A Human Body Model with Active Muscles for Simulation of Pre-Tensioned Restraints in Autonomous Braking Interventions

Objective: The aim of this work is to study driver and passenger kinematics in autonomous braking scenarios, with and without pre-tensioned seat belts, using a whole-body finite element (FE) human body model (HBM) with active muscles. Methods: Upper extremity musculature for elbow and shoulder flexion-extension feedback control was added to an HBM which was previously complemented with feedback controlled muscles for the trunk and neck. Controller gains were found using a radial basis function meta-model sampled by making 144 simulations of an 8 ms−2 volunteer sled test. The HBM kinematics, interaction forces, and muscle activations were validated using a second volunteer dataset for the passenger and driver positions, with and without 170 N seat belt pre-tension, in 11 ms−2 autonomous braking deceleration. The HBM was then used for a parameter study in which seat belt pre-tension force and timing were varied from 170 N to 570 N, and from 0.25 s before to 0.15 s after deceleration onset, in an 11 ms−2 autonomous braking scenario. Results: The model validation showed that the forward displacements and interaction forces of the HBM correlated with those of corresponding volunteer tests. Muscle activations and head rotation angles were overestimated in the HBM when compared with volunteer data. With a standard seat belt in11 ms−2 autonomous braking interventions, the HBM exhibited peak forward head displacements of 153 mm and 232 mm for the driver and passenger positions. When 570 N seat belt pre-tension was applied 0.15 s before deceleration onset, a reduction of peak head displacements to 60 mm and 75 mm was predicted. Conclusions: Driver and passenger responses to autonomous braking with standard and pre-tensioned restraints were successfully modelled in a whole-body FE HBM with feedback controlled active muscles. Variations of belt pre-tension force level and timing revealed that belt pre-tension 0.15 s before deceleration onset had the largest effect in reducing forward head and torso movement caused by the autonomous brake intervention. The displacement of the head relative to the torso for the HBM is quite constant for all variations in timing and belt force; it is the reduced torso displacements that lead to reduced forward head displacements