1. Geometrical and Mechanical Engineering
Drawing – CAPE Unit II
Clutches
A clutch is a mechanical device that engages and disengages the power transmission, especially
from driving shaft to drive shaft. Clutches are used whenever the transmission of power or
motion must be controlled either in amount or over time (e.g., electric screwdrivers limit how
much torque is transmitted through use of a clutch; clutches control whether automobiles
transmit engine power to the wheels).
Friction Clutch
The purpose of friction clutches is to connect a moving member to another that is moving at a
different speed or stationary, often to synchronize the speeds, and/or to transmit power.
Usually, as little slippage (difference in speeds) as possible between the two members is
desired.
Materials
Various materials have been used for the disc-friction facings, including asbestos in the past.
Modern clutches typically use a compound organic resin with copper wire facing or
a ceramic material. (Ceramic materials are typically used in heavy applications such as racing or
heavy-duty hauling, though the harder ceramic materials increase flywheel and pressure plate
wear.)
Dampers
A clutch damper is a device that softens the response of the clutch
engagement/disengagement. In automotive applications, this is often provided by a mechanism
in the clutch disc centres. In addition to the damped disc centres, which reduce driveline
vibration, pre-dampers may be used to reduce gear rattle at idle by changing the natural
frequency of the disc. These weaker springs are compressed solely by the radial vibrations of an
idling engine. They are fully compressed and no longer in use once the main damper springs
take up drive.
Push/Pull
Friction-disc clutches generally are classified as push type or pull type depending on the location
of the pressure plate fulcrum points. In a pull-type clutch, the action of pressing the pedal pulls
the release bearing, pulling on the diaphragm spring and disengaging the vehicle drive. The
opposite is true with a push type, the release bearing is pushed into the clutch disengaging the
vehicle drive. In this instance, the release bearing can be known as a thrust bearing (as per the
image above).

2. Single-Plate Clutch
A single disc or plate clutch consists of a clutch plate whose both sides are faced with a frictional
material. It is mounted on the hub which is free to move axially along the splines of the driven
shaft. The pressure plate is mounted inside the clutch body which is bolted to the flywheel. Both
the pressure plate and the flywheel rotate with the engine crank shaft or the driving shaft. The
pressure plate pushes the clutch plate towards the flywheel by a set of strong springs which are
arranged radially inside the body. The three levers (also known as release levers or fingers) are
carried on pivots suspended from the case of the body. These are arranged in such a manner so
that the pressure plate moves away from the flywheel by the inward movement of a trust
bearing. The bearing is mounted upon a forked shaft and moves forward when the clutch pedal
is pressed.
Advantages: simpler assembly, cheaper, more reliable, takes up less space longitudinally, can be
used to completely disengage the drive
Disadvantages: requires larger cross-sectional space, less torque capacity

3. Multi-plate Clutch
This type of clutch has several driving members interleaved or "stacked" with several driven
members. Clutches are assembled in a basket with metal surfaces for multiple friction surfaces
to contact.
Advantages: decreased moment of inertia, increased torque conversion, decreased force
require to operate the clutch resulting in smoother shifting, less slippage
Disadvantages: more expensive, does not completely disengage the drive
Uses: some modern automobiles, diesel locomotives

4. Centrifugal Clutch
A centrifugal clutch is a clutch that uses centrifugal force to connect two concentric shafts, with
the driving shaft nested inside the driven shaft. It engages more at higher speeds. As
engine RPM increase, weighted arms in the clutch swing outward and force the clutch to
engage. The most common types have friction pads or shoes radially mounted that engage the
inside of the rim of a housing. On the centre shaft there are an assorted number of extension
springs, which connect to a clutch shoe. When the central shaft spins fast enough, the springs
extend causing the clutch shoes to engage the friction face. When the engine reaches a certain
speed, the clutch activates, working somewhat like a continuously variable transmission. As the
load increases, the speed drops, disengaging the clutch, letting the speed rise again and
reengaging the clutch. If tuned properly, the clutch will tend to keep the speed at or near the
torque peak of the engine.
Advantages: no control mechanism needed, cheaper than other, prevents internal combustion
engine from stalling
Disadvantages: loss of power due to slippage and stopping, not suitable for heavy load or high
torque requirements
Uses: chain-saws, mopeds, go-karts, paramotor (propulsion of a para-glider)
Wet Clutch
A wet clutch is immersed in a cooling lubricating fluid that also keeps surfaces clean and
provides smoother performance and longer life. Wet clutches, however, tend to lose some
energy to the liquid. Since the surfaces of a wet clutch can be slippery (as with a motorcycle
clutch bathed in engine oil), stacking multiple clutch discs can compensate for the lower
coefficient and so eliminate slippage under power when fully engaged. The Hele-Shaw
clutch was a wet clutch that relied entirely on viscous effects, rather than on friction.

5. Dry Clutch
A dry clutch, as the name implies, is not bathed in liquid and should be, literally, dry.
Pressure Plate
Pressure plates are, as the name implies, round, metallic devices containing springs and fingers,
or levers, and controlled by the release fork connected to the shifter. All of the clutch
components are enclosed in the bell housing of the transmission, between the rear of the
engine and the front of the gearbox.
Clutch Disc
A disk clutch is used in a vehicle's manual transmission and is sandwiched between the flywheel
and the pressure plate. In some high-performance applications, a multiple disk clutch is used to
better harness the high amounts of horsepower and torque produced by the engine. This
device can be made up of organic materials, metal and iron compounds, and even Kevlar in
high-performance applications.
Flywheel
A flywheel is a rotating mechanical device that is used to store rotational energy. Flywheels
have a significant moment of inertia and thus resist changes in rotational speed. The amount of
energy stored in a flywheel is proportional to the square of its rotational speed. Energy is
transferred to a flywheel by applying torque to it, thereby increasing its rotational speed, and
hence its stored energy. Conversely, a flywheel releases stored energy by applying torque to a
mechanical load, thereby decreasing its rotational speed.