Gears
also changed the direction of rotation. For instance, in the differential
between the rear wheels of your car, the power is transferred by a shaft that
runs down the center of the car and the difference has to turn that power 90
degrees to apply it to the wheels
There
are many intricacies in the different types of gear. In this article, we'll
learn exactly how the teeth on the gear work, and we'll talk about the
different kinds of gears you find and all sorts of Mechanical gadgets.
Contents,
·
Gear Basics
·
Helical Gears
·
Spur Gears
·
Bevel Gears
·
Worm Gears
·
Rack and pinion
Gears
·
Planetary Gear
sets and Gear Ratio
·
Detail on involute
Gear Profiles
1.
Gear Basics
You
have in probably heard of gear ratios, mostly when it comes to cars. The gear
ratio is the number of rotates the production shaft makes while the input shaft
turns one time. If the gear ratio is 2:1, then the smaller gear is rotating two
times while the larger gear rotating just once. It also means that the larger
gear has twice as many teeth as the smaller gear. The larger gear is just
called a "gear" while the smaller gear is also called a pinion.
One
of the earliest kinds of gear we could look at would be a wheel with wooden
pegs sticking out of it. The problem with this kind of gear is that the
distance from the center of each gear to the point of contact makes a
difference as the gears rotate. This means that the gear ratio changes as the
gear rotate, meaning that the output speed also changes. If you used a gear
like this in your car, it would be impossible to continue at a hurry-up speed
you would be accelerating and decelerating constantly.
Many
modern gears are used a special tooth profile called an involute. This profile
has the very important property of maintaining a constant speed ratio between
the two gears. Like the peg wheel above, the contact point moves, but the
configuration of the involute gear tooth compensates for this movement.
Now
let's look at some of the different types of gears
2. Helical Gears
The
teeth on the helical are cut at the angle of the face of the gear, when two
teeth gears on a helical gears system engage, the contact starts at one ending
of the teeth and gradually grows as the gears rotate until the two teeth are in
full engagement.
The
gradual appointment of helical gears makes them operate much more smoothly and
quietly than spur gears. For this reason, helical gears are used in practically
all car transmissions.
Because
of the angle of the teeth on helical gears, they generate a thrust load on the
gear when they mesh. Devices that used helical gears have bearings that can
support these thrust loads.
The
bent teeth of helical gears mean they have to be staggered, with the teeth of
the next gear goings in the opposite way so the teeth can mesh. Each gear is
called "right-hand" or "left-hand" when it meshes with
another gear on parallel shafts. If the angles of the gear teeth are correct,
helical gears can also be placed on perpendicular shafts adjusting the rotation
Angles by 90 degrees.
3. Spur Gears
Spur
gears are the most common types of gears they have straight teeth and are
mounted on parallel shafts. Sometimes, many spur gears are used at once to
create a very large gear reduction.
Spur
gears are used in many devices that you can see all over How Stuff Works, like
the electric screwdriver, dancing monster, oscillating sprinkle, windup alarm
clock, Washing Machine, and cloth dryer. But you won’t find it in your car.
This
is because the spur gear can be really loud. Each time a gear tooth engages a
tooth on the other gear, the teeth collide, and this impact makes a noise. It
also increases the stress on the gear teeth.
To
reduce the noise and stress in the gears, most of the gears in your car are
helical which we will explain next.
4. Bevel Gears
Bevel
Gears are useful when the direction of the shaft's rotation needs be to
changed. They are cone-shaped and
usually mounted on shafts that are 90 degrees apart, but they can be designed
to work at another angle as well.
The
teeth on bevel gears can be straight, spiral, or hybrid. Straight bevel gears
teeth actually have the same problems as straight spur gears teeth as each
tooth engages, it impacts the corresponding tooth Just as with spur gears, the
solution to this problem is to curve the gear teeth. These spiral teeth engage
just like helical teeth: the contact starts at one end of the gear and all at
once.
Just
as with spur gears, the solution to this problem is to curve the gear teeth.
These spiral teeth engage just like helical teeth: the contact starts at one
end of the gear and progressively, across the whole tooth. On straight and
spiral bevel gears, the shafts must be perpendicular to each other and in the
same plane. If you were to extend the two shafts past the gears, they would
intersect. The hypnoid, on the other hand, can engage with the axes in different
planes.
5. Worm Gears
This
feature is used in many cars different. The ring gear of the different and the
inputs pinion gear are both hypoid. This allows the input pinion to be produced
lower than the axis of the ring gear. The figure at left shows the input pinion
engaging the ring gear of the differential. Since the drive shaft of the car is
coupled to the input pinion, this also lowers the drive's haft. This means that
the drive shaft does not intrude into the passenger section of the car as much,
making more room for cargo.
Worm
gears are cylinders with a spiral thread wrapped around the outsides that
meshes with another gear to turn it. They are used when larger gears reductions
are needed. It is common for worm gears to have reductions of 20; 1 and even up
to 300; 1 are greater.
Mostly
worm gears have an interesting property that no other gear set has: The worm
gears can easily turn the gears, but the gears cannot turn the worm. This is
because the angle on the worm is so shallow that when the gears tried to spin
it, the friction between the gears and the worm holds the worm in place.
These
features are used for machines such as conveyor systems, in which the locking
features can act as a brake for the conveyor when the motor is not turning.
Worm gears are also used in the torsion difference, which increases torque for
some high- performances cars and trucks.
6.
Rack and Pinion Gears
Earlier
we mentions that went two gears mesh, the smaller is one called the pinion. A
rack is a straight bar with gears teeth’s that meshes with the pinion. So you
can probably imagine how rack and pinion gear is used to convert rotation
into linear motion. Perfect examples of these are the steering system of many
cars. The steering wheel rotates a gear, which engaged the rack. As the gears
turn, it slides the rack either to the right or left depending on which way
you turn the wheel.
Rack
and pinion gear are also used in some scales to turn the dial that displays
your weight.
7.
Planetary Gear sets and Gear Ratios
Any
Planetary Gear set has three main components.
·
Sun Gears
·
Planet Gears and
the Planet Gears Carrier
·
Ring Gears
Each
of these three components can be the input or the output, or they can be held
stationary. Choosing which pieces plays which role determined the gear ratio
for the gear set. Let’s take a look at the single planetary gear set.
One of the planetary gears set from our transmission has ring gears with 72 teeth and sun gears with 30 teeth. We can get lots of different gear ratios out of the gear set.
Gear set table
HOWSTUFFWORKS
Locking
any two of the three components together will lock up the whole device at a 1:1
gears reduction. Notice that the first gear ratio listed above is a reduction in the output speed is slower than the input speeds. The second is an overdrive
the output speed is faster than the input speed. The last is a reduction
again, but the output direction is reversed. There are several other ratios that
can be got out of this planetary gears set,
But
these are the ones that are relevant to our automatic transmission.
This
one set of gears can produce all of these different gears ratio without having to
engage or disengage any other gear. With two of these gear sets in a row, we
can get as many forward gears and one reversed gear as our transmission needs.
We will put the two sets of gears together in the next section.
8.
Details on involute gear Profiles
On
an involute profile gears tooth, the contacted point starts closer to one
gear, and as the gears spin, the contacted point moved away from that gear and
toward the other. If you were to follow the contact point, it would describe
a straight line that starts near one gear and end up near the other. This means
that the radius of the contacted point gets larger as the teeth engage.
The
pitch diameter is defined as "the imaginary diameter for which the width
of the threads and the grooves are equal," according to science Direct.
Since the contact diameter is not constant, the pitch diameter is really the
average contact distance. As the teeth first start to engage, the top gears
tooth contacted the bottom gears tooth inside the pitch diameter. But the parts
of the top gears tooth that contacted the bottom gears tooth are very narrow
at this point. As the gears turn, the contacted point slides up onto the
thicker part of the top gears tooth. This pushes the top gears ahead, so it
compensates for the smaller slightly contracted diameter.
As
the teeth continue to rotate, the contacted point moves even farther away,
going outsides the pitch diameter — but the profiles of the bottom tooth
compensate for this movement. The contact point starts to slide onto the
narrowed parts of the bottom tooth, subtracting a little bit of velocity from
the top gears to compensate for the increased diameter of contact. The end
result is that even though the contacted point diameter changes continually, the
speed remains the same. So, an involute profile gears tooth produced a constant
ratio of rotational speed.