Load limiting seatbelt retractor

1. A seatbelt retractor comprising:

a housing;

a spool rotatably supported by the housing on a rotational axis;

a load limiter fixed to the spool and lockable with the housing, the load limiter being on the rotational axis;

the load limiter having a first coupling and a second coupling spaced from the first coupling along the rotational axis;

the first coupling having a first male segment and a first female segment receiving the first male segment defining a first cavity therebetween, the first male segment and the first female segment being moveable relative to each other along the rotational axis;

the first coupling having a first energy absorber retained in the first cavity, the first energy absorber being compressible relative to the first male segment and the first female segment;

the second coupling having a second male segment and a second female segment receiving the second male segment defining a second cavity therebetween, the second male segment and the second female segment being moveable relative to each other along the rotational axis; and

the second coupling having a second energy absorber retained in the second cavity, the second energy absorber being compressible relative to the second male segment and the second female segment.

2. The seatbelt retractor of claim 1 , wherein the first male segment includes threads and the first female segment includes threads engaged with the threads of the first male segment.

3. The seatbelt retractor of claim 2 , wherein the second male segment includes threads and the second female segment includes threads engaged with the threads of the second male segment.

4. The seatbelt retractor of claim 1 , wherein the first energy absorber is resiliently compressible between the first male segment and the first female segment and the second energy absorber is resiliently compressible between the second male segment and the second female segment.

5. The seatbelt retractor as set forth in claim 1 , wherein the first energy absorber is a compressible fluid sealed in the first cavity between the first male segment and the first female segment and the second energy absorber is a compressible fluid sealed in the second cavity between the second male segment and the second female segment.

6. The seatbelt retractor as set forth in claim 1 , wherein the first energy absorber and the second energy absorber each include a liquid and hydrophobic nanoporous particles in the liquid.

7. The seatbelt retractor as set forth in claim 1 , wherein the first energy absorber is compressible between the first male segment and the first female segment to a compressed position in response to compressive load between the first male segment and the first female segment that exceeds a first threshold, and the second energy absorber is compressible between the second male segment and the second female segment to a compressed position in response to compressive load between the second male segment and the second female segment that exceeds a second threshold, the second threshold being greater than the first threshold.

8. The seatbelt retractor as set forth in claim 1 , wherein the load limiter includes a first member fixed to the spool and a second member lockable with the housing, the first coupling and the second coupling being between the first member and the second member.

9. The seatbelt retractor as set forth in claim 8 , wherein the first member includes one of the first male segment or the first female segment and the second member includes one of the second male segment or the second female segment.

10. The seatbelt retractor as set forth in claim 9 , wherein the load limiter includes an intermediate member between the first member and the second member, the intermediate member including the other of the first male segment or the female segment, and the intermediate member including the other of the second male segment or the second female segment.

11. The seatbelt retractor as set forth in claim 8 , further comprising a locking device between the housing and a second member.

12. The seatbelt retractor as set forth in claim 1 , wherein the load limiter includes a first member fixed to the spool, a second member lockable with the housing, and an intermediate member between the first member and the second member, the first coupling being between the first member and the intermediate member and the second coupling being between the second member and the intermediate member.

13. The seatbelt retractor as set forth in claim 12 , wherein:

the first member includes one of the first male segment or the first female segment and the intermediate member includes the other of the first male segment or the first female segment; and

the second member includes one of the second male segment or the second female segment and the intermediate member includes the other of the second male segment or the second female segment.

14. The seatbelt retractor as set forth in claim 13 , wherein the first energy absorber is a compressible fluid sealed in the first cavity between the first male segment and the first female segment and the second energy absorber is a compressible fluid sealed in the second cavity between the second male segment and the second female segment.

15. The seatbelt retractor as set forth in claim 14 , wherein the first energy absorber and the second energy absorber each include a liquid and hydrophobic nanoporous particles in the liquid.

16. The seatbelt retractor as set forth in claim 12 , wherein the first energy absorber is compressible between the first male segment and the first female segment to a compressed position in response to compressive load between the first male segment and the first female segment that exceeds a first threshold, and the second energy absorber is compressible between the second male segment and the second female segment to a compressed position in response to compressive load between the second male segment and the second female segment that exceeds a second threshold, the second threshold being greater than the first threshold.