Retractor spool

Abstract

Force limitation in retractors is needed to avoid injury to an occupant from the seat belt itself particularly at high crash impact loads. The invention provides a seat belt retractor comprising a spool including force limiting means for allowing further payout of the seat belt webbing after the spool has locked, under the influence of an occupant's forward momentum in the crash condition. In one aspect the force limiting means is provided by a plurality of fins provided on the outer surface of the spool, each fin having a section which extends in a generally radial direction and a section which extends circumferentially, the circumferentially extending section of one fin overlapping the circumferentially extending section of an adjacent fin and supported by the radial extending section of that adjacent fin, so that a force tending to tighten the webbing on the spool, acts in a direction to crush the radial sections of the fins and to slide the circumferential sections over each other, thus reducing the effective outer circumference of the spool. In another aspect the force limiting means comprises an energy absorbing member connecting the spool to the spool shaft, the connection being rigid below a predetermined force, and above the predetermined force there being relative rotation of the spool with respect to the spool shaft to allow pay-out of belt webbing.