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Technical Briefs

Analysis and Synthesis of Spool Valves With Arbitrary Metering Area Variation

[+] Author and Article Information
Zongxuan Sun

e-mail: zsun@umn.edu
Mechanical Engineering Department,
University of Minnesota,
Minneapolis, MN 55455

1Corresponding author.

Contributed by the Dynamic Systems Division of ASME for publication in the Journal of Dynamic Systems, Measurement, and Control. Manuscript received April 24, 2012; final manuscript received April 21, 2013; published online July 3, 2013. Assoc. Editor: Nariman Sepehri.

J. Dyn. Sys., Meas., Control 135(5), 054503 (Jul 03, 2013) (11 pages) Paper No: DS-12-1119; doi: 10.1115/1.4024364 History: Received April 24, 2012; Revised April 21, 2013

This paper presents a systematic method for analyzing and designing the notches on the spool of a flow control valve to influence the area-schedule, i.e., relationship between the spool position and the metering area. The motivation for such a flow control valve comes from a novel hydraulic actuator intended for camless valve actuation in internal combustion engines. The proposed actuator has a unique hydromechanical internal feedback system in which the motion of the flow regulator's spool is directly coupled to the motion of the actuator. Lack of direct control of the spool position necessitates the appropriate modification of the spool design in order to control the variation of the effective area across the valve. The design modifications required to realize the desired area-schedules are first discussed. A systematic procedure which combines computational fluid dynamics (CFD) analysis and geometry based analysis is then developed to characterize the variation of the effective area for various spool designs. It is shown that the mean area available for the fluid flow through the entire notch serves as a better approximation of the metering characteristics when compared to the traditional approach of using the minimum area. The proposed analysis procedure is validated with experimental data from a prototype spool valve. The fast turn around time of the proposed analysis technique is then used to develop an automated procedure to design the 3D features (notches) on the spool required to realize any specified area-schedule.

Copyright © 2013 by ASME
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References

Figures

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Fig. 1

Electrohydraulic engine valve actuation system: (a) schematic, (b) corresponding control block diagram

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Fig. 2

Schematic of a spool valve: (a) conventional design, (b) modified design with notches on the spool lands

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Fig. 3

CAD model showing the valve body and the spool with the notches

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Fig. 4

(a) 1/6th of the fluid volume corresponding to the spool and the valve body illustrating the metering geometry, (b) fluid volume corresponding to a displaced spool

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Fig. 5

(a) The discretized fluid volume (mesh) and the boundary conditions, (b) simulation results showing the path and speed of the fluid in various sections of the valve

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Fig. 6

(a) Variation of mass flow rate at different pressure drops, (b) effective area calculated using the orifice equation

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Fig. 7

Various notch geometries analyzed using the CFD based method

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Fig. 8

The effective areas corresponding to the notches shown in Fig. 7

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Fig. 9

Pressure distribution inside the valve for both configurations (a) centered spool, (b) deflected spool

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Fig. 10

Data required for the geometric analysis (a) region exposed to the groove in the valve body for the center position, (b) region corresponding to 50% spool deflection

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Fig. 11

(a) Nomenclature used in the analysis of the notch geometry, (b) sample cross-sections corresponding to various values of θ overlaid on the notch geometry

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Fig. 12

(a) Comparison of the cross-sections, (b) cross-sectional area-variation as a function of θ for each value of spool deflection x

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Fig. 13

The values predicted by the “min” approximation: (a) metering areas, (b) discharge coefficients

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Fig. 15

The variation of discharge coefficient with respect to the Reynolds number for (a) the “min” approximation, (b) the “mean” approximation

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Fig. 14

The values predicted by the “mean” approximation: (a) metering areas, (b) discharge coefficients

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Fig. 16

(a) The experimental test setup for characterizing the spool with notches, (b) comparison of the effective orifice area obtained from the experiment and the CFD based analysis

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Fig. 17

(a) The metering area calculated using the two approximations from the geometric analysis procedure, (b) The corresponding estimated discharge coefficient

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Fig. 18

Illustration of the axisymmetric notch design (a) 2D representation, (b) 3D feature

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Fig. 19

Method for calculating the notch design for a given area-schedule: (a) Flow chart for the overall procedure, (b) illustration of the process for updating the estimate of the notch radius, (c) corresponding 3D notch geometry

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Fig. 20

(a) Notch radii obtained from the design procedure, the corresponding 3D geometry for case 1 (b) and case 2 (c)

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Fig. 21

Comparison of the area-schedules (desired and actual) for (a) case 1 and (b) case 2

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