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 a significant energy consumption disadvantage due to the need to control flow and pressure by throttling flow and bypassing unused flow to pressures below the discharge pressure. An inlet metering valve-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 paper presents a theoretical model for inlet metered pump efficiency. The work considers additional sources of energy loss unique to the inlet metering system. Experimental results associated with inlet metered 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.

Pressure-compensated pumps are routinely used for supplying fluid power for hydraulic control systems. These pumps traditionally exhibit significant overshoot and oscillation before reaching a steady-state pressure condition, thus requiring the use of downstream safety valves to prevent over pressurization. In addition to over pressurizing the hydraulic control system, the response of the traditional pressure-compensated pump often induces excessive noise and creates instability for other components within the system. In this paper, a nontraditional pressure-compensated hydraulic pump is studied based upon the paradigm that has been offered by diesel-engine technology. This technology uses an inlet-metered pump to provide pressurized fuel for the high-pressure, fuel-injector rail. The analysis of this paper shows that a system of this type may be used to produce a first-order pressure response with no overshoot and oscillation, and that the characteristic time constant and settling time may be designed by specifying parameters that are identified in this research. The problem of cavitation damage is also discussed based upon preliminary testing done at the University of Missouri, and it is suggested that by using hardened machine parts cavitation damage may be prevented in these machines. In conclusion, this paper shows that continued development of the inlet-metered pump may be warranted for those applications where pressure overshoot and oscillation cannot be tolerated due to safety, noise, or other dynamical considerations.

This project developed the inlet metering system. An inlet metering system represents a new option in hydraulic pump design. Traditional pressure controlled hydraulic pumps rely on either swashplate displacement (for variable displacement pumps) or bleed off valves (for fixed displacement pumps). Variable displacement pumps require mechanically complex parts which are expensive to machine and prone to break down. Bleed off valves represent a significant loss in system efficiency. In contrast, the inlet metering system is able to make use of a fixed displacement pump (which is relatively inexpensive and mechanically robust) and a two-way spool valve. This dissertation goes through the process of designing the valve and pump dimensions, presents a theoretical dynamic analysis, studies the control law associated with this pump, and examines the energy requirements associated with inlet metering system operation. A prototype of the design was constructed and experimental data was used to validate the efficiency analysis. The major finding associated with this work was that the inlet metering system can be designed to display a first order pressure response. This means that when the inlet metering system is operated, the actual pressure in the system will never exceed the desired pressure. In contrast, traditional hydraulic systems will display up to 60% pressure overshoot, meaning the systems must be designed to handle pressures significantly greater than operating pressures. Additionally it was found that the inlet metering system is more efficient than using a bleed off valve, but less efficient than using a variable displacement pump.