Estimation of vehicle speed in all-wheel-drive vehicle
A vehicle includes an electric machine and a controller. The controller is programmed to responsive to a threshold difference, indicative of wheel slip, between average wheel speed and a vehicle speed that is based on a difference between wheel acceleration and measured vehicle acceleration, command a speed to the electric machine to reduce the wheel slip.
1. A vehicle comprising:
an electric machine; and
a controller programmed to:
receive a driver-demanded torque,
responsive to an average wheel speed exceeding a threshold that is based on a vehicle speed and is indicative of wheel slip, command a speed-control torque to the electric machine based on an error between a target speed, derived from the vehicle speed, and a measure speed of the electric machine to reduce the wheel slip, wherein the vehicle speed is based on a difference between wheel acceleration and measured vehicle acceleration, and
command a torque to the electric machine based on the driver-demanded torque when the average wheel speed is less than the threshold.
2. The vehicle of claim 1 further comprising primary and secondary axles, wherein the electric machine powers one of the primary and secondary axles.
3. The vehicle of claim 2 further comprising a second electric machine that powers the other of the primary and secondary axles.
4. The vehicle of claim 3 , wherein the controller is further programmed to:
responsive to an average wheel speed of the other of the primary and secondary axles exceeding the threshold, command a speed-control torque to the second electric machine based on an error between a target speed, derived from the vehicle speed, and a measure speed of the second electric machine to reduce the wheel slip of the other of the primary and secondary axles.
5. The vehicle of claim 1 , wherein the vehicle speed is further based on wheel measured speed.
6. The vehicle of claim 1 , wherein the vehicle speed is further based on a grade offset acceleration.
7. The vehicle of claim 6 , wherein the grade offset acceleration is based on a derivative of a measured speed of a slowest wheel.
8. The vehicle of claim 1 further comprising speed sensors each associated with one of the wheels and configured to output a signal indicative of wheel speed.
9. The vehicle of claim 1 further comprising an internal combustion engine configured to power wheels.
10. A method of controlling a vehicle comprising:
commanding torque to an electric machine based on a driver-demanded torque; and
when a speed difference between average wheel speed and a vehicle speed exceeds a threshold indicative of wheel slip, commanding a speed-control torque to the electric machine such that a product of the average wheel speed and wheel rolling radius converges toward the vehicle speed to reduce the wheel slip, wherein the vehicle speed is based on a difference between wheel acceleration and measured vehicle acceleration.
11. The method of claim 10 , wherein the vehicle speed is further based on a grade offset acceleration.
12. The method of claim 11 , wherein the grade offset acceleration is based on a derivative of a measured speed of a slowest wheel.
13. The method of claim 10 , wherein the vehicle speed is further based on measured wheel speed.
14. The vehicle of claim 1 , wherein the target speed is based on a quotient of the vehicle speed and an effective rolling radius of a wheel.
15. The vehicle of claim 1 , wherein the target speed is equal to a quotient of the vehicle speed and an effective rolling radius of a wheel multiplied by a speed ratio between the electric machine and the wheel.
16. A vehicle comprising:
an electric machine; and
a controller programmed to:
command torque to the electric machine based on a driver-demanded torque; and
when a speed difference between average wheel speed and a vehicle speed exceeds a threshold indicative of wheel slip, command a speed-control torque to the electric machine such that a product of the average wheel speed and wheel rolling radius converges toward the vehicle speed to reduce the wheel slip, wherein the vehicle speed is based on a difference between wheel acceleration and measured vehicle acceleration.