Piston Pin: Wear and Rotating Motion

Abstract

In new engines, running conditions for piston pin bushes have become very severe due to combustion pressure and temperature increase. Moreover, the lead removal from the bush material has strongly reduced the capability of the antifriction material to accept asperity contacts, geometrical defects or edge loading. Today, it is usual that wear and seizure occur in the piston pin bushes during the first steps of engine development. In order to propose basic design recommendations avoiding damage, during the early steps of engine development, it is necessary to have quick numerical simulations. In these calculations, the mixed lubrication in the piston pin bearings must be taken into account. To obtain a simple realistic tool, a refined contact model is implemented in a simple hydrodynamic lubrication program. Then, the general behaviour of the piston pin is described before focusing on the combustion cycle phases when damage may occur. The oil film thickness variations during cycle are described and show what the critical phases are. Several parameters like pin diameter, temperature, pressure-viscosity coefficient have been investigated in order to understand their influence. To have an efficient wear modelling a special emphasis is put on the description of asperity contacts in order to built a wear model for bearings located on the piston pin. In this wear model, the surface topography parameters are taken into account in order to have a realistic approach and to identify the optimal roughness parameters.