Patent ID: 6085522
Filing Date: 2000-07-11
Classification: B60T

Abstract:
A braking device for a motor vehicle, comprising a master cylinder filled with a brake fluid and equipped with a main hydraulic piston which receives an actuating force composed of an input force and of a boost force, both acting in an axial direction, and a pneumatic booster which is operated by applying the input force to an operating rod secured to a plunger, thereby controlling opening of a three-way valve, so as to exert the actuating force on the main hydraulic piston;whereby the booster includes a rigid casing divided in leaktight fashion into at least two chambers by at least one moving partition, which is acted upon by a difference in pressure between the two chambers resulting from the opening of the three-way valve; and wherein the moving partition moves a pneumatic piston, bearing the three-way valve and transmitting at least the boost force;wherein the main hydraulic piston of the master cylinder includes a hollow moving cylinder receiving at least part of the boost force, a reaction piston axially slidable in the hollow cylinder, in leaktight fashion and capable of receiving at least the input force, and first elastic means exerting a first elastic force between the reaction piston and the hollow cylinder, urging the reaction piston in the axial direction;wherein there is at least one opening in the hollow cylinder allowing communication between an interior of the hollow cylinder and an interior of the master cylinder;wherein the reaction piston includes a normally open two-way valve means, capable of interrupting the communication between the interior of the master cylinder and the interior of the hollow cylinder;wherein the reaction piston includes a first part which abuts the hollow cylinder, when the main hydraulic piston is in the position of rest, under the effect of the first elastic means, and a second part sliding, in leaktight fashion, in the first part, and second elastic means exerting a second elastic force on the second part in a direction opposite the axial direction, such that the second part abuts the first part, when the main hydraulic piston is in the position of rest;a stepped third piston sliding, in leaktight fashion, in a stepped bore of the hollow cylinder and urged by third elastic means in a direction opposite the axial direction, such that the third piston abuts the first part, when the main hydraulic piston is in the position of rest, with the third piston having a central opening allowing the interior of the moving cylinder to communicate with the interior of the master cylinder;wherein the second elastic means is between the second part and the third piston;wherein the two-way valve means includes a seat located either on the second part or the third part; andwherein a diameter of a front portion of the stepped bore is smaller than a diameter of a rear portion of the stepped bore.