| The variable valve technology has made flexible variable valve timing, variable vale lift possible and can greatly improve the energy efficiency and dynamic performance of the automobile engines. But the traditional variable valve greatly depends on the profile of valve cam. Fully variable valve timing and variable valve lift can not be achieved. So it is necessary to investigate new method of variable valve actuator to replace valve cam.This paper investigated the basic principle of variable valve system base on electro-hydraulic theory. The research includes the study of key components of the system, i.e. the electro-mechanical converter, the control circuit and both the simulation and experiments based on peak and hold control method. We established the theoretical and FEM model of the high speed electro-mechanical converter to analyze how different paramenters affect the output performance of the high speed converter. Optimal parameters were abtained after the analysis. Furthermore, this paper proposed peak and hold method to enhance the prequency response of the system and analytical relationship between the control signal and the valve stroke was deduced. Optimal control parameters were obtained by SIMULINK simulation.This paper chose proportional electro-magnet to be the electro-machanical converter of the system. High speed control circuit was designed based on PWM method. Some experiments were carried out to validate the correctness of the propesed method and the simulation models.This paper is organized as follows:In chapter 1, the history and research status of variable valve system were introduced. Four typical variable valve actuators were detailly illustrated. Then, we compared the advanrage and disadvantage of the four different actuators. After that, typical control methods and control circuits were introduced. At the end of this chapter, the research backgrounds, contents and procedures of this project with analysis of research significance were descripted briefly.Chapter 2 focused on the study of the electro-mechanical converter. Firstly, the impact of the characteristics of magnetic materials on the electro-magnet was studied. We studied the heat treatment characteristics, frequency characteristics and temperature characteristics of the material. Then, both the analytical and empirical temperature rising model of the electro-magnet was established. After that, analytical solution of the cylindrical electro-magnet was presented. We analyzed the relationship between the time constant of the electro-magnet and the design specifications. The calculation of the electro-magnetic force was also presented. At the end of this chapter, we built the FEA models by Ansoft and compared the calculation results of analytical solutions and FEA solutions.Chapter 3 firstly descripted the system implementation schematic and its work principles under flow and pressure control circumstances respectively. Then, the theoretical models of the variable valve system based on electro-hydraulic pressure reducing valve was established and deduced. In this chapter, peak and hold method was proposed and explained in detail. According the theoretical model, we built simulation models in SIMULINK in order to obtain the optimal Tpeak of the proposed peak and hold method. Summary conclutions were drawn at the end of this chapter.Chapter 4 firstly described the experimental test rig of the electro-hydraulic vaiable valve system. Then, some experiments by employing proposed peak and hold method and standard control method were carried out respectively. Experiment results were basically consistent with the simulation results; hence the correctness and fleability of this design were proved once again, which could meet the design goals of this system. Summary conclutions were drawn at the end of this chapter.The chapter 5 was the conclusions and prospects. The major research conclusions and results were summarized in this chapter, and future planning steps together with research directions are also proposed. |
PDF Full Text Request