The inclusion of lubricant shear thinning in journal bearing models

The Short Bearing Approximation is often used in the preliminary design stages of automotive engine bearings. However, amongst its many limitations, the assumption is made that the lubricant is Newtonian. Modern automotive lubricants are multigrade oils containing polymeric additives at treat rates of several percent. This results in the lubricant viscosity having a significant dependence on shear rate (temporary shear thinning). This paper extends the Short Bearing Model to allow for lubricant shear thinning, as described by the Cross model. The modified model has been applied to a modern automotive con-rod bearing for various automotive multigrade lubricants.