Brake control system for vehicles

Brake control system including a fluid reservoir, hydraulic pressure source means, brake control valve means, means for actuating said brake control valve means, and brake means including at least one brake actuating means connected with said brake control valve means, said brake control valve means including at least one brake pressure control valve comprising a valve housing having an axial bore provided with an inlet port for connection with said hydraulic pressure source means, an outlet port for connection with said brake actuating means and a return port for connection with said fluid reservoir, a valve spool slidably disposed in said axial bore of said valve housing, said valve spool having land means defining within said valve housing a first control chamber at one side of said land means and a second control chamber at the other side, means provided in said valve spool for connecting said inlet port with said outlet port when said valve spool is slidably displaced toward a first direction in said axial bore of said valve housing, means provided in said valve spool for connecting said outlet port with said return port when said valve spool is slidably displaced toward a second direction in said axial bore of said valve housing, said outlet port being so disposed that pressure therein serves to bias said valve spool toward the second direction, said first and second control chambers being so disposed that pressure in said first chamber biases said valve spool toward the second direction while pressure in said second chamber biases said valve spool toward the first direction, first and second restricted passages connecting, through said first and second chambers respectively, said hydraulic pressure source means to said fluid reservoir, means provided in at least one of said first and second restricted passages for regulating pressure in said first and second chambers, and means for actuating said regulating pressure means upon detection of braking force conditions which exceed or are below certain predetermined levels, and wherein said means for actuating said brake control valve means includes means for actuating said valve spool toward the first direction.