| Suspension system has an essential influence on vehicle’s ride comfort and safety.Semi-active suspension has become an important research direction of intelligent suspension for its excellent vibration isolation,high reliability and low power consumption.As to semi-active suspension,the main research refers to adjustable dampers and semi-active control algorithms.Electrorheological dampers have simple structure,homogenous liquid,sensitive response and low energy consumption,which show great potential for application.At present,road information is rarely exploited to compute semi-active control input,which is always generated according to current state variables.Besides,complicated constraint problem of semi-active system is hardly addressed while optimizing control input.Hence,in this paper,an easily implemented preview control algorithm of semi-active suspension is deliberately designed.On one hand,the algorithm incorporates road information,explicitly addresses system constraint and optimizes on each step for optimal performance.On the other hand,the algorithm is improved to avoid on-line optimization and sate observation thus being easy to implement.Methods of theoretical derivation,numerical simulation and bench test are applied to study the semi-active preview control system.The main contribution of the dissertation is as follows:1)Suspension system modeling.Vehicle and road surface models are established and methods to evaluate performance of suspension system are presented.Electrorheological damper is tested to get the characteristic data to identify the model parameters.Then,the relationship between parameters and voltage is established.Finally,a precise and reversible model is acquired.2)Design of optimal preview control for semi-active suspension.The essence of semi-active control,which is a multi-objective optimization problem of weighted indexes,is analyzed by optimal control.Then,optimal preview controller is designed with road information.Simulation result indicates that preview control can improve the ride comfort and road holding at the same time;in addition,considering the economy of implementation,wheel-based preview control is studied and numerical simulation shows it can improve vehicle performance,especially for rear axle;at last,the improvement of preview on delay is analyzed.3)Design of model predictive control of semi-active suspension with available road preview.MPC design explicitly incorporates all hard constraints and generates control over receding horizon,so applying the methodology of MPC can address the issues of control saturation and states constraint.Simulation results indicate MPC can achieve better ride comfort and road holding comparing with optimal preview.Besides,an improved algorithm is established to solve the problem of computing efficiency.The method of least squares and system identification are applied to obtain control parameters.The results indicate that the above approach can be implemented in real time and achieve approximated effect.4)Hardware in the loop test for semi-active preview control.Based on shock absorber as physical hardware,HIL real-time operating system is developed to verify the response effect.A set of impulse and random tests are conducted comparing with skyhook and ADD.the results show the proposed algorithm can improve ride comfort as well as road holding. |
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