GB984312A - Improvements in or relating to internal shoe drum brakes - Google Patents

Abstract

984,312. Internal shoe drum brakes. AUTOMOTIVE PRODUCTS CO. Ltd. March 1, 1963 [March 2, 1962], No. 8266/62. Heading F2E. An internal shoe drum brake having two floating shoes normally engaged with a surrounding drum by energization of a single twopiston hydraulic servo, is also provided with a linkage separately operable to apply the shoes, e.g. when a car in which the brake is used has been parked, the linkage consisting of two thrust members mounted side-by-side and simultaneously moved in opposite directions to engage the brake, the thrust members being pivoted to a floating lever itself acted upon by a pull-rod arranged transversely to the plane of the brake. Transverse movement of the thrust members is opposed either by their interconnection with the brake shoes, which are themselves prevented by their mountings from moving in a parallel direction, or alternatively one of the thrust members contacts the brake back-plate. In one form, a pull-rod 51, Fig. 2, pivots at 50 on a floating lever 48 mounting by pivots 47, 49 two oppositely-movable struts 39, 41. The strut 39 carries at one end a roller 44 running on the brake backplate 45, to take the pull of the rod 51, and is formed with a notch 46 engaging the web of one brake-shoe 23. The other strut 41 engages at its end a carrier 27 supporting another brakeshoe 26, and passes through a hole in a support lug 43. When the pull-rod 51 is operated, the two struts 39, 41 separate the shoes 23, 26 and apply the brake, a disengaging spring 52 acting to restore the struts to the disengaged position. The carrier 27, Fig. 1, is of U-shaped cross-section to receive the web of the shoe 26, a link 28 between the web and the carrier allowing the shoe to move circumferentially. One end of the carrier 27 is engaged by a slotted pusher 29 acted upon by the piston 30 of an hydraulic servo, the other end of the carrier engaging the rounded end 33 of an adjustable-length thrust-rod 21, supported in a bearing housing 18 and engaging at its other end the web of the shoe 23. An enlargement 22 on the thrust-rod 21 limits its sliding movement in one direction. The other end of the shoe 23 engages a second piston 24 of the hydraulic servo, a flange 25 on this piston limiting the extent to which the piston can be forced into the servo cylinder. Brake disengaging springs 35, 36 draw the shoes 23, 26 towards each other. Rotation of a drum surrounding the shoes in a direction clockwise of Fig. 1 causes relative movement of the shoes 23, 26, the thrust-rod 21, the pistons 24, 30 &c. on application of the brake, and thereby causes a self-servo brake engagement. Rotation of the drum in the other sense tends to cause brake disengagement, in opposition to the brake-applying force. In a modification, a pull-rod 92, Fig. 7, pivots on a floating lever 88 on which are pivoted at 89, 91 two struts 83, 86. The strut 83 has two arms 83a, Fig. 9, which embrace one end of the strut 86, itself having two arms at its other end to embrace the strut 83. One end of the strut 86 has a notch 87 engaging the web of a brake-shoe 61, the other end of this strut engaging the edge of the strut 83. The strut 83 is deeply slotted to embrace the webs both of the shoe 61 and of a second shoe 68, and engages a carrier 69 mounting the shoe 68. On actuation of the pull-rod 92, the struts 83, 86 separate the two shoes 61, 68 for brake application, the whole transverse reaction to the load applied by the pull-rod being transmitted through the links &c. to the brake-shoe webs, and thence to the back plate 74. In a similar construction. Fig. 11 (not shown), a reaction plate is welded to the back plate and is slidably engaged by the web of the brake-shoe 61, to support the reaction against the pull-rod. The shoes 61, 68 are supported against transverse movement by engagement of their webs in deep slots 75, Fig. 6, at opposite ends of a support 73 fast with the back plate 74, and in deep slots in a thrust-rod 65 slidable through a support 66 on the back plate. Additionally, tubes 76, Fig. 10, carried on the back plate 74, are engaged by the sides of the shoe webs, springs 79 acting through rods 78 to hold the parts together. The shoe 68, Fig. 6, is permitted to move circumferentially in the carrier 69 by a U-shaped link 77, the shoes normally being applied to a surrounding drum by energization of an hydraulic servo 64. Two pistons within the servo act upon the shoes 61, 68, a piston 63 acting through a rod 62 directly upon the web of the shoe 61 and a piston 71 acting through a rod 72 upon the carrier 69 and the shoe 68. Circumferential movement of the shoe 68 in one direction is limited by its contacting the support 73, and an enlargement 67 limits sliding of the push-rod 65. A single spring 81 biases the struts 61, 68 to the disengaged position.