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Technical Briefs

Soft Switching Approach to Reducing Transition Losses in an On/Off Hydraulic Valve

[+] Author and Article Information
Michael B. Rannow

Center for Compact and Efficient Fluid Power, Department of Mechanical Engineering,  University of Minnesota, Minneapolis, MN 55455rann0018@umn.edu

Perry Y. Li1

Center for Compact and Efficient Fluid Power, Department of Mechanical Engineering,  University of Minnesota, Minneapolis, MN 55455pli@me.umn.edu

1

Corresponding author.

J. Dyn. Sys., Meas., Control 134(6), 064501 (Sep 24, 2012) (6 pages) doi:10.1115/1.4006620 History: Received August 24, 2009; Revised March 07, 2012; Published September 24, 2012

A method for significantly reducing the losses associated with an on/off controlled hydraulic system is proposed. There has been a growing interest in the use of on/off valves to control hydraulic systems as a means of improving system efficiency. While on/off valves are efficient when they are fully open or fully closed, a significant amount of energy can be lost in throttling as the valve transitions between the two states when the switching times are not negligible. A soft switching approach is proposed as a method of eliminating the majority of these transition losses. The operating principle of soft switching is that fluid can temporarily flow through a check valve or into a small chamber while valve orifices are partially closed. The fluid can then flow out of the chamber once the valve has fully transitioned. Thus, fluid flows through the valve only when it is in its most efficient fully open state. A model of the system is derived and simulated, with results indicating that the soft switching approach can reduce transition and compressibility losses by 81% and total system losses by 64%. The soft switching approach has the potential to improve the efficiency of on/off controlled systems and is particularly beneficial as switching frequencies are increased. The soft switching approach will also facilitate the use of slower on/off valves for effective on/off control; in simulation, a valve with soft switching matched the efficiency of an on/off valve that was 4.4 times faster.

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Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Virtual variable displacement pump using a three-way on/off valve

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Figure 2

Three-way circuit with split tank and load valves, check valve, and soft switch

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Figure 3

Area profiles for 1 PWM period

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Figure 4

Inlet pressure profile for a three-way circuit with a relief valve

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Figure 5

Diagram of the soft switch chamber

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Figure 6

Power loss over 1 PWM period for a system with a relief valve

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Figure 7

Power loss over 1 PWM period for a system with a check-valve-only

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Figure 8

Pressure profile for a system with soft switching

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Figure 9

Flow rates in a soft switching system

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Figure 10

Position of the soft switch piston over 1 PWM period

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Figure 11

Power loss over 1 PWM period for a system with soft switching

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Figure 12

Reduction in energy lost/switch (J) from the check valve to the soft switching case

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