Patent ID: 8042758

Claim:
A pretensioner for a seat belt retractor of a vehicle, comprising; a torsion bar on which a webbing is wound; a gear member connected to the torsion bar; a base member with which the gear member is meshed and through which the torsion bar passes; a cylinder having a movement guide hole formed therein to supply a gas upon rapid deceleration of the vehicle; a piston having a rack with a plurality of teeth formed at a side surface thereof in a longitudinal direction configured to be meshed with the gear member and to be moved along the movement guide hole upon supply of a gas from an initial position substantially within the cylinder to a deployed position substantially out of the cylinder, and; a cylindrical sealing operation part integrally formed with a bottom of the piston and projecting therefrom; and a sealing part coupled to an outer periphery of the sealing operation part to seal between the piston and an inner wall of the cylinder, wherein the base member has a hooking means engaging the piston to retain the piston in the initial position relative to the base member prior to movement of the piston and the rack along the guide hole upon the supply of gas into the deployed position, the hooking means having a shape corresponding to the teeth of the rack of the piston and being in meshed engagement therewith.