Vacuum booster device

Claim 1

A vacuum booster device comprising a booster shell, a booster piston axially slidably positioned in said booster shell, a piston diaphragm having inner and outer peripheral edges secured to the rear surface of said booster piston and the inner peripheral surface of said booster shell, a front side first working chamber and a rear side second working chamber defined in said booster shell by said booster piston and said piston diaphragm, said first working chamber communicating with a vacuum supply source, said second working chamber selectively communicating with said first working chamber or the external atmosphere through a control valve, an input rod located opposite to said booster piston for movement toward and away from said booster piston, said input rod being connected to said control valve to produce a pressure difference between said working chambers for causing said booster piston to follow the forward movement of said input rod, tie rods extending through said booster piston and said piston diaphragm for connecting the front and rear walls of said booster shell, said piston diaphragm having a plurality of through holes for passage of said tie rods, sealing means positioned between said tie rods and booster piston for permitting the free movement of said booster piston, said sealing means including a first annular bead integrally formed around the inner peripheral edge of said piston diaphragm, a plurality of second annular beads integrally formed around the peripheral edges of each of said through holes, and a plurality of paired straight beads formed on one side of said piston diaphragm and extending between said first bead and said second beads along common tangential lines with respect to said first bead and said second beads.