Abstract
Besides the well-known zinc dithiophosphates (ZDTP) phosphorus and sulfur containing ashless additives are used to improve the lubrication properties of modern engine and hydraulic oils. It is generally accepted that a wear reducing reaction layer is formed by additive tribofragmen-tation reactions in the friction zone of the metal surface. The composition of those reaction layers and the formation mechanism relative to the used additive is quite unknown. By systematic modification of monothiophosphates the influence of molecule parameters on the wear reducing properties were investigated (1).