The Technology Behind Airbags

Before the 1970s, car accidents were a major concern, not only to the general public and to drivers, but to automotive manufacturers as well. However, this was about to change. The change had in fact begun to unfold in 1953. Because that year, American John Petrick was issued US Patent # 2,649,311. The patent was for a safety cushion for the automobile – the airbag.

Airbags gained commercial recognition in the seventies. The modern airbag uses some clever technology to restrain people in their seats instantly in the event of a crash, and greatly reducing the chances of the driver or passengers hurting themselves by hitting objects inside the car like the steering wheel or the dashboard.

The airbag works by means of a central airbag control unit (ACU), a specific type of electronic control unit (ECU). The ACU monitors various sensors in the vehicle, including wheel speed, gyroscopes, brake pressure and seat occupancy. Signals from the sensors are fed to the ACU which then determines the severity of a crash and the angle of impact. Depending on the evaluation, the ACU deploys the airbag, and if necessary, other safety aids such as seatbelt pre-tensioners and curtain airbags (which cover the side windows). Each of these devices is typically activated using one or more pyrotechnic devices, commonly called initiators or electric matches. An electrical match consists of an electrical conductor wrapped in a combustible material, and activates with a current pulse of 1 to 3 amps, in under 2 milliseconds. The current flowing through the conductor causes it to heat up. When it is hot enough, it ignites the combustible material and this in turn triggers the gas generator. In an airbag the initiator is used to ignite solid propellant inside the airbag inflator. The burning propellant produces inert (non-reactive) gas, which instantly inflates the airbag, taking usually between 20 and 30 milliseconds.

Generally the decision to deploy airbags in case of a head-on collision is made within 15 to 30 milliseconds after the impact, and both driver and passenger airbags are fully inflated in about 60 to 80 seconds after impact.

Today almost all automotive manufacturers in India offer airbags, but these come as standard equipment only in the top-of-the line models. The most plausible explanation for this seems to be as follows. Firstly airbags do not guarantee safety during an accident- they only decrease-marginally- the likelihood of grievous injury. Moreover with reference to the highways in India where traffic moves faster than the city’s dull crawl, the top speeds are not as high as they are in other countries. Most economy cars in India are not designed to exceed 160 kph (100 mph), and this reduces the necessity of airbags. An airbag can be deployed only once, and if used when not needed, can cause more harm than good (examples are suffocation of children in the car, and momentarily blinding the driver, which actually increases the probability of a catastrophic accident).

All in all, the airbag strives to serve a good cause – that of keeping its patrons safe. But just how crucial it will be to road safety can only be answered in due course of time – as the airbag is pitted against the ever-increasing advancement in automotive technology which drives the desire to build cars that relentlessly push the limits of speed and performance.

-by Abhishek Neeli

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