Gears are used to transmit rotational motion between shafts. The main types are spur gears, helical gears, bevel gears, worm gears, and rack and pinion gears. Gear trains use multiple gears meshed together to increase or decrease speed and torque. Simple gear trains use two gears on parallel shafts. Compound gear trains use multiple gears on one shaft. Planetary gear trains use a sun gear engaging planet gears fixed to a carrier, which engage an outer ring gear. They provide higher gear ratios and are used in automatic transmissions.

2. GEAR…..
• Power transmission is the movement of energy from its place of
generation to a location where it is applied to performing useful
work
• A gear is a component within a transmission device that transmits
rotational force to another gear or device

3. TYPES OF GEARS
1. According to the position of axes of the shafts.
a. Parallel
1.Spur Gear
2.Helical Gear
3.Rack and Pinion
b. Intersecting
Bevel Gear
c. Non-intersecting and Non-parallel
worm and worm gears

4. Applicationsof Gears
• Control gears– long life, low noise, precision gears
kinematic & stress analysis
• Aerospace gears– light weight, moderate to high load
kinematic & stress analysis
• Power transmission– long life, high load and speed
kinematic & stress analysis
• Appliance gears– long life, low noise & cost, low to
moderate load
kinematic & some stress analysis
• Toys and Small Mechanisms– small, low load, low cost
kinematic analysis

5. Types of Gears
Spur gears – tooth profile is parallel to the
axis of rotation, transmits motion
between parallel shafts.
Pinion (small gear)
Gear (large gear)
Internal gears
– teeth are inclined to the
axis of rotation, the angle provides
more gradual engagement of the
teeth during meshing, transmits
motion between parallel shafts.
Helical gears

6. SPUR GEAR
• Teeth is parallel to axis of rotation
• Transmit power from one shaft to
another parallel shaft
• Used in Electric screwdriver,
oscillating sprinkler, windup alarm
clock, washing machine and
clothes dryer

7. Herringbone gears
• To avoid axial thrust, two
helical gears of opposite
hand can be mounted side
by side, to cancel resulting
thrust forces
• Herringbone gears are
mostly used on heavy
machinery.

8. Rack and pinion
• Rack and pinion gears are used to
convert rotation (From the pinion)
into linear motion (of the rack)
• A perfect example of this is the
steering system on many cars

9. Bevel gears
• Bevel gears are useful when the direction of a shaft's
rotation needs to be changed
• They are usually mounted on shafts that are 90
degrees apart, but can be designed to work at other
angles as well
• The teeth on bevel gears can be straight, spiral or
hypoid
• locomotives, marine applications, automobiles,
printing presses, cooling towers, power plants, steel
plants, railway track inspection machines, etc.

10. Straight and Spiral Bevel
Gears

11. WORMAND WORM GEAR
• Worm gears are used when large gear reductions are
needed. It is common for worm gears to have
reductions of 20:1, and even up to 300:1 or greater
• Many worm gears have an interesting property that
no other gear set has: the worm can easily turn the
gear, but the gear cannot turn the worm
• Worm gears are used widely in material handling
and transportation machinery, machine tools,
automobiles etc

12. WORMAND WORM GEAR

13. Types of Gears
Bevel gears – teeth are formed on a
conical surface, used to transfer
motion between non-parallel and
intersecting shafts.
Straight
bevel gear
Spiral
bevel gear

14. Types of Gears
Worm gear sets – consists of a helical
gear and a power screw (worm), used
to transfer motion between non-
parallel and non-intersecting shafts.
Rack and Pinion sets – a special case of
spur gears with the gear having an
infinitely large diameter, the teeth
are laid flat.
Rack
Pinion

15. Gear Design and Analysis
• Kinematics of gear teeth and gear trains.
• Force analysis.
• Design based on tooth bending strength.
• Design based on tooth surface strength.

16. Mechanical
Engineering
Dept.
16
Nomenclatureof SpurGear Teeth
= (tooth spacing)driven gear – (tooth thickness)driver , measured on
the pitch circle.
Backlash
Pitch circle
gear diam.
Fillet radius
Clearance
Base Circle

17. UsefulRelations
P = N / d
P = diametral pitch, teeth per inch
N = number of teeth
d = pitch diameter (gear diameter)
m (module, mm) = d / N
Metric system
p (circular pitch) = πd / N
Pp = π

18. StandardToothSpecifications
Pressure angle
Two mating gears must have the same diametral pitch, P, and pressure angle,
φ.
Pitch
line
Line of centers
Base
circle
Base
circle
Pitch
circle
Pitch
circle
Pressure angle φ
Standard pressure angles, 14.5o
(old), 20o
, and 25o

19. Kinematics
(ωp / ωg) = (dg / dp) = (Ng / Np) = VR (velocity ratio)
P = (Ng / dg) = (Np / dp)
Spur, helical and bevel gears
ωg
dg
ωp
dp
Rack and pinion
Velocity of the rack
Displacement of the rack
Δθ is in radians
,

20. Kinematicsof Gear Trains
Conventional gear trains
ω3
ω2
=
N2
N3
ω3 ω4
=
, ω5
ω4
=
N4
N5
,
mV = e = train value
Speed ratio
ω5
ω2
=
output
input
=
Reverted gear train – output shaft is
concentric with the input shaft. Center
distances of the stages must be equal.

21. Kinematicsof Gear Trains
Planetary gear trains
gear = arm + gear/arm
F/arm = F - arm , L/arm = L - arm
= e (train value)

22. Kinematicsof Gear Trains
Determine the speed of the sun gear if the arm rotates at 1 rpm.
Ring gear is stationary.
2 degrees of freedom, two inputs are needed to control the system

23. PlanetaryGear Trains- Example
For the speed reducer shown, the input
shaft a is in line with output shaft b. The
tooth numbers are N2=24, N3=18, N5=22,
and N6=64. Find the ratio of the output
speed to the input speed. Will both
shafts rotate in the same direction? Gear
6 is a fixed internal gear.
Train value = (-N2 / N3)(N5 / N6) = (-24/18)(22/64) = -.4583
-.4583 = (ωL – ωarm) / (ωF – ωarm) = (0 – ωarm) / (1 – ωarm)
ωarm = .125, reduction is 8 to 1
Input and output shafts rotate in the same direction
d2 + d3 = d6 – d5

24. HarmonicDrive
The mechanism is comprised of three components: Wave Generator,
Flexspline, and Circular Spline.
Wave Generator
Consists of a steel disk and a specially design bearing. The outer surface
has an elliptical shape. The ball bearing conforms to the same elliptical
shape of the wave generator. The wave generator is usually the input.
Flexspline
The Flexspline is a thin-walled steel cup with gear teeth on the outer
surface near the open end of the cup. Flexspline is usually the output.
Circular Spline
Rigid internal circular gear, meshes with the external teeth on the
Flexspline.

25. HarmonicDrive
Teeth on the Flexspline
and circular spline
simultaneously mesh at
two locations which are
180o
apart.
As the wave generator travels 180o
,
the flexspline shifts one tooth with
respect to circular spline in the
opposite direction.
ω Circular Spline = 0
ω Flexspline = output
ωWave Generator = input
The flexspline has two less teeth than the circular
spline.
Gear Ratio = - (Nflex spline)/ 2
, ,

26. NOMENCLATURE….
• Pitch surface: The surface of the imaginary rolling
cylinder (cone, etc.) that the toothed gear may be
considered to replace.
• Pitch circle: A right section of the pitch surface.
• Addendum circle: A circle bounding the ends of the
teeth, in a right section of the gear.
• Root (or dedendum) circle: The circle bounding the
spaces between the teeth, in a right section of the gear.
• Addendum: The radial distance between the pitch circle
and the addendum circle.
• Dedendum: The radial distance between the pitch circle
and the root circle.
• Clearance: The difference between the dedendum of one
gear and the addendum of the mating gear.

27. NOMENCLATURE….
• Face of a tooth: That part of the tooth surface lying outside
the pitch surface.
• Flank of a tooth: The part of the tooth surface lying inside the
pitch surface.
• Circular thickness (also called the tooth thickness): The
thickness of the tooth measured on the pitch circle. It is the
length of an arc and not the length of a straight line.
• Tooth space: pitch diameter The distance between adjacent
teeth measured on the pitch circle.
• Backlash: The difference between the circle thickness of one
gear and the tooth space of the mating gear.
• Circular pitch (Pc) : The width of a tooth and a space,
measured on the pitch circle.
N
D
Pc


28. NOMENCLATURE….
• Diametral pitch (Pd): The number of teeth of a gear unit
pitch diameter. The diametral pitch is, by definition, the
number of teeth divided by the pitch diameter. That is,
Where
Pd = diametral pitch
N = number of teeth
D = pitch diameter
• Module (m): Pitch diameter divided by number of teeth.
The pitch diameter is usually specified in inches or
millimeters; in the former case the module is the inverse
of diametral pitch.
m = D/N
D
N
Pd 

29. VELOCITY RATIO OF
GEAR DRIVE
d = Diameter of the wheel
N =Speed of the wheel
ω = Angular speed
velocity ratio (n) =
2
1
1
2
1
2
d
d
N
N





30. 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

31. 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

32. Simple Gear Train

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

34. Planetary Gear Train (Epicyclic GearTrain)

35. 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.

36. Planetary Gear Train…
• Because there are three red gears instead of one, this gear train
is extremely rugged.
• planetary gear sets is that they 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.

37. 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