Perception of Low Frequency Vibrations by Heavy Vehicle Drivers

Abstract

A study was initiated to identify the levels and frequencies of heavy articulated vehicle body vibrations at which the drivers perceive the ride as uncomfortable. The study involved conducting a subjective assessment survey in which a panel of truck drivers were asked to rate the ride quality provided by a number of road sections with different surface roughness characteristics. The study's objective was achieved by correlating the mean panel ratings (MPRs) to road surface roughness contents in different one-third-octave bands of the roughness spectrum. The results showed that at 100 km/h, truck drivers object mainly to motions resulting from roughness excitations of the low frequency vibration modes of the truck body in the range 1.42 -5.7 Hz. These results were validated by correlating MPRs with the levels of whole body vibrations measured on the driver's seat in a representative vehicle while traversing some test sections. MPRs were found to correlate well with the measured overall vibration total values and the likely comfort reactions to various magnitudes of overall vibration total values given by ISO 2631-1. The influence on MPRs of vehicle and driver related factors were also investigated and commented upon. INTRODUCTIONThe ride environment of the truck driver is the product of the applied excitation and the response properties of the truck (Gillespie, 1985). Road surface roughness is a major source of excitation in addition to the rotating tyre/wheel assemblies, the driveline and the engine (Gillespie, 1985). When a vehicle traverses a rough road pavement, surface irregularities excite different vibration modes of the vehicle body at different frequencies. Past research has shown that heavy vehicle ride is most sensitive to excitations of the low frequency modes in the range 1-8 Hz (Gillespie, 1985). At these frequencies, modes such as body bounce, pitch, roll, frame bending and axle hop are excited. The resulting motions affect the ride quality perceived by the occupants and their comfort as at these frequencies humans are most sensitive to vertical (4-10 Hz) lateral and longitudinal (0.5-2 Hz) vibrations (IS0-2631-1, 1997).The aim of this paper is to report on the results of a study conducted for the purpose of identifying the levels and frequencies of heavy articulated vehicle body vibrations, excited by road roughness, at which the drivers perceive the ride as uncomfortable. The study involved conducting a subjective assessment survey to collect drivers' ratings of the ride quality provided by a number of road sections with varying roughness levels and spectral characteristics. Further, Whole Body Vibrations (WBV) transmitted through the driver's seat were measured at highway speed on a number of test sections.Driver's perception of ride is influenced by factors other than the vibrations present in the vehicle's cabin. They include factors related to the road, the vehicle

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