GB1431096A - Automatic slack adjuster for a brake - Google Patents

Abstract

1431096 Slack adjusters; lining-wear indicators G WIRMSBERGER 18 April 1973 18859/73 Heading F2E In a drum brake including brake shoes 2, 3 and a brake shoe carrier 1 there is an automatic slack adjuster, to compensate for wear of the brake linings, comprising a locking teeth mechanism which is formed by at least two mutually engaging racks which lock together in one direction when the brake is released and slide upon each other when the brake is operated; the racks work together with a lost-motion device, i.e. a pin and slot connection 15, 16, having a clearance proportional to the predetermined slack which device is actuated before the racks are moved relatively to each other so that the relative motion of the racks and the adjustment takes place only if the clearance of the device is consumed, at least one of the racks being pivotable. Two racks 9, 14, Fig. 1, which provide length adjustment in one direction only, are held together by leaf-springs 12, 13 extending from U-shaped staples 10, 11; one rack 9 is pivoted to a hand brake lever 7 and the other rack 14 has a slot 15 within which slides a pin 16 fixed to a brake carrier part 17 or a shoe 3. Initially the pin 16 abuts the right-hand slot end and upon actuation the racks 9, 14 are moved rightwardly, helped by a tension spring 18, until the pin abuts the left hand slot end; further movement due to wear causes the rack 9 to move relative to the rack 14. Alternatively, levers 24, 25, Fig. 3, spring-biased to engage brake shoes 27, 28, act on the racks 14, 30 via a gear train 26, 26a, 26b. A contact 31 is engaged by the rack 30 or a part 32 therewith to provide a maximum shoe wear signal. Only one shoe may actuate the racks 14, 30 via one lever. For wedge shoes, the levers are pivoted on arcuate guides extending from the shoes. Fig. 4 shows a member 34 pivoted to a shoe and causing leftward movement of a bar 35 until a fixed pin 37 abuts the right-hand end of a slot therein; subsequent movement causes relative movement of two racks 41, 40 connected to the member 34 and bar 35 via levers 38, 39, respectively, the levers swinging about fixed pivots. Alternative embodiments are:-a lever abutting a shoe and causing clockwise rotation of a pinion upon shoe actuation, the pinion moving a rack therewith until the rack is arrested by a pin-slot engagement thus producing rack-pnion relative movement; two levers abutting cams on respective brake shoes and connected directly to and via a pin-and-slot connection to respective engaging racks; a shoe abutting lever connected via a pin-and-slot connection to a pinion moving lever, the pinion engaging a pawl; a directly movable pinion engaging a pivoted pawl which is able to move through a part circumferential orbit. The pin-and-slot connection may be replaced by a flanged piston sliding between two stops in a cylinder, and there may be provided three racks for interengagement. The engaging flanks of the teeth may be 70 or 90 degrees to the longitudinal plane. The racks are disengaged during repair &c. by actuation through spring-biased cables. A cable tensioner comprises one rack coupled to the cable and the other rack to a support or lever via a pin-and-slot connection. A tension-spring between the racks provides the constant tension.