Patent GB-1443013-A (GB)
Title: Disc brake caliper assemblies
IPC: F16D65/14
Filed: 1973-11-15
Abstract: 1443013 Spot-type disc brakes GENERAL MOTORS CORP 15 Nov 1973 [29 Nov 1972] 52975/73 Heading F2E The invention in its broadest aspect is very detailed: this aspect is expressed in the first of the following paragraphs. The disc-brake caliper assembly 18 has a housing 46 open at one end and contains a hollow piston 60 of an actuator mechanism for moving a brake pad 70 on the piston head 68 against a brake disc 22, the piston 60 being movable hydraulically and also mechanically by a screw-and-nut device 134, 122, in the housing 46, the screw being axially held, and the nut 122 extending into and slidably engaging an adjuster member 86 movable partly within and relative to the hollow piston 60 to a position limiting excessive return movement of the piston 60 due to brake wear; piston 60 and adjuster member 86 have normally-engageable coneclutch surfaces 104, 102, urged together by a spring 132; housing 46 has an inner cylindrical chamber (unreferenced) extending from the closed end 56 of the housing to a shoulder 54 at the junction of two wall portions 48, 52, of the housing, this inner chamber opening into an outer cylindrical chamber (unreferenced) of greater diameter than the inner one and extending from the shoulder 54 to the open end of the housing; the outer chamber has the hollow piston 60 slidably mounted therein with its open end facing the head 98 of the cup-shaped piston 86, which constitutes the adjuster member, and is slidably and rotatably mounted in the inner chamber; the wall portions 48, 52 of the housing, the shoulder 54 and the two pistons 60, 86 together define a first variablevolume pressure chamber 100 connectible through a passage 112 to a brake line for pressure-fluid brake-applying movement of the hollow piston 60, the wall portion 52, the closed end 56 of the housing and the cup-shaped piston 86 together defining a second variable-volume pressure chamber 114 connectible through another passage 116 to a separate brake line for pressure-fluid brake-applying movement of hollow piston 60 by movement of the cupshaped piston 86; the hollow piston 60 has an effective area in the first pressure chamber 100 less than the effective area of the cup-shaped piston 86 in the second pressure chamber 114, the cup-shaped piston 86 being movable to move the hollow piston 60 upon sufficient pressurization of the second variable-volume pressure chamber 114 as to overcome the force of a spring 130 acting between the cup-shaped piston 86 and the nut 122 (this spring normally maintaining the nut and cup-shaped piston in engagement with each other); axially-fixed screw 134 is rotationally fixed during hydraulic operation, and rotary movement of the nut occurs by fluid pressure, acting through spring 130, only when the cone-clutch surfaces 104, 102, have been disengaged by excessive movement (due to lining wear) of hollow piston 60, such rotary (and hence axial) movement of the nut being transmitted to cup-shaped piston 86 until the cone-clutch surfaces are re-engaged, defining a new rest position for piston 60. (To prevent over-adjustment at higher brake pressures, spring 130 yields at such pressures; otherwise it remains solid). As shown, the caliper assembly 18, and hence pad assembly 78, is fixed, while disc 22 is slidably mounted in front wheel 38; the return movement of the hollow piston 60 is effected by the retractile force of a seal 64. For manual operation, lever 144 is rotated, which causes adjuster nut 122 to be moved axially since it is locked by engagement of the clutch surfaces, so both pistons are moved towards the disc.