Brake booster

A brake booster comprising a housing, a piston structure dividing the housing internally into two chambers, distribution valve means arranged in a valve body which is connected with the piston structure and actuable by means of an input member to generate selectively a pressure differential between the chambers, the valve means comprising a plunger mounted axially and slidably in a central bore of the valve body and connected to the input member, the plunger having at least one first shoulder and defining at an 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 stressing the input member in a direction opposite the flap seats, and means for positioning the plunger which is arranged in the valve body and which interacts with the plunger to assign to the plunger at least two separate specific positions relative to the valve body, characterized in that the positioning means comprises the combination of a first positioning member fastened in the valve body and having an inner end capable of interacting with a first zone of the first shoulder of the plunger to position the plunger in a specific position of retraction relative to the valve body, and a second positioning member mounted pivotally in the valve body and having a first portion capable of interacting with a second zone of the first shoulder of the plunger and a second portion capable of interacting, in the vicinity of a position of rest of the booster, with a stationary element connected to the housing in order, at least in the position of rest, to place the second positioning member in a specific angular position which positions the plunger, via the first portion of the second positioning member, in a specific position of rest relative to the valve body, the first zone of the first shoulder of the plunger and the second portion of the second positioning member interacting with the stationary element being located on one and the same side relative to a diametral plane of the plunger, and the second zone of the first shoulder and first portion of the second positioning member being located on the other side of the diametral plane.