Lecture Note 8-1 Hydraulic Systems

System Analysis Spring 2015

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Lecture Note 8-1Hydraulic Systems


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Vehicle Model - Brake Model

Brake Model

BrakePedal

VacuumBooster

MasterCylinder

ProportionnigValve

FontWheel

RearWheel

Brake Pedal

Vacuum Booster

Master Cylinder

ProportioningValve

Fundamental structure of a hydraulic brake


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Conservation of Mass, Force and Pressure

mi mom q q

1 1 1

2 2 2

22 1 1 2

1

1 1 23 2 1

2 2 1

)

( )

iii f p Af p A

Af f P PAL L Af f fL L A

Force

1 1 2 2

12 1

2

)i Volume A dx A dxAdx dxA

2 1) Prii essue p p gh


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Hydraulic Excavator

Boom Up

Boom Down

Arm Dump

Arm CrowdBucket Crowd

Bucket Dump

Swing(선회)

Travel(주행)


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유압굴삭기 회로도


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Hydraulic Brake Systems

Brake System

1 ) Wheel Cylinder2 ) Brake Light3 ) Brake Pedal4 ) Rear Brake Lines5 ) Stop Light Switch (Mechanical)6 ) Front/Rear Balance Valve7 ) Pressure Differentiavl Valve8 ) Brake Warning Lamp9 ) Brake Fluid

10) Brake Pad11) Master Cylinder


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Vehicle Model - Brake Model

Brake Model

BrakePedal

VacuumBooster

MasterCylinder

ProportionnigValve

FontWheel

RearWheel

Brake Pedal

Vacuum Booster

Master Cylinder

ProportioningValve

Fundamental structure of a hydraulic brake


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• Pneumatically controlled dexterous hand

• Hydraulically powered dexterous arm

Applications of Fluid Power• Space shuttle Columbia

• Space shuttle vehicle


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Applications of Fluid Power• Hydraulically powered Sky-tram

• Hydraulic power brush drive

• Hydraulically driven turntable

• Oceanography


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Automatic Transmission


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Press


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Linear Actuators

Airplane

PressMotion Simulator

Robot


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Landing gear system of AIRBUS A330

Hydraulic Systems : Landing Gear System


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1P 2P

Tank

Load

Control valve

)( 21 PPAF P

(70 ~ 210 )Hydraulic actuator bar

Hydraulic Systems

Hydraulic pump

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Why hydraulic ?Internal combustion EngineTurbineElectric motorHydraulic actuator……

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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

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Disadvantages1. 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

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Primary Functions of a Hydraulic Fluid


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Conservation of Mass, Force and Pressure

mi mom q q

1 1 1

2 2 2

22 1 1 2

1

1 1 23 2 1

2 2 1

)

( )

iii f p Af p A

Af f P PAL L Af f fL L A

Force

1 1 2 2

12 1

2

)i Volume A dx A dxAdx dxA

2 1) Prii essue p p gh


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Gear Pumps (External)– fixed displacement pump– uses spur gear (teeth are parallel to the axis of the gear)– noisy at relatively high speeds


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Internal Gear Pump


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Internal Gear Pump

• Gerotor Pump


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Internal Gear Pump

• Lobe Pump


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Simple Vane Pump


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Balanced Vane Pump


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Piston Pump (Swash Plate Type)


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Piston Pump


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Pump

Electric Motor or Engine


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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: cm3/rev, cc/rev, cm3/rad, cc/rad


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Pump Torque• Mechanical power supplied to pump

• Hydraulic power delivered by pump

• Therefore

: :

pH PQ

P pressure rise across the pumpQ delivery rate

th th p

th p

T PQ P D

T PD

mH T

]/3[ : radmDp 배제용적펌프여기서


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Hydraulic Motors and Actuators


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Hydraulic Systems : Valve-motor Combination


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Application of Hydraulic Motors


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Gear Motors


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Valve-piston combination

Hydraulic Systems : Valve-piston Combination


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Hydraulic Excavator

Boom Up

Boom Down

Arm Dump


Bucket Dump

Swing(선회)

Travel(주행)


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Hydraulic Excavator


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Automotive Application

Active Suspension


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Rough terrain forklift driven by hydraulic cylinders


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Double-acting Cylinder Design


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Cylinder Construction


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Types of Valves: shearing elements


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Types of Valves: seating elements


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Directional Control Valve


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Schematic of a single stage electrohydraulic

servovalve connected to a motor with

inertia load

Hydraulic Systems : Single Stage Electrohydraulic Servovalve


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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


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Operation of Solenoid to Shift of Valve


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Schematic of a two-stage electrohydraulic

servovalve with force feedback controlling

a motor with inertia load

Hydraulic Systems : Two-stage Electrohydraulic Servovalve


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Solenoid-controlled, Pilot-operated Valve


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Servo Valve StructureMoog 760 Series

Moog 30 Series


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N N

SS

N S

Operation of Servo Valve


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Operation of Servo Valve: Torque MotorTorque Motor

Hydraulic Amplifier


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Operation of Servo Valve: Valve Spool

Valve Spool


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Hydraulic Servo Systems


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Hydraulic Excavator

Boom Up

Boom Down

Arm Dump


Bucket Dump

Swing(선회)

Travel(주행)


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Valve-piston combination

Hydraulic Systems : Valve-piston Combination


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Operation of Solenoid to Shift of Valve


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PV 11 PV 22

mRTPV

1

,

V PV

where Compressibility

1 2 2 1

1

, ( )

1 ;

1 1 1

1

B

B

B

PV

VP dP V V V V V dV

dPV K Bulk modulusdV

dP dV K dVV V

dP dVKdt V dt

Hydraulic Servo System : Compressibility


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Basic Modeling of Dynamic Cylinder• Generalized Flow - Continuity equation

• Equation of motion

dtdPV

dtdVQ

e

1111 0

dtdPV

dtdVQ

e

22220

dtdPVuAQ

e

1111

dtdPVuAQ

e

2222

LfbvdtdvmAPAP 2211

v

load

1Q 2Q

1P 2P

1A 2A1V 2V

Lf

mass m


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0P SP 0P

2Q 1Q

2P 1P

:SP supply pressure

piston

servosystem

21 1

2 ( ) /

: , :

: , :

d S

d

Q C a x P P m s

a area gradient x displacement

density C discharge coefficient

spool

2 2 0

2 0

2 ( )

2 ( 0)

d

d

Q C a x P P

C a x P P

Hydraulic Servo System

x

y


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no leakage, no compressibility

1 2 1 2 1 2

1 2 1 2

1 2

1 2

2 , 2

,2 2

22

s s

L S L S L

S L S L

S Ld S L

Q Q P P P P P P

P P P P P P P P P P

P P P PP P

P PQ Q Q C a x C x P P

P S L

S L

dyQ A C x P Pdt

dy C x P Pdt



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, , ,

( , ) ( ) ( )

1 1( ) ( ) ( )2

L L

S L L L L

L L Lx P x PL

S L L L

S L

d y C x P P y y y x x x P P Pdt

dy f ff x P x x P Pdt x P

d y C P P x x C x P Pdt P P

1

1

0, 0 , 0

( ).( )

L

S

d yif x Pdt

dy C P x K xdt

KY sT FX s S



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0P

1Q 2Q

SP

12 11 21 22

Ap

0P

1P2P

:sP supply pressure

x

ypA

0

11 0 1

12 0 1

1 11 12

0 ,

2( ) ( )

2( ) ( 0 )

d S

d

x A A

Q C A ax P P

Q C A ax P

Q Q Q

21 0 2

22 0 2

2 22 21

2( ) ( )

2( ) ( 0 )

d S

d

Q C A ax P P

Q C A ax P

Q Q Q


Flow equations :


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Assume no leakage 21 QQ

11

1 21 2

1 2

0,

1 1

1 1 ( )

0,

1 1 1 1( ), ( )p P

y

dP dVdt V dt

QV

y

dp dpQ A y Q A ydt V dt V

1 2

1 2

( )

( )

p

p

my A p p by

my by A p p

Equation of motion :



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Hydraulic Servo System Model

1 2

11

1

22

2

1 11 12 0 1 0 1

2 22 21 0 2 0 2

1 2

( )

1 1 ( )

1 1 ( )

2 2( ) ( ) ( ) ( 0 )

2 2( ) ( 0 ) ( ) ( )

p

p

P

d S d

d d S

my by A p p

dp Q A ydt V

dp Q A ydt V

Q Q Q C A ax P P C A ax P

Q Q Q C A ax P C A ax P P

Q Q


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1 2 1 2

0 1 2 0 1 2

1 2 1 2

0 1 2 1 2

0

2 2 2 2( ) ( ) ( ) ( )

0,

2 2 2 2( ) ( )

2 2 2 2( ) ( ) 0

d S d S

d S S

d S S

Q Q Q Q

C A ax P P P C A ax P P P

when x

C ax P P P P P P

C A P P P P P P

To make an identical equati

1 2 1 2 1 2

1 2 1 2

, ,

, ,2 2

s s s

s L s LL

Pon P P P P P P P P

P P P Plet P P P P P

Hydraulic Servo System : Linearization


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Operating point :

1 11 1 0, 0 0, 0

10, 0 1

10, 0 0 2

1 2 2

1 21 2

0, 0

( , ) (0,0) ( 0) ( 0)

12

1

,

L L

L

L

L

L x p x p LL

x p d S

x p dL S

L L

LL

x p

Q QQ x p Q x px p

Q C a p Kx

Q C A Kp p

Q K x K p Q Q

dp dp dpp p pdt dt dt

Hydraulic Servo System : Linearization

1 0 01 1( ) ( ) ( ) ( )

( , )

d s L d s L

L L L

Q C ax A P P C A ax P P

Q Q x P


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11 2

1 1

21 2

2

1 2

1 2

1 1 1 1( ) ( )

1 1 ( )

1 1 (2 2 2 )

( ) ( ) :( )

p L

L p L p

L p

LL p

my by A p

dp Q A y K x K p A ydt V V

dp K x K p A ydt V

let V V

dp K x K p A ydt V

Y s cubic equation formX s



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Simplification : No compressibility, No leakage

1 2 12

21

2 2

1 22 2

2 2

1 ( )

( )( ) ( 1)

,

L p

L L p L p

pp

p

p p

my by p A

Q K x K p A y p K x A yK

A Kmy b y A xK K

Y s KX s s Ts

K A mKK TK b A K b A



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End of Hydraulic systems 8-1

Lecture Note 8-1 Hydraulic Systems

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