Transcript
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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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