Structure Borne Noise and Vibration Reduction of a Sports Utility Vehicle by Body-Mount Dynamic Stiffness Optimization

Among the key parameters that decide the success of a vehicle in today's competitive market are quietness of passenger cabin (in respect of both airborne and structure-borne noise) and low levels of disturbing vibration felt by the occupants. To control these values in body-on-frame construction vehicles, it is necessary to identify major transfer paths and optimize the isolation characteristics of the elastomeric mounts placed at several locations between a frame and the enclosed passenger cabin of the vehicle. These body mounts play a dominant role in controlling the structure-borne noise and vibrations at floor and seat rails resulting from engine and driveline excitations, and they are also a vital element in the vehicle ride comfort tuning across a wide frequency range.

In the work described in this paper, transfer path tracking was used to identify root cause for the higher noise and vibration levels of a diesel-powered sports utility vehicle. It was found that the one of the most important paths was the connection at the body mount locations. The mounts exhibited very high dynamic stiffness at frequencies above 50 Hz under installed conditions due to their geometric configuration, resulting in poor isolation of power train-induced vibrations between the frame and the body. New mounts of significantly different geometry were designed and evaluated at various stiffness values to optimize in-cab noise, structure vibration, and secondary ride quality. This resulted in noise-level reductions up to 4 dB(A) at passenger's ear levels through out the engine speed range together with floor vibration reduction in the range of 70 % without adversely affecting the ride qualities of the vehicle.