Research Papers

Phase-Shift High-Speed Valve for Switch-Mode Control

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

Department of Mechanical Engineering, Worcester Polytechnic Institute, 100 Institute Road, Worcester, MA 01609vandeven@wpi.edu

Allan Katz

Department of Mechanical Engineering, Worcester Polytechnic Institute, 100 Institute Road, Worcester, MA 01609akatz@wpi.edu

J. Dyn. Sys., Meas., Control 133(1), 011003 (Nov 23, 2010) (11 pages) doi:10.1115/1.4002706 History: Received September 25, 2008; Revised June 10, 2010; Published November 23, 2010; Online November 23, 2010

Hydraulic applications requiring a variation in the speed or torque of actuators have historically used throttling valve control or a variable displacement pump or motor. An alternative method is switch-mode control that uses a high-speed valve to rapidly switch between efficient on and off states, allowing any hydraulic actuator to have virtually variable displacement. An existing barrier to switch-mode control is a fast and efficient high-speed valve. A novel high-speed valve concept is proposed that uses a phase shift between two tiers of continuously rotating valve spools to achieve a pulse-width modulated flow with any desired duty ratio. An analysis of the major forms of energy loss, including throttling, compressibility, viscous friction, and internal leakage, is performed on a disk spool architecture. This analysis also explores the use of a hydrodynamic thrust bearing to maintain valve clearance. A nonoptimized design example of a phase-shift valve operating at 100 Hz switching frequency at 10 l/min demonstrates an efficiency of 73% at a duty ratio of 1 and 64% at 0.75 duty ratio. Numerous opportunities exist for improving this efficiency including design changes and formal optimization. The phase-shift valve has the potential to enable switch-mode hydraulic circuits. The valve has numerous benefits over existing technology yet requires further refinement to realize its full potential.

Copyright © 2011 by American Society of Mechanical Engineers
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Figure 1

Hydraulic circuit for a series hydraulic hybrid vehicle with four-quadrant operation of a fixed displacement pump/motor to make a virtually variable displacement unit. The high-speed three-way valve controls the virtual displacement and thus the torque, while the four-way directional valve controls the torque direction. The check valves are used to minimize pressure spikes during valve transitions, as discussed in Sec. 2.

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Figure 9

Thrust bearing schematic with defined dimensional variables. Through a cut-away in the valve disk, subfigure (a) shows the thrust bearing pads as arranged on the inside of the valve ports. Subfigure (b) gives dimensions for the fixed-incline thrust bearing pads.

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Figure 10

A plot of the viscous torque due to the hydrodynamic thrust bearing as a function of the height of the inclined plane. Note that the torque required increases significantly when departing from the minima at sh=15 μm.

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Figure 11

Instantaneous power loss due to throttling for a single valve rotation when the hydraulic unit is acting as a motor. Note that the throttling through the high-speed valve during the opening and closing of the pressure branch dominates the power loss contributions.

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Figure 12

The viscous power loss components as a function of valve disk rotating frequency. Note the dominance of the viscous losses on the port plate due to the larger acting radius.

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Figure 2

Schematic representation of the phase shift switching valve at two phases of rotation. Each valve section directs flow from one of the two input ports to a single output port by the rotating valve spool, shown in gray. For clarity, the flow path through the valve for the current positions in subfigures (a) and (b) is highlighted. Note that subfigure (b) has rotated π/2 rad past subfigure (a). The architecture shown creates a two-position three-way valve with two full switches per rotation cycle.

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Figure 3

Plot of the flow diversion in the various sections of the valve during a full rotation for a given phase shift. Note that sections 1A and 1B remain synchronized during operation. Shifting the phase angle between the tier 1 sections and section 2 controls the duty ratio of the valve, observable in the bottom plot of the figure. The port labels correspond to those in Fig. 2. Gray areas denote when section 2 is receiving flow from the tier 1 section.

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Figure 4

Schematic of the two tier valve where the previously divided first tier valve sections are combined into a single section. The first tier section has two outputs, port 2b entering the center of the spool and passing through an internal passage to the upper right region of valve section 1 and port 2a entering a groove outside the center of the spool and connecting to the lower left region of the section 1 valve.

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Figure 5

Simplified high-speed valve and check valves used for analysis purposes. The two check valves have been added to avoid extreme pressure fluctuations occurring when flow is completely blocked during valve transitions.

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Figure 6

Annotated schematic of the disk style three-way phase-shift valve geometry. Fluid enters a valve section through the fixed port when it is unobstructed by the valve spool. Fluid leaves each valve section through a center port.

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Figure 7

Open area of the internal ports of the valve as a function of the rotation angle. The areas of the tier 1 ports are displayed in the top plot, while the lower plot shows the area of the tier 2 ports. Note the phase shift of π/4 rad between the first and second tier ports.

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Figure 8

Flow through and pressure drop across the high-speed valve in motoring mode. The bottom subfigure is a zoomed plot of the center subfigure, highlighting the smaller magnitude pressure drop corresponding to the switches to the tank branch.



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