Method for detecting a deflated tire on a vehicle

Claim 3

Method as in claim 1 wherein said between column variation SSC is formed by subtracting the speed total X from four times the column sum SUMV j for each wheel to form four deviations, squaring the deviations, and adding the squared deviations, whereby ##EQU11##

Claim 4

Method as in claim 1 wherein said between row variation SSR is formed by squaring the four column sums SUMV j and adding the squared column sums to form a total of squared column sums ##EQU12## squaring the measured speeds V ij of each of the four wheels, adding the squared speeds (V ij ) 2 for each wheel to form four column sums of squared speeds ##EQU13## and adding the column sums of squared speeds SUM2V j to form a total sum of squared speeds ##EQU14## subtracting said total of squared column sums from said total sum of squared speeds, whereby ##EQU15##

Claim 5

Method as in claim 1 wherein F=SSC/SSR.

Claim 6

Method as in claim 1 further comprising, when F does not exceed said first predetermined threshold, comparing F to a first predetermined sub-threshold which is smaller than said first predetermined threshold, measuring the speeds of each of the four wheels a plurality of times in a second time interval which is cumulative to said first time interval when F exceeds said first sub-threshold, forming said value F based on said plurality of measured wheel speeds in said second time interval, comparing said value F to a second predetermined threshold corresponding to a second predetermined pressure loss which is smaller than said first predetermined pressure loss, and actuating a driver warning device when F exceeds said second predetermined threshold.

Claim 7

Method as in claim 5 further comprising, when F does not exceed said second predetermined threshold, comparing F to a second predetermined sub-threshold which is smaller than said second predetermined threshold, measuring the speeds of each of the four wheels a plurality of times in a third time interval which is cumulative to said second time interval when F exceeds said second sub-threshold, forming said value F based on said plurality of measured wheel speeds in said third time interval, comparing said value F to a third predetermined threshold corresponding to a third predetermined pressure loss which is smaller than said second predetermined pressure loss, and actuating a driver warning device when F exceeds said third predetermined threshold.

Claim 8

Method as in claim 1 further comprising determining wheel calibration factors for each of the four wheels prior to said first time interval, said wheel calibration factors discounting variations in rolling radii of the four wheels, and modifying said wheel speeds by said wheel calibration factors during said first time interval and any subsequent time intervals.

Claim 9

Method as in claim 1 further comprising normalizing all measured wheel speeds, said normalizing comprising calculating a vehicle reference speed V iref and dividing each measured wheel V ij speed by said vehicle reference speed V iref to obtain a normalized wheel speed V ij nor .

Claim 10

Method as in claim 8 wherein said vehicle reference speed is the average of the angular speeds of the four wheels times a virtual tire radius.

Claim 11

Method as in claim 8 further comprising measuring the speeds of each of the four wheels a plurality of times (m) prior to said first time interval, determining wheel calibration factors for each of the four wheels prior to said first time interval, said wheel calibration factors each being determined as a rolling radius R j * according to ##EQU16## modifying said wheel speeds V ij by said wheel calibration factors R j * during said first time interval and any subsequent time interval.

Claim 12

Method as in claim 1 further comprising determining when said vehicle is cornering, and excluding wheel speeds measured during cornering from steps used to form said value F.

Claim 13

Method as in claim 10 wherein cornering is determined by determining a difference between a speed of the left front wheel and a speed of the right front wheel, determining a difference between a speed of the left rear wheel and a speed of the right rear wheel, comparing the difference between the front wheel speeds to the difference between the rear wheel speeds, and determining that said vehicle is cornering when said differences are greater than a predetermined minimum and both within the same predetermined limits.

Claim 14

Method as in claim 1 further comprising determining when one of said wheels is accelerating or decelerating, and excluding wheel speeds measured when one of said wheels is accelerating or decelerating from steps used to form said F value.

Claim 15

Method as in claim 13 wherein accelerating and decelerating are determined by determining a time rate of change dV ij /dt, determining that a wheel is accelerating when dv ij /dt exceeds a positive threshold, and determining that one of said wheels is decelerating when dV ij /dt falls below a negative threshold.

Claim 16

Method as in claim 1 further comprising determining when any of said vehicle is travelling uphill or downhill, and excluding wheel speeds measured when said vehicle is travelling uphill or downhill form steps used to form said value F.

Claim 17

Method as in claim 15 wherein uphill or downhill travel are determined by determining a difference between a speed of the left front wheel and a speed of the left rear wheel, determining a difference between a speed of the right front wheel and a speed of the right rear wheel, comparing the difference between the left wheel speeds to the difference between the right wheel speeds, and determining uphill or downhill travel when said differences are greater than a predetermined minimum and both within the same predetermined limits.

Claim 18

Method for detecting the loss of pressure in a tire of a motor vehicle having four wheels and a tire on each wheel, said method comprising measuring the speeds V ij of each of the four wheels a plurality of times (m) in a calibration time interval, determining wheel calibration factors four each of the four wheels based on said plurality (m) of measured speeds for each of said four wheels, said wheel calibration factors discounting variations in rolling radii of the four wheels, measuring the speeds V ij of each of the four wheels a plurality of times (n) in a first time interval subsequent to said calibration time interval, modifying said wheel speeds by said calibration factors during said first time interval and any subsequent time intervals, adding the plurality of speeds for each wheel to produce four wheel speed column sums SUMV j where ##EQU17## and j=1, 2, 3, 4, adding the four wheel speed column sums SUMV j to form a speed total X, forming a between column variation SSC based on the four column sums SUMV j and the speed total X, forming a between row variation SSR based on the four column sums SUMV j and the wheel speeds V ij , forming a value F based on the ratio SSC/SSR, comparing F to a first predetermined threshold corresponding to a first predetermined pressure loss, and actuating a driver warning device when said F value exceeds said first predetermined threshold.

Claim 19

Method for detecting the loss of pressure in a tire of a motor vehicle having four wheels and a tire on each wheel, said method comprising measuring the speeds V ij of each of the four wheels a plurality of times (m) in a calibration time interval, determining wheel calibration factors four each of the four wheels based on said plurality (m) of measured speeds for each of said four wheels, said wheel calibration factors discounting variations in rolling radii of the four wheels, measuring the speeds V ij of each of the four wheels a plurality of times (n) in a first time interval subsequent to said calibration time interval, modifying said wheel speeds by said calibration factors during said first time interval and any subsequent time intervals, adding the plurality of speeds for each wheel to produce four wheel speed column sums SUMV j where ##EQU17## and j=1, 2, 3, 4, adding the four wheel speed column sums SUMV j to form a speed total X, forming a between column variation SSC based on the four column sums SUMV j and the speed total X, forming a between row variation SSR based on the four column sums SUMV j and the wheel speeds V ij , forming a value F based on the ratio SSC/SSR, comparing F to a first predetermined threshold corresponding to a first predetermined pressure loss, and actuating a driver warning device when said F value exceeds said first predetermined threshold.