1.00 10.00 Hz 1.00e-6 0.01 Log g 2 1.00 10.00 26.8e-6 3.72e-6 889e-6 447e-6 227e-6 37.5e-6 144e-6 128e-6 F AutoPower STRL:DRVR:+Z RANDOM 10 mm F AutoPow er STRL:DRVR:+Z RANDOM 5 mm F AutoPower STRL:DRVR:+Z FLORIDA F AutoPower STRL:DRVR:+Z BLUE-KAY (a) 1.00 10.00 Hz 1.00e-6 0.01 Log g 2 1.00 10.00 5.09e-6 16.8e-6 344e-6 94.4e-6 59.9e-6 247e-6 84.1e-6 29.0e-6 AutoPower STRL:DRVR:-Z RANDOM 10 mm AutoPow er STRL:DRVR:-Z RANDOM 5 mm AutoPower STRL:DRVR:-Z FLORIDA AutoPower STRL:DRVR:-Z BLUE-KAY (b) Fig.7 Comparison of the driver seat rail output auto-power spectrum in the four poster test cases reported in the legend and for (a) the semi-active suspension equipped car and (b) the active suspension equipped one Again a good agreement has been reached, not only between proving ground tests performed on the two different roads, as shown in Fig.10a, but also between proving ground and four poster tests, as shown in Figures 10b and 10c. In all the cases there are small discrepancies between the eigenfrequencies, with quite well correlated modes. Higher discrepancies are achieved on damping ratios, even because dissipation is more difficult to be estimated. Eigenfrequency [Hz] Damping ratio [%] 4P mode 5 mm random Blue-kay Florida 5 mm random Blue-kay Florida 1st (heave) - 1.10 1.27 - 13.42 13.73 2nd (roll) 1.86 1.58 1.80 14.83 7.86 7.45 3rd (pitch) - 2.30 2.14 - 10.68 17.40 Tab.1 Semi-active suspension equipped car: Comparison of the modal parameters estimated in different four poster tests (random excitation proved to be not reliable in the frequency range from 0 to 3 Hz) Eigenfrequency [Hz] Damping ratio [%] PG mode Blue-kay Florida Blue-kay Florida 1st (heave) 1.08 1.19 7.05 15.52 2nd (roll) 1.46 1.55 14.92 19.67 3rd (pitch) 1.77 2.19 9.07 12.82 Tab.2 Semi-active suspension equipped car: Comparison of the modal parameters estimated in different proving ground tests 4.2 The active suspension equipped car In the case of the vehicle equipped with the novel, prototypic suspension system, higher damping values are expected, due to the active operation and performance of the system itself. As it is possible to see from the recalled comparison proposed in Fig.7, indeed, in the case of this second vehicle, the active system operation reduces the output energy levels in the frequency range of interest (0 to 3 Hz) for all the tests performed. As a consequence it becomes more difficult to extract the information from corresponding sets of data, with respect to the semiactive system equipped car. 320
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