Brake booster with a hinged positioning member

A brake booster comprising a housing, a piston structure dividing the housing internally into two chambers, distribution valve means arranged in a valve body integral with the piston structure and actuatable by means of an input member to generate selectively a pressure differential between the chambers, the valve means comprising a plunger mounted axially and slideably in a coaxial central bore of the valve body and connected to the input member, the plunger having at least one peripheral shoulder and defining, at one plunger end, a first flap seat, a second flap seat formed in the valve body concentrically relative to the first flap seat and flap means mounted in the valve body and stressed elastically toward the first and second flap seats, a restoring spring bearing in the valve body and axially stressing the input member in a direction away from the flap seats, and means for positioning the plunger arranged in a radial opening of the valve body opening into the central bore and interacting with the plunger to assign to the plunger at least two separate specific axial positions relative to the valve body, characterized in that the positioning means comprises a combination of a first positioning member mounted fixably in the radial opening and having an inner end zone extending in the central bore and of a second positioning member mounted rockingly in the radial opening and comprising an inner end zone extending in the central bore between the first shoulder of the plunger and the inner end zone of the first positioning member and interacting with the first positioning member in hinged contact, a central portion and an outer end capable of interacting, in the vicinity of a rest position of the booster, with a stationary element connected to the housing to cause the second positioning member to rock from a first position in which the inner end zones are axially adjacent and a second position, in the rest position of the booster, in which the second positioning member, bearing against the first shoulder by means of the associated inner end zone, is set angularly at a distance from the first positioning member, the distance increasing in a direction away from the inner end zones and toward said outer end, the inner end zone of the first positioning member having a U-shaped profile with two lateral arms having ends situated, in an assembly configuration, on the axis side of the central bore away from the outer end of the second positioning member, the inner end zone of the second positioning member having a U-shaped profile with two lateral arms having end portions extending axially above the ends of the lateral arms of the inner end zone of the first positioning member in order to provide said hinged contact therebetween, the positioning members located adjacent one another within the valve body.