Modeling and analysis of active valve control of a digital pump-motor

Kyle Joseph Merrill, Purdue University

Abstract

This work involves the development of a hydraulic pump/motor that incorporates actively controlled high speed on/off valves connected to each piston cylinder displacement chamber. The fluid is commutated between the ports and the displacement chamber by the on/off valves and there is no longer a need for the valve plate. Unit displacement is electronically controlled by on/off valve timing, not by a swash plate or other typical means. Pump/motors of this design can have increased efficiency due to reduction of friction, leakage, and compressibility losses as well as increased displacement control bandwidth. A unique contribution of this work is the development of a coupled dynamic model of a digital hydraulic pump/motor that is crucial for understanding the design tradeoffs and operating characteristics. The simulation model is used to characterize and predict pump/motor efficiency, define the dynamic response and flow requirements of on/off valves required to provide significant improvements in efficiency and dynamic response over traditional pump/motors, and perform design optimization studies. Different operating strategies have been analyzed to characterize the effects on pump/motor efficiency and flow ripple (valve timing effects, partial fill methods, etc.). A three-piston pump/motor unit was used to experimentally validate the model, design, and operating strategies of a digital pump/motor. For a digital pump/motor with direct acting valves, sequential flow-limiting showed the best efficiency followed closely by sequential flow-diverting and partial flow-limiting. The partial flow-diverting method had the worst efficiency results. The key enabling technology for the digital pump/motor is the on/off valves. The largest simulated losses were due to the throttling across the valves and the electrical energy consumption required too actuate the valves.

Degree

Ph.D.

Advisors

Lumkes, Purdue University.

Subject Area

Agricultural engineering|Mechanical engineering

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