Switched Control For Vehicle Suspension System With Magnetorheological Damper

With the development of society and the advances in technology, people havehigher requirement for vehicle riding comfort, while the reducing vibration ofsuspension systems always is a key factor that affects the improving of thisperformance. In the last century, the invention of a megnetorheological damperpromotes the development of the reducing vibration techniques. Themegnetorheological damper has many advantages such as strong anti-interferencecapability, fast response and low energy consumption and so on. This presents achance to its application in the vehicle suspension system. Since themegnetorheological damper has complex nonlinear physical character, the controlsystem of the suspension system based on a megnetorheological damper usuallyadopt the strategy of the intelligent control or the Skyhook control, but theintelligent control algorithm has some disadvantages such as low control precisionand slowly frequency response and so on, and the Skyhook control strategy hasfailed to make full use of the merit that the coulomb force of a megnetorheologicaldamper can be continuous controlled, so it is difficult to further improve theperformance of the megnetorheological suspension system based on the intelligentcontrol or the Skyhook control. This thesis will research how to solve the problemsexisting in the current control strategies.In this thesis, that how to establish the model of the suspension system basedon the megnetorheological damper is discussed firstly. In the processes ofestablishing model, a new processing method that handles megnetorheologicaldamping force in Bingham model is proposed. This method separates the coulombforce only related with the speed direction from megnetorheological damping forceto make megnetorheological coulomb force for the suspension system be equivalentto an active execution force in form and under some particular state conditions. Andthen a linearization method is given, which introduce the fitting function of the static nonlinear inverse function of megnetorheological coulomb force to the frontof the megnetorheological damper so as to eliminate the complex nonlinear. Finally,based on the control system point of view and according to the above processing,the thorough theoretical analysis of the megnetorheological damper suspensionsystem is presented and a relatively perfect control system model of themegnetorheological damper suspension system is established. In addition,according to the condition of road surface, a perturbation model and a comfortevaluation index are set up. This builds the foundation for the control systemanalysis and performance evaluation of the suspension system with themegnetorheological damper.Secondly, the vehicle riding comfort and handing stability of the suspensionsystem with the Skyhook control and the passive suspension system aresystematically studied in this thesis, and then multiple segmented coulomb forceswitched control method is put forward, this method takes advantages of both theSkyhook control and the passive suspension. The numerical simulation results showthat this method not only can gain vehicle riding comfort better than the Skyhookcontrol but also can obtain vehicle handing stability better than the passivesuspension system.Furthermore, aimed at the megnetorheological damper suspension system withinput saturation and uncertain, put forward a multiple feedback matrix switchedcontrol method based on the state feedback closed loop control and the stability ofthis switched control system has be analyzed and proved by common Lyapunovfunction. Based on the running characteristics of the megnetorheological dampersuspension system, three different state feedback matrixes, one of the feedbackmatrixes can let the corresponding closed-loop sub-system obtain the optimal H∞performance thereby ensure that the suspension system under this closed loopcontrol mode can get the best vibration reduction performance, are designedrespectively. Then according to the state running track of the suspension system todesign a switched law to guarantee the suspension system can provide vehicle with better riding comfort in any switched state.In addition, considering some state variables are often difficult to be measuredin the actual engineering, which limits the switched control based on the statefeedback matrix switching be used in the practical engineering, for this reason, anew control method based on multiple output feedback parameters switching isproposed for the megnetorheological damper suspension system with the inputsaturation and uncertain parameters in this thesis. The method, according to thedesigned switching control law, lets the suspension system alternately run underthree kinds of closed-loop sub-system control modes to ensure better rideperformance of the vehicle. Using ILMI technology which reduces the solvingconservatism, the BMI constraints based on H∞optimization performance istransformed into LMI constraints. Then by the alteration iteration method, one ofthe closed-loop control sub-systems static output feedback controller parameters aregot to ensure the suspension system running in this closed-loop control mode canobtain the best vibration reduction performance. The numerical simulation resultsshow that the control method based on the multiple output feedback parametersswitching has obvious effect on the vibration reduction of the suspension system.Lastly, the vibration experiment bench of the megnetorheological dampersuspension system is designed, and then the semi-physical simulation experimenthas been done for the megnetorheological damper suspension system based on statefeedback matrixes switched control. Experimental results show that the presentedswitched control method for the megnetorheological damper suspension system iseffective and is likely to be successfully applied to practical engineering in thefuture.