Einfluss von Mikrostruktur und Einlaufprozedur auf Reibung und Verschleißintensität im Nocken-Stößel Tribosystem: Ganzheitliche Prozess- und Oberflächenstrukturentwicklung

The tribological interaction of cam and bucket tappet in the valve-train system of combustion engines is characterized by the high wear intensity of the tappet surface in the first hours of the run-in period. The present paper describes the potential of a defined surface structure on a micrometer level with regard to improved wear and friction. Furthermore, the machining process to generate the surface was developed and integrated into the camshaft manufacturing. The theoretical approach is based on the numerical simulation of the three-dimensional EHL-contact. On this basis an optimized surface texture was defined for the experimental investigations. For experimental validation, a unique cam-tappet test-rig was built, copying the valve train kinematics and tribological environment of a combustion engine. Integrated sensors enable online monitoring of the operating behaviour of the tappet by measuring the rotational tappet-speed and frictional forces. The wear performance is captured by surfacemeasurements before, during and after the running-in period. In order to transfer the theoretical results to a manufactured surface pattern it was required to develop a highly dynamic and high-precision mechanical process. As a useful method the machining process single-grain scratching was chosen and further developed for the camtappet application. At first a prototype test facility was created for texturing of variable cam geometries. In the second stage a complete manufacturing line was set up, including a very precise tool positioning. For this purpose pyramid-shaped and partically sharped natural or synthetic diamonds serve as a tool