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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.

The object of this study is to investigate the possibility of improving ride comfort, and develop a new damping control system. We supposed and analyzed the ideal damping control for vehicle suspension system using optimal control strategy. The parameter study shows the effect of reducing vehicle acceleration from road excitation. To achieve the same performance with a more simple and lower cost control strategy, we introduce another control strategy called ‘Skyhook model’ proposed by D.Karnopp. Continuously damping control system is developed based on this to avoid some problems that might be caused in the case of a two-stage switching system. Further more, variable control gain depends on vehicle vibration circumstances introduced to realize the adaptation of various road conditions. Using computer simulation and testing the experimental vehicle, effectiveness of this system is evident and the possibility of ride comfort improvement is verified by using this control.

The adaptation of the active control technology to practical suspension systems of vehicles has remarkably improved the safety and ride-comfort of vehicles. This paper presents a study on the practical realization methods of an active suspension system that combines high response and low energy dissipation. The effects of active control on the stability of vehicle motion and ride-comfort were investigated by practical tests using an experimental vehicle. The integrated active suspension system consists of a motor-controlled oil pump, which is active power source, and a motor-controlled variable orifice, which is semi-active adjustable element. Multi-controller computer systems for individual controls of each suspension unit and an integrated control of the whole body behavior are also installed.