A new apparatus to evaluate friction modifier additives for engine oil((c))

Friction reducing additives are commonly blended with engine and transmissi on lubricants to improve efficiency. A wide range of laboratory scale tests is used to predict their performance in full-scale applications. In most i nstances, 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 co nditions in which anti-wear additives are largely unneeded. The majority of existing test geometries do not produce accurate friction forces tinder su ch light contact pressures. Clearly, a new approach was required. This pape r describes an apparatus that measures the force needed to restrain a wire that is wrapped around a rotating cylinder or capstan. This novel arrangeme nt produces high friction forces from a low contact stress. ore importantly , an exponential relationship exists be tween friction force and friction c oefficient. Minute changes in friction coefficient are readily observed and the design is appreciably more sensitive to friction modifier additives th an conventional test geometries. The test successfully differentiates comme rcially 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 lu bricant rheology.