EFFECTS OF SMALL TRAVEL SPEED VARIATIONS ON ACTIVE VIBRATION CONTROL IN MODERN VEHICLES

A stochastic optimal control procedure, based on a perturbation criterion, is developed to study effects of small travel speed variations on active suspensions of vehicles. The vehicle speed is regarded as an uncertain parameter that randomly varies around a measured (equilibrium) mean value. The approach here separates the active suspension forces into two control (laws) forces. The first force is termed steady (unperturbed) control force that isolates a vehicle body from a roadway disturbance and functions in large (mean) nominal speed variations starting from low to very high. The second force is termed a perturbation control force that accommodates changes in the steady force due to small speed variations. Eventually, after justifying the perturbation approach, it is shown how these two control forces could be combined to function only in terms of measured signals. The investigation is made of two different suspension structures for two levels of roadway roughness. Although the approach to the problem is approximate and needs perfect knowledge of all the state variables, the results show that there are noticeable variations to the steady control laws for even small deviations from nominal travel speed. In fact, the control procedure developed here as a design tool is meaningful since optimum vibration control problems are not easy to formulate when non-stationary random vibrations are considered. Also, it can be generalized with care to handle some parametric uncertainty problems.