Brakes

Brakes
By : Ratnadeepsinh Jadeja

Introduction
• Brakes are one of the most important control components of the vehicle. They
contribute very much in the running and control the vehicle. On the efficiency
of the brakes depends the lives and comfort not only of the driver and the
passengers but other persons moving on the road.
• The braking system used most frequently operates hydraulically, by pressure
applied through a liquid.
• On some trucks and buses, the braking system is operated by air pressure
(pneumatically).
• In addition all cars have a parking brake system which is mechanically operated
by a separate foot or hand lever.
• Breaking efficiency is the ratio between the retarding force (or force of friction
between the lining and the drum) and the weight of the vehicle. It is expressed
as %.

Functions of Brakes
Breaks perform the following
functions:
1. To stop the moving vehicle in
the shortest possible time.
2. To help in controlling the
speed of the vehicle and to
reduce the speed at turnings
and other crowded places.
3. To hold the vehicle in its
stationary position, without
the presence of the operator,
after it has been brought to
stop.

Requirements of a good braking system
The requirements of a good braking system are as follows:
1. The brakes should stop the vehicle within a reasonable distance. The retardation shall be
smooth and free from jerk.
2. The braking system should be very reliable to promote highest degree of safety on the
road.
3. The braking system should not affected by water, heat, road grit or dust etc.
4. Pedal effort applied by the driver should not be more so as not to strain the driver.
5. Brakes should work equally good in all weathers.
6. The wear and tear of the brake lining should be minimum for its longer life.
7. The brake design system should be capable of dissipating heat generated by friction very
quickly.
8. All the components and levers of the braking system should be strong enough to take the
mechanical stresses and strain while braking.
9. No braking system can work at its best through worn out or incorrectly inflated tyres.
good tyres are prime essential for the efficient braking.

The capacity of a brake depends upon the following factors:
1. The unit pressure between the braking surface.
2. The coefficient of friction between the braking surfaces.
3. The peripheral velocity of the brake drum.
4. The projected area of the friction surfaces.
5. The ability of the brake to dissipate heat equivalent to the energy being
absorbed.

Classification of Brakes
Brakes may be classified as follows:
1. Mechanical Brakes
2. Hydraulic Brakes
3. Power Brakes

Mechanical Brakes
The brakes which are operated mechanically by means of levers, linkages,
pedals, cams, bell cranks, etc. are known as mechanical brakes.
1. Internal Expanding Mechanical Brake.
2. Hand Brake. (Parkin Brake)
3. Disc Brakes

Internal Expanding Mechanical Brake

Hydraulic Brakes
• Brakes which are operated by means of hydraulic pressure are known as
hydraulic brakes.
• In hydraulic system, when the brakes are applied, the pressure is
increased sufficiently in the system to produce equal and uniform braking
action on all the four wheels.
• The hydraulic brakes function on the principle of pascal’s law:
“Pressure applied to a liquid is transmitted equally in all directions.”
• The hydraulic braking system contains two important components upon
which the system is mostly dependent, these are :
1. Master cylinder
2. Wheel cylinder.

Master cylinder
It serves the following objects in the system.
1. It builds up hydraulic pressure to operate the brakes.
2. It maintains a constant volume of fluid in the system owing to its
reservoir.
3. It serves as a pump to bleed or force air out of the hydraulic system.
There are two types of master cylinders.
1. Single master cylinder for all the front and rear wheel cylinders.
2. Tandem master cylinder containing separate units for front and rear
wheel cylinders.

Wheel cylinder (Slave cylinder)

Power Brakes
• Brakes operated by power other than physical effort applied at brake pedal, are
known as power brakes. The power may be exerted by air pressure, engine
vacuum or electrical energy.
• Main features of the power brake system are:
1. Time lag or the time internal between the moment when pedal is pressed
down and the moment when the brakes are put on must be very small.
2. The force applying the brakes should be closely proportional to the force
exerted by the driver on the brake pedal.
These days following systems are predominantly used for actuating the brakes:
1. Air Brakes
2. Air Hydraulic brakes.
3. Vacuum brakes.
4. Electric brakes.

An exhaust brake is a means of
slowing a diesel engine by
closing off the exhaust path
from the engine, causing the
exhaust gases to be
compressed in the exhaust
manifold, and in the cylinder.
Since the exhaust is being
compressed, and there is no
fuel being applied, the engine
works backwards, slowing
down the vehicle. The amount
of negative torque generated
is usually directly proportional
to the back pressure of the
engine.
Engine Exhaust Brakes

It is auxiliary brake and should be used under the following circumstances:
1. In traffic situations demanding slowing down over a long stretch of road.
2. While travelling on long downhill gradient.
The exhaust brake serves the following purposes.
1. Improves the life and efficiency of the service brakes.
2. Increases the life of the service brake linings and drums.
3. Reduces overheating of service brakes.
The main component of the engine brake system are:
1. Pressure regulator,
2. Foot control valve.
3. Air cylinder.
Engine Exhaust Brakes

Anti lock Braking
System
• An anti-lock braking system
(ABS) is a safety anti-skid
braking system used on
aircraft and on land
vehicles, such as cars,
motorcycles, trucks, and
buses. ABS operates by
preventing the wheels from
locking up during braking,
thereby maintaining tractive
contact with the road
surface.

Brake Effectiveness
The following factors contribute to the effectiveness of the brakes:
1. Amount of pressure applied to the shoe brakes.
2. Area of brake lining.
3. Radius of brake drum.
4. Radius of car wheel.
5. Coefficient of friction of braking surfaces.
6. Coefficient of friction between tyre and road surface.

Factors controlling the stop of an automobile
The following factors control the stop of an automobile.
1. Speed and load
2. Road surface
3. Tyre tread
4. Gradient
5. Number of wheels braking
6. Coefficient of friction of braking surfaces
7. Braking force of engine
8. Pressure applied through energization
9. Weight transfer

Brakes

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