Patent ID: 7255408
Filing Date: 2007-08-14
Classification: B60T

Abstract:
1. A vacuum booster comprising; a housing having a pressure chamber therein; a movable wall provided in the housing for being movable forward and backward and for separating the pressure chamber into a constant pressure chamber and a variable pressure chamber; a power piston having a first vacuum valve seat and a radial directional bore and unitarily formed with the movable wall; an input rod provided in the power piston for being movable forward and backward relative to the power piston; a plunger having a first flange portion and a second flange portion, connected to the input rod, inserted into the power piston slidably in a longitudinal direction relative to the power piston, and formed with an atmosphere valve seat; an output member for outputting a driving force of the power piston outside of the vacuum booster in accordance with a movement of the movable wall; a valve seat member having a second vacuum valve seat and being approximately concentric with the first vacuum valve seat and being movable forward and backward relative to the power piston; a valve mechanism provided in the power piston and having a movable portion facing the first vacuum valve seat and a fixing portion provided concentric with the movable portion; drive means for moving the valve seat member towards the movable portion by a predetermined amount when a forward moving amount of the plunger relative to the power piston is equal to or greater than a predetermined value; holding means for holding the valve seat member at a predetermined position in the power piston when the forward moving amount of the plunger relative to the power piston is less than the predetermined value; an engaging member for engaging the holding means with the power piston; a key member inserted into the radial directional bore and moving between the first flange portion and the second flange portion of the plunger in the longitudinal direction for restricting a longitudinal direction moving amount of the plunger relative to the power piston; noise restriction means mounted on the plunger for restricting a contact noise between the key member and the second flange portion of the plunger; wherein the noise restriction means comprises second drive means with a predetermined preload, the valve seat member moving backward by a predetermined amount towards the movable portion against a biasing force of the second drive means when the forward moving amount of the plunger relative to the power piston is equal to or greater than the predetermined value; wherein the noise restriction means comprises: a retainer provided on an outer periphery of a rear cylindrical portion of the plunger; a snap ring fitted in an annular groove formed on the outer periphery of the rear cylindrical portion of the plunger for restricting a forward movement of the retainer; and wherein the valve seat member includes a rear end surface contacting a front end surface of a ring portion of the retainer, the retainer including an inclined connecting portion, and the plunger including an incline portion provided between a rear cylindrical portion of the plunger and a rear flange portion of the plunger.