Method and apparatus for determining tire condition using ideal gas law

1. An apparatus for determining a tire operating condition comprising:

a tire-based sensor for sensing tire pressure and temperature and transmitting a signal indicative thereof;

a vehicle ignition system;

a vehicle-based receiver/controller for receiving the signal from the tire-based sensor and for detecting the state of the vehicle ignition system, said controller providing an error signal when the sensed tire pressure is less than a set threshold value P set and resetting the error signal when the sensed tire pressure is greater than a reset threshold value P rst , the vehicle-based receiver/controller determining the set threshold value P set and the reset threshold value P rst as a function of a calculated warm tire pressure value P warm , determining a mole value N of the tire pressure and adjusting the determined set threshold value P set and the reset threshold value P rst in response to the vehicle ignition state and a change in the determined mole value N; and

a display the displaying the error signal from the vehicle-based receiver/controller.

2. The apparatus of claim 1 wherein said mole count N is equal to the sensed tire pressure divided by the sensed tire temperature.

3. The apparatus of claim 1 wherein said vehicle-based receiver/controller calculates the warm tire pressure value P warm equal to a recommended tire pressure value P rec times a measured tire temperature value T meas divided by a learned value of cold tire pressure temperature T cold .

4. The apparatus of claim 3 wherein learned value the cold tire pressure temperature T cold is adjusted in response to a change in the determined mole value N.

5. The apparatus of claim 3 wherein the set threshold P set =P warm plus a pressure tolerance value P tol .

6. The apparatus of claim 3 wherein the reset threshold P rst =P warm minus a pressure tolerance value P tol .

7. A method for determining a tire operating condition comprising the steps of:

sensing tire pressure;

sensing tire temperature;

providing a signal indicative of the sensed tire pressure and tire temperature;

sensing a state of the a vehicle ignition system;

providing an error signal when the sensed tire pressure is less than a set threshold value P set ;

resetting the error signal when the sensed tire pressure is greater than a reset threshold value P rst ;

calculating warm tire pressure value P warm

determining the set threshold value P set and the reset threshold value P rst as a function of the calculated warm tire pressure value P warm ;

determining a mole value N of the tire pressure;

adjusting the determined set threshold value P set and the reset threshold value P rst in response to the vehicle ignition state and a change in the determined mole value N; and

displaying the provided error signal for the vehicle operator.

8. The method of claim 7 wherein said step of determining a mole value N is determined by dividing the sensed tire pressure by the sensed tire temperature.

9. The method of claim 7 wherein said step of calculating the warm tire pressure value P warm includes multiplying a recommended tire pressure value P rec times a measured tire temperature value T meas divided by a learned value of cold tire pressure temperature T cold .

10. The method of claim 9 wherein learned value the cold tire pressure temperature T cold is adjusted in response to a change in the determined mole value N.

11. The method of claim 9 wherein the set threshold P set is set equal to P warm plus a pressure tolerance value P tol .

12. The method of claim 9 wherein the reset threshold P rst is set equal to P warm minus a pressure tolerance value P tol .