Patent ID: 8434831

Claim:
A vehicle brake device of an electronic hydraulic brake system comprising: an input shaft coupled to a brake pedal; a pedal operation detector which detects pedal force of a driver; a pedal simulator coupled to the input shaft in a control housing to supply pedal repulsive force; a master cylinder which delivers a hydraulic pressure to a wheel brake when a braking pressure is formed by the brake pedal; a control piston which is adjacent to a first piston of the master cylinder to deliver a hydraulic pressure to the first piston; a control chamber which controls a pressure of the master cylinder between the control piston and the pedal simulator; and a hydraulic pressure supply which delivers a hydraulic pressure to the control chamber as required by a driver, wherein the pedal simulator includes: a first simulator piston which slidably moves in the control housing; a pressing member which reciprocates corresponding to reciprocating motion of the input shaft in the first simulator piston; a second simulator piston provided in the first simulator piston to slidably move corresponding to movement of the pressing member; and a push rod which is accommodated in the pressing member while being spaced apart from a bottom wall of a guide groove of the pressing member by passing through the first simulator piston and the second simulator piston from the control piston to the input shaft such that the input shaft is mechanically separated from the first piston of the master cylinder in a normal operation mode, said push rod and pressing member are arranged to slidably move relative to each other on corresponding surfaces thereof, wherein a diameter of the master cylinder is greater than a diameter of the second simulator piston, and a diameter of the control piston is greater than the diameter of the master cylinder, and the second simulator piston is arranged to slidably move on a surface of the push rod.