A new apparatus to evaluate friction modifier additives for engine oil©

Friction reducing additives are commonly blended with engine and transmission lubricants to improve efficiency. A wide range of laboratory scale tests is used to predict their performance in full-scale applications. In most instances, the laboratory equipment was originally designed to measure wear under accelerated conditions by using artificially high contact pressures. However, many friction modifiers are more effective under lightly-loaded conditions in which anti-wear additives are largely unneeded. The majority of existing test geometries do not produce accurate friction forces tinder such light contact pressures. Clearly, a new approach was required. This paper describes an apparatus that measures the force needed to restrain a wire that is wrapped around a rotating cylinder or capstan. This novel arrangement produces high friction forces from a low contact stress. ore importantly, an exponential relationship exists be tween friction force and friction coefficient. Minute changes in friction coefficient are readily observed and the design is appreciably more sensitive to friction modifier additives than conventional test geometries. The test successfully differentiates commercially available engine oils that are marketed as being energy-conserving from those that are not. Preliminary results, reported elsewhere, indicate correlation with Sequence VI, VIA and VIB engine data when combined with lubricant rheology.