Patent ID: 7104058
Filing Date: 2006-09-12
Classification: B60T

Abstract:
1. A vehicle braking system comprising: a master cylinder in which a master piston with its back turned to a boosted hydraulic pressure chamber is slidably housed in a casing; a backup piston which is slidably housed in the casing with its front face turned to the boosted hydraulic pressure chamber and with its backward limit fixed, to push the master piston directly from behind in response to operation of a brake operating member when the hydraulic pressure of the boosted hydraulic pressure chamber decreases; and pressure regulating means which applies output hydraulic pressure of a hydraulic power source to the boosted hydraulic pressure chamber after regulating the output hydraulic pressure according to brake operating input from the brake operating member; the master cylinder being connected to wheel brakes, wherein the backup piston comprises a piston body which is slidably fitted in the casing with substantially the same seal diameter as a seal diameter of the master piston, and a pusher which is slidably fitted in the casing with a seal diameter smaller than the seal diameters of the master piston and the piston body and which coaxially extends to the front end of the piston body so as to abut against and push the rear end of the master piston, wherein an annular input chamber is formed between the backup piston and the casing so as to be communicated with the hydraulic power source, with axially opposite ends of the annular input chamber sealed by sealing members interposed between the piston body and the casing and between the pusher and the casing, respectively, wherein the backup piston contains pressure regulating means interposed between an output chamber and the input chamber which are connected to the boosted hydraulic pressure chamber, so as to communicate the input chamber with the output chamber and to communicate the output chamber with a reservoir when the output hydraulic pressure of the hydraulic power source decreases, and wherein when the pusher pushes the master piston forward, amount of volume increased in the boosted hydraulic pressure chamber is set to be substantially equal to amount of volume decreased in the input chamber.