Research Papers

Design and Validation of a Soft Switch for a Virtually Variable Displacement Pump

[+] Author and Article Information
Brandon K. Beckstrand

Department of Mechanical Engineering,
University of Minnesota,
111 Church Street SE,
Minneapolis, MN 55455
e-mail: becks033@umn.edu

James D. Van de Ven

Department of Mechanical Engineering,
University of Minnesota,
111 Church Street SE,
Minneapolis, MN 55455
e-mail: vandeven@umn.edu

Contributed by the Dynamic Systems Division of ASME for publication in the JOURNAL OF DYNAMIC SYSTEMS, MEASUREMENT, AND CONTROL. Manuscript received September 23, 2015; final manuscript received September 27, 2017; published online December 22, 2017. Assoc. Editor: Umesh Vaidya.

J. Dyn. Sys., Meas., Control 140(6), 061006 (Dec 22, 2017) (11 pages) Paper No: DS-15-1460; doi: 10.1115/1.4038536 History: Received September 23, 2015; Revised September 27, 2017

Switch-mode hydraulic control is a compact and theoretically efficient alternative to throttling valve control or variable displacement pump control. However, a significant source of energy loss in switch-mode circuits is due to throttling during valve transitions. Hydraulic soft switching was previously proposed as a method of reducing the throttling energy loss, by absorbing, in a small variable volume chamber, the flow that would normally be throttled across the transitioning high-speed valve. An active locking mechanism was previously proposed that overcomes the main challenge with soft switching, which is a lock mechanism that releases quickly and with precise timing. This prior work demonstrated a reduction in energy losses by 66% compared to a control circuit. In this paper, a numerical model is developed for a switch-mode virtually variable displacement pump (VVDP) circuit, utilizing the proposed soft switch. The model is then used as a means of designing a proof of concept prototype to validate the model. The prototype design includes methods for controlling the soft switch spring preload, travel distance, piston displacement required to unlock the soft switch, valve command duty cycle, switching cycle period, and load pressure. Testing demonstrated that the soft switch circuit performed as expected in a baseline condition. The operating region for this prototype was found to be quite narrow. However, the model does a good job of predicting the displacement of the soft switch.

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Fig. 1

Soft switch concept as proposed by Van de Ven (Adapted from Ref. [9])

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Fig. 2

Virtually variable displacement pumping circuit

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Fig. 3

Graphical representation of high-speed valve spool displacement relative to tank and load port openings

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Fig. 4

Three-way valve orifice area as a function of time, with a 60% duty cycle and a period of 0.15 s

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Fig. 5

Open area of check valves corresponds to the dotted cylindrical surface area between the check valve disk and seat

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Fig. 6

Open area of the soft switch internal port to tank. The port is comprised of 6 radial holes through the cylinder sleeve.

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Fig. 7

Leakage flow paths past the soft switch piston. The path represented by the dotted line goes from the switched volume at the front of the piston to the volume behind the piston. The path represented by the dashed lines travel from the back of the soft switch to tank via two paths, as a result of the internal porting of the piston.

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Fig. 13

Experimentally measured soft switch piston displacement and pressure profiles for baseline parameters

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Fig. 12

Experimentally measured switched volume pressure profile for control case with the soft switch locked. The switched volume pressure spike reaches 9.02 MPa.

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Fig. 11

The soft switch hydraulic test circuit layout. Three pressure transducers and two flow meters gathered pertinent information regarding system behavior.

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Fig. 10

Soft switch test bed setup with component labels

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Fig. 9

Cross-sectional view of the assembled soft switch, including three-way control valve and manifold

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Fig. 8

Numerical model performance plots, showing the behavior of the soft switch for one complete switching cycle

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Fig. 14

Experimentally measured high and low system load pressure cases resulting in operation failure: (a) high load pressure of 5.72 MPa and (b) low load pressure of 5.52 MPa

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Fig. 15

Experimentally measured high and low valve switching period cases resulting in operation failure: (a) high valve switching period of 0.152 s and (b) low valve switching period of 0.138 s

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Fig. 16

Comparison between the experimental measurements and the numerical model for the baseline case

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Fig. 17

Comparison between the experimental measurements and the numerical model for the high switching period case. The switched volume pressure is not accurately predicted due to slow unlocked piston movement.



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