Abstract: A seat belt retractor has a spool having seat belt webbing wound thereon mounted for rotation in a frame. A toothed ratchet wheel is connected to the spool and rotates therewith. The retractor has a crash sensor. A locking pawl is arranged to be pivotable from a first position in which it is spaced from the ratchet wheel to a second position in which it engages with the ratchet wheel to lock the spool against rotation, in response to activation of the crash sensor. A pretensioner is responsive to the crash sensor to rapidly rewind webbing onto the spool. A venting arrangement for the pretensioner includes a chamber having an inside side wall and an inside wall. A vent hole is formed in the side of the chamber with a seal for the vent hole. An axially slidable member is mounted in the chamber and biased away from one end of the chamber. The slidable member is connected to the locking pawl, so that it slides in the chamber when the locking pawl pivots.

Abstract: A pretensioner for a seat belt system has first and second piston-cylinder arrangements arranged generally one on each side of a spool shaft so that in travelling along the respective cylinder, each piston engages the periphery of the spool shaft and causes it to rotate. A sensor is responsive to a crash situation to detonate a first piston drive means, and means for detonating a drive means for the second piston at the end of the stroke of the first piston. The spool shaft may be a component of a seat belt retractor. Alternatively, the spool shaft is wound with a cable that pulls on a seat belt or seat belt buckle.