Stability test for semi-active suspensions with base disturbance

Previous investigations by the authors (Storey et al. 2006; Storey et al. 2009; Storey 2011) indicate that controlled suspensions are capable of being “soft” (have a low damping rate) under placid conditions, and “hard” (high damping rate) when required to improve “tracking” (staying close to the middle of and avoiding hitting suspension limits). The question arises then whether such suspensions are safe. On the one hand, vehicles have had relatively high mandated suspension damping rates after Ralph Nadar (1972) famously found that cars with soft suspensions were prone to rollover. On the other hand, improved isolation and tracking should make suspensions more resilient to destructive harmonics. ... For our analysis we compared three controls, two linear and one piecewise linear. ... The main disadvantage of the skyhook is that it cannot be implemented in full by a controlled damper in a semiactive suspension. In the experiments described below, however, we investigated the simplest damping control possible, in which the damper is either on or off.... Results of our numerical experiments show that the switched skyhook greatly improves on the linear passive. Figure 1 shows an example of transmissibility against frequency (as a proportion of the natural frequency). In this example each control has a damper with the same damping rate, �� = √2. As shown in Figure 1, the switched skyhook can greatly reduce the response amplitude (much less than one) at the resonant frequency, even with relatively high damping rates. It also provides a much smoother response at higher frequencies.