Method of diagnosing a vehicle brake system using brake pedal position and vehicle deceleration

• US 6,405,117 B1
• Filed: 06/21/2001
• Issued: 06/11/2002
• Est. Priority Date: 06/21/2001
• Status: Expired due to Fees

• Current Assignee: GM Global Technology Operations Incorporated (Motors Liquidation Co. GUC Trust)
• Original Assignee: General Motors Corporation (Motors Liquidation Co. GUC Trust)
• Inventors: Thatcher, David Alan, Leppek, Kevin Gerard, Walenty, Allen John
• Primary Examiner(s): ARTHUR JEANGLAUDE, GERTRUDE
• Application Number:
  US09/885,191
• Time in Patent Office: 355 Days
• Field of Search: 701/29, 701/30, 701/33, 701/35, 701/36, 701/34, 701/70, 701/71, 701/74, 701/75, 731/21, 731/171, 731/181, 731/29
• US Class Current: 701/70
• CPC Class Codes: B60T 17/221 Procedure or apparatus for checking or keeping in a correct functioning condition of brake systems hydraulic pressure systems in general F15B19/00, F15B21/04; testing structures or apparatus G01M
• CPC Class Codes: B60T 2270/406 Test-mode; Self-diagnosis
• CPC Class Codes: B60T 8/885 using electrical circuitry
• CPC Class Codes: G01L 5/28 for testing brakes

Abstract

An improved method of diagnosing conditions of a vehicle braking system that degrade the braking effectiveness informs the driver of the condition so that repair or adjustment can be timely made. The relationship between brake pedal position and vehicle deceleration is determined during a calibration interval to construct a calibration table of brake effectiveness, and then periodically over the life of the braking system to develop a current brake effectiveness table. Braking system abnormalities that impair the braking effectiveness are diagnosed by analyzing the table values.

Claims

1. A method of diagnosing an operation of a motor vehicle braking system including a driver positioned brake pedal, the method comprising the steps of:

periodically measuring vehicle deceleration and a brake pedal position during activation of the braking system;

storing calibration brake effectiveness data characterizing a relationship between the measured vehicle deceleration and measured brake pedal position during a calibration interval;

periodically storing current brake effectiveness data characterizing the relationship between the measured vehicle deceleration and measured brake pedal position during a diagnostic interval subsequent to said calibration interval; and

diagnosing abnormalities that impair the operation of the braking system based on the stored data.

2. The method of claim 1, wherein the vehicle includes front and rear wheels, the braking system includes rear wheel brakes that require periodic adjustment, and the method includes the steps of:

measuring speeds of the front and rear wheels; and

diagnosing a condition of non-adjusted rear wheel brakes when the speed of the rear wheels exceeds the speed of the front wheels by a reference value for at least a predefined time interval.

3. The method of claim 2, wherein the reference value varies as a function of the measured brake pedal position.

4. The method of claim 1, including the step of:

suspending the steps of storing the calibration and current brake effectiveness data if the measured vehicle deceleration exceeds a predefined threshold.

5. The method of claim 1, including the step of:

suspending the steps of storing the calibration and current brake effectiveness data when the measured brake pedal position decreases during the braking system activation.

6. The method of claim 1, including the step of

disabling the steps of storing the calibration and current brake effectiveness data when the measured brake pedal position increases at a rate in excess of a reference rate.

7. The method of claim 1, including the step of:

disabling the steps of storing the calibration and current brake effectiveness data if the measured vehicle deceleration is less than a predefined threshold.

8. The method of claim 1, including the step of compensating the measured vehicle deceleration based on a vehicle deceleration in effect prior to activation of the braking system.

9. The method of claim 1, wherein the step of storing the calibration brake effectiveness data is repeated after servicing of the vehicle braking system.

10. The method of claim 1, wherein the stored current brake effectiveness data is determined by averaging measured brake pedal position values corresponding to predefined vehicle deceleration levels during a first predefined number of braking system activations.

11. The method of claim 10, wherein the stored calibration brake effectiveness data is determined by averaging measured brake pedal position values corresponding to predefined vehicle deceleration levels during a second predefined number of braking system activations which is greater than said first predefined number.

12. The method of claim 1, wherein the step of diagnosing abnormalities includes the steps of:

determining an expected vehicle deceleration from the calibration brake effectiveness data based on a measured brake pedal position value;

computing a deceleration loss based on a difference between the measured vehicle deceleration and the expected vehicle deceleration when the measured vehicle deceleration is less than the expected vehicle deceleration ; and

diagnosing impaired operation of the braking system when the computed deceleration loss exceeds a loss threshold for a predefined time interval.

13. The method of claim 12, wherein the step of diagnosing impaired operation of the braking system includes the steps of:

determining a braking system temperature; and

diagnosing a condition of brake fading when the computed deceleration loss exceeds the loss threshold for a predefined time interval and the determined braking system temperature exceeds a threshold temperature.

14. The method of claim 13, wherein the step of diagnosing impaired operation of the braking system includes the step of:

diagnosing a condition of brake fluid leakage when the computed deceleration loss exceeds the loss threshold for a predefined time interval and the determined braking system temperature is less than the threshold temperature.

15. The method of claim 12, including the steps of:

periodically incrementing a counter when the computed deceleration loss exceeds the loss threshold;

periodically decrementing the counter when the computed deceleration loss is below a secondary threshold which is lower than said loss threshold; and

diagnosing impaired operation of the braking system when the counter reaches a value corresponding to said predefined time interval.

16. The method of claim 15, including the step of:

resetting the diagnosis of impaired operation when said counter is decremented to a zero threshold.

17. The method of claim 1, wherein the step of diagnosing abnormalities includes the steps of:

comparing the calibration brake effectiveness data to the current brake effectiveness data to determine a brake wear value when the current brake effectiveness data indicates less braking effectiveness than the calibration brake effectiveness data; and

diagnosing a condition of brake wear when the determined brake wear value exceeds a brake wear threshold for a predefined time interval.

18. The method of claim 17, wherein the calibration and current brake effectiveness data include measured brake pedal positions corresponding to predefined vehicle deceleration values, and the method includes the steps of:

retrieving brake pedal positions from the calibration and current brake effectiveness data for at least one vehicle deceleration value;

comparing the retrieved brake pedal positions, and determining the brake wear value based on a difference between the retrieved brake pedal positions when the brake pedal position retrieved from the current brake effectiveness data is greater than the brake pedal position retrieved from the calibration brake effectiveness data.

19. The method of claim 18, including the steps of:

periodically incrementing a counter when the determined brake wear value exceeds the brake wear threshold;

periodically decrementing the counter when the determined brake wear value falls below the brake wear threshold; and

diagnosing the condition of brake wear when the counter reaches a value corresponding to said predefined time interval.

20. The method of claim 19, wherein the steps of retrieving and comparing brake pedal positions and periodically incrementing and decrementing the counter are repeated for each of a plurality of vehicle deceleration values.

21. The method of claim 19, including the step of:

resetting the diagnosis of the condition of brake wear when said counter is decremented to a zero threshold.