Patent ID: 6935705
Filing Date: 2005-08-30
Classification: B60T

Abstract:
1. A pneumatic brake booster ( 10 ) for actuating a brake master cylinder ( 28 ) of a motor vehicle, having a rigid casing ( 12 ) in which a transverse partition ( 14 ) sealingly moves while delimiting a front chamber ( 16 ) subjected to a first, engine depression, pressure (P 1 ) and a rear chamber ( 18 ) subjected to a second pressure (P 2 ) that varies between the engine depression and atmospheric pressure (P a ), a moving piston ( 22 ) that is secured to the moving partition ( 14 ) with a front face ( 26 ) that acts on a rod ( 34 ) for actuation of the master cylinder, a rod ( 46 ) that moves in the piston ( 22 ) to selectively control of the booster ( 10 ) as a function of an axial input force exerted forwards against a return force exerted on the rod ( 38 ) by a return spring ( 50 ), a plunger ( 56 ) which is arranged in front of the control rod ( 46 ) in the piston ( 22 ) having rear end that comprises at least one annular rear seat ( 58 ) for a three-way valve ( 60 ) progressively moves between a position in which, with the control rod ( 56 ) at rest, the front chamber ( 16 ) and the rear chamber ( 18 ) are in communication, and a position in which, with the control rod ( 56 ) actuated, the second pressure (P 2 ) in the rear chamber ( 18 ) increases as the valve ( 60 ) places the rear chamber ( 18 ) in communication with atmospheric pressure (P a ), and a first feeler ( 62 ) formed on a front end of the plunger ( 56 ) that passes through the piston ( 22 ) when the control rod ( 46 ) is in the rest position and is arranged a first determined jump distance (d 1 ) away from a reaction disc ( 44 ) inserted between the rod ( 34 ) for actuation of the master cylinder ( 28 ) and the front face ( 26 ) of the moving piston ( 22 ), and when the control rod ( 46 ) is actuated at a rate lower than a determined rate by the plunger ( 56 ) to moves through the first jump distance (d 1 ) and then penetrate the reaction disc ( 44 ) in such a way as to transmit to the plunger ( 56 ) and to the control rod ( 46 ) the reaction force of the master cylinder ( 28 ), characterized in that said three-way valve ( 60 ) includes a tubular bushing ( 64 ) which is slidably mounted on the plunger ( 56 ) and has a front portion ( 66 ) that passes through the piston ( 22 ) with an end thereof that comprises a second feeler ( 68 ) and a rear tubular portion ( 72 ) that is slidably mounted in a complementary rear bore ( 74 ) of the piston ( 22 ), said second feeler ( 68 ) including in annulus that is slidably mounted an the cylindrical front end ( 67 ) of the bushing ( 64 ), said second feeler ( 68 ) when the control rod ( 46 ) is actuated at a rate higher than a determined rate being pushed into the reaction disc by a shoulder front face ( 69 ) of the bushing ( 64 ) by the plunger ( 56 ) and immobilized with respect to the piston ( 22 ) by a one-way engagement device ( 70 ) in an axial position that can vary depending on the rate at which the control rod is actuated and then is driven by the piston to cause the second feeler ( 68 ) to penetrate the reaction disc ( 44 ) to allow the first feeler ( 62 ) to apply a rapid braking force against an antagonistic reaction force of the master cylinder ( 28 ) which is reduced along a second, variable, jump distance (d 2 ) greater than the first jump distance (d 1 ).