Model And Performance Studies Of Electro-hydraulic Valve Actuators On Gasoline HCCI Engine

In order to alleviate contradiction between limited reserves of petroleum andincreasing demands, many countries begin to use biofuels including ethanol, methanol andbiodiesel, as alternative to petroleum-based fuels. The contradiction among utilization ofbio-energy， food supply, and capacity limit of ecological environment also exists.Technologies and methods of improving efficiency of internal combustion engine to saveexisting petroleum-based energy and bio-energy, and reducing emissions of carbon dioxideand pollutants can alleviate the energy crisis. HCCI combustion has potential to reduceemissions, in part load condition which reaches a considerable low level emission withoutexhaust gas aftertreatment. Different valve control strategies to control percentage ofexhaust gas trapped into the cylinder and control the mixing process of working fluid, canoptimize HCCI combustion process.Variable valve is the key technology to achieve gasoline HCCI combustion at engine.To support the973project of low-temperature combustion research and developing HCCIengine, a dual-piston-driven hydraulic variable valve train (HVVT) is self-developed toovercome the shortcomings of existing valve system. Method of regulating the open andclose trigger signal from VCU achieves a wide range of variable valve timing. The HVVTlift is adjustable by adjusting the electro-hydraulic proportional valve. In order to masterthe design method of HVVT, the mathematical models of electro-hydraulic valve motion isestablished. A physical prototype and a virtual prototype platform are built to explorefactors that affect performance of HVVT. Main contents of this article are listed below.In chapter Ⅰ, HCCI combustion engine with HVVT is reviewed. Exhaust gas trappedby adjusting variable valve train (VVT), can achieve HCCI combustion without intake airheated and changing compression ratio. Different valve control strategies can adjustamount of burnt residual gas in cylinder (burnt gas fraction, BRF), to adjust heat releaserate of HCCI combustion and rise rate of cylinder pressure. In recent years, many fullyvariable valve trains were designed, such as electronically controlled mechanical variablevalve train, electro-magnetic fully variable valve train, electro-pneumatic fully variablevalve train, electro-hydraulic fully variable valve train, and cam coupled with electronicallycontrolled fully variable valve. HVVTs are promising to replace the traditional valve,which are classified. Chapter Ⅱ, work process of the dual piston driven hydraulic valve train is analyzedand a mathematical model of HVVT is established. Design parameters are determinedbased on the cylinder head of a ZS1105four-stroke engine. Based on mathematical modelsand physical prototypes, a simulation platform is built with AMEsim, Adams and Matlab,using Visual Fortran as a solver and Visual C++as a unified compiler, to establish platformof the dual piston driven Fully Variable Valve System（FVVS） model.Chapter Ⅲ, buffer mechanisms including spring buffer, orifice+spring buffer, andmulti-orifices buffer are used to reduce shock in the buffer stage of valve piston fully openand seated. After establishing and analyzing the buffer mechanisms and submodels ofFVVS, structural parameters are analoged. Assuming deceleration is uniform in the seatingprocess, Newton interpolation algorithm is used to optimize the number, diameters andarrangement of orifices. In conjunction with the simulation model of the hydraulicvalvetrain, the parameters of the hydraulic valve buffer simulation model are analyzed.Chapter Ⅳ, utilizing hydraulic valve train model established in the previous chapter，golden section algorithm and trial method are applied to get reasonable parameter values ofhydraulic valve mechanism. Larger piston diameter, smaller piston diameter and orificediameters and other key parameters are optimized by a genetic algorithm.Chapter Ⅴ, HVVT key parameters that affect open delay and close delay are analyzedby simulating and test. The effect of pipe length, hydraulic line diameter, oil viscosity andoil temperature is analyzed. Statistical analysis is undertaken to determine the delayfluctuation of valve open and close in different temperatures. With engine speed increasing,valve open frequency increases, the impact of valve open and close delay increases,continuous fully open state extends. Based on the hydraulic valve train models,controllability of HVVT operating in high frequency is analyzed.Finally, the hydraulic valve train is tested at engine. In order to achieve an accuratecontrol of the electro-hydraulic valve delay to meet requirements of the nonlinear delay ofthe electro-hydraulic valve train，a fuzzy and PID control system with three-dimensionalmap of open and close delay is established to control hydraulic valve. According to thehydraulic valve engine test results, the hydraulic mechanism parameters of HVVT aredetermined and an electro-hydraulic valve control strategy is built for HCCI engine.