Patent ID: 6591734
Filing Date: 2003-07-15
Classification: B60T

Abstract:
A pneumatic servomotor for an assisted braking of a motor vehicle, said servomotor having a rigid casing with a movable transverse partition wall therein that defines in an airtight manner a front chamber under a first engine negative pressure and a rear chamber under a second pressure, said second pressure varying between said first pressure and atmospheric pressure; said movable wall including an integral piston that biases a rear end of an actuating rod for a brake master cylinder, said actuating rod being slidably arranged in relation to said piston against a first return spring mounted inside said front chamber; and a control rod that moves inside of said piston in a selective manner as a function of an axial input force exerted in the forward direction against a return force applied to said control rod by a second return spring; said control rod being biased towards either an intermediate actuation position or an end actuation position resulting from the applying of said input force at a predetermined high speed; a plunger, arranged at a front part of said control rod inside of said piston, and a three-way valve, including at least an annular seat borne by a rear section of said plunger, and said three-way valve varying the second pressure prevailing within said rear chamber particularly by connecting said front chamber with said rear chamber when said control rod is in a rest position and by gradually connecting said rear chamber with atmospheric pressure when said control rod is actuated by an input force; said plunger having a finger-forming front end that biases a reaction disk integral with a rear end of said actuating rod in an end actuation position for said control rod to transmit the reaction force from said actuating rod through said plunger into said control rod; characterised in that said piston has a front bore that opens into a cup that is integral with a rear end of said actuating rod, said cup receiving said reaction disk with said cup being slidably mounted on a cylindrical bearing surface of said piston and said servomotor including a unidirectional clutch device that is activated when an input force is applied to said control rod at a predetermined speed to lock said actuating rod in relation to the said piston in an end front axial position in which a corresponding reaction force is transmitted to said piston, independently of the reaction disk and independently of a position of said plunger and said control rod, said unidirectional clutch device including an expandable means for an axial insertion, in the active position, between said piston and said rear end of said actuating rod to lock said actuating rod in said end front axial position.