Pressure generating device and operating method comprising an electrically driven dual-action reciprocating piston

Abstract

A pressure generating device may comprise a piston-cylinder unit having a bilaterally acting piston with two effective surfaces defining two respective, separate working spaces in a sealing manner. Each working space is connected via a hydraulic line to a hydraulic circuit, wherein at least one hydraulic chamber of a consumer is connected to each hydraulic circuit, and wherein a drive drives the piston. Each working space may be in communication with a reservoir for hydraulic medium, via a respective hydraulic line having a respective switching valve. Alternatively, one or both working spaces may be in communication with a reservoir for hydraulic medium via a hydraulic line, with a switching valve in one or both hydraulic lines, and/or a respective outlet valve may be associated with one or more hydraulic chambers of the consumer, and a further connecting line having a switching valve may connect the pressure chambers and/or hydraulic lines.

Claims

1. A pressure generating device comprising: a piston-cylinder unit, which comprises a bilaterally acting piston that separates two working spaces in the cylinder of the piston-cylinder unit from one another in a sealing manner, wherein the piston has two, different-sized effective surfaces, and wherein each effective surface of the piston respectively defines a respective one of the two working spaces, respective hydraulic lines connecting each of the respective working spaces to a respective hydraulic circuit, wherein at least one hydraulic chamber of a hydraulic consumer is connected to each hydraulic circuit, and a drive configured to drive the piston of the piston-cylinder unit, wherein each working space is in communication by means of a hydraulic line with a reservoir vessel for a hydraulic medium, wherein in each respective hydraulic line connecting a working space with the reservoir vessel, at least one first switching valve is arranged for the optional closure or opening of the respective hydraulic line, wherein the drive of the piston-cylinder unit has a linear actuator in the form of a linear motor or rotation motor and gear mechanism, and wherein the pressure generating device is adapted to build up and reduce pressure by driving the linear actuator by a predetermined pressure rod path which is calculated taking into account an effective surface in a backward or forward stroke.

2. The pressure generating device according to claim 1, wherein pressure build-up in the hydraulic circuits is done simultaneously, one after the other, or with a time offset.

3. The pressure generating device according to claim 1, wherein the effective surfaces are different and are in a ratio of 1.5:1 to 2.5:1 to one another.

4. The pressure generating device according to claim 1, wherein the working spaces, the hydraulic lines, or the hydraulic circuits are connected to one another via a connecting line, wherein at least one second switching valve is arranged in the connecting line for the optional opening or closure of the connecting line, such that pressure build-up or pressure reduction is done with the acting or effecting working space.

5. The pressure generating device according to claim 1, wherein non-return valves with a closing direction from the working space of the pressure generating unit to the reservoir vessel are arranged parallel to the first switching valves.

6. The pressure generating device according to claim 1, wherein at least one pressure sensor measures pressure in at least one of the hydraulic lines.

7. The pressure generating device according to claim 1, wherein an actual pressure is calculated via a phase current of the electric drive measured with one of more redundant current sensors and a torque calculated from a torque constant, as well as one of the effective surfaces, and is used for pressure regulation.

8. The pressure generating device according to claim 1, wherein a third switching valve is associated with each hydraulically acting working space of the hydraulic consumers for the optional closure or opening of the respective hydraulic line to the pressure supply device.

9. The pressure generating device according to claim 1, wherein for pressure reduction in a respective one of the hydraulic consumers, hydraulic fluid is enabled to flow through the respective working space to the reservoir vessel or directly via an outlet valve into the reservoir vessel, wherein in each hydraulic connection to the respective one of the hydraulic consumers, a third switching valve is arranged between the respective working space and the respective one of the hydraulic consumers.

10. The pressure generating device according to claim 8, wherein in a case of pressure reduction in the reservoir vessel via the working space or spaces as well as well as via the first switching valves, the control device uses a pressure calculated by one or more pressure sensors in one or both hydraulic circuits and/or calculated from a phase current sensor, for regulation.

11. The pressure generating device according to claim 1, wherein, by adjusting the piston, the pressure is increased and/or reduced simultaneously or partly simultaneously in at least two hydraulic consumers.

12. The pressure generating device according to claim 1, wherein pressure supply to at least two of the hydraulic consumers is done with a multiplex operation.

13. The pressure generating device according to claim 1, wherein the pressure supply unit supplies at least two hydraulic consumers with pressure, wherein one consumer is a vehicle clutch, a chamber of a change speed selector, or a gear mechanism.

14. The pressure generating device according to claim 1, wherein the pressure supply unit supplies with pressure at least one of the hydraulic consumers having two hydraulic chambers and a bilaterally acting piston between.

15. The pressure generating device according to claim 1, wherein the pressure supply unit supplies at least two hydraulic consumers with pressure, wherein one hydraulic consumer is a valve hydraulic chamber in a cylinder head of an internal combustion engine and serves for the actuation of one or two gas exchange valves.

16. A method for the optional pressure build-up and pressure reduction in first and second hydraulic circuits to which at least two hydraulic chambers of one or more consumers are connected, with a pressure generating device which comprises a piston-cylinder unit that has a bilaterally acting piston, which separates first and second working spaces in the cylinder from one another in a sealing manner, and a drive configured to drive the piston of the piston-cylinder unit, wherein the drive has a linear actuator in the form of a linear motor or rotation motor and gear mechanism, wherein the piston has two effective surfaces and each effective surface of the piston respectively defines a working space of the first and second working spaces, wherein the pressure generating device is adapted to build up and reduce pressure by driving the linear actuator by a predetermined pressure rod path which is calculated taking into account the effective surface in a backward or forward stroke, wherein each of the first and second working spaces is connected via a hydraulic line to a respective hydraulic circuit, wherein at least one hydraulic chamber of a consumer is connected to respective ones of the first and second hydraulic circuits, wherein pressure build-up in one hydraulic chamber of a consumer associated with one hydraulic circuit is carried out by a forward stroke or return stroke of the piston via a working space, wherein both working spaces are switchable hydraulically connected with a reservoir, the method comprising: performing pressure reduction in one or both hydraulic circuits separately or at the same time, in a way that either: a) the pressure reduction in the first hydraulic circuit takes place by a return stroke of the piston which enlarges the first working space, wherein hydraulic fluid from the second working space is released through a hydraulic connection and a corresponding opened valve into the reservoir and/or the pressure reduction in the first hydraulic circuit is done via the first working space and the hydraulic line and the corresponding opened valve into the reservoir; or b) the pressure reduction in the second hydraulic circuit takes place by a forward stroke of the piston which enlarges the second working space, wherein hydraulic fluid from the first working space is released through a hydraulic connection and a corresponding opened valve into the reservoir and/or the pressure reduction in the second hydraulic circuit is done via the second working space and the hydraulic line and the corresponding opened valve into the reservoir.

17. The method according to claim 16, further comprising performing pressure build-up in the hydraulic circuits simultaneously, one after the other, or with a time offset.

18. The method according to claim 16, wherein the effective surfaces are different and are in a ratio of 1.5:1 to 2.5:1 to one another.

19. The method according to claim 16, wherein the pressure chambers, the hydraulic lines, or the hydraulic circuits are connected to one another via a connecting line, wherein at least one switching valve is arranged in the connecting line for the optional opening or closure of the connecting line, such that pressure build-up or pressure reduction is done with an acting or effecting working space.

20. The method according to claim 16, wherein a respective non-return valve with a closing direction from a respective working space of the pressure generating unit to the reservoir vessel is arranged parallel to a respective one of the valves associated with the respective working space and hydraulic connection to the reservoir.

21. The method according to claim 16, further comprising measuring pressure in at least one of the hydraulic lines leading to at least one of the consumers using at least one pressure sensor.

22. The method according to claim 16, further comprising: calculating an actual pressure via a phase current of the electric drive, measured with one of more redundant current sensors, and a torque calculated from a torque constant, as well as an effective piston surface; and performing pressure regulation using the calculated actual pressure.

23. The method according to claim 16, wherein a switching valve is associated with each hydraulically acting working space of the consumers for the optional closure or opening of a respective hydraulic line to the pressure supply device.

24. The method according to claim 16, further comprising enabling hydraulic fluid to flow through the respective working spaces to the reservoir vessel or to flow directly via an outlet valve into the reservoir vessel for pressure reduction in at least one consumer, wherein in each hydraulic connection to a respective consumer a switching valve is arranged between one of the working spaces and the respective consumer.

25. The method according to claim 24, wherein in the case of the pressure reduction in the reservoir vessel via the working space or spaces as well as via the switching valves, the control device uses the pressure calculated by one or more pressure sensors in one or both hydraulic circuits and/or calculated from the phase current sensor for regulation.

26. The method according to claim 16, further comprising at least partly simultaneously increasing or reducing pressure in at least two consumers by adjusting the piston.

27. The method according to claim 16, wherein the pressure supply of at least two consumers is done with a multiplex operation.

28. The method according to claim 16, wherein the pressure supply unit supplies at least two consumers with pressure, wherein one consumer is a vehicle clutch, a chamber of a change speed selector, or a gear mechanism.

29. The method according to claim 16, wherein the pressure supply unit supplies at least one consumer with two hydraulic chambers and a bilaterally acting piston between.

30. The method according to claim 16, wherein the pressure supply unit supplies at least two consumers with pressure, wherein one consumer is a valve hydraulic chamber in the cylinder head of an internal combustion engine and serves for the actuation of one or two gas exchange valves.

Description

DESCRIPTION OF THE FIGURES

(1) Various possible embodiments of the pressure generating device according to the invention are described in more detail hereinafter with the aid of the drawings, in which:

(2) FIG. 1a: shows the basic construction of a pressure generating device with double-stroke piston, hereinafter also termed double-stroke piston pressure regulating unit, with motor gear mechanism unit for the pressure supply of two hydraulic circuits with pressure reduction valves;

(3) FIG. 1b: shows the basic construction of the double-stroke piston pressure regulating unit with motor gear mechanism unit for the pressure supply of two hydraulic circuits with pressure reduction valves and shifting valve;

(4) FIG. 1c: shows the basic construction of the double-stroke piston pressure regulating unit with motor gear mechanism unit for the pressure supply of two hydraulic circuits with one, alternatively two, pressure reduction valves as well as switching valves in the hydraulic circuits for further degrees of freedom in the pressure regulation;

(5) FIG. 2: shows the basic construction of the pressure generating device with a linear drive without gear mechanism;

(6) FIG. 3a: shows a pressure regulating method taking into account the switchable surfaces;

(7) FIG. 3b: shows the pressure regulating method in the coupling actuation with different consumers and hydraulic effective cross-sectional surfaces;

(8) FIG. 4: shows the use of the pressure generating device as a piston actuator for two hydraulic consumers (in particular couplings) with additional use of a ShV valve and switching valves at the consumers for multiplex operation;

(9) FIG. 5: shows the use of the pressure generating device as a piston actuator as well as switching actuator for more than two consumers (in particular two couplings and two switching actuators with pressure regulation of the coupling and of the switching actuators in the multiplex method);

(10) FIG. 6: shows the use of the pressure regulating unit as coupling actuator and switching actuator for consumers with two hydraulic effective surfaces (e.g. change speed selector, steering mechanism) as well as optionally further consumers with multiplex operations.

(11) FIG. 1a shows the basic construction of a first possible embodiment of the pressure generating device according to the invention, which can also be termed a pressure regulation and volume conveying unit, hereinafter also double-stroke piston pressure regulating unit. This has a bilaterally acting piston 1, hereinafter also called double-stroke piston DHK, which can be displaced via a pressure rod 2 with a linear drive, consisting of electric motor M and gear mechanism, which in particular is a ball-type linear gear mechanism, in both directions over the path sk. An angle transmitter 6a and phase current measurement sensor(s) 6b are provided on the actuator M. As an alternative to the angle transmitter a sensor can be used directly to determine the piston stroke position (6c). This is helpful in improving the position regulation particularly in case of slippage in the gear mechanism. The double-stroke piston 1 defines a first working space and pressure chamber 3a and a second working space and pressure chamber 3b. Both working spaces 3a, 3b are connected via non-return valves 4a and 4b to a storage container 5. The non-return valves 4a, 4b have a large opening cross-section, so that a throttling action is avoided.

(12) The pressure generating device regulates the pressure in the two hydraulic circuits K1 and K2. Pressure sensors 7 and 7a are arranged in the feed lines H3, H4 between the working spaces 3a, 3b and the hydraulic circuits K1 and K2. The pressure sensors 7 or 7a can be dispensed with for the regulation if the torque of the motor M is calculated via the phase current measurement and the system pressure in the hydraulic line H3, H4 is calculated via the effective cross-sectional surface, in which no pressure sensor is present. However, for safety considerations and in order to calibrate the pressure volume characteristic line at least one pressure sensor is desirable. Also, the phase current measurement can be designed to be redundant so as to be able to completely dispense with the pressure sensors.

(13) In addition, two switchable valves PD1 or PD2 are provided, which can also be termed pressure reduction valves, which are arranged in the hydraulic line H1, H2 connecting the respective working space 3a, 3b with the reservoir vessel 5. A pressure reduction from both working spaces 3a, 3b into the reservoir vessel 5 is thus possible. By opening one or both valves PD1 or PD2 the pressure can be reduced in a controlled manner during the forward or reverse stroke via path control of the path sk or stopping the double-stroke piston 1. In this connection, at least one of the two pressure sensors 7, 7a or the current measurement is used for the pressure reduction regulation. This is particularly advantageous compared to a pressure regulation via conventional outlet valves with PWM (pulse-width modulation) operation, since the pressure can be reduced in a controlled manner with a high degree of accuracy. With conventional outlet regulation with upstream connected closed switching valves (e.g. outlet valve between SV1 and consumer V1 or outlet valve between consumers V2 and SV2) this pressure regulation accuracy is not possible, since no pressure sensor can be used for the pressure reduction regulation in such an arrangement as is normal in brake regulation systems.

(14) FIG. 1b shows a further possible embodiment of the pressure generating device according to the invention, in which the working space 3a is bounded by the effective surface A1 and the second working space 3b is bounded by the effective surface A2 of the piston 1. The ratio of the surfaces A1 and A2 is approximately 2:1, but is at least 1.5:1 however and at most 2.5:1. In addition a switchable pressure compensation valve ShV is arranged between the chambers 3a, 3b. The switchable valve ShV is in the case of highly dynamic systems designed as a switching valve without a throttle function and consequently has a large flow cross-section. The connecting line containing the switching valve ShV and connecting the pressure chambers 3a, 3b and the hydraulic lines H3, H4 leading from these to the consumers, is as short as possible and begins at least at one pressure chamber as far as possible directly at the outlet of the piston-cylinder unit. In particular elements that increase the flow resistance, such as additional valves, etc., should be avoided as far as possible in this region. Alternatively, instead of a switching valve ShV multiple switching valves can also be connected in parallel in the connecting line H5. By means of such a parallel connection standard valves from large-scale mass production can be used by means of such a parallel arrangement. By switching the pressure compensation valve ShV a connection can be produced between the front side and rear side of the double-stroke piston 1 and during the piston stroke different effective surfaces can be realised by pressure compensation. With a less dynamic system or the use of fewer consumers in the system the flow cross-section of the switching valve ShV and the flow resistance of the hydraulic lines that connect the working chambers of the double-stroke piston are less relevant and the connection can also be made via multiple valves, for example in the hydraulic circuits.

(15) Two hydraulic circuits K1 and K2 are supplied by the pressure generating device. When the valve ShV is closed the circuit 1 is supplied with pressure in the forward stroke and the circuit 2 is supplied with pressure in the reverse stroke. When the valve ShV is open, in the forward stroke and reverse stroke both the circuit K1 and K2 are jointly supplied with pressure via the effective surface A1-A2 (in the forward stroke) and A2 (in the reverse stroke). The pressure in at least one hydraulic line H3, H4 is determined by means of a pressure sensor 7, optionally also by means of the two pressure sensors 7, 7a. A pressure sensor can be dispensed with for the regulation if the torque of the motor M is calculated via the phase current measurement and the system pressure is calculated via the effective cross-sectional area.

(16) FIG. 1c shows an expansion of the pressure generating device of FIG. 1b, in which further switching valves SV1, SV1a and SV2 are provided in the hydraulic lines H3, H4. In this arrangement the switching valves SV1 and SV2 are arranged at the outputs of the front chamber 3a and rear chamber 3b and the switching valve ShV directly connects the hydraulic circuit K1 to the chamber 3b. The switching valve SV1a is then arranged in front of the connecting line H5 and the hydraulic circuit K1.

(17) This expansion produces a larger functional scope for the regulation of the consumers. In this connection the double-stroke piston 1 has via the stroke control, partially with the use of the pressure volume characteristic curve and the pressure sensor 7a and 7b (see the implementation in FIG. 3b) the following degrees of freedom in this embodiment: pressure build-up individually in circuit K1 and circuit K2; pressure build-up jointly in circuit K1 and circuit K2; pressure reduction individually in circuit K1 and circuit K2; pressure reduction jointly in circuit K1 and circuit K2; simultaneous pressure build-up in circuit 1 and pressure reduction in circuit 2; simultaneous pressure build-up in circuit 2 and pressure reduction in circuit 1.

(18) For the implementation of these functions the valves in FIG. 1c are switched as follows. In this connection it should be noted that the valve PD2 as well as the hydraulic line H2 can also be dispensed with for the regulations described hereinafter, since it is always operated closed in the executed functions and therefore corresponds in its function to a non-return valve.

(19) TABLE-US-00001 Double-stroke Pressure build-up P.sub.auf. K1 Pressure build-up P.sub.auf K2 piston stroke Forward Reverse Forward Reverse direction stroke stroke stroke stroke ShV 0 1 With 0 SV1 1 0 switching 0 SV2 0 0 FIG. 1 PD1 0 0 1b ShV, SV2 0 PD2 0 0 open 0

(20) TABLE-US-00002 Double-stroke Pressure reduction p.sub.ab. K1 Pressure reduction p.sub.ab.K2 piston stroke Forward Reverse Forward Reverse direction stroke stroke stroke stroke ShV 1 1 0 With SV1 0 1 0 switching SV2 0 0 1 4a(SV1 at PD1 1 0 1 the PD2 0 0 0 consumer) SV2 and ShV open

(21) TABLE-US-00003 Pressure reduction Pressure reduction Double-stroke p.sub.abK1 + K2 p.sub.abK1 + K2 piston stroke Forward Reverse Forward Reverse direction stroke stroke stroke stroke ShV 1 1 1 1 SV1 1 0 1 0 SV2 1 1 1 1 PD1 0 0 0 1 PD2 0 0 0 0
Designations:
0 Valve closed
1: Valve opened

(22) Further degrees of freedom of the simultaneously regulated pressure build-up and pressure reduction can be used if the valve PD1 and also the valve PD2 are provided and employed. In this way, in addition to the aforementioned possibilities the pressure in in each case one of the two hydraulic circuits K1, K2 or also in both hydraulic circuits K1 and K2 pressure regulated via the chambers 3a, 3b of the double-stroke piston can be reduced in a controlled manner by using the pressure sensors 7 and 7a and the valves PD1, PD2.

(23) FIG. 2 describes the same pressure generating device as in FIG. 1a, but with the difference that the pressure rod piston 2 can be actuated via a linear actuator, consisting of an armature 15 with permanent magnets 15a, a stator with excitation coils 16 and a linear path sensor 17. The function is the same as in FIG. 1a. Linear actuators have advantages compared to motor screw drives if the double-stroke piston is designed for small stokes and small forces occur in the system. Optionally the connecting valve ShV is used, which has the same mode of action as described in FIG. 1b.

(24) FIG. 3a describes the regulation strategy for the accurate pressure regulation via the formation of a pressure-volume (path) characteristic curve in a relationship between pressure rod path sk and pressure p. The pressure sensor 7 of FIGS. 1a, 1b, 1c is used to produce the pressure-volume characteristic curve. The pressure-volume characteristic curve can be compensated in operation.

(25) This method is used in particular in the pressure build-up and pressure reduction of coupling actuators and further consumers, such as for example change speed selectors, if no simultaneous pressure build-up and pressure reduction is necessary, i.e. either a coupling or a change speed selector is operated in sequence.

(26) A ratio of the chamber areas of the double-stroke piston of approximately A1/A2=2 is used as the basis in the representation. The pressure build-up begins starting from an initial pressure sO.sub.A1. A desired regulating pressure p1 is adjusted by modulating the linear actuator during the pressure build-up paid with area A1, for example in the forward stroke up to the position S.sub.p1, and during the pressure build-up p.sub.aufII with area A2, for example in the reverse stroke up to the position Sp.sub.3. The pressure-path characteristic curve forms the basis for the regulation, and illustrates the non-linear connection between pressure and path. Also pressures lower than p1 can also be adjusted via the pressure-path characteristic curve. On switching to the effective surface A2 the pressure-volume characteristic curve is displaced, and a new reference path S.sub.p3 is formed. Pressure changes can be adjusted by adjusting difference paths Dsk. The path-controlled pressure regulating strategy has the advantage that the pressure can be adjusted significantly more effectively if the regulation is performed by stroke and not by using the pressure sensor, since in this way pressure fluctuations and elasticities of the pressure line cannot influence the regulation as interference quantities and no stringent demands need be placed in the accuracy of pressure sensors.

(27) If the pressure regulation unit according to FIG. 1b is used, i.e. with pressure reduction valve PD1, the pressure can be regulated via the path control sk also in the pressure reduction via the pressure-path relationship (p.sub.abI). For this purpose the piston 1 is operated in reverse stroke. In this connection it must be ensured that the volume in the second chamber 3b is not compressed, i.e. can escape via PD2 into the reservoir vessel. A comparable pressure reduction (P.sub.abII) can also be regulated in the forward stroke with a smaller effective surface. For this, the volume is released via the reservoir vessel PD2 into the reservoir vessel. An equivalent effect is achieved in the pressure reduction method P.sub.abII) if the ShV valve is opened in the reverse stroke. In this case no PD1 or PD2 valve is required for the pressure reduction. The displaced volume is conveyed from the rear chamber 3b into the front chamber of the double-stroke piston.

(28) FIG. 3b describes the regulation process with simultaneous pressure build-up and pressure reduction via both chambers of the double-stroke piston (for example with the actuation of two couplings in the system construction according to FIG. 5). There slightly different pressure-volume characteristic curves of two slave cylinders are used as a basis or alternative identical pressure-volume characteristic curves of the slave pistons and a double-stroke piston design with a surface ratio of the hydraulic surfaces A1/A2=S2/S1.

(29) For this purpose, starting from the position S1 the piston is adjusted in the reverse stroke from the position S1 to the position S2. The pressure of the coupling K1 is reduced from the operating pressure P.sub.K1 to approximately zero, while at the same time the pressure in the coupling K2 is increased from approximately zero to p.sub.K2. The actuator is then moved further to the position S2 until the operating pressure pK2 is reached. In the reverse stroke movement the missing volume is conveyed from the storage chamber via the non-return valves to the front chamber of the double-stroke piston, in order to avoid a negative pressure. Compared to a sequential method this method has the significant advantage that one coupling K1 can be released very quickly, while the coupling K2 is applied at the same time.

(30) This is achieved in particular for a switching process with minimum time delay, which is required with a double coupling system. In addition, the pressure in one coupling can be used as energy source, so that only a drive motor with a minimum power demand is necessary, and the dynamics of the switching process compared to a two-actuator system with the same motor can be significantly improved in the switching process, since the stored hydraulic energy can be utilised in the switching process.

(31) By using a ShV valve and corresponding actuation the control can in addition be optimised, for example in that the procedure for releasing a coupling K1 is synchronised with the application procedure of the second coupling, i.e. the procedure is terminated with an adjustment path in the middle between S1 and S2 (i.e. S=0.5(S1+S2)).

(32) In particular in the reverse procedure (i.e. coupling K2 is released from the operating pressure pK2 by an adjustment path S2), the use of the AV valve is desirable, otherwise the operating pressure pK1 of the coupling K1 is exceeded. A remedy is also the use of discharge valves (PD1 or PD2) or further outlet valves in the system. Here the PD1 valve is important, since the pressure reduction in the coupling K1 can be accurately controlled via the discharge valve PD1 using the pressure sensor in K1, even without using a ShV valve. PD1 and ShV are therefore alternatives and both are not absolutely necessary. The PD2 valve has a similar importance when the surface ratio A1/A2 is approximately equal and the coupling actuator K2 has a larger volume.

(33) As an alternative to the pressure supply unit, also the double-stroke piston pressure supply unit with a valve switching as illustrated in FIG. 2 can be used.

(34) FIG. 4 represents an embodiment of the pressure generating device according to the implementation in FIG. 1b, in which the potential of the double-stroke piston 1 is used. The pressure generating device can also be used in the configuration according to FIG. 1c, in which the switching valves SV1 and SV2 are part of the pressure supply unit (SV1a =SV1, SV2=SV2). Each working space 3a, 3b is connected to a slave cylinder V1K, V2K of the two couplings V1 and V2. This system arrangement allows the pressure reduction of the coupling K1 (p.sub.red.K1) via the front chamber 3a of the double-stroke piston while at the same time the pressure build-up in the coupling K2 (p.sub.aufK2) is carried out via adjustment in the reverse stroke direction of the double-stroke piston. The simultaneous pressure build-up and pressure reduction can also take place in the forward stroke direction. In this case the pressure in the consumer B2 is reduced and the pressure in the consumer B1 is increased by the forward stroke movement of the double-stroke piston. To assist this, both PD1 and PD2 can be used for the pressure reduction regulation. The ShV valve can likewise be opened for the pressure reduction and also for the pressure build-up regulation, and the pressure varying over the movement of the double-stroke piston can be influenced, in which the circuits K1 and K2 are connected.

(35) Thanks to the provision of outlet valves, in a system introduction the advantage of an exact pressure build-up regulation via piston path control as well as the simultaneous pressure change possibility (pressure reduction in chamber V1k, pressure build-up in chamber V2K) via the mode of operation of the double-stroke piston can be used in a first step, especially in the actuation of two couplings that have to be switched simultaneously.

(36) In addition, the valve ShV with an area ratio A1/A2 of approximately 2:1 can be used with the same volume management of the couplings V1 and V2 for the downsizing of the torque of the drive motor. In this way, starting from a specific operating pressure (ca. 50% of the operating pressure) in the forward stroke the hydraulically effective surface can be halved and is then approximately twice as large as in the reverse stroke.

(37) The currentless open switching valves SV1 and SV2 mean that when the target pressure of the coupling is reached by flow of current they are closed and the pressure in the slave piston hydraulics is maintained with a low valve current. In this way the power load of the motor M and the performance requirement can be reduced and the regulation can be facilitated, in particular when the target pressure is reached the consumer can be disconnected and in a sequential step the other consumer can be adjusted to the target pressure value via the pressure volume control.

(38) As an alternative to the pressure supply unit the pressure generating device can also be used with a valve switching as illustrated in FIG. 2. The valve switching of FIG. 2 can also be adapted comparably as in FIG. 1b to FIG. 1c. The same applies to the following system descriptions in FIGS. 5 and 6.

(39) FIG. 5 shows an expansion of the system described in FIG. 4 for the additional actuation of multiple consumers V3, V4 with the simultaneous omission of a pressure sensor in the circuit K2. Alternatively, a pressure sensor in the circuit K2 is also possible and the pressure sensor is dispensed with in the circuit K1. For this, switching vales SV1, SV2, SV3, SV4 are provided for each consumer V1-V4. The change speed selectors are controlled in the so-called multiplex method, i.e. by actuating hydraulic consumers VS3 or VS4 the currentless open switching valves of the coupling actuators are closed, so that the pressure is maintained by current flowing through the solenoid valves and the pressure is not raised by the actuation. The pressure of the slave piston of the consumer V3 or V4 is, as already described, increased or reduced (p.sub.MUX,V3, p.sub.MUX,V4) via the double-stroke piston having regard to the pressure-volume characteristic curve. When the pressure is reached the switching valve SV3 or SV4 is closed, and in a following sequence a further consumer can be actuated. This method is as a rule performed sequentially especially when change speed selectors are used, since no simultaneous actuation of change speed selector is carried out and in a double coupling gear mechanism and moreover the change speed selection procedure does not take place at the same time as the coupling actuation procedure. The method however offers the possibility of the simultaneous or partially simultaneous pressure build-up and pressure reduction, as is known from the multiplex operation of the inventor.

(40) Due to the expansion of the coupling actuation system to further consumers the system can be significantly simplified compared to conventional double coupling systems, in which a drive mechanism is provided for each change speed selector and each coupling. Since switching valves are comparatively favourable and light also with a low flow resistance, significant cost savings and weight reduction can thereby be achieved.

(41) FIG. 6 shows an alternative to FIG. 5, in which in the multiplex operation two chambers V1K1 and V1K2 of a consumer V1 as well as a second consumer V2 are charged with pressure with the pressure generating device according to the invention. In contrast to FIG. 5 the piston of the consumer V1 can be adjusted in both directions, wherein with the adjustment of the rod in V1 both hydraulic circuits K1 and K2 are used, in which in one chamber of the double-stroke piston the pressure is reduced and, by displacing the piston, in another chamber the pressure is increased. The valves PD1, PD2 or ShV are additionally used for the regulation, wherein only at most two valves are necessary for the regulation. An outlet valve AV.sub.K3 can also be connected between a hydraulic chamber of a consumer, here for example illustrated for the consumer V3, and the respective switching valve SV3, via which the pressure can be dissipated from the chamber V3k via a separate hydraulic line H8 directly to the reservoir vessel 5.

(42) In this implementation the pressure is supplied in the chamber V1K2 or V1K2 and the piston is adjusted very accurately with the pressure regulating method according to the invention. In the application the consumers can for example represent a steering mechanism or change speed selector (V1) as well as a coupling (V2).

(43) Further consumers V3, V4 with upstream connected switching valves SV4 and SV5 with the operating principle of the consumers V1 and/or V2 can be connected to the hydraulic circuits K1 and K2 and operated in multiplex operations. Thus, for example, a complete double coupling gear mechanism (with 2 couplings, 4 change speed selectors) or a plurality of couplings as well as a steering mechanism can be operated with a pressure supply unit and other hydraulic systems with a central actuator can be supplied with pressure (e.g. electrohydraulic valve operation).

LIST OF REFERENCE NUMERALS

(44) 1 Bilaterally acting piston or double-stroke piston 2 Pressure rod piston 3a Chamber 4a Non-return valve 4b Non-return valve 5 Reservoir vessel 6a Non-return valve 6b Non-return valve 7 Pressure sensor 8 Ball-type linear drive 9a Bearing 9b Bearing 10 Rotor 11 Stator 12 Excitation coils 13 Housing 14 Transducer 15 Armature 15a Permanent magnets 16 Stator with excitation coils 17 Linear path sensor 20 Pressure regulating unit 21a Pressure build-up valve 21a Pressure release valve 22a Pressure build-up valve 22b Pressure release valve 23 Line 24 Line 32a Line 32b Line 33a Solenoid valve 33b Solenoid valve 34 Control piston cylinder unit 35 Pressure chamber 36 Seal 37 Pressure piston 38 Spring 39 Active piston 40 Control piston cylinder unit 41 Pressure chamber 42 Pressure chamber 43 Control piston 44 Seal 45 Sniffing hole seal 46 Reservoir vessel 47 Pressure sensor 48 Path simulator 48 Pedal unit 50 Hydraulic circuit 51 Hydraulic circuit 52 Pressure sensor 53 Pressure sensor 54 Path sensor 55 Electric control and regulating unit (ECU) AV Switchable pressure compensation valve D1 Seal D2 Seal K1 Hydraulic circuit K2 Hydraulic circuit SiV Safety valve Sk Path TV Isolation valve V1 Consumer V2 Consumer V3 Consumer and coupling actuation V4 Consumer and brake system