Automotive Variable Engine Valve Lift Mechanism Controlled by a Hydraulic 3-Step Rotary Actuator

Abstract

Variable valve lift (VVL) system for automotive engines is one of the key technologies to attain improvement of fuel economy and power output and a reduction of emission. This paper presents a highly reliable VVL mechanism controlled by a hydraulic 3-step rotary actuator. A 3-step VVL with a high-, middle- and low-valve lift of the inlet or exhaust valve, is realized by the pivot shifting of an intermediate cam placed between a camshaft and valve tappet. The hydraulic actuator with no electric device is installed in a cylinder head and its rotary positioning generates 3-step rotation of a specially-designed sprag cam. The actuator can work in low supply pressure of 0.2MPa from the engine oil pump and control 3-step angles within the interval in which the valve is at rest during camshaft rotation. This paper describes the analytical simulation model of the VVL system, and the experimental evaluation for the developed VVL mechanism and hydraulic 3-step rotary actuator.