Vacuum booster device

Claim 1

In a vacuum booster device comprising a booster shell, a booster piston axially slidably accommodated in said booster shell, first and second working chambers defined in said booster shell separately from each other by said booster piston, said first working chamber being held in communication with a vacuum source, said second working chamber being selectively placed in communication with said first working chamber or the atmosphere through a control valve means, an input rod arranged in said booster piston for forward and rearward movement and connected to said control valve means so as to produce a pressure difference between both of said first and second working chambers effective to cause said booster piston to follow the forward movement of said input rod, tie rod means extending through said booster piston for connection of front and rear walls of said booster shell, sealing means arranged between said tie rod means and said booter piston to allow the operation of said piston, and a return spring compressed in said first working chamber for biasing said booster piston in its retracting direction, the improvement which comprises a spring retainer plate supporting the fixed end of said return spring, said spring retainer plate being abutted against the front wall of said booster shell and having a pair of bosses integrally projected at its both ends, each of said bosses being provided at its inner end with an intercepted round concave hole; said tie rod means including at least two tie rods having integral mounting bolts formed at ends thereof so as to project outwardly of said booster shell, said tie rods each having an intercepted round flange disposed thereon, said spring retainer plate being fixed to said front wall by the two tie rods penetrating through said bosses thereby preventing relative rotation of the spring retainer plate with respect to the front wall of the booster shell, the intercepted round flange of each of the tie rods being fitted in the intercepted round concave hole formed on each of the bosses thereby holding each tie rod in a rotation-proof manner.