HYDRAULIC BRAKE DEVICE FOR VEHICLE

A vehicle hydraulic brake system of the brake-by-wire type which is free of the problem of deterioration in brake operating feeling. An input piston (14) and a master piston (18a) configured to be actuated under hydraulic pressure introduced into a second fluid chamber (C2) are mounted in the housing (16) so as to be movable relative to each other through a partition wall (17a) and a first fluid chamber (C1). The piston (18a) defines therein a communication passage (20) which extends from a fourth fluid chamber (C4) to the first fluid chamber (C1) and in which a check valve (21) is mounted. When the piston (18a) is advanced under hydraulic pressure introduced into the second fluid chamber (C2), the volume of the fourth fluid chamber (C4) decreases, while the volume of the first fluid chamber (C1) increases. This allows brake fluid in the fourth fluid chamber (C4) to be quickly released into the first fluid chamber (C1) through the communication passage (20) and through a pipe line (30) in which an electromagnetic on-off valve (3) are mounted. This in turn reduces fluctuations in hydraulic pressure in the first fluid chamber (C1) when the volume of the fourth fluid chamber (C4) decreases and the volume of the first fluid chamber (C1) increases, and thus reduces fluctuations in the reaction force to brake operating force applied to the brake pedal. It is thus possible to prevent deterioration in brake operating feeling.