Viscosity Influence on Friction Conditions and Fuel Economy of Automobiles - Some Basic Considerations

Decreasing viscosity for improving the fuel economy by reducing the mechanical friction under hydrodynamic conditions simultaneously will cause increased areas of mixed film lubrication regimes. As a consequence, higher wear has to be taken into account. Therefore, a balance between improved fuel economy on one side and increasing wear by lower viscosities on the other side has to be established.

Based on an efficiency analysis of automobil gears and engines the influence of the mechanical efficiencies on the fuel economy will be estimated. In doing so, influences of viscosity, of viscosity index, of temperature and shear rate on viscosity will be analyzed regarding their effect on fuel economy.