Road Frequency&Vehicle Load Adaptive Semi-active Suspension Control Strategy

The suspension system is a critical component that can influence the vehicle ride andhandling performance. Establishing a semi-active suspension system, which can becontrolled according to the road surface and vehicle load conditions, is an importantapproach to improving automotive comfort and security. In this paper, a simple, reliable andinexpensive semi-active suspension control system is described. On one hand, the proposedcontrol system can estimate the essential vehicle states accurately in different vehicle loadconditions. On the other hand, it can adjust the control parameters online according to theroad conditions to improve the vehicle performance. In this paper, the methods of theoreticalanalysis, numerical simulation and road testing are applied to study the development of theproposed semi-active suspension control system. The main contributions of the dissertationinclude the following:1) The method and indicators used to evaluate the performance of the automotivesuspension system are discussed. The vibration characteristic and the effect of thesuspension parameters on vertical vibration are mainly analyzed based on a linear2DOFvehicle model. Then,by using the notion of variance gain, the approximate FR for thenonlinear semi-active control systems is computed.2) Using the Kalman Filter theory, a state estimator based on2DOF vehicle model forestimating the required state variables is designed, and then, the state estimator is extendedinto full-car application. To avoid the state estimation error inducing by vehicle loadvariation, an vehicle load adaptive state estimator is proposed in this paper, where the onlinevehicle sprung mass can be calculated by Recursive Least-Squares Estimation.3) To improve the vehicle suspension performance (ride comfort and wheel handling)for all frequency regions of road disturbances, a road-frequency adaptive control forsemi-active suspension systems is investigated. In order to achieve this aim, the control law is extended from the conventional skyhook control, and the controller gains are scheduledfor various frequency regions of road disturbances, where the road disturbance frequenciesare estimated by using a first order zero-crossing algorithm. The efficiency of the proposedcontrol is shown through numerical simulations.4) At last, a semi-active suspension controller, based on MotoHawk rapid prototypingsystem, was developed in the C131test vehicle. A set of impulse input tests under differentvehicle load were conducted, the test result shows that compared with the passive suspensionand the conventional skyhook suspension the proposed control system can improve thevehicle performance in different load conditions. Random road tests were carried out, to testthe vehicle performance in different road input conditions. Experimental studies show thatthe frequency adaptive controller can effectively improve the vehicle ride comfort indifferent road conditions.