Patent ID: 6269731
Filing Date: 2001-08-07
Classification: B60T

Abstract:
A pneumatic brake-booster comprising: a rigid casing; a moving partition delimiting, in leaktight fashion, a front chamber and a rear chamber inside the casing, said front chamber in operation being subjected to a first pressure and said rear chamber being selectively connected to said front chamber or subjected to a second pressure higher than said first pressure; a pneumatic piston moving with said moving partition; an operating rod moving in said piston as a function of an input force selectively exerted in an axial actuating direction orientated towards said front chamber, and of a return force exerted by a main return spring in an axial return direction opposite of said axial actuating direction, said return force urging said operating rod into a return position, and an input force urging said operating rod into an intermediate actuating position or into an extreme actuating position, depending on whether an input force is applied at a rate that is lower or higher than a determined limiting rate; a plunger housed in said piston and driven along by said operating rod; a three-way valve having an annular seat borne by a rear section of said plunger, said three-way valve connecting said rear chamber to said front chamber when said operating rod is in a position of rest, said three-way valve subjecting said rear chamber to said second pressure when said operating rod is in an actuating position; force-transmission means capable of receiving and of transmitting at least a boost force exerted by a front face of said piston when said three-way valve subjects said rear chamber to the second pressure, said force-transmission means including reaction means capable of reacting against said input force with a reaction force dependent on said boost force, characterized in that said plunger comprises a front section connected to the rear section by a secondary spring exerting, between the front and rear sections, a mutual-contact force that is lower than the return force, and in that the front section and the force-transmission means respectively comprise a reversible retention means capable of securing said front section to the piston when a boost force exceeds a determined threshold while said operating rod is in an extreme actuating position.