Home' Australian Automotive Aftermarket Magazine : Australian Auto Aftermarket e-Zine - Feb 13 Contents AUTOMOTIVE AFTERMARKET MAGAZINE FEBRUARY 2013 19
This then enables the control unit to
determine the direction of the impact and its
severity and trigger the deployment of
appropriate restraint systems.
Airbags are designed not to activate
during sudden braking or while driving on
rough or uneven pavement.
In fact, the most severe braking is only a
small fraction of the deceleration necessary
to activate the airbag system.
Modern airbags are designed to inflate
with variable volume depending on the
severity of the crash.
Many of these variable volume airbags use
multi stage inflators that deploy less forcibly
in moderate crashes than in very severe
Driver and passenger airbags inflate in
frontal crashes protecting their heads from
hitting the steering wheel, instrument panel
or other parts of the vehicle's interior.
For belted drivers, airbags reduce
fatalities by about 25 percent and serious
head injuries by 60 percent.
Frontal airbags deploy in around 50
milliseconds; about half the time it takes to
blink an eye.
Frontal airbags are an integral part of the
steering wheel system or instrument panel
and are typically 30 to 60 litres in size --
about the size of a large beach ball when fully
Curtain airbags form a cushion between
the occupant and side glass protecting the
occupant's head from striking the side of the
car or intruding vehicles in side impact
Side airbags are usually located in the
backrest of the seat and inflate between the
door and the seat occupant, keeping the
occupant away from the impact zone and
dampening the blow from the intruding
vehicle in a side impact.
Due to the close proximity of occupant to
a side impact, side airbags are inflated four
times faster (around 12 milliseconds) than
Knee airbags are designed to reduce leg
injury which, although not fatal, often cause
lifelong injury and represent about 23
percent of active life years lost in frontal
The knee airbag also provides benefits for
the head and chest by keeping the occupant
in the proper position for maximum
protection afforded by the front airbag (i.e.
New airbag applications expected in the
market in the forthcoming future include seat
cushion airbags which inflate under the driver
and passengers knees lifting the knees to
prevent submarining and a front centre
airbag to prevent front passengers from
colliding with each other during side impacts
ACTIVE HEAD RESTRAINTS
An effective method to minimise the load
applied to an occupant's neck in a rear
impact is to quickly hold the head in position
so it's not thrown rearward.
Active head restraints are designed to
During normal driving, the active head
restraints are positioned as far forward as
possible without detracting from comfort.
If the vehicle is hit from behind, the force
with which the occupant presses into the
seatback is instantaneously used to move the
The head restraint's forward movement
prevents excessive rearward inclination of the
neck, greatly mitigating the load applied to
INFLATABLE SEAT BELTS
Auto companies have begun introducing
inflatable seat belts to help compensate for
the inability to install airbags in the rear seat
Ford and Lexus introduced this feature
first in 2012 and it is expected to be released
by Mercedes-Benz in its new generation S
class in 2013.
Should the crash sensors detect a severe
frontal impact; the airbag control unit will
trigger deployment and inflation of the seat
belt.A gas generator then inflates the multi-
layered belt strap, with Velcro seams, to
nearly three times its normal width.
The resulting larger surface area is able
to better distribute the force acting on the
seat occupant, thereby reducing the risk of
The seat belt does not need to expand as
rapidly as an airbag and a short time after
inflation the seat belt expels the gas through
the strap fabric and deflates to allow the
passenger to exit the vehicle.
It is claimed that this seat belt is able to
reduce the risk of injury to rear passengers in
a head-on collision by lessening the strain
placed on the ribcage.
Earlier this year Volvo announced the
introduction of the world's first pedestrian
airbag for its V40 model.
The motivation for introducing this feature
is the reduction of traffic fatalities involving
pedestrians, which in Europe and USA
number around 13 percent and 25 percent
while in China, far higher numbers of
pedestrians are injured.
The most serious head injuries involving
pedestrians are caused by the hard structure
under the hood panel, the windscreen's lower
edge and the A-pillars.
Seven sensors embedded in the front of
the car transmit signals to a control unit.
When the car comes into contact with an
object the control unit evaluates the signals
and, if it registers what it interprets as a
human leg, the pedestrian airbag is deployed.
The bonnet hinges are each equipped
with pyrotechnic release mechanisms which,
when the system is activated, pull out a pin
to release the rear of the bonnet panel.
At the same time, the airbag is activated
which starts filling with gas and during the
inflation sequence raises the hood.
It is lifted 10 centimetres and stays in the
The added gap between the hood and the
hard components in the engine compartment
gives space for the bonnet to deform,
creating a dampening effect when it is hit by
In its inflated position, the airbag covers
the entire windscreen wiper recess, about
one-third of the windscreen and the lower
part of the A-pillars.
The entire sequence from activation of the
system to full inflation takes a few
hundredths of a second.
The system is active at speeds between
20kph and 50kph as 75 percent of all
accidents involving pedestrians take place at
up to 40kph.
Acknowledgement of assistance in
preparation of this article to Mercedes-Benz,
Volvo, Mazda, Automotive Safety Council,
Volkswagen, Autoliv and TRW.
Mercedes Benz Inflatable Seat Belt
Volvo Pedestrian Airbag
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