Contact-Triggered Active Bonnet System for Pedestrian Head Injury Mitigation: Multibody Modelling and Experimental Validation.

Pedestrian head injuries represent one of the most severe consequences of vehicle-pedestrian collisions, primarily resulting from the impact between the pedestrian head and the vehicle hood or windshield region. Active bonnet systems have been developed to mitigate injury severity by increasing the clearance between the hood and rigid engine components during impact; however, their effectiveness strongly depends on rapid impact detection and timely deployment. This study proposes an approach for analysing pedestrian impact dynamics and evaluating the design performance of a contact-triggered active bonnet system using MATLAB/Simulink and Simscape Multibody. The pedestrian-vehicle interaction is reproduced using spatial contact force models, while the bonnet deployment is initiated through a contact-based trigger mechanism coupled with a simplified actuator integrated into the hood hinge. The model was experimentally validated using controlled pedestrian impact tests at 17 km/h and 29 km/h, including frame-by-frame kinematic analysis and measured head acceleration signals. Additional simulations were performed at multiple vehicle velocities with and without bonnet deployment to evaluate the influence of impact configuration and pedestrian trajectory on head injury severity. The results indicate that the active bonnet system can reduce peak head acceleration and HIC15 values under several investigated impact conditions. The comparative simulations further show that the protective effect is influenced by pedestrian positioning and head trajectory relative to the vehicle front-end geometry, with higher effectiveness when the head impact remains within the deformable bonnet region.