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1
TSM363 Fluid Power Systems
Pumps and Actuators
Tony Grift
Dept. of Agricultural & Biological EngineeringUniversity of Illinois
2
Agenda
• Units, Pumps, Pressure Relief Valve• Cylinders
• Double acting/ Single acting• Single rod, Double rod
• Cylinder construction• Pressure, Flow, Work and Power in cylinders• Pressure, Flow, Torque and Power in
pump/motors• Volumetric and Torque efficiency of
pump/motors• Pump implementations
3
Hydraulic Units (SI)
rad
mD
Nm
s
NmP
NmW
NF
mA
s
mq
m
Np
3
2
3
2
nt Displaceme
T Torque
ow Power
Work
Force
Area
Flow
Pressure
Pascal
Newton
Watt
Pascal 1010 Bar 1 52
5
m
N
4
Control can take place in various ways. Power is pressure times flow rate
• Pressure control• Pressure relief valve• Pressure reducing valve (regulator)• Pressure compensation: Only provide the pressure needed to
move the load(s). In idle reduce energy loss by providing a open center condition
• Pressure compensated pump. Make the pressure independent of the flow required to move the load at a preset speed. Deal with multiple cylinders that need to move simultaneously
• Flow control• Throttle (needle valve, very crude, Orifice equation applies)• Pressure compensated Flow Control Valve: Assure a preset flow
rate independent of the pressure drop across the valve• Pressure and Flow control
• Load sensing systems: combine pressure and flow control to reduce energy losses
5
Choice of pump depends on these factors
• Application• Max and working Pressure and Flow rate requirements• Constant rate / Variable rate• Pump efficiency• Leakage• Noise level• Contamination sensitivity
• Price
6
Pump ‘family tree’
7
Video 8: Power units (3:26)
• Power supply unit• Converts Mechanical energy into hydraulic energy• Hydraulic Fluid is conditioned (cooled, cleaned)
• Components• Drive motor• Safety valve• Oil reservoir • Pump
• External Gear pump function (constant delivery)• Where teeth unmesh, volume increases, oil enters• Where teeth mesh, volume decreases, oil leaves
• Pressure only builds when there is a resistance (load)• Safety valve needed to prevent failure when cylinder stalls
• Pressure Relief Valve diverts flow back to tank when cylinders are stalled
• Reservoir• Cools oil• Cleans oil from suspended particles, water and air which takes time
(Capacity)• Filters trap impurities• 70% of all malfunctions are due to impurities
8
• In case of a motor shaft, the Work can be found by multiplying a force through a distance. Suppose we assume a force at a distance . The total work per radian of the shaft is now equal to
Mechanical Torque in a pump/motor
r
F
1 Radian
r
rFWMECH *
9
Mechanical Power in a pump/motor
• The power is now equal to this value divided by the time per radian.
• If the shaft is turning at it takes seconds per radian.
• Since for Power we have to divide the Work by time, this leads to:
s
rad1
T
MECH rFrF
t
WPow **
1*
Nms
rad
s
Nm
TPowMECH
*
*
10
Hydraulic Power in pump/motor ( )
qpPowHYD *
outin qq
11
Pump/Motor flow is proportional to the speed of rotation and the displacement per revolution
*Dq
Pump displacement is a volume per angular displacement (radian).Assuming the volumetric efficiency is 1.0 (no leakage)
10,** VVDq
More realistic, with Volumetric Efficiency (why in numerator?)
12
Torque Required to drive a pump is proportional to Pressure
More realistic, with Torque Efficiency (why in the denominator?)
10,*
TT
DpT
(No losses here)
***
*DpPow
Dq
qpPowHYD
HYD
Constant
**
**DpT
TPow
DpPow
MECH
HYD
13
Power Efficiency of Pumps
VV
T
qDq
DpT
***
*
From before:
And
TPowMECH *
TVTVMECH
pqDp
D
qTPow
*
***
**
Power Efficiency: Without loss
Efficiencies
14
Data sheet Eaton MHT vane pump
15
A Pressure Relief Valve (PRV) provides overload protection
• In the symbol there are• Main pressure lines (solid)• Sense lines (dashed)• Spring return• Adjust arrow• Direction arrow• Pressure and Tank connections
16
Some questions about a PRV
• Is this valve normal open or normal closed• Closed / open, think of a door
• Where is the pressure sensed, upstream or downstream and why ?
• What is the pressure at the tank port ? • Why is a PRV adjustable ?
17
Cylinders
18
Video 9: Hydraulic actuators (6:58)
• Cylinders convert hydraulic energy into linear motion• Motors generate rotary motion• Single acting cylinder: One working port
• Can do work in only one direction (extension)• External force retracts the cylinder• No perfect seal, over time oil passes on to unpressurized
side: need for drain• Good for high load single lift (scissor platform)• Return stroke through gravity or spring return• Plunger (ram) cylinders: Cap end only, very powerful and
stiff• Double acting cylinder: Two working ports
• Pressure advances and retracts the cylinder: push and pull• Cylinder retracts faster than it extends due to different
areas of cap end and rod end side
19
Video 9: Hydraulic actuators (6:58) cont.
• Example: ratio of cap and rod end side area is 2:1.
• Assume • During extension rod end pressure =0• During retraction cap end pressure =0
2*
* * 2*
*
CAP ROD
CAPEXT CAP EXT RET RET
RODRET ROD
A AA
F p A F F FA
F p A
22
*N
F N p A mm
20
Video 9: Hydraulic actuators (6:58) cont.
• Example: ratio of cap and rod end side area is 2:1.
2*
1* *
2
CAP ROD
RODEXT EXT RET RET
CAP CAP
RETROD
A A
Aqv v v v
A A
qv
A
* m NmF N v P Watt
s s
• Linear Power: *Pow F v
3
2
mq
smv
s A m
21
Hydraulic Cylinder
22
Cylinder construction
1 2 3 4 5 6
7
8 9 10 11 12 13
23
1 2 3 4 5 6
7
8 9 10 11 12 13
1. Tie rod ( keeps cylinder assembly together )2. Rod end head ( mounting point )3. Rod end port ( fluid entrance/exit point )4. Piston seals ( dynamic, seals cap end from rod end
pressure)5. Cap end head ( mounting point)6. Cap end port ( fluid entrance/exit point )7. Rod bearing ( lateral support of the rod )8. Rod wiper ( keeps dirt out )9. Rod seal (dynamic, seals fluid from
environment )10. Barrel ( cylinder )11. Piston rod ( mechanical force output )12. Piston ( pressure to force converter )13. Static seal ( seals fluid from environment )
24
Cylinders are perfect for linear motion
• Single rod (most common)
• Dual rod (power steering)
25
Telescopic cylinder
26
Basic Circuit with Double Acting Cylinder
Pump
Actuator
OverloadProtection
Reservoir
Pressuregage
Electric Motor
27
Question: Can the cylinder be moved ?
1) Cylinder:• Double acting, differential area
2) Fluid is incompressible3) Rod and cap end connected
Check in FluidSim
28
Hydraulic Work (rod end pressure = 0)
AR AC
F
pR pC
s Cq
0
***
R
CC
p
sApsFW
29
AR AC
Cq Rq
F
FR FC
pR pC
s
R
R
C
C
RR
R
CC
C
A
q
A
q
vAt
sAq
vAt
sAq
Differential area cylinder: Flow and displacement
30
Differential area cylinder: Force equilibrium
RC F
RR
F
CC ApApF
AR AC
Cq Rq
F
FR FC
pR pC
s
31
Differential area cylinder: Work
RRCC ApApsFsW
AR AC
Cq Rq
F
FR FC
pR pC
s
0Rp
32
Differential area cylinder: Power
RRCC ApApsFsW
RRCC
q
RR
q
CC qpqp
t
sAp
t
sAp
t
sF
t
WPow
RC
AR AC
Cq Rq
F
FR FC
pR pC
s
33
Dual rod cylinder: Power
CRCC ApApsFsW
p
RCC
q
CR
q
CC ppq
t
sAp
t
sAp
t
sF
t
WPow
CC
AR AC
Cq Rq
F FR FC
pR pC
s
34
Power if (as in motors and pumps)
pqPow *
AR AC
Cq Rq
F FR FC
pR pC
s
qqq outin
35
Question: Will the cylinder extend ?
Check in FluidSim
36
Video 5: Pressure transmission (0:53)
• Pressure intensification in hydraulic systems:• Differential area cylinders cause this effect• Max pressure in the system is NOT PRV setting !
*
* * *CAP CAP CAP
CAPROD ROD ROD CAP CAP ROD ROD ROD CAP
RODCAP ROD
F p AA
F p A p A p A p pA
F F
PRVp
Check in FluidSim
37
Question in ‘Customary Units’
• Given• PRV Setting 15 MPa• pump displacement of 10.54 cm3/rev• the speed of the pump is 1800 rpm
• Required• Torque needed to drive the pump • Power needed to drive the pump
• Neglect friction
38
Answer in ‘Customary Units’
s
Nm 4743188.495*Nm25.163*
Nm 25.163615*66775.1*
188.495min
60
1*2*
min1800
66775.110
1*
2
1*54.10
61515
2
3
3
3
3
6
3
2
s
radTPow
m
NE
rad
mEpDT
s
rad
srev
radrev
rad
mE
cm
m
rad
rev
rev
cmD
m
NEMPap
PRV
PRV
39
Question in ‘Customary Units’
• Given• PRV Setting• pump displacement of • the speed of the pump
• Required• Torque needed to drive the pump • Power needed to drive the pump .
• Neglect friction
40
Answer in SI Units
*
*
TPow
pDT
MECH
PRVMECH
41
Types of Pumps and Motors
• External Gear• Internal Gear• Vane• Axial Piston• Radial Piston
42
External Gear pump
• Poorly sealing• Low flow rates• Low pressures• Fixed displacement• Low cost
43
Internal Gear pump
• Poorly sealing• Low flow rates• Medium pressures• Fixed displacement• Medium cost
44
Vane pump
• Medium sealing• Higher pressures• Inexpensive• Fixed or variable
flow rate
45
Axial piston pump with swash plate. In this case the swash plate angle is variable, which results in a variable delivery pump
• Excellent sealing• High pressures• Relatively simple design• Variable flow rate• No need for valves• Expensive
46
Axial piston pump with swash plate. In this case the swash plate angle is constant, which results in a constant delivery pump
• Here fixed flow rate
47
Radial piston pump with variable rate through changing eccentricity between shaft and ‘pintle’
• Excellent sealing• High pressures• Relatively expensive• Variable flow rate• Valves are needed• Complex design
48
Radial piston pump with variable rate through changing eccentricity between shaft and ‘pintle’
• Excellent sealing• High pressures• Relatively expensive• Variable flow rate
49
External Gear
Fixed Displacement
50
Pump ‘family tree’
51
TSM363 Fluid Power Systems
Pumps and Actuators
The End
Dept. of Agricultural & Biological EngineeringUniversity of Illinois