Effects of Mechanical and Pneumatic Return Springs on Valve Train Dynamics

Abstract

The dynamic analysis of a cam transmission derived from an engine valve train is performed in frequency and time domain, by means of a combined lumped-distributed parameters models, capable of predicting the effects of the higher harmonics of the cam lift profile on system performances, in particular as concerning the return spring device. Dynamic stiffness of the transmission in frequency domain and time history of contact force between cam and follower are evaluated, highlighting the limits of the transmission at high-speed camshaft operations caused by the spring behavior. The aim of the study is to developed a comparison on the performances of the cam mechanism working with the original mechanical spring from design or with a pneumatic return device based on a pneumatic spring and a pressure control circuit.