Introduction:
The Automobile Braking System is
one of the most important system on a vehicle from a safety standpoint. The
brake system is designed to slow down and halt the motion of vehicle. The
braking system converts the kinetic energy of the moving vehicle into the heat
(Thermal) energy. If the brake fails, there may be a crash, people may be
injured and even die. In order to guarantee personal safety, the driver should
have some basic knowledge about the brake system and inspect the brake
regularly, make sure it is in good condition. Also, automobile brake system is
an essential element to measure the performance of an automobile. The performance
of brake system directly affects the other properties of the vehicles. When
stepping on the brakes, the driver commands a stopping force several times as
powerful as the force that puts the car in motion and dissipates the associated
kinetic energy as heat. Brakes must be able to arrest the speed of a vehicle in
a short periods of time regardless how fast the speed is. As a result, the
brakes are required to have the ability to generating high torque and absorbing
energy at extremely high rates for short periods of time. Brakes may be applied
for a prolonged periods of time in some applications such as a heavy vehicle
descending a long gradient at high speed. Brakes have to have the mechanism to
keep the heat absorption capability for prolonged periods of time.
The brake engineer has two challenges:
·
Create
enough deceleration to stop the vehicle as quickly as the driver wishes,
without exceeding the drivers comfort level with regard to pedal effort or
pedal travel,
·
Manage the resulting heat energy so as not to
damage the brake system or the rest of the vehicle.
Various components are used in braking system to convert the momentum
(Kinetic energy) in to heat energy using friction. Two forms of friction play
important role in automotive braking:
·
Kinetic friction,
·
Static friction.
Factor governing braking:
There are four basic factors determine the braking power of the system.
·
Pressure – amount of friction generated between moving surfaces contacting one
another depends in part on the pressure exerted on the surfaces. The hydraulic
force is used to move brake pads or brake shoes against spinning rotors or
drums mounted on the wheels.
·
Coefficient of Friction – In automotive brakes, the COF expresses the frictional relationships
between pads and rotors or shoes and drums and is carefully engineered to
ensure maximum performance. [COF 0.25 to 0.55]
·
Frictional Contact surface- It is the amount of surface or area that is in contact. Bigger brakes stop
the car more quickly.
·
Heat Dissipation – A large amount of heat is produced in brakes. The weight and the speed
of the vehicle determine the braking mechanism.
Principle
of Braking System.
The
principle of braking in road vehicles involves the conversion of kinetic energy
into thermal energy (heat). When stepping on the brakes, the driver commands a
stopping force several times as powerful as the force that puts the car in
motion and dissipates the associated kinetic energy as heat. Brakes must be
able to arrest the speed of a vehicle in a short periods of time regardless how
fast the speed is. As a result, the brakes are required to have the ability to
generating high torque and absorbing energy at extremely high rates for short
periods of time. Brakes may be applied for a prolonged periods of time in some
applications such as a heavy vehicle descending a long gradient at high speed.
Brakes have to have the mechanism to keep the heat absorption capability for prolonged periods of
time.
Types of Braking
System
Brakes can be broadly classified into
following types;
Ø Mechanical brakes
·
Disc brake
·
Drum brake
Ø Hydraulic Brakes
Ø Power Brakes
·
Air brake
·
Air Hydraulic brake
·
Vacuum brakes
·
Electro-mechanical brake or electric brake
MECHANICAL BRAKES
a) Disc Brake
It is a type of brake that uses calipers
to squeeze pair of pads against disc or rotor which is attached to the wheel by
creating frictional force between them and retards the motion of rotating shaft
connected to it. A disc brake work on the principle of transmission of fluid
pressure. This law states that,” the pressure exerted anywhere in a confined
incompressible fluid is transmitted in all directions throughout the fluid such
that the pressure ratio remains same.”
b) Drum Brakes
A drum brake is that brake which uses
friction caused by set of shoes or pads that press outward against a rotating
cylinder part called as brake drum. It
is commonly used in vehicles where high amount of brake force is required like
heavy duty vehicles, medium vehicles, etc.
c) Hydraulic Brakes
A hydraulic braking system is piston
cylinder arrangement consisting of incompressible fluid typically glycol ethers
or diethylene glycol which multiplies force significantly. It works on Pascal’s
law and transfers hydraulic pressure.
d) Power Brakes
Ø Air brakes
Ø Air hydraulic
brakes
Ø Vacuum brakes
Ø Electro-mechanical
brakes
Anti-lock Brake System
Anti-lock brake systems make braking safer and more
convenient, Anti-lock brake systems modulate hydraulic pressure of brake system
to prevent the brakes from locking and the tires from skidding on slippery
pavement or during a panic stop. So some sources predict that all cars will
offer anti-lock brakes to improve the safety of the car.
Anti-lock systems modulate brake application force several times per second
to hold the tires at a controlled amount of slip; all systems accomplish this
in basically the same way. One or more speed sensors generate alternating
current signal whose frequency increases with the wheel rotational speed. An
electronic control unit continuously monitors these signals and if the
frequency of a signal drops too rapidly indicating that a wheel is about to
lock, the control unit instructs a modulating device to reduce hydraulic
pressure to the brake at the affected wheel. When sensor signals indicate the
wheel is again rotating normally, the control unit allows increased hydraulic
pressure to the brake. This release-apply cycle occurs several times per second
to “pump” the brakes like a driver might but at a much faster rate. In
addition to their basic operation, anti-lock systems have two other things in
common. First, they do not operate until the brakes are applied with enough
force to lock or nearly lock a wheel. At all other times, the system stands
ready to function but does not interfere with normal braking. Second, if the
anti-lock system fails in any way, the brakes continue to operate without
anti-lock capability. A warning light on the instrument panel alerts the driver
when a problem exists in the anti-lock system. (Automobile Brake System, 2016)
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