The objective of this paper is to present an update on the research conducted by the National Highway Traffic Safety Administration (NHTSA) to assess the performance of roof glazing in production vehicles and certain countermeasure designs in preventing occupant ejections.
Federal Motor Vehicle Safety Standard (FMVSS) No. 226 “Ejection mitigation” set requirements for ejection mitigation systems to reduce the likelihood of complete and partial ejections of vehicle occupants through side windows during rollovers or side impact events.
In the preamble of the final rule establishing the standard (Jan 2011), the agency stated “NHTSA is interested in learning more about roof ejections and would like to explore this area further...” It also stated that while sun/moon roof ejection could be potentially cost effective to mitigate, the agency was not in a position to extend coverage to roof glazing in the final rule because the agency wanted to research a viable performance test procedure.
The assessment of ejection protection offered by sunroofs was made using a guided impactor (18 kg) directed toward roof glazing (pre-broken) from inside the vehicle, based on the procedures developed in the FMVSS No. 226 regulation 2 , with test speeds of 14, 16, and 20 kilometers per hour.
Tests were conducted on production and countermeasure sunroof designs for the 2016 Ford F-150, production sunroofs for 2012 Toyota Prius, and production sunroofs provided by the Aisin Technical Center of America. For sunroofs with both a fixed and a moving panel (F-150, Aisin), the movable panels presented more challenges to contain the headform than fixed panels. For the moving panels, the sunroof attachment structure separated at the inserts (into the rails). Fixed panels had higher excursions at unsupported transverse edges or edges without any metal encapsulation frames. The F-150 fixed rear panel had front and rear transverse unsupported edges, while the Aisin had longitudinal edges without metal frames. Laminated glazing panes with thicker polyvinyl butyral (PVB) inner layer in and polyethylene terephthalate (PET) film with tempered panes used as countermeasures for the F-150 sunroof reduced glazing stretch (and ram excursions). However, this transferred more forces to the edges and presented a greater challenge for movable panel containment at rail attachments.
The fixed polycarbonate panel used in the Prius had low ram excursions but high ram decelerations.
Meeting some excursion limit will require designs that have strong attachments to the vehicle roof or rails. Deformation of the glazing and encapsulation frame should be limited when impacted at the center of the panel. Any tear/rip of the plastic layer would add to the excursion of the ram.
The number of vehicle designs tested was limited by the availability of laminated glazing used in production or countermeasure designs.
This paper details performance of selected production and countermeasure sunroof designs in limiting headform excursions. Some of the fixed sunroof designs had excursions of less than 100 millimeters. The movable sunroof designs tested will require additional countermeasures to perform at this level.