RESUMEN
Not only is it important to know how large the overall change in vibration should be for occupants to perceive an improvement in comfort, but also how large this change should be in specific frequency bands. Relative difference thresholds (RDT) of primary (0.5-4 Hz) and secondary (9-80 Hz) ride are estimated for 14 automotive engineers seated in a vehicle on a 4-poster test rig over two roads. Resulting stimuli differed in magnitude and spectral shape. The median RDTs estimated for primary and secondary ride were 16.68% and 13.82% on the smooth road, and 9.50% and 24.67% over the rough road. Statistically significant differences were found in the medians of the RDTs between (1) primary and secondary ride on the two roads and (2) the two roads for changes in the primary and secondary ride, suggesting that Weber's law does not hold.
Relative difference thresholds of primary and secondary ride are estimated that can be used to evaluate whether modifications to vehicle characteristics result in perceivable changes of vehicle vibration. Results suggest that Weber's law does not hold implying that relative difference thresholds should be used that closely match the stimuli characteristics.
RESUMEN
The study aim was to determine whether a relationship exists between the cardiovascular response, measured by HR and HRV and the magnitude of whole-body vibration. Cardiovascular response of sixty male participants in four groups, was measured during three states i.e. (1) no vibration, (2) a reference vibration and (3) an alternative vibration. The reference vibration was the same for all groups with the alternative vibrations different for each group. Weighted vertical seat vibration was 0.66 m.s-2, root-mean-square for the reference and 0.70, 0.73, 0.76, and 0.79 m.s-2, root-mean-square for the alternative vibrations. Vibrations only differed in magnitude with the difference between alternative vibrations based on relative difference thresholds. Nonparametric tests compared cardiovascular indicators between groups at State 3 adjusted for state of departure i.e. State 2. No significant differences between groups were found for most of the indicators, suggesting no relationship between cardiovascular response and the magnitude of whole-body vibration. Practitioner summary: The cardiovascular response to the magnitude of whole-body vibration on an automobile seat was investigated. Results suggest that no relationship exists between the magnitude and cardiovascular response and that the latter may not be as effective as other objective measures (e.g. acceleration) in evaluating the human's response to whole-body vibration.
Asunto(s)
Automóviles , Vibración , Aceleración , Humanos , Masculino , Vibración/efectos adversosRESUMEN
Improving vibration-induced discomfort often requires a reduction in the vibration experienced by vehicle occupants. Simulation software and test equipment are able to measure changes in vibration that are too small for humans to perceive. It is therefore important to know how large the change in vibration should be, i.e. the difference threshold, for occupants to perceive an improvement in comfort. This study estimates difference thresholds for ten automotive engineers seated in a vehicle on a 4-poster test rig. Participants were exposed to multi-axis vibration. Component ride values were calculated by applying BS 6841 frequency weightings and multiplication factors to seat accelerations in the six directions. Difference thresholds were estimated for two road profiles using the vertical component ride value and combined point ride value (i.e. the root-sums-of-squares of the six component ride values). The two road profiles had different magnitudes, but the same spectral shape, resulting in median vertical component ride values of 0.58 and 1.01 m.s.-2, root-mean-square. An up-down transformed response rule was used with a three-down-one-up response grouping to estimate difference thresholds at a 79.4% probability level. The median relative difference threshold for the two roads was 10.13% and 8.58% considering the vertical component ride value, and 10.99% and 9.24% considering the combined point ride value. No statistically significant difference was found between the medians of the relative difference threshold over the two roads considering either of the two ride values (p-value = 0.995 in both instances), suggesting that Weber's law holds.