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Relative rollover conditions of a heavy vehicle are analyzed to establish an array of potential dynamic rollover indicators towards development of an early warning device. A relative roll instability indicator defined as Roll Safety Factor (RSF) is proposed and shown to be a highly reliable indicator regardless of vehicle configurations and operating conditions. The correlation of various potential rollover indicators with the roll safety factor are then investigated for a 5-axle tractor semi-trailer combination using a comprehensive directional dynamic analysis model to determine the reliability of the proposed indicators over a range of operating conditions. The indicators are further examined in terms of measurability, lead time, and potential for application in an early warning system. The study shows that the trailer lateral acceleration and axle roll angles are closely correlated with the RSF.

In this paper, the driver ride comfort in a heavy vehicle (city bus) is studied under the sky-hook semi-active damping force policy. A new hybrid dynamic model composed of a continuous system and a discrete system are integrated in the current work. The chassis of the vehicle is assumed as the continuous beam supported on the discrete suspension springs and dampers. The driver and the seat are also considered as a discrete vibrating system. The dynamic equations are solved by using the assumed mode method, where the mode shapes of a free-free beam have been employed. The results of the semi-active system are compared with those of the passive one through simulations. The results indicate that the new hybrid dynamic model represents more degrees-of-freedom of the system for driver ride analysis compared to the discrete model. In addition, the results show that the semi-active system has a superior performance in terms of the ride comfort.