Vehicle drum brakes and adjusting means therefor

Claim 2

In an internal shoe drum brake including a drum and brake shoes and having power actuating means and auxiliary mechanical actuating means for applying the shoes to the drum, an automatic wear compensating adjuster comprising first and second relatively rotatable strut parts in screw-threaded engagement with each other and constituting an adjustable strut acting to define a retracted position for said shoes, a pivoted pawl lever rotatable about a pivotal axis transverse to said strut and engageable with one said strut part for effecting rotation thereof, a coil spring prestressed in torsion with its axis aligned with said pivotal axis and having an end directly engaged with said lever to urge the same in a direction for effecting rotation of said strut parts in a wear compensating direction solely under the influence of said spring in response to greater than normal movement of said auxiliary actuating means due to wear of said brake shoes, and means carried by said auxiliary actuating means for preventing said torsion spring from moving said lever in a wear compensating direction when said brakes are released.

Claim 3

An internal shoe drum brake comprising a pair of opposed, arcuate brake shoes, movably mounted on a fixed brake structure, power-actuated service brake means for expanding the shoes against the drum, auxiliary, mechanical actuating means including an actuating lever engaging one shoe and a strut for transmitting auxiliary actuating forces to the other shoe, the strut including relatively rotatable screw-threaded parts so that the strut is adjustable in length to compensate for wear of the brake shoe linings, a pivoted lever for effecting relative rotation of the strut parts in response to excessive travel of the brake shoes upon brake application by the auxiliary actuating means, a prestressed coil torsion spring coupled to the said lever to urge the pivoted lever for effecting wear compensating adjustment as required in response to operation of said auxiliary means, said spring being adapted to yield to avoid over adjustment under high-braking loads, and a shaft mounted for rocking movement about a transverse axis, said shaft rotatably supporting said actuating lever and said operating lever, said coil torsion spring being mounted on said shaft to surround the same.

Claim 4

An internal shoe drum brake comprising a pair of opposed, arcuate brake shoes, movably mounted on a fixed brake structure, power-actuated service brake means for expanding the shoes against the drum, auxiliary, mechanical actuating means including an actuating lever engaging one shoe and a strut for transmitting auxiliary actuating forces to the other shoe, the strut including relatively rotatable screw-threaded parts so that the strut is adjustable in length to compensate for wear of the brake shoe linings, a pivoted lever for effecting relative rotation of the strut parts in response to excessive travel of the brake shoes upon brake application by the auxiliary actuating means, a prestressed coil torsion spring coupled to the said lever to urge the pivoted lever for effecting wear compensating adjustment as required in response to operation of said auxiliary means, said spring being adapted to yield to avoid over adjustment under high-braking loads, and a shaft mounted for rocking movement about a transverse axis, said shaft rotatably supporting said actuating lever and said operating lever, said coil torsion spring being mounted on said shaft to surround the same.

Claim 5

A brake according to claim 2, wherein the shaft is coupled to the actuating lever for rotation therewith, the pivoted lever is rotatable relative to the shaft and the actuating lever, the said spring serving to transmit rotational forces from the shaft and actuating lever to the pivoted lever up to a maximum value determined by the preload in the spring.

Claim 6

A brake according to claim 2, wherein said torsion spring is also prestressed as a compression spring and acts against said pivoted lever to urge it into operative engagement with said strut.