Gears
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Transcript of Gears
Gears
Introduction to Gears Types of Gears Design of Gears according to their Types Advantages And Disadvantages Applications
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
1. According to the position of axes of the shafts.
a. Parallel 1.Spur Gear 2.Helical Gear 3.Herringbone Gear 4.Rack and Pinion
b. Intersecting Bevel Gear
c. Non-intersecting and Non-parallel worm and worm gears
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
The teeth on helical gears are cut at an angle to the face of the gear
This gradual engagement makes helical gears operate much more smoothly and quietly than spur gears
One interesting thing about helical gears is that if the angles of the gear teeth are correct, they can be mounted on perpendicular shafts, adjusting the rotation angle by 90 degrees.
Helical Gear is used in Automobile gear box because it produces less noise than spur gear
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.
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
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.
A worm drive is a cylindrical gear with a shallow spiral thread that engages the worm gear in a non-intersecting, perpendicular axes configuration.
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
The gear ratio is the "size of the worm gear - to - 1" The worm can easily turn the gear, but the gear cannot
turn the worm Typical worm drives can only be turned in one direction
due to self-locking depends on the lead angle, the pressure angle, and the coefficient of friction
Worm gears are used widely in material handling and transportation machinery, machine tools, automobiles etc
One of the newest designs for differentials is called the Torsen differential. It uses a combination of worms and worm gears that make each wheel independent of the other wheels. These differentials are found in Hummers, large earth-moving vehicles and some off-road vehicles.
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
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
For large velocities,
compound
arrangement is
preferred
Two or more gears
may rotate about a
single axis
Nearly all automatic transmissions rely on planetarygear sets to transfer power and multiply enginetorque to the drive axle.
A simple planetary gear set consists of three parts:
a) sun gear,b) Planet carrierc) ring gear
All gears in a planetary gear set are in constantmesh. The torque flow through a planetary gear set,both input and output, occurs along a single axis.
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.
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.
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
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.
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
DP
c
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
NPd
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
ADVANTAGES
Spur gears have high power transmission efficiency
They are compact and easy to install.
Unlike belt drives, spur gear drives have no Slip.
They can be used to transmit large amount of power (of the order of 50,000 kW)
DISADVANTAGES
Spur gear drives are costly when compared to belt drives
Spur gears produce a lot of noise when operating at high speeds.
They cannot be used for long distance power transmission.
ADVANTAGES
Helical gears are much less noisy. The teeth engage a little at a time rather than the entire face at once.
They can handle more load then a spur gear of equivilant width and tooth size. They tooth is effectively longer because it is diagonal.
They can be made to engage at angles. Effeciency is lost as the angle becomes greater.
DISADVANTAGES
Helical gears have a higher load capacity but are expensive to manufacture.
They have an axial thrust, This can however be overcome by the use of double helical gears by
having teeth with a 'v' shape.
ADVANTAGES
This gear makes it possible to change the operating angle.
Differing of the number of teeth (effectively diameter) on each wheel allows mechanical advantage to be changed. By increasing or decreasing the ratio of teeth between the drive and driven wheels one may change the ratio of rotations between the two, meaning that therotational drive and torque of the second wheel can be changed in relation to the first, with speed increasing and torque decreasing, or speed decreasing and torque
increasing.
DISADVANTAGES
One wheel of such gear is designed to work with its complementary wheel and no other.
The shafts' bearings must be capable of supporting significant forces
Must be precisely mounted.
ADVANTAGES
Worm gear drives operate silently and smoothly.
They occupy less space. They have good meshing
effectiveness. They can be used for
reducing speed and increasing torque.
DISADVANTAGES
Worm gear materials are expensive.
Worm drives have high power losses and low transmission efficiency.
They produce a lot of heat,due to resistance between them.
Spur Gear: Metal cutting machines Power plants Watches Fuel pumps Rack and pinion mechanisms Rolling mills Automobile gear boxes. Electric screwdrivers, windup alarm clocks & pumps are just a few
everyday machines where internal gears are used.
Bevel Gear: Bevel gears are used in differential drives, which can transmit power to
two axles spinning at different speeds, such as those on a cornering automobile.
Its is used in Mining Machine equipment. It also used in Printing press Machine. Spiral bevel gears are important components on rotorcraft drive systems
Worm Gear: Gates and Conveyor Belts – Typical worm drives can only be turned in
one direction, which means that conveyor belts and security gates lock-up when not being used, Automatic security gates will often adopt two worm drives, one to open and another to close.
Elevators/Lifts – worm gears can often be found in the machinery of common elevators/lifts because of their compact size and non-reversible properties.
Hoisting machines Automobile steering mechanisms Conveyors.
Helical Gears: Helical gears are also used in machine tools, turbine drives,
feed drives, sand mullers, rolling mills & marine applications And in Actuators.
Rack and pinion:
Rack and pinion Mechanism is Commonly used in Cranes and Actuators
It is also used in Car steering Mechanism. Used in Rack Railways.
Gears Use in Automatic TransmissionEpi-cyclic gear or planetary gear is a gear system consisting of one or
more outer gears, or planet gears, revolving about a central, or sun gear. Typically, the planet gears are mounted on a movable arm or carrier
which itself may rotate relative to the sun gear. It is used in automatic transmission!