Seat belt retractor with energy absorbing mechanism

1. A seatbelt retractor for a seat belt device in a vehicle, the retractor comprising: a frame;

a spool configured to be fixed to one end of a webbing so that the webbing may be wound around the spool, the spool being rotatably mounted at both ends to the frame and configured to rotate in a webbing extraction direction and a webbing retraction direction;

a primary torsion bar positioned in the spool, a first end of the primary torsion bar being coupled to a torsion bar cam and a second end of the primary torsion bar being connected to a pinion, wherein the torsion bar cam is configured to engage the spool;

a pretensioner coupled to the second end of the primary torsion bar via the pinion, the pretensioner configured to rotate the pinion in a webbing retraction direction when the pretensioner activates in response to an acceleration of the vehicle greater than a predetermined high acceleration;

a secondary torsion bar positioned in the spool, a first end of the secondary torsion bar being connected to the torsion bar cam and a second end of the torsion bar being engaged with a locking mechanism mounted to the frame;

wherein the primary and secondary torsion bars are configured to be locked at the second ends and the first ends are configured to rotate relative to the second ends so that the primary and secondary torsion bars deform to absorb force.

2. The seatbelt retractor of claim 1 , further comprising a release mechanism for unlocking the second end of the secondary torsion bar so that the secondary torsion rotates at both ends with the spool and only the primary torsion bar deforms to absorb force.

3. The seat belt retractor of claim 2 , wherein the release mechanism comprises a pyrotechnically driven piston.

4. The seat belt retractor of claim 1 , wherein the locking mechanism includes a rotatable locking ring with internal teeth engaged with a lock base, wherein the lock base is directly engaged with the second end of the secondary torsion bar.

5. The seat belt retractor of claim 4 , wherein the lock base includes a movable locking pawl that engages at least one of the internal teeth of the locking ring in response to a predetermined vehicle acceleration to thereby prevent rotation of the locking base relative to the locking ring.

6. The seat belt retractor of claim 5 , wherein the locking ring is engaged by a movable release pawl connected to the frame to thereby prevent rotation of the locking ring relative to the frame.

7. The seat belt retractor of claim 6 , further comprising a release mechanism for moving the release pawl out of engagement with the locking ring, and wherein the release mechanism includes a pyrotechnic actuator.

8. The seat belt retractor of claim 7 , wherein the pyrotechnic actuator includes a piston and cylinder arrangement and wherein movement of the piston in the cylinder causes a corresponding movement of the release pawl out of engagement with the locking ring.

9. The seat belt retractor of claim 6 , wherein the release pawl is moved out of engagement with the locking ring in response to a predetermined condition to thereby permit rotation of the first and second ends of the secondary torsion bar with the spool.

10. A seatbelt retractor for a seat belt device in a vehicle, the retractor comprising: a frame;

a spool configured to be fixed to one end of a seat belt webbing so that the webbing may be wound around the spool, the spool being rotatably mounted at both ends to the frame and configured to rotate in a webbing extraction direction and a webbing retraction direction;

primary and secondary torsion bars positioned end to end in the spool along an axis of rotation of the spool, wherein adjacent first ends of the torsion bars are coupled to an interior surface of a torsion bar cam and wherein the torsion bar cam engages the spool;

wherein the primary and secondary torsion bars are configured to be locked at second ends of the torsion bars opposite to the first ends, and wherein the first ends are configured to rotate relative to the second ends so that the primary and secondary torsion bars deform to absorb force when the vehicle experiences an acceleration greater than a predetermined value.

11. The seat belt retractor of claim 10 , wherein the retractor is configured so that the second end of the secondary torsion bar is released to rotate with the first end of the secondary torsion bar while, at the same time, the second end of the primary torsion bar remains locked.

12. The seat belt retractor of claim 11 , further comprising a pyrotechnically actuated release mechanism for releasing the second end of the secondary torsion bar.

13. The seat belt retractor of claim 10 , further comprising a pretensioner for driving the spool in the webbing retraction direction and locking the second end of the first torsion bar.

14. The seat belt retractor of claim 10 , further comprising a locking mechanism for locking and preventing rotation of the second end of the secondary torsion bar, wherein the locking mechanism includes a locking ring rotatable relative to the frame.

15. The seat belt retractor of claim 14 , further comprising a movable release pawl connected to the frame that engages the locking ring to prevent rotation of the locking ring relative to the frame.

16. The seat belt retractor of claim 15 , wherein the movable release pawl is driven out of engagement with the locking ring by pyrotechnic actuator in response to a predetermined condition to thereby permit rotation of the second end of the secondary torsion bar with the first end of the secondary torsion bar and the spool.

17. A seatbelt retractor for a seat belt device in a vehicle, the retractor comprising:

a frame;

a spool configured to be fixed to one end of a webbing so that the webbing may be wound around the spool, the spool being rotatably mounted in the frame and configured to rotate in a webbing extraction direction and a webbing retraction direction;

a primary torsion bar positioned in the spool, a first end of the primary torsion bar being coupled to a torsion bar cam that is coupled to the spool and a second end of the primary torsion bar being configured to be locked;

a secondary torsion bar positioned in the spool, a first end of the secondary torsion bar being located adjacent to the first end of the primary torsion bar, wherein the first end of the secondary torsion bar is coupled to the torsion bar cam and a second end of the secondary torsion bar being engaged with a locking mechanism mounted to the frame;

wherein the second ends of the primary and secondary torsion bars are configured to be locked when vehicle acceleration exceeds a predetermined value and wherein the first ends are configured to rotate with the spool relative to the second ends so that the primary and secondary torsion bars deform to absorb force; and

wherein the retractor includes a release mechanism for unlocking the second end of the secondary torsion bar in response to a predetermined condition so that the secondary torsion rotates at both ends with the spool and only the primary torsion bar absorbs force.

18. The seat belt retractor of claim 17 , wherein the locking mechanism includes a locking ring rotatable relative to the frame.

19. The seat belt retractor of claim 18 , further comprising a movable release pawl connected to the frame that engages the locking ring to prevent rotation of the locking ring relative to the frame.

20. The seat belt retractor of claim 19 , wherein the movable release pawl is driven out of engagement with the locking ring by a pyrotechnic actuator in response to a predetermined condition to thereby permit rotation of the second end of the secondary torsion bar with the first end of the secondary torsion bar and the spool.