The Electrohydraulic Servovalve Coloring Book. Rosamond Dolid, PMP MTS Systems Corporation

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1 The Electrohydraulic ervovalve Coloring Book Rosamond Dolid, PMP MT ystems Corporation 2010

2 Acknowledgements The CAD rendering and drawings were contributed by Nathan Milner and Kristin Haag, undergraduate mechanical engineering students at the University of Minnesota. Content review was provided by Professor Will Durfee, Department of Mechanical Engineering, University of Minnesota. Permission to reproduce photographs was granted by MT ystems Corporation and by Moog Inc. upport for this project was provided by MT ystems Corporation and by the Center for Compact and Efficient Fluid Power, an NF Engineering Research Center. For information on this project, contact the author, Roz Dolid at 2

3 About this book This purpose of this book is to facilitate understanding of a basic electrohydraulic servovalve. This is not a guide to valve design, nor does it provide proprietary information regarding design or manufacturing of valves. The primary audience for this book is degreed engineers working in the fluid power industry who may not have received a fluid power education or who may not be familiar with servovalves. Versions of this book have been used to train newly hired engineers at MT ystems Corporation since The underlying concept of this book is that the act of coloring components helps your brain to fully understand where those components are located and how they contribute to the operation of the valve. The inspiration to use coloring as a means to understand complex ideas is The Anatomy Coloring Book by Kapit and Elson, which has long been used by medical school students to deepen their understanding of how the human body works. o, grab your colored pencils or crayons and get started! Twelve colors are sufficient to complete this book, by re-using each color once. Twenty-four colors are enough for every item to have its own color throughout the book. Colored pencils are a better choice than crayons or markers. Use the same color for the same part throughout the book as much as possible this allows the color itself to be a memory trigger for the part it is associated with. For the first part of the book, which covers servovalve components, choose distinct colors for adjacent parts. Later, when coloring in the oil flow paths, color represents a pressure state. Choose a color sequence that shows pressure level in an order that makes sense, for example a light spectrum sequence of red, orange, yellow, green, blue, purple. 3

uni-directional or reciprocating mechanical motion. ervovalves were invented during the late 1940 s for military use.

4 Introduction: What is a ervovalve? An electrohydraulic servovalve is a device that takes an electrical current and turns it into hydraulic flow which can then create linear, rotational, uni-directional or reciprocating mechanical motion. ervovalves were invented during the late 1940 s for military use. In the 1960 s MT ystems Corporation began using servovalves in displacement and force controlled test equipment. There are several types of servovalves, including the flapper nozzle style 4-way valve, which is presented in this book. Two stage MT valve built by Moog, Inc Three stage MT valve, with two stage Moog valve used as the pilot stage 4

5 First tage: Armature assembly A. Permanent Magnet (2) B. Wire Coils (2) C. Armature Assembly D. Upper Pole Piece E. Lower Pole Piece A B F. Ferrous Core or Armature G. Flexure Tube H. Flapper J. Feedback Wire K. Nozzles D B B E C C C C K K A F F F F F H G H J Armature Detail The first stage of an electrohydraulic servovalve converts the input electrical current signal into a hydraulic flow. 5

6 First tage: Flapper-Nozzle Interaction G G Null K K H G G Activated K K H Use the same color for these parts as on the previous page. Notice that the flapper on the activated valve is closer to the nozzle on the left, which throttles the flow running through the left nozzle. 6

7 econd tage: Components J L L L L L L M M N M M N J. Feedback Wire L. pool M. Filter N. Fixed Orifice O. Variable Orifice Notes: 1. Use brown or black for the filter 2. The variable orifices in this view are closed so there is no space to color. Pages following will reveal the orifices. 7

8 econd tage: pool Features Q Q Q Q R R Q. The wider portions of the spool are called lands. R. The precision machined edges that define the variable orifice openings are called metering edges. Only two metering edges are visible in this drawing. 8

9 econd tage: Variable Orifices When the valve is in its null position, all of the variable orifices are closed. There is a small amount of leakage through this type of valve even in the null position, which must be taken into account when sizing a system for an application. O O When the valve is activated by a command signal, some of the variable orifices open while others remain closed. The arrows indicate the direction of oil flow through the open orifices. O O. Variable orifice 9

10 Full Valve: Oil Pressures Null Position U U Y Y W W W W U U Y W T W T T T Color in the pressure legend according to the colors used in the picture. upply pressure T. Filter pressure U. pool pressure W. Working pressure Y. Return pressure Notes: 1. Color the filter brown or black 2. Working pressures are equal so there is no flow to the next device (actuator or spool) 10

11 Full Valve: Oil Pressures Activated Position U V Y O Y X W U X O W O Y X T T T T W V Color in the pressure legend according to the colors used in the picture. upply pressure T. Filter pressure U. Higher pool pressure V. Lower pool pressure W. C1 working pressure X. C2 working pressure Y. Return pressure O. Variable Orifice Notes: 1. Color the filter brown or black 2. Use the same color for variable orifices as previous pages 11

12 Full Valve: Oil Flows Using one color, draw the path of an oil particle traveling through the valve when the valve is in the null (top) and activated (bottom) positions, remembering that there are four different pathways for an oil particle to travel through when the valve is activated. 12

ervovalve Parts 1 3 4 2 5 1. pool 2. Nozzle 3. Fixed Orifice 4.

13 ervovalve Parts pool 2. Nozzle 3. Fixed Orifice 4. Tubular Filter 5. Disc Filter Courtesy of MT ystems Corporation 13

Torque Motor Armature Assembly 2 4 3 1 1. Upper and lower pole pieces 2.

14 Torque Motor Armature Assembly Upper and lower pole pieces 2. Permanent magnet 3. Electromagnet coil 4. Feedback wire Courtesy of MT ystems Corporation 14

Torque Motor Assembly 1 3 2 4 1. Torque motor armature assembly with signal connector 2. Permanent magnet 3.

15 Torque Motor Assembly Torque motor armature assembly with signal connector 2. Permanent magnet 3. Electromagnet coil 4. Armature/flexure tube/flapper/feedback wire assembly Courtesy of MT ystems Corporation 15

Three tage ervovalve 1 3 2 4 1. Torque motor armature assembly 2. 2 nd stage spool 3.

16 Three tage ervovalve Torque motor armature assembly 2. 2 nd stage spool 3. Manifold block (porting between 2 nd and 3 rd stage spools) 4. 3 rd stage spool Courtesy of MT ystems Corporation 16

17 ervovalve and Hydraulic Piston Actuator Courtesy of MT ystems Corporation 17

18 References 1. Dolid, R., "What Makes a Bicycle? A Coloring Activity to Teach Basic Mechanical Concepts presented at the 2006 AME International Mechanical Engineering Congress and Exposition, November 5-10, 2006, Chicago, IL. 2. Kapit, W. and L. Elson, The Anatomy Coloring Book, 3 rd ed., Benjamin Cummings, Merritt, H.E., Hydraulic Control ystems, New York, John-Wiley & ons, Moog Inc., Electrohydraulic Valves, a Technical Look, 5. Wang, D., Dolid, R., Donath, M. and Albright, J., Development and Verification of a Two- tage Flow Control ervovalve Model, presented at the 1995 AME International Mechanical Engineering Congress and Exposition, November 12-17, 1995, an Francisco, CA. 18

LECTURE 27 SERVO VALVES FREQUENTLY ASKED QUESTIONS

LECTURE 27 SERVO VALVES FREQUENTLY ASKED QUESTIONS 1. Define a servo valve Servo valve is a programmable orifice. Servo valve is an automatic device for controlling large amount of power by means of very