Class7-Servo-Hydraul..

ME 4232: FLUID POWER CONTROLS LAB Class #7 Servo-Hydraulic Systems

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: Course Like • 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 4

Previously Discussed: Directional Control Valves

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Single Stage Proportional Valves Solenoids

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Solenoids Create Spool Displacement LVDT Spool Position Feedback Spring (sometimes) for Safety 6

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 motors needed. – Low end market ….. 7

Multi-stage valves

• Use hydraulic force to drive the spool ….. 8

Electrohydraulic servo-valve • • • • •

Multi-stage valve Typically uses a flapper-nozzle pilot stage Built-in feedback via feedback wire Very high dynamic performance Bandwidth = 100-200+Hz

Pilot 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 9

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) 10

Servo Valve Function

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First Stage – Torque-motor-armature Transforms electrical current into torque, which changes relative nozzle pressures

A. Permanent Magnet (2) - yellow B. Wire Coil - pink C. Armature Assembly – light blue D. Upper Pole Piece – light green E. Lower Pole Piece – dark green 12

First Stage - Armature rotation

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First Stage – Nozzle and Flapper

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Second Stage J. Feedback wire – orange K. Nozzles – red L. Spool – dark blue M. Filter – brown N. Fixed Orifice – light green O. Variable orifice – dark green

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Null Position – Oil Flow path 1. Supply pressure - red 2. Filter pressure – light blue 3. Spool press. – orange 4. Return press – light green

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Activated Position – Oil Flow Path 1. Supply - red 2. Filter – light blue 3. Spool hi-side – pink 4. Spool lo-side – yellow 5. C1 – orchid/magenta 6. C2 – dark blue 7. 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 2nd Stage to 1st Low Mass Torque Motor Large ΔP in 1st Stage Frictionless / Isolated 1st 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

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