Dual Stage Pretensioning and High Pay-In Capacity Pretensioning Retractor

A dual pretensioner 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 and having a spindle adapted for winding the webbing, the spindle assembly further having a first and a second pretensioner pinion,
• a first rotopretensioner assembly for causing the first pinion to rotate the spindle for pretensioning the belt webbing upon activation of the first pretensioner assembly, the first rotopretensioner assembly having a first pretensioner tube, with first engagement elements therein, and a first gas generator, wherein upon activation of the first gas generator, the first engagement elements are driven to travel in the first pretensioner tube and engage the first pinion to drive the spindle to rotate,
• a second pretensioner assembly for causing the second pinion to rotate the spindle for pretensioning the belt webbing upon activation of the second pretensioner assembly, the second rotopretensioner assembly having a second pretensioner tube, with second engagement elements therein, and a second gas generator, wherein upon activation of the second gas generator, the second engagement elements are driven to travel in the second pretensioner tube and engage the second pinion to drive the spindle to rotate, and
• one of the first or the second pretensioner assembly having locking means for locking the respective first or the second pinion to the frame after the activation thereof, and the other of the first or the second pretensioner assembly allowing rotation of the respective first or the second pinion relative to the frame after the activation thereof.

A dual pretensioner 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 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 spindle hub, the first and second torsion bars arranged end to end and meeting at a rim, the rim coupled with a second pretensioner pinion, and a first pretensioner pinion coupled to the spindle and a end thereof opposite the second pretensioner pinion,
• a tread head assembly mounted to the retractor frame and engaging the spindle 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,
• a first rotopretensioner assembly for causing the first pinion to rotate the spindle for pretensioning the belt webbing, and
• a second rotopretensioner assembly for causing the second pinion to rotate the spindle for pretensioning the belt webbing and for locking the pinion to the frame with tension loads acting on the seat belt produce torque on the spindle are coupled through the first torsion bar section, thereby providing a high seat belt load limiting function, and wherein upon locking of the tread head assembly the seat belt produce torque on the spindle are coupled through the second torsion bar section, thereby providing a low load level limiting function.