Investigation into the rising air pressure inside the door during side impacts

A crucial point in side impacts is the rapid intrusion of the side structure of the door into the passenger compartment. In the initial stage of the crash it is essential to provide sufficient space between occupant and door trim to enable a proper unfolding of the side airbag. This problem can be alleviated by using the rising air pressure inside the door as an additional input for crash sensing. When combined with the common acceleration sensing on the centre tunnel or B-Pillar it is feasible to increase the sensitivity of the impact detection so that an earlier airbag triggering in side impacts can be achieved. However, because of the introduction of more demanding side impact test configurations this phenomenon still needs to be investigated. In the early development process side impact simulations are usually employed to estimate the available space for airbag unfolding. But these simulations have shown some discrepancies if kinematics of the door trim intrusion during the airbag unfolding phase is compared to the experiments. This can be attributed to a lack of consideration of the air inside the door. A method to simulate this phenomenon which incorporates fluid-structure interaction is given in LS-DYNA. Recent developments in this software allow the use of an Arbitrary Lagrangian-Eulerian (ALE) solver and therefore make it possible to simulate the airflow inside and out of the door during a side impact. Using this approach, the dynamic pressure distribution inside the door and the loss of pressure due to outflowing air was simulated. Within the scope of this study the predictability of the pressure signal recorded for crash sensing and the additional air-induced intrusion of the door trim which reduces space for airbag unfolding is investigated in comparison to the different side and pole impact experiments.