EP3943440A1 - Hydraulic system for a fallback support and tool - Google Patents

Abstract

The invention relates to a hydraulic system (10) for operating a hydraulic fallback support of a working implement (1), comprising at least one hydraulic fallback support cylinder (12) for tracking and limiting movements of a boom (4) of the working implement, and a hydraulic pump (14) by means of which the Fallback support cylinder and at least one other consumer can be supplied with hydraulic fluid. According to the invention, a shut-off valve (16) with a shut-off position and an open position is connected between the hydraulic pump and the fall-back support cylinder, by means of which a load-bearing cylinder space of the fall-back support cylinder can be shut off, and a hydraulic accumulator (20) connected to the load-bearing cylinder space is provided between the shut-off valve and the fall-back support cylinder.

Description

The present invention relates to a hydraulic system for operating a hydraulic fallback support of a working device according to the preamble of claim 1 and a working device, in particular a mobile crane or cable excavator, with such a hydraulic system.

In a number of work devices such as crawler cranes or cable excavators, it is known to use so-called fallback supports to increase operational safety in difficult weather conditions. To illustrate the principle of a fallback support, the figure 1 a generic crawler crane 1 in a side view. The crane 1 has an undercarriage 2 with an undercarriage (e.g. crawler undercarriage, caterpillar undercarriage, etc.) and an uppercarriage 3 which is mounted on the undercarriage 2 so that it can rotate about a vertical axis and to which a boom 4 is bolted so that it can pivot about a horizontal axis so that its angle of inclination is relatively to the superstructure 3 is adjustable. The boom 4 is adjusted via a luffing rope 5 by means of a luffing winch 6 . By operating the hoist winch 9, the free length of the hoist rope 8 can be changed in order to raise or lower hoist loads attached to the load-carrying means 7.

The weight of the jib 4 together with the lifting load generates a load moment M acting counterclockwise around the pivot point of the jib 4 on the superstructure 3. This load moment M is counteracted by the rope force of the luffing rope 5, which means that it is tensioned and the jib 4 is in a defined angular position to the superstructure 3 is held.

The boom 4 offers wind a large attack surface. Wind load from the front (in the figure 1 from the left) thus counteracts the load moment M and reduces the rope force in the pull-in rope 5. This means there is a risk that the load moment M will be exceeded; the result is slack rope formation of the pull-in rope 5 and, in extreme cases, the jib 4 tipping over backwards, which would lead to machine damage and personal injury. As a countermeasure, it is known to limit the maximum achievable jib angle to values below 90° by a mechanical stop or by switching off the luffing winch 6 in good time. Furthermore, a maximum wind speed can be defined, if exceeded, machine operation is to be stopped and the boom 4 is to be laid down on the ground.

In order to be able to allow steeper boom angles and higher wind speeds, the use of fallback supports 12 has proven itself: hydraulically operated cylinders, which support the effect of the load moment M with their power and are arranged between the boom 4 and the superstructure 3. The one or more fallback support cylinders 12 maintain constant contact with the boom 4 and follow all of its movements. These can be movements from the activity of the luffing winch 6 (i.e. working movements with a large cylinder stroke - typically in the range of several decimetres) or smaller movements such as elastic deformation of the entire system due to load change reactions when lifting or setting down hoisting loads (i.e. very small movements with a very small cylinder stroke - typically in the range of a few centimetres).

In known devices, the power supply to the fallback supports is usually provided by means of hydraulic pumps built specifically for this purpose build up pressure in the fallback support cylinders over the entire duty cycle. During operation, the piston surfaces of the fallback support cylinders are typically permanently subjected to pressure from the specially provided hydraulic pumps. In an advantageous and proven design, these pumps are demand-controlled (so-called "Load Sensing"), so that they adapt the oil delivery quantity to the movement status of the fallback support cylinder at constant pressure and thus keep the power consumption within limits.

A disadvantage of such known energy supply systems is that every built-in hydraulic pump consumes base load with 100% of the duty cycle of the primary energy source (bearing friction, splashing losses, energy requirements of control devices, etc.) and thus reduces the efficiency of the entire working device. With diesel-powered machines, this fact has mostly been ignored in the past. In the meantime, however, efforts to avoid unnecessary emissions are increasing. In the case of electric drives with accumulators, on the other hand, there is, for example, a greater economic and technical interest in saving the base load. Furthermore, installation space and the number of pump mounting locations on the primary energy source are limited.

Against this background, the object of the present invention is to reduce the energy requirement for providing the fallback support function in such working devices and to ensure an energy-efficient compensation for minimal movements of the boom.

According to the invention, this object is achieved by a hydraulic system having the features of claim 1. Accordingly, a hydraulic system for operating a hydraulic fallback support of a working device is provided, which comprises at least one hydraulic fallback support cylinder for tracking and limiting movements of a boom of the working device and a hydraulic pump, by means of which the at least one fallback support cylinder and at least one additional hydraulic consumer can be supplied with hydraulic fluid . The hydraulic pump is therefore not only intended to supply the fallback support cylinder. Rather, it serves as a primary energy source to supply a wide variety of consumers such as cooler drives, winches or the like, and is also used to supply the backup support function.

According to the invention, a check valve is connected between the hydraulic pump and the fallback support cylinder, which can assume a blocked position and an open position and by means of which a load-bearing cylinder chamber of the fallback support cylinder can be shut off.

Switching the shut-off valve to the shut-off position shuts off the load-carrying cylinder space of the backup prop cylinder, preventing energy from being exchanged with the rest of the hydraulic system. As a result, the hydraulic pressure that prevailed in the shut-off area or in the load-bearing cylinder chamber was that at the moment when the shut-off valve was shut off. The hydraulic pump therefore no longer has to provide energy for the fallback support function if the boom is not to move, which reduces the energy requirement or the base load of the primary energy source and increases the overall efficiency. In the case of an active movement of the boom, i.e. a movement desired by the operator of the implement, the check valve can be switched to the open position in order to allow hydraulic fluid to be supplied or drained and thus to allow the fallback support cylinder to be repositioned.

Since the jib is not moved via the safety prop cylinder, but rather via an adjusting device, for example a retractable winch, no energy has to be provided by the hydraulic pump when the jib is raised, i.e. when the piston rod of the safety prop cylinder is retracted, but only while maintaining a specific energy Pressure in the load-bearing cylinder chamber derived hydraulic fluid or fed to a tank. Supply via the hydraulic pump only has to be provided when the fallback support cylinder is extended, i.e. when the boom is lowered. The same can apply to an assembly company if the fallback support cylinder is detached from the boom.

According to the invention, a hydraulic accumulator connected to the load-bearing cylinder chamber is also provided between the check valve and the fallback support cylinder. As a result, minor movements of the boom can be compensated for even when the load-bearing cylinder chamber is shut off by means of the check valve and is thus decoupled from the hydraulic pump or a tank. The fallback support cylinder can thus follow the smallest movements of the boom, with the hydraulic fluid flow required for this being taken from or supplied to the hydraulic accumulator.

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

In one embodiment, at least two fallback support cylinders are provided, each with a check valve and each with a hydraulic accumulator, which can be supplied with hydraulic fluid jointly by the hydraulic pump.

In a further embodiment, a pressure relief valve is provided between the check valve and the fallback support cylinder. This can be used in particular for pressure protection in the event of malfunctions and is therefore preferably not involved in the function of the fallback support in normal operation. However, it is also conceivable that the pressure-limiting valve is used to control or regulate the pressure and the flow rate of the hydraulic fluid flow from and to the fall-back support when the shut-off valve is open at the same time, i.e. in the open position, in order to reduce the hydraulic pressure when the boom is repositioned in the load-bearing cylinder space in an optimal range. The value of the maximum pressure ensured by the pressure relief valve can be adjustable.

In a further embodiment, a check valve is provided, which shuts off the area of the hydraulic system that can be shut off by the shut-off valve in the direction of the hydraulic pump. The check valve can be connected in parallel to the check valve, so be independent of the switching state of the check valve in operation, or be acted upon only in the locked position of the check valve, ie only to Used when the check valve is in the locked position. In the latter case, the check valve can in particular be part of the check valve. With the non-return valve, it is possible, in particular, before opening the shut-off valve for the purpose of tracking the fall-back support cylinder when the boom moves, to first establish a pressure equalization on both sides of the shut-off valve and thereby reduce or avoid load change reactions during the transitions between different operating phases.

In a further embodiment, it is provided that a further valve, which can preferably be switched electrically, is arranged between the check valve and the hydraulic pump. The valve can be a directional valve, in particular a 4/2 or 4/3 directional valve. A possible function of the additional valve is the decoupling of the check valve from the hydraulic pump or the tank. Alternatively or additionally, it is conceivable that it is used to control or regulate the pressure and the flow rate of the hydraulic fluid flow from and to the fall-back support when the shut-off valve is open at the same time, in order to keep the hydraulic pressure in the load-bearing cylinder chamber at an optimum level when the boom is being repositioned to hold area. The valve can be electrically controllable. If there are several fallback support cylinders, only a single such valve is preferably provided.

In a further embodiment it is provided that the load of the fallback support cylinder can be detected by means of a load measuring device which preferably comprises a pressure sensor arranged between the check valve and the fallback support cylinder. This allows a load-sensing application to be implemented, for example. In particular, this makes it possible to control or regulate the pressure and the flow rate of the hydraulic fluid flow from and to the fallback support and to enable optimal tracking of the fallback support cylinder.

In a further embodiment, a pressure adjustment device is provided, by means of which the pressure and volumetric flow or flow rate to and from the fallback support cylinder can be adjusted and preferably regulated as a function of a measured load of the fallback support cylinder. As a result, when tracking the Boom to keep the hydraulic pressure in the load-bearing cylinder chamber of the fallback support cylinder in an optimal range. When retracting the fallback support cylinder, in particular due to a corresponding active movement of the boom, a resistance is generated by the pressure control device, which ensures optimal tracking while maintaining the fallback support function.

In a further embodiment, it is provided that the pressure control device is a recuperation device on/in the backup support cylinder, in which hydraulic fluid flows off to the opposite side of the backup support cylinder piston, at least one pressure-limiting valve that is arranged between the check valve and the hydraulic pump and is in particular electrically controllable, a load-sensing arrangement and/or a Means for controlling a valve arranged between the hydraulic pump and check valve described above. The last-mentioned valve can be controlled or controlled hydraulically-mechanically or software-supported electrically. Values of a load-sensing arrangement can be taken into account.

In a further embodiment it is provided that the shut-off valve can be controlled hydraulically by means of an in particular electrically controllable switching valve. The switching valve is preferably arranged between the hydraulic pump and a control connection of the blocking valve and can have a blocking position and an open position, for example.

In a further embodiment, it is provided that the shut-off valve can be controlled hydraulically and has a control connection which is connected to the outlet of a hydraulic shuttle valve, with one inlet of the shuttle valve preferably being connected to a non-load-bearing cylinder chamber of the fallback support cylinder and the other inlet being connected to an electrically controllable chamber switching valve is connected. With the help of the shuttle valve, it is possible to switch the check valve in two ways: either by applying pressure to the non-load-bearing cylinder chamber of the fallback support cylinder (e.g. in an assembly operation) or by actuating the switching valve (e.g. in normal operation, in which no pressure is applied to the non-load-bearing cylinder chamber, but the fallback support cylinder is retracted by "pushing" the actuated boom).

In a further embodiment, it is provided that the hydraulic accumulator is designed to compensate for slight movements of the fallback support cylinder when the load-bearing cylinder chamber is blocked off by the check valve by removing and releasing hydraulic fluid. This takes place in particular with a moderate change in pressure and thus force according to the charging characteristic of the hydraulic accumulator.

The present invention also relates to a working device, in particular a mobile crane or cable excavator, comprising a swiveling arm, an adjusting device for adjusting the arm, at least one fallback support cylinder connected to the arm and following its movements, and a hydraulic system according to the invention for operating the at least one fallback support cylinder. This obviously results in the same advantages and properties as for the hydraulic system according to the invention, which is why a repeated description is dispensed with at this point.

In one embodiment it is provided that the shut-off valve is in the shut-off position and shuts off a load-bearing cylinder space of the fallback support cylinder when the boom is not actively moved by means of the actuating device. This reduces energy consumption or the base load when the boom is not being moved by the operator.

In a further embodiment, a controller is provided, by means of which the shut-off valve and preferably the actuating device can be controlled directly or indirectly and which is set up to switch the shut-off valve to the open position when the actuating device is actuated, so that hydraulic fluid can be conveyed to the load-bearing cylinder chamber or drained from it to keep the pressure in an optimal range for the purpose of tracking the boom.

In a further embodiment, a further valve arranged between the shut-off valve and the hydraulic pump and a non-return valve per fallback support cylinder are provided, as described above, with the controller being set up to receive a signal from an input unit to actuate the actuating device for the purpose of moving the boom, and then the valve to switch to a through position and to leave the shut-off valve in the shut-off position, after opening the check valve to switch the shut-off valve to the through position (and possibly to close the other valve) and then to actuate the actuating device. As a result, sufficient pressure can initially be built up by the hydraulic pump in the area of the hydraulic system that is not shut off. As soon as the non-return valve opens (and thus a pressure equalization is established), the shut-off valve is opened so that hydraulic fluid can be pumped into or drained from the load-bearing cylinder chamber in the event of a subsequent movement of the boom, which leads to the retraction or extension of the backup support cylinder.

Figur 1:

einen gattungsgemäßen Raupenkran mit Rückfallstütze in einer Seitenansicht;

Figur 2:

einen Schaltplan eines ersten Ausführungsbeispiels des erfindungsgemäßen Hydrauliksystems; und

Figur 3:

einen Schaltplan eines zweiten Ausführungsbeispiels des erfindungsgemäßen Hydrauliksystems.

Further features, details and advantages of the invention result from the exemplary embodiments explained below with reference to the figures. Show it:

Figure 1:

a generic crawler crane with backup support in a side view;

Figure 2:

a circuit diagram of a first embodiment of the hydraulic system according to the invention; and

Figure 3:

a circuit diagram of a second embodiment of the hydraulic system according to the invention.

the figure 1 shows a schematic side view of a generic crawler crane 1 and has already been described at the outset, so that at this point repeated explanations are omitted. The working device 1 according to the invention can in principle be such a crawler crane which, in contrast to known devices, is equipped with a hydraulic system 10 according to the invention. At the in the figure 1 Crawler crane 1 shown, the luffing winch 6 arranged on the superstructure 3 represents the actuating device. It is also possible for an A-frame to be pivoted about a horizontal axis on the superstructure 3, which is coupled to the boom 4 via guying means, for example guy rods, and this can be pivoted together by actuating the pull-in winch 6 . However, other jib configurations and adjusting devices for the jib movement are also conceivable without this having any effect on the functioning of the fallback support or the hydraulic system 10 according to the invention.

In the figure 2 a circuit diagram of the hydraulic system 10 according to the invention is shown according to a first exemplary embodiment. The hydraulic system 10 serves to operate the fallback support function of a working device 1, for the two exemplary embodiments discussed below of a crawler crane 1 according to FIG figure 1 is assumed. A hydraulic pump 14 which is driven by a motor 15 and operates a series of hydraulic consumers 50 (not shown in detail) serves as the primary energy source. This can be, for example, cooler drives or winches such as the hoisting winch and the pull-in winch 6 , 9 . According to the invention, the hydraulic pump 14 also supplies two fallback support cylinders 12 whose piston rods are pivotably coupled to the boom 4 of the implement 1 .

Instead of the system configuration shown here with two symmetrically connected fallback support cylinders 12, other configurations with only one or more than two fallback support cylinders 12 are of course also possible. The exact design of the primary energy source 14, 15 is not relevant to the functioning of the invention. The functioning of the hydraulic system 10 is explained below using one of the two symmetrical branches.

The fallback support cylinder 12 is separated from the outlet of the hydraulic pump 14 by an electrically switchable check valve 16, which has a locked position and an open position. In the locked position, a check valve 24 blocks the load-bearing cylinder space 18 of the fallback support cylinder 12; the blocking direction therefore points towards the hydraulic pump 14. In the open position, hydraulic fluid can be supplied or drained to and from the fallback support cylinder 12. A hydraulic accumulator 20 and a pressure sensor 28 are located between the shut-off valve 16 and the fallback support cylinder 12, i.e. in the area that can be shut off.

An electrically switchable 4/3-way valve 26 connects the hydraulic pump 14 to the hydraulic lines that lead to the check valve 16 and to the non-load-bearing cylinder space or annular space 19 of the fallback support cylinder 12 . In the figure 2 the directional control valve 26 is in the (middle) blocking position, so that the connection between the hydraulic pump 14 and the blocking valve 16 is disconnected. The "cross" switching position of the directional control valve 26 on the left in the figure is not required in normal operation, since retraction of the fallback support cylinder 12 does not take place hydraulically, but mediated by the actively actuated boom 4 . This switch position is required, for example, for an assembly operation in which the implement is partially dismantled for transport, ie the boom 4 is removed from the superstructure 3 and the fallback support cylinder 12 protruding beyond the superstructure 3 is retracted to prepare it for dispatch. In the case of a working device without a transport situation or assembly operation, the use of a simpler 4/2-way valve without a cross position would also be possible.

Furthermore, a pressure-limiting valve 30 is arranged between the directional control valve 26 and the check valve 16 . Another such valve 30 is located in the line that connects the directional control valve 26 to the annular space 19 . The value of the maximum pressure limited by the pressure relief valve 30 can be adjusted electrically. By means of the pressure-limiting valve 30, in cooperation with the directional control valve 26, it is possible to control the pressure and delivery quantity of the hydraulic fluid flow or oil flow to and from the fallback support cylinder 12.

All electrically switchable or controllable valves 16, 26, 30 are controlled by a controller of the implement 1, which in particular also controls various actuators of the implement 1, such as the hoist winch 9 or pull-in winch 6. The controller also receives values from the pressure sensor 28 with regard to the pressure prevailing in the load-bearing cylinder chamber 18 of the fallback support cylinder 12, as a result of which a load-sensing function is implemented. For this purpose, further sensors can be provided inside and/or outside of the hydraulic system 10 .

In contrast to known systems with a fallback support function, in the case of the hydraulic system 10 according to the invention, there is no need for a permanent supply of the fallback support cylinder 12 via a specially provided hydraulic pump. Instead, the hydraulic pump 14 of the implement 1, which is already present anyway, is used in order to provide energy for the fallback support function only in certain situations. If the boom 4 is not moved by actuation of the luffing winch 6, the load-bearing cylinder chamber 18 and the area connected to the pressure sensor 28 and hydraulic accumulator 20 are shut off by the check valve 16, so that no energy exchange takes place with the rest of the system. The cylinder pressure prevailing before the last switching of the check valve 16 into the locked position is thus maintained in the closed volume. Only the other consumers 50 are then supplied by the hydraulic pump 14 .

The hydraulic accumulator 20 is provided in order to ensure a fallback support function of the boom 4 in the event of minimal movements of the boom 4 caused by external forces, for example when lifting or setting down lifting loads, gusts of wind, etc., when the load-bearing cylinder chamber 18 is closed off. The required hydraulic fluid flow is taken from this when the fall-back support cylinder 12 is extended or added when the fall-back support cylinder 12 is retracted, so that the fall-back support cylinder 12 can follow the smallest movements of the boom 4 . The hydraulic accumulator 20 thus acts both as an energy source and as an energy sink for micro-movements of the boom 4.

When the operator actuates the luffing winch 6 for the purpose of an active movement of the boom 4, the shut-off valve 16 is opened, i.e. switched to the open position. When lowering boom 4, ie extending fallback support cylinder 12, the necessary pressure in hydraulic accumulator 20 or in load-bearing cylinder chamber 18 for tracking boom 4 can be maintained or set by supplying hydraulic fluid. For this purpose, the directional control valve 26 is also switched to an open position. When the boom 4 is raised, i.e. when the fallback support cylinder 12 is retracted, the directional control valve 26 remains in the blocked position, so that hydraulic fluid is now discharged from the load-bearing cylinder chamber 18 to the tank 36 against the resistance generated by the pressure relief valve 30. Due to the adjustable resistance of the pressure relief valve 30, an optimal tracking of the fallback support cylinder 12 can also be ensured when the boom 4 is raised.

Thus, the hydraulic pump 14 only has to supply the fallback support cylinder 12 overall when the boom 4 is lowered or in an assembly operation that may be provided. Optionally, it can be provided that when the boom 4 is lowered, the check valve 16 is not switched to the open position, but instead hydraulic fluid is supplied via an opening in the check valve 24 .

The non-return valve 24 has, inter alia, the function of reducing load change reactions which occur when there is a change in the operating phase, but is not absolutely necessary. An advantageous operating method of the hydraulic system 10 when raising the boom 4 is described below. In the initial situation, in which there is no active movement of the boom 4, the blocking valve 16 and the directional control valve 26 are each in the blocking position, so that the hydraulic line between these valves 16, 26 is pressureless. On the other hand, the line between the check valve 16 and the fallback support cylinder 12 is acted upon by accumulator pressure. The operator of the working device 1 now wants to raise the boom 4 or make it steeper and makes a corresponding entry via an input unit.

The controller switches the directional valve 26 to the open position ("parallel" position), as a result of which the pressure in the line up to the check valve 16, ie the pressure present at the check valve 24, increases. If the pressure generated by the hydraulic pump 14 exceeds the accumulator pressure in the shut-off area, the check valve 24 opens and the pressure in the hydraulic accumulator 20 is equal. Optionally, the directional control valve 26 can be closed after this point in time.

Only now does the controller switch the check valve 16 to the open position. Optionally, however, this step can be omitted and hydraulic fluid can be supplied via the check valve 24 if required (i.e. if the cylinder force falls below the minimum permissible level). Then the luffing winch 6 is actuated to raise the boom 4 . As a result, the fallback support cylinder 12 is retracted against the resistance of the pressure-limiting valve 30, so that the fallback support cylinder 12 follows suit with a corresponding pressure in the load-bearing cylinder chamber 18 or with a corresponding restraining force.

the figure 3 shows a second embodiment of the hydraulic system 10 according to the invention. Compared to the first embodiment of FIG figure 2 the shut-off valve 16, which is biased into the blocking position, can be switched hydraulically here and is connected to the output of a hydraulic shuttle valve 34 at the control input. The shuttle valve 34 is connected at an input to the annular space 19 of the fallback support cylinder 12 so that the check valve 16 can be switched to the open position by pressurizing the annular space 19 in a targeted manner. However, this does not take place during normal working operation of the implement 1 since retraction of the fallback support cylinder 12 takes place mechanically via the boom 4 .

The other input of the shuttle valve 34 is connected to an electrically switchable switching valve 32 . The blocking valve 16 can be switched to the open position by the control valve 32 being activated by the controller. The latter has no check valve in the blocking position, but the check valve 24 is permanently connected in parallel here. How the hydraulic system works However, FIG. 10 corresponds to the mode of operation illustrated in the context of the first exemplary embodiment.

Furthermore, an additional pressure-limiting valve 22 is provided in the lockable area of the hydraulic system 10, which serves to protect against pressure in the event of a malfunction and is not involved in the function of the hydraulic system or the fallback support during normal operation.

• Energiebedarf für die Versorgung der Rückfallstützenfunktion ist nur noch notwendig, wenn der Rückfallstützenzylinder 12 ausgefahren wird. Dies ist im Betrieb des Arbeitsgeräts 1 nur bei "Ausleger senken" der Fall oder in einem ggf. vorgesehenen Montagebetrieb.
• Minimalbewegungen des Auslegers 4, welche durch Krafteinwirkung von außen auftreten, werden durch den Hydraulikspeicher 20 ausgeglichen, um so eine Rückfallstützenfunktion zu gewährleisten.

Overall, the main advantages of the hydraulic system 10 according to the invention can be summarized as follows:

• Energy requirement for the supply of the fallback support function is only necessary when the fallback support cylinder 12 is extended. This is the case when operating the working device 1 only when "lowering the boom" or in an assembly operation that may be provided.
• Minimal movements of the boom 4, which occur due to external forces, are compensated for by the hydraulic accumulator 20 in order to ensure a fallback support function.

Reference list:

1

implement

2

Undercarriage with chassis

3

superstructure

4

boom

5

pulling rope

6

adjusting device (retracting winch)

7

Load handling device (load hook)

8th

hoist rope

9

hoist winch

10

hydraulic system

12

fallback prop cylinder

14

hydraulic pump

15

engine

16

check valve

18

Load bearing cylinder space

19

Non-load bearing cylinder space

20

hydraulic accumulator

22

pressure relief valve

24

check valve

26

valve

28

pressure sensor

30

pressure relief valve

32

switching valve

34

shuttle valve

36

tank

50

consumer

M

load moment

Claims (15)

Hydraulic system (10) for operating a hydraulic fallback support of a working implement (1), comprising at least one hydraulic fallback support cylinder (12) for tracking and limiting movements of a boom (4) of the working implement (1) and a hydraulic pump (14) by means of which the fallback support cylinder (12) and at least one other consumer (50) can be supplied with hydraulic fluid,
characterized,
that between the hydraulic pump (14) and the fallback support cylinder (12) there is a blocking valve (16) with a blocking and an open position, by means of which a load-bearing cylinder chamber (18) of the fallback support cylinder (12) can be shut off, and that between the blocking valve (16) and A fallback support cylinder (12) is provided with a hydraulic accumulator (20) connected to the load-bearing cylinder chamber (18). Hydraulic system (10) according to Claim 1, characterized in that at least two fallback support cylinders (12) are provided, each with a check valve (16) and a hydraulic accumulator (20) which can be supplied with hydraulic fluid jointly by the hydraulic pump (14). Hydraulic system (10) according to Claim 1 or 2, characterized in that a pressure-limiting valve (22) is provided between the check valve (16) and the fallback support cylinder (12). Hydraulic system (10) according to one of the preceding claims, characterized in that a non-return valve (24) is provided, which shuts off the area of the hydraulic system (10) which can be shut off by the shut-off valve (16) in the direction of the hydraulic pump (14), the non-return valve ( 24) is connected in parallel to the shut-off valve (16) or is only acted upon in the shut-off position of the shut-off valve (16). Hydraulic system (10) according to one of the preceding claims, characterized in that between the check valve (16) and the hydraulic pump (14) there is a further valve (26), in particular a directional control valve, which is preferably electrically switchable. Hydraulic system (10) according to one of the preceding claims, characterized in that the load of the fallback support cylinder (12) can be detected by means of a load measuring device which preferably comprises a pressure sensor (28) arranged between the check valve (16) and the fallback support cylinder (12). Hydraulic system (10) according to one of the preceding claims, characterized in that a pressure control device is provided, by means of which the pressure and flow rate to and from the fallback support cylinder (12) can be adjusted and preferably regulated as a function of a detected load of the fallback support cylinder (12). Hydraulic system (10) according to Claim 7, characterized in that the pressure adjustment device comprises a recuperation device on/in the fallback support cylinder (12), at least one pressure-limiting valve (30) arranged between the check valve (16) and the hydraulic pump (14), a load-sensing arrangement and/or or a means for driving a valve (26) according to claim 5. Hydraulic system (10) according to one of the preceding claims, characterized in that the shut-off valve (16) can be controlled hydraulically by means of an in particular electrically controllable switching valve (32). Hydraulic system (10) according to one of the preceding claims, characterized in that the check valve (16) can be controlled hydraulically and has a control connection which is connected to the outlet of a hydraulic shuttle valve (34), an inlet of the shuttle valve (34) preferably being connected to a non-load-bearing cylinder space (19) of the fallback support cylinder (12) and the other input is connected to an in particular electrically controllable switching valve (32). Hydraulic system (10) according to one of the preceding claims, characterized in that the hydraulic accumulator (20) is designed, when the load-bearing cylinder chamber (18) is shut off by the check valve (16), by removing and releasing hydraulic fluid, slight movements of the fallback support cylinder (12). compensate. Working device (1), in particular a mobile crane or cable excavator, comprising a pivotable boom (4), an adjusting device (6) for adjusting the boom (4), at least one fallback support cylinder (12) connected to the boom and following its movements, and a hydraulic system ( 10) according to any one of the preceding claims. Working device (1) according to Claim 12, characterized in that the shut-off valve (16) is in the shut-off position when the boom (4) is not being actively moved by means of the adjusting device (6). Working device (1) according to Claim 12 or 13, characterized in that a controller is provided, by means of which the check valve (16) and preferably the adjusting device (6) can be controlled directly or indirectly and which is set up, when the adjusting device (6) is actuated switch the check valve (16) to the open position. Implement (1) according to Claim 14, characterized in that a valve (26) according to Claim 5 and a non-return valve (24) according to Claim 4 are provided for each fallback support cylinder (12), the controller being set up to receive a signal from an input unit for actuation of the adjusting device (6) for the purpose of moving the boom (4), then switching the valve (26) to a through position and leaving the check valve (16) in the locked position, after opening the check valve (24) the check valve ( 16) to the open position and then to actuate the adjusting device (6).

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