Patent ID: 6089140
Filing Date: 2000-07-18
Classification: B60T

Abstract:
A brake booster including a tubular valve body slidably disposed within a shell and having a rear tubular portion, the outer periphery of which slidably extends through an opening in the shell while maintaining a hermetic seal, a power piston mounted on the valve body, a constant and a variable pressure chamber defined across the power piston, a valve mechanism disposed within the valve body, a constant pressure passage which provides a communication between the valve mechanism and the constant pressure chamber, a variable pressure passage which provides a communication between the valve mechanism and the variable pressure chamber, an atmosphere passage which provides a communication between the valve mechanism and the atmosphere, an input shaft coupled to the valve mechanism and is adapted to be driven back and forth in response to a brake pedal, and an output shaft driven forward as the valve body is driven forward, an axial relative movement being permitted between the valve body and the power piston, and the valve mechanism including a vacuum valve seat formed on an inner periphery of the valve body, a valve plunger slidably fitted into the valve body and coupled to the input shaft, an annular atmosphere valve seat formed on a rear part of the valve plunger, and a valve element urged forwardly by a spring for movement into engagement with or disengagement from the both valve seats;characterized by an arrangement which prevents a reaction applied to the output shaft from being transmitted to the valve plunger as the brake booster is actuated;further comprising a reaction piston slidably disposed on either the power piston or the valve body;pseudo-reaction imparting means for transmitting to the valve plunger a force which urges the reaction piston due to a pressure differential between the variable pressure chamber and the constant pressure chamber as a pseudo-reaction;a tubular cover connected to said opening of the shell and surrounding said rear tubular portion of the valve body;and bellows disposed between a rear end of the tubular cover and an end of the valve element which is fitted into the inner periphery of the valve body, a space being defined between the tubular cover and the bellows and communicating with the constant pressure chamber;a diameter of the vacuum valve seat, a diameter of the atmosphere valve seat and an effective diameter of the bellows being chosen to be substantially equal to each other.