Intake and/or exhaust-valve timing control sytem for internal combustion

Abstract

A valve timing control system for an internal combustion engine is provided. This system includes a sprocket assembly in driven connection with a crankshaft of the engine, a camshaft assembly disposing cams for opening and closing intake- and/or exhaust valves, and a ring gear assembly functioning as a piston slidably disposed between the sprocket assembly and the camshaft assembly for modifying a phase angle relation between the sprocket assembly and the camshaft assembly. The system further includes first and second pressure chambers for exerting fluid pressure on the ring gear assembly to be displaced over a range of first, second, and third positions which correspond to phase angle relations respectively suitable for low, intermediate, and high engine load levels. The ring gear assembly is responsive to fluid pressures in the first and second pressure chambers both below a threshold valve to be arranged at the first position, responsive to elevation in the fluid pressure in the first pressure chamber above the threshold value to be arranged at the second position, and responsive to elevation in the fluid pressures in the first and second pressure chambers both above the threshold value to be arranged at the third position.