Evaluation of Discomfort Due to Vertical Feet Vibration at a Driver's Sitting Posture

Floor vibration in a passenger car is getting more interest with the improvement of its NVH quality. International standard ISO 2631 provides frequency weightings for the evaluation of vibration on floor as well on seat at a sitting posture and has been widely used in automotive industry. However, since these frequency weightings were originally derived from an erect sitting posture and vibration magnitude of more than 0.5 m/s², it can not describe well human response to the feet vibration in a passenger car any longer because of the two reasons; First reason is that the erect posture gives quite different dynamic characteristics of a human body compared to the inclined sitting posture in a passenger car. Second reason is magnitude level of 0.5 to 5 m/s² where the frequency weightings of ISO 2631 were determined can not stand for the real situation of floor vibration of a passenger car of nowadays. Recent studies showed frequency weighting curves depend on the vibration magnitude, and therefore it is necessary to determine a new frequency weighting for the feet vibration in a passenger car.

This study aims to suggest an equal discomfort contour, reciprocal of frequency weighting, due to vertical feet vibration in the frequency range of 8 to 25 Hz and in the magnitude level of 0.125 to 0.8 m/s². Twenty subjects joined the test and judged the relative discomfort between a test vibration stimulus and a reference vibration stimulus. The results showed the slope of frequency weighting curve is much less than that in ISO 2631, which means the current weighting underestimates discomfort at higher frequencies.