The remaining useful life of a transmission fluid in a vehicle is continually
estimated by a transmission control computer module during vehicle operation using
both an oxidation model and a shift energy model. The oxidation model uses experimentally
determined remaining useful fluid life values obtained at temperatures experienced
by the fluid in transmission usage and subtracts incremental values from said life
based on the temperature-time experience of volume fractions of the fluid in the
sump and torque converter. The shift energy model starts with an estimated maximum
number of shifts and continually obtains a current remaining useful life by deducting
for actual shifts and estimated shift energy inputs based on fluid temperature.
Notice of end of fluid useful life is given when one of the models first determines
no remaining useful fluid life.
