Vehicle Active Suspension Control Strategies And Simulation Study

The suspension system is one of the important devices of automobile. It has great effect on vehicle' s usage performances, such as ride quality, handling stability and passing ability. Nowadays, the common suspension composing of spring and absorber has utilization on a large scale. With a passive suspension system, enhancing ride quality and handling simultaneously has limitations if the vehicle ride at a high speed in various road conditions, therefore, in order to overcome the limitations, in rent years, the active suspension is a new approach to improve the suspension s performance. It is able to provide optimal feedback control according to various road profile and actual condition of riding to maintain optimal riding indexes.An electromagnetic active suspension is the object of the thesis. Because the electromagnetic activ suspension has the advantages of simply structure, no actuator of serve-valve and step-advance motor and quick response in comparison with electrohydraudic or pneumatic suspension. The two-degree-of freedom vehicle models have been built for an electromagnetic suspension and an ideal suspension. Three performance indexes are proposed: verticle acceleration of the vehicle body, suspension deflection and tyre deflection. The control theory of suspension is presented.There are many control strategy for the active suspension. Fuzzy logic has been choosed because it is independence on the exact mathematical model of the system, sensitivenessless to the variant and good robustness. Besides, fuzzy logic is very fit to the model of non-linear, time-chageable and delay characteristics. The control algorithm of fuzzy logic base on several control rules and is simple. Then, the fuzzy logic controller has been designed.Because PID control algorithm regarded as a classical and practical algorithm has some advantages such as little work of accounting, good real-time trait and easy achievement, PID control strategy has also been applied. Then, the PID controller has been designed.Fuzzy-PID control combined fuzzy logic and PID control is able to achieve the parameters's self-adapative on-time status. It can furtherly improved the performance of the PID controller in order to adaptive to the changeable variant and changeable condition of the control model. Fuzzy-PID controller that combines the two control strategies discussed above to eliminate the disadvantages of the singles has been designed.Using the software MATLAB/Simulink, simulation models are built under the three control strategies. Computer simulations are carried out on the typical road input (include high, middle and low frequencies). The results show that ride qulity and vehicle maneuverability can be markedly improved by the active suspension and the performances of the active suspension markedly excel the passive suspension. The performances of the active suspension have been compared under the three control strategies. Among the three control strategies, fuzzy-PID controller excel fuzzy one, and fuzzy logic controller excel PID controller. The designed active suspension system also shows robust performance under the three control stragegies.Some theoretic and numerical reference can be given in experimental reseach and development of automobile active suspension in this thesis.