Article : What is airbag ? | Airbag introduction | Airbag overview

Since their invention in 1968, car airbags have become a standard safety feature in automobiles that significantly reduce automobile-related deaths and injuries.

In this section, we would like to introduce the airbag system that protects the driver or passengers in the event of a collision.

1. What is an Airbag ?

Supplementary Restraint System for the driver and/or passenger safety in the event of a collision.

Basic mechanism: A thin nylon fabric pocket in the steering wheel/top glove compartment will inflate in the event of a collision, and prevent the driver/passenger from hitting the steering wheel/dashboard.

There are two main types of airbags: Mechanically Triggered, and Electrically triggered.

Link Toyota Crash Test – Airbag:

2. Vehicle restraint system

For many years, reliable seat belts have provided the only form of passive restraint in our cars. There have been debates about their safety, especially in relation to children, but over time, many countries have passed mandatory seat belt laws.

Statistics have shown that using seat belts has saved thousands of lives that could have been lost in crashes.

Airbags have been in development for many years, the suction force of a soft pillow to land in a collision must be very strong. The first patent for an inflatable landing gear for an airplane was filed during World War II.

In the 1980s, the first commercial airbags appeared in cars.

To date, statistics show that airbags reduce the risk of death in a frontal collision by about 30%.

• Effect of the restraint systems during minor accidents:

In small crashes, the bodywork absorbs only a portion of the impact energy of components such as bumpers and shock absorbers.

Seat belts (seta belts) provide adequate protection; belt tensioner restricts vehicle occupants to their seats.

The belt force limiter reduces the risk of injury to the belt. In this case, the airbags are not activated.

• Effect of the restraint systems during serious accidents:

In serious accidents, the car body will absorb the impact energy. The passenger compartment is still intact and the airbags are activated.

In addition to the protection provided by seat belts, restraint systems protect front occupants from more serious upper body and head injuries.

The vehicle's central locking system is unlocked.

3. Conponents that make up the airbag system

4. Airbag Control Unit:

The airbag ECU usually contains the following:

• Center sensor:

Usually a solid-state deceleration sensor.

Main sensor for starting squib ignition.

Must be properly mounted on the centerline of the vehicle.

• Safety sensor:

Designed to prevent unintentional ignition of air bags.

Mounted in series with the squib power supply.

The airbag will only deploy when the safety sensor is closed.

Usually a mechanical switch (mercury switch or roller and ramp)

• Ignition and Drive module:

The brain of the ECU.

Contains a microprocessor, which burns the squib when the safety switch is closed and the input data compares with the programmed crash data stored in its ROM memory. .

• Diagnostic and memory module:

Works in conjunction with warning lights. (Legal requirements for electrically triggered system, construction and use of Regs)

When the vehicle starts, the warning light stays on for about 5 seconds, while a self-test of the system is performed. If no problems are detected, the

warning light goes out and the system is ready to go.

If a problem is detected, the light stays on and the system goes down (disabled)

While in operation, the system is continuously monitored and any malfunction will be stored in the fault memory as an error code and the system will stop working until the error code is removed. Problems are reported through an indicator on the control panel.

Error diagnosis: The error memory can be accessed through a code reader, which will normally indicate the exact error detected (e.g. squib open circuit drivers). Some systems may also have facilities to use flash codes.

Safety: Due to the dangers associated with the airbag system, only fully trained personnel should attempt to repair the airbag system.

For safety, most airbag systems have a dedicated wire loom that is coded (yellow).

• Back-up power source:

Safety: Due to the possibility of the battery/conductor being damaged in a head-on collision, backup power may be required.

This will usually be a capacitor that can store enough charge to power the squib's ignition.

It is recommended to disconnect from the power source for 10 minutes before working on the system.

Links explain how an airbag works:

5. Airbag & Qquib module:

Contains both an inflator unit and a light-weight fabric airbag located inside:

Steering wheel hub

Above the glove compartment (Above glove compartment)

Proximity side compartments (separate/combined head/side/window curtain).

Airbag: The airbag itself is made of thin, nylon fabric, folds neatly into the steering wheel or dashboard, or more recently the seat or door, and inflates with a large balloon upon impact. touch.

Airbag's inflation system: Contains a number of sodium azide (NaN3) pellets that are electrically burned to produce N2 and the product reacts with potassium nitrate (KNO3) and SiO2 respectively to produce gas. Nitrogen (N2). Hot explosions produce nitrogen gas that inflates the air sacs.

Chemical reaction 1: 2NaN₃ --> 2Na + 3N₂

The signal from the deceleration sensor ignites the gas-generating mixture with an electrical pulse during head-on collision, creating the high temperature conditions needed for sodium asides to decompose at 300°C. This causes a relatively slow type of detonation (combustion) that releases a pre-calculated amount of N2 gas through a series of chemical reactions, filling the airbag.

Chemical reaction 2: 10Na + 2KNO₃ --> K₂O + 5Na₂O + N₂

Podium is the product of this reaction and potassium nitrate produces extra N2, which also helps to fill the air sacs.

Chemical reaction 3: K₂O + Na₂O + SiO₂ --> Alkaline silicate

This reaction causes potassium oxide and sodium oxide to react with a third compound Silicon dioxide and form alkaline silicate (glass) which is a safe and stable substance that is not flammable.

NaNO3 is very toxic in nature (0.2 mg/m3 is only allowed for use in the workplace) which is converted to alkaline silicate.

The metal Na is explosive in nature, converted to alkaline silicate using KNO3 and SiO2.

Airbag inflation device:

Both the airbag and the airbag tensioner are deployed singly, i.e. must be replaced after a collision.

Rotary Coupler:

A rotary coupling or clock spring is sometimes called a spiral flat wiring loom. It allows the connection between the ECU and the Squib during full rotation of the steering wheel.

It is therefore important that it be mounted according to the manufacturer's instructions, as it will be manufactured in a straight forward, fully locked left-hand or all-right-hand position.

If it is not installed properly, it will fail almost immediately.

6. Airbag Deployment

Frontal crash scenario: Vehicle crashes into an obstacle (hard wall) at 20 mph

Sensors detect the deceleration and the inflator unit activated.

Deployment sensitivity: To prevent accidental inflation during hard braking, sensors detect collisions with a solid barrier at speeds greater than 8-14 mph only upon impact.

The current used to heat a filament (filament wire) ignites the NaN₃ capsules, producing N₂:

2NaN₃ --> 2Na + 3N₂

10Na + 2KNO₃ --> K₂O + 5Na₂O + N₂

K₂O + Na₂O + SiO₂ --> Alkaline silicate (Safe, non-flammable)

130g produces 67 liters of N2

The airbag will then deploy safely at speeds > 320 mph within 0.05s after impact. To ensure safety, occupants must fasten their seat belts and sit 10 inches away from the steering wheel.

Immediately after fully inflated, the airbag deflates through the small holes in the surface within 0.3s to have an absorbing effect.

The whole process happens in the blink of an eye and will certainly be much faster than what the slow motion video below shows:

7. Smart Restraint System

Is one that adjusts shape, performance or behavior to accommodate different external forces and/or occupants.

Must be able to distinguish between: RFIS & child seats, child, adult, empty, subset of possible seating positions. For above (< / > 10 inches)

With belt/without belt, severity of incident, direction of impact.

That is: an intelligent constrain system must be able to update itself on the following: occupant's attributes, occupant's location

It is then decided: Which airbag will be deployed when fully inflated/compressed, seat belt pre-tension, parts retracted/retracted, deployment direction, deployment action posting time sequence.

Detection types: Mechanical, space, other

Detection means: Weight distribution, seat belt, Active Infrared, ultrasonic, Radar/microwave, capacitance, tags for RFIS & mart keys, height sensor in seat/belt

Advance meth (requires high computational power, complex): Passive infrared, video system, biometric sensor.

Right system: right sequence and timing, extremely reliable, work in different car interior lighting and atmospheres, discriminatory camouflage, low price.

8. More information

Most airbag systems are designed to work in conjunction with seat belt pre-tensioners. However, it is imperative to wear a seat belt when operating a vehicle with an airbag, as failure to do so will result in the Airbag becoming ineffective.

Most modern vehicles are equipped with more complex systems than simply a driver airbag. These will include passenger airbags, side airbags (built into the seat) and possibly up to 20 different airbags.

These more complex systems will of course be accompanied by more advanced collision sensors (there can be up to 5 sensors arranged around the vehicle).

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