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An important issue in automotive seat comfort is reducing driver fatigue during long-term driving. In this paper, a finite element model of the seat and the human body was developed, and stress analyses around the lumbar vertebrae of the human body were carried out. A long-term driving test on a compact car seat was conducted by using a driving simulator, and increases in the stress hormone adrenaline in the urine of the subjects were measured. Correlations between physical seat data and increases in adrenaline were analyzed, and the seat parts causing body fatigue were identified. The results of the long-term driving test were compared with the results of the finite element analysis, and an attempt was made to clarify the mechanism responsible for the fatigue.

transient vibrations caused by a sudden change in the road surface under steady-state random vibration subject the human body to unpleasant sensations. However, it is very difficult to examine each part of the seat structure and physical properties because the measurement position of acceleration sensors with the conventional evaluation method are limited to the hipbone on the seat cushion and lumbar on the seat back. In this paper, in order to evaluate three kinds of driver seats having different structures and physical properties, we dynamically measured body pressure distribution, which are mainly made with static measurements, on a pavement inducing transient vibrations. We analyzed each part of measurement data by means of a new human engineering index, which is body pressure change rate over time. We next investigated the correlation between the analyzed data and the subjective evaluation, and found the mechanism causing unpleasant sensations during transient vibrations.