Vehicle wheel slip control on split coefficient surface

Claim 1

A method of controlling slip between the left and right wheels of an axle of a vehicle and a road surface, the method comprising the steps of: determining left and right wheel speeds; determining vehicle speed; controlling the right wheel speed to establish a predetermined function of the determined right wheel speed at a right wheel target value in response to an excessive slip condition of the right wheel; controlling the left wheel speed to establish a predetermined function of the determined left wheel speed at a left wheel target value in response to an excessive slip condition of the left wheel; sensing a vehicle yaw condition when one of (A) a first predetermined function of the difference between the determined left and right wheel speeds exceeds a first threshold while the determined vehicle speed is less than a vehicle speed threshold and (B) a second predetermined function of the difference between the left and right wheel speeds exceeds a second threshold while the vehicle speed is greater than the vehicle speed threshold; and when a yaw condition is sensed (A) determining which one of the left and right wheels is on a higher coefficient of friction surface and (B) decreasing the target value of the one of the left and right wheels on the higher coefficient of friction surface.

Claim 2

A method of controlling slip between the left and right wheels of an axle of a vehicle and a road surface, the method comprising the steps of: determining left and right wheel speeds; determining vehicle speed; controlling the right wheel speed to establish a predetermined function of the determined right wheel speed at a right wheel target value in response to an excessive slip condition of the right wheel; controlling the left wheel speed to establish a predetermined function of the determined left wheel speed at a left wheel target value in response to an excessive slip condition of the left wheel; sensing a vehicle yaw condition when one of (A) a first predetermined function of the difference between the determined left and right wheel speeds exceeds a first threshold while the determined vehicle speed is less than a vehicle speed threshold and (B) a second predetermined function of the difference between the left and right wheel speeds exceeds a second threshold while the vehicle speed is greater than the vehicle speed threshold; and when a yaw condition is sensed (A) determining which one of the left and right wheels is on a higher coefficient of friction surface and (B) decreasing the target value of the one of the left and right wheels on the higher coefficient of friction surface.

Claim 6

A method of controlling slip between the left and right wheels of an axle of a vehicle and a road surface, the method comprising the steps of: determining left and right wheel speeds; determining vehicle speed; controlling right wheel speed to a right wheel target speed value ω rdes in response to an excessive slip condition of the right wheel when the determined vehicle speed is less than a predetermined threshold; controlling left wheel speed to a left wheel target speed value ω ldes in response to an excessive slip condition of the left wheel when the determined vehicle speed is less than the predetermined threshold; controlling right wheel slip to a right wheel target slip value λ rdes in response to an excessive slip condition of the right wheel when the determined vehicle speed is greater than the predetermined threshold; controlling left wheel slip to a left wheel target slip value λ rdes in response to an excessive slip condition of the left wheel when the determined vehicle speed is greater than the predetermined threshold; determining a wheel speed index in accordance with the expression (C.sub.ω *ω dd )+ω dd +ω rdes -ω ldes , where C 107 is a constant, ω dd is the difference between the left and right wheel speeds and ω dd is the rate of change in ω dd ; determining a wheel slip index in accord with the expression (C.sub.λ *λ dd )+λ dd +λ rdes -λ ldes , where C.sub.λ is a constant, λ dd is the difference between the left and right wheel speeds divided by vehicle speed and λ dd is the rate of change in λ dd ; sensing a vehicle yaw condition (A) when the wheel speed index exceeds a first threshold while the vehicle speed is less than the vehicle speed threshold and (B) when the wheel slip index exceeds a second threshold while the vehicle speed is greater than the vehicle speed threshold; and when a yaw condition is sensed (A) determining which one of the left and right wheels is on a higher coefficient of friction surface and (B) when the vehicle speed is less than the vehicle speed threshold, repeatedly decreasing the one of the target speed values ω ldes and ω rdes associated with the wheel on the higher coefficient of friction surface until the wheel speed index is equal to the first threshold and when the vehicle speed is greater than the vehicle speed threshold, repeatedly decreasing the one of the target slip values λ rdes and λ ldes associated with the wheel on the higher coefficient of friction surface until the wheel slip index is equal to the second threshold.

Claim 7

A method of controlling slip between the left and right wheels of an axle of a vehicle and a road surface, the method comprising the steps of: determining left and right wheel speeds; determining vehicle speed; controlling right wheel speed to a right wheel target speed value ω rdes in response to an excessive slip condition of the right wheel when the determined vehicle speed is less than a predetermined threshold; controlling left wheel speed to a left wheel target speed value ω ldes in response to an excessive slip condition of the left wheel when the determined vehicle speed is less than the predetermined threshold; controlling right wheel slip to a right wheel target slip value λ rdes in response to an excessive slip condition of the right wheel when the determined vehicle speed is greater than the predetermined threshold; controlling left wheel slip to a left wheel target slip value λ rdes in response to an excessive slip condition of the left wheel when the determined vehicle speed is greater than the predetermined threshold; determining a wheel speed index in accordance with the expression (C.sub.ω *ω dd )+ω dd +ω rdes -ω ldes , where C 107 is a constant, ω dd is the difference between the left and right wheel speeds and ω dd is the rate of change in ω dd ; determining a wheel slip index in accord with the expression (C.sub.λ *λ dd )+λ dd +λ rdes -λ ldes , where C.sub.λ is a constant, λ dd is the difference between the left and right wheel speeds divided by vehicle speed and λ dd is the rate of change in λ dd ; sensing a vehicle yaw condition (A) when the wheel speed index exceeds a first threshold while the vehicle speed is less than the vehicle speed threshold and (B) when the wheel slip index exceeds a second threshold while the vehicle speed is greater than the vehicle speed threshold; and when a yaw condition is sensed (A) determining which one of the left and right wheels is on a higher coefficient of friction surface and (B) when the vehicle speed is less than the vehicle speed threshold, repeatedly decreasing the one of the target speed values ω ldes and ω rdes associated with the wheel on the higher coefficient of friction surface until the wheel speed index is equal to the first threshold and when the vehicle speed is greater than the vehicle speed threshold, repeatedly decreasing the one of the target slip values λ rdes and λ ldes associated with the wheel on the higher coefficient of friction surface until the wheel slip index is equal to the second threshold.