Patent GB-1247245-A (GB)
Title: Improvements in back stops for internal shoe drum brakes and to internal shoe drum brakes incorporating such back stops
Inventor: QUINEY KENNETH MAURICE
IPC: F16D51/20
Filed: 1969-03-01
Abstract: 1,247,245. Internal shoe drum brakes; dismantling. GIRLING Ltd. 26 Feb., 1970 [1 March, 1969; 18 Oct., 1969], Nos. 11032/69. and 51267/69. Heading F2E. The invention is concerned with a brake which may be applied mechanically, in emergency or for parking, by a lever 9, Fig. 1, pivoted at 10 to the web of shoe 1 and coupled at its other end by an abutment 19 to a cable 11 passing through an opening 12 in the back-plate 4, Fig. 2. At an intermediate point in its length the lever 9 acts on the left-hand end (between bifurcated portions 15) of a strut 13 whose other end (also provided with bifurcated portions 15) engages the web of shoe 2. (The brake drum is not shown). The effective length of the strut 13 is adjustable by automatic adjustment means 14. The invention makes provision for holding the lever 9, when the brake is off, in a position corresponding to less than full retraction of the shoes 1, 2, during all braking operations. Such provision consists of a back stop 17, Fig. 2, which extends into the brake through an opening 18 in the back-plate 4 to hold lever 9, by contact with lever abutment 19, in the position mentioned. The invention thus facilitates removal of the drum when one of the brake shoes has worn a groove in it by preventing full retraction of the shoes until the drum is to be removed, thereby providing greater clearance at that time. Prior to drum removal, the back-stop 17 is removed, or merely manipulated, to permit lever 9 to move to the left (as seen in Fig. 2) whereupon the pull-off springs 7, 8, Fig. 1 (still under tension), retract the shoes fully. The back-stop may be a single closed-ended tube of deformable or resilient plastics material with a retaining rib (Fig. 3, not shown), the closed end contacting abutment 19 (see Fig. 2). The modification of Fig. 4 differs only in having the end wall partly chamfered, portion 27 normally being in contact with abutment 19, and the tube being merely rotated to bring portion 26 into contact, prior to drum-removal. (The Fig. 3 embodiment has to be removed). A manipulating rod may be inserted through holes 25. In Fig. 7 the back-stop comprises a piston 32 in a sleeve 30, the sleeve being located in opening 18 in back-plate 4 by a groove 38. Initially, piston 32 is moved inwards (leftwards) until nose 31 engages rib 36; thereafter, adjuster 14, Fig. 1, is manipulated to bring abutment 19 into contact with piston head 33, and further adjusted until abutment 19 has pushed head 33 into contact with the end of sleeve 30, as shown. Prior to drum removal the whole assembly is removed, whereupon abutment 19 moves towards back-plate 4. In Fig. 8 the back stop is assembled by pushing piston 43 in a right-hand direction into sleeve 40 (ring 52 not being present at this stage) before the assembly is located by its groove 51 in opening 18 in back-plate 4. Thereafter the piston 43 is moved and adjuster 14 manipulated as described above for Fig. 7 until the positions are as shown in Fig. 8. Ring 52, preventing ingress of foreign matter, deflects when piston 43 is moved axially inwards. A double-ended piston and cylinder assembly 5, Fig. 1, is provided for service braking.