The present invention relates to slack adjusters of the type which comprise part of a lever used to connect a power actuator with the brake shaft of a vehicle braking system whereby linear motion of the actuator produces rotation of the brake shaft to apply the brakes. Slack adjustment is necessary because the clearance between the brake linings and the drum against which they are applied grows during wear of the linings and must be compensated. It is therefore common practice to build a slack adjuster into the lever assembly so that the rotational position of the brake shaft can be adjusted while maintaining the angular excursion of the lever substantially constant, since the motion of the actuator is limited.
A common type of slack adjuster comprises a bushing which is attached to the brake shaft, and an arm which has a hub member rotatable on the bushing, but has means for adjusting the angular position of the hub member with respect to the bushing carried by the brake shaft. One common expedient is to use a worm carried by the hub of the arm and engaging teeth around the periphery of the bushing, which comprises a worm wheel attached to the brake shaft so that the position of the arm can be selectively adjusted with respect to the angular position of the bushing.
Another way of fixing the position of the bushing relative to the hub of the arm is shown in U.S. Pat. No. 2,948,558 to Schultz, which provides a flange on the bushing having teeth around its shoulder which is located adjacent to a bearing surface on which the hub of the arm is rotatable, the arm also having a set of teeth on a surface which lies parallel to the shoulder so that the two annular series of teeth mesh with each other. A washer and nut are provided on the bushing to maintain the two series of teeth tightly locked together except during periods of adjustment. U.S. Pat. No. 2,631,472 to MacDougall shows a similar structure using interlocking teeth to maintain the adjusted position of the bushing with respect to the hub of the arm.
U.S. Pat. No. 2,648,996 to MacDougall shows intermeshing ratchet teeth maintaining the adjusted position of the bushing with respect to the hub of the arm, and in this patent the mesh of the teeth is yieldably maintained by spring means. U.S. Pat. No. 2,697,497 to Shively shows a similar structure in which the engagement between the teeth is spring loaded. These are both automatic slack adjusters.
Copies of the above four patents are filed with the specification in lieu of a prior art statement.