Braking system.pptx....Braking system.pptx

Brake
 The device used to stop any vehicle by
applying frictional forces.
 One of most important control components
of vehicle.
 They are required to stop vehicle within
smallest possible distance.
 This is done by converting kinetic energy of
vehicle into heat energy which is dissipated
into atmosphere.

Functions of Brake
• It is used as emergency to avoid accident.
• It holds vehicle stationary on slope or steep
road for parking.
• It control the vehicle to be retained when
descending a hill.
• To retard or stop the vehicle within minimum
possible distance, in consistent with safety and
without wheel skidding.

Braking Requirements
1. Brakes must be strong enough to stop vehicle with in a
minimum distance in an emergency.
2. Brakes must have good antifade characterstics i.e. their
effectiveness should not decrease with prolonged
application. This requirement demands cooling of
brakes should be very efficient.
3. The brake must operate with minimum effort of the
driver.
4. It should not cause wheel skidding.
5. The brake must strong enough to sustain sudden large
braking force.

Basic terms related to braking.
• 1.Brake Torque
Brake torque is the force applied at the brake wheel to stop
the motion of the moving vehicle.
It is twisting or torsional action caused by the disc or drum
on the brake shoes during application of brake.
• 2.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.
After prolong application of brake the coefficient of friction
reduces which causes less braking effect.

• 3.Stoppping distance:
It depend upon
1.Tyre deflection.
2.Air resistance.
3.Inertia force.
The distance required to stop the vehicle is proportional to
the square of the speed at which the brakes are applied.
It is inversely proportional to braking efficiency.
It is defined as the distance between point of application of
brake and to the point where vehicle comes to the rest.
Stopping distance=V2
/2a Meters.
V-Velocity in M/Sec
a- De acceleration in M/Sec

Stopping time
• Stopping time :It is the duration required
between the brake application and when the
vehicle comes to rest. It is inversely proportional
to brake efficiency and proportional to the speed.
Stopping Time= V/a
• Braking Efficiency:
It is the ratio of Maximum retarding force applied
at the wheel to the weight of the vehicle.
When retarding force is equal to the weight of the
vehicle and =1 then the retardation is 9.81 m/S2
and the braking efficiency is 100%.

Principle of Braking.
• The brake works on the principle of conversion of
energy. It converts kinetic energy of wheels into heat
energy by means of friction between two moving
surfaces of brake drum.
• The brake torque applied at the wheels produces a
retarding effort by the adhesion available between
brake lining and brake drum.
• The heat generated at contact surfaces depends upon
the intensity of force and coefficient of friction of two
materials.
• FB=B*WB
• WB –Normal force on the brake shoes.

Classification of brake
• The brakes of an automobile are classified
according to as :-
1. Purpose
2. Location
3. Construction
4. Method of actuation
5. Extra braking effort
6. Application

• Purpose:- From this point of view Brakes are classified as service
or primary and parking or secondary brakes.
• Location:- From this point of view brakes are located at wheels(2
or 4) or at transmission.
• Construction:-From this point of brakes are drum brakes and disc
brakes.
• Method of actuation:- This criterion gives following brake type :
a) Mechanical Brakes
b) Hydraulic Brakes
c) Electric Brakes
d) Vacuum Brakes
e) Air Brakes
f) By-wire Brakes

• According to extra braking effort:
1) servo brake or power assisted brake
2) Power brakes or power operated brakes.
• According to application
1) Foot brake
2) Hand Brake

DRUM BRAKE or Internal expanding brake

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Working
• The drum encloses the complete brake mechanism and protect it from dust and
moisture.
• The backing plate holds the all braking assembly.
• The backing plate is attached to the vehicle axle housing and act as base or frame
for fastening the brake shoe and the operating cam mechanism with linkages.
• The brake shoe are hinged to back plate at one end by an anchor pin and other
end rest on the cam or toggle.
• As the Brake pedal is pressed the cam turn by expanding brake shoes outward
against the retractor spring force.
• The brake lining comes in contact with brake drum causes friction between them.
• This force of friction opposes the direction of rotation and reduce speed or stop
the vehicle.
• When brake pedal is released the retractor spring pulls the brake shoe inward and
brake are released.
• Drum brakes have more parts than disc brakes and are harder to service, but they
are less expensive to manufacture.

Disc Brakes
• A disc brake consists of a cast iron disc bolted to
wheel hub and stationary housing called caliper.
• Caliper having a piston and friction pad is
connected to some stationary part of vehicle like
axle.
• When brakes are applied, piston move friction
pads into contact with disc, applying equal and
opposite force on disc.
• On releasing brakes, the rubber sealing rings act
as return springs and retract piston and friction
pads away from disc.

Mechanical Brakes
• Mechanical brakes are assemblies consisting of mechanical
elements for the slowing or stopping of vehicle. They use
levers or linkages to transmit force from one point to another.
• There are several types of mechanical brakes. Band brakes,
the simplest brake configuration, have a metal band lined
with heat and wear resistant friction material. Drum brakes,
which are commonly used on automobile rear wheels work
when shoes press against a spinning surface called a drum.
Disc breaks are constructed of brake pads, a caliper, and a
rotor. During operation, the brake pads are squeezed against
the rotor. Cone brakes are made with a cup and a cone,
which is lined with heat and wear resistant material. During
actuation, the cone is pressed against the mating cup surface.

Band Brakes
• The principle is that a band is wrapped part
round a rotating drum. Tension can be applied
to the band using a lever. The restraining
torque results from the difference in tension
between the two ends of the belt.

Hydraullic Brakes
• The hydraulic brake is an arrangement of braking
mechanism which uses brake fluid specialy ehtylene
glycol to transfer pressure from the controlling unit
to the actual brake mechanism of the vehicle.
• Parts of hydaullic brakes:-
1. Brake Pedal
2. Push rod
3. Master cylinder assembly
4. Brake calliper assembly

System Operation
• as the brake pedal is pressed, a pushrod exerts force on the piston(s)
in the master cylinder.
• This forces fluid through the hydraulic lines toward calipers.
• The brake caliper piston(s) then apply force to the brake pads. This
causes them to be pushed against the spinning rotor, and the friction
between the pads and the rotor causes a braking torque to be
generated, slowing the vehicle.

• In a hydraulic brake system, when the brake pedal is pressed, a pushrod
exerts force on the piston(s) in the master cylinder, causing fluid from the
brake fluid reservoir to flow into a pressure chamber through a
compensating port. This results in an increase in the pressure of the entire
hydraulic system, forcing fluid through the hydraulic lines toward one or
more calipers where it acts upon one or more caliper pistons sealed by one
or more seated O-rings (which prevent leakage of the fluid).
• Alternatively, in a drum brake, the fluid enters a wheel cylinder and presses
one or two brake shoes against the inside of the spinning drum. The brake
shoes use a similar heat-tolerant friction material to the pads used in disc
brakes.
• Subsequent release of the brake pedal/lever allows the spring(s) in the
master cylinder assembly to return the master piston(s) back into position.
This action first relieves the hydraulic pressure on the caliper, then applies
suction to the brake piston in the caliper assembly, moving it back into its
housing and allowing the brake pads to release the rotor.

• There are two main chambers i.e fluid reservoir and
compression chamber in which piston operates .The fluid
in the reservoir compensates for any change in the fluid
volume in the pipelines due to temperature variation and
due to leakage.
• Towards brake line side of the compressor ,there is fcv
with rubber cup inside .it serves to retain the residual
pressure in the brake line even when the brakes are
released.
• There are number of holes in the piston heads on the
primary high pressure side. Two holes connect at the
fluid reservoir to the compression chamber .the smaller
one out of these is abut 0.7 mm dia and is called bypass
or compensation port.

• The second hole is called intake port. Besides there is vane in
the cap ,to keep the brake fluid at atmospheric pressure .
• The push rod is operated with foot brake pedal through linkage.
As the pedal is pressed, push rod moves to the left against the
force of spring, till it cover bypass port.
• Further movement of the push rod causes building up of
pressure in the compression chamber finally when sufficient
pressure has built up, inner rubber cup of fluid check valve is
deflected, forcing the fluid under pressure in the lines.
• This fluid enters wheel cylinder or the caliper and moves the
piston thereby applying the brakes.
• When the brake pedal is release ,the spring pressure the master
cylinder moves the piston to the right extreme position.
• The same force of spring keeps the fluid check valve pressed on
its seat for sometime and thereby delays return of fluid from
the lines into the compression chamber again.

Power Brakes
• These are the brakes in which power of engine or
battery is used to enhance the braking effort.
• These are of four types:- Vaccum Brakes, Air Brakes,
Hydraulic Booster Brake and Electro-Hydraulic Booster
brake.
1. Vaccum Brakes:- Vacuum brake system is controlled
through a brake pipe connecting a brake valve in the
driver's cab with braking equipment on every
vehicle. The operation of the brake equipment on
each vehicle depends on the condition of a vacuum
created in the pipe by an ejector or exhauster.

• 2. Air Brakes:- The operatiom of air brakes is
similar to hydraulic brake except that
compressed air is used to apply brakes instead
of hydraulic pressure. Air brake are commonly
used on heavy vehicles like trucks, buses etc

Working
• The compressor takes air from the atmosphere
through the filter and the compressed air is sent to the
reservoir through the unloader valve, which gets lifted
at a predetermined pressure and relieves the
compressor of load.
• From the reservoir air goes to various accessories and
also to the brake chambers also called the diaphragm
units at each wheel ,through the brake valve.
• The control of brake valve is with the driver who can
control the intensity of braking according to the
requirements.

• 3. Antilock Brake System (ABS):- Due to excessive
braking brakes are locked which causes skidding.
Skidding is avoided by releasing braking pressure
just before wheels are lock up and then reapplying
same. This process is calles pressure modulation. A
modern ABS consists of an electronic control unit
(ECU)., one sensor on each wheel,an electrically
driven hydraullic pump and pressure accumlator.
Accumlator is used to store hydraulic fluid to
maintain high pressure in braking system. It is
charged with nitrogrn gas. ECU monitors and
controls the antilock function when required.

Braking system.pptx....Braking system.pptx

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Braking system.pptx....Braking system.pptx