GB1446552A - Brake assemblies - Google Patents

Abstract

1446552 Air removal from drum brake actuators; slack adjuster GIRLING Ltd 5 Dec 1973 [6 Dec 1972] 56168/72 Headings F2E and F2F A hydraulic actuator for a brake system is provided with a slack adjuster within the working chamber of the actuator, the slack adjuster comprising a tappet member 35 having a blind bore 102, an adjuster member 39 or 39a having an external screwthread meshing with an internal screw thread in the blind bore of the tappet member (to form a non-reversible connection 40), an adjuster mechanism 84 or 84a for turning the adjuster member relatively to the tappet member in response to a requirement for adjustment, and conduit means 107 interconnecting the inner end of the blind bore 102 with a space 104 at the end of the adjuster member 39 remote from the inner end of the blind bore 102 to facilitate the removal of air bubbles from the blind bore inner end during brake bleeding. Fig. 1 shows half an actuator, for a shoe drum brake, symmetrical about centre line 103. Adjuster member 39 has an inclined abutment surface engageable with an inclined abutment surface 44 on part 45 of a cylinder body 34; member 39 also has an internal conical friction surface 49 cooperating with a friction surface 77 on a drive ring 75. The drive ring 75 has a reversible screw-threaded connection 76 with an axially and rotationally fixed screw 74, axial clearance at this screw-thread accommodating normal piston travel. The conduit means 107 facilitating air bubble removal during brake bleeding is described later. In operation, when lining wear has occurred, movement of tappet member or piston 35 to the right under hydraulic actuation is accompanied by separation of member 39 from ring 75. A spring 51 thereupon forces ring 75 to rotate on screw 74 until contact is re-established with member 39. On brake release, the clearance at connection 76 is fully taken up before member 39 engages abutment surface 44, so because friction surfaces 49, 77, in engagement, prevent relative rotation between member 39 and ring 75, the brake return spring (not shown) forces these two components to rotate together within piston 35, in the sense to increase the length of the assembly, until member 39 engages surface 44 once more. Conduit means 107, Figs. 2, 3, has a stem 81 extending axially through member 39, Fig. 1, into a perforate spring guide member 80, and fingers 113, Figs. 3 and 1, between which air can escape from between the end of member 39 and wall 108 of piston 35 to the interior of stem 81. Air thus reaching chamber 104 is discharged through a bleed port (not shown). Inflow for hydraulic fluid is provided by grooves 112 in the shank of member 39. Fig. 4 is a single unit shown in its entirety. Here, member 39a has a non-reversible screwthread connection 40 with piston 35 as before, a reversible screwthread connection 76a with drive ring 75, and inclined abutment surface 44a engageable with cylinder body 34a. Ring 75 now has its friction surface 77 engageable with cylinder body 34a also. Operation is similar to that of Fig. 1. The stem 81a of conduit means 107 does not extend the full length of bore 109. In both cases piston 35 is normally prevented from rotating but may be rotated manually for re-setting