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TECHNICAL PAPERS

Using Steady Flow Force for Unstable Valve Design: Modeling and Experiments

[+] Author and Article Information
Qinghui Yuan

Department of Mechanical Engineering, University of Minnesota, Minneapolis, Minnesota 55455

Perry Y. Li1

Department of Mechanical Engineering, University of Minnesota, Minneapolis, Minnesota 55455pli@me.umn.edu

1

Author to whom correspondence should be addressed.

J. Dyn. Sys., Meas., Control 127(3), 451-462 (Sep 15, 2004) (12 pages) doi:10.1115/1.1997166 History: Received July 25, 2003; Revised September 15, 2004

In single stage electrohydraulic valves, solenoid actuators are usually used to stroke the main spools directly. They are cheaper and more reliable than multistage valves. Their use, however, is restricted to low bandwidth and low flow rate applications due to the limitation of the solenoid actuators. Our research focuses on alleviating the need for large and expensive solenoids in single stage valves by advantageously using fluid flow forces. For example, in a previous paper, we proposed to improve spool agility by inducing unstable transient flow forces by the use of negative damping lengths. In the present paper, how steady flow forces can be manipulated to improve spool agility is examined through fundamental momentum analysis, CFD analysis, and experimental studies. Particularly, it is found that two often ignored components—viscosity effect and non-metering momentum flux, have strong influence on steady flow forces. For positive damping lengths, viscosity increases the steady flow force, whereas for negative damping lengths, viscosity has the tendency to reduce steady flow forces. Also, by slightly modifying the non-metering port geometry, the non-metering flux can also be manipulated to reduce steady flow force. Therefore, both transient and steady flow forces can be used to improve the agility of single stage electrohydraulic valves. Experimental results confirm the contributions of both transient and steady flow force in improving spool agility.

Copyright © 2005 by American Society of Mechanical Engineers
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Figures

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Figure 1

Typical configuration of a four way direction flow control valve. The two “Q” ports are connected to the load (hydraulic actuator), Ps is connected to the supply pressure, and Pt is connected to the return. In a single stage valve the spool is stroked directly by solenoid actuators. Damping length L is defined to be L≔L2−L1.

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Figure 2

Meter-in valve chamber. The lower gray block is the control volume (C.V.) which includes all the fluid in the chamber, and is surrounded by the sleeve, rod, land ends and the inlet/outlet surfaces.

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Figure 3

Meter-out valve chamber

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Figure 4

Two fluid volume models for a given xv used in the CFD study corresponding to two damping lengths. Each model corresponds to half of the fluid in the valve. The orifice is at the right-hand side port. To model the meter-in chamber (left chamber in Fig. 1), the right-hand side port is the entry port, and the left-hand port is the outlet port. To model the meter-out chamber (right chamber in Fig. 1), the left-hand side port is the entry port, and the right-hand side port is the outlet port.

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Figure 5

Flow patterns used to estimate the jet angles for the meter-in case: (from left to right) xv=−0.635, −1.27, −1.905, and −2.54 mm

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Figure 6

Flow patterns used to estimate the jet angles for meter-out case (from left to right) xv=0.635, 1.27, 1.905 and 2.54 mm

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Figure 7

CFD computed metering orifice momentum versus ρQ2∕Ao(xv). The four clusters of data, from the lower left corner to the upper right corner, correspond to xv=0.635, 1.27, 1.905, and 2.54 mm. The dashed line is the estimate based on the least squares fit with cos(θ)∕Cc=0.454.

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Figure 8

Metering orifice fluxes as a function of damping length L, for various spool displacements xv. The dashed lines are directly obtained from CFD computation, while the solid lines are estimated using Eq. 5 based on cos(θ)∕Cc=0.454.

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Figure 9

Non-metering flow pattern with the port designed to be normal to the spool axis. Note that the flow direction for (a) is downward at the port, while the flow direction for (b) is upward at the port.

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Figure 12

CFD computed sleeve force Fsleeve as the function of μQL. The sixteen diamond points correspond to the sleeve forces computed from sixteen CFD models, and the dotted line is the least squares fit. The solid line is calculated from Eq. 7 or Eq. 14 with α computed from Eq. 8.

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Figure 13

Steady flow forces computed from various methods as a function of the orifice displacement. Four different damping lengths are considered.

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Figure 15

Steady flow forces and their estimates in a two chamber four way valve as a function of the damping length for fours sets of spool displacements. “A” takes into account non-metering flux, “B” does not take into account non-metering flux. The horizontal bars at L=0 indicate the estimates if viscosity effect is ignored.

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Figure 16

Non-metering flow pattern for a 2D CFD model with the port rotated +30° clockwise from the normal direction to the spool axis. Note that the flow direction for (a) is downward at the port, while the flow direction for (b) is upward at the port.

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Figure 17

Non-metering port flow pattern for a 2D CFD model with the port rotated -30° clockwise from the normal direction to the spool axis. Note that the flow direction for (a) is downward at the port, while the flow direction for (b) is upward at the port.

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Figure 18

The diagram of experimental setup for measuring the steady flow forces

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Figure 19

The custom-built valve allows for different (both positive and negative) damping lengths L. The valve sleeve has eleven (11) ports, fitted with quick couplers for connection to the inlets and outlets. The ports that are not connected are blocked. By connecting the supply and return to different ports, the dimensions L1 and L2 in Fig. 1 and the damping length L≔L2−L1 can be changed. Although both meter-in and meter-out chambers (see Sec. 2) can be achieved simultaneously, our experiments investigate each single chamber separately so that either L1=0 or L2=0. The spool consists of a threaded hardened precision anodized aluminum shaft on which several bronze lands can be arbitrarily positioned to be consistent with the chosen inlet/outlet locations. By connecting the inlet/outlet and actuator to the various ports, different damping lengths can be achieved. The configuration shown in Fig. 1 has only one valve chamber.

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Figure 20

Measurements (“squares” and dashed lines) and estimation (“triangles” and solid lines) of steady flow forces as a function of the damping length for various flow rates. The dashed lines are regression lines of the experimental data assuming a constant kL≔Fsteady∕∂L for each flow rate. Top: Q=2.2LPM, middle: Q=4.0LPM, bottom: Q=6.0LPM.

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Figure 21

Relationship between flow force sensitivity to damping length kL, and flow rate Q. The squares correspond to the slopes of the dashed lines in Fig. 2 that are the regression lines of the experimental data. The dashed line is the curve fit of the squares, whose slope should be αμ.

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Figure 22

Modified control volume of the valve with tapered lands. The metering orifice land area is also smaller than the area of the left hand side land. The control volume is the gray colored block.

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Figure 23

Measurements (“squares” and dashed lines) and estimation (“triangles” and solid lines) of steady flow forces as a function of the damping length for various flow rates. The estimates take into account limitation of the experimental setup via Eq. 22. The dashed lines are regression lines of the experimental data assuming a constant kL≔∂Fsteady∕∂L for each flow rate. Top: Q=2.2LPM, middle: Q=4.0LPM, bottom: Q=6.0LPM.

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Figure 24

Schematic of the experimental setup used to investigate the effect of the damping length on spool agility

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Figure 25

Current driver circuit for solenoid. “Coil” refers to the coil of the solenoid. The current through the coil is Vc∕R in which R=1.1Ω is the sensing resistor.

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Figure 26

Spool displacement trajectories for various damping lengths (from left to right: L=0.216, 0.118, −0.118, −0.216 m), when a step input of Vc=1.6V is applied at the instant t=0.5s

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Figure 27

Work done by the sum of the transient flow forces, solenoid force, and the spring force; and by the steady flow force, as functions of xv(tf) when step voltage input of Vc=1.6V is applied, for damping lengths L=±0.216m.

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Figure 11

Estimated cin and cout for various spool displacements and damping lengths L in a 2D CFD model. Top: Various xv and L=0.15m. Bottom: Various L and xv=0.645mm.

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Figure 10

Non-metering flux as a function of Q2 for the sixteen 3D CFD models. The regression lines correspond to cin=4.26×106Ns2m−6 and cout=1.79×106Ns2m−6.

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Figure 14

Steady flow forces as a function of the single chamber damping length

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