Abstract :
I am
introducing to you the ceramic disc brakes. Cast iron is extensively used as
the material for manufacturing disc brakes. This is much heavier and thus
reduces initial acceleration and causes more fuel consumption. For reducing
these effects, we use ceramic brakes.
Today’s
technology is in need for speed, but at the same time, we need safety as well.
For safety, we need deceleration to the maximum extent. These two things are
moreover contradictory factors. For speed, we need engines of maximum efficiency
and for keeping this speed in bounds, we need brakes of latest technology. For
coping up with today’s speed, new
materials are introduced in the manufacture of brakes.
The ceramic
disc brakes possess the following advantages:
Its weight
is half the weight of conventional disc brakes.
It
increases the fuel efficiency of the vehicle.
It
functions well in wet conditions as well.
One of the
most important control system of an automobile is BRAKE SYSTEM They are required to stop the vehicle within the
smallest possible distance and is done by converting kinetic energy of the
vehicle into heat energy which is dissipated into atmosphere.
The main
requirements of brakes are given below:-
The brakes
must be strong enough to stop the vehicle within the minimum possible distance
in an emergency. But this should also be consistent with safety. The driver
must have a proper control over the vehicle during emergency braking and the
vehicle must not skid.
The brakes
must have good antifade characteristics and their effectiveness should not
decrease with constant prolonged application.
The actual
stopping distance of vehicle while braking depends on the following factors:-
1. Vehicle
speed
2.
Condition of the road surface
3.
Condition of tyre tread
4.
Coefficient of friction between the tyre tread and the road surface
5.
Coefficient of friction between the brake drum/disc and brake lining/friction
pad
6. Braking
force applied by the driver
DISC BRAKES
As shown in
fig a disc brake consists of a cast iron disc bolted to the wheel hub and a
stationary housing called caliper. The caliper is connected to some stationary
part of the vehicle, like the axle casing or the stub axle and is cast in two
parts, each part containing a piston. In between each piston and disc there is
a friction pad held in position by retaining pins, spring plates etc., passages
are drilled in the caliper for the fluid to enter or leave each housing. These
passages are also connected to another one for bleeding.
When the
brakes are applied hydraulically actuated pistons move the friction pads into
contact with the disc, applying equal and opposite forces the later. On
releasing the brakes the rubber sealing rings act as return springs and retract
the pistons and the friction pads away from the disc.
CONSTRUCTIONAL
FEATURES
Two types
brake discs are generally used the solid type and the ventilated type. The
ventilated type more efficient since it provides better cooling. But they are
thicker and heavier than solid type, they are liable to wrap at severe braking
conditions, the dirt accumulates in the vents which affects cooling and apart
produces wheel imbalance.
The discs
of the brakes are made of pearlite gray cast iron. The material is cheap and
has good antiwear properties. Cast steel discs have also been employed in
certain cases, which wear still less and provide higher coefficient of
friction. Their main drawback is the non uniform frictional behavior.
The other
materials used for the manufacture of disc are
1. Aluminium
2. Ceramic
Obviously,
cast-iron disc is the heaviest part of a brake - about 8 kg each, or 32 kg per
car. Aluminium alloy discs are used in the Lotus Elise. Though light, they were
less resistant to heat and fade, thus more powerful Elises still employ
conventional cast-iron disc.
In contrast, carbon-fiber disc is most
heat-resisting yet is by far the lightest, however, it requires very high
working temperature, and otherwise braking power and response will be
unacceptable.
Ceramics
are inorganic, non-metallic materials that are processed and used at high
temperatures. They are generally hard brittle materials that withstand
compression very well but do not hold up well under tension compared to the
metals. They are abrasive-resistant, heat resistant (refractory) and can
sustain large compressive loads even at high temperatures. The nature of the
chemical bond in the ceramics is generally ionic in character, and the anions
play an important role in determination of the properties of the material.
Typical anions present are carbides, borides, nitrides and oxides. The
different types of ceramics are clays, refractories, glasses etc.
Cast iron
has been the material of choice for brakes rotors since the introduction of
disc brakes during the 50’s.Elise made a new era, being the first road
production road car to use aluminium metal matrix composite discs inserted on
four wheels. Aluminium is better rotor material than cast iron due to two main
reasons: its density is as one third as cast iron but its thermal conductivity
is three times greater. These factors made it possible to construct a much
lighter brake disc.
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