Hydraulic braking systems for vehicles

Hydraulic braking system for vehicles of the four wheel type having a pair of front wheels, a pair of rear wheels, a front brake on each said front wheel, and a rear brake on each said rear wheel, said system comprising first brake-applying fluid pressure generating means for generating a pressure for applying said front wheel brakes, second pressure-generating means for generating a pressure for applying said rear wheel brakes, wherein said pressure generated by said second pressure-generating means is dependent upon said pressure applied to at least one of said front wheel brakes by said first pressure generating means, sensing means responsive to the behavior of said rear wheels, at least one solenoid-operated valve responsive to signals from said sensing means, and a fluid-powered unit for controlling operation of said rear brakes under the control of said solenoid-operated valve, wherein said fluid powered unit comprises a stepped de-boost piston working in a stepped bore and having a first portion of smaller area exposed to said rear brake, and a second portion of larger area defining a pressure-responsive control member, an isolating valve, and a double-seated solenoid-operated valve, said de-boost piston normally being sustained in an advanced position by a pressure differential action across said control member, in which position said control member holds said isolating valve open, and said solenoid-operated valve acts in a first position to establish said pressure differential, movement of said solenoid-operated valve into a second position in response to a signal from said sensing means acting to destroy said pressure differential with the result that said piston moves into a retracted position, initially to permit said isolating valve to close and isolate said fluid pressure supply from said brakes and thereafter to increase the effective volume of a smaller portion of said bore in which said first portion works, whereby to relieve any pressure applied to said brakes.

Hydraulic braking system for vehicles of the four wheel type having a pair of front wheels, a pair of rear wheels, a front brake on each said front wheel, a brake-pressure modulator for each said front brake, and a rear brake on each said rear wheel, said system comprising first brake-applying fluid pressure generating means for generating a pressure for applying said front wheel brakes, second pressure-generating means for generating a pressure for applying said rear wheel brakes, wherein said pressure generated by said second pressure-generating means is dependent upon said pressure applied to at least one of said front wheel brakes by said first pressure generating means, sensing means responsive to the behavior of said rear wheels, at least one solenoid-operated valve responsive to signals from said sensing means, and a fluid-powered unit for controlling operation of said rear brakes under the control of said solenoid-operated valve, wherein a pneumatically-operated booster-assisted tandem hydraulic master cylinder is adapted to apply said front wheel brakes, and a second solenoid-operated valve means is provided to control operation of said booster independently of a foot pedal and in response to signals from wheel speed sensors associated with both front wheels, whereby said master cylinder is operated to apply the brakes but said brake on the non-spinning front wheel is prevented from being applied by said modulator for that wheel, and said brakes on said rear wheels are prevented from being applied by simultaneous energization of the solenoid-operated valve means for anti-lock control of the rear wheels.