Reserve protection for hydraulic systems and working machines

Abstract

To reduce a required amount of energy to be supplied to a preliminary protection function, and to secure efficient balance of energy in a minimum operation of a boom of a work machine.SOLUTION: A hydraulic system for controlling preliminary protection of a hydraulic pressure of a work machine, includes: at least one preliminary protection cylinder 12 for hydraulic pressure, tracking and limiting an operation of a boom of a work machine; a hydraulic pump 14 used in the preliminary protection cylinder; and at least one hydraulic reservoir 20 capable of supplying a hydraulic oil. A shut-off valve 16 having a closed position and a passing position, is connected between the hydraulic pump and the preliminary protection cylinder. By the shut-off valve, a load-bearing cylinder space 18 of the preliminary protection cylinder is closable, and the hydraulic reservoir connected to the load-bearing cylinder space is provided between the shut-off valve and the preliminary protection cylinder.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a hydraulic system for operating a hydraulic reserve protection of a work machine according to the preamble of claim 1, and to a work machine, in particular a mobile crane or a cable excavator, having such a hydraulic system. [Background technology]

[0002] To increase operational safety under difficult weather conditions, it is known to use so-called backup protection in many working machines, such as crawler cranes or cable excavators. To explain the principle of backup protection, FIG. 1 shows a side view of a crawler crane. The crane 1 comprises a chassis 2 with a running body (e.g. crawler running body, crawler chain running body, etc.), a superstructure 3 supported on the chassis 2 for rotation about a vertical axis, and a boom 4 supported for rotation about a horizontal axis so that the angle of inclination can be adjusted relative to the superstructure 3. The adjustment of the boom 4 is performed by a pulling winch 6 via a pulling rope 5. The load suspension means 7 or the crane hook is connected to a hoist winch 9 via a hoist rope 8. The natural length of the hoist rope 8 can be changed by moving the hoist winch 9 to increase or decrease the suspended load of the load suspension means 7.

[0003] The load of the boom 4, including the lifting load, generates a load torque M acting counterclockwise on the pivot of the boom 4 on the superstructure 3. This load torque M counteracts the rope force of the retraction rope 5, thereby tensioning the latter and holding the boom 4 at a defined angle relative to the superstructure 3. Summary of the Invention [Problem to be solved by the invention]

[0004] The boom 4 has a large surface exposed to the wind. Wind forces from the front (from the left in FIG. 1) therefore counteract the load torque M and reduce the rope force of the retracting rope 5. There is therefore a risk that the load torque M will become excessive. As a result, slack will form in the retracting rope 5 and, in the worst case, the boom 4 will flip backwards. This can lead to mechanical damage and personal injuries. Measures are known that limit the upper boom angle at the right time to below 90°, either by mechanical contact or by switching off the retracting winch 6. A maximum wind speed is further defined, at which the machine operation should be stopped and the boom 4 should be placed on the ground.

[0005] The use of this backup protection makes it possible to tolerate steeper boom angles and higher wind speeds: hydraulically operated cylinders are arranged between the boom 4 and the superstructure 3, whose forces complement the effect of the load torque M. One or more backup protection cylinders 12 are in permanent contact with the boom 4 and are associated with all its movements. They can be movements from the action of the pulling winch 6 (i.e. working movements with large cylinder strokes, usually in the range of several tens of decimeters) or smaller movements (i.e. micro movements with very small cylinder strokes, usually in the range of a few centimeters), such as elastic deformations of the whole system under the action of load changes due to an increase or decrease in the lifting load.

[0006] The energy supply of the backup protection is generally carried out by known units specifically assembled for that purpose and by a number of hydraulic pumps which apply pressure to the backup protection cylinders over the entire operating time. In this respect, the piston surfaces of the backup protection cylinders are generally constantly acted upon by the pressure of the hydraulic pumps, which are specifically applied during the working operation. In an advantageous and demonstrated embodiment, these pumps are controlled as required (by so-called "load sensing") and they adapt the oil delivery volume at a given pressure to the operating state of the backup protection cylinders, so that the output is kept within limits.

[0007] A drawback of such known energy supply systems is that every hydraulic pump installed consumes a load (friction in the bearings, splash losses, energy requirements of the regulating equipment, etc.) 100% of the time, thus reducing the efficiency of the entire working machine. Usually, this situation was ignored in past machines operated with diesel. However, in the meantime, the effort to avoid unnecessary emissions is increasing. Meanwhile, the economic and technical interest of reducing the load, for example electric drives with rechargeable batteries, is growing. In addition, the installation and installation space of several pumps as the main energy source is also limited.

[0008] Against this background, an underlying object of the present invention is to reduce the amount of energy required to supply a backup protection function and ensure an efficient balance of energy at minimum movement of the boom of the work machine. [Means for solving the problem]

[0009] This object of the invention is achieved by a hydraulic system having the features of claim 1. The hydraulic system for operating a hydraulic backup protection provided on a work machine comprises at least one hydraulic backup protection cylinder for tracking and limiting the movement of the boom of the work machine, and a hydraulic pump for supplying hydraulic fluid to the backup protection cylinder and to at least one hydraulic consumer. The hydraulic pump is therefore not provided exclusively for supplying the backup protection cylinder, but rather is used as the main energy source for supplying various consumers such as radiator drives, winches, etc., and additionally for supplying the backup protection function.

[0010] In the present invention, the shut-off valve is connected between the hydraulic pump and the backup protection cylinder and is switchable between a closed position and a passing position, thereby closing the load-bearing cylinder space of the backup protection cylinder.

[0011] To prevent the exchange of energy remaining in the hydraulic system, the load-bearing cylinder space of the backup protection cylinder can be closed by switching the shut-off valve to the closed position. The hydraulic pressure therefore remains in the shut-off area or the load-bearing cylinder space that was present when the shut-off valve was closed. Therefore, if no boom movement is intended, the hydraulic pump does not need to provide energy for the backup protection function, reducing the energy requirements and the underlying load of the primary energy source and increasing the overall efficiency. With active movement of the boom, i.e. the movement required by the operator of the work machine, the shut-off valve can be switched to the pass-through position to allow the induction of hydraulic oil in and out and to allow the tracking of the backup protection cylinder.

[0012] Since the boom does not move via the backup protection cylinder, but rather via an adjustment device, such as a retraction winch, the energy provided by the hydraulic pump is not required for the lifting of the boom, i.e. the retraction of the piston rod of the backup protection cylinder. Instead, hydraulic oil needs to be directed to be discharged or supplied to a tank while potential pressure is maintained in the load-bearing cylinder space. Supply via the hydraulic pump only needs to be provided during the extension of the backup protection cylinder, i.e. the lowering of the boom. The same applies in assembly operations, where the backup protection cylinder is removed from the boom.

[0013] In the present invention, a hydraulic reservoir connected to the load-bearing cylinder space is further provided between the shut-off valve and the backup protection cylinder, so that the boom micro-movements are guaranteed even if the load-bearing cylinder space is closed with the aid of the shut-off valve and is isolated from the hydraulic pump or tank. The backup protection cylinder can remove or provide the hydraulic oil flow required for the boom micro-movements from or to the hydraulic reservoir following the boom micro-movements.

[0014] Advantageous embodiments of the invention result from the dependent claims and the following description.

[0015] In an embodiment, at least two backup protection cylinders are provided, each having a shut-off valve and a hydraulic reservoir, both of which may be fed with hydraulic fluid by a hydraulic pump.

[0016] In a further embodiment, a pressure relief valve is provided between the shutoff valve and the backup protection cylinder. This provides a back-up pressure especially for abnormal operation and is therefore not included in the backup protection in normal operation. However, it is conceivable that the pressure relief valve, together with the synchronous opening of the shutoff valve, i.e. the shutoff valve in the pass-through position, can be used to control or regulate the transfer of hydraulic fluid flow to the pressure or backup protection to keep the hydraulic pressure in the load-bearing cylinder space in the optimum range for tracking the boom. The maximum pressure value guaranteed by the pressure relief valve can be set.

[0017] In a further embodiment, a check valve is provided, which closes off an area of ​​the hydraulic system that can be closed by the shut-off valve in the direction of the hydraulic pump. The check valve can be connected in parallel with the shut-off valve, independent of the switching state of the shut-off valve in operation, or can only operate in the closed position of the shut-off valve, i.e. can only be used when the shut-off valve is in the closed position. In the latter case, the check valve can in particular be part of the shut-off valve. It can in particular be provided with a check valve in order to initially establish a pressure balance on both sides of the shut-off valve before opening the backup protection cylinder in the operation of the boom, and to reduce or avoid load change reactions during transitions between different operating states.

[0018] A further embodiment is provided in which a further valve, preferably electrically switchable, is arranged between the shut-off valve and the hydraulic pump. The valve may be a directional valve, in particular a 4 / 2-way or 4 / 3-way valve. A possible function of the additional valve is decoupling of the shut-off valve from the hydraulic pump or the tank. Alternatively or additionally it may be conceivable that, together with the simultaneous opening of the check valve, it is used to control or regulate the pressure and the flow rate of the hydraulic fluid to / from the backup protection in order to keep the hydraulic pressure in the load-bearing cylinder space in the optimum range for tracking the boom. The valve may be electrically controllable. With several backup protection cylinders, preferably only one such valve may be provided.

[0019] A further embodiment is provided in which the load of the backup protection cylinder can be measured by a load measuring device, preferably a pressure sensor arranged between the shut-off valve and the backup protection cylinder, whereby a load sensing application is implemented, which in particular allows the pressure and the flow rate of hydraulic fluid to and from the backup protection to be controlled or regulated, thus allowing an optimal tracking of the backup protection cylinder.

[0020] Further embodiments include a pressure regulator that is used to allow setting of the pressure and flow or transfer rate to and from the backup protection cylinder, possibly adjustable based on the measured load of the backup protection cylinder, so that the hydraulic pressure in the load bearing cylinder space of the backup protection cylinder can be kept in an optimal range for tracking of the boom. Particularly upon retraction of the backup protection cylinder in response to active movement of the boom, the pressure regulator provides resistance to ensure optimal tracking while the backup protection function is maintained.

[0021] In a further embodiment, the pressure regulating device comprises a recovery device arranged in a reserve protection cylinder, in which the hydraulic fluid flowing therein is discharged on the opposite side of the piston, at least one pressure relief valve arranged between the shut-off valve and the hydraulic pump, and in particular an electrically controllable load sensing arrangement and / or means for controlling the above-mentioned valve arranged between the hydraulic pump and the shut-off valve. The control or regulation of the latter valve can be performed hydraulically, mechanically or in an electrical manner based on software. The value of the load sensing arrangement can be taken into account in this process.

[0022] In a further embodiment, the shut-off valve is hydraulically controllable, in particular by means of an electrically controllable switching valve, which is preferably arranged between the hydraulic pump and the control connection of the shut-off valve and which can have, for example, a closed position and a through position.

[0023] In a further embodiment, the closing valve is hydraulically controllable and has a control connection connected to the outlet of a hydraulic reciprocating valve, the outlet of which is possibly connected to a non-load-bearing cylinder space of the backup protection cylinder, and the other inlet of which is connected to a switching valve, in particular electrically controllable. With the aid of the reciprocating valve, the closing valve can be switched in two ways: either by controlling the switching valve in the event of action on the non-load-bearing cylinder space of the backup protection cylinder, for example in an assembly operation, or in the event of contraction of the backup protection cylinder, caused for example by "hitting" on the actuated boom, rather than in normal operation, in which no pressure action on the non-load-bearing cylinder space occurs.

[0024] In a further embodiment, the hydraulic reservoir is configured to compensate for the micro-movements of the backup protection cylinder with the load bearing cylinder space closed by the shutoff valve removing or withdrawing hydraulic fluid, which in particular results in force variations and moderate pressures associated with the inherent refilling of the hydraulic reservoir.

[0025] The invention further relates to a working machine, in particular a mobile crane or a cable excavator, comprising a swivellable boom, an adjustment device for adjusting the boom, at least one backup protection cylinder connected to the boom and following its movement, and a hydraulic system according to the invention for operating the at least one backup protection cylinder, which in this respect obviously has the same advantages and features as the hydraulic system according to the invention, and therefore a repeated description will be omitted.

[0026] In a further embodiment, when the boom is disabled by the adjustment device, the shut-off valve is in a closed position to close the load-bearing cylinder space of the backup protection cylinder, thereby reducing energy consumption or underlying load when the boom is not being moved by the operator.

[0027] In a further embodiment, a control is provided that allows the shut-off valve, and preferably the regulator, to be indirectly or directly controllable, and upon actuation of the regulator the shut-off valve is switched to a through position, whereby hydraulic fluid can be transferred to the load bearing cylinder space or removed therefrom to keep pressure in the optimum range for boom tracking.

[0028] In a further embodiment, as described above, a shut-off valve, a hydraulic pump and a check valve are provided for one backup protection cylinder, with a control configured to receive a signal from an input device for actuating the regulator for boom movement, and configured to switch the valve to a pass position to hold the shut-off valve in a closed position, switch the shut-off valve to a pass position (additionally closing other valves) after the check valve opens, and then actuate the regulator. Thereby, the pressure in the unclosed area of ​​the hydraulic system can be initially fully boosted by the hydraulic pump. As soon as the check valve is opened (and thus pressure equilibrium is established), the shut-off valve is opened and the backup protection cylinder can be retracted or extended by the subsequent movement of the boom, and hydraulic oil can be correspondingly sent or evacuated to the load-bearing cylinder space. Effect of the Invention

[0029] Further features, details and advantages of the invention are shown in the following description of the embodiments with reference to the figures. [Brief description of the drawings]

[0030] [Figure 1] FIG. 1 is a side view of a crawler crane with backup protection. [Diagram 2] FIG. 1 is a circuit diagram of a first embodiment of a hydraulic system according to the invention. [Diagram 3] FIG. 2 is a circuit diagram of a second embodiment of a hydraulic system according to the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] FIG. 1 is a schematic side view of a crawler crane, which has already been described above and will not be described again here. The working machine 1 according to the invention can in principle be a crawler crane equipped with a hydraulic system 10 according to the invention, unlike known machines. In the crawler crane shown in FIG. 1, the pull-in winch 6 arranged on the superstructure 3 represents the adjustment device. The A-frame is connected to the superstructure 3 so as to be pivotable about a horizontal axis by an articulated connection. The boom 4 is connected to the A-frame via a support means, for example a support rod, and can be pivoted together by the operation of the pull-in winch 6. However, other boom configurations and adjustment devices are also conceivable as is the boom operation, without any influence on the preliminary protection according to the invention or on the function of the hydraulic system 10.

[0032] In Fig. 2, a circuit diagram of the hydraulic system 10 for the first embodiment is shown. The hydraulic system 10 operates the function of the backup protection of the working machine 1 in the crawler crane 1 shown in Fig. 1 in the state assumed in the second embodiment described below. A hydraulic pump 14, driven by a motor 15 and operating a number of hydraulic consumers 50, which will not be described in detail, serves as the main energy source. The hydraulic consumers 50 include, for example, a radiator drive and winches such as hoist ropes and pulling winches 6, 9. In the context of the present invention, the hydraulic pump 14 also supplies two backup protection cylinders 12, the piston rods of which are pivotally connected to the boom 4 of the working machine 1.

[0033] Instead of a system with two symmetrically connected backup protection cylinders 12, other systems can be constructed with one or more backup protection cylinders 12. The exact form of the primary energy sources 14, 15 is not relevant to the functioning of the invention. The functioning of the hydraulic system 10 will be explained according to one of two symmetrical branches:

[0034] The backup protection cylinder 12 is branched off from the outlet of the hydraulic pump 14 by an electrically switchable shut-off valve 16 which has a closed position and a through position. In the closed position, a check valve 24 closes the load-bearing cylinder space 18 of the backup protection cylinder 12 in the direction opposite the hydraulic pump 14. In the through position, hydraulic fluid can be fed to or returned from the backup protection cylinder 12. A hydraulic reservoir 20 and a pressure sensor 28 are arranged in the area between the shut-off valve 16 and the backup protection cylinder 12, i.e. in the closable area.

[0035] An electrically switchable 4 / 3-way valve 26 connects the hydraulic lines leading from the hydraulic pump 14 to the shut-off valve 16 and to the non-load-bearing cylinder space or annular space 19 of the backup protection cylinder 12. In FIG. 2, the directional valve 26 is in the (middle) closed position so that the connection between the hydraulic pump 14 and the shut-off valve 16 is inoperative. The "cross" switching position of the directional valve 26, located on the left side in the figure, is not required in normal operation, since the retraction of the backup protection cylinder 12 is not caused by hydraulic pressure but by emergency movements of the boom 4. This switching position is required, for example, when the working machine is partially disassembled for transport, i.e. the boom 4 is removed from the superstructure 3 and the backup protection cylinder 12 protruding above the superstructure 3 is retracted to finish preparing for transport. In working machines without transport or assembly situations, it is also possible to use a simple 4 / 2-way valve without the cross position.

[0036] Furthermore, a pressure relief valve 30 is arranged between the directional valve 26 and the shut-off valve 16. The valve 30 is arranged in the path connecting the directional valve 26 with the annular space 19. The maximum pressure value limited by the pressure relief valve is electrically settable. It is possible by means of the pressure relief valve 30 in cooperation with the directional valve 26 to control the pressure and the flow rate of hydraulic oil or its flow to / from the backup protection cylinder 12.

[0037] All electrically switchable or adjustable valves 16, 26, 30 are controlled by the control of the working machine 1, in particular to take over the various actuators of the working machine 1, such as the hoist winch 9 and the pulling winch 6. In addition, the control receives the values ​​of the pressure sensor 28 relating to the pressure in the load-bearing cylinder space 18 of the backup protection cylinder 12, thereby performing a load sensing function. For this purpose, further sensors may be provided inside and outside the hydraulic system 10.

[0038] Unlike known systems with a backup protection function, continuous supply of the backup protection cylinder 12 by the hydraulic pump is not mandatory in the hydraulic system 10 according to the invention. Instead, the hydraulic pump 14 of the existing working machine 1 is used only to provide energy for the backup protection function in certain situations. If the boom 4 is not moved by the actuation of the retraction winch 6, the area connected to the pressure sensor 28 and the hydraulic reservoir 20, as well as the load-bearing cylinder space 18, are closed by the shut-off valve 16 so that no energy exchange with other systems takes place. The cylinder pressure present before the shut-off valve 16 is switched to its final closed position is kept in the closed volume. Only the remaining consumption 50 is supplied by the hydraulic pump 14.

[0039] The hydraulic reservoir 20 is additionally provided to ensure a backup protection function for the boom 4 in the event of minimal movement of the boom 4 due to the closed load-bearing cylinder space 18 caused by external forces, e.g., an increase or decrease in lift due to wind loads such as gusts of wind. The backup protection cylinder 12 can guide the fine movement of the boom 4, with the necessary hydraulic oil flow being removed therefrom by extension of the backup protection cylinder 12 or being added thereto by contraction of the backup protection cylinder 12. The hydraulic reservoir 20 thus acts as both a source and sink of energy for the fine movement of the boom 4.

[0040] In the actuation of the pulling winch 6 by operation aimed at active movement of the boom 4, the shut-off valve 16 is opened, i.e. switched to the passing position. In the lowering of the boom 4, the backup protection cylinder 12 is extended and the pressure required for pulling the boom 4 is maintained or adjusted in the hydraulic reservoir 20 or in the load-bearing cylinder space 18 by the supply of hydraulic oil. The directional valve 26 is also switched to the passing position for this purpose. In contrast, in the raising of the boom 4, the backup protection cylinder 12 is contracted and the directional valve 26 is maintained in the closed position, so that the hydraulic oil is guided from the load-bearing cylinder space 18 back to the tank 36 against the resistance offered by the pressure relief valve 30. The settable resistance of the pressure relief valve 30 ensures an optimal tracking of the backup protection cylinder 12 in the raising of the backup protection cylinder 12.

[0041] Therefore, the supply of hydraulic pressure to the backup protection cylinder 12 by the hydraulic pump 14 only needs to be performed during overhaul or additional assembly work with the boom 4 lowered. When the boom 4 is lowered, additional provision is made by not switching the shut-off valve 16 to the through position, but rather by the supply of hydraulic oil via the opening of the check valve 24. The check valve 24 has the function, among other things, of reducing the load change reaction when changing the operating state, but this is not essential. An advantageous operating method of the hydraulic system 10 when raising the boom 4 is explained below. In a starting position, in which no active movement of the boom 4 takes place, the shut-off valve 16 and the directional valve 26 are each in a closed position, and there is no pressure in the hydraulic path between them. In contrast, the hydraulic path between the shut-off valve 16 and the backup protection cylinder 12 is acted upon by the stored pressure. If the operator of the working machine 1 then wants to raise or erect the boom 4, he makes a corresponding input via the input device.

[0042] By this control, the directional valve 26 is switched to the through position ("parallel" position), which increases the pressure in the hydraulic path upstream of the shut-off valve 16, i.e. the pressure acting on the check valve 24. If the pressure generated by the hydraulic pump 14 exceeds the pressure stored in the closed area, the check valve 24 opens and a pressure balance is established in the hydraulic reservoir 20. The directional valve 26 can additionally be closed after this point.

[0043] The control also switches the shutoff valve 16 to the pass position. However, this step can additionally be omitted and the supply of hydraulic oil can be provided via the check valve 24 when necessary (i.e. when it falls below the minimum permitted cylinder force). The retraction winch 6 is then actuated so that the boom 4 rises. This causes the backup protection cylinder 12 to contract against the resistance of the pressure relief valve 30 and a corresponding pressure in the load-bearing cylinder space 18 or a corresponding holding force causes the backup protection cylinder 12 to follow.

[0044] Figure 3 shows a second embodiment of the hydraulic system 10 according to the invention. In comparison with the first embodiment shown in Figure 2, here the shut-off valve 16 is preset in the closed position with hydraulic switching enabled and its control input is connected to the outlet of a hydraulic reciprocating valve 34. The reciprocating valve 34 is connected on the input side to the annular space 19 of the backup protection cylinder 12, so that the shut-off valve 16 can be switched to the through position by the pressure action determined in the annular space 19. However, since the retraction of the backup protection cylinder 12 is performed mechanically via the boom 4, this does not occur during normal work operation of the work machine 1.

[0045] The other input side of the reciprocating valve 34 is connected to an electrically switchable switching valve 32. The shutoff valve 16 can be switched to a through position by controlling the switching valve 32. The shutoff valve 16 does not function as a check valve in the closed position, but rather the check valve 24 here is continuously connected in a parallel state. However, the function of this hydraulic system 10 corresponds to that shown as the first embodiment.

[0046] An additional pressure relief valve 22 provides pressure back-up for abnormal operation and may be included in the shut off area of ​​the hydraulic system 10 either as a function of the hydraulic system or as an additional protection during normal operation.

[0047] The substantial advantages of the hydraulic system 10 of the present invention can be summarized as follows: The energy required to supply the backup protection function is only required when the backup protection cylinder 12 is extended. This is only in the case of the "Lower Boom" operation of the working machine 1 or an additionally provided mounting operation. The minimum movement of the boom 4 caused by the action of external forces is compensated by the hydraulic reservoir 20 to ensure a backup protection function. [Explanation of symbols]

[0048] 1. Work Machinery 2. A vehicle equipped with a chassis 3 Superstructure 4. Boom 5. Pull Rope 6 Adjustment device (retraction winch) 7 Load suspension means (load hook) 8 Hoist Rope 9 Hoist winch 10 Hydraulic System 12 Backup protection cylinder 14 Hydraulic pump 15 Motor 16 Shut-off valve 18 Load-bearing cylinder space 19 Non-load bearing cylinder space 20 Hydraulic reservoir 22 Pressure relief valve 24 Check valve 26 Valves (directional valves) 28 Pressure Sensor 30 Pressure relief valve 32 Switching valve 34 Reciprocating Valve 36 Tank 50 consumables M Load Torque

Claims

1. A work machine (1), The work machine (1) comprises: A rotatable boom (4); an adjustment device (6) for adjusting the boom (4); At least one hydraulic consumer (50); a hydraulic system (10) for operating a hydraulic backstop of the work machine (1); The hydraulic system (10) comprises: at least one hydraulic backstop cylinder (12) connected to and following the movement of the boom (4) for tracking and limiting the movement of the boom (4); a hydraulic pump (14) for operating said backstop cylinder (12) and said at least one hydraulic consumer (50); a switchable shut-off valve (16) disposed between the hydraulic pump (14) and the backstop cylinder (12) and having a closed position and a passing position; The backstop cylinder (12) has a load cylinder space (18) on which pressure can act, and a non-load cylinder space (19) on which pressure can act during an assembly operation; The load cylinder space (18) of the backstop cylinder (12) can be closed by the shutoff valve (16); The hydraulic system (10) comprises: a hydraulic reservoir (20) disposed between the shutoff valve (16) and the backstop cylinder (12) and connected to the load cylinder space (18); a check valve (24) for closing off an area of ​​the hydraulic system (10) that can be closed by the shut-off valve (16) in the direction of the hydraulic pump (14); a further electrically switchable valve (26) disposed between the shutoff valve (16) and the hydraulic pump (14); The check valve (24) is connected in parallel with the shutoff valve (16) or operates only when the shutoff valve (16) is in a closed position. Working machinery.

2. A hydraulic system comprising at least two backstop cylinders (12), each having a shut-off valve (16) and a hydraulic reservoir (20) to which hydraulic fluid can be both supplied by the hydraulic pump (14).

2. The work machine of claim 1.

3. A pressure release valve (22) is provided between the shutoff valve (16) and the backstop cylinder (12). A work machine according to claim 1 or 2.

4. The load of the backstop cylinder (12) can be measured by a load measuring device including a pressure sensor (28) disposed between the shutoff valve (16) and the backstop cylinder (12). A work machine according to any one of claims 1 to 3.

5. Further comprising a pressure adjusting device, said pressure regulator allows the pressure and transfer rate to and from said backstop cylinder (12) to be set and adjusted based on the measured load of said backstop cylinder (12); A work machine according to any one of claims 1 to 4.

6. The shutoff valve (16) is hydraulically controllable by an electrically controllable switching valve (32). A work machine according to any one of claims 1 to 5.

7. The shut-off valve (16) is hydraulically controllable and has a control connection connected to an outlet of a hydraulic reciprocating valve (34); One inlet of the hydraulic reciprocating valve (34) is connected to the unloaded cylinder space (19) of the backstop cylinder (12), and the other inlet is connected to an electrically controllable switching valve (32). A work machine according to any one of claims 1 to 6.

8. The hydraulic reservoir (20) is configured to compensate for minute movements of the backstop cylinder (12) by removing and releasing hydraulic oil when the load cylinder space (18) is closed by the shut-off valve (16). A work machine according to any one of claims 1 to 7.

9. The shut-off valve (16) is in a closed position when the boom (4) is not actively moved by the adjustment device (6). A work machine according to any one of claims 1 to 8.

10. A control device capable of indirectly or directly controlling the shut-off valve (16) and the regulating device (6) and configured to switch the shut-off valve (16) to a passing position when the regulating device (6) is actuated. A work machine according to any one of claims 1 to 9.

11. The control device is configured to receive a signal from an input device to actuate the regulating device (6) to move the boom (4), switch the further valve (26) to a pass position, hold the shut-off valve (16) in a closed position, switch the shut-off valve (16) to a pass position after the check valve (24) is opened, and thereafter actuate the regulating device (6).

11. A work machine according to claim 10.

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