| 摘要 |
A drum brake (10) includes a rotatable brake drum (16) and a pair of brake shoes (12, 14) which are engageable with the brake drum. A non-rotatable backing plate (24) slidably carries the pair of brake shoes. The brake shoes pivotally anchor at one end to a pin (32) secured to the backing plate. An extendible member (36) adjustably spaces apart the other ends of the brake shoes to maintain a desired running clearance between the brake shoes and the brake drum. One of the brake shoes carries a lever (48) which drivingly engages a ratchet wheel (46) of the extendible member. The lever carries a pin (60) which is slidably and rotatably received in an arcuate guide slot (58) of the backing plate. A brake application with forward brake drum rotation causes the lever to slide along the arcuate slot and to remain substantially stationary relative to the extendible member. A reverse brake application causes the one brake shoe to shift in a direction nearly perpendicular to the arcuate guide slot so that the lever is pivoted relative to the extendible member. The lever engages with a successive tooth of the ratchet wheel if the running clearance of the brake is greater than the desired value. An adjustment of the extendible member is effected to diminish the running clearance of the brake to the desired value. |
