Brake booster with high kick-off emergency valve

摘要

A braking device for a motor vehicle, including a master cylinder ( 2 ) with a primary piston ( 3 ) subjected to an actuating force of an input force exerted by a manual operating member ( 4 ) and a boost force exerted by a booster ( 6 ) coupled to the manual operating member ( 4 ) and an emergency assist valve (VA). Valve (VA) comprises: a reaction piston ( 19 ) sliding in a bore ( 20 ) of the primary piston ( 3 ) and urged toward a position of rest by by an elastic return member ( 22 ); a rapid piston ( 32 ) having a cross section smaller than the reaction piston ( 19 ) and sliding in a sealed manner in a bore ( 31 ) of a bushing ( 30 ) in bore ( 200 ; and a ratio control ( 27 ) actuated by a plunger distributor ( 10 ) driven by the manual operating member ( 4 ). The elastic return member ( 22 ) is arranged outside of the primary piston ( 3 ) and a transmission element (T) is provided to transmit a return force of the elastic return member ( 22 ) to the reaction piston ( 19 ).