Brake rotors of disc brakes rotate
with the wheels, and brake pads, which are fitted to the brake calipers, clamp
on these rotors to stop or decelerate the wheels. The brake pads pushing
against the rotors generate friction, which transforms kinetic energy into
thermal energy.
This thermal energy generates heat,
but since the main components are exposed to the atmosphere, this heat can be
diffused efficiently. This heat-dissipating property reduces brake fade, which
is the phenomenon where braking performance is influenced by the heat. Another
advantage of disc brake is its resistance to water fade, which occurs when the
water on the brakes significantly reduces braking force. When the vehicle is in
motion, the rotor spins at high speeds and this rotational motion discharges
the water from the rotors themselves, resulting in stable braking force.
The brake rotor (disc) which rotates
with the wheel, is clamped by brake pads (friction material) fitted to the
caliper from both sides with pressure from the piston(s) (pressure mechanism)
and decelerates the disc rotation, thereby slowing down and stopping the
vehicle.
Circular disc bolted to the wheel hub
that spins with the wheel. Rotors are most commonly made of cast iron or steel;
however, some very high-end cars use a carbon ceramic rotor. Rotors can be
slotted or drilled for better heat dissipation.
2)Brake pads
The component that pushes into the
rotor, creating the friction that slows and stops a car. They feature a metal
portion called a shoe and a lining that is attached to the shoe. The lining is
what actually comes in contact with the rotor and wears away with use. Linings
are made of different materials and fall into three categories: organic,
semi-metallic and ceramic. The lining material chosen will impact the length of
brake life, the amount of noise heard when the brakes are applied, and how
quickly the brakes bring a car to a halt.
3)Piston
Cylinder connected to the brake
system hydraulics. The piston is what moves the brake pads into the rotor when
the driver presses the brake pedal. Some brake systems have a single piston
that moves both pads, while others have two pistons that push the brake pads
from each side of the rotor. Others still have four, six, or even eight pistons
for higher braking power, at the expense of added cost and complexity.
4)
Caliper
Housing that fits over the rotor and
holds the brake pads and pistons, as well as contains ducting for brake fluid.
There are two types of brake calipers: floating (or sliding) and fixed.
Floating calipers “float” over the rotor, and only have pistons on a single
side. When the driver presses the brakes, the pistons press the brake pads on
one side into the rotor, which causes the caliper to slide over so that the
pads on the non-piston side of the caliper also contact the rotor. Fixed
calipers are bolted in place, and instead, have pistons on both sides of the
rotor that move when the driver applies the brakes. Fixed calipers apply brake
pressure more evenly and clamp more firmly on the rotor, however floating
calipers are found on most cars and are perfectly adequate for everyday driving.
5)Sensors
Some vehicles have brakes that
contain sensors embedded in the brake pads which work to tell the driver when
the pads are worn out. Other brake sensors play a part in the vehicle’s ABS
system.
Disc brakes are generally used in
passenger cars, but due to their stable performance at higher speeds and
resistance to brake fade, they are gradually spreading into the commercial
vehicle segment, where drum brakes were traditionally chosen for their longer
service life.
WORKING PRINCIPLE
When the driver steps on the brake
pedal, the power is amplified by the brake booster (servo system) and changed
into a hydraulic pressure (oil-pressure) by the master cylinder. The pressure
reaches the brakes on the wheels via tubing filled with brake oil (brake
fluid). The delivered pressure pushes the pistons on the brakes of the four
wheels. The pistons in turn press the brake pads, which are friction material,
against the brake rotors which rotate with the wheels. The pads clamp on the
rotors from both sides and decelerate the wheels, thereby slowing down and stopping
the vehicle.
• When the brake pedal is pressed, the
high-pressure fluid from the master cylinder pushes the piston outward.
• The piston pushes the brake pad
against the rotating disc.
• As the inner brake pad touches the
rotor, the fluid pressure exerts further force and the caliper moves inward and
pulls the outward brake pad towards the rotating disc and it touches the disc.
• Now both the brake pads are pushing
the rotating disc, a large amount of friction is generated in between the pads
and rotating disc and slows down the vehicle and finally, let it stop.
• When a brake pad is released, the
piston moves inward, the brake pad away from the rotating disc. And the vehicle
again starts to move.
TYPES OF DISC BRAKES
There are two types of disc brakes.
One is called the "opposed piston type disc brake" which has pistons
on both sides of the disc rotor, and the other is the "floating type disc
brake" which has a piston on only one side. The floating type disc brakes
are also called the sliding pin type disc brakes.
1)
Opposed Piston Type Disc Brakes
The opposed piston type is a disc
brake which has pistons on both sides of the disc rotors.
The opposed piston type disc brake
features stable braking force as well as a high level of controllability.
The swept areas of the brake pads are
enlarged to increase braking force, and here opposed piston types are favored.
This is because of its advantage where the number of pistons can be increased
to realize even distribution of pressure on the rotors from both sides.
Depending on the size of the brake pads, there are several types, including the
4-pot type which has two pistons on each side for a total of four, and the
6-pot type which has three pistons on each side for a total of six.
2(Floating Type Disc Brakes
Floating type is a disc brake which
has a piston on only one side and is also called the sliding type disc brake.
On the floating type disc brakes, the
piston pushes the inner brake pad against the rotor when the brakes are
engaged. This generates a reaction force that moves the caliper itself along
with the slide pin, pushing the outer pad against the rotor to clamp it from
both sides.
Many passenger car disc brakes are of
the floating caliper type since this type has a relatively simple and
lightweight construction, which allows for lower manufacturing costs.
Floating type disc brakes for
commercial vehicles Disc brakes are used mainly for passenger cars, but due to
their consistent performance at higher speeds and resistance to brake fade,
they are gradually spreading into the commercial vehicle segment, where drum
brakes were traditionally chosen for their resistance against wear.
TYPES OF ROTOR
1(Smooth Rotors
Smooth rotors are identified by their
flat, smooth surface. For most cars and trucks on the road, smooth rotors are
original equipment (OE) because of their versatility for many driving
conditions. The main benefit of smooth rotors is that they tend to wear evenly,
helping your brake pads last longer. If you want to keep the smooth rotor but still
go for the upgrade, look for premium metal that absorbs more heat.
2)
Drilled or Dimpled Rotors
Drilled rotors are identified by the
pattern of holes that have been drilled all the way through the rotor disc.
Dimpled rotors are similar, though instead of holes there are dimples that have
been drilled to the rotor’s minimum thickness level, retaining more structural
integrity than a fully drilled rotor. These rotor types help the brake pads to
better grip the rotor, giving it more initial bite and increasing stopping
power.
3)Slotted
Rotors
Slotted rotors are recognized by
carved lines found on the rotor. These carved slots help to cool the rotor
during high-performance use. They also help to remove dirt and other debris
from the disc and brake pad, helping to maintain consistent contact for more
efficient braking. Slotted rotors are perfect for vehicles that see frequent,
heavy towing.
4)
Drilled/Dimpled and Slotted Rotors
Rotors that are both drilled (or
dimpled) and slotted, while effective, are best for trucks that want the added
aesthetic, such as those with wheels that have a more open design. Not only
will they look great through an open wheel, but the drilled holes assist with
an initial bite while the slots are designed to remove dust and debris from
between the rotor and brake pad.
ROTOR MATERIALS
Brake rotors can be made of six
different materials, each with its own advantages. Let’s take a look at each.
1)Cast Iron
This is the very definition of old
school when it comes to a brake rotor. It’s one or two pieces and gets the job
done. In fact, it’s the most common material for brake rotors. The right design
(usually two-piece) can even work well in a performance vehicle. However, it’s
also the heaviest option, which affects the overall weight of your car and its
handling, since that weight is right up there with your front wheels. 2)Steel
Steel has been the racer’s choice for
years because a steel brake rotor is thinner, weighs less and handles heat
better. The downside: Steel rotors aren’t as durable as some others, and warped
rotors can cause noise and a pulsating pedal when you brake.
3)Layered Steel
Layering sheets of steel together and
laminating them makes them resistant to the warping you might find in a
straight steel brake rotor. It’s a favorite of racers who don’t want frequent
brake rotor replacement and repair, but manufacturers are currently only
targeting professional racers and production is limited, so it’s not terribly
common in passenger vehicle applications.
4)
Aluminum
Aluminum brake rotors dissipate heat
quickly, but they also melt at a lower temperature than other options. Aluminum
is a favorite for motorcycles, which weigh less and are easier on the rotors
when braking than a heavy car, truck or SUV.
5)High Carbon
These are iron, but with a lot of
carbon mixed in. They can take a lot of heat and dissipate it quickly. The
metallic content helps the rotor avoid cracking under high stress, and brake
noise and vibration are reduced as well. The only downside is the price, which
is significantly higher than straight iron or aluminum.
6)Ceramic
What’s your favorite super-car?
Ferrari? Porsche? Lamborghini? Odds are it’s packing ceramic brake rotors. They
offer the highest heat capacity (85 percent higher than cast iron) and superior
dissipation, and they maintain a more consistent force and pressure as the
temperature of the rotors rises. Ceramic is the highest-performance brake rotor
available today.
Advantages
1. It is lighter than drum brakes.
2. It has better cooling ( because the braking surface is directly exposed
to the air(
3. It offers better resistance to fade.
4. It provides uniform pressure distribution
5. Replacement of brake pads is easy.
6. By design, they are self-adjusting brakes.
Disadvantages
1. It is costlier than drum brakes.
2. Higher pedal pressure is required for stopping the vehicle. This brake
system is installed with vacuum booster.
3. No servo action is present.
It is difficult to attach a suitable parking
attachment
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