Combined effects of ZnDTP and ashless dispersant on friction in boundary lubrication

摘要

A high level of friction between pulleys and elements is required to increase the torque transmission capacity of metal-pushing-belt type Continuously Variable Transmissions (belt-type CVTs). Contacts areas between pulleys and elements are in boundary lubrication regimes and are lubricated with a CVT fluid, which is required to achieve a higher friction coefficient and thus to form a steady boundary layer. Friction coefficients of PAO (poly alpha olefin) with ZnDTP (Zinc-dithiophosphate) alone, with ZnDTP plus an ashless dispersant and with ZnDTP plus Ca sulfonate were measured using an SRV friction tester. In the case of PAO with ZnDTP alone, high and low friction coefficients were observed in spite of the uniform test conditions. In the case of PAO with ZnDTP and ashless dispersant, friction coefficients were high and stable; repeatability was also good. In the case of PAO with ZnDTP and Ca sulfonate, the friction coefficient decreased with time. Ashless dispersant inhibits ZnDTP from adsorbing iron oxide, and restrains the decomposition of ZnDTP. because of these effects, ashless dispersant seems to hinder the formation of an unsteady boundary layer, and exhibits a stable and high friction coefficient.