Inlet metering pump analysis and experimental evaluation with application for flow control
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Axial piston pumps with variable volumetric displacement are often used to control flow and pressure in hydraulic systems. The displacement control mechanism in these pumps occupies significant space and accounts for significant cost in the pump design. Fixed displacement pumps have lower cost and a more compact design but suffer from significant energy consumption disadvantage due to the need for flow and pressure control by throttling flow and bypassing unused flow to pressures below the discharge pressure. An inlet metering valve (IMV) controlled pump marks a recent development in pumping technology for hydraulic systems. In this design, an inlet metering valve restricts inlet flow reducing inlet pressure so that the specific volume of the fluid is increased as it enters a fixed displacement pump. By altering the specific volume of the working fluid, the inlet metering valve permits precise control over the pump discharge flow. This study presents a theoretical model for inlet metering pump efficiency. The work considers additional sources of energy loss unique to the inlet metering system. Experimental results associated with inlet metering pump efficiency are presented. A comparison of the theoretical model and the experimental results is also included. It is determined that the current efficiency model accurately predicts efficiencies determined using experimental data. In addition, a velocity control system is considered which utilizes the inlet metering valve controlled pump. The stability and the performance of the velocity control system were studied for the open-loop and the closed-loop with a PID, H∞, and a two degrees of freedom controllers. The simulation showed that the velocity control system is stable and has good performance characteristics.
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