Im­pact!

In a crash, this is the ex­plo­sion you’ll want to hear

Herald Sun - Motoring - - How Stuff Works - Stu­art Martin

THE most com­mon airbag is the one mounted in the cen­tre hub of the steer­ing wheel but bags are now in­cluded for the pas­sen­ger (in front and to the side) as well as side and cur­tain airbags for the rear-out­board pas­sen­gers in high­end lux­ury cars. There are even knee airbags for front oc­cu­pants.

The airbag— most com­monly made from ny­lon— is packed away with lu­bri­cat­ing powder in the hub be­neath the cov­er­ing trim (which has seams on the in­side to al­low it to split when re­quired).

The airbag is linked to nu­mer­ous sen­sors— im­pact sen­sors and ac­celerom­e­ters among oth­ers— to recog­nise de­cel­er­a­tion on im­pact and trig­ger the car’s safety sys­tems and de­ploy the sup­ple­men­tal re­straint sys­tems.

The airbag sys­tem uses ni­tro­gen gas, which is fired by a solid-pro­pel­lant in­fla­tor sys­tem, to det­o­nate the bag from the steer­ing wheel hub in 0.05sec and at up to 300km/h, bal­loon­ing up in front of the driver’s head and torso and slowly de­flat­ing to lessen the oc­cu­pant’s im­pact on hard in­te­rior sur­faces such as the dash­board or steer­ing wheel.

Early airbags were some­times la­belled as do­ing more harm than good (in some cases caus­ing death) be­cause of their ex­ces­sive force of de­ploy­ment.

The more mod­ern sys­tems match the airbag force with the crash im­pact and whether the oc­cu­pant is us­ing a seat belt.

For comic ef­fect, Hol­ly­wood would have you be­lieve they stay in­flated for comic ef­fect but most airbags de­flate shortly af­ter the im­pact has dis­si­pated, al­though some side-cur­tain airbags will re­main in­flated for longer to main­tain pro­tec­tion in a rollover.

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