ADAPTIVE LOAD LIMITING SEAT BELT RETRACTOR

摘要

A safety seat belt arrangement comprises a retractor or spool assembly including a spool 20, carrying the seat belt, rotatable in a frame 18 unless blocked by a blocking mechanism 25, the spool assembly including a head member 22 cooperating with the blocking mechanism. A load limiting torsion bar assembly within the spool and acting between the head member and the spool comprises a first, high level, torsion bar portion 24, a second, low level, torsion bar portion 26 and an intermediate torsion element in the form of a torsion pipe 36 fixed at its ends with respect to the ends of the torsion bar portion 26. A torque tube 32 initially provides a direct drive connection between the outer end of the spool 20 and the outer end 24A of the high level torsion bar portion, so that, in a frontal impact situation, in which the blocking mechanism blocks rotation of the head member, the torque applied to the spool by the belt tension is transferred to the head member principally via the torsion bar part 24, limiting the belt tension to a relatively high level, until the torque tube is disconnected from the outer end of the spool in a changeover operation effected by a changeover mechanism 28, 40, 42, after which the belt tension is limited by twisting of the bar portion 26 and the torsion pipe 36 together, until the torsion pipe breaks, leaving rotation of the spool restrained only by twisting of the low level torsion bar part 26. The provision of the torsion pipe substantially eliminates any undesired dip in the belt restraining force during the changeover operation.