Research On Electromagnetic Fully Variable Valve Of Engine Lift Control Based On Model

Automobile fuel consumption and emission regulations put forward higher requirements on engine performance.The application of electric fully variable valve mechanism to achieve flexible adjustment of engine ventilation is an important research direction to improve engine performance.To achieve flexible control of valve lift,valve phase and opening duration,it is necessary to accurately control the electric fully variable valve mechanism.In this paper,a new electric fully variable valve mechanism composed of electromagnetic linear actuator and magnetorheological buffer is proposed.In order to overcome the influence of system nonlinearity and complex working environment to achieve accurate valve control,the control of electric fully variable valve mechanism was studied by means of system characteristics,mathematical modeling,simulation analysis and experimental research.The thesis mainly carries out the following aspects of research:(1)The system characteristics of electric fully variable valve mechanism are studied.Firstly,the composition and working principle of the system are introduced.Secondly,the static characteristics,dynamic characteristics and hysteresis characteristics of the system are analyzed through simulation and test,and the influence of nonlinear factors of the system is clarified.Finally,the requirements of accurate valve motion control and system robustness are proposed.(2)The nonlinear mathematical model of electric fully variable valve mechanism is established.Based on the static characteristics of the system,the electromagnetic force model based on the equivalent magnetic circuit model is constructed and verified.Aiming at the friction hysteresis in the process of valve movement,the Lu Gre friction model of the system was built and its parameters were identified.The model of valve force was obtained by data fitting method.Finally,the overall model of electric fully variable valve mechanism was built,and the system simulation model was established based on Matlab/Simulink.(3)A composite control strategy for electric fully variable valve system based on H∞robust control is proposed.In order to facilitate the design of the control method,the nonlinear model is linearized by precise linearization method.The control strategy of H∞ controller combined with disturbance observer was proposed to solve the problem that electric fully variable valve is affected by disturbance and parameter variation.Through simulation analysis,the feasibility and rationality of the composite control strategy in the transition process and the seating process are verified,and the robustness of the system is analyzed.(4)Set up the system test platform and conduct experimental research.The test platform of electric fully variable valve system was built,and the control strategy applied to electric fully variable valve system was tested based on the test platform.The effectiveness of the control strategy and the robustness of the system are verified by the experimental study of valve movement process,valve variable parameters and cycle consistency.