Hierarchical brake controller

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.sub.c in accord with an operator commanded braking value;
• means for generating a front brake pressure command P.sub.cf having a value Y*P.sub.c where Y is a desired front-to-rear proportioning brake pressure ratio;
• means for generating a rear brake pressure command P.sub.cr having a value (1-Y)P.sub.c ;
• front brake pressure control means for controlling the brake pressure applied to each of the front wheel brakes to the value P.sub.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.sub.cr when the value P.sub.cr is less than a maximum value P.sub.rm and to the maximum value P.sub.rm when the value P.sub.cr is greater than P.sub.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.sub.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.sub.c to a maximum value P.sub.cm having a value (1/(1-Y))P.sub.rm, whereby the front brake pressure command P.sub.cf is limited to a maximum front wheel pressure before an incipient wheel lockup condition will occur.

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.sub.c in accord with an operator commanded braking value;
• generating a front brake pressure command P.sub.cf having a value Y*P.sub.c where Y is a desired front-to-rear proportioning brake pressure ratio;
• generating a rear brake pressure command P.sub.cr having a value (1-Y)P.sub.c ;
• controlling the brake pressure applied to each of the front wheel brakes to the value P.sub.cf ;
• controlling the brake pressure applied to each of the rear wheel brakes to the lesser of the value P.sub.cr or a value P.sub.rm determined to prevent a rear wheel lock-up condition;
• and
• limiting the brake pressure command value P.sub.c to a maximum value P.sub.cm having a value (1/(1-Y))P.sub.rm, whereby the front brake pressure command P.sub.cf is limited to a value preventing front wheel lock-up based on the rear brake pressure value P.sub.rm determined to prevent a rear wheel lock-up.