Patent ID: 6773079
Filing Date: 2004-08-10
Classification: B60T

Abstract:
A boosted braking device for use in a motor vehicle, comprising: a master cylinder for controlling the pressure in at least one brake circuit; a primary piston mounted to slide in the master cylinder to create therein a variation in pressure, said primary piston being subjected to an actuating force made up of an input force exerted by a manual-control member and of a boost force exerted by a booster that is coupled to a manual-control member; an emergency assist valve comprising a reaction piston that slides in a sealed manner in a first bore of said primary piston, said first bore having a front part that is in communicating with an interior volume of said master cylinder, a rapid piston having a cross section that is smaller than a cross section of said reaction piston and sliding in a sealed manner in a second bore of corresponding diameter of said primary piston, and a ratio control actuated by a plunger distributor driven by said manual-control member, said primary piston, reaction piston and rapid piston being arranged in such a way that under emergency braking, a hydraulic reaction is exerted only on said smaller cross section of the rapid piston, characterized in that said reaction piston and said rapid piston form one and the same stepped piston having a part of large cross section and a part of small cross section, said large cross section part defining within said first bore of the primary piston an annular chamber, said annular chamber having a volume that varies according to a displacement of the stepped reaction piston relative to the primary piston and said separation/communication means and being controlled by the displacement of the stepped reaction piston so that the pressure of the liquid is exerted on said large cross section part of the stepped reaction piston when said reaction piston occupies a position of rest or is to the rear of said position of rest, and on only said small cross section part when the stepped reaction piston is displaced forward relative to said primary piston under emergency braking, said separation/communication means comprise a blind bore located in said stepped reaction piston and open forward, said blind bore communicating, toward its interior end, via at least one hole, with the periphery of the said small cross section part of said rapid piston, while a sealing means, connected to said primary piston, is provided in said annular chamber, around said small cross section part of said rapid piston, to collaborate with said one hole in said small cross section part of said rapid piston.