Drivetrain

1. A drivetrain comprising a friction clutch for decoupling a transmission from an internal combustion engine having an input part, at least one output part that can be decoupled from the input part and at least one disengagement device, the at least one output part in the force-free state being decoupled from the input part and, by means of the at least one disengagement device, being brought into frictional engagement with the input part, and the at least one disengagement device being formed of a master cylinder and a slave cylinder that is in operative connection with the master cylinder via a hydraulic line, wherein in the hydraulic line between the master cylinder and the slave cylinder is a pressure relief device that sets back a pressure applied between the master cylinder and the slave cylinder when actuated, wherein the pressure relief device is operable by the driver via an actuating device.

2. The drivetrain as described in claim 1 , wherein the friction clutch is implemented as a dual clutch having an input part and output parts that are each rotationally connected to a transmission input shaft, in each case a disengagement device actuating an axially displaceable annular part that is rotationally connected to the input part.

3. The drivetrain as described in claim 2 , wherein the two disengagement devices are each provided with a pressure relief device.

4. The drivetrain as described in claim 3 , wherein the two pressure relief devices are operable via a single actuating device.

5. The drivetrain as described in claim 1 , wherein two pressure relief devices for a dual clutch are mounted within one housing.

6. The drivetrain as described in claim 1 , wherein at least one pressure relief device is integrated in a master cylinder or slave cylinder.

7. The drivetrain as described in claim 1 , wherein the actuating device is a selection lever for selection of the drive mode of the transmission by the driver in operative connection with a pressure relief device.

8. The drivetrain as described in claim 7 , wherein the pressure relief device is operated as a function of the position of the selection lever.

9. The drivetrain as described in claim 8 , wherein an operation of the pressure relief device occurs at least in the drive mode Neutral (N) and/or Park (P).

10. The drivetrain as described in claim 8 , wherein on operation of the pressure relief device does not occur at a selection position Drive (D) or Reverse (R) or in a manual drive mode (+, −).

11. The drivetrain as described in claim 8 , wherein the operation of the pressure relief device is delayed for 0.1 to 1 s when there is shifting between the drive modes Drive (D) and Reverse (R) when passing through the selection lever position for Neutral (N).

12. The drivetrain as described in claim 8 , wherein operation of the pressure relief device is delayed after selection of the drive mode Neutral (N) by a specified delay time.

13. The drivetrain as described in claim 12 , wherein the delay time lies in the range between 0.1 and 1 s.

14. The drivetrain as described in claim 7 , wherein the operative connection is a Bowden cable connected to the actuation device.

15. The drivetrain as described in claim 7 , wherein the operative connection is an electrical operative connection.

16. The drivetrain as described in claim 15 , wherein the operative connection acts on an electrically actuated valve that is in connection with a switch provided on the actuation device.

17. The drivetrain as described in claim 15 , wherein the electrical operative connection is in connection with an electrical valve that directly forms the pressure relief device.

18. The drivetrain as described in claim 15 , wherein the electrical operative connection actuates the pressure relief device in the de-energized state.

19. The drivetrain as described in claim 7 , wherein the operative connection is an actuated pin that is connected to an electrically operated switch that is connected to the actuation device.

20. The drivetrain as described in claim 1 , wherein the pressure relief device has an input-side feed and an output-side discharge and between them a chamber is provided with a dead volume that is expandable via an axially displaceable piston that is sealed off from the chamber against the action of an energy storage device if the force on the piston due to the pressure in the pressure line is greater than the axial force of the energy storage device acting on the piston, and the piston with regard to its axial displacement is released from the operative connection.