Patent ID: 8534773

Claim:
A hydraulic booster for use in a hydraulic brake system, comprising an auxiliary hydraulic pressure source including a power pump and a pressure accumulator, a pressure regulator including a spool valve and configured to adjust hydraulic pressure supplied from the auxiliary hydraulic pressure source to a value corresponding to an operating amount of a brake operating member by displacement of the spool valve and to introduce the thus adjusted hydraulic pressure into a boost chamber, and a boost piston for producing an assisting force under the hydraulic pressure introduced into the boost chamber, thereby actuating a master piston of a master cylinder with the assisting force, wherein the hydraulic booster further comprises at least one hydraulic line which bypasses the pressure regulator and through which one of the boost chamber and a pressure chamber of the master cylinder is connected to one of the auxiliary hydraulic pressure source and an atmospheric pressure reservoir, and at least one check valve provided in the hydraulic line and configured to allow only a discharge of hydraulic pressure from said one of the boost chamber and the pressure chamber of the master cylinder to said one of the auxiliary hydraulic pressure source and the atmospheric pressure reservoir.