Motor vehicle braking system

Claim 1

A motor vehicle braking system comprising a brake pedal, a booster having opposed variable and fixed pressure chambers, first valve means operable by said brake pedal to supply pressure to said booster, and a first sensor for detecting the force generated by said brake pedal upon movement thereof in a brake applying direction, a second sensor for determining vehicle deceleration by detecting the rotational retardation of at least one wheel, a second electrically operated valve for supplying pressure to said booster, a data processing unit for comparing data determined by said first and second sensors and generating a signal to operate said second valve for adjusting pedal controlled pressure in said booster to provide a predetermined vehicle deceleration commensurate with a detected pedal force, said second valve having a first port connected to the fixed pressure chamber of said booster, a second port connected to the variable pressure chamber of said booster and a third port connected to a source of high pressure fluid, a movable valve element in said second valve, first spring means biasing said movable valve element against a fixed valve seat disconnecting said second and third ports while connecting said first and second ports, a movable valve seat in said valve engageable with said movable valve element to disconnect said first and second ports and then lift said movable valve element from said fixed valve seat to connect said third and second ports, a valve plunger carrying said movable valve seat and which is displaceable, in response to a signal generated by said data processor unit, axially by an electromagnet in a direction which is opposite to the direction in which said movable valve element is biased by said first spring, a second spring carried by said plunger which upon axial movement of said plunger towards said movable valve element, engages and exerts a force on said movable valve element as said movable valve seat is moved into engagement with said movable valve element, said first spring being predetermined stronger than said second spring whereby the force exerted by said movable valve seat on said movable valve element to open the same is lessened by the difference in the forces of the respective springs, and the sensitivity of said second valve is thereby enhanced.