Vibration in vehicles: its effect on comfort

This thesis examines procedures for predicting the effect of vibration on the comfort of vehicle occupants. A three part literature review investigates: parameters of vibration which have been shown to influence comfort; studies in which objective measures of vehicle vibration have been compared with subjective assessments; deficiencies inherent in procedures for model I ing discomfort. Important deficiencies concerning the effect of seating on modifying the vibration input to vehicle occupants, the evaluation of vehicle rides containing low frequency and/or impulsive components are investigated systematically in a programme of experimental work culminating in the development of a revised procedure for evaluating vehicle ride. In the first of two studies of vehicle seating, the effect of subject weight on the transmission of vertical vibration through a suspension seat was found to be small. The second study demonstrated that seat construction was an important source of variability in the performance of six suspension seats designed for use in the same articulated truck. These results confirmed that measurements of vibration received by a single subject seated in vehicles could be used in a model of vehicle ride to predict the discomfort of a group of subjects. In a simulation of vehicle ride, the vertical vibration recorded on the seats of six trucks as each was driven over a test track was reproduced in the laboratory. Despite the limited nature of the simulation there was good agreement between assessments of the rides made in the laboratory and field situations. It was concluded that Iaboratory simulation of vehicle ride offered a convenient alternative to extensive field testing of vehicles. Fundamental studies of the reaction of seated subjects to vertical vibration in the frequency range 0.5 to 5.0 Hz were conducted. The shape of the equivalent comfort contour obtained was independent of vibration magnitude. Similar shaped contours were obtained using sinusoidal and random motion. An additional study to investigate the sensitivity of subjects to lateral seat motion in the same frequency range was also conducted. The results of these studies together with information obtained from two experiments which investigated the reaction of subjects to vertical impulsive motion, were incorporated into an enhanced model of vehicle ride. The mode I was validated in a I aboratory simulation of dual axis rides recorded in six articulated trucks. The evolved model was superior, in terms of predicting the discomfort due to vibration, than guidance given in the current International Standard (ISO 2631, 1978). Implications for the future development of models of vehicle ride are discussed. Areas to which future research might usefully be directed are suggested