class7 servo hydraulics

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

class7 servo hydraulics

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