Download - emergency braking system
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Emergency Braking System
Introduction We have pleasure in introducing our new project “emergency braking system”, which
is fully equipped by Infrared Sensor sensors circuit and pneumatic breaking circuit. It is a
genuine project which is fully equipped and designed for automobile vehicles. This forms an
integral part of best quality.
The “pneumatic braking circuit” can stop the vehicle within 2to 3 seconds running at
a speed of 50 km. The intelligent braking system is a fully automated.
This is an era of automation where it is broadly defined as replacement of manual
effort by mechanical power in all degrees of automation. The operation remains an essential
part of the system although with changing demands on physical input as the degree of
mechanization is increased.
1 Braking System
Braking action on wheeled vehicles is the use of a controlled force to hold,
stop, or reduce the speed of a vehicle. Many factors must be considered when
designing the braking system for an automotive item. The vehicle weight, size of tires,
and type of suspension are but a few that influence the design of a system.
The power needed to brake a vehicle is equal to that needed to make it go.
However, for safety reasons, brakes must be able to stop the car in a very short
distance. As an example, a passenger car equipped with an 80-HP engine can
normally accelerate from a Standstill to 60 MPH in about 36 seconds. On the
other hand, the brakes must be able to decelerate the vehicle from 60 MPH to a stop
in 4 1/2 seconds. You can therefore see the braking force is about eight times greater than
the power developed by the engine.
Each part in the braking system must operate with a very positive action to
accomplish this tremendous braking effort. The job of a wheeled vehicle mechanic is
to maintain the braking components in a state of repair that ensures serviceable brakes
when needed. For you to keep brake system components in a working shape, you
must understand how the system works. In this lesson, we will discuss the principles of
operation for components contained in various types of braking systems.
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Braking action is the use of a controlled force to slow the speed of or stop a
moving object, in this case a vehicle. It is necessary to know what friction is to
understand braking action.
Friction is the resistance to movement between two surfaces or objects that
are touching each other. An example of friction is the force which tries to stop your
hand as you apply pressure and slide it across a table or desk. This means that by forcing
the surface of an object that is not moving (stationary) against a moving object's surface,
the resistance to movement or the rubbing action between the two surfaces of the
objects will slow down the moving surface. Automotive vehicles are braked in this
manner.
1.1 Principles Of Braking
Brakes on early motor vehicles were nothing more than modified wagon brakes
used on horse-drawn wagons. These were a hand-operated, mechanical, lever-type
brakes that forced a piece of wood against one or more of the wheels. This caused friction
or a drag on the wheel or wheels.
There is also friction between the wheel and ground that tries to prevent the
wheel from sliding or skidding on the ground. When a vehicle is moving, there is a
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third force present. This force is known as kinetic energy. This is the name given the force
that tries to keep any object in motion once it has started moving.
When the brakes are applied, the wheel will either roll or skid, depending on
which is greater, the friction between the braking surfaces or between the wheel
and the road. Maximum retardation (slowing down) is reached when friction between the
brake surfaces is just enough to almost lock the wheel. At this time, friction between the
brake surfaces and wheel and road are almost the same. This is all the friction that
can be used in retarding (slowing down) the motion of the vehicle. The amount of
friction between
The road and the wheel is what limits braking. Should friction between the
braking surfaces go beyond this, the braking surfaces will lock and the wheels will
skid.
When a wheel rolls along a road, there is no movement between
(relative motion) the wheel and road at the point where the wheel touches the road.
This is because the wheel rolls on the road surface; but, when a wheel skids, it
slides over the surface of the road, and there is relative motion because the wheel is
not turning while moving over the road. When a wheel skids, friction is reduced, which
decreases the braking effect. However, brakes are made so that the vehicle operator is able
to lock the wheels if enough force to the brake lever or pedal is applied.
1.2 Braking Requirements
Most of us know that to increase a vehicle's speed requires an increase
in the power output of the engine. It is just as true that an increase in speed requires
an increase in the braking action necessary to bring a vehicle to a stop. Brakes must
not only be able to stop a vehicle, but must stop it in as short a distance as
possible.
Because brakes are expected to decelerate (slow down) a vehicle at a faster rate than
the engine can accelerate it, they must be able to control a greater power than that developed
by the engine. This is the reason that well-designed, powerful brakes have to be used to
control the modern high-speed motor vehicle. The time needed to stop is one-eighth the
time needed to accelerate from a standing start. The brakes then can handle eight times
the power developed by the engine.
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1.3 Factors Controlling Retardation
The amount of retardation (slowing down) obtained by the braking system
of a vehicle is affected by several factors. For wheel brakes used on today's motor
vehicles, these factors are the pressure exerted on the braking surfaces (lining and
drum), the weight carried on the wheel, the overall radius of the wheel (the distance
from the centre of the wheel to the outer tread of the tire), the radius of the brake
drum, the amount of friction between the braking surfaces, and the amount of friction
between the tire and the road. The amount of friction between the tire and the road
determines the amount of retardation that can be obtained by the application of the
brakes. The things that affect the amount of friction between the tires and the road are
the amount and type of tread in contact with the road surface and the type and
condition of the road surface. There will be much less friction, and thus much less
retardation, on wet or icy roads than on good dry roads.
1.4 Driver's Reaction Time
Another factor that affects the time and distance required to bring a vehicle to a stop is
the driver’s reaction time. Reaction time is the time required for the driver to move
his/her foot from the accelerator pedal to the brake pedal and apply the brakes. While the
driver is thinking of applying the brakes and reacting to do so, the vehicle will move
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a certain distance. How far it will move depends on its speed. After the brakes are
applied, the vehicle will travel an additional distance before it is brought to a stop.
The total stopping distance of a vehicle is the total of the distance covered during the
driver's reaction time and the distance during which the brakes are applied before the
vehicle stops. This illustration shows the total stopping distance required at various vehicle
speeds. This is assuming an average reaction time of three-quarters of a second and
that good brakes are applied under the most favourable road conditions.
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Brakes2.1.1 Types of Braking
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
Based on the above considerations, brakes are classified with respect to
Following factors.
1. With respect to application,
A. Foot brake
B. Hand brake
2. With respect to the number of wheels,
A. Two wheel brakes
B. Four wheel brakes
3. With respect to the method of braking contact
A. Internal expanding brakes
B. External contracting brakes
4. With respect to the method of applying the braking force.
A. Single acting brake
B. Double acting brakes.
5. With respect to the brake gear,
A. Mechanical brake
B. Power brakes
6. With respect to the nature of power employed
A. Vacuum brake
B. Air brake
C. Hydraulic brake
D. Hydrostatic brake
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E. Electric brake
7. With respect to power transmission,
A. Direct acting brakes
B. Geared brakes
8. With respect to power unit,
A. Cylinder brakes
B. Diaphragm brake
The foot brake or service brake is always applied by a pedal, while the
parking brake is applied by a hand lever. The parking brake is intended chiefly to hold the
car in position. The parking brake can be set in the “ON” position by means of a latch while
the service brake remains on only as long as the driver presses down on the pedal.
The hand brake is normally used only after the driver has stopped the car by using the
foot brake. Its other use is as an emergency brake to stop the car if the foot braked system
should fail. The hand or parking brakes operates on a pair of wheels, frequently the rear
wheels. When drum type rear brakes are used, the same shoes can be used for both hand and
foot control.
The drum type of brake may either be a band brake or a shoe brake. Both
band brakes and shoe brakes may be either external or internal. The band brakes
generally are external and shoe brakes internal. In drum brakes the drum is
attached to the wheel and revolves with it. Friction to slow the drum is applied
from inside by the shoes which do not rotate but are mounted on a stationary metal
back plate. There are different types of drum brakes such as a two leading shoe
arrangement - which gives an augmented response to pedal effort because of its
self-applying arrangement. A leading-trailing shoe is a cheaper and better
alternative as it is equally effective whether the car is going forward or backwards.
Manufacturers design drum brakes so that rain, snow or ice or grit cannot get inside
and decrease braking efficiency for moisture greatly reduces the friction between the linings
and the drum.
The dissipate quickly the considerable amount of heat generated when
braking a fast moving heavy car large brake drums would be required. Disc brakes
do the job more efficiently, for the cooling air can get to the rubbing 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 calliper for the fluid to enter or leave the each
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housing. These passages are also connected to another one for bleeding. Each
cylinder contains a rubber selling ring between the cylinder and the piston.
The brakes are applied, hydraulically actuated piston 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.
2.1.2 Mechanical Brake:
In a motor vehicle, the wheel is attached to an auxiliary wheel called
drum. The brake shoes are made to contact this drum. In most designs, two shoes
are used with each drum to form a complete brake mechanism at each wheel. The
brake shoes have brake linings on their outer surfaces. Each brake shoe is hinged at
one end by on anchor pin; the other end is operated by some means so that the
brake shoe expands outwards. The brake linings come into contact with the drum.
Retracting spring keeps the brake shoe into position when the brakes are not
applied. The drum encloses the entire mechanism to keep out dust and moisture.
The wheel attaching bolts on the drum are used to contact wheel and drum. The
braking plate completes the brake enclosure, holds the assembly to car axle, and
acts the base for fastening the brake shoes and operating mechanism.
2.1.3 Hydraulic Brakes:
The hydraulic brakes are applied by the liquid pressure. The pedal force is
transmitted to the brake shoe by means of a confined liquid through a system of force
transmission.
The force applied to the pedal is multiplied and transmitted to brake shoes
by a force transmission system. This system is based upon Pascal’s principle,
which states that “The confined liquids transmit pressure without loss equally in all
directions”.
It essentially consists of two main components - master cylinder and wheel
cylinder the master cylinder is connected by the wheel cylinders at each of the four
wheels. The system is filled with the liquid under light pressure when the brakes
are not in operation. The liquid is known as brake fluid, and is usually a mixture of
glycerine and alcohol or caster-oil, denatured alcohol and some additives Spring
pressure, and thus the fluid pressure in the entire system drops to its original low
valve, which allows retracting spring on wheel brakes to pull the brake shoes out of
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contact with the brake drums into their original positions. This causes the wheel
cylinder piston also to come back to its original inward position. Thus, the brakes
are released.
2.1.4 Air Brake:
Air brakes are widely used in heavy vehicle like buses and trucks which
require a heavier braking effort that can be applied by the driver’s foot. Air brakes
are applied by the pressure of compressed air, instead of foot pressure, acting flexible
diaphragms in brake chamber. The diaphragms are connected to
the wheel brakes. These diaphragms are controlled through a hand or foot
operated valve. The brake valve controls brake operation by directing the flow of
air from a reservoir against diaphragms in the brake chamber when the brakes are
applied and from brake chambers to tube atmosphere when the brakes are released.
The air compressor, driven by the engine furnishes compressed air to the reservoir
fall below a set valve.
2.1.4 Electric Brake:
Electric Brakes are also used in some motor vehicles, although these are not very
popular. Warner electric brake is one of the examples of such brakes. An electric brake
essentially consists of an electromagnet within the brake drum. The current from the battery
is utilized to energize the electromagnet, which actuates the mechanism to expand the brake
shoe against the brake drum, thus applying the brakes. The severity of braking is controlled
by means of a rheostat, which is operated by the driver through the foot pedal.
Electric brakes are simpler. These brakes do not require complicated
operating linkage. Only cable is required to take current from the battery to the
electromagnet. Also, these are very quick in action as compared to other types of
brakes.
2.1.5 Vacuum Brakes / Servo Brakes:
A serve mechanism fitted to the braking system reduces the physical effort
the driver has to use on the brake pedal most servo mechanisms are of the vacuum
assistance type. A pressure differential can be established by subjecting one side
of the piston to atmospheric pressure and the other side to a pressure below
atmospheric pressure by exhausting air from the corresponding end of the servo
cylinder.
2.1.6 Regenerative Braking:
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Electricity powered vehicles use regenerative braking for stopping the vehicle. With
regenerative braking pressing the brake pedal does not necessarily activate a conventional
friction brake. The motor controller controlling the vehicle is treated as a generator which
slows the vehicle and simultaneously provides an output for charging the battery. The
effectiveness of regenerative braking falls off with vehicle speed. Electric vehicles will have
to be fitted with conventional hydraulic friction brakes as well as with regenerative systems.
2.2 Brakes in Details 2.2.1 External-Contracting and Internal-Expanding Brakes
There are several types of braking systems. All systems require the use of a rotating
(turning) unit and a nonrotating unit. Each of these units contains braking surfaces that,
when rubbed together, give the braking action. The rotating unit on military
wheeled vehicle brakes consists of a drum secured to the wheel. The nonrotating unit
consists of brake shoes and the linkage needed to apply the shoes to the drum. Brakes
are either the external-contracting or internal-expanding type, depending on how the
nonrotating braking surface is forced against the rotating braking surface.
When a brake shoe or a brake band is applied against the outside of a rotating brake
drum, the brake is known as an external-contracting brake. On this type of brake, the
nonrotating braking surface must be forced inward against the drum to produce the
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friction necessary for braking. The brake band is tightened around the drum by moving the
brake lever. Unless an elaborate cover is provided, the external-contracting brake is
exposed to dirt, water, and other foreign matter which rapidly wears the lining and drum.
This is particularly true with wheel brakes.
The nonrotating unit may be placed inside the rotating drum with the drum acting
as a cover for the braking surfaces. This type of brake is known as an internal-
expanding brake because the nonrotating braking surface is forced outward against the
drum to produce braking action. This type of brake is used on the wheel brakes of cars
and trucks because it permits a more compact and economical construction. The brake
shoes and brake-operating mechanism may be mounted on a backing plate or brake
shield made to fit against and close the open end of the brake drum. This protects the
braking surfaces from dust and other foreign matter. Some vehicles are fitted with a third
type of brake system known as disk brakes. The rotating member is known as the rotor. A
brake pad is positioned on each side of the rotor. The brakes operate by squeezing together and
grasping the rotor to slow or stop the disk.
2.2.2 Brake Drums
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The brake drums are usually made of pressed steel, cast iron, or a combination of
the two metals. Cast-iron drums dissipate the heat produced by friction more rapidly
than steel drums and have better friction surfaces. However, if a cast-iron drum is made as
strong as it should be, it will be much heavier than a steel drum.
To provide light weight and enough strength, some drums are made of steel with
a cast-iron liner for the braking surface. This type is known as a centrifuge brake drum.
Cooling ribs are sometimes added to the outside of the drum to give more strength and
better heat dissipation. Braking surfaces of drums may be ground, or they may be machined to
a smooth finish.
For good braking action, the drum should be perfectly round and have a uniform
surface. Brake drums become "out of round" from pressure exerted by the brake shoes or
bands and from the heat produced by the application of the brakes. The brake drum surface
becomes scored when it is worn by the braking action. When the surface is badly scored or
the drum is out of round, it is necessary to replace the drum or regrind it or turn it down in
a lathe until the drum is again smooth and true.
2.2.3 Brake Shoes
Brake shoes are made of malleable iron, cast steel, drop-forged Steel, pressed
steel, or cast aluminium. Pressed steel is usually used because it is cheaper to produce in
large quantities. Steel shoes expand at approximately the same rate as the drum when
heat is produced by brake application, thereby maintaining the clearance between the
brake drum and the brake shoe under most conditions.
A friction lining riveted or bonded to the face of the shoe makes contact with the
inner surface of the brake drum when the brake is applied. On the riveted-type lining, brass
rivets are usually used because brass does not unduly score the drum when the lining is worn.
Aluminium rivets are not very satisfactory because they are corroded very readily by salt
water. The bonded lining is not riveted but is bonded directly to the shoe with a special cement.
Differences in brake design and conditions of operation make it necessary
to have various types of brake linings.
- The molded brake lining is made of dense, hard, compact materials and is cut
into blocks to fit different sizes of brake shoes. Its frictional qualities are low
because it has a smooth surface, but it dissipates heat rapidly and wears longer than the
woven type.
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- The woven brake lining is made of asbestos fiber, cotton fiber, and copper or
bronze wire. After being woven, the lining is treated with compounds intended to
lessen the effects of oil and water if they should come in contact with the lining.
However, oil, in particular, will reduce the frictional quality of the lining even after
treatment. The lining is also compressed and heat treated before being installed.
The main advantage of a woven lining is its frictional qualities. However, it does
not dissipate heat as rapidly or wear as well as molded brake linings. This type of lining is
generally not used in automotive vehicles.
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2.2.4 Disk Brakes
The disk brake, like the drum brake assembly, is operated by pressurized
hydraulic fluid. The fluid, which is routed to the callipers through steel lines and
flexible high-pressure hoses, develops its pressure in the master cylinder. Once the brake
pedal is depressed, fluid enters the calliper and begins to force the piston(s)
outward. This outward movement forces the brake pads against the moving rotor. Once
this point is reached, the braking action begins. The greater the fluid pressure exerted on
the piston(s) from the master cylinder, the tighter the brake pads will be forced against
the rotor. This increase in pressure also will cause an increase in braking effect. As the
pedal is released, pressure diminishes and the force on the brake pads is reduced. This allows
the rotor to turn more easily. Some callipers allow the brake pads to rub lightly against
the rotor at all times in the released position. Another design uses the rolling action of
the piston seal to maintain a clearance of approximately 0.005 inches when the brakes are
released.
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Both the disk and brake drum assemblies used on modern vehicles are well-designed
systems. Each system exhibits certain inherent advantages and disadvantages. The most
important points of interest are discussed below. One major factor that must be discussed in
automotive brakes, as well as all other brake systems, is the system’s ability to dissipate heat. As
discussed previously, the by-product of friction is heat. Because most brake systems use this
concept to develop braking force, it is highly desirable for brake systems to dissipate heat as
rapidly and efficiently as possible. The disk brake assembly, because of its open design, has the
ability to dissipate heat faster than the brake drum. This feature makes the disk brake assembly
less prone to brake fade due to a build-up of excess heat. The disk assembly also may have
additional heat transfer qualities due to the use of a ventilated rotor. This type of rotor has built-
in air passages between friction surfaces to aid in cooling.
While the brake drum assembly requires an initial shoe-to-drum clearance adjustment
and periodic checks, the disk brake assembly is self-adjusting and maintains proper adjustment
at all times. The disk assembly automatically compensates for lining wear by allowing the piston
in the calliper to move outward, thereby taking up excess clearance between pads and rotor.
The disk system is fairly simplistic in comparison to the drum system. Due to this design
and its lack of moving parts and springs, the disk assembly is less likely to malfunction. Over-
hauling the disk brake assembly is faster because of its simplistic design. It also is safer due to
the fact that the disk brake assembly is open and asbestos dust from linings is less apt to be
caught in the brake assembly. Like brake drums, rotors may be machined if excessive scoring is
present. Rotors also are stamped with a minimum thickness dimension which should not be
exceeded. The drum brake assembly requires that the drum be removed for lining inspection,
while some disk pads have a built-in lining wear indicator that produces inaudible high-pitch
squeal when linings are worn excessively. This harsh squeal is a result of the linings wearing to
a point, allowing metal indicator to rub against the rotor as the wheel turns. Because of its small
frictional area and lack of self-energizing and servo effect, the disk brake assembly requires the
use of an auxiliary power booster to develop enough hydraulic pressure for satisfactory braking.
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Hydraulic brake systemsIn hydraulic braking systems, the pressure applied at the brake pedal is transmitted to
the brake mechanism by a liquid. Since a liquid cannot be compressed under ordinary
pressures, force is transmitted solidly just as if rods were used. Force exerted at any point
upon a confined liquid is distributed equally through the liquid in all directions so
that all brakes are applied equally.
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In a hydraulic brake system, the force is applied to a piston in a master
cylinder. The brake pedal operates the piston by linkage. Each wheel brake is provided with
a cylinder. Inside the cylinder are opposed pistons which are connected to the brake shoes.
When the brake pedal is pushed down, linkage moves the piston within the
master cylinder, forcing the brake liquid or fluid from the cylinder. From the master
cylinder, the fluid travels through tubing and flexible hose into the four wheel
cylinders.
The brake fluid enters the wheel cylinders between the opposed pistons.
The pressure of the brake fluid on the pistons causes them to move out. This forces
the brake shoes outward against the brake drum. As pressure on the pedal is increased, more
hydraulic pressure is built up in the wheel cylinders and more force is exerted against
the ends of the brake shoes.
When the pressure on the pedal is released, retracting (return) springs on
the brake shoes pull the shoes away from the drum. This forces the wheel cylinder
pistons to their release positions and also forces the brake fluid back through the flexible
hose and tubing to the master cylinder.
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The master cylinder housing is an iron casting which contains the cylinder and
a large reservoir for the brake fluid. The reservoir carries enough reserve fluid to
ensure proper operation of the braking system. It is filled through a hole at the top
which is sealed by a removable filler cap containing a vent. The cylinder is
connected to the reservoir by two drilled holes or ports, a large intake port, and a small
bypass port.
The master cylinder piston is a long, spool-like member with a rubber secondary cup
seal at the outer end and a rubber primary cup which acts against the brake liquid
just ahead of the inner end. The primary cup is kept against the end of the piston by a
return spring. The inner piston head has several small bleeder ports that pass
through the head to the base of the rubber primary cup. A steel stop disk, held in the outer
end of the cylinder by a retaining spring (snap ring), acts as a piston stop. A rubber
boot covers the piston end of the master cylinder to prevent dust and other foreign
matter from entering the cylinder. This boot is vented to prevent air from being compressed
within it.
In the outlet end of the cylinder is a combination inlet and outlet valve which is
held in place by the piston return spring. This check valve is a little different from most
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check valves that will let fluid pass through them in one direction only. If enough pressure
is applied to this valve, fluid can go either through or around it in either direction.
This means it will keep some pressure in the brake lines. The check valve consists of a
rubber valve cup inside a steel valve case which seats on a rubber valve seat that fits in the
end of the cylinder. In some designs, the check valve consists of a spring-operated outlet
valve seated on a valve cage rather than a rubber cup outlet valve. The principle of
operation is the same. The piston return spring normally holds the valve cage against
the rubber valve seat to seal the brake fluid in the brake line.
The wheel cylinder changes hydraulic pressure into mechanical force that
pushes the brake shoes against the drum. The wheel cylinder housing is mounted on the
brake backing plate. Inside the cylinder are two pistons which are moved in opposite
directions by hydraulic pressure and which, at the same time, push the shoes against
the drum. The piston or piston stems are connected directly to the shoes. Rubber piston
cups fit in the cylinder bore against each piston to prevent the escape of brake liquid.
There is a light spring between the cups to keep them in position against the pistons.
The open ends of the cylinder are fitted with rubber boots to keep out foreign matter.
Brake fluid enters the cylinder from the brake line connection between the pistons.
At the top of the cylinder, between the pistons, is a bleeder hole and screw through
which air is released when the system is being filled with brake fluid.
On some vehicles, a stepped wheel cylinder is used to compensate for the
faster rate of wear on the front shoe than on the rear shoe. This happens because
of the self-energizing action. By using a larger piston for the rear shoe, the shoe
receives more pressure to offset the self-energizing action of the front shoe.
If it is desired that both shoes be independently self-energizing, it is necessary to
have two wheel cylinders, one for each shoe. Each cylinder has a single piston and
is mounted on the opposite side of the brake backing plate from the other cylinder.
So far, we have discussed the parts needed to make up a hydraulic brake
system. Now let's see what happens to these parts when the brakes are applied and
released. Let's assume the master cylinder is installed on a vehicle and the hydraulic
system is filled with fluid. As the driver pushes down on the brake pedal, linkage
moves the piston in the master cylinder. As the piston moves inward, the primary cup
seals off the bypass port (sometimes known as the compensating port).
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With the bypass port closed, the piston traps the fluid ahead of it and creates
pressure in the cylinder. This pressure forces the check valve to open and fluid passes into
the brake line. As the piston continues to move, it forces fluid through the lines into
the wheel cylinders. The hydraulic pressure causes the wheel cylinder pistons to move
outward and force the brake shoes against the brake drum. As long as pressure is kept on
the brake pedal, the shoes will remain pressed against the drum.
When the brake pedal is released, the pressure of the link or pushrod is removed from
the master cylinder piston. The return spring pushes the piston back to the released
position, reducing the pressure in front of the piston. The check valve slows down the
sudden return of fluid from the wheel cylinders. As the piston moves toward the
released position in the cylinder, fluid from the master cylinder supply tank flows
through the intake port and then through the bleeder holes in the head of the
piston. This fluid will bend the lips of the primary cup away from the cylinder wall,
and the fluid will flow into the cylinder ahead of the piston.
When the pressure drops in the master cylinder, the brake shoe return springs pull the
shoes away from the drum. As the shoes are pulled away from the drum, they squeeze the
wheel cylinder pistons together. This forces the brake fluid to flow back into the master
cylinder.
The returning fluid forces the check valve to close. The entire check valve is then
forced off its seat, and fluid flows into the master cylinder around the outer edges of the
valve. When the piston in the master cylinder has returned to its released position
against the stop plate, the primary cup uncovers the bypass port and any excess fluid
will flow through the bypass port to the reservoir. This prevents the brakes from
"locking up” when the heat of the brakes causes the brake fluid to expand.
When the piston return spring pressure is again more than the pressure of
the returning fluid, the check valve seats. The valve will keep a slight pressure in the
brake lines and wheel cylinders. The brake system is now in position for the next brake
application.
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4
Infrared Sensor4.1 Sensors
A sensor is a transducer used to make a measurement of a physical variable. Any
sensor requires calibration in order to be useful as a measuring device. Calibration is
the procedure by which the relationship between the measured variable and the converted
output signal is established.
Care should be taken in the choice of sensory devices for particular tasks. The
operating characteristics of each device should be closely matched to the task for which it is
being utilized. Different sensors can be used in different ways to sense same conditions and
the same sensors can be used in different ways to sense different conditions.
4.2 Types of Sensor:
Passive sensors detect the reflected or emitted electro-magnetic radiation from natural
sources, while active sensors detect reflected responses from objects which are irradiated
from artificially generated energy sources, such as radar. Each is divided further in to non-
scanning and scanning systems.
A sensor classified as a combination of passive, non-scanning and nonimaging
method is a type of profile recorder, for example a microwave radiometer. A sensor
classified as passive, non-scanning and imaging method, is a camera, such as an aerial survey
camera or a space camera, for example on board the Russian COSMOS satellite.
Sensors classified as a combination of passive, scanning and imaging are classified
further into image plane scanning sensors, such as TV cameras and solid state scanners, and
object plane scanning sensors, such as multi-spectral scanners (optical-mechanical scanner)
and scanning microwave radiometers.
An example of an active, non-scanning and non-imaging sensor is a profile recorder
such as a laser spectrometer and laser altimeter. An active, scanning and imaging sensor is
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radar, for example synthetic aperture radar (SAR), which can produce high resolution,
imagery, day or night, even under cloud cover.
The most popular sensors used in remote sensing are the camera, solid state scanner,
such as the CCD (charge coupled device) images, the multi-spectral scanner and in the
future the passive synthetic aperture radar.
Laser sensors have recently begun to be used more frequently for monitoring air
pollution by laser spectrometers and for measurement of distance by laser Altimeters.
In our project IR transmitter and IR receiver are used to detect the obstacle. These
sensors are fitted at the front side of the vehicle.
4.3 Infrared Transmitter:
The IR transmitting circuit is used in many projects. The IR transmitter sends 40
kHz (frequency can be adjusted) carrier under 555 timer control. IR carriers at around
40 kHz carrier frequencies are widely used in TV remote controlling and ices for
receiving these signals are quite easily available.
4.4 Infrared Receiver:
The transmitted signal reflected by the obstacle and the IR receiver circuit receives
the signal and giving control signal to the control unit. The control unit activates the
pneumatic breaking system, so that break was applied.
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5
Components and Description5.1 Selection of Pneumatics:
Mechanization is broadly defined as the replacement of manual effort by mechanical
power. Pneumatics is an attractive medium for low cost mechanization particularly for
sequential or repetitive operations. Many factories and plants already have a compressed
air system, which is capable of providing both the power or energy requirements and the
control system (although equally pneumatic control systems may be economic and can
be advantageously applied to other forms of power).
The main advantages of an all-pneumatic system are usually economy and simplicity,
the latter reducing maintenance to a low level. It can also have outstanding advantages in
terms of safety.
5.2 Pneumatic Components and Its Description
The pneumatic bearing press consists of the following components to fulfil the
requirements of complete operation of the machine.
1) Pneumatic Single Acting Cylinder
2) Solenoid Valve
3) Flow Control Valve
4) IR Sensor Unit
5) Wheel and Brake Arrangement
6) PU Connector, Reducer, Hose Collar
7) Stand
8) Single Phase Induction Motor
1) Pneumatic Single Acting Cylinder:
Pneumatic cylinder consist of
A) Piston B) Cylinder
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The cylinder is a Single acting cylinder one, which means that the air pressure
operates forward and spring returns backward. The air from the compressor is passed through
the regulator which controls the pressure to required amount by adjusting its knob.
A pressure gauge is attached to the regulator for showing the line pressure. Then the
compressed air is passed through the single acting 3/2 solenoid valve for supplying the air to
one side of the cylinder.
One hose take the output of the directional Control (Solenoid) valve and they are
attached to one end of the cylinder by means of connectors. One of the outputs from the
directional control valve is taken to the flow control valve from taken to the cylinder. The
hose is attached to each component of pneumatic system only by connectors.
Parts of Pneumatic Cylinder Piston:
The piston is a cylindrical member of certain length which reciprocates inside
the cylinder. The diameter of the piston is slightly less than that of the cylinder bore diameter
and it is fitted to the top of the piston rod. It is one of the important parts which convert the
pressure energy into mechanical power.
The piston is equipped with a ring suitably proportioned and it is relatively soft rubber
which is capable of providing good sealing with low friction at the operating pressure. The
purpose of piston is to provide means of conveying the pressure of air inside the cylinder to
the piston of the oil cylinder.
Generally piston is made up of
Aluminium alloy-light and medium work.
Brass or bronze or CI-Heavy duty.
The piston is single acting spring returned type. The piston moves forward when the
high-pressure air is turned from the right side of cylinder.
The piston moves backward when the solenoid valve is in OFF condition. The piston
should be as strong and rigid as possible. The efficiency and economy of the machine
primarily depends on the working of the piston. It must operate in the cylinder with a
minimum of friction and should be able to withstand the high compressor force developed
in the cylinder and also the shock load during operation.
The piston should possess the following qualities.
A. The movement of the piston not creates much noise.
B. It should be frictionless.
C. It should withstand high pressure.
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Piston Rod
The piston rod is circular in cross section. It connects piston with piston of other
cylinder. The piston rod is made of mild steel ground and polished. A high finish is essential
on the outer rod surface to minimize wear on the rod seals. The piston rod is connected to the
piston by mechanical fastening. The piston and the piston rod can be separated if necessary.
One end of the piston rod is connected to the bottom of the piston. The other end of
the piston rod is connected to the other piston rod by means of coupling. The piston
transmits the working force to the oil cylinder through the piston rod. The piston rod is
designed to withstand the high compressive force. It should avoid bending and withstand
shock loads caused by the cutting force. The piston moves inside the rod seal fixed in the
bottom cover plate of the cylinder. The sealing arrangements prevent the leakage of air
from the bottom of the cylinder while the rod reciprocates through it.
Cylinder Cover Plates
The cylinder should be enclosed to get the applied pressure from the
compressor and act on the pinion. The cylinder is thus closed by the cover plates on both the
ends such that there is no leakage of air. An inlet port is provided on the top cover plate and
an outlet ports on the bottom cover plate. There is also a hole drilled for the movement of the
piston.
The cylinder cover plate protects the cylinder from dust and other particle and
maintains the same pressure that is taken from the compressor. The flange has to hold the
piston in both of its extreme positions. The piston hits the top plat during the return stroke
and hits the bottom plate during end of forward stroke. So the cover plates must be strong
enough to withstand the load.
Cylinder Mounting Plates:
It is attached to the cylinder cover plates and also to the carriage with the help of ‘L’
bends and bolts.
2. Solenoid Valve with Control Unit:
The directional valve is one of the important parts of a pneumatic system. Commonly
known as DCV, this valve is used to control the direction of air flow in the pneumatic system.
The directional valve does this by changing the position of its internal movable parts.
This valve was selected for speedy operation and to reduce the manual effort
and also for the modification of the machine into automatic machine by means of
using a solenoid valve. A solenoid is an electrical device that converts electrical energy into
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straight line motion and force. These are also used to operate a mechanical operation which
in turn operates the valve mechanism. Solenoids may be push type or pull type. The push
type solenoid is one in which the plunger is pushed when the solenoid is energized
electrically. The pull type solenoid is one is which the plunger is pulled when the solenoid is
energized.
The name of the parts of the solenoid should be learned so that they can be recognized
when called upon to make repairs, to do service work or to install them.
Parts of a Solenoid Valve
1. Coil
The solenoid coil is made of copper wire. The layers of wire are separated by
insulating layer. The entire solenoid coil is covered with a varnish that is not affected by
solvents, moisture, cutting oil or often fluids. Coils are rated in various voltages such as 115
volts AC, 230 volts AC, 460 volts AC, 575 Volts AC, 6 Volts DC, 12 Volts DC, 24 Volts
DC, 115 Volts DC & 230 Volts DC. They are designed for such frequencies as 50 Hz to
60 Hz.
2. Frame
The solenoid frame serves several purposes. Since it is made of laminated sheets, it is
magnetized when the current passes through the coil. The magnetized coil attracts the metal
plunger to move. The frame has provisions for attaching the mounting. They are usually
bolted or welded to the frame. The frame has provisions for receivers, the plunger. The wear
strips are mounted to the solenoid frame, and are made of materials such as metal or
impregnated less fibre cloth.
3. Solenoid Plunger
The Solenoid plunger is the mover mechanism of the solenoid. The plunger is made
of steel laminations which are riveted together under high pressure, so that there will be no
movement of the lamination with respect to one another. At the top of the plunger a pin hole
is placed for making a connection to some device. The solenoid plunger is moved by a
magnetic force in one direction and is usually returned by spring action. Solenoid operated
valves are usually provided with cover over either the solenoid or the entire valve. This
protects the solenoid from dirt and other foreign matter, and protects the actuator. In many
applications it is necessary to use explosion proof solenoids.
Working Of 3/2 Single Acting Solenoid (Or) Cut off Valve:
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The control valve is used to control the flow direction is called cut off valve or
solenoid valve. This solenoid cut off valve is controlled by the emergency push button. The
3/2 Single acting solenoid valve is having one inlet port, one outlet port and one exhaust port.
The solenoid valve consists of electromagnetic coil, stem and spring. The air enters to the
pneumatic single acting solenoid valve when the push button is in ON position.
4. IR Sensor Unit:-
The IR transmitter and IR receiver circuit is used to sense the obstacle. It is fixed to
the back side of the frame stand with a suitable arrangement. The pneumatic cylinder is
controlled by the flow control valve, single acting solenoid valve and control unit.
At Normal Condition:
The IR transmitter sensor is transmitting the infrared rays with the help of 555 IC
timer circuit. These infrared rays are received by the IR receiver sensor. The Transistor T1,
T2 and T3 are used as an amplifier section. At normal condition Transistor T5 is OFF
condition. At that time relay is OFF, so that the vehicle running continuously.
At Obstacle Condition:
At Obstacle conditions the IR transmitter and IR receiver, the resistance across the
Transmitter and receiver is high due to the non-conductivity of the IR waves. So the output of
transistor T5 goes from OFF condition to ON stage. In that time the relay is ON position. In
that time, the solenoid valve is on so that the vehicle stops.
5. Wheel and Braking Arrangement:
The simple wheel and braking arrangement is fixed to the frame stand. Near the brake
drum, the pneumatic cylinder piston is fixed.
6. Connectors, Reducer and Hose collar:
In our pneumatic system there are two types of connectors used; one is the hose
connector and the other is the reducer. Hose connectors normally comprise an adapter
(connector) hose nipple and cap nut. These types of connectors are made up of brass or
Aluminium or hardened steel. Reducers are used to provide inter connection between two
pipes or hoses of different sizes. They may be fitted straight, tee, “V” or other
configurations. These reducers are made up of gunmetal or other materials like hardened
steel etc.
7. STAND:
This is a supporting frame and made up of mild steel.
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6
Single Phase Induction Motor It is found to drive the roller shaft which fixed on the end of the frame structure. The
free end of the shaft in the motor a large pulley is found around which the belt runs. The
other specification about the motor is discussed in design part of the machine.
6.1 Single-Phase Theory
Because it has but a single alternating current source, a single-phase motor can only
produce an alternating field: one that pulls first in one direction, then in the opposite as the
polarity of the field switches. A squirrel-cage rotor placed in this field would merely twitch,
since there would be no moment upon it. If pushed in one direction, however, it would spin.
The major distinction between the different types of single-phase AC motors is how
they go about starting the rotor in a particular direction such that the alternating field will
produce rotary motion in the desired direction. This is usually done by some device that
introduces a phase-shifted magnetic field on one side of the rotor.
The figure the performance curves of the four major types of single-phase AC motors.
They are described below.
6.2 Split-Phase Motors:
The split phase motor achieves its starting capability by having two separate windings
wound in the stator. The two windings are separated from each other. One winding is used
only for starting and it is wound with a smaller wire size having higher electrical resistance
than the main windings. From the rotor's point of view, this time delay coupled with the
physical location of the starting winding produces a field that appears to rotate. The apparent
rotation causes the motor to start.
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A centrifugal switch is used to disconnect the starting winding when the motor
reaches approximately 75% of rated speed. The motor then continues to run on the basis of
normal induction motor principles.
6.3 Capacitor-Start Motors
Capacitor start motors form the largest single grouping of general purpose single
phase motors. These motors are available in a range of sizes from fractional through 3HP.
The winding and centrifugal switch arrangement is very similar to that used in a split
phase motor. The main difference being that the starting winding does not have to have high
resistance. In the case of a capacitor start motor, a specialized capacitor is utilized in a series
with the starting winding.
The addition of this capacitor produces a slight time delay between the
magnetization of starting poles and the running poles. Thus the appearance of a rotating field
exists. When the motor approaches running speed, the starting switch opens and the motor
continues to run in the normal induction motor mode.
This moderately priced motor produces relatively high starting torque, 225 to 400% of
full load torque. The capacitor start motor is ideally suited for hard to start loads such as
conveyors, air compressors and refrigeration compressors. Due to its general overall desirable
characteristics, it also is used for many applications where high starting torque may not be
required. The capacitor start motor can usually be recognized by the bulbous protrusion on
the frame where the starting capacitor is located.
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6.4 Permanent-Split Capacitor Motors
The capacitor of this motor is left in series with the starting winding during normal
operation. The starting torque is quite low, roughly 40% of full-load, so low-inertia loads
such as fans and blowers make common applications.
Running performance and speed regulation can be tailored by selecting an appropriate
capacitor value. No centrifugal switch is required.
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7
7 Block Diagram of Emergency Braking System
7.1 Circuit Diagram
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7.2 Layout of the Intelligent Braking System
7.3 Working Operation
The important components of our project are,
• IR transmitter
• IR receiver
• Control Unit with Power supply
• Solenoid Valve
• Flow control Valve
• Air Tank (Compressor)
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The IR TRANSMITTER circuit is to transmit the Infra-Red rays. If any obstacle is
there in a path, the Infra-Red rays reflected. This reflected Infra-Red rays are received by the
receiver circuit is called “IR RECEIVER”.
The IR receiver circuit receives the reflected IR rays and giving the control signal to
the control circuit. The control circuit is used to activate the solenoid valve.
If the solenoid valve is activated, the compressed air passes to the Single Acting Pneumatic
Cylinder. The compressed air activate the pneumatic cylinder and moves the piston rod.
If the piston moves forward, then the breaking arrangement activated. The breaking
arrangement is used to break the wheel gradually or suddenly due to the piston movement.
The breaking speed is varied by adjusting the valve is called “FLOW CONTROL VALVE”.
In our project, we have to apply this breaking arrangement in one wheel as a model.
The compressed air drawn from the compressor in our project. The compressed air
flow through the Polyurethane tube to the flow control valve. The flow control valve is
connected to the solenoid valve.
7.4 Applications and Advantages
• For automobile application
• Industrial application
Advantages
•Brake cost will be less.
•Free from wear adjustment.
•Less power consumption
•Less skill drivers is sufficient to operate.
•It gives very simplified operation.
•Installation is simplified.
•To avoid other burnable interactions viz.… (Diaphragm) is not used.
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ConclusionThis project work has provided us an excellent opportunity and experience, to use our
limited knowledge. We gained a lot of practical knowledge regarding, planning, purchasing,
assembling and machining while doing this project work. We feel that the project work is a
good solution to bridge the gap between Institution and industries.
We are proud that we have completed the work with the limited time successfully.
The Emergency Braking System is working with satisfactory conditions. We are able to
understand the difficulties in maintaining the tolerances and also quality. We have done to
our ability and skill making Maximum use of available facilities.
In conclusion remarks of our project work, let us add a few more lines about our
impression project work. Thus we have developed an “Emergency Braking System” which
helps to know how to achieve low cost automation. The application of pneumatics produces
smooth operation. By enhancing this Technique, the system can be modified and developed
according to the applications.
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References1. G.B.S. Narang, “Automobile Engineering”, Khanna Publishers, Delhi, pp 671.
2. William H. Crowse, “Automobile Engineering”.
3. Donald. L. Anglin, “Automobile Engineering”.
4. Pneumatic Control System----Stroll & Bernaud, Tata Mc Graw Hill
Publications.
5. Pneumatic System----Majumdhar, New Age India International (P) Ltd
6. Automotive electronics in passenger cars -A.Numazawa
Web sites:
Www. Profc.udec.cl/~gabriel/tutorials.com
Www.carsdirect.com/features/safetyflatures
Www.hwysafety.org
Www.Wikipedia.com
Www.Crazyengineers.com
Www.howstuffworks.com
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