Tandem-type brake booster

Claim 1

A tandem-type brake booster comprising a closed shell assembly composed of front and rear chambers defined by a partition member therein and first and second power pistons coaxially disposed in said front and rear chambers, respectively, said power pistons being operatively coupled with each other and passing through a substantially central portion of said partition member, each of said front and rear chambers including a constant-pressure chamber subjected to a vacuum and a variable-pressure chamber, respectively, and means for selectively communicating said variable pressure chamber of said rear chamber with said constant pressure chambers and atmosphere, said constant-pressure chambers in said front and rear chambers being held in communication with each other, said variable-pressure chambers in said front and rear chambers being in communication with each other, said power pistons being axially movable in unison by pressure differences between said constant-pressure chambers and said variable-pressure chambers, respectively, one of said front and rear chambers having an outside diameter smaller than that of the other chamber and that of the power piston disposed in said other chamber, and the power piston in said other chamber having an outer peripheral portion overlapping an outer peripheral portion of said one chamber when said power piston are moved forward or returned to inoperative positions thereof wherein said closed shell assembly further comprises a cup-shaped front shell having an open rear end and a rear shell coupled to said open rear end of said front shell, and wherein said partition member further comprises a cup-shaped reinforcement member having a diameter smaller than that of said front shell and reinforcing said front shell and a partition closing a rear opening in said reinforcement member.