EP1182302B1 - Method for supporting a hydraulically actuated, mobile working machine on a rail track and working machine for carrying out said method - Google Patents

Abstract

Before the excavator is moved with its rail wheels (6) on the track, the actual relative position between upper body and lower chassis is determined using a detector unit (20). This generates a relative position signal and transmits it to a regulator device (22) with computer (21). The device generates a control signal, which causes connection of the rod chambers (23) of two piston-cylinder-units (8.1,8.2), and hydraulic connection between the cylinder chambers (25.1,25,2) of the units and an oil reservoir (28).

Description

The present invention relates to a (working) method for supporting a hydraulic operated, movable working device, in particular a two-way excavator, on one Trajectory, as in the preamble of claim 1 (also with respect to the essential features the work equipment to be supported) is described.

Furthermore, the present invention relates to a hydraulically actuated working device for Implementation of the aforementioned method according to the preamble of claim 5, ie esp. In the literature and practice also referred to as two-way excavator hydraulic excavator in the manner of a track railroad vehicle with a working tool in the manner of a spoon, gripper or the like ..

For a better understanding of the subject invention and the hitherto in the prior art The present problem with generic methods and devices should first be that it is so-called. Wegwechselfahrzeuge in two-way excavators, ie Vehicles, which due to special (possibly also additional) facilities the traffic route can change. Because you usually only at a transition from a Verkehrswegart to only one is interested, one speaks in practice i.a. also of two-way vehicles. In this case, in addition to road-water vehicles esp. So-called. Spurbahn road vehicles of which again esp. The rail-road vehicles particular importance have attained. Again, these include the i.a. hydraulic operated two-way excavator.

Two-way (hydraulic) excavators form rail-road "vehicles" in their purest form. Because she lead their two types of chassis (for rail or road operation) - unlike so-called. unreal rail-road vehicles in which the example. Trained as a semi-trailer Road vehicle on two railway wheeled sets, with draw and push devices provided supporting frames placed and locked with these frictionally, and in which the road undercarriage i.a. must be cranked up constantly with.

While in rail-road vehicles, which are intended for transport i.a. four so-called Idler wheels with flanges are intended for rail travel, and carried on the road trip Tire wheels are mounted by means of bolts on the wheel flanges and (i.a. in a Sledge guide), rail-way excavators are generally used in longitudinal and / or transverse direction offset from one another, always firmly mounted (i.a., four) rail wheels and (i.a., four) pneumatic tires which, depending on the respective mode of operation, alternatively are to be used: If the excavator moves on the rails of a track, so are the For road driving certain pneumatic tire wheels with sufficiently large vertical distance above the Gauge railway; If, on the other hand, a two-way excavator is used for road transport, then the each by means of a hydraulic lifting device such esp. A piston-cylinder unit held on the frame of the excavator rail wheels relative to the i.a. firmly on the equipment frame stored pneumatic tire wheels by means of their lifting devices so far up, that the excavator not only on its (i.a. four) pneumatic wheels on the ground supported, but that between the rail wheels and the ground so much Freedom of profile prevails that when moving the excavator from the track to a road as well as on road driving not to damage the rail wheels and the other parts their suspension can come.

While it is, for example, permissible and predominantly customary in the Federal Republic of Germany, in that the road wheels of a two-way excavator designed as pneumatic tire wheels are used in the course of a railway on rails of the track railway stand such. shown in DE-A1-4041970 and both the drive and the braking forces transferred, so that the rail wheels i.w. merely exercise a leadership function is such a way of working in other states - eg in France as well as all other UIC states, which have joined European railway regulations (UIC) - inadmissible. In these states, the clearance gauge must remain free around the rails, so that the Road wheels must not be allowed to stand on the rails, so the rail wheels are driving and need to be braked.

Such two-way excavator are so far designed so that when switching from road travel on track railway operation in road operation by means of hydraulic lifting devices upwards retracted rail wheels or at their end portions with these provided rail wheel axles with the piston-cylinder units ("hydraulic cylinders") the rail wheel lifting devices each up to the rod-side stops the Piston-cylinder units extended down and the track rail operation - so not only in stationary use of the implement, but also in the process of the excavator on the Trajectory - are held in this working position, the lifting height determining Cylinder length is chosen so that the road wheels at a sufficient height above the track be located when the excavator by means of its (i.a four) rail wheels on the rails of Railway track is supported.

This design and operation obviously produces a completely rigid four-point support, with the result that it is already at relatively low unevenness of the track rail tracks To derailment can occur, so that rail travel at high speed are not possible, and even a rail operation with relatively low speed is at risk of derailment.

The present invention is based on the object, the method of the beginning or in Preamble of claim 1 described genb to improve in that with little technical and control engineering effort - always a statically determined (Three-point) support by means of its rail wheels on the rails of the track supported excavator is to ensure and ensure, so that even at considerable Rail unevenness and / or gauge railway operation with relatively high driving speed none Danger of derailment exists. In addition, a generic working device, esp. A Two-way hydraulic excavator are created in which the inventive Abstützverfahren not only at all, but in a particularly simple, expedient manner and practiced with a relatively low investment and labor.

The solution of the procedural part of the above object is achieved according to the invention by the characterizing features of claim 1, i.w. in that preferably Immediately after supporting the implement on the track rail tracks, but at the latest before his method, respectively, the instantaneous relative position between the working tool holding upper part and the lower part of the implement - and thus the current arrangement (Pivot position) of the working tool or a holding this boom or the like., and thus its current spatial allocation to one of the four (working) quadrant means a corresponding detector device is determined, as well as a corresponding from this (Relativstellungs-) signal generated and to the (provided with a computer) Control device is transmitted, which in turn (at least) a corresponding Generates control signal which triggers the following functions:

On the one hand, the so-called rod spaces (that of the piston rods of the piston-cylinder units interspersed chambers) of two piston-cylinder units with each other connected, and on the other hand i.w. at the same time the so-called cylinder chambers (ie the respective not interspersed by the piston rods sections of the piston-cylinder units) this two piston-cylinder units hydraulically connected to an oil reservoir, which thereby absorbs that volume of oil which compensates for unevenness of the rail corresponds, as explained below with reference to an embodiment in detail becomes.

It is apparent to solve the above-described problem is particularly appropriate if the rod spaces of two adjacent piston-cylinder units hydraulically connected to each other in a two-way hydraulic excavator, the at its relative to its lower part rotatable or at least pivotable upper part regularly has a counterweight on the opposite side of the implement, the rod spaces of the two adjacent to the counterweight or under the counterweight located piston-cylinder units.

Thus, for example, when supported on a rail wheels on rails of the track railway Two-way hydraulic excavator holding at its free end the working tool Boom from its front lying on the longitudinal center axis basic position to one or pivoted to the other side or to the rear (and thus into another of the four fixed Work quadrant), so in the previous working position due to the invention Procedure limited from their stop position retracted piston of the relevant two piston-cylinder units first - by emptying the (oil) memory by means of high pressure application - extended back to its stop position, so that temporarily turn all four piston-cylinder units in their fully extended rod-side stop position are located. Then the upper part with the working tool pivoted into his new working position, which, however, in stationary operation possibly also in in reverse order, and it will in any case be the new relative position between the upper part and the lower part of the excavator by means of the corresponding detection device detected. The generated by this, transmitted to the Steurereinrichtung corresponding signal causes by the controller (by means of their computer) a Control signal is generated, which now the two rod spaces of those two piston-cylinder units hydraulically interconnects, now under the counterweight lie the excavator, and it also causes the cylinder chambers of these two Piston-cylinder units now in the manner already described with the memory get connected.

Preferred embodiments of the present invention are defined in the subclaims described.

The invention is based on an embodiment with reference to a Drawing further explained.

Fig. 1:

eine Seitenansicht eines auf den Schienen einer Spurbahn abgestützten Zwei-Wege-Hydraulikbaggers in Richtung des Pfeiles I' in Fig. 2 gesehen;

Fig. 2:

eine (Teil-)Draufsicht auf den Bagger gem. Fig. 1 in Richtung des Pfeiles II in Fig. 1 gesehen; und

Fig. 3:

einen hydraulischen Schaltplan für den Bagger gem den Fig. 1 und 2, aufgrund dessen sich das erfindungsgemäße Verfahren in besonders einfacher und zweckmäßiger Weise praktizieren läßt.

It shows:

Fig. 1:

a side view of a supported on the rails of a track rail two-way hydraulic excavator seen in the direction of arrow I 'in Figure 2;

Fig. 2 :

a (partial) top view of the excavator gem. Fig. 1 seen in the direction of arrow II in Fig. 1; and

3 :

a hydraulic circuit diagram for the excavator according to FIGS. 1 and 2, due to which the method according to the invention can be practiced in a particularly simple and expedient manner.

Figs. 1 and 2 show a generally designated 1 two-way hydraulic excavator four in pairs on both sides of an i.w. right-angled (above and below also Undercarriage 2 (which in Fig. 2 for reasons of better clarity I. W. has been omitted) arranged, drivable, designed as pneumatic tire wheels Road wheels 3, which are connected in pairs with a front axle 4 and a rear axle 5 and at the respective end portions of the axles 4, 5 are arranged. In the in Fig. 1 state, the four road wheels 3 are not on the ground, since the excavator 1 is in the state of rail operation, and therefore four at the corner areas of the undercarriage 2 arranged rail wheels 6, which by means of a hydraulic Lifting device from a relative to the road wheels 3 raised rest position in the illustrated in Fig. 1, lowered working position (driving position) on the two rails 7, 7 are lowered a track railway. The rail wheels 6 are by means of a not in the drawing to drive in detail shown (Schienenräder-) suspension, and by means of a brake not also shown in detail. As the rail wheels 6 are at road travel of the excavator 1 in a raised rest position, is the excavator 1 then of course by means of a separate (road wheels) suspension to drive and decelerate by means of an associated braking device.

The lifting device is i.w. four hydraulic piston-cylinder units 8, which are each associated with a rail wheel 6, so that singular relative movements of Rail wheels 6 to the undercarriage 2 and the machine frame 2 ', on which the road wheels. 3 are stored stationary, are possible. For carrying out the method according to the invention it only partially possible, the two arranged in the main direction of travel 9 front of the excavator 1 Piston-cylinder units 8 on one of the two front rail wheels 6 connecting front axle and / or the two in the main direction 9 rear piston-cylinder units 8 acting on one of the two rear rail wheels 6 connecting rear axle as in the prior art in previously known two-way hydraulic excavators be the case here or a similar education the case can.

Furthermore, the excavator 1 by means of a hydraulic rotary drive relative to Undercarriage 2 about a vertical pivot axis 10 rotatable or pivotable upper carriage 11th on, the above and below also referred to as "top" of the excavator 1. The superstructure 11 has u.a. a driver's pulpit 12, a multi-part boom 13, one at the free End arranged working tool 14 (such as a spoon or gripper), as well as at his opposite, rear end portion on a counterweight 15.

In addition, the excavator 1 has a controller 22 (including a computer), by means of which the lifting device 8 for the rail wheels 6 and the other components of the excavator 1 are to be controlled.

Fig. 3 shows in a conventional schematic representation of a (i.w. hydraulic) circuit diagram for the excavator 1 gem. Figs. 1 and 2, due to which the inventive method in optimal way to practice. The two front rail wheels 6.1 and 6.2 and the two rear rail wheels 6.3 and 6.4 for the sake of easier understanding for attribution reasons, with one of the two front rail wheels 6.1 and 6.2 connecting front axle 16 and one of the two rear rail wheels 6.3 and 6.4 connecting rear axle 17 are shown, also referred to as "rail axes" be, but - as has already been stated - not necessarily necessarily exist must be, since - as has already been stated - a singular relative movement the rail wheels 6 to the device frame 2 'is sought, and this for optimal Practicing the method according to the invention may even be required, although an axle connection of the rail wheel pairs 6.1, 6.2 or 6.3, 6.4 do not oppose that got to.

After moving the excavator 1 from the road (in which he on the road wheels 3 is supported, and in which the rail wheels 6 by means of their associated piston-cylinder units 8 are retracted up) on track railway operation are the four rail wheels 6.1, 6.2, 6.3 and 6.4 for supporting the excavator 1 on the rails 7 by means of each assigned piston-cylinder units 8.1 or 8.2 or 8.3 or 8.4 completely extended downwards, i. the piston rods 18.1, 18.2, 18.3 and 18.4 are respectively extended to its rod-side stop 19.1 or 19.2 or 19.3 or 19.4, as can be seen in Fig. 3 with respect. The piston-cylinder units 8.3 and 8.4, when recording the track railway operation or during the track rail operation after a pivoting of the jib 13 - at the latest before a method of the excavator 1 on the track rail. 7 also with respect to the piston-cylinder units 8.1 and 8.2 of the front rail axis 16 of the case is, so that the excavator 1 then - as in the prior art - initially rigid at four points (and thus statically indefinite) is supported.

In this state, however, the excavator 1 takes its (deviating from the prior art) its Operation not yet on; esp. it will not be moved in this state yet. Rather, it will then preferably immediately the instantaneous relative position between the upper part 11th and the lower part 2 is detected by means of a detector device 20 which is between the superstructure (= Upper part) 11 and the lower carriage (= lower part) 2 is arranged, and a relative position signal generated, which to the provided with a computer 21 control device 22 is transmitted.

The controller 22 then generates based on the received relative position signal Control signals for controllable shut-off between the piston-cylinder units 8, which are recognizable in FIG. 3 and arranged as follows:

The so-called rod spaces 23 of all four piston-cylinder units 8 are through rod space connecting lines 24 connected to each other, and the cylinder chambers 25 of the piston-cylinder units 8 are interconnected via cylinder space connection lines 26, however, both the rod space connecting lines 24 and the cylinder space connecting lines 26 first by a respective of the controller 22nd controllable shut-off device (valve unit) 27 are closed.

Thus, the rod space 23.1 of the piston-cylinder unit 8.1 with the rod space 23.2 of Piston-cylinder unit 8.2 via a rod space connecting line 24.1 / 2 and with the Rod space 23.3 of the piston-cylinder unit 8.3 via a rod space connecting line 24.1 / 3 connected; the latter with the rod space 23.4 of the piston-cylinder unit 8.4 via a rod space connection line 24.3 / 4; and the rod space 23.4 of the Piston-cylinder unit 8.4 with the rod space 23.2 of the piston-cylinder unit 8.2 via a rod space connecting line 24.2 / 4, between the rod space connecting lines 24.1 / 2 and 24.3 / 4 runs.

The cylinder chamber 25.1 of the piston-cylinder unit 8.1 is connected to the cylinder chamber 25.2 of Piston-cylinder unit 8.2 connected via a cylinder space connecting line 26.1 / 2, and with the cylinder space 25.3 of the piston-cylinder unit 8.3 via a cylinder connecting line 26.1 / 3, while the cylinder chamber 25.3 with the cylinder chamber 25.4 of Piston-cylinder unit 8.4 connected via a cylinder space connecting line 26.3 / 4 is, and the latter with the cylinder chamber 25.2 of the piston-cylinder unit 8.2 via a cylinder space connecting line 26.2 / 4, between the cylinder space connecting lines 26.1 / 2 and 26.3 / 4.

In addition, an (oil) piston accumulator 28 is provided, which forms a pump as such, and the cylinder chamber 28 'via a storage line 29.1 / 2 with the cylinder space connecting line 26.1 / 2 is connected, of which a memory line 29.2 / 4 and a Branch line 29.1 / 3 branches off, the former leads to valve unit 27.2 / 4, and the latter to Valve unit 27.1 / 3. From the memory line 29.1 / 3 branches a memory line 29.3 / 4 a valve unit 27.3 / 4, so that all four cylinder chambers 25 optionally with the piston accumulator 28 are connectable.

The shut-off devices 27.1 / 2, 27.1 / 3, 27.3 / 4 and 27.2 / 4 respectively comprise the two adjacent ones Piston-cylinder units 8 rod side and cylinder-side connecting lines 24 and 26, respectively, and the branching of the latter memory line 29, and each have a Control line 30 connected to the control device 22, the obturator 27.1 / 3 so with the control line 30.1 / 3 u.s.f., with the following aim:

Once by means of the detector device 20, the instantaneous arrangement (pivot position) of the Jib 13 and thus its current local assignment to one of the four imaginary determined working quadrants I, II, III and IV determined and a corresponding relative position signal generated and transmitted to the controller 22 generates this one Control signal for the corresponding obturator 27 of the two in this position under the Counterweight 15 located piston-cylinder units 8, which causes on the one hand the rod spaces 23 of these two piston-cylinder units with each other, as well as on the other the cylinder chambers 25 are hydraulically connected to the piston accumulator 28, so on the one hand, that the respective rod and piston chambers can exchange with each other, and moreover, it is made possible that the piston accumulator serving as a storage element 28 each accommodates that volume of oil, which regularly balancing an existing Rail unevenness corresponds.

In the presentation acc. Figs. 1 and 2 are thus in so far the two rear-mounted piston-cylinder units 8.3 and 8.4, which are arranged under the counterweight 15 are (at the indicated in Fig. 2 with dash-2-dot lines pivot position to the Piston-cylinder units 8.2 and 8.4), while Fig. 3 shows a pivoting position of the boom 13 (and thus also arranged on the upper carriage 11 counterweight 15) based is at which the two front piston-cylinder units 8.1 and 8.2 currently are under the counterweight 15.

This results from the fact that these two piston-cylinder units 8.1 and 8.2 not are more in their rod-side stop position, as this originally the case was, and in the piston-cylinder units 8.3 and 8.4 is still the case, but that the piston rod 18.1 of the piston-cylinder unit 8.1 arranged with its at one end Piston 31.1 from its rod-side stop position by a stroke length h1 in the Cylinder 32.1 of the piston-cylinder unit has moved 8.1, and the piston rod 18.2 the piston-cylinder unit 8.2 with its piston 31.2 by the stroke length h2 in the cylinder 32.2 of the piston-cylinder unit 8.2. This was done by opening the valve unit 27.1 / 2 allows, so by connecting the rod spaces 23.1 and 23.1 on the now open rod space connection line 24.1 / 2, continue to connect the cylinder chambers 25.1 and 25.2 via the cylinder space connecting line 26.1 / 2, and an opening the memory line 29.1 / 2 leading from the latter to the memory 28. In this way, therefore with simple means quickly, safely and easily in any relative position between Upper and lower part of the excavator 1 due to the quasi-elastic support of the excavator. 1 by means of its rail wheels 6 on the rails 7 to a statically determined support create.

If later the superstructure 11 with the boom 13 and the counterweight 15 in another the four quadrants I-IV pivots, so first the piston accumulator 28 by means of High pressure deflates, which in turn all four cylinders 31.1 - 31.4 in their final position with rod-side stop 19.1 - 19.4 are pressed, so that in turn a starting situation present, as it was at the start of rail operation, and after the superstructure 11 has been pivoted to the next / another quadrant then in a corresponding manner, the two below the counterweight 15 lying piston-cylinder units 8 connected to each other and to the memory 28, as this further described above by way of example. The investment required for this is the same As low as the operating costs, especially the respective control fully or semi-automatic can be done, and therefore it is due to the present invention with certainty avoid derailing, as in conventional two-way excavators so far relatively often the case.

LIST OF REFERENCE NUMBERS

1

Two-way hydraulic excavators

2

Undercarriage (lower part) (from 1)

2 '

implement frame

3

road wheels

3 '

Longitudinal axis (from 1)

4

Front axle (for 3)

A, B

axes

5

Rear axle (for 3)

6

rail wheels

7

rails

8th

Piston-cylinder units

9

Main direction of travel

10

swivel axis

11

Uppercarriage (= upper part) (from 1)

12

leader pulpit

13

boom

14

Working tool (spoon)

15

counterweight

16

Front axle (for 6.1, 6.2)

17

Rear axle (for 6.3, 6.4)

18

piston rods

19

rod-side stops (from 8)

20

detector device

21

computer

22

control device

23

Barrooms (from 8)

24

Rod chamber connecting lines

25

Cylinder chambers (from 8)

26

Cylinder chamber connecting lines

27

Shut-off valve (from 24 or 26)

28

(Oil) Piston accumulators

28 '

cylinder space

29

storage line

30

control line

31

piston

32

cylinder

Claims (5)

1. A method of supporting a hydraulically actuated mobile working machine, particularly a two-way excavator (1), on a rail track (7), comprising:

   a bottom part (2) with a frame (2') and four rail wheels (6) disposed thereon to support the machine (1) on the rail track (7), each rail wheel being adjustable as to height relatively to the machine frame (2') by means of a hydraulically actuated piston and cylinder unit (8), and being controllable by means of a control device (22),

   and an upper part (11) which carries the working tool (14), for example a bucket or grab, and which is pivotable or rotatable relatively to the bottom part (2) about a vertical pivot axis (1'), and is provided with a counterweight (15) on its side remote from the working tool (14),

   wherein two diagonal axes (A, B), which each extend substantially through a front rail wheel (e.g. 6.1) and the rear rail wheel (6.4) disposed on the other side, divide the working machine (1) into - in plan view - four imaginary working quadrants (I, II, III, IV),

   wherein the piston rods (18) of the four piston and cylinder units (8.1, 8.2, 8.3, 8.4) each connected to a rail wheel (6) or to a rail wheel axle (16; 17) are extended, to support the working machine (1) on the rail track (7), from a piston position retracted into the cylinders (32) in each case as far as their stop (19) on the piston rod side, characterised in that at the latest before the working machine (1) supported on its rail wheels (6) on the rail track (7) is moved:

   the instantaneous relative position between the upper part (11) and the bottom part (2) of the working machine is detected by a detector device (20) and a corresponding relative position signal is generated and transmitted to the control device (22) - which is provided with a computer (21);

   and the control device (22) in response to the received relative position signal generates at least one control signal by means of which:

   on the one hand the rod chambers (23) of two piston and cylinder units (e.g. 8.1, 8.2) are interconnected and

   on the other hand the cylinder chambers (25.1, 25.2) of these two piston and cylinder units (8.1, 8.2) are hydraulically connected to an oil accumulator (28).
2. A method according to claim 1, characterised in that before the working machine (1) is moved the rod chambers (e.g. 23.1, 23.2) of two adjacent piston and cylinder units (8.1, 8.2) are hydraulically interconnected.
3. A method according to claim 2, characterised in that the rod chambers (e.g. 23.1, 23.1) of the two piston and cylinder units (e.g. 8.1, 8.2) adjacent or beneath the counterweight (15) are interconnected.
4. A method according to any one of the preceding claims, particularly according to claim 3, characterised in that on pivoting of the working tool (14) situated in one of the four working quadrants (I, II, III, IV) into another quadrant first of all the two pistons (e.g. 31.1, 31.2) of the associated piston and cylinder units (e.g. 8.1, 8.2) which pistons have been retracted to a limited degree from their stop position on connection of their rod chambers (e.g. 23.1, 23.2) on the one hand and on connection of their cylinder chambers (e.g. 25.1, 25.2) to the oil accumulator (28) on the other hand, are extended into their stop position by emptying of the accumulator (28) by the application of high pressure; in that the upper part (11) is swung with the working tool (14) into its new working position; in that the new relative position between the upper part (11) and the bottom part (2) is detected by the detector device (20) and a corresponding signal is transmitted to the control device (22); and in that then the two rod chambers (23) of two piston and cylinder units (8), preferably of the piston and cylinder units now situated beneath the counterweight (15), are interconnected and their cylinder chambers (25) are connected to the accumulator (28).
5. A hydraulically operated working machine, particularly a two-way hydraulic excavator (1), in the form of a rail track or rail or road vehicle, with four at least partially drivable road wheels (3) which are disposed in pairs on both longitudinal sides of a substantially rectangular chassis (2) and which are generally connected in pairs to a front and back axle (4 and 5 respectively); with four rail wheels (6) which are disposed at the corner zones of the chassis (2) and which are lowerable by a hydraulic lifting device out of a raised position of rest into a lowered working position or position of travel on to the rails (7) of a rail track, and which are drivable by means of a rail wheel running gear, and are adapted to be braked by a braking device, wherein the lifting device comprises a hydraulic piston and cylinder unit (8) for each rail wheel (6); with a superstructure (11) which is rotatable or pivotable about a vertical pivot axis (10) relative to the chassis (2) by means of a generally hydraulic rotary drive, and which at its free end has a jib (13) provided with a working tool (14), a counterweight (15) disposed on the opposite side, and generally a driver's cab (12); and with a control device by means of which the lifting device and the other components of the working machine (1) are controllable, for performing the method according to any one or more of the preceding claims, characterised in that the four piston and cylinder units (8.1, 8.2, 8.3, 8.4) of the lifting device are so controlled by the control device (22), on extension of the rail running gear out of its raised position of rest into its lowered working position or position of travel, that they initially move into their extended end position; in that a detector device (20) is provided by means of which the instantaneous relative position of the superstructure and chassis can be detected and a corresponding signal generated; in that on the one hand the rod chambers (23) of the four piston and cylinder units (8) are each connected to the rod chambers (23) of the other piston and cylinder units (8) via rod chamber connecting lines (24) each provided with a shut-off member (27) actuatable by the control device (22) and on the other hand the cylinder chambers (25) of the four piston and cylinder units (8) are each connected to the cylinder chambers (25) of the other piston and cylinder units (8) via cylinder chamber connecting lines (26) between adjacent piston and cylinder units (8), which cylinder chamber connecting lines (26) are provided with a shut-off member (27) actuatable by the control device (22); and in that at least one accumulator (28) is provided which is connected to the cylinder chamber connecting lines (26) between adjacent piston and cylinder units (8) via an accumulator line (29) in each case, which line leads to the cylinder chamber (25) of the associated piston and cylinder units (8) and is provided with a shut-off member (27) actuatable by the control device (22).

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