VIBRATION COMFORT OF THE VEHICLE EXPRESSED BY SEAT EFFECTIVE AMPLITUDE TRANSMISSIBILITY

Research of the human body vibrations, carried out under controlled laboratory conditions, shows that human body is the most sensitive to vibrations in the frequency range that matches the biomechanical resonance. In the vertical direction, the resonance of the body is approximately 5 Hz, while in the horizontal direction the resonance occurs at frequencies less than 2 Hz. The vibrations of the vehicle have been transferred to the driver and passengers over the seats, which have the ability to attenuate or to amplify vibrations which human body is exposed to while driving. One way to determine the vibration behaviour of the seat is to measure the SEAT (seat effective amplitude transmissibility) factor, which represents the ratio between the vibrations measured on the seat and vibration measured directly on the floor under the seat. Measurement of vibrations in these two positions must be performed simultaneously. If the value of SEAT is less than 1, a seat attenuates vibrations and meets vibrational comfort, the value of SEAT greater than 1 indicates that a seat amplifies vibration, reducing vibration comfort. This paper gives results of SEAT factor investigation done on a hybrid vehicle, for different types of road surface and different modes of driving (electric power and internal combustion engine).