The multi-planar and multiple impact long duration accident sequence of a real world rollover results in multidirectional vehicle acceleration pulses and multi-planar occupant motions not typically seen in a planar crash sequence. Various researchers have documented that, while contemporary production emergency locking seat belt retractors (ELRs) have been found to be extremely effective in the planar crashes in which they are extensively evaluated, when subjected to multi-planar acceleration environments their response may be different than expected. Specifically, accelerations in the vertical plane have been shown to substantially affect the timeliness of the retractors inertial sensor moving out of its neutral position and locking the seat belt. An analysis of the vehicle occupant motions relative to the acceleration pulses sensed at the retractor location indicates a time phase shift that, under certain circumstances, can result in unexpected seat belt spool out and occupant excursions in these multi-planar, multiple impact crash sequences. This paper will review the various previous studies focusing on the retractors response to these multidirectional, including vertical, acceleration environments and review statistical studies based upon U.S. government collected data indicating a significant difference in belt usage rates in rollover accidents as compared to all other planar accident modes. A significant number of real world accident case studies will be reviewed wherein the performance of ELR equipped seat belt systems spooled out. Finally, the typical occupant injury and the associated mechanism due to belt spool out in real world accidents will be delineated. (Author/publisher)
Abstract