| 摘要 |
A brake assembly having a pair of brake shoes each moved an equal distance into engagement with a brake drum by a brake actuator and each positionally adjusted relative to the drum by a brake adjuster an equal distance corresponding to brake lining wear during movement of the shoes toward the drum. The actuator is a wedge type brake having a pair of tines movable by an air motor an amount sufficient to force a pair of properly adjusted shoes into engagement with the drum. Each tine engages a jackscrew contacting the upper end of one of the shoes. A ratchet wheel is secured to one element of each jackscrew and is rotated by movement of a pawl. The pawls are interconnected for corresponding movement and receive energy via a torsional spring which in turn is energized in response to movement of the tines. When the shoes effect braking of the drum, the axial force on each jackscrew prevents relative rotation of the jackscrew elements regardless of the rotational force exerted by the pawls, causing the torsional spring to act as a "lost motion" mechanism. The force needed to rotate the ratchet wheels is transmitted to the pawls via the torsional springs only after the tines have moved a sufficient distance to cause engagement of properly adjusted shoes with the drum. The actuator and adjuster are enclosed dustproof housing. A wedge shaped plate is secured to a frame that is used to support the shoes for displacement into contact with the drum. Angular sides on the plate engage the lower ends of the shoes. Shoes having worn linings can be replaced without disassembling the adjuster by removing the plate, moving the shoes away from the drum and then withdrawing the shoes from the drum.
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