DE102021212944B3 - Hydraulic circuit with a hydraulic cylinder - Google Patents

Abstract

Disclosed is a hydraulic circuit with a hydraulic cylinder, in particular a press cylinder, and with a hydrostatic displacement machine with a variable direction of displacement, via which the hydraulic cylinder can be driven in gears, for which its high pressure, depending on the gear, can be fluidically connected to at least one of the cylinder chambers of the hydraulic cylinder, of which one, in particular for protection against pressure peaks or overload, can be fluidically connected to a pressure medium sink via a pressure limiting device of the circuit.

Description

The invention relates to a hydraulic circuit with a hydraulic cylinder, in particular a press cylinder, according to the preamble of claim 1.

The pamphlet DE 10 2014 219 734 A1 shows a circuit with a hydraulic cylinder via which a suspended load can be moved. In this case, mutually opposing piston surfaces are supplied with pressure medium via a hydrostatic transmission by a hydraulic machine that can be driven with variable speed and direction of rotation and has a constant displacement volume. Pressure peaks or pressure surges in the cylinder chambers are reduced to a tank or an almost pressure-free pressure medium reservoir via a respective pressure-limiting valve to protect against overloading and to maintain a specified force-velocity-time profile.

The disadvantage of this is that once the pressure medium has been released, it has to be fed back into the hydrostatic transmission and brought to the appropriate pressure level, which on the one hand entails a technical complexity in the form of large suction valves and on the other hand is energetically unfavorable.

From the DE 10 2018 203 367 A1 a hydrostatic linear drive is known. The hydrostatic linear drive has a speed and a power cylinder and two hydraulic machines, which can be connected to the cylinders via switching valves. The power cylinder has a regeneration flow path that connects the two opposing cylinder spaces. Thus pressure medium can be regenerated from one cylinder space to another. The disadvantage here is that the hydrostatic linear drive requires two hydraulic machines.

In contrast, the invention is based on the object of creating a more energy-efficient hydraulic circuit.

This problem is solved by a hydraulic circuit with the features of patent claim 1.

Advantageous developments of the hydraulic circuit are described in patent claims 2 to 9.

A hydraulic circuit has a hydraulic cylinder, in particular a press cylinder of a press, for example a press brake. In order to enable a plurality of possible gaits of the hydraulic cylinder—and thus of the press—in terms of force and/or speed, the hydraulic cylinder is preferably multi-acting, in particular double-acting. It is particularly preferably designed as a tandem cylinder. In order to supply it with pressure medium in the different gaits, the circuit also has a hydrostatic displacement machine that is designed to be operable in different directions of displacement. At least it can be operated in different conveying directions during pump operation. It can preferably also be operated in different consumption directions during engine operation. Depending on the gait of the hydraulic cylinder, a high-pressure or high-pressure chamber of the displacement machine can be fluidically connected to at least one of the cylinder chambers of the hydraulic cylinder. At least one of the cylinder chambers can be fluidically connected to a pressure medium sink, in particular to another of the cylinder chambers, via a pressure limiting device, in particular via at least one regeneration flow path, of the circuit, in particular to protect against pressure peaks or overload. According to the invention, the cylinder spaces connected by the at least one regeneration flow path are delimited by two piston surfaces that each have the same effect.

In contrast to the prior art, in which a pressure surge or a pressure peak is relieved via the pressure limiting device in a tank or an external pressure medium reservoir from which the hydraulic machine or the hydraulic cylinder draws, the pressure medium remains within the hydraulic circuit according to the invention. As a result, less pressure medium has to be replenished in order to keep the pressure medium quantity of the hydraulic cylinder constant, and replenishment valves can be designed to be smaller or can even be omitted. A risk of cavitation during suction is reduced. In this way, a more energy-efficient hydraulic circuit is created.

Furthermore, the pressure medium can be relieved via the regeneration flow path from the loaded cylinder space into the other cylinder space with the same acting piston surface. The pressure medium can be fed to the hydrostatic displacement machine via the other cylinder space and regenerated in this way.

In a further development, the displacement machine can be driven or is driven by an electric motor, in particular by means of a variable-speed, position-controllable stepper or servomotor of the circuit. The displacement machine can be designed with a constant displacement volume or with an adjustable displacement volume. The latter variant, in conjunction with a variable-speed electric machine as the drive machine, enables particularly high dynamics to control a Force and/or speed profile of the hydraulic cylinder. The displacement machine is preferably designed as an axial piston machine with a swash plate or swash plate design. A reversal of the direction of rotation of the drive machine and the displacement machine can even be dispensed with if the displacement machine is designed with a reversible displacement volume, ie displacement volume that can be adjusted through zero and on both sides.

In a preferred development, one of the remaining cylinder chambers is assigned as a pressure medium sink to one cylinder chamber, depending on the gait. This means that depending on the gait, another of the remaining cylinder chambers can represent the pressure medium sink for one cylinder chamber. In this way, a number of regeneration paths for reducing pressure peaks can be formed. Specifically trained.

In a preferred design of the hydraulic cylinder, it has three hydraulically active or activatable piston surfaces. In particular, these are a second and a third, which have the same effect as one another, and a first, which counteracts the second and third piston surfaces. The design is also referred to as a tandem cylinder.

So that there is no difference in volume when the piston moves and, as a result, regeneration of the pressure medium between the cylinder chambers in different gear types and without a compensation volume or a hydraulic accumulator is possible, in a further development the sum of the surface areas of the second and third piston surfaces, which have the same effect, is equal to a surface area of the they counteracting first piston surface. Here "equal" is to be understood as sufficiently equal, since a slight leakage between the cylinder chambers can influence the real ratio of the surface areas.

In a development, one of the cylinder chambers, which, as mentioned above, can be connected fluidically to the other cylinder chamber—the pressure medium sink—as mentioned above, is delimited by the third piston surface. The third piston surface is preferably arranged in such a way that it acts against the force of gravity when pressurized medium is applied.

So that pressure medium displaced from the third cylinder chamber can be regenerated in the first cylinder chamber, a first regeneration flow path is provided in a further development, via which the third piston surface can be fluidically connected to the first piston surface acting in the opposite direction, or in other words the third cylinder chamber to the first cylinder chamber . The first regeneration flow path is preferably active or opened when the piston is lowered, in particular when the piston is lowered quickly with comparatively little force—ie in rapid downward motion.

In order to prevent excessive forces when retracting or raising the piston - i.e. in particular in an upward rapid traverse - a first pressure limiting valve is arranged in a first pressure limiting path, parallel to the first regeneration flow path Cylinder chamber passes, wherein the first piston surface counteracts the lifting effective third piston surface. When the first pressure-limiting valve responds, the raising pressure force in the third cylinder chamber is reduced on the one hand and the lowering pressure force in the first cylinder chamber is also increased. In this way, in particular, a mechanical connection of the piston with its piston rod, on which a load is suspended, can be secured against excessive tensile forces. It is therefore a matter of protecting the hydraulic cylinder from damage caused by excessive forces when retracting.

So that pressure medium displaced from the third cylinder chamber can be regenerated in the second cylinder chamber, a second regeneration flow path is provided in a further development, via which the third cylinder chamber can be fluidically connected to the second piston surface acting in the same way, or in other words the third cylinder chamber to the second cylinder chamber is. The second regeneration flow path is preferably active or opened when the piston is lowered, in particular when the piston is lowered comparatively slowly at high force—ie in a downward force gear. The aforementioned first regeneration path is then closed.

To ensure that the circuit does not have any unwanted operating states, only one of the named regeneration paths is opened, at least in rapid traverse and in power gear, with the respective other one being closed.

As already mentioned, the first regeneration path is opened and the second regeneration path is closed in rapid traverse downwards. If, for example, a ram moved by the piston is placed on a die of the press, the press force of the hydraulic cylinder must be increased in order to form the desired force-time profile. To do this, it is necessary to switch from rapid traverse downwards to force traverse downwards, which requires the two regeneration paths to be switched over. The switching process must be optimized for the specific application in order, for example, to introduce the lowest possible acceleration into the system. Depending on the application, it may be necessary for the regeneration paths must not be activated at the same time.

In a further development, particularly in such applications, the first regeneration path is therefore closed before the second regeneration path is opened. Since pressure medium flows from the third cylinder chamber into the first cylinder chamber when the first regeneration path is open, the closing of the first regeneration path can result in a pressure surge in the third cylinder chamber.

In a further development, the circuit therefore has a second pressure-limiting path, parallel to the second regeneration flow path, in which a second pressure-limiting valve is arranged. In the case of the above-described pressure surge, it can be released into the second cylinder chamber via the second pressure-limiting valve. This is the cylinder space from which the displacement machine draws in pressure medium in the power gear down, so that the derived pressure medium according to the invention remains in the hydraulic circuit and is made available to the displacement machine on the suction side.

In a further development, a valve is provided in the respective regeneration flow path, either a switching valve or, in order to make the opening and closing control less abrupt, a continuously adjustable directional control valve. The respective valve can be actuated depending on the gait or a change of gait, in particular it can be controlled on and off.

The rapid traverse downwards or outwards corresponds to a first direction of movement of the hydraulic cylinder, with a low pressure of the displacement machine being fluidically connected to the second cylinder chamber delimited by the second piston surface and the high pressure of the displacement machine being fluidically connected to the first cylinder chamber delimited by the first piston surface, and the first regeneration flow path being opened and the second regeneration flow path is controlled.

The downward or extending power gear corresponds to the first direction of movement of the hydraulic cylinder, with the low pressure of the displacement machine being fluidically connected to the second cylinder chamber delimited by the second piston area and the high pressure of the displacement machine being fluidically connected to the first cylinder chamber delimited by the first piston area, and the first regeneration flow path being controlled and the second regeneration flowpath is turned on.

An upward or retracting rapid traverse corresponds to a second direction of movement of the hydraulic cylinder, with the low pressure of the displacement machine being fluidically connected to the first cylinder chamber delimited by the first piston surface and the high pressure of the displacement machine being fluidically connected to the second cylinder chamber delimited by the second piston surface, and the first regeneration flow path being opened and the second regeneration flow path is controlled.

In a further development, the gearshift has a control unit for control purposes, which is set up so that the gaits can be controlled and changed via it.

In a further development, the control unit is set up so that the direction of displacement can be controlled and changed via it, and that the valve or valves can be controlled via it.

• 1 eine hydraulische Schaltung gemäß einem Ausführungsbeispiel, in einem Eilgang abwärts,
• 2 die hydraulische Schaltung gemäß 1, beim Umschalten vom Eilgang abwärts in einen Kraftgang abwärts,
• 3 die hydraulische Schaltung gemäß 1 und 2 im Kraftgang abwärts, und
• 4 die hydraulische Schaltung gemäß den 1 bis 3 in einem Eilgang aufwärts.

An exemplary embodiment of a circuit according to the invention is explained in more detail below in four drawings. Show it:

• 1 a hydraulic circuit according to an embodiment, in a rapid traverse downwards,
• 2 the hydraulic circuit according to 1 , when switching from rapid traverse downwards to a power traverse downwards,
• 3 the hydraulic circuit according to 1 and 2 in power gear down, and
• 4 the hydraulic circuit according to the 1 until 3 in a rapid traverse upwards.

1 shows a hydraulic circuit 1 with a hydraulic cylinder 2, which acts as a pressing cylinder. The hydraulic cylinder 2 is designed as a tandem cylinder and accordingly has two cylinder tubes 4 , 6 which are separated from one another by a central base 8 . The hydraulic cylinder 2 has a first piston 10 running in the cylinder tube 4 and a second piston 12 running in the cylinder tube 6 . The pistons 10, 12 are coupled via a rod 14 which passes through the central base 8. A piston rod 16 extends from the second piston 12 through a cylinder base 18 which closes the cylinder tube 6 in the pressing direction.

According to 1 the piston 12 divides the interior of the cylinder tube 6 into a first cylinder chamber 20 and a third cylinder chamber 22. A first piston surface 24 delimits the first cylinder chamber 20 and a third piston surface 26 delimits the third cylinder chamber 22. The piston surfaces 24, 26 are on the piston 12 formed and arranged in opposition to each other. Furthermore, the piston 10 separates the interior of the cylinder tube 4 into a second cylinder chamber 28 and a fourth cylinder chamber 30. The first-mentioned cylinder chamber is delimited by a second piston surface 32. last The latter is delimited by a fourth piston surface 34 and can be connected to it via a check valve 36 that opens to atmosphere (pressure p0).

A ram (not shown) is arranged on the piston rod 16 and can be moved onto a mattress of the press (also not shown) for the pressing process. The hydraulic cylinder 2 is usually arranged in such a way that the piston rod 16 is extended in the direction of gravity. Of course, different arrangements or positions of the hydraulic cylinder 2 are also possible.

To move the hydraulic cylinder 2, more precisely its piston and rod arrangement 10, 14, 12, 16, an electrohydraulic drive with a variable-speed electric machine 38 and a hydrostatic displacement or hydraulic machine 40 coupled thereto is provided. This is designed for operation in all four quadrants, ie for operation in both directions of rotation as well as for pump operation and motor operation. The pump operation enables the active displacement of the piston rod 16, the motor operation enables the recuperation of hydraulic pressure medium energy and thus contributes to energy efficiency. In addition, the hydraulic machine 40 is designed with an adjustable displacement volume. In this specific case, it is designed as an axial piston machine with a swash plate design, with the displacement volume being measured in 1 the swivel angle α of the swash plate is indicated. The displacement volume of the hydraulic machine 40 is reversible in the exemplary embodiment, ie adjustable on both sides from a pivoting angle a equal to zero (corresponds to zero displacement) in the negative direction (a−) and positive direction (α+). With the direction of rotation remaining the same, this allows the pressure side of the hydraulic machine 40 to change, that is to say a change in the direction of displacement, for all operating modes (pump, motor operation).

A working port of hydraulic machine 40 is fluidically connected to first cylinder chamber 20 via a first working line 42 , and another of its working ports is fluidically connected to second cylinder chamber 28 via a second working line 44 . A third working line 46 branches off from the first working line 42 , via which the latter working connection can be fluidically connected to the third cylinder chamber 22 . An electromagnetically actuable 2/2-way switching valve 48 with a spring-loaded blocking position a and an actuatable flow position b is arranged in the third working line 46 for opening and closing the pressure medium connection of the hydraulic machine 40 with the third cylinder chamber 22 . A first regeneration flow path 46 can be formed between the cylinder chambers 20 , 22 via the first working line 42 , the switching valve 48 and the third working line 46 . A first pressure-limiting valve 50 is arranged in a pressure-limiting path 52 in a parallel connection to the first switching valve 48 .

In addition, the third cylinder chamber 22 can be fluidically connected to the second cylinder chamber 28 via a second regeneration path 54 . To open and close the second regeneration path 54, an electromagnetically actuable 2/2-way switching valve 56 with a spring-loaded blocking position a and an actuatable flow position b is also provided here. A second pressure-limiting valve 58 is arranged in a second pressure-limiting path 60 in a parallel connection to the second switching valve 56 .

The hydraulic cylinder 2 is designed in such a way that the sum of the surface areas of the piston surfaces 26, 32 that act in the same way is equal to the surface area of the first piston surface 24 that acts in opposition to them. As a result, when the pistons 10, 12 are moved, pressure medium can be conveyed between the cylinder chambers 22, 20 and 22, 28 in a closed circuit via the working lines 42, 44, 46 and the regeneration flow paths 42, 46 and 54, without a differential volume flow occurring. In order to be able to replace a possible leakage volume, suction valves can be provided in the circuit 1, via which suction valves in the respective cylinder chambers 20, 28 and 22 are made possible.

The first piston surface 24 is larger than the counteracting third piston surface 26, which in turn is larger than the second piston surface 32, which acts in the same way as the first piston surface 24.

A first pressure detection unit 64 is fluidly connected to the first working line 42 , a second pressure detection unit 62 is fluidly connected to the second working line 44 and a third pressure detection unit 66 is fluidically connected to the third working line 46 . The pressure detection units 62, 64, 66 are signal-connected to a control unit 68 of the circuit 1 via a respective signal line. The valves 48, 56, more precisely their electromagnets, are signal-connected to the control unit 68 via a respective signal line. In addition, the pressure limiting valves 50, 58 can be adjusted in terms of their limiting pressure and for this purpose can be signal-connected to the control unit 68 via a respective signal line.

The following is a description of how the circuit 1 works using the types of gears of the hydraulic cylinder 2. These are a rapid traverse down, a transition from rapid traverse down to a power gear down, the power gear down and a rapid traverse up.

1 shows the circuit 1 in rapid downwards, which is symbolized by the arrow pointing downwards. In this gait, the piston and rod assembly 10, 14, 12, 16 is moved downwardly toward the die (not shown) at high speed (large length of arrow) and low force (small thickness of arrow). For the sake of clarity of further consideration, it is assumed that a change in the direction of displacement of the hydraulic machine 40 is brought about solely by a change in the direction of rotation of the electric machine 38 . A description that reversing the swivel angle α from positive to negative values—and vice versa—can also bring about the change in the direction of displacement is therefore dispensed with. The hydraulic machine 40 accordingly has a swivel angle α, or a displacement volume Vg, which is greater than or equal to zero in every gear. Rapid down is according to 1 the first switching valve 48 is actuated in its flow position b, while the second switching valve 56 is tensioned in its blocking position a when not actuated. Accordingly, the first regeneration path 42, 46 is opened and the second regeneration path 54 is closed. The hydraulic machine 40 is driven by the electric machine 38 and conveys pressure medium from the second cylinder chamber 28 into the first cylinder chamber 20. Due to the different surface areas of the piston surfaces 32, 24, the pressure medium volume flow sucked in via the second working line 44 is not sufficient to pump the first cylinder chamber 20 at the requested travel speed to be sufficiently charged with pressure medium. However, the differential volume flow resulting from the difference in area is made available via the first regeneration flow path 46 and the first switching valve 48 from the third cylinder chamber 22, so that the required displacement speed is achieved with a very reduced pump output at the same time. This occurs when the downwardly moving piston 12 reduces the third cylinder chamber 22 and thus displaces pressure medium from it via the third working line 46, the first switching valve 48 and the first working line 42 into the first cylinder chamber 20.

If the punch arranged on the piston rod 16 touches the die (not shown), the rapid traverse is terminated. There follows a transition from rapid traverse downwards to power or press traverse downwards, which 2 is explained.

The touchdown is determined by a displacement detection unit or by continuous pressure measurement. On the one hand, the touchdown leads to a drastic reduction in the driving speed, which can be determined via the position detection unit, and on the other hand, the pressure in the first cylinder chamber 20 increases with the touchdown. At the same time, the pressure conditions in the second and third cylinder chambers 28, 22 also change. The pressure is measured continuously via the previously mentioned pressure detection units 62, 64, 66. The control unit 68, depending on the pressures and the piston surfaces 32, 24, 26 assigned to them, calculate the cylinder force. This changes significantly when you put it on.

In the control unit 68, a switchover force of the cylinder force is stored in a predetermined manner, from which point onwards the rapid traverse is ended and the switchover to the force gear down is started, which is based on 2 is described. This means that the cylinder ratio can be switched over depending on the load and the cycle time can be improved.

As previously explained, the switching positions are still in accordance with when putting on 1 active. If the switching force is determined via the control unit 68, the valves 48, 56 are switched sequentially, with according to FIG 2 first valve 48 is closed and valve 56 remains closed. Accordingly, the regeneration from the third cylinder chamber 22 via the valve 48 into the first cylinder chamber 20 is first interrupted. At that point in time, the two cylinder chambers 22, 20 are still at about the same high pressure as when they touched down. At the same time, the valve 56 is still closed. Since the regeneration volume flow is abruptly interrupted via the valve 48, a pressure surge can occur in the third cylinder chamber 22. This must be limited to prevent damage to components and because the hydraulic cylinder 2 is required to follow an exact speed and force-time profile in order to ensure the quality of the product to be pressed. Empirical values show that the amplitudes of the pressure surges can reach 50 bar with pressure gradients of up to 2000 bar/s. If the pressure peaks were diverted into a tank or a low-pressure reservoir, anti-cavitation valves would have to be designed very large due to this low preload, which leads to low dynamics. Here, according to the invention, the second pressure-limiting valve 58 becomes effective and relieves the pressure surge in the second cylinder chamber 28 via the pressure-limiting path 60. In other words, the second pressure-limiting valve 58 opens as soon as the pressure difference between the third cylinder chamber 22 and the second cylinder chamber 28 exceeds an application-specific pressure.

According to the invention, the pressure surge is not blown off against ambient pressure or tank pressure, but the pressure medium of the pressure surge remains in the hydraulic cylinder 2. It therefore does not have to be sucked in again and existing ones Anti-cavitation valves of circuit 1 can be made smaller or can be omitted.

Only with a small time delay according to 3 the second valve 56 in the second regeneration path 54 is opened, whereby as the piston 12 is lowered further, pressure medium is supplied from the third cylinder chamber 22 via the second valve 56, the second cylinder chamber 28 and the second working line 44 to the hydraulic machine 40 (on its suction side). With the direction of rotation of the hydraulic machine 40 remaining the same and the swivel angle α reduced, the power transmission can now take place with high force and low speed down to zero speed, which is symbolized by the short, bold arrow. This is done by the in 2 thick and short arrow that follows the long and thin arrow of the rapid traverse.

Decompression occurs at the end of the downward power cycle.

This can be followed by a power or press run upwards, for example to overcome the adhesive forces of the press. Here comes the same circuit as in 3 (Press gear downwards), but with a changed direction of rotation of the hydraulic machine 40, for use. The hydraulic machine 40 conveys pressure medium via the second working line 44 into the second cylinder chamber 28 and via the activated second regeneration flow path 54 also into the third cylinder chamber 22. The working pressure is therefore present in both cylinder chambers 28, 22 and from the sum of the second and third piston areas 26, 32 results in a high upward piston force. By lifting the piston 12, pressure medium is displaced from the first cylinder chamber 20 and is thus available to the hydraulic machine 40 on the suction side. With the piston force directed upwards and possibly high adhesive forces, a high tensile load can be associated with a mechanical connection point of the piston rod 16 with the piston 12 . To protect the components and in particular to protect the connection point against failure, the first pressure-limiting valve 50 is provided, which responds when the pressure in the third cylinder chamber 22 is too high, and opens the first pressure-limiting path 52 . The solution according to the invention applies here too, that the pressure medium discharged via the pressure-limiting path 52 remains in the hydraulic circuit and thus does not have to be replenished. In the exemplary embodiment shown, the opening pressure of the second pressure-limiting valve 52 is set to 160 bar.

This is followed by rapid traverse upwards, according to 4 . The same switching constellation of the valves 48, 56 as in 1 (rapid traverse downwards) for use. That is, valve 56 is closed and valve 48 is switched open. The direction of rotation of the hydraulic machine 40 is still the same as in the above-described power or press gear, ie inversely to the rapid feed, downwards 1 . As a result, the hydraulic machine 40 conveys pressure medium via the second working line 44 solely into the second cylinder chamber 28 with the comparatively small piston area 32. The first regeneration flow path 54 is closed. Due to the lifting of the piston 12, pressure medium is displaced from the first cylinder chamber 20 towards the hydraulic machine 40 (suction side) and via the open valve 48 towards the third cylinder chamber 22 (regeneration).

Disclosed is a hydraulic circuit with a hydraulic cylinder, in particular a press cylinder, with cylinder chambers, at least one of which is protected by a pressure-limiting valve whose pressure medium outlet can be fluidically connected or is connected to another of the cylinder chambers.

The use of the at least one pressure-limiting valve according to the invention enables components to be protected in the event of an unexpected pressure build-up and in the event of a suboptimal switching timing between the gear types.

The pressure protection according to the invention takes place within the hydraulic cylinder, in that the pressure medium sink of the pressure-limiting valve is formed by one of the cylinder chambers. It therefore also takes place within the controlled system. This minimizes the pressure medium volume to be replenished and cavitation is avoided as far as possible.

Claims (9)

Hydraulic circuit (1) with a hydraulic cylinder (2), in particular a press cylinder, and with a hydrostatic displacement machine (40) with a variable direction of displacement, via which the hydraulic cylinder (2) can be driven in gears, for which its high pressure is dependent on the gear with at least one of Cylinder chambers (20, 22, 28) of the hydraulic cylinder (2) can be fluidically connected, one of which, in particular for protection against pressure peaks or overload, via at least one regeneration flow path (54) of the circuit (1) fluidically with another of the cylinder chambers (20, 22, 28) can be connected, characterized in that the cylinder chambers (22, 28) connected by the at least one regeneration flow path (54) are delimited by two piston surfaces (26, 32) each having the same effect. circuit after claim 1 , wherein parallel to the regeneration flow path (54), which fluidly acts the same piston surfaces (26, 32). connects, a pressure relief path (60) is arranged with a pressure relief valve (58). Circuit (1) after claim 1 or 2 , wherein the pressure medium sink can be formed or is formed depending on the gait. Circuit (1) according to one of Claims 1 until 3 , wherein a second piston surface (32) and third piston surface (26) of the piston surfaces (24, 26, 32, 34) act in the same way and a first piston surface (24) of the piston surfaces of the second piston surface (32) and the third piston surface (26) is counteracting. Circuit (1) after claim 4 , wherein a sum of the surface areas of the second piston surface (32) and the third piston surface (26) that act in the same way is equal to a surface area of the first piston surface (24) that acts in opposition to them. Circuit (1) after claim 4 or 5 , wherein one of the cylinder chambers (22), which is protected in particular against pressure peaks or overload, is delimited by the third piston surface (26). Circuit (1) according to one of Claims 4 until 6 with a regeneration flow path (46) via which the third piston surface (26) can be fluidically connected to the first piston surface (24) acting in opposition to it. circuit after claim 7 , With a further pressure-limiting path (52), parallel to the regeneration flow path (46), which fluidly connects the two counteracting piston surfaces (24, 26), in which a further pressure-limiting valve (50) is arranged. Circuit (1) after claim 2 or 7 with a controllable respective valve (48, 56) in the regeneration flow path (46, 54), via which this can be controlled on and off depending on the gait.

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