154 E. Bonisoli et al. 10 20 30 Swingarm-Wheel Mode [-] 0 100 200 300 400 500 600 700 800 Motorbike frequency [Hz] 0 10 20 30 40 50 60 70 80 90 Fig. 14.3 Rear sub-assembly vs motorbike 10 20 Chassis Mode [-] 0 100 200 300 400 500 600 700 800 Chassis-Engine frequency [Hz] 0 10 20 30 40 50 Fig. 14.4 Chassis vs chassis +engine sub-assembly In Fig. 14.4 the three horizontal lines correspond to the frequencies of the selected modes of the front sub-assembly (8, 12 and 13). It is clear that only the mode 16 of the chassis at 615 Hz has a high influence on the sub-assembly modal behaviour. This is probably due to the effect of the engine and its link that strongly modify the modal properties of the sub-assembly with respect to the chassis component. The influence of swingarm and wheel in the operative dynamics of the rear sub-assembly is shown in Figs. 14.5 and 14.6. In both figures, blue, red and black lines are relative to the natural frequencies of the three rear sub-assembly modes selected in Fig. 14.4 (modes 14, 22 and 16). The swingarm modes 8 and more 9 have an effect on the dynamics of the sub-assembly, both with wheel modes 11, 14 and 15. It is very interesting to notice that mode 8 of swingarm at a frequency of 290 Hz has a strong effect on the two modes of the rear-subsystem. Therefore, it is necessary to act on the stiffness or on the mass distribution of the component to change its modal influence and to move the natural frequency of that mode out of the critical working frequency range.
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