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Abstract
Prolonged exposure to whole-body vehicular vibration and shock is known to contribute significantly to the degradation of health and comfort of seated drivers. Off-road vehicle drivers are considered particularly at risk in view of the severe nature of the vibration environment caused by the vehicle-terrain interactions. The effectiveness of secondary vehicle suspensions in reducing the vibration exposure levels is investigated through development and analyses of suspension seat and suspended cab models. The analytical models are validated through extensive laboratory tests of an off-road vehicle suspension seat and of a prototype suspended cab. A comprehensive whole-body vehicular vibration simulator (WBVVS) is developed to study the suspension seat and human driver response characteristics under deterministic and random vibration, and shocks. A methodology is developed for computing the shock response characteristics of a suspension seat, with and without travel limiting bump stop impacts.
A four-degree-of-freedom linear biodynamic model of the seated driver is developed to account for the influence of human body dynamics on the suspension seat vibration attenuation performance. The model parameters for a seated driver maintaining a well defined posture are identified from measurements of the driving-point mechanical impedance and idealized values of seat-to-head transmissibility magnitude and phase characteristics, using optimization techniques. The biodynamic response characteristics are shown to be highly affected by the seated posture and the nature of the vibration excitation. The combined suspension seat-human driver model developed in this study correlates better with the measured response characteristics than the suspension seat model defined with a rigid driver mass representation.
Seat and cab suspension design guidelines are defined to minimize the vibration exposure levels of off-road vehicle drivers under different types of excitations. This is performed upon integrating the various proposed whole-body vibration and shock exposure assessment methods and health criteria into the response computations using the validated models. The vibration exposure levels differ considerably under random and shock excitations, particularly when bump stop interactions occur. Effective design and tuning of the secondary suspension systems can provide a significant reduction in vibration exposure levels. The design guidelines of such systems, however, must provide a distinction between the conditions involving high level shocks and those with low level shocks or continuous excitations.
