Method of estimating engine lubricant condition

1. A method of estimating the useful life of lubricating oil in an internal combustion engine, comprising the steps of:

measuring variables relating to operation of the internal combustion engine;

estimating a depletion rate for a TBN in the lubricating oil from the measured variables;

estimating an accretion rate for a TAN in the lubricating oil from the measured variables; and

determining a time span until the TBN and the TAN equal one another as an estimate of remaining useful life of the lubricating oil.

2. A method of estimating the useful life of lubricating oil as set forth in claim 1 , wherein the internal combustion engine is installed on a motor vehicle, the method further comprising the step of:

relating the determined time span to a distance and displaying the distance to an operator of the vehicle; and

warning the operator when TBN and TAN equal one another.

3. A method of estimating the useful life of lubricating oil as set forth in claim 2 , further comprising the step of:

estimating depletion of an active zinc number in the lubricating oil; and

comparing the accumulated depletion of the active zinc number to a fixed minimum limit to determine a maximum limit of lubricating oil useful life.

4. A method of estimating the useful life of lubricating oil as set forth in claim 3 , further comprising the steps of:

relating the maximum limit of lubricating oil useful life based on the active zinc number depletion rate to a distance; and

setting the distance until the lubricating oil change to the lesser of the distance based on the accumulated depletion of the active zinc number and the determined time span and displaying the distance.

5. A method of estimating the useful life of lubricating oil as set forth in claim 4 , wherein the steps of estimating the depletion of the TBN and the accretion of the TAN further comprise:

independently relating engine load, ignition timing and oil temperature to the depletion of the TBN and accretion rate of the TAN.

6. A method of estimating the useful life of lubricating oil as set forth in claim 5 , the method further comprising the steps of:

equating a depletion rate for the TBN to a TBN equivalent operating hours factor;

equating an accretion rate for the TAN to a TAN equivalent operating hours factor;

providing a TBN look up table indexed by TBN equivalent operating hours;

providing a TAN look up table indexed by TAN equivalent operating hours;

using the TBN equivalent operating hours factor as an input to the TBN look up table to recover an estimated TBN; and

using the TAN equivalent operating hours factor as an input to the TAN look up table to recover an estimated TAN.

7. A motor vehicle comprising:

an internal combustion engine having a lubricating system;

a lubricating oil temperature sensor;

an engine crankshaft position sensor;

a fuel injection means for setting fuel flow controller responsive to the engine crankshaft position sensor and the fuel flow;

lubricating oil for circulating in the lubricating system, the lubricating oil including buffers for neutralizing acid infiltration of the oil and metal salts for enhancing the lubricity of the oil; and

data processing means programmed for equating oil temperature, fuel rates and ignition timing for estimating depletion of the buffers, accretion of acid, and depletion of the metal salts.

8. A motor vehicle as set forth in claim 7 , further comprising:

a programming executable on the data processing means for expressing rates of buffer depletion and acid accretion to equivalent operating hours for each variable independently;

a look up table of buffer concentration indexed to equivalent operating hours for the buffer; and

a look up table of acid concentration indexed to equivalent operating hours for the total acid.

9. A motor vehicle as set forth in claim 8 , further comprising:

means for comparing the acid concentration and base concentration figures returned from the look up tables as an indication of end of lubricating oil useful life.

10. A motor vehicle as set forth in claim 9 , further comprising:

means responsive to the base concentration exceeding the acid concentration for projecting an operating time duration until the base concentration and acid concentration are equal; and

means for relating the projected operating duration to a distance for display.

11. A motor vehicle as set forth in claim 10 , further comprising:

programming executable on the data processing means for equating oil temperature and engine operation in terms of fuel rates and ignition timing from the engine crankshaft position sensor and fuel injection controller for estimating depletion of the metal salts; and

determining a projected operating endurance until depletion of the metal salts reaches a limit and comparing the projected operating duration to determine an oil change interval distance.

12. A motor vehicle as set forth in claim 10 , further comprising:

memory accessible by the data processing means; and

look up tables stored in memory and accessible to the programming executables to provide estimates of depletion of buffers and accretion of acids in the lubricating oils, indexed in terms of equivalent operating hours.