Flywheel Ppt

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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The Fluctuation Turning Moment can be controlled to some extent

by increasing number of cylinders (Multi-cylinder engines)

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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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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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2/14/2006 ACR/ME209/2006

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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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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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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Keyway Types for Keyways

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Keyway Types for Keys

Rectangular keys



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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

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Flywheel Ppt