Tribological aspect of the surface topography variations for injection cams

Other conference contribution, 2008

In automotive industry, the environmental demands of low emissions, low fuel consumptions and long lifecycles lead to higher and higher engineering constraints. For example, high pressures on injection cams are needed for an improved combustion. Therefore friction and wear are constant problems encountered in camshaft development. The contact between roller and cam is a mix of sliding and rolling which leads to a wide range of failure modes. The uniqueness of this contact is also due to variations all around the cam depending on a multitude of parameters such as radius of curvature, load, sliding velocity. A previous study described surface topography as a function of cam shape and running time. The different types of wear mechanisms are strongly linked to contact pressures which are also dependent on roughness. This paper deals with the repercussion of observed variations of surface topography on the tribological behaviour of the cam roller contact. A number of cams have been mapped. The measurements are made by a non-contact light interferometer to monitor changes in the surface roughness. The Greenwood-Williamson contact model has been developed and applied to those measurements in order to collect characteristics of the microscopic pressures distribution. The results of the study show the significant effect of topography variations on the tribological behaviour of the cam roller contact. Cam angle roughness fluctuations are studied as well as running time dependency. The flat part of the cams with a high amount of peaks of sharp radii gives the worst tribological conditions and the running-in study shows the beneficial effect of peak smoothening on contact pressures. Tribological characteristics such as pressure distribution are valuable results which are helping to build characteristics of a recommended surface more able to face wear problems. In that case, an interesting prospect will be to virtually screen surfaces produced with different finishing processes and find out the best ones in order to reduce wear. The study of different roller processes will be as well of great interest.