flywheel ppt
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7/21/2019 Flywheel Ppt
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ME 209: Machine Design I
Design of a Flywheel
Asanga Ratnaweera
Department of Mechanical Engineering
Faculty of Engineering
University of Peradeniya
2/14/2006 ACR/ME209/2006
Flywheel A flywheel acts as an energy reservoir, which stores energy during
the period when the supply of energy is more than the
requirement and releases energy during the period when the
requirement is more than the supply.
FLYWHEEL
Manual press Combustion engines Power press
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IC Engines: The basic operation
In internal combustion engines, the energy is developed during
the power (expansion) stroke and the engine runs for the whole
cycle on the energy supplied during that stroke.
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IC Engines: The basic operation
Power is produced only during the power stroke
Intake Compression Power Exhaust
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IC Engines: The basic operation Pressure and temperature rapidly increases during the
combustion and hence the piston is pushed down. Therefore,
there is a significant fluctuation of energy during once engine
cycle
IVO - intake valve opens, IVC – intake valve closes
EVO – exhaust valve opens, EVC – exhaust valve closes
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IC Engines: Turning Moment
The torque at the crank shaft or theturning moment is largely dependent on; The in-cylinder gas pressure
The inertia force of the reciprocating parts
As explained above the gas pressurefluctuates over a complete cycle
The acceleration and deceleration of the
piston assembly also changes during themotion over a cycle
Therefore the Turning Moment alsofluctuates over an engine cycle
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IC Engines: Turning Moment
The Fluctuation Turning Moment can be controlled to some extent
by increasing number of cylinders (Multi-cylinder engines)
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IC Engines: Turning Moment
There are two common configurations used in multi-cylinder
engines
Inline Engine V Engine
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IC Engines: Turning Moment Practically it is not possible to build engines with cylinders beyond
a certain number. (depends on the capacity)
Therefore, a complete smoothness can not be achieved by only
increasing the number of cylinders
A flywheel is usually coupled to the crank shaft to limit the
fluctuation of turning moment and hence the fluctuation of speed.
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Design of a Flywheel This design exercise deals with the design of a flywheel to
bring the fluctuation of the engine speed to a required
limit.
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Design of a Flywheel: Procedure
Selection of the engine Data tables will be provided and select the problem based on the serial
number
Calculation of Turning Moment calculation of torque due to inertia forces
calculation of torque due to pressure forces the indicator diagram of the engine will be provided
Obtain the turning moment and hence find the meantorque
Calculation of the Moment of Inertia of the Flywheel tolimit the speed fluctuation to given value
Design of the flywheel with the required Moment ofInertia
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Design of a Flywheel: Procedure
Calculation of torque due to inertia forces
[ ]α θ coscos)1( nr r r n x −−+=
r
l=nr
θ
α
x
TDC
[ ]α θ coscos lr r l x −−+=
θ α sinsin r nr =
n
n 2/122 )sin(
cos θ
α −
=
The total Inertia force where M is the mass of the
reciprocating parts
..
x M Q =
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Design of a Flywheel: Procedure Calculation of torque due to inertia forces
2/122 )sin(cos)1( θ θ −−−+= nr r r n x
⎥⎦
⎤⎢⎣
⎡+×=
nr x
θ θ ω 2cos
cos2
..
..
x M Q =
M is the mass of reciprocating parts
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Design of a Flywheel: Mass Mass of the reciprocating parts are largely due to
Mass of the piston
Contribution from the connecting rod
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Design of a Flywheel: Mass
Calculation of the contribution from the connecting
rod
l
l 2 l 1
G
A B
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Design of a Flywheel: Mass
Find the equivalent mass system
l
l 2 l 1
G
A
B
m 1 m 2
If the mass of the connecting rod = m
m = m1 + m2
m2 x l 2 = m1 x l 1
Therefore;
Usually for internal combustion
engines;
l 2= 3 x l
1
Mass of the con. Rod = 10g/mm
mll
lm
)( 21
12
+=
Therefore the total mass
M = piston mass + m2
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Design of a Flywheel: Procedure Calculation of torque due to pressure force
r
l=nr
θ
α
h
P
S
α cosS P =
cosShT =
PhT =
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Design of a Flywheel: Procedure Calculation of pressure force (P)
Use the Indicator diagram
The pressure force at given
crank angle can be obtained
using the indicator diagram
The indicator diagram of an engine canexperimentally be obtained bymeasuring the in-cylinder gas pressure
and plotting the variation of pressure
against the volume over one cycle
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Design of a Flywheel: Procedure Calculation of resultant torque
r
l=nr
θ
α
h
P
S
hQPT )( −=
Q
QhPhT −=
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Design of a Flywheel: Procedure
Draw the given indicator diagram on the drawing sheet
Calculate the scale factors for pressure axis and displacementaxis Consider the given maximum pressure and the stroke of the engine
Draw the configuration diagram to obtain h at each crank
position
Tabulate the pressure and the value of h at each crank position.
Tabulate the gas torque, inertia torque and the total torque ateach crank position.
Draw the Turning Moment diagram and the mean torque line
Calculate the maximum fluctuation of energy
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Design of a Flywheel: Fluctuation of
Energy
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Design of a Flywheel: Fluctuation of
Energy
Use the Planimeter to calculate the area hence the energyfluctuation
Then calculate the moment of inertia of the flywheel2
2
2
12
1
2
1ω ω I I E ×−×=∆
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Design of a Flywheel: Planimeter
Area = Planimeter constant x number of revolutionsNote : Planimeter constant = 10.
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Design of a Flywheel The two basic types of flywheels
Rim type Disc type
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2/14/2006 ACR/ME209/2006
Design of a Flywheel The major components
Rim
Arms
Hub
Key and Keyways
Shaft
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Design of a Flywheel: Key and
Keyway Keys are used to transmit torque from a component to
the shaft.
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Design of a Flywheel: Key and
Keyway Types for Keyways
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Design of a Flywheel: Key and
Keyway Types for Keys
Rectangular keys
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Design of a Flywheel: Key and
Keyway Failure modes
A key has two failure mechanisms:
It can sheared off
It can be crushed due to the compressive bearing forces.
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Design of a Flywheel: Shaft The diameter of the shaft should be large enough to
prevent from failure due to the torque on it.
r J
T τ =
T = torque on the shaft
J = Polar second moment of area
32
4 D
J π =
r = distance from the centre
D = diameter of the shaft
τ = shear stress on the shaft at radius r
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Design of a Flywheel: Rim and arms
If the speed of rotation is ω;
Centrifugal force on the element
2dmdF 2 R
××= ω
222F ω ρ AR=
A
F =σ
Arms can be designed as specified in Mechanical Engineering Handbooks or
any acceptable standards
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Design of a Flywheel
The End