Page 342 - 05. Subyek Teknik Mesin - Automobile Mechanical and Electrical Systems Automotive Technology Vehicle Maintenance and Repair (Vehicle Maintenance Repr Nv2) by Tom Denton

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324 Automobile mechanical and electrical systems

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Figure 3.133 Air bag deployment: sequence of events in a frontal impact

4 At 40 ms after impact, the air bag will be fully infl ated and the driver’s
momentum will be absorbed by the air bag.
5 About 120 ms after impact, the driver will be moved back into the seat and
the air bag will have almost defl ated through the side vents, allowing driver
visibility.

Passenger air bag deployment events are similar to the previous description. The
position is different but the basic principle of operation is the same. The positions
of the side and rear air bags are shown in Figs 3.134 and 3.135 , and the ECU in
Fig. 3.136 .
A block diagram of an air bag circuit is shown in Fig. 3.137 . A digitally based
system, using electronic sensors, has about 10 ms at a vehicle speed of 50 km/h,
to decide whether the restraint systems should be activated. In this time, about
10 000 computing operations are necessary. Data for the development of these
algorithms is based on computer simulations, but digital systems can also
remember the events during a crash, allowing real data to be collected.
Taking the ‘slack’ out of a seat belt in the event of an impact is a good
Safety fi rst
contribution to vehicle passenger safety. The decision to take this action is the
Taking the ‘slack’ out of a seat belt in same as for the air bag. The two main methods are:
the event of an impact contributes to
●
passenger safety. spring tension
pyrotechnic.
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When the explosive charge is fi red, the cable pulls a lever on the seat belt reel,
which in turn tightens the belt ( Fig. 3.138 ). The unit must be replaced once
deployed. This feature is sometimes described as anti-submarining.