Adaptive wheel slip threshold

Claim 1

A system for controlling a pressure applied to a brake of a vehicle wheel traveling over a road surface, the pressure applied establishing a braking force between the wheel and road surface, the system composed of: means for measuring an amount of slip present between the vehicle wheel and the road surface; means for detecting an incipient wheel lock condition when the measured slip exceeds an adjustable slip threshold value; means for decreasing pressure to the brake of the vehicle wheel in response to the detected incipient wheel lock condition; means for measuring a coefficient of friction between the vehicle wheel and the road surface; means for determining a critical slip value, s c , at which the braking force is a maximum for the measured coefficient of friction; means for adjusting the adjustable slip threshold value equal to the determined critical slip value; means for detecting a wheel recovery condition resulting from the amount of slip falling below the adjustable slip threshold value; and means for increasing pressure applied to the brake of the vehicle wheel in response to the detected recovery condition.

Claim 2

A system for controlling a pressure applied to a brake of a vehicle wheel traveling over a road surface, the pressure applied establishing a braking force between the wheel and road surface, the system composed of: means for measuring an amount of slip present between the vehicle wheel and the road surface; means for detecting an incipient wheel lock condition when the measured slip exceeds an adjustable slip threshold value; means for decreasing pressure to the brake of the vehicle wheel in response to the detected incipient wheel lock condition; means for measuring a coefficient of friction between the vehicle wheel and the road surface; means for determining a critical slip value, s c , at which the braking force is a maximum for the measured coefficient of friction; means for adjusting the adjustable slip threshold value equal to the determined critical slip value; means for detecting a wheel recovery condition resulting from the amount of slip falling below the adjustable slip threshold value; and means for increasing pressure applied to the brake of the vehicle wheel in response to the detected recovery condition.

Claim 4

A method for limiting a pressure applied to a brake of a vehicle wheel traveling over a road surface comprising the steps of: measuring an amount of slip between the vehicle wheel and the road surface; detecting an incipient wheel lock condition when the measured amount of slip exceeds an adjustable slip threshold value; decreasing pressure to the brake of the vehicle wheel in response to the detected incipient wheel lock condition; measuring a coefficient of friction between the vehicle wheel and the road surface; determining a critical slip value, s c , at which the braking force is a maximum for the measured coefficient of friction in accord with the expression s c =s d +f.sub.μ * μ r where s d is a calibrated value of slip, f.sub.μ is a calibrated factor for determining a variance from the calibrated value of slip and μ r is the measured coefficient of friction between the vehicle wheel and the road surface; adjusting the adjustable slip threshold value equal to the determined critical slip value s c ; detecting a wheel recovery condition resulting from the amount of slip falling below the adjustable slip threshold value; and increasing pressure applied to the brake of the vehicle wheel in response to the detected recovery condition.

Claim 5

A method for limiting a pressure applied to a brake of a vehicle wheel traveling over a road surface comprising the steps of: measuring an amount of slip between the vehicle wheel and the road surface; detecting an incipient wheel lock condition when the measured amount of slip exceeds an adjustable slip threshold value; decreasing pressure to the brake of the vehicle wheel in response to the detected incipient wheel lock condition; measuring a coefficient of friction between the vehicle wheel and the road surface; determining a critical slip value, s c , at which the braking force is a maximum for the measured coefficient of friction in accord with the expression s c =s d +f.sub.μ * μ r where s d is a calibrated value of slip, f.sub.μ is a calibrated factor for determining a variance from the calibrated value of slip and μ r is the measured coefficient of friction between the vehicle wheel and the road surface; adjusting the adjustable slip threshold value equal to the determined critical slip value s c ; detecting a wheel recovery condition resulting from the amount of slip falling below the adjustable slip threshold value; and increasing pressure applied to the brake of the vehicle wheel in response to the detected recovery condition.

Claim 6

A method for limiting a pressure applied to a brake of a vehicle travelling over a road surface comprising the steps of: measuring an amount of slip between the vehicle wheel and the road surface; detecting an incipient wheel lock condition when the measured amount of slip exceeds an adjustable slip threshold value; measuring an amount of pressure present at the brake of the vehicle wheel when the incipient lock condition is detected; weighting the amount of pressure measured such that (a) a small value of pressure is weighted to be indicative of a low coefficient of friction between the vehicle wheel and the road surface, (b) a moderate value of pressure is weighted to be indicative of a medium coefficient of friction between the vehicle wheel and the road surface, and (c) a large value of pressure is weighted to be indicative of a high coefficient of friction between the vehicle wheel and the road surface; decreasing pressure to the brake of the vehicle wheel in response to the detected incipient wheel lock condition; measuring an amount of vehicle wheel reacceleration resulting from the decrease in brake pressure; determining a peak value of vehicle wheel reacceleration; weighting the peak value of vehicle wheel reacceleration such that (a) a small value of peak reacceleration is weighted to be indicative of a low coefficient of friction between the vehicle wheel and the road surface, (b) a moderate value of peak reacceleration is weighted to be indicative of a medium coefficient of friction between the vehicle wheel and the road surface, and (c) a large value of peak reacceleration is weighted to be indicative of a high coefficient of friction between the vehicle wheel and the road surface; averaging the pressure weight and peak reacceleration weight to arrive at a value representative of a measured coefficient of friction between the vehicle wheel and road surface; determining a critical slip value, s c , at which the braking force is a maximum for the measured coefficient of friction using the expression s c =s d +f.sub.μ * .sub.μr where s d is a calibrated value of slip, f.sub.μ is a calibrated factor for determining a variance from the calibrated value of slip and .sub.μr is the measured coefficient of friction between the vehicle wheel and the road surface; adjusting the adjustable slip threshold value equal to the determined critical slip value s c ; detecting a wheel recovery condition resulting from the amount of slip falling below the adjustable slip threshold value; and increasing pressure applied to the brake of the vehicle wheel in response to the detected recovery condition.

Claim 7

A method for limiting a pressure applied to a brake of a vehicle travelling over a road surface comprising the steps of: measuring an amount of slip between the vehicle wheel and the road surface; detecting an incipient wheel lock condition when the measured amount of slip exceeds an adjustable slip threshold value; measuring an amount of pressure present at the brake of the vehicle wheel when the incipient lock condition is detected; weighting the amount of pressure measured such that (a) a small value of pressure is weighted to be indicative of a low coefficient of friction between the vehicle wheel and the road surface, (b) a moderate value of pressure is weighted to be indicative of a medium coefficient of friction between the vehicle wheel and the road surface, and (c) a large value of pressure is weighted to be indicative of a high coefficient of friction between the vehicle wheel and the road surface; decreasing pressure to the brake of the vehicle wheel in response to the detected incipient wheel lock condition; measuring an amount of vehicle wheel reacceleration resulting from the decrease in brake pressure; determining a peak value of vehicle wheel reacceleration; weighting the peak value of vehicle wheel reacceleration such that (a) a small value of peak reacceleration is weighted to be indicative of a low coefficient of friction between the vehicle wheel and the road surface, (b) a moderate value of peak reacceleration is weighted to be indicative of a medium coefficient of friction between the vehicle wheel and the road surface, and (c) a large value of peak reacceleration is weighted to be indicative of a high coefficient of friction between the vehicle wheel and the road surface; averaging the pressure weight and peak reacceleration weight to arrive at a value representative of a measured coefficient of friction between the vehicle wheel and road surface; determining a critical slip value, s c , at which the braking force is a maximum for the measured coefficient of friction using the expression s c =s d +f.sub.μ * .sub.μr where s d is a calibrated value of slip, f.sub.μ is a calibrated factor for determining a variance from the calibrated value of slip and .sub.μr is the measured coefficient of friction between the vehicle wheel and the road surface; adjusting the adjustable slip threshold value equal to the determined critical slip value s c ; detecting a wheel recovery condition resulting from the amount of slip falling below the adjustable slip threshold value; and increasing pressure applied to the brake of the vehicle wheel in response to the detected recovery condition.