Method for detecting a deflated tire on a vehicle

• US 6,285,280 B1
• Filed: 06/26/2000
• Issued: 09/04/2001
• Est. Priority Date: 06/26/2000
• Status: Active Grant

• Current Assignee: Robert Bosch Corporation (Robert Bosch GmbH)
• Original Assignee: Robert Bosch Corporation (Robert Bosch GmbH)
• Inventors: Wang, Orson Szu-Han
• Primary Examiner(s): TRIEU, VAN THANH
• Application Number:
  US09/605,686
• Time in Patent Office: 435 Days
• Field of Search: 340/442, 340/443, 340/444, 340/446, 340/447, 731/461, 731/462
• US Class Current: 340/444
• CPC Class Codes: B60C 23/061 by monitoring wheel speed measuring distance traversed on the ground by vehicles G01C22/00

Abstract

A method for detecting the loss of pressure in a tire of a motor vehicle having first and second wheels on a driven axle and a tire on each of the wheels. Each of the tires has a grip-rate. The method includes measuring the wheel speeds of the first wheel and the second wheel a plurality of times n, calculating a difference in wheel speed value between the first wheel and the second wheel for each of the plurality of times n, determining a value representative of the tractive force for the first wheel and the second wheel for each of the plurality of times n, pairing each difference in wheel speed value with the corresponding value representative of the tractive force, performing a linear regression on the n pairings of the difference in wheel speed values and the values representative of the tractive force, and analyzing the linear regression to determine whether a tire on one of the first and the second wheels is deflated. Preferably, determining the value representative of the tractive force includes determining either a driven wheel force value or a driven wheel slip value for each of the plurality of times n. Analyzing the linear regression preferably includes determining the slope of a best-fit line.

Claims

1. A method for detecting loss of pressure in a tire of a motor vehicle having first and second wheels on a driven axle and a tire on each of the first and second wheels, the method comprising:

measuring the wheel speeds of the first wheel and the second wheel a plurality of times n;

calculating a difference in wheel speed, NORM_DIFF, between the first wheel and the second wheel for each of the plurality of times n;

reading a wheel force value, F, for the first and second wheels for each of the plurality of times n;

pairing each NORM_DIFF value with the corresponding F value;

performing a linear regression on the n pairings of the NORM_DIFF values and the F values to determine the slope of a best-fit line; and

analyzing the slope of the best-fit line to determine whether a tire on one of the first and the second wheels is deflated.

2. The method of claim 1, further including

filtering the n pairings of the NORM_DIFF values and the F values to eliminate pairings obtained during vehicle braking.

3. The method of claim 1, further including

filtering the n pairings of the NORM_DIFF values and the F values to eliminate pairings obtained during vehicle maneuvering.

4. The method of claim 1, further including

filtering the n pairings of the NORM_DIFF values and the F values to eliminate pairings obtained during low-speed operation of the vehicle.

5. The method of claim 1, wherein analyzing the slope of the best-fit line includes determining an absolute value of the slope and comparing the absolute value of the slope to a predetermined slope threshold, the predetermined slope threshold being selected to substantially differentiate between a zero slope and a non-zero slope.

6. The method of claim 1, wherein analyzing the slope of the best-fit line includes performing significance of regression testing to determine an F₀ value and comparing the F₀ value to a predetermined F₀ threshold, the predetermined F₀ threshold being selected to substantially differentiate between a zero slope and a non-zero slope.

7. The method of claim 6, wherein F₀ is determined according to $F_o=\frac{{\mathrm{SS}}_R*\left(n-2\right)}{{\mathrm{SS}}_E},\mathrm{where}$${\mathrm{SS}}_R=\mathrm{Slope}*S_{\mathrm{xy}},$

Sxy=∑

i=1n

NORM—



DIFFi*Fi-(∑

i=1n

NORM—



DIFFi)2

(∑

i=1n

Fi)n,

Slope=SxySxx,where$S_{\mathrm{xx}}=\underset{i=1}{\overset{n}{\sum <br><br>}}<br><br>F_i^2-\frac{{\left(\underset{i=1}{\overset{n}{\sum <br><br>}}<br><br>F_i\right)}^2}{n},<br><br>{\mathrm{SS}}_E=S_{\mathrm{yy}}-{\mathrm{SS}}_R,\mathrm{and}$$S_{\mathrm{yy}}=\underset{i=1}{\overset{n}{\sum <br><br>}}<br><br>{\mathrm{NORM}}_{\mathrm{—<br><br>}}<br><br>{\mathrm{DIFF}}_i^2-\frac{{\left(\underset{i=1}{\overset{n}{\sum <br><br>}}<br><br>{\mathrm{NORM}}_{\mathrm{—<br><br>}}<br><br>{\mathrm{DIFF}}_i\right)}^2}{n}.$

8. The method of claim 1 further including

issuing a warning when the slope of the best-fit line is determined to be non-zero.

9. The method of claim 1, wherein the driven axle is a first driven axle and the vehicle further includes a second driven axle having thereon a third wheel with a tire and a fourth wheel with a tire, the method further comprising:

measuring the wheel speeds of the third wheel and the fourth wheel a plurality of times n;

calculating a difference in wheel speed, NORM_DIFF′

, between the third wheel and the fourth wheel for each of the plurality of times n;

reading a wheel force value, F′

, for the third and fourth wheels for each of the plurality of times n;

pairing each NORM_DIFF′

value with the corresponding F′

value;

performing a linear regression on the n pairings of the NORM_DIFF′

values and the F′

values to determine the slope of a best-fit line; and

analyzing the slope of the best-fit line to determine whether a tire on one of the third and the fourth wheels is deflated.

10. The method of claim 1 further including

calculating a vehicle reference speed, and wherein NORM_DIFF is calculated according to ${\mathrm{NORM}}_{—}$



DIFF=V—



LD-V—



RDV—



REF,

where

V_LD is the speed of the first wheel,

V_RD is the speed of the second wheel, and

V_REF is the vehicle reference speed.

11. The method of claim 1, wherein the slope of the best-fit line is determined according to $\mathrm{Slope}=\frac{S_{\mathrm{xy}}}{S_{\mathrm{xx}}},\mathrm{where}$$S_{\mathrm{xy}}=\sum _{}^{}$

i=1n

NORM—



DIFFi*Fi-(∑

i=1n

NORM—



DIFFi)

(∑

i=1n

Fi)n

 



and$S_{\mathrm{xx}}=\underset{i=1}{\overset{n}{\sum <br><br>}}<br><br>F_i^2-\frac{{\left(\underset{i=1}{\overset{n}{\sum <br><br>}}<br><br>F_i\right)}^2}{n}.$

12. A method for detecting loss of pressure in a tire of a motor vehicle having first and second wheels on a driven axle, third and fourth wheels on an un-driven axle, and a tire on each of the wheels, the method comprising:

measuring the wheel speeds of each of the wheels a plurality of times n;

calculating a difference in wheel speed, NORM_DIFF, between the first wheel and the second wheel for each of the plurality of times n;

calculating a driven wheel slip value, NORM_SLIP, for each of the plurality of times n;

pairing each NORM_DIFF value with the corresponding NORM_SLIP value;

performing a linear regression on the n pairings of the NORM_DIFF values and the NORM_SLIP values to determine the slope of a best-fit line; and

analyzing the slope of the best-fit line to determine whether a tire on one of the first and the second wheels is deflated.

13. The method of claim 12, further including

filtering the n pairings of the NORM_DIFF values and the NORM_SLIP values to eliminate pairings obtained during vehicle braking.

14. The method of claim 12, further including

filtering the n pairings of the NORM_DIFF values and the NORM_SLIP values to eliminate pairings obtained during vehicle maneuvering.

15. The method of claim 12, further including

filtering the n pairings of the NORM_DIFF values and the NORM_SLIP values to eliminate pairings obtained during low-speed operation of the vehicle.

16. The method of claim 12, wherein analyzing the slope of the best-fit line includes determining an absolute value of the slope and comparing the absolute value of the slope to a predetermined slope threshold, the predetermined slope threshold being selected to substantially differentiate between a zero slope and a non-zero slope.

17. The method of claim 12, wherein analyzing the slope of the best-fit line includes performing significance of regression testing to determine an F₀ value and comparing the F₀ value to a predetermined F₀ threshold, the predetermined F₀ threshold being selected to substantially differentiate between a zero slope and a non-zero slope.

18. The method of claim 17, wherein F₀ is determined according to $F_o=\frac{{\mathrm{SS}}_R*\left(n-2\right)}{{\mathrm{SS}}_E},\mathrm{where}$${\mathrm{SS}}_R=\mathrm{Slope}*S_{\mathrm{xy}},$

Sxy=∑

i=1n

NORM—



DIFFi*NORM—



SLIPi-(∑

i=1n

NORM—



DIFFi)2

(∑

i=1n

NORM—



SLIPi)n,

Slope=SxySxx,where$S_{\mathrm{xx}}=\underset{i=1}{\overset{n}{\sum <br><br>}}<br><br>{\mathrm{NORM}}_{\mathrm{—<br><br>}}<br><br>{\mathrm{SLIP}}_i^2-\frac{{\left(\underset{i=1}{\overset{n}{\sum <br><br>}}<br><br>{\mathrm{NORM}}_{\mathrm{—<br><br>}}<br><br>{\mathrm{SLIP}}_i\right)}^2}{n},<br><br>{\mathrm{SS}}_E=S_{\mathrm{yy}}-{\mathrm{SS}}_R,\mathrm{and}$$S_{\mathrm{yy}}=\underset{i=1}{\overset{n}{\sum <br><br>}}<br><br>{\mathrm{NORM}}_{\mathrm{—<br><br>}}<br><br>{\mathrm{DIFF}}_i^2-\frac{{\left(\underset{i=1}{\overset{n}{\sum <br><br>}}<br><br>{\mathrm{NORM}}_{\mathrm{—<br><br>}}<br><br>{\mathrm{DIFF}}_i\right)}^2}{n}.$

19. The method of claim 12 further including

issuing a warning when the slope of the best-fit line is determined to be non-zero.

20. The method of claim 12 further including

calculating a vehicle reference speed, and wherein NORM_DIFF is calculated according to ${\mathrm{NORM}}_{—}$



DIFF=V—



LD-V—



RDV—



REF,

where

V_LD is the speed of the first wheel,

V_RD is the speed of the second wheel, and

V_REF is the vehicle reference speed.

21. The method of claim 12, wherein the slope of the best-fit line is determined according to $\mathrm{Slope}=\frac{S_{\mathrm{xy}}}{S_{\mathrm{xx}}},\mathrm{where}$$\begin{array}{c}{S}_{\mathrm{xy}}=\end{array}$



∑

i=1n

NORM—



DIFFi*NORM—



SLIPi- 



(∑

i=1n

NORM—



DIFFi)

(∑

i=1n

NORM—



SLIPi)n$\mathrm{and}<br><br>\text{\hspace{1em}<br><br>}<br><br>S_{\mathrm{xx}}=\underset{i=1}{\overset{n}{\sum <br><br>}}<br><br>{\mathrm{NORM}}_{\mathrm{—<br><br>}}<br><br>{\mathrm{SLIP}}_i^2-\frac{{\left(\underset{i=1}{\overset{n}{\sum <br><br>}}<br><br>{\mathrm{NORM}}_{\mathrm{—<br><br>}}<br><br>{\mathrm{SLIP}}_i\right)}^2}{n}.<br><br>\text{\hspace{1em}<br><br>}$

22. A method for detecting loss of pressure in a tire of a motor vehicle having first and second wheels on a driven axle and a tire on each of the wheels, each of the tires having a grip-rate, the method comprising:

measuring the wheel speeds of the first wheel and the second wheel a plurality of times n;

calculating a difference in wheel speed value between the first wheel and the second wheel for each of the plurality of times n;

determining a value representative of the tractive force for the first wheel and the second wheel for each of the plurality of times n;

pairing each difference in wheel speed value with the value representative of the tractive force;

performing a linear regression on the n pairings of the difference in wheel speed values and the values representative of the tractive force; and

analyzing the linear regression to determine whether a tire on one of the first and the second wheels is deflated.

23. The method of claim 22, wherein determining the value representative of the tractive force includes determining a driven wheel force value for each of the plurality of times n.

24. The method of claim 22, wherein determining the value representative of the tractive force includes determining a driven wheel slip value for each of the plurality of times n.

25. The method of claim 22, wherein analyzing the linear regression includes determining the slope of a best-fit line.