Vacuum brake booster with a valve for allowing atmospheric air into a variable pressure chamber, the position for opening of the valve being adjustable

Claim 1

A brake booster of the vacuum type, comprising a casing within which is located a piston which, by means of a diaphragm, defines a front chamber connected permanently to a vacuum source and a rear chamber connected to said vacuum source when the booster is at rest, valve means establishing a pressure difference between the two chambers during actuation of a control rod capable, by means of a plunger, of bearing on one face of a reaction disk integral with a push rod intended for actuating a master cylinder, said valve means comprising a first shutter for coming to bear on a first shutter seat integral with said piston and determining, at rest, communication between said front and rear chambers, a second shutter bearing, at rest, on a second shutter seat integral with said plunger in order to close communication between the rear chamber and the outside of said booster, said second shutter being equipped with a stop for limiting its stroke while accompanying said plunger, and a spring tending to keep said first and second shutters apart from one another, said seats and shutters being arranged in such a way that, during operation, said first shutter closes communication between said front and rear chambers before said second shutter opens communication between the rear chamber and the outside of the booster.