Patent ID: 7100997
Filing Date: 2006-09-05
Classification: B60T

Abstract:
1. A boosted brake ( 10 ) for a motor vehicle comprising a pneumatic brake booster ( 12 ) for actuating a master cylinder ( 14 ), said booster ( 12 ) comprises a rigid casing ( 16 ) inside which moves a transverse partition ( 18 ) sealably delimiting a front chamber ( 20 ) subjected to a first pressure (P 1 ) and a rear chamber ( 22 ) subjected to a second pressure (P 2 ) varying between the first pressure (P 1 ) and a pressure (P a ) greater than the first pressure (P 1 ), a moving piston ( 24 ) fixed to the moving partition ( 18 ) and comprising a front face ( 26 ) which acts on a primary piston ( 54 ) of the master cylinder ( 14 ) by way of a reaction disk ( 28 ) housed in a cage ( 30 ) interposed between the moving piston ( 24 ) and the primary piston ( 54 ), a control rod ( 32 ) which moves in the piston ( 24 ) selectively as a function of a first axial input force exerted forward against a return force exerted on the rod ( 32 ) by a return spring ( 34 ), a plunger ( 36 ) which is arranged in front of the control rod ( 32 ) in the piston ( 24 ) and a rear end ( 38 ) with at least one annular rear seat of a three-way valve ( 40 ) which progressively moves between a position in which, with the control rod ( 32 ) at rest, the front chamber ( 20 ) and the rear chamber ( 22 ) are in communication, and a position in which, with the control rod ( 32 ) actuated, the second pressure (P 2 ) prevailing in the rear chamber ( 22 ) increases, the valve ( 40 ) placing the rear chamber ( 22 ) in communication with the pressure (P a ) which is greater than the first pressure (P 1 ), and a feeler ( 42 ), arranged at the front end of the plunger ( 36 ) and passing through a bore ( 44 ) leading from the piston ( 24 ), which, when the control rod ( 32 ) is in the rest position, is arranged at a defined jump distance (d) from the reaction disk ( 28 ) and which, when the control rod ( 32 ) is actuated with an input force whose intensity is greater than a first defined intensity, comes into contact with the reaction disk ( 28 ) in such a way as to transmit to the plunger ( 36 ) and to the control rod ( 32 ) a reaction force of the master cylinder ( 14 ), the ratio of the area of the reaction disk ( 28 ) in contact with the cage ( 30 ) to the area of the feeler ( 42 ) in contact with the reaction disk ( 28 ) defining a first defined boost ratio, and said cage ( 30 ) comprises at least one moving decompression wall ( 46 ) which, when the control rod ( 32 ) is actuated with a second axial input force whose intensity is greater than a second defined intensity greater than said first axial input force, moves to create in the cage ( 30 ) an additional volume in which a front part ( 48 ) of the reaction disk ( 28 ) expands in order to reduce the reaction force transmitted to the feeler ( 42 ) by way of the rear face ( 50 ) of the reaction disk ( 28 ), the ratio of the area of the reaction disk ( 28 ) in contact with the cage ( 30 ) to the area of the feeler ( 42 ) in contact with the reaction disk ( 28 ) defining a second boost ratio, which is greater than the first boost ratio, characterized in that said control rod ( 32 ) comprises an independent push rod ( 52 ) which is interposed between the reaction disk ( 28 ) and the primary piston ( 54 ) of the master cylinder, and which comprises: a rear section ( a tubular front section (