SAFETY AIRBAGS IN CARS
ACKNOWLEDGEMENTS
It is with great satisfaction and euphoria that I am submitting the Technical
seminars report on “SAFETY AIRBAGS IN CARS”. I have completed it as a part of
the curriculum of our university.
I would like to thank H.O.D. Dr. K.J.Sudhakar, Prof. C P S Prakash for his support
and guidance in assistance provided at every stage.
I would extremely thank my Principal Dr. Netaji Ganesan, DSCE, Bangalore who
has always been a great source of inspiration & has encouraged me all through.
SIDDHARTH SINGH
ABSTRACT
The present topic is about safety airbags in cars. No safety device
has consumed more attention and resources than the airbag. It is known
with high confidence that when a crash occurs , the presence of
airbag reduces fatality risk to drivers.
Airbags are subject of serious government and industry
research. My seminar takes you to the history, development and working
aspects of airbag.
1. INTRODUCTION
For years, the trusty seat belt provided the sole form of passive restraint in
our cars. There were debated about their safety, especially relating to
children. But over time, mush of the country adopted mandatory seat-belt
laws. Statistics have shown that the use of seat belts has saved thousands
of lives that might have been lost in collisions.
Air Bags have been under development for many years. The attraction
of a soft pillow to land against in a crash must be very strong – the first
patent on an inflatable crash-landing device for airplanes was filed during
World War II. In the 1980’s the first commercial air bags appeared in
automobiles.
Since 1988, all new cars have been required to have air bags on both
driver and passenger sides (Light Trucks came under the rule in 1999). To
date, Statistics show that air bags reduce the risk of dying in a direct frontal
crash by 30 percent. Newer than steering Wheel mounted or Dashboardmounted
bags, but not so widely used, are seat-mounted and door mounted
side air-bags. Some experts say that within the next few years, our cars will
go from having dual air bags top having six or even eight air bags. Having
evoked some of the controversy that surrounded seat-belt use in its early
years, air bags are the subject of serious government and industry research
and tests.
2. THE BASICS OF AIR BAGS
Before looking at specifics, let’s review our knowledge of the laws of the
motion. First, we know that moving objects have momentum (the product of
the mass and velocity of an object. Unless an outside force acts on an
object, the object will continue to move its present speed and direction.
Cars consist of several objects, including the vehicle itself, Loose objects in
the car and, of course, passengers. If these objects are not restrained, they
will continue moving at whatever speed the car is traveling at, even if the
car is stopped by a collision.
Stopping an object’s momentum requires force acting over a period of
time. When a car crashes, the force required to stop an object is very great
because the car’s momentum has changed instantly while the passengers’
has not much time to work with. The goal of any supplemental restraint
system is to help stop the passenger while doing as little damage to him or
her as possible.
What an air bag wants to do is to slow the passengers’ speed to zero
with little or no damage. The constraints that it has to work within are
huge. The air bag has the space between the passenger and the steering
wheel or dashboard and a fraction of a second to work with. Even that tiny
amount of space and time is valuable, however, if the system can slow the
passenger evenly rather than forcing an abrupt halt to his or her motion.
3. DEVELOPMENT OF AIR BAGS
The idea of using a rapidly inflating cushion to prevent crash injuries has a
long history. The first patent on an inflatable crash-landing device for
airplanes was filed during World War II.
Early efforts to adapt the air bag for use in cars bumped up against
prohibitive prices and technical hurdles involving the storage and release of
compressed gas.
· If there was enough room in a car for a gas canister.
· Whether the gas would remain contained at high pressure for the
life of the car.
· How the bag could be made to expand quickly and reliably at a
variety of operating temperatures and without emitting an ear-splitting
bang.
They needed a way to set off a chemical reaction that would produce the
nitrogen that would inflate the bag. Small solid-propellant inflators came to
rescue in the 1970’s.
In the early days of auto air bags, experts cautioned that the new device
was to be used in tandem with the seat belt. Seat belts were still completely
necessary because airbags worked only in front-end collisions occurring at
more than 6 Kmph. Only Seat belts could help in side swipes and crashes
(Although side-mounted air bags are becoming more common now), rear
end collisions and secondary impacts. Even as the technology advances, air
bags still are only effective when used with a lap/Shoulder seat belt.
4.MAIN PARTS OF AIR BAG
There are three parts to an air bag that help to accomplish this feat:
1. Bag
2. Sensor
3. Inflation system
BAG
The bag itself is made of a thin, nylon fabric, which is folded into the
steering wheel or dashboard or, more recently, the seat or door. The
powdery substance released from their sir bag, by the way, is regular
8
cornstarch or talcum powder, which is used by the air bag manufacturers to
keep the bags pliable and lubricated while they’re in storage.
SENSOR
The sensor is the device that tells the bag to inflate. It works with the
control module to discriminate between crash and non-crash events. These
sensors measure the severity of the impact. Inflation happens when there is
a collision force equal to running into a brick wall at 16 to 24 Km per hour.
They are setup so that sudden negative acceleration will cause the contacts
to close, telling the control module that a crash before airbag deployment.
INFLATION SYSTEM
The air bag’s inflation system reacts sodium azide(NaN3) with potassium
nitrate (KNO3) to produce large volume of nitrogen gas. Hot Blasts of the
nitrogen inflate the air bag from its storage site up to 322Kmph. A Second
later, the gas quickly dissipates through a tiny holes in the bag, thus
deflating the bag so you can move.
CONSTRUCTION OF AIR BAGS
Airbag are assemblies consisting of the airbag (made of Nylon), inflator
modules and sensor housing, electrical connectors (Clock spring), airbag
retainer and the cover. The driver’s side bag is mounted in the center of the
steering wheel as shown in fig. 1.