Patent ID: 8231181

Claim:
A brake system comprising: a master cylinder which generates brake-fluid pressure in response to a braking operation of a driver; an electrically-driven hydraulic pressure generator which communicates with the master cylinder, includes a rear fluid chamber and a front fluid chamber, and generates, based on the driver's braking operation, brake-fluid pressure when driven by an electrically-controllable actuator; and a plurality of wheel cylinders which communicate with the rear fluid chamber and the front fluid chamber, respectively, and which generate a braking force to brake wheels, wherein when the electrically-driven hydraulic pressure generator fails, brake-fluid pressure generated by the master cylinder is used to actuate the wheel cylinders, and wherein the hydraulic pressure generator includes: a rear piston and a front piston which are moved forward by the actuator so as to generate brake-fluid pressure in the rear fluid chamber and in the front fluid chamber, respectively; a rear inlet port and a rear outlet port formed in the rear fluid chamber, and connected to the master cylinder and the wheel cylinders, respectively; a rear supply port formed at a rear of and adjacent to the rear inlet port, and connected to the master cylinder; a front inlet port and a front outlet port formed in the front fluid chamber, and connected to the master cylinder and the wheel cylinders, respectively; a front supply port formed at a rear of and adjacent to the front inlet port, and connected to the master cylinder so as to be supplied with brake fluid from the master cylinder; a first rear cup seal disposed at a front end of the rear piston so as to face forward; a second rear cup seal disposed at a rear end of the rear piston so as to face forward; a first front cup seal disposed at a front end of the front piston so as to face forward; a second front cup seal disposed at a rear end of the front piston so as to face rearward; a third front cup seal disposed forwardly of the second front cup seal of the front piston so as to be adjacent to the second front cup seal and to face forward; and a stopper which limits a distance by which the front piston can move rearward; wherein the electrically-driven hydraulic pressure generator causes the wheel cylinders to generate the braking force when the rear piston and the front piston are moved forward past the rear inlet port and the front inlet port, respectively; and wherein the front supply port is formed between the second front cup seal and the first front cup seal.