| With the development of science and microelectronics technique, the trend of the future is that there are breakthroughs improvement in Grand Scale Integration of microcomputer and technology of transducer. All the world will enter the stage of equipments revolution taking the integrity of machine and electron as the core, which will make the bulldozer get quick development, such as apparent improvement in working function, dependability, maintainability, safety and fuel economy. In order to reform the maneuverability of the working device of bulldozer and make production abroad be homemade, digital proportional decompression valve which substitutes for the original PPC valve is used as pilot valve to make up of digital electro-hydraulic proportional directional valve with multiple-unit valve in this article, which fulfills digitized control of working device for bulldozer. The working device of bulldozer takes advantage of the hydraulic system to drive and control cylinder of shovel to complete the homework, such as pushing soil, loading soil etc.The digital electro-hydraulic proportional control system, in the article, comprises of control handlebar (electric potential device), electronic control unit (ECU), pilot valve (proportional decompression valve), multiple-unit valve and oil cylinder.When manipulator manipulates control handlebar, it sends instruction signal that is converted into PWM signal (Pulse-Width Modulation) dealt with by electricity control system. Then this signal is amplified by the switch type of power-amplifying circuit, current-amplifying circuit, to drive pilot proportional decompression valve and control each working position of main control valve, in order to fulfill kinds of actions of shovel, such as rising and falling, pitching etc. After manipulator manipulates pilot valve, pressure outputs to the both ends of main valve according to linear proportion, which makes main valve move between two directions to realize change of its direction. Because pilot valve is a small flux piece, the journey of slide valve and force of restitution of spring can be designed much smaller, which cuts down the manipulating moment greatly, so as to meet the character of PPC-short of manipulating handlebar. In addition, layouts of main valve and pilot one are the same as original layouts of system, for there is no rigid conjunction between them.This designed system has two advantages: first, the movement of valve core responds the average value of PWM signal, which makes valve core work in tiny vibration situation and decreases stagnant wreath of proportional valve greatly; second, amplifier is in good economical function only working in switch (on or off) situation, for current amplifying circuit of PWM signal is a switch type of enlarging circuit.The main parts of this hydraulic system are proportional valve and multiple units one. First, model and simulate them individually, then analyze the whole system. The characteristic analyzing and modeling of proportional decompression valveElectro-hydraulic proportional decompression valve is controlled by PWM signal. In a modulating period T as to an ideal decompression valve voltage wave is complete the same as the displacement wave of valve core. But, because electro-hydraulic proportional decompression valve is affected by the responding ability of electromagnetic coil and the time of valve moving, in fact it is impossible for valve core responding to follow variety of Pulse-Width signal always in time. And its respond character varies much with the period of PWM (or frequency) and the variety of occupy.Make use of the modern control theories and conclude the following state equations about proportional compression valve: Based above state equations, work out simulated diagram of compression valve subsystem with MATLAB and acquire simulated curve of relation between fluxes and time accordingly. Through studying characteristic analysis of proportional compression valve, we can conclude that proportion...
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