Research On Control Strategy Of Vehicle Air Suspension System Under Straight-line Driving Condition

Compared with other vehicle suspension,the air suspension system with auxiliary chamber has the functions of active changing vehicle body height and adjusting suspension stiffness,which can greatly improve vehicle performance.It is one of the development directions of vehicle suspension,and its core is the related control strategy.Therefore,this paper takes the air suspension system system with auxiliary chamber as the research object.On the basis of theoretical research and mathematical models,the control strategies of the suspension system when the vehicle runs stably in a straight line and under the non-emergency braking condition are proposed and the simulation experiments are conducted to verify the effectiveness of the control strategies.The main research contents and results are as follows:(1)The mathematical model and simulation model of the air suspension system system with auxiliary chamber are established.On this basis,the 1/4 and 1/2 vehicle models are established by using the equivalent spring force to replace the the air suspension with auxiliary chamber.Simulation experiments are conducted on the basis of the air spring with auxiliary chamber model and the 1/4 vehicle model,and the results show that the simulation results are basically consistent with the experimental results of the related references.(2)In order to improve the comprehensive performance when the vehicle runs stably in a straight line,the fuzzy analytic hierarchy process,the range normalization method and the linear weighted sum method are used to transform the multi-objective optimization problem of suspension parameters into a single-objective optimization problem,and the Artificial Immune-Fuzzy hierarchical control strategy is proposed to improve the comprehensive performance of the vehicle.The upper controller applies the artificial immune algorithm to optimize the volume of the auxiliary chamber and the damping coefficient of the damper online,while the lower controller applies the fuzzy rule to control the internal gas quality of the spring when the volume of the auxiliary chamber changes.The simulation experiments about the vehicle performance are conducted when the vehicle runs stably in a straight line is simulated.The results show that the RMS(root mean square)of the vertical acceleration of the vehicle body is reduced by 32.26%,the RMS of the dynamic loads of the the front and rear tire are increased by 5.45% and 2.55%,and the RMS of the deflection of the front and rear suspension are reduced by 3.17% and 7.69%.(3)In order to suppress the vehicle body pitching motion during the non-emergency braking process,a method of closing the valve between the main and the auxiliary chamber to make the main chamber work independently is proposed.Based on the Backstepping control strategy,the front and rear air springs(the main chambers)are charged and deflated to suppress the pitching motion of the vehicle body during the non-emergency braking process.The simulation experiments about the vehicle performance are conducted when the vehicle is in the process of non-emergency braking.The results show that the maximum pitch angle of the vehicle body,the RMS of the pitch angle acceleration of the vehicle body,the maximum vertical displacement of the vehicle body,and the RMS of the vertical acceleration of the vehicle body are reduced by 79.43%,80.10%,78.57% and 82.30%.(4)In order to further verify the effectiveness of the control strategies proposed in this paper,the joint simulation model is built by TruckSim and Simulink software and the joint simulation is carried out.The results show that when the vehicle runs stably in a straight line,the RMS of the vertical acceleration of the vehicle body is reduced by 30.50%,the RMS of the dynamic loads of the the front and rear tire are increased by 3.31% and 2.74%,and the RMS of the deflection of the front and rear suspension are reduced by 5.66% and 7.57%;and when the vehicle is under the non-emergency braking condition,the maximum pitch angle of the vehicle body,the RMS of the pitch angle acceleration of the vehicle body,the maximum vertical displacement of the vehicle body,and the RMS of the vertical acceleration of the vehicle body are reduced by 79.24%,79.21%,77.65% and 81.96%.