Valve gear for internal combustion engines

Claim 1

Valve gear for an internal combustion engine, said valve gear including a first cam mounted to rotate about a first axis, a second cam mounted to rotate about a second axis which is substantially parallel to said first axis, said first and second cams having respective actuating profiles, a phase-change mechanism arranged selectively to vary the phase of one of said cams relative to the other of said cams, a valve member movable along a valve axis, biassing means urging said valve member in a first direction along said valve axis and a cam follower which has first and second contact surfaces, said contact surfaces being arranged to be engaged by the actuating profile of said first and second cams, respectively, and being arranged to transmit movement from said cams to said valve member being movable with respect to said valve member, said actuating profile of said first cam including an ascending portion to move said valve member in a second direction opposite to said first direction and a descending ramp to control movement of said cam follower with respect to said valve member, said actuating profile of said second cam including a descending portion to control movement of said valve member in said first direction and an ascending ramp to control movement of said cam follower with respect to said valve member, the gradient of said ascending ramp and of said descending ramp being substantially the same over at least part of their length and the phase of said two cams being such that the times for which said ascending and descending ramps contact said follower at least partially overlap at a time during which said valve member is stationary in a closed position wherein said cam follower moves with respect to said valve member.