Slip regulation algorithm for an automotive vehicle using a normal force estimate and a predetermined peak wheel slip value

1 . A control system for an automotive vehicle having a wheel and wheel brake comprising:

a wheel speed sensor generating a rotational speed signal; and

a controller coupled to the wheel speed sensor, said controller determining a vehicle speed, calculating an actual wheel slip based upon the vehicle speed and the rotational speed, estimating a normal force on the wheel, calculating a modified brake torque signal in response to a saturation function of a threshold slip and the actual wheel slip, an approximated friction curve slope, and the normal force, and actuating the wheel brake in response to the modified brake torque signal.

2 . A system as recited in claim 1 further comprising a vehicle speed sensor, said controller determining vehicle speed from the vehicle speed sensor.

3 . A system as recited in claim 2 wherein the vehicle speed sensor comprises plurality of wheel speed sensors.

4 . (canceled)

5 . A system as recited in claim 1 wherein said controller measures a wheel deceleration from the wheel speed sensor; when the wheel deceleration is above a threshold applying the modified torque.

6 . A system as recited in claim 5 wherein said controller applies an unmodified torque when the wheel deceleration is below a threshold.

7 . A method of controlling a vehicle having a wheel and wheel brake comprising:

measuring rotational speed of a wheel;

determining a vehicle speed;

calculating an actual wheel slip based upon the vehicle speed and the rotational speed;

estimating a normal force on the wheel;

calculating a modified brake torque signal in response to a saturation function of a threshold slip and the actual wheel slip, an approximated friction curve slope, and the normal force; and

actuating the wheel brake in response to the modified brake torque signal.

8 . (canceled)

9 . A method as recited in claim 7 further comprising measuring a wheel deceleration; when the wheel deceleration is above a threshold applying a modified brake torque.

10 . A method as recited in claim 9 further comprising applying an unmodified torque when the wheel deceleration is below a threshold.

11 . A method as recited in claim 7 further comprising when the vehicle speed is above a speed threshold, performing calculating wheel slip based upon the vehicle speed and the rotational speed, estimating a normal force on the wheel, calculating a modified brake torque signal in response to the wheel slip and the normal force, and actuating the wheel brake in response to the modified brake torque signal when a wheel deceleration is below a threshold.

12 . A method as recited in claim 7 wherein calculating an actual wheel slip comprises calculating a normalized wheel slip value.

13 . A method as recited in claim 7 wherein determining a vehicle speed comprises determining a vehicle speed in response to the wheel speed.

14 . A method of controlling braking of an automotive vehicle having a plurality of wheels and brakes comprising:

measuring rotational speed of the plurality of wheels;

determining a vehicle speed;

calculating a respective actual wheel slip for the plurality of wheels based upon the vehicle speed and a respective rotational speed;

estimating a normal force on the plurality of wheels;

calculating a respective modified brake torque signal in response to a saturation function of a threshold slip and the actual wheel slip, an approximated friction curve slope, and the normal force for each of the plurality of wheels; and

actuating a respective brake in response to the respective modified brake torque signal.

15 . (canceled)

16 . A method as recited in claim 14 further comprising measuring a wheel deceleration; when the wheel deceleration is above a threshold applying the respective modified torque, and applying an unmodified torque when a wheel deceleration is below a threshold.

17 . A method as recited in claim 14 wherein calculating a respective wheel slip comprises calculating a respective normalized wheel slip value.

18 . A method as recited in claim 14 wherein determining a vehicle speed comprises determining a vehicle speed in response to the wheel speed.

19 . A system as recited in claim 1 wherein the controller calculates a modified brake torque signal in response to a saturation function of a difference of a threshold slip and the actual wheel slip, an approximated friction curve slope, and the normal force.

20 . A system as recited in claim 1 wherein the controller calculates a modified brake torque signal in response to a saturation function of a difference of a threshold slip, the actual wheel slip and a boundary later thickness, an approximated friction curve slope, and the normal force.

21 . A system as recited in claim 1 wherein the controller calculates a modified brake torque signal in response to a saturation function of a difference of a threshold slip, the actual wheel slip and a boundary later thickness, a convergence factor, an approximated friction curve slope, and the normal force.

22 . A method as recited in claim 7 wherein calculating a modified brake torque signal in response to a saturation function of a threshold slip and the actual wheel slip, an approximated friction curve slope, and the normal force comprises calculating a modified brake torque signal in response to a saturation function of a difference of a threshold slip and the actual wheel slip, an approximated friction curve slope, and the normal force.

23 . A method as recited in claim 7 wherein calculating a modified brake torque signal in response to a saturation function of a threshold slip and the actual wheel slip, an approximated friction curve slope, and the normal force comprises calculating a modified brake torque signal in response to a saturation function of a difference of a threshold slip, the actual wheel slip and a boundary later thickness, an approximated friction curve slope, and the normal force.

24 . A method as recited in claim 7 wherein calculating a modified brake torque signal in response to a saturation function of a threshold slip and the actual wheel slip, an approximated friction curve slope, and the normal force comprises calculating a modified brake torque signal in response to a saturation function of a difference of a threshold slip, the actual wheel slip and a boundary later thickness, a convergence factor, an approximated friction curve slope, and the normal force.

25 . A method as recited in claim 14 wherein calculating a respective modified brake torque signal in response to a saturation function of a threshold slip and the actual wheel slips, an approximated friction curve slope, and the normal force for each of the plurality of wheel comprises calculating a respective modified brake torque signal in response to a saturation function of a difference of a threshold slip and the actual wheel slips, an approximated friction curve slope, and the normal force for each of the plurality of wheel.

26 . A method as recited in claim 14 wherein calculating a respective modified brake torque signal in response to a saturation function of a threshold slip and the actual wheel slips, an approximated friction curve slope, and the normal force for each of the plurality of wheel comprises calculating a respective modified brake torque signal in response to a saturation function of a difference of a threshold slip, the actual wheel slips and a boundary later thickness, an approximated friction curve slope, and the normal force for each of the plurality of wheel.

27 . A method as recited in claim 14 wherein calculating a respective modified brake torque signal in response to a saturation function of a threshold slip and the actual wheel slips, an approximated friction curve slope, and the normal force for each of the plurality of wheel comprises calculating a respective modified brake torque signal in response to a saturation function of a difference of a threshold slip, the actual wheel slips and a boundary later thickness, a convergence factor, an approximated friction curve slope, and the normal force for each of the plurality of wheel.