Pneumatic booster

Claim 1

A pneumatic booster comprising a housing, power piston including means for partitioning the interior of the housing into a front chamber and a rear chamber, means for connecting said front chamber permanently to a source of a first reference pressure, a valve mechanism for selectively connecting said rear chamber with said front chamber and a source of second reference pressure which is higher than the first reference pressure, an output shaft receiving the output force from said power piston, an input shaft coupled with said valve mechanism for receiving an input force and for actuating said valve mechanism in response thereto and engagable by sid output shaft for receiving the reaction force of the output force, reaction force changing means on said output shaft for changing the reaction force transmitted to the input shaft with respect to the output force, said changing means including a resilient reaction disk disposed in front of the end of the input shaft which is toward said output shaft, a plurality of separate members interposed between the surface of the reaction disk which is toward said output shaft and the end of the output shaft which is toward said input shaft and having different areas abutting said surface of the reaction disk which is toward said output shaft, said members being selectively engageable by the output shaft when the output shaft is in different rotational positions sot as to change the effective area in which the reaction disk receives a reaction force from the output shaft in transmitting the output force from the reaction disk to the input shaft, and a mechanism for rotating the output shaft around the axis thereof to different rotational positions.