Importance

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Abstract

Variable valve lift in an engine is achieved by varying the location of the pivot of the rocker arm or finger follower. The pivot shaft and rocker arm or finger follower have engaging teeth that mate. The pivot shaft rolls across a stationary rack of teeth to change the ratio of valve lift to cam lift, while, for a given position of the pivot shaft, preventing the pivot shaft from rotating. The pivot shaft rides in a bearing block whose movement is constrained by a bearing guide of the same shape as the stationary rack. The shape of the toothed rack on the rocker arm or finger follower is part of a circular cylinder whose radius is determined by the position and angles of the cam and valve. The shape of the stationary rack and bearing guide may vary from that of the rocker arm to allow for altered adjustment clearance with different valve lifts. The relationship between adjustment clearance and pivot shaft position yields controlled variation of phase and duration. At full lift the clearance would be within usual limits, while at partial lift reduced contact velocities allow greater clearance without increasing idle noise, and thus opening of valves may be delayed, and closing advanced.

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First Claim