Adaptive compensation method for an anti-lock brake control

• US 20030045989A1
• Filed: 08/31/2001
• Published: 03/06/2003
• Est. Priority Date: 08/31/2001
• Status: Active Grant

• Current Assignee: GM Global Technology Operations LLC (General Motors Company)
• Original Assignee: GM Global Technology Operations Incorporated (General Motors Company)
• Inventors: Thatcher, David Alan, Leppek, Kevin Gerard, Walenty, Allen John
• Granted Patent: US 6,859,712 B2
• Time in Patent Office: Days
• US Class Current: 701/71
• CPC Class Codes: B60T 2270/403 Brake circuit failure
• CPC Class Codes: B60T 2270/602 ABS features related thereto
• CPC Class Codes: B60T 8/17636 Microprocessor-based systems
• CPC Class Codes: B60T 8/50 having means for controlling the rate at which pressure is reapplied to or released from the brake
• CPC Class Codes: B60T 8/885 using electrical circuitry

Abstract

An improved anti-lock control method for a vehicle brake system identifies various factors that degrade the effectiveness of the brake system and adaptively adjusts a brake apply rate during anti-lock brake control to compensate for the identified degradation so that the optimal tractive force during anti-lock brake control is more nearly realized. The identified factors include fading due to brake heating, hydraulic leakage, mis-adjusted and non-releasing rear brakes, brake wear and excessive vehicle weight.

Claims

1. A method of operation for a vehicle braking system including a driver activated brake pedal, a brake pressure modulator, and an anti-lock brake control that activates the brake pressure modulator to modulate vehicle braking upon detection of an insipient wheel lock condition, the method comprising the steps of:

periodically measuring vehicle deceleration and a brake pedal position during activation of the braking system when said insipient wheel lock condition is not detected;

identifying conditions of degraded braking effectiveness based on the periodically measured deceleration and brake pedal position; and

adaptively adjusting a brake pressure control parameter of said anti-lock brake control when a condition of degraded braking effectiveness is identified so as to compensate for the identified condition.

2. The method of claim 1, wherein the anti-lock brake control releases and then re-applies brake pressure at a determined apply rate upon detection of an insipient wheel lock condition, and the step of adaptively adjusting a brake control parameter includes adjusting the determined apply rate in a manner to provide an increased rate of brake pressure application.

3. The method of claim 1, wherein the identified condition of degraded braking effectiveness is brake wear, and the determined apply rate is increased by a predefined factor.

4. The method of claim 1, wherein the anti-lock brake control releases and then re-applies brake pressure at a determined apply rate upon detection of an insipient wheel lock condition, the method including the steps of:

estimating a road surface coefficient of friction based on the periodically measured deceleration and brake pedal position;

determining said apply rate based on the estimated road coefficient of friction when conditions of degraded braking effectiveness are not identified; and

determining said apply rate based on the estimated road coefficient of friction and a measure of braking effectiveness degradation when the condition of degraded braking effectiveness is identified.

5. The method of claim 4, wherein the step of determining the apply rate when the condition of degraded braking effectiveness is identified includes the steps of:

compensating the estimated road surface coefficient of friction for error due to the identified condition of degraded braking effectiveness; and

determining the apply rate based on the compensated estimate of road surface coefficient of friction and the measure of braking effectiveness degradation.

6. The method of claim 4, wherein the identified condition of degraded braking effectiveness is brake fading, and the measure of braking effectiveness degradation is determined according to an amount by which an estimate of brake temperature exceeds a nominal brake temperature.

7. The method of claim 4, wherein the identified condition of degraded braking effectiveness is fluid leakage, and the measure of braking effectiveness degradation is determined according to an estimated rate of the fluid leakage.

8. The method of claim 4, wherein the braking system includes an adjustable brake, the identified condition of degraded braking effectiveness is mis-adjustment of said adjustable brake, and the measure of braking effectiveness degradation is determined according to a difference in wheel speeds attributable to such mis-adjustment.

9. The method of claim 4, wherein the identified condition of degraded braking effectiveness is excessive vehicle weight, and the measure of braking effectiveness degradation is determined according to an amount by which an estimate of vehicle weight exceeds a reference weight.