Hierarchical brake controller

• US 4,850,650 A
• Filed: 09/02/1988
• Issued: 07/25/1989
• Est. Priority Date: 09/02/1988
• Status: Expired due to Fees

• Current Assignee: General Motors Corporation (General Motors Company)
• Original Assignee: General Motors Corporation (General Motors Company)
• Inventors: Boustany, Nader M., Eckert, Steve J., Salman, Mutasim A.
• Primary Examiner(s): Halvosa, George E. A.
• Assistant Examiner(s): Graham, Matthew C.
• Application Number:
  US07/239,908
• Time in Patent Office: 326 Days
• Field of Search: 303/9.62, 303/9.69, 303/9.71, 303/93, 303/94, 303/95, 303/100, 303/107, 303/108, 303/109, 303/113, 303/100, 364/426.02, 188/182
• US Class Current: 303/9.62
• CPC Class Codes: B60T 13/662 characterised by specified functions of the control system components
• CPC Class Codes: B60T 13/745 acting on a hydraulic system, e.g. a master cylinder
• CPC Class Codes: B60T 8/1766 Proportioning of brake forces according to vehicle axle loads, e.g. front to rear of vehicle
• CPC Class Codes: B60T 8/266 using valves or actuators with external control means B60T8/261 takes precedence
• CPC Class Codes: B60T 8/326 Hydraulic systems

Abstract

A hierarchical brake controller is described having two control levels, a high level supervisory controller and a low local controller. The supervisory controller receives a vehicle deceleration rate command from the vehicle operator and determines a commanded brake line pressure value to establish the actual vehicle deceleration at the operator commanded rate. The supervisory controller then proportions the commanded brake line pressure between the front and rear brakes based on a determined proportioning factor. The local controller at each wheel functions to establish the respective commanded front or rear brake line pressure. In addition, the local controller for each of the rear brake limits the applied brake pressure in response to a sensed incipient wheel lockup condition to prevent lockup of the braked wheel. The local controller for a rear brake that is limiting brake pressure to prevent a lockup condition provides a maximum allowable rear brake pressure value to the supervisory controller. The supervisory controller then limits the commanded brake line pressure and therefore the commanded front brake line pressure to values based on the maximum allowable rear brake pressure and the proportioning value between the front and rear brakes.

Claims

1. A system for controlling the brake pressure applied to the brakes of the front and rear wheels of a vehicle, the system comprising in combination:

means for generating a brake pressure command value P_c in accord with an operator commanded braking value;

means for generating a front brake pressure command P_cf having a value Y*P_c where Y is a desired front-to-rear proportioning brake pressure ratio;

means for generating a rear brake pressure command P_cr having a value (1-Y)P_c ;

front brake pressure control means for controlling the brake pressure applied to each of the front wheel brakes to the value P_cf ;

rear brake pressure control means, the rear brake pressure control means including means for controlling the brake pressure applied to each of the rear wheel brakes to the lesser of the value P_cr or a value P_rm determined to prevent a rear wheel lock-up condition; and

means for limiting the brake pressure command value P_c to a maximum value P_cm having a value (1/(1-Y))P_rm, whereby the front brake pressure command P_cf is limited to a value preventing front wheel lock-up based on the rear brake pressure value P_rm determined to prevent a rear wheel lock-up.

2. The system of claim 1 wherein the operator commanded braking value is a commanded vehicle deceleration value and the means for generating the brake pressure command value P_c includes (A) means for sensing vehicle deceleration and (B) means for adjusting the brake pressure command value P_c to establish the sensed vehicle deceleration at the commanded vehicle deceleration value.

3. A system for controlling the brake pressure applied to the brakes of the front and rear wheels of a vehicle traveling over a road surface, the system comprising in combination:

means for generating a brake pressure command value P_c in accord with an operator commanded braking value;

means for generating a front brake pressure command P_cf having a value Y*P_c where Y is a desired front-to-rear proportioning brake pressure ratio;

means for generating a rear brake pressure command P_cr having a value (1-Y)P_c ;

front brake pressure control means for controlling the brake pressure applied to each of the front wheel brakes to the value P_cf ;

rear brake pressure control means, the rear brake pressure control means including for each rear wheel (A) means for controlling the rear wheel brake pressure to the rear brake pressure command value P_cr when the value P_cr is less than a maximum value P_rm and to the maximum value P_rm when the value P_cr is greater than P_rm, (B) means for detecting an incipient wheel lockup condition and (C) means responsive to an incipient wheel lockup condition to establish the value of P_rm at the maximum brake pressure that can be attained before an incipient wheel lockup condition will occur; and

means for limiting the brake pressure command value P_c to a maximum value P_cm having a value (1/(1-Y))P_rm, whereby the front brake pressure command P_cf is limited to a maximum front wheel pressure before an incipient wheel lockup condition will occur.

4. The system of claim 3 wherein the operator commanded braking value is a commanded vehicle deceleration value, the means for generating the brake pressure command value P_c includes (A) means for sensing vehicle deceleration and (B) means for adjusting the brake pressure command value P_c to establish the sensed vehicle deceleration at the commanded vehicle deceleration value.

5. The system of claim 4 further including (A) means for determining the normal weight W_f (t) on the road surface at the front wheels as a predetermined function of vehicle deceleration and for determining the normal weight W_r (t) on the road surface at the rear wheels as a predetermined function of vehicle deceleration and (B) means for determining the value of Y in accord with the expression Y=W_f (t)/(W_f (t)+W_r (t)).

6. A method of controlling the brake pressure applied to the brakes of the front and rear wheels of a vehicle, the method comprising the steps of:

generating a brake pressure command value P_c in accord with an operator commanded braking value;

generating a front brake pressure command P_cf having a value Y*P_c where Y is a desired front-to-rear proportioning brake pressure ratio;

generating a rear brake pressure command P_cr having a value (1-Y)P_c ;

controlling the brake pressure applied to each of the front wheel brakes to the value P_cf ;

controlling the brake pressure applied to each of the rear wheel brakes to the lesser of the value P_cr or a value P_rm determined to prevent a rear wheel lock-up condition; and

limiting the brake pressure command value P_c to a maximum value P_cm having a value (1/(1-Y))P_rm, whereby the front brake pressure command P_cf is limited to a value preventing front wheel lock-up based on the rear brake pressure value P_rm determined to prevent a rear wheel lock-up.