Comparison of Methods Between an Acceleration-Based In-Situ and a New Hybrid In-Situ Blocked Force Determination

The NVH-development cycle of vehicle components often requires a source characterization separated from the vehicle itself, which leads to the implementation of test bench setups. In the context of frequency based substructuring and transfer path analysis, a component can be characterized using Blocked Forces. The following paper provides a comparison of methods between an acceleration-based in-situ and a new hybrid in-situ Blocked Force determination, using measurements of an artificially excited electric power steering (EPS). Under real-life conditions on a test rig, the acceleration-based in-situ approach often shows limitations in the lower frequency range, due to relatively bad signal-to-noise ratio at the indicator sensors, while delivering accurate results in the higher spectrum. Due to considerable loads on components in operation, the stiffness of the test-rig cannot be decreased arbitrarily. Therefore, the new in-situ hybrid approach is developed to compensate these deficiencies using also force gauges as indicators for the Blocked Force calculation. The force gauges have a higher signal-to-noise ratio in the lower frequency range than the accelerometers on a relatively stiff set-up. This leads to a higher quality of the Blocked Forces using the hybrid in-situ method in the lower frequency range while remaining a high quality in the high frequency range. The acceleration-based in-situ method could not create similarly good results as the hybrid method even when the number of indicator sensors were chosen equally. This higher overdetermination of the matrix inverse is shown to be irrelevant compared to the influence of the type of additional sensors used in the in-situ method. This study also investigates how many additional force gauges are needed to create higher Blocked Force qualities considering their higher costs. Depending on the complexity of the excitation of the active component, there will be diminishing return for additional force sensors. A cost-effective choice of force gauges, thus, requires very good understanding of the active component.