Lecture Note 8-1 Hydraulic Systems 1
Vehicle Model - Brake Model Brake Model Font Wheel Brake Pedal Vacuum Booster Master Cylinder Proportionnig Valve Vacuum Booster Rear Wheel Master Cylinder Proportioning Valve Brake Pedal Fundamental structure of a hydraulic brake 2
Conservation of Mass, Force and Pressure m q q mi mo i) Volume A dx A dx dx A 1 2 1 A2 iii) Force f p A f 1 1 2 2 dx ii) Pressue p p gh 1 1 1 2 1 pa 2 2 2 A f f ( P P) 2 2 1 1 2 A1 L L A f f f 1 1 2 3 2 1 L2 L2 A1 3
Hydraulic Excavator Arm Dump Boom Up Arm Crowd Bucket Crowd Boom Down Swing( 선회 ) Bucke t Dump Travel( 주행 ) 4
유압굴삭기회로도 5
Hydraulic Brake Systems Brake System 1 ) Wheel Cylinder 2 ) Brake Light 3 ) Brake Pedal 4 ) Rear Brake Lines 5 ) Stop Light Switch (Mechanical) 6 ) Front/Rear Balance Valve 7 ) Pressure Differentiavl Valve 8 ) Brake Warning Lamp 9 ) Brake Fluid 10) Brake Pad 11) Master Cylinder 6
Vehicle Model - Brake Model Brake Model Font Wheel Brake Pedal Vacuum Booster Master Cylinder Proportionnig Valve Vacuum Booster Rear Wheel Master Cylinder Proportioning Valve Brake Pedal Fundamental structure of a hydraulic brake 7
Applications of Fluid Power Pneumatically controlled dexterous hand Space shuttle Columbia Hydraulically powered dexterous arm Space shuttle vehicle 8
Applications of Fluid Power Hydraulically powered Sky-tram Hydraulic power brush drive Hydraulically driven turntable Oceanography 9
Automatic Transmission 10
Press 11
Linear Actuators Motion Simulator Press Airplane Robot 12
Hydraulic Systems : Landing Gear System Landing gear system of AIRBUS A330 13
Hydraulic Systems Hydraulic pump Control valve Tank P1 P2 Load Hydraulic actuator (70 ~ 210 bar) F A ( P ) P 1 P2 14
Why hydraulic? Internal combustion Engine Turbine Electric motor Hydraulic actuator 15
Why hydraulic? 1. smaller and lighter horsepower to weight ratio > 2 hp/lb 2. heat/lubrication long component life 3. no saturation and losses - saturation and losses in magnetic materials of electrical machine - torque limit only by safe stress levels 4. high natural frequency/high speed of response/high loop gains - electrical motors, a simple lag device from applied voltage to speed 5. dynamic breaking with relief valve without damage 16
Disadvantages 1. not so readily available 2. small allowable tolerances result in high costs 3. hydraulic fluids imposes upper temperature limit. 4. fluid contamination: dirt and contamination 5. basic design procedures are lacking and difficult, complexity of hydraulic control analysis 6. not so flexible, linear, accurate, and inexpensive as electronic and/or electromechanical devices 17
Primary Functions of a Hydraulic Fluid 18
Conservation of Mass, Force and Pressure m q q mi mo i) Volume A dx A dx dx A 1 2 1 A2 iii) Force f p A f 1 1 2 2 dx ii) Pressue p p gh 1 1 1 2 1 pa 2 2 2 A f f ( P P) 2 2 1 1 2 A1 L L A f f f 1 1 2 3 2 1 L2 L2 A1 19
Gear Pumps (External) fixed displacement pump uses spur gear (teeth are parallel to the axis of the gear) noisy at relatively high speeds 20
Internal Gear Pump 21
Internal Gear Pump Gerotor Pump 22
Internal Gear Pump Lobe Pump 23
Simple Vane Pump 24
Balanced Vane Pump 25
Piston Pump (Swash Plate Type) 26
Piston Pump 27
Pump Electric Motor or Engine 28
Hydraulic Pump the heart of a hydraulic system converts mechanical energy into hydraulic energy hydrostatic pump Displacement the amount of fluid ejected per revolution unit: cm 3 /rev, cc/rev, cm 3 /rad, cc/rad 29
Pump Torque Mechanical power supplied to pump H m T Hydraulic power delivered by pump Therefore H p PQ P : pressure rise across the pump Q : delivery rate T PQ P D T th th p th PD p 여기서D p : 펌프배제용적[ m3/ rad] 30
Hydraulic Motors and Actuators 31
Hydraulic Systems : Valve-motor Combination 32
Application of Hydraulic Motors 33
Gear Motors 34
Hydraulic Systems : Valve-piston Combination Valve-piston combination 35
Hydraulic Excavator Arm Dump Boom Up Arm Crowd Bucket Crowd Boom Down Swing( 선회 ) Bucke t Dump Travel( 주행 ) 36
Hydraulic Excavator 37
Automotive Application Active Suspension 38
Rough terrain forklift driven by hydraulic cylinders 39
Double-acting Cylinder Design 40
Cylinder Construction 41
Types of Valves: shearing elements 42
Types of Valves: seating elements 43
Directional Control Valve 44
Hydraulic Systems : Single Stage Electrohydraulic Servovalve Schematic of a single stage electrohydraulic servovalve connected to a motor with inertia load 45
Solenoid-Actuated Valves Solenoid-actuated, three-position, spring-centered, four-way, directional control valve Single solenoid-actuated, two-position, spring-offset, four-way, directional control valve 46
Operation of Solenoid to Shift of Valve 47
Hydraulic Systems : Two-stage Electrohydraulic Servovalve Schematic of a twostage electrohydraulic servovalve with force feedback controlling a motor with inertia load 48
Solenoid-controlled, Pilot-operated Valve 49
Servo Valve Structure Moog 760 Series Moog 30 Series 50
Operation of Servo Valve N N N S S S 51
Operation of Servo Valve: Torque Torque Motor Motor Hydraulic Amplifier 52
Operation of Servo Valve: Valve Valve Spool Spool 53
Hydraulic Servo Systems 54
Hydraulic Excavator Arm Dump Boom Up Arm Crowd Bucket Crowd Boom Down Swing( 선회 ) Bucke t Dump Travel( 주행 ) 55
Hydraulic Systems : Valve-piston Combination Valve-piston combination 56
Operation of Solenoid to Shift of Valve 57
Hydraulic Servo System : Compressibility V P1 1 V 2 P2 V P V 1 where, Compressibility PV mrt 1 P V V P dp, V V V ( V V ) dv 1 2 2 1 1 dp V KB ; Bulk modulus dv 1 1 1 dp dv KB dv V V dp 1 dv KB dt V dt 58
59
Basic Modeling of Dynamic Cylinder Generalized Flow - Continuity equation Q 1 0 0 Q 2 dv dt dv dt 1 2 V1 e V2 e dp dt 1 dp dt 2 Q 1 A u 1 V1 e dp dt 1 Q 2 A u 2 V2 e dp dt 2 Equation of motion P 1 A 1 P2 A2 m dv dt bv f L Q Q 1 2 P P 1 2 V1 V2 A1 A2 v f L load mass m 60
Hydraulic Servo System x P0 PS P0 spool PS : supply pressure servo system y Q Q 2 1 P2 P1 piston 2 2 1 ( 1 ) d S / Q C ax P P m s a : area gradient, x : displacement : density, C : discharge coefficient d 2 Q2 Cd ax ( P2 P0 ) 2 Cd ax P2 ( P0 0) 61
Hydraulic Servo System no leakage, no compressibility Q Q P P P P P P 1 2 s 1 2 s 1 2 P PP P P P 2 P, P P 2P L 1 2 S L 1 S L 2 P P P P P, P 2 2 2 PS PL QQ1 Q2 C ax Cx P P 2 dy Q A Cx P P dt dy dt d S L P S L Cx P P S L S L S L 1 2 62
Hydraulic Servo System dy Cx PS PL, y yy, xxx, PL PL PL dt dy f f f( x, PL ) ( x x ) ( PL PL ) x PL x PL dt x P dy 1 1 C PS PL ( x x ) ( Cx ) ( PL PL ) dt 2 P P dy if x 0, PL 0, 0 dt dy dt C P x K x S 1 Y() s TF. X () s K S 1 L S L 63
Hydraulic Servo System x 0, A A 0 P 0 P S 12 11 21 22 Q1 Q2 P 0 x Ps : supply pressure y Flow equations : 2 Q11 Cd ( A0 ax) ( PS P1 ) 2 Q12 Cd ( A0 ax) ( P1 0 ) P 2 A p P 1 Q Q Q 1 11 12 2 Q21 Cd ( A0 ax) ( PS P2 ) 2 Q22 Cd ( A0 ax) ( P2 0) A p Q Q Q 2 22 21 64
Hydraulic Servo System Assume no leakage Q1 Q2 y 0, dp 1 1 dv dt V dt y 0, 1 1 ( Q1 ) V 1 dp 1 1 dp 1 1 ( Q A y), ( Q APy) dt V dt V 1 2 1 p 2 1 2 Equation of motion : my A ( p p ) by p 1 2 my by A ( p p ) p 1 2 65
Hydraulic Servo System Model my by A ( p p ) dp dt 1 dp dt 2 1 2 1 2 p 1 2 1 1 ( Q2 AP y ) V 2 2 Q1 Q11 Q12 Cd ( A0 ax) ( PS P1) Cd ( A0 ax) ( P10 ) 2 2 Q2 Q22 Q21 Cd ( A0 ax) ( P2 0) Cd ( A0 ax) ( PS P2) Q 1 1 ( Q1 Ap y ) V Q 66
Hydraulic Servo System : Linearization Q Q Q Q 0 1 2 1 2 2 2 2 2 Cd ( A0ax) ( PS P1) P2 Cd ( A0 ax) P1 ( PS P2) when x 0, 2 2 2 2 Cax d ( PS P1) P2 P1 ( PS P2) 2 2 2 2 CdA0 ( PS P1) P2 P1 ( PS P2) 0 To make an identical equation, P P P, P P P P P P s 1 2 1 s 2 s 1 2 P P P P let PL P P, P, P 2 2 s L s L 1 2 1 2 67
Hydraulic Servo System : Linearization 1 1 Q 1 Cd( ax A0) ( Ps PL) Cd( A0 ax) ( Ps PL) Q Q (, x P) L L L Operating point : x 0, p 0 L Q Q Q ( x, p ) Q (0,0) ( x0) ( p 0) 1 1 1 L 1 x0, pl0 x0, pl0 L x pl Q x 1 Q p 1 L 1 2C a p K x0, p 0 d S 1 L 1 C A K p x0, p 0 d 0 2 L S Q K xk p Q Q 1 2 L 2 dpl dp dp pl p1 p2, dt dt dt L 1 2 68
Hydraulic Servo System my by A p p L dp1 1 1 1 1 ( Q A y) ( K xk p A y) dt V V L p 1 2 L p 1 1 dp dt 2 1 1 ( Kx 1 K2pL) Ay p V 2 let V dp dt L V 1 2 1 1 (2 Kx 1 2 K2pL 2 Ay p ) V Ys () X() s (): cubic equation form 69
Hydraulic Servo System Simplification : No compressibility, No leakage my by p A L p 1 Q K xk p A y p ( K xa y ) L 1 2 L p L 1 p K2 A 2 p K1 my b y Ap x K 2 K2 Ys () K X() s s( Ts1) K KA mk, T Kb A Kb A 1 p 2 2 2 2 p 2 p 70
End of Hydraulic systems 8-1 71