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II-C Power & Energy SystemsDennis Buckmaster
dbuckmas@purdue.eduhttps://engineering.ecn.purdue.edu/~dbuckmas/
OUTLINE
Internal combustion engines
Hydraulic power circuits Mechanical power transmission
Electrical circuit analysis (briefly)
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References
Engineering Principles of
Agricultural Machinery, 2nd
ed. 2006. Srivastava,
Goering, Rohrbach,
Buckmaster. ASABE.
Off-Road Vehicle
Engineering Principles.2003. Goering, Stone, Smith,
Turnquist. ASABE.
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Other good sources
Fluid Power Circuits and
Controls: Fundamentals
and Applications. 2002.
Cundiff. CRC Press.
Machine Design for
Mobile and Industrial
Applications. 1999. Krutz,Schueller, Claar. SAE.
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Engines
Power and Efficiencies
Thermodynamics
Performance
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Engine Power Flows
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Power&
Efficiencies
Fuel equivalent
Pfe,kW = (HgkJ/kgf,kg/h)/3600
[Hg = 45,000 kJ/kg for No. 2 diesel] Indicated
Pi,kW = pime,kPaDe,lNe,rpm/120000
BrakePb,kW = 2TNmNe,rpm/60000
Friction
Pf
= Pi
-Pb
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Power &
Eff iciencies
Indicated Thermal
Eit = Pi/Pfe
MechanicalEm = Pb/Pi
Overall (brake thermal)
Ebt = Pb/Pfe = Eit*Em Brake Specific Fuel Consumption
BSFC= f,kg/h/Pb,kW
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Dual Cycle
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Related equations
Compression ratio = rr = V1/V2
Displacement
De,l = (V1-V2)*(# cylinders)= (borecm)
2(strokecm)*(# cyl)/4000
Ideal gas
p1V1/T1 = P2V2/T2 Polytropic compression or expansion
p2/p1 = rn
[n = 1 (isothermal) to 1.4 (adiabatic), about 1.3 during
compression & power strokes]
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Air intakea,kg/h = .03De,lNe,rpma,kg/cu mv,decimal
From Stoichiometry (fuel chemistry) A/F = air to fuel mass ratio = 15:1 for cetane
Related equations
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What is the displacement of a 6 cylinder
engine having a 116 mm bore and 120 mm
stroke?
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For this same engine (7.6 l displacement, 2200 rpm rated speed), what is the air
consumption if it is naturally aspirated and has a volumetric efficiency of 85%?
Assume a typical day with air density of 1.15 kg/m3.
With a stoichiometric air to fuel ratio based on cetane, at what rate could fuel
theoretically be burned?
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Consider the this same (595 Nm, 137 kW @ 2200 rpm) engine which has a high
idle speed of 2400 rpm and a torque reserve of 30%; peak torque occurs at 1300
rpm. Sketch the torque and power curves (versus engine speed).
Torque (Nm)
Speed (rpm)
Power (kW)
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17
A quick problem
Diesel engine generating 60 kW at 2300 rpm
Q: torque available
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Power Hydraulics
Principles
Pumps, motors
Cylinders
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About Pressure
14.7 psia STP (approx __ in Hg)
Gage is relative to atmospheric
Absolute is what it says absolute & relative to
perfect vacuum
What causes oil to enter a pump?
Typical pressures: Pneumatic system
Off-road hydraulic systems
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20
Liquids Have no Shape of their own
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21
Liquids are
Practically Incompressible
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Pascals Law
Pressure Exerted on a Confined Fluid is
Transmitted Undiminished in All Directions
and Acts With Equal Force on Equal Areas
and at Right Angles to Them.
22
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Application Principles
1 lb (.45kg)Force
1 sq in (.65cm2)
Piston Area
1 psi
(6.9kpa)
10 sq in
(6.5cm2)
Piston Area
10 lbs (4.5kg)
23
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24
Hydraulic lever
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25
Types of Hydraulic Systems
Open Center
Closed Center
The control valve that regulates the flow from the pump
determines if system is open or closed.
Do not confuse Hydraulics with the Closed Loop of thePower Train. (Hydro)
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Trapped Oil
Closed Center HydraulicsOpen Center
Flow in Neutral
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Extend 27
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Retract 28
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Neutral Again 29
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Pumps
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Pump Inefficiency
Leakage: you get less flow from a pump
than simple theory suggests.
Increases with larger pressure difference
Friction: it takes some torque to turn a
pump even if there is no pressure rise
Is more of a factor at low pressures
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Efficiency of pumps & motors
Em mechanical efficiency < 1 due to
friction, flow resistance
Ev
volumetric efficiency < 1 due to
leakage
Eo =overall efficiency = Em * Ev
Eo
= Power out/power in
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Speed
Flow
Qgpm = Dcu in/rev Nrpm /231
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Pressure Rise
Torque
Required
Tinlb = Dcu in/revPpsi /(2)
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Pressure
Flow
Theoretical pump
Effect of leakage
Relief valve or pressure
compensator
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Pressure
Flow
Constant power curve
Php = Ppsi Qgpm/1714
1 If t t
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1a. If a pump turns at
2000 rpm with a
displacement of 3
in3/rev, theoretically,how much flow is
created?
1b. If the same pump is
95% volumetrically
efficient (5%
leakage), how muchflow is created?
Example pump
problems
2 If 8 i i d
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Example pump
problems
2a. If 8 gpm is required
and the pump is to turn
at 1750 rpm, what
displacement istheoretically needed?
2b. If the same pump willreally be is 90%
volumetrically efficient
(10% leakage), what is
the smallest pump tochoose?
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3a. A 7 in3/rev pump is to
generate 3000 psi
pressure rise; how much
torque will it theoreticallytake to turn the pump?
3b. If the same pump is91% mechanically
efficient (9% friction &
drag), how much torque
must the prime moverdeliver?
Example pump
problems
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Example motor
problemIf a motor with 2 in3/rev
displacement and 90%
mechanical and 92%volumetric efficiencies
receives 13 gpm at
2000 psi
a. How much fluid poweris received?
b. What is its overall
efficiency?c. How fast will it turn?
d. How much torque will
be generated?
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Cylinders
Force balance on
piston assembly: FexternalP1 * A1 P2 * A2
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42
3000 psi system
2 bore cylinder
Extends 24 inches in 10seconds
Q: max force generated
max work done
power used
flow required
Example cylinder
problem
Tractor source with 2500 psi
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Tractor source with 2500 psiand 13 gpm available
Return pressure tax of 500 psi
Cylinder with 3 bore, 1.5 roddiameters
Q1: How much force will thecylinder generate?
Q2: How long will it take to
extend 12 inches?
Example cylinder
problem
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Power Transmission
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Transmissions transform power
a torque for speed torque tradeoff
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Gears
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Planetary Gear Sets
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Belt & Chain Drives
Speed ratio determined by sprocket teeth
or belt sheave diameter ratio
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FIRST GEAR
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First gear speeds if Input shaft: 1000 rpm
Main countershaft: 1000 (22/61) = 360 rpm
Ratio = input speed/output speed = 1000/360 = 2.78
Ratio = output teeth/input teeth = 61/22 = 2.78Secondary countershaft: 360 rpm (41/42) = 351 rpm
Output shaft: 351 rpm (14/45) = 109 rpm
RATIO: input speed/output speed = 1000/109 = 9.2
Product of output teeth/input teeth = (61/22)(42/41)(45/14) = 9.2
FIRST GEAR
If 50 kW @ 2400 d iE l
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If 50 kW @ 2400 rpm drives a
pinion gear with 30 teeth and
the meshing gear has 90
teeth (assume 98%efficiency)
Q1: What is the speed of the
output shaft? Q2: How much power leaves
the output shaft?
Q3: How much torque leaves
the output shaft?
Example gear
problem
If th f l tE l l t
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If the sun of a planetary gear
set turns at 1000 rpm, what
speed of the ring would
result in a still planetcarrier? Teeth on gears are
sun: 20 and ring: 100.
Example planetary
gear problem
If a belt dri e from a 1750 rpmE l b lt
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If a belt drive from a 1750 rpm
electric motor is to transmit
5 hp to a driven shaft at 500
rpm and the small sheavehas a pitch diameter of 4
Q1: What should the pitch
diameter of the other pulleybe?
Q2: Which shaft gets the small
sheave?
Q3: How much torque doesthe driven shaft receive?
Example belt
problem
Php = Tft-lbNrpm/5252
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Electricity
Voltage = Current * Resistance
Vvolts = Iamps * Rohms
Power = voltage times current
PWatts = Vvolts*Iamps
VI R
Th T f Ci it
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Three Types of Circuits
SeriesSame current, voltage divided
+
-12 v.
Parallel
Same voltage, current divided
Series / Parallel
A 12 V DC solenoid aE l 12 V DC
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A 12 V DC solenoid a
hydraulic valve has a 5 amp
fuse in its circuit.
Q1: What resistance would
you expect to measure as
you troubleshoot its
condition?Q2: How much electrical
power does it consume?
Example 12 V DC
problem
Q1: Identify specifications forE l 12 V DC
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Q1: Identify specifications for
a relay of a 12 V DC lighting
circuit on a mobile machine
if the circuit has four 60Wlamps.
Q2: Would the lamps be wiredin series or parallel?
Example 12 V DC
problem
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Good luck on the PE Exam!
My email address:dbuckmas@purdue.edu
My web page:https://engineering.ecn.purdue.edu/~dbuckmas/
Note ASABE members can access ASABEtexts electronically at:
http://asae.frymulti.com/toc.asp
mailto:dbuckmas@purdue.eduhttp://cobweb.ecn.purdue.edu/~dbuckmas/http://asae.frymulti.com/toc.asphttp://asae.frymulti.com/toc.asphttp://cobweb.ecn.purdue.edu/~dbuckmas/mailto:dbuckmas@purdue.eduRecommended