Patent ID: 6955407

Claim:
A negative pressure brake hydraulic pressure generating device comprising, a constant pressure chamber connected to a negative pressure source, a variable pressure chamber into which when a brake is operated, atmospheric air of an amount corresponding to the brake operating amount is introduced, a fixed shell for separating said negative pressure chamber and said constant pressure chamber from outside, an input shaft actuated by an operating force applied to a brake operating member, a piston which receives a pressure in said variable pressure chamber and a pressure in said constant pressure chamber on pressure receiving surfaces thereof and produces an advancing thrust by a differential pressure between said pressures, a spring for biasing said piston in a retracting direction, a power plate which receives said pressures in said variable pressure chamber and said constant pressure chamber on pressure receiving surfaces thereof and transmits an advancing thrust under said differential pressure, a control valve built in said piston for controlling the pressure in said variable pressure chamber by selectively bringing said variable pressure chamber into communication with the atmosphere or said negative pressure source depending on the relative movement between said input shaft and said piston, said power plate and said piston being axially movable relative to each other, and a slide resistance imparting arrangement provided between said piston and said fixed shell, said slide resistance imparting arrangement producing a slide resistance between said piston and said fixed shell that is sufficient to cancel a slide resistance produced between said power plate and said piston.