Patent ID: 6082109
Filing Date: 2000-07-04
Classification: B60T

Abstract:
Master cylinder with hydraulic reaction for a pneumatic brake booster, comprising:a body pierced with a main bore;a cylindrical main piston located without leaking, in said main bore to to delimit a working chamber which during operation is subjected to hydraulic pressure, said main piston having first end located outside of said body for receiving a boost force directed in a first direction and being pierced with a stepped secondary bore;hydraulic reaction means including a reaction piston mounted with leaktight sliding in a cross section of a first diameter of the secondary bore which it closes off, and having an first end outside said body for receiving an actuating force, said boost force having a delay that increases with the rate of application of the actuating force;characterized in that said hydraulic reaction means further comprise:a shut-off seat mounted on a front face of said the reaction piston and pointing toward the working chamber;an annular wall arranged some distance from said reaction piston in said first direction, said annular wall forming a reduced diameter of the secondary bore and delimiting a central passage which has a second diameter smaller than said first diameter of said secondary bore whereby the cross section of said first diameter of the secondary bore communicates with said working chamber;a ratio-change piston which is tubular and open to said working chamber, said ratio-change piston having a downstream external cross section which passes with leaktight sliding through said central passage of said annular wall, said ratio-change piston having a first retaining stop which cooperation with said annular wall on a same side as said working chamber, said ratio-change piston being pushed back by a first spring some distance from said shut-off seat when said main piston is in a condition of rest, and by which it is closed off when said main piston is actuated quickly; andan annular floating piston mounted with leaktight sliding in said cross section of said first diameter of said secondary bore and around an upstream external cross section of said ration-change piston, said floating piston, together with said annular wall, delimiting a low-pressure annular chamber, a second spring being located in said lower-pressure annular chamber for urging said floating piston in a second direction that is opposite of said first direction and toward said reaction piston and a second stop of said ratio-change piston.