Class #7Servo-Hydraulic SystemsME 4232:FLUID POWER CONTROLS LAB2Notes• 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 Session3Agenda• Feedback: Course• Servo Valves– Function– Characteristics– Experimental System– Open-Loop System Identification– Force Analysis4Feedback: CourseLike• Interesting / Hands-on Labs• Seeing Components in Class• Explanations in Class• Discussion of ResearchDislike• Grading Inconsistency• Hard to Absorb all Info• Want Well Defined Labs• Hard to See Board in Video• Condense lecturesSuggestions• “Can we visit the hybrid vehicle lab?”− Tuesday, 10 am5Previously Discussed: Directional Control Valves6Single Stage Proportional ValvesSolenoids• Solenoids Create Spool Displacement• LVDT Spool Position Feedback• Spring (sometimes) for Safety7Single 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 …..8Multi-stage valves• Use hydraulic force to drive the spool …..9Electrohydraulic servo-valvePilot stageMain stageFor 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+Hz10ServovalvesServo-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)11Servo Valve Function12First Stage – Torque-motor-armatureA. Permanent Magnet (2) - yellowB. Wire Coil - pinkC. Armature Assembly – light blueD. Upper Pole Piece – light greenE. Lower Pole Piece – dark greenTransforms electrical current into torque, which changes relative nozzle pressures13First Stage - Armature rotation14First Stage – Nozzle and Flapper15Second StageJ. Feedback wire – orangeK. Nozzles – redL. Spool – dark blueM. Filter – brownN. Fixed Orifice – light greenO. Variable orifice – dark green16Null Position – Oil Flow path1. Supply pressure - red2. Filter pressure – light blue3. Spool press. – orange4. Return press – light green17Activated Position – Oil Flow Path1. Supply - red2. Filter – light blue3. Spool hi-side – pink4. Spool lo-side – yellow5. C1 – orchid/magenta6. C2 – dark blue7. Return press – light green18Servo Valve Parts19Torque Motor Parts20Three Stage Valve21MTS Systems Corp – 4000 gpm Valve22Nozzle & Flapper vs. Jet Tube23Typical Flow vs. Pressure Curve24Servo Valve Benefits / Characteristics• Feedback from 2ndStage to 1st• Low Mass Torque Motor• Large ΔP in 1stStage• Frictionless / Isolated 1stStage• Mechanically / Hydraulically Symmetric• 300-1000 Hz Natural Frequency• Good Linearity25Negatives• Contamination Susceptible– < 3 micron filtration• High Cost– Torque motor– Critically Lapped26Servovalve vs. Proportional