FR3084710A1 - HYDRAULIC ACTUATION SYSTEM WITH MANUAL AND AUTOMATIC CONTROLS OF A CLUTCH DEVICE, PARTICULARLY FOR A MOTOR VEHICLE - Google Patents

Abstract

The invention relates to a hydraulic actuation system in particular of a clutch device, in particular for a motor vehicle, capable of operating in manual control mode or in automatic control mode of the clutch device, which comprises, for manual control, a clutch pedal (2) operable by an operator, a hydraulic sending cylinder (4) intended to cause a transfer of hydraulic fluid, under the control of the clutch pedal to a receiving cylinder (17) of actuation of the clutch device (1), and, for automatic control, an electric pump unit (3) intended for the transfer of hydraulic fluid to the receiving cylinder. The system is characterized in that it comprises a hydraulic actuator cylinder (22) which comprises a main internal piston (23) which ensures the transfer of the hydraulic fluid to the receiving cylinder, either under the control of the clutch pedal (2) when the system operates in manual mode, or under the control of the electropump group (3) when the system operates in automatic mode. The invention can be used for motor vehicles.

Description

The invention relates to a hydraulic actuation system in particular of a clutch device, in particular for a motor vehicle, capable of operating in manual control mode or in automatic control mode of the clutch device, which comprises , for manual control, a clutch pedal operable by an operator, a hydraulic transmitter cylinder intended to cause a transfer of hydraulic fluid, under the control of the clutch pedal, to a cylinder actuating receiver of the device clutch, and, for automatic control, an electric pump unit intended for transferring hydraulic fluid to the receiving cylinder.

A clutch actuation system of this type is already known from document WO 2015191308. This known system has the major drawback that it includes a valve for selecting the control mode of the clutch device, which must be perfectly watertight, otherwise the clutch cannot be controlled properly with the pedal or remain open without permanent operation of the system. However, such a perfectly sealed valve is difficult to produce.

The invention aims to provide a system of the type indicated above, which ensures satisfactory operation of the system.

To achieve this object, the clutch actuation system according to the invention is characterized in that it comprises a main actuator hydraulic cylinder, which comprises an internal piston which ensures the transfer of the hydraulic fluid to the receiving cylinder, either under the control of the clutch pedal, when the system is operating in manual mode, or under the control of the electric pump unit, when the system is operating in automatic mode.

According to a characteristic of the invention, the main piston allows the transfer to the receiving cylinder of the fluid emitted by the emitting cylinder when the system operates in manual mode, or by the displacement of a secondary piston of the actuator cylinder, by fluid coming from the electric pump group.

According to another characteristic of the invention, the main and secondary pistons are located in the actuator cylinder axially separated from one another and delimit in the cylinder three chambers of variable volume by the displacement of the pistons, namely an outlet chamber intended to contain the fluid to be transferred to the receiving cylinder, a chamber for receiving the fluid from the electric pump group and an intermediate chamber defined between the two pistons.

According to yet another characteristic of the invention, each piston comprises a peripheral seal adapted to prevent the passage of fluid from one side of the piston to the other.

According to yet another characteristic of the invention, in the rest state of the system, with the clutch device closed, the secondary piston bears against a stop inside the actuator cylinder so that the fluid pump receiving chamber has its minimum volume, and in that the main piston is in abutment against an axial projection of the secondary piston.

According to yet another characteristic of the invention, the connection between the emitting cylinder and the actuating cylinder comprises at least one orifice opening into the intermediate chamber, near the main cylinder, when the latter is in its position of rest.

According to yet another characteristic of the invention, a reservoir is associated with the outlet chamber of the actuator cylinder, which is intended to ensure the filling of this chamber with hydraulic fluid.

According to yet another characteristic of the invention, during a manual control of the clutch device by pressing on the clutch pedal, the main piston is moved by the hydraulic fluid discharged from the emitting cylinder and the fluid which acts on the piston of the receiving cylinder is the fluid discharged from the chamber of the actuating cylinder.

According to yet another characteristic of the invention, the connection between the emitting cylinder and the actuating cylinder comprises a second orifice which opens into the outlet chamber, near the main piston, when the latter is in its position rest, and in that the surface of the second orifice is greater than the surface of the first orifice, so as to ensure the immobility of the main piston and reduce the wear of its seal when the operator presses on the pedal in order open and check the clutch device.

According to yet another characteristic of the invention, in the case of manual control of the clutch device by pressing on the clutch pedal, the secondary piston is in its rest position bearing on a stop, the main piston is in abutment against an axial projection of the secondary piston and the emitting cylinder is in communication with the intermediate chamber of the actuator cylinder to cause the displacement of the main piston and the transfer through it of the hydraulic fluid in the receiving cylinder .

According to yet another characteristic of the invention, the actuator actuator comprises a sensor for the position of the main piston.

According to yet another characteristic of the invention, the main piston is provided with a magnet allowing the establishment of the position of the piston in cooperation with the position sensor.

According to yet another characteristic of the invention, the system comprises a two-position solenoid valve, which is normally open interposed between the output of the actuator cylinder and the receiver cylinder.

According to yet another characteristic of the invention, the solenoid valve is controlled by the electronic computer integrated in the electric pump group.

According to yet another characteristic of the invention, the second orifice is adapted to reduce the dead travel (x) of the main piston.

According to yet another characteristic of the invention, in the absence of pressing on the pedal, in order to achieve an automatic opening of the clutch device, the electric pump group causes the displacement of the secondary piston and of the main piston in abutment on a axial projection of the secondary piston in order to move the appropriate volume of fluid from the chamber to the receiving cylinder.

According to yet another characteristic of the invention, when the clutch device is open and the solenoid valve is in its position for interrupting the communication between the actuating cylinder and the receiving cylinder, the secondary piston can be moved by the electric pump group so that it creates a pressure in the intermediate chamber which acts on the piston of the emitting cylinder so that it opposes the pedal an effort identical to the effort resulting from pressing on the pedal in the case of manual control.

The invention will be better understood, and other objects, characteristics, details and advantages thereof will appear more clearly in the explanatory description which follows, made with reference to the appended drawings given solely by way of example illustrating a embodiment of the invention and in which:

- Figure 1 is a diagram illustrating the clutch actuation system according to the invention in the closed state of the clutch;

- Figure 2 is a diagram illustrating an example of the relationship between the EC compressive force exerted on the clutch diaphragm and the stroke x of the piston of the receiving cylinder and dry type clutch characteristic;

- Figure 3 is an axial sectional view of the actuator cylinder according to the invention;

- Figures 4A to 4D are views illustrating the actuator cylinder in two operating phases (at rest 4A and 4C or actuated 4B and 4D);

- Figure 5 is a schematic view, on a larger scale of the part indicated in V in Figure 3;

- Figure 6 is a perspective view of the system according to the invention, showing the various components thereof in the assembled state;

- Figure 7 is a diagram of the system according to the invention, showing it during a clutch pedal operation, with the electric pump unit stopped and the solenoid valve open;

- Figure 8 is a diagram of the actuation of the actuator cylinder for the automatic opening of the clutch;

- Figure 9 is a diagram of the regulation loop of the clutch actuator cylinder for the system according to the invention;

- Figure 10 is a diagram illustrating the clutch in the state kept automatically open;

- Figure 11 is a diagram illustrating the end of the automatic clutch opening mode without depressing the clutch pedal;

- Figure 12 is a diagram illustrating the reproduction of the pedal force by the actuator, the clutch being kept open by the solenoid valve;

- Figure 13 is a diagram illustrating the end of the automatic clutch opening mode with depressing on the clutch pedal;

FIG. 14 is a diagram illustrating a first variant of the system according to the invention, and

- Figure 15 is a diagram illustrating a second variant of the system according to the invention.

Figure 1 illustrates, schematically, a hydraulic actuation system of a clutch device, in particular for a motor vehicle, according to the invention, that is to say a so-called parallel clutch system, allowing control of the clutch device, either manually by actuation by an operator of a clutch pedal, or automatically using an electric pump group controlled by an integrated electronic computer, according to certain operating parameters emitted by the vehicle computer.

In Figure 1, which shows the system in the rest state, with the clutch device closed, the clutch device is designated by the reference 1, the references 2 and 3 respectively designate the pedal clutch and the pump set. With the pedal 2 is associated a hydraulic cylinder 4 emitting a hydraulic fluid, which comprises a piston 5 which is actuated by the pedal 2, and a sensor 6 of the position of the piston. The cylinder is associated with a hydraulic fluid reservoir 7. The electric pump group 3 includes a positive displacement pump 10, an electric motor 11 for driving the pump in rotation, with the integrated electronic computer. The pump sucks in hydraulic fluid, from a reservoir 12.

The clutch device 1 which comprises, in a manner known per se a flywheel 14 and a clutch disc 15 is actuated by a hydraulic receiving cylinder 17 whose piston 18 moves the clutch disc 15 under the effect of the hydraulic fluid sent into the chamber 19 of the jack against a spring 20 constituting the clutch diaphragm. This diaphragm is intended to keep the clutch closed when the pedal is in its rest position.

According to an essential characteristic of the invention, the system comprises a hydraulic actuator clutch actuator 22 illustrated in FIGS. 3 to 5, which comprises two separate internal pistons, namely a main piston 23 and a secondary piston 24. The main piston has the function of sending hydraulic fluid to the receiving cylinder 17 to control the opening of the clutch device 1, through a two-position solenoid valve 26, against a return spring 21 disposed in the chamber 25 of the cylinder delimited between the piston 23 and the end on the solenoid valve 26. The hydraulic control solenoid valve with piloted valve, normally open, is located at outlet 44 of the chamber 25 in the hydraulic connection connecting the actuator cylinder 22 to the receiving cylinder. It allows, in its interrupted communication position, to keep the clutch open and the pump unit to stop. In its rest position, the main piston is in abutment against an axial projection 27 of the secondary piston 24 when the latter is in its rest position in which it is in abutment against a stop 28 provided on the internal wall of the other end of the jack, on the electric pump side. Between the piston 24 and this end of the jack is delimited a chamber 29. This chamber 29 is in fluid communication with the outlet of the pump 10, so that the piston is axially displaceable in the jack when the pump is activated and a pressure is created at the outlet of the pump. This pressure is generated by a restriction 31 placed in the hydraulic connection between the pressure outlet of the pump and the reservoir 12. The pistons 23 and 24 define between them an intermediate chamber 33. The chambers 25, 29 and 33 are of course of volume variable by the displacement of the pistons. It is important to note that each piston is provided on its peripheral face with a seal. The seal of the main piston 23 has the reference 35 and that of the secondary piston 24 the reference 36. These seals have the function of guaranteeing the hydraulic seal on either side of the piston, between the peripheral surface of the latter and the internal face of the cylinder body. The main piston 23 further carries on its circular face on the side of the secondary piston 24 a magnet 38 which, in cooperation with a position sensor 40 located outside the cylinder, makes it possible to know the position of the main piston 23 in the cylinder . The information on the positioning of this piston will make it possible to know and control the movement of the clutch when the electropump group is activated, as will be explained below. The dimensions of the actuator hydraulic cylinder, of these internal pistons and of these chambers must take into account the dispersions of the system (temperature, expansion of the pipes, wear of the disc, etc.) in order to ensure the transfer of the volume of oil necessary for movement. of the receiving cylinder. Whatever the conditions of use of the vehicle, the volume of the chamber 25 of the actuator hydraulic cylinder 22 must in particular be at least greater than the maximum necessary volume of the chamber 19 of the receiving cylinder

17.

The actuator cylinder is also in fluid communication with the transmitter cylinder 4. To this end, the cylinder body has two hydraulic ports of a hydraulic connection 41 to the transmitter cylinder, which open on either side of the main piston seal 23, in the jack, when the piston is in its rest position, namely an orifice 42 opening into the chamber 25 on the side of the solenoid valve 26 and an orifice 43 opening into the chamber 33 delimited between the two pistons.

It should be noted that, to limit the risk of wear-related failure, the hydraulic ports 42 and 43 are dimensioned so as to ensure the immobility of the main piston when the clutch pedal is actuated. , as a function of the forces of the seals and the stiffness of the spring 21. As shown in particular in FIG. 5, the section S1 of the hydraulic orifice 42 towards the chamber 25 is greater than the section S2 opening into the intermediate chamber . Thus, in the case of actuation of the pedal on the part of the driver of the vehicle, in order to open the clutch, the piston 23 remains stationary in its rest position. The illustrated geometry of the openings opening into the jack also makes it possible to limit the dead travel indicated at x in FIG. 5. In FIGS. 3 and 4A to 4D, we see, in addition to what has already been mentioned above, the outlet to the valve 26, which is designated by the reference 44 and is located on the lateral side with respect to the connection to the emitting cylinder 7. The cylindrical body of the cylinder is closed at the opposite end of the outlet 44 by a plug 46. The connection to the electric pump unit is noted 48.

Figure 6 shows the various components of the system according to the invention, assembled so as to form a compact unit and a small footprint. Reference 56 designates the electronic housing. FIG. 1 shows electrical connections, namely a connection a to an energy source 50 such as a battery, for supplying electric power to the motor 11, a connection b for exchanging information between the vehicle computer denoted 52 and the electronic computer 54 integrated into the engine, an integrated connection ç between the engine 11 and the position sensor 40 of the main piston 23, an integrated control connection d between the engine and the solenoid valve 26, a connection e connecting the computer 52 of the vehicle and the position sensor 6 of the emitting cylinder 7.

The operation of the system will be described below in three distinct situations of use of the clutch control.

The first situation is the case of an operation of the clutch pedal by the operator, that is to say the driver of the vehicle, for example, when changing the gearbox ratio. clutch / clutch speeds, without actuation of the electric pump group or of the solenoid valve 26 which is therefore open. Figure 7 illustrates this situation. Pressing the pedal 2 moves the piston 5 of the emitting cylinder 4, which causes a transfer of fluid to the actuating cylinder 22. Since the electric pump group is stopped, the chamber 29 is therefore without pressure and the secondary piston 24 is in its rest position resting on the stop 28. It will therefore remain stationary, the seal not allowing fluid to pass into the chamber 29 on the pump unit side. The main piston also remains stationary in abutment against the stop 27 of the secondary piston, as indicated above, owing to the fact that the orifice 42 is larger than the orifice 43. The volume of fluid of the emitting cylinder is therefore directly transferred through the chamber 25 of the actuator cylinder to the receiving cylinder 17 which, under the effect of the diaphragm 20 causes an increase in the hydraulic pressure and makes it possible to open the clutch so that there is no longer any transmission of torque between the disc 15 and the flywheel 14. In FIG. 7, the pressure zones of the emitting, receiving and actuating cylinders are indicated in gray. It can be seen that the volume 25 on the outlet side of the jack 22 is filled with a pressurized fluid, like the chamber 33 between the two pistons and the chambers of the transmitter 4 and receiver 17 cylinders.

The second situation is that where the system will proceed to an automatic opening of the clutch, in particular in the absence of support by the driver on the vehicle pedals, such as the clutch, brake and accelerator pedals. An automatic clutch is opened, for example for freewheeling of the vehicle, that is to say so that there is no longer any transmission of the engine torque to the primary shaft of the gearbox of speeds. Figure 8 illustrates the automatic opening of the clutch. The hydraulic pressure zones are indicated in gray, namely the chambers 29 and 25 of the actuator cylinder 22 and the chamber 19 of the receiver cylinder.

In this second situation, after analysis of the signals received from the computer 52 of the vehicle, via the vehicle network, the integrated electronic computer 54 will then trigger a rotation of the engine 11 and therefore of the pump 10. The latter will increase its flow rate and the hydraulic pressure through the restriction 31 in order to move the secondary piston 24. Since the main piston 23 is in abutment against the axial projection 27 of the secondary cylinder 24, the displacement of the latter causes the displacement of the main piston 23 and the latter then moves and transfers pressurized hydraulic fluid to the receiving cylinder 17 through the solenoid valve 26 which is open. The displacement of the secondary piston 24 is ensured by the sealing of its seal which prevents the fluid from passing to the other side of the piston and from going up in the reservoir 7 of the clutch transmitter 4. The sealing ensured by the seal 35 of the main piston 23 makes it possible to move the volume of fluid necessary towards the receiving cylinder 17 and thus open the clutch 1.

The diagram in Figure 9 illustrates the chain of components for controlling the position of the main piston 23 of the actuator 22 depending on the speed of the engine 11 and the position of the main piston detected by the position sensor 40 The diagram in FIG. 9 shows that, to ensure control, the electronic computer 54 receives information on the measured speed of the engine 11 by connection b, information on the position of the main piston 23 by connection ç and certain operating parameters emitted by the vehicle computer (52) via the connection f. The principle of control, with the regulation loops shown in FIG. 9 is described in patent EP 3 279 494 and therefore does not need to be explained here. The only difference lies in the position of the position sensor 40, which is no longer at the receiving cylinder, but at the main piston 23 of the clutch actuator. This new positioning also contributes to simplifying the integration of the system into the vehicle environment. The displacement sensor 40 measures the position of the main piston thanks to its magnet 33 incorporated in the main piston and sends this information to the electric pump group 3 and thus to be able to determine when the volume of fluid strictly necessary to move will be reached to open the clutch. , depending on the control loop.

The invention also takes into account the dead stroke x of the main piston, distance during which a certain amount of fluid can flow to the reservoir 7 of the clutch pedal. As indicated above, this distance is small thanks to the geometry illustrated in Figure 5.

When the position of the main piston 23 of the actuator cylinder is stabilized, thus ensuring a controlled opening of the clutch, the system will then activate the solenoid valve 26 in order to cut the communication between the hydraulic lines on both sides. other of the solenoid valve. This makes it possible, on the one hand, to maintain the pressure, therefore in position, of the piston of the receiving cylinder 17 and, on the other hand, to be able to optionally stop or reduce the speed of rotation of the electric pump unit in order to reduce its consumption. energy. In addition, in the event of a solenoid valve failure, the clutch can remain open by simple actuation of the electropump group.

The diagram in Figure 10 illustrates this mode of operation. In this figure, the zones subjected to hydraulic pressure are indicated in gray. It can be seen that only the receiving chamber 19 of the receiving cylinder 17 is under pressure.

The third situation is the case where it is necessary to close or not close the clutch when it is in the conditions described above of the opening of the clutch, that is to say when the solenoid valve 26 interrupts the communication between the cylinders 22 and 17 or when the electric pump group is activated in order to keep the clutch open by pressurizing and moving the pistons of the hydraulic actuator cylinder.

Depending on the information sent by the vehicle computer 52, the electronic computer 54 integrated into the engine 11 will have to choose between two different control modes. If the information is not intended to move the clutch transmitter, i.e. if the driver only wants to accelerate or brake, the system according to the invention will close the clutch automatically, without causing discomfort to the driver, that is to say smoothly. If the information indicates a displacement of the clutch transmitter, with action of the driver on the clutch pedal, the invention will guarantee both the closing of the clutch, without discomfort for the driver, and ensure a force feedback to the pedal similar to the effort during a manual maneuver as shown in FIG. 7 as will be explained later.

In all other situations, of the operation of the vehicle than that involving the use of the clutch pedal, requiring the closure of the latter, the system is managed automatically. Indeed, the speed of rotation of the electric pump group, always subject to the reading of the position of the main piston 23, will decrease as a function of the information received by the computer from the vehicle computer. The decreasing pressure, the main 23 and secondary 24 pistons will come back to their initial position in abutment in the actuator cylinder, in particular at the end of the race under the effect of the return spring 24, and thus allow the clutch to close. . FIG. 11 illustrates the end of this phase of automatic closing of the clutch. Areas under pressure are shown in gray. It can be seen that the chambers 25 and 29 of the actuator 22 and the chamber 19 of the receiving actuator 17 are under pressure.

In the aforementioned situation where the driver uses the clutch pedal, in the most complex case, two strategies are involved: that where the driver finally decides not to close his clutch and that where he will actually close it (or to skate). When the driver of the vehicle decides to press the clutch pedal without the desire to close it (the clutch being kept open), the actuator actuator 22 of the clutch will only reproduce the effort on the pedal that the driver should feel manually, the clutch remaining held open by the solenoid valve in closed control. Using the signal from the position sensor of the clutch transmitter cylinder 4, the clutch actuator cylinder will then adapt the force, via the hydraulic pressure resulting from the flow passing through the restriction 31, on the secondary piston

24, in order to move it and thus be able to reproduce the same force (by integrating the possible ratio of the sections of the emitting and receiving cylinders) of compression EC such as that exerted on the clutch diaphragm, in accordance with FIG. 2. In this case , the main piston 23 remains stationary since the solenoid valve is in its position for interrupting the communication of fluid between the actuator cylinder and the receiver cylinder, as shown in FIG. 12. The relationship between the force and the stroke to be reproduced is illustrated by the diagram in FIG. 2. This relationship is defined by a target speed recorded or memorized in the computer. Of course, this non-linear force characteristic of dry clutches could, if necessary, be adapted and configured according to user requests from the vehicle.

This operating phase continues as long as the position of the transmitter does not exceed a certain threshold which is a function of the force curve in FIG. 2 In the situation where the driver finally decides to close or to skate its clutch open automatically, that is to say when the position sensor of the emitting cylinder exceeds the previously mentioned threshold value and when the hydraulic pressures are identical between the circuit regulated by the electric pump group and that maintained in pressure on the receiver side clutch, the integrated electronic computer 54 will deactivate the solenoid valve 26 and put the hydraulic connection between the transmitter 4 and receiver 17 cylinders back into communication through the actuator cylinder 22. As the pressures are identical on either side of this actuator, there is no pressure peak likely to disturb the driver by a rise in the pedal via the cylinder é director. FIG. 13 illustrates this phase where the solenoid valve 26 opens, the zones subjected to hydraulic pressure being in gray. It can be seen that the three chambers of the cylinder 22 are under pressure, as well as the working chambers of the transmitter and receiver cylinders.

Therefore, pressing the pedal directly controls the force on the pedal, the speed of the electric pump unit decreases gradually until it comes to a complete stop, thus allowing the secondary piston to return to abutment, that is to say - say in its initial position, in the actuator cylinder. The cylinder spring makes it possible to return the main piston to its original position in abutment against the projection of the secondary piston, that is to say in its dead travel zone where there is no longer any hydraulic pressure applied and which can, therefore, allow a direct hydraulic connection between the transmitter and receiver cylinders. The system then finds itself in the same characteristics as those described in FIG. 7.

It emerges from the above description, that the system according to the invention provides two major advantages for a parallel system, capable of operating in manual or automatic clutch control mode. The system according to the invention makes it possible to maintain a direct hydraulic connection between the clutch transmitter and receiver, on the one hand, and to guarantee an identical feeling of the driver whatever the clutch actuation command, thanks to to a pedal-driven effort recreation control mode.

Figures 15 and 16 illustrate two variants of the system according to the invention. In these variants, there is no longer a direct hydraulic link between the emitter 7 and receiver 17 cylinders, but the possibilities of manual and automatic clutch control are preserved.

In the variant according to Figure 14, there is only one orifice corresponding to the orifice 43 for connection with the actuator between the two pistons 23 and 24. This variant has the disadvantage of the systematic displacement of the main piston and therefore superior wear of the seal in the case of manual actuation with the clutch pedal. Its advantage is to know more regularly, with the analysis of the position of the main piston, the possible evolution of the wear of the clutch.

The variant shown in Figure 15 provides an additional hydraulic connection to an additional tank 55, however with the constraint of being able to locate this tank in the restricted vehicle environment. However, this variant guarantees filling of the chamber 25 of the actuator jack 22, and this even in the case of a fluid leak between the actuator and the receiver jack 17.

The invention has been described above in its application to a clutch device, but it is also applicable to other applications requiring in particular control in position of hydraulic cylinders.

Claims (17)

1. Hydraulic actuation system, in particular of a clutch device, in particular for a motor vehicle, capable of operating in manual control mode or in automatic control mode of the clutch device, which comprises, for manual control, a clutch pedal operable by an operator, a hydraulic sending cylinder intended to cause a transfer of hydraulic fluid, under the control of the clutch pedal to a receiving cylinder actuating the clutch device, and, for controlling automatic, an electric pump unit intended for the transfer of hydraulic fluid to the receiving cylinder, characterized in that it comprises a hydraulic actuating cylinder (22) which comprises a main internal piston (23) which ensures the transfer of the hydraulic fluid to the receiving cylinder, under the control of the clutch pedal (2) when the system is operating in manual mode, or under the control of the electric pump unit (3) when the The system operates in automatic mode. 2. System according to claim 1, characterized in that the main piston (23) allows the transfer to the receiving cylinder of the fluid emitted by the emitting cylinder (4) when the system operates in manual mode, or by moving a secondary piston (24) of the actuator cylinder (22), by fluid coming from the electric pump group (3). 3. System according to claim 2, characterized in that the main (23) and secondary (24) pistons are located in the actuator cylinder (22) axially separated from each other and delimit in the cylinder three chambers of variable volume by the displacement of the pistons, namely an outlet chamber (25) intended to contain the fluid to be transferred to the receiving cylinder (17), a chamber (29) for receiving the fluid from the electric pump group (3) and an intermediate chamber delimited between the two pistons (33). 4. System according to claim 3, characterized in that each piston (23, 24) comprises a peripheral seal (35, 36) adapted to prevent the passage of fluid from one side of the piston to the other. 5. System according to one of claims 2 to 4, characterized in that, in the system rest state, with the clutch device closed, the secondary piston (24) is in abutment against a stop (28) inside the actuator cylinder (22) so that the chamber (29) for receiving the fluid from the electric pump group has its minimum volume, and in that the main piston (24) is in abutment against an axial projection (27) secondary piston (23). 6. System according to one of claims 3 to 5, characterized in that the connection (41) between the emitter cylinder (4) and the actuator cylinder (22) comprises at least one orifice (43) opening into the intermediate chamber ( 33), near the main cylinder (23), when the latter is in its rest position. 7. System according to claim 6, characterized in that a reservoir (55) is associated with the outlet chamber (25) of the actuator cylinder, which is intended to ensure the filling of this chamber with hydraulic fluid. 8. System according to one of claims 6 or 7, characterized in that, during a manual control of the clutch device by pressing on the clutch pedal, the main piston (23) is moved by the hydraulic fluid discharged from the sending cylinder (4) and the fluid which acts on the piston of the receiving cylinder (17) is the fluid discharged from the chamber (25) of the actuating cylinder (22). 9. System according to claim 6, characterized in that the connection (41) between the emitting cylinder (4) and the actuator cylinder (22) comprises a second orifice (42) which opens into the outlet chamber (25), proximity of the main piston, when the latter is in its rest position, and in that the surface (S1) of the second orifice (42) is greater than the surface (S2) of the first orifice (43), so as to ensure the immobility of the main piston (23) and reduce the wear of its seal (35) when the operator presses on the pedal (1) in order to open and check the clutch device (1). 10. System according to claim 9, characterized in that, in the case of a manual control of the clutch device (1) by pressing on the clutch pedal, the secondary piston (24) is in its rest position pressing on a stop (28), the main piston (23) is pressing against an axial projection (27) of the secondary piston (24) and the emitting cylinder (4) is in communication with the intermediate chamber (33) of the cylinder actuator (22) to cause the displacement of the main piston and the transfer through it of the hydraulic fluid in the receiving cylinder (17). 11. System according to one of claims 1 to 10, characterized in that the actuator cylinder (22) comprises a sensor (40) of the position of the main piston (23). 12. System according to claim 11, characterized in that the main piston (23) is provided with a magnet (38) allowing the establishment of the position of the piston in cooperation with the position sensor (40). 13. System according to one of claims 1 to 12, characterized in that it comprises a solenoid valve (26) with two positions, which is normally open interposed between the outlet (44) of the actuator cylinder (22) and the receiver cylinder (17). 14. System according to claim 13, characterized in that the solenoid valve (26) is controlled by the electronic computer integrated in the electric pump group. 15. System according to one of claims 8 to 14, characterized in that the second orifice (42) is adapted to reduce the dead travel (x) of the main piston (23). 16. System according to one of claims 2 to 15, characterized in that, in the absence of pressure on the pedal, to achieve automatic opening of the clutch device (1), the electric pump unit (3) causes displacement of the secondary piston (24) and of the main piston (23) bearing on an axial projection (27) of the secondary piston (24) in order to move the appropriate volume of fluid from the chamber (25) to the receiving cylinder. 17. System according to one of claims 11 to 16 characterized in that when the clutch device (1) is open and the solenoid valve (26) is in its position for interrupting the communication between the actuating cylinder (22 ) and the receiving cylinder (17), the secondary piston (24) can be moved by the electric pump unit (3) so that it creates in the intermediate chamber (33) a pressure which acts on the piston (5) of the cylinder transmitter (4) so that it opposes the pedal (2) an effort identical to the effort resulting from pressing the pedal in the case of a manual control.