Hydraulic booster device

Abstract

A hydraulic booster device comprises a booster cylinder coupled with a rear end of a cylinder body of a master cylinder, a booster piston slidably received in a piston guide mounted in the booster cylinder and spring-biased in a retreating direction, a valve piston connected to an operating member and slidably received in the booster piston, an output hydraulic pressure chamber defined to face a back of the booster piston, an input hydraulic pressure chamber leading to a hydraulic pressure supply source, an inlet valve interposed between the input and output hydraulic pressure chambers and opened in response to the advancing operation of the valve piston relative to the booster piston, an outlet valve interposed between the output hydraulic pressure chamber and an outlet chamber leading to an oil reservoir and closed in response to the advancing operation of the valve piston relative to the booster piston, and a booster chamber facing a back of the operating piston and defined between the operating piston and a guide member disposed rearwardly of the operating piston to be able to abut against a leading end of the booster piston. The valve piston has a leading end which is oil-tightly and movably passed through the guide member to project into said booster chamber, and the valve piston is perforated with an oil supply passage which permits the communication between the input hydraulic pressure chamber and the booster chamber as the inlet valve is opened.