Method and system for detecting and correcting vehicle speed reference signals in anti-lock brake systems

A method of detecting and correcting overestimated reference speeds for a vehicle having a front-right wheel, a front-left wheel, and a rear axle with two rear wheels, the vehicle being capable of generating a first speed signal representative of a speed of the front-right wheel, a second speed signal representative of a speed of the front-left wheel, and a third speed signal representative of a speed of at least one wheel on the rear axle, the vehicle further being capable of calculating a first reference speed for the front-right wheel, a second reference speed for the front-left wheel, and a third reference speed for at least one wheel on the rear axle, the method comprising the steps of:

• (a) computing a first speed quantity representative of the speed of the front-right wheel, a first slip quantity representative of a slip of the front-right wheel, and a first acceleration quantity representative of an acceleration of the front-right wheel, based on the first speed signal;
• (b) computing a second speed quantity representative of the speed of the front-left wheel, a second slip quantity representative of a slip of the front-left wheel, and a second acceleration quantity representative of an acceleration of the front-left wheel, based on the second speed signal;
• (c) computing a third speed quantity representative of the speed of at least one rear wheel, a third slip quantity representative of a slip of at least one rear wheel, and a third acceleration quantity representative of an acceleration of at least one rear wheel, based on the third speed signal;
• (d) comparing the first slip quantity to a first slip threshold;
• (e) comparing the second slip quantity to a second slip threshold;
• (f) comparing the third slip quantity to a third slip threshold;
• (g) comparing the first speed quantity to a first speed threshold;
• (h) comparing the second speed quantity to a second speed threshold;
• (i) comparing the third speed quantity to a third speed threshold;
• (j) comparing the first acceleration quantity to a first lower acceleration threshold and a first upper acceleration threshold;
• (k) comparing the second acceleration quantity to a second lower acceleration threshold and a second upper acceleration threshold;
• (l) comparing the third acceleration quantity to a third lower acceleration threshold and a third upper acceleration threshold;
• (m) incrementing a count if the first slip quantity exceeds the first slip threshold, the second slip quantity exceeds the second slip threshold, the third slip quantity exceeds the third slip threshold, the first speed quantity exceeds the first speed threshold, the second speed quantity exceeds the second speed threshold, the third speed quantity exceeds the third speed threshold, the first acceleration quantity is less than the first upper acceleration threshold and greater than the first lower acceleration threshold, the second acceleration quantity is less than the second upper acceleration threshold and greater than the second lower acceleration threshold, and the third acceleration quantity is less than the third upper acceleration threshold and greater than the third lower acceleration threshold;
• (n) reducing the count by one if the first slip quantity exceeds the first slip threshold, the second slip quantity exceeds the second slip threshold, the third slip quantity exceeds the third slip threshold, the first speed quantity exceeds the first speed threshold, the second speed quantity exceeds the second speed threshold, the third speed quantity exceeds the third speed threshold, at least one of the first, second, and third acceleration quantities is greater than the corresponding first, second, and third upper acceleration threshold or less than the corresponding first, second, and third lower acceleration threshold, and the count is not equal to zero;
• (o) setting the first reference speed equal to the first speed quantity if the count attains a predetermined count threshold;
• (p) setting the second reference speed equal to the second speed quantity if the count attains the predetermined count threshold;
• (q) setting the third reference speed equal to the third speed quantity if the count attains the predetermined count threshold;
• and
• (r) controlling the anti-lock brake system based on the first reference speed, the second reference speed, and the third reference speed;
• wherein steps (a) through (r) are repeated.

A system for detecting and correcting an overestimated reference speed condition for a vehicle having a plurality of wheels and an anti-lock brake system, the vehicle being capable of generating a speed signal based upon the speed of each wheel in a selected subset of the plurality of wheels and capable of calculating at least one reference speed, the system comprising:

• computing means, operatively associated with the speed signals, for computing test quantities for each corresponding wheel of the selected subset of wheels based on %he corresponding speed signal;
• decision means, operatively associated with the computing means, for determining a consistency of the test quantities with the overestimated reference speed condition by comparing the test quantities to predetermined thresholds;
• detecting means, operatively associated with the decision means for detecting the overestimated reference speed condition based upon the consistency of the test quantities with the overestimated reference speed condition;
• correcting means, operatively associated with the detecting means, for modifying at least one reference speed when the overestimated reference speed condition is detected;
• and
• controlling means, operatively associated with the correcting means, for controlling the anti-lock brake system based on the modified reference speed.

A system for detecting and correcting overestimated reference speeds for a vehicle having a front-right wheel, a front-left wheel, and a rear axle with two rear wheels, the vehicle being capable of generating a first speed signal representative of a speed of the front-right wheel, a second speed signal representative of a speed of the front-left wheel, and a third speed signal representative of a speed of at least one wheel on the rear axle, the vehicle further being capable of calculating a first reference speed for the front-right wheel, a second reference speed for the front-left wheel, and a third reference speed for at least one wheel on the rear axle, the system comprising:

• first computing means, operatively associated with the first speed signal, for computing a first speed quantity representative of the speed of the front-right wheel, a first slip quantity representative of a slip of the front-right wheel, and a first acceleration quantity representative of an acceleration of the front-right wheel, based on the first speed signal;
• second computing means, operatively associated with the second speed signal, for computing a second speed quantity representative of the speed of the front-left wheel, a second slip quantity representative of a slip of the front-left wheel, and a second acceleration quantity representative of an acceleration of the front-left wheel, based on the second speed signal;
• third computing means, operatively associated with the third speed signal, for computing a third speed quantity representative of the speed of at least one rear wheel, a third slip quantity representative of a slip of at least one rear wheel, and a third acceleration quantity representative of an acceleration of at least one rear wheel, based on the third speed signal;
• first comparison means, operatively associated with the first, second, and third computing means, for comparing the first, second, and third slip quantities to corresponding first, second, and third slip thresholds;
• second comparison means, operatively associated with the first, second, and third computing means, for comparing the first, second, and third speed quantities to corresponding first, second, and third speed thresholds;
• third comparison means, operatively associated with the first, second, and third computing means, for comparing the first, second, and third acceleration quantities to corresponding first, second, and third upper acceleration thresholds and corresponding first, second, and third lower acceleration thresholds;
• a counter, operatively associated with the first, second and third comparison means, wherein the counter is incremented if the first slip quantity exceeds the first slip threshold, the second slip quantity exceeds the second slip threshold, the third slip quantity exceeds the third slip threshold, the first speed quantity exceeds the first speed threshold, the second speed quantity exceeds the second speed threshold, the third speed quantity exceeds the third speed threshold, the first acceleration quantity is less than the first upper acceleration threshold and greater than the first lower acceleration threshold, the second acceleration quantity is less than the second upper acceleration threshold and greater than the second lower acceleration threshold, and the third acceleration quantity is less than the third upper acceleration threshold and greater than the third lower acceleration threshold;
• decrement means, operatively associated with the counter and the first, second, and third comparison means, for reducing the counter by one if the first slip quantity exceeds the first slip threshold, the second slip quantity exceeds the second slip threshold, the third slip quantity exceeds the third slip threshold, the first speed quantity exceeds the first speed threshold, the second speed quantity exceeds the second speed threshold, the third speed quantity exceeds the third speed threshold, at least one of the first, second, and third acceleration quantities is greater than the corresponding first, second, and third upper acceleration threshold or less than the corresponding first, second, and third lower acceleration threshold, and the counter is not equal to zero;
• first setting means, operatively associated with the counter, for setting the first reference speed equal to the first speed quantity if the counter attains a selected threshold;
• second setting means, operatively associated with the counter, for setting the second reference speed equal to the second speed quantity if the counter attains the selected threshold;
• third setting means, operatively associated with the counter, for setting the third reference speed equal to the third speed quantity if the counter attains the selected threshold;
• and
• controlling means, operatively associated with the first setting means, the second setting means, and the third setting means, for controlling the anti-lock brake system based on the first reference speed, the second reference speed, and the third reference speed.