge pressure compensator ADW from one to a control surface 66 pending pressure signal generated.

The additional valve device 60 is by means of a control line 67 to the control surface 65 the inlet pressure compensator ZDW and by means of a control line 68 to the control surface 66 the pressure compensator ADW connected. Furthermore, the additional valve device 60 by means of a branch line 70 connected to the tank line TL, by means of a branch line 71 with one of the supply lines LN, LM, LH, in the illustrated embodiment with the supply line LN, and by means of a branch line 72 with a pilot control line 73 connected, in which a default pressure as Δp setpoint is pending.

The additional valve device 60 connects in the first control position 60a the to the control surface 65 the inlet pressure compensator ZDW guided control line 67 and those to the control surface 66 the pressure compensator ADW guided control line 68 with the pilot control line 73 , so on both control surfaces 65 . 66 the same default pressure is pending and both the inlet pressure compensator ZDW and the outlet pressure compensator ADW are active. In the second control position 60b connects the additional valve device 60 the control line 67 the inlet pressure compensator ZDW with the pilot control line 73 and the control line 68 the pressure compensator ADW with the supply line LN. As a result, the default force at the discharge pressure compensator ADW is increased and the discharge pressure compensator ADW is switched off, in which it is reset by the pressure P3 of the constant pressure level PN in the control line 68 is acted upon in the connection position VS. In the second control position 60b Thus, only the supply pressure compensator ZDW is active. In the third control position 60c connects the additional valve device 60 the control line 67 the inlet pressure compensator ZDW with the tank line TL and the control line 68 the pressure compensator ADW with the pilot control line 73 , As a result, the default force at the inlet pressure compensator ZDW is reduced and the supply pressure compensator ZDW is switched off. In the third control position 60c So only the pressure compensator ADW is active.

The additional valve device 60 thus defines, depending on the load pressure of the consumer drive VA, the Δp at the inlet pressure compensator ZDW and at the outlet pressure compensator ADW and adjusts the Δp at the inlet pressure compensator ZDW and at the outlet pressure compensator ADW as a function of the load pressure of the consumer drive VA. With a positive load on the consumer drive VA, wherein the additional valve device 60 in the second control position 60b is actuated to turn off the discharge pressure compensator ADW, thus preventing that on the discharge side of the consumer drive VA, a Δp is adjusted. With a negative load on the consumer drive VA, wherein the additional valve device 60 in the third control position 60c is actuated to turn off the supply pressure compensator ZDW, thus preventing that on the inlet side of the consumer drive VA, a Δp is adjusted.

The springs 61 . 62 generated spring preload of the additional valve device 60 in the neutral position 60a ensures that at low load pressures of the consumer drive VA, the inlet pressure compensator ZDW and the outlet pressure compensator ADW are active, so that a Δp is adjusted both on the inlet side and on the outlet side of the consumer drive VA. As a result, a clamping of the consumer drive VA is achieved and improved its dynamic response to load changes.

To switch off the supply pressure compensator ZDW is of the additional valve device 60 in the third control position 60c through the connection of the control surface 65 with the tank pressure T, the Δp of the inlet pressure compensator ZDW set to zero. To switch off the discharge pressure compensator ADW is of the additional valve device 60 in the second control position 60b through the connection of the control surface 66 with the supply line LN to the control surface 66 the pressure P3 is passed, which is higher than Δp, so that the discharge pressure compensator ADW is actuated in the connection position VS.

With one in the 4 Limit load control device, not shown, can be supplied in operating states in which more power is supplied by the consumer drives VA than can be supplied by the pump module PUM, ie the pressure fluid reservoir of the pressure fluid storage module DM falls below a predetermined minimum pressure, the default pressure in the pilot control line 73 , which corresponds to the Δp setpoint, decreases and decreases become. If each consumer drive VA with a to the pilot control line 73 connected additional valve device 60 is reduced by lowering the default pressure in the central pilot line 73 the volume flow at all consumer drives VA corresponding to the opening cross-section of the metering restrictors MZ.

The control valve 10 the control module SM of 2 to 4 thus serves to specify the direction of movement and due to the constant Δp the speed of movement of the consumer drive VA. In addition, the control valve is used 10 of the 2 to 4 in addition, by means of the load pressure taps 16 . 18 To report the load pressure of the consumer drive VA to the inlet pressure compensator ZDW and to the outlet pressure compensator ADW.

In the constant pressure system according to the invention 1 serves the driven by the drive motor pump module PUM to charge the pressure fluid storage module DM, which has a pressure fluid store for each constant pressure level PH, PN, PM, with pressure medium. For loading the accumulator module DM, the drive motor AM and the pump module PUM are operated at a certain operating point. In the 5 to 9 are various embodiments of a pump module PUM of the constant pressure system according to the invention 1 represented, with which the consumer drives VA all pressure levels of the constant pressure system 1 can be made available.

In the 5 The pump module PUM comprises a single pump PU which is designed as a variable displacement pump and is driven by the drive motor AM and charges the pressure accumulator of the constant pressure level PM with the mean pressure level P2. The variable displacement pump PU is designed as a pump designed in the open circuit, the pressure medium from a container 100 sucks and into a delivery line 101 promotes, with the interposition of a blocking to the pump PU check valve 102 is connected to the supply line LM. Via a rotary transformer T1, the pressure medium delivered by the pump PU is translated to the constant pressure level PH with the higher pressure level P1. Via a further rotary transformer T2, the pressure medium delivered by the pump PU is translated to the constant pressure level PN with the lower pressure level P3.

In the 6 The pump module PUM comprises a single pump PU which is designed as a variable displacement pump and is driven by the drive motor AM and charges the pressure accumulator of the constant pressure level PM with the mean pressure level P2. The variable displacement pump PU is designed as a pump designed in the open circuit, the pressure medium from a container 100 sucks and into a delivery line 101 promotes, with the interposition of a blocking to the pump PU check valve 102 is connected to the supply line LM. Via a linear transformer T1, the pumped by the pump PU pressure medium is translated to the constant pressure level PH with the higher pressure level P1. Via a further linear transformer T2, the pressure medium conveyed by the pump PU is translated to the constant pressure level PN with the lower pressure level P3. The linear transformers T1, T2 are each designed as a double-piston transformer, which can be operated in both directions of movement. For the reciprocal operation of the linear transformers T1, T2 is in each case a valve device 105 . 106 provided that allows the double piston transformer in both directions of movement of a piston device 107 . 108 a supply of higher or lower pressure levels with pressure medium allows.

The transformers T1, T2 of 5 and 6 have a constant gear ratio, so that it is ensured that the ratio of the pressure levels in the supply lines LH, LM, LN does not change. Pressure medium, which is recovered from a consumer drive VA, can be evenly distributed with the transformers T1, T2 to all pressure fluid reservoir of the pressure medium storage device DM.

The transformer T1 the 5 respectively. 6 serves to translate the pumped by the pump PU pressure fluid to the supply line LH of the constant pressure level PH with the higher pressure level P1 and thus to load the pressure fluid reservoir. The transformer T2 of 5 respectively. 6 serves to translate the pumped by the pump PU pressure medium to the supply line LN of the constant pressure level PN with the lower pressure level P3 and thus to load the pressure fluid reservoir.

For the pump module PUM the 5 and 6 Thus, the pump PU is a supply line of the constant pressure system 1 , In the illustrated embodiment, the supply line LM of the constant pressure level PM with the average pressure level P2, loaded and the transformers T1, T2 distribute the power to the other supply lines of the constant pressure system 1 in the illustrated embodiment, the transformer T1 on the supply line LH of the constant pressure level PH with the higher pressure level P1 and the transformer T2 on the supply line LN of the constant pressure level PN with the lower pressure level P3.

In the 7 For example, the pump module PUM for each constant pressure level PH, PN, PM on a separate pump PU1, PU2, PU3, each Pump PU1, PU2, PU3 is designed as adjustable in the delivery volume variable pump.

The pump PU1 is operated in an open circuit and sucks pressure medium via a suction line 110 from the container 100 at. The pump PU1 supplies the constant pressure level PH with pressure medium and for this purpose conveys it into a delivery line, which is connected to the supply lines LH of the constant pressure level PH.

The pump PU2 is operated in an open circuit and sucks pressure medium via a suction line 111 from the container 100 at. The pump PU2 supplies the constant pressure level PM with pressure medium and for this purpose conveys into a delivery line, which is connected to the supply lines LM of the constant pressure level PM.

The pump PU3 is operated in an open circuit and sucks pressure medium via a suction line 112 from the container 100 at. The pump PU3 supplies the constant pressure level PN with pressure medium and for this purpose conveys into a delivery line, which is connected to the supply lines LN of the constant pressure level PN.

The pumps PU1, PU2 and PU3 can be operated in the same direction of rotation both as pump and motor, which are designed for this purpose as adjusting pumps adjustable on both sides in the delivery volume. By means of the pump PU1 which can be operated as a motor, pressure medium from the supply line LH of the constant pressure level PH can be translated into another constant pressure level PM, PN. By means of the pump PU2 which can be operated as a motor, pressure medium from the supply line LM of the constant pressure level PM can be translated into another constant pressure level PH, PN. Correspondingly, pressure medium from the supply line LN of the constant-pressure level PN can be translated into another constant-pressure level PH, PM by the motor PU3 that can be operated as a motor.

In the 8th is a pump module PUM shown that differs from the 7 only differs in that the pump PU1 can only be operated as a pump, which is designed for this purpose as a variable in the delivery volume variable displacement pump. The pump PU1 supplies the constant pressure level PH with pressure medium and for this purpose conveys it into a delivery line which, with the interposition of a non-return valve blocking in the direction of the pump PU1 115 is connected to the supply lines LH of the constant pressure level PH.

In the 7 and 8th a control can regulate the sum of the torques of all pumps PU1, PU2, PU3. If at least one of the pumps designed as variable-displacement pumps can be operated both as a pump and as a motor, pressure fluid can be translated from a constant pressure level into another constant-pressure level of the constant-pressure system as a result of the motor operation of the pump.

In the 9 is a pump module PUM of a constant pressure system according to the invention 1 represented, which has a single pump PU, which is designed as variable in the delivery volume variable pump and is connected by means of a Umschaltventileinrichtung UV to the constant pressure levels PH, PM, PN to supply the constant pressure levels PH, PM, PN as needed with pressure medium.

The pump PU is operated in an open circuit and sucks pressure medium via a suction line 120 from the container 100 at. The pump PU conveys into a delivery line 121 the interposition of a blocking in the direction of the pump PU check valve 122 is connected to the switching valve device UV.

In the illustrated embodiment, the Umschaltventileinrichtung UV a switching valve 125 on, the input side to the delivery line 121 is connected and the output side is connected to the supply lines LM, LN. The switching valve 125 has a neutral position 125a on, in which the connection of the delivery line 121 to the supply lines LM, LN is shut off. In a first switching position 125b is the support line 121 connected to the supply line LM. In a second switching position 125c is the support line 121 connected to the supply line LN.

The supply line LH is to the delivery line 121 between the check valve 122 and the switching valve 125 connected. The switching valve device UV has a check valve 126 on, which is arranged in the supply line LH and locks in the direction of the pump PU.

In the neutral position 125a the switching valve 125 Thus, the pump PU can supply the supply line LH with pressure medium. In the first switching position 125b the switching valve 125 Thus, the pump PU supply the supply line LM with pressure medium. Accordingly, in the second switching position 125c the switching valve 125 the pump PU supply the supply line LN with pressure medium.

The pump module PUM of the 9 thus consists of a single driven by the drive motor AM pump PU, which supplies all constant pressure levels of the constant pressure system with pressure medium and loads the pressure fluid reservoir of the pressure medium storage module DM of the individual pressure levels of the constant pressure system as needed. The Execution of the pump PU as a variable pump makes it possible to compensate for the fluctuating pressure level at the pump PU when conveying to the appropriate pressure levels by gradually adjusting the delivery volume.

In the 10 to 12 are various embodiments of a pressure medium storage module DM of a constant pressure system according to the invention 1 shown.

The accumulator module DM the 10 has an independent accumulator D1, D2, D3 for each constant pressure level PH, PM, PN. The pressure fluid reservoirs D1, D2, D3 are each in the form of a pressure accumulator, for example bladder accumulator BS, which is under a gas bias, for example nitrogen.

The accumulator D1 is associated with the high constant pressure level PH and connected to the supply line LH at a fluid side. The accumulator D2 is assigned to the mean constant pressure level PM and connected to the supply line LM on one side of the fluid. The accumulator D3 is associated with the low constant pressure level PN and connected at a fluid side to the supply line LN.

The accumulator module DM still has an independent accumulator D4, which is assigned to the prestressed tank line TL. The pressure medium accumulator D4 is designed as a pressure accumulator, for example bladder accumulator BS, which is under a gas bias, for example nitrogen. The pressure medium accumulator D4 is connected to the tank line TL at a fluid side.

By the operation of the drive motor AM when loading the accumulator module DM in a certain, constant operating point is in a constant pressure system according to the invention 1 limited the torque provided by the drive motor AM, so that not at any time pressure differences between the separate and independent under a gas bias pressure accumulators D1, D2, D3 of the individual pressure levels can be compensated. In the case of a pressure medium storage module DM, which has a separate and independent gas pressure biasing accumulator D1, D2, D3 for each constant pressure level PH, PM, PN, a compensation of these pressure differences can take place according to the 11 , in which a further education of 10 is shown. additional compensation pistons 130 . 140 are used, which are designed as differential cylinders, and are connected to the piston side and the piston rod side to two different pressure levels of the constant pressure system.

In the 11 is designed as a differential cylinders compensating piston 130 connected at the piston side with the supply line LM of the mean constant pressure level PM and at the piston rod side with the supply line LH of the high constant pressure level PH. The designed as a differential cylinders compensation piston 140 is connected at the piston side with the supply line LN of the low constant pressure level PN and at the piston rod side with the supply line LM of the mean constant pressure level PM.

These extra compensation pistons 130 . 140 of the 11 make it possible to compensate for deviations of the pressure ratio of two pressure levels of the constant pressure system.

The accumulator module DM the 12 has for each constant pressure level PH, PM, PN designed as a piston accumulator K1, K2, K3 accumulator D1, D2, D3. The accumulator D1, D2, D3 are connected to a common downstream gas storage GS, such as a nitrogen storage, as a gas volume (nitrogen volume).

The gas storage GS is in this case designed as a pure gas storage and thus as a pure gas volume for the pressure fluid reservoirs D1, D2, D3.

The pressure medium reservoirs D1, D2, D3 designed as piston accumulators K1, K2, K3 are each provided with a fluid side F and a gas side S.

The pressure medium accumulator D1 is assigned to the high constant pressure level PH and connected to the supply line LH on the fluid side F. The accumulator D2 is assigned to the mean constant pressure level PM and connected to the fluid side F to the supply line LM. The accumulator D3 is assigned to the low constant pressure level PN and connected to the fluid side F to the supply line LN. The gas sides G of all accumulator D1, D2, D3 are connected to the common gas storage GS.

The piston accumulator K2, which is assigned to the mean constant pressure level PM, has a longitudinally displaceable in a housing G piston K, which has the same size surfaces on the fluid side F and the gas side S.

The piston accumulator K1, which is associated with the high pressure level PH, and the piston accumulator K3, the low pressure level PN is assigned, in each case as a differential piston accumulator is formed, which has different sized surfaces on the fluid side F and the gas side S.

The piston accumulators K1, K3 designed as differential piston accumulators each have a piston K, which is longitudinally displaceable in a housing G and is provided on one side with a piston rod KS, so that the differential piston accumulators have a piston side with a large area and a piston rod side with a smaller area.

In the designed as a differential piston accumulator piston K1, which is associated with the high pressure level PH, the piston rod side is formed as a fluid side F and the piston side as a gas side S.

In the designed as a differential piston accumulator piston K3, which is associated with the low pressure level PN, the piston side is formed as a fluid side F and the piston rod side as the gas side S.

The accumulator module DM the 12 also has a pressure accumulator D4 which is under a gas bias and which is designed as a bladder accumulator BS and is connected to the tank line TL.

In the accumulator module DM the 12 This results in a direct pressure coupling via the common gas storage GS. In the piston accumulators K1, K2, K3, the piston volume corresponds to the storage volume of pressure medium. By the piston accumulator K1, K2, K3, which are connected to the common gas storage GS, and pressure differences between the individual pressure levels PH, PM, PN can be compensated, since designed as a differential piston accumulator piston K1, K3 have a transformer function.

In the 13 is the circuit diagram of a first embodiment of a constant pressure system according to the invention 1 shown. In the constant pressure system 1 is a pump module PUM according to 8th provided with a pump PU1, PU2, PU3 for each supply line LH, LM, LN and a pressure medium storage module DM according to the 12 provided with three designed as piston accumulators K1, K2, K3 accumulators D1, D2, D3, which are connected to a common downstream gas storage GS. In the 13 is the valve device VE for controlling the consumer drive VA according to the 4 built up. The valve device VE consists of the control valve 10 , By means of which the direction of movement and the speed of movement of the consumer drive VA can be specified, the inlet pressure compensator ZDW, the outlet pressure compensator ADW and the additional valve device 60 which controls the pressure difference at the inlet pressure compensator ZDW and at the outlet pressure compensator ADW as a function of the load pressure of the consumer drive VA.

The tank line TL is - as from the 13 can be seen - via a spring-loaded preload valve 15 , which is preferably designed as a check valve, with the container 100 connected. The spring preload of the preload valve 150 defines the tank bias voltage TV of the tank line TL.

The pump module PUM of the 13 allows by the pumps PU2, PU3 a transformer operation.

In the 13 can by a limit load control of the default pressure in the pilot control line 73 are lowered, if in the pressure medium stores D1, D2, D3, a minimum pressure is reached.

In the 14 is the circuit diagram of a second embodiment of a constant pressure system according to the invention 1 shown. In the constant pressure system 1 is a pump module PUM according to 6 with a single pump PU, which charges the supply line LM with pressure medium, and two transformers T1, T2, which distribute the power to the other supply lines LH and LM, and a pressure medium storage module DM according to the 10 provided with independent pressure fluid reservoirs D1, D2, D3, D4, each of which is designed as a pressure reservoir, for example bladder accumulator BS, which is under a gas bias, for example nitrogen. In the 14 is the valve device VE for controlling the consumer drive VA according to the 4 constructed and further comprises the locking device 50 for the pressure compensator ADW according to the 3 connected to the switching valve 52 can be actuated, for pressure upshift on the consumer drive VA.

In the diagram of 15 are the throttling losses of a constant pressure system 1 of the 13 shown. In the diagram, the pressure is plotted against the pressures P1, P2, P3 of the constant pressure levels PH, PM, PN over time t.

In the left half of the 15 the losses during operation of the consumer drive VA are shown at a positive load. The line 200 corresponds to that in the consumer line 13 pending load pressure of the consumer drive VA and the line 201 the pressure in the supply line 11 downstream of the inlet pressure compensator ZDW. The distance between the lines 201 . 200 corresponds to the Δp at the upstream measuring throttle MZ of the control valve 10 ,

With a positive load, throttling losses fall through the control valve 10 at. In addition, throttling losses occur that arise due to the throttling of the storage pressures of the accumulator D1, D2, D3 and thus the pressures P1, P2, P3 to the required load pressure of the consumer drive VA. At a required load pressure of the consumer drive VA, the pressure medium is throttled from the next-higher constant pressure level and thus pressure level P1 or P2 or P3 to the load pressure. These losses are in the left half of the 15 illustrated by the hatched areas.

wobei

P1

dem Druck des höchsten Konstantdruckniveaus PH

N

der Anzahl der verschiedenen Konstantdruckniveaus

∆p

dem Druckabfall über die zulaufseitigen Messdrossel des Steuerventils

Q

dem Volumenstrom

entspricht. Assuming a uniform occurrence of all load pressures results in a mean power loss P _loss according to the following formula:

in which

P1

the pressure of the highest constant pressure level PH

N

the number of different constant pressure levels

Ap

the pressure drop across the inlet side throttle of the control valve

Q

the volume flow

equivalent.

In the right half of the 15 the losses during operation of the consumer drive VA are shown at a negative load. The line 205 corresponds to that in the consumer line 14 pending load pressure of the consumer drive VA and the line 206 the pressure downstream of the discharge pressure regulator ADW. The resulting in a negative load losses, ie energy that can not be recovered in the pressure fluid reservoirs D1, D2, D3 are in the right half of 15 illustrated by the hatched areas.

In the diagram of 16 are the throttling losses of a constant pressure system 1 of the 14 shown, with the locking device 50 is provided for the pressure compensator ADW for pressure upshift on the consumer drive VA. In the diagram, the pressure with the pressures P1, P2, P3 of the constant pressure levels PH, PM, PN is plotted over time.

In the 16 only the losses during operation of the consumer drive VA are shown at a positive load. The line 210 corresponds to that in the consumer line 13 pending load pressure of the consumer drive VA and the line 211 the pressure in the supply line 11 downstream of the inlet pressure compensator ZDW. The distance between the lines 210 . 211 corresponds to the Δp at the upstream measuring throttle MZ of the control valve 10 ,

The pressure upshift by the locking device 50 leads to reduced throttling losses in operating points in which a large distance of the load pressure to the next higher constant pressure level and thus pressure level P1 or P2 or P3 occurs, from which the consumer drive VA is supplied. By the pressure upshift through the locking device 50 the losses during operation of the consumer drive VA at a positive load compared to the 15 be halved.

The constant pressure system according to the invention 1 has the valve device VE with the hydraulically controlled Zulaufdruckwaage ZDW and the hydraulically controlled Ablaufruckwage ADW a simple design with low construction costs for the valve device VE, since no pressure sensors for detecting the load pressure of the consumer drives VA are required. Due to the purely hydraulically controlled inlet pressure compensator ZDW and the purely hydraulically controlled discharge jaw ADW, an automatic selection of the constant pressure level takes place without the need for additional external control.

The pressure upshift by the locking device 50 leads to reduced throttle losses at positive loads.

The constant pressure system according to the invention 1 has by the valve device VE invention further a faster response of Verbraucheranriebe VA and thus improved dynamics.

In addition, results in the constant pressure system according to the invention 1 an independence of the consumer drives VA, whereby the vote one with the constant pressure system according to the invention 1 equipped working machine is simplified and facilitated.

Claims (34)

Hydraulic constant pressure system ( 1 ) for a mobile work machine having at least two constant pressure levels (PH; PM; PN) with different pressure levels (P1; P2; P3) from which at least one consumer drive (VA) is supplied with pressure medium, one of a drive motor (AM) , in particular an internal combustion engine, driven pump module (PUM) is provided, the at least two constant pressure levels (PH; PM; PN), wherein the constant pressure levels (PH; PM; PN) each have a supply line (LH; LM; LN) which are in communication with a pressure medium storage module (DM), with a valve device (VA) for controlling each consumer drive (VA). VE) is provided, characterized in that the valve device (VE) of each consumer drive (VA) is a control valve ( 10 ), by means of which the direction of movement and the speed of movement of the consumer drive (VA) is controllable, wherein the control valve ( 10 ) to a supply line ( 11 ) for supplying pressure medium from the supply lines (LH; LM; LN) to a drain line ( 12 ) for discharging pressure medium into the supply lines (LH; LM; LN) and to consumer lines ( 13 . 14 ) connected to the control valve ( 10 ) connect to the consumer drive (VA), wherein a first selector valve (AV1) is provided, the connection of the supply line ( 11 ) of the control valve ( 10 ) with the supply lines (LH; LM; LN), and a second selector valve (AV2) is provided which controls the connection of the drain line ( 12 ) of the control valve ( 10 ) with the supply lines (LH; LM; LN). Hydraulic constant pressure system according to claim 1, characterized in that the first selection valve (AV1) is designed as an inlet pressure compensator (ZDW), which is dependent on the pressure drop at an inlet-side measuring throttle (MZ) of the control valve (FIG. 10 ) is controlled. Hydraulic constant pressure system according to claim 2, characterized in that the inlet pressure compensator (ZDW) by means of branch lines ( 25 . 26 . 27 ) is connected to the supply lines (LH, LM, LN) of all constant pressure levels (PH, PM, PN), wherein the inlet pressure compensator (ZDW) has a shut-off position (AS) in which the connections of the supply lines (LH, LM, LN) to Supply line ( 11 ), and one of the number of constant pressure levels (PH, PM, PN) corresponding number of control positions (ST1, ST2, ST3), wherein in a first control position (ST1) the supply line ( 11 ) is connected to the supply line (LN) of the lowest constant pressure level (PN) and in each further control position (ST2, ST3) the supply line ( 11 ) is additionally connected to the supply line (LM; LH) of the next higher constant pressure level (PM; PH). Hydraulic constant pressure system according to claim 3, characterized in that except for the branch line ( 27 ), which connects the inlet pressure compensator (ZDW) with the highest constant pressure level (PH), in all other branches ( 25 . 26 ) each one in the direction of the inlet pressure compensator (ZDW) opening check valve ( 28 . 29 ), in particular check valve, is arranged. Hydraulic constant pressure system according to claim 3 or 4, characterized in that the inlet pressure compensator (ZDW) of the upstream of the upstream measuring throttle (MZ) of the control valve ( 10 ) pending pressure in the direction of the shut-off position (AS) and of the downstream of the inlet-side measuring throttle (MZ) of the control valve ( 10 ) is applied in the direction of the control positions (ST1, ST2, ST3). Hydraulic constant pressure system according to one of claims 2 to 5, characterized in that the control valve ( 10 ) upon actuation the pressure downstream of the upstream measuring throttle (MZ) of the control valve ( 10 ) and forwarded to the inlet pressure compensator (ZDW). Hydraulic constant pressure system according to one of claims 3 to 6, characterized in that the inlet pressure compensator (ZDW) is acted on by a default force in the direction of the control positions (ST1; ST2; ST3). Hydraulic constant pressure system according to claim 7, characterized in that the default force of a spring device ( 31 ) is given. Hydraulic constant pressure system according to one of claims 1 to 8, characterized in that the supply line ( 11 ) of the control valve ( 10 ) by means of a connecting line ( 32 ) with a tank line (TL) of the constant pressure system ( 1 ), wherein in the connecting line ( 32 ) in the direction of the supply line ( 11 ) opening check valve ( 33 ), in particular check valve, is arranged. Hydraulic constant pressure system according to one of claims 1 to 9, characterized in that the second selection valve (AV2) is designed as a discharge pressure compensator (ADW), which is dependent on the pressure drop across an outlet-side measuring throttle (MA) of the control valve (FIG. 10 ) is controlled. Hydraulic constant pressure system according to claim 10, characterized in that the discharge pressure compensator (ADW) by means of branch lines ( 40 . 41 . 42 ) to a tank line (TL) of the constant pressure system ( 1 ) and to the constant pressure level (PH) with the highest pressure level (P3) to the supply lines (LM, LN) of all other constant pressure levels (PM, PN) is connected, wherein the discharge pressure balance (ADW) has a connection position (VS), in the the drain line ( 12 ) is connected to the tank line (TL) and the supply lines (LM, LN) and has a number of control positions (ST1, ST2, ST3) corresponding to the number of constant pressure levels (PH, PM, PN), wherein in a first control position ( ST1) the connection of the drain line ( 12 ) to the connected constant pressure levels (LN, LM) and the connection of the drain line ( 12 ) is shut off to the tank line (TL) and in each additional control position (ST2, ST3) in addition the connection of the drain line ( 12 ) to the supply line (LN; LM) of the next higher constant pressure level (PN, PM). Hydraulic constant pressure system according to claim 10, characterized in that except for the branch line ( 40 ), which connects the discharge pressure compensator (ADW) to the tank line (TL), in all other branches ( 41 . 42 ) in each case one in the direction of the discharge pressure balance (ADW) blocking check valve ( 43 . 44 ), in particular check valve, is arranged. Hydraulic constant pressure system according to claim 11 or 12, characterized in that the discharge pressure compensator (ADW) of the upstream of the outlet-side measuring throttle (MA) of the control valve ( 10 ) pressure in the direction of the control positions (ST1; ST2; ST3) and of the downstream of the downstream measuring throttle (MA) of the control valve (FIG. 10 ) applied pressure in the direction of the connection position (VS) is applied. Hydraulic constant pressure system according to one of claims 10 to 13, characterized in that the control valve ( 10 ) upon actuation, the pressure upstream of the outlet side throttle (MA) of the control valve ( 10 ) and sends it to the expiry pressure gauge (ADW). Hydraulic constant pressure system according to one of claims 11 to 14, characterized in that the discharge pressure compensator (ADW) is acted on by a default force in the direction of the connection position (VS). Hydraulic constant pressure system according to claim 15, characterized in that the default force of a spring device ( 46 ) is given. Hydraulic constant pressure system according to one of claims 1 to 16, characterized in that the drain line ( 12 ) of the control valve ( 10 ) by means of a connecting line ( 47 ) is connected to the supply line (LH) of the highest constant pressure level (PH), wherein in the connecting line ( 47 ) in the direction of the drain line ( 12 ) blocking check valve ( 48 ), in particular check valve, is arranged. Hydraulic constant pressure system according to one of claims 10 to 17, characterized in that the discharge pressure compensator (ADW) with a locking device ( 50 ) is provided, which locks the discharge pressure compensator (ADW) in the first control position (ST1) in a locking position and prevents actuation of the discharge pressure compensator (ADW) in the connection position (VS). Hydraulic constant pressure system according to claim 18, characterized in that the locking device ( 50 ) of a latching device which can be brought into operative connection with the discharge pressure balance (ADW) ( 51 ) is formed. Hydraulic constant pressure system according to claim 19, characterized in that the latching device ( 51 ) is hydraulically or electrically actuated between a locking position and a release position. Hydraulic constant pressure system according to claim 20, characterized in that the latching device ( 51 ) is hydraulically actuated, wherein a switching valve ( 52 ) is provided, by means of which in a first switching position ( 52a ) a control surface ( 53 ) of the locking device ( 51 ) to the tank line (TL) for actuating the locking device ( 51 ) is relieved in the release position and in a second switching position ( 52b ) the control surface ( 53 ) of the locking device ( 51 ) with a pressure source for actuating the locking device ( 51 ) is connectable to the locking position. A constant pressure hydraulic system according to claim 21, characterized in that the pressure source is formed by one of the constant pressure levels (PH; PM; PN) and the switching valve ( 52 ) by means of a connecting line ( 54 ) is connected to one of the supply lines (LH; LM; LN). Hydraulic constant pressure system according to claim 21 or 22, characterized in that the switching valve ( 52 ) of a spring ( 55 ) and the pressure in the supply line ( 11 ) in the direction of the first switching position ( 52a ) and the pressure in the drain line ( 12 ) in the direction of the second switching position ( 52b ) is actuated. Hydraulic constant pressure system according to claim 23, characterized in that the switching valve ( 52 ) of the pressure selected by means of the inlet pressure compensator (ZDW) in the direction of the second switching position ( 52b ) is actuated. Hydraulic constant pressure system according to one of claims 7 to 24, characterized in that an additional valve device ( 60 ) is provided, by means of which the default force on the inlet pressure compensator (ZDW) and / or the default force on the discharge pressure compensator (ADW) is variable. Hydraulic constant pressure system according to claim 25, characterized in that the additional valve device ( 60 ) a first control position ( 60a ), in which the inlet pressure compensator (ZDW) and the discharge pressure balance (ADW) are active, a second control position ( 60b ), in which the supply pressure compensator (ZDW) is active and the discharge pressure balance (ADW) is switched off, and a third control position ( 60c ), in which the discharge pressure compensator (ADW) is active and the supply pressure compensator (ZDW) is switched off. Hydraulic constant pressure system according to claim 26, characterized in that the additional valve device ( 60 ) in the first control position ( 60a ) at the inlet pressure compensator (ZDW) and at the outlet pressure compensator (ADW) generates an equally large predetermining force, in the second control position (FIG. 60b ) increases the default force at the outlet pressure balance (ADW) and in the third control position ( 60c ) reduces the default force at the inlet pressure compensator (ZDW). Hydraulic constant pressure system according to claim 26 or 27, characterized in that the additional valve device ( 60 ) at a positive load on the consumer drive (VA) in the second switching position ( 60b ) and at a negative load on the consumer drive (VA) in the third switching position ( 60c ) is actuated. Hydraulic constant pressure system according to one of claims 7 to 28, characterized in that the default force at the inlet pressure compensator (ZDW) from one to a control surface ( 65 ) is generated and the default force at the discharge pressure balance (ADW) from one to a control surface ( 66 ) Pending pressure signal is generated. Hydraulic constant pressure system according to claim 29, characterized in that the additional valve device ( 60 ) in the first control position ( 60a ) one to the control surface ( 65 ) of the inlet pressure compensator (ZDW) guided control line ( 67 ) and one to the control surface ( 66 ) the pressure compensator (ADW) guided control line ( 68 ) with a pilot control line ( 73 ), in which a default pressure is pending, in the second control position ( 60b ) the control line ( 67 ) of the inlet pressure compensator (ZDW) with the pilot control line ( 73 ) and the control line ( 68 ) the discharge pressure balance (ADW) connects to one of the supply lines (LH; LM; LN), and in the third control position ( 60c ) the control line ( 67 ) of the inlet pressure compensator (ZDW) with the tank line (TL) and the control line ( 68 ) the discharge pressure balance (ADW) with the pilot control line ( 73 ) connects. Hydraulic constant pressure system according to claim 30, characterized in that the default pressure is lower than the lowest constant pressure level (PN). Hydraulic constant pressure system according to one of claims 26 to 31, characterized in that the first control position ( 60a ) as a spring-biased neutral position of the additional valve device ( 60 ) is trained. Hydraulic constant pressure system according to one of claims 26 to 32, characterized in that the additional valve device ( 60 ) in dependence on the downstream of the upstream measuring throttle (MZ) of the control valve ( 10 ) pending pressure in the direction of the second control position ( 60b ) and in dependence on the upstream of the downstream measuring throttle (MA) of the control valve ( 10 ) pending pressure in the direction of the third control position ( 60c ) is acted upon. Hydraulic constant pressure system according to one of claims 30 to 33, characterized in that a limit load control device is provided, by means of which the default pressure in the pilot control line ( 73 ) is reducible.

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