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An Active Independent Front Steering (AIFS) offers attractive potential for realizing improved directional control performance compared to the conventional Active Front Steering (AFS) system, particularly under more severe steering maneuvers. The AIFS control strategy adjusts the wheel steer angles in an independent manner so as to utilize the maximum available adhesion at each wheel/road contact and thereby compensate for cornering loss caused by the lateral load transfer. In this study, the performance potentials of AIFS are explored for vehicles experiencing greater lateral load transfers during steering maneuvers such as partly-filled tank trucks. A nonlinear yaw plane model of a two-axle truck with limited roll degree-of-freedom is developed to study the performance potentials of AIFS under different cargo fill conditions.

It has been widely reported that the overall vibration comfort performance of static and dynamics seats is strongly influenced by the biodynamic behaviour of the seated human body. The contributions of the seated occupant to the overall vibration attenuation of the coupled seat-occupant system are experimentally investigated as functions of the nature of excitation, static and dynamic properties of the seat, and the sitting posture. The study involved two different seats with natural frequencies in the vicinity of 1.5 Hz and 4 Hz, which would characterize the low natural frequency suspension as well as high natural frequency seats employed in automobiles and some industrial vehicles. The vibration isolation properties of the seats are evaluated with a rigid mass and two human subjects under different vibration excitations, including swept sine, broad-band random and standardized vibration spectra of selected vehicles.

The longitudinal load transfer encountered in a partly-filled ellipsoidal tank truck, subject to a straight-line braking maneuver, is investigated as a function of the location of partition walls, deceleration and the fill level. The response characteristics of the truck equipped with a compartmented tank are evaluated in terms of dynamic load transfer, stopping distance, braking time and time lag between the front and rear axle wheel lock-up. The braking response characteristics are derived as a function of the load shift, and number and location of partition walls. Road tests were performed on an airport fuel truck, equipped with a 3 m long tank with two movable partition walls. The simulation results derived from the test vehicle model are compared to the road test data to demonstrate the validity of the analytical model. The results show good correlation with the measured data acquired under straight-line braking maneuvers performed under different fill levels and initial speeds.

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.

A six degrees-of-freedom ride dynamic model of a cab-over-engine supported on elastomer mounts is developed using lumped parameters. The lumped parameter model is analyzed for its free vibration response, while assuming the cab structure to be rigid. A finite element model of the suspended cab is developed and analyzed to establish the influence of flexibility of the cab structure on the ride dynamics of the tilt cab. The vibration modes of analytical lumped parameter and finite element models are compared to the dominant ride frequencies of the vehicle measured in the field. The lumped parameter model is then modified to achieve a comprehensive ride dynamic model for its further use in ride performance analyses.