Patent ID: 7296669

Claim:
An actuator for the control of a friction clutch in the drive train of a motor vehicle, the actuator comprising: a cylinder/piston unit generating a contact pressure for the friction clutch; a reversible electric motor/pump unit ( 3 ) selectively providing a pressure medium; and a self-regulating valve unit ( 2 ) fluidly coupling the cylinder/piston unit and the reversible electric motor/pump unit such that the friction clutch is controlled by actuating the motor/pump unit ( 3 ), the self-regulating valve unit ( 2 ) having a dump valve ( 8 ; 8 ′; 28 ; 38 ) having a sleeve ( 10 ; 10 ′) and a slide ( 12 ; 12 ′; 32 ) disposed within the sleeve, the dump valve further having a first opening ( 11 , 11 ′) through which pressure medium from the cylinder/piston unit ( 1 ) can flow to a sump, the slide ( 12 ; 12 ′; 32 ) being movable between a first position exposing the first opening ( 11 ; 11 ′) and a second position concealing the first opening ( 11 ; 11 ′), the slide being spring biased in to the first position to permit the flow of pressure medium from the cylinder/piston unit to the sump when the reversible electric motor/pump unit is deactivated, the slide being positionable in the second position in response to positive pressure of the pressure medium from the reversible electric motor/pump unit and positionable in the first position in response to negative pressure of the pressure medium from the reversible electric motor/pump unit; and a nonreturn valve ( 9 ; 29 ) fluidly coupling the cylinder/piston unit and the reversible electric motor/pump unit, the nonreturn valve being movable between a closed position and an opened position, the nonreturn valve being biased in the closed position, the nonreturn valve permitting flow of pressure medium therethrough only from the reversible electric motor/pump unit ( 3 ) to the cylinder/piston unit ( 1 ) in the opened position.