Vacuum booster device

Claim 1

A vacuum booster device comprising a booster shell having a front wall and a rear wall, an axially slideable booster piston accommodated in the booster shell, a first working chamber defined in the booster shell by said front wall and the booster piston and held in communication with source of vacuum supply, a second working chamber defined in the booster shell by said rear wall and the booster piston and slectively placed in communication with the first working chamber or the external atmosphere through a control valve means, an input rod arranged opposite the booster piston for movement toward and away from the latter and connected to the control valve means so as to produce a pressure difference between both the working chambers effective to cause the booster piston to follow forward movement of the input rod, tie rods extending through the booster piston interconnecting said front and rear walls of the booster shell and passing through a through hole in said piston, flexible bellows surrounding each of the tie rods and having opposite ends fixed to an end of the tie rod adjacent said front wall and around said opening in the booster piston, respectively, so that the inside of the flexible bellows communicates continuously with the second working chamber, an adjustable stop means provided on the input rod for defining a retraction limit of the latter so as to create a pressure difference between said first and second working chambers when the input rod is in it is full-retreated position and the control valve means is held in a neutral postion keeping the second working chamber cut off from its communication with both the first working chamber and external atmosphere so that the bellows becomes expansive owing to said pressure difference between the working chambers, a piston diaphragm which cooperates with said booster piston to divide the interior of said booster housing into said first and second working chambers, said flexible bellows having a rear end tightly fixed to said through hole of the booster piston while said piston diaphragm having a through hole for said tie rod passing therethrough, and an annular bead being integrally formed around a peripheral edge of said through hole of the piston diaphragm, which annular bead has it front surface separably mated with said rear end of the flexible bellows to provide a seal to said through hole of the piston diaphragm.