15751 g12 Gear Trains Repeat

8/3/2019 15751 g12 Gear Trains Repeat

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GEAR TRAIN. Combination of two

or more gears when

they made to mesh

each other to

transmit power

from one shaft toanother.



TYPES OF GEAR TRAIN. Simple Gear Train

Compound Gear Train

Riveted Gear train

Epicycle Gear

Train



SIMPLE GEAR TRAIN

W

hen there is onlyone gear on each

shaft.



Module

t=Number of teeth on the gear

D=Pitch circle diameter,

N=speed in rpm

m=module=D/t

Module must be same for all gears

otherwise they would not mesh.



The velocity v of any point on the circle must be the

same for all the gears, otherwise they would be

slipping.

r = Dcle. v =on the cir velocityv = linear

.r velocity= angula

= m t Dand = m t D;= m t D

t

D=

t

D=

t

Dm =

C C B B A A

C

C

B

B

A

A

[[

[

2



C C B B A A

C C B B A A

C C B B A A

C C B B A A

C

C

B

B

A

A

t N t N t N

revof termsinor

t t t

t mt mt m

D D D

D D D

v

!!

!!

!!

!!

!!!

min/

222

[[[

[[[

[[[

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valueTrain gear driver of Speed

gear drivenof Speed

N

N

If

eSpeed valuoSpeed ratit

t

N

N

C A

speed Output speed Input GR

A

C

A

C

C

A

thecalledis

/ascalledalsoGR

output;theisgear andinputtheisgear If

asdefinedisratiogear The

!

!!

!



PO W ER TRANSMISSION

The power transmitted by a torque is given by

In an ideal gear box, the input and output

powers are the same so;

60

2 T N P

T

!

GR

N

N

T

T T N T N

T N T N

P

!!!

!!

2

1

1

2

2211

2211

60

2

60

2 TT



C

OMPOUND GEAR TRAIN When there aremore than one gear

on a shaft,it iscalled a

compound gear train



GEAR 'A'

GEAR 'B'

GEAR 'C'

GEAR 'D'

Compound Gears

A

C

B D

Output

Input

COMPOUND GEAR TRAIN

For large velocities ratios,compound gear train

arrangement is preferred.

The velocity of each tooth

on A and B are the same so:

[A tA = [B tB

-as they are simple gears.

Likewise for C and D,

[C tC = [D tD.



C

D

A

B

D B

C A

C

D D

A

B B

C A

C

D D

C

A

B B

A

C

D

D

C

A

B

B

A

t

t

t

t

t

t

t

t

T

t and

t

t

t t

and

t t

v!

v

v

v

v

v

!v

v

!

v

!

!!

[[

[[

[[

[[

[

[

[

[

[[[[



GEAR 'A'

GEAR 'B'

GEAR 'C'

GEAR 'D'

Compound Gears

A

C

B D

Output

Input

GRt

t

t

t

Out N

In N aswritten

bemayratio gear The

N Since

GRt

t

t

t

shaft sametheonareC and B gear Since

C

D

A

B

C

D

A

B

D

A

C B

!v!

vv!

!v!

!

:

2 T[

[

[

[[



REVERTED GEAR TRAIN

When the axes of the first

driver and the last driven

are co-axial, then thegear train is known as

reverted gear train.

In a reverted gear train, the

motion of the first gear and

the last gear is same.



EPIC Y CLIC GEAR TRAIN

Epicyclic means one

gear revolving upon and

around another. Thedesign involves planet

and sun gears as one

orbits the other like a

planet around the sun.



EPIC Y CLIC GEAR TRAIN

A small gear at the

center called the

sun, several

medium sized gears

called the planets

and a large externalgear called the ring

gear.



VELOCITY RATIO OF

EPIC Y CLIC GEAR TRAIN velocity ratio;

velocity ratio of epicyclic gear train is the ratio of thespeed of the driver to the speed of the driven or follower.

The following two methods may be used for finding out the

velocity ratio of an epicyclic gear train.

1.Tabular method

2. Algebraic method



1. TABULAR MET HODTA = Number of teeth on gear A

T B = Number of teeth on gear B.

Suppose that the arm is f ixed.

Therefore, the axes of both the gears are also

f ixed relative to each other. When the gear Amak es one revolution anticlockwise, the gear B

will mak e TA / TB

NB / NA = TA / TB

Since NA = 1 revolution, therefore

NB = TA / TB

Assuming the anticlockwise rotation as positive

and clockwise as negative.



2. ALGEBRAIC MET HOD

In this method, the motion of each elementof the epicyclic train relative to the arm is

set down in the form of equations. The

number of equations depends upon the

number of elements in the gear train. Letthe arm C be fixed in an epicyclic gear

train as shown in Fig

Therefore,

Seed of the gear A relative to the armC= N(A)- N(C)

S peed of the gear B relative to the arm

C= N(B) ±N(C)



COMPOUND EPIC Y CLIC GEAR TRAIN

(SUN AND PLANET GEAR)



ADVANTAGES OF RIVERTED

GEAR TRAIN

The reverted gear trains are used in automotive

transmissions, lathe back gears, industrial speedreducers, and in clocks (where the minute and hour

hand shafts are co-axial).



ADVANTAGES OF EPIC Y CLIC

GEAR TRAIN They have higher gear ratios.

They are popular for automatic transmissions in

automobiles.

They are also used in bicycles for controlling power

of pedaling automatically or manually.

They are also used for power transmission betweeninternal combustion engine and an electric motor.



ANY QUESTION ?

15751 g12 Gear Trains Repeat

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