Patent ID: 8286903

Claim:
A seat belt retractor comprising: a spindle for retracting a webbing; a torsion bar including a first shaft part and a second shaft part having a different torsional rigidity and an intermediate portion connecting the first and second shaft parts, the torsion bar being inserted into an interior of the spindle and joined to the spindle by an end portion of the first shaft part; a tread head joined to an end portion of the second shaft part of the torsion bar; a male screw portion that is joined to the tread head, the male screw portion having a cylindrical shape projecting into the interior of the spindle, wherein the male screw portion includes a first male screw groove on an outer surface thereof; a slide nut that is disposed in the interior of the spindle and spaced away from the tread head by a first distance, the tread head being configured to slide relative to the spindle but incapable of rotating relative to the spindle, the slide nut comprising a female screw groove formed on an inner surface thereof and configured to mesh with the first male screw groove of the male screw portion, wherein the slide nut moves toward the tread head while rotating by a mesh between the first male screw groove and the female screw groove, wherein the tread head is prevented from rotating by a predetermined lock mechanism and the spindle rotates in a direction for unreeling the webbing; and a slider that slides relative to the intermediate portion but that is incapable of rotating relative to the intermediate portion, the slider comprising a second male screw groove that meshes with the female screw groove of the slide nut, wherein the second male screw groove is spaced away from the female screw groove by a second distance, and wherein the slider slides toward the slide nut by a mesh between the female screw groove and the second male screw groove when the slide nut slides toward the tread head while rotating, wherein a torsional rigidity of the second shaft part is greater than a torsional rigidity of the first shaft part, and the second distance is eliminated before the first distance such that the slide nut and the slider are integrated.