1. GEAR
&
GEAR TRAINS
See the background of slide....!!!
For pre-info about journey we are about
to begin…….

2. LETS START WITH OUR
JOURNEY….
INTRODUCTION TO
GEARS AND GEAR
TRAINS
START
TYPES OF
GEARS
MANUFACTURING
GEAR TRAINS
APPLICATIONS
END

3. WHAT ARE GEARS???
• A friction wheel with teeth cut on it,
i.e. ; a synchronous arrangement of
projections and recesses on a wheel.
projections
recess

4. And Gear Trains???
Friction
Wheels
Gear
Trains
When two or more
gears are mesh
together to transmit
power from one
shaft to another;
then such
combination is called
train of tooth
wheels or gear
trains.

5. + and – ‘s of GEAR
TRAINS
Over belts , ropes and chain drives.
+
Transmits exact VELOCITY RATIO*
Compact layout and higher EFFICIENCY.
_
Making of Gears require special tools and
equipments.
Noise and vibrations are produced during
their usage.
* This is the true principle of gearing

6. Velocity Ratio
Ratio of the distance moved by the EFFORT
POINT and LOAD POINT.
2
1
1
2
1
2
d
d
N
N
RATIO 





7. VARIOUS TYPES OF
GEARS
• PARALLEL
• INTERSECTING
• NON-INTERSECTING AND NON-
PARRALEL
POSITION OF
AXES OF
SHAFTS
• LOW VELOCITY.
• MEDIUM VELOCITY.
• HIGH VELOCITY.
PERIPHERAL
VELOCITY OF
GEARS
• EXTERNAL GEARING.
• INTERNAL GEARING
• RACK AND PINION.
TYPE OF
GEARING
BASIS

8. POSITION OF AXES OF
SHAFT

9. POSITION OF AXES OF
SHAFT

10. PERIPHERAL VELOCITY
OF GEARS
• VELOCITY LESS THAN 3m/s : LOW
• VELOCITY b/w 3m/s AND
5m/s:MEDIUM
• VELOCITY GREATER THAN
15m/s:HIGH

11. TYPES OF GEARING
External Gearing Internal Gearing Rack and Pinion

12. MANUFACTURING
MATERIALS FOR GEARS
TYPE OF MATERIAL USED DEPENDS ON:
• STRENGTH
• SERVICE CONDITIONS LIKE NOISE,WEAR,etc.
GEARS ARE MANUFACTURED BY:
(commercially available)
• METALLIC: CAST IRON,BRONZE AND STEEL.
• NON-METALLIC: WOOD,SYNTHETIC RESINS like
NYLON, especially used to reduce NOISE.

13. METALLIC GEARS are
basically used for rough
mechanical purposes
METAL
USED
SPECIFICATIONS
CAST IRON
(employed
where smooth
action is not
that
important )
GOOD WEARING
PROPERTIES,EXCELLENT
MACHINABILITY AND EASE
OF PRODUCING COMPLEX
SHAPES USING CASTING
PROCESSES.
steel Used where high strength
gears are required and
usually heat treated to
provide toughness and tooth
strength.
Phosphor
bronze
Used in worm gears to
reduce wear which will be
max. with cast iron.

14. MORE ON
MANUFACTURING
SOME TERMS ARE REQUIRED TO BE CONSIDERED WHEN WE
DESIGN GEARS such as:
MODULE: THIS IS THE RATIO OF PITCH CIRCLE DIAMETER (in
mm) TO THE NO. OF TEETH
m=(pitch circle diameter(in mm))/(No. of teeth)=D/T.
RECOMMENDED SERIES OF MODULES IN INDIAN STANDARDS
ARE 0.5,1,1.5,2,2.5,3,4,5,6,8,10,12,16,20.
CIRCULAR PITCH: IT IS THE DISTANCE BETWEEN A POINT ON
ONE TOOTH TO THE CORRESPONDING POINT ON NEXT TOOTH.
PITCH= ∏D/T.
REMEMBER: A LITTLE CONSIDERATION SHOWS THAT FOR
GEARS TO MESH PROPERLY,IT IS NECESSARY THAT THEIR
CIRCULAR PITCH IS SAME.

15. Resuming sree’s talk on
GEAR TRAINS
• A gear train is two or more gear working
together by meshing their teeth and
turning each other in a system to
generate power and speed
• It reduces speed and increases torque
• Electric motors are used with the gear
systems to reduce the speed and
increase the torque

16. Types of Gear Trains
• Simple gear train
• Compound gear train
• Planetary gear train
Simple Gear Train
• The most common of the gear train is the
gear pair connecting parallel shafts. The
teeth of this type can be spur, helical or
herringbone.
• Only one gear may rotate about a single axis

17. Simple Gear Train

18. Compound Gear Train
• For large velocities,
compound
arrangement is
preferred
• Two or more gears
may rotate about a
single axis

19. Planetary Gear Train
(Epicyclic Gear Train)
EXTERNAL INTERNAL

20. Planetary Gear Train…
• In this train, the blue gear has six times the
diameter of the yellow gear
• The size of the red gear is not important because
it is just there to reverse the direction of
rotation
• In this gear system, the yellow gear (the sun)
engages all three red gears (the planets)
simultaneously
• All three are attached to a plate (the planet
carrier), and they engage the inside of the blue
gear (the ring) instead of the outside.

21. Planetary Gear Train…
• Because there are three red gears
instead of one, this gear train is
extremely rugged.
• Planetary gear sets can produce different
gear ratios depending on which gear you
use as the input, which gear you use as
the output, and which one you hold still.

22. Planetary 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 train
between internal combustion engine and
an electric motor

23. APPLICATIONS
DIFFERENTIAL DRIVER: A MIRACULOUS MECHANISM
STARTING FROM A BASIC ASSEMBLY USING GEAR
TRAINS
A vehicle's wheels rotate at different speeds,
especially when turning corners. The differential is
designed to drive a pair
of wheels with equal force, while allowing them to
rotate at different speeds

24. Input torque is applied to the ring gear (blue),
which turns the entire carrier (blue), providing
torque to both side gears (red and yellow), which
in turn may drive the left and right wheels. If the
resistance at both wheels is equal, the planet
gear (green) does not rotate, and both wheels
turn at the same rate.

25. If the left side gear (red) encounters resistance,
the planet gear (green) rotates about the left
side gear,
in turn applying extra rotation to the right side
gear
(yellow).

26. BIBLIOGRAPHY
• “THEORY OF MACHINES” by
PROF. KHURMI,R.S.
• ARTICLES FROM
WIKIPEDIA:”GEARS”.CITED ON
5/4/2011.
• “THEORY OF MACHINES”,by
SHINGLEY,JOSEPH
EDWARD;JOHN UICKER.

27. THANK YOU
Deepak Sharma
IIT Mandi
Copyright 2013 Deepak Sharma IIT Mandi
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