Load-limiting seatbelt retractor

1. A restraint system comprising:

a retractor housing;

a spool rotatably coupled to the retractor housing and defining an axis of rotation;

a threaded rod lockable relative to the retractor housing and elongated along the axis;

a nut threaded on the threaded rod; and

a spring elongated from a first end to a second end, the first end fixed relative to the spool, and the second end rotationally and axially fixed relative to the nut.

2. The restraint system of claim 1 , wherein the spring is a compression spring positioned coaxially around the threaded rod.

3. The restraint system of claim 1 , further comprising an emergency locking mechanism movable between an engaged state and a disengaged state, wherein the emergency locking mechanism in the engaged state locks the threaded rod to the retractor housing, and the emergency locking mechanism in the disengaged state permits rotation of the threaded rod relative to the retractor housing.

4. The restraint system of claim 3 , wherein when the emergency locking mechanism is in the disengaged state, the threaded rod is rotatable with the spool relative to the retractor housing.

5. The restraint system of claim 1 , further comprising a rod plate oriented orthogonal to the axis and fixed relative to the threaded rod, wherein the threaded rod is lockable to the retractor housing via the rod plate.

6. The restraint system of claim 5 , wherein the spool extends along the axis from a first end to a second end, and the rod plate is positioned at the second end of the spool.

7. The restraint system of claim 6 , wherein the spool includes an end plate oriented orthogonal to the axis and positioned at the first end of the spool, and the first end of the spring is fixedly attached to the end plate.

8. The restraint system of claim 7 , wherein the spring is a first spring, the restraint system further comprising a second spring elongated coaxially with the first spring from a first end to a second end, wherein the first end of the second spring is fixedly attached to the end plate.

9. The restraint system of claim 5 , wherein the nut is threadedly movable along the threaded rod from a starting position to an ending position, and the nut in the starting position abuts the rod plate.

10. The restraint system of claim 9 , wherein when the nut is in the ending position, the spring is in a fully compressed state.

11. The restraint system of claim 10 , wherein the spring is a first spring, the restraint system further comprising a second spring elongated from a first end to a second end, wherein the first end of the second spring is fixed relative to the spool, and the second end of the second spring is positioned between the starting position and the ending position of the nut.

12. The restraint system of claim 1 , wherein the threaded rod includes threading, the nut is threadedly movable along the threaded rod in a rotational and axial direction defined by the threading, and the threading is oriented such that when the threaded rod is locked to the retractor housing and the spool rotates in an extractive direction, the nut moves in a direction tending to compress the spring.

13. The restraint system of claim 1 , wherein the spring is a first spring, the restraint system further comprising a second spring elongated from a first end to a second end, wherein the first end of the second spring is fixed relative to the spool.

14. The restraint system of claim 13 , wherein the second end of the second spring is free.

15. The restraint system of claim 13 , wherein the second spring extends coaxially with the first spring.

16. The restraint system of claim 13 , wherein a stiffness of the first spring is greater than a stiffness of the second spring.

17. The restraint system of claim 13 , wherein the first spring in a relaxed position is longer than the second spring in a relaxed position.