Research On Modeling And Control Of Vehicle Height Adjustment System For Automobile With Double Wishbone ECAS

In automobiles,the air spring and the double wishbone suspension generally form the electronic control air suspension(ECAS).In addition to its excellent vibration isolation ability due to its variable stiffness characteristics,the automobile double wishbone ECAS can adjust the vehicle height by charging and discharging operation to improve vehicle fuel economy,handling stability and trafficability.However,the vehicle height adjustment system for automobile with double wishbone ECAS has some problems,such as insufficient modeling accuracy and easy oscillation in vehicle height adjustment.This thesis takes the double wishbone ECAS for automobiles as the research object,and conducts research on perfecting the model,improving the adjustment accuracy of the vehicle height adjustment system and reducing the calculation the control algorithm.The main research contents are as follows:The model of vehicle height adjustment system for automobile with double wishbone ECAS ignores the influence of geometry and kinematics of double wishbone suspension,which makes the model shows larger error compared with actual model.Firstly,the mechanism model of air spring is derived based on the thermodynamic theory.Combined with the dynamic model of the double wishbone air suspension based on kinematic analysis and dynamic modeling,the model of the vehicle height adjustment system for automobile with double wishbone ECAS is established.Then,on this basis,the influence of kinematics and geometry of double wishbone suspension on the vehicle height adjustment system is analyzed quantitatively.Finally,the results of the quarter car test rig and Simulink-Adams co-simulation show that the accuracy of the vehicle height adjustment model is improved effectively.The vehicle height adjustment system has strong nonlinearity and is easily affected by road disturbance,which leads to oscillation in vehicle height adjustment.A double loop controller is designed specifically,which includes a model predictive main controller based on the extended state observer and a fuzzy PID auxiliary controller.Firstly,the extended state observer is used to observe the linearization error of the model and the road disturbance.On this basis,the main controller performs optimized control and finally the auxiliary controller performs timely compensation,which realizes the improvement of the vehicle height adjustment accuracy and the suppression of oscillation.The simulation results under four vehicle height modes show that the double loop controller not only can effectively adjust the vehicle height,but also can effectively control the acceleration of vehicle body and the opening/closing states of solenoid valve.For the problem of how to reduce the calculation amount of the control algorithm while maintaining the control accuracy when dynamically adjusting the vehicle height,an event triggered double loop controller is proposed.Through the analysis of algorithm complexity theory,it is clear that the calculation amount of the algorithm mainly depends on the model predictive control.Then,the event-triggered strategy is introduced for the model predictive control and the optimization of the model predictive control is judged according to the trigger condition.Finally,through simulations of static and dynamic vehicle height adjustment,the effectiveness of the event-triggered double loop controller is verified with the evaluation indexs of control accuracy and trigger times.