Disc brake caliper assembly

Claim 1

A disc brake caliper assembly comprising: a housing having a stepped cylinder formed therein with first and second stepped chambers defined by a first cylinder wall, a second cylinder wall of smaller diameter than said first cylinder wall and joined thereto by a shoulder, and an end wall; first and second brake pressure supply passages respectively connecting with said first and second stepped chambers of said cylinder; a cup-shaped first piston reciprocably and sealingly received in said first stepped chamber and opening toward said second chamber, said first piston having a head, a skirt section with a first clutch surface and a cylinder wall formed therein, and means on the head thereof non-rotatably mounting a brake pad assembly; a cup-shaped second piston reciprocably and rotatably and sealingly received in said second stepped chamber and said first piston cylinder wall and opening toward said end wall, said second piston having a head with a second clutch surface thereon cooperating with said first piston first clutch surface to define a clutch and a skirt section with an axial force transmitting surface therein; an adjuster nut non-rotatably received in said second piston skirt section and axially movable therein and having an axial force transmitting surface thereon engageable with said second piston axial force transmitting surface; a threaded shaft received in said second chamber and mounted in said base wall and having said adjuster nut threaded thereon for combined rotary and axial movement; and pre-loaded spring means having a first section acting on said second piston and said end wall and said adjuster nut and a second section acting on said end wall, said first section urging said second piston away from said end wall and said clutch into engagement and said second section urging said adjuster nut toward axial engagement with said second piston at said axial force transmitting surfaces; said first and second cylinder walls and said shoulder and said first and second pistons cooperating to define a first pressure actuating chamber, and said second cylinder wall and said end wall and said second piston cooperating to define a second pressure actuating chamber fluidly separated from said first pressure actuating chamber, said first and second pressure actuating chambers respectively being fluid connected with said first and second brake pressure supply passages, said first piston having an effective area in said first pressure actuating chamber which is less than the effective area of said second piston in said second pressure actuating chamber; said first piston moving in the brake apply direction Upon pressurization of said first pressure actuating chamber and said second piston moving in the brake apply direction upon sufficient pressurization of said second pressure actuating chamber to overcome said spring means acting between said second piston and said adjuster nut, said clutch preventing rotary movement of said second piston and said adjuster nut and therefore preventing axial movement of said adjuster nut until the forces holding said clutch surface in clutching engagement are decreased by first piston movement in the brake apply direction, and said adjuster nut and said second piston then rotating and moving axially to reengage said clutch surfaces in non-slipping clutching relation, thereby adjusting said brake caliper.