Research On Test And Nonlinear Control Of Electro-hydraulic Fully Variable Valve System

The technology of diesel engine fully variable valve is one of the effective methods to improve the combustion performance,power,economy and emission of diesel engine through intake and exhaust optimization.The electro-hydraulic fully variable valve mechanism can realize the flexible adjustment of parameters such as valve lift,phase and opening duration,and has significant advantages in adapting to different working conditions of diesel engine valve process.For an electro-hydraulic variable valve actuator,it is necessary to realize its tracking control of the target lift curve,accurate mathematical modeling and experimental verification.The electro-hydraulic system is a typical nonlinear system,especially in the high-speed operation of diesel engine,its remarkable nonlinear characteristics will bring great difficulty to the realization of control strategy.Based on a kind of proportional valve control actuator,this paper completed the construction of variable valve test bench,tested and identified the control valve,and tested the key parameters and characteristics of the system,which created conditions for improving the mathematical model,studying the nonlinear characteristics and control characteristics of the system.By analyzing the structure and working principle of the system,the third-order nonlinear mathematical model of the actuator system is established.The simulation verification is realized on the Simulink simulation platform,and the calibration is carried out through the test data.In order to realize the control of the nonlinear system,the mathematical model of the system is approximated and the variable is replaced.Then a terminal sliding mode control method is used to realize the real-time tracking control of the system.In view of the difficulty of state feedback,the filter estimation method is used to realize the observation of state and the real-time estimation of control pressure.Based on this,an output feedback control algorithm based on state observation is designed and verified by simulation.In view of the variable valve performance requirements of diesel engine,a full variable valve lift control reference signal output function is designed by using hyperbolic tangent function,and the simulation shows that the tracking control of the valve lift reference signal can achieve the stable maintenance of the target lift and the smooth buffer of the valve seat at 500 rpm.The results show that the control strategy can track the smooth lift curve,and the designed lift function of the valve can meet the requirements of various working conditions.It provides a method for the adaptation and optimization of diesel engine’s off design conditions,and a reference for the application of electro-hydraulic fully variable valve system in diesel engine.