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8/12/2019 Class7 Servo Hydraulics
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Class #7Servo-Hydraulic Systems
ME 4232:FLUID POWER CONTROLS LAB
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Notes Class Next Week
Data Acquisition & Controls Hardware
System Dynamics Review Assignment Due Wed/Thurs lab after break (3/21-22) Counts as a lab assignment
Upcoming Labs: Lab 14: Integrated Lab
Make-Up & Help Session
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Agenda
Feedback: Course
Servo Valves Function Characteristics
Experimental System Open-Loop System Identification Force Analysis
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Feedback: CourseLike Interesting / Hands-on
Labs Seeing Components in
Class
Explanations in Class Discussion of Research
Dislike Grading Inconsistency
Hard to Absorb all Info Want Well Defined Labs Hard to See Board in
Video Condense lectures
Suggestions Can we visit the hybrid vehicle lab?
Tuesday, 10 am
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Previously Discussed:
Directional Control Valves
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Single Stage Proportional ValvesSolenoids
Solenoids Create Spool Displacement LVDT Spool Position Feedback Spring (sometimes) for Safety
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Single Stage Proportional Valves Advantages:
Simple design
Reliable Cost effective
Disadvantages : Poor dynamic performance (bandwidth) At high flow rates and bandwidths, large stroking
force is needed
Large (and expensive) solenoids / torque motorsneeded.
Low end market ..
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Multi-stage valves
Use hydraulic force to drive the spool ..
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Electrohydraulic servo-valvePilot stage
Main stage
For a fun place to learn how a servo-valve works:R. Dolid
Electrohydraulic Valve Coloring Book
http://www.lulu.com/items/volume_67/7563000/7563085/3/print/Servovalve_Book__091207.pdf
Multi-stage valve Typically uses a flapper-nozzle pilot stage Built-in feedback via feedback wire Very high dynamic performance Bandwidth = 100-200+Hz
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Servovalves
Servo-Valve Diagrams from:Dolid, R., 2010, The Electrohydraulic Servovalve Coloring Book,(http://www.lulu.com/items/volume_67/7563000/7563085/3/print/Servovalve_Book__091207.pdf )
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Servo Valve Function
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First Stage Torque-motor-armature
A. Permanent Magnet (2) - yellowB. Wire Coil - pinkC. Armature Assembly light blueD. Upper Pole Piece light greenE. Lower Pole Piece dark green
Transforms electricalcurrent into torque,which changesrelative nozzle
pressures
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First Stage - Armature rotation
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First Stage Nozzle and Flapper
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Second Stage
J. Feedback wire orangeK. Nozzles redL. Spool dark blue
M. Filter brownN. Fixed Orifice light greenO. Variable orifice dark green
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Null Position Oil Flow path1. Supply pressure - red2. Filter pressure light blue3. Spool press. orange
4. Return press light green
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Activated Position Oil Flow Path1. Supply - red2. Filter light blue3. Spool hi-side pink4. Spool lo-side yellow
5. C1 orchid/magenta6. C2 dark blue7. Return press light green
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Servo Valve Parts
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Torque Motor Parts
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Three Stage Valve
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MTS Systems Corp 4000 gpm Valve
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Nozzle & Flapper vs. Jet Tube
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Typical Flow vs. Pressure Curve
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Servo Valve Benefits / Characteristics
Feedback from 2 nd Stage to 1 st
Low Mass Torque Motor Large P in 1 st Stage Frictionless / Isolated 1 st Stage Mechanically / Hydraulically Symmetric 300-1000 Hz Natural Frequency
Good Linearity
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Negatives
Contamination Susceptible < 3 micron filtration
High Cost
Torque motor Critically Lapped
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Servovalve vs. Proportional Valve