Patent ID: 6161464
Filing Date: 2000-12-19
Classification: B60T

Abstract:
A brake booster including a tubular valve body slidably disposed within a shell and having a rear end, 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 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 the 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 both said valve seats;characterized by an arrangement which prevents a reaction applied to the output shaft as the brake booster is actuated from being transmitted to the valve plunger, in combination with pseudo-reaction imparting means which transmits a pseudo-reaction which depends on an output from the output shaft to the brake pedal;the pseudo-reaction imparting means comprising a reaction piston slidably mounted on at least one of the power piston and the valve body, a second constant pressure chamber disposed rearward of the reaction piston and into which a pressure in the constant pressure chamber is introduced, and a second variable pressure chamber disposed forward of the reaction piston and into which a pressure in the variable pressure chamber is introduced, the reaction piston being urged rearward by a pressure differential between the second constant pressure chamber and the second variable pressure chamber to transmit the force with which it is urged as a pseudo-reaction to the valve plunger;further characterized by a first spring which normally urges the valve body forward and a second spring which urges the power piston and the valve body away from each other, the first and the second spring being disposed in the variable pressure chamber.