GB1068648A - Internal shoe drum brake - Google Patents

Abstract

1,068,648. Internal shoe drum brakes. SOC. ANON. D.B.A. April 15, 1965 [April 20, 1964; March 26, 1965], No. 16313/65. Heading F2E. An internal shoe drum brake of the kind having both ends of each of two shoes 4, 6 actuable by a pair of hydraulic cylinders 18, 20, each cylinder having two pistons 26, 28 engaging directly, or via rollers 56, respective lugs on the shoe webs, the shoes are arranged to operate as a two-trailing shoe brake in both directions of rotation of the drum by the provision of slots (14), 16 in the opposite ends of the web of each brake shoe, two of these ends being cranked to enable the webs to overlie each other and the slots being shaped such that pins 10, 12 secured to anchor plate 6 each engage in a slot (14) of one shoe (Fig. 7, not shown) and a slot 16 of the other with both circumferential and radial play, whereby the shoes can move radially to align themselves with the drum in addition to anchoring automatically at their trailing ends. Each slot (14), whose edge 44 nearest the extremity of the shoe web engages the respective anchor pin in the forward direction of rotation f, has this edge formed as a ramp inclined at an angle of about 15 degrees to the line joining the pins 10, 12, so that the reaction of the pin on the shoe passes through the centre of pressure of the lining on the drum, while the corresponding edge 46 of each slot 16 is inclined at an angle of about 45 degrees to this line so that the pin cams the shoe over towards the adjacent side of the drum during reverse braking, so reducing the shock when the shoes move circumferentially. Further cushioning is provided in both directions of circumferential movement of the shoe, when changing from one direction of rotation to the other, by providing within the cylinders 18, 20 domed partition members 30, each having a restricted aperture 41 to retard flow of fluid from the chamber 37 on one side of member 30 to the other chamber 39, and vice versa. Chambers 39 of the two cylinders are interconnected by external piping, the lower one of chambers 37 being connected to the hydraulic feed and the higher one having a bleed hole sealed by a removable plug.' Any air bubbles pass to the latter chamber 37 since the domed shape of partitions 30 facilitates their passage through the apertures 41. The lugs of the shoes co-operating with the pistons are of unequal length so that pistons 28 are further in than pistons 26 in the brakes released position. This allows for greater lining wear of the trailing end of the lining in the forward direction of running and the fact that return springs 32 bias the shoes towards the forward running position. Manually-operated cams 43 are provided to adjust for lining wear, such adjustment reducing the amount of circumferential movement of the shoes when braking in the reverse direction. Hold-down clips 40 for the shoes pass through apertures 38 in the shoe webs.