EP2667038A2 - Hydraulic circuit assembly - Google Patents

Abstract

The device has hydraulic lines (12,14) connected to hydraulic fluid inlet and hydraulic fluid return line for lifting/lowering hydraulic load. A drain control valve (26) is opened/closed to control flow of hydraulic fluid from load. A pilot valve (30) controls pilot pressure in control input (28) of drain control valve for opening pilot valve. A pressure-measuring device measures pressure in line (14) during lowering of load. A control device (42) controls pilot valve based on measured pressure such that preset pressure prevails in line (14) for opening drain control valve.

Description

The invention relates to a hydraulic circuit arrangement for a hydraulically operated machine. Hoisting winches are hydraulically operated on many lifting vehicles, in particular by hydraulic motors. The hoisting winches are used for lifting and lowering loads. Via hose lines, the hydraulic motor is connected to a control valve, which doses a coming from a pump hydraulic fluid flow in the amount and determines its direction for lowering or lifting the load.

So that in a line break or hose rupture of the hydraulic motor extending hydraulic lines no uncontrolled falling of the load is possible, usually lowering brake valves are provided which are locked in a normal position and are opened, for example by the pressure in a supply line to the hydraulic motor. In known lowering brake valves, a volume flow is conducted via a check valve to the hydraulic motor for lifting the load and from there to a tank. The lifting thus happens almost lossless, since only the unavoidable throttle losses incurred in the valve. To lower the load, the hydraulic fluid is then passed from the control valve to the hydraulic motor. From this line also a control pressure is tapped, which acts on a valve spool opening. Only then can the hoist winch be set in motion to lower the load. The load pressure of the winch is thus supported on the lowering brake valve.

Usually hydraulic motors are hydraulically clamped, so that the lowering of the load can be done without vibration. This means that the lowering brake valve, for example, only opens at an inlet pressure of 15 bar and is only fully opened, for example, at a pressure of 50 or 60 bar. This in turn means that even when lowering a load due to its own weight without feeding an external power would decrease, a large proportion of power, namely the total volume flow supplied with the necessary for lowering pressure, must be supplied. In this case, considerable amounts of power are throttled, in particular converted into heat.

Based on the explained prior art, the present invention seeks to provide a hydraulic circuit arrangement for a hydraulically operated machine, which reduces the power losses with high security against uncontrolled lowering of a load.

This object is achieved according to the invention by the subject matter of claim 1. Advantageous embodiments can be found in the dependent claims, the description and the figures.

The invention solves this problem by a hydraulic circuit arrangement for a hydraulically operated machine, comprising at least one hydraulic load for selectively lifting or lowering a load, and a first and a second connected to the hydraulic consumer hydraulic line, wherein for lifting the load a hydraulic fluid inlet for the hydraulic consumer via the first hydraulic line is carried out and a hydraulic fluid return from the hydraulic consumer via the second hydraulic line, and wherein for lowering the load is a hydraulic fluid inlet for the hydraulic consumer via the second hydraulic line and takes place a hydraulic fluid return from the hydraulic consumer via the first hydraulic line, at least one drain control valve, which in the open state a flow of when lowering the load as return from the hydraulic consumer coming Hydraulikflü liquid and in a closed ground state for one such flow of hydraulic fluid blocks, at least one connected to the second hydraulic line pilot valve, wherein the pilot valve, a pilot pressure at a first control input of the drain control valve for opening the drain control valve is controllable, a pressure measuring device that measures the pressure in the second hydraulic line, at least when lowering the load , And a control device, which controls based on the pressure measured by the pressure measuring device, the pilot valve for opening the drain control valve, that in the second hydraulic line, a predetermined pressure prevails.

The work machine may be a lift truck, e.g. a crane, act. The work machine may e.g. comprise a hoisting winch with which a load is raised or lowered, the hoisting winch being driven by the hydraulic consumer, e.g. a hydraulic motor, is driven. The circuit arrangement comprises a main control valve which selectively connects the first hydraulic line to the pump and the second hydraulic line to the tank for lifting a load or connects the second hydraulic line to the pump and the first hydraulic line to the tank for lowering a load. The hydraulic fluid may be hydraulic oil in a manner known per se. When lifting the pump flow is passed through the main control valve and, for example, an inlet check valve through the first hydraulic line to the hydraulic consumer and from there into the second hydraulic line and back to the main control valve in the tank. This happens almost lossless.

When lowering the load, however, the pump flow is passed through the main control valve through the second hydraulic line to the hydraulic consumer and from there into the first hydraulic line, from which it reaches the drain control valve. This is initially closed in a basic position, so that the hydraulic fluid can not flow through the drain control valve. Thereby Among other things, the pressure increases in the second hydraulic line serving as an inlet. This pressure is measured by the pressure measuring device, for example at regular intervals or continuously and the measurement results are given to the control device. For this purpose, the pressure measuring device comprises at least one pressure sensor, which measures the pressure in the second hydraulic line when lowering the load and possibly also when lifting the load. By means of the control device, the pressure in the second hydraulic line is regulated on this basis to a defined predetermined pressure, that is, a target pressure. This is done according to the invention by means of a pilot valve, which is controlled by the control device. By means of the pilot control valve, the pilot pressure acting on the first control input of the drain control valve is set in a suitable manner for opening the drain control valve. On the first control input of the drain control valve thus acts a mediated by the pilot valve control pressure, which then leads to the opening of the drain control valve. When open, hydraulic fluid can flow to the tank via the drain control valve. On the basis of the measured values of the pressure measuring device, control of the opening cross section of the pilot valve is carried out by means of the control device in such a way that such an opening cross section is provided by the drain control valve that the set pressure prevails as precisely as possible in the second hydraulic line.

The pilot valve is supplied by the second hydraulic line serving as a supply line to the hydraulic consumer when lowering the load. If the hydraulic consumer, for example a hydraulic motor, becomes too fast and over-revving due to a very large load to be lowered, this leads to a drop in the inlet pressure in the second hydraulic line. This in turn automatically causes the pressure in the pilot control line to the drain control valve to decrease and the drain control valve to close. Through this structure, the inventive circuit arrangement at low inlet pressures automatically to a classic lowering brake valve, which prevents over-rotation and cavitation of the hydraulic load, such as a Windernnotors. In addition, another important safety function is fulfilled. At least the drain control valve is in its basic state in a closed position. If, for example, when lowering the load, a line break occurs and a sudden drop in pressure occurs in the system, sufficient pressure is no longer available to open the drain control valve. This therefore closes and uncontrolled falling of the load is reliably prevented. The pilot valve may also be in its basic state in a closed position according to an embodiment. But it is also possible in principle that the pilot valve is open in its basic position and is influenced by the control device in the course of pressure control of the opening cross section in a suitable manner.

The function of lowering the load according to the invention corresponds to a supply pressure control. In particular, the supply pressure to the hydraulic consumer is regulated to a specific desired value with the aid of the drain control valve. With a conventional counterbalance valve, the inlet pressure opens the drain control valve directly. This often causes vibrations in the system, which can only be prevented by high damping measures. Often only a high hydraulic clamping of the consumer of 60 bar and more leads to success. By contrast, the hydraulic circuit arrangement according to the invention effects a decoupling of the second hydraulic line serving as a supply line during lowering from the drain control valve, since the inlet pressure does not immediately open the drain control valve, but the pilot valve is interposed. The pressure required for the vibration-free lowering of a load is achieved by the hydraulic circuit arrangement according to the invention therefore considerably reduced. This reduces power losses. In addition, it is possible to provide targeted further vibration-reducing measures by the control device.

The pilot valve may open according to an embodiment in the open state, a connection between the second hydraulic line and the first control input of the drain control valve for opening the drain control valve and close in a closed state, this connection. The pilot valve may be arranged in particular in a connecting line between the second hydraulic line and the first control input of the drain control valve. The pilot valve thus establishes in its open state via its working channel a connection between the second hydraulic line and a first control input of the drain control valve. Achieved, for example, when starting the hydraulic consumer, the pressure in the second hydraulic line, the target pressure, the control device controls the pilot valve in such a way that it is brought from a closed state to an open state and thus also opens the drain control valve. But it is also possible that the pilot valve is arranged in a branched off from the connecting line between the second hydraulic line and the first control input of the drain control valve bypass line. The bypass line forms a bypass to the drain control valve. In this case, the pilot pressure to the first control input of the drain control valve is thus influenced by the open-arranged in the bypass line pilot valve is opened or closed.

The drain control valve may be, for example, a 2/2-way valve. The pilot valve may be, for example, a 3/2-way valve. The drain control valve may be closed leak-free in its basic position. The pilot valve may have a connection for leak oil. After a particularly practical design The pilot valve may be an electrically controllable pilot valve, which is electrically controlled by the control device. The controller may include a microcontroller. The evaluation of the measuring signals of the pressure measuring device and the control of the pilot valve and thus the control to a constant inlet pressure in the second hydraulic line when lowering a load are then carried out by the microcontroller. By such, for example, as "onboard electronics" designed microcontroller extensive control rules can be implemented in a simple and cost-effective manner.

The drain control valve and / or the pilot valve may be a proportional valve. As a result, the regulation to a constant pressure in the second hydraulic line serving as a supply line during lowering is possible in a particularly simple and precise manner. The pilot valve may in particular be an electrohydraulic valve with proportional solenoids.

According to a further embodiment may act on the second control input of the drain control valve, a spring force biasing the drain control valve in a closed position, for example, a constant spring force. The control device can act on a first control input of the pilot valve, wherein a spring force, for example a constant spring force acts on the second control input of the pilot valve. This can bias the pilot valve in a closed position. The second control inputs of the drain control valve and / or the pilot control valve may each be connected to the tank. By acting on the second control inputs spring forces is ensured in a particularly simple and reliable manner that the pilot valve and the drain control valve are biased in the closed position.

According to another embodiment, it can be provided that the control device only activates the pilot control valve for opening the drain control valve when a predetermined limit pressure is measured by the pressure measuring device. As a result, the required hydraulic clamping and thus avoiding vibrations of the system when lowering the load is ensured. At the same time, as explained above, in the hydraulic circuit arrangement according to the invention a significantly lower pressure is required for the clamping than in the prior art. By way of example only given are predetermined limiting pressures in the range of 20 to 30 bar. These depend on the specific application.

As already mentioned, the pressure measuring device comprises at least one pressure sensor, which measures the pressure in the second hydraulic line at least when lowering the load. According to a further embodiment, the pressure measuring device may comprise at least two pressure sensors, each measuring the pressure in the second hydraulic line at least when lowering the load. As a result, a higher level of security is realized, for example, in the event that one of the pressure sensors fails. The measured values of both pressure sensors are present as inputs to the control device and can for example be compared with one another by the control device. For example, when a predetermined limit difference between the pressure measured values compared with one another is exceeded, an error message can then be output by the control device and / or the lowering of the load can be stopped. If one of the pressure sensors indicates erroneous measured values, this is thus recognizable by the control device and suitable countermeasures can be taken. It is also possible according to a further embodiment that the pressure sensors are different pressure sensors. For example, the pressure sensors can be designed for different pressure ranges. Hereby are Also, to rule out systematic errors that can occur in certain configurations of load and pressure sensors.

According to a further embodiment, a non-return valve which opens in the direction of flow when the load is lowered as a return from the hydraulic consumer and opens in the opposite direction of flow can be provided. This ensures that when lifting the load a hydraulic fluid supply is possible at any time, and that when lowering the load, a hydraulic fluid return is only possible via the drain control valve. The check valve can be integrated into the drain control valve.

According to a particularly practical embodiment can be provided that branches off from the first hydraulic line, a third hydraulic line, wherein when lowering the load a hydraulic fluid return from the hydraulic consumer via the first hydraulic line and the third hydraulic line, and wherein the drain control valve is disposed in the third hydraulic line , When lowering the load, the hydraulic fluid flow passes via the branch into the third hydraulic line to the drain control valve arranged therein. An outflow via the first hydraulic line downstream of the branch into the third hydraulic line is not possible. For this purpose, it may be provided that the check valve in the first hydraulic line in the flow direction of the hydraulic fluid when lowering the load downstream of the branch is arranged in the third hydraulic line. The third hydraulic line can branch off at a branch point from the first hydraulic line and open at a mouth location back into the first hydraulic line. The check valve may then be disposed between the tap site and the mouth location in the first hydraulic line. The third hydraulic line forms in this embodiment, a bypass line for bypassing the in the first hydraulic line arranged check valve. The drain control valve is thus arranged parallel to the check valve. By the check valve is ensured in a particularly simple manner that when lowering a load of the hydraulic fluid flow must be done via the third hydraulic line, while lifting the load a hydraulic fluid inlet via the first hydraulic line is possible. Via the main control valve, when the load is lowered, the hydraulic fluid can then flow out to the tank through the third and optionally the first hydraulic line.

As already mentioned, the hydraulic consumer can be a hydraulic motor. It can then be further provided a speed measuring device which measures the speed of the hydraulic motor and gives the measured values to the control device. According to a further embodiment, the control device may be designed to take into account individual application parameters for the control process, in particular the weight of the load, a setpoint and / or maximum speed when lowering the load and / or a setpoint and / or maximum speed of the hydraulic load when Lowering the load.

The control device, for example a microcontroller of the control device, can therefore be provided with additional signals for the evaluation in addition to the pressure measurement values. For example, based on a speed sensor of a winch motor, the microcontroller can detect the speed of the wind when lowering the load and depending on wind speed, for example, use different target pressures for the control. Also, for example, from a central crane control data to the control device, such as a microcontroller of the control device, could be passed. An example in this regard would be a setpoint for the lowering speed of a load. These further parameters can then be taken into account by the control device by a each appropriate target pressure is selected as the inlet pressure when lowering the load to which the control device then controls.

Fig. 1

eine erfindungsgemäße hydraulische Schaltungsanordnung nach einem ersten Ausführungsbeispiel,

Fig. 2

eine erfindungsgemäße hydraulische Schaltungsanordnung nach einem zweiten Ausführungsbeispiel, und

Fig. 3

eine erfindungsgemäße hydraulische Schaltungsanordnung nach einem dritten Ausführungsbeispiel.

Embodiments of the invention will be explained in more detail with reference to drawings. They show schematically:

Fig. 1

A hydraulic circuit arrangement according to the invention according to a first embodiment,

Fig. 2

a hydraulic circuit arrangement according to the invention according to a second embodiment, and

Fig. 3

a hydraulic circuit arrangement according to the invention according to a third embodiment.

Unless otherwise indicated, like reference characters designate like items throughout the figures. The inventive circuit arrangement according to the in FIG. 1 The first embodiment shown has a main control valve 10 and a first hydraulic line 12 and second hydraulic line 14 connected to the main control valve 10. Between the first and second hydraulic line 12, 14 there is a hydraulic consumer, in the present case a hydraulic motor 16. The hydraulic motor 16 serves to raise or lower a load by a hydraulic working machine, for example a lifting vehicle with a hoist winch driven by the hydraulic motor 16. At a branch point 18, a third hydraulic line 20 branches off from the first hydraulic line 12. At a mouth 22, the third hydraulic line 20 opens again into the first hydraulic line 12. Between the branch point 18 and the mouth 22 there is a check valve 24th in the first hydraulic line 12. To lift the load hydraulic fluid is conveyed via the main control valve 10 by means of a pump from a tank into the first hydraulic line 12, in which they return via the check valve 24 to the hydraulic motor 16 and from there via the second hydraulic line 14 to the main control valve 10 passes, through which it is discharged into the tank. In this conveying direction of the hydraulic fluid opens the check valve 24. In the opposite direction blocks the check valve 24th

In addition, a drain control valve 26, in the present case a 2/2-way proportional valve, is located in the third hydraulic line 20. In the basic position shown in the figure, which is also assumed when lifting a load, the drain control valve 26 blocks for a flow of hydraulic fluid through the third hydraulic line 20. A first control input 28 of the drain control valve 26 is connected to the output of a pilot valve 30, in this case one 3/2-way proportional valve, in particular an electrically controllable pilot valve 30. A second control input 32 of the drain control valve 26 is at tank pressure level, with a spring force acting on the second control input 32. As a result, the above-described closed basic position is ensured. In the pilot valve 30, the first control input 34, as mentioned, electrically controllable. The second control input 36 in turn is at tank pressure level, with a spring force also acting on the second control input 36 of the pilot control valve 30. As a result, the pilot valve 30 is biased in the closed basic position shown in the figure. In this basic position, the pilot valve 30 connects the first control input 28 of the drain control valve 26 with tank pressure level.

The hydraulic circuit arrangement according to the first embodiment further comprises a pressure measuring device with two pressure sensors 38, 40, which in each case control the pressure in the second hydraulic line 14 measure, for example at regular intervals or continuously. The measurement results are given by the pressure sensors 38, 40 to a control device 42 of the hydraulic circuit arrangement according to the invention. The control device 42 includes a microcontroller, which is electrically supplied via a line 44. Via an electrical line 46, the control device 42, the first control input 34 of the pilot valve 30 to open the pilot valve 30 to control. It should be mentioned that near the main control valve 10 of the second hydraulic line 14 branches off a compensation line 48, which is connectable via a pressure relief valve 50 to the tank. By the pressure relief valve 50, the maximum inlet pressure in the second hydraulic line is limited. By the pressure limiting valve 50 and sudden supply pressure changes can be limited, whereby the first existing control error (target-actual error) can be limited even at high attenuation.

The hydraulic circuit arrangement according to the first embodiment operates as follows: The lifting of a load with the circuit arrangement according to the invention has been explained above. To lower a load, hydraulic fluid is conveyed from the tank into the second hydraulic line 14 via the main control valve 10 by means of a pump. Due to the check valve 24, a drainage of the hydraulic fluid via the first hydraulic line 12 to the main control valve 10 and thus to the tank is not possible. Rather, the hydraulic fluid at the branch point 18 enters the third hydraulic line 20. As long as the drain control valve 26 and the pilot valve 30 are in their closed position, the drain control valve 26 also blocks a drainage of the hydraulic fluid through the third hydraulic line 20. On the inlet side of the hydraulic motor 16 increases So the pressure on. The pressure sensors 38, 40 measure, for example, at regular intervals or continuously the pressure in the second hydraulic line 14 and give their measured values to the control device 42. The control device 42 is now to regulate the pressure in the second hydraulic line 14 to a desired pressure. Purely by way of example, it is assumed that this target pressure is 30 bar. As soon as the pressure measured by the pressure sensors 38, 40 reaches this value, the pilot valve 30 is actuated by the control device 42 via the line 46, so that it assumes an open state. In this open state, the pilot valve 30 establishes a connection via the line 52 between the second hydraulic line 14 and the first control input 28 of the drain control valve 26. In this open state of the drain control valve 26, hydraulic fluid can flow via the third hydraulic line 20 and the mouth 22 through the first hydraulic line 12 to the main control valve 10 and thus to the tank. The control device 42 controls the opening cross section of the pilot valve 30 and also the opening cross section of the drain control valve 26 so that in the now taking place lowering the load in the second hydraulic line 14 as accurately as possible, the target pressure of for example 30 bar. Thus, regardless of the load and the lowering speed, a constant inlet pressure arises on the inlet side of the hydraulic motor 16.

In this case, a comparison of the measured values of the two pressure sensors 38, 40 can take place in the control device 42. If critical deviations are detected, this indicates an error of at least one of the pressure sensors 38, 40. It can then be taken by the control device 42 suitable countermeasures, for example, a stop of the lowering process and / or an error message. It is also possible that the two pressure sensors are designed differently in order to rule out systematic errors.

This in Fig. 2 shown second embodiment of a hydraulic circuit arrangement according to the invention corresponds in structure and function as far as possible in Fig. 1 shown embodiment. In contrast to the embodiment according to Fig. 1 is the pilot valve 30 'at the in Fig. 2 however, in the second embodiment shown in FIG Fig. 2 shown basic state, thus establishes a connection between the second hydraulic line 14 and the first control input 28 of the drain control valve 26. For pressure control, the pilot valve 30 'is controlled by the control device 42 via the line 46, so that in turn the first control input 28 of the drain control valve 26 supplied pilot pressure is controlled in a suitable manner for pressure control, as in principle above to Fig. 1 was explained.

Also in Fig. 3 shown third embodiment of the circuit arrangement according to the invention corresponds in structure and function as far as possible in Fig. 1 shown first embodiment. Unlike the ones in the FIGS. 1 and 2 shown first and second embodiments of the invention is in the third embodiment after Fig. 3 However, the pilot valve 30 "not in a connecting line between the second hydraulic line 14 and the first control passage 28 of the drain control valve 26, but in a bypass line 52 branching off from this connecting line, through which the drain control valve 26 can be bypassed .. The bypass line 52 is connected to tank pressure level. In the in Fig. 3 In this state, the pressure acting on the first control input 28 of the drain control valve 26 acts via a throttle point 54 of the pressure acting in the second hydraulic line 14. For the pressure control, the pilot control valve 30 "of the pressure control device 42 via the line 46 are brought into an open state, so that in turn the on the first control gear 28 of the drain control valve 26 acting pilot pressure can be influenced. As the pilot valves 30 and 30 'from the FIGS. 1 and 2 it is also in the pilot valve 30 "off Fig. 3 around a proportional valve, in this case a 2/2-way proportional valve.

In the circuit arrangement according to the invention according to all embodiments, the pressure required to lower a load, can be significantly reduced. This results in a considerable energy saving potential. The hydraulic oscillating circuit can be decoupled and, if necessary, vibration-reducing measures can be taken via the microcontroller of the regulating device 52. By supplying the pilot valve 30, 30 ', 30 "with the second hydraulic line 14, which acts as a supply line when the load is lowered, the intake pressure drops, for example, if the hydraulic motor 16 overruns with a very large driving load At the same time, for example, in the event of a line break and an associated sudden pressure drop in the system, it is ensured that the pilot valve 30, 30 ', 30 "and the drain control valve 26 move in their closed position, so that an uncontrolled fall of the load is excluded.

Claims (21)

Hydraulic circuit arrangement for a hydraulically operated working machine, comprising - At least one hydraulic consumer for selectively raising or lowering a load, and a first and a second connected to the hydraulic consumer hydraulic line (12, 14), wherein for lifting the load, a hydraulic fluid inlet for the hydraulic consumer via the first hydraulic line (12) and a hydraulic fluid return from the hydraulic consumer via the second hydraulic line (14) takes place, and wherein for lowering the load, a hydraulic fluid inlet for the hydraulic consumer via the second hydraulic line (14) and a hydraulic fluid return from the hydraulic consumer via the first hydraulic line (12) he follows, - At least one drain control valve (26), which allows a flow of when lowering the load as a return from the hydraulic consumer incoming hydraulic fluid in the open state and blocks in a closed ground state for such a flow of hydraulic fluid, - At least one with the second hydraulic line (14) connected pilot valve (30, 30 ', 30 "), wherein by the pilot valve (30, 30', 30") a pilot pressure at a first control input (28) of the drain control valve (26) for Opening the drain control valve (30, 30 ', 30 ") is controllable, - A pressure measuring device that measures the pressure in the second hydraulic line (14) at least when lowering the load, and a control device (42) based on the pressure from the device measured pressure, the pilot valve (30, 30 ', 30 ") so to open the drain control valve (26) controls that in the second hydraulic line (14) there is a predetermined pressure. Hydraulic circuit arrangement according to claim 1, characterized in that the pilot valve (30, 30 ', 30 ") in the open state, a connection between the second hydraulic line (14) and the first control input (28) of the drain control valve (26) for opening the drain control valve (26). 26) opens and closes this connection in a closed state. Hydraulic circuit arrangement according to one of claims 1 or 2, characterized in that the pilot valve (30, 30 ', 30 ") is arranged in a connecting line between the second hydraulic line (14) and the first control input (28) of the drain control valve (26). Hydraulic circuit arrangement according to one of claims 1 or 2, characterized in that the pilot valve (30, 30 ', 30 ") branches off in one of the connecting line between the second hydraulic line (14) and the first control input (28) of the drain control valve (26) Bypass line (52) is arranged. Hydraulic circuit arrangement according to one of the preceding claims, characterized in that the pilot valve (30, 30 ', 30 ") is an electrically controllable pilot valve (30, 30', 30"), which is electrically controlled by the control device (42). Hydraulic circuit arrangement according to one of the preceding claims, characterized in that the control device (42) comprises a microcontroller. Hydraulic circuit arrangement according to one of the preceding claims, characterized in that the drain control valve (26) and / or the pilot control valve (30, 30 ', 30 ") is a proportional valve. Hydraulic circuit arrangement according to one of the preceding claims, characterized in that acts on the second control input (32) of the drain control valve (26) has a spring force which biases the drain control valve (26) in a closed position. Hydraulic circuit arrangement according to one of the preceding claims, characterized in that the control device (42) acts on a first control input (34) of the pilot valve (30, 30 ', 30 ") and that on the second control input (36) of the pilot valve (30 , 30 ', 30 ") a spring force acts. Hydraulic circuit arrangement according to one of the preceding claims, characterized in that the control device (42), the pilot valve (30, 30 ', 30 ") only to open the drain control valve (26) controls when a predetermined limit pressure is measured by the pressure measuring device. Hydraulic circuit arrangement according to one of the preceding claims, characterized in that the pressure measuring device at least two pressure sensors (38, 40) each measuring the pressure in the second hydraulic line (14) at least when lowering the load. Hydraulic circuit arrangement according to claim 11, characterized in that the pressure sensors (38, 40) are different pressure sensors (38, 40). Hydraulic circuit arrangement according to one of the preceding claims, characterized in that in the flow direction of when lowering the load as return from the hydraulic consumer coming hydraulic fluid blocking and opening in the opposite direction of flow check valve (24) is provided. Hydraulic circuit arrangement according to claim 13, characterized in that the check valve is integrated in the drain control valve (26). Hydraulic circuit arrangement according to one of the preceding claims, characterized in that from the first hydraulic line (12) branches off a third hydraulic line (20), wherein when lowering the load a hydraulic fluid return from the hydraulic consumer via the first hydraulic line (12) and the third hydraulic line ( 20), and wherein the drain control valve (26) is arranged in the third hydraulic line (20). Hydraulic circuit arrangement according to claims 13 and 15, characterized in that the check valve (24) in the first hydraulic line (12) is arranged in the flow direction of the hydraulic fluid when lowering the load downstream of the branch into the third hydraulic line (20). Hydraulic circuit arrangement according to one of claims 15 or 16, characterized in that the third hydraulic line (20) at a Abzweigungsort (18) branches off from the first hydraulic line (12) and opens at a mouth location (22) again in the first hydraulic line (12) , Hydraulic circuit arrangement according to claims 16 and 17, characterized in that the check valve (24) between the Abzweigungsort (18) and the mouth location (22) in the first hydraulic line (12) is arranged. Hydraulic circuit arrangement according to one of the preceding claims, characterized in that the hydraulic consumer is a hydraulic motor (16). Hydraulic circuit arrangement according to claim 19, characterized in that a speed measuring device is provided which measures the rotational speed of the hydraulic motor (16) and outputs the measured values to the control device (42). Hydraulic circuit arrangement according to one of the preceding claims, characterized in that the control device (42) is designed to take into account individual application parameters for the control process, in particular the weight of the load, a desired and / or maximum speed when lowering the load and / or a target and / or Maximum speed of the hydraulic load when lowering the load.

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