GB731757A - Improvements in self-adjusting mechanism for hydraulic wheel brakes - Google Patents

Abstract

731,757. Automatic adjusting mechanism for brakes. H. & T. INDUSTRIES, Ltd. Feb. 3, 1954 [May 7, 1953], No. 12791/53. Class 103 (1). In a self-adjusting mechanism mounted in the hydraulic wheel brake cylinder of an internal shoe-drum brake, the device comprises two pistons 1; one of which carries a central spigot 2 which projects axially therefrom and is formed with ratchet teeth 3. The piston carrying the spigot is provided with a protuberance 4 adjacent the spigot on which is mounted a sealing washer 5. The second piston is formed with an axial extension 6 which is provided with an axial blind boring 7 into which the spigot enters. The extension 6 also provides a mounting for a second washer 5a; both sealing washers 5 and 5a providing a good seal under pressure of the hydraulic fluid which enters the fixedly mounted cylinder 18 through a boring 8. The extension 6 is formed with an annular groove 9 into which is fitted a pawl 10 (Fig. 4). A circlip 14 is then pushed over the end of the extension 6 into a position in which it springs into the groove 9 and forms a shoulder against which the pawl 10 can abut, its movement being thus restricted to the width of the groove. The pistons and their associated parts will be maintained in the position shown by the usual coil springs (not shown) which hold the brake shoe 17 out of engagement with the brake drum. On depression of the brake pedal, fluid is forced into the space between the pistons and, as a result, the pawl 10 will move into engagement with the circlip 14 and then if wear has occurred on the faces of the linings the inwardly turned extremities 13 of the pawl will over-ride on one or more teeth on the ratchet which will have the effect of reducing the clearance between the linings and the drum when the brakes are not in operation, thus compensating for wear. The clearance between the linings and the drum will thus finally be determined by the width of the groove. Two alternative constructions are illustrated and described in the Specification; one being such that the cylinder is mounted for axial movement and the hydraulic fluid acts between a single piston and a transverse wall of the cylinder, the latter carrying the spigot 2; the other construction being of the kind used in connection with two leading brake shoes, there being two fixed cylinders arranged diametrically opposite one another, each cylinder forming an anchorage for a pivotally mounted shoe. A modified form of pawl is also described which permits a finer degree of adjustment.