Importance of Vehicle Body Elements and Rear Axle Elements for Describing Road Booming Noise

Abstract

For investigating influences of vehicle components on the acoustic comfort at low frequencies, e.g., the booming noise behavior of a vehicle, building a whole car simulation model is useful. To reduce the model’s complexity and to save resources in the validation process, we first identify relevant components before building the model. Based on previous studies, we focus on the vehicle’s body and the rear axle. In this paper, we analyze which axle and body elements are crucial for describing road booming noise. For this purpose, we use impact measurements to examine noise transfer functions of the body and a vibro-acoustical modal analysis to identify coupled modes between the body’s structure and the interior cavity. For investigating relevant force paths from the rear axle to the body, we used a chassis test bench. We identify the main transmission paths of road booming noise and highlight which axle and body components have an influence on them. Mainly the rear axle in its upright direction in combination with a rigid body movement of the rear tailgate coupled with the first longitudinal mode of the airborne cavity causes road booming noise. Furthermore, the rear axle steering, the active roll stabilization and the trim elements of the vehicle’s body are essential to describe road booming noise. The results can be used to set priorities in the validation of individual axle and body components for future simulation models. We found that the ventilation openings, the front seats, the headliner, and the cockpit of a vehicle have little influence on its noise transfer functions from the rear axle connection points to the driver’s ear between 20 and 60 Hz.

Describing Road Booming Noise with a Hybrid Simulation Model Using a Time Segmentation of the Excitation Load Approach

“…Since only the transfer paths of the rear axle (excluding the rear springs) are relevant for the description of road booming noise [8], only the six marked connection points of the chassis to the body are used. There are three directions per point, i.e., 18 internal forces.…”

“…We focus on the road booming noise, which is mainly excited by non-uniform road profiles [4,5]. The excitation introduced into the chassis primarily causes the rear axle to resonate in a pitching and lifting motion [6][7][8]. The vehicle's body responds with a coupled vibration mode formed by the first bending mode of the body, a rigid-body motion of the tailgate and the first longitudinal mode of the air cavity [8].…”

“…The excitation introduced into the chassis primarily causes the rear axle to resonate in a pitching and lifting motion [6][7][8]. The vehicle's body responds with a coupled vibration mode formed by the first bending mode of the body, a rigid-body motion of the tailgate and the first longitudinal mode of the air cavity [8]. Passengers experience this phenomenon as ear pressure and booming noise at low frequencies [4,9].…”

Strategies for Reducing Booming Noise Generated by the Tailgate of an Electric Sport Utility Vehicle

“…Selvaraj et al [2] analyzed low-frequency noise and vibration problems in bus bodies, which stem from imbalances in large bus propeller shafts, using the operational deflection shape (ODS) technique. Herrmann et al [3] investigated the mechanisms behind the booming noise generated by coupling modes between the rear axle and vehicle body, which subsequently affect the fore-aft behavior of tailgates and the acoustics within the vehicle interior. Lim et al [4] identified the origins of structure-borne and airborne booming noise originating from the rigid modes of air-conditioning pipes through transmission path analysis and ODS analysis.…”