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In a tractor-trailer, ride comfort affected by horizontal human body motions, so called “wavy” and “shaky” feelings, is at issue. Insight about “wavy” and “shaky” feelings which is important for efficient vehicle development is not enough. Experiments using 6-axis motion generator and motion capture and inverse-analysis using multi-body human model indicated the characteristics of each feeling. Motion observation and transfer function indicated that while a bad subjective score of “wavy” feeling corresponds to same-phase roll motion of chest and pelvis up to 0.7Hz, “shaky” correlates to an antiphase of them around 2Hz. By multiple regression, dominant vibration components of the human body and the vehicle to subjective evaluation of the feelings above were identified. Explanatory variables for the “wavy” feeling are roll rate and lateral jerk and those for the “shaky” are lateral acceleration and longitudinal acceleration.

In recent years, requests for automotive comfort are increasing, and the development of seats that cause little fatigue, even for long distance driving, has been required. Until now, seat riding comfort has been studied mainly using dynamic vibration analysis; and there are few studies that give importance to the sensory characteristics of the driver and passengers. In order to apply to the design of comfortable seating, we developed a new seat evaluation method that emphasizes the interaction between the human body and seat. For static seating comfort, we determined seat compliance as a new evaluation index by using a human body pressure distribution that is calculated by dividing the seat into 16 segments, and is related to seat flexion. For dynamic riding comfort, speed of the human body pressure distribution, and the acceleration of each human body part were made into an index.