Improved car occupant safety by expandable A-pillars

Abstract

There are contradictory requirements on the A-pillar of a modern passenger vehicle. The A-pillar needs to be strong to help withstand the forces, as in a rollover situation, and maintain the occupant cell integrity in rollover and high-speed offset frontal crashes. The A-pillar needs to be slim to ensure good visibility for the driver and should be light to contribute to lower fuel consumption. An ideal A-pillar, which is folded during normal operation but is expanded by high-pressure gas in a crash, resulting in a signficant increase in cross-section and strength, should combine these contradictory requirements. Such an A-pillar was developed in this project. The A-pillar was initially folded and sealed. The goal was to develop an A-pillar that was lighter, had a smaller obscuration angle and had the same level of safety for the occupant as a state-of-the-art A-pillar. Expansion and pressurisation of the folded sealed A-pillar was accomplished by generating a high internal pressure using pyrotechnics, which is a cost- and weight-efficient way to generate high pressures. The development was carried out by combining full-vehicle crash simulations with mechanical tests. The load cases used in the development of the expandable A-pillar were an offset deformable barrier crash at 64 km/h and a roof crush test according to FMVSS 216. The expandable A-pillar concept was subsequently built and mechanically tested. The A-pillar model was validated by means of mechanical testing. Generally, there was a clear correlation between the predicted A-pillar shape and the shape of the expanded mechanical A-pillar. The developed expandable A-pillar combined the goals of high strength, smaller cross-section and lower mass. The developed A-pillar reduced the obscuration angle by 25% and the mass by 8% (excluding brackets and gas generator) relative to a state-of-the-art A-pillar, while maintaining the level of safety for the occupant.