# Clutch ,Fly Wheels, Friction How Clutches Work Abstract : If you

```Clutch ,Fly Wheels, Friction
How Clutches Work
Abstract :
If you drive a manual transmission car ,you may be surprised to find out that
it has more than one clutch. And it turns out that folks with automatic
transmission cars have clutches, too. In fact, there are clutches in many things
you probably see or use every day: Many cordless drills have a clutch ,chain
saws have a centrifugal clutch and even some yo-yos have a clutch.
Clutch Image Gallery
Diagram of car showing clutch location. See
more clutch images.
works and find out some interesting, and perhaps surprising, places where
clutches can be found .
Clutches are useful in devices that have two rotating shafts. In these devices,
one of the shafts is typically driven by a motor or pulley, and the other shaft
drives another device. In a drill, for instance, one shaft is driven by a motor
and the other drives a drill chuck. The clutch connects the two shafts so that
they can either be locked together and spin at the same speed, or be
decoupled and spin at different speeds .
In a car, you need a clutch because the engine spins all the time, but the car's
wheels do not. In order for a car to stop without killing the engine, the wheels
need to be disconnected from the engine somehow. The clutch allows us to
smoothly engage a spinning engine to a non-spinning transmission by
controlling the slippage between them .
To understand how a clutch works, it helps to know a little bit about friction,
which is a measure of how hard it is to slide one object over another .Friction
is caused by the peaks and valleys that are part of every surface -- even very
smooth surfaces still have microscopic peaks and valleys. The larger these
peaks and valleys are, the harder it is to slide the object. You can learn more
about friction in How Brakes Work .
A clutch works because of friction between a clutch plate and a flywheel.
We'll look at how these parts work together in the next section .
Fly Wheels, Clutch Plates and Friction
In a car's clutch, a flywheel connects to the engine ,and a clutch plate
connects to the transmission .You can see what this looks like in the figure
below.
.Exploded view of a clutch
When your foot is off the pedal, the springs push the pressure plate against
the clutch disc, which in turn presses against the flywheel. This locks the
engine to the transmission input shaft, causing them to spin at the same speed .
Photo
courtesy
Pressure plate
Carolina
Mustang
The amount of force the clutch can hold depends on the friction between the
clutch plate and the flywheel, and how much force the spring puts on the
pressure plate. The friction force in the clutch works just like the blocks
described in the friction section of How Brakes Work ,except that the spring
presses on the clutch plate instead of weight pressing the block into the
ground
.
.
How a clutch engages and releases
When the clutch pedal is pressed, a cable or hydraulic piston pushes on the
release fork, which presses the throw-out bearing against the middle of the
diaphragm spring. As the middle of the diaphragm spring is pushed in, a
series of pins near the outside of the spring causes the spring to pull the
pressure plate away from the clutch disc (see below). This releases the clutch
from the spinning engine .
Clutch plate
Note the springs in the clutch plate. These springs help to isolate the
transmission from the shock of the clutch engaging .
This design usually works pretty well, but it does have a few drawbacks .
We'll look at common clutch problems and other uses for clutches in the
following sections .
Common Problems
From the 1950s to the 1970s, you could count on getting between 50,000 and
70,000 miles from your car's clutch. Clutches can now last for more than
80,000 miles if you use them gently and maintain them well. If not cared for,
clutches can start to break down at 35,000 miles. Trucks that are consistently
overloaded or that frequently tow heavy loads can also have problems with
relatively new clutches.
The most common problem with clutches is that the friction material on the
disc wears out. The friction material on a clutch disc is very similar to the
friction material on the pads of a disc brake or the shoes of a drum brake -after a while, it wears away. When most or all of the friction material is gone,
the clutch will start to slip, and eventually it won't transmit any power from
the engine to the wheels
The clutch only wears while the clutch disc and the flywheel are spinning at
different speeds. When they are locked together, the friction material is held
tightly against the flywheel, and they spin in sync. It's only when the clutch
disc is slipping against the flywheel that wearing occurs. So ,if you are the
type of driver who slips the clutch a lot, you'll wear out your clutch a lot
faster.
Sometimes the problem is not with slipping, but with sticking. If your clutch
won't release properly, it will continue to turn the input shaft. This can cause
grinding, or completely prevent your car from going into gear. Some
common reasons a clutch may stick are:
Broken or stretched clutch cable - The cable needs the right amount of
tension to push and pull effectively.
Leaky or defective slave and/or master clutch cylinders - Leaks keep the
cylinders from building the necessary amount of pressure.
Air in the hydraulic line - Air affects the hydraulics by taking up space the
fluid needs to build pressure.
the wrong amount of force.
Mismatched clutch components - Not all aftermarket parts work with your
clutch.
A "hard" clutch is also a common problem. All clutches require some amount
of force to depress fully. If you have to press hard on the pedal, there may be
something wrong. Sticking or binding in the pedal linkage, cable, cross shaft,
or pivot ball are common causes. Sometimes a blockage or worn seals in the
hydraulic system can also cause a hard clutch.
Another problem associated with clutches is a worn throw-out bearing ,
sometimes called a clutch release bearing. This bearing applies force to the
fingers of the spinning pressure plate to release the clutch. If you hear a
rumbling sound when the clutch engages, you might have a problem with the
throw-out.
Clutch Diagnostic Test
If you find that your clutch has failed, here is an at-home diagnostic test that
anyone can perform:
.1Start your car, set the parking break, and put the car in neutral.
.2With your car idling, listen for a growling noise without pushing the clutch
in. If you hear something, it's most likely a problem with the transmission. If
you don't hear a noise, proceed to step three.
.3With the car still in neutral, begin to push the clutch and listen for noise. If
you hear a chirping noise as you press, it's most likely the clutch release, or
throw-out bearing. If you don't hear a noise, proceed to step four.
.4Push the clutch all the way to the floor. If you hear a squealing noise, it's
probably the pilot bearing or bushing.
If you don't hear any noise during these four steps, then your problem is
probably not the clutch. If you hear the noise at idle and it goes away when
the clutch is pressed, it may be an issue in the contact point between the fork
and pivot ball
In the next section, we'll examine some different types of clutches and how
they are used
Types of Clutches
There are many other types of clutches in your car and in your garage.
An automatic transmission contains several clutches. These clutches engage
and disengage various sets of planetary gears .Each clutch is put into motion
using pressurized hydraulic fluid. When the pressure drops, springs cause the
clutch to release. Evenly spaced ridges ,called splines, line the inside and
outside of the clutch to lock into the gears and the clutch housing. You can
An air conditioning compressor in a car has an electromagnetic clutch. This
allows the compressor to shut off even while the engine is running. When
current flows through a magnetic coil in the clutch, the clutch engages. As
soon as the current stops, such as when you turn off your air conditioning, the
clutch disengages.
Most cars that have an engine-driven cooling fan have a thermostatically
controlled viscous clutch -- the temperature of the fluid actually drives the
clutch. This clutch is positioned at the hub of the fan, in the airflow coming
through the radiator. This type of clutch is a lot like the viscous coupling
sometimes found in all-wheel drive cars. The fluid in the clutch gets thicker
as it heats up ,causing the fan to spin faster to catch up with the engine
rotation. When the car is cold, the fluid in the clutch remains cold and the fan
spins slowly, allowing the engine to quickly warm up to its proper operating
temperature.
Many cars have limited slip differentials or viscous couplings, both of which
use clutches to help increase traction. When your car turns, one wheel spins
faster than the other, which makes the car hard to handle. The slip differential
makes up for that with the help of its clutch .
When one wheel spins faster than the others, the clutch engages to slow it
down and match the other three. Driving over puddles of water or patches of
viscous couplings in How Differentials Work.
Gas-powered chain saws and weed eaters have centrifugal clutches, so that
the chains or strings can stop spinning without you having to turn off the
engine. These clutches work automatically through the use of centrifugal
force. The input is connected to the engine crankshaft. The output can drive a
chain, belt or shaft .As the rotations per minute increase, weighted arms
swing out and force the clutch to engage. Centrifugal clutches are also often
found in lawn mowers ,go-karts, mopeds and mini-bikes. Even some yo-yos
are manufactured with centrifugal clutches.
Car air conditioning compressor with magnetic
clutch
Clutches are valuable and necessary to a number of applications
Refrence:
http://auto.howstuffworks.com/clutch.htm
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