Patent ID: 7216577

Claim:
A vacuum booster comprising: a housing having a forward side, a rearward side and a longitudinal axis extending therebetween, the housing defining a control volume; a diaphragm separating the control volume into an apply chamber and a vacuum chamber, the diaphragm being movable along the longitudinal axis; a power piston movable along the longitudinal axis and having a rearward end and a forward end, the power piston extending through and engaging the diaphragm, and including an axial bore; wherein the rearward end of the power piston is exposed to atmospheric pressure a valve assembly positioned in the axial bore controlling a diaphragm pressure differential acting on the diaphragm; an output rod extending along the longitudinal axis through the forward side of the housing, the output rod engaging the forward end of the power piston to transmit an output force; and an output rod collar connected to the output rod, the output rod collar having a forward portion exposed to atmospheric pressure, wherein a surface area of the forward portion of the output rod collar is greater than a surface area of the rearward end of the power piston such that a pressure differential is established to urge the power piston in a rearward direction.