Comparison of Different Kinematic Solutions for Mechanical Continuously Variable Valve Lift Systems

Abstract

Variable valve timing represents one of the key technologies in further development of automotive engines. Different valve lift profiles and variable valve timing in the engine operation map offer the flexibility to better meet the load specific engine requirements regarding the intake flow conditions, the exhaust gas control and the efficiency of load exchange, mixture preparation and combustion. Mechanical solutions for continuously variable valve lift and timing are based on different principles such as: - systems, which perform the variable valve lift and timing by superposition of the opening and closing flank of two continuously rotating cams - systems, which translate a fixed cam profile into a variable valve movement by varying the position of an oscillating transmission link This paper describes the specific kinematics of different mechanical principles and illustrates the resulting properties and restrictions considering lift/event-ratio, phasing of the opening event, minimum and maximum valve lift, valve acceleration, as well as precision requirements. The thermodynamic characteristics like benefits in full-load performance, reductions in pumping losses, support of mixture preparation and idle quality will be discussed on the base of load exchange calculations as well as test bench results.