Abstract:Reducing fuel consumption is a prime objective in the automotive industry in order to meet regulatory and customer demands. Variable valve actuation offers many opportunities for improving the spark ignition engine's performance in areas such as fuel economy and pollutant emissions. Our studies revealed that the ability to control maximum intake valve lift does indeed offer the ability to control intake air mass, but also has the added benefit that it improves the fuel-air mixing process thanks to an increased turbulence, caused by the increased intake flow velocity. This is particularly important at idle and low part loads when low maximum lifts are to be used for improving the fuel economy or for achieving the required power. The paper focuses on the experimental results obtained when approaching idle operation with different intake valve laws. Results indicating the potential of using low intake valve lift for fuel economy and cyclic dispersion improvement are presented in this paper.

This paper presents an original continuously variable intake valve lift mechanism designed for the automotive spark ignition engines. The paper first presents the analytical kinematic synthesis of the variable intake valve lift mechanism, which consists in finding out the required intake cam profile starting from an imposed intake valve lift law. Then, by using the obtained cam profile, a computer-aided kinematic analysis of the variable intake valve lift mechanism is performed using commercial CAD software. The accuracy of the motion conversion performed with CAD software is validated by checking the degree of correlation between the resulted intake valve lift law and the imposed law used when performing the analytical synthesis. The goals of the kinematic analysis are first to find the partial laws of the intake valve lift, corresponding to the engine part loads and second, to find the transfer functions of the elements used to command the mechanism, i.e. the dependency between these elements and the intake valve lift law. The designed variable intake valve lift mechanism is successfully operated on an engine prototype and proved its energetic improvement potential.