Patent ID: 8220735

Claim:
An adaptive load limiting seat belt retractor for seat belt webbing of a motor vehicle occupant restraint system, comprising: a retractor frame adapted to be mounted to the motor vehicle, a spindle assembly supported for rotation by the retractor frame assembly and having a spindle with a hollow interior and an outer surface adapted for winding the webbing, a first torsion bar and a second torsion bar positioned end to end and at least partially disposed within the spindle hollow interior, the first torsion bar having an end fixed to the spindle, the second torsion bar having an end coupled to a tread head hub, the first and second torsion bars arranged end to end and meeting at a rim, the rim coupled with a pretensioner pinion, a tread head mounted to the retractor frame and engaging the tread head hub to lock the spindle to the frame in response to inertial loads acting on the retractor, and upon locking with the spindle, tension loads acting on the seat belt produce torque on the spindle carried through the first and second torsion bars, which provides a low seat belt load limiting function, and a pretensioner assembly for causing the pinion to rotate the spindle for pretensioning the belt webbing and locking the pinion to the frame with tension loads acting on the seat belt produce torque on the spindle are coupled through the torsion bar rim and pinion and carried by the first torsion bar section, thereby providing a high seat belt load limiting function; a torque transfer tube positioned around at least one of the torsion bars and connected with the torsion bar rim at one end thereof and with the pretensioner pinion at another end thereof; and a connection between the torque tube and the tread head hub enabling limited relative rotation therebetween, and upon the limited relative rotation being exceeded, the torque tube and the tread head hub being rotationally coupled to transfer torque therebetween, whereupon the tension loads acting on the seat belt produce torque on the spindle carried by the first torsion bar, and provide the high seat belt load limiting function.