Seat belt retractor with multi-level load limiting

#The present invention relates to a seat belt retractor having multilevel load limiting.

#A seat belt retractor generally comprises a cylindrical bobbin or spool with a circular cross-section. Seat belt webbing is attached to and wound around the spool and the spool is mounted on a spool shaft to be rotatable in the retractor to wind in webbing under action of a retractor spring and to pay-out webbing under the influence of relatively gentle forward directed movement of a vehicle occupant, for example to allow for normal movement associated with vehicle occupancy such as reaching forwards to activate in-car controls (for a radio or a window) or to reach a glove compartment or door pocket. In the event of a crash situation, the more extreme momentum of the vehicle occupant activates a crash sensor which locks the spool against rotation and thus prevents forward motion of the vehicle occupant and injury due to impacting the interior structure of the vehicle such as the steering wheel, dashboard or windscreen.

#However, this sudden locking of the seat belt spool in a crash can sometimes cause injury to the vehicle occupant due to sudden impact of the torso with the belt webbing. This is particularly true in severe crashes. In recent years this problem has been recognized and some solutions have been proposed.

#FIG. 1 is an isometric view of a known seat belt retractor that can be adapted according to one embodiment of the present invention.

#FIG. 2 is a cross-sectional view of a spool, before load limiting, according to the present invention that could be adapted to the seat belt retractor of FIG. 1.

#FIG. 3 is an exploded view of part of the seat belt retractor of FIGS. 1 and 2.

#The arrangement of the invention is used in a traditional seat belt retractor that is well known to a person skilled in the art. Such a seat belt retractor is shown in general in FIG. 1 and comprises a cylindrical retractor spool 1 mounted for rotation in a frame 8 to wind in and pay-out seat belt webbing (not shown).

#In a crash, a sensor, positioned generally at 30, but not specifically illustrated, activates a locking mechanism to move a lockbar 10 to engage teeth on a locking ring 3 which is fixed to one end of the spool 1. Subject to further movement due to load limiting arrangements the spool 1 is then locked against further rotation. The other end of the spool 1 is connected to a rewind spring mechanism 5 which comprises a clock type coiled spring that biases the spool 1 to a webbing rewound condition.

#FIG. 2 shows the spool 1 according to the present invention and adaptable to the prior art seat belt retractor of FIG. 1 in cross section and shows a load limiting torsion bar 2 mounted along the spool axis and fixed at one end to the locking ring 3 by engagement of splines 32 in a correspondingly shaped hole 33 (shown more clearly in FIG. 3) in the locking ring 3. A wire 4 is wound around the spool 1 in a recess 31 to form coils 6, and is fixed to the torsion bar 2 at its end connected to the locking ring 3. The wire 4 is not attached to the spool. As shown in FIG. 3 the other end 34 of the torsion bar 2 is connected to the spool 1 at the side of the retractor at which the rewind spring 5 is attached to the spool 1.