Performance analysis of restraint systems for reclined occupant in side pole impact collisions

Safety restraint systems have enhanced occupants' safety in case of collision. However, they are designed to protect occupants in standard sitting posture and different sitting postures are not evaluated in current legal and rating tests. The goal of this study was to address the reclined posture under oblique pole side impact conditions. Different airbag systems were proposed and analyzed for protecting reclined occupants, providing a general overview of the restraint systems performance across these conditions.

Simulations were performed with a subsystem Finite Elements (FE) vehicle model developed and validated against side impact tests. A reclined occupant position was analyzed using WorldSID 50th male dummy under Euro NCAP oblique pole side impact test conditions. Three different seat-mounted side restraint system solutions optimized according to standard EuroNCAP position were proposed to enhance reclined occupant safety. Additionally, three time-to-fire strategies were considered, a conventional time-to-fire and two pre-crash triggering that lead to an earlier deployment of the restraint systems.

In the reclined posture, the conventional time of activation led to higher occupant injury values for all the restraint systems proposed. As the firing time was brought forward, the measured injury values were reduced. The double side airbag head + thorax-pelvis system with a pre-crash triggering (time-to-fire -5 ms) was predicted as the safest case scoring the higher overall rating and five Euro NCAP stars.

This study investigated three side airbag systems capable of providing good protection under Euro NCAP oblique pole side impact conditions (upright posture), considering triggering times earlier than conventional in combination with optimized airbag design parameters, these systems were able to provide also adequate protection (4-5 stars) in reclined occupant positions. The results showed that the airbag inflation time is significant in reclined positions.