Download Lecture: Introduction to Hydraulics

TSM363 Fluid Power
Systems
Fluid Power Introduction
and Applications
Dr. Tony E. Grift
Dept. of Agricultural & Biological Engineering
University of Illinois
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Agenda
• Energy Transfer Systems
• Pascal’s Law
• Basic Hydraulic Systems
• Pump
• Actuators
• Pressure Relief Valve (PRV)
• Applications
• Agriculture
• Construction/mining
• Forestry
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Video: Modern Marvels Hydraulics
Ch1: 0-11:03 (11:03)
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Introduction
Power steering
Hydraulic brakes
Thrill rides
Basic fluid power
Jack
History
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Units are irrelevant if everything is kept in Pure SI:
• Distance in m
• Area in m2
• Volume in m3
• Time in seconds (s)
• Flow rate in m3/s
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Force in Newton (N = kgm/s2)
Pressure in Pascal (Nm-2)
Work (energy) is Force through a Distance (Nm)
Torque is also Force times a Distance (Nm)
Power is Work per unit of Time (Nm/s)
• Viscosity in Pascal*second (Pa*s)
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Video 1: Introduction (3:20)
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Power supplies cannot directly move loads
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Fluid properties are important
Advantages
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Hydraulics can lift large loads in linear fashion (bucket of dump truck)
Conversion into useable form and transmission to work location
Compressed fluid is the energy carrier
Force can be applied in accurate amounts
Hydraulics have good power/weight ratio (mobile applications)
Precise positioning possible
Hydraulic motion is uniform and speeds are variable
Hydraulic systems can be started under maximum load (platform lift)
Overload protection easily implemented (PRV)
Forms of hydraulic systems
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Stationary systems
Mobile systems
• Construction equipment
• Vehicles (Off-road and On-road), ships
• Aircraft
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A hydraulic system is nothing more than an Energy
Transfer System
• Fluid Power Advantages
• multiplies forces
• constant torque at all speeds
• can work remotely and around
corners
• High power density
• Easy to implement linear motion
• Only two actuators, linear and
rotary
• Disadvantages
• Leakages
• Sensitive to contamination
• Can be dangerous
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Caterpillar 797 Dump Truck (world’s biggest until
2004)
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3400 HP
360 Tons capacity
40 MPH Fully loaded
Mechanical drive
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Liebherr 282B 400 Ton Mining truck (record holder
2005)
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2,700 HP Detroit Diesel
505,000 lb (229,000 kg)
267 yd3 (204 m3)
400 tons (363 tonnes)
Electric AC Drive
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Video 7: Hydraulic system design (1:13)
• Three system components
• Power supply unit: external either electric, internal
combustion engine or human (hydraulic jacks)
• Power control section (valves, many types,
functions and implementations)
• Drive unit (actuators: cylinder and motors)
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Fluid Power Energy Transfer System
vo, Fo
ni, Ti
M
P1
P4
Q1
Q4
Energy Level
no, To
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Video 2: Pressure Fluids (2:02)
• Function of hydraulic fluids
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Transmit pressure energy
Serve as lubricant
Protect metal from corrosion
Dissipate heat from oil flow
Carry away abraded particles to the filter
• Fluid properties
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Viscosity is resistance to flow
Lubricated properties
Mineral or sythetic oils used in hydraulic systems
Additives make oil suitable for certain applications
Only 7% compressible by volume
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Basic Principles
• Liquids form in the shape of the container (like the
lines for transmitting fluid power)
• Liquids can be considered incompressible
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Energy Transfer Methods
• Fluid power is one method of energy
transmission:
• It transfers potential energy in fluid medium to do
desired work.
• Other methods of energy transmission:
• Mechanical transmission
• Electrical transmission
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Video 3: Pascal’s Law (2:41)
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Pressure determines work output
P  FA
Pressure applied to surface give Force
Closed system: same pressure is present everywhere
V
(Pascal’s law)
Q
Operating speed determined by flow rate
t
• Pressure applied to a confined liquid is transmitted undiminished
in all directions, and acts with equal force on equal areas, and at
right angles to them.
Blaise Pascal
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Pascal’s Law: Pressure in static closed system
(confined fluid) is the same everywhere
100 N
10 N
1 m2
10 m2
10 N/m2
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Video 4: Force transmission (1:35)
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Pressure propagation transmits force
P
Equal diameters>equal forces
Different diameters> different forces
Force can be transmitted or stepped down
Large masses can be moved with small forces
through cycling pumps (manual jack)
 FA
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Conservation of Energy
10 m2
1 m2
100 N
Fi  Li  Fo  Lo
1m
10 m
10 N
10 N/m2
Energy can be neither created nor destroyed
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Elements of Fluid Power systems
• Power is transmitted by pushing a confined liquid.
• Input component is a positive displacement pump.
• Flow from pump is dependent on speed
• Flow from pump is independent of system pressure
• Output components are called actuators
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Positive Displacement Pump
• Except for efficiency, pump output is constant regardless of
pressure.
• Pump outlet is sealed from inlet.
• Fluid at the inlet is forced to the outlet.
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Linear Actuators
F  p1  A1  p2  A2
A1
A2
F
p1
p2
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Linear Actuators
• Cylinders
Double acting
Differential area
Double acting
Dual Rod
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Rotary Actuators
• Motors
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Advantages of Fluid Power
• Variable Speed
• Actuators can be driven from a high to low speed using a
flow control valve.
• Reversible
• Hydraulic actuators can be instantly reversed in direction of
motion.
• Overload Protection
• A pressure relief valve protects a hydraulic circuit from
overload.
• Also, a pressure relief valve provides a set clamping force.
• Can Be Stalled
• A load can stall a fluid power circuit without damage.
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Where do we find Hydraulics?
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John Deere Utility tractor with dual pumps
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Valtra introduces powerful new hydraulics with output
of 160 liters/minute
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Mining & Construction
Equipment
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Mining Equipment
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Hydraulics is the Energy Transfer System on most
mining equipment
Cylinders
Motors
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Backhoe arm
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Forestry Equipment
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Feller-bunchers fell trees and drop them in a pile
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Cut-to-length feller heads
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Timberjack experimental felling ant?
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Skidders pull trees out of the forest to a collection site
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Forwarders stack trees for transport
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TSM363 Fluid Power
Systems
Introduction
to Hydraulics
The End
Dept. of Agricultural & Biological Engineering
University of Illinois
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