Actuation device for a clutch

An actuation device and a method for actuating a clutch, in particular for a hybrid drive, include a master cylinder having an interior separated by a master piston into master and slave oil chambers. The slave oil chamber is connected, via a valve in a first valve position, to a tank line leading to an oil reservoir and in a second valve position, to a pressure line of the oil reservoir. The master oil chamber is connected via a working line to an oil chamber of a slave cylinder and to a compensating tank via a compensating line as a function of the position of the master piston. The compensating tank has a compensating volume which has, at its highest point, an overflow which is connected to the tank line and in its first position the valve connects the slave oil chamber to the compensating tank via a return line.

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates to an actuation device for a clutch, in particular for a hybrid drive, having a master cylinder whose interior space is divided by a master piston into a slave oil chamber and a master oil chamber, with the slave oil chamber being connected by means of a valve to a tank line to an oil reservoir in a first valve position and to a pressure line from the oil reservoir in a second valve position, and with the master oil chamber being connected via a working line to the oil chamber of a slave cylinder and via a compensating line, as a function of the position of the master piston, to a compensating tank.

The invention also relates to a method for actuating a clutch, in particular for a hybrid drive, in which method, to activate a working piston in a slave cylinder which is assigned to a clutch, a slave oil chamber of a master cylinder is filled with oil via a valve which connects the slave oil chamber to a pressure line of an oil reservoir, with the oil being pressed from a master oil chamber of the master cylinder via a working line into an oil chamber of the slave cylinder, and moving the working piston into its activating position, as a result of a movement of a master piston, wherein in order to restore the working piston, the slave oil chamber of the master cylinder is separated from the pressure line and connected to a tank line by means of the valve and is emptied, wherein in the initial position of the master piston, the master oil chamber is ventilated via a compensating tank and a lack of oil volume is compensated.

Hybrid drives have the aims not only of providing a reduction in fuel consumption and pollutant emissions but also of providing an increase in comfort, an increase in performance and zero-emissions driving. To achieve some of these aims, it is necessary to shut down the internal combustion engine and drive under purely electric power (for example: zero-emissions driving). In the parallel architecture of a hybrid drivetrain, it is necessary for this purpose to arrange an additional clutch between the internal combustion engine and the electric machine in order to separate the internal combustion engine from the drivetrain. Said clutch must be activated, corresponding to a driving strategy, as a function of the operating state.

In the case of a hydraulic actuation device of a clutch, such as is known for example from DE 43 09 901A1, use is made of a master cylinder which displaces a defined oil quantity into a slave cylinder. Said slave cylinder finally activates, for example as a central release unit, a clutch. In the master cylinder, in the rear end position, that is to say without activation, a hydraulic connection to a compensating tank is opened up. The system is firstly ventilated via said connection during regular operation, and secondly, an automatic adjustment of the clutch takes place by means of said connection with progressive wear of said clutch. For an automatic actuation of the clutch, a hydraulic controller is required. As a result, two hydraulic circuits are formed: the hydraulic actuation device and the hydraulic clutch activation path with associated compensating tank.

A disadvantage of the known actuation device is that, in the case of an additional clutch, a corresponding amount of additional installation space must be reserved for the entire hydraulic activation means. The additional compensating tank entails a certain amount of additional expenditure, for example regular monitoring of the filling level in the compensating tank. Furthermore, DE 196 33 420 A1 discloses a method and a device for the hydraulic activation of a clutch. Here, the slave oil chamber and the master oil chamber are connected by means of a common proportional valve to an oil reservoir. It is a disadvantage here that, although compensation of the clutch wear is possible as a result of a connection of the master oil chamber via the proportional valve to the tank line of the oil reservoir, operational ventilation is possible at best to a limited extent as a result of the lack of a separate compensating tank.

BRIEF SUMMARY OF THE INVENTION

It is therefore an object of the present invention to propose an actuation device and a method for actuating a clutch which enables as compact and low-maintenance a system as possible. Here, both the functionality of the operational ventilation and also the compensation of the clutch wear should be maintained.

The object with regard to the actuation device of a clutch is achieved in that the valve, in its first position, connects the slave oil chamber via a return line to the compensating tank and in that the compensating tank has a compensating volume which, at its highest point, has an overflow which is connected to the tank line.

Since the compensating tank has an overflow which is connected to the tank line and the slave oil chamber is connected not directly to the tank line but rather via the compensating volume or the compensating tank to the oil reservoir, it is possible for the compensating tank or its compensating volume to be designed to be considerably smaller than in the prior art. As a result of the integration of the compensating tank or compensating volume into a hydraulic circuit, the compensating volume is re-filled with every activation of the master cylinder. At the same time, the functionality of the operational ventilation and also the compensation of the clutch wear are maintained. Furthermore, it is advantageous that the system, upon initial operation or after maintenance work on the hydraulic clutch activation path, can be filled automatically with hydraulic oil by means of repeated activation.

According to a second preferred embodiment of the invention, the master cylinder, the compensating tank and the valve are arranged in a housing and form an actuation unit. In this way, a compact and low-maintenance activation unit is obtained which may be of identical design for both clutches of a hybrid drive.

According to a further preferred embodiment of the invention, the activation unit has an external working connection for connecting to the slave cylinder, an external tank connection and an external pressure connection for connecting to the oil reservoir, and a valve control connection for connecting a control unit to a valve actuation device of the valve. This permits simple assembly or simple exchange of the actuation unit.

According to a further preferred embodiment of the invention, when an equal pressure level prevails on both sides of the master cylinder, the master piston has equal-sized hydraulically acting piston surfaces pointing toward the slave oil chamber and toward the master oil chamber. When different pressure levels prevail on the two sides of the master cylinder, the master piston may have different-sized hydraulically acting piston surfaces pointing toward the slave oil chamber and toward the master oil chamber. Here, the ratio of piston areas on the master and slave sides produces a pressure boost or pressure reduction.

According to a further preferred embodiment of the invention, between the master piston and master cylinder, a seal is arranged in an annular groove in such a way that, in an end position of the master piston when the slave oil chamber is empty, the opening of the compensating line to the master oil chamber is exposed, with a passage which connects the master oil chamber to the opening of the compensating line being formed in a region, which is situated upstream of the seal in the direction of the master oil chamber, between the piston circumference and the adjacent cylinder inner wall. In said position, the master oil chamber is ventilated to the compensating volume, or a differential volume in the master oil chamber resulting from wear of the clutch can be filled with oil from the compensating tank, or compensated.

The seal which seals off the piston with respect to the master oil chamber during a movement may be arranged both in an encircling groove of the master piston and also in an encircling groove of the master cylinder wall.

With regard to the method for actuating a clutch, the object is achieved in that the slave oil chamber, in order to be emptied, is connected by means of the valve to the compensating tank and the latter is filled, with excess oil being supplied back to the oil reservoir via an overflow of the compensating tank via the tank line which is connected to the overflow.

In this way, during the return stroke of the master piston, the actuation oil volume is conducted from the slave oil chamber into the compensating tank and excess oil flows back into the oil reservoir of the hydraulic controller via the overflow. The compensating volume is thus re-filled with every activation of the master piston. At the same time, the compensating tank ensures operational ventilation of the clutch activation path. As a result of the overflow and the connection to the oil reservoir, it is possible for the compensating tank to be designed to be relatively small, that is to say with a smaller compensating volume, while maintaining the same function as the known compensating tanks. The method according to the invention eliminates the need for monitoring the filling level of the compensating tank.

According to a further embodiment of the invention, in the event of the clutch activation path being completely empty, the master cylinder is actuated repeatedly in order to completely fill the master oil chamber and compensating tank. In this way, the system can be filled automatically with hydraulic oil upon initial operation or after maintenance work on the hydraulic clutch activation path.

DESCRIPTION OF THE INVENTION

The actuation device1of a clutch is composed substantially of an actuation unit2, a hydraulic controller3, a control unit4and a slave cylinder5for actuating a clutch.

The actuation unit2is composed of a master cylinder6whose interior space is divided by a longitudinally movable master piston into a slave oil chamber8and a master oil chamber9. Arranged in the master oil chamber9is a pressure spring10which presses the master piston7into its initial position in the slave oil chamber8in the unpressurized state. In the initial position of the master piston7, the master oil chamber is connected via a compensating line11to a compensating tank12. The master piston7has in each case one annular groove13,14pointing in the direction of the slave oil chamber8and in the direction of the master oil chamber9respectively, in each of which annular grooves is held a seal15,16for sealing off with respect to the cylinder inner wall17adjacent to the piston. In addition to the master cylinder6and the compensating tank12, a valve18is also arranged in the actuation unit2. The valve18, when in a first position, connects the slave oil chamber8via a return line19to the compensating tank12.

The compensating tank12has a compensating volume20which, at its highest point, has an overflow21which is connected via a tank connection22to the tank line23to an oil reservoir24of the hydraulic controller3. In a second position, the valve18connects a pressure line26, which is fed from the oil reservoir24or the hydraulic controller3, to the slave oil chamber8via an external pressure connection27of the actuation unit2. The valve18is controlled by a valve actuation device28which is connected via a control line30to the control unit4via an external valve control connection29of the actuation unit2.

The master oil chamber9is connected via an external working connection31of the actuation unit2to a working line33which leads to an oil chamber32of the slave cylinder5.

During a return stroke of the master piston7, the actuation volume is conducted, when the valve18is in the first valve position, from the slave oil chamber8into the compensating tank12via the return line19. Here, the compensating volume20is filled and excess oil is conducted via the overflow21and the tank line23into the oil reservoir24of the hydraulic controller3. The compensating volume20or the compensating tank12is thus refilled with every activation of the master piston7. Here, operational ventilation of the clutch activation path is ensured via the compensating line11. A sufficiently large cross section of the compensating line11as a connection between the compensating volume20and master oil chamber9ensures the function of the automatic initial filling and refilling by means of repeated activation. The size of the cross section of the hydraulic connection or of the compensating line11is selected here such that the oil can flow unforced from the compensating volume20of the compensating tank12into the master oil chamber9.

The filling process begins, when the clutch activation path is completely empty, with the actuation of the master piston7by means of the hydraulic controller3. During the return stroke of the master piston7, the actuation oil volume is displaced from the slave oil chamber8into the compensating volume20and, in the end position of the master piston7, flows through the compensating line11into the master oil chamber9. The next actuation causes the oil which has passed into the master oil chamber9to be displaced into the slave cylinder5. The slave cylinder5is hereby partially filled with oil. Since the actuation unit2is situated at the highest point of the hydraulic system, air from the slave cylinder5is displaced into the master oil chamber9of the master cylinder6during the return stroke. At the same time, the actuation oil is in turn displaced from the slave oil chamber8of the master cylinder6into the compensating volume20or the compensating tank12and flows from here into the master oil chamber9. This is followed by a suitable number of further activations until the slave cylinder5is completely filled in the above-described way, and the master oil chamber9is ventilated and the compensating tank12is completely filled. The adjustment of the clutch (not illustrated) with progressive wear is likewise realized as a result of the connection of the compensating volume20to the external tank connection22. As the clutch lining wears, the clutch can engage progressively further than it can in the new state. This results in a differential oil volume which must be conveyed out of the slave cylinder5in order to fully close the clutch. During the return stroke, the master piston7accommodates the actuating volume defined by the piston diameter and stroke, and when the hydraulic connection is opened up, the differential oil volume escapes into the compensating volume20and from there via the overflow21into the oil reservoir24of the hydraulic controller3.

In the exemplary embodiment ofFIG. 2, the master cylinder6′ has a stepped master piston7′. Here, the ratio of the slave-side piston surface area34′ to the hydraulically acting master-side piston surface areas35′,36′ yields a pressure boost.

In the exemplary embodiment ofFIG. 3, a pilot piston37is positioned upstream of the master piston7″ of the master cylinder6″ in the direction of the slave oil chamber8″. This yields a pressure reduction.

In the exemplary embodiment ofFIG. 4, the master cylinder6′″ has an annular duct38which ensures a sufficient cross section of the hydraulic connection between the compensating tank12and the master oil chamber9′″.

In the exemplary embodiment ofFIG. 5, the master cylinder6″″ has an annular groove39with a seal40for sealing off the master oil chamber9″″ with respect to the master piston7″″. In its unpressurized initial position, the master piston7″″ has a flattened portion41adjacent to the seal40. The flattened portion41is likewise intended to ensure a sufficient cross section of the hydraulic connection between the compensating volume20and master oil chamber9″″.

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