An approach for estimating the reliability of transmission oils

This paper deals with an approach for estimating the reliability of transmission oils. Forecasting oil degradation, especially oil oxidation allows to adjust the right oil change intervals in order to save costs and expand the transmission´s lifetime. A brief overview about the machine component transmission oil imparts fundamental knowledge. Afterwards definitions of oil failures and combining them to an oil failure system are explained. The oil lifetime line describes the relationship between possible oil temperature and oil lifetime. Such a line is the keystone in order to describe the oil´s failure behavior caused by oil oxidation. That´s why two approaches are presented to derive an oil lifetime line. Both approaches use a certain oil failure criteria explained in the paper. The first approach is based on the pitting damage accumulation hypothesis. This hypothesis is expanded with the effect of oil degradation what enables to derive an oil lifetime line out of the results of a back-to-back spur gear rig test. Second a General Log Linear Model is used with available data to estimate the gears pitting lifetime depending on oil degradation. With the defined oil failure criteria it was possible to derive an oil lifetime line for mineral oil based fluids. Further work will include the estimation of an oil lifetime line with a probability and confidence intervals. Synthetic oil based fluids need to be investigated more intensive in order to create a suitable oil lifetime line for such fluids.