Patent ID: 6966616

Claim:
A hydraulic brake apparatus for applying braking force to each wheel of a vehicle in response to depression of a brake pedal, comprising: a master cylinder for advancing a master piston in response to operation of said brake pedal to pressurize brake fluid in an atmospheric pressure reservoir and discharge the pressurized brake fluid; an assisting device for assisting said master piston to be advanced in response to operation of said brake pedal; an auxiliary piston having a large diameter portion with an effective cross-sectional area larger than an effective cross-sectional area of said master piston and a small diameter portion with an effective cross-sectional area smaller than the effective cross-sectional area of said master piston, defining a first pressure transmitting chamber between said large diameter portion and said master piston, and defining a second pressure transmitting chamber between said small diameter portion and said master piston, said auxiliary piston connecting said large diameter portion with said assisting device; a first valve member for closing said first pressure transmitting chamber when said master piston is assisted by said assisting device through said auxiliary piston, and communicating said first pressure transmitting chamber with said atmospheric pressure reservoir, when said master piston is not assisted by said assisting device, and after said assisting device has exceeded an assisting limit thereof; a second valve member for normally allowing a flow of the brake fluid from said first pressure transmitting chamber to said second pressure transmitting chamber, and preventing a flow of the brake fluid from said second pressure transmitting chamber to said first pressure transmitting chamber to hold the hydraulic pressure in said second pressure transmitting chamber; and a valve opening mechanism for opening said first valve member, and mechanically connecting said second valve member with said first valve member, to open said second valve member when said auxiliary piston is retracted from an advanced state thereof to an initial position of said auxiliary piston.