A comparison of two methods of simulating seat suspension dynamic performance

Abstract

Many off-road machines are equipped with a suspension seat intended to minimize the vibration exposure of the operator to vertical vibration. The optimization of the isolation characteristics of a suspension seat involves consideration of the dynamic responses of the various components of the seat. Ideally, the seat components would be optimized using a numerical model of the seat. However, seat suspensions are complex with non-linear characteristics that are difficult to model; the development of seat suspensions is therefore currently more empirical than analytical. This paper presents and compares two alternative methods of modelling the non-linear dynamic behaviour of two suspension seats whose dynamic characteristics were measured in the laboratory. A ‘lumped parameter model’, which represented the dynamic responses of individual seat components, was compared with a global ‘Bouc–Wen model’ having a non-linear degree-of-freedom. Predictions of the vibration dose value for a load placed on the seats were compared with laboratory measurements. The normalized r.m.s. errors between the predictions and the measurements were also determined. The median absolute difference between the measured and predicted seat surface vibration dose values over all test conditions for both models was less than 6% of the measured value (with an inter-quartile range less than 20%). Both models were limited by deficiencies in the simulation of top end-stop impacts after the load lifted from the seat surface. The lumped parameter model appears best suited to the development of the overall design of a suspension seat. The Bouc–Wen model can provide a useful simulation of an existing seat and assist the optimization of an individual component in the seat, without measuring the dynamic properties of components in the seat except those of the component being optimized.