Dead reckoning system

1. A method of dead reckoning navigation for a vehicle using a plurality of accelerometers, comprising:

determining an orientation between the sensor frame of reference and a body frame of reference for the vehicle using sensed accelerations from the accelerometers; and

determining a dead-reckoning longitudinal acceleration for the vehicle by converting sensed accelerations from the accelerometers according to the determined orientation between the sensor frame of reference and the body frame of reference, wherein determining the orientation of the vehicle comprises:

with the vehicle in a state selected from the set consisting of a stationary state and an un-accelerated state, calculating a pitch angle and a roll angle between the sensor frame of reference and a body frame of reference for the vehicle using sensed accelerations from the accelerometers; and

with the vehicle accelerated without turning, calculating a yaw angle between the sensor frame and the body frame using sensed accelerations from the accelerometers.

2. The method of claim 1 , further comprising:

sensing a heading for the vehicle; and

integrating the dead-reckoning longitudinal acceleration according to the heading to provide a dead-reckoning-determined location for the vehicle.

3. The method of claim 1 , wherein determining the dead-reckoning longitudinal acceleration comprises converting sensed accelerations from the accelerometers according to the roll, pitch, and yaw angles.

4. The method of claim 3 , wherein determining the pitch and roll angles comprises:

with the vehicle in the state selected from the set consisting of a stationary state and an unaccelerated state, calculating a scale factor for the accelerometers; and

converting the sensed accelerations according to the scale factor into accelerations according to a yawed frame of reference.

5. The method of claim 4 , wherein calculating the yaw angle is a function of a longitudinal acceleration in the yawed frame of reference and a lateral acceleration in the yawed frame of reference.

6. The method of claim 5 , wherein the function comprises calculating an arc-tangent of a ratio of the longitudinal acceleration in the yawed frame of reference and the lateral acceleration in the yawed frame of reference.

7. The method of claim 6 , further comprising:

with the vehicle accelerated without turning, sensing a reference longitudinal acceleration for the vehicle using a GPS system; and

scaling the ratio according to the reference longitudinal acceleration before calculating the arc tangent.

8. The method of claim 1 , wherein determining the dead-reckoning longitudinal acceleration further comprises:

determining a reference longitudinal acceleration for the vehicle using a GPS system;

comparing the reference longitudinal acceleration for the vehicle to the dead-reckoning longitudinal acceleration to obtain a scale factor and a bias for each of the accelerometers; and

converting the sensed accelerations according the scale factor and the bias to provide a corrected dead-reckoning longitudinal acceleration.

9. The method of claim 8 , wherein the comparing act comprises kalman filtering a difference between the reference longitudinal acceleration for the vehicle and the dead-reckoning longitudinal acceleration.

10. A vehicle navigation system, comprising:

a set of accelerometers operable to sense accelerations for the vehicle according to a sensor frame of reference;

a GPS navigation system operable to determine a reference longitudinal acceleration for the vehicle; and

a processor operable to calculate a pitch angle and a roll angle between the sensor frame of reference and a body frame of reference for the vehicle using sensed accelerations from the accelerometers with the vehicle in a state selected from the set consisting of a stationary state and an un-accelerated state and to calculate a yaw angle between the sensor frame and the body frame using the senses accelerations with the vehicle accelerated without turning, the processor being further operable to convert the sensed accelerations according to the pitch angle, the roll angle, and the yaw angle to provide converted accelerations and to calculate a dead-reckoning longitudinal acceleration for the vehicle using the converted accelerations.

11. The vehicle navigation system of claim 10 , further comprising:

a heading sensor for the vehicle, wherein the processor is further operable to integrate the dead-reckoning longitudinal acceleration according to a heading sensed by the heading sensor to calculate a dead-reckoning-determined location for the vehicle.

12. The vehicle navigation system of claim 11 , wherein the heading sensor is a yaw-rate gyroscope.

13. The vehicle navigation system of claim 11 , wherein the GPS navigation system is integrated with the set of accelerometers and the heading sensor.

14. The vehicle navigation system of claim 10 , wherein the GPS navigation system is adapted to provide a graphical representation of a location for the vehicle according to the dead-reckoning-determined location if GPS satellite signal reception is unavailable.