Belt tightener for seat belt

摘要

A pre-loader device that quickly tighten a seat belt after a sudden deceleration of a vehicle is detected is disclosed herein. The pre-loader device includes a mass body and a casing housing the mass body with the mass body being movable in the longitudinal direction of the vehicle within the casing. A holder is positioned by a weak coil spring, and a strong coil spring is disposed between a flange part of the mass body and a flange part of the holder. A retainer and the holder hold therebetween stoppers disposed at the tip of plate springs that extend from the rear end of the mass body so as to position the mass body and maintaining the coil spring in a compressed state. A wire connects the rear end of the mass body to a seat belt buckle.