Gears are machine components that determine the capability and reliability of many technical products. Continuous demand for higher efficiency and reliability, increased load carrying capacity and endurance life, smaller size, lower noise and vibrations, prolonged service intervals, low environmental impact and low costs will remain the main driving forces in the development of gear drives in the future. The fatigue of contacting surfaces in gears is often the life-limiting factor in transmissions which should, ideally, operate reliably for 20 years or more. Low oil levels - and, thus, reduced oil quantities - are sometimes used for the reduction of no-load losses in dip-lubricated automotive and industrial transmissions. Specifically, a higher efficiency can be obtained by reducing no-load power losses such as squeezing, splashing and ventilation losses. These losses can be reduced by lowering the oil volume, namely the oil level in dip-lubricated transmissions and the oil flow rate with oil injection lubrication. In these cases, the oil amount required for lubrication may be sufficient, but there may be a lack of cooling oil. This leads to high gear bulk temperatures resulting in thin separating films with higher friction and wear on the mating surfaces and, therefore, an increased risk of gear failures such as scuffing, pitting, micropitting and low-speed wear. Therefore the objective of this study was to investigate the limits concerning possible reduction of lubricant quantity in gears that could be tolerated without detrimental effects on their load carrying capacity.
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