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Research Papers

Soft Switch Lock-Release Mechanism for a Switch-Mode Hydraulic Pump Circuit

[+] Author and Article Information
James D. Van de Ven

Department of Mechanical Engineering,
University of Minnesota,
111 Church St. SE,
Minneapolis, MN 55455

Contributed by the Dynamic Systems Division of ASME for publication in the JOURNAL OF DYNAMIC SYSTEMS, MEASUREMENT, AND CONTROL. Manuscript received December 4, 2012; final manuscript received December 11, 2013; published online January 29, 2014. Assoc. Editor: Evangelos Papadopoulos.

J. Dyn. Sys., Meas., Control 136(3), 031003 (Jan 29, 2014) (12 pages) Paper No: DS-12-1401; doi: 10.1115/1.4026327 History: Received December 04, 2012; Revised December 11, 2013

Switch-mode hydraulic circuits are a theoretically efficient, compact, fast responding, and inexpensive control option. Despite the many potential benefits of switch-mode hydraulic circuits, the control method suffers from large energy losses during transitions of the high-speed valve due to throttling and fluid compressibility. Rannow and Li previously proposed utilizing soft switching to minimize the throttling energy loss (Rannow and Li, “Soft Switching Approach to Reducing Transition Losses in On/Off Hydraulic Valve,” J. Dyn. Syst., Measure. Control (in press)). A major challenge of this approach is a locking soft switch that releases quickly and with precise timing, while under load. In this paper, a novel soft switch locking mechanism is presented that utilizes the pressure signal in the switched volume to trigger the release. A dynamic model is developed of three unique soft switch circuits and two control circuits that create a virtually variable displacement pump. The model is used to perform a grid search optimization of the soft switch parameters for the three circuits. The three soft switch circuits reduce the throttling and compressibility energy losses between 49% and 66% compared with the control circuit. The simulation results demonstrated that the soft switch circuits perform as expected for duty cycles and pressures below the design conditions. At higher duty cycles and pressures, the short time the circuit is connected to tank prevented the soft switches from resetting between cycles, preventing proper function. This novel lock and release soft switch mechanism enables soft switching in switch-mode hydraulic circuits, which significantly reduces throttling and compressibility energy losses during valve transitions. Lower losses during valve transition allow the use of slower switching valves, lowering energy consumption, and cost.

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References

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Figures

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Fig. 1

Circuit (a) is a generic virtually variable displacement pump circuit. Circuit (b) is equivalent to circuit (a), but uses two 2-way valves instead of a single 3-way valve. The relief valve and check valve illustrate two ways of reducing pressure rises during valve transitions. Circuit (c) illustrates the soft switching concept.

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Fig. 2

Cross-sectional view of the novel soft switch lock and release mechanism

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Fig. 3

Diagrams of the virtually variable displacement pump soft switch circuits a–c

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Fig. 4

Illustrating the implementation of the pressure-release soft switch concept on a virtually variable displacement motor circuit

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Fig. 5

High-speed valve orifice areas as a function of time during a switching period with a duty cycle of 60%. The vertical gridlines correspond with the beginning and end of each phase of the valve transition.

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Fig. 6

Simulation results for the relief valve circuit illustrating the pressure in the switched volume, flow rate through the various valves, and throttling power loss as a function of time during a single switching cycle at a duty cycle of 60%. Note, the vertical gridlines mark the beginning and end of the valve transitions shown in Fig. 5.

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Fig. 7

Results of the simulation for the circuit with a check valve in parallel with the pressure valve at a duty cycle of 60%

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Fig. 8

Simulation results for the soft switch circuit using the diaphragm, Fig. 3(a), at 60% duty cycle

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Fig. 9

Simulation results for the soft switch circuit illustrated in Fig. 3(b) at 60% duty cycle

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Fig. 10

Simulation results for the soft switch circuit illustrated in Fig. 3(c) at 60% duty cycle

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Fig. 11

Energy loss during one second of operation for the five circuits as a function of duty cycle

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Fig. 12

Fraction of energy loss versus the fraction of energy delivered to the high pressure rail for the five circuits

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