A clutch is a mechanism in engine for transmitting rotation that is engaged and
disengaged. Clutch is useful in
auto parts that have
two rotating shafts. In these devices, one shaft is typically driven by
a motor or pulley, and the other shaft drives another device. The clutch connects the two shafts so that they
can either be locked together and spin at the same speed (engaged), or
be decoupled and spin at different speeds (disengaged). In a drill, for
instance, one shaft is driven by a motor, and the other drives a drill
Single plate friction clutch
This type of clutch is used almost exclusively in automobiles and trucks
and has three main parts:
1. Driving member
2. Operating member
Multiple plate friction clutch
This type of clutch has several driving members interleaved with several
driven members. It is used in motorcycles and in some diesel locomotives
with mechanical transmission.
Wet and dry
A 'wet clutch' is immersed in a cooling lubricating fluid, which also
keeps the surfaces clean and gives smoother performance and longer life.
Wet clutches, however, tend to lose some energy to the liquid. A 'dry
clutch', as the name implies, is not bathed in fluid.
There are many different vehicle clutch designs but most are based on
one or more friction discs, pressed tightly together or against a
flywheel using springs. The friction material varies in composition
depending on whether the clutch is dry or wet, and on other
considerations. Clutches found in heavy duty applications such as trucks
and competition cars use ceramic clutches that have a greatly increased
friction coefficient, however these have a "grabby" action and are
unsuitable auto parts for road cars. The spring pressure is released
when the clutch pedal is depressed thus either pushing or pulling the
diaphragm of the pressure plate, depending on type, and the friction
plate is released and allowed to rotate freely.
When engaging the clutch, the engine speed may need to be increased from
idle, using the manual throttle, so that the engine does not stall.
However, raising the engine speed too high while engaging the clutch
will cause excessive clutch plate wear. Engaging the clutch abruptly
when the engine is turning at high speed causes a harsh, jerky start.
This kind of start is necessary and desirable in drag racing and other
competitions where speed is more of an issue than comfort.
Operation in automobiles
This plastic pilot shaft guide tool is used to align the clutch disk as
the spring-loaded pressure plate is installed. The transmission's drive
splines and pilot shaft have an identical shape. A number of such
devices fit various makes and models of drivetrains.
These cogs have matching teeth, called dog teeth, which means that the
rotation speeds of the two parts have a synchronizer, a device that uses
frictional contact to bring the two parts to the same speed, and a
locking mechanism called a blocker ring to prevent engagement of the
teeth (full movement of the shift lever into gear) until the speeds are
In all car the clutch is operated by the left-most pedal using
hydraulics or a cable connection from the pedal to the clutch mechanism.
Even though the clutch may physically be located very close to the
pedal, such remote means of actuation (or a multi-jointed linkage) are
necessary to eliminate the effect of slight engine movement, engine
mountings being flexible by design. With a rigid mechanical linkage,
smooth engagement would be near-impossible, because engine movement
inevitably occurs as the drive is "taken up." No pressure on the pedal
means that the clutch plates are engaged (driving), while pressing the
pedal disengages the clutch plates, allowing the driver to shift gears
A manual transmission contains cogs for selecting gears.
Non-powertrain in automobiles
There are other clutches found in a car. For example, a belt-driven
engine cooling fan may have a clutch that is heat-activated. The driving
and driven elements are separated by a silicone-based fluid and a valve
controlled by a bimetallic spring. As the temperature of the spring
rises, it unwinds and opens the valve, allowing fluid past the valve
which allows the fan to spin at about 60% to 90% of shaft speed
depending on whether it a regular or heavy-duty clutch. There are also
electronically engaged clutches that use magnetic force to lock the
drive and driven shafts together.
Operation in motorcycles
On most motorcycles, the clutch is operated by the clutch lever,
located on the left handlebar. No pressure on the lever means that the
clutch plates are engaged (driving), while pulling the lever back
towards the rider will disengage the clutch plates, allowing the rider
to shift gears. Motorcycle clutches are usually made up of a stack of
alternating plain steel and friction plates. The plates are forced
together by a set of coil springs when the clutch is engaged. Racing
motorcycles often use slipper clutches to eliminate the effects of