ABSTRACT

In today’s world, braking is the most important system in an Automobile. Brakes are energy

conversion devices, which convert kinetic energy of the vehicle into thermal energy.

In recent years, with advancement in design & technology, Disc brakes are fast replacing

drum brakes. In Antilock Braking System, we can prevent the locking of the wheel and hence

skidding, using an Electro Mechanical Control System.

ABS was first developed for Aircrafts braking system but soon started replacing the

conventional braking system in trucks and cars. Recent improvements in ABS allows to prevent

wheel when accelerated on wet or slippery surface.

CONTENT

1. INTRODUCTION

2. HISTORY

2.1 EARLY SYSTEM

2.2 MODERN SYSTEM

3. IMPORTANCE OF ANTILOCK BRAKE SYSTEM

4. OPERATING PRINCIPAL OF ABS

5. WORKING OF ABS

6. TYPES OF ABS

6.1 FOUR CHANNEL FOUR SENSOR

6.2 THREE CHANNEL FOUR SENSOR

6.3 THREE CHANNEL THREE SENSOR

6.4 TWO CHANNEL FOUR SENSOR

6.5 ONE CHANNEL ONE SENSOR

7. COMPONENTS OF ABS

7.1 SPEED SENSOR

7.2 VALVE

7.3 PUMP

7.4 CONTROLLER

8. CRASH AVOIDENCE WITH ABS

9. EFFECTIVINESS

10. APPLICTIONS

11. ADVANTAGES

12. DISADVANTAGES

13. FUTURE WORK

14. CONCLUSION

REFRENCES

1. INTRODUCTION

A brake is one of the most important parts of any type of vehicle. Brake is used to retard or stop a

vehicle. Here Kinetic energy transferred into Heat energy. The kinetic energy increases with the

square of the velocity. So, K.E.=1/2mv² .

An anti-lock braking system is a safety system that allows the wheels on a motor vehicle to continue

interacting tractively with the road surface as directed by driver steering inputs while braking,

preventing the wheels from locking up (that is, ceasing rotation) and therefore avoiding skidding.

Stopping a car in a hurry on a slippery road can be very challenging. Anti-lock braking systems

(ABS) take a lot of the challenge out of this sometimes nerve-wracking event. In fact, on slippery

surfaces, even professional drivers can't stop as quickly without ABS as an average driver can with

ABS.

An ABS generally offers improved vehicle control and decreases stopping distances on dry and

slippery surfaces for many drivers; however, on loose surfaces like gravel or snow-covered

pavement, an ABS can significantly increase braking distance, although still improving vehicle

control.

2. History

2.1 Early systems

ABS was first developed for aircraft use in 1929 by the French automobile and aircraft pioneer

Gabriel Voisin,[citation needed] as threshold braking on airplanes is nearly impossible. These

systems use a flywheel and valve attached to a hydraulic line that feeds the brake cylinders. The

flywheel is attached to a drum that runs at the same speed as the wheel. In normal braking, the

drum and flywheel should spin at the same speed. However, if a wheel were to slow down, then

the drum would do the same, leaving the flywheel spinning at a faster rate. This causes the valve

to open, allowing a small amount of brake fluid to bypass the master cylinder into a local reservoir,

lowering the pressure on the cylinder and releasing the brakes. The use of the drum and flywheel

meant the valve only opened when the wheel was turning. In testing, a 30% improvement in braking

performance was noted, because the pilots immediately applied full brakes instead of slowly

increasing pressure in order to find the skid point. An additional benefit was the elimination of

burned or burst tires.

By the early 1950s, the Dunlop Maxaret anti-skid system was in widespread aviation use in the

UK, with aircraft such as the Avro Vulcan and Handley Page Victor, Vickers Viscount, Vickers

Valiant, English Electric Lightning, de Havilland Comet 2c, de Havilland Sea Vixen, and later

aircraft, such as the Vickers VC10, Hawker Siddeley Trident, Hawker Siddeley 125, Hawker

Siddeley HS 748 and derived British Aerospace ATP, and BAC One-Eleven being fitted with

Maxaret as standard. Maxaret, while reducing braking distances by up to 30% in icy or wet

conditions, also increased tyre life, and had the additional advantage of allowing take-offs and

landings in conditions that would preclude flying at all in non-Maxaret equipped aircraft.

In 1958, a Royal Enfield Super Meteor motorcycle was used by the Road Research Laboratory to

test the Maxaret anti-lock brake. The experiments demonstrated that anti-lock brakes can be of

great value to motorcycles, for which skidding is involved in a high proportion of accidents.

Stopping distances were reduced in most of the tests compared with locked wheel braking,

particularly on slippery surfaces, in which the improvement could be as much as 30 percent.

Enfield's technical director at the time, Tony Wilson-Jones, saw little future in the system, however,

and it was not put into production by the company.

A fully mechanical system saw limited automobile use in the 1960s in the Ferguson P99 racing

car, the Jensen FF, and the experimental all wheel drive Ford Zodiac, but saw no further use; the

system proved expensive and unreliable.

The first fully electronic anti lock system was developed in the late 60s for the Concorde aircraft.

2.2 Modern systems

Chrysler, together with the Bendix Corporation, introduced a computerized, three-channel, four-

sensor all-wheel ABS called "Sure Brake" for its 1971 Imperial. It was available for several years

thereafter, functioned as intended, and proved reliable. In 1970, Ford added an antilock braking

system called "Sure-track" to the rear wheels of Lincoln Continentals as an option; it became

standard in 1971. In 1971, General Motors introduced the "Trackmaster" rear-wheel only ABS as

an option on their rear-wheel drive Cadillac models and the Oldsmobile Toronado. In the same

year, Nissan offered an EAL (Electro Anti-lock System) as an option on the Nissan President,

which became Japan's first electronic ABS.

Fig. ABS in cars

In 1972, four wheel drive Triumph 2500 Estates were fitted with Mullard electronic systems as

standard. Such cars were very rare however and very few survive today.

In 1985 the Ford Scorpio was introduced to European market with a Teves electronic system

throughout the range as standard. For this the model was awarded the coveted European Car of the

Year Award in 1986, with very favourable praise from motoring journalists. After this success Ford

began research into Anti-Lock systems for the rest of their range, which encouraged other

manufacturers to follow suit.

In 1988, BMW introduced the first motorcycle with an electronic-hydraulic ABS: the BMW K100.

Honda followed suit in 1992 with the launch of its first motorcycle ABS on the ST1100 Pan

European. In 2007, Suzuki launched its GSF1200SA (Bandit) with an ABS. In 2005, Harley-

Davidson began offering ABS as an option for police bikes.

3. IMPORTANCE OF ANTILOCK BRAKE SYSTEM

The objectives of antilock braking system are three ford :

1. to reduce stopping distance

2. to improve stability

3. to improve steerability during brakes

Fig. Reduce stopping distance

these are explained below

Stopping distance: The distance to stop the function of the mass of the vehicle, the initial velocity,

and the braking force .by maximizing the braking force the stopping distance will be minimized if

all other factor remain constant. However, on all types of surface, to a greater or lesser extant,

there exists a peak in friction coefficients.

Stability: Although decelerating and stopping constitutes a fundamental purpose of braking system

maximum friction force may not be desired in all cases, for example not if the vehicle is on a so –

called p-slit surface (asphalt and ice),such that significantly ore braking force is obtained on one

side of the vehicle than on the other side.

Applying maximum breaking force on both side will result in a yaw moment that will tend to pull

the vehicle to the high friction side and contribute to vehicle instability

Steerability: Good peak friction force control is necessary in order to achieve satisfactory lateral

forced and, therefore, satisfactory. steerability while braking is important not only for inor course

corrections but also for the possibility of steering around an obstracle. tyre characteristics play vn

important in the braking and steering response a wheel.

4. OPERATING PRINCIPLES OF ABS

Limiting the pressure to any wheel which decelerates too rapidly is the basic principle employed

in ABS.

A speed sensor is used for measuring the speed of the wheel and sends it constantly to the computer.

Depending on the initial brake pressure and the speed of the wheel, the computer modulates the

brake pressure as fast as fifteen times per second.

Initially when the driver applies pressure on the brake if the pressure applied is too hardly then

there is a large amount of pressure on the wheel due to that ECU activates the valves to release the

pressure so that braking force applied reduces and hence the wheel maintains to its normal speed

and vice versa.

5. WORKING OF ABS

A typical ABS includes a central electronic control unit (ECU), four wheel speed sensors,

and at least two hydraulic valves within the brake hydraulics. The ECU constantly monitors

the rotational speed of each wheel; if it detects a wheel rotating significantly slower than the others,

a condition indicative of impending wheel lock, it actuates the valves to reduce hydraulic pressure

to the brake at the affected wheel, thus reducing the braking force on that wheel. The wheel then

turns faster. Conversely, if the ECU detects a wheel turning significantly faster than the others,

brake hydraulic pressure to the wheel is increased so the braking force is reapplied, slowing down

the wheel. This process is repeated continuously and can be detected by the driver via brake pedal

pulsation. Some anti-lock system can apply or release braking pressure 16 times per second.

Fig.Working of ABS

The ABS equipment may also be used to implement a traction control system(TCS) on

acceleration of the vehicle. If, when accelerating, the tire loses traction, the ABS controller can

detect the situation and take suitable action so that traction is regained. More sophisticated versions

of this can also control throttle levels and brakes simultaneously.

6. TYPES OF ABS

Anti-lock braking systems use different schemes depending on the type of brakes in use.

They can be differentiated by the number of channels: that is, how many valves that are individually

controlled—and the number of speed sensors.

6.1 Four-channel, four-sensor ABS

This is the best scheme. There is a speed sensor on all four wheels and a separate valve for

all four wheels. With this setup, the controller monitors each wheel individually to make sure it is

achieving maximum braking force.

6.2 Three-channel, four-sensor ABS

There is a speed sensor on all four wheels and a separate valve for each of the front wheels,

but only one valve for both of the rear wheels. Older vehicles with four-wheel ABS usually use

this type.

6.3 Three-channel, three-sensor ABS

This scheme, commonly found on pickup trucks with four-wheel ABS, has a speed sensor

and a valve for each of the front wheels, with one valve and one sensor for both rear wheels. The

speed sensor for the rear wheels is located in the rear axle. This system provides individual control

of the front wheels, so they can both achieve maximum braking force. The rear wheels, however,

are monitored together; they both have to start to lock up before the ABS will activate on the rear.

With this system, it is possible that one of the rear wheels will lock during a stop, reducing brake

effectiveness. This system is easy to identify, as there are no individual speed sensors for the rear

wheels.

6.4 Two-channel, four sensor ABS

This system, commonly found on passenger cars from the late 80's through early 2000's

(before government mandated stability control), uses a speed sensor at each wheel, with one control

valve each for the front and rear wheels as a pair. If the speed sensor detect lock up at any individual

wheel, the control module pulses the valve for both wheels on that end of the car.

6.5 One-channel, one-sensor ABS

This system is commonly found on pickup trucks with rear-wheel ABS. It has one valve,

which controls both rear wheels, and one speed sensor, located in the rear axle. This system

operates the same as the rear end of a three-channel system. The rear wheels are monitored together

and they both have to start to lock up before the ABS kicks in. In this system it is also possible that

one of the rear wheels will lock, reducing brake effectiveness. This system is also easy to identify,

as there are no individual speed sensors for any of the wheels.

Fig. Types of ABS

7. COMPONENT OF ABS

1.Speed Sensor

2.Valve

3.Pump

4.Controller

7.1 SPEED SENSORS

Sensors use a magnet and a coil of wire to generate a signal. The rotation of the wheel or

differential induces a magnetic field around the sensor. The fluctuations of this magnetic field

generate a voltage into the sensor. A schematic of this system is shown in figure below. The ABS

controller interprets this signal.

Fig.speed sensor

Since the voltage inducted on the sensor is a result of the rotating wheel, this sensor can become

inaccurate at slow speeds. The slower rotation of the wheel can cause inaccurate fluctuations in the

magnetic field and thus cause inaccurate readings to the controller.

The speed sensor is used to determine the acceleration or deceleration of the wheel. A picture of

this sensor is shown in Figure. These sensors use a magnet and a coil of wire to generate a signal.

The rotation of the wheel or differential induces a magnetic field around the sensor. The

fluctuations of this magnetic field generate a voltage into the sensor.The ABS controller interprets

this signal. Since the voltage inducted on the sensor is a result of the rotating wheel, this sensor can

become inaccurate at slow speeds. The slower rotation of the wheel can cause inaccurate

fluctuations in the magnetic field and thus cause inaccurate readings to the controller.

7.2 VALVES:-

Fig. Valves

The valves within an ABS serve three distinct functions. The first function of the valves is

to open and allow the hydraulic fluid from the brake pedal or the pump to reach the braking system.

The second function of the valves is to maintain the current pressure provided to the braking

system. This is accomplished by closing the valve to resist further pressure from the brake pedal.

The third function of these valves is to reduce the amount of hydraulic pressure at the braking

system. This is accomplished by opening the valves to allow the hydraulic fluid to be released from

the braking system.

7.3 PUMPS:-

When the ABS system operates the brake lines lose pressure. The pump re-pressurizes the

system. ABS Pumps; since the ABS modulator/valves can release pressure from the individual

wheels brakes there needs to be a way to restore the pressure when required. That is what the ABS

pumps job is. When the pump is cycling the driver may experience a slight pedal vibration. This

cycling is happening many times per second and this slight vibration is nature.

Fig. Pump used in ABS

The pump in the ABS is used to restore the pressure to the hydraulic brakes after the valves

have released it. A signal from the controller will release the valve at the detection of wheel slip.

After a valve release the pressure supplied from the user, the pump is used to restore a desired

amount of pressure to the braking system. The controller will modulate the pumps status in order

to provide the desire amount of pressure and reduce slipping.

The valves within an ABS serve three distinct functions. The first function of the valves is

to open and allow the hydraulic fluid from the brake pedal or the pump to reach the braking system.

The second function of the valves is to maintain the current pressure provided to the braking

system. This is accomplished by closing the valve to resist further pressure from the brake pedal.

The third function of these valves is to reduce the amount of hydraulic pressure at the braking

system. This is accomplished by opening the valves to allow the hydraulic fluid to be released from

the braking system. A picture of a standard ABS valve and pumping system is show in Figure.

The majority of problems with the valve system occur due to clogged valves. When a valve is

clogged it is unable to open, close, or change position. An inoperable valve will prevent the system

from modulating the valves and controlling pressure supplied to the brakes.

7.4 CONTROLLER:-

Fig. Controller

The controller is an ECU type unit in the car which receives information from each

individual wheel speed sensor, in turn if a wheel loses traction the signal is sent to the controller,

the controller will then limit the brake force (EBD) and activate the ABS modulator which actuates

the braking valves.

During braking, the ECU uses voltage pulses from each wheel speed sensor to determine

wheel speed changes. If the ECU determines that the pulse rate of the sensed wheels indicates

imminent lock-up, it cycles the ABS modulator valves to modify brake air pressure as needed to

provide the best braking possible.

The ECU sends signals to the ABS malfunction indicator lamp or blink code lamp to

communicate ABS faults. It also sends signals to the retarder control to disengage the retarder when

the ABS is working. When the ABS stops modulating the brake pressure, the ECU permits retarder

use once again. Technicians can communicate with the ECU through a standard SAE J1587

diagnostic connector (See Fig. 1). Technicians can read and clear fault codes stored in the ECU

and run various diagnostic tests with this connector.

The type of ECU used and its location (in-cab or frame) vary by manufacturer and

application. A detailed description of all the different ECU types used today is beyond the scope

of this manual. Consult either the vehicle or component manufacturer’s service information for

specifics.

8. CRASH AVOIDENCE WITH ABS

Fig. Crash Avoidance by ABS

Crash avoidance behavior has significantly different outcomes for a vehicle equipped with

ABS and for a vehicle which is not. An ABS equipped vehicle has a safe side during crashes

particularly when emergency braking.

If a driver is too close to a vehicle ahead when it applies its brakes, they will apply their

own brakes suddenly and - realising they will not stop in time - will turn the steering wheel in order

to avoid a collision. If their vehicle is not ABS equipped the wheels can then lock meaning the

driver will lose control of the vehicle, possibly leading to a collision. If the vehicle has been

equipped with ABS the wheels won't lock so the vehicle is always under control. ABS may also

reduce the braking distance enough such that there is no need to swerve.

9. EFFECTIVINESS

A 2004 Australian study by Monash University Accident Research Centre found that ABS:

Reduced the risk of multiple vehicle crashes by 18 percent,

Increased the risk of run-off-road crashes by 35 percent.

Fig. Effect of ABS

On high-traction surfaces such as bitumen, or concrete, many (though not all) ABS-

equipped cars are able to attain braking distances better (i.e. shorter) than those that would be

possible without the benefit of ABS. In real world conditions, even an alert and experienced driver

without ABS would find it difficult to match or improve on the performance of a typical driver

with a modern ABS-equipped vehicle. ABS reduces chances of crashing, and/or the severity of

impact. The recommended technique for non-expert drivers in an ABS-equipped car, in a typical

full-braking emergency, is to press the brake pedal as firmly as possible and, where appropriate, to

steer around obstructions. In such situations, ABS will significantly reduce the chances of a skid

and subsequent loss of control.

In gravel, sand and deep snow, ABS tends to increase braking distances. On these surfaces,

locked wheels dig in and stop the vehicle more quickly. ABS prevents this from occurring. Some

ABS calibrations reduce this problem by slowing the cycling time, thus letting the wheels

repeatedly briefly lock and unlock. Some vehicle manufacturers provide an "off-road" button to

turn ABS function off. The primary benefit of ABS on such surfaces is to increase the ability of

the driver to maintain control of the car rather than go into a skid, though loss of control remains

more likely on soft surfaces such as gravel or on slippery surfaces such as snow or ice. On a very

slippery surface such as sheet ice or gravel, it is possible to lock multiple wheels at once, and this

can defeat ABS (which relies on comparing all four wheels, and detecting individual wheels

skidding). Availability of ABS relieves most drivers from learning threshold braking.

Fig. Effect while taking a turn

A June 1999 National Highway Traffic Safety Administration (NHTSA) study found that ABS

increased stopping distances on loose gravel by an average of 27.2 percent.

According to the NHTSA,

"ABS works with your regular braking system by automatically pumping them. In vehicles not

equipped with ABS, the driver has to manually pump the brakes to prevent wheel lockup. In

vehicles equipped with ABS, your foot should remain firmly planted on the brake pedal, while

ABS pumps the brakes for you so you can concentrate on steering to safety."

When activated, some earlier ABS systems caused the brake pedal to pulse noticeably. As most

drivers rarely or do not brake hard enough to cause brake lock-up, and drivers typically do not read

the vehicle's owners manual, this may not be noticeable until an emergency. Some manufacturers

have therefore implemented a brake assist system that determines that the driver is attempting a

"panic stop" (by detecting that the brake pedal was depressed very fast, unlike a normal stop where

the pedal pressure would usually be gradually increased, Some systems additionally monitor the

rate at the accelerator was released)[citation needed] and the system automatically increases

braking force where not enough pressure is applied. Hard or panic braking on bumpy surfaces,

because of the bumps causing the speed of the wheel(s) to become erratic may also trigger the

ABS. Nevertheless, ABS significantly improves safety and control for drivers in most on-road

situations.

Anti-lock brakes are the subject of some experiments centred around risk compensation

theory, which asserts that drivers adapt to the safety benefit of ABS by driving more aggressively.

In a Munich study, half a fleet of taxicabs was equipped with anti-lock brakes, while the other half

had conventional brake systems. The crash rate was substantially the same for both types of cab,

and Wilde concludes this was due to drivers of ABS-equipped cabs taking more risks, assuming

that ABS would take care of them, while the non-ABS drivers drove more carefully since ABS

would not be there to help in case of a dangerous situation.[21]

10. APPLICTIONS

There are many different variations and control algorithms for use in ABS. One of the

simpler systems works as follows:

The controller monitors the speed sensors at all times. It is looking for decelerations in the

wheel that are out of the ordinary. Right before a wheel locks up, it will experience a rapid

deceleration. If left unchecked, the wheel would stop much more quickly than any car could. It

might take a car five seconds to stop from 60 mph (96.6 km/h) under ideal conditions, but a wheel

that locks up could stop spinning in less than a second.

The ABS controller knows that such a rapid deceleration is impossible, so it reduces the

pressure to that brake until it sees an acceleration, then it increases the pressure until it sees the

deceleration again. It can do this very quickly, before the tire can actually significantly change

speed. The result is that the tire slows down at the same rate as the car, with the brakes keeping the

tires very near the point at which they will start to lock up. This gives the system maximum braking

power.

This replaces the need to manually pump the brakes while driving on a slippery or a low

traction surface, allowing to steer even in the most emergency braking conditions.

When the ABS is in operation the driver will feel a pulsing in the brake pedal; this comes

from the rapid opening and closing of the valves. This pulsing also tells the driver that the ABS

has been triggered. Some ABS systems can cycle up to 16 times per second.

Fig. Impact of ABS on Braking system

11. ADVNTAGES OF ABS

1. Stopping on ice\water:- As mentioned above, an ABS prevents lock-ups and skidding,

even in zero slippery conditions. Anti-lock brakes have been proven to save lives in some

situations by helping drivers keep control of a vehicle.

Fig. ABS prevent skidding on wet road

2. Lower insurance costs:- Because it is a thoroughly tested safety device with a track record

of effectiveness, insurers often give customers specific discounts for having an ABS system

on their vehicle.

3. Higher resale value:- As a feature on a car or truck, an ABS raises the market value of the

vehicle. Nowadays, where ABS technology has become standard on many vehicles, not

having it could result in a lower price for resale.

4. Traction control:- An ABS shares some of the infrastructure of a traction control system,

where new technology helps ensure that each wheel has traction on the road. That makes it

easy for manufacturers to install both of these features at the factory.

12. DISADVNTAGES OF ABS

Despite the fact that anti-lock brakes are proven to be a safety feature in most situations,

and insurers consider them to significantly lower risk for a vehicle, not all drivers are sold on this

option for a car or truck. Here are some of the down sides that drivers find in this kind of brake

system.

1. Inconsistent stop times :- Anti-lock brakes are made to provide for surer braking in

slippery conditions. However, some drivers report that they find stopping distances for

regular conditions are lengthened by their ABS, either because there may be errors in the

system, or because the clunking or noise of the ABS may contribute to the driver not braking

at the same rate.

2. Expense :- An ABS can be expensive to maintain. Expensive sensors on each wheel can

cost hundreds of dollars to fix if they get out of calibration or develop other problems. For

some, this is a big reason to decline an ABS in a vehicle.

3. Delicate systems :- It's easy to cause a problem in an ABS by messing around with the

brakes. Problems include disorientation of the ABS, where a compensating brake sensor

causes the vehicle to shudder, make loud noise or generally brake worse.

13. FUTURE WORK

In this work system is non linear model nd controller is linear type hence the effictiveness

of the controller may not be good .in this time , as a future work well known linear controller like

neural networks, neuro-fuzzy and fuzzy PID systems may be employed. Also, real tie impliention

of the control logic is needed with on board micro-controller mounted over a small model of the

vehicle.

14. CONCLUSION

Because of its role in preventing the wheels from locking and better steering control during

braking, Antilock Braking System should be made mandatory for all vehicles.

As we have already seen the advantages of antilock brake system that it has good traction

control on the wheels when they run on the road so this will not only reduce the slipping and

skidding of the wheels but it directly reduces the accidental cases.

We can also say that antilock brake systems are the future brakes ot the automobile industry

.They are now used in approximately in every vehicles or we can say that they are becoming the

status symbol for the vehicle.

REFRENCES

The Journals of Society Of Automotive Engineers India (SAE INDIA).

Theories of machines by R.S. Khurmi

Wikipedia/Disc Brakes

www.edmunds.com/anti+lock+bracking+system

www.howstuffworks.com

En.wikipedia.org/anti-lock_brking_system