5 CONCLUDING REMARKS In this paper, Operational Modal Analysis is proposed as a tool for the performance assessment of different type of suspension systems for passenger cars. Of course the idea can be extended to other classes of vehicles. Two different suspension architectures have been, in particular, considered equipping the same model of car, a Ford S-MAX. The former is a semi-active commercial suspension system, the latter is a novel prototypic active one. Two different in-operation types of test have been then performed on both the vehicles: Proving ground tests on different road profiles and laboratory tests carried out on a four poster test rig. In the latter case, not only the same road profiles considered in the former one have been reproduced on the test rig, but also four uncorrelated white noise sequences have been utilised as input excitations, sent to the four actuators. By OMA-processing the output responses acquired in the different testing conditions and by comparing the results, it is shown how this tool can be effectively utilised to verify the operation and the performance of those systems, by only carrying out a simple, cost-effective road test. In particular, the suspension operation has been analysed by OMA-estimating the modal parameters in the frequency range from 0 to 3 Hz, which the heave, roll and pitch modes are expected to belong to. These modes have been actually identified for both the vehicles considered. Regarding the heave mode, in particular, the damping ratio estimated in the case of the active system equipped vehicle, has been found to be quite higher than that obtained in the other vehicle case, due to the operation of the active suspension system. From excitation point of view, it is useful to stress that in the case of road input, the lower are the considered frequencies, the higher is the energy level in the band and, consequently, the better excited are the included modes, with respect to random input, that can be, instead, effectively utilised to identify only higher-frequency structural deformation modes. Road tests are in conclusion suggested for the performance assessment of suspension operation. ACKNOWLEDGEMENTS The presented research is conducted in the frame of the Flanders’ Drive project InAST (Integrated Active Safety Technology) and the European Commission FP7 project MoDe (“Maintenance on Demand”) coordinated by Volvo Trucks (grant agreement nr. 233890). The financial contribution from the EC is gratefully acknowledged. REFERENCES [1] BRINCKER R., HENNING KIRKEGAARD P., Editors, Special Issue: Operational Modal Analysis, Mechanical Systems and Signal Processing, Vol. 24 (5), pp 1209-1323, 2010. 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