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!