Lecture Note 8-1 Hydraulic Systems

System Analysis Spring 2015

1

Lecture Note 8-1

Hydraulic Systems

System Analysis Spring 2015

2

Vehicle Model - Brake Model

Brake Model

Brake Pedal

Vacuum Booster

Master Cylinder

Proportionnig Valve

Font Wheel

Rear Wheel

Brake Pedal Vacuum

Booster

Master Cylinder

Proportioning Valve

Fundamental structure of a hydraulic brake

System Analysis Spring 2015

3

Conservation of Mass, Force and Pressure

mi mo

m   q  q

1 1 1

2 2 2

2

2 1 1 2

1

1 1 2

3 2 1

2 2 1

)

( )

iii f p A

f p A

f A f P P

A

L L A

f f f

L L A





 

 

Force

1 1 2 2

1

2 1

2

)

i Volume A dx A dx dx A dx

A



 

2 1

) Pr

ii essue p  p   gh

System Analysis Spring 2015

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Hydraulic Excavator

Boom Up

Boom Down Arm Dump

Arm Crowd Bucket Crowd

Bucke t Dump

Swing(

)

Travel(

)

System Analysis Spring 2015

5

유압굴삭기 회로도

System Analysis Spring 2015

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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

System Analysis Spring 2015

7

Vehicle Model - Brake Model

Brake Model

Brake Pedal

Vacuum Booster

Master Cylinder

Proportionnig Valve

Font Wheel

Rear Wheel

Brake Pedal Vacuum

Booster

Master Cylinder

Proportioning Valve

Fundamental structure of a hydraulic brake

System Analysis Spring 2015

8

• Pneumatically controlled dexterous hand

• Hydraulically powered dexterous arm

Applications of Fluid Power

• Space shuttle Columbia

• Space shuttle vehicle

System Analysis Spring 2015

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Applications of Fluid Power

• Hydraulically powered Sky-tram

• Hydraulic power brush drive

• Hydraulically driven turntable

• Oceanography

System Analysis Spring 2015

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Automatic Transmission

System Analysis Spring 2015

11

Press

System Analysis Spring 2015

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Linear Actuators

Airplane

Press

Motion Simulator

Robot

System Analysis Spring 2015

13 Landing gear system of AIRBUS A330

Hydraulic Systems : Landing Gear System

System Analysis Spring 2015

14

P

P

Tank

Load Control valve

) ( P

P

A

F 

 

(70 ~ 210 ) Hydraulic actuator bar

Hydraulic Systems

Hydraulic pump

15

Why hydraulic ?

Internal combustion Engine Turbine

Electric motor

Hydraulic actuator

……

16

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

17

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

18

Primary Functions of a Hydraulic Fluid

System Analysis Spring 2015

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Conservation of Mass, Force and Pressure

mi mo

m   q  q

1 1 1

2 2 2

2

2 1 1 2

1

1 1 2

3 2 1

2 2 1

)

( )

iii f p A

f p A

f A f P P

A

L L A

f f f

L L A





 

 

Force

1 1 2 2

1

2 1

2

)

i Volume A dx A dx dx A dx

A



 

2 1

) Pr

ii essue p  p   gh

System Analysis Spring 2015

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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

System Analysis Spring 2015

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Internal Gear Pump

System Analysis Spring 2015

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Internal Gear Pump

• Gerotor Pump

System Analysis Spring 2015

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Internal Gear Pump

• Lobe Pump

System Analysis Spring 2015

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Simple Vane Pump

System Analysis Spring 2015

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Balanced Vane Pump

System Analysis Spring 2015

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Piston Pump (Swash Plate Type )

System Analysis Spring 2015

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Piston Pump

System Analysis Spring 2015

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Pump

Electric

Motor or

Engine

System Analysis Spring 2015

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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: cm 3 /rev, cc/rev, cm 3 /rad, cc/rad

System Analysis Spring 2015

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Pump Torque

• Mechanical power supplied to pump

• Hydraulic power delivered by pump

• Therefore

: :

H p PQ

P pressure rise across the pump Q delivery rate



th th p

th p

T PQ P D T PD

   



H m  T 

] /

3 [

: m rad

D

펌프 배제용적

여기서

System Analysis Spring 2015

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Hydraulic Motors and Actuators

System Analysis Spring 2015

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Hydraulic Systems : Valve-motor Combination

System Analysis Spring 2015

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Application of Hydraulic Motors

System Analysis Spring 2015

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Gear Motors

System Analysis Spring 2015

35 Valve-piston combination

Hydraulic Systems : Valve-piston Combination

System Analysis Spring 2015

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Hydraulic Excavator

Boom Up

Boom Down Arm Dump

Arm Crowd Bucket Crowd

Bucke t Dump

Swing(

)

Travel(

)

System Analysis Spring 2015

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Hydraulic Excavator

System Analysis Spring 2015

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Automotive Application

Active

Suspension

System Analysis Spring 2015

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Rough terrain forklift driven by hydraulic cylinders

System Analysis Spring 2015

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Double-acting Cylinder Design

System Analysis Spring 2015

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Cylinder Construction

System Analysis Spring 2015

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Types of Valves: shearing elements

System Analysis Spring 2015

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Types of Valves: seating elements

System Analysis Spring 2015

44

Directional Control Valve

System Analysis Spring 2015

45 Schematic of a single stage electrohydraulic

servovalve connected to a motor with inertia load

Hydraulic Systems : Single Stage Electrohydraulic Servovalve

System Analysis Spring 2015

46

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

System Analysis Spring 2015

47

Operation of Solenoid to Shift of Valve

System Analysis Spring 2015

48 Schematic of a two- stage electrohydraulic servovalve with force feedback controlling a motor with inertia load

Hydraulic Systems : Two-stage Electrohydraulic Servovalve

System Analysis Spring 2015

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Solenoid-controlled, Pilot-operated Valve

System Analysis Spring 2015

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Servo Valve Structure

 Moog 760 Series

 Moog 30 Series

System Analysis Spring 2015

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N N

S S

N S

Operation of Servo Valve

System Analysis Spring 2015

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Operation of Servo Valve: Torque Motor

 Torque Motor

 Hydraulic Amplifier

System Analysis Spring 2015

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Operation of Servo Valve: Valve Spool

 Valve Spool

System Analysis Spring 2015

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Hydraulic Servo Systems

System Analysis Spring 2015

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Hydraulic Excavator

Boom Up

Boom Down Arm Dump

Arm Crowd Bucket Crowd

Bucke t Dump

Swing(

)

Travel(

)

System Analysis Spring 2015

56 Valve-piston combination

Hydraulic Systems : Valve-piston Combination

System Analysis Spring 2015

57

Operation of Solenoid to Shift of Valve

System Analysis Spring 2015

58

V

P

V

P

mRT PV 

1

,

V P

V

where Compressibility





  



1 2 2 1

1

, ( )

1 ;

1 1 1

1

B

B

B

P V V

P dP V V V V V dV

V dP K Bulk modulus dV

dP dV K dV

V V

dP dV

dt K V dt







 



         

  

    

   

Hydraulic Servo System : Compressibility

System Analysis Spring 2015

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System Analysis Spring 2015

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Basic Modeling of Dynamic Cylinder

• Generalized Flow - Continuity equation

• Equation of motion

dt dP V

dt Q dV

e 1 1 1

1

0

 





dt dP V

dt Q dV

e 2 2 2

0

 





dt dP u V

A Q

e 1 1 1

1

   dt

dP u V

A Q

e 2 2 2

2

   



f L

dt bv m dv A

P A

P 1 1  2 2   

v

load

Q

Q

P

P

A

A

V

V

f

mass m

System Analysis Spring 2015

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Q2 Q₁

P2 P₁

S

:

P supply pressure

piston servo

system

2

1 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

System Analysis Spring 2015

62 no leakage, no compressibility

1 2 1 2 1 2

1 2 1 2

1 2

1 2

2 , 2

2 , 2

2

2

s s

L S L S L

S L S L

S L

d S L

Q Q P P P P P P

P P P P P P P P P P

P P P P

P P

P P

Q Q Q C a x C x P P



      

        

 

  

        

P S L

S L

Q A dy C x P P dt

dy C x P P dt

    

  

Hydraulic Servo System

System Analysis Spring 2015

63

, , ,

( , ) ( ) ( )

1 1

( ) ( ) ( )

2

L L

S L L L L

L x P x P L L

L

S L L L

S L

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

dt

dy f f

f x P x x P P

dt x P

d y C P P x x C x P P

dt P P

           

 

      

 

        



1

1

0 , 0 , 0

. ( )

( )

L

S

if x P d y

dt

dy C P x K x

dt

K T F Y s

X s S

  

   

  

Hydraulic Servo System

System Analysis Spring 2015

64

P

Q

Q

P

12 11 21 22

A

P

P

P

s

:

P supply pressure

x

y

A

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





  

  

 

Hydraulic Servo System

Flow equations :

System Analysis Spring 2015

65

Assume no leakage Q

 Q

1 1

1 2

1 2

1 2

0,

1 1

1 1 ( ) 0,

1 1 1 1

(

), (

)

y

dP dV

dt V dt

V Q y

dp dp

Q A y Q A y

dt V dt V





 



   

  



    





 

1 2

1 2

( )

( )

p

p

my A p p by

my by A p p

  

  

 

 

Equation of motion :

Hydraulic Servo System

System Analysis Spring 2015

66

Hydraulic Servo System Model

1 2

1

1 1 2

2 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 y

dt V

dp Q A y

dt 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





 

 

  

 

  

   

   

           

   

   

   

   

           

   

   



 





System Analysis Spring 2015

67

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 L

L

on P P P P P P P P P

P P P P

let P P P P P

      

 

    

Hydraulic Servo System : Linearization

System Analysis Spring 2015

68

Operating point :

1 1

1 1 0, 0 0, 0

1

0, 0 1

1

0, 0 0 2

1 2 2

1 2

1 2

0, 0

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

2 1

1

,

L L

L

L

L

L x p x p L

L

x p d S

x p d

L S

L L

L L

x p

Q Q

Q x p Q x p

x p

Q C a p K

x

Q C A K

p p

Q K x K p Q Q

dp dp dp

p p p

dt dt dt





   

 

 

 

 

     

 

   



     

 

   

   



Hydraulic Servo System : Linearization

1 0 0

1 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

 

     



System Analysis Spring 2015

69

 

   

1

1 2

1 1

2

1 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

L

L p

my by A p

dp Q A y K x K p A y

dt V V

dp K x K p A y

dt V

let V V

dp K x K p A y

dt V

Y s cubic equation form X s

 





 

    

   



  

 

 

 





Hydraulic Servo System

System Analysis Spring 2015

70

Simplification : No compressibility, No leakage

1 2 1

2 2

1

2 2

1 2

2 2

2 2

1 ( )

( )

( ) ( 1)

,

L p

L L p L p

p

p

p

p p

my by p A

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

K

A K

my b y A x

K K

Y s K

X s s Ts

K A mK

K T

K b A K b A

 

     

 

       

 

 



 

 

 

 

 

Hydraulic Servo System

System Analysis Spring 2015

71

End of Hydraulic systems 8-1