Moorthy, S., Rao, M., Raghavendran, P., and Babu, S., "Analysis and Elimination of Howling Noise in Compact Utility Vehicle," SAE Technical Paper 2017-28-1922, 2017.
NVH is becoming one of the major factor for customer selection of vehicle along with parameters like fuel economy and drivability. One of the major NVH challenges is to have a vehicle with aggressive drivability and at the same time with acceptable noise and vibration levels.This paper focuses on the compact utility vehicle where the howling noise is occurring at higher rpm of the engine. The vehicle is powered by three cylinder turbocharged diesel engine. The noise levels were higher above 2500 rpm due to the presence of structural resonance. Operational deflection shapes (ODS) and Transfer path analysis (TPA) analysis was done on entire vehicle and powertrain to find out the major reason for howling noise at higher engine rpm. It is observed that the major contribution for noise at higher rpm is due to modal coupling between powertrain, half shaft and vehicle sub frame. The acoustic transfer function levels from the body and the sub-frame connection point to driver ear were also higher at the problematic frequency where structural resonance were observed in operational measurements. Structural modification on powertrain, half shaft and installation of tuned mass damper on sub frame reduced the howling noise to great extent. The effect of powertrain torsional vibration and its contribution to this higher noise levels were also discussed.