Adaptive load limiting retractor

An adaptive load limiting seat belt retractor particularly adapted for motor vehicle applications. The retractor provides multiple levels of load limiting through the use of a pair of internal torsion bar elements. The torsion bar elements control the tension force on the seat belt webbing during an impact in a manner which provides desirable crash management characteristics. The retractor can be switched between high and low load limiting modes through activation of a pyrotechnic pretensioner. When the pyrotechnic pretensioner is not activated, the retractor provides a low load level characteristic. Pretensioner activation switches the retractor into a high load level operating condition. A high load limiting level is provided when the pretensioner is not activated if the spindle rotation exceeds a limited level in the low load limiting condition. A degressive load limiting feature may be provided to cause load limiting to begin at a higher level than the high load limiting level, and then step down the high load limiting level.