Servomotor for braking assistance with reduced stroke of actuation

Claim 1

Servomotor for braking assistance, of a vacuum type, including a first chamber (22) intended to be connected to a vacuum source, a second chamber (26) separated from the first chamber by a driving piston (20) connected to an output member, said driving piston comprising a distribution valve (30) actuable by an input push rod (36) to selectively put said second chamber in communication with said first chamber or with the atmosphere, said valve comprising a movable annular valve poppet (32) resiliently axially biased and capable of coming alternately into sealing abutment against a movable seat (34) integral with said push rod and against an annular seat (40) defined in said driving piston around said movable seat, said movable seat being constructed at one end of a plug (50) mounted axially slidingly within said driving piston, said valve poppet being in abutment against said movable seat and spaced apart from said annular seat in the rest position of the servomotor, characterized in that it comprises a movable stop (60) extending approximately perpendicularly to the axis of said rod and resiliently axially biased so as to normally bear in abutment against a bearing surface (51) which is fixed relative to the driving piston, in said rest position, and in that said stop cooperates with an abutment surface (61) of said push rod to maintain in said rest position said movable valve poppet at a short distance (d) from said annular seat, thereby reducing the idle stroke of actuation of the servomotor.