Patent ID: 6931979

Claim:
A pneumatic brake booster having a casing ( 1 ) divided into a front chamber ( 7 ) and a rear chamber ( 9 ) by a sealed moving wall ( 11 ) of a pneumatic piston ( 13 ), said pneumatic piston ( 13 ) having a bore therein for retaining a three-way valve ( 19 ) that is actuated by an actuating rod ( 21 ) connected at a first end to a brake pedal and at a second end opposite the first end to a distributor ( 22 ), said three-way valve ( 19 ) on being actuated by said actuating rod ( 21 ) controlling the development of a pressure differential that moves said sealed wall ( 11 ) to create an actuation force that is provided as an output force for pressurizing fluid in a master cylinder to effect a brake application, characterized in that the distributor ( 22 ) contacts a reaction arrangement ( 235 ) through which the output force is communicated to the master cylinder and the output force is a functional ratio of said input force and wherein said functional ratio is modified by a reaction disc ( 33 ) and elastic means ( 230 , 330 ) during a brake application such that during the brake application said reaction arrangement ( 235 ) functions as a rigid member until the input force reaches a first predetermined input force level Fd and where a first boost ratio remains in effect until a second predetermined force level Fe is reached and a second boost ratio is in effect until a third predetermined input force level Ff is reached and a third boost ratio remains in effect until a fourth predetermined fource level is reached and as a result the output force is sequentially increased with increases in the input force, said reaction arrangement ( 235 ) including a cage ( 37 ) having a cylindrical body with a first diameter ( 39 ) separated from a second diameter ( 41 ) by a shoulder ( 43 ), said first diameter ( 39 ) being closed by an end that is connected to a push rod ( 31 ) through which an output force is communicated to the master cylinder; a first spring ( 230 ) of said elastic means has a first end that engages said end of said cage; a second spring ( 330 ) of said elastic means is concentric to said first spring ( 230 ) and has a first end that engages said end of said cage; a floating piece ( 49 ) consisting of a central first piece ( 249 ) and an annular second piece ( 340 ); a washer ( 47 ) that engages said shoulder ( 43 ), is fixed in said second diameter 41 ) of said cage ( 37 ) and engages said first piece ( 249 ) and second piece ( 340 ) to preload said first spring ( 230 ) and said second spring ( 330 ), said washer ( 47 ) having a central passage ( 51 ) for receiving said floating piece ( 49 ); said reaction disc ( 33 ) being located in said second diameter ( 41 ) and having a face that engages said washer ( 47 ), said second piece ( 340 ) and said first piece ( 249 ); said pneumatic piston ( 13 ) having an radial notch to define guide means ( 24 ) for receiving said second diameter ( 41 ) of said cage ( 37 ) to maintain said putput push rod ( 31 ) in alignment with said distributor ( 22 ).