A computer model was developed to study the dynamic behavior of a pushrod/hydraulic tappet configured valve train. For accurate simulation, the model had 21 degrees of freedom, nine of which were used to model the valve spring. The model's damping values, and the stiffness of the hydraulic tappet, were empirically derived by correlating the model with experimental data. To achieve excellent correlation, two of the model's dampers had to be non-linear. This study did not include the impact of cylinder pressure.
The computer model was used to study component loads and stresses over a broad engine speed range. The valve train was found to behave as a linear mechanical system with two significant modes of vibration. The harmful consequences of strongly exciting these resonant modes is covered, as well as ways to minimise these resonant responses.