EP1170512B1 - Fluid pressure actuator with mechanical locking device when unpressurized - Google Patents

Abstract

The cylinder has an internal thread (7) in the boring of its piston (6), in working connection with the thread of a threaded spindle (9). This spindle has a coupling profile at the lower end, on which a locking disk (11) with first gear crown can move axially. This gear crown is engaged with a second gear crown (17) on a fixed locking disk (18).

Description

The invention relates to a working cylinder with mechanical Path blocking for use in hydraulic or pneumatic operated mechanisms, their movement in the event of failure the pressure energy through a mechanically acting locking system is hindered.

Mechanical are from the general state of the art Locking systems for working cylinders known by a positive or non-positive blocking of the movement of the Piston rod act, systems with non-positive Blockage prevail. For example, friction bodies by spring forces on the inner or outer Jacket of the piston rod, or inner jacket of the working cylinder tube pressed to by means of the frictional engagement achieved the movement of those under axial load To prevent or block the piston rod.

DE 35 10 643 A1 describes a clamping head for fixing a rod by means of an attack on it from the outside Clamping element with an oblique guide surface, the from a slidable by means of servo pistons, under spring preload standing clamping element is actuated.

A similar solution to a blocking clamp is described in the publication DE 38 11 225 C2. Several jaws that can be moved axially in guides pressed by spring elements to block the piston rod. The opening position is guided by a cylinder Servo piston reached.

A device for clamping an axially moving rod is also disclosed in the publication DE 37 07 046 A1. Here, the clamping takes place by means of a clamping sleeve with outer cone, on which the inner cone is spring-loaded standing piston acts.

This described clamping heads is in addition to a complex Manufacturing together that generally occurs when large dynamic forces due to static friction none exact positioning is possible. It has a disadvantageous effect the clamping also on the service life of functional parts, here the piston rod, because of the static friction considerable wear is caused. The dimensions of a Working cylinders with such clamping devices are essential larger or attached outside the cylinder Clamping devices are radially wide.

With almost the same disadvantages of wear from functional parts is that in the publication DE 3810183 A1 disclosed solution of a device for locking a Piston rod of a piston-cylinder arrangement affected. For locking purposes, the piston has slidable springs Disc segments on the ring-shaped, piston-like Control elements with conical control elements conical surfaces are pressed on the disc surfaces and so the disc segments against the pressure of the springs inwards pull. The disc segments are in a depressurized state pressed against the inner jacket of the cylinder tube and block the piston movement.

Another solution where the movement is blocked a piston rod is achieved, describes the document DE 33 07 644 A1. In the hollow piston rod is one Device for non-positive clamping installed, whereby Clamping segments with friction linings on a support tube through a Cone on an operating rod with a control piston connected in a control cylinder and via a spring is biased into the clamping position for blocking be pressed against the inner wall of the piston rod.

A special version of a continuously adjustable working cylinder, who is able to take his position under To hold the load reliably in any intermediate position, is disclosed in the document DE 38 07 669 C2. achieved this effect is achieved by means of a hollow piston rod an inner profile in which a slidable, axial spring-loaded rod with a ball recirculation channel with balls, which engage in the profiling of the piston rod, is arranged. The rod is with an actuating piston connected in an actuating cylinder that the rod at Pressurization with the pressure medium of the working cylinder so that the balls run freely can and in the event of pressure drop brought into the blocking position the piston rod will continue to move is hindered.

The document DE 297 20 838 U1 describes a working cylinder with integrated lifting brake, which essentially consists of a brake cone and a brake piston, whereby in the depressurized state, a non-positive coupling between this is present. The brake cone is with a through the working piston movement by means of a spindle nut, driven, Threaded spindle connected in the hollow piston rod. The brake piston with a compression spring in a spring chamber is arranged in the bottom closure part. For releasing the lifting brake this will be for the actuation of the working cylinder existing print medium is used by using a 4/3 Valve and a separate connection on the working cylinder is guided into the piston chamber of the brake piston and this removed from the brake cone against the spring preload becomes. The pressure is at the same time on the brake piston and Piston on, so that the release is always under Load without force-free decoupling. in principle is this version of a lifting brake, with near the Central axis of the working cylinder arranged frictionally Brake can only be used for very small locking torques. A working cylinder designed for this principle large locking torques as they are accurate for heavy loads as well Positionings are required, should be done with a radially widely protruding screw cap to accommodate the lifting brake be executed, making a manufacturing and costly Construction would arise, its more practical Applicability is limited.

A pneumatic working cylinder for presetting the cylinder with active or passive brake is in the publication EP 0 648 942 A1. In a hollow piston rod with a working piston with a threaded sleeve a threaded rod arranged with a brake disc is connected, their rotation and thus the piston movement, is braked or blocked by means of a friction element. The The friction element is located on a locking element two interconnected piston elements in one separate piston chamber with its own connection for the Print medium are arranged displaceably. Dependent on the brake can be used during the installation of the Working cylinder designed as an active or passive brake his. In any case, to release or apply the brake an additional, separately controlled pressure medium connection required. The position of the working piston is with the help a signal generator coupled to the threaded rod evaluated. Due to the type of execution as well as the interaction of the brake disc and friction element is one Working cylinders also only when necessary Locking torques can be used sensibly.

Another cylinder with locking means is in the Document US 2 804 053. This also points a working piston with a hollow piston rod, spindle nut, Threaded spindle and a connected to it, axially displaceable brake part in the form of a brake disc, the under spring preload with another brake part in the form of a friction element in the depressurized state in Intervention stands up. To release the brake is a special one Release piston with plunger, which when pressurized Brake disc stands out from the friction element in an additional Piston chamber with separate pressure medium connection. This complex solution is also due to the friction brake only suitable and limited for relatively low locking torques an additional pressure medium connection for the release piston as well as an additional control.

The document US 2 879 746 proposes 2 versions of one Working cylinder with means for mechanically locking the Piston movement before. Among other things, there is also a working piston with hollow piston rod, spindle nut, threaded spindle and a brake element connected thereto Form of a disc available. When depressurized between the shoulder of the brake disc and one firmly in the Working cylinder arranged counterpart by means of a Spring preload, specially designed piston, with its own piston chamber and separate pressure medium supply, a frictional connection is established. The brake is released by pressurizing the specially trained Piston, which is axially displaced. The proposed one Working cylinder with mechanical locking by means of Friction is only for applications with low locking torques suitable.

Furthermore, US Pat. No. 3,442,176 a elaborate cylinder lock system in the form of a, only ratchet lock acting in one direction of rotation, with a Working piston with spindle nut, hollow piston rod, threaded spindle, in which a loose extension rod from the closed End of the piston rod can be moved and a locking mechanism mounted thereon. The ratchet lock is made from a first one, on wedges axially displaceable, ratchet wheel on a disc on the Threaded spindle and one, in the locking part of the cylinder assembled, second ratchet wheel formed. If the teeth the ratchet wheels are engaged, the threaded spindle can only turn in one direction, gradually. The Both ratchet wheels are spring-loaded from each other kept separate, with a small piston rod a special piston in a separate piston chamber one, arranged in this spring, an axial displacement the disc with the first ratchet wheel. This spring acts as a second spring, with higher preload, in a drilled piston chamber of a second special Towards the piston on the sliding ratchet wheel. The second special piston is from the loose extension rod then shifted when the piston rod of the working cylinder is in a predetermined position when retracting, whereby the second special piston with the Disc of the ratchet wheel until it engages with the fixed one Ratchet wheel moves and the piston rod extends again is prevented. To extend the piston rod First the piston chamber of the special piston with pressure medium acted upon so that the engaged Ratchet wheels are separated and only then the cylinder space to extend the piston rod by means of a necessary Hydraulic reversal pressurized.

In GB 683 633 a working cylinder according to the preamble of claim 1.

The object of the invention is a pressure medium operated Working cylinders with mechanical path locking develop, the locking device integrated in the working cylinder which is accurate positioning and instant reliable blocking in the event of pressure loss guaranteed, no additional auxiliary energy as well as additional external Control elements and control lines for the and locking requires a compact design as well allows.

The object is achieved by those listed in claim 1 Features solved. Preferred further developments result from the subclaims.

The basic idea of the invention is training a working cylinder with integrated mechanical locking the translatory movement of a hollow piston rod, which is coupled to a pierced piston, wherein the inside of the bore of the piston has a thread, the one with an external thread, inside the hollow piston rod arranged with a threaded spindle Coupling profile is engaged at its lower end, and a movable locking disc on the coupling profile, with a ring gear on the underside, form-fitting is axially displaceably mounted on a sprocket the top of a fixed locking washer in the bottom part of the Working cylinders in a pressureless state with each other are coupled, the two sprockets of the Locking washers have a positive locking that inhibits the first ring gear or form a positive coupling.

In particular, the axial gear ring can be advantageous Change sliding locking washer for repair purposes. For the thread pairing between the piston and the threaded spindle is preferably a non-self-locking thread used with a large incline to ensure smooth, free rotation of the threaded spindle, which in high quality Plain bearings is supported. The slope of the Thread determined depending on the value of the piston rod acting force and the coefficients of friction between the functional parts of the working cylinder the value of resulting negative reverse torque.

The locking device is pressure-dependent. It is through a control integrated in the bottom part of the working cylinder always put into the blocked state when there is no operating pressure a fluid is present or the pressure fails. When the working pressure is applied to the working cylinder the locking device is first released by the spring-loaded, axially movable locking disk with the ring gear by means of an unlocking piston via plunger opposite the ring gear of the fixed locking disc is raised so far that only after that the movement of the main piston of the working cylinder is made possible. During the movement of the, coupled with the piston rod Parts of the gear to be moved against twisting secured piston in the cylinder barrel will turn the threaded spindle with the positively coupled, axial movable locking disc causes. Regardless of the direction of movement of the piston occurs when the operating pressure is not present immediate mechanical blocking of the piston movement, by rotating the threaded spindle in the thread of the piston through the positive coupling of the two ring gears of the locking disks is blocked. in this connection the cylinder chamber of the unlocking piston is also depressurized, whereby the spring-loaded, with the Threaded spindle coupled positively, axially displaceable Locking disk presses the unlocking piston back over the plunger and with the ring gear against the ring gear of fixed locking disc pressed, a positive coupling is produced and the rotation of the threaded spindle locks immediately.

The control integrated in the base part of the working cylinder, that for that essentially from the rotating lead screw and the two locking washers with sprockets existing, mechanical locking system works, works with the normal operating pressure of the working cylinder. The Control has one in the main axis of the working cylinder Slightly displaceable around a central position against spring forces Middle slide with fluid return channels on the is in neutral neutral position when depressurized, this fluid return channels with the unlocking piston chamber communicate with the unlocking piston chamber Depressurise so that it unlocked Fluid into the respective flow-oriented connection Check valves flow out and through the spring preload the axially movable locking disc over this and the plunger the unlocking piston is pressed into its starting position becomes.

During the unlocking process, the pressurized flows first Fluid through the channels leading to the unlocking piston chamber and piston chamber of the working cylinder. In these Channels are non-return valves with a defined preload installed, which initially discharges into the piston chambers prevent, with the extent of the pressure increase, only the Middle slide is moved to its end position, and after that the unlocking piston is pressurized. The unlocking piston moves the movable locking disc via ram against the action of the locking spring so that the unlocked state is given.

The preload valves that prevent the fluid from flowing into the prevent each piston chamber are in their preload set 10% higher than the preloaded check valves, which the free inflow into the unlocking piston chamber prevent. In this way, the safe guarantee for the onset of movement of the piston only after it has been completed Unlocking the form lock given.

The preload valves leading to the piston chambers of the working cylinder lead to the outflow of the fluid from the respective Piston chamber check valves connected in parallel. Conveniently, the cylinder tube is double-walled with channels formed on the inner tube, whereby the fluid to as also from the piston rod area without additional external lines via the control in the bottom part of the working cylinder is directed.

For the safe function of the positive or non-positive coupling of the two ring gears of the locking washers Size of the axial force of the spring for the preload of the axially movable locking washer be dimensioned so that this with sufficient locking quality, taking into account that on the working cylinder dynamic loads, at least corresponds to the return torque impressed by the external load.

It is also conceivable for the positive coupling of the two sprockets of the locking washers by a purely frictional To replace coupling.

The displacement of the unlocking piston is advantageous Ensuring that it can be moved freely without oil held by inevitable leak oil on every stroke the unlocking piston to unlock the form or frictional coupling of the two ring gears of the locking washers through one in the central axis of the working cylinder arranged leak oil line via a check valve in the fluid circuit is pushed back.

The advantages of the invention are in particular the reliable, immediate blocking of the movement of the piston rod of the working cylinder when pressure is not present Fluid.

The current position of the piston rod is without braking distance fixed.

Wear of functional parts of the working cylinder does not occur.

There are no additional external controls, and Lines required.

The twisting of the working cylinder is caused by flattening on the bottom part. and corresponding counterparts at the installation site prevented, or in simple execution via the thru axle the spherical bearing.

The size of the working cylinder with mechanical path locking does not differ in the radial dimensions and in the axial dimensions only slightly of those a comparable working cylinder without blocking.

Fig. 1 als Schnitt A-A durch den Arbeitszylinder im verriegelten Zustand;

Fig. 2 als Teilschnitt A-A durch den Arbeitszylinder im Bereich des BodenTeils im entriegelten Zustand;

Fig. 3 als Schnitt B-B durch die Rückströmkanäle und den Rückschlagventilraum des Fluids aus dem Entriegelungskolbenraum;

Fig. 4 als Schnitt C-C durch das doppelwandige Zylinderrohr;

Fig. 5 als Schnitt D-D mit der Darstellung der Abströmleitung aus dem Kolbenraum zur Umgehung der Vorspannventile;

Fig. 6 als Teilschnitt E-E zur Darstellung des Vorspannventils näher erläutert.

The invention is described as an embodiment using

Figure 1 as a section AA through the cylinder in the locked state.

2 shows a partial section AA through the working cylinder in the area of the base part in the unlocked state;

3 shows a section BB through the return flow channels and the check valve chamber of the fluid from the unlocking piston chamber;

4 shows a section CC through the double-walled cylinder tube;

5 shows a section DD with the representation of the outflow line from the piston chamber to bypass the preload valves;

Fig. 6 is explained in more detail as a partial section EE to illustrate the bias valve.

According to Fig. 1 and Fig. 2, a working cylinder 1 with its Main axis 2 in a double-walled cylinder tube 3 with Channels 4 and radial groove 5 a piston 6 with an internal thread 7, which is coupled to a hollow piston rod 8, on. In the hollow piston rod 8 protrudes as part of the locking system a threaded spindle 9, at its lower end Square 10 for positive coupling with a sliding Locking disk 11 with a first ring gear 12, which is pre-tensioned by means of locking spring 13, integrally formed is. For deriving leakage oil from a cubic capacity 14 an unlocking piston 15, which via plunger 16 (16.1; 16.2) the first ring gear 12 with the axially displaceable Locking disc 11 from a second ring gear 17 a fixed Locking disk 18 presses are in the threaded spindle 9 in the area the displacement 14 has a bore 19 in the main axis 2 a check valve 20 and with an axial bore 21 in Connected radial bores 22 are arranged.

In a bottom part composed of several individual parts 23 with an inflow connection 24, which via an upper Line 25 with an inner annular chamber 26 and an upper one Connection line 27 with an upper check valve chamber 28 with an upper check valve 29 in connection stands; a drain port 30 that communicates with a room 31, via a lower connecting line 32, an outer one Ring channel 33 and a line 34 with an oil return Valve communicates with valve chamber 35 a center slide 36 for controlling the pressurization of the unlocking piston 15 is arranged.

The central slide 36 is depressurized by springs 37 held in the defined middle position, being over its backflow channels 38 and a backflow bore 39 a Connection between an unlocking piston chamber 40 and the check valves 29; 35 exists.

In the bottom part 23 there are also an upper locking tube 41, an oil return-leading locking tube 42, which according to FIG. 5 and FIG. 6 a non-parallel check valve 43 (43.1; 43.2) is switched, which via an annular chamber 44 and a bore 45 (45.1; 45.2) in the locking tube 41; 42 opens arranged. The upper locking tube 41 is shown in FIGS. 1 and 2 via a left annular chamber 46 and lines 47 (47.1; 47.2) with the channels 4 in the double-walled cylinder tube 3 and thus further via the radial groove 5 with a piston rod space 48 connected. The oil return leading Locking tube 42 is connected via a further line 49 to a Piston chamber 50 connected.

From Fig. 2 continue the connections between the Unlocking piston chamber 40 and the inner annular chamber 26 via an upper connecting channel 51 with another biased check valve 52 as well as between the outer Ring channel 33 via a lower connecting channel 53 with additional biased check valve 54 and Unlocking piston chamber 40 emerges.

4 are the double-walled Cylinder tube 3 with its channels 4 and the threaded spindle 9 with axial bore 21 and those connected to it Radial bores 22 shown.

The mechanical locking system in one double acting Working cylinder 1 lies in its main axis 2, wherein the autonomous control is arranged in the bottom part 23 and only by the pressure of the inflow and outflow of the fluid to the normal operation is operated. It essentially exists from a threaded spindle 9, an axially displaceable Locking disc 11 with a first ring gear 12 which on the Square 10 is secured against rotation, positively and a fixed locking disk 18 with a second ring gear 17. When the working cylinder 1 is depressurized, the teeth are of the first ring gear 12 of the displaceable locking disk 11 and that of the second ring gear 17 of the fixed locking disk 18 engaged, positively coupled, the sliding Locking disc 11 by means of the locking spring 13 in this Locked position on the square 10 was moved.

The sliding locking disk 11 and the fixed locking disk 18 with the sprockets 12; 17, the mating of the thread the threaded spindle 9 with the internal thread 7 of the piston 6 and the locking spring 13 are the crucial functional elements of the mechanical locking system, the locking, positive engagement of the teeth of the two sprockets 12; 17 works as a mold. It is sized that it is against the action of the reverse torque, which over the coupling of the internal thread 7 of the piston 6 with the threaded spindle 9 due to external forces on the piston rod 8 arises, a sufficient rest quality is guaranteed. The firm Lock washer 18 is in a known manner with the bottom part 23 detachable, but non-positively and positively connected. On the outer jacket of the bottom part 23 can be in a suitable place Flats have been incorporated for a non-rotating ensure external coupling of the working cylinder 1 if larger reverse torques must be safely absorbed. smaller Reverse torques can be on the axis of the working cylinder 1 to be counteracted by a torque with the piston rod 8 connected thru axle bearings.

The function of the system for mechanically blocking the Working cylinder 1 will follow two essential Functional states explained in more detail.

State 1 - the locked system should be retracted Piston rod 8 by the inflow of a pressurized Fluids are unlocked.

The pressurized port 24 is the pressurized Fluid is introduced and enters via the upper line 25 the inner annulus 26 from which it continues through the upper Connection line 27 into the upper check valve chamber 28 arrives, which enables the outflow into the upper locking tube 41. According to Fig. 1 and Fig. 2, the locking tubes 41; 42 a biasing valve 55 (55.1; 55.2). The blocking tubes 41; 42 are the check valves 43.1; 43.2 switched antiparallel to the backflow out the respective run-oriented piston rod space 48 or To allow piston chamber 50. The preload of the preload valves 55.1; 55.2 is dimensioned so that the guarantee for it is given that the central slide 36, which is in the unpressurized Condition via the springs 37 in a defined central position is held when the piston rod 8 is retracted into its right end position is pressed before the preload valve 55.1 the fluid via line 47.1, channels 4 and the radial groove 5 can flow into the piston rod space 48. In the right end position of the central slide 36 are Reverse flow channels 38 moved so that the unlocking piston 15 are pressurized to be pressurized with the fluid can.

After the middle slide 36 reaches its right end position has, flows through the upper connecting channel 51 and through the further biased check valve 52 in the Unlocking piston chamber 40, whereby the unlocking piston 15 axially, against the action of the bias of the locking spring 13 via the displaceable locking disk 11 and the plunger 16.1; 16.2. The unlocking piston 15 moves over the plunger 16.1; 16.2 the sliding Lock washer 11 axially on the square 10 of the threaded spindle 9, whereby the engagement - the positive coupling the toothing of the first ring gear 12 and the second Sprocket 17 are lifted, the locked state is lifted is. The pressure of the fluid required to maintain the lockout condition by moving the unlocking piston 15 its value is at least 10% higher than that required to move the central slide 36 Print. Only after moving the unlocking piston 15, the unlocking achieved with this, and another Pressure increase of at least another 10% compared to Pressure to move the unlocking piston 15 opens the bias valve 55.1 of the upper locking tube 41, the The fluid flows to the piston rod chamber 48.

With the then possible and successful postponement of Piston 6, which has its internal thread 7 with the thread of Threaded spindle 9 is in positive coupling, results their rotating movement and thus that of the Square 10 positively coupled sliding locking disc 11. The movement of the piston 6 and with it coupled piston rod 8 always causes a rotation of the Threaded spindle 9 and the elements coupled to it.

That during the retracting movement of the piston rod 8 Fluid to be discharged from the piston chamber 50 flows over the further line 49 through the check valve 43.2, the Annulus 44 and the bore 45.2 in the oil return Locking tube 42 and further via the oil return valve with valve chamber 35, line 34, the outer ring channel 33, the lower connecting line 32 to the drain connection 30th

State 2 - the unlocked system should enter Piston rod 8 due to a sudden drop in pressure of the fluid, for example damage to the pressure line, immediately locked to lower the external load prevent.

Due to the lack of pressure in the working cylinder 1, the Middle slide 36 through the springs 37 in the middle position moved, the return flow channels 38 via the return flow bore 39 with the unlocking piston chamber 40 in drain-oriented Be brought under cover and the fluid from Unlocking piston 15 by the bias of Locking spring 13 via the displaceable locking disk 11 and the plunger 16 (16.1: 16.2) is pushed back out of the Unlocking piston chamber 40 is pressed.

At the same time it causes the toothing of the ring gears 12; 17 of the locking disks 11, 18 again in engagement come and the twist-proof coupling through positive locking is made. The size of the force of the locking spring 13 is dimensioned so that this is due to the effect of an external Load on the piston rod 8 via the rotating threaded spindle 9 brought back torque held against rotation becomes.

Leakage oil from the displacement 14 and the area of the locking spring 13 are known in each stroke of the unlocking piston 15 Way through the check valve 20 in the piston chamber 50 dissipated.

In the practical version of the working cylinder described 1 is the threaded spindle 9 as is technically usual received by a plain bearing and using a thrust washer and retaining ring held.

Reference symbols used

1

working cylinder

2

main axis

3

double-walled cylinder tube

4

channels

5

radial groove

6

piston

7

inner thread

8th

piston rod

9

screw

10

square

11

sliding lock washer

12

first ring gear

13

locking spring

14

capacity

15

unlocking

16

Plunger (16.1; 16.2)

17

second ring gear

18

fixed lock washer

19

drilling

20

check valve

21

axial bore

22

radial bores

23

the bottom part

24

inlet connection

25

top line

26

inner annulus

27

upper connecting line

28

upper check valve space

29

upper check valve

30

outflow

31

room

32

lower connecting line

33,

outer ring channel

34

management

35

oil return valve with valve chamber

36

means slide

37

feathers

38

return flow

39

Rückströmbohrung

40

Entriegelungskolbenraum

41

upper locking tube

42

oil returning locking tube

43

Check valve (43.1; 43.2)

44

annular chamber

45

Bore (45.1; 45.2)

46

left ring chamber

47

Lines (47.1; 47.2)

48

Piston rod space

49

further management

50

piston chamber

51

upper connection channel

52

another preloaded check valve

53

lower connection channel

54

additional preloaded check valve

55

Preload valve (55.1; 55.2)

Claims (4)

1. Pressure medium-operated working cylinder (1) having integrated, pressure-dependent mechanical locking of the translatory movement of a piston rod (8), having a control device for supplying and draining a pressure medium, a double-walled cylinder pipe (3), a base part (23) with a fixed locking disc (18), a piston rod guide, a partially hollow piston rod (8) on a bored-through piston (6) with an internal thread (7) which is operatively connected to the thread of a threaded spindle (9) which, at the lower end, has a coupling profile on which a locking disc (11) is axially displaceably mounted in a form-fit manner, which locking disc is coupled in the unpressurised state to the fixed locking disc (18) in the base part (23) of the working cylinder (1) by means of resilient pretensioning,
   characterised in that
   the locking disc (11) is coupled in a form-fit manner by a first toothed ring (12) to a second toothed ring (17) of the fixed locking disc (18) and
   in the base part (23) a control device for the form-fit coupling of the two toothed rings (12; 17) of the locking discs (11; 18) is disposed, which control device is dependent upon the pressure of the fluid for operating the working cylinder (1), operates without additional external control elements and has no separate pressure medium connection and in that force-free unlocking is effected by an unlocking piston (15) by means of pretensioning valves (55) and a central slide valve (36), and the piston rod chamber (48) or piston chamber (50) are each subjected to the pressure fluid only after the locking system has been unlocked by this fluid.
2. Working cylinder as claimed in claim 1, characterised in that the thread pairing between the internal thread (7) of the piston (6) and the thread of the threaded spindle (9) consists of a non-self-locking thread with a steep pitch.
3. Working cylinder as claimed in claims 1 or 2, characterised in that coupling is effected between the displaceable locking disc (11) and the fixed locking disc (18) by means of friction linings.
4. Working cylinder as claimed in claims 1 to 3, characterised in that a swept volume (14) of an unlocking piston (15) is kept free of oil by its displacement effect during unlocking.

Images