Research Of Vehicle Semi-active Suspension Based On Fractional Calculus

The vehicle suspension system decides the ride comfort and the handling stability. As the developing of science and technology, a few of new suspension systems with advanced control strategy have been emerging constantly. In this thesis, the Fractional Calculus Theory (FC) is introduced into the control strategy of semi-active suspension, using the Magneto Rheological (MR) damper as an actuating mechanism, and then the dynamic properties of semi-active suspension based on FC is investigated.Firstly, a brief introduction is given about the vehicle suspension system and its model establishment and simulation, and then this thesis sums up the definition of FC. Furthermore, taking a vehicle vibration model of a quarter body as an object of study, the semi-active suspension based on fractional order skyhook damping is proposed. A simulating model is established by using the Oustaloup approximation algorithm.?The results demonstrate that, the fractional order system can achieve a better performance than the ordinary integral order system. Considering the nonlinearity and uncertainty of vehicle suspension, a nonlinear semi-active suspension dynamic model is established.?Using fractional order skyhook damping system as reference model, a new excellent sliding mode control strategy for suspension systems is proposed. Also, establish a simulating model for the above nonlinear suspension with the new strategy. Afterwards, the simulation results clearly illustrate that, the semi-active suspension system based on FC obtains a better performance than integral order system.Finally, a new numerical algorithm for response computation of linear or nonlinear dynamic equation with fractional order control items is presented in this thesis, and the precise integral method is adopted in this algorithm to improve the computational accuracy and stability. The examples show that regardless of linear systems or nonlinear systems, the answers of this algorithm are of accuracy and stability. This numerical algorithm in general may substitute the simulation in Simulink, and its answer almost coincides with the Oustaloup approximation algorithm.