Variable valve timing lift device

Abstract

A variable valve timing and lift mechanism consists of low and high speed cams provided in phase on the camshaft of an overhead camshaft engine, the high speed cam having larger lift than the low speed cam although the base circle diameter of the two is the same. The low speed cam is coupled to port opening/closing valve(s) via a direct-driven tappet and the high speed cam is coupled to the same valve via a piston-type tappet consisting of a pair of pistons sealed in a support with an oil chamber interposed in between. The oil chamber is connected to the lubricating oil circuit of the engine by an oil passage provided with a control valve. This variable valve timing and lift device with the so-called direct attack-type dynamic valve mechanism, where the cam drives the valves directly without using any rocker arm and connecting mechanism, solves the problems created by the inability of the rocker arm, etc. to keep pace with the valve at high speed because of inadequate rigidity of the dynamic valve system; it yields high output at both low and high speeds; it does not suffer from lift loss; it can correctly select valve timing and valve lift in conformity with the high or low speed of the engine; and it has small valve acceleration.