GB2047794A

GB2047794A - Power unit

Info

Publication number: GB2047794A
Application number: GB8013047A
Authority: GB
Original assignee: KNAEBEL H
Current assignee: KNAEBEL H
Priority date: 1979-04-21
Filing date: 1980-04-21
Publication date: 1980-12-03
Also published as: FR2454548B1; AT368922B; IT8048442A0; DE2916191C2; FR2454548A1; GB2047794B; SE8002791L; IT1128516B; BE882786A; DE2916191A1; ATA162080A

Abstract

Power unit for use as a drive mechanism e.g. for deforming a workpiece, comprising a working piston 3 movable in a cylinder (2), or a rotary piston, Fig. 5 (not shown), a working member (4), an energy store 14 which is connected constantly to a primary cylinder space 10 generating the drive power, while the secondary cylinder space 11 on the other side of the working piston contains a pressure medium which provides before the start of a working stroke a counterbalancing force on the working piston, and a control device for the expansion of the secondary cylinder space (11), comprising at least one auxiliary piston (27 to 30) which in use abruptly increases the volume of the secondary cylinder space and thereby effects a rapid expansion of the secondary cylinder space, the working piston (3) being couplable with the working member (4) in the working direction for the transmission of the drive energy and being uncouplable in the opposite direction. <IMAGE>

Description

SPECIFICATION Power unit for use as a drive mechanism This invention relates to a power unit for use as a drive mechanism, for example for deforming, compressing, pressing or beating a workpiece. Such a power unit comprising a working piston displaceable in a cylinder and having a piston rod is known from German OLS 2,600,948, in which a primary cylinder space supplying the working force remains permanently under the pressure of a gas cushion which is compressed before each working stroke, while the cylinder space on the other side of the piston, namely the secondary cylinder space, is filled with a pressure medium which provides before the start ofworkthe force compensation of the working piston, as well as a control valve and valve body for the expansion of the secondary cylinder space.With this known power unit the valve body comprises a large-area auxiliary piston and is displaceable fluid tightly in a cylinder space which it divides into a branch space adjacent the secondary cylinder space and enlarged in relation to the diameter of the auxiliary piston and into a space serving for the return and guidance of said valve body, the auxiliary piston fluid tightly separating on the end side a pressurerelieved control space from the branch space. The auxiliary piston is controllable from the control space by a force for the purpose of lifting from its end-side sealing face, due to which the pressure medium of the secondary cylinder causes an abrupt displacement of the auxiliary piston within a few milliseconds or fractions thereof and consequently just as rapid an expansion of the secondary cylinder space.

Such a power unit has, among other things, the advantage that the force action is effected, e.g. on a workpiece, abruptly, that is within a very short period of time, e.g. after touch contact between the tool and workpiece, since the flow cross sections between the secondary cylinder space and the space released by the auxiliary piston can be made practically as large as desired and also the piston face of the auxiliary piston can be made large in relation to the working piston.The known power unit is controllable with simple means, permits the industrial utilisation of the advantages of high-performance forming and offers a small accident risk and also a small noise development in comparison with known devices, especially those working by the so-called Dynapack process, especially due to the fact that the force action is effected e.g. only after contact in a closed system. Moreover, the known power unit is, among other things, applicable to forging, hammer forging, impact extrusion, embossing, deepdrawing, shearing and puching. Furthermore, it can also be used for compacting powders of ceramic and metallurgical materials.In so doing, such a device can also be employed for the above-mentioned areas of application in conjunction with hydraulic or mechanical presses or in conjunction with a counterpunch driven e.g. by a crank assembly.

The object of the invention is to provide a power unit in which the released energy to be transmitted to the working member is preselectable, sensitively controliable and maximally limitable and the working member is not prevented by the mechanism itself from transmitting the energy to the working material (e.g. workpiece, material, bedrock, earth) to be machined, to be loaded, to be deformed, to be driven and the like.

According to the invention, there is provided a power unit for use as a drive mechanism comprising a working piston movable in a cylinder, a working member, an energy store which is connected constantly to a primary cylinder space generating the drive power and which maintains a pressure medium pressure in the primary cylinder space, while the secondary cylinder space on the other side of the working piston contains a pressure medium which provides before the start a working stroke a counterbalancing force on the working piston, and a control device for the expansion of the secondary cylinder space comprising at least one auxiliary piston which is guided movably and fluid tightly in a cylinder and which in use abruptly increases the volume of the secondary cylinder space and thereby effects a rapid expansion of the secondary cylinder space, the working piston being couplable with the working member in the working direction for the transmission of the drive energy and being uncouplable in the opposite direction and the drive energy is dosable due to the expansion volume for the secondary cylinder space which is made available preselectably or adjustably by said at least one auxiliary piston.

The power unit according to the invention can be used both as a pressure unit and as a traction and/or rotational unit. It is thereby possible e.g. to use such a power unit not only for forming, but also for ramming, for carrying out demolition work, for earth tamping, smashing, percussion screwing and drilling, e.g. percussion drilling.

It is possible in all cases to execute both progressive and intermittent working movements.

Due to the separation of the working piston from the working member a power unit according to the invention is proof against overloading and against accidents.

With all work operations the energy supply can be adapted sensitively to the respective working process, due to which short effective times and high working frequencies are possible.

The energy dosing can be effected mechanically or in dependence on time.

An especial advantage of a power unit according to the invention is also to be seen in the fact that it works especially silently, which is of considerable importance especially with outside work such as ramming or demolition work.

The working member may have on both sides of a portion adapted to engage the working piston pressure active faces of equal area. The working member can then be moved until the energy transmitted by the working piston is consumed, namely independently of the expansion volume made available to the secondary space. A further movement of the working member does not lead to any noteworthy pressure peaks in the secondary cylinder space.

Alternatively, the working member may have pressure active faces of differing areas on each side of the portion adapted to engage the working piston.

Such an arrangement has the advantage of large possibilities of variation for the application of engaging and breaking forces. In a continuous action the working piston acts as a safety valve.

In order to compensate for or overcome the differential forces resulting from the pressure-active differential faces on the working member and/or working piston, pistons and/or springs and/or weights may be employed to effect an engaging movement orto bring about the starting position.

In one preferred embodiment, a stepped working piston is used which allows, despite the one-sided outlet of a working member designed as a piston rod, the pressure-active faces to be equal on both sides of the working piston. A compact structural form results, since at least one auxiliary piston is arranged concentrically with the working member and the working piston and the auxiliary piston is brought fluid tightly against the working member or the working piston.

The reaction forces of the cylinder may be resiliently absorbed by a weight or by the inertia of the cylinder housing mass or an additional mass. The power unit then does not need to be installed in a machine frame of a press or the like. Rather, it is possible to use such as power unit as a separate machine, e.g. as a manually operable machine for the tamping of earth orthe like. In principle, such an embodiment can be designed for all conceivable possibilities for absorbing forces of reaction. The housing or additional mass may be brought into its starting position hydraulically, pneumatically, or by means of one or more springs. Even large reaction travels can be recovered therewith with a small force. Since the action time is very short and can be influenced via the dosing facility, such a power unit can be handled easily and without danger.

The or each auxiliary piston may be arranged tangentially to or coaxially with the working piston and/or working member. A simple production and functional arrangement of the parts results in a very simple maintenance. Finally, this arrangement permits a compact construction.

The inlet to the or each auxiliary piston may be formed by a plurality of slots, the overall crosssection of which is adjusted to the rate of expansion of the secondary cylinder space. Wide-ranging possibilities of adaptation of the expansion rate of the secondary space are thus obtained. Moreover, this expansion rate is adjustable to the separating force activated between two auxiliary pistons. If the separating force between the auxiliary pistons is to be kept constant, it is desirable to effect this hydraulically. With a gas pressure support between the two auxiliary pistons there results a strongly degressive and strongly progressive force.

A progressive and effective stop damping may be obtained if this is effected either hydraulically or pneumatically.

Due to a constant connection of the primary and secondary cylinder spaces and due to an optionally adjustable bypass a rapid pressure compensation is achieved between the two cylinder spaces after the working phase. This pressure compensation can, if required, be influenced in time, e.g. by an adjustable choke inserted in the bypass.

In a further preferred embodiment, a first working cylinder in the form of a lifting cylinder and a second working cylinder in the form of a turning cylinder are connected to one another so that the working member undergoes both linear and rotary movements. Such a unit can be used e.g. as a drilling machine e.g. for drilling in concrete or metals, as a gallery advance machine for tunelling or for driving drill rods in the search for petroleum or natural gas.

The possibility arises of adjusting optimally to one another the drive energies causing the straight advancing movement and the turning movement and to control these movements according to the work process. The power unit causing the straight movement may be separated from the power unit driving the rotary movement, in which case both working movements can be executed in a manner phase-shifted in time, while these movements can be effected simultaneously with a connection of the secondary cylinder spaces which conducts the pressure medium. Especially in the latter case a further simplification of the mechanism results e.g. due to the fact that only at least one auxiliary piston which receives the necessary expansion volume needs to be provided for the two secondary cylinder spaces of the power units for the straight and rotary movements.

The invention is illustrated with reference to several exemplary embodiments partly schematically in the drawing wherein: Figure 1 is a partial longitudinal section through a first embodiment of a power unit according to the invention.

Figure 2 is a further embodiment likewise in partial longitudinal section.

Figure 3 is a section along the line Ill-Ill of Figure 1 or of Figure 2.

Figure 4 is a further embodiment likewise in partial longitudinal section.

Figure 5 is a partial cross-section through yet another embodiment.

Figure 6 is a side view of a power unit for use as a drawing mechanism.

Figure 7 is a side view of a power unit for use as a ram.

Figures 8 and 9 are two partial sections of two further embodiments of the invention.

The reference numeral 1 designates in all the embodiments shown in the drawing a housing in which a cylinder 2 is arranged.

The embodiments according to Figures 8 and 9 have, among other things, the advantage that the mass of the working pistons to be braked can be kept extremely small, so that no pressure peaks occur in the energy dosing possible also with all the other embodiments. The freewheel system required in the embodiment according to Figure 5 is omitted in these embodiments.

In the embodiment according to Figure 1 a working piston 3 is guided longitudinally displaceably and fluid tightly in the cylinder 2. The working piston 3 is mounted displaceably on a working member4 passing axially through the cylinder 2 and designed as a piston rod. The working member 4 has at one free end an annular shoulder 5 and a spring element 7 designed in the embodiment illustrated as a compression spring which extends between said shoulder and a housing cover 6.

Spaced from the shoulder 5 is a collar 8 which, like the shoulder 5, is formed in one piece with the piston rod 4.

The piston rod 4 has on both sides of the collar 8 the same diameter, that is d, = d2.

Figure 1 also shows that the piston rod 4 emerges from the housing 1 with its free end remote from the collar 8. Suitable coupling means not shown can be provided on this side for the attachment of a tool or the like. However, it is also possible to construct the free end of the piston rod 4 itself as a tool.

A cylindrical recess 9 is provided in the housing 1 which is adapted in diameter to the outside diameter of the collar 8 and serves for extreme-position damping.

A primary cylinder space 10 is connected to an energy store 14 via a channel 12 and a line 13. There opens into the line 13 a supply line 15 which is fed by a pressure medium source not shown in detail with pressure medium, especially a suitable hydraulic pressure liquid. A gas cushion 16 is provided in the energy store. Alternatively spring loading or weight loading can be used instead thereof.

A secondary cylinder space 11 is likewise connected via a channel 17 to an expansion device to be described hereinafter in detail in connection with Figure 3.

The primary cylinder space 10 is connected via the line 18 to the expansion device in a pressure medium - conducting manner (Figure 3).

In the embodiment of Figure 2 the same reference numerals have been used for parts having the same function. This embodiment differs from that of Figure 1 in that the diameter d1 is largerthan the diameter d2 of the piston rod 4. There thereby results a pressure-active face which becomes active in the direction Y, that is opposite to the working direction X.

A plunger 19 is guided longitudinally displaceably and fluid tightly in a cylinder 20. The cylinder 20 is connected via a line 21 to a solenoid valve 22 which is designed as a three-way valve and has a line 24 leading to a tank 23 and a line 25a connected to the supply line 15. In the position shown in Figure 2 the cylinder 20 is relieved via the three-way valve 22 to the tank 23.

Provided between the primary and secondary spaces 10 and 11 is an adjustable bypass which connects the spaces 10 and 11. Such a bypass can also be provided in all other embodiments of the invention.

As shown in Figure 3, the expansion device is arranged tangentially to the cylinder 2. This expansion device has two bushes 25 and 26. A first and a second auxiliary piston 27, 28 and 29, 30 are guided longitudinally displaceably and fluid tightly in each bush 25 and 26 respectively.

All the auxiliary pistons are arranged coaxiallyto one another.

The first auxiliary pistons 27 and 29 situated between the two outer second auxiliary pistons 28 and 30 are supported on the end sides fluid tightly via an annular shoulder 31 and 32 respectively on a valve seat 33 integral with the housing. Both the first auxiliary piston 27 and the first auxiliary piston 29 thereby form with the valve seat integral with the housing and their annular shoulder a control space 34 which is connected in a pressure - medium - conducting manner via a channel 35 and a line 36 to the cylinder spaces 37 and 38 which are remote from the first auxiliary pistons and in which the second auxiliary pistons 28 and 30 are guided longitudinally displaceably and tightly.

Housing covers 39 and 40 close the cylinder spaces 37 and 38 of the second auxiliary pistons 28 and 30 in a pressure - medium -tight manner and lock the bushes 25 and 26.

The two first auxiliary pistons 27 and 29 have central cylinder spaces into which a piston-like extension 41 and 42 ofthe associated second auxiliary pistons 28 and 30 respectively can be inserted. The piston-like extension 41 or 42 is connected respectively in one piece to the associated second auxiliary piston 28 or 30. As may be seen from Figure 3, each first auxiliary piston 27 and 29 has an extremeposition damping 43 and 44 in the form of a recess into which the associated piston-like extension 41 or 42 of the respective second auxiliary piston 28 or 30 can be inserted and displace the pressure medium present therein.

The respective cavity 45 or 46 of the first auxiliary piston 27 or 29 is connected via several slots 47 and 48 passing through its peripheral face, on the one hand, and via channels 49 and 50 respectively via the line 18 to the primary cylinder space 10. On the other hand, these slots 47 and 48 are connected in a pressure - medium - conducting manner to the secondary cylinder space 11 via several control slots 51 and 52 and the channel 17.

The pressure-active face, adjacent the cylinder space 37 or 38, of the respective second auxiliary piston 28 or 30 is larger than the pressure-active face, adjacent the valve seat, of the associated first auxiliary piston 27 or 29. The second auxiliary pistons 28 and 30 are thereby capable of overcoming the respective first auxiliary piston 27 or29 and of applying it against its valve seat 33.

In the embodiment illustrated the difference of the faces is connected via channels 53 and 54 to a leakage line 55 so that the respective differential face is not pressure-active.

The cylinder spaces 37 and 38 and the control space 34 are connected in a pressure - medium conducting manner via a solenoid valve 56 designed as a three-way valve to a tank 57 or via the line 58 to the secondary cylinder space 11 depending on the switching position of the said valve.

The mode of operation of the embodiments ill ustrated in Figures 1 to 3 is as follows: In the embodiment of Figures 1 and 3, due to the connection of the primary and secondary cylinder spaces 10 and 11 the pressure medium pressures are compensated in these cylinder spaces. If in the posi tion of the parts as shown in Figure 1 the three-way valve 56 (Figure 3) is activated, the cylinder spaces 37 and 38 and the control space 34 are relieved of pressure. The second auxiliary pistons 28 and 30 thereby move outwards, that is away from one another, while the first auxiliary pistons 27 and 29 are held against the valve seat 33 under the action of the pressure-active space formed by the piston-like extensions 41 and 42.

If the three-way valve 56 is disconnected, the cylinder spaces 37 and 38 and also the control space 34 are put under pressure medium pressure. On the one hand, this results in the fact that the first auxiliary pistons 27 and 29 lift abruptly and suddenly from their valve seats and move in the direction of the associated second auxiliary pistons. However, also the two second auxiliary pistons 28 and 30 are simultaneously set in motion due to the pressure-medium loading of the cylinder spaces 37 and 38 in a direction opposite to the movement of the first auxiliary pistons and overcome the associated first auxiliary pistons 27 and 29 after a damped encounter and push the respective first auxiliary piston back again into its tight extreme position shown in Figure 3.

Due to the control of the first auxiliary pistons 27 and 29 the volume of the secondary cylinder space 11 is enlarged abruptly and suddenly practically within a few milliseconds or within fractions thereof.

This results in the fact that the working piston 3 is set in motion just as abruptly and suddenly in the direction X and the working member which drives the piston rod 4 in the direction X drives same only until the expansion volume provided by the first auxiliary pistons 27 and 29 is used up. The working piston 3 then stops, while the working member 4 moves further in the direction X, namely until the energy is used up on the workpiece.

Due to the fact that the first auxiliary pistons 27 and 29 have been brought again into their extreme position, the primary and secondary cylinder spaces are again connected to one another, so that the compression spring 7 can move the working member and consequently the working piston back again in the direction Y into their starting positions.

This mode of operation applies, in principle, also to the embodiment according to Figure 2, but with the difference that due to the surface difference caused by the different diameters the working piston 3 and working member 4 are moved back again in the direction Y into their starting positions after the first auxiliary pistons 27 and 29 have been applied again.

In the embodiment according to Figure 2 there is present due to the pressure-active differential face a force which acts constantly in the direction Y and which must be overcome by the plunger 19 for the engagement. This is effected due to the fact that the three-way valve 22 is activated, owing to which the line 21 is connected to the pressure medium supply.

The feed travel can be determined by limit switches or by application to the workpiece to be machined.

Also in the embodiment according to Figure 4the reference numerals already used for the abovedescribed embodiments have been used for parts having the same function.

In the embodiment according to Figure 4the working piston 3 is designed as a stepped piston and the cylinder 2, also, has sections with different diameters d2 and d3, while the diameter of the working member 4 designed as a piston rod is designated by d,. There thereby result pressure-active faces which are defined as follows: A, &commat;(d2-d1) A2 &commat; d3 These pressure-active faces A1 and A2 are equal or slightly different so that corresponding engaging or recoil forces result.

The expansion device consisting of a first auxiliary piston 59 and a second auxiliary piston 60 is arranged coaxially to the working member 4 or to the working piston 3. Said second auxiliary piston is inserted with the piston - rod - shaped extension 61 into a cavity 62 of the first auxiliary piston 59, whereby there is play both on the end side and radially between the piston - rod - shaped extension of the second auxiliary piston 60.

In the position of the parts which is shown in Figure 4the first auxiliary piston 59 lies with an annular shoulder 63 tightly on the collar 8 designed as a valve seat and forms therewith a control space 64.

This control space 64 is connected in a pressure medium - conducting way to the cylinder space 69 of the second auxiliary piston 60 by a bore 65 running coaxially in the piston rod 4, a connecting channel 66, an annular space 67 and a line 68. This second auxiliary piston 60 is supported against the housing 1 via a spring 70 which has the job of applying tightly against the collar 8 the entire expansion device consisting of the first and second auxiliary pistons 59 and 60.

The first and second auxiliary pistons 59 and 60 have equal pressure-active faces.

The gas space 16 of the energy store 14 is connected via a line 21 and via a choke 72 to a channel 73 which opens into an annular space 74 of the second auxiliary piston 60 and this annular space 74 is connected via at least one groove 75 to the cavity 62 of the first auxiliary piston 59.

The annular space 76 of the first auxiliary piston 59 is connected via a channel 77 to a line 78 to the energy store 14, whereby a pressure - medium conducting connection is provided to the secondary cylinder space 11 via at least one slot 79. Since the primary cylinder space 10 is likewise connected via the line 80 to the energy store 14 and consequently to the line 78, the annular space 76 and the secondary cylinder space 11 are also connected to the primary cylinder space 10.

A supply line 81 is connected to a pressure medium source not shown, for example a hydraulic pump.

Athree-way solenoid valve 82 can provide, on the one hand, via a line 83 a connection to the cylinder space 69 of the second auxiliary piston 60 and, on the other hand, via a line 84 a connection to the secondary cylinder space 11.

If the solenoid valve 82 is energized, the cylinder space 69 ofthe second auxiliary piston 60 is relieved via the line 83 and the valve 82 to a tank 85.

Regarding the mode of operation of the expansion device formed by the first and second auxiliary pistons, reference may be made to the statements in connection with the embodiments according to Figures 1 to 3 with the difference that the active force between the first and second auxiliary pistons 59 and 60 is not constant, but is formed due to the presence of a compressible gas.

In Figure 5the same reference numerals have been used for parts having the same function as in the description of the embodiments according to Figures 1 to 3.

With this embodiment the working piston 3 is designed as a rotor which is coupled via a freewheel system 86 to the working member 4 designed as a drive shaft in one direction, in the illustrated embodiment in the direction Z. The resetting can be effected via a spring element not shown, e.g. via a torsion spring.

The freewheel system not illustrated in detail can be designed as a needle-type freewheel system.

Due to the working piston (rotor) 3 made sectorshaped on sides lying diametrically opposite one another primary and secondary cylinder spaces 10 and 11 result in pairs. Radial forces are thereby compensated in every position of the rotor.

Due to energisation of the three-way valve 56 the first and second auxiliary pistons 27,28 and 29,30 are actuated in the same way as in connection with Figure 3, due to which the secondary cylinder spaces 11 are relieved abruptly, suddenly and instantaneously and the working member 4 and a tool, e.g. a drill, optionally coupled therewith are thereby driven via the free wheel system 86 in the direction Z under the action of the stored energy. In this embodiment the energy is taken from two energy stores 14.

Figures 6 and 7 illustrated a power unit which is used, on the one hand, for drawing (Figure 6) and, on the other hand, for ramming (Figure 7).

This power unit is suspended via a spring element 87 on a crane or the like not shown. This suspension is effected according to Figure 6 for drawing on additional weights 88 and 89 of the housing 1, while for ramming the suspension is effected on a clamping head 90.

In orderto use the power unit according to Figures 6 and 7 for different uses, the power unit is, as shown, turned merely through 180" and hung onto the spring element 87.

The impact drive is effected via the working member 4 in the direction of the marked arrow.

The forces of reaction are absorbed by the additional weights 88, 89. For drawing the resetting is effected via springs 87 by the crane orthe like not shown, while for ramming (Figure 7) the resetting is effected undergravity (weight).

As can be seen in Figures 6 and 7, the expansion device and the energy store are accommodated in the additional weight 89.

The embodiment according to Figure 1 represents a power unit suitable for the transmission of traction and/or pressure. This power unit can be applied for cold and hot forming, ramming, demolition work, earth tamping, smashing and shearing.

Figure 2 illustrates a power unit which is suitable for the application of pressures. It can be applied with advantage for shearing, embossing, upsetting, and testing, especially for conducting internal pressure tests.

The embodiment according to Figure 4 is suitable for the transmission of tractive forces; it can be applied with advantage for testing, drawing and shearing.

The power unit illustrated in Figure 5 can be used as a torsional percussion element, e.g. for percussion screw driving, percussion drilling, testing and shearing, especially torsional shearing.

Figures 8 and 9 illustrate two different alternative solutions to Figure 5, the same reference numerals being used for parts having the same function as with the above-described embodiments.

In the embodiment shown in Figure 8 the working member constructed as a drive shaft is provided with two radially projecting cams which are connected materially in one piece and which can be connected operatively to two segments which correspond to the working piston.

The primary and secondary cylinder spaces and the various connecting channels correspond to those of the embodiment according to Figure 5 in respect of their arrangement and mode of operation.

With the embodiment according to Figure 9 the hollow working member 4 likewise designed as a drive shaft is, again, provided with radially outwardly projecting cams designed in one piece, the working piston consisting of two rotary pistons 3 which can be connected operatively to the cams 8.

One spring element 91 is connected fixedly, that is drivably and loadablyto each of the cams 8. Each of these spring elements 91 can be e.g. a leaf spring.

Each spring element 91 has the tendency to hold the associated rotary piston 3 in the position illustrated, that isto restore itto its starting position shown in Figure 9.

Moreover, with this embodiment the arrangement and function of the primary and secondary cylinder spaces 10 and 11 and the connecting channels correspond in their function and arrangement to the embodiment according to Figure 5.

The two embodiments illustrated in Figures 8 and 9 can, if required, be considered for the same areas of application as the embodiment according to Figure 5.

The embodiments according to Figures 8 and 9 has, among other things, the advantage that the mass of the working pistons to be braked can be kept extremely small, so that no pressure peaks can occur due to the energy dosing which is possible also in all other embodiments. The freewheel system required for the embodiment according to Figure 5 is omitted in these embodiments.

Claims

1. Power unit for use as a drive mechanism, comprising a working piston movable in a cylinder, a working member, an energy store which is connected constantly to a primary cylinder space generating the drive power and which maintains a pressure medium pressure in the primary cylinder space, while the secondary cylinder space on the other side of the working piston, contains a pressure medium which provides before the start of a working stroke a counterblancing force on the working piston, and a control device for the expansion of the secondary cylinder space comprising at least one auxiliary piston which is guided movably and fluid tightly in a cylinder and which in use abruptly increases the volume of the secondary cylinder space and thereby effects a rapid expansion of the secondary cylinder space, the working piston being couplable with the working member in the working direction for the transmission of the drive energy and being uncouplable in the opposite direction and the drive energy is dosable due to the expansion volume for the secondary cylinder space which is made available preselectably or adjustably by said at least one auxiliary piston.

2. Power unit according to claim 1, wherein the energy dosing is effected or is adjustable in dependence on time by means of at least one optionally adjustable mechanical stop, the drive energy being maximally limitable by the maximum stroke.

3. Power unit according to claim 1 or 2, wherein the working member has pressure-active faces of equal area on both sides of a portion adapted to engage the working piston.

4. Power unit according to claim 1 or 2, wherein the working member has pressure-active faces of differing areas on each side of a portion adapted to engage the working piston.

5. Power unit according to any preceding claim, wherein the starting position and/or the engaging movement of the working member are effectable by at least one piston and/or spring and/orweights.

6. Power unit according to any preceding claim wherein the pressure-active faces on the working piston and/or on the working member in the primary and secondary cylinder spaces are made equal or different by a stepped piston.

7. Power unit according to any preceding claim, wherein the supporting of the reaction forces of the cylinder is effected rigidly by a machine frame or resiliently by a weight or by the inertia ofthe housing mass or an additional mass.

8. Power unit according to claim 7, wherein the housing or additional mass is brought into its starting position hydraulically, pneumatically or by means of springs.

9. Power unit according to any preceding claim, wherein the auxiliary piston or pistons serving for the expansion of the secondary cylinder space is (are) arranged tangentially or coaxially to the working piston and/orto the working member.

10. Power unit according to any preceding claim, wherein the inlet cross-section to the auxiliary piston or pistons is formed by slots which are adjusted to the rate of expansion of the secondary cylinder space.

11. Power unit according to any preceding claim, wherein the active force between the auxiliary pistons is formed by a rod face loaded with pressure medium pressure, especially hydraulic pressure, or by the gas pressure varying with the retraction and advance of the second auxiliary piston.

12. Power unit according to claim 11, wherein the stop damping of the two auxiliary pistons is effected hydraulically or pneumatically.

13. Power unit according to any preceding claim, wherein there is arranged between the primary cylinder space and the secondary cylinder space an optionally adjustable bypass via which the primary and secondary cylinder spaces are connected to one another in a manner conducting the pressure medium.

14. Power unit according to any preceding claim, wherein a working cylinder designed as a lifting cylinder and one designed as a turning cylinder are connected to one another in such a way that the working member describes both straight and rotary movements.

15. Power unit according to claim 14, wherein the power units for the straight and the rotary movements have separate secondary cylinder spaces or in that their secondary cylinder spaces are connected to one another in a manner conducting the pressure medium, whereby the expansion is effected by the auxiliary piston or pistons both for the straight and for the rotary movements in a manner phase-shifted in time or simultaneously.

16. Power unit according to claim 14, wherein the working member has several cams which are engageable operatively with correspondingly several segments as a working piston.

17. Power unit according to claim 16, wherein the segments are designed as rotary pistons.

18. Power unit according to claim 16 or 17, wherein each segment or each rotary piston is returnable by at least one spring element to the respective cam of the working member.

19. Power unit substantially as herein described with reference to the accompanying drawings.