Traction control for performance and demonstration spin

1. A method for controlling a powertrain of a vehicle with wheels and a driver-actuated pedal, comprising:

controlling a wheel slip to a first amount, independent of a driver requested output torque during a first road condition; and

controlling the wheel slip to a second amount based on the driver requested output torque during a second road condition, the second road condition having higher friction than the first road condition.

2. The method of claim 1 , wherein the first amount is based on one of a friction coefficient (μ) and a vehicle speed.

3. The method of claim 2 , wherein the driver requested output torque is overridden during the first road condition.

4. The method of claim 1 , wherein the second amount is a function of a pedal position.

5. The method of claim 1 , wherein a road condition is a friction coefficient (μ) between road surface and tires.

6. The method of claim 5 , wherein the second amount is further based on an ambient temperature.

7. The method of claim 6 , wherein the second amount is responsive to a vehicle speed.

8. The method of claim 7 , wherein controlling the wheel slip to the second amount includes increasing the wheel slip when the vehicle speed is less than a first threshold.

9. The method of claim 8 , wherein the second amount increases as the friction coefficient and the ambient temperature increase.

10. The method of claim 9 , wherein the second amount decreases as the vehicle speed is greater than the first threshold.

11. The method of claim 10 , wherein the second amount decreases to the first amount when the vehicle speed is greater than the first threshold and less than a second threshold.

12. A method for controlling a powertrain of a vehicle with wheels, the vehicle having a pedal actuated by a driver, the method comprising:

when wheel slip is present and traction control is enabled,

overriding a driver request for an output torque and controlling a wheel slip to a first amount during a first road condition by at least increasing wheel braking torque, the first amount independent of the driver request and selected to reduce the wheel slip; and

overriding the driver request and controlling the wheel slip to a second amount during a second road condition, the second amount proportional to the driver request and adjusted based on a vehicle speed, where the controlled wheel slip is reduced as the vehicle speed increases, the second road condition having higher friction than the first road condition; and

providing engine output responsive to the driver request otherwise.

13. The method of claim 12 , wherein the first amount is determined based on one of a road friction coefficient (μ) and the vehicle speed.

14. The method of claim 13 , wherein the road conditions include friction between road surface and tires.

15. The method of claim 14 , wherein increasing controlling the wheel slip is further based on an ambient condition.

16. The method of claim 15 , wherein the ambient condition includes an ambient temperature.

17. The method of claim 16 , wherein the controlled wheel slip is increased as the road friction coefficient (μ) increases and the ambient temperature increases.

18. A vehicle comprising:

wheels;

an accelerator pedal actuated by a driver;

a powertrain to provide an output torque; and

a traction control system configured to override a driver requested output torque to control a wheel slip to a first amount during a first road condition and increase the wheel slip from the first amount to a second amount by the accelerator pedal during a second road condition when a vehicle speed is less than a first threshold,

wherein the second road condition has a higher road-tire friction than the first road condition.

19. The vehicle of claim 18 , wherein the second amount is responsive to an ambient temperature.

20. The vehicle of claim 19 , wherein the second amount increases as the road-tire friction and the ambient temperature increase.