Threshold Time-to-fire Determination for SRS to Control Occupant Injuries in Real World Accidents

Supplementary Restraints Systems (SRS) are provided in automobiles for occupant protection in severe accidents. Real world accidents are a varied mix of types and severities; thereby a need exists to engineer such systems for adequate performance robustness. Statistical data suggests high serious to fatal occupant injuries due to inadvertent SRS deployments, or sub-optimal Time-to-Fires (TTF) which lead to bag induced injuries.

This paper explains the work done on a project to establish requirements of SRS deployments in different load cases of low, medium and high severity. LSDyna and MADYMO CAE applications have been used for this work and final validation through physical tests. The study considers different real world accident types and involves analysis of occupant-restraints system interactions. It includes variations in occupant types and seat belt configurations. Injury values, occupant displacements and its proximity to airbags were the main criteria to arrive at deployment threshold parameters. Vehicle dependent accident speed determination which could necessitate SRS activation was estimated through this approach. The deployment matrix was thereby a combination of load case, time-to-fire and vehicle speed. The input parameters for electronics sensing calibration were derived and trade-off was validated. The restraints “no fire” and “must fire” threshold definition was established with clarity on transition zone. The study shall ascertain a robust “no fire” in slow speed accidents that drive insurance premiums for customers.