GB1240222A - Improvements in or relating to automatic adjusting devices for vehicle brakes - Google Patents

Abstract

1,240,222. Slack-adjusters for vehicle brakes; fluid and mechanical actuation. AUTOMOTIVE PRODUCTS CO., Ltd. 19 Feb., 1970 [17 March, 1969], No. 13904/69. Heading F2E. Applying-means, shown applied to a spot-type disc brake, Fig. 1, comprise (diagrammatically) a piston 14 movable by fluid pressure in a cylinder 15, the piston 14 being also movable by a lever 16 pivoted at 17 on a slidable plate 11 and acting through a thrust member 18 which incorporates the slack-adjusting means. A stop to prevent movement, beyond a predetermined position, of the thrust member in the brakereleasing direction, is provided, and as shown, takes the form of a stop 19 on plate 11 for cooperation with lever 16. As shown in Fig. 2 the thrust member 18 comprises a screw-threaded stem 21 provided with a head (unreferenced) which is engaged by a spring 23 to urge the stem leftwards into contact with lever 16. The spring bears against a plate 24 retained by a clip-ring 25 inserted in the cylinder bore. The cylinder 15 is fixed relative to the plate 11, and the lever being forced against stop 19 indirectly by spring 23, is also fixed relative to the plate in this rest position. Thus stem 21, when retracted, has a fixed position relative to the cylinder 15. Rotation of stem 21 is prevented by "flats" 26 engaging groove 27 in lever 16. The thrust member also comprises a nut 22, the mating threads on nut and stem having a clearance so that the nut is capable of a small predetermined linear axial movement on the stem. The nut is urged to the right, so that frusto-conical faces 32, 33 on nut and piston respectively are in contact, by a spring 28 reacting against a clip ring 31 fixed in the piston, and acting through a ball thrustbearing 34. On fluid-pressure actuation, piston 14 is urged to the right to apply pad 13, Fig. 1, while reaction thrust in the cylinder through plate 11 applies pad 12. Fluid pressure in the cylinder assists spring 23 to hold stem 21 against movement relative to cylinder 15, whereas spring 28 urges nut 22 to follow outward movement of piston 14. Until the clearance in the screwthreads is taken up, the nut 22 moves linearly, but if piston 14 moves through a distance greater than this, it tends to move ahead of nut 22, separating faces 32 and 33. Consequently, spring 28 rotates nut 22 to keep the faces in contact. When fluid pressure is relieved, piston 14 is free to move back only to the extent permitted by the thread clearance, nut 22 being held against rotation by friction at faces 32, 33. Thus the clearances between pads 12, 13 and disc 10 respectively are kept substantially constant. On mechanical actuation, by pulling on lever 16, thrust is transmitted through member 18 and piston 14 to pad 13, while reaction thrust at pivot 17 is transmitted through plate 11 to pad 12. Backward rotation of nut 22 on stem 21 is prevented because the thrust, being transmitted through the nut from stem 21 to piston 14, causes high friction both at the screw-threads and at the co-operating faces 32, 33. Because of the automatic adjustment, lever travel is kept constant, so a high leverage ratio may be used in the connecting linkage. In a modification (Fig. 3, not shown), two parts replace nut 22, namely: a nut (35), (the mating threads on this nut and the stem 21 having only normal working clearance), and a separate component (36) which carries face 32, and is keyed to nut (35) and is slidable axially on it through a small distance. Spring 28 acts on member (36), not on nut (35). During fluid pressure application, after appropriate pad wear, component (36) first moves with piston 14 relative to nut (35), to its limit, after which component (36) and nut (35) are rotated together by pressure of spring 28 to follow movement of the piston.