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The objectives of the research project were to investigate the limits concerning possible reduction of lubricant quantity in gears without detrimental influence on the load carrying capacity. The investigations covered the influence of the oil level in dip lubricated systems as well as the oil flow rate in spray lubricated systems namely oil-air supply systems on power loss, heat generation and load carrying capacity. The load carrying capacity in terms of characteristic gear failure modes was determined and was compared to the results using conventional lubricant volumes with dip lubrication. Therefore in back-to-back gear tests the parameters speed, load and oil quantity were varied for examination of the four main gear flank damages: scuffing, wear, pitting and micropitting. The investigations showed the application potential of oil/air lubrication also for heavy duty transmissions nevertheless there exists a natural limitation for lowering the oil quantity in transmissions without detrimental influence on the load carrying capacity.

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Purpose-The purpose of this paper is to make an attempt to evaluate the pitting load carrying capacity under increased thermal conditions. This is the basis for an estimated lifetime which is one of the most important parameters defining transmission reliability. Design/methodology/approach-Recommendations related to pitting load carrying capacity calculation of case hardened gears running at high gear bulk temperatures are formulated. These factors are based on extensive experimental data, obtained in pitting tests with high oil injection temperatures, high oil sump temperatures or high operational gear bulk temperatures due to a lack of heat dissipation caused by minimised lubrication. Findings-Testing of gear type C-PT on FZG back-to-back test rig at high gear bulk temperatures by either heating up the lubricant or caused by a lack of heat dissipation as it appears with poor lubrication conditions resulted in a decrease of up to 30 per cent of the endurance strength in various investigations. This results in a reduction of the material strength due to tempering effects and high surface shear stress due to low oil film thicknesses caused by low operating oil viscosities. Originality/value-The present calculation method in the standard DIN/ISO is not valid for high gear bulk temperatures. Nevertheless, the present calculation algorithms of the standards DIN/ISO are valid for low and moderate thermal operating conditions when using oil temperatures of up to 80 (90)8C in the case of a sufficient cooling oil supply to the gear mesh. With the presented modifications higher gear bulk temperatures (. 1208C) can be taken into account.