In a motor vehicle having a direct or an indirect injection engine containing lubricating oil which has a useful life that varies in accordance with engine operating conditions, a method for advising the operator of the vehicle of the need to change oil, such method comprising the steps of:
Periodically calculating an effective engine revolutions value over predetermined intervals during a present engine operation in accordance with a product of measured engine revolutions and engine oil temperature and engine oil contaminant penalty factors which operate to increase the effective engine revolutions value to compensate for engine operating conditions that tend to cause increased degradation of the engine oil, the oil temperature and oil contaminant penalty factors being determined as a function of engine oil temperature and engine oil contaminant values, respectively;
Decreasing a stored remaining allowed revolutions value indicative of the remaining number of engine revolutions allowed for the useful life of the engine oil by subtracting the calculated effective engine revolutions value; and
Actuating an indicator advising the operator that the engine oil needs to be changed when the stored remaining allowed revolutions value falls below a predetermined threshold value indicative of the end of the useful life of the engine oil.
2. A method as in claim 1 further comprising the step of calculating the engine oil temperature value in accordance with engine parameters prior to calculating the effective engine revolutions value.
3. A method as in claim 1 further comprising the step of determining the engine oil temperature value by measuring an engine oil temperature from an engine oil temperature sensor prior to calculating the effective engine revolutions value.
4. A method as in claim 1 further comprising the step of calculating the engine oil contaminant value in accordance with an oil temperature value, fuel injection timing, fuel quantity and engine rotational speed prior to calculating the effective engine revolutions value.
5. A method as in claim 2 wherein the step of calculating the engine oil temperature value includes the steps of:
When the engine oil temperature value is in a warm up range, calculating the oil temperature in accordance with a measured initial coolant temperature at the beginning of a current engine operation and a sum of engine revolutions since the beginning of the current engine operation; and
When the engine oil temperature value is in an equilibrium range, calculating the oil temperature in accordance with a measured coolant temperature, engine rotational speed, fuel quantity, intake air temperature and vehicle speed.
6. A method as in claim 2 wherein the step of calculating the engine oil temperature value includes the steps of:
When the engine oil temperature value is in a warm up range, calculating the oil temperature in accordance with a warm up equation T.sub.o =T.sub.ic +k.sub.1 R.sub.e wherein T.sub.ic is an initial coolant temperature at the beginning of a current engine operation, R.sub.e is sum of the engine revolutions since the beginning of the current engine operation and k.sub.1 is a constant; and
When the engine oil temperature value is within an equilibrium range, calculating the oil temperature in accordance with an equilibrium equation T.sub.o =k.sub.2 +k.sub.3 S.sub.e +k.sub.4 T.sub.c +k.sub.5 F.sub.q -k.sub.6 T.sub.a.+-.k.sub.7 V.sub.s wherein S.sub.e is engine rotational speed, T.sub.c is a coolant temperature, F.sub.q is fuel quantity, T.sub.a is an air intake temperature, V.sub.s is vehicle speed, and k.sub.2, k.sub.3, k.sub.4, k.sub.5, k.sub.6 and k.sub.7 are constants.
7. A method as in claim 4 wherein the step of calculating the engine oil contaminant value includes the steps of:
calculating the engine oil contaminant value, C, from an equation
C=k.sub.8 +k.sub.9 I.sub.t +k.sub.10 F.sub.q +k.sub.11 T.sub.o +T.sub.o +k.sub.12 S.sub.e,
wherein I.sub.t is fuel injection timing, F.sub.q is fuel quantity, T.sub.o is the calculated oil temperature value, S.sub.e is engine rotational speed, and k.sub.8, k.sub.9, k.sub.10, k.sub.11 and k.sub.12 are constants.