The Application And Research Of Vehicle's Chassis Control With Fractional Calculus Theory

Both vehicle's suspension and steering system which are the main effect on vehicle stability and smooth performance are the cores of vehicle chassis control. The comfortableness to passenger and the operation security to driver are directly determined by the suspension system and the steering system performance. In past decade,the fractional order control which based on fractional calculus theory has got a lot of attentions of researcher aboard. But in the field of vehicle control, only few scholars have applied this control strategy on vehicle's suspension control and those researches are yet at the beginning stage. In this thesis, the fractional calculus theory is introduced for the control of vehicle chassis system and the computer simulation works are carried out to demonstrate the effectiveness and validity of the fractional methodology.Firstly, the definitions, characters, calculus methods and control methods of fractional calculus are introduced. Then, three kinds of a quarter car models based on fractional calculus theory are designed through the study and research of control strategy on suspension system and combining the vibration control theory and technique in this thesis. That is the active suspension with LQ optimal control technology, the active suspension with CRONE control method and the semi-active CRONE suspension based on Magneto-Rheological (MR) technique. Using the Matlab/Simulink software,the models of the suspension control system respectively are built and the simulations are carried out under three different kind of control strategies . The conclusions of the simulations under the prompting of the B level road turn out that the acceleration of the sprung mass and the deflections of tire are greatly reduced and the deflections of vehicle body become relatively smaller than other integer-order control method. Therefore, the smooth and the security of vehicle are well improved and the probability of crashing is reduced in high and low of suspension. In particular, the latter two kinds of models have certain robustness and the energy consumption is reduced.Finally, through studying the steering characters and researching the laws of dynamics and kinematics, the dynamics model of four-wheel steering system is built, and the stable and transient responses are analyzed under the promptings of the front wheel corner. Then the four wheels steering system of the forward feed control strategy and the synthesis of forward feed and feedback control strategy are proposed based on fractional calculus theory. The modeling and simulations are accomplished with Matlab/Simulink software. From the conclusions of the simulations, no matter the mobility in the low speed or the stability in the high speed is greatly improved. Though the steering performances are relatively worse comparing with the 4WS, the steering radius is relatively much smaller, so the flexibility of vehicle steering is meliorated.