Abstract

Prolonged exposure to vehicular vibration and shocks has been related to discomfort, reduced work efficiency and various health and safety risks for the drivers, specifically for the off-road vehicle drivers. Enhancement of shock and vibration environment of such vehicles involves characterization of vibration environment, biodynamic response of the driver, design and analysis of secondary suspension, and seating dynamics. Relationships between biodynamic measures are derived through analysis of measured data and selected biodynamic models. The magnitude of variations in subject characteristics and test conditions can be significantly reduced by representing 'to-the-body' biodynamic characteristics in terms of apparent mass (APMS) and by identifying a range of test conditions applicable to off-road vehicle driving. It is further shown that normalized APMS correlates well with the 'through the body' biodynamic function, expressed in terms of seat-to-head transmissibility (STHT). A synthesis of reported data is performed to propose a range of idealized biodynamic response characteristics. A three degree-of-freedom biodynamic model of the occupant is developed using measured response characteristics. Occupant-seat interactions are investigated through measurement and analysis of contact force and area. The results are utilized to propose a nonlinear and asymmetric seat cushion model. A nonlinear suspension seat model is further developed to incorporate asymmetric force-velocity and nonlinear force-deflection characteristics of the damper and elastic end-stops, respectively. A combined human-suspension seat model is finally derived upon integrating the proposed occupant, cushion and suspension models. The results show that the model is an effective tool for assessment of seating dynamic comfort and whole-body vibration exposure. The results of a comprehensive parametric study clearly 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. The suspension performance under continuous and shock excitations is assessed in terms of Seat Effective Amplitude Transmissibility (SEAT) and Vibration Dose Value (VDV) ratio, respectively. Two different optimization problems are formulated to minimize the SEAT and VDV ratios. The results suggest that soft and lightly damped suspension with low degree of damping asymmetry coupled with low friction and large mass can enhance vibration isolation performance. Thick and soft elastic buffers with linear stiffness characteristics result in low VDV ratio response. The proposed design with optimal suspension and buffer parameters yields considerable reduction in both SEAT and VDV ratio response under selected classes of excitations