The lubrication of gears has two major functions: Reducing friction and wear as well as dissipating heat. The
power losses, especially the no-load losses, decrease with decreasing immersion depth using dip
lubrication. The load-dependent gear power losses are nearly unaffected by minimized lubrication. However,
the gear bulk temperatures rise dramatically by using minimized lubrication due to a lack of heat dissipation. .
With minimized lubrication the scuffing load carrying capacity decreased by up to more than 60% comparedto
rich lubrication conditions. The dominating influence of the bulk temperature is therefore very clear. Starved
lubrication leads to more frequent metal – to contact and the generation of high local flash temperatures must
be considered. An additional factor for the scuffing load carrying capacity calculation in case of minimized
lubrication conditions is proposed.
Concerning pitting damage test runs showed that by lowering the oil level the load cycles without pitting
damage decreased by approximately 50% up to 75% for minimized lubrication compared to the results with
rich lubrication conditions. The allowable contact stress is clearly reduced (up to 30%) by minimized
lubrication. A reduced oil film thickness as a consequence of increased bulk temperatures results in more
frequent metal-to-metal contacts causing a higher surface shear stress. In combination with a decreased
material strength due to a possible tempering effect at high bulk temperatures the failure risk of pitting damage
is clearly increased. The common pitting load carrying capacity calculation algorithms according to DIN/ISO
are only valid for moderate oil temperatures and rich lubrication conditions. For increased thermal conditions,
the reduction of the pitting endurance level at increased gear bulk temperatures can be approximated with the
method of Knauer (FZG TU Munchen, 1988). An advanced calculation algorithm for pitting load carrying
capacity calculation at high gear bulk temperatures (valid for high oil temperatures as well as for minimized
lubrication) is proposed.