| Because of continuous variable compression ratio, free piston engine(FPE) has the capacity of more efficiency and more clear combustion than traditional internal combustion engine. As the amount of non-renewable energy are decreasing and the criterion of environmental protection is increasing,there is a good development prospect for FPE. Since 1950s, many countries and research institutes have paid much attention to FPE study in the world. So far, the researching of FPE is attracting more interest interiorly.According to the techniques of saving energy, FPE is divided into electromagnetic free piston engine and hydraulic free piston engine (HFPE).The chemical energy of fuel is transformed into electric energy by electromagnetic free piston engine, while it is transformed into pressure energy by hydraulic free piston engine,and then transported to high pressure accumulator,which is used to drive hydraulic motor and the hydraulic motor exports rotary inertia.The subject investigated in this paper is opposed-piston hydraulic free piston engine system, this engine adopts uniflow scanveging,has the advantage of less coefficient residual gas. The researching work mainly contains the optimization of electromagnetic coefficient and hydraulic coefficient for solenoid valve which is used in HFPE system, opposed-piston HFPE hydraulic system simulation, control strategy development and simulation and so on. Verification of the control strategy developed is carried out by the union simulation between AMESim and Matlab software.On the basement of experiment study of large flow fast response solenoid valve, improving the function of solenoid valve, the large flow fast response solenoid valve is replaced by the combination of two solenoid valves. The assembling of two solenoid valves contains one high pressure large flow rate solenoid valve and one high pressure small flow rate solenoid valve, the first valve is responsible for large amount fluid flowing and the second valve is charge of reducing the pressure difference between the assemble of two solenoid valve. The electromagnetic force is increased by 44.6% after the optimization, and this is beneficial to the response of solenoid valve.Opposed-piston HFPE system model is made in AMESim software, this model includes engine model, crankcase model, solenoid valve model, plunger assemble model and so on. This opposed-piston HFPE system model is working successfully, by modulating the injection timing, solenoid valves closing and opening timing. Under the condition of no damping between the plungers assemble, the system hydraulic efficiency is calculated and the peak value of it is 98.9%.Opposed-piston HFPE control strategy is developed and a model for this control strategy is made by Matlab, of which the theory is based on two freedom PI feedback control and predictive working state feedforward control. The steady and continuous working cycles for opposed-piston HFPE are achieved by union simulation between AMESim and Matlab software, the developed control strategy is used in union simulation and is proved that the robustness of the control strategy is good. The union simulation is important to opposed-piston HFPE bench test in the future, and has the guiding significance for further control strategy development of opposed-piston HFPE. |
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