Cylinder in a pretensioner for seat belt retractor and pretensioner for seat belt retractor employing the same

摘要

Provided is a pretensioner for a seat belt retractor. The pretensioner for a seat belt retractor (38) of a vehicle includes a torsion bar (250) on which a webbing (16) is wound; a gear member (550) connected to the torsion bar (250); a base member (500) with which the gear member (550) is meshed and through which the torsion bar passes; a cylinder (610) having a movement guide hole (612) formed therein to supply a gas upon rapid deceleration of the vehicle; a piston (630) having a rack (633) formed at a side surface thereof in a longitudinal direction to be meshed with the gear member (550) and moved along the movement guide hole (612) upon supply of a gas, and; a cylindrical sealing operation part (632) integrally formed with a bottom of the piston (630) and projecting therefrom; and a sealing part (640) coupled to an outer periphery of the sealing operation part (632) to seal between the piston (630) and an inner wall of the cylinder (610), wherein the base member (500) has a hooking means (510) for hooking the piston (630) to a rack. Since the rack of the piston is hooked by the hooking means and assembled thereto, it is possible to form an appropriate gap (or a marginal space) between the sealing part and the straight movement guide hole.