ACSM: Crash safety module

The Crash Safety Module (ACSM) is the control unit for the safety system. No sensors are installed in the Crash Safety Module. The Crash Safety Module performs a self test after the ignition is switched on. During this time, the airbag indicator light lights up (approx. 3 to 5 seconds). The airbag indicator lamp goes out as soon as the safety system is ready for operation.

All gas generators and sensors of the safety system are connected directly to the Crash Safety Module. The Crash Safety Module evaluates the acceleration data (longitudinal and lateral acceleration) of the sensors and thus determines the direction and severity of the accident in a collision. Comprehensive tests are used to define triggering thresholds for all possible types of accident. This results in different trigger thresholds for activation of the various restraint systems (airbags, seatbelt tensioners, etc.). When an impact occurs the Crash Safety System decides whether deployment is required and which gas generators (belt tensioners, airbags, crash-active head restraints, etc.) must be activated. The Crash Safety Module also triggers the safety battery terminal.

The restraint systems are triggered only when 2 independent sensors detect the corresponding threshold.

The Crash Safety Module sends a message to other bus users when the restraint systems are triggered. The individual control units execute various functions according to the severity of the accident. For example, the footwell module (FRM) or front electronic module (FEM) or the Body Domain Controller (BDC) activates the interior lights and hazard warning flashers. The Crash Safety Module transmits a signal to the Combox over a direct wire. The Combox automatically initiates an emergency call which also includes the location of the vehicle.

When the restraint systems trigger, certain data are written to a read only memory in the Crash Safety Module. The data is relevant to accident research (no access for service). After 3 crash signals, the data memory is full. The airbag warning lamp lights up. The Crash Safety Module must be replaced.

For the seat belt warning, the signals of the belt buckle switch are picked up separately.

The crash safety module contains an ignition capacitor. If the power supply is interrupted in the event of an impact, the ignition capacitor serves as an energy reserve for the crash safety module.

Fig 1: Identifying Crash Safety Module And Plug Connection

Courtesy of BMW OF NORTH AMERICA, INC.