Equivalent comfort contours for vertical seat vibration: effect of vibration magnitude and backrest inclination

Abstract

This study determined how backrest inclination and the frequency and magnitude of vertical seat vibration influence vibration discomfort. Subjects experienced vertical seat vibration at frequencies in the range 2.5–25 Hz at vibration magnitudes in the range 0.016–2.0 ms⁻² r.m.s. Equivalent comfort contours were determined with five backrest conditions: no backrest, and with a stationary backrest inclined at 0° (upright), 30°, 60° and 90°. Within all conditions, the frequency of greatest sensitivity to acceleration decreased with increasing vibration magnitude. Compared to an upright backrest, around the main resonance of the body, the vibration magnitudes required to cause similar discomfort were 100% greater with 60° and 90° backrest inclinations and 50% greater with a 30° backrest inclination. It is concluded that no single frequency weighting provides an accurate prediction of the discomfort caused by vertical seat vibration at all magnitudes and with all backrest conditions.

Practitioner Summary: Vertical seat vibration is a main cause of vibration discomfort for drivers and passengers of road vehicles. A frequency weighting has been standardised for the evaluation of vertical seat vibration when sitting upright but it was not known whether this weighting is suitable for the reclined sitting postures often adopted during travel.

Keywords:

• backrest angle
• ride comfort
• frequency weighting

Acknowledgements

This study was conducted with the support from the Ministry of Higher Education of Malaysia and Universiti Teknikal Malaysia, Melaka. The authors are grateful to Dr Miyuki Morioka for technical advice and assistance in providing software used to control the experiment.