Research On Motion Characteristics And Semi-Active Control Of Automotive Suspension System

During vehicle driving,road-infuced excitation will give different frequencies excitation of the vehicle body.When the frequency of road excitation is close to or equal to the resonance frequency of human organs,the human body will have an uncomfortable response.With the rapid growth of the number of passenger cars,road safety accidents are on the rise.Especially,vehicles with poor handling stability are prone to roll over during sharp turns,emergency braking and acceleration,and high-speed driving.As an important part of the vehicle,the performance of the suspension system has a crucial impact on the ride comfort and handling stability of the vehicle.Studies have shown that passive suspension can not solve the problem of coordination between ride comfort and maneuvering stability,active suspension can carry out real-time control according to road condition and vehicle running state,but it has high cost and large energy consumption.Semi-active suspension system has the advantages of simple structure,high reliability.In order to make the vehicle better adapt to various driving conditions,this article adopted magnetorheological shock absorber to develop semi-active suspension with adjustable damping force in multiple working conditions.Based on modal energy distribution method,the design of the whole vehicle suspension sliding mode control system was carried out,and the accuracy of the dynamic model was verified by real vehicle test.Considering the vertical motion of sprung and unsprung masses,a dynamic model of single-wheel suspension was established to study the vibration transfer characteristics of the system with different damping.Aiming at the active safety problem under special working conditions,considering the roll and pitch motion of the body,the four degrees of freedom model of roll and pitch of the suspension system and the seven degrees of freedom model of the whole vehicle were established respectively,and the modal frequencies and modes of the system were determined,which laid a foundation for the follow-up work.In order to analyze the dynamic characteristics of the vehicle,modal energy method was used to identify the main motion modes of the vehicle.Simulation analysis showed that the energy intensity of each mode changes with time,and the mode with the largest energy proportion at a certain instant is the dominant mode of the vehicle.In order to solve the problem of uncertainty and disturbance in suspension system,the sliding mode variable structure method was used to design the controller.In vertical mode,taked the single-wheel semi-active suspension model as the research object,taked the minimum vertical vibration response of the body as the control objective,the sliding mode control method based on the nominal model was adopted,the expected damping force was obtained.In order to improve the roll stability of vehicle,semi-active suspension model with roll mode was established.With the roll angle and roll angular velocity of vehicle body as the control objective,a sliding mode controller based on inverse design was adopted to obtain expected roll moment.Using the same method,the pitch mode controller was designed.The modal energy distribution method was used to multiply the damping force of each moving mode,and then the expected damping force of each damper was obtained.According to the inherent hysteretic characteristics of actual dampers,the Bouc-Wen model was adopted.The force-velocity characteristic of the damper was linearized and the decision current was obtained.Under different driving conditions,the simulation results of the integrated control suspension were compared with passive suspension.The results showed that under the condition of double lane change,the roll mode is the dominant mode,and the maximum and root mean square acceleration of the body roll angle decrease greatly.Under the condition of highway,the vertical modal is the dominant mode,the maximum and root mean square value of vertical acceleration decrease greatly.The comprehensive control of suspension improves the ride comfort and handling stability of the vehicle.Vibration characteristics of suspension system were tested.In order to improve ride comfort,the vibration transmission rate in resonance zone of suspension system should be reduced.With the increase of vehicle speed,the vibration peaks of the axle and body increase.Based on the drop test method,the modal identification of vehicle was carried out.The experimental values are compared with the simulation values based on the dynamic model.The reliability of the drop test and the accuracy of the dynamic model were verified.The factors that cause errors and affect the test accuracy were analyzed.