Anti-lock brake control system

• US 4,750,124 A
• Filed: 11/19/1986
• Issued: 06/07/1988
• Est. Priority Date: 11/19/1986
• Status: Expired due to Term

• Current Assignee: General Motors Corporation (Motors Liquidation Co. GUC Trust)
• Original Assignee: General Motors Corporation (Motors Liquidation Co. GUC Trust)
• Inventors: Zarei, Shahram, Lin, William C. W.
• Primary Examiner(s): Chin, Gary
• Application Number:
  US06/932,401
• Time in Patent Office: 566 Days
• Field of Search: 364/426, 364/566, 180/197, 303/100, 303/104, 303/110, 303/111, 303/112, 303/97, 303/DIG. 4
• US Class Current: 701/79
• CPC Class Codes: B60T 8/17636 Microprocessor-based systems
• CPC Class Codes: B60T 8/326 Hydraulic systems
• CPC Class Codes: B60T 8/5056 Pressure reapplication using memory devices
• CPC Class Codes: Y10S 303/04 Pressure signal used in electrical speed controlled braking circuit

Abstract

A wheel lock control system is described for a wheel braking system in which the brake pressure producing the critical slip value and therefore the peak braking effort is precisely determined. The brake pressure that is reapplied following an incipient wheel lockup condition is determined as a function of (A) the brake pressure and wheel deceleration corresponding in time to the peak calculated tire torque tending to accelerate the wheel during braking prior to the detection of an incipient wheel lockup condition and (B) the brake pressure and wheel acceleration corresponding in time to the peak calculated tire torque tending to accelerate the wheel during wheel speed recovery following an incipient wheel lockup condition. By using these parameters, the precise brake pressure for establishing the critical wheel slip is determined so that the maximum braking effort may be established following a detected incipient lockup condition.

Claims

1. A method of limiting the brake pressure applied to the brake of a vehicle wheel, the method comprising the steps of:

determining the brake pressure applied to the brake;

determining the rate of change in wheel speed;

determining the maximum tire torque tending to accelerate the wheel during each period of application of brake pressure;

storing the determined brake pressure and the determined rate of change in wheel speed correspponding in time to the determined maximum tire torque during each period of application of brake pressure;

detecting an incipient wheel lockup condition;

reducing the brake pressure in response to a detected incipient wheel lockup condition to allow wheel speed recovery;

determining the maximum tire torque tending to accelerate the wheel during wheel speed recovery following each reduction of brake pressure in response to a sensed incipient wheel lockup condition;

storing the determined brake pressure and the determined rate of change in wheel speed corresponding in time to the determined maximum tire torque during wheel speed recovery following each reduction of brake pressure in response to a detected incipient wheel lockup condition; and

applying brake pressure to the brake following wheel speed recovery with a value that is a predetermined function of the stored brake pressure and rate of change in wheel speed during the period of application of brake pressure prior to a detected incipient wheel lockup condition and the stored brake pressure and rate of change in wheel speed during wheel speed recovery after the detected incipient wheel lockup condition.

2. A wheel lock control system for limiting the brake pressure applied to the brake of vehicle wheel, the system comprising:

means for sensing wheel speed and

control means, the control means including

means for determining the brake pressure applied to the brake,

means for determining the rate of change in the sensed wheel speed,

means for detecting an incipient wheel lockup condition,

means for reducing the brake pressure in response to a detected incipient wheel lockup condition to allow wheel speed recovery,

means for determining the maximum tire torque tending to accelerate the wheel (A) during each period of application of brake pressure prior to a detected incipient wheel lockup condition and (B) during wheel speed recovery following each reduction of brake pressure in response to a detected incipient wheel lockup condition,

means for storing the determined the brake pressure and the determined rate of change in wheel speed corresponding in time to the determined maximum tire torque during each period of application of brake pressure prior to a detected incipient wheel lockup condition,

means for storing the determined brake pressure and the determined rate of change in wheel speed corresponding in time to the determined maximum tire torque during wheel speed recovery following each reduction of brake pressure in response to a detected incipient wheel lockup condition and

means for applying brake pressure to the brake following wheel speed recovery with a value that is a predetermined function of the stored brake pressure and rate of change in wheel speed during the period of application of brake pressure prior to a detected incipient wheel lockup condition and the stored brake pressure and rate of change in wheel speed during wheel speed recovery after the detected incipient wheel lockup condition.

3. A wheel lock control system for limiting the brake pressure applied to the brake of a vehicle wheel, the system comprising:

means for sensing wheel speed and

control means, the control means including

means for determining the brake pressure applied to the brake,

means for determining the rate of change ω

in the sensed wheel speed,

means for detecting an incipient wheel lockup condition,

means for reducing the brake pressure in response to a detected incipient wheel lockup condition to allow wheel speed recovery,

means for determining the maximum value of tire torque T_t tending to accelerate the wheel (A) during each period of application of brake pressure prior to a detected incipient wheel lockup condition and (B) during wheel speed recovery following each reduction of brake pressure in response to a detected incipient wheel lockup condition,

means for storing a brake pressure value P₁ of the determined brake pressure and a rate of change value ω

_m in the determined rate of change in wheel speed corresponding in time to the determined maximum tire torque during each period of application of brake presusre prior to a detected incipient wheel lockup condition,

means for storing a brake pressure value P₂ and a rate of change value ω

_r in the determined rate of change in wheel speed corresponding in time at the determined maximum tire torque during wheel speed recovery following each reduction of brake pressure in response to a sensed incipient wheel lockup condition and

means for applying brake pressure to the brake following wheel speed recovery with a value P_c defined by the expression P_c =(ω

_r P₁ -ω

_m P₂)/(ω

_r -ω

_m).

4. The wheel lock control system of claim 3 wherein T_t is defined by the expression T_t =I_w ω

+P_b K_b where I_w and K_b are predetermined constants and P_b is the brake pressure.