Dynamic Analysis of a Valve-Train System with EHD Contacts

The aim of this paper has been the evaluation of the elasticity constant which characterizes the cam-follower contact in a valve train system. Such parameter has been no more assumed as a constant value, because the system dynamic and lubrication have been considered. In particular, the system dynamic response has been simulated by means of a concentrated parameter model, where: a) the valve-follower contact is modeled by means of constant linear spring and viscous damper; b) the system helical springs are considered as multi-mass springs; c) the cam-follower contact is modeled through a viscous damper and variable linear spring whose value is achieved by evaluating the oil minimum film thickness and the pressure field under EHD conditions. However, such a computation requires some efforts. In fact, an iterative approach is needed because the EHD contact conditions and the dynamic analysis of the overall system are mutually dependent. Once convergence is reached, the obtained function, which represents the elasticity of the cam-follower contact, affects the system dynamics significantly. In fact, the obtained results are rather different from those obtained by assuming a constant value of such elasticity. Nevertheless, the novel approach allows a more accurate modeling of the valve-train system.