Digital hydraulic systems : a theoretical comparative efficiency analysis of hydraulic systems with real pump models
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[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI SYSTEM AT REQUEST OF AUTHOR.] Digital hydraulic systems are a highly disputed technology in the field of fluid power. A digital hydraulic system controls load flow using a fixed-displacement pump and a digital pulse-width modulation (PWM) valve instead of using a variable displacement pump, like other common control systems. The digital valve, also known as an on-off valve, intermittently changes between completely closed and wide-open position through operator input or a control system that alters the valve duty-ratio. This type of operation theoretically increases system efficiency by reducing the throttling losses experienced in traditional valves when the valve is partially opened to the load. Much work has been done to improve efficiency of the digital valve designs, but very little research has been done to compare the efficiency of these systems to conventional systems to see if the technology is worth investigating. The only comparative efficiency analysis performed included an ideal pump model, which does not account for losses in the input power to the hydraulic system. This paper will derive the governing equations of digital hydraulic system efficiency with a real pump model, then compare it to the conventional pressure relief, pressure compensating, and load sensing systems. A numerical code is also written to analyze and plot the efficiency of all systems to determine the ideal operating regimes for each system. It is revealed that the load sensing system dominates the other three systems for most operating conditions. However, in high pressure applications, the pressure relief and pressure compensating systems are favorable. The digital on-off system has the highest efficiency for low pressure, high flow operating conditions.
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