Man--tractor system dynamics: towards a better suspension system for human ride comfort.

Abstract It is found that tractor drivers suffer from a number of disorders of the spine and supporting structures at low frequency and high amplitude vibrations that are encountered in their field activities. In this paper the occupant - tractor system is modelled as a lumped parameter system; the composite model is analysed, by computer simulation, (for vertical and rotational (pitch) vibrational response to ground reaction simulating steady state sinusoidal forcing function inputs), for (a) relaxation type seat suspension and (b) relaxation type suspensions for both the seat and the front axle. These responses are compared to responses for (c) rigid seat and front axle, and (d) standard type front axle suspensions, as determined by previous investigators. It is found that the intensity of these (harmful) vibrations, is reduced by selecting these suspension parameters such that the responses of the human body parts are minimized in the frequency range of 0.5–11 Hz. Both the types of suspensions are the compared for their vibration isolation characteristics.