The Prediction of Passenger Riding Comfort from Acceleration Data

Various methods for evaluating ride quality in automobiles are investigated by means of a field study involving two different automobiles, seventy-eight different passengers, and eighteen different roadway sections. Passenger rating panels were used to obtain subjective evaluation of the various rides, and measured vibration spectra were compared on the basis of various evaluation techniques to determine their ability to predict the subjective ratings. Included in the evaluation criteria considered are the ISO (International Standards Organization) Standard, the UTACV (Urban Tracked Air Cushion Vehicle) Specification, and the Absorbed Power method of Lee and Pradko. Excellent correlation was found to exist between the subjective ride ratings and simple root mean square acceleration measurements at either the vehicle floorboard or the passenger/seat interface. Equations were developed to predict the subjective ride rating from measured vibration spectra. Introduction The acceptance of any new transportation system is affected by the vibrations or "ride quality" to which passengers are exposed. Study of the response of passengers to a vehicle vibration environment has therefore become increasingly important to assist in the development of these new systems. While underdesign of a system with regard to allowed vibration levels can cause it to be unacceptable to the traveling public, overdesign can lead to excessive system costs. It is therefore imperative that we understand the relationships between allowed vibration levels and passenger acceptance. This study is a detailed study of these relationships for the automobile, a presently well accepted mode of transportation within the common experience of the traveling public. This provides a baseline comparison for examination of other, newer modes of transportation. Method The collection of data for the study here described included the measurement of passenger subjective response (ratings) to a variety of riding vibrations in different automobiles over different roadways. Acceleration measurements of the corresponding vibrations were also recorded, including both vertical and lateral floorboard and vertical and lateral seat/passenger interface accelerations. The subjective (passenger ratings) and objective (acceleration measurements) measures of the ride were then compared via a variety of proposed ride rating methods to determine the method which best predicts the subjective ratings using the objective measurements. Methods compared include the ISO Standard, the UTACV Specification, the Absorbed Power method of Lee and Pradko, and frequency weighting techniques utilizing various proposed curves relating human sensitivity to vibration as a function of frequency. Findings and Results A variety of the frequency weighting schemes investigated relate reasonably well to the subjective passenger responses. Of these, the simple r.m.s. acceleration measures, the simplest to use, are also consistently as good of predictors as the more elaborate schemes. Measured at the floorboard, the vertical r.m.S. acceleration is an excellent predictor. while at the nassenger/seat interface, the lateral r.m.s. acceleration is the better predictor. The magnitude (defined as the square root of the sum of the squares of the vertical and lateral r.m.s. values) acceleration is a good predictor for either the floorboard or passenger/seat interface vibrations.