Braking system for estimating vehicle reference speed in a vehicle during a wheel slip event

1. A method for updating a vehicle reference speed of an all-wheel drive vehicle during acceleration, the all-wheel drive vehicle having a plurality of wheels, the method comprising:

repeatedly increasing brake torque to at least one wheel of the plurality of wheels on at least one axle until it is determined, via an electronic control unit: (1) that a first wheel speed of the at least one wheel on the at least one axle is not less than a second wheel speed of another wheel of the plurality of wheels on the same axle and (2) that a predetermined brake torque limit threshold has been reached, the predetermined brake torque limit threshold being preprogrammed into a memory of the electronic control unit as a function of an engine torque of the all-wheel drive vehicle;

holding the brake torque at the predetermined brake torque limit threshold for a predetermined amount of time; and

updating a prior estimate of the vehicle reference speed of the vehicle based upon the first wheel speed.

2. The method of claim 1 , further comprising:

determining that each of the plurality of wheels are potentially experiencing wheel slippage.

3. The method of claim 2 , further comprising determining that each of the plurality of wheels are potentially experiencing wheel slippage for greater than a predetermined amount of time.

4. The method of claim 1 , further comprising:

releasing the brake torque at the at least one wheel.

5. The method of claim 1 , wherein applying brake torque further comprises increasing brake torque to an alternating wheel.

6. The method of claim 1 , wherein applying brake torque further comprises increasing brake torque to at least one rear wheel of the plurality of wheels.

7. The method of claim 1 , wherein the predetermined braking torque threshold is based on an engine torque of the all-wheel drive vehicle.

8. A method for updating a vehicle reference speed of an all-wheel drive vehicle during acceleration, the all-wheel drive vehicle having a plurality of wheels, the method comprising:

determining each wheel of the plurality of wheels is potentially experiencing wheel slippage;

repeatedly increasing brake torque to at least one wheel of the plurality of wheels on at least one axle until it is determined, via an electronic control unit: (1) that a first wheel speed of the at least one wheel on the at least one axle is not less than a second wheel speed of another wheel of the plurality of wheels on the same axle and (2) that a predetermined brake torque limit threshold has been reached, the predetermined brake torque limit threshold being preprogrammed into a memory of the electronic control unit as a function of an engine torque of the all-wheel drive vehicle;

holding the brake torque at the predetermined brake torque limit threshold for a predetermined amount of time; and

updating a prior estimate of the vehicle reference speed of the vehicle based upon the first wheel speed.

9. The method of claim 8 , further comprising determining that each of the plurality of wheels are potentially experiencing wheel slippage for greater than a predetermined amount of time.

10. The method of claim 8 , further comprising:

releasing the brake torque at the at least one wheel.

11. The method of claim 8 , wherein applying brake torque further comprises increasing brake torque to an alternating wheel.

12. The method of claim 8 , wherein applying brake torque further comprises increasing brake torque to at least one rear wheel of the plurality of wheels.

13. The method of claim 8 , wherein the predetermined braking torque limit threshold is based on an engine torque of the all-wheel drive vehicle.

14. A braking system for a vehicle that updates a vehicle reference speed of an all-wheel drive vehicle during acceleration, the all-wheel drive having a plurality of wheels, the braking system comprising:

a braking system;

an electronic control unit (ECU) for controlling the braking system, the ECU configured to:

repeatedly increase brake torque to at least one wheel of a plurality of wheels on at least one axle until it is determined (1) that a first wheel speed of the at least one wheel on the at least one axle is not less than a second wheel speed of another wheel of the plurality of wheels on the same axle and (2) that a predetermined brake torque limit threshold has been reached, the predetermined brake torque limit threshold being preprogrammed into a memory of the electronic control unit as a function of an engine torque of the all-wheel drive vehicle;

hold the brake torque at the predetermined brake torque limit threshold for a predetermined amount of time; and

update a prior estimate of the vehicle reference speed of the vehicle based upon the first wheel speed.

15. The braking system of claim 14 , wherein the ECU is further configured to determine each wheel of the plurality of wheels are potentially experiencing wheel slippage.

16. The braking system of claim 14 , wherein the ECU is further configured to determine each wheel of the plurality of wheels are potentially experiencing wheel slippage for greater than a predetermined amount of time.

17. The braking system of claim 14 , wherein the ECU is further configured to release the brake torque at the at least one wheel.

18. The braking system of claim 14 , wherein the predetermined braking torque limit threshold is based on an engine torque of the all-wheel drive vehicle.

19. The braking system of claim 14 , wherein the ECU is further configured to increase brake torque to an alternating wheel.

20. The braking system of claim 14 , wherein the ECU is further configured to increase brake torque to at least one rear wheel of the plurality of wheels.