Disc Brake System
ABSTRACTThe current tendencies in automotive industry need
intensive investigation in problems of interaction of active safety
systems with brake system equipments. At the same time, the
opportunities to decrease the power take-off of single components,
disc brake systems. Disc brakes sometimes spelled as "disk" brakes,
use a flat, disc-shaped metal rotor that spins with the wheel. When
the brakes are applied, a calliper squeezes the brake pads against
the disc (just as you would stop a spinning disc by squeezing it
between your fingers), slowing the wheel.The disc brake used in the
automobile is divided into two parts: a rotating axis symmetrical
disc, and the stationary pads. The hydraulic disc brake is an
arrangement of braking mechanism which uses brake fluid, typically
containing ethylene glycol, to transfer pressure from the
controlling unit, which is usually near the operator of the
vehicle, to the actual brake mechanism, which is usually at or near
the wheel of the vehicle.The frictional heat, which is generated on
the interface of the disc and pads, can cause high temperature
during the braking process. Hence the automobiles generally use
disc brakes on the front wheels and drum brakes on the rear wheels.
The disc brakes have good stopping performance and are usually
safer and more efficient than drum brakes. The four wheel disc
brakes are more popular, swapping drums on all but the most basic
vehicles. Many two wheel automobiles design uses a drum brake for
the rear wheel. Brake technology began in the '60s as a serious
attempt to provide adequate braking for performance cars has ended
in an industry where brakes range from supremely adequate to
downright phenomenal. One of the first steps taken to improve
braking came in the early '70s when manufacturers, on a widespread
scale, switched from drum to disc brakes. Since the majority of a
vehicle's stopping power is contained in the front wheels, only the
front brakes were upgraded to disc during much of this period.
Since then, many manufacturers have adopted four-wheel disc brakes
on their high-end and performance models as well as their low-line
economy cars. Occasionally, however, as in the case of the 1999
Mazda Protgs, a manufacturer will revert from a previous four-wheel
disc setup to drum brakes for the rear of the car in order to cut
both production costs and purchase price.
CHAPTER-1
INTRODUCTION
A brake is a mechanical device which inhibits motion. Most
commonly brakes use friction to convert kinetic energy into heat,
though other methods of energy conversion may be employed. For
example regenerative braking converts much of the energy to
electrical energy, which may be stored for later use. Other methods
convert kinetic energy into potential energy in such stored forms
as pressurized air or pressurized oil. Eddy current brakes use
magnetic fields to convert kinetic energy into electric current in
the brake disc, fin, or rail, which is converted into heat. Still
other braking methods even transform kinetic energy into different
forms, for example by transferring the energy to a rotating
flywheel.Brakes are generally applied to rotating axles or wheels,
but may also take other forms such as the surface of a moving fluid
(flaps deployed into water or air). Some vehicles use a combination
of braking mechanisms, such as drag racing cars with both wheel
brakes and a parachute, or airplanes with both wheel brakes and
drag flaps raised into the air during landing.
Since kinetic energy increases quadratically with velocity (),
an object moving at 10m/s has 100 times as much energy as one of
the same mass moving at 1m/s, and consequently the theoretical
braking distance, when braking at the traction limit, is 100 times
as long. In practice, fast vehicles usually have significant air
drag, and energy lost to air drag rises quickly with speed.
Almost all wheeled vehicles have a brake of some sort. Even
baggage carts and shopping carts may have them for use on a moving
ramp. Most fixed-wing aircraft are fitted with wheel brakes on the
undercarriage. Some aircraft also feature air brakes designed to
reduce their speed in flight. Notable examples include gliders and
some World War II-era aircraft, primarily some fighter aircraft and
many dive bombers of the era. These allow the aircraft to maintain
a safe speed in a steep descent. The Saab B 17 dive bomber used the
deployed undercarriage as an air brake.Friction brakes on
automobiles store braking heat in the drum brake or disc brake
while braking then conduct it to the air gradually. When travelling
downhill some vehicles can use their engines to brake.When the
brake pedal of a modern vehicle with hydraulic brakes is pushed,
ultimately a piston pushes the brake pad against the brake disc
which slows the wheel down. On the brake drum it is similar as the
cylinder pushes the brake shoes against the drum which also slows
the wheel down.
HISTORY OF DISC BRAKE
Ever since the invention of the wheel, if there has been "go"
there has been a need for "whoa." As the level of technology of
human transportation has increased, the mechanical devices used to
slow down and stop vehicles has also become more complex. In this
report I will discuss the history of vehicular braking technology
and possible future developments.
Before there was a "horse-less carriage," wagons, and other
animal drawn vehicles relied on the animals power to both
accelerate and decelerate the vehicle. Eventually there was the
development of supplemental braking systems consisting of a hand
lever to push a wooden friction pad directly against the metal
tread of the wheels. In wet conditions these crude brakes would
lose any effectiveness.
The early years of automotive development were an interesting
time for the designing engineers, "a period of innovation when
there was no established practice and virtually all ideas were new
ones and worth trying. Quite rapidly, however, the design of many
components stabilized in concept and so it was with brakes; the
majority of vehicles soon adopted drum brakes, each consisting of
two shoes which could be expanded inside a drum."
In this chaotic era is the first record of the disc brake. Dr.
F.W. Lanchester patented a design for a disc brake in 1902 in
England. It was incorporated into the Lanchester car produced
between 1906 through 1914. These early disc brakes were not as
effective at stopping as the contemporary drum brakes of that time
and were soon forgotten. Another important development occurred in
the 1920s when drum brakes were used at all four wheels instead of
a single brake to halt only the back axle and wheels such as on the
Ford model T. The disc brake was again utilized during World War II
in the landing gear of aircraft. The aircraft disc brake system was
adapted for use in automotive applications, first in racing in
1952, then in production automobiles in 1956. United States auto
manufacturers did not start to incorporate disc brakes in lower
priced non-high-performance cars until the late 1960s.
CHAPTER-2
CHARACTERISTICSBrakes are often described according to several
characteristics including:
Peak force The peak force is the maximum decelerating effect
that can be obtained. The peak force is often greater than the
traction limit of the tires, in which case the brake can cause a
wheel skid.Continuous power dissipation Brakes typically get hot in
use, and fail when the temperature gets too high. The greatest
amount of power (energy per unit time) that can be dissipated
through the brake without failure is the continuous power
dissipation. Continuous power dissipation often depends on e.g.,
the temperature and speed of ambient cooling air.Fade As a brake
heats, it may become less effective, called brake fade. Some
designs are inherently prone to fade, while other designs are
relatively immune. Further, use considerations, such as cooling,
often have a big effect on fade.Smoothness A brake that is grabby,
pulses, has chatter, or otherwise exerts varying brake force may
lead to skids. For example, railroad wheels have little traction,
and friction brakes without an anti-skid mechanism often lead to
skids, which increases maintenance costs and leads to a "thump
thump" feeling for riders inside.Power Brakes are often described
as "powerful" when a small human application force leads to a
braking force that is higher than typical for other brakes in the
same class. This notion of "powerful" does not relate to continuous
power dissipation, and may be confusing in that a brake may be
"powerful" and brake strongly with a gentle brake application, yet
have lower (worse) peak force than a less "powerful" brake.Pedal
feel Brake pedal feel encompasses subjective perception of brake
power output as a function of pedal travel. Pedal travel is
influenced by the fluid displacement of the brake and other
factors.
Drag Brakes have varied amount of drag in the off-brake
condition depending on design of the system to accommodate total
system compliance and deformation that exists under braking with
ability to retract friction material from the rubbing surface in
the off-brake condition.Durability Friction brakes have wear
surfaces that must be renewed periodically. Wear surfaces include
the brake shoes or pads, and also the brake disc or drum. There may
be tradeoffs, for example a wear surface that generates high peak
force may also wear quickly.Weight Brakes are often "added weight"
in that they serve no other function. Further, brakes are often
mounted on wheels, and unsprung weight can significantly hurt
traction in some circumstances. "Weight" may mean the brake itself,
or may include additional support structure.
Noise Brakes usually create some minor noise when applied, but
often create squeal or grinding noises that are quite loud.
2.1 Types of Braking Systems:-Brakes may be broadly described as
using friction, pumping, or electromagnetic. One brake may use
several principles: for example, a pump may pass fluid through an
orifice to create friction:
Frictional brakes are most common and can be divided broadly
into "shoe" or "pad" brakes, using an explicit wear surface, and
hydrodynamic brakes, such as parachutes, which use friction in a
working fluid and do not explicitly wear. Typically the term
"friction brake" is used to mean pad/shoe brakes and excludes
hydrodynamic brakes, even though hydrodynamic brakes use
friction.Friction (pad/shoe) brakes are often rotating devices with
a stationary pad and a rotating wear surface. Common configurations
include shoes that contract to rub on the outside of a rotating
drum, such as a band brake; a rotating drum with shoes that expand
to rub the inside of a drum, commonly called a "drum brake",
although other drum configurations are possible; and pads that
pinch a rotating disc, commonly called a "disc brake". Other brake
configurations are used, but less often. For example, PCC trolley
brakes include a flat shoe which is clamped to the rail with an
electromagnet; the Murphy brake pinches a rotating drum, and the
Ausco Lambert disc brake uses a hollow disc (two parallel discs
with a structural bridge) with shoes that sit between the disc
surfaces and expand laterally.Pumping brakes are often used where a
pump is already part of the machinery. For example, an
internal-combustion piston motor can have the fuel supply stopped,
and then internal pumping losses of the engine create some braking.
Some engines use a valve override called a Jake brake to greatly
increase pumping losses. Pumping brakes can dump energy as heat, or
can be regenerative brakes that recharge a pressure reservoir
called a hydraulic accumulator.
Electromagnetic brakes are likewise often used where an electric
motor is already part of the machinery. For example, many hybrid
gasoline/electric vehicles use the electric motor as a generator to
charge electric batteries and also as a regenerative brake. Some
diesel/electric railroad locomotives use the electric motors to
generate electricity which is then sent to a resistor bank and
dumped as heat. Some vehicles, such as some transit buses, do not
already have an electric motor but use a secondary "retarder" brake
that is effectively a generator with an internal short-circuit.
Related types of such a brake are eddy current brakes, and
electro-mechanical brakes (which actually are magnetically driven
friction brakes, but nowadays are often just called electromagnetic
brakes as well).
Brakes are one the key parts of any vehicle, without which it is
virtually not possible to use the vehicle for travel. Clearly, a
brake, which serves to slow down the vehicle, should not be too
weak. But interestingly, when designing a brake system, it should
also be taken care that its not too efficient. A too strong a brake
would expose us continuously to the ill effects of a sudden brake
application in bus or car. If a vehicle is stopped abruptly or
strongly, the passenger may hit the front seat or whatever is
there. Hence, too efficient a brake system is not required!
The braking system is strongly relation to Newtons laws of
motion. Indeed, the above phenomenon is linked to Newtons second
law of motion, which states A body continues to be in its state of
rest or of motion unless external force acts on the same.
On the other hand, if a brake system is too weak, the stopping
distance would increase and hence may lead to accidents. Thus, a
brake system should be perfect enough to stop the vehicle at
minimum safe distance, without affecting the comfort of the
passenger. In an endeavour to achieve this there have been a lot of
developments in the brake system technology, right from Mechanical
brakes to Air brakes in automobiles. In this article we would like
provide the relevant information regarding the same
CHAPTER-3
WORKING OF A BRAKEWe all know that pushing down on the brake
pedal slows a car to a stop. But we do not how does this happen,
how does our car transmit the force from our leg to its wheels and
how does it multiply the force so that it is enough to stop
something as big as a car.
Fig 1: Braking fundamentals
Friction and how it applies to automobilesA brake system is
designed to slow and halt the motion of vehicle. To do this,
various components within the brake system must convert vehicles
moving energy into heat. This is done by using friction.
Friction is the resistance to movement exerted by two objects on
each other. Two forms of friction play a part in controlling a
vehicle: Kinetic or moving, and static or stationary. The amount of
friction or resistance to movement depends upon the type of
material in contact, the smoothness of their rubbing surfaces and
the pressure holding them together.Thus, in a nutshell a car brake
works by applying a static surface to a moving surface of a
vehicle, thus causing friction and converting kinetic energy into
heat energy. The high-level mechanics are as follows.
As the brakes on a moving automobile are put into motion,
rough-textures brake pads or brake shoes are pressed against the
rotating parts of vehicle, be it disc or drum. The kinetic energy
or momentum of the vehicle is then converted into heat energy by
kinetic friction of the rubbing surfaces and the car or truck slows
down.
When vehicle comes to stop, it is held in place by static
friction. The friction between surfaces of brakes as well as the
friction between tires and roads resists any movement. To overcome
the static friction that holds the car motionless, brakes are
released. The heat energy of combustion of in engine is converted
into kinetic energy by transmission and drive train, and the
vehicle moves.
Fig 2: Typical Braking SystemCHAPTER-4
BRAKE BASICS
When you depress your brake pedal, your car transmits the force
from your foot to its brakes through a fluid. Since the actual
brakes require a much greater force than you could apply with your
leg, your car must also multiply the force of your foot. It does
this in two ways:
Mechanical advantage (Leverage)
Hydraulic force multiplicationThe brakes transmit the force to
the tires using friction, and the tires transmit that force to the
road using friction also. Before we begin our discussion on the
components of the brake system, let's cover these three
principles:
Leverage
Hydraulics
Friction
4.1 LEVERAGE
The pedal is designed in such a way that it can multiply the
force from your leg several times before any force is even
transmitted to the brake fluid.
Fig 3: LeverageIn the figure above, a force F is being applied
to the left end of the lever. The left end of the lever is twice as
long (2X) as the right end (X). Therefore, on the right end of the
lever a force of 2F is available, but it acts through half of the
distance (Y) that the left end moves (2Y). Changing the relative
lengths of the left and right ends of the lever changes the
multipliers.
4.2 HYDRAULIC SYSTEMS
The basic idea behind any hydraulic system is very simple: Force
applied at one point is transmitted to another point using an
incompressible fluid, almost always an oil of some sort. Most brake
systems also multiply the force in the process.4.3 FRICTION
Friction is a measure of how hard it is to slide one object over
another. Take a look at the figure below. Both of the blocks are
made from the same material, but one is heavier. I think we all
know which one will be harder for the bulldozer to push.
Fig 4 : Friction force versus weight
To understand why this is, let's take a close look at one of the
blocks and the table: Fig 5: Close look at one of the blocksEven
though the blocks look smooth to the naked eye, they are actually
quite rough at the microscopic level. When you set the block down
on the table, the little peaks and valleys get squished together,
and some of them may actually weld together. The weight of the
heavier block causes it to squish together more, so it is even
harder to slide.
Different materials have different microscopic structures; for
instance, it is harder to slide rubber against rubber than it is to
slide steel against steel.
The type of material determines the coefficient of friction, the
ratio of the force required to slide the block to the block's
weight. If the coefficient were 1.0 in our example, then it would
take 100 pounds of force to slide the 100-pound (45 kg) block, or
400 pounds (180 kg) of force to slide the 400-pound block. If the
coefficient were 0.1, then it would take 10 pounds of force to
slide to the 100-pound block or 40 pounds of force to slide the
400-pound block.
So the amount of force it takes to move a given block is
proportional to that block's weight. The more weight, the more
force required. This concept applies for devices like brakes and
clutches, where a pad is pressed against a spinning disc. The more
force that presses on the pad, the greater is the stopping
force.
A SIMPLE BRAKE SYSTEMThe distance from the pedal to the pivot is
four times the distance from the cylinder to the pivot, so the
force at the pedal will be increased by a factor of four before it
is transmitted to the cylinder. The diameter of the brake cylinder
is three times the diameter of the pedal cylinder. This further
multiplies the force by nine. All together, this system increases
the force of your foot by a factor of 36. If you put 10 pounds of
force on the pedal, 360 pounds (162 kg) will be generated at the
wheel squeezing the brake pads.
There are a couple of problems with this simple system. What if
we have a leak? If it is a slow leak, eventually there will not be
enough fluid left to fill the brake cylinder, and the brakes will
not function. If it is a major leak, then the first time you apply
the brakes all of the fluid will squirt out the leak and you will
have complete brake failure. CHAPTER-5
TYPES OF BRAKES
TYPES OF BRAKES1. DRUM BRAKES
2. DISC BRAKES (CALLIPER BRAKES)
Fig 6: Types of Brakes5.1 DRUM BRAKESThe drum brake has two
brake shoes and a piston. When you hit the brake pedal, the piston
pushes the brake shoes against the drum. This is where it gets a
little more complicated. as the brake shoes contact the drum, there
is a kind of wedging action, which has the effect of pressing the
shoes into the drum with more force. The extra braking force
provided by the wedging action allows drum brakes to use a smaller
piston than disc brakes. But, because of the wedging action, the
shoes must be pulled away from the drum when the brakes are
released. This is the reason for some of the springs. Other springs
help hold the brake shoes in place and return the adjuster arm
after it actuates. 5.2 DISC BRAKE The disc brake has a metal disc
instead of a drum. It has a flat shoe, or pad, located on each side
of the disc. To slow or stop the car, these two flat shoes are
forced tightly against the rotating disc, or rotor. Fluid pressure
from the master cylinder forces the pistons to move in. This action
pushes the friction pads of the shoes tightly against the disc. The
friction between the shoes and the disc slows and stops the
disc.CHAPTER-6TYPES OF DISC BRAKESThe Three Types of Disc Brakes
Are:-
1. FLOATING CALIPER DISC BRAKES
2. FIXED CALIPER DISC BRAKES
3. SLIDING CALIPER DISC CALIPER6.1 FLOATING-CALIPER DISC
BRAKES
The calliper is the part that holds the brake shoes on each side
of the disc. In the floating-calliper brake, two steel guide pins
are threaded into the steering-knuckle adapter. The calliper floats
on four rubber bushings which fit on the inner and outer ends of
the two guide pins. The bushings allow the calliper to swing in or
out slightly when the brakes are applied
When the brakes are applied, the brake fluid flows to the
cylinder in the calliper and pushes the piston out. The piston then
forces the shoe against the disc. At the same time, the pressure in
the cylinder causes the calliper to pivot inward. This movement
brings the other shoe into tight contact with the disc. As a
result, the two shoes pinch the disc tightly to produce the braking
action
Fig 7: Floating calliper Disc Brake6.2 FIXED-CALIPER DISC BRAKE
This brake usually has four pistons, two on each side of the disc.
The reason for the name fixed-calliper is that the calliper is
bolted solidly to the steering knuckle. When the brakes are
applied, the calliper cannot move. The four pistons are forced out
of their calliper bores to push the inner and outer brake shoes in
against the disc. Some brakes of this type have used only two
pistons, one on each side of the disc
Fig 8: Fixed Caliper Disc Brake
6.3 SLIDING-CALIPER DISC BRAKE
The sliding-calliper disc brake is similar to the
floating-calliper disc brake. The difference is that
sliding-calliper is suspended from rubber bushings on bolts. This
permits the calliper to slide on the bolts when the brakes are
applied.
Proper function of the brake depends on (1) the rotor must be
straight and smooth, (2) the calliper mechanism must be properly
aligned with the rotor, (3) the pads must be positioned correctly,
(4) there must be enough "pad" left, and (5) the lever mechanism
must push the pads tightly against the rotor, with "lever" to
spare.
Most modern cars have disc brakes on the front wheels, and some
have disc brakes on all four wheels. This is the part of the brake
system that does the actual work of stopping the car
The most common type of disc brake on modern cars is the
single-piston floating calliper. MAIN PARTS:The main components of
a disc brake are:
The brake pads The calliper, which contains a piston
The rotor, which is mounted to the hub
BRAKE PAD
Fig 9: Brake PadCALIPER AND ROTOR
Fig 10: Caliper and Rotor
CHAPTER-7COMPONENTS OF HYDRAULIC DISC BRAKE
Now that we understand hydraulics let's take a look at the
different parts which make up the hydraulic brake. The entire
braking system can be broken down into the following main parts: 1.
Master cylinder (Lever)2. Lines
3. Fluid
4. Slave cylinder (Calliper)
5. Pads
6. RotorNext we will explain these components in more
detail.
Fig 11: The layout of a typical brake system
7.1 MASTER CYLINDER
Converts mechanical force from the brake pedal, power booster
and push rod into hydraulic pressure
Contain pistons, piston seals, return springs and internal brake
fluid ports.
Also has a fluid reservoir that may either be an integral part
of the unit or remotely mounted. The reservoir itself will have a
removable cap with a rubber diaphragm seal that must be in good
condition to seal properly.
Most reservoirs also have a low brake fluid level switch to
alert the driver of a low fluid condition.
Master Cylinder/Lever
The master cylinder, mounted to the handlebar, houses the brake
lever and together they produce the input force needed to push
hydraulic brake fluid to the slave cylinder (or calliper) and cause
the brake pads to clamp the rotor. The lever stroke can be divided
into 3 categories: 1. Dead-stroke - This is the initial part of the
lever stroke when the primary seal pushes fluid toward the
reservoir before it goes on to push fluid on to the calliper via
the brake lines.
2. Pad Gap Stroke - This is the part between the calliper
beginning to push the pistons out of their housings and the pads
contacting the disc (as the dead space between the pads and rotor
is taken up).3. Contact & Modulation - The pads are now
clamping the rotor and by stroking the lever further, additional
brake power will be generated. Modulation is rider controlled and
not necessarily a characteristic of the braking system; however
some brakes may allow the rider to better modulate or control the
braking forces than others.
7.2 MASTER CYLINDER - OPEN OR CLOSEDMaster cylinder systems can
be categorized into two groups - open and closed.An open system
includes a reservoir and bladder which allow for fluid to be added
or removed from the braking system automatically during use.
Reservoirs are the overflow for fluid which has expanded due to
heat produced by braking. The bladder has the ability to expand and
contract therefore as the fluid expands the bladder will compensate
without any adverse effects on the 'feel' of the brake. Reservoirs
also provide the additional fluid needed as the pads begin to wear
resulting in the need for the pistons to protrude further to
compensate for the reduced pad material.A closed system also
utilizes a reservoir of brake fluid however the lack of an internal
bladder to compensate for the expansion in brake fluid and also to
compensate for pad wear means that any adjustments to the levels of
brake fluid within the working system need to be made manually. 7.3
BRAKE LINESHydraulic brake lines or hoses play the important role
of connecting the two main working parts of the brake, i.e. the
master cylinder and slave cylinder. We've already mentioned that
hydraulic systems can be very versatile in that their lines or
hoses can be routed almost anywhere so let's take a closer
look.
Hose Construction
Hydraulic hoses are multi-layered in their construction and
usually consist of 3 layers:
1. Inner Tube - This layer of tubing is designed to hold the
fluid. Teflon is usually the material of choice here as it does not
react or corrode with brake fluid.2. Aramid (Kevlar) Layer -
provides the strength and structure of the hose. This woven layer
is flexible and handles the high pressures of the hydraulic system
efficiently in that it should not expand. Kevlar is also very
light, which is a desirable attribute for any cycle component, and
also it can be cut easily and re-assembled using standard hose
fittings.3. Outer Casing - Serves as a protection layer for both
the Kevlar layer and the bike frame to reduce abrasions.
Fig 12: The layers that make up an average hydraulic brake
line
Steel Braided Brake Lines
Steel braided hoses can provide some advantages over standard
hydraulic hoses. Steel braided hoses are also usually a 3-layer
construction, the inner most layer contains the brake fluid and
there is an outer most layer which provides protection against
abrasions. The key difference is in the middle layer which is made
up of a stainless steel braid.This stainless steel layer is
designed to be more resistant against expansion than that of
standard lines. This can be an advantage because when the brake
lever is applied we want all of the force we put in to be
transferred to the calliper to cause braking. Any expansion in the
hydraulic line due to the pressures within will mean that some of
that pressure will not be transferred to the calliper. This will be
wasted effort and will require additional lever input by the rider
to compensate.Steel braided lines may also be more appealing
aesthetically. Many riders believe that they look better than the
standard, boring black hoses that are supplied with the vast
majority of brakes on the market.
Fig 13:2011 Formula R1 brake with braided brake lines
7.4 BRAKE FLUIDHydraulic braking systems typically use one of
two types of brake fluid - DOT fluid or mineral oil. An important
thing to note before we get into the properties of each is that the
two fluids should never be mixed. They are made up of very
different chemicals and the seals within the braking system are
suited to either fluid or not both; therefore mixing or replacing
one fluid with the other is likely to corrode the internals of your
brake.On the other hand, mixing fluid from the same family is
allowed but not generally advised. For example you may mix DOT 4
fluid with DOT 5.1 without harming your braking system.
DOT Brake Fluid
DOT brake fluid is approved and controlled by the Department of
Transportation. It has to meet certain performance criteria to be
used within braking systems and is classified by its performance
properties - mainly its boiling points.DOT 3, 4 and 5.1 brake
fluids are glycol-ether based and are made up of various solvents
and chemicals. Glycol-ether brake fluids are hygroscopic, which
means they absorb water from the environment even at normal
atmospheric pressure levels. The typical absorption rate is quoted
to be around 3% per year. This water content within the brake fluid
will affect the performance by reducing its boiling points that is
why it is recommended to change brake fluid every 1-2 years at
most.The table below shows DOT brakes fluid in its various
derivatives with its corresponding boiling temperatures. Wet
boiling point refers to fluid with water content after 1 years'
service. DOT FluidDry Boiling PointWet Boiling Point
DOT 3205 C (401 F)140 C (284 F)
DOT 4230 C (446 F)155 C (311 F)
DOT 5260 C (500 F)180 C (356 F)
DOT 5.1
270 C (518 F)
190 C (374 F)
DOT brake fluid is commonly used in Avid, Formula, Hayes and
Hope brakes.
DOT 5 Brake Fluid
DOT 5 brake fluids (not to be mistaken for DOT 5.1) are very
different from other DOT fluids as it is silicone based and not
glycol-ether based. This silicone based brake fluid is hydrophobic
(non water absorbing) and must never be mixed with any other DOT
brake fluid.
DOT 5 can maintain an acceptable boiling point throughout its
service life although the way in which it repels water can cause
any water content to pool and freeze/boil in the system over time -
the main reason that hygroscopic fluids are more commonly used.
Mineral Oil
Mineral oil is less controlled as a brake fluid, unlike DOT
fluid which is required to meet a specific criteria, therefore less
is known regarding its performance and boiling points from brand to
brand.Manufacturers such as Shimano and Magura design their brakes
around their own brand of mineral oil and should never be
introduced to DOT brake fluid as this will likely have an adverse
effect on the brake's seals.An advantage of mineral oil is that,
unlike most DOT fluids, it does not absorb water. This means that
the brake will not need to be serviced as often, but any water
content within the braking system could pool and freeze/boil
adversely affecting the performance of the brake.
Mineral oil is also non-corrosive meaning handling of the fluid
and spillages are less of a concern.
7.5 SLAVE CYLINDER/CALLIPERThe brake callipers reside at each
wheel and respond to the lever input generated by the user. This
lever input is converted to clamping force as the pistons move the
brake pads to contact the rotor. Callipers can be fixed by a rigid
mount to the frame or floating. Fixed callipers are combined with a
fixed rotor which offers the only way of achieving zero free
running drag one drawback of this design is that it is much less
tolerant of rotor imperfections. Floating callipers slide axially
and self-centre with each braking application.
Construction
Calliper construction can fall into two categories - mono-block
and two piece. The difference here is the 'bridge' design, the
bridge is the part of the calliper above the pistons which connects
the two halves together and provides the strength to endure the
clamping forces generated by the pistons.
1. Mono-block - A mono-block calliper is actually a one piece
design formed from one piece of material. This can offer a unique
design and usually a lighter calliper as there is no need for steel
bolts joining both halves as in a two piece design. Also the lack
of a transfer port seal means there is one less opportunity for
fluid leaks at the half way seam. Servicing a mono-block calliper
can be tricky however and manufacturing and assembly are usually
more difficult.2. Two piece - These two piece callipers are
constructed as two separate halves and are then held together with
steel bolts which can provide additional strength over a mono-block
design. Servicing, manufacturing and assembly are simplified. Steel
bolts and additional seals are a means of additional weight and can
be problematic during servicing.
Fig 14: Exploded view of an Avid two-piece calliper design
Pistons
The pistons are the cylindrical components housed within the
calliper body. Upon lever input they protrude to push the brake
pads which contact the rotor. The number of pistons within a
calliper or brake can differ. Many hydraulic mountain bike brakes
have 2 piston callipers, some may have 4 pistons. Whereas some
automobile brake callipers have 6 or even 8 pistons. It is an
important note that brake power is not determined by piston
quantity. A more reliable indicator would be total piston contact
area, e.g. 4 smaller pistons can be just as powerful as 2 larger
pistons.
Pistons can be either opposed or single sided. Opposed pistons
both protrude with lever input to push the brake pads equal amounts
to meet the rotor at both sides. Whereas single sided calliper
pistons stroke on one side and float the rotor to the opposite
pad.
7.6 BRAKE PADSChoosing the right brake pads can mean the
difference between a great and a poor performing brake. With the
sheer diversity of brake pad materials out there it is quite easy
to get it wrong when the time comes to replace the pads.Let's jump
right in and take a look at the different pad materials available
and their properties.
Organic
Organic brake pads contain no metal content. They are made up of
a variation of materials which used to include asbestos until its
use was banned. These days you will commonly find materials such as
rubber, Kevlar and even glass. These various materials are then
bonded with a high-heat-withstanding resin. An advantage of organic
pads is that they're made up of materials that don't pollute as
they wear. They are also softer than other brake pads and as a
result quieter. Also they inflict much less wear upon the brakes'
rotor. However organic pads wear down faster and they perform
especially poorly in wet gritty conditions (UK readers take
note).Organic pads then are probably more suited to less aggressive
riding in mostly dry conditions. Fig 15: Organic Brake
padsSemi-metallic
The metallic content of semi-metallic pads can vary from
anything between 30% and 65%. The introduction of metal content
into the friction material changes things slightly. It can improve
the lifespan of the pad quite significantly as metal wears slower
than organic materials. Also heat dissipation is improved as it is
transferred between the pad material and the backing plate. Some
disadvantages can include increased noise during use and the harder
compound means increased wear on the rotor.
Fig 16: Semi-metallic padsSintered
Sintered brake pads are made up of hardened metallic ingredients
which are bound together with pressure and high temperature. The
advantages of this compound are better heat dissipation, a longer
lasting pad, better resistance to fading and superior performance
in wet conditions. The trade-offs are more noise, longer bed-in
time and a poor initial bite until the friction material has chance
to warm.
Fig 17: Sintered Brake padsCeramic
Ceramic brake pads are now seen more and more as an
alternative/upgrade mountain bike brake pad. Traditionally ceramic
brake pads would only be seen on high performance racing cars with
brakes which need to perform under intense heat. Heat like that is
not usually a problem for the average mountain bike brake and
therefore for most people ceramic pads would be overkills however
they might have other desirable properties. The advantages of a
ceramic material then is one which can cope with extreme heat and
keep performing strongly; this is in part down to its great
dissipating abilities. They also last longer than other pads and
noise is less of an issue. They're also easier on brake rotors and
produce a lot less dust that other brake pad compounds.
Fig 18: Ceramic Brake pads7.7 ROTORSRotor size has a direct
effect on braking power. The larger the brake rotor the more power
will be produced for any given input. This can be a concern with
larger rotors as they tend to have more of a 'grabby' feel making
the brake more difficult to modulate. Mountain bike rotors tend to
range in size from 160mm to 203mm, with smaller rotors geared
toward XC type riding and larger rotors designed for downhill
riding.
Rotor Design
Important specifications of rotor design include hardness,
thickness and rub area.The material used to manufacture rotors must
be hard and durable due to the aggressive forces inflicted upon
them from the pad friction material. This has a direct impact on
rotor wear.
Rotors must also have no thickness variations. Differences in
thickness around the circumference of the rotor can have undesired
effects on the braking system including pulsing as thicker and
thinner sections pass between the pads. Rotors also need to run
true. Any lateral wobble in the rotor during use can cause the
brake to contact the pads intermittently during riding.
Fig 19: Left to right: Formula Lightweight, Avid G3 Clean Sweep,
AshimaAiRotor
A rotor's rub area can take the form of many different designs.
The three rotors above show this in detail. Rub area design can
affect the weight and strength of the rotor. It also has a direct
effect on pad lifetime.
TYPES OF ROTORSThe two types of rotor on the market today are
ISO standard 6-bolt rotors and CenterLock rotors. Both have their
pros and cons.6 Bolt - Readily available and interchangeable
between many brake models, this is the most common rotor fixing
system in use today and was adopted by all manufacturers in the
late 1990's. With no shortage of hub options, cross-compatibility
with other products is rarely a problem. However installation of
six fixing bolts can be cumbersome and there is always the risk of
stripping a thread on fixing bolts and hub mounting points.
CenterLock - The Shimano CenterLock system eliminates the risk
of stripping threads as there are no bolts to worry about, just one
centre locking ring. Installation and removal is also simplified,
although you will need a CenterLock tool. Lack of mass-market
adoption means that hub choices are limited and brake choice may
also be limited due to odd sized rotors. CenterLock rotors are also
generally slightly heavier and can come at a price premium.
Fig 20: Left to right: ISO standard 6-bolt, Shimano
CenterLock
2-Piece Rotors
2-Piece rotors are supplied as standard with some higher priced
brake sets and can also be bought separately as an upgrade.
In contrast to standard stainless steel rotors, 2-piece rotors
combine a stainless steel rub area with an aluminium carrier (or
spider). The advantage of the alloy carrier is a cooler running
disc as aluminium has superior heat dissipation qualities to that
of stainless steel. This will also help to keep your pads, calliper
and fluid cooler. Aluminium is also lighter than stainless steel so
a reduction in weight can be expected.
Fig 21: Formula 2-Piece Stainless Steel / Aluminium Rotor
Reason why Brakes Fail
Hydraulic brakes can fail or temporarily stop working for
numerous reasons such as a simple (but potentially catastrophic)
fluid leak or eventual brake fade after prolonged use. Knowing the
causes of brake failure can be valuable knowledge in curing the
problem and preventing future episodes.As we know there are a
couple of important principles behind hydraulic brakes. Hydraulics
relies on pressure within the system and brakes rely on friction.
Absence of either will result in failure of the system. For
example, a loss of brake fluid will decrease the pressure within
the system as the lever has nothing to transfer the input forces
to. On the other hand if brake fluid contacts the brake pads or
rotor, a loss of friction will occur due to the lubricating nature
of brake fluid.The above examples should be obvious to most but
what about the less obvious causes of brake failure? Earlier we
mentioned brake fade, a term which I bet many of you have heard,
however did you know that there are multiple types of brake fade?
Below is an overview of the three different types.
Pad Fade
All friction material (the stuff your pads are made of) has a
coefficient of friction curve over temperature. Friction materials
have an optimal working temperature where the coefficient of
friction is at its highest. Further hard use of the brake will send
the friction material over the optimal working temperature causing
the coefficient of friction curve to decline.This high temperature
can cause certain elements within the friction material to melt or
smear causing a lubrication effect; this is the classic glazed pad.
Usually the binding resin starts to fail first, and then even the
metallic particles of the friction material can melt. At very high
temperatures the friction material can start to vaporize causing
the pad to slide on a layer of vaporized material which acts as a
lubricant.The characteristics of pad fade are a firm, non-spongy
lever feel in a brake that won't stop, even if you are squeezing as
hard as you can. Usually the onset is slow giving you time to
compensate but some friction materials have a sudden drop off of
friction under high temperatures resulting in sudden fade.
Green Fade
Green fade is perhaps the most dangerous type of fade which
manifests itself on brand new brake pads. Brake pads are made of
different types of heat resistant materials bound together with a
resin binder. On a new brake pad these resins will cure when used
hard on their first few heat cycles and the new pad can hydroplane
on this layer of excreted gas.Green fade is considered the most
dangerous as it can catch users unaware given its quick onset. Many
people would consider new brake pads to be perfect and may be used
hard from the word 'go'.Correct bedding-in of the brake pads can
prevent green fade. This process removes the top layer of the
friction material and keys the new pad and rotor together under
controlled conditions.
Fluid Fade
Fluid fade is caused by heat induced boiling of the brake fluid
in the callipers and brake lines. When used under extreme
conditions heat from the pads can transfer to the calliper and
brake fluid causing it to boil, producing bubbles in the braking
system. Since bubbles are compressible this results in a spongy
lever feel and prevents the lever input from being sent to the
calliper.The major cause of fluid fade is absorbed water from the
air under normal atmospheric conditions which reduces the boiling
temperature of the brake fluid. DOT brake fluid has an affinity for
absorbing water from the air around it, especially in hot humid
conditions. This is the main reason why we replace brake fluid on
an annual basis.Fortunately fluid fade has a gradual onset giving
the user time to compensate for potential loss of braking.
CHAPTER-8
WORKING OF HYDRAULIC DISC BRAKES
Fig 22: Working of hydraulic disc brakes
The master cylinder is where the brake fluid starts. The pedal
is attached to the master cylinder plunger. When the pedal is
depressed it pushed the plunger which pushes the brake fluid down
the brake lines. The brake lines are connected to the slave
cylinders. When the brake fluid reaches the slave cylinders it
presses out a piston to which is attached a brake pad. The brake
pad then clamps against the rotor. All air must be bled from the
system. (Air is compressible and if you have any in the system you
will have a soft pedal.) As oil is virtually uncompressible it
works as a solid link from pedal to brake.
8.1 THE MASTER CYLINDER IN ACTIONAs you can see in figure there
are two pistons (primary and secondary) and two springs inside the
master cylinder.
When the brake pedal is pressed, a push rod moves the primary
piston forward which begins to build pressure in the primary
chamber and lines. As the brake pedal is depressed further, the
pressure continues to increase.
Fluid pressure between the primary and secondary piston then
forces the secondary piston forward and pressurizes the fluid in
the secondary circuit.
If the brakes are operating properly, the pressure will be the
same in both circuits.
Fig 23: Brakes released
Fig 24: Brakes applied If there is a leak in one of the brake
circuits, that circuit will not be able to maintain pressure.
Figure shows what happens when one of the circuits develops a leak.
In this example, the leak is in the primary circuit and the
pressure between the primary and secondary pistons is lost. This
pressure loss causes the primary piston to mechanically contact the
secondary piston and the master cylinder now behaves as if it has
only one piston. The secondary circuit will continue to function
correctly, however the driver will have to press the pedal further
to activate it. In addition, since only two wheels now have
pressure, the braking power will be reduced.
Fig 25: Functioning of the brakes8.2 COMPENSATING PORTSSmall
holes those are located between the master cylinder reservoir and
the front side, or pressure side, of the master cylinder
pistons.
When the master cylinder pistons are in the at-rest position (no
braking-figure 9), the piston seals uncover the compensating ports
and open the passages between the reservoir and the wheel brake
channel.
Allow for the normal expansion and contraction of brake fluid
due to changes in temperature.
Fig 26: Compensating Ports
Assist in fluid return after brake release (See Bypass Port
section below).
Note: When the brakes are released, the piston seals on both the
primary and secondary pistons are located between the compensating
port and the bypass port. During braking, the piston seals close
the compensating port passages to the reservoir which prevents high
pressure fluid from entering the reservoir.
8.3 BYPASS PORTSThe bypass ports, like the compensating ports,
are passages that are open between the reservoir and the master
cylinder chambers (fig. 10). However, the bypass ports are open to
the low pressure or back side of the pistons.
Allow the master cylinder pistons to return to the at-rest
position rapidly.
Fig 27: Bypass Ports
During brake release, the following occurs:
Strong springs in the master cylinder force the pistons back to
the at-rest position faster than the brake fluid can return through
the hydraulic channels. The pistons must return rapidly so they can
be ready for another forward stroke, if necessary. This rapid
piston return movement could create a vacuum in the master cylinder
high pressure chambers, which would delay brake release.
The bypass ports allow brake fluid from the reservoir to fill
the low-pressure piston chambers.
Brake fluid from the low pressure chambers then passes through
holes in the pistons and bypasses the piston lip seals. The pistons
can then return without any dragging.
Since this return action causes additional fluid to be moved to
the front of the piston, it results in an excess amount of fluid
being present there, as even more fluid returns from the callipers
and wheel cylinders. This excess fluid is easily returned to the
reservoir through the now-open compensating ports.
Note: Piston dragging can also occur if the seals are installed
backward.
Fig 28: Master Cylinder Return Operation: applied (left);
releasing (right)
8.4 SELF ADJUSTMENT OF DISC BRAKES:
Disc brakes are self adjusting. Each piston has a seal on it to
prevent fluid leakage. When the brakes are applied, the piston
moves toward the disc. This distorts the piston seal. When the
brakes are released, the seal relaxes and returns to its original
position. This pulls the piston away from the disc. As the brakes
linings wear, the piston over travels and takes a new position in
relation to the seal. This action provides self-adjustment of disc
brakes.8.5 EMERGENCY BRAKES:In cars with disc brakes on all four
wheels, an emergency brake has to be actuated by a separate
mechanism than the primary brakes in case of a total primary brake
failure. Most cars use a cable to actuate the emergency brake.
Fig 29: Emergency BrakesSome cars with four-wheel disc brakes
have a separate drum brake integrated into the hub of the rear
wheels. This drum brake is only for the emergency brake system, and
it is actuated only by the cable; it has no hydraulics.
CHAPTER-9
BRAKE FADE
Vehicle braking system fade, or brake fade, is the reduction in
stopping power that can occur after repeated or sustained
application of the brakes, especially in high load or high speed
conditions. Brake fade can be a factor in any vehicle that utilizes
a friction braking system including automobiles, trucks,
motorcycles, airplanes, and even bicycles.
Brake fade is caused by a build-up of heat in the braking
surfaces and the subsequent changes and reactions in the brake
system components and can be experienced with both drum brakes and
disc brakes. Loss of stopping power, or fade, can be caused by
friction fade, mechanical fade, or fluid fade. Brake fade can be
significantly reduced by appropriate equipment and materials design
and selection, as well as good cooling.
Brake fade occurs most often during high performance driving or
when going down a long, steep hill. Owing to their configuration
fade is more prevalent in drum brakes. Disc brakes are much more
resistant to brake fade and have come to be a standard feature in
front brakes for most vehicles.
9.1 BRAKE MODIFICATION TO REDUCE FADE
High performance brake components provide enhanced stopping
power by improving friction while reducing brake fade. Improved
friction is provided by lining materials that have a higher
coefficient of friction than standard brake pads, while brake fade
is reduced through the use of more expensive binding resins with a
higher melting point, along with slotted, drilled, or dimpled
discs/rotors that reduce the gaseous boundary layer, in addition to
providing enhanced heat dissipation. Heat build-up in brakes can be
further addressed by body modifications that direct cold air to the
brakes.
The "gaseous boundary layer" is a hot rod mechanics explanation
for failing self-servo effect of drum brakes because it felt like a
brick under the brake pedal when it occurred. To counter this
effect, brake shoes were drilled and slotted to vent gas. In spite
of that, drum brakes were abandoned for their self-servo effect.
Discs do not have that because application force is applied at
right angles to the resulting braking force. There is no
interaction.
Drum brake fade can be reduced and overall performance enhanced
somewhat by an old "hot rudder" technique of drum drilling. A
carefully chosen pattern of holes is drilled through the drum
working section; drum rotation centrifugally pumps a small amount
air through the shoe to drum gap, removing heat; fade caused by
water-wet brakes is reduced since the water is centrifugally driven
out; and some brake-material dust exits the holes. Brake drum
drilling requires careful detailed knowledge of brake drum physics
and is an advanced technique probably best left to professionals.
There are performance-brake shops that will make the necessary
modifications safely.9.2 DISC BRAKE VENTS
Fig 30: Brake Modification to Reduce Fade
A moving car has a certain amount of kinetic energy, and the
brakes have to remove this energy from the car in order to stop it.
How do the brakes do this? Each time you stop your car, your brakes
convert the kinetic energy to heat generated by the friction
between the pads and the disc. Most car disc brakes are vented.
Brake fade caused by overheating brake fluid (often called Pedal
Fade) can also be reduced through the use of thermal barriers that
are placed between the brake pad and the brake calliper piston.
These reduce the transfer of heat from the pad to the calliper and
in turn hydraulic brake fluid. Some high-performance racing
callipers already include such brake heat shields made from
titanium or ceramic materials. However, it is also possible to
purchase aftermarket titanium brake heat shields that will fit your
existing brake system to provide protection from brake heat. These
inserts are precision cut to cover as much of the pad as possible.
These Titanium Brake shims are an easy to install, low cost
solution that are popular with racers and track day
enthusiasts.
Another technique employed to prevent brake fade is the
incorporation of fade stop brake coolers. Like titanium heat
shields the brake coolers are designed to slide between the brake
pad backing plate and the calliper piston. They are constructed
from a high thermal conductivity, high yield strength metal
composite which conducts the heat from the interface to a heat sink
which is external to the calliper and in the airflow. They have
been shown to decrease calliper piston temperatures by over twenty
percent and to also significantly decrease the time needed to cool
down. Unlike titanium heat shields, however, the brake coolers
actually transfer the heat to the surrounding environment and thus
keep the pads cooler.CHAPTER-10
ADVANTAGES10.1 ADVANTAGES OF DISC BRAKES OVER DRUM BRAKES
As with almost any artifact of technology, drum brakes and disc
brakes both have advantages and disadvantages. Drum brakes still
have the edge in cheaper cost and lower complexity. This is why
most cars built today use disc brakes in front but drum brakes in
the back wheels, four wheel discs being an extra cost option or
shouted as a high performance feature. Since the weight shift of a
decelerating car puts most of the load on the front wheels, the
usage of disc brakes on only the front wheels is accepted
manufacturing practice.
Drum brakes had another advantage compared to early disc brake
systems. The geometry of the brake shoes inside the drums can be
designed for a mechanical self-boosting action. The rotation of the
brake drum will push a leading shoe brake pad into pressing harder
against the drum. Early disc brake systems required an outside
mechanical brake booster such as a vacuum assist or hydraulic pump
to generate the pressure for primitive friction materials to apply
the necessary braking force. All friction braking technology uses
the process of converting the kinetic energy of a vehicles forward
motion into thermal energy: heat. The enemy of all braking systems
is excessive heat. Drums are inferior to discs in dissipating
excessive heat:"The common automotive drum brake consists
essentially of two shoes which may be expanded against the inner
cylindrical surface of a drum.The greater part of heat generated
when a brake is applied has to pass through the drum to its outer
surface in order to be dissipated to atmosphere, and at the same
time (the drum is) subject to quite severe stresses due to the
distortion induced by the opposed shoes acting inside the open
ended drum.The conventional disc brake, on the other hand, consists
essentially of a flat disc on either side of which are friction
pads; equal and opposite forces may be applied to these pads to
press their working surfaces into contact with the braking path of
the discs. The heat produced by the conversion of energy is
dissipated directly from the surfaces at which it is generated and
the deflection of the braking path of the disc is very small so
that the stressing of the material is not as severe as with the
drum."
The result of overheated brakes is brake fade...the same amount
of force at the pedal no longer provides the same amount of
stopping power. The high heat decreases the relative coefficient of
friction between the friction material and the drum or disc. Drum
brakes also suffer another setback when overheating: The inside
radii of the drum expand, the brake shoe outside radii no longer
matches, and the actual contact surface is decreased.
Another advantage of disc brakes over drum brakes is that of
weight. There are two different areas where minimizing weight is
important. The first is unsprung weight. This is the total amount
of weight of all the moving components of a car between the road
and the suspension mounting points on the cars frame.
Auto designs have gone to such lengths to reduce unsprung weight
that some, such as the E-type Jaguar, moved the rear brakes
inboard, next to the differential, connected to the drive shafts
instead of on the rear wheel hubs. The second "weighty" factor is
more of an issue on motorcycles: gyroscopic weight. The heavier the
wheel unit, the more is gyroscopic resistance to changing
direction. Thus the bikes steering would be higher effort with
heavier drum brakes than with lighter discs. Modern race car disc
brakes have hollow internal vents, cross drilling and other weight
saving and cooling features.
Most early brake drums and discs were made out of cast iron.
Current OEM motorcycle disc brakes are usually stainless steel for
corrosion resistance, but after-market racing component brake discs
are still made from cast iron for the improved friction qualities.
Other exotic materials have been used in racing applications.
Carbon fibre composite discs gripped by carbon fibre pads were
common in formula one motorcycles and cars in the early 1990s, but
were outlawed by the respective racing sanctioning organizations
due to sometimes spectacular failure. The carbon/carbon brakes also
only worked properly at the very high temperatures of racing
conditions and would not get hot enough to work in street
applications.
A recent Ducati concept show bike uses brake discs of selenium,
developed by the Russian aerospace industry, which claim to have
the friction coefficient of cast iron with the light weight of
carbon fibre.
Another area of development of the disc brake is the
architecture of the brake calliper. Early designs had a rigidly
mounted calliper gripping with opposed hydraulic pistons pushing
the brake pads against a disc mounted securely to the wheel hub.
Later developments included a single piston calliper floating on
slider pins. This system had improved, more even pad wear. Most
modern automobiles and my 1982 Kawasaki motorcycle use this type
calliper. Current design paradigm for motorcycle brakes have up to
six pistons, opposed to grip both sides of a thin, large radius
disc that is "floating" on pins to provide a small amount of
lateral movement; two discs per front wheel.
Improvements in control have been made available with the
application of Anti-Lock Brake technology. Wheel sensors convey
rotation speed of each wheel to a computer that senses when any of
them are locked up or in a skid, and modulates individual wheel
brake hydraulic pressure to avoid wheel skidding and loss of
vehicular control.
The use of exotic materials for additional weight savings would
be likely for the future of motor vehicle braking. Discs mounted to
the wheels rim gripped by an internally located calliper are not
necessarily a new design (Porsche, 1963) but could be a futuristic
looking option for motorcycle wheels. Electric vehicles of the
future will likely utilize regenerative braking, the electric
motors become generators to convert kinetic energy back to
electricity to recharge the batteries. As production vehicles
become increasingly quicker, the need for "whoa" will always
accompany the "go".10.2 REASON FOR HIGH EFFICIENCY OF DISC BRAKES
Flat brake disc (axial brake) under high pressure versus round
brake drum (radial brake) during braking Full friction surface of
the brake pad on the plane brake disc. No loss of brake power due
to overheating or partial contact from brake drum parts expansion.
Disc brakes can withstand higher loads and its efficiency is
maintained considerably longer even under the highest stresses
Higher residual brake force after repeating braking Brake discs can
withstand extremely high temperatures Full contact of brake pads
achieves maximum effect. No verification of brake pads. Dangerous
fading or slipping is almost completely eliminated.10.3 BETTER
BRAKING BEHAVIOUR OF HYDRAULIC DISC BRAKES Driver friendly braking
behaviour. Sensitive braking in all situations and better Sensitive
brake application and better brake feeling Uniform braking from
small fluctuations in brake forces Retardation values retained even
under heavy stresses Minimal "pulling to one side" due to uneven
brake forces Disc brake axial arrangement permits a simple and
compact design Linear characteristics lead to an even progression
of brake force Basic design principle makes for higher efficiency
Low hysteresis is particularly suitable to ABS control cycles10.4
HIGHER SAFETY RESERVES Minimal braking effect from high
temperatures and extreme driving requirements Minimal heat fading
No brake disc distortion from extreme heat due to internal
ventilation with directional stability and large power reserve
under high stress The decisive safety aspects of the disc brake
design are shorter braking distances High power and safety reserves
for emergencies Constant braking power under high stresses
Shortened braking distance under emergency braking with
considerably improved directional stability
CHAPTER-11LIMITATIONS
The limitations of hydraulic disc brakes: Braking systems fails
if there is leakage in the brake lines. The brake shoes are liable
to get ruined if the brake fluid leaks out. Presence of air inside
the tubing ruins the whole system. Pad wear is more. Hand brakes
are not effective if disc brakes are used in rear wheels also.
(Hand brakes are better with mechanical brakes).
CHAPTER-12
APPLICATIONSThe applications of Hydraulic Disc Brakes are:
Hydraulic Disc brakes are used primarily in motor vehicles, tanks,
but also in machinery and equipment, and aircraft, bicycles,
carriages and railway. The disc brakes have been widely used in
cars and trucks, especially in the premium sedan. The disc brakes
on the new mine hoist brake. The disc brake inertia is small, fast
action, high sensitivity, and adjustable braking torque. The
multi-rope friction hoist all use disc brakes.
II. CONCLUSION
Many trucks and buses are equipped with hydraulic actuated disc
brakes. The high contact forces are transmitted mechanically via
needle mounted actuating device.In view of the fact that the air
can circulate freely between the disc and the brake shoe, disc
brakes are cooled much better, especially since it is possible to
do so ventilated discs extra holes. The gases resulting from
friction, dust, dirt, do not stay on the working surfaces. These
brakes are not sticky.The disc brakes have been widely used in cars
and trucks, especially in the premium sedan. The disc brakes on the
new mine hoist brake. The disc brake inertia is small, fast action,
high sensitivity and adjustable braking torque.III. REFERENCES
TechCenter By Karl Brauer, Editor in Chief, Edmunds.com
http://cars.about.com/od/thingsyouneedtoknow/ig/Disc-brakes
http://en.wikipedia.org/wiki/Disc_brake
http://www.kobelt.com/pdf/brochure_brake.pdf
http://auto.howstuffworks.com/auto-parts/brakes/brake-types/disc-brake.htm
http://www.sae.org/search?searchfield=brake%20system
http://www.hinduonnet.com/thehindu/2000/05/25/ceramic brake disc
Automotive Engineering International Online Global Viewpoints, Nov_
199954