The effect of tyre damping on the performance of vibration absorbers in an active suspension

Abstract

In advanced active suspension concepts, damped vibration absorbers may be fitted to the axles to control wheel hop oscillations. The optimal tuning and damping ratios for the vibration absorber to minimize wheel-bounce on a random road are computed for a linear two-degree-of-freedom system as functions of the relative tyre damping rate and mass ratio. The optimum damping for the vibration absorber is fairly insensitive to tyre damping, but the latter has quite a significant effect in reducing the r.m.s. tyre deflection, particularly for mass ratios, μ, less than about 0·5, and is worth taking into account. In an example, the r.m.s. dynamic tyre deflection for an isolated system comprising the unsprung mass and tyre fitted with a vibration absorber is shown to be only 27% greater than that of the tyre in a conventional passive suspension, taking the tyre damping into account in both cases. The damping of the bounce mode, however, is comparatively low. Some possible means of improving the performance are suggested.