Belt retractor utilizing active material actuation

1. A seat belt retractor adapted for use with a seat belt presenting a first tensile load, said retractor comprising:

a tensioning mechanism coupled to the belt and including an active material element operable to undergo a reversible change in fundamental property when exposed to or occluded from an activation signal,

said mechanism being configured to selectively adjust the tension in the belt to a second tensile load, as a result of the change, wherein the mechanism includes first and second inter-engaged parts, and the first part is able to transmit a first maximum torque or force to the second part when the element is activated and a second maximum torque or force when deactivated, a plurality of torque-transmitting spheres are fixed to a first of the parts and contact the other, so as to be intermediately disposed therebetween, and the element is operable to cause the parts to relatively translate so as to reduce or increase the plurality of spheres.

2. The retractor as claimed in claim 1 , wherein the mechanism is further configured to gradually adjust the tension, so as to present digressive load limiting.

3. The retractor as claimed in claim 1 , wherein the mechanism includes a multi-component torsion bar operable to present first and second torsional strengths when the element is activated and deactivated respectively.

4. The retractor as claimed in claim 3 , wherein the bar includes inner and outer concentric tubes having respective torsional strengths, and the tubes are caused to inter-engage by the change.

5. The retractor as claimed in claim 1 , further comprising:

a controller communicatively coupled to the mechanism; and

at least one sensor communicatively coupled to the controller, and operable to detect a condition or event,

said controller and sensor being cooperatively configured to cause the element to be exposed to or occluded from the signal upon detection of the event.

6. The retractor as claimed in claim 5 , wherein said at least one sensor includes a pre-crash, or crash sensor.

7. The retractor as claimed in claim 6 , wherein said at least one sensor is operable to determine a crash characteristic selected from the group consisting essentially of closing velocity, vehicle crush pulse, and the type of object being impacted.

8. The retractor as claimed in claim 1 , wherein the element is formed of an active material selected from the group consisting essentially of shape memory alloys, electroactive polymers, and piezoelectric materials.