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Figure 5 FD damping force [kN] response; experimental (dotted) and simulated (solid) The control variables are, respectively, solenoid current for the MRD, and hydraulic actuator pressure for the FD. Drive dynamics upon which damper responses rely under feedback control have also been accurately modelled.

Figure 5 FD damping force [kN] response; experimental (dotted) and simulated (solid) The control variables are, respectively, solenoid current for the MRD, and hydraulic actuator pressure for the FD. Drive dynamics upon which damper responses rely under feedback control have also been accurately modelled.

Related Figures (7)

Figure 2. Schematic of the MRD
Figure 2. Schematic of the MRD
Figure 3. Schematic of the FD Figures 4 and 5 depict, respectively, the MRD and FD modelled and measured static force vs velocity characteristics. Dynamic response identification and validation has also been carried out. Both models provide a good prediction of the experimentally measured responses.
Figure 3. Schematic of the FD Figures 4 and 5 depict, respectively, the MRD and FD modelled and measured static force vs velocity characteristics. Dynamic response identification and validation has also been carried out. Both models provide a good prediction of the experimentally measured responses.
Figure 4 MRD Damping force [kN] response; experimental (dotted) and simulated (solid)
Figure 4 MRD Damping force [kN] response; experimental (dotted) and simulated (solid)
able 1 Performance assessment of passive and semi-active systems
able 1 Performance assessment of passive and semi-active systems
It is finally worth drawing an analogy in the behaviour of the semi-active response, when the gain factor varies, with a linear system varying the viscous damping ratio. Close to resonance a highly damped system with high gain (b = 3) performs well; conversely above the resonant frequency a low gain system (b = 1.25) behaves better and, analogously to a linear system, there exists a frequency at around 2 Hz where the three trends tend to cross one another and the behaviour is almost independent of the value of the control gain. Figure 6 Acceleration transmissibility for the MRD seat suspension, varying gain factor b
It is finally worth drawing an analogy in the behaviour of the semi-active response, when the gain factor varies, with a linear system varying the viscous damping ratio. Close to resonance a highly damped system with high gain (b = 3) performs well; conversely above the resonant frequency a low gain system (b = 1.25) behaves better and, analogously to a linear system, there exists a frequency at around 2 Hz where the three trends tend to cross one another and the behaviour is almost independent of the value of the control gain. Figure 6 Acceleration transmissibility for the MRD seat suspension, varying gain factor b
On the same picture the effect of closed-loop gain changes from 2 to 3.33 is examined; b is the reciprocal of the friction coefficient in the Coulomb friction model, and hence its increase from 2 to 3.33 can be treated as equivalent to a decrease of the friction coefficient from 0.5 to 0.3. The performance with the ‘reduced’ friction shows some deterioration over part of the frequency range: this is to be expected since with a lower assumed friction coefficient, the force cancellation is smaller, resulting in higher accelerations. Figure 7
On the same picture the effect of closed-loop gain changes from 2 to 3.33 is examined; b is the reciprocal of the friction coefficient in the Coulomb friction model, and hence its increase from 2 to 3.33 can be treated as equivalent to a decrease of the friction coefficient from 0.5 to 0.3. The performance with the ‘reduced’ friction shows some deterioration over part of the frequency range: this is to be expected since with a lower assumed friction coefficient, the force cancellation is smaller, resulting in higher accelerations. Figure 7
Figure 8 Comparison of tyre fluctuations and vertical acceleration: passive vs semi-active control
Figure 8 Comparison of tyre fluctuations and vertical acceleration: passive vs semi-active control
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