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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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