Working Mechanism of Organic Friction Modifiers on Steel and Paper Materials

The effect of organic Friction Modifiers (FMs) on friction properties at steel and paper clutch materials is investigated, and their working mechanisms are assessed by the observation of reaction and adsorption films formed on the surface.
FMs are essential additives for drivetrain lubricants to manage friction properties. Recently developed fuel efficient transmission systems such as Continuously Variable Transmission (CVT) require precise and complicated friction control. As a result it is extremely important for the detailed behaviour of the FMs and in particular their reactions with the surfaces to be elucidated.
In this study, friction properties of organic friction modifiers, oleic acid, oleyl alcohol and glycerol mono-oleate, were evaluated by TE77 and MTM using steel and paper specimens, which simulate two major components of CVT; a steel belt-pulley mechanism and a paper clutch system. The surface films on the post-test materials were studied by SEM, EDX, XPS and ATR-FTIR to assess the influence of the FMs.
The results indicate that the friction properties are strongly affected by the substrate material and test temperature as well as the chemical structure of the FMs. In addition, interactions between the FMs and the other additives play an important role for the friction modification mechanism. In order to discuss the working mechanism of the FMs, the relationship between the friction properties and the chemical nature of the surface films was considered. Furthermore, the chemical structure of the FMs and its formulation suitable for CVT fluids are discussed.