Brake booster

A brake booster comprising a substantially tubular valve body slidably disposed in a shell, a power piston mounted on the valve body to divide the interior of the shell into a constant pressure chamber and a variable pressure chamber, a valve plunger slidably mounted on the valve body and driven by an input shaft to move back and forth to switchably control a flow path, an output shaft slidably mounted on the valve body and driven back and forth in interlocked relationship with the valve body, a reaction disc disposed between the output shaft and the valve body for transmitting a brake reaction from the output shaft to the valve body and the valve plunger, and a valve mechanism comprising an annular, first valve seat formed on the valve body, a second valve seat formed on the rear end of the valve plunger, and a valve element disposed within the valve body and adapted to be seated on the first and second valve seats:

• characterized in that a servo ratio regulating member is disposed on the front end face of the valve body, abuts against a rear end face of the reaction disc and has a small diameter engagement portion pressure fitted into an engagement portion of the valve body and a front part formed with a large diameter abutting portion which abuts the reaction disc, the external diameters of the surface of the servo ratio regulating member that abuts against the reaction disc and the reaction disc being greater than the external diameter of a stem portion of the valve element clamped to an inner peripheral surface of the valve body.