Air Bag Control Module: Description and Operation

12-pin Control Unit, Driver Airbag:

As of 09/87 or 01/88, the airbag restraint system has a new control unit with integral reserve power source and voltage transformer. This means that the reserve power source and voltage transformer previously accommodated in separate housings are no longer required.

Function:
The control unit processes the vehicle deceleration during a frontal collision and is rigidly coupled on a support bracket with the transmission tunnel of the vehicle (as before). By means of an integral safety switch which interrupts the ignition circuits for the driver airbag and belt tensioner restraint system during normal driving, the airbag and belt tensioners can only be triggered by an actual acceleration. This prevents any malfunctions.

An acceleration sensor installed in the control unit detects the deceleration acting on the vehicle in the longitudinal direction and sends an appropriately conditioned signal to the trigger switches for evaluation. If the fixed triggering thresholds of both trigger switches are exceeded, the output stages are activated as is appropriate for the circumstances detected via the belt buckle switch (buckle latch in/not in belt buckle) This results in triggering of the system (see table below). If the power supply is interrupted during a collision, the driver airbag can still be triggered within 100 ms, but not the two belt tensioners. The warning lamp lights up if the vehicle voltage is < 9.5 V for longer than 10 s. The lamp goes out at a voltage > 10 V.

The housing and the electrical connections have been designed in such a way as to virtually exclude malfunctions due to electrical interference in the vehicle electrical system caused by the switching of electric consumer units on and off, and by electromagnetic radiation on public highways.

Belt Buckle, Except Coupe:

Belt Buckle, Coupe:

In order to detect whether the buckle latches are inserted in the belt buckles or not, new belt buckles with separate switches and resistors were necessary. This results in the triggering logic listed below.

Release Logic, Driver's Airbag and Belt Tensioner:

Explanation:
In a minor accident, in which the safety belt provides adequate protection, only the belt tensioner is activated when the first release threshold is passed, provided the belt buckle is fastened.

In a more serious accident, whereby the second threshold is passed, the airbag is also activated.

Release Logic, Driver's and Front Pass. Airbag and Belt Tensioner:

Explanation:
In a minor accident, in which the safety belt provides adequate protection, only the belt tensioner is acuvated when the first release threshold is passed, provided the belt buckle is fastened.

If the belt buckles are not fastened or the second release threshold is passed, the driver's and passenger's airbags will be activated instead of, or in addition to, the belt tensioners.