| The independent metering technique can separately control the meter-in and meter-out orifices of actuator by adopting two spools. And it can simultaneously improve the controllability and energy-saving effect for hydraulic system by increasing system control degrees of freedom, which is difficult for other methods. Currently, the electro-hydraulic proportional valve or servo valve is widely used in the research of hydraulic system, and the control signal is analog.As a new hydraulic component, digital valve can be connected to computer directly without D/A converter. At the same time the digital valve has become a development trend of hydraulic control system for its advantages of simple structure, good manufacturability, strong anti-jamming and anti-pollution ability, and stable reliability. Currently, the high-speed on-off valve is widely used, but it can only be applied to pilot control and the small flow control for its limitation of structure. This paper presents a new kind of digital pilot flow amplification valve, of which the pilot stage is digital valve and the main stage is Valvistor valve. And the new valve is applied to the independent metering control system to achieve requirements of controllability and energy-saving for valve controlled cylinder system, which can lay a foundation for intelligent control of the hydraulic system.In this paper, the pilot stage of the new digital pilot flow amplification valve is HSV3143S3 which is two way three port and normally closed, made by Guizhou Honglin Machinery CO., LTD, and the main stage is cartridge structure with 16 DN Valvistor made by VICKERS, and the flow control of the new valve can be achieved by controlling duty ratio of digital pilot stage.The model of digital pilot flow amplification valve is established in multi-disciplinary co-simulation software SimulationX and the flow-duty ratio characteristics is studied. And the experiment is carried out to obtain the flow-displacement characteristics of main stage and flow-duty ratio characteristics of pilot stage, so the correctness of the simulation model can be verified. And then the accuracy of the simulation model for digital flow valve is improved by optimal correction.In order to achieve the compound control of pressure and flow when hydraulic cylinder is under different working mode, the hydraulic circuit with independent metering system constituting of six new digital pilot amplification flow valves and three check valves is proposed according to flow control characteristics.According to feedforward-feedback compound control strategy, flow feedback of the system can be achieved by the calculation of the flow feedback method. The simulation model is established according to the system control principle. And according to cylinder control characteristic under power extension mode and high side regeneration extension mode, the piston rod velocity control characteristic is researched during the process of starting, velocity response and load response. And it is verified that the velocity of hydraulic cylinder can be controlled by the independent metering system based on digital pilot flow amplification valve. Through theoretical analysis and simulation it can be concluded that the new flow valve can reach optimal control for hydraulic cylinder when carrier frequency is 125Hz, flow valve inter-stage cavity is 1L, and the main valve pre-opening amount is 0.4mm. |
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