Rheological Properties of Engine Crankcase and Gear Oil Components in Elastohydrodynamic Oil Films

Techniques are described by which the response of viscosity to both pressure and shear may be determined from measurements of elastohydrodynamic oil film thickness. The methods are applied to three aspects of lubricant behaviour. The response of viscosity to pressure is first determined for a range of mineral, hydrocracked, polyalphaolefin and ester base stocks. Changes in this property when a dispersant/inhibitor additive package is introduced are then examined to determine whether relationships can be established between base oil and solution properties. A relatively simple outcome would allow the properties of commercial lubricants to be estimated from a much narrower range of base oil data. Finally, the response of a polymeric viscosity modifier to the high shear regime of the elastohydrodynamic inlet zone is investigated. The behaviour of the polymer is shown to depend on the relationship between polymer and base oil compositions.