Key Technologies For Engine Variable Valve Actuator System Based On High-Speed Electro-hydraulic Valve

The serious problem automobiles raise is high energy consumption and high pollution while automobiles have brought convenience. Conventional gasoline engine drives intake valve and exhaust valve by using mechanical camshaft. This kind of engine can not adapt to different distributing programs in various working conditions because valve timing, lift and duration are fixed, and therefore fuel economy and dynamic property are not high. In order to optimize distributing parameter in all working conditions, improve fuel economy and power performance and reduce exhaust emission , variable valve technique is much in demanded.Therefore, a variable valve actuator system with adoption of high-speed electro-hydraulic valve and single rod hydraulic cylinder is proposed to offset the disadvantages of present distributing mechanism based on camshaft drive. The actuator system has simple structure and can achieve soft adjustment of valve timing, lift and duration. In order to solve the valve shock problem during opening-closing process in electro-hydraulic variable valve actuator system, a high-speed valve buffer structure characterized by its multiple openings throttle and spring buffer is well proposed in this paper. The buffer structure can effectively reduce valve opening and closing velocity and shock, and therefore efficiently achieve valve buffer in high speed. In the purpose of addressing the problem of low dynamic response of present electro-hydraulic valve, a drive for high-speed electro-hydraulic valve was successful developed owning to the power scheme, which is based on small number of turns, large current and reversed polarity discharge. The driving performace and dynamic response of the high-speed electro-mechanical converter was analyzed and the optimized structure parameters were obtained by the finite element model of the high-speed electro-mechanical converters. The experimental results show that the high-speed proportional valve and on/off valve take 5.6ms and 2.2ms to reach 1.4mm travel respectively by using the drive and optimizing structure parameters, and therefore the dynamic response of the electro-hydraulic valve was effectively improved .Finally, in order to solve the problem of low dynamic response of the electro-hydraulic variable valve, a high-speed large flow electro-hydraulic valve of without spring, pressure feedback structure was proposed. The valve is a two-position and three-way valve based on slide valve, and therefore can effectively reduce flow force. It can achieve large flow gain because of small valve diameter and short stroke. The electro-hydraulic proportional and on/off variable valve actuator system were built based on the high-speed large flow valve. The optimized structure parameters were obtained by way of analyzing the influence of key structure parameters in dynamic performance of the electro-hydraulic proportional and on/off variable valve actuator system respectively. The experimental results show that the maximum dynamic response frequency of the optimized proportional actuator system can reach to 50Hz and it can be used to control 1500r/min engine valve and the maximum dynamic response frequency of the optimized on/off actuator system can reach to 133Hz and it can be used to control 4000r/min engine valve.In chapter 1, the meaning of studying on engine variable valve technique was illustrated by analyzing the shortage of camshaft valvetrain system. The classification of variable valve technique was introduced and the advantages and disadvantages of the electro-hydraulic variable valve actuator system were obtained by contrasting all kinds of variable valve actuator system. The key techniques which were used to solve the disadvantages of the electro-hydraulic variable valve actuator system were put forward and present research status of the key techniques were introduced. Finally, research background, research significance and research contents were summarized.In chapter 2, a variable valve actuator system scheme by adopting the electro-hydraulic high-speed valve plus single rod hydraulic cylinder was given by analyzing mechanism of electro-hydraulic variable valve system. The structure of the electro-hydraulic variable valve actuator system was introduced and the working principles of the electro-hydraulic variable valve actuator system based on high-speed proportional valve and high-speed on/off valve were illustrated respectively. In order to achieve high-speed and large- power control, a high-speed electro-hydraulic valve with adoption of no spring and pressure feedback structure was proposed. The working principles of the high-speed proportional valve and on/off valve were introduced. According to the research objectives, the structure parameters of the key components of the electro-hydraulic variable valve actuator system were obtained according to the research objectives.In chapter 3, the demands of the high-speed electro-hydraulic variable valve actuator system on the control components was analyzed. The key techniques improving the dynamic performance of the electrical-mechanical converter were introduced in detail. In order to improve dynamic response of the electrical-mechanical converter, a power scheme for driving the high-speed electro-hydraulic valve, which is based on small number of turns , large current and reversed polarity discharge, was proposed, while the working principles and the circuit module were introduced in detail as well.. The working performances of the high-speed proportional and on/off electrical mechanical converter were introduced respectively. The influences of key structure parameters on driving performance and dynamic response were analyzed and optimized structure parameters were obtained by the finite element model of the electrical-mechanical converter. The influences of the key structure parameters of the high-speed electro-hydraulic valve on flow performance were analyzed by the mathematical models of the high-speed proportional and on/off valve respectively.In chapter 4, a high-speed valve buffer scheme of multiple opening throttle and spring buffer was proposed by analyzing present buffer techniques. Based on buffer scheme, the detailed buffering structure and buffering mechanism were analyzed. The buffering structure parameters were obtained and the number of throttle, the hole diameter and distributing position were optimized by Monte Carlo. Finally, the influences of key structure parameters on buffering performance were analyzed by building the mathematical model of the electro-hydraulic on/off variable valve actuator system with high-speed valve buffer.In chapter 5, the system components of the electro-hydraulic variable valve actuator system were introduced. According to the physical model of the system, the mathematical model was modeled. The simulated models of the electro-hydraulic variable valve actuator system based on high-speed proportional valve and on/off valve were built in AMESim. Based on the simulated models, the controllability of valve parameters, system stability and the valve feedback control of the electro-hydraulic proportional variable valve actuator system were analyzed; the controllability of valve parameters of the electro-hydraulic on/off variable valve actuator system was analyzed. In order to optimize system, the influences of key structure parameters on dynamic performance were analyzed and optimized structure parameters were obtained. The dynamic responses of the proportional and on/off variable valve actuator system were analyzed after optimizing. Finally, the feasibilities of increasing freauency responses of the electrohydraulic proportional and on/off actuator system were analyzed.In chapter 6, the experimental rig of the electro-hydraulic variable valve actuator system based on the high-speed electro-hydraulic valve was introduced and the components and working principle were introduced in detail. The controllability of valve parameters of the electro-hydraulic variable valve actuator system based on the high-speed proportional and on/off valve was experimentally studied respectively. The system stability of the proportional system was also analyzed. The influences of key structure parameters, such as spring stiffness, pre-tightening force and pulse width, on dynamic performance were experimentally evaulated. The experiment was carried on after optimizing the system. Finally, the differences between the electrohydraulic proportional and on/off variable valve actuator system were discussed.In chapter 7, all achievements of the dissertation are summarized and the further researches are prospected.