Patent ID: 7117831

Claim:
An internal combustion engine having a crankshaft and a valve mechanism, wherein the valve mechanism comprises a gas exchange poppet valve, a camshaft rotatable in synchronism with the engine crankshaft and having a cam for operating the valve, a valve actuator acting on the poppet valve to open and close the valve, the valve actuator having a part-cylindrical contact surface, a pivot shaft that is moveable relative to the camshaft along a predetermined path in response to rotation of the pivot shaft about its own axis, and an intermediate rocker mounted on the pivot shaft and having a follower acted upon by the cam and a contoured surface that acts on the part-cylindrical contact surface of the valve actuator to open and close the valve in synchronism with the rotation of the cam, wherein movement of the pivot shaft along the predetermined path causes movement of intermediate rocker, and movement of the intermediate rocker in turn causes the valve lift to vary, and said predetermined path is such that, while the cam follower is on the base circle of the cam, the valve actuator remains stationary and a substantially constant clearance is maintained between the contoured surface of the intermediate rocker and the valve actuator during displacement of the pivot shaft along the path.