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In recent years, research on occupant behavior models has been promoted for vehicle motion control that includes occupant comfort as a control target. In previous research, modeling and verification focusing mainly on behavior, such as occupant head motion, has been conducted. But in order to accurately predict occupant comfort with a model, it is necessary to model and verify not only the behavior but also the joint torque required to maintain posture. When the occupants maintain their posture against the inertial force associated with the motion of the vehicle, they utilize the seat reaction force with the joint torque. So, in order to accurately model the joint torque, it is necessary to measure and model the joint torque and the seat reaction force separately. Therefore, in this research, we tried to make a occupants behavior model and parameter identification method that predicts joint torque and seat reaction force separately. We focused on the occupant’s head and torso motion among the whole body, and these are modeled in the form of an inverted double pendulum. And the seatback reaction force is set as an input in order to accurately predict the joint torque exerted by the occupants. Then, by utilizing existing occupant behavior analysis technology and we measured joint torque and seat reaction force in addition to the behavior of seated occupants and identified each parameter of the model. The model is experimentally verified, and as an example of the use of the proposed method, experiments and parameter identification are performed on occupants with different gaze points, and the changes in occupant’s joint torque control when view conditions are different were quantitatively clarified.

To achieve simple and accurate modeling of human-like behavior with the aim of realizing a model-based design (MBD) methodology incorporating vehicle occupants, this research applied a simplified two-mass system for the upper body of a vehicle occupant and control laws derived based on natural human characteristics. To express the behavior of a seated occupant in response to lateral inputs, the motion of the upper body with respect to the vehicle and the motion of the head with respect to the upper body are modeled using a two-mass system projected onto a plane that includes the horizontal and vertical vehicle axes. Torques to maintain the posture calculated by the control laws were applied to each joint. This research focused on somatic and vestibular sensations as natural human characteristics. Somatic sensations are a source of information concerning the relative spatial and positional relationships between the body and its supporting surfaces (in this research, a vehicle). Seated occupant behavior to hold the upper body upright in the vehicle was defined as somatic feedback, which calculates torque based on the upper body posture angle. On the other hand, vestibular sensations are a source of information concerning the acceleration applied to the head. The vestibular system contains two types of receptor organs: the semicircular canals and the otoliths. The semicircular canals are the receptor organs for rotational acceleration of the head and are sensitive to rapid head motions. The otoliths are the receptor organs for linear acceleration of the head and are sensitive to slow head motions. In this research, we focused on the otoliths and otolithic feedback was defined as the tilting motion of the head against lateral acceleration, which generates torque based on the head posture angle and the lateral acceleration of the head. Validation experiment was performed on a test bench using a vibration generator and vehicle tests confirmed that the proposed model is capable of generally reproducing occupant behavior in response to lateral acceleration inputs.