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ENGINE MECHANICS
FUNDAMENTALS
N. V. MARATHESr. Deputy Director, Powertrain Engineering
ARAI, Pune (India)[email protected]
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.recap of topics covered in past
2 days
Basics of Engine Thermodynamics
Basics of Engine Combustion
CRDI Emission Formation & Control
Breathing and Valve train
Exposure to Engine tests
Exposure to Port testing
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CONTENTS of the moduleEngine Mechanism Fundamentals
Engine Classifications parameters
Crank mechanism Kinematics & Forces
Engine balancing
Torsional vibrations
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Engine Classification Purpose
Stationary engineelectric power plants, pumping units, etc
Variable speed engine - motor vehicles, off-road,
locomotive, ships
Type of fuel
Light liquid fuelpetrol, kerosene
Heavy liquid fueldiesel, fuel oil, bio-fuel, etc.
Gaseous fuelnatural gas, propane, hydrogen, etc
Mixed fuel
Nature of energy conversion to mechanical work
Internal Combustion (IC) enginesconventional piston engine External combustion enginesgas turbine
Method of mixture formation
External mixture formationpetrol engine
Internal mixture formationdiesel engine
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Method of ignition Positive ignition - spark ignitiongasoline engine
Compression ignitiondiesel engine
Pre-chamber ignition
Open chamber ignition Piston strokes per cycle Two stroke
Four stroke
Nature of Aspiration Naturally Aspirated ( NA ) engine
Supercharged engine
Turbocharged engine
Engine Classification
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Method of load controlcomposition of mixture Quantity control - quantity of mixture is controlled
composition of mixture unchangedpetrol engines
Quality control fuel mass is controlledcomposition of
mixture changed - diesel engines
Cooling method Liquid cooling
Air cooling
Cylinder arrangement
Inlinevertical, horizontal
V
Opposed piston
Radial
Engine Classification
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Vee AngleFor even firing pulses the
product of the vee angle and
the number of cylinders must
be a multiple of 360.
60o: V-6 or V-12
90o: V-8
Changing the vee angle (for
package dimensions, use of
common tooling, etc.) results
in uneven firing..
Vee Engine Design Considerations
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Engine that converts thermal energy to
mechanical work
Particularly, the architecture comprising all the
subsystems required to convert this energy to
work
Sometimes extends to drive train, whichconnects power train to end-user of power
What is a Power Train ?
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Basic Characteristics of Vehicle engines Reliability
Efficiency of conversion of heat energy into mechanical work Engine power and torque capacity
Specific powerpower per litre
Specific massengine power per unit of engine mass
Package volume - size
Exhaust emissions Noise
Reliable starting in all conditions
Durability - service life of all design elements
Design complexity
Manufacturing cost Operating cost
Service interval - Oil change period
Access to assembly and dis-assembly
Recycling
Customer perception and acceptance
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Typical Cross-section of an Engine
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Cylinder Block
Part of engine framethat contains
cylinders in which
piston moves
Supports liners &head
Structural Components
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Cylinder Head/Assembly
Serves to admit, confine, and release fuel/air
Cover to cylinder block Supports valve train
Crankcase
Engine frame section that houses the crankshaft
Oil sump
Reservoir for collecting and holding lube oil
Structural Components
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Three Groupsaccording to motion
Reciprocating only (pistons and valves)
Reciprocation & rotary (connecting rods)
Rotary only (crankshafts and camshafts)
Structural Components
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Piston Acted on by combustion gases
Lightweight but strong/durable
Piston Rings
Transfer heat from piston to
cylinder Seal cylinder & distribute lube
oil
Piston Pin
Pivot point connecting pistonto connecting rod
Connecting Rod
Connects piston & crankshaft
reciprocating rotating
motion
Structural Components
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Crankshaft Combines work done by each piston
Drives camshafts, generator, pumps, etc.
Flywheel Absorbs and releases kinetic energy of piston
strokes.
Smoothens rotation of crankshaft
Structural Components
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Valves Intake: open to admit air to
cylinder (with fuel in Otto
cycle)
Exhaust: open to allowgases to be rejected
Camshaft & Cams
Used to time the addition ofintake and exhaust valves
Operates valves via
pushrods & rocker arms
Moving Components
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Pushrod OHV (Type 5) HEMI 2-Valve (Type 5) SOHC 2-Valve (Type 2)
2-V train layout of an engine
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SOHC 4-Valve (Type 3) DOHC 4-Valve (Type 2)
DOHC 4-Valve (Type 1)Desmodromic
4-V train layout of an engine
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Air flow is an easier variable to
change than thermal efficiency
90% of restriction of induction
system occurs in cylinder head Cylinder head layouts allowing
the greatest airflow will have
highest specific power potential
Peak flow from poppet valveengines primarily a function of
total valve area
More/larger valves provide
greater valve area
Valve- train layoutSpecific Power = f(Air Flow, Thermal efficiency)
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Cam Drive Configuration - Example
GM ECOTEC 1.8 2.2L in-line DOHC 4cylinder
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Increased pressure of combustion
gases acts on piston. Reciprocating
motion converts to rotary motion
Can be 2 or 4 stroke engines
2-stroke: 1 power stroke per 1crankshaft rev
4-stroke: 1 power stroke per 2
crankshaft rev
Engine Operation
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Engine stroke
A stroke is a single
traverse of the
cylinder by the
piston (from TDC to
BDC)
1 revolution of
crankshaft =
2 strokes of piston
Engine Operation
R
L
Stroke S
BDC
TDC
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Vc= Clearance Volume
Vd= Displacement or Swept Volume
Vt= Total Volume
TC or TDC=
Top or Top Dead Center Position
BC or BDC=
Bottom or Bottom Dead CenterPosition
Compression Ratio (CR)c
cd
V
VVCR
Compression Ratio
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Intake stroke Intake valve open, exhaust
valve shut
Piston travels from TDC to
BDC Air or Charge drawn in
4-Stroke engine
Compression stroke
Intake and exhaust valves shut
Piston travels from BDC to TDC
Temperature and pressure of air or Charge increase
Fuel is injected at the end of the stroke ( CI engines )
Spark is ignited towards the end of the stoke ( SI engines)
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Power stroke Intake and exhaust valves shut
Fuel injected gets ignited and pressure develops
Piston forced from TDC to BDC
4-Stroke engine
Exhaust stroke Intake valve shut, exhaust
valve open
Piston moves from BDC toTDC
Combustion gases expelled
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Air system
Supplies & removes air/gases
Air supplied at constant pressure by
blower/compressor
Fuel System
Carburetor: mixes air & fuel in properproportion (NOT on diesels)
Fuel injector: sprays fuel in (more efficient)
Engine Supporting systems
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Ignition system Diesel has compression ignition
Gasoline has spark plugs
Cooling system Uses fresh water and/or salt water to cool
Lubrication system Provide lubrication and cooling
Engine Supporting systems
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Characteristics
Slider-crank mechanism has high mechanicalefficiency (piston skirt rubbing is source of 50-60% of all firing friction)
Piston-cylinder mechanism has high single-stage compression ratio capabilityleads tohigh thermal efficiency capability
Reciprocating I C engine
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Engine Mechanics
Kinematics
Static force analysis
Inertial effects
Balancing
Overview
Some simplifying assumptions are made throughout:
(a) gravity forces are small, and are ignored
(b) friction is ignored
(c) the components are rigid
(d) the motions are planar (two dimensional)
(e) the length ratio between crank-throw and con-rod issmall enough to make some simplifications
(f) the con-rod can be represented as a two-mass system.
Mechanics of I C engine
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approximate expression for the distance x between thecrankshaft rotation centre O and the piston centre B :
where n is a geometric ratio between the length of thecon-rod AB and the length of the crank throw OA.
O
A
B
y
x
r n r
Fig 1.2: crank-slider geometry
coscos nrrx
2/stroker
)2/stroke/(lengthconrodn
Mechanics of I C engine
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for transverse crankpin displacement,
Or,
since
then
sinsin nrr
cos ( sin ) 1 2
sin1
1cos 22
n
nrrx
sin1
sin
n
O
A
B
y
x
r n r
Fig 1.2: crank-slider geometry
Mechanics of I C engine
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Mechanics of I C engine
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2cos1
2
11cos
2
nnrx
2sin2
1sin
nrx
)2cos1
cos2sin2
1sin
2
n
rn
rx
Applying binomial theorem expansion and neglecting higher terms of
mn/1
Piston displacement
Piston velocity
Piston acceleration
M h i f I C i
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-15000
-10000
-5000
0
5000
10000
15000
20000
25000
0 30 60 90 120 150 180
Crank Angle (deg)
Accelera
tion(m/s2)
0
5
10
15
20
25
30
0 30 60 90 120 150 180
Crank Angle (deg)
Velocity(m/s)
4.3
2
Peak piston velocity increases and advances towards
BDC as n reduces Peak piston acceleration at BDC positionincreases as n reduces
0.00
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0 30 60 90 120 150 180
Crank angle BDC - TDC (deg)
PistonpositionBDC-TDC(m)
4.3
2
BDC
TDC
Mechanics of I C engine
Pistondisplacement--
Con
rod CD
Crank
rad
(0.5 x
stroke)
Peak
piston
velocity
Piston
acceln
at BDC
n l r Vp(max) Ap(bdc)
reduce
s
reduce
s
(shortercon rod
length)
increase
s
(longerstroke)
increase
s and
shifts
towardsBDC
increase
s
BDC TDC TDCBDC
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Con Rod and Piston Stroke ratioThon e rod-to-stroke ratio is the ratio of the length of the
connecting rod to the length of the piston stroke.
A longer rod will reduce the sidewise pressure of the piston on
the cylinder wall and the stress forces, hence increasingengine life. It also increases cost and engine height and
weight.
A square engineis an engine with a bore diameter equal to
its stroke length.
An engine where the bore diameter is larger than its stroke
length is an oversquareengine.
an engine with a bore diameter that is smaller than its stroke
length is an undersquareengine
Mechanics of I C engine
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Heat Transfer Losses
As Bore/Stroke increases, surface to
volume ratio near TDC increases,
causing increased heat transfer losses.
Valve Flow Area
As Bore/Stroke decreases, there is less
room in the head for valves, and the
valve flow area decreases.
Piston Speed
As Bore/Stroke decreases, the longer
stroke dimension requires the piston to
travel further in the same amount of time.
Bore / Stroke Ratio Optimization
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Bore to Stroke Ratio Optimization
(Example taken for 2L per cylinder at 1800 RPM)
0
2
4
6
0
10
20
30
40
4
6
8
10
0.4 0.6 0.8 1.0 1.2 1.4 1.6
Bore to Stroke Ratio
Mean Piston Speed (100 ft/min)
Pressure drop across intake valves (psi)
Surface area to Volume at TDC (1/in.)
Optimum Range
Bore / Stroke Ratio Optimization
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Rotational forcedue to mass
spinning at
some offset from
the shaft
centerline
Inertia force associated
with accelerating anddecelerating
reciprocating mass
Gas pressure
forces transmittedthrough piston to
connecting rod
Moment generated bygrouping of cylinders
whose net forces try
to pivot the system
about some axis
Forces Generated within the Engine
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FRecip
FR
R
L
Frecip is the reciprocating forcegenerated by accelerating and
decelerating the piston, rings, pin, and
upper portion of the connecting rod.
FRRecip is the reaction force
transmitted to the block at the mainbearing saddle
Frotate is the rotating force generated
by the mass of the crankshaft and
lower portion of the connecting rodoffset from the crankshaft centerline.
FRRotate is the reaction force
transmitted to the block at the main
bearing saddle.
Forces Acting on the Engine System
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Reciprocating forces are calculated from Newtons
Second Law:
onAcceleratiMassForce
The mass is that of the piston, rings, piston pin, and
the upper portion of the connecting rod.
The acceleration is calculated by taking the time
derivative of the piston velocity as a function of crank
angle.
Reciprocating Forces
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The piston velocity versus crank angle is given by the series
expression:
Piston acceleration versus crank angle is then given by:
...4cos162cos4cos 422 aaR
dt
dV
V 2R s in 2a2s in2 4a
4s in4 ...
where: a2
LR
14RL
2 116
RL
4 15512
RL
6 ...a
4 L
R164
RL
4
3256
RL
6
...
Reciprocating Forces
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By Newtons Second Law the reciprocating forces are then:
The higher order terms are very small and can be safely
neglected. 4a2is approximately R / L, so the equation simplifies
to:
First Order Second Order
Frecip MPiston Assy dVdt
MPiston Assy
2Rcos4a
2
cos216a4
cos4...
Frecip MPiston Ass y 2
R cosRLcos2
Reciprocating Forces
Reciprocating Forces Engine Vibration Order
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ReciprocatingFor
ce
TDC 0o BDC 180o TDC 360o
First Order
Second Order
Resultant
90o 270o
Reciprocating Forces Engine Vibration Order
Engine Vibration Order= Frequency of vibration / system characteristicfrequency
For engine, the system characteristic frequency is taken as crankshaftspeed
A first order vibration is one where the force cycle repeats onceeverycrankshaft revolution
1 stroke 2 stroke
1 revolution
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BDC
Crank Angle
TDC 90o
Piston velocityis not sinusoidal, but is skewed
It shows higher velocities near TDC than BDC
As shown in the four-cylinder diagram,
pistons 1 and 4 nearing TDC are
decelerating at a faster rate than pistons 2
and 3 nearing BDC, resulting in anet
upward force.
One-half revolution later, pistons 2 and 3
approach TDC, while 1 and 4 approach
BDC, and the force is repeated
What is 1st& 2ndorder forces ?
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Engine Balancing
Engine balance is the design,
construction and tuning of an engineto runsmoothly.
http://en.wikipedia.org/wiki/Enginehttp://en.wikipedia.org/wiki/Engine8/12/2019 8. Engine Mechanics Fundamentals
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Engine Balancing
Primary balance is the balance achieved bycompensating for the eccentricities of the masses inthe rotating system, including the connecting rods.
Primary balance is controlled by adding or removing
mass to or from the crankshaft, typically at each end, at
the required radius and angle. It varies both due to
design and manufacturing tolerances.
Theoretically, any conventional engine design can bebalanced perfectly for primary balance.
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Engine Balancing
Secondary balance can include compensating for :
kinetic energy of the pistons
non-sinusoidal motion of the pistons
motion of the connecting rods
sideways motion of balance shaftweights
The second of above is the main consideration for secondary balance.
There are two main control mechanisms for secondary balance
matching the phasing of pistons along the crank, so that their
second order contributions cancel,
the use of Lanchester balance shafts, which run at twice engine
speed, and so can provide a counteracting force.
http://en.wikipedia.org/wiki/Balance_shafthttp://en.wikipedia.org/wiki/Balance_shafthttp://en.wikipedia.org/wiki/Balance_shafthttp://en.wikipedia.org/wiki/Balance_shaft8/12/2019 8. Engine Mechanics Fundamentals
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Primary forces are balanced
Secondary forces sum up. This produces a vibration in
the vertical plane at a frequency twice that of the speed of
the crank.
Direction of Primary and secondary forces in an in-line 4-cylinder engine
EXAMPLE
Engine Balancing
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Static Balance
Unbalanced Couplewhen shaft spins
Concept of Dynamic Couples
massestwothebetweenshaftalongcetanDisL
velocityangularshaftfromdistanceradialMass
masseachbygeneratedforceOutwardF
:where
LFMoment
2
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Couple balanced by adding
equal and opposite couple
Concept of Dynamic Couples
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The mass associated
with each cylinder
creates two equal and
opposite couples, and
forces transmitted into
the block cancel oneanother. However, two
internal couples, and
resulting moments, place
high loads on the 1, 3,
and 5 main bearings.
Counterweights asshown are used to cancel
these internal moments,
and reduce main bearing
loads.
Four Cylinder Crankshaft Representation
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Summary of unbalance forces & couples
Engine
Configurati
on
Unbalance Forces Unbalance Couples
Primary Seconda
ry
Rotary Primary Seconda
ry
Rotary
Single cyl
PRESEN
T
PRESEN
T
PRESEN
TX X X
2-cyl (1800) X PRESEN
T
X PRESE
NT
X PRESENT
2-cyl (5400)
PRESENT
PRESEN
T
PRESEN
T
X X X
3-cyl X X X PRESENT
PRESEN
T
PRESENT
4-cyl X PRESEN
T
X X X Internal
couple
In-line Engines
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Solutions for Engine Balancing
Primary balancer shaft rotating at the speed of
the engine
Balance mass on the pulley
Pair of secondary balancer shafts rotating at double
speed of the engine and in the opposite direction
of each other
Counter weights on the crank-throw
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Each fraction of the
counterweight has the
effect of the mass ofthat fraction acting at
its radius from the
crankshaft centerline
Reducing the arc over which
the counterweight is sweptmakes each element of mass
more effective, and reduces
overall crankshaft mass, but
increases required crankcase
size
This design eliminates mass in
the least effective areas, and aids
in packaging, with some increase
in crankcase diameter
Crankshaft Counterweights
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Counterweights may be shaped for
reduced aerodynamic drag
This will slightly increase overall
crankshaft mass
Counterweight Design
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Benefits of engine balancing
reduced vibrationand other stresses
reliability of the engine
Tolerates higher engine speeds
improved performance and efficiency
reduced stress on other machinery
and people near the engine
improved cost of ownership
http://en.wikipedia.org/wiki/Vibrationhttp://en.wikipedia.org/wiki/Stress_(physics)http://en.wikipedia.org/wiki/Stress_(physics)http://en.wikipedia.org/wiki/Vibration8/12/2019 8. Engine Mechanics Fundamentals
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Focus areas to achieve engine balancing
( additional to basic design principles )
Balancing the physical engine components, is called
BLUEPRINTING
Careful machining and matching of components as a
seteach engine being unique
Flywheel, bearings, piston & rings, connecting rods,
piston pins, crank
Balancing the engine dynamics
Differing compression ratio will create imbalance and
Vibrations
Compression ratio is affected by many parameterssuch as damaged
Cylinder wall, gasket imperfections, poor valve seating,
poor spark plug
or injector sealing, camshaft uneven wear, etc.
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Convert reciprocating motion of pistons to rotarymotion Work extraction
Repeated cycle
Components and specific functions Connecting rod - link between reciprocating and
rotary components Crankshaft - Transfers work from engine, and definespiston travel
Vibration dampener - minimizes torsional vibration
Flywheel - minimizes cyclic speed fluctuation
Crankshaft functional requirements
Critical Crankshaft Dimensions
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Critical region for
durability
Journal Overlap
Web Thickness
Main Bearing
Rod Bearing
Fillet Radii
Critical Crankshaft Dimensions
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Crankshaft failure
mode is simple
bending across
diagonal section
Main Bearings
TDC Firing
Tensile
Compressive
TDC Valve Overlap
Compressive
Tensile
Rod Bearings
Bending across crankshaft web
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Fillet RadiusMax.P
rincipalStressinRodFillet Inertia Load
Firing Load
Stress
Load
d
e
a
c
b
Bearing
Web
abc
de Strain gage
locations
Importance of fillet radius
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Axial Loading
Bending perpendicular to crankshaft
Results from transfer of cylinder pressure and reciprocating
forces, and relationship between rod and crankshaft
position versus timeBending parallel to crankshaft
Results from crankshaft bending, or misalignments
between power cylinder and slider-crank components
Tensile loads due
to reciprocating
forces
Compressive loads due to
combination of cylinder pressure and
reciprocating forces
Connecting rod loading
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Torsional vibration is angular vibrationof an object,commonly a shaft, along its axis of rotation.
Torsional vibration is often a concern in power
transmissionsystems using rotating shafts or couplings.
It can cause failures, if not controlled.
In ideal power transmission systems using rotating parts,
the torquesapplied or reacted are "smooth" leading toconstant speeds.
In reality this is not the case. The torques generated may
not be smooth (e.g., internal combustion engines)
Torsional Vibration
http://en.wikipedia.org/wiki/Vibrationhttp://en.wikipedia.org/wiki/Power_transmissionhttp://en.wikipedia.org/wiki/Power_transmissionhttp://en.wikipedia.org/wiki/Torquehttp://en.wikipedia.org/wiki/Internal_combustion_engineshttp://en.wikipedia.org/wiki/Internal_combustion_engineshttp://en.wikipedia.org/wiki/Torquehttp://en.wikipedia.org/wiki/Power_transmissionhttp://en.wikipedia.org/wiki/Power_transmissionhttp://en.wikipedia.org/wiki/Vibration8/12/2019 8. Engine Mechanics Fundamentals
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Torsional vibration is a concern in the crankshaftsofinternal combustion engines because of several factors.
Alternating torques are generated by the slider-crank
mechanism of the crankshaft, connecting rod, and piston. The motion of the piston mass and connecting rod
mass generate alternating torques often referred to as
"inertia" torques
The cylinder pressure due to combustion is not
constant through the combustion cycle.
The slider-crank mechanism does not output a smooth
torque even if the pressure is constant (e.g., at Top
Dead Centerthere is no torque generated)
Torsional Vibration
http://en.wikipedia.org/wiki/Crankshaftshttp://en.wikipedia.org/wiki/Top_Dead_Centerhttp://en.wikipedia.org/wiki/Top_Dead_Centerhttp://en.wikipedia.org/wiki/Top_Dead_Centerhttp://en.wikipedia.org/wiki/Top_Dead_Centerhttp://en.wikipedia.org/wiki/Crankshafts8/12/2019 8. Engine Mechanics Fundamentals
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If torsional vibration is not controlled in acrankshaft, it can cause failure of the crankshaft
or other accessories that are being driven by the
crankshaft (typically at the front of the engine).
The inertia of the flywheel normally reduces the
vibrational motion at the rear of the engine.
Engines with several cylinders can have very
flexible crankshafts due to their long length.
Inherently little damping in a crankshaft does
not reduce the vibration
Torsional Vibration
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These curves show the amplitude
of relative twist between thevarious crankpins during the
course of one revolution.
The greater portion of the crank
twists from clockwise to
anticlockwise, while the flywheeland small portion of crank at the
rear twist in the opposite
direction.
The node is the point of zero twist
- it is the weakest point. And this
is where a crankshaft usually
breaks.
Torsional VibrationThe torsional twist varies along
the length of a crankshaft.
Each crankpin assembly is
represented by a disc that has the
same deflection properties.
NODE
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A FREQUENCY is the vibration at a specific number of cycles per
second. For example, 400 cycles per second ("hertz"), or how f requently
the oscillation occurs.
An ORDER is a specific multiple of a basic frequency. For example aneven-firing eight-cylinder, four-stroke engine produces eight torque
pulses per cycle that is four torque pulses per revolution. This is called
a fourth order excitation.
If the crankshaft in an 8-cyl engine operates at 6000 rpm, then the
frequency of the fourth order excitation is 4 x 6000 / 60 = 400 hertz,
whereas the same 4th order excitation at 7200 RPM is a frequency of
480 hertz.
Torsional Vibration
DEFINITIONS
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For Inline Engines
3 Cylinder : 1.5, 3, 4.5, 6,----
4 Cylinder : 2, 4, 6, 8,----
6 Cylinder : 3, 6, 9, 12,----
Major Critical Orders
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A crankshaft, like a plain torsion-bar, has mass and a
torsional spring rate. This causes the crankshaft system
to have its own torsional resonant frequency.
The torque peaks and valleysplus the inertia loads fromthe accelerationof the reciprocating components cause
the engine crankshaft itself to deflect (rotationally)
forward and backward while it is operating. When those
pulses (excitations) are near the crankshaft resonantfrequency, they can cause the crank to vibrate
uncontrollably and eventually break.
Torsional Vibration
http://www.epi-eng.com/piston_engine_technology/torsional_excitation_from_piston_engines.htmhttp://www.epi-eng.com/piston_engine_technology/piston_motion_basics.htmhttp://www.epi-eng.com/piston_engine_technology/piston_motion_basics.htmhttp://www.epi-eng.com/piston_engine_technology/piston_motion_basics.htmhttp://www.epi-eng.com/piston_engine_technology/piston_motion_basics.htmhttp://www.epi-eng.com/piston_engine_technology/torsional_excitation_from_piston_engines.htm8/12/2019 8. Engine Mechanics Fundamentals
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The torsional resonant frequency of the crankshaft
system is a function of :
crankshaft length; crankshaft torsional stiffness;
crankshaft stroke;
Bob-weight mass;
moments of inertia of rotating items attached to
or driven by the engine.
Torsional Vibration
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71
Cam and accessory drive durability
Gear train
Chain or belt drives
Crank durability?
Magnitude of stress resulting from
torsionals
Noise
Torsional Vibration - importance
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Developing an Equivalent Rotor System Determination of Natural Frequencies -
HolzersForced Tabulation Method
Eigen Value Matrix Method
Fast Fourier Transformation of T- Curve. Conversion of
periodic function to harmonic function
Identification of major & minor Critical Orders
Construction of Phaser & Vector diagrams
Order Analysis for forced Vibration Amplitudes. Estimation of
Resonance & resonance amplitude.
Damper design, if required
Torsional Vibration Analysis Steps
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Equivalent Rotor SystemExample for a 3 Cyl Engine
5-Rotor system representing 3 Cyl Engine crank train
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-0.2
0
0.2
0.4
0.6
0.8
1
1.2
0 1 2 3 4
MODAL
VALUE
LOCATION
HOLZER
MATRIX
NATURALFREQENCY
Modal Value
Pulley Cyl. 1 Cyl.2 Cyl. 3 Flywheel
471 Hz 1 0.8752 0.66 0.328 -0.0497
1245 Hz 1 0.1275 -0.648 -0.619 0.0122
Method FundamentalFrequency
Second HigherFrequency
Holzer Table 471 Hz 1245 Hz
Eigen Matrix 470.5 Hz 1244.6 Hz
Modal AnalysisNatural frequency estimationExample for a 3 Cyl Engine
Mode
Shape
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Forcing Function
Resultant Force (Combined) curve based on cylinder pressure and inertia forces.Torque curve is developed based on Combined force data.
Combined
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-600
-400
-200
0
200
400
600
800
1000
1200
1400
0 100 200 300 400 500 600 700 800
Torque(N-m
)
Turning Moment Diagram
-150
-100
-50
0
50
100
150
0 100 200 300 400 500 600 700 800
Torque(N-M
)
1 st order harmonic
-250
-200
-150
-100
-50
0
50
100
150
200
250
0 100 200 300 400 500 600 700 800
Torque(N-m
)
2 nd order harmonic
-200
-150
-100
-50
0
50
100
150
200
0 100 200 300 400 500 600 700 800
Torque(N-m
)
6 th order harmonic
3 Cylinder Engine Case Study
Gas Torque curve
order
1storder
3rdorder
FFT analysis of Gas Torque curve
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Torsional Vibration Control
A DAMPER is a device which dissipates energy,
mainly in the form of heat.
An ABSORBER is a device which is designed to
oscillate in direct opposition to a vibration at
either a specific frequency or a specific order,depending on the design.
DEFINITIONS
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The potentially damaging torsional
vibration is often controlled by a torsional
damper that is located at the front nose of
the crankshaft, often integrated into thefront pulley.
Tuned Rubber Damper
Viscous Damper
Torsional Vibration Control
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Tuned absorber type of "dampers" often
referred to as a harmonic dampers orharmonic balancers
The tuned rubber vibration damper has a
rubber mass interposed between an
outer inertia ring and a central hub. It istypically tuned to the first torsional
natural frequency of the crankshaft.
This type of damper reduces the
vibration at specific engine speeds of
interest. Vibration amplitudes increases
at other non-critical speeds.
It is effectively employed in single speed
control engines such as constant speed
genset engines.
Torsional Vibration ControlTuned Rubber Damper
CHARACTERISTIC HELP GRAPH - 1
0
10
20
30
40
50
60
70
80
90
0 500 1000 1500 2000 2500
FREQUENCY (rad/sec)
DYNAMIC
MAGNIFICATION LOCK_TD
UNIT_TD
O_TD
OPT_TD
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Viscous dampers consist of an
inertia ring in a viscous silicon
fluid.Its viscocity changes very
little with temperature. The
torsional vibration of the
crankshaft forces the fluid throughnarrow passages that dissipates
the vibration as heat. Shearing
force in the fluid damp the
vibrations.The viscous torsional damper is
analogous to the hydraulic shock
absorberin a car's suspension.
Torsional Vibration Control Viscous Damper
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Effectiveness of TV Damper CASE STUDY ( 6 cyl diesel
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Test Engine - 6 Cylinder inline, TC
Rated Power - 200 HP @2500rpm
Test - Full Load test , Speed Sweep Test
Test Carried out with & without Damper
High Speed Data Acquisition is used to record Rotary
oscillations of Crankshaft
Accelerometer along with HSDA is used to recordsurface vibrations on the block (g levels of crankcase)
Effectiveness of TV Damper - CASE STUDY ( 6 cyl diesel
Engine )
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0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
1800 1900 2000 2100 2200 2300 2400 2500 2600
ENGINE SPEED (RPM)
AMPLITUDE(deg)
EXP
PRED
4.5 th
6 th
9 th
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0.2
1800 2000 2200 2400 2600
ENGINE SPEED (RPM)
AMPLITUDE(deg)
EXP
PRED 6 th
4.5 th
9th
Without DamperWith Damper
Effectiveness of TV Damper - CASE STUDY ( 6 cyl diesel Engine )
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Signature Analysis
(Speed Sweep Test)
0 20 40 60 80 100 120 140
-100
0
100
g(g)
secs
max 190.3
min -196.1
Range 386.4
sd 16.16
0 20 40 60 80 100 120 1401000
1500
2000
2500ENGINE SPEED(rpm)
secs
max 2524
min 983.8
Range 1540
sd 431.7
0 20 40 60 80 100 120
-50
0
50
g(g)
secs
max 93.04min -92.5Range 185.5
sd 9.406
0 20 40 60 80 100 120
1500
2000
2500ENGINE SPEED(rpm)
secs
max 2516min 1012Range 1503
sd 521.5
Without Damper With Damper
Effectiveness of TV Damper - CASE STUDY ( 6 cyl diesel Engine )
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Campbell Diagram
1000 1500 2000 2500
0
100
200
300
400
ENGINE SPEED (rpm)
3
5
6
7
9
12 10.2
:
1000 1500 2000 2500
0
100
200
300
400
ENGINESPEED (rpm)
Frequency(Hz.)
3
5
6
7
9
1213.1
Without Damper With Damper
Effectiveness of TV Damper - CASE STUDY ( 6 cyl diesel Engine )
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Thank You
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