The present invention relates to a shift gearbox, a control unit and at least one electric motor-driven piston-cylinder unit with a piston, which delimits at least one working chamber, which is connected via hydraulic lines to multiple shift gearbox units of the shift gearbox and shifts them, wherein the shift gearbox units comprise at least one gear selector unit and at least one clutch unit.
 From DE 10 2006 038 446 A1 a shift gearbox with an electric motor-driven piston-cylinder unit is described, in which one or two piston-cylinder units operate four gear selectors and two clutches. The piston-cylinder unit generates the pressure required to shift the gear selectors and clutches, wherein a pressure sensor measures the pressure generated. DE 10 2006 038 446 A1 describes two possible embodiments for this purpose. In the first embodiment clutches and gear selectors are shifted via so-called multiplex valves for an actuation, by means of the piston-cylinder unit. In this connection the pressure build-up and also the pressure reduction can take place via the piston-cylinder unit. However, it is also possible that additional outlet valves are provided for some or all loads, via which the pressure in the individual loads can be lowered in a regulated manner.
OBJECT OF THE INVENTION
 The object of the invention is to further improve the shift gearbox known from DE 10 2006 038 446 A1.
 This object is achieved according to the invention with a shift gearbox having the features of claim 1. Advantageous embodiments of this shift gearbox are obtained from the features of the sub-claims.
 Through the displacement control of the piston, which corresponds to a volume control, a cost-effective structure is provided in which the number of valves used can be advantageously reduced. On account of the displacement or volume control at least one shift gearbox unit can in a simple manner have more than two switching positions, without a complicated pressure control, since on account of the incompressibility of the hydraulic medium over a predetermined delivered volume the respective shift gearbox unit can be shifted specifically in one of the possible positions. Through the displacement or volume control the shift gearbox units can also be shifted accurately and quickly, and also components (switching valves, seals of piston units of gear selectors or clutch plates) can be diagnosed for leakage, as well as hydraulic flow resistances. Thus, it is advantageously possible that initially a rapid shifting is carried out, and by decelerating, the shift gearbox unit is smoothly shifted to its target position.
 By the use of at least one pressure sensor, a pressure regulation for pressure build-up and also alternatively for pressure reduction can be provided for some shift gearbox units in an advantageous further development, so that by means of the same piston-cylinder unit a displacement control and/or a volume control and also a pressure control results. By additionally providing a pressure regulation using a pressure sensor, a precisely adjustable required force can also be applied to loads, such as, for example, the clutch.
 Pressure regulation can also be achieved without the use of a pressure sensor via targeted piston displacement control or via targeted electrical energisation of the electric motor. In the pressure control, the non-linear relationship between pressure and piston adjustment path is recorded and stored in a performance map. This map is used in the pressure control in such a way that the piston travels a certain distance, which corresponds to a certain pressure. If the performance map changes due to temperature or air bubbles, it is recalibrated and recorded. Various methods are available for this, such as adjustment via pressure transducer, adjustment via path control, and use of the current of the electric motor.
 Alternatively, a torque can be regulated via the current of the electric motor. For an accurate torque determination, the torque constant kt of the electric motor, which represents the relationship between the torque of the electric motor and phase current, can for example be used. The torque constant kt in the case of electric motors can be determined for example during manufacture or initial start-up and is characterised in that kt changes slightly over time and essentially changes linearly only due to temperature influences. As an alternative to the phase current, the supply current of the electric motor can also be used.
 If no pressure sensor is available for the calibration, a pressure estimate can be made by means of a model. Such a model can according to the invention consist of a motor with a transmission, which for example presses on or possibly retracts a single-acting or double-acting hydraulic piston. For a sufficiently good pressure estimate for a gearbox unit, the parameters in the subunits (motor torque constant kt, transmission efficiency and hydraulic piston cross-sectional area, friction due to seals) must either be subjected to minor influences or the parameter variations must be adjusted at regular intervals.
 An accurate model can be realised in such a way that the aforementioned parameter changes of the model, which interfere in the pressure estimation or pressure control, are detected during operation. For example, pressure sensors that are only active in partial operation or an indirect pressure calculation can be employed.
 A method for the indirect measurement of the pressure via the current of the electric motor can be calculated by the position of the clutch piston in the slave cylinder and by the acting cross-sectional area of the piston of the master cylinder, by means of knowledge of the clutch release spring and the diameter of the clutch slave cylinder. Thus, a system based on a pressure transducer can be completely avoided, which leads to significant cost savings since pressure transducers are primary cost drivers of hydraulic systems. In series applications a pressure transducer is about 4 times more expensive than a switching valve and comparably expensive as a proportional valve.
 By using a dual-action reciprocating piston, which can convey, via its two working chambers in both stroke directions of the dual-action reciprocating piston, hydraulic medium into or out of one of the shift gearbox units, inter alia a short design of the piston-cylinder unit can advantageously be achieved. Thus, the two piston surfaces can either have the same size, so that the same volume is conveyed with the same displacement of the piston during the forward stroke and the return stroke. It is however also possible that the piston surfaces have different sizes, e.g. in the ratio of 1.5-2:1, so that in the forward stroke 1.5 to 2 times the volume is conveyed as in the return stroke, so that in the forward stroke, volume can be conveyed faster in terms of a rapid pressure build-up and thus rapid actuation of the clutch or a rapid gear operation is promoted. In this way very short switching times of a double-clutch shift gearbox can be achieved, especially if at the same time in another clutch the pressure in the reservoir is reduced via a solenoid valve and the speed-torque characteristic curve of an electric motor can thus be optimally used for a given supply voltage.
 Also, the volume ratio 2:1 can be used expediently in such a way that a volume compensation between two working chambers of a dual-action reciprocating piston can be achieved via a switching valve (31) and the axial force load on the shift gearbox is thus reduced, since in the forward stroke and in the return stroke only half the area acts on the shift gearbox unit. This is sensible especially at high pressures, since the axial force reduces the gear load and thus enables the use of a cost-effective plastic trapezoidal spindle drive. The advantage of the dual-action reciprocating piston compared to a continuously operating pump is that the pressure generating unit has to be operated only during a switching operation.
 The following advantages can thus be achieved with the shift gearbox according to the invention:
- a) Lower weight by reducing the number of components, especially by reducing the number of valves, sensors, filter, pressure accumulator and pump.
- b) Improvement of the reliability by introducing diagnostic methods for leak testing and calibration methods for detecting a change in flow resistances
- c) Reduction of Costs of the System
Simplified gear position by using only two hydraulic piston-cylinder units (GS1 and GS2) for the actuation of more than 2 gear selectors (8-10 gears)
Use of a cost-effective motor spindle unit for the pressure supply with trapezoidal spindle gears instead of recirculating ball gears
Reduction of the number of sensors by the derivation of alternative measured variables such as motor current and motor piston position.
- d) Functional Improvement
Use of a position-controlled dual-action reciprocating piston as conveying unit for continuous conveyance for open system
Use of a position-controlled dual-action reciprocating piston as pressure supply with pressure reduction via the pressure supply unit for closed systems
Optimal use of the torque-speed characteristic curve of an electric motor in the sense of a quick actuation of one or two clutches
- e) Improved Reliability
Diagnostic method for checking the components (valves, tightness of piston of the gear and clutch plates as well as the pressure supply unit), for tightness via piston control
Measurement of the hydraulic system by measuring the hydraulic resistances in the system and detecting changes in operation
Measuring methods for checking the flow resistances of the hydraulic system and its components (for example valves, lines) and determining the adjustment forces of the pistons of gear selectors and clutch actuators
- f) Platform concept for automated gear shifting and dual clutches with as few changes as possible of the components in the system.
 Advantageous possible embodiments of the shift gearbox according to the invention are explained in more detail with reference to the drawings, in which:
 FIG. 1: System structure of an automated shift transmission gearbox (AMT) with clutch and gear selector;
 FIG. 1a : System structure according to FIG. 1 with dual-action reciprocating pistons;
 FIG. 1b : An automated shift transmission gearbox with clutch, gear selectors and four valves in the closed hydraulic circuit;
 FIG. 2: System structure of an AMT (automated shift transmission) or double-clutch shift gearbox with one to two clutches as well as four gear selectors; the clutch is adjusted in multiplex mode in the closed hydraulic circuit;
 FIG. 3: System structure of an AMT (automated manual transmission) or DCT (double-clutch transmission) with one to two clutches and four gear selectors, in which the actuation of the clutches occurs via inlet and outlet valves;
 FIG. 3a : System structure with gear selectors with double-acting piston, in which the piston surfaces of the dual-action reciprocating piston are the same size;
 FIG. 3b : System structure with different size piston surfaces of the dual-action reciprocating piston;
 FIG. 3c : System structure as FIG. 3a , but with 2/2-way valves instead of 3/2-way valves;
 FIG. 4a : System structure of an AMT (automated shift transmission) or DCT (double-clutch transmission) with one to two clutches as well as four gear selectors, in which the actuation of the clutches occurs by means of inlet and outlet valves via a double-acting piston with a ratio of the piston surfaces of 1:1 or suitably chosen other ratio, e.g. 1:2;
 FIG. 4b : System structure as in FIG. 4 but with only one 2/2-way valve per gear selector instead of two, wherein in each case only one chamber of the dual-action reciprocating piston is hydraulically connected in each case to only one chamber of a gear selector;
 FIG. 5 Cross-sectional view of a possible embodiment of a pressure supply unit, in which a spindle is driven by an electric motor, in particular a BLC motor, whereby by means of preferably a trapezoidal thread drive a piston is displaced in a pressure chamber.
 FIG. 1 shows a first possible embodiment of the shift gearbox according to the invention, which is designed as an automated shift gearbox. Here, an electric motor-driven actuating unit consisting of motor 1, shift gearbox 2 and piston-cylinder unit 3 actuates a clutch 7 and two gear selector units 10, 11, which in turn actuate a gear selector mechanism 12, 13. The motor 1 is activated only during a switching operation, whereby the system does not have to be permanently in operation, as is the case with systems with pumps and a pressure accumulator unit. The gear selectors 10, 11 may have two or more positions, to which the gear selector mechanisms 12, 13 can be adjusted. Normally the gear selector 10 has the positions left, middle, right. On the other hand, the gear selector 11 may also have more than three positions. By conveying predetermined fluid volumes in or out, the gear selector mechanisms 12, 13 can thus be adjusted from a starting position to a target position, in which the volume of fluid necessary for this is conveyed or displaced by the piston-cylinder unit 3.
 The electric motor-driven actuating unit 1, 2 is for reasons of cost and space preferably in the form of a trapezoidal screw drive, alternatively executed by means of a ball screw drive or similar types of gears.
 The hydraulic piston-cylinder unit 3 is actuated with the aid of the electric motor-driven actuating unit 1, 2, wherein here a pressure control takes place by using the pressure sensor 5. By adjusting a target pressure by means of the piston 3 a (reducing the working chamber 3 b) the fluid is displaced from the working chamber 3 b via a 2/2-way valve 9 in the direction of the clutch unit 7 and thus opens the unpressurised closed clutch, which is monitored via the centrally arranged pressure sensor 5.
 After actuation of the clutch 7, the 2/2-way valve 9 is closed and the clutch 7 is thus held in the open state.
 By opening the 2/2-way valve 16 and closing the 2/2-way valve 14 further volume can be displaced via the piston-cylinder unit 3 into the cylinder 10 a of the gear selector unit 10, whereby a rotation is exerted on the gear selector mechanism 12, which preferably has three possible switch positions. For this purpose, the 2/2-way valves 15 must be opened and the 2/2-way valve 17 must be closed at the same time. To adjust the gear selector, no pressure control is applied by means of the pressure sensor 5 however, but a volume control is carried out by driving the piston by a predetermined distance Δs, so that a defined amount of fluid is displaced into the cylinder 10 a or 10 b of the gear selector, whereby the gear selector mechanism 12 is rotated by a certain angle and thus to its desired set position.
 In order to complete the switching process further, fluid is displaced via the 2/2-way valve 18 into the gear selector unit 11, whereby the gear selector mechanism 13 is moved to one of preferably three possible switching positions, preferably to one of the two end positions, whereby a spring 14 of the gear selector 11 is tensioned. Here too a volume control is applied, so that separate sensors for detecting the gear selector position could be dispensed with, which however may not be sensible in some cases, so that it is completely within the meaning of the invention to provide such position sensors at one or both gear selectors 10, 11. Only a slight pressure is needed to compensate for the spring forces of the piston-cylinder unit 3. The resetting of the gear selector 11 to its initial position can be carried out by the tensioned spring alone.
 After the engagement of the selected gear via the gear selector mechanism 12, 13, the 2/2-way valve 9 is opened and the volume contained therein is moved back via the piston-cylinder unit 3 to its working chamber 3 b, whereby the clutch 7 moves back in a controlled manner to its starting position and thus closes. Through the check valve 4 volume can be aspirated from a reservoir 6 into the piston-cylinder unit 3.
 FIG. 1a shows a second possible embodiment of a shift gearbox according to the invention, which is a modification of the shift gearbox according to FIG. 1. Instead of a piston-cylinder unit with only one working chamber, the second embodiment has a dual-action reciprocating piston 34 a, which hermetically separates the two working chambers 34 b, 34 c from one another. The two working chambers 34 b, 34 c are connected to one another by means of a connecting line HLV, wherein a switching valve 31 is arranged in the connecting line. The two piston surfaces 34 d, 34 e delimiting the working chambers 34 b, 34 c are of different sizes, the piston surface 34 e being 1.5 to 2 times smaller than the piston surface 34 d. In the return stroke of the piston 34 a (move to the left) and with the switching valve 31 closed, the fluid or hydraulic medium is thus conveyed from the working chamber 34 c to the hydraulic line HL. In the forward stroke, i.e. when adjusting the piston 34 a to the right, the switching valve 31 must be open, whereby the piston 34 a conveys fluid from the working chamber 34 b to the hydraulic line HL or HLV. Since however the other working chamber 34 d increases and the pressure in the hydraulic line is greater than the atmospheric pressure, fluid flows from the hydraulic line HL into the working chamber 34 c. If the piston surface ratio of the piston surfaces 34 d, 34 e is 2:1, just as much hydraulic medium is conveyed to the respective shift gearbox unit in the forward stroke as in the return stroke.
 When pressure is reduced in the gear selector 10 via the outlet valves 14, 15, with the valves 16, 17 closed, pressure can be built up at the same time in the clutch 7 and the other gear selector 11.
 FIG. 1b shows another possible embodiment of the shift gearbox according to the invention, which is designed as an automated shift gearbox. Here, an electric motor-driven actuating unit consisting of a motor 1 with rotation angle sensor 70, shift gearbox 2 and piston-cylinder unit 3 operates a clutch 7 and two gear selector units 10, 11, which in turn actuate a gear selector mechanism 12, 13. The motor 1 is activated only during a switching operation, whereby the system does not have to be permanently in operation, as is the case with systems with pumps and a pressure accumulator unit. The gear selectors 10, 11 may have two or more positions into which the gear selector mechanisms 12, 13 can be shifted. The gear selector 10 normally has two to three positions. On the other hand, the gear selector 11 can also have more than three positions. By conveying predetermined fluid volumes in or out, the gear selector mechanisms 12, 13 can thus be adjusted from a starting position to a target position, wherein the volume of fluid necessary for this is conveyed or displaced by the piston-cylinder unit 3.
 The electric motor-driven actuating unit 1, 2 is for reasons of cost and space preferably in the form of a trapezoidal screw drive, or alternatively implemented by means of a ball screw drive or similar types of shift gearbox.
 The hydraulic piston-cylinder unit 3 is actuated by means of the electric motor-driven actuating unit 1,2. The regulation of the individual hydraulic units in the form of the clutch 7 and gear selector 10, 11 is carried out via the piston movement for conveying the required hydraulic volumes. In this case the displaced volume can be calculated via the piston travel of the actuating unit 3 and therefore need not be measured individually with sensors in the individual hydraulic receivers 10 a, 10 b, 11, 7. This means that the function of the AMT actuator can only take place with an angle sensor 70 in the motor-shift gear-box-piston unit. Sensors such as for example a pressure transducer 5 a or position sensor 71 in the clutch 7 can be used for diagnosis and can guarantee the functionality or evaluate the state of the system. However, they are not absolutely necessary. Assuming that the clutch actuator valve 9 has a leakage and the clutch 7 opens slowly, this can be determined by means of the differential rotational speed of the crankshaft and vehicle gearbox and an additional position or pressure sensor (5 a, 71) is therefore not absolutely necessary. In addition, position sensors P1, P2 can also be provided at the gear selectors GS1 and GS2, which can be provided for example for leakage testing. These can however also be used instead of pressure transducers to control the position of the gear selector. In all embodiments which are shown and described in the figures, corresponding sensors Pi can be provided with the gear selectors, which can fulfil the above mentioned functions.
 After actuation of the clutch 7, the 2/2-way valve 9 is closed and the clutch 7 is thus held in the open state.
 By opening the 2/2-way valve 16 and closing the 2/2-way valve 14, which is closed current-free, further volume can be displaced via the piston-cylinder unit 3 to the cylinder 10 a of the gear selector unit 10, whereby a rotation is exerted on the gear selector mechanism 17, which preferably has three switching possibilities. For this purpose, the 2/2-way valves 14 must be opened at the same time and the 2/2-way valve 16 must be closed. However, for adjusting the gear selector, no pressure control by means of a pressure sensor is used, but a volume control is carried out by driving the piston by a predetermined distance Δs, so that a defined amount of fluid is displaced into the cylinder 10 a or 10 b of the gear selector, whereby the gear selector mechanism 17 is rotated by a certain angle and is thus rotated to its required position.
 In order to complete the switching process further fluid is displaced via the 2/2-way valve 18 to the gear selector unit 11, whereby the gear selector mechanism 13 is moved to one of preferably three possible switching positions, preferably to one of the two end positions, whereby a spring 15 of the gear selector 11 is tensioned. In this case as well a volume control is applied, so that separate sensors for detecting the gear selector position could be dispensed with, which however is not expedient in some cases, so it is completely within the meaning of the invention to provide such position sensors with one or both gear selectors 10, 11. Only a slight pressure is required to compensate the spring forces of the piston-cylinder unit 3. The resetting of the gear selector 11 to its initial position can be done by the tensioned spring alone.
 After engaging the selected gear via the gear selector mechanism 12, 13, the 2/2-way valve 9 is opened and the volume contained therein is displaced via the piston-cylinder unit 3 back to its working chamber 3 b, whereby the clutch 7 moves back in a controlled manner to its starting position and thus closes. Through the check valve implemented as a collar seal on the piston, volume can be aspirated from a reservoir 6 into the piston-cylinder unit 3. An excess of volume can thus be generated in the closed hydraulic system, which restricts the pressure or also the position control in the further course of events. Excessive volume can be drained via the valves 14 and 16 into the reservoir. Alternatively, the hydraulic piston 3 can for this purpose also drive into a position while the clutch 7 is depressed, where a pressure reduction is subsequently executed without any problem.
 FIG. 2 shows a third possible embodiment of the shift gearbox according to the invention which is designed as a double-clutch gearbox. In contrast to FIG. 1, in each case two gears are selected via a gear selector. Preferably four to five gear selectors (7- or 9-speed shift gearbox) are installed in a system.
 In the initial state preferably one of the two clutches 7, 19 is closed, whereas the other is in the open state.
 With a gear change from first to second gear, volume is displaced via the hydraulic piston-cylinder unit to the hydraulically open gear selector system. The inlet valves of all gear selectors and the currently not activated clutch 19 are closed. By opening the 2/2-way valve 23 b and simultaneously opening the outlet valve 26, the second gear is engaged by displacement of the piston in the gear selector 27 b, following which the valve 23 b is closed. A displacement or pressure control of the piston can be carried out here. For the change from first to second gear, volume is now displaced from the piston-cylinder unit 3 to the preferably hydraulically closed clutch unit system. The clutch C1 7 is closed and thus the first gear of the gear selector 27 a is in the power train. The clutch C2 19 is in the open state in the starting position. By means of two 2/2-way valves 9, 20 the pressure reduction in clutch 7 and sequentially the pressure build-up in clutch 19 is carried out in the so-called multiplex operation. The pressure sensor 5 serves in this case for the pressure-volume control. For a gear change from second to third gear again all the inlet valves of the clutches and gear selectors as well as the outlet valve 26 are closed and the inlet valve 24 a and the outlet valve 25 are opened. Via the control of the electric motor-driven actuating unit, the hydraulic fluid is displaced via the piston-cylinder unit to the piston chamber of the piston-cylinder unit 29 a and third gear is thus engaged. The completion of the gear change operation is accomplished by opening or closing the clutches 7, 19 in multiplex mode.
 A simplification of the hydraulic circuit diagram and a reduction in the number of valves is achieved by the use of one check valve per gear selector-piston chamber. In this connection for example the piston chambers of the gears 3, 4, 7, R can be hydraulically combined. A connection to the reservoir 6 is formed via an outlet valve 26.
 FIG. 3 shows a third possible embodiment of the shift gearbox according to the invention, which is also designed as a double clutch drive.
 In contrast to FIG. 2, the two clutches are implemented as a hydraulically open system with the additional outlet valves 32, 35. For this system two pressure sensors 5, 33 are installed to improve the pressure reduction control accuracy, each one sensing the pressure in the corresponding clutch. The pressure sensors 5, 33 are expediently arranged behind the inlet valves 9, 20. The change of gears is carried out as described in FIG. 2. The exemplary pressure build-up in clutch 7 is carried out as before via the control of the electric motor-driven actuating unit, whereby the hydraulic fluid is displaced via the piston-cylinder unit and the inlet valve 9 to the clutch 7. The pressure reduction at the other clutch 19 can be carried out via a PWM control of the outlet valve 35, whereby the pressure reduction gradient is determined. This has a significant influence on the closing behaviour of the clutch. The pressure sensor can be dispensed with since the initial pressure of the piston-cylinder unit of the clutch 7, which is adjusted via path control during the pressure build-up via path control, is stored and is released in a controlled manner in the pressure reduction via a hydraulic model by appropriate timing control of the outlet valves. For the control accuracy, the hydraulic resistances determined by the measurement method are used in the modelling of the hydraulic model.
 The pressure build-up can also take place without a pressure transducer via a path control, in which the pressure-volume characteristic curve should then be taken into account and a pressure estimate is made by measuring the phase current of the electric motor. However, for safety reasons it is expedient to provide at least one pressure transducer also for adjusting the model.
 The dual-action reciprocating piston can be implemented as a continuous pressure supply unit, which is used only as required, in which the check valves 4, 4 a and 36 are employed. With an area ratio of the two piston surfaces or piston ring surfaces of 2:1, the same volume is conveyed to the system both in the forward stroke and the return stroke. In the forward movement of the dual-action reciprocating piston the volume is conveyed from the forward stroke piston 34 b via the check valve 36 on the one hand to the return stroke chamber 34 c, and on the other hand the other half of the volume is made available to the system. In a reverse movement of the dual-action reciprocating piston, volume is made available via the check valve 4 in the forward stroke chamber 34 b and the volume is fed from the return stroke chamber 34 c to the system.
 On account of the hydraulic connection of the forward and return stroke chambers 34 b, 34 c, the effective piston area is the difference between the piston forward stroke surface and piston return stroke surface, or only the return stroke surface. This area must be taken into consideration for the design of the engine torque and/or the shift gearbox. The unit can be designed so that axial forces are reduced as much as possible, which can allow the use of a plastic transmission.
 FIG. 3a shows a further fourth possible embodiment, which differs from the embodiment of FIG. 3 in that the four gear selectors 37 a to 37 d have double-acting piston-cylinder systems, wherein the directional valves 42 a-d and 43 a-d in one of their positions act as inlet valves and in their other position act as outlet valves, so-called 3/2 valves. In the inlet position the valve 42 a-d connects the working chamber 38 a-d to the hydraulic line HL and thus to the piston-cylinder unit 34. The same applies to the valves 43 a-d, which in their first position connect the working chambers 39 a-d to the hydraulic line HL. In their second positions the valves 42 a-d and 43 a-d connect the respective working chambers to the hydraulic line HLR2 and the reservoir 6.
 FIG. 3b shows a fifth possible embodiment, in which the working chambers 34 b, 34 c are arranged with check valves 36, 36 a connecting to the hydraulic line, so that only hydraulic medium can be conveyed to the hydraulic line with the drive unit 1, 2, 34 for the pressure build-up. If the piston surfaces 34 d, 34 e are of different sizes, more fluid is conveyed to the hydraulic line HL in the forward stroke than in the return stroke. The pressure reduction in the shift gearbox units takes place via the outlet valves 9 a, 35 at the clutches 7, 19 and via the valves 42 a-d and 43 a-d. In this way a quicker pressure build-up or higher volume conveyance in the forward stroke than in the return stroke is possible. This can be used advantageously for fast or slow switching operations.
 FIG. 3c shows a further embodiment of the shift gearbox according to the invention, which is also designed as a double-clutch gearbox. The pressure supply is implemented here in the form of a so-called dual-action reciprocating piston with two check valves 4, 36, wherein each further combination of valves for the dual-action reciprocating piston 34 can be selected.
 In contrast to FIG. 3a the more expensive and often leak afflicted 3/2-way valves were replaced by cheap and low-leakage 2/2-way valves. These are used in modern braking systems and are preferred for diagnostic purposes. Due to the large production volumes these are very inexpensive and should therefore preferably be used. Here either valves directly from brake systems can be used, or valves with slight modifications, which can also be manufactured inexpensively and reliably as regards their functions. The operation of the clutches 7 and 19 is performed as described by means of the pressure supply unit 34. For the actuation of the gear selector 37 a to the right, volume from the pressure supply unit 34 is conveyed via the open 2/2-way valve 68 a and simultaneously closed 2/2-way valve 69 a to the chamber 38 a of the gear selector 37. Due to the differently large piston surfaces delimiting the working chambers 38 a and 38 b a differential force acts on the piston 40 a, whereby the volume is conveyed from the chamber 39 a of the gear selector 37 a to the chamber 38 a and the piston moves to the right. In order to move the gear selector 37 a to the left, volume is conveyed from the pressure supply unit directly to the chamber 39 a of the gear selector 37 a. For this purpose, simultaneously the valve 69 a must be open and the valve 68 a must be closed.
 FIG. 4a shows an eighth possible embodiment of the shift gearbox according to the invention, which is also designed as a double clutch drives.
 In contrast to FIG. 3, a piston-cylinder unit is preferably driven in the embodiment of a double-acting piston unit 34 by the electric motor-driven actuator. In this case the so-called forward stroke chamber 34 b with the clutch 7 and the return stroke chamber 34 c with the clutch 19 are hydraulically connected. As regards the gear selectors, in each case one hydraulic chamber is connected to the forward stroke chamber 34 b and the other hydraulic chamber is connected to the return stroke chamber 34 c. Likewise two outlet valves 50, 51 are also provided, in each case in one of the two hydraulic circuits that are connected to the reservoir 6.
 The volume from the forward stroke chamber 34 b can conveyed via the 2/2-way valve 20 to the clutch 7. At the same time the volume can be displaced from clutch 19 to the return stroke chamber 34 c. For a change of the pressure gradient the outlet valve 50 can in addition be electrically energized in PWM control. The closing or opening operation of the individual clutches can thus be influenced. On actuation of a gear selector the volume of the forward stroke chamber is used for example for the pressure build-up in a gear selector, and at the same time the volume is displaced from the second chamber of the gear selector to the return stroke chamber of the double-acting piston unit 34.
 FIG. 4b shows a further embodiment of the shift gearbox according to the invention, which is also designed as a double-clutch gearbox. The pressure supply is implemented in the form of a dual-action reciprocating piston.
 Preferably the piston 34 e is in a middle position before the start of its travel, since it cannot be predicted whether first gear or reverse gear is engaged when the vehicle is started. Thus, for both manoeuvres a corresponding volume is present in the chambers 34 b and 34 c for actuating a gear selector and a clutch. Alternatively, the piston 34 e would have to be moved to the correct position with the valves 50 and 51 open.
 Contrary to the embodiment shown in FIG. 4, in each case the 2/2-valves 24 a, 24 b, 24 c, 24 d can be dispensed with. It is important in this connection that one chamber of the dual-action reciprocating piston is connected respectively to one chamber of each gear selector. Through this separate arrangement of the connecting lines HL1 and HL2, a gear change can be executed as follows. For a gear change from first to second gear, first of all second gear must be engaged. For this, the piston 34 a is moved to the left, whereby volume is displaced to the gear selector 2/4. The valve 68 b is in this case also opened to allow the shift of the gear selector 2/4, since otherwise the gear selector 2/4 would be hydraulically locked. As soon as second gear is engaged, the piston 34 e is shifted further to the left and volume is displaced via the 2/2-way valve 20 to the clutch C2 19, which leads to the closure of the clutch C2 19. At the same time the clutch C1 must be opened. For this, the 2/2-way valve 9 is opened and the volume is displaced from there either to the increasingly larger piston chamber 34 b, or alternatively the valve 51 is additionally opened, whereby the pressure in the reservoir can be reduced. After the clutch C2 is completely closed and the clutch C1 is opened, the next gear can be preselected. In order now to engage third gear, the dual-action reciprocating piston 34 is moved to the right, whereby volume is conveyed through the open valve 68 a to the chamber 38 a of the gear selector 37 a. The volume from the chamber 39 a of the gear selector is at the same time conveyed to the chamber 34 c of the dual-action reciprocating piston.
 FIG. 5 shows a cross-sectional representation through a possible embodiment of a pressure supply unit 3, in which a spindle 62 is driven by an electric motor (stator 65, rotor 66), in particular a BLC motor. The electric motor is arranged substantially in the housing half 67.
 The spindle 62 is connected to the rotor 66 and drives the axially displaceably mounted spindle nut 63, which is arranged in a torque-proof manner with its collar in the second housing part 60. The spindle nut 63 forms as it were with its front end 64 the piston of the piston-cylinder unit. The working chamber 3 b is delimited by the first housing part 60 and the piston 64. Seals 69 ensure that no fluid can move in the direction of the electric motor 65, 66. A trapezoidal spindle 63 made of plastic is preferably used, since only low pressures have to be built up for a shift gearbox and thus only small forces are exerted. The working chamber 3 b is connected to the hydraulic line HL, not shown, via the channel 68.
 The spindle nut 63 of the pressure supply unit according to FIG. 5 can also drive a dual-action reciprocating piston via a push rod, which hermetically divides the working chamber 3 b into two working chambers, wherein a partition, which is penetrated by the push rod, must then also be introduced between the spindle nut and the working chamber 3 b. In addition to the channel 68 another channel must then be provided in the housing 60, which connects the second formed working chamber to the hydraulic lines.
LIST OF REFERENCE NUMERALS
- 1 EC motor
- 2 shift gearbox
- 3 piston-cylinder unit
- 4, 4 a check valve with hydraulic connection to the reservoir 65
- 5 a pressure sensor
- 6 reservoir
- 7 clutch unit 1
- 8 return spring clutch unit 1
- 9 2/2-way valve
- 10 gear selector unit 1 (rotational movement)
- 10, 10 b piston-cylinder units of the gear selector 10
- 11 gear selector unit 2 (linear movement)
- 12 gear mechanism 1 rotation (3 positions)
- 13 gear mechanism 2 translation (3 positions)
- 14-17 2/2-way valve
- 19 clutch unit 2
- 20 2/2-way inlet and outlet valves
- 21 a-d check valve
- 22 a-d check valve
- 23 a-d inlet valve
- 24 a-d inlet valve
- 25 outlet valve
- 26 outlet valve
- 27 a gear selector (1/3 gear)
- 27 b gear selector (2/4 gear)
- 27 c gear selector (5/7 gear)
- 27 d gear selector (6/R gear)
- 28 a-d left piston-cylinder unit of the gear selector 27 a-d
- 29 a-d right piston-cylinder unit of the gear selector 27 a-d
- 31 2/2-way valve
- 32 outlet valve
- 33 pressure sensor
- 34 double-acting piston-cylinder unit
- 34 a dual-action reciprocating piston
- 34 b, 34 c working chambers of the piston-cylinder unit 24 with dual-action reciprocating piston 34 a
- 34 d, 34 e piston surfaces of the dual-action reciprocating piston 34
- 35 outlet valve
- 26 check valve
- 37 a-d gear selector
- 38 a-d first working chamber of the piston-cylinder unit of the gear selector 37 a-d
- 39 a-d second working chamber of the piston-cylinder unit of the gear selector 37 a-d
- 40 a-d piston of the piston-cylinder unit of the gear selector 37 a-d
- 41 a-d piston rod of the piston-cylinder unit of the gear selector 37 a-d
- 42 a-d 2/2-way inlet and outlet valve for first working chamber 38 a-d
- 43 a-d 2/2-way inlet and outlet valve for second working chamber 39 a-d
- 46 2/2-way valve
- 50, 51 2/2-way valve
- 60 first housing part
- 61 working chamber
- 62 spindle
- 63 spindle nut also forms the piston
- 64 collar of the spindle nut for torque bracing
- 65 stator
- 66 rotor
- 67 second housing part
- 68 a-d 2/2-way inlet and outlet valve for gear selector 37 a-d
- 69 a-d 2/2-way inlet and outlet valve for gear selector 37 a-d
- 70 angle of rotation sensor for motor commutation
- 71 position transducer of the clutch actuator C1
- 72 pistons of the clutch actuator C1
- HLxxx hydraulic line
- HL1, HL2 main hydraulic line
- HLR1,2 hydraulic feedback of the pressure regulator unit
- HLR3,4 hydraulic feedback of the gear selector unit
- P1, P2 sensors, in particular position sensors, e.g. Hall switch