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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10https://www.hitachicm.com/global/ourbusiness/products/large-excavators-loading-shovels/

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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13https://www.valmet.com/globalassets/media/downloads/white-papers/roll-services/wpr_rollmoddeflcomp.pdf

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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