Side airbags utilize a different type of system for
deployment. They are usually packaged into the backrest of the front seats and
deploy by splitting the seam of the covering.
Though a few manufacturers place the bag into the center post between
the doors. The system is set up with a pressure sensor in each door and each
door has a sealed covering inside the inner door trim to maintain it as a
sealed cavity. When the door gets hit, the change in pressure from the outer
panel crushing sends the signal to the ACU, which then sends the trigger signal
to the appropriate airbag(s). The airbag
will then deploy in a manner similar to how the front airbags do.
Some manufacturers, such as Saab,
have developed a two-stage side airbag where the lower or torso section of the
bag deploys first, and then a split second later the upper section deploys. This
is intended to prevent the whipping motion that would cause the head to strike
the side door.
Certain
vehicles use a head curtain airbag in place of or sometimes in conjunction with
the seat-mounted side airbag. Head curtain airbags deploy from the same signal
as a side airbag from the pressure sensor in the door. They also deploy in a similar method, but deploy
downward from the inside of the roof-rail. Head curtain airbags can offer an
additional protection if the vehicle is equipped with a rollover sensing
system. If so equipped, the head curtain airbag can deploy in the event of a
rollover to prevent injury, and can possibly even prevent ejection from the
vehicle.
Gyroscopes and accelerometers that
determine the angle of inclination, the speed and direction of travel, and send
their signals to the ACU actuate rollover systems. This in turn, analyzes the signals and
deploys the airbag or bags if needed. These sensors are the same ones, which
actuate a fuel shutoff in the event of a rollover. Usually on four-wheel drive
vehicles there is a manual switch to shut off the rollover system if the
operator is going off-roading.
There are
also some vehicles that are equipped with either knee or torso frontal airbags.
These systems work similar to and read the same signals as the front airbags.
Seat-belt
pretensioners are an important part of most airbag systems. When the trigger
signal is sent to the airbag, the same signal goes to the seat-belt
pretensioners for the front seat occupants. Each seatbelt unit has a small tube,
usually about six inches long with an actuating charge at the lower end, attached
to the recoil mechanism on the seat belt retractor. When the unit receives a
trigger signal, the charge goes off, locking the belt and propelling the lock
up the tube, which pulls in three to four inches of slack from the seatbelt and
locking it in place to restrain the person occupying that seat.
When locked, the seat belt may be
pulled so tight that it might have to be cut it if the latch cannot be
released. While working as a Saab technician, I had to remove and replace a
seat belt unit under warranty. The defective unit was to be returned after
replacement, but we were not allowed to ship it charged, so I detonated it for
shipment. I have to say that it was about as loud as setting off an M80
firecracker. I also detonated an airbag
for the same reason.
To detonate an airbag, Saab
supplied an actuator button which had two leads attached to it, one to connect
to a car battery, and the other about fifteen feet long to connect to the
airbag. We placed the airbag backside down on the pavement outside the building,
attached the leads and detonated it. The bag actually jumped about four to five
feet into the air and the sound was extremely loud. My only thought was, ‘did I
really want something like that going off in my face?’ However, considering the possible alternatives
in the event of a serious crash, I guess I would appreciate it after all.
Next week
we will review anti-whiplash head restraints. Some information for this article was obtained from www.wikipedia.org.
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