Seat belt retractor with load limiting

#The present invention relates to a seat belt retractor with 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. 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 forwardly directed movement of a vehicle occupant, for example normal movement associated with reaching the controls for a radio or a window or to reach a glove compartment or door pocket. In a crash the more extreme momentum of the vehicle occupant activates a crash sensor that locks the spool against rotation and prevents forward motion of the vehicle occupant and collisions with the interior fixtures of the vehicle. 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. In recent years this problem has been recognized and some solutions proposed.

#One known solution is to effect load limiting by interposing a plastically or elastically deformable member in the force path. For example, a torsion bar may be incorporated into the spool. A torsion bar is made of steel that twists when high torque is applied to it and can rotate up to seven or eight times before breaking. It is connected to both ends of a split spool. One end of the spool is held against rotation by a locking ring engaged by a load bearing pawl in a crash. The other end of the spool is prevented from rotating by its connection to the locking ring via the torsion bar, but when the crash forces exceed a predetermined level the torsion bar will twist and allow a limited controlled further pay-out of belt webbing. The additional pay-out of belt webbing is generally in proportion to the momentum of the vehicle occupant at the moment of a crash. This pay-out of belt webbing lessens the otherwise severe restraining forces on the vehicle occupant at high vehicle speeds, especially during the initial moments of a crash.

#FIG. 1 is a perspective view of a seat belt retractor according to the present invention including a spool of the type shown in subsequent figures.

#FIG. 2 is a cross sectional view of the spool of the seat belt retractor of FIG. 1 prior to load limiting.

#FIG. 3 is an end view of the spool for FIG. 2.

#The seat belt retractor shown in FIG. 1 comprises a cylindrical retractor spool 1 mounted for rotation about a spindle 9 concentric with the spool axis in a frame 21 to wind in and pay-out seat belt webbing.

#In a crash a sensor positioned at a location indicated by reference character 23 activates a locking pawl 22 to engage a toothed locking ring 3 fixed to one end of the spool to prevent rotation and begin the spool locking process. The other end of the spool is connected to a rewind spring which is a clock type coiled spring which biases the spool to a webbing rewound condition.

#When a crash is detected the locking ring 3 is engaged by the locking pawl 22 and prevented from rotating. Subject to further movement due to load limiting arrangements the spool 1 is then locked against further rotation.