EP3109485B1 - Hydraulic system for pressure supply of a hydro-cylinder with three separate pressurisable surfaces and method for operating the hydraulic system - Google Patents

Description

Field of the invention

The invention relates to a hydraulic system according to claim 1.

Furthermore, the invention relates to a method for operating the hydraulic system according to the invention according to method claim 12.

Background of the invention

In known hydraulic systems, in particular those for the pressure medium supply of a hydraulic cylinder with separate druckmittelbeaufschlagbaren active surfaces, which are used for example as adjusting device for wind turbines, hydraulic presses or plastic injection machines, is usually in the integration of additional functions, such as an emergency operation and to compensate for leakage and differential volume large low-pressure accumulator required from which a hydraulic machine can suck in pressure medium or excess pressure medium from the cylinder and / or the system can be recorded, which in addition to increased space requirements increased production costs and / or operating costs. Next is a complex corrosion protection in the hydraulic cylinder used in known solutions operate, especially in Gleichzugzylindern with internal construction, which further increased production costs.

The document D 10 2012 012 142 A1 describes a hydraulic adjusting device having a control function for a working and a special operation. A dedicated double-acting actuator cylinder can be acted upon by a working pressure medium and to fulfill the control function in special operation with a pressure medium storage connected, which has a separate from the working pressure medium compressed gas.

The document EP 2 420 681 A2 describes a hydraulic linear drive with a running with three pressure chambers hydraulic cylinder, the active surfaces are coordinated so that in a rapid traverse and in a power stroke, a drive of the hydraulic cylinder with pressure medium supplying hydraulic machine operates in about the same speed / torque range.

Disclosure of the invention

In contrast, the invention is based on the object to provide a hydraulic system for supplying pressure medium of a hydraulic cylinder with three separate druckmittelbeaufschlagbaren effective areas, which is less expensive to manufacture and / or to operate.

This object is achieved by a hydraulic system having the features of patent claim 1.

Furthermore, it is an object of the present invention to operate the hydraulic system according to the invention in a simple manner.

This object is achieved by a method for operating the hydraulic system according to the invention with the features of the independent method claim.

Advantageous developments of the invention are described in the subclaims. A hydraulic system according to the present invention includes a hydraulic cylinder having at least three separate pressure-sensitive surfaces. There are one first active surface and a second active surface for a movement of a piston / rod member of the hydraulic cylinder in its extension direction druckmittelbeaufschlagbar. In the hydraulic system, a memory switching valve is provided, by means of which the second active surface can be acted upon by a pressure medium of a charged memory in the extension direction, in particular during an emergency operation for fast and / or maximum extension of the piston / rod element.

An advantage of the hydraulic system according to the present invention is that the solution according to the invention that the second active surface for extending the piston / rod element can be acted upon by pressure medium from the charged reservoir,
allows a simpler special design of the hydraulic cylinder and thus saves on manufacturing costs.
The hydraulic system according to the invention is advantageously used, for example, in wind power plants for hydraulic pitch adjustment, in particular of a rotor or of rotor blades. In particular, in an emergency operation, in which the rotor is to be rotated from the wind, thus the second active surface in addition to the first effective area for the movement of the piston / rod element in the direction of the preferred position druckmittelbeaufschlagbar, whereby a quick adjustment is possible.

According to the invention, a charging valve is provided, by means of which, in particular during a charging operation in which the accumulator is charged with pressure medium, a first working area delimited by the first working space of the hydraulic cylinder is fluidically connectable to a second working area bounded by the second working area of the hydraulic cylinder. Thus, the memory, in particular after execution of the emergency operation, can be charged with pressure medium. During the charging operation, the piston / rod element is advantageously moved completely counter to the extension direction in order to convey pressure medium from the second working space back into the hydraulic circuit when the storage switching valve and charging valve are open.
A further advantage of the hydraulic system according to the invention is that a low-pressure accumulator, from which pressure medium can be sucked by the hydraulic machine, can be dimensioned considerably smaller than the known hydraulic systems of this type. The memory from which the second active surface can be acted upon with pressure medium is advantageously designed as a high-pressure accumulator. Advantageously, the inventive hydraulic system is thus, in addition to the above-mentioned wind turbines, also in hydraulic presses and plastic injection machines, and generally used in hydraulic systems with a high-pressure accumulator and a low-pressure accumulator.
Advantageously, in the first working space during a normal operation, a negative pressure, in particular a vacuum, can be generated, in particular due to a movement of the piston / rod element in its extension direction and because the second working space in Normal operation is completed because of the energized and thus closed state of the memory switching valve. In normal operation, the piston / rod element is movable in the closed second working space in or against the extension direction. Thus, no moisture can be present in the second working space during normal operation, which eliminates the need for expensive and costly anticorrosive treatment and thus further reduces the costs of the hydraulic system according to the invention.

According to the invention, a hydraulic machine is provided, by means of which in each case the first active surface or a third active surface of the hydraulic cylinder in a closed hydraulic circuit can be acted upon with pressure medium, wherein the third active surface for moving the piston / rod element against the extension direction can be acted upon with pressure medium. Thus, the first working space and the third working space are each directly controllable. In particular, during normal operation, only the first active surface for moving the piston / rod element in the extension direction is acted upon by a pressure medium and the third active surface is acted upon to move the piston / rod element against the extension direction with a pressure medium.
The hydraulic machine can in particular be designed to be variable in speed and / or in particular drivable to rotate and / or swivel through in the direction of rotation.
Advantageously, as already explained above, no pressure medium can flow into the second working space during normal operation of the hydraulic cylinder. Thus, a synchronous behavior of the hydraulic cylinder is achieved during normal operation, since advantageously the first effective area is the same size as the third effective area. The second effective area may deviate from the size of the two other active areas, in particular be larger than the first effective area or the third effective area. In emergency mode thus a differential behavior of the hydraulic cylinder is given.
Advantageously, the, in particular hollow cylindrical design, hydraulic cylinder in its housing a, in particular cylindrical, guide pin, on which the piston / rod member is mounted axially displaceable. In this case, the first working space of the guide pin and the piston / rod element is limited, and the second Working space is limited by the guide pin and the piston / rod element and the housing. In addition, the third working space is limited by the piston / rod member and the housing. The inventive special design of the hydraulic cylinder allows a space-saving execution of the same and thus a reduction in space requirements.

In particular, the piston / rod member has a substantially annular radial collar at an open end portion, or at a position between a closed end portion of the piston / rod member and the open end portion. Advantageously, the respective working spaces delimited by the piston / rod element, in particular the second working space and the third working space, are limited by means of the radial collar or by means of its annular surfaces.

In particular, the piston / rod element protrudes with its closed end from an end section of the housing which points essentially in the direction of extension and from which a cylinder head is formed.

The guide pin can be arranged on a substantially pointing away from the extension direction end portion of the housing, of which a cylinder bottom is formed. In particular, the guide pin is fixedly connected to the housing or formed integrally with the housing.

The first active surface may be arranged at the closed end portion of the, in particular hollow cylinder-shaped, piston / rod element on an inner contour, wherein the first active surface points substantially towards the cylinder base and away from the extension direction.

The second active surface may be arranged on an outer contour, in particular formed as an annular radial collar, of the piston / rod element, wherein the second active surface points substantially toward the cylinder base and away from the extension direction.

The third active surface may be arranged on the, in particular designed as an annular radial collar, the outer contour of the piston / rod element, wherein the third active surface is substantially toward the cylinder head and towards the extension direction.

According to the invention, the storage switching valve is connected in a storage flow path between the storage and the second working space, and the charging valve is connected in an intermediate branch of the storage flow path between the storage switching valve and the second working space. In addition, the intermediate branch between the first working space and a pressure medium source is fluidly connected to a first flow path. Thus, a simple change of the operating modes, for example between normal operation and emergency operation or between emergency operation and recharging operation is guaranteed.
Advantageously, the storage switching valve is normally open and energized closed. Thus, the emergency operation is executable in a power failure and, for example, a rotor of a wind turbine automatically rotatable from the wind.
Advantageously, the second working space is divided into a first chamber and a second chamber by means of a fluid-tight partition wall or plate or steel plate. Thus, a complete retraction of the piston / rod element in the charging operation is not necessary, since the resulting during normal operation in the first chamber negative pressure or the resulting vacuum is effectively separated by the partition from a pressure medium present in the second chamber. Thus, the charging operation can be terminated at an almost arbitrary position, without negatively affecting the subsequent normal operation. Another advantage of the partition is that, because pressure medium is kept away from the negative pressure / vacuum in the first chamber, so that outgassing dissolved in the pressure medium moisture and / or air or gas and thus cavitation is avoidable.
Advantageously, the partition wall is annular and arranged axially displaceable on the guide pin. In this case, the partition, in particular during emergency operation, by means of a pressure medium from the memory in the extension direction displaced, in particular together with the piston / rod element.

In particular, during the Aufladebetriebs the partition by means of a pressure medium loading of the third active surface on the piston / rod member against the extension direction displaced, directly or via a pressure medium, which may be present in the first chamber. Further advantageously, the partition wall is held in its respective position by means of a retaining device and / or a frictional force between the partition wall and the housing. Thus, during normal operation, a travel path of the piston / rod element in the extension direction is marked by a cylinder-head-side extension stop on the housing and marked against the extension direction by a cylinder-bottom retraction stop on the housing or a position of the dividing wall.

The retaining device may be formed as a spring element, polyurethane being used as the material in particular.

Advantageously, the partition by means of a return device, in particular independently of the piston / rod element, against the extension direction displaced. Thus, the memory is independent of the piston / rod element, in particular after execution of the emergency operation, charged with pressure medium.

The restoring device can be designed as a spring element, wherein a gas filling of the first chamber, in particular with nitrogen, acts as a spring element.

The second active surface may be arranged on an annular outer contour of the dividing wall, wherein the second active surface points substantially toward the cylinder base and away from the extension direction.

Advantageously, a drain valve is provided in the partition, which, in particular designed as a check valve, is permeable in the direction of the memory and can be flowed via the pressure medium from the first chamber into the second chamber. Thus, a leakage amount of the hydraulic cylinder, which is sucked because of the negative pressure / vacuum in the first chamber, in particular during the Aufladebetriebs, in the hydraulic circuit back conveyed. The restoring device is advantageously designed as a particular consisting of polyurethane spring element.

Advantageously, a pressure monitoring device is provided, by means of which a pressure in the memory is monitored. In particular, the pressure monitoring device is provided in the high-pressure accumulator and / or in the low-pressure accumulator. Thus, an increased leakage safety of the hydraulic cylinder is ensured. Furthermore, as a result of the leakage, the hydraulic system is able to automatically reset itself to an original state and thus delay service. In particular, with the above-described execution of the charging operation, a leakage amount can be returned to the hydraulic circuit.

• Schließen und/oder Geschlossenhalten des Speicherzuschaltventils und Schließen und/oder Geschlossenhalten des Aufladeventils zum Ausführen des Normalbetriebs,
• Öffnen und/oder Offenhalten des Speicherzuschaltventils und Schließen und/oder Geschlossenhalten des Aufladeventils zum Ausführen eines Notbetriebs zum, insbesondere schnellen und/oder maximalen, Ausfahren des Kolben-/Stangenelements,
• Schließen und/oder Geschlossenhalten des Speicherzuschaltventils und Öffnen und/oder Offenhalten eines Aufladeventils zum Ausführen eines Zurücksetzens des hydraulischen Systems nach Ausführen des Notbetriebs mit Laden des Speichers, insbesondere zum Bewegen des Kolben-/Stangenelements entgegen der Ausfahrrichtung.

An inventive method for operating the hydraulic system according to the present invention comprises the following steps:

• Closing and / or keeping closed the storage switching valve and closing and / or keeping the charging valve closed to perform the normal operation,
• Opening and / or holding open the storage switching valve and closing and / or keeping closed the charging valve for performing an emergency operation for, in particular fast and / or maximum, extension of the piston / rod element,
• Closing and / or keeping closed the storage switching valve and opening and / or holding open a charging valve for performing a reset of the hydraulic system after performing the emergency operation with loading of the memory, in particular for moving the piston / rod member against the extension direction.

An advantage of the method according to the invention is that it allows the hydraulic system according to the invention to be operated in a simple and effective manner, thus saving costs.

Advantageously, the charging operation is carried out after the emergency operation. Thus, the memory, in particular the high pressure accumulator, after the emergency operation can be recharged with pressure medium. Normal operation can then be performed again.

Brief description of the drawings

• Figur 1 ein erfindungsgemäßes hydraulisches System gemäß einem ersten Ausführungsbeispiel mit einem in einem Längsschnitt dargestellten Hydrozylinder in einem geschlossenen hydraulischen Kreis,
• Figur 2 ein erfindungsgemäßes hydraulisches System gemäß einem zweiten Ausführungsbeispiel mit einem in einem Längsschnitt dargestellten Hydrozylinder in einem geschlossenen hydraulischen Kreis während eines Normalbetriebs,
• Figur 3 ein erfindungsgemäßes hydraulisches System gemäß Figur 2 während eines Notbetriebs, und
• Figur 4 ein erfindungsgemäßes hydraulisches System gemäß Figur 2 während eines Aufladebetriebs.

Several Embodiments An exemplary embodiment of the invention will be explained in more detail below with reference to schematic drawings. Show it:

• FIG. 1 A hydraulic system according to the invention according to a first embodiment with a hydraulic cylinder shown in a longitudinal section in a closed hydraulic circuit,
• FIG. 2 a hydraulic system according to the invention according to a second embodiment with a hydraulic cylinder shown in a longitudinal section in a closed hydraulic circuit during normal operation,
• FIG. 3 an inventive hydraulic system according to FIG. 2 during an emergency operation, and
• FIG. 4 an inventive hydraulic system according to FIG. 2 during a recharge operation.

Detailed description of the illustrated embodiments

This in FIG. 1 illustrated first embodiment of the hydraulic system 1 according to the invention includes a hydraulic cylinder 2, which has a special construction according to the invention and can be referred to as differential cylinder in differential construction.

In a housing 4 of the hydraulic cylinder 2, a cylindrical guide pin 6 is arranged on an end portion of the housing 4 pointing away from a direction of extension 8, of which a cylinder base 10 is formed. The guide pin 6 is here formed integrally with the housing 4, alternatively it may be firmly connected to the housing 4.

On the guide pin a hollow cylinder-shaped piston / rod member 12 is mounted axially displaceable. A first working space 14 is bounded by the guide pin 6 and the piston / rod element 12. A second working space 16 is bounded by the guide pin 6 and the piston / rod element 12 and the housing 2. A third working space 18 is bounded by the piston / rod element 12 and the housing 4. The piston / rod element 12 protrudes in the illustrated Position with a closed end portion 20 of a substantially in the extension direction 8 facing end portion of the housing 4, of which a cylinder head 22 is formed.

From the first working chamber 12, a first flow path 24 extends to a pressure medium source 26. The pressure medium source 26 is formed as a pump unit, which is a drive 28, here a variable speed and reversible controllable electric motor, and a hydraulic machine 30, which is designed here as a hydraulic pump is. Fluidically parallel to the hydraulic machine 30, a low-pressure accumulator 32 is connected, from which the hydraulic machine 30 via each one designed as a check valve Nachsaugventil 34 pressure medium can vacuum.

From the second working space 16 extends a storage flow path 36 up to a high-pressure accumulator designed memory 38. From the storage flow path 36 leads a branch 39 to a second flow path 40, which extends from the hydraulic machine 30 to a third working space 18. In the branch 39, a check valve 41 is arranged, which blocks in the direction towards the second flow path 40.

In the storage flow path 36, a storage switching valve 40 is disposed between the second working chamber 16 and the memory 38, here a 2/2-way valve, which is normally open. Between the second working space 16 and the storage switching valve 42, an intermediate branch 44 of the storage flow path 36 can be fluidically connected to the first flow path 24 via a charging valve 46. The charging valve 46 is designed here as a normally closed 2/2-way valve.

A first active surface 48 is arranged on a closed end section 20 on an inner contour of the piston / rod element 12. The first active surface 48 points substantially toward the cylinder bottom 10 and away from the extension direction 8.

The second active surface 50 is arranged on an outer contour of the piston / rod element 12 which is designed here as an annular radial collar, wherein the second active surface 50 points essentially toward the cylinder base 10 and away from the extension direction 8. The Radial collar is disposed at an open end portion 51 of the piston / rod member 12.

A third active surface 52 is arranged on the outer contour of the piston / rod element 12, which is embodied here as an annular radial collar, the third active surface 52 pointing essentially toward the cylinder head 22 and towards the extension direction 8.

The operation and various modes of the hydraulic system according to the invention will be described below.

In a normal operation is for a movement of the piston / rod member 12 in its extension direction 8, the first active surface 48 is acted upon via the first flow path 24 by means of the hydraulic machine 30 with pressure medium. Pressure medium present in the third working space 18 is returned to the hydraulic machine 30 via the storage flow path 36, the branch 39 and the second flow path 40. In this case, the storage switching valve 42 is energized and thus closed and the charging valve 46 is de-energized and thus closed. A movement of the piston / rod member 12 against its extension direction 8 takes place in the same circuits of the valves 42, 46 analogous thereto.

Since the memory switching valve 42 is energized and thus closed during normal operation, a negative pressure or a vacuum is produced in the first working space 16 due to the movement of the piston / rod element 12 in the extension direction 8.

In an emergency operation, the memory switching valve 42 is de-energized and thus open, whereby the second active surface 50 is acted upon by pressure medium from the memory 38 and the piston / rod member 12 is moved in its extension direction 8. If the storage switching valve 42 is switched off during normal operation, the second active surface 50 is acted upon in addition to the first active surface 48 with pressure medium - the first active surface 48, as described above, with pressure medium from the pressure medium source 26 and the hydraulic machine 30. In a power failure, which has a failure of the drive 28, for example, the electric motor, the result, the memory switching valve 42 is thereby quasi automatically de-energized and only the second active surface 50 with pressure medium from the memory 38 is applied. Thus, in emergency operation, the hydraulic cylinder 2 is also adjustable without the drive 28.

After performing the emergency operation, a charging operation must be performed to recharge the reservoir 38 with pressure medium and to promote pressure medium from the second working chamber 16 back into the hydraulic circuit. In this case, the memory switching valve 42 is energized and is thus closed and the charging valve 46 energized and is thus open. Thus, when moving the piston / rod member 12 against its extension direction 8 pressure medium from the hydraulic machine 30 via the second flow path 40 in the third working space 18 is promoted. In this case, pressure medium from the first working chamber 14 and pressure medium from the second working chamber 16 is conveyed back into the hydraulic circuit, wherein pressure medium from the second working space 16 in the intermediate branch 44 from the storage flow path 36 via the open charging valve 46 in the first flow path 24 and towards the low pressure side the hydraulic machine 30 is promoted. Pressure fluid from the first working chamber 14 is conveyed via the first flow path 24 toward the low-pressure side of the hydraulic machine 30. From the high-pressure side of the hydraulic machine 30 pressure medium is conveyed via the branch 39 and the flow-through in the flow direction check valve 41 into the memory 38 and the memory 38 thus recharged. Normal operation can then be performed again.

FIG. 2 shows a second embodiment of the hydraulic system according to the invention in normal operation.

The in the hydraulic circuit in addition to the in FIG. 1 illustrated hydraulic elements are standard elements that will not be described further here.

Unlike the in FIG. 1 1, the hydraulic cylinder 2 of the second embodiment has a partition wall 54 in the second working space 16, whereby it is divided into a first chamber 56 arranged adjacently to the open end section 51 and a second chamber 58 arranged adjacently to the cylinder bottom 10.

The resulting in normal operation because of the movement of the piston / rod member 12 in the extension direction 8 when energized and thus closed Speicherschaltaltventil 42 negative pressure / vacuum thus arises in the first chamber 56th

A travel of the piston / rod member 12 in the extension direction 8 is marked in normal operation by a cylinder head side extension stop on the housing 4 and marked against the extension direction 8 of a position of the partition 54.

The partition 54 is in an intermediate position between the cylinder head side extension stop on the housing 4 and a cylinder bottom side retraction stop on the housing 4 and separated in the second chamber 58 pressure fluid effectively from the force acting in the first chamber 56 negative pressure / vacuum.

In the partition wall 54 designed as a check valve drain valve 60 is provided, which is permeable in the direction of the memory 38 out and on the pressure medium from the first chamber 56 into the second chamber 58 can be flowed.

FIG. 3 shows that too FIG. 2 described second embodiment of the hydraulic system according to the invention in emergency operation.

In that too FIG. 1 described emergency operation here the formed on an annular outer contour of the partition 54 second active surface 50 is acted upon with pressure medium from the memory 38 to move the piston / rod member 12 in the extension direction 8 with power amplification. The partition wall 54 shifts axially on the guide pin 6 until it rests against the piston / rod element 12 or at its annular radial collar, as in FIG. 3 shown. The partition wall 54 is then moved together with the piston / rod element 12 in the extension direction 8 until the piston / rod element 12 bears against the housing 4 on the cylinder head side extension stop.

FIG. 4 shows that too FIG. 2 described second embodiment of the hydraulic system according to the invention in the charging mode.

Unlike the in FIG. 1 shown and described above first embodiment of the hydraulic system 1 according to the invention in the second embodiment of the hydraulic system 1 according to the invention in Aufladebetrieb a complete retraction of the piston / rod member 12 is no longer required. At the second embodiment, the partition 54 is displaced by the piston / rod member 12 against the extension direction 8 in the charging operation and thus at each position of the partition 54 is an effective separation of pressure medium in the second chamber 58 of normal pressure in the first chamber 56 resulting negative pressure / Vacuum guaranteed. In this way, a travel of the piston / rod member 12 and thus a measure of the movement of the piston / rod member 12 against the extension direction 8 during charging operation is relatively freely selectable. An optionally occurring leakage quantity of the hydraulic cylinder 2, which is sucked into the first chamber 56 because of the negative pressure / vacuum, can be conveyed back into the hydraulic circuit via the drain valve 60, in particular during the charging operation.

Disclosed is a hydraulic system with a special hydraulic cylinder, in particular a differential cylinder in differential construction, which has three separate druckmittelbeaufschlagbare active surfaces. Operable in normal operation with a Gleichgangscharakteristik, developed the hydraulic cylinder in emergency operation, a differential characteristic. This is advantageous when using the hydraulic system according to the invention, for example in a wind power plant for the hydraulic pitch adjustment of a rotor or its rotor blades.

LIST OF REFERENCE NUMBERS

1

Hydraulic system

2

hydraulic cylinders

4

Housing of the hydraulic cylinder

6

spigot

8th

of extension

10

cylinder base

12

Piston / rod member

14

First workroom

16

Second workspace

18

Third workspace

20

Closed end portion of the piston / rod element

22

cylinder head

24

First flow path

26

Pressure medium source

28

drive

30

hydromachine

32

Low-pressure accumulator

34

cavitation valve

36

Memory flow path

38

Storage

39

junction

40

Second flow path

41

check valve

42

Speicherzuschaltventil

44

between branch

46

Aufladeventil

48

First effective area

50

Second effective area

51

Open end portion of the piston / rod element

52

Third active surface

54

partition wall

56

First chamber

58

Second Chamber

60

drain valve

Claims (12)

1. Hydraulic system having a hydraulic cylinder (2) which has at least three separate pressurizable surfaces (48, 50, 52), wherein a first surface (48) and a second surface (50) can be pressurized for a movement of a piston/rod element (12) of the hydraulic cylinder (2) in its extension direction (8), wherein a reservoir connection valve (42) is provided, by means of which the second surface (50) can be pressurized in the extension direction (8) with a pressure medium from a charged reservoir (38), and wherein a charging valve (46) is provided, by means of which a first working chamber (14) of the hydraulic cylinder (2), which is delimited by the first surface (48), can be connected fluidically to a second working chamber (16) of the hydraulic cylinder (2), which is delimited by the second surface (50), and wherein a hydraulic machine (30) is provided, by means of which the first surface (48) or a third surface (52) of the hydraulic cylinder (2) can respectively be pressurized with pressure medium in a closed hydraulic circuit, wherein the third surface (52) can be pressurized with pressure medium to move the piston/rod element (12) counter to the extension direction (8), and wherein the reservoir connection valve (42) is connected in a reservoir flow path (36) between the reservoir (38) and the second working chamber (16), and wherein the charging valve (46) is connected in an intermediate branch (44) of the reservoir flow path (36) between the reservoir connection valve (42) and the second working chamber (16), and wherein the intermediate branch (44) between the first working chamber (14) and the hydraulic machine (30) is connected fluidically to a first flow path (24), and wherein the reservoir flow path (36) extends from the second working chamber (16) as far as the reservoir (38) formed as a high-pressure reservoir, and wherein a branch (39) leads from the reservoir flow path (36) as far as a second flow path (40), which extends from the hydraulic machine (30) as far as a third working chamber (18) delimited by the third surface (52), and wherein a non-return valve (41), which blocks in the direction towards the second flow path (40), is arranged in the branch (39).
2. Hydraulic system according to Claim 1, wherein, during a normal operation, a negative pressure can be produced in the second working chamber (16).
3. Hydraulic system according to Claim 1 or 2, wherein, during a normal operation of the hydraulic cylinder (2), no pressure medium can flow into the second working chamber (16).
4. Hydraulic system according to one of Claims 1 to 3, wherein the hydraulic cylinder (2) has in its housing (4) a guide pin (6), on which the piston/rod element (12) is axially displaceably mounted, wherein the first working chamber (14) is delimited by the guide pin (6) and the piston/rod element (12), and wherein the second working chamber (16) is delimited by the guide pin (6) and the piston/rod element (12) and the housing (4), and wherein a third working chamber (18) is delimited by the piston/rod element (12) and the housing (4).
5. Hydraulic system according to one of the preceding Claims 1 to 4, wherein the reservoir connection valve (42) is open when de-energized.
6. Hydraulic system according to one of the preceding Claims 1 to 5, wherein the second working chamber (16) is subdivided into two chambers (56, 58) by means of a partition (54) that is designed to be fluid-tight.
7. Hydraulic system according to Claim 6, wherein the partition (54) is formed in the shape of a ring and is axially displaceably arranged on the guide pin (6), and wherein the partition (54) can be displaced in the extension direction (8) by means of pressurization from the reservoir (38) or, by means of pressurization of the third surface (52) via the piston/rod element (12), is indirectly or directly displaceable counter to the extension direction.
8. Hydraulic system according to Claim 6 or 7, wherein the partition (54) can be displaced counter to the extension direction (8) by means of a restoring device.
9. Hydraulic system according to Claim one of Claims 6 to 8, wherein an outlet valve (60), which is permeable in the direction of the reservoir (38), is provided in the partition (54).
10. Hydraulic system according to Claim 8 or 9, wherein the restoring device is arranged in the first chamber (56) and is formed as a gas filling or as a spring element consisting substantially of polyurethane.
11. Hydraulic system according to one of Claims 1 to 10, wherein, in an emergency operation, the second surface (50) can be pressurized in the extension direction (8) with pressure medium from the charged reservoir (38).
12. Method for operating the hydraulic system according to one of Claims 1 to 11,
    characterized by the following steps:

    closing and/or keeping closed the reservoir connection valve (42) and closing and/or keeping closed the charging valve (46) in order to carry out the normal operation for moving the piston/rod element (12) in or counter to the extension direction (8),

    opening and/or keeping open the reservoir connection valve (42) and closing and/or keeping closed the charging valve (46) in order to carry out an emergency operation for moving the piston/rod element (12) in the extension direction (8), and/or

    closing and/or keeping closed the reservoir connection valve (42) and opening and/or keeping open a charging valve (46) in order to carry out resetting of the hydraulic system following the carrying out of the emergency operation with charging of the reservoir (38).

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