Development of a multi-body simulation model of a Winston Cup valvetrain to study valve bounce

Abstract

Valvetrain dynamics is an important factor in the development of engines that operate at high rotational speeds. Valve bounce, which occurs at different speeds in the operating range of the engine, can severely limit the ability of the engine to develop peak power owing to the inability of the valves to seal appropriately. The objective of the work reported in this paper is to develop a model of a Winston Cup (WC) engine valvetrain that can predict the dynamics of the valvetrain at high speed. This model can then be used to develop a more complete understanding of the valvetrain motion and to aid effective design of valvetrains. The model is developed in the ADAMS environment. It contains a flexible pushrod, a flexible rocker arm and lift-off among all components, the mass of the valve springs, and a fluctuating rocker arm ratio. Also included in the model is damping in the valve spring and friction at the rocker arm pivot. Finite element analyses (FEAs) were conducted in order to obtain accurate data for pushrod and rocker arm stiffnesses, and to obtain the frequency response characteristics of the valve springs. The model data represent an actual engine used in WC racing. The model is run at different speeds to determine its dynamic characteristics and to verify its response with models developed previously by other researchers. Valve bounce predictions from the simulation model are compared with measured data from a Spintron test of an identical valvetrain configuration. The results indicate that the model accurately predicts the speeds of maximum valve bounce.