BRAKING SYSTEMS
INTRODUCTION:
Braking is the mechanism in the motor
vehicle which is used
to slowing down and stopping the vehicle to
rest in the shortest possible
distance.
Principle of Braking system: While operating the braking system the KINETIC
ENERGY of moving
vehicle is converted in to HEAT ENERGY.
Braking of a vehicle depends upon the static function that
acts between tyres and road surface.
“The kinetic energy due to motion of the vehicle is
dissipated in the form of heat energy due to friction between moving parts and
stationary parts of vehicle”.
Functions of Brakes: Brakes have the following functions.
1.It is used to stop the vehicle.
2.It is used to control the speed where and
when required.
3.It is used to control the vehicle while
descending along the slope.
4.To park the vehicle and held it in
stationary position without the presence of
Driver.
Requirements of Automobile Brakes:
1.It should work efficiently irrespective
of road condition and quality.
2.The retardation must be uniform
throughout its application.
3.The pedal effort must be within the
convenient capacity of the driver.
4.It must be reliable and should not be
effected by heat water and dust.
5.It should be in minimum weight.
6.It should have long life.
7.It should be easy to maintain and adjust.
8.Noise and vibrations are to be minimum.
9.There should
be provision for secondary brake or parking brake.
(a) To slow down or stop the vehicle.
(b) To control the speed of vehicle.
CLASSIFICATION OF BRAKES
Classification of Brakes: The following are the classifications of Brakes:
1.BY METHOD OF POWER
a) Mechanical brakes
b) Hydraulic brakes
c) Vacuum brakes
d) Air brakes
e) Electrical brakes
f) Magnetic brakes
g) Air assisted hydraulic brakes
2.By method of application/ Actuation:
a) Service or foot brakes, operated
by foot pedal.
b) Parking or hand brakes, operated
by hand.
3.By method of operation:
a) Manual
b) Servo
c) Power operation
4. By method of Braking contact
a. Internal
Expanding Brakes
b. External Contracting Brakes.
5. By Method of Applying Brake force:
a. Single Acting Brakes.
b. Double Acting Brakes.
Types of Mechanical Brakes:
a. Drum Brakes (Internal Expanding or
External Contracting)
b. Disc Brakes (Single or Two calliper)
Drum Brakes:
Construction: The main components of drum
brakes are
1. Brake drum
2. Back plate
3. Brake shoes
4. Brake Liners
5. Retaining Springs
6. Cam
7. Brake
Linkages
ON THE BASIS OF ACTION ON FRONT OR REAR WHEELS
(a) Front-wheel brakes
(b) Rear-wheel brakes.
AIR BRAKES
Air brakes are applied by the pressure of compressed air.
Air pressure applies force on brakes shoes through suitable linkages to operate
brakes. An air compressor is used to compress air. This compressor is run by
engine power.
Construction and working of Air Brake
System:
The air brake system consists of two-stage
air-compressor driven by the
crankshaft or gearbox shaft. It takes air
from atmosphere, compresses it and
delivers to the air reservoir through
un-loader valve. Where the pressure of
the reservoir reaches the maximum degree,
the un- loader valve opens to the
atmosphere. Then the compressed air is
directed in to the atmosphere
directly.
VACUUM BRAKES
Vacuum brakes are a piston or a diaphragm operating in a
cylinder.
ELECTRIC BRAKES
In electrical brakes an electromagnet is used to actuate a
cam to expand the brake shoes. The electromagnet is energized by the current
flowing from the battery. When flow of current is stopped the cam and brake
shoes return to their original position and brakes are disengaged. Electric
brakes are not used in automobiles as service brakes.
HYDRAULIC BRAKES
The brakes which are actuated by the hydraulic pressure
(pressure of a fluid) are called hydraulic brakes. Hydraulic brakes are
commonly used in the automobiles.
The master cylinder is connected to all the four-wheel
cylinders by tubing or piping. All cylinders and tubes are fitted with a fluid
which acts as a link to transmit pedal force from master cylinder to wheel
cylinders.
BRAKE FLUID
The fluid filled in the hydraulic brake system is known as
brake fluid. It is a mixture of glycerine and alcohol or castor oil and some
additives.
Master cylinder consists of a piston which is connected to
peal through connecting rod. The wheel cylinder consists of two pistons between
which fluid is filled.
Each wheel brake consists of a cylinder brake drum. This
drum is mounted on the inner side of wheel. The drum revolves with the wheel.
Two brake shoes which are mounted inside the drum remain stationary. Heat and wear
resistant brake linings are fitted on the surface of the brake shoes.
APPLICATION OF BRAKES
When brake pedal is pressed to apply the brakes, the piston
in the master cylinder forces the brake fluid. This increases the pressure of
fluid. This pressure is transmitted in all the pipes and upto all wheel
cylinders according to Pascal’s law. This increased pressure forces out the two
pistons in the wheel cylinders. These pistons are connected to brake shoes. So,
the brake shoes expand out against brake drums. Due to friction between brake
linings and drum, wheels slow down and brakes are applied.
As shown in Figure 6.2, two pipes carrying braked fluid are
connected to front wheel cylinders which may be same as rear wheel cylinders.
The front wheels may also have same type of brakes (drum brakes) as shown in
the rear wheels. But, in modern cars, there are disc brakes in the front wheels
and drum brakes in the rear wheels.
MECHANICAL BRAKE (INTERNAL EXPANDING TYPE)
RELEASE OF BRAKES
When pedal is released, the piston of master cylinder
returns to its original position due to retractor spring provided in master
cylinder. Thus, fluid pressure drops to original value. The retractor spring
provided in the wheel cylinders pulls the brake shoes and contact between drum
and brake linings is broken. Therefore, brakes are released.
Braking System brings back shoes in their original position
when brakes are not applied. The brake drum closes inside it the whole
mechanism to protect it from dust and first. A plate holds whole assembly and
fits to car axle. It acts as a base to fasten the brake shoes and other
operating mechanism.
DISC BRAKES
Modern motor cars are fitted with disc brakes instead of
conventional drum type brakes. In Santro car and Maruti-800, front wheels are
provided with disc brakes whereas rear wheel are provided with drum brakes. A
disc brake consists of a rotating disc and two friction pads which are actuated
by hydraulic braking system as described earlier. The friction pads remain free
on each side of disc when brakes are no applied. They rub against disc when
brakes are applied to stop the vehicle. These brakes are applied in the same
manner as that of hydraulic brakes. But mechanism of stopping vehicle is
different than that of drum brakes.
PARKING BRAKE OR EMERGENCY BRAKE
1.Push button for Automated Parking Brake at
dashboard
2.ESP hydraulic unit with APB software
3.Calipers with locking
device
Parking brakes or emergency brakes are essentially
mechanical brakes operated by hand. These are used to prevent the motion of
vehicle when parked at a place or when parked on slopes. In cars, these brakes
are generally attached to rear wheels. In this type, a cable connects the hand
lever to the brake. Brakes are applied by pulling the lever and released by
pushing a button (provided on lever) and pressing the lever down.
When air enters, into the brake system and any brake line is
disconnected, bleeding of brakes has to be done. Since air is compressible so
any presence of air inside brake lining does not allow to transmit brake force
to apply brakes. Therefore, the system must be free from presence of air.
Bleeding is the process of removal of air from the braking system.