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. We also used TAN (total acid number) and LCC (load-carrying capacity) as oil evaluation criteria for determining the details of the oil deterioration process. Also, NMR (nuclear magnetic resonance) spectroscopy was used to identify the deterioration process of additives.
The results of the FZG test were similar to those of the field test with respect to oil deterioration. Also, the NMR analysis showed that the deterioration process of ZnDTP in the FZG tests and the field tests were similar. Therefore, the FZG test method can be used as a means to deteriorate T/M oils.
The results of the FZG tests indicate that the life of synthetic-based T/M oil is at least twice as long as that of mineral-based oil.