Knechten, T., Morariu, M., and van der Linden, P., "Improved Method for FRF Acquisition for Vehicle Body NVH Analysis," SAE Technical Paper 2015-01-2262, 2015, doi:10.4271/2015-01-2262.
Structural and vibro-acoustic transfer functions still form an essential part of NVH data in vehicle development programs. Excitation in the three DOFs at all body interface connection locations to target responses gives information on local dynamics stiffness and the body sensitivity for that specific path in an efficient manner. However, vehicles become more compact for fuel efficiency, production costs and to meet the market demand for urban vehicles. Alternative driveline concepts increase the electronic content and new mount locations. To achieve the optimum on road noise NVH, handling performance while conserving interior space and trunk volume requires a complex suspension layout. On top of that, customers put weight on safety and comfort systems which result to a higher packaging density. These trends imply ever limiting accessibility of the interface connections on the body structure. A modal hammer and a traditional shaker cannot reach all connections The FRF result is very sensitive for local mass loading, alignment errors and parasitic moment input during excitation. Even the most compact inertia shaker encounters challenges accessing all relevant points on the body structure in three directions. The reciprocal method allows the measurement of the (vibro-)acoustic body noise transfer function but not the local dynamic stiffness or local structural FRFs.In this paper a method is proposed which enables the engineer to obtain all relevant FRFs in and around the body structure.The method is based on multiple excitations in a locally rotated coordinate system which are re-combined to obtain the desired FRFs in the three global directions. In this way the engineer is able to select excitation orientations which are accessible. This process is evaluated using new hard- and software tools. The process is validated experimentally on an automotive trimmed body and compared with traditional methods.