Effects of Steering Wheel Center Module Mass on Driver Airbag Deployment Behavior and Resulting Occupant Injury

This study investigated the effects of the steering wheel center module mass on driver airbag deployment and driver injury through finite element analyses under FMVSS 208 frontal-impact conditions. The module mass was varied up to 500 g and extended to 1500 g to identify where HIC15 approaches the regulatory limit. Increasing the mass progressively delayed the early deployment; the time for the cushion volume to reach 10 L was delayed by 1.57 ms at 500 g. After 40 ms, differences in cushion volume and shape largely disappeared, indicating that the mass mainly affected the early deployment timing rather than the final deployed state. HIC15 decreased by 16.9%, from 578.8 without the module to 481.0 at 500 g, and then increased, exceeding the FMVSS 208 limit of 700 at 1500 g (718.9). The head–cushion contact initiation time advanced from 50 to 47 ms (500 g) and was then delayed to 53 ms (1500 g). These results indicate that the effect of an integrated module on head injury should be evaluated together with the early deployment and head–cushion contact timing, rather than by added mass alone. The findings provide preliminary reference data for jointly assessing module integration and airbag packaging in function-integrated steering wheels.