Engine Friction and Bearing Wear. III. The Role of Elasticity in Bearing Performance

Oils containing polymers have been shown to give better bearing performance—lower friction and lower wear—than straight mineral oils of the same low-shear viscosity, in spite of their non-Newtonian character. This unexpected behavior has been investigated further in studies on solutions of different polymer types, using a range of molecular weights and concentrations for each type and blending all solutions to the same low shear viscosity. The viscosity and elasticity of these solutions were measured at different rates of shear in an ultrasonic crystal viscometer. The governing parameter controlling bearing performance appears to be the recoverable shear, which is related to the elastic modulus of the system. Polymer type, also appears to be important in determining the critical value of recoverable shear required for good bearing performance.