Method and apparatus for determining tire position on a vehicle

1. An apparatus for determining a position of a tire on a vehicle comprising:

a tire-based sensing unit, each tire on the vehicle having an associated tire-based sensing unit, each tire-based sensing unit including,

a first sensor mounted for rotation with the tire and for generating a first sensor signal indicative of such rotation;

a second sensor mounted for rotation with the tire and for generating a second sensor signal indicative of such rotation;

a transmitter for transmitting a signal indicative of a phase relationship between the first and second sensor signals;

axle position sensor for determining each tire-based sensing unit position relative to a front and rear axle of the vehicle and providing an axle position signal for each tire-based sensing unit; and

a controller for monitoring the transmitted phase signals of each tire-based sensing unit and the determined axle position signals, said controller including,

means for comparing the tire-based sensing unit phase relationships for possible tire locations considering the determined axle positions of the tire-based sensing units,

means for determining a confidence value by weighting the compared phase relationships,

means for comparing the phase difference of each tire-based sensing unit relative to the phase difference of other tire-based sensing units for each possible vehicle tire location, and

means for associating each tire-based sensing unit with a vehicle location in response to the confidence values.

2. The apparatus of claim 1 wherein the first sensor is a gravitational sensor.

3. The apparatus of claim 2 wherein said gravitational sensor is an accelerometer.

4. The apparatus of claim 1 wherein the second sensor is a magnetic field sensor.

5. The apparatus of claim 4 wherein said magnetic field sensor includes a coil.

6. The apparatus of claim 1 further including a tire condition sensor for sensing condition of the tire and for transmitting a signal indicative of the sensed tire condition.

7. The apparatus of claim 1 further including receiver means for determining the received signal strength of the transmitted signals, where the receiver is closer to one of the axles, in order to determine the axle positions of the tire mounted sensors.

8. The apparatus of claim 1 further including low frequency initiation means located on or near one of the axles, in order to determine the axle positions of the tire mounted sensors.

9. A method for determining a position of a tire on a vehicle comprising the steps of:

sensing tire rotation by a first method and generating a first signal indicative of sensed rotation;

sensing tire rotation by a second method and generating a second signal indicative of sensed rotation;

transmitting a signal indicative of a phase relationship between the first and second signals;

measuring signal strength of the transmitted sensor signals; and

monitoring via a controller the phase relationship of the transmitted signals, determining confidence value weights from the monitored phase relationships, monitoring the received signal strength of the transmitted signals, and correlating location of each tire-based sensing unit with vehicle location responsive to the confidence values.