RKDF INSTITUTE OF SCIENCE & TECHNOLOGY, BHOPAL

EXPERIMENT NO. - 08

AIM: -To study Barking system of an automobile.

INTRODUCTION:
It goes without saying that brakes are one of the most important control components of vehicle.
They are required to stop the vehicle within the smallest possible distance and this is done by
converting the kinetic energy of the vehicle into the heat energy.

BRAKING REQUIREMENTS:
1. The brakes must be strong enough to stop the vehicle within a minimum distance in an
emergency. But this should also be consistent with safety. The driver must have proper
control over the vehicle during emergency braking and the vehicle must not skid.
2. The brakes must have good ant fade characteristics i.e. their effectiveness should not
decrease with control over the vehicle during emergency braking and the vehicle must
not skid.
Thus the actual stopping distances will be more than the values given in given in table which
is based upon some points
1. Vehicle speed.
2. Condition of the road surface.
3. Condition of tyre tread.
4. Coefficient of friction between the tyre tread and the road surface.
5. Coefficient of friction between the brake drum and the brake lining (between the disc and
the friction pad in case of disc brakes)
6. Braking force applied by the driver.

TYPES OF BRAKES:
The brakes for automotive use may be classified according the following considerations:

1. Purpose 2. Location.
3. Construction 4. Method of actuation
5. Extra braking effort.

Purpose:
From this point of view the brakes may be classified as the service or the primary and the
parking or the secondary brakes. The service brakes are the main brakes used for stopping the
vehicle while in motion, whereas the parking brakes are meant to hold the vehicle on a slope.

Location:
The brakes may be located either at the transmission or at the wheels. The wheel brakes are
definitely better from heat dissipation point of view on account of two reasons. Firstly the
location of transmission brakes from this view point is very poor and secondly there is only one
brake drum, whereas in case of wheel brakes we may have four brake drums i.e. one on each
wheel which increases the area available for heat dissipation . Further as in case of transmission
brakes the whole of the braking torque has to be transmitted through the universal joints,
propeller shaft, differential and the rear axle, suitable provision must be made in their design and
their sizes increased proportionally. However, if the brakes are located on the transmission, the

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braking torque is equally divided automatically by the differential between the two wheels and
no special compensation is needed. Further because of the reduction at the differential, the
transmission brakes would be stronger than the brakes of similar capacity at the wheels.
In case of automobiles, the wheel brakes are used universally.
Construction
From construction point of view, two categories are the drum brakes and the disc brakes. These
have been explained in detail in Art 8 and 9.\

Method of Actuation
This criterion gives the following brake types:
(a) Mechanical brakes
(b) Hydraulic brakes
(c) Electric brakes
(d) Vacuum brakes
(e) Air brakes.
These will be described in detail in the later sections:
Disc Brakes
Construction
As shown in Fig.1. a disc brake consists of a cast iron disc bolted to the wheel hub and a
stationary housing called caliper. The caliper is connected to some stationary part of the vehicle,
like the axle casing or the stub axle and is cast in two parts, each part containing a piston. In
between each piston and the disc, there is a friction pad held in position by retaining pins, spring
plates etc. Passages are drilled in the caliper for the fluid to enter or leave each housing. These
passages are also connected to another one of bleeding. Each cylinder conations a rubber sealing
ring between the cylinder and the piston (Fig.1.)
When the brakes are applied, hydraulically actuated pistons move the friction pads into contact
with the disc, applying equal and opposite forces on the later. On releasing the brakes, the rubber
sealing rings act as return springs and retract the pistons and the friction pads away from the disc.

Fig. 1 Disc brake with fixed caliper.

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MECHANICAL BRAKES
Mechanical brakes are obsolete now as service brakes. However, these are still used on rear
wheels in many cars, as parking or emergency brakes.
Break Shoe operation
The brake shoes are operated by means of a cam or toggle lever (Fig.2.) which itself is actuated
through various mechanical linkages which will be discussed in the Art. Earlier the drum brakes
were mostly mechanically operated. These days their use is limited to parking brakes. However,
some large tucks and articulated trailers also employ such type of brakes. Fig shows one method
of making both shoes leading by mechanical means. This is known as the Girling type
mechanism. When the brakes are applied, the expander pushes the arm of upper bell crank lever.
This transmits its motion through the vertical strut to the lower bell crank and thus the lower arm
of the bell crank tends to move towards the left. But as the adjuster mechanism is there, it cannot
actually move to the left; it gets a reaction and there by the whole of the brake shoe at the lower
end moves towards the right, acting as a leading shoe. The other shoe is already leading. This
type has got one obvious disadvantage. On reverse, both the shoes will become trailing, thus
reducing the braking effect considerably As explained already this is not objectionable
ordinarily, but if desired the defect can be remedied by using the arrangement on both shoes as
shown in Fig.2. 10.19 When the vehicle is in reverse, the shoes bear against the expanding
mechanism and consequently become leading, thus obviating the disadvantage of the one-strut
arrangement in reverse. Alternatively, the two leading shoes are employed only on front brakes,
where braking effort is required on account of transfer weight.

Fig. 2. Mechanical expander breaks (a) Cam-operated (b) Toggle

HYDRAULIC BRAKES
Layout and components
Most of the cars today use hydraulically operated foot brakes on all the four wheels with an
additional hand brake mechanically operated on the rear wheels. An outline of the hydraulic
braking system is shown in Fig. The main component in this is master cylinder, which contains
reservoir for the brake fluid Master cylinder is operated by the brake pedal and is further
connected to wheel cylinders in each wheel through steel pipelines, unions and flexible hoses. In

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Fig. 3. Hydraulic brake system.

Case of Hindustan Ambassador car, on front wheels each brake shoe is operated by separate
wheel cylinder (thus making the brake two shoe- leading), whereas in case of rear wheels there is
only one cylinder on each wheel which operates both the shoes (thus giving one leading and one
trailing shoe brakes). As the wheel cylinders are also operated mechanically with the hand brake,
they are made floating. Further all the shoes in the Ambassador car are of the floating anchor
type.
Master Cylinder
This can be rightly named as heart of the hydraulic braking system. There are two main
chambers viz. the fluid reservoir and compression chamber in which the piston operates (Fig.4.)

Fig. 4. Master Cylinder.

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The fluid in the reservoir compensates for any change in the fluid volume in the pipelines due to
temperature variations and to some extent due to leakage. To prevent leakage there are rubber
seals on both ends of the piston in the compression chamber. The fluid always surrounds the
reduced diameter region of the piston. A rubber boot covers the push rod end of the master
cylinder to prevent the dirt from entering inside. Towards the brake lines side of the compression
chamber, there is a fluid checl valve with a rubber cup inside. It serves to retain the residual
pressure in the brake lines even when the brakes are released
The push rod is operated with the foot brake pedal through linkage (Fig. 4.) As the pedal is
pressed, push rod moves moves the piston to left (Fig.4) agaiast the force of the spring, till it
covers the by-pass port. Further movement of the push rod causes building up of pressure in the
compression Chamber. Forcing the fluid under pressure in the lines. This fluid enters the wheel
cylinder or the caliper and moves the pistons thereby applying the brakes.
When the brake pedal is released, the spring pressure in the compression chamber moves the
piston to the right extreme position. This same force of the spring keeps the fluid check valve
pressed on its seat for sometime and there by delays the return of fluid from the lines into the
compression chamber again. Some delay is also caused by the inertia of the fluid in the lines

Wheel Cylinder
(Fig.5.) Wheel cylinders in the brake system are meant to force the brake shoes against the drum
the construction is very simple. Each wheel cylinder is provided with pistons, rubber seals
(cups), cup spreaders, spring and dust covers (boots.) The brake line from the master cylinder is
attached to the inlet port and bleeder screw with a cover is provided to beed air from the system
whenever required Wheel cylinders are mounted on the back plate.

Fig. 5. Wheel cylinder.

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When brakes are applied the fluid under pressure from the master cylinder enters the inlet port
and forces the pistons to move outward to push the shoes against the drum. Similarly when the
brakes the released, the brake shoe retractor springs force the brake fluid out of the wheel
cylinder by pushing the pistons in ward.

BRAKE SYSTEM FOR MARUTI (SUZUKI) 800 CAR

Fig. 6. Layout of braking system for Maruti (Suzuki) 800 car

ELECTRIC BRAKES
The type of brakes, though not very popular, as service brakes, have been commonly used on
trailers. One such example is Warner electric brake.
The current from the battery is utilized to energize an electromagnet within the brake drum,
which in turn actuates the mechanism (usually a cam) to expand the brake shoes. When current
stops, the cam and brake shoes are returned to the release position by retractor springs. The
severity of braking is controlled by means of a rheostat, which is operated by the driver through
the foot pedal.
As an alternative to the foot-operated rheostat, hydraulic pressure has also been used to apply
electric brakes. As pedal is pressed more, hydraulic pressure actuates the rheostat to increase
current to the electromagnet still another method uses an inertia weight to uncover a light . As
the brakes are applied for the main vehicle, it slows down due to which the weight or pendulum
in the trailer brake control device moves forward, exposing a light-sensitive diode to more of the

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light beam. This increases the current to the electromagnet in the trailer brake, thereby applying
these brakes.
Advantage of electric brakes

1. The operating linkage much simplified in electric brakes. Instead of complicated linkage
as in mechanical brakes or pipelines as in hydraulic brakes, these require only one cable
for each drum.
2. Being electrically operated there is much less time-lag between the pressing of the brake
pedal and application of brakes at the wheels, as compared to other systems.
3. For trailer brakes, this type offers much simplified connections. Simply one cable has to
be carried to the trailer side.

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