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Transcript of V. Machines (A,B,C,J) Dennis Buckmaster [email protected] dbuckmas/ [email protected] OUTLINE...
V. Machines (A,B,C,J)Dennis Buckmaster
[email protected]://engineering.purdue.edu/~dbuckmas/
OUTLINE
• Internal combustion engines
• Hydraulic power circuits
• Mechanical power transmission
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.
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.
Free & Online
http://hydraulicspneumatics.com/learning-resources/ebooks
ASABE members can access ASABE texts & Standards electronically at:
http://elibrary.asabe.org/toc.asp
Engines
• Power and Efficiencies
• Thermodynamics
• Performance
Engine Power Flows
Power & Efficiencies
• Fuel equivalent
Pfe,kW = (HgkJ/kg∙ṁf,kg/h)/3600
[Hg = 45,000 kJ/kg for No. 2 diesel]• Indicated
Pi,kW = pime,kPaDe,lNe,rpm/120000
• Brake
Pb,kW = 2πTNmNe,rpm/60000
• Friction
Pf = Pi-Pb
Power & Efficiencies
• Indicated Thermal
Eit = Pi/Pfe
• Mechanical
Em = Pb/Pi
• Overall (brake thermal)
Ebt = Pb/Pfe = Eit*Em
• Brake Specific Fuel Consumption
BSFC= ṁf,kg/h/Pb,kW
Dual Cycle
Related equations• Compression ratio = r
r = V1/V2
• Displacement
De,l = (V1-V2)*(# cylinders)
= π(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]
• Air intake
ṁa,kg/h = .03De,lNe,rpmρa,kg/cu mηv,decimal
From Stoichiometry (fuel chemistry)• A/F = air to fuel mass ratio = 15:1 for cetane
Related equations
What is the displacement of a 6 cylinder engine having a 116 mm bore and 120 mm stroke?
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?
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)
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)
Alternative fuels
What has to be similar?
•Self Ignition Temperature
•Energy density
•Flow characteristics
•Stoichiometric A/F ratio
Power Hydraulics
• Principles
• Pumps, motors
• Cylinders
• Pressure compensated & load sensing systems
• Electrohydraulics introduction
21
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
22
Liquids Have no Shape of their own
23
Liquids are Practically Incompressible
Pascal’s 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.
24
Application Principles1 lb (.45kg)Force
1 sq in (.65cm2)Piston Area
1 psi
(6.9kpa)
10 sq in (6.5cm2)Piston Area
10 lbs (4.5kg)
25
26
Hydraulic “lever”
27
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 the Power Train. (Hydro)
28
Trapped Oil
Closed Center HydraulicsOpen CenterFlow in Neutral
Extend 29
Retract 30
Neutral Again 31
Pumps
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
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
Speed
Flow
Qgpm = Dcu in/rev Nrpm /231
Speed
Flow
Qgpm = Dcu in/rev Nrpm /231
Pressure Rise
TorqueRequired
Tinlb = Dcu in/rev ∆Ppsi /(2π)
Pressure Rise
TorqueRequired
Tinlb = Dcu in/rev ∆Ppsi /(2π)
Pressure
Flow
Theoretical pump
Effect of leakage
Relief valve or pressure compensator
Pressure
Flow
Constant power curve
Php = Ppsi Qgpm/1714
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 much flow is created?
Example pump problems
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 much flow is created?
Example pump problems
Example pump problems
2a. If 8 gpm is required and the pump is to turn at 1750 rpm, what displacement is theoretically needed?
2b. If the same pump will really be is 90% volumetrically efficient (10% leakage), what is the smallest pump to choose?
Example pump problems
2a. If 8 gpm is required and the pump is to turn at 1750 rpm, what displacement is theoretically needed?
2b. If the same pump will really be is 90% volumetrically efficient (10% leakage), what is the smallest pump to choose?
3a. A 7 in3/rev pump is to generate 3000 psi pressure rise; how much torque will it theoretically take to turn the pump?
3b. If the same pump is 91% mechanically efficient (9% friction & drag), how much torque must the prime mover deliver?
Example pump problems
3a. A 7 in3/rev pump is to generate 3000 psi pressure rise; how much torque will it theoretically take to turn the pump?
3b. If the same pump is 91% mechanically efficient (9% friction & drag), how much torque must the prime mover deliver?
Example pump problems
Example motor problem
If a motor with 2 in3/rev displacement and 90% mechanical and 92% volumetric efficiencies receives 13 gpm at 2000 psi …
a. How much fluid power is received?
b. What is it’s overall efficiency?
c. How fast will it turn?
d. How much torque will be generated?
Example motor problem
If a motor with 2 in3/rev displacement and 90% mechanical and 92% volumetric efficiencies receives 13 gpm at 2000 psi …
a. How much fluid power is received?
b. What is it’s overall efficiency?
c. How fast will it turn?
d. How much torque will be generated?
Example motor problem
If a motor with 2 in3/rev displacement and 90% mechanical and 92% volumetric efficiencies receives 13 gpm at 2000 psi …
a. How much fluid power is received?
b. What is it’s overall efficiency?
c. How fast will it turn?
d. How much torque will be generated?
Cylinders
Force balance on piston assembly: Fexternal
P1 * A1P2 * A2
51
• 3000 psi system• 2” bore cylinder• Extends 24 inches in 10
seconds• Q: max force generated• max work done• power used• flow required
Example cylinder problem
• Tractor source with 2500 psi and 13 gpm available
• Return pressure “tax” of 500 psi• Cylinder with 3” bore, 1.5” rod
diameters
• Q1: How much force will the cylinder generate?
• Q2: How long will it take to extend 12 inches?
Example cylinder problem
• Pressure builds due to resistance
• A fixed displacement pump delivering flow with the capability of 3000 psi does not always deliver 3000 psi!
• How much pressure does a pump deliver?
• What limits pressure delivered?
Load Sensing Advantage
Open CenterPump size & speed sets flowRelief valve sets pressure
Pressure compensated Pump
Pressure Compensated Circuit
Load Sensing Advantage
Open CenterPump size & speed sets flowRelief valve sets pressure
Closed Center, Pressure CompensatedCompensator adjusts displacement & flowCompensator sets pressure
LOAD SENSING CIRCUIT
Load Sensing Advantage
Open CenterPump size & speed sets flowRelief valve sets pressure
Closed Center, Pressure CompensatedCompensator adjusts displacement & flowCompensator sets pressure
Load SensingCompensator adjusts displacement & flowLoad sensing compensator sets pressure
HYDRAULIC PLUMBING
-- SIZE
Pulse Width Modulation
Spool valve
Typical Valve Performance
Power Transmission
Transmissions transform powera torque for speed tradeoff
Gears
Planetary Gear Sets
Belt & Chain Drives
• Speed ratio determined by sprocket teeth or belt sheave diameter ratio
FIRST GEAR
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 = 2.78
Secondary 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 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 the sun of a planetary gear set turns at 1000 rpm, what speed of the ring would result in a still planet carrier? Teeth on gears are sun: 20 and ring: 100.
Example planetary gear problem
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 sheave has a pitch diameter of 4” …
Q1: What should the pitch diameter of the other pulley be?
Q2: Which shaft gets the small sheave?
Q3: How much torque does the driven shaft receive?
Example belt problem
Php = Tft-lbNrpm/5252
THE END
• Skip what follows
ElectricityElectricityVoltage = Current * Resistance
Vvolts = Iamps * Rohms
Power = voltage times current
PWatts = Vvolts*Iamps
V
I R
Three Types of CircuitsThree Types of Circuits
Series
Same current, voltage divided
+
-12 v.
Parallel Same voltage, current divided
Series / Parallel
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 for a relay of a 12 V DC lighting circuit on a mobile machine if the circuit has four 60W lamps.
Q2: Would the lamps be wired in series or parallel?
Example 12 V DC problem
Good luck on the PE Exam!
• My email address:
• My web page:
https://engineering.purdue.edu/~dbuckmas/
Note … ASABE members can access ASABE texts electronically at:
http://elibrary.asabe.org/toc.asp