Research On Nonlinear Characteristics Modeling And Control Of Air Suspension Based On High Order Statistical Theory

As an important part of the vehicle,the performance of air suspension system determines vehicle comfort and handing stability.However,it is difficult to improve the control and performance of air suspension,because of its complexity and nonlinear characteristics.Based on the research of the project team,selected the air suspension with additional air chamber as research object.This thesis focuses on the reconstruction of road microscopic characteristics based on high-order statistical theory,the nonlinear dynamic characteristics influencing factors and change rules of air suspension with additional air chamber.Then,the fuzzy controller and the sliding mode controller are designed.They are based on the reference model of hybrid control and fuzzy control strategy respectively.By simulation analysis the control effect.The main research contents are as follows:1)The road input is an important part of vehicle simulation model.Based on the frequency characteristics of the road,the three-dimensional reconstruction of the road is carried out by using the method of harmonic superposition.From the perspective of mathematical statistics theory proofs the random and stationary ergodic characteristics of the road.This thesis introduces the theory of high-order statistics,selects the standard road spectrum to establish four-wheel road and reconstructed Road.By Matlab High-order Statistics toolbox calculates the third-order cumulant about the two kinds of roads.From the comparison of road contour and micro road features,the correctness and accuracy of road reconstruction are explained.It also provides a new road feature extraction method.The three-dimensional features of five common standard pavements are constructed,which can be used as a reference for judging the current pavement grade.It can as a reference for judging the road surface grade of the current driving road.It has a great significance to vehicle control.2)To research the nonlinear characteristics of the air suspension with an additional air chamber,the mathematical models of the main air chamber,the additional air chamber and orifice model of throttle valve are derived.The equivalent stiffness and damping model of the nonlinear air suspension with additional air chamber are established by using the method of small deviation linearization.The equivalent model of the stiffness and damping of the air suspension with an additional air chamber is simulated and analyzed.The thesis provided the influence rule about the initial air pressure,the volume ratio of the main and auxiliary chambers,the area of the orifice and the excitation frequency.The nonlinear dynamic characteristics of the air suspension with an additional air chamber are obtained.The thesis also established the quarter vehicle modelt to verify the effect of the equivalent model.Then,it is extended to the whole vehicle and established the equivalent seven degree of freedom vehicle model of the additional air chamber air suspension.3)In order to meet the requirements of high precision and short response time of vehicle control,the air suspension fuzzy controller based on fuzzy control strategy is designed.Compared with no control,With fuzzy controller of equivalent air suspension,its RMS of body acceleration,pitch angle acceleration,roll angle acceleration and dynamic deflection of four-wheel front and rear suspension are reduced by 18.8%,23.2%,17.2%,15.6%(left front),15.58%(right front),9.65%(left rear)and 9.3%(right rear),respectively The root mean square of suspension dynamic load increases by 10.2%(left front),4.9%(right front),3.07%(left rear)and 9.25%(right rear).The results show that the fuzzy control can effectively reduce the vibration of the vehicle body and improve the ride comfort of the vehicle.4)Taking into account the comfort and handling stability of the vehicle,based on the reference model of hybrid control strategy of sky-hook and ground-hook control design sliding modle controller.The simulation results show that the performance of the equivalent air suspension with additional air chamber under the sliding mode control better than hybrid control strategy of sky-hook control and ground-hook control.The root mean square of the body acceleration is reduced by10.18%,the root mean square of the pitch angle acceleration is reduced by 3.22%,the root mean square of the body roll angle acceleration is reduced by8.78%,the root mean square of the dynamic deflection of the four-wheel front and rear suspension is reduced by 22.31%(left front),22.88%(right front),26.85%(left rear)and27.35%(right rear).The root mean square of dynamic load of four-wheel front and rear suspension increased by 17.02%(left front),17.76%(right front),24.48%(left rear),23.85%(right rear).The results show that the sliding model control can effectively suppress the body vibration,increase the tire dynamic load and significantly improve the vehicle comfort and handling stability.