Comprehensive injury assessment of reclined occupants across varied seat configurations with the THUMS human body model

The development of autonomous driving technology will liberate the space in the car and bring more possibilities of comfortable and diverse sitting postures to passengers, but the collision safety problem cannot be ignored. The aim of this study is to investigate the changes of injury pattern and loading mechanism of occupants under various reclined postures. A highly rotatable rigid seat and an integrated three-point seat belt were used, with a 23g, 50kph input pulse. Firstly, the sled test and simulation using THOR-AV in a reclined posture were conducted, and the sled model was verified effective. Based on the sled model, the latest human body model, THUMS v7, was used for collision simulation. By changing the angle of seatback and seat pan, 5 seat configurations were designed. Through the calculation of the volunteers' pose regression function, the initial position of THUMS body parts in different seat configurations was determined. The responses of human body parts were output, including kinematics, biomechanics and kinetics. The results show that the bending state of spine in motion changes with the reclined posture changing, and more attention should be paid to the injuries of the neck, chest, lumbar vertebra and pelvis. As the tilt increased, there was an increased likelihood of submarining and abnormal belt-neck contact, the z-deflection of the ribcage became larger, and the loading mechanism of the lumbar spine changed. Raising the seat pan could prevent high pelvis excursion and reduce the possibility of submarining. The findings will help to guide the design of inclined occupant protection and provide theoretical guidance for future crash safety evaluation.