Psychoacoustic analysis of high frequency elasto-acoustic emissions from hollow driveshaft tubes

Abstract

Lightly damped non-linear systems such as vehicular drivelines undergo a plethora of Noise, Vibration and Harshness (NVH) problems. The clonk phenomenon is one concern which occurs as the result of impulsive torque input in the form of sudden clutch actuation or throttle tip-in and back-out. The resulting impact of meshing gear pairs propagate structural waves down the driveline. With lightly damped thin-walled tubes having high modal density, elasto-acoustic coupling occurs. High frequency noise emission is of metallic nature and quite disconcerting to vehicle occupants as well as passers-by. It is perceived as structural failure and/or poor-quality build. Therefore, the occurrence of the phenomenon is a concern to vehicle manufacturers and progressively constitutes a warranty concern. This paper investigates the clonk phenomenon through use of a long-wheel base rear drive light truck test rig. The investigation uses psychoacoustic metrics to establish the severity of clonk noise in different maneuvers. This is an attempt to quantify the effect of transient clonk event which is usually ascertained through subjective evaluation ratings in a customer/jury clinic in industry. Alternatively, detailed numerical analysis is carried out with parametric studies to quantify different clonk events, a very time consuming approach which is not usually correlated with occupants’ perception of the event. Therefore, the experimental NVH monitoring-psycho-acoustic approach is new for the case of clonk and not hitherto reported in literature. The study corroborates the results and conclusions of previous work, pointing to the loudness and sharpness of high frequency short-lived “metallic” response, which is attuned to human aural perception. The psychoacoustic analysis has shown this to be as the result of short duration hard impact (accelerative period). This hard impact duration accounts for the bulk loudness and sharpness of the overall event. Therefore, effective palliation should focus on the attenuation of particular frequency bands, which carry the main contribution to loudness and sharpness.