Transmission of fore–aft vibration to a car seat using field tests and laboratory simulation

Abstract

The transmission of fore–aft vibration to the seat cushion and backrest of a small car has been investigated by means of a field test and laboratory simulation methods. In the field test, transmissibilities to the seat backrest and the seat pan were computed using both single-input single-output and two-input one-output system models. The results showed that in the car the fore–aft vibration at the seat pan and the backrest depended not only on the fore–aft vibration of the floor but also on the vertical vibration of the floor. In the laboratory simulation, the transmissibilities were measured with 12 subjects and five different vibration stimuli. It was found that the fore–aft transmissibilities to both the backrest and the seat pan exhibited three resonance frequencies in the ranges 4–5, 25–30 and 45–50 Hz. The laboratory test also revealed that for the backrest and the seat pan, the resonance frequencies and the peak transmissibility at resonance changed with vibration magnitude, indicating non-linearity involving both seat–person systems. The field test and the laboratory test methods have different advantages. The correct vibration input spectra and the correct subject posture can be used in a field test, whereas a higher coherency can be obtained using the laboratory test. It was found that the low coherency in the field test when using the single-input and single-output assumption could be improved by adopting a two-input and one-output system model.