Variable timing valve operating mechanism, eg for i.c. engines

摘要

The mechanism comprises a cam 12, a rocker 20, which may operate a pair of valves, and a pivotally-mounted lever 50 having points of contact with both the cam 12 and the rocker 20. Adjustment means which comprise a shaft 24 and eccentric 53 are operable to move the axis 52 of the lever 50 relative to the axes 16,22 of the cam 12 and of the rocker 20 so that the point of contact between the cam 12 and the lever 50 is shifted and hence the timing of the valve relative to the rotation of the cam can be varied. The lever 50 comprises two cam followers 60,62 which are arranged to engage the cam 12 at different orientations relative to the axis 16 of the cam. Cam follower 62 is mounted on a carriage 70 which can be pivoted by an actuator 72. At low engine speeds, only follower 60 engages the cam 12 but at higher speeds the actuator 72 also presses follower 62 against the cam to hold the valve open for longer.