Patent ID: 7334512

Claim:
A vacuum type booster device comprising: a housing having a pressure space formed inside; a movable member provided in the housing to be movable in a forward-backward direction and partitioning the pressure space into a variable pressure chamber and a vacuum chamber; a power piston secured to the movable member; an input member and an output member carried in the power piston to be movable relative to each other in the forward-backward direction; a valve mechanism including an atmosphere valve seat and a vacuum valve seat respectively provided on the input member and the power piston, an atmosphere valve contactable to the atmosphere valve seat for making the variable pressure chamber communicate with, or blocked from, the atmosphere, and a vacuum valve contactable with the vacuum valve seat for making the variable pressure chamber communicate with, or blocked from, the vacuum chamber; a reaction force applying mechanism for transmitting a reaction force from the output member to the input member; a vacuum valve seat retracting mechanism for moving the position of the vacuum valve seat backward relative to the power piston by a first distance, wherein the first distance is a predetermined ratio of a second distance, wherein the power piston is moved relative to the housing by the second distance, when the advance of the input member causes the atmosphere valve seat to be separated from the atmosphere valve to advance the power piston; wherein: the vacuum valve seat is composed of a fixed vacuum valve seat provided on the power piston and a movable vacuum valve seat formed on a movable valve seat member which is air-tightly fitted in an internal surface of the power piston movably in the forward-backward direction; and the vacuum valve seat retracting mechanism is composed of a spring for urging the movable valve seat member backward relative to the power piston and a lever member radially passing through the power piston; wherein the lever member is carried on one end side thereof to be inclinable about a fulcrum point on the power piston, is in contact with the housing at the other end portion thereof and is engaged with the movable valve seat member at a mid portion thereof so that the movable vacuum valve seat is movable backward relative to the fixed vacuum valve seat by the first distance which is a predetermined lever ratio of the second distance.