Vehicle hydraulic braking system with independent brake circuits

Claim 1

An hydraulic braking system for vehicles comprising a plurality of independent brake circuits; a master cylinder assembly including a housing having a plurality of bores, a plurality of master cylinders arranged in said housing corresponding in number to said master cylinders and each master cylinder is connected in at least one of said circuits, and booster means in said housing for at least partially operating all of said master cylinders by fluid pressure, said booster means being arranged so that a failure in one brake circuit does not affect the operation of the remaining master cylinders; a source of hydraulic fluid under pressure; and manually operated valve means for controlling the supply of fluid from said source to said booster means, said booster means comprising a booster chamber in said housing, and a plurality of modulator pistons working in said bores to operate said master cylinders, being movable between retracted and advanced positions, each modulator piston being of stepped outline and having a first end exposed to said booster chamber, a second opposite end of an area less than that of said first end and acting to operate a corresponding one of said master cylinders, and an intermediate portion of an area greater than that of said first end and providing a reaction face of an effective area greater than that of said first end and exposed to a portion of said bore on the side of said intermediate portion remote from said first end which defines a control space, a plurality of control valves each providing communication between said booster chamber and a corresponding one of said control spaces and movable between a closed position and an open position, and a plurality of anti-skid sensing means each responsive to deceleration of a braked wheel in one of said brake circuits to control operation of the one said control valve which controls communication between said booster chamber and said control space for the master cylinder which control the said one of said brake circuits, each anti-skid sensing means being operative when the deceleration of the corresponding braked wheel exceeds a predetermined value to open the said control valve controlled thereby and connect said control space to said booster chamber whereby equal fluid pressure acting over different areas of said modulator piston apply thereto a resultant force to urge said modulator piston into said retracted position to relieve the braking effect of said braked wheel independently of operation of the other of said master cylinders.