Patent ID: 7007642

Claim:
An hydraulic valve actuator for activating a gas-exchange valve in a combustion cylinder of an internal combustion engine, comprising: a housing; an operating piston accommodated in the housing, the operating piston being axially displaceable within the housing to an upper limit position which closes the gas-exchange valve and to a lower limit position which maximally opens the gas-exchange valve; an intake line; a return line having upper and lower discharge openings that are mutually connected and are disposed in the housing with axial clearance; lower and upper variable-volume pressure chambers axially delimited by the operating piston, the lower pressure chamber being delimited by a first effective area of the operating piston and being situated so as to be permanently acted on by fluid pressure, the upper pressure chamber being delimited by a second effective area of the operating piston and situated to enable alternate pressurization and depressurization via the intake line and the return line, the first effective area being smaller than the second effective area; and a restrictor coupled to the upper discharge opening; wherein the lower discharge opening is disposed in the displacement path of the operating piston such that the lower discharge opening is closed by the operating piston before the operating piston reaches the upper limit position, and wherein the lower discharge opening is axially displaceable relative to the operating piston.