Hydraulics
KON-C2004 Mechatronics BasicsJyrki Kajaste 14.11.2018
Slides by Tapio Lantela & Jyrki Kajaste
Lecture topics
Intro & basics
Hydraulic actuators
Controlling hydraulic systems
FLUID
” Fluid, any liquid or gas or generally any material that cannot sustain a
tangential, or shearing, force when at rest and that undergoes a continuous
change in shape when subjected to such a stress”Reference: Encyclopædia Britannica
”FLUID POWER” covers both hydraulics (liquids, oil/water hydraulics) and
pneumatics (gas, air).
Hydraulics – power transmission
Mechanical power (T, ω) hydraulic power (qV, p) with pump- The medium transmitting the power is “incompressible” fluid (oil, water, etc.)
Pressure 𝒑 =𝑭
𝑨[SI unit Pa]
Power 𝑷 = 𝒒𝒗𝚫𝐩 [SI units m3/s and Pa]
A B
Source NeedPower transmission
Pump Actuator
Power transmissionTechnology of converting power to a more useable form and distributing it to where it is needed. (by NFPA)https://www.nfpa.com/home/AboutNFPA/What-is-Fluid-Power.htm Mechanical Hydraulic Mechanical
Hydraulic system types
Hydrostatic system Hydrodynamic system
m m
Force and power
mostly linked to
pressure p
Force and power
mostly linked to
flow qV
Change in momentummass flow rate and velocity
(pressure dependent) Force
p= gh
h
F= pAF F
Hydraulic force conversion
If
- Same pressure
- Different area
Then
- Different force
- Different speed
And
• Same power
- (if no friction or leakage)
• power transmission
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https://www.britannica.com/technology/hydraulic-press/images-videos/Illustration-of-Pascals-principle-at-work-in-a-hydraulic-press/170703
Hydraulic car brakes
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http://www.weblumen.com/index.php/tools-supplies/tools/83-tools-supplies/tools/72-disc-brake-spreaders
In this application
Power transmission is not central.
Force control is.
Hydraulic press
Deep drawing press- Forming sheets by pressing them
into a mold with a huge force
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Actuator types
Applications: cranes
Telescoping hydraulic boom
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Applications: mining machinery
Hydrostatic driveline
Boom & bucket
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Applications: harvester
Hydrostatic driveline
Hydraulic boom
Hydraulic harvester
head
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Pump and motor
Saw motor
Applications: other mobile machinery
Wheel loader with
Hydrostatic driveline
Boom & bucket
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Dump truck
Tractor with
Hydraulic lift
3 point hitch
Applications: paper machine
Hundreds of hydraulic actuators- Roll positioning
- Roll geometry compensation
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deflection-compensated rolls
Applications: airplanes
Elevator, rudder
Landing gear
Brakes
Cargo doors, stairs
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Application: Robots
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Atlas leg actuation
Hydraulic cylinders
Controlled with servo
valves
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https://www.bostondynamics.com/atlas
Boston DynamicsAtlas humanoid robot
Applications: every day stuff
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Hydraulic log splitter Hydraulic bottle jack Hydraulic power steering
Example system
- Valve controlled
- Power source electric motor
Depending on application
- Pressure level 10400 bar
- Flow rates 0.11000+ l/min
Hydrostatic systems – basic structure
Control of power
mNeed for power
Generationof power
Need for power
Linear movement
cylinder
Rotary movement
motor
Components
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Mechanical power hydraulic power : pump
Hydraulic power mechanical power: actuator
Power converters of hydraulic systems
Fixed
displacement
pump
Variable
displacement
pump
Cylinder Fixed
displacement
motor
Variable
displacement
motor
Semi-rotary
motor
Pumps
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http://www.designworldonline.com/a-quick-and-easy-guide-to-hydraulic-pump-technology-and-selection/#_
Pumps
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Produced flow rate 𝒒𝒗 = 𝒏𝑽𝒓𝜼𝒗
Required torque 𝑻 =𝚫𝐩𝐕𝒓
𝟐𝝅𝜼𝒉𝒎
Required power 𝑷 =𝒒𝒗𝚫𝐩
𝜼𝒕𝒐𝒕
Pump equations
Bosch Rexroth
n = Rotational speed [r/s]
Vr = Displacement [m3/r]
p = Pressure difference between inlet
and outlet [Pa]
qV = Flow rate [m3/s]
v = Volumetric efficiency []
hm = Hydromechanical efficiency []
t = Overall efficiency []
= v hm
More torque and rotational speed input power
needed because of
• Friction (hydromechanical efficiency)
• Leakages (volumetric efficiency)
than in ideal pumps
Ideal and real values for flow, torque and power
Efficiencies < 1
Pump efficiency
hmvt
n : rotational speed
v : volumetric efficiency (leaks)
hm : hydromechanical efficiency (flow and mechanical frictions)
t : overall efficiency
p0
0
40
20
60
80
100
n = constant
[%]hmv
t
n0
0
40
20
60
80
100
p = constant
[%]
v
t
hm
p : pressure difference
Motors
Often exactly the same structure as in a pump
Types- Axial piston
• Bent axis
- Radial piston
- Gear
• Gerotor
- Vane
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http://www.hyspecs.com.au/how-stuff-works/hydraulic-motor/
Parker F11/F12 - motor/pumpsF11 (and F12) are bent axis, fixed displacement heavy-duty motor/pumps.
Often used as a saw motor
Motor
V= 4.9 ccm
m= 5 kg
Ppeak.theor= 41 kW
V= 30 ccm
m= 12 kg
Ppeak.theor= 170 kW
F11 and F12
performance
Flow rate in 𝒒𝒗 =𝒏𝑽𝒓
𝜼𝒗
Produced torque 𝐓 =𝚫𝐩𝐕𝒓𝜼𝒉𝒎
𝟐𝝅
Power in 𝑷 = 𝒒𝒗𝚫𝐩 =𝐓𝝎
𝜼𝒕
Motor equations
Bosch Rexroth
n = rotational speed [r/s]
= angular velocity [rad/s]
Vr = swept volume [m3/r]
T = load torque [Nm]
p = pressure difference between
in- and outlet [Pa]
qV = flow rate [m3/s]
v = volumetric efficiency []
hm = hydromechanical efficiency []
t = overall efficiency []
= v hm
Hydrostatic transmission
Generalized performance characteristics of hydraulic motors:
Motor parameters
Bosch Rexroth
Low speed Tmax 1125 kNm
motors nmax 11000 r/min
t 0,80,95
Middle speed Tmax 501000 Nm
motors nmax 2001500 r/min
t 0,70,9
High speed Tmax 103000 Nm
motors nmax 2006000 r/min
t 0,80,9
Parker F11 efficiency
F11-19 motors can be
equipped with Power
Boost
which in high speed
applications can
decrease the
mechanical losses by
up to 15%.
F11-5 motor
https://www.parker.com/literature/Literature%20Files/hydraulicpump/cat/english/F11-F12_HY17-8249-US.pdf
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Low Speed High Torque Hydraulic motor
Bosch – Rexroth - Hägglunds CBm radial piston motor
Maximum torque 1.97 MNm
Diameter 1.46 m
Height 1.3 m
Weight 7500 kgTotal efficiency exceeds 97%
Semi-rotary motors (torque motors)
GenerallyRotation angle max 90720°Torque Tmax 10300 kNm
Efficiency t 0,60,85
http://nptel.ac.in/courses/112103174/module6/lec4/4.html
Energy storage and regeneration
Pressure accumulator- Nitrogen gas compressed by the fluid
acts as energy storage
- Pressure depends on loading condition
- Types: bladder, piston, diaphragm
http://www.womackmachine.com/engineering-toolbox/design-data-sheets/tips-on-sizing-accumulators.aspx
http://www.machinerylubrication.com/Read/2305/hydraulic-accumulators
Applications: PSA Hybrid ”air”
Hydraulic hybrid
passenger car
Development on hold
”AIR” means
• Gas (nitrogen) filled
pressure accumulator
• Accumulator high power
for short time acceleration
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http://www.popularmechanics.com/cars/hybrid-electric/a9252/how-it-works-the-hybrid-air-car-15724045/
Applications: delivery trucks
Hydraulic parallel
hybrid
Energy recovery to
pressure accumulator
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http://www.wired.com/2012/10/ups-hydraulic-hybrids/
https://www.stle.org/images/pdf/STLE_ORG/BOK/LS/Hydraulics/Power%20to%20Spare_Hydraulic%20Hybrids_tlt%20article_Feb12.pdf
Cylinders
Double or single acting- Single acting returned by external force.
Symmetric or asymmetric
Generally
- Maximum pressure pmax 16 25 40 MPa
- Total efficiency ηt 0,8 0,9
- Piston diameter Dp 0,01 0,5 m
- Stroke length l 0,1 10,0 m
http://www.bluebird-
electric.net/oceanography/Ocean_Plastic_International_Rescue/SeaVax_
Hydraulics_Actuators_Autonomous_Robotics_For_Ships_Boats.htm
http://www.globalspec.com/learnmore/fluid_power_components/hydraulic_equipment_components/hydraulic_cylinders
• 100 mm (diameter)
• 350 bar
275 kN
Flow rate 𝒒𝒗𝟏 =𝑨𝟏𝒗
𝜼𝒗
Force balance 𝒑𝟏𝑨𝟏 =𝑭
𝜼𝒉𝒎+ 𝒑𝟐𝑨𝟑
Required power 𝑷 = 𝒒𝒗𝟏(𝐩𝟏 −𝐀𝟑
𝐀𝟏𝐩𝟐) =
𝐅𝐧𝐞𝐭𝐯
𝜼𝒕
Cylinder equations
A1 A
3
F
v
A2
1p
2p
V1q
V2q
A1 = piston area on the working chamber [m2]
A3 = piston area on the opposing chamber [m2]
v = piston speed [m/s]
F = external load force [N]
pout = pressure on the opposing chamber [Pa]
v = volumetric efficiency []
hm = hydromechanical efficiency []
t = overall efficiency []
Telescopic cylinders
Long stroke
Often single acting
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http://hydraulicspneumatics.com/200/TechZone/Cylinders/Article/False/21653/TechZone-Cylinders
Typically for
• dump trailers
• dump trucks
Cylinder size
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http://www.offshore-technology.com/contractors/hydraulics/ruhfus-systemhydraulik/ruhfus-systemhydraulik5.html
D= 500 mm
@ 400 bar
7.7 MN
AIRBUS A380 - Superjumbo
• 3 jacks
• Cylinders made in Finland
• Empty mass 277 000 kg
Hydraulic fluid
Oil- Good lubricant
- Environmental hazard
- Health risk
• Food industry
- Expensive
- Fire hazard
- Viscosity index
Filtering- Metal chips, water, air
Water- Needs additives to lubricate
- ”Clean”
- More expensive components
- Fire safe
- Can freeze
- Corrosion
• Stainless steel must be used (or even plastics for low pressures)
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Hydraulic systems
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Valve control
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- = p
p
p
Vq
Vq
Vq
Vq
1p
2p
1p
2p
2
q
V
2
AC
qp
4/3 directional
spool valve
• 4-way
• 3-position
𝑞v = 𝐶𝑞𝐴02∆𝑝
𝜌
Pdissipation= pqv heat
ThrottlingControl of flow
with flow area
Throttling means dissipation
Generation of system pressure
Pump -> produces flow rate
Pressure is reaction,
depending on loads!
• External loads
- Force/torque loads on actuators
• Internal loads
- Friction losses
- Throttling
• Control valves
• Piping and hoses
pam
F
A hp
External
LOAD Friction
ppipe
ppipe
pthrottle
Lifting
FlowFlow rate
qv
pload
ppump
Pipe 2
Pipe 1
Throttle
Pressure
increases
Atmospheric
pressureTank/Reservoir
Generation of system pressure
0
p
Measurement points
1
2
3
4
5
6
7
8
1 2 3 4 5 6 7 8
pp
p
p
pppp
p p p p p p p p
Throttle valve
Directional valve
Check valveFilter
F
T
1p
2p
6p
3p
4p
8p
7p
5p
Pressurereliefvalve
Pump
Tank
If you know actuators’ velocities you know also the flow rates and you can
calculate system pressures by starting from the end, the tank.
Finally the pump
pressure Start from here
Manual valves
Controlling booms etc.
Usually spool type
Proportional or logic (ON/OFF)
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Electric valvesElectric actuators as electric interfaces
• Solenoids ON/OFF
• Proportional solenoids proportional valves
• Torque motors servo valves
• Voice coils ”proportional valves”
Servo valve with torque motor Proportional control valve with proportional solenoid
S S
N N
S N
Torque motor (Proportional) solenoid
Other valves
Pressure relief valves- To protect from over pressure
- Usually connects the protected line to tank
- Necessary component in practice
Check valves- Block reverse flow direction
Shuttle valves- Choose the larger pressure level
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Pump control
Produce only the required
fluid with the pump
Options
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Control of power
mNeed for power
Generationof power
Need for power
• Inverter controlled motor
• Servomotor
• Variable displacement pump
Direct Drive Hydraulics
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• Direct Drive Hydraulics (DDH)• Motion of actuators is controlled by
electric motor’s rotation
• Basically valves are not needed
• Pressure losses minimized• Servo motor
• Inverter controlled motor
Direct Drive Hydraulics in the laboratory
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frastructure in the laboratory
Test benches in the Fluid Power Laboratory are unique. The best
place in the world to study the systems.
• DDH systems by leading manufacturers (Bosch-Rexroth, Parker)
• Own architectures and prototypes
• Hydraulic hybrid test system
”Dolores” (Parker)
”Rex” (Bosch-Rexroth)
”DDH-LITE”
Student project developed during
MEC-E5004 - Fluid Power Systems
MEC-E5002 - Mechatronics Project
Actuator control
Variable displacement motors
Multi chamber cylinders (digital hydraulics)
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http://www.norrhydro.com/media/files/pdf/linjama_vihtanen_sicfp09.pdf
Control of power
mNeed for power
Generationof power
Need for power
Connect the chambers to
different pressure sources
- Low pressure
- High pressure
Multiple different forces
Control of force
Control of velocity
Control of position
Summary of control methods
Q = flow rate
p = pressure
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Mechatronics in Fluid Power
• Proportional control valves, integrated
• Hydraulic spool valve
• Spool position sensor (LVDT)
• Control electronics (spool position control)
• Option: CAN Bus operated
• Digital hydraulic valves
• Valve units (digital flow control units, DFCU)
• Consisting of multiple ON/OFF valves
• Fast and leak free
• Optimized magnetic circuit, integrated electronics
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Examples
Valves for control systems (1)
Proportional Directional Control Valve
Rexroth 4WRPH6Step response at 100 % step < 10 ms
Spool valve
Separate control electronics
Proportional Solenoid operated proportional control valves
Proportional solenoidLVDT position sensor
Electronics
can be
also
integrated
into the
valve!
Frequency response of
spool displacement
[Hz]
[Amplitude, dB]
[Phase, ]
Response is
displacement
amplitude
dependent
- Stroke
amplitude
- Phase lag
+/- 5%
+/- 100%
Proportional solenoid
56
https://www.magnet-schultz.com/fileadmin/Daten/Vertrieb/PR4/GRC_GHP/GRCY037045063_e.pdf
https://www.magnet-schultz.com/fileadmin/Daten/Vertrieb/PR4/GRC_GHP/GHPY037045063_e.pdf
Rated magnetic force 47 N
Working stroke 2 mm
Solenoid weight 0.410 kg
Armature weight 0.040 kg
Proportional solenoid ON/OFF solenoid
Valves for control systems (2)
http://www.parker.com/literature/Hydraulic%20Controls%20Europe/Manuals%20UK/D_FP_20%205715-658%20UK.pdf
Voice Coil operated Proportional Directional
Control Valve - Parker DFplus
Nominal flow up to 40 l/min @ 35 bars
Step response at 100 % step < 3.5 msMeasured with load (100 bar pressure drop/two control edges)
Spool valve
Voice coilControl electronicsVoice Coil operated proportional control valves
http://www.parker.com/literature/Hydraulic%20Controls%20Europe/HY11-3500UK/PDF_2013/D1FP%20UK.pdf
Size:
NG06 / CETOP 03 / NFPA D03Moving Coil Assembly
v vPermanent
Magnetic Field Assembly
Moving Coil Actuator
Distributed control systems
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Danfoss
Distributed control system
for boom operations.
Based on
• Microcontroller
• Proportional valves
• Joystick operation
• CAN Bus
Digital Hydraulic valvesTapio Lantela’s (Aalto) research
Digital valve system based on
pilot operated miniature valves (pilot main)
4 x 8 on/off valves
Response time < 2 ms
Flow capacity 78 l/min @ 35 bar
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Magnetic sub-
system simulation
Pilot and main valve
Laminated
valve body
Digital hydraulic valves
Selective Laser Melted manifold Enables optimization of flow paths
Enhanced 3D printed version
also made and tested
http://www.tandfonline.com/doi/full/10.1080/14399776.2017.1358025
Improved flow channels
pressure loss reduced up to 49%
Misc.
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Sensing
Force/velocity control can be based on- Crude estimation
• estimated pump flow and system pressure
- Better estimation
• measured actuator flow and pressure
- Best estimation
• measured speed and force or torque
Important quantities in hydraulics- Pressure, force, position
- Flow rate
- Temperature
• Fluid viscosity
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Flow measurements
Gear
Turbine
Operation principles- Gear
- Turbine
- Ultrasound
- Orifice plate
Vq
Vq
p1 2
p
p
Turbulent orifice
Integrated actuators
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MoogEaton
Servo cylinder with integrated valveCylinder with integrated position sensor
Efficiency
Hydraulic components have often good efficiency
Traditionally designed hydraulic systems have often bad
efficiency- Valve control – throttling
- Constantly rotating pump
- Not recovering kinetic and potential energy
Well designed hydraulic systems can be very efficient
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Pros and cons
Advantages- High power/weight –ratio
- Linear and rotary movement
- Ease and accuracy of control
- Protection against overloading
- Flexible power routing
- Power regeneration readiness
• lifting/lowering
• acceleration/deceleration
Deficiencies- Mediocre efficiency
- Characteristics of fluid
• Possible leakages
- Maintenance
If requirements for
- high force or torque and small component weight and size
- flexible power transmission routing
Consider using hydraulics!
Summary
Hydraulics is a power transmission method- High forces nad power from compact actuators
- Good efficiency actuators, often bad efficiency systems (bad design)
- Input power from outside (electric motor/combustion engine)
Hydraulic system consists of- Power source + pump
- Actuators: motor, cylinder, semi-rotary devices
- Valves: on/off, proportional, check, pressure relief
- Sensors: pressure, flow, position, force, temperature
- Fluid: oil, water
- Pressure accumulator, heat exchanger, filters, tank?
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