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The ride dynamics of typical North-American soil compactors were investigated via analytical and experimental methods. A 12-degrees-of-freedom in-plane ride dynamic model of a single-drum compactor was formulated through integrations of the models of various components such as driver seat, cabin, roller drum and drum isolators, chassis and the tires. The analytical model was formulated for the transit mode of operation at a constant forward speed on undeformable surfaces with the roller vibrator off. Field measurements were conducted to characterize the ride vibration environments during the transit mode of operation. The measured data revealed significant magnitudes of whole-body vibration of the operator-station along the vertical, lateral, pitch and roll-axes. The model results revealed reasonably good agreements with ranges of the measured vibration data.

A two-stage preview strategy is proposed to characterize steering control properties of commercial vehicle drivers. The strategy includes a near and a far preview points to describe the driver control of lateral path deviation and vehicle orientation. A human driver model comprising path error compensation and dynamic motions of the limb is subsequently formulated and integrated to a yaw-plane model of an articulated vehicle. The coupled driver-vehicle model is analyzed under an evasive steering maneuver to identify limiting values of the driver control parameters through minimization of a generalized performance index comprising driver's steering effort, path deviations and selected vehicle states. The performance index is further analyzed to identify relative contributions of different sensory feedbacks, which may provide important guidance for designs of driver-assist systems (DAS).

The human body is most sensitive to low frequency whole body vibrations. Ride vibrations of off-road vehicles, caused primarily by irregular terrains, predominate in the 0.5 - 5 Hz frequency range. A suspension seat offers the simplest means to improve vehicle ride by reducing ride vibrations transmitted to the driver. A computer model of an off-road vehicle suspension seat was developed which can aid the designer in the selection of optimal suspension parameters. A parametric study was performed to determine the frequency response characteristics of the validated suspension model via computer simulation to investigate the influence of suspension parameters on the vibration transmission performance of suspension seats.

A closed-loop articulated vehicle-driver model, incorporating the path errors, lateral accelerations of the two units and the rate of steering, is proposed to study the directional control behavior of the driver. The closed-loop driver-vehicle model is formulated upon integrating the yaw-plane model of a five-axle articulated vehicle and a comprehensive driver model. The driver model, incorporating the delays associated with the limb movement and muscle activities, is developed with an objective to minimize the lateral acceleration of vehicle, and the lateral position and orientation errors between the previewed and the actual path of the tractor. Various parameters required to describe the driver's contributions are identified through minimizing a weighted performance index subject to an array of limit constraints established from the reported data.

Development of a micro-processor based early warning safety device that can detect and warn the drivers of impending dynamic instabilities is discussed to improve the operational safety of articulated freight vehicles. Directional dynamics of articulated freight vehicles are investigated to determine the key dynamic response parameters that can best describe the onset of rollover and jackknife instabilities. The feasibility of identified key response parameters is further investigated in view of various vehicle design and operating conditions, and ease of on-line acquisition and analyses. The study concludes that a general stability criteria can be established to identify impending roll and jackknife instabilities, and a safety monitor can be conceived to provide an early warning to the driver.

This paper proposes a new evaluation method of analyzing stability and design of a controller for an electric power steering (EPS) system. The main purpose of the EPS system’s control design is to ensure a comfortable driving experience of drivers, which mainly depends on the assist torque map. However, the high level of assist gain and its nonlinearity may cause oscillation, divergence and instability to the steering systems. Therefore, an EPS system needs to have an extra stability controller to eliminate the side effect of assist gain on system stability and attenuate the unpleasant vibration. In this paper, an accurate theoretical model is built and the method for evaluating system quality are suggested. The bench tests and vehicle experiments are carried out to verify the theoretical analysis.

Human-seat interactions are investigated through measurement and analysis of distribution of interface contact force and area under vertical vibration. The time histories of dynamic ischium pressure, effective contact area and contact force on a soft seat revealed significant asymmetry, under large magnitude vibration excitations occurring near the resonant frequency of the human-seat system. The asymmetric response characteristics of the cushion are mostly attributed to the nonlinear force-deflection properties of polyurethane foam materials, contour shape of human buttocks, body-hop motion and cushion bottoming tendencies. The results are utilized to propose a nonlinear and asymmetric seat cushion model incorporating body hop motion and cushion bottoming under vertical vibration. A combined human-seat model is derived upon integrating the proposed cushion model with a bio-dynamic model of the seated occupant.

A coupled human-seat-suspension model is developed upon integrating asymmetric and nonlinear models of the cushion, suspension and elastic end-stops with a three degrees-of-freedom biodynamic model of the occupant. The validity of the model is examined under harmonic and stochastic vibration excitations of different classes of vehicles, using the laboratory measured data. The suspension performance under continuous and shock excitations, assessed in terms of Seat Effective Amplitude Transmissibility (SEAT) and Vibration Dose Value (VDV) ratio, revealed that attenuation of continuous and shock-type excitations pose conflicting design requirements. It is thus proposed to develop suspension design for optimal attenuation of continuous vibration, while the severity of end-stop impacts caused by shock-type excitations be minimized through design of optimal buffers. Two different optimization problems are formulated to minimize the SEAT and VDV ratios.