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In consideration of environmental protection, it has recently become necessary to extend the drain intervals of gear oils. For the evaluation of oil life, field tests are generally used, but they are extremely time-consuming and expensive. For gear oils, a laboratory evaluation method mutually related to in-vehicle life has not yet been presented in papers. Because of the importance of evaluating the life of developing oils, the goal of this study was to establish a laboratory evaluation method mutually related to in-vehicle deterioration. With this method, appropriate evaluation is carried out easily and quickly. In our research, we used an FZG gear machine (power circulating gear test rig) to test for T/M (transmission) oil deterioration. The FZG gear machine was operated under severe conditions to accelerate the deterioration of the oil.

Austempered ductile iron (ADI) is a material having excellent mechanical properties and damping capacity. However practical mass production of ADI gears has not been possible due to ADI's poor machinability and distortion during the austempering heat treatment. With a new process method of carrying out hobbing before austempering when the material is in its soft condition, then austempering it and lastly, conducting the shave finishing process, we have diminished the above defects and developed practical ADI gears. These new gears generate less noise than ordinary nitrocarburized steel gears and are superior in pitting resistance.