Human subjective response to steering wheel vibration caused by diesel engine idle

Abstract

This study investigated the human subjective response to steering wheel vibration of the type caused by a 4-cylinder diesel engine idle in passenger cars. Vibrotactile perception was assessed using sinusoidal amplitude modulated vibratory stimuli of constant energy level (0.41 r.m.s. m/s2) having a carrier frequency of 26 Hz (i.e. engine firing frequency) and modulation frequency of 6.5 Hz (half engine order). Evaluations of seven levels of modulation depth parameter m (0.0, 0.1, 0.2, 0.4, 0.6, 0.8, 1.0) were performed in order to define the growth function of human perceived disturbance as a function of amplitude modulation depth. Two semantic descriptors were used (unpleasantness and roughness) and two test methods (Thurstone paired comparison and Borg CR-10 direct evaluation scale) for a total of four tests. Each test was performed using an independent group of 25 individuals. The results suggest that there is a critical value of modulation depth m = 0.2 below which human subjects do not perceive differences in amplitude modulation and above which the stimulus-response relationship increases monotonically with a power function. Stevens’ power exponents suggest that the perceived unpleasantness is nonlinearly dependent on modulation depth m with an exponent greater than 1 and that the perceived roughness is dependent with an exponent close to unity.