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Technical Committee Lubricants

Determination of the Frictional Behaviour of Gears Lubricated with EP-Oils at Mixed and Boundary Lubrication Conditions (Frictional Behaviour EP Additive Systems)

The frictional behaviour of lubricants decisively affects the friction and therefore the efficiency of gearings. The lubricant determines the coefficient of friction between mating gears by the type of base oil (mineral oil / synthetic lubricant), viscosity, and additive package.

The efficiency of any gearing can be enhanced by an optimised lubrication formulation (base oil plus additive package). For applications which run at mixed and boundary lubrication conditions the additives’ influence on the coefficient of friction and therefore on friction forces, power loss and the efficiency of the gearing is predominant, but its impact is not yet known. Neither the tendency nor the quantity of an additive’s effect on friction can be predicted. By using certain EPadditives with low friction the power losses in gears and bearings at mixed and boundary friction conditions can be reduced. Therefore the oil and bulk temperatures decrease which allows higher safety against scuffing, micropitting, pitting and wear failures. Lubricant aging is slowed down. Furthermore the local surfaces shear stresses at mixed and boundary lubrication can also be influenced advantageously by appropriate additive packages which in turn diminishes risk of micropitting and pitting.

This research project comprises a systematic investigation of the frictional behaviour of different additive packages at mixed and boundary lubrication conditions particularly for the application in gears. Therefore 12 model additives based on sulphur, phosphorus, and PD (plastic deformation) are investigated as well as 6 market-ready lubricants provided by lubricant manufacturers.

Bernd-Robert Höhn et al.
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