Investigation of the Relationship between Passenger Comfort and Body Behavior during Autonomous Braking

In autonomous vehicles, if the driving operation patterns of a self-driving vehicle differ from the driving operation patterns that drivers are accustomed to performing, there is a possibility that the passengers may feel anxiety and discomfort. Such a deviation has conventionally been discussed from the viewpoint of safety during braking, and it is known that the timing of the start of braking is important. However, in addition to safety, ride comfort is also considered to be important. Koto et al. pointed out that not only the timing of the start of braking but also the deceleration profile, such as the maximum g-force timing, influences the sensory evaluation of braking, and there are large differences between individuals. This suggests that the most comfortable braking differs between individual passengers. Regarding this, as well as subjective evaluation and evaluation of the physical quantities of a vehicle, it is also effective to evaluate the riding comfort of an automobile based on human body behavior. Therefore, in this study, the relationship between human body behavior and riding comfort was studied in order to clarify the factors that affect individual differences in riding comfort during braking, and the effects of changes in situations were also investigated. The obtained results suggested the following: (1) Shoulder angle contributes to the ride comfort evaluation of braking, (2) Individual differences in ride comfort evaluation may be affected by differences in the timing of the body posture with respect to braking g-force, (3) Changes in the situation may change the timing of the body posture for braking.