Patent GB-779889-A (GB)
Title: Automatic adjustor for internal shoe-drum brakes
IPC: F16D65/56
Filed: 1955-05-12
Abstract: 779,889. Internal shoe-drum brakes. BENDIX AVIATION CORPORATION. May 12, 1955 [June 1, 1954], No. 13756/55. Class 103 (1). In an internal shoe-drum brake having an automatic adjustor, a ratchet wheel is situated on a thrust link connected to one brake shoe end and co-operates with a strut connected to the other adjacent brake shoe end, said ratchet wheel co-operating with an operating member adapted to be displaced with respect to the ratchet wheel when the brake is applied and adapted, by spring means, to turn said ratchet wheel when the brake is released such that a flexible linkage associated with one brake shoe has an operative connection at its one end with a fixed member and at its other end with the spring loaded operating member. In the embodiment illustrated in Figs. 1 and 3 (a section through 3-3 of Fig. 1) an internal shoe-drum brake is provided with an automatic adjustment mechanism in the form of a thrust link or strut 30, which engages articulated shoe ends 26 and 28, and consists of an adjusting nut 32, socket 34 and an externally threaded link 36 received in threaded opening 38 provided in nut 32. The link 36 has a transversely located serrated ratchet wheel 40. An adjusting mechanism 46 comprises a positioning portion 48, an integral U-shaped convolution 50, a lever portion 52 provided with a tooth 54 adapted to engage the serrations on the ratchet wheel 40. The adjustor 46 is actuated by means of an adjustable flexible cable 58 connected at one end to the anchor post 24 and at the other end to the lever 52 of adjustor 46 and is provided intermediate its length at 60 with an operative connection with the shoe 12 to produce tension of cable 58 when shoe 12 is moved in one direction to actuate adjustor 46; shield 62 preventing the cable 58 from sliding directly on spring 25. The positioning portion 48 of the adjustor 46 is formed with flats which prevent the relative turning of ratchet wheel 40 on strut 30 and a non-rotatable washer 66 is mounted on the flat side 44 of socket 34 of strut 30 and located between ratchet wheel 40 and positioning portion 48. The washer 66 is permitted lateral sliding movement into abutment with tooth 54 on adjustor 46 to disengage tooth 54 from the serrations on ratchet wheel 40. In order to ensure the brake adjustment is not carried out when the drum 17 is overheated or when the brake components are subjected to excessively high temperatures which cause thermal distortion and other heat phenomenal, the brake is only adjusted when the vehicle is moving in the reverse direction of motion when temperatures are normal and the brake components are substantially undistorted since the kinetic energy to be absorbed is usually much lower than during forward speeds due to the lower reversing speed of the vehicle. In reverse direction of motion of the vehicle when end 22 of shoe 12 is actuated into frictional engagement with brake drum 17 by wheel-brake cylinder 18, the shoe 12 will be provided with a self-energizing action to assist in applying shoe 10. This movement of shoe 12 produces a tensile force in flexible cable 58 and automatic adjustor 46 is actuated to move tooth 54 upwardly if the shoe is moved sufficiently to cause tooth 54 to engage a successive serration on ratchet wheel 40. When the brake is released the shoe 12 returns to its retracted position relaxing the tensile force in flexible cable 58 and the U-shape convolution 50 urges tooth 54 into engagement with the ratchet wheel to a retracted position to cause the ratchet wheel to be rotated, advancing threaded link to the right and spreading the articulated shoe ends slightly apart. The tooth 54 may be brought out of engagement with the serrations on ratchet wheel 40 to enable manual adjustment of the brake to be effected. Other alternative embodiments of the invention are illustrated in the Specification; a typical case being the arrangement shown in Fig. 10, wherein the flexible actuating cable 58c is positioned between the lining and rim of the brake shoe such that when a tensile force is set up in flexible cable 58c due to movement of the shoe 12 the tooth 54c is moved to a successive serration 42c when the extent of the shoe travel is sufficient, so that when the brake is released, the tooth 54c is urged into the retracted position by convolution 50c, thus causing turning of the ratchet wheel 40c and sleeve 69c to spread the adjacent articulated shoe ends apart through the adjustable strut 30c. Specifications 551,726 and 779,890 are referred to.