Abstract
Influences on the wear of hydraulic pivot elements for valve trains were investigated by using the RNT-method. The tests were carried out with a motored cylinder head test rig. The test program was divided into two main sections in order to investigate the assumed influences separately. In the first section, the relative movement between the contact partners was varied by using different oil viscosities, oil temperatures, engine speeds and also by an additional thinning of the oil. In the second section, the wear-protection ability of the oil was changed by using oil without anti-wear additives, by adding artificial soot and by running the cylinder head with aged oil from Diesel and Gasoline engines. From the analysis of returned parts from affected vehicles, a critical wear rate was derived, at which a wear amount which is critical with regard to the function of the pivot element would be expected. As no influence of the relative movement of the contact partners was observed, a viscosity drop due to fuel thinning is not assessed as a main influence on the wear rate. Despite the same oil grade and a comparable driving profile, the usage of aged oil from Diesel engines generated much higher wear rates than with the usage of used oil from Gasoline engines, although the content of Diesel soot was on a low level of only 0.5 %. The usage of new oil without anti-wear additives exhibited higher wear rates than the usage of original new oil, but they were nevertheless lower then those of used oil from Diesel engines. The highest wear rate was achieved by adding 1 % artificial soot to the fresh oil. So the quantity as well as certain qualities of the soot has a significant effect on the wear behavior of the investigated components. It is concluded that the effect of soot cannot exclusively be a negative influence on the anti-wear additives for this tribological contact system.
Keywords: (Hydraulic lash adjusters, Wear; Soot, Additives, Oil