GB1418681A - Internal shoedrum brakes - Google Patents

Abstract

1418681 Internal shoe drum brakes; slack adjusting GIRLING Ltd 1 March 1973 [3 March 1972 9 March 1972] 9920/72 and 10952/72 Heading F2E Between the pair of shoes at one end is located an actuator for separating them, and between them at the other end is located an abutment unit comprising a body fixed to the stationary back plate, two normally non- rotatable members slidable in the body, each for co-operation with the end of one of the shoes, and an intermediate component extending between the members and including one or more stops adapted to engage with a part of the body to limit movement of one member towards the other. In Fig. 3, "member" 9 co-operates with one shoe and "member" 10 with the other. Between them an "intermediate component" in the form of spindle 15 is threaded in member 9 and in nut 17 which is slidable (but need not be) in member 10. Drive ring 21 on steep thread 20 is urged by spring 23 against an internal frustoconical face 22 of shoulder 16, so member 10 is spaced at 18 from the right side of shoulder 16. Spindle collar 19 forms a stop which bears on the left side of shoulder 16. In operation besides the application of fluid pressure to a wedge device at the upper ends of the shoes, fluid pressure is applied between the members 9, 10. With counter-clockwise (normal) rotation of the brake drum, one shoe forces member 9 against the fluid pressure; this force is transmitted via spindle collar 19 to shoulder 16, not to member 10; member 10 is urged outwardly by the fluid pressure, urging the lower end of its shoe to the drum, so both shoes act as leading shoes. With reverse rotation, the right-hand shoe acts on member 10, and, because of clearance 18, indirectly on member 9, so the brake acts as a duo-servo brake. When the desired minimum shoe clearance (allowed for by play in the various screw-threaded connections) is exceeded by shoe-lining wear, movement of member 10 leftwards moves drive ring 21 leftwards but also tends to move spindle 15 further, so ring 21 is forced to rotate on it by spring 23; (rotation of spindle 15 is prevented by spring 24): adjustment is thus provided for but not yet actually made (nor on subsequent brake release). When the brake is next applied during normal drum rotation, ring 21 meets face 22 before collar 19 meets shoulder 16, and because of pressure on spindle 15, this is forced to rotate in ring 21; the threaded engagements with members 9, 10 are of opposite hand, so members 9, 10 are moved apart. The ratio of pitch of thread 20 to the pitch of the "member" threads ensures that only about one thirtieth of the wear is taken up at each adjustment. A spigot connection 11 is provided between member 9 and tappet 12 so that member 9 may be rotated by a tool applied to teeth 26 on it to reduce the length of the abutment unit when necessary. In Fig. 6 the spindle is replaced by two threaded studs 57, 60, each co-operating with an inclined face 67 or 68 on an abutment 66 of the body; part 63 may be an extension of stud 57, slides in stud 60 and carries drive ring 70; as shown, however, part 63 is separate from stud 57, having a head 73 in clutching engagement with its inner end. Independent and alternative adjustments for members 53 and 54 are provided according to the direction of rotation of the drum. Fig. 4 (not shown) resembles Fig. 3, but provision for applying fluid pressure between members 9, is omitted. The brake now acts as a leading-trailing shoe brake in the forward direction but still as a duo-servo brake in the reverse direction. The modified brake incorporating the abutment unit of Fig. 5 (not shown), acts as a twoleading-shoe brake in both directions of rotation.