Transcript
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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.
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TYPES OF GEAR TRAIN. Simple Gear Train
Compound Gear Train
Riveted Gear train
Epicycle Gear
Train
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SIMPLE GEAR TRAIN
W
hen there is onlyone gear on each
shaft.
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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.
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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
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[
2
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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
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thecalledis
/ascalledalsoGR
output;theisgear andinputtheisgear If
asdefinedisratiogear The
!
!!
!
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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
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C
OMPOUND GEAR TRAIN When there aremore than one gear
on a shaft,it iscalled a
compound gear train
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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.
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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
!
!!
[[
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[
[
[
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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[
[
[
[[
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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.
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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.
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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.
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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
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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.
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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)
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COMPOUND EPIC Y CLIC GEAR TRAIN
(SUN AND PLANET GEAR)
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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).
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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.
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ANY QUESTION ?
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