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Distinguishing physical modes from mathematical modes in the modal analysis of complex systems, such as full vehicle structures, is a difficult and time-consuming process. The major tools frequently used are stabilization diagrams, mode indicator functions, or modal participation factors. When closely spaced modes are to be identified, the stabilization diagrams and mode indicator functions are no longer effective. Even the reciprocities of mode shapes and modal participation factors cannot be well satisfied to indicate whether a mode is a physical one, when measurement errors are large. To overcome these difficulties, an optimization procedure is developed, whereby physical modes can be sorted out in a given frequency range while the error between measured and synthesized frequency responses is minimized. An optimal subset selection algorithm is used in this procedure.

An investigation of the effect of rack-housing rubber bushings on the handling characteristics of a vehicle is presented using a sophisticated three-dimensional vehicle model based on multibody dynamic analysis method. Previous research on this problem has been limited to a transfer function model for a simplified one- or two-dimensional steering subsystem. This paper uses a multibody modeling approach to find the effects of the steering-system compliance on the complete vehicle system. Sample simulations for circular cornering and pulse steering show that the steering-system compliance is the source of the frequency peak in the yaw rate to hand-wheel angle response function.

A tire longitudinal and lateral flexibility model has been developed which shows considerable advantages over the other available models or methods. Most of the available methods indirectly considers tire lateral flexibility effect by the inclusion of a time-lag function, whereas the developed model is a multibody representation of a wheel/tire subsystem so that the resultant dynamics are similar to those of an actual physical system. Sample simulations with a realistic three-dimensional vehicle model show the effectiveness of the developed model.

This paper presents a look-ahead driver model with potential application to autonomous cruising of vehicles on highways. The driver model has two physically meaningful parameters: the look-ahead distance and the steering sensitivity. The two parameters are scheduled with respect to the vehicle speed using a preprocessor that converts open-loop steering response data to pseudo-closed-loop steering response data. Sample simulations with a realistic three-dimensional multibody vehicle model are presented for a lane-change scenario. The results indicate that the proposed driver model performs well for a wide range of vehicle speeds.

This paper presents an analytical approach for a three dimensional tire model used for the steady-state simulations of vehicles. The functional relationship of slip ratios of the SAE definition and new definition suitable for vehicle dynamics analysis is first studied. New formula for friction is used and a contact pressure change is considered during driving/braking. The compliances of carcass, braker, and tread are employed for longitudinal and lateral elastic deformation. Rolling resistance force, plysteer, and conicity are also included in the explicit formulations of longitudinal force, lateral force, and aligning torque due to comprehensive slips.

This paper presents a systematic methodology and formulation for determining optimal strategies for four-wheel steering of vehicles. The methodology is based on multibody dynamics, design sensitivity, and optimization techniques, and is applicable to a wide variety of mechanical systems. The particular application discussed in this paper considers a vehicle model with four-wheel steering capability, and the presented methodology determines an optimal steering angle ratio strategy for the vehicle. It is shown that such a strategy can improve the ride stability of the vehicle, during a variety of maneuvers, when compared against similar strategies obtained from linearized and simplified vehicle models.

This paper presents a comprehensive approach for the mathematical and computer modeling of subsystems required in vehicle dynamic simulations. Three dimensional models for tire-terrain interaction, traction, braking, steering, and suspension systems are presented. The tire-terrain interaction model provides the necessary tire forces and moments which are determined by explicit formulation or experimental data based model. For the suspension subsystem, such elements as bushing, leaf spring, and stabilizer bar are reviewed. For the steering, traction, and braking subsystems, simplified models are discussed. The models developed here can easily be implemented in a three dimensional multibody simulation program.