Low frequency terrain-induced vibrations transmitted to off-road vehicle operators are quite severe and exceed ISO specified “fatigue-decreased-proficiency” (FDP) limits. Ride improvement of an agricultural tractor is investigated via passive suspensions at the seat and/or cab for their relatively simpler adaptability to an existing tractor construction. The investigation has been carried out in three phases, namely: seat suspension incorporating bounce, longitudinal, lateral, roll, and pitch modes on a rigidly mounted cab; cab suspension with a rigidly mounted seat; seat suspension in bounce, bounce-lateral, and bounce-roll, mounted on a suspended cab. Optimum suspension parameters in each phase of study are selected to maintain all translational acceleration PSDs at the operator’s location within 4 hours’ exposure-FDP limits, and to minimize roll and pitch acceleration PSD response. The relative displacement in each case is constrained to a selected minimum. Ride improvement achieved during each phase of investigation is compared to ISO-FDP acceleration PSD limits, and conclusions are drawn. Contribution of factors such as seat-location and cab-geometry to ride improvement is also presented.

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