Drum brake apparatus

A drum brake apparatus, comprising:

• a pair of brake shoes disposed opposed to an inner peripheral surface of a brake drum and elastically supported movably on a backing plate;
• a wheel cylinder interposed between a one-side adjoining ends of the paired brake shoes for expanding the paired brake shoes respectively;
• an anchor portion fixed to the backing plate and contactable by another-side adjoining ends of the paired brake shoes;
• an adjuster interposed between the one-side adjoining ends of the paired brake shoes existing near the wheel cylinder for adjusting a shoe clearance;
• an expansion mechanism arranged in series with the adjuster and, on receiving an operation force, for expanding the paired brake shoes respectively;
• a switch lever mechanism rotatably mounted on one of the brake shoes and rotatable by an action force of a given or higher value from the expansion mechanism;
• and
• a switch strut interposed. between the anchor-portion side adjoining ends of the paired brake shoes and, following the rotation of the switch lever mechanism, for expanding the anchor-portion side adjoining ends of the paired brake shoes, wherein
• the switch lever mechanism includes a first switch lever rotatably supported on one of the brake shoes by a first fulcrum pin for serving as an input side, and a second switch lever rotatably supported on the one of the brake shoes by a second fulcrum pin for serving as an output side rotatable following the first switch lever;
• and
• the first switch lever receives an action force from the expansion mechanism between a slide contact point of the first swich lever and the second switch lever and the first fulcrum pin.