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Continuing interest in energy conservation and friction reduction, driven primarily by environmental concerns, provides opportunities to develop energy saving lubricants. The greatest potential energy savings come from reductions in hydrodynamic friction as typified by main and connecting rod journal bearings in automotive engines. The main approach to minimise friction losses in these bearings is to reduce the lubricant viscosity. However, this approach will inevitably reduce oil film thickness and impose even higher stresses on the lubricant. The problem is compounded by the use of multigrade oils, which contain relatively high molecular weight polymeric components, and exhibit both temporary and permanent shear thinning. Thus these lubricants exhibit non-Newtonian flow behaviour under the extreme conditions imposed by engine bearings.

An instrument is described which allows the load bearing capacity of a lubricant to be measured under pressures, shear rates and dynamic loadings typical of those found in automotive crankshaft journal bearings. Using Newtonian lubrication approximations, a theoretical analysis of the Journal Bearing Simulator has been carried out. Good agreement between theory and experiment is found demonstrating that the instrument is a fundamentally sound method for measuring lubricant load bearing capacity.