The elastohydrodynamic friction and film forming properties of lubricant base oils

The stringent and often competing requirements of high fuel economy and low emissions are placing increasing emphasis on the selection of appropriate base oils Soi modem engine lubricants. Two properties now recognized as imp ortant in engine oil design are the elastohydrodynamic (EHD) traction coeff icient and the pressure-viscosity coefficient. The former determines the le vel of friction in high pressure contacts such as cams, while the latter pl ays a major role in determining the EHD film thickness. Unfortunately, for many fluids there is a broad correlation between the two properties so that a low traction coefficient implies a low pressure viscosity coefficient an d thus film thickness. This paper measures the traction and film-forming pr operties of a wide range of base oil types at realistic engine oil temperat ures in order to both explore the extent of this coil-elation and to determ ine the dependence of EHD lubricant properties on base oil compositions.