Abstract: A seat belt retractor is provided with a pretensioner which comprises a wound-wire tightening mechanism and a drive means. The wound-wire tightening mechanism is composed of a pulley fixedly mounted on an end portion of a take-up spindle and a wire wound around the pulley with a small space left therebetween. The drive means comprises a piston connected to a free end of the wire, a cylinder with the piston movably received therein, a compression coil spring disposed in the cylinder to bias the piston in the pulling direction of the wire, and a trigger unit releasably holding the piston relative to the cylinder such that the piston can be maintained at a biased position against the resilient force of the compression coil spring but the holding of the piston at the biased position can be released responsive to an acceleration of at least a predetermined value.

Abstract: A retractor with both emergency and automatic locking mechanisms is provided. The retractor has take-up spindle means; a ratchet wheel; a pawl member engageable with the ratchet wheel and displaceable between a first position, where the pawl member prevents any further rotation of the take-up spindle means in the webbing-releasing direction, and a second position where the pawl member is maintained out of engagement with the ratchet wheel, said pawl member normally assuming the second position; control means for bringing the pawl member to the first position when the webbing is wound on the take-up spindle means after release of the webbing over at least a predetermined first length from the take-up spindle means and then to the second position when the webbing has been taken up over at least a predetermined second length; and an emergency locking mechanism for sensing an emergency state to prevent any further rotation of the take-up spindle means in the webbing-releasing direction.

Abstract: A retractor is equipped with an emergency locking mechanism and an automatic locking mechanism. It is allowed to change the automatic locking mechanism from a state ready to actuate to a state not ready to actuate and vice versa by suitably changing the wound state of the webbing on a take-up spindle.