The Occupant Response to Autonomous Braking: A Modeling Approach That Accounts for Active Musculature

Abstract

Objective: The aim of this study is to model occupant kinematics in an autonomous braking event by using a finite element (FE) human body model (HBM) with active muscles as a step toward HBMs that can be used for injury prediction in integrated precrash and crash simulations.

Methods: Trunk and neck musculature was added to an existing FE HBM. Active muscle responses were achieved using a simplified implementation of 3 feedback controllers for head angle, neck angle, and angle of the lumbar spine. The HBM was compared with volunteer responses in sled tests with 10 ms⁻² deceleration over 0.2 s and in 1.4-s autonomous braking interventions with a peak deceleration of 6.7 ms⁻².

Results: The HBM captures the characteristics of the kinematics of volunteers in sled tests. Peak forward displacements have the same timing as for the volunteers, and lumbar muscle activation timing matches data from one of the volunteers. The responses of volunteers in autonomous braking interventions are mainly small head rotations and translational motions. This is captured by the HBM controller objective, which is to maintain the initial angular positions. The HBM response with active muscles is within ±1 standard deviation of the average volunteer response with respect to head displacements and angular rotation.

Conclusions: With the implementation of feedback control of active musculature in an FE HBM it is possible to model the occupant response to autonomous braking interventions. The lumbar controller is important for the simulations of lap belt–restrained occupants; it is less important for the kinematics of occupants with a modern 3-point seat belt. Increasing head and neck controller gains provides a better correlation for head rotation, whereas it reduces the vertical head displacement and introduces oscillations.

Keywords:

• Active muscle
• Feedback control
• Finite element
• Human body model
• Occupant kinematics
• Autonomous braking

ACKNOWLEDGMENTS

This work was carried out at SAFER: Vehicle and Traffic Safety Centre at Chalmers, Sweden. It was funded as part of the SAFER project B8: Development of Active HBM in Frontal Impact Situations. The simulations were performed on resources provided by the Swedish National Infrastructure for Computing (SNIC) at C3SE. The authors thank Merete Östman and Niklas Höglund, PhD, at Volvo Car Corporation for support with the seat model and Volvo Car Corporation for supplying it. We are also grateful to Susumu Ejima, PhD, of the Japan Automotive Research Institute, for supplying plot data for Figures 4, 5, and 6.