The document discusses the key components and principles of automotive braking systems. It explains that braking systems use friction to convert the kinetic energy of a moving vehicle into heat through the contact of brake pads or shoes with rotors or drums. The system is hydraulic, using brake fluid to transfer pressure from the brake pedal to the calipers or wheel cylinders. Drum brakes expand shoes outward to contact the inner drum surface, while disc brakes use calipers to squeeze pads against a rotor. The document also covers factors like pressure and surface area that influence braking capability.
2. Braking System
An automotive braking
system is a group of
mechanical, electronic
and hydraulically
activated components
which use friction / heat
to stop a moving
vehicle.
3. Principle of Braking
Common principles on which a braking
system depends when stopping a car is
friction and heat. By applying resistance, or
friction, to a turning wheel, a vehicle's
brakes cause the wheel to slow down and
eventually stop, creating heat as a
byproduct. The rate at which a wheel can
be slowed depends on several factors
including vehicle weight, braking force and
total braking surface area.
5. Overview
Brakes convert kinetic energy into
heat by creating friction
System must have very high
reliability
6. Brake system is actually an energy conversion
device that converts kinetic energy (car in
motion possessing momentum) to potential
energy (car stopping) through dissipating heat
and noise to the surrounding air. The friction
surfaces of the brake pads on a disc brake, or
the brake shoes on a drum brake convert the
forward motion of the vehicle into heat. Heat is
what causes the friction surfaces
7. Requirement of Braking System
Most engines generate a large amount of
power to get the car up to speed quickly
To stop the car, an equal amount of power
must be expended to stop the car.
Brakes turn the power of the rolling wheel
to heat.
The quicker you stop, the more power is
required, the more heat is generated
8. Requirement of brakes:
The function of brakes is to stop the vehicle within the
required time. The brake of the vehicle absorbs all the
energy given by the engine plus that due to the momentum
of the vehicle. This energy must then be dissipated. In most
of the vehicles, the energy is absorbed by the brakes in the
form of heat and dissipated into the stream of air passing
around the vehicle.
Apart from stopping the vehicle the brakes should
perform the others function too like the vehicle should stop
without any jerk and the retardation should be smooth. Also
the rate of retardation should be equal to the pedal effort and
the effort applied by the driver to stop the vehicle should not
be excessive. The rate of wear should also be low. The brake
system should not be affected by water, heat, and dust etc. It
should require a very low maintenance and durable.
9. Factors Governing Braking
Pressure
The amount of friction generated between moving
surfaces contacting one another depends in part on
the pressure exerted on the surfaces.
Coefficient of friction
The amount of friction between 2 surfaces (pads and
rotors or shoes and drums)
Determined by dividing the force required to pull an
object across a surface by the weight of the object
11. Factors Governing Braking
Frictional Contact Surface
The amount of surface, or area, that is in
contact.
Simply put, bigger brakes stop a car more
quickly than smaller brakes used on the same
car.
Heat Dissipation
The tremendous heat created by the rubbing
brake surfaces must be conducted away from
the pad and rotor (or shoe and drum) and be
absorbed by the air.
12. Importance of Brakes
Loss of brakes can cause accidents,
death, and injury
When working on brakes, keep in
mind that peoples lives are at stake
If in doubt, seek help
13. Brake rules
The car must have four wheel brakes operated by
a single control.
It must have two independent hydraulic circuits
with independent fluid reserves.
The brake system must be capable of locking all
four (4) wheels, and stopping the vehicle in a
straight line.
The braking systems must be protected with
scatter shields from failure of the drive train )
A brake pedal over-travel switch must be installed.
This switch must kill the ignition and cut the power
to any electrical fuel pumps.
The car must be equipped with a red brake light
that illuminates when ever the brakes are applied
14. How does a braking system work?
When the brake pedal is depressed, the
pressure on the brake pedal moves a
piston in the master cylinder, forcing the
brake fluid from the master cylinder
through the brake lines and flexible hoses
to the calipers and wheel cylinders. The
force applied to the brake pedal produces
a proportional force on each of the
pistons.
15. continued
The calipers and wheel cylinders contain
pistons, which are connected to a disc brake
pad or brake shoe. Each output piston pushes
the attached friction material against the surface
of the rotor or wall of the brake drum, thus
slowing down the rotation of the wheel. When
pressure on the pedal is released, the pads and
shoes return to their released positions. This
action forces the brake fluid back through the
flexible hose and tubing to the master cylinder.
16. Classification of brakes
In automobile generally two types
of brakes are used :-
Mechanical brakes
Air brakes & vaccum brakes
17. Mechanical Brakes
Mechanical brakes all act by
generating frictional forces as two
surfaces rub against each other.
The stopping power or capacity of
a brake depends largely on the
surface area of frictional surfaces
as well as on the actuation force
applied. The friction and wear
encountered by the working
surfaces are severe. Thus, the
durability of a brake or service life
between maintenance depends
heavily on the type of material
used to line the shoe or pad.
18. Air Brakes
The compressed air is used for obtaining brake
application. The brake pipe and feed pipe run
throughout the length of the coach. Brake pipe and
feed pipe on consecutive coaches in the train are
coupled to one another by means of respective hose
couplings to form a continuous air passage from the
locomotive to the rear end of the train. The
compressed air is supplied to the brake pipe and
feed pipe from the locomotive. The magnitude of
braking force increases in steps with the
corresponding reduction in brake pipe pressure and
vice-versa.
20. Vacuum Brakes
The vacuum brake system derives its brake
force from the atmospheric pressure acting on
the lower side of the piston in the vacuum brake
cylinder while a vacuum is maintained above
the piston. The train pipe runs throughout the
length of the coach and connected with
consecutive coaches by hose coupling. The
vacuum is created in the train pipe and the
vacuum cylinder by the ejector or exhauster
mounted on the locomotive.
22. Drum Brakes
With drum brakes, fluid
is forced into the wheel
cylinder, which pushes
the brake shoes out so
that the friction linings
are pressed against the
drum, which is attached
to the wheel, causing
the wheel to stop.
24. PARTS OF DRUM BRAKING SYSTEM
Brake Shoes
Like the disk pads, brake shoes consist of a steel
shoe with the friction material or lining riveted or
bonded to it. Also like disk pads, the linings
eventually wear out and must be replaced. If the
linings are allowed to wear through to the bare metal
shoe, they will cause severe damage to the brake
drum.
Backing Plate
The backing plate is what holds everything
together. It attaches to the axle and forms a solid
surface for the wheel cylinder, brake shoes and
assorted hardware. It rarely causes any problems.
25.
26. CONTINUED
Brake Drum
Brake drums are made of iron and have a machined
surface on the inside where the shoes make
contact. Just as with disk rotors, brake drums will show
signs of wear as the brake linings seat themselves
against the machined surface of the drum. When new
shoes are installed, the brake drum should be machined
smooth. Brake drums have a maximum diameter
specification that is stamped on the outside of the drum.
When a drum is machined, it must never exceed that
measurement. If the surface cannot be machined within
that limit, the drum must be replaced.
27. Drum Brakes
Expanding shoes
create force on the
inner surface of the
drum
Used on the rear of
some trucks and
SUV’s
Self-energizing design
requires less
activation force
Require periodic
adjustment
31. Construction
Disc brakes use a cast iron
rotor, inboard of the vehicle
wheel.
Both sides of the rotor are
machined smooth for the
brake pads to rub against.
Usually the 2 surfaces are
separated by a finned centre
section for better cooling
(ventilated rotors).
The pads are attached to
metal shoes, which are
actuated by pistons housed in
the brake calliper.
32. Disc Brake Operation
A piston inside the
caliper pushes the
brake pads toward
each other
The rotor is located
between the pads
The squeezing effect
causes friction which
slows the car
33. Disk Brakes
Caliper squeezes
pads to create force
on the surfaces of
the rotor.
Used in most
automotive
applications.
Benefits:
Simple design
Self adjusting
Rotor venting
allows faster heat
dissipation
34. 2 Types of disk brake calipers
Floating caliper
Piston pushes
pad against the
inner rotor
surface, reaction
force causes the
caliper to slide
and contact the
outer surface
35. 2 Types of disk brake calipers
Fixed caliper has at
least one piston on
each side
Each piston drives
it’s corresponding
pad into contact
with the rotor
36. Disc Brake Material
A disc brake
usually made of
cast iron or
ceramic
composites
(including
carbon, Kevlar
and silica).
37. DESIGN
The design of the disc varies
somewhat. Some are simply solid
cast iron, but others are hollowed
out with fins or vanes joining
together the disc's two contact
surfaces. This "ventilated" disc
design helps to dissipate the
generated heat and is commonly
used on the more-heavily-loaded
front discs.
Many higher performance brakes
have holes drilled through them.
This is known as cross-drilling A cross-drilled disc on a modern
motorcycle
40. Power Assistance
Power booster reduces
pedal force required to stop
vehicle
Engine vacuum is used to
actuate a large diaphragm
When the pedal is
depressed, vacuum is
applied to only one side of
the diaphragm and force is
applied to the master
cylinder push rod
Booster stores sufficient
vacuum for several brake
applications if the engine
fails.
42. Vacuum Assist Units
Uses engine
vacuum to add to
the force of you foot
when applying
brakes
Leaking seals
can cause lose
of assist
(hard brakes) or
lose of brake fluid
