GB1007804A - Improvements in or relating to internal shoe-drum brakes - Google Patents

Abstract

1,007,804. Internal shoe-drum brakes; bearings. ROCKWELL-STANDARD CORPORATION. Oct. 11, 1963, No. 40265/63. Headings F2A and F2E. In an internal shoe drum brake having brake shoes pivotally mounted on one end at 20, 22, on a fixed support 14, a floating cam means 86 is located between the other ends of the brake shoes 24, 26 and is adapted to spread the shoes apart to actuate the brake against a return spring means 156, the primary shoe 24 being provided with a brake lining 40, 42 of predetermined thickness initially larger than the thickness of the lining 68 of the secondary shoe 26, automatic adjusting means 164, 178 being provided to compensate for wear of the brake linings, the floating cam means 86 being adapted to follow the adjusted position of the primary shoe towards the brake drum as the brake - linings wear. The thickness of the linings of the primary and secondary shoes are of such proportions that both linings will wear out at the same time. The lining of the primary shoe may be of higher coefficient of friction than that of the secondary shoe so that even wear of the linings results. Both shoes are provided with a greater thickness of lining at the centre of the brake shoe where the travel and wear is greatest to compensate for increased wear at this point. The ends of the brake shoes adjacent the cam means 86 are provided with rollers 52, 76 which abut the cam means. The automatic adjusting means, shown in Fig. 4, comprises a first elongated member 164 pivoted to the brake support 14 with a clearance 192 corresponding to the required brake clearance. The end 162 of the first elongated member 164 is secured to the secondary shoe 26 by means of the return spring means 156. The second elongated member 178 slides relatively to the first elongated member 164 and is connected to the primary shoe 24 and friction means 176 provides a predetermined frictional resistance to relative sliding movement between the elongated members which together form a unidirectional extensible strut. The camshaft 88 is mounted for rotation in a universal bearing assembly 101 comprising a bushing of synthetic plastic material housed in a socket assembly 110 attached to a flange 116 secured to the vehicle axle or frame. As shown in Fig. 1, the cam 86 is initially located on the side of a geometric brake centre line 30 opposite to the end of the primary shoe 24. During the course of successive applications of the brake the brake shoe centre line 28 will progressively advance towards the centre line 30 of the brake support 14 swinging about a point 32 due to lining wear on the primary brake shoe 24. An alternative embodiment is disclosed in the Specification wherein the cam-shaft is completely sealed against the ingress of dirt. U.S.A. Specifications 2,923,579 and 2,928,506 are referred to.