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©2009 Bo R Andersson
Hydraulic systems for Mobile Applications
Sid 1
TMMS10 Fluida system och transmissioner2014-05-08
Bo R Andersson
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©2009 Bo R Andersson 2
Mobile Hydraulics”Continously operated by a human being”
Difficulties and challenges:• Wide operating range
• No consistency between flow and speed
• Simultanous operation of several functions
• Saturation of pump flow
• Low efficiency and heat generation
• Safety and stability
• Low natural frequency and low damping
• Cost
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©2009 Bo R Andersson 3
Mobile Hydraulics”Continously operated by a human being”
Difficulties and challenges:• Wide operating range
• No consistency between flow and speed
• Simultanous operation of several functions
• Saturation of pump flow
• Low efficiency and heat generation
• Safety and stability
• Low natural frequency and low damping
• Cost
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©2009 Bo R Andersson 4
Content
Low natural frequency and low damping- Oscillations of hydro-mechanical systems- Natural frequency- Damping by the hydraulic system- Simulations of different types of systems- Load Holding Valves
May 08, 2014Bo R Andersson
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©2009 Bo R Andersson 5
Control of position by control of velocity(change of velocity, acceleration, deceleration)
Open-Center Valves
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©2009 Bo R Andersson Linköpings universitetSid 6
A mobile application
- Steady state performace very important
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©2009 Bo R Andersson Linköpings universitetSid 7
A mobile application
- Steady state performace very important- Dynamic performance still more important!
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©2009 Bo R Andersson Linköpings universitetSid 8
Car Suspension
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©2009 Bo R Andersson Linköpings universitetSid 9
Car suspension damping
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©2009 Bo R Andersson Linköpings universitetSid 10
Damping of a hydraulic operated boom?
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©2009 Bo R Andersson Linköpings universitetSid 11
Oscillations of hydro-mechanical systemsNatural Frequency
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©2009 Bo R Andersson Sid 12
Oscillations of hydro-mechanical systemsNatural Frequency
Video
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©2009 Bo R Andersson Sid 13
Natural Frequency of an arm with a load
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©2009 Bo R Andersson Sid 14
Natural Frequency of an arm with a load
Higher working pressure
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©2009 Bo R Andersson Sid 15
New machines will have even lower natural frequency!New machines will be even more lika a ”fishing pole”!New machines will have even lower damping!
Even more important to avoid oscillations!!
EgenfrekvensNatural Frequency
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©2009 Bo R Andersson Linköpings universitetSid 16
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©2009 Bo R Andersson Linköpings universitetSid 17
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©2009 Bo R Andersson Sid 18
0
10
20
30
40
50
60
70
80
90
100
0 2 4 6 8 10 12
Cp = oo
Cp = 0
dP
dQ
Cp =dQ
dP
05
1015202530354045
0 5 10 15 20 25 30 35
0
5
10
15
20
25
30
35
0 5 10 15 20 25 30 35
Cp
M
pQ diagramEgenfrekvens, dämpning
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©2009 Bo R Andersson
Mobile Valve Systems from a dynamic Point of View
19
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©2009 Bo R Andersson 20
Constant Pressure SystemThrottle Valve (Variable orifice)
Simulation
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©2009 Bo R Andersson Sid 21
Qp-Diagram for Closed-Center Valve
0
10
20
30
40
50
60
70
80
90
100
0 20 40 60 80 100
Q Load %
p L
oad
% dQ
dp
20% 30% 40%
50%
60%
70%
80%
100%
pQ-diagram, Closed-Centre Valve
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©2009 Bo R Andersson 22
Constant Flow System – Open-CentreThrottle Valve (Variable orifice)
Simulation
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©2009 Bo R Andersson Sid 23
pQ-diagram, open-centre valve
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©2009 Bo R Andersson 24
Damping by a LS valve
Simulation
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©2009 Bo R Andersson 25
Damping by a LS-valveIncreased damping by use of meter-out restriction
Simulering
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©2009 Bo R Andersson Sid 26
Dämpning med LS-ventil
Va/Vb = 1/3 - 3/1, = 0.5
Va/Vb = 1/3 - 3/1, = 1.0
b
a
V
V21
4/3
1
e
bccbm m
VAK
Meter-out dampingDamping by a LS-valve:
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©2009 Bo R Andersson Sid 27
Fig. 11, 12
CMX-valvePressure feedback
Danfoss PVG 32 has a special version with a pressure control spool
Parker has two types of pressure feedback
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©2009 Bo R Andersson 28
Damping by a LS-valveIncreased damping by use of pressure feedback
Simulation
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©2009 Bo R Andersson Sid 29
Crane without pressure feedback
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©2009 Bo R Andersson Sid 30
Crane with pressure feedback
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©2009 Bo R Andersson 31
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©2009 Bo R Andersson Sid 32
Safety ...
Slangbrott: “s”
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©2009 Bo R Andersson 33
Over-center valves have the following functions :
- Hose rupture safety
- Load holding with 0 leakage
- Important part of over-load system
- Control of lowering speed
- Relief and chock valve
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©2009 Bo R Andersson Sid 34
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©2009 Bo R Andersson
Load Holding Valvesof
Over-Centre Type
Easily start to oscillate! Why?
High power losses! Why?
35
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©2009 Bo R Andersson Sid 36
Lorry Crane
Typical Over-Centre Valve
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©2009 Bo R Andersson Sid 37
Load goes over-centre
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©2009 Bo R Andersson Sid 38
Meter-in control
Load goes over-centre
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©2009 Bo R Andersson Sid 39
P T
Hoist sustem
Avoid cavitation by ”pumping down” the load
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©2009 Bo R Andersson Sid 40
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©2009 Bo R Andersson Sid 41
Crane arm controlled by an open-center valveand an over-center valve
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©2009 Bo R Andersson 42
Steady state control of LHV
Areaförhållande: 1
2
A
A 0
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©2009 Bo R Andersson Sid 43
Analyze of an over-centre valve system
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©2009 Bo R Andersson Sid 44
Analyze of an over-centre valve system
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©2009 Bo R Andersson Sid 45
Oscillating hydro-mechanical system
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©2009 Bo R Andersson Sid 46
Pressure oscillations
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©2009 Bo R Andersson Sid 47
Simulering
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©2009 Bo R Andersson 48
Over-centre valves in crane ssytems
Use of Over-Center Valves:-Hose Rupture Safety Protection-Low Leakage-Active part of OLP System-Speed Control-Pressure Relief function
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©2009 Bo R Andersson 49
Use of Over-Center Valves:-Hose Rupture Safety Protection-Low Leakage-Active part of OLP System-Speed Control-Pressure Relief function
Difficult to avoid oscillations!
Waste of energy!
Over-centre valves in crane ssytems
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©2009 Bo R Andersson Sid 50
3G - New Load Holding Valve
How does it work?
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©2009 Bo R Andersson Sid 51
3G - Load holding Valve
How does it eliminate power losses?
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©2009 Bo R Andersson Sid 52
3G - Load holding Valve
How does it eliminate power losses?
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©2009 Bo R Andersson Sid 53
3G - LHV
Conclusions:
- Hose rupture safety without compromising safety or performance
- Elimination of tendency to oscillate associated with over-centre valve systems
- Elimination of power losses when lowering gravity loads