Patent ID: 6718863
Filing Date: 2004-04-13
Classification: B60T

Abstract:
A vacuum booster, comprising:a booster shell; a booster piston accommodated in said booster shell to divide the interior of said booster shell into a front vacuum chamber communicating with a vacuum source and a rear operating chamber; a valve cylinder connected to said booster piston; a valve piston fitted into said valve cylinder so as to be slidable forward and backward; an input rod connected to said valve piston at a front end thereof; an input return spring urging said input rod backward; and a control valve arranged within said valve cylinder, for changing over the communication of said operating chamber with one of said vacuum chamber and the atmosphere in accordance with the forward and backward movement of said input rod, said control valve including: a ring-shaped vacuum introduction valve seat formed in said valve cylinder; an atmosphere introduction valve seat formed in said valve piston and disposed inside said vacuum introduction valve seat; a valve element having: a ring-shaped attachment bead portion securely held with respect to an inner wall of said valve cylinder; an elastic cylinder axially extending from said attachment bead portion; and, an annular valve portion connected in a flange shape to a front end of said elastic cylinder and facing said vacuum introduction valve seat and said atmosphere introduction valve seat, on which said valve portion is to be seated; and a valve spring urging said valve portion in a direction that said valve portion is seated on said vacuum introduction valve seat and said atmosphere introduction valve seat, wherein a first port that communicates with said vacuum chamber is opened to an outer periphery side of said vacuum introduction valve seat, a second port that communicates with said operating chamber is opened between said vacuum introduction valve seat and said atmosphere introduction valve seat, and an inner periphery side of said valve portion is communicated with the atmosphere, further wherein said valve portion is fitted with said valve cylinder so as to be slidably contacted with the inner wall of said valve cylinder, to define a front annular chamber and a rear annular chamber within said valve cylinder, said front annular chamber being closed by a front face of said valve portion when said valve portion is seated on said vacuum introduction valve seat, said rear annular chamber being formed so that the rear of said valve portion is faced thereto, and further wherein said front annular chamber communicates with said first port, and said rear annular chamber communicates with said second port to introduce atmosphere into said rear annular chamber to reduce operating forces during normal braking conditions.