Dynamic Modelling for Automobile Acceleration Response and Ride Quality Over Rough Roadways

Current interest in dynamics and vibration of ground transportation vehicles arises from the fact that excessive levels can lead to unsafe operation and give an uncomfortable ride to passengers. Current work by the U.S. Department of Transportation in high-speed tracked air-cushion and magnetically levitated vehicles centers around suspension design (both active and passive) for isolating guideway roughness effects from the main body of the vehicle. The work described herein arose from a need to evaluate vibration acceptance criteria for use in both vehicle systems design and guideway specification. This report deals with the first part of a study of automobile riding quality. Three different models of an intermediate sedan together with two different models for roadway roughness are compared. Roadway models compared are, first, a random input single track model with statistics governed by a power spectral density proportional to the square of the wavelength and, second, a model using a data sequence with a zero order hold where the data sequence is obtained from measured evaluation profiles of actual roadway sections. Frequency weighted rms acceleration responses are compared with serviceability indices of roadway test sections. It is concluded that the commonly used roadway model is inadequate and that more complete roadway information regarding statistics of right and left wheel tracks, together with a vehicle model including body roll motions, is necessary to predict ride quality. Use of the ISO Standard on Whole Body Vibration Tolerances as a basis of frequency weighting provides a good correlation with subjective response measured in terms of the roadway servicability index.