1. Hydraulics KON-C2004 Mechatronics Basics Jyrki Kajaste 14.11.2018
Slides by Tapio Lantela & Jyrki Kajaste

2. 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).

3. 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= 𝒒 𝒗 𝚫𝐩 [SI units m3/s and Pa]
Power transmission
Technology of converting power to a more useable form and distributing it to where it is needed.
(by NFPA)
Power transmission
Pump
Actuator
Pressure -> force transmission.
Pressure * flow rate = power transmission.
The mechanical power must be created with some other method such as an electric motor or internal combustion engine.
Hydraulic power is transferred via piping to desired point (actuator) and transformed back to mechanical power
Hydraulic fluid is not truly incompressible but close enough for many applications. Commonly the fluid compressibility can be neglected but for more accurate modelling compressibility must be taken to account.
Demo with syringe. Pressure level depends on the load pressure.
Mechanical  Hydraulic  Mechanical

4. Hydraulic system types
Hydrostatic system Hydrodynamic system
Change in momentum
mass flow rate and velocity
(pressure dependent)
 Force h
F= pA F F
p= gh
Force and power mostly linked to pressure p
Force and power mostly linked to flow qV
Almost all systems are hydrostatic.
Torque converter (momentinmuunnin) used in automatic transmissions is hydrodynamic.
Image shows the principle of a hydraulic cylinder, the most common hydraulic actuator.

5. Hydraulic force conversionIf
Same pressure
Different area
Then
Different force
Different speed
And
Same power
(if no friction or leakage)
 power transmission
Pressure level inside a fluid volume is constant if there is no flow rate or restrictions.
Relatively small force can create a very high force.
The same goes for mechanical gear systems, however, mechanical gears for very high torques are often expensive large and heavy.

6. Hydraulic car brakes In this application
Power transmission is not central.
Force control is.
Very little movement in brake calipers. Mainly force transmission.
First mechanical force amplification with pedal lever and joint positioning. Then hydraulic force amplification with small master cylinder and a larger brake caliper cylinder.
Image shows unassisted hydraulic brakes. Normally the braking power is amplified with the power from the car motor.

7. Hydraulic press Deep drawing press
Forming sheets by pressing them into a mold with a huge force

8. Actuator types
Thus, very large forces are usually produced with hydraulic actuators.
Micrometer level accuracy possible with hydraulics. Higher accuracies with electric actuators.
Pneumatics introduced in Other actuators lecture.

9. Applications: cranes
Telescoping hydraulic boom

10. Applications: mining machinery
Hydrostatic driveline Boom & bucket
Diesel engine in the back.

11. Applications: harvester
Pump and motor
Hydrostatic driveline Hydraulic boom Hydraulic harvester head
Diesel engine in the back.
High power required in the harvester head for moving logs and cutting them. Small actuators and flexible power routing. Power density of electric motors limited
Saw motor

12. Applications: other mobile machinery
Wheel loader with
Hydrostatic driveline
Boom & bucket
Tractor with
Hydraulic lift
3 point hitch
Dump truck

13. Applications: paper machine
deflection-compensated rolls
Hundreds of hydraulic actuators
Roll positioning
Roll geometry compensation
Positioning of rolls, maintaining correct pressure between them, compensating for the bending of rolls.
Hundreds of hydraulic actuators.

14. Applications: airplanes
Elevator, rudder Landing gear Brakes Cargo doors, stairs
Also in ships steering and cargo hatches are operated with hydraulics.
Common with the aforementioned examples: large, heavy and expensive industrial machines.

15. Application: Robots Height 1.5 meters, weight 75 kg. 28 joints.

16. Atlas leg actuation Hydraulic cylinders Controlled with servo valves
Boston Dynamics
Atlas humanoid robot
One hydraulic cylinder for the knee joint, an other for the ankle joint (not visible in images).

17. Applications: every day stuff
Hydraulic log splitter Hydraulic bottle jack Hydraulic power steering
Hydraulic log splitting thingie.
Hydraulic power steering in cars.
Hydraulic bottle jack.

18. Hydrostatic systems – basic structure
Linear movement
 cylinder
Rotary movement
 motor
Example system
Valve controlled
Power source electric motor
Depending on application
Pressure level 10400 bar
Flow rates 0.11000+ l/min
Hydraulic circuit – hydraulic symbols
Convert power from mechanical to hydraulic. Then convert it back to mechanical where needed.
Valves commonly used to control actuator direction and velocity.
Pressure level: atmospheric pressure ~1 bar. Car tire pressure ~2 bars. Water pressure at depth of 100m ~10 bar. -> 400 bar is a lot.

19. Components

20. Power converters of hydraulic systems
Mechanical power  hydraulic power : pump Hydraulic power  mechanical power: actuator
Fixed
displacement
pump
Variable
displacement
pump
Cylinder
Fixed
displacement
motor
Variable
displacement
motor
Semi-rotary
motor
Most power converters can be used in either direction. For example a cylinder can work as a pump.
Often the structure of motors and pumps is basically the same. Some differences in for example sealing.

21. Pumps
Gear pumps simple and cheap. Can be noisy. Gerotor pump is an improved version. Fixed displacement
Piston pump for high pressure. Good efficiency. Can be variable displacement. Axial version driven by an angled swash plate. Also radial piston pumps available.
Vane pumps are quiet. Can also be variable displacement.
Friction and leakage.
Generally:
Gear type: pmax  17  25 MPa ηt  0,7  0,85
Vane type: pmax  7  25 MPa ηt  0,8  0,9
Piston type: pmax  16  45 MPa ηt  0,85  0,95
Displacements: Vk  1  1000 cm3/r
Motor types are basically the same.

22. Pumps

23. Pump equations Ideal and real values for flow, torque and power
Efficiencies  < 1
Ideal and real values for flow, torque and power
Produced flow rate 𝒒 𝒗 =𝒏 𝑽 𝒓 𝜼 𝒗 Required torque 𝑻= 𝚫𝐩 𝐕 𝒓 𝟐𝝅 𝜼 𝒉𝒎 Required power 𝑷= 𝒒 𝒗 𝚫𝐩 𝜼 𝒕𝒐𝒕
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
Displaced volume per rotation Vr can be variable. Vr depends on the pump type and its geometry.
Often we talk about rpm but remember that the Si unit is rad/s.
Bosch Rexroth

24. p : pressure difference
Pump efficiency
n : rotational speed
p : pressure difference
v : volumetric efficiency (leaks)
hm : hydromechanical efficiency (flow and mechanical frictions)
t : overall efficiency
Every power conversion includes losses in form of friction and leaks. These are descripted with efficiencies.
In simple equations efficiencies are considered to be constant, in reality they depend on pressure, rotation speed/velocity and fluid viscosity (which depends on temperature).

25. Motors Often exactly the same structure as in a pump Types
Axial piston
Bent axis
Radial piston
Gear
Gerotor
Vane
Motors tolerate pressure also in inlet side unlike most pumps.
Right top: tractor wheel motor

26. Parker F11/F12 - motor/pumps
Often used as a saw motor
Parker F11/F12 - motor/pumps
F11 (and F12) are bent axis, fixed displacement heavy-duty motor/pumps.

27. F11 and F12 performance Motor V= 4.9 ccm m= 5 kg Ppeak.theor= 41 kW

28. Motor equations
Flow rate in 𝒒 𝒗 = 𝒏 𝑽 𝒓 𝜼 𝒗 Produced torque 𝐓= 𝚫𝐩 𝐕 𝒓 𝜼 𝒉𝒎 𝟐𝝅 Power in 𝑷= 𝒒 𝒗 𝚫𝐩= 𝐓𝝎 𝜼 𝒕
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
Same equations as for pump but efficiencies in different place.
Again, Vr can be variable. Enables continuously variable tarnsmisison by varuing either pump
Bosch Rexroth

29. Hydrostatic transmission
Again, Vr can be variable. Enables continuously variable transmisison by varying either pump displacement, motor displacement or both.

30. Motor parameters
Generalized performance characteristics of hydraulic motors:
Low speed Tmax  1125 kNm
motors nmax  11000 r/min
t  0,80,95
Middle speed Tmax  501000 Nm
motors nmax  2001500 r/min
t  0,70,9
High speed Tmax  103000 Nm
motors nmax  2006000 r/min
t  0,80,9
Bosch Rexroth
Generally, rotating speed lower than with electric motors, produces higher torque.

31. Parker F11 efficiency F11-5 motor
F11-19 motors can be equipped with Power Boost
which in high speed applications can decrease the
mechanical losses by up to 15%.

32. 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 kg
Total efficiency exceeds 97%
2/6/2020

33. Semi-rotary motors (torque motors)
Generally
Rotation angle max  90720°
Torque Tmax  10300 kNm
Efficiency t  0,60,85
More torque than with a normal hydraulic motor.
Vane type: less than full turn rotation.

34. 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
Piston accumulator is a hydraulic cylinder without the rod.
Corresponds roughly to electric capacitor, not electric battery. Can receive very large powers but cannot store large amounts of energy.
Hydraulic diagram shows a system where the actuator can maintain force without the pump running constantly.

35. 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
”Compressed air” engine. In reality that is just marketing talk. There is not air anywhere in the powertrain. ”Compressed air” refers here to nitrogen used in the hydraulic accumulators. Air cannot be used in accumulators because it might explode when mixed with oil in high pressure.
Development put on hold in 2015 due to money and legislation problems

36. Applications: delivery trucks
Hydraulic parallel hybrid Energy recovery to pressure accumulator
Excellent for city driving with constant stops.
Garbage trucks, buses etc.

37. Cylinders Double or single acting Symmetric or asymmetric Generally
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
 100 mm (diameter)
350 bar
 275 kN
Volumetric efficiency usually very good but piston seals cause friction against the cylinder bore. A compromise between tight seals with high friction and leaking but easily sliding seals.
Force balance. Atmospheric pressure.

38. Cylinder equations
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 []
Flow rate 𝒒 𝒗𝟏 = 𝑨 𝟏 𝒗 𝜼 𝒗 Force balance 𝒑 𝟏 𝑨 𝟏 = 𝑭 𝜼 𝒉𝒎 + 𝒑 𝟐 𝑨 𝟑 Required power 𝑷= 𝒒 𝒗𝟏 ( 𝐩 𝟏 − 𝐀 𝟑 𝐀 𝟏 𝐩 𝟐 )= 𝐅𝐧𝐞𝐭𝐯 𝜼 𝒕
v=q_v/A
Force production is not the same in both directions with an asymmetric cylinder because the rod reduces the area affected by the pressure.
Atmospheric pressure on A2 neglected. Atmospheric pressure considered “base” pressure.

39. Telescopic cylinders Long stroke Often single acting Typically for
dump trailers
dump trucks
Commonly used in dump trucks.
Usually single acting, therefore and external load is required for the return movement.
Collapsed length 20 to 40 % of extended length.

40. Cylinder size D= 500 mm @ 400 bar  7.7 MN AIRBUS A380 - Superjumbo
3 jacks
Cylinders made in Finland
Empty mass kg
If piston diameter 0.5 m, produced force at 40 Mpa ~7854 kN which equal lifting kg.

41. Hydraulic fluid Oil Filtering Water 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)
Usually it is assumed that the fluid is incompressible. This is not exactly true, especially if there are small air bubbles mixed in the fluid.
Water has a lower viscosity and a higher bulk modulus (it is less compressible) than oil.
Lower viscosity means more leakage.
Better lubrication increases component life.

42. Hydraulic systems

43. Valve control Pdissipation= pqv  heat Throttling 𝑞 v = 𝐶 𝑞 𝐴 0 2∆𝑝 𝜌
Throttling means dissipation
Pdissipation= pqv  heat
Valve control
Throttling
𝑞 v = 𝐶 𝑞 𝐴 ∆𝑝 𝜌
Control of flow with flow area
4/3 directional spool valve
4-way
3-position
Valve control
System power input (qV·p) exceeds the power need of actuators, valves produce power losses to control the output power
results into typically low system efficiency
Restricting flow – generating pressure loss

44. Generation of system pressure
External
LOAD
Friction
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
pload
Lifting
Flow
Flow rate qv
Pipe 2
ppipe
Throttle
pthrottle
Pipe 1
ppipe
Pressure increases
ppump
In hydraulics, absolute pressure often does not matter but the pressure difference over a device.
Atmospheric pressure
Tank/Reservoir

45. Generation of system pressure
If you know actuators’ velocities you know also the flow rates and you can calculate system pressures by starting from the end, the tank.
Pump
Finally the pump pressure
When system is operating, the pressure at different points of system is different. Minimizing pressure losses maximizes system efficiency. Part of the pressure losses are control related.
Often coupled with combustion engines which cannot be used for pump control efficiently.
Tank pressure can be considered zero. In hydraulics, the main thing is pressure difference, not absolute pressures i.e. tank pressure = atmospheric pressure = zero.
In the image, if the actuators do not move, all the flow rate goes through the pressure relief valve and its cracking pressure determines the pressure level at pump outlet.
Supply line divided for two actuators. Valves used to direct flow. If both actuators active, flow goes where the pressure level is lowest.
What if the hose to the cylinder breaks?
Pitäisikö tässä vaiheessa piirrellä taululle se oma systeemi, näyttää vapaakierto, PRV, jne.
Start from here
Tank

46. Manual valves
Controlling booms etc. Usually spool type Proportional or logic (ON/OFF)
Common in mobile machinery

47. Electric valves Electric actuators as electric interfaces
Solenoids  ON/OFF
Proportional solenoids  proportional valves
Torque motors  servo valves
Voice coils  ”proportional valves”
Torque motor (Proportional) solenoid
Pilot/direct operated.
Control command to the control electronics can be voltage signal, current signal or digital signal (various buses).
Servo valve with torque motor Proportional control valve with proportional solenoid

48. Other valves Pressure relief valves Check valves Shuttle 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

49. Pump control Produce only the required fluid with the pump Options
Inverter controlled motor
Servomotor
Variable displacement pump
Pump controlled systems:
System power input (qV·p) is matched to the power need of actuators. This is done by controlling the swept volume of the pump. ->results into higher system efficiency

50. Direct Drive Hydraulics
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

51. Direct Drive Hydraulics in the laboratory
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
”DDH-LITE”
Student project developed during
MEC-E Fluid Power Systems
MEC-E Mechatronics Project
”Dolores” (Parker)
”Rex” (Bosch-Rexroth)
Koivusaari & Smolander

52. http://www. norrhydro. com/media/files/pdf/linjama_vihtanen_sicfp09
Actuator control
Variable displacement motors Multi chamber cylinders (digital hydraulics)
Connect the chambers to different pressure sources
Low pressure
High pressure
Multiple different forces
Control of force
Control of velocity
Control of position
Actuator control aka secondary control
Reverse thinking: controlling the swept volume of actuators affects to the qV and p need of actuator in certain loading condition (i.e. required speed and force or torque).
Controlling of the swept volume of hydraulic motor enables better matching of the characteristics of the motor to the characteristics of the load or/and the system pump.
 results into higher system efficiency
Control of swept volume is also possible with some special cylinders, e.g., so called digital cylinders. In these the construction of the cylinder enables selection of typically 2 to 3 different effective piston areas.

53. Summary of control methods
Q = flow rate p = pressure

54. Mechatronics in Fluid Power
Examples
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

55. Valves for control systems (1)
Separate control electronics
Valves for control systems (1)
Proportional Solenoid operated proportional control valves
Electronics can be also integrated into the valve!
Frequency response of spool displacement
+/- 5%
+/- 100%
Proportional solenoid
[Amplitude, dB]
LVDT position sensor
Spool valve
Response is
displacement
amplitude dependent
Stroke amplitude
Phase lag
[Phase, ]
[Hz]
Proportional Directional Control Valve
Rexroth 4WRPH6
Step response at 100 % step < 10 ms

56. Proportional solenoid
Rated magnetic force 47 N
Working stroke 2 mm
Solenoid weight kg
Armature weight kg
Proportional solenoid
ON/OFF solenoid

57. Valves for control systems (2)
Voice Coil operated proportional control valves
Control electronics
Size:
NG06 / CETOP 03 / NFPA D03
Voice coil
Moving Coil Assembly v
Permanent Magnetic Field Assembly
Moving Coil Actuator
Nominal flow up to bars
Step response at 100 % step < 3.5 ms
Measured with load (100 bar pressure drop/two control edges)
Spool valve
Voice Coil operated Proportional Directional Control Valve - Parker DFplus

58. Distributed control systems
Distributed control system for boom operations.
Based on
Microcontroller
Proportional valves
Joystick operation
CAN Bus
Danfoss
2/6/2020

59. Digital Hydraulic valves Tapio 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 bar
Laminated valve body
Pilot and main valve
Magnetic sub-system simulation

60. Digital hydraulic valves
Enhanced 3D printed version also made and tested
Selective Laser Melted manifold
 Enables optimization of flow paths
Improved flow channels  pressure loss reduced up to 49%

61. Misc.

62. 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
In fluid power systems the most important/interesting quantities are the ones related to transforming, transferring and controlling of power.
 pressure
 flow rate
 position (linear and rotational motion)
 speed (linear and rotational motion)
 acceleration (linear and rotational motion)
 force
 torque
 temperature (!)
 characteristics of fluid
If measuring of force or torque is required, transducers for these are typically installed externally between the actuator and its load. (Estimation of values of these quantities is also possible by measuring the inlet and outlet pressures of the actuator.)
Pressure transducer can also be integrated in the valve controlling the actuator.

63. Flow measurements Operation principles Gear Turbine Ultrasound
Orifice plate
Gear
Turbine

64. Integrated actuators Cylinder with integrated position sensor
Eaton
Moog
Cylinder with integrated position sensor
When a transducer is integrated into actuator, it typically is
- position transducer (cylinders)
- velocity transducer (cylinders and motors)
- pressure transducer (cylinders and motors)
Actuators equipped with transducers (integrated or external) are generally referred as servo actuators and they are to be used in feedback control systems.
Valve controlling the servo actuator is typically installed as close to the actuator as possible (minimization of fluid volume)
 small elasticity  high stiffness  accuracy  but also possible vibration problems  need for controllers
Servo cylinder with integrated valve

65. 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

66. Pros and cons Advantages Deficiencies If requirements for
high force or torque and small component weight and size
flexible power transmission routing
Consider using hydraulics!
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
Actuators tolerate impacts and overloading unlike mecanical transmission, for example a ball screw.
Easier to route power than with mechanical transmission systems. Flexible hoses etc.

67. 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?