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Optimal trailer design for tractor-trailer transportation depends on accurate and reliable estimates of typical lifetime loading duty cycles. On-the-road testing was done to measure the vertical acceleration response of three different trailers in forest logging conditions. The test conditions included various trailer axle and load configurations, weight transported, and road surfaces including both gravel and paved roads. It was concluded that the rigid trailer body bounce and pitch, the non-rigid body trailer bending, and the wheel hop are the primary components of the vertical response. These results establish approximately what types of operational amplitudes are to be expected for these operations and will provide the basis for the development of a more general trailer frame load prediction model.

Ride quality of articulated vehicles is investigated via computer simulation in view of secondary suspension parameters. A tractor-semitrailer vehicle is modelled incorporating primary as well as secondary suspension. The ride vibration levels at the cab floor and at the driver-seat interface are evaluated using power spectral density approach. The effect of various vehicle parameters, such as secondary suspensions, primary suspensions, axle loads and tires on the vehicle ride quality is presented, and the significance of secondary vehicle suspension is specifically emphasized. A software package is developed to evaluate and assess the ride performance of articulated vehicles with suspended seat and cab. A limited validation of the computer ride model is achieved via field measurements.

Low frequency terrain induced vibrations transmitted to the off-road vehicle operators are quite severe and exceed I.S.O specified “fatigue decreased proficiency” limits. In this paper, the ride improvement of an agricultural tractor is sought through effective designs of passive seat suspensions. The dynamic analysis of existing bounce suspension seats is carried out to establish its ride performance behaviour. Optimal bounce seat suspension parameters are selected with an objective to maintain the ride vibration levels within 4 hours exposure “fatigue decreased proficiency” limits. The roll and pitch ride vibrations, perceived by the operators, can be attenuated through a gimbal arrangement mounted to the bounce suspension seat. The optimal parameters of the combined seat isolator are selected using parametric optimization techniques. Also a horizontal isolator, attachable to the bounce or the combined seat isolator, is configured.

The unique difficulties associated with low frequency and large amplitude ride vibrations of off-road tractor are summarized. Concept of a cab suspension system for improving the ride quality of off-road tractors in the bounce, longitudinal, lateral, pitch and roll modes is explored. Influence of suspension parameters on the ride performance is presented followed by selection of optimal suspension parameters. It is shown that a cab suspension would provide improved performance in the longitudinal and pitch modes alone. Ride analysis of the cab suspension with a sprung seat reveals satisfactory bounce ride. Roll and lateral ride of the off-road tractor can be improved significantly through alterations in the cab geometry. The ride performance of the optimal suspensions is assessed with reference to ISO (International Standards Organization) specified “fatigue decreased proficiency” (FDP) boundaries.