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AIRBAG SAFETY SYSTEMS

by

K.Jayakishore M.TECH

GRIET

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ABSTRACT

This seminar is about airbags, which act as one of the

safety systems in automobile accidents to save the occupants

from fatalities. The development of airbags began with the

idea for a system that would restrain automobile drivers and

passengers in accidents. It is an occupant restraint system

consisting of a flexible envelope designed to inflate rapidly in

an automobile collision, to prevent vehicle occupants from

striking interior objects such as the steering wheel,

instrument panel, windscreen or windows.

In this seminar we will discuss different types of airbags,

how airbags work, the chemistry behind airbags, use of

airbags and latest development

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Contents

Motivation 4

Automotive safety – Classification 5

Airbags Introduction 6

Airbags – Classification 7

How airbags works 14

Chemistry behind air bags 18

force-deployment 21

post-deployment 23

Final words 26

Bibliography 27

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Motivation

40% of fatalities are due to automotive crashes.

Introduction of restraint systems in automotives has

resulted in significant reduction of fatalities in

accidents.

Airbags are important restraint systems in

automotives.

Airbags act in conjunction to other restraints systems

like seat belts to protect the occupants in automotives.

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Automotive Safety - Classification

Automotive Safety

ACTIVE Safety

Examples: - ABS- ESP

- Automatic BRAKES

PASSIVE Safety

ACTIVE Restraint System

Examples:

- Seats-

Seatbelts-

Headrest

PASSIVE Restraint SystemExample

s:- Airbags

- Collapsib

le steering column

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Airbags – Introduction

Airbags are balloon shaped …

First invented by ?

First fixed in ? commercial car

An airbag is a vehicle safety device. It is an

occupant restraint consisting of a flexible envelope

designed to inflate rapidly in an automobile collision, to

prevent vehicle occupants from striking interior objects

such as the steering wheel or window.

An American inventor, John Wenrick, a retired

industrial engineer, designed the original safety cushion

for automotive use in 1952 at his kitchen table.

General Motors' first bags, in the 1970s, were

marketed as the Air Cushion Restraint System.

Common terms in North America include Supplemental

Restraint System (SRS) and Supplemental Inflatable

Restraint (SIR)

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Airbags - Classification

AIRBAGS

FRONTAL Airbags

SIDE Airbags

CURTAIN Airbags

KNEE Airbags

New inventions (seat belt airbags, foot airbags, etc.)

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Frontal Airbags

Frontal Airbags are introduced in 1980; Mercedes-Benz

introduced the airbag in Germany. As an option on its high-

end S-Class (W126). In the Mercedes system, the sensors

would automatically pre-tension the seat belts to reduce

occupant's motion on impact, and then deploy the airbag on

impact. This integrated the seat belts and airbag into a

restraint system, rather than the airbag being considered an

alternative to the seat belt

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Side Airbags

By the end of the decade, it was very rare to find a mass

market car without an airbag, and some late 1990s products,

such as the Volkswagen Golf Mk4 also featured side airbags.

The Peugeot 306 was a classical example of how

commonplace airbags became on mass market cars during

the 1990s. On its launch in early 1993 most of the range did

not even have driver airbags as an option. By 1999 however,

side airbags were available on several variants.During the

2000s side airbags were commonplace on even budget cars,

such as the smaller-engined versions of the Ford Fiesta and

Peugeot 206.

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Curtain Airbags

There are essentially two types of side airbags commonly

used today, the side torso airbag and the side curtain airbag.

Side-impact airbags or side torso airbags are a category of

airbag usually located in the seat, and inflate between the

seat occupant and the door. These airbags are designed to

reduce the risk of injury to the pelvic and lower abdomen

regions. Some vehicles are now being equipped with

different types of designs, to help reduce injury and ejection

from the vehicle in rollover crashes. Curtain airbags have

been said to reduce brain injury or fatalities by up to 45% in

a side impact with an SUV.

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Knee Airbag

The first driver's side and separate knee airbag was used in

the 1996 model Kia Sportage vehicle and has been standard

equipment since then. The airbag is located beneath the

steering wheel. The Toyota Avensis became the first vehicle

sold in Europe equipped with a driver's knee airbag. The

EuroNCAP reported on the 2003 Avensis, "There has been

much effort to protect the driver's knees and legs and a knee

airbag worked well." the glove compartment in a crash.

Knee airbags are designed to reduce leg injury.

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Seat belt airbags

In 2009, the S-class ESF safety concept car showcased

seatbelt airbags. They will be included standard on the

production Lexus LFA in late 2010, and the 2011 Ford

Explorer will offer rear seatbelt airbags as an option.

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Rear-window-curtain airbags

In 2008, the Toyota iQ launched featuring the first

production rear curtain shield airbag to protect the rear

occupants' heads in the event of a rear end impact.

In 2009, Toyota developed the first production rear-

seat center airbag designed to reduce the severity of

secondary injuries to rear passengers in a side collision. This

system deploys from the rear center console first appearing

in on the redesigned Crown Majesta.

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How Airbags Work ?

What triggers an airbag? (Sensors)

Airbag inflator

Chemistry behind airbags

Airbag gases (new technology –inert gases)

Airbag material

Airbag vents (Pressure controlled)

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What triggers an airbag?

Sensors triggers an airbags.

They are

accelerometer

impact sensors

side pressure sensors

wheel speed sensors

gyroscopes

brake pressure sensors

seat occupancy sensors

The signals from the various sensors are fed into the Airbag

control unite.

The airbag sensor is a MEMS accelerometer, which is a

small integrated circuit with integrated micro mechanical

elements. The microscopic mechanical element moves in

response to rapid deceleration, and this motion causes a

change in capacitance, which is detected by the electronics

on the chip that then sends a signal to fire the airbag. The

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most common MEMS accelerometer in use is the ADXL-50

by Analog Devices, but there are other MEMS

manufacturers as well. Initial attempts using mercury

switches did not work well. Before MEMS, the primary

system used to deploy airbags was called a "rolamite". A

rolamite is a mechanical device, consisting of a roller

suspended within a tensioned band. As a result of the

particular geometry and material properties used, the roller

is free to translate with little friction or hysteresis. This

device was developed at Sandia National Laboratories. The

rolamite, and similar macro-mechanical devices were used in

airbags until the mid-1990s when they were universally

replaced with MEMS.

Nearly all airbags are designed to automatically deploy in

the event of a vehicle fire when temperatures reach 150-200

°C (300-400 °F). This safety feature, often termed auto-

ignition, helps to ensure that such temperatures do not cause

an explosion of the entire airbag module

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Airbag inflator

When the frontal airbags are to deploy, a signal is sent

to the inflator unit within the airbag control unit.

An igniter starts a rapid chemical reaction generating

primarily nitrogen gas(N2) to fill the airbag.

Some airbags technologies use compressed nitrogen or

argon gas with a pyrotechnic operated valve.

Some airbag technologies use compressed

nitrogen or argon gas with a pyrotechnic operated valve

("hybrid gas generator"), while other technologies use

various energetic propellants. Propellants containing

the highly toxic sodium azide (NaN ) to fill the airbag

making it deploy ) were common in early inflator

designs. However, propellants containing sodium azide

were widely phased out during the 1990s in pursuit of

more efficient, less expensive and less toxic alternatives.

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Chemistry behind airbags

When sensors fire! Temperature reaches 150-200 °c

chemical capsules form in gases with in 0.008 seconds.

An igniter starts a rapid chemical reaction generating

nitrogen gas (N₂).

Incomplete combustion of sodium azide produce of

Carbon monoxide and nitrogen(II)oxide as by-products.

The azide-containing pyrotechnic gas generators

contain a substantial amount of the propellant. The

driver-side airbag would contain a canister containing

about 50 grams of sodium azide. The passenger side

container holds about 200 grams of sodium azide. The

incomplete combustion of the charge due to rapid

cooling leads to production of carbon monoxide (CO)

and nitrogen(II) oxide as reaction by-products.

The alternative propellants may incorporate, for

example, a combination of nitroguanidine, phase-

stabilized ammonium nitrate (NH tetrazoles, triazoles,

and their salts). The burn rate modifiers in the mixture

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may be an alkaline metal nitrate (NO NO ) or other

nonmetallic oxidizer, and a nitrogen-rich fuel different

than azide (e.g. -) or nitrite (NO formers may be e.g.

clay, silica, alumina, glass, etc. -), dicyanamide or its

salts, sodium borohydride (NaBH ), etc. The coolants

and slag Other alternatives are e.g. nitrocellulose based

propellants (which have high gas yield but bad storage

stability, and their oxygen balance requires secondary

oxidation of the reaction products to avoid buildup of

carbon monoxide), or high-oxygen nitrogen-free organic

compounds with inorganic oxidizers (e.g., di or

tricarboxylic acids with chlorates (ClO (HClO -) or

perchlorates ) and eventually metallic oxides; the

nitrogen-free formulation avoids formation of toxic

nitrogen oxides).

From the onset of the crash, the entire deployment and

inflation process is about 0.04 seconds — faster than the

blink of an eye (about 0.2 seconds). Because vehicles

change speed so quickly in a crash, airbags must inflate

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rapidly to reduce the risk of the occupant hitting the

vehicle's interior.

Airbag gases (new technology- inert gasses)

Compressed nitrogen

Argon gas with hybrid gas generator

Highly toxic sodium azide

Driver side airbag would contain about 50 grams of

sodium azide.

Passenger side container holds about 200 grams of

sodium azide.

Inert gasses.

Airbag material and Airbag vents

Airbags material nylon fabric bag.

After deploy airbag gas escape through small vent

holes.

Variable-force deployment

These systems use multi-stage inflators that deploy less

force fully in stages in moderate crashes.

Occupant sensing devices(mass/weight of the persons).

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ACU determine whether airbags should be suppressed

or deployed.

Advanced airbag technologies are being developed to tailor

airbag deployment to the severity of the crash, the size and

posture of the vehicle occupant, belt usage, and how close

that person is to the actual airbag. Many of these systems use

multi-stage inflators that deploy less forcefully in stages in

moderate crashes than in very severe crashes. Occupant

sensing devices let the airbag control unit know if someone is

occupying a seat adjacent to an airbag, the mass/weight of

the person, whether a seat belt or child restraint is being

used, and whether the person is forward in the seat and close

to the airbag. Based on this information and crash severity

information, the airbag is deployed at either a high force

level, a less forceful level, or not at all.

Adaptive airbag systems may utilize multi-stage airbags to

adjust the pressure within the airbag. The greater the

pressure within the airbag, the more force the airbag will

exert on the occupants as they come in contact with it. These

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adjustments allow the system to deploy the airbag with a

moderate force for most collisions; reserving the maximum

force airbag only for the severest of collisions. Additional

sensors to determine the location, weight or relative size of

the occupants may also be used. Information regarding the

occupants and the severity of the crash are used by the

airbag control unit, to determine whether airbags should be

suppressed or deployed, and if so, at various output levels.

Post-deployment

Once an airbag deploys, deflating begins immediately as

the gas through vents.

Dust consists of cornstarch,french chalk, or talcum

powder, which are used to lubricate the airbag during

deployment.

Chemicals can cause miner irritation to the eyes and or

open wounds, some times irritate throat and eyes.

In some cases death causes.

Newer design –harmless talcum powders/cornstarch

and N₂.

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A chemical reaction produces a burst of nitrogen to

inflate the bag. Once an airbag deploys, deflation begins

immediately as the gas escapes through vent(s) in the

fabric (or, as it's sometimes called, the cushion) and

cools. Deployment is frequently accompanied by the

release of dust-like particles, and gases in the vehicle's

interior (called effluent). Most of this dust consists of

cornstarch, French chalk, or talcum powder, which are

used to lubricate the airbag during deployment. Newer

designs produce effluent primarily consisting of

harmless talcum powder/cornstarch and nitrogen gas.

In older designs using an azide-based propellant

(usually NaN ), varying amounts of sodium hydroxide

nearly always are initially present. In small amounts

this chemical can cause minor irritation to the eyes

and/or open wounds; however, with exposure to air, it

quickly turns into sodium bicarbonate (baking soda).

However, this transformation is not 100% complete,

and invariably leaves residual amounts of hydroxide ion

from NaOH. Depending on the type of airbag system,

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potassium chloride may also be present. Post-

deployment view of a SEAT Ibiza airbag.

For most people, the only effect the dust may produce is

some minor irritation of the throat and eyes. Generally,

minor irritations only occur when the occupant remains

in the vehicle for many minutes with the windows closed

and no ventilation. However, some people with asthma

may develop a potentially lethal asthmatic attack from

inhaling the dust.

Improvements

Fist generation airbags.

Second generation airbags.

Third generation airbags(sensing and gas generator

technology reduce injury risk factor).

The increasing use of airbags may actually make rescue

work for firefighters, emergency medical service and police

officers more dangerous, because of the risk of deployment

while the emergency responder is assisting or extracting

vehicle occupants.

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Improvements in sensing and gas generator technology have

allowed the development of third generation airbag systems

that can adjust their deployment parameters to size, weight,

position and restraint status of the occupant. These

improvements have demonstrated a reduced injury risk

factor for small adults and children who had an increased

risk of injury with first generation airbag systems.

Final Words

Please buy cars with airbags !

Always wear seat belts !

Always Drive Safely ! It is always better to be Mr. Late

than Late Mr. !!!

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Bibliography

1. http://en.wikipedia.org/wike/Airbag

2. http://www.airbagcrash.com/contactusetc.html

3. http://www.iihs.org/ratings/ratingsbyseries.aspx?id=527

4. http://www.theautochannel.com/news/

2007/07/23/055878.html. Retrieved 2009-12-08

5. http://www.toyoda-gosei.com/news/2003/030630.html.

Retrieved 2009-12-08

6. http://www.audi.com/audi/com/en2/tools/glossary/safety/

airbag_control_unit.html

7. http://www.patentstorm.us/patents/5806888-

description.html

8. http://www.motorcyclenews.com/MCN/News/

newsresults.html

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