PRESENTED BYRAJESH KUMAR UPADHAYAY

M.TECH(MD) 2011-201311MTMEMD002

Air bag: A Supplementary Restraint System (SRS)

Triggering conditions

INTRODUCTION:Air bags are designed to keep occupants head, neck, and chest from slamming into the dash, steering wheel, or windshield in a front-end crash in a fraction of second. Air bags are fabric bags that are filled quickly with a gas to provide supplement protection for vehicle passengers during some collisions Air bags come out when vehicle

crashing into a solid wall at 8 to 14 miles per hour

Purpose of air bags

Designed for frontal impact crashes which can cause more than half of passengers deaths.

Designed to limit head and chest injuries.Protect occupant from hitting the interior parts

of carThese are stowed in the steering wheel (driver)

and the instrument panel (front passenger). While seatbelts are the primary restraint, air

bags offer supplemental protection and reduce the risk of serious head injury.

How air bag works? One or more sensors detect intensity

and direction of vehicle deceleration during a collision.

The sensor sends an electric signal to start a chemical reaction that inflates the air bag with harmless nitrogen gas.

Air bags have vents, so they deflate immediately after cushioning you.

On impact, air bag system senses the crash, inflate, and then deflate all in the blink of an eye.

Based on Newtons Laws

To study an auto accident, it is necessary to study the changes in momentum that a car faces during the collision. According to Newton's laws, "A body in motion will stay in motion until it is acted up by an outside force." For example when we are traveling along in a car at 90 mile per hour, we do not feel as though we ourselves are traveling that fast, but we feel as though it is the car that is going that fast, but really, it is both we and the car traveling this fast. The only way we can really notice exactly how fast we are going would be if we had to hit the brake. We would feel our body sliding forward in our seat and the only reason why we do not fly out of our seat is because we are wearing our seat belt. This is the same idea when it comes to an accident. An accident is the same as if we were to stop immediately and go from 50 miles per hour to 0 in less than a second. The amount of momentum our body has is still 50 miles per hour where as the car has now stopped. This is where airbags help in the event of an accident. Before our head gets the chance to smash into the steering wheel .

CONSTRUCTION

Airbags are consists of following main units.

1. Control Unit. 2. The Inflation Unit. 3. Airbag Unit. 4. Impact Sensor.

CONTROL UNIT Crash sensors and their associated wiring harnessDiagnostic module with readiness indicatorElectrical SystemAirbag Modules With Inflators

THE INFLATION UNIT

Chemistry behind airbags The mixture present in the airbags is of sodium azide (NaN3),

together with the fiberfrax material of potassium nitrate (KNO3) and silica (SiO2). This mixture is ignited through an electrical impulse and causes relatively slow detonation called as ‘Deflagration’.

This liberates precalculated volume of nitrogen gas which in turn fills the bag.

NaN32Na+3N2

Additional nitrogen gas is provided as,

10Na+2KNO3K20+5Na20+N2 

Now the two oxides react with silica forming alkaline silicate which is safe stable and unignitable compound.

 K20+Na20+siO2Alkaline silicates (Glass)

 

AIRBAG UNIT Typical driver sides airbags are constructed of

light weight nylon fabric measuring 714 mm in diameter are 152 mm deep and fill volume of 65 liters

Passenger side airbags may be as much several times larger, and are designed to hold 100-300 liters.

Driver side airbags are of circular shape and passenger side airbags are of tear drop shaped

IMPACT SENSORS Impact sensors are important components in

inflatable restraint systems. To prevent an injury or death to the driver/occupant, it’s critical that the airbags be activated immediately upon the impact. Typically several sensors are mounted in remote frontal areas of the vehicle, wired in series or parallel combination with a safing sensors located with the system diagnostics. The primary function of the safing sensors is to prevent an accidental detonation from shocks and jolts not related to the accidents.

Types Of Sensors :Electromechanical Sensor Electronic Sensor Silicon Micro Machined Sensors

Airbag Before Collision

Airbag After Collision

DRIVERS AIRBAG

Side-Impact Air Bags

APPLICATIONS(SUPPLEMENTARY RESTRAINT SYSTEM)

Function of SRS Airbag Absorbs kinematic energy of occupants Protect occupants from interior trims Protect occupants from broken glass Reduce occupants neck load by kinematically restraining spin of neck. Major Components SRS CM LABELS FOR INFORMATION STEERING COLUMN & WHEEL CLOCK SPRING D.A.B MODULE SEAT BELT PRETENSIONER SRS SRI BUCKLE SWITCH WIRING HARNESS

Operating SequenceCrashCrash SensingIgniting the InflatorProduce gas to deploy AirbagBag deployingFull deployment of the bagProtect the front occupantsVent gas (bag deflation)Air bag system completed

Aerospace Applications

NASA engineers test the Mars Pathfinder air bag landing system on simulated Martian terrain.

CONCLUSION Inflating in a fraction of a second immediately after a

serious crash begins, airbags become energy-absorbing buffers between people and the hard interior surfaces of vehicles

The airbags help keep people's heads and chests from hitting the steering wheel, instrument panel, or windshield.

They prevent people from being thrown from their vehicles. Side airbags are expected to offer increased protection

from intruding objects such as trees, poles, and the fronts of striking vehicles, particularly taller vehicles, such as pickup trucks and SUVs.

As belts offer more protection in other than frontal type of crashes by preventing ejection from the vehicles, air bags are only to supplement safety belts and not to replace them.

THANX