ACSM: Crash Safety Module

The Crash Safety Module (ACSM) is the control unit for the safety system.

The 4th generation Crash Safety Module (ACSM) with its integrated sensor system incorporates four internal sensors; among the parameters that the system employs for its calculations of vehicle dynamics and impact recognition are the following:

• Longitudinal acceleration and vehicle inclination in longitudinal direction
• Lateral acceleration and vehicle inclination in transverse direction
• Yaw rate (rotation about the vertical axis)
• Roll rate (rotation around the longitudinal axis)

Following start, the Crash Safety Module (ACSM) initiates a self-test. During this time, the airbag indicator light lights up (approx. 3 to 5 seconds). When the safety system is functional, the airbag warning lamp goes out.

All the gas generators and sensors in the safety systems are directly connected with the Crash Safety Module (ACSM). The Crash Safety Module (ACSM) evaluates the acceleration data (longitudinal and lateral acceleration) of the sensors and thus determines the direction and severity of the accident in the event of a crash. 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.).

In the event of a crash, the Crash Safety Module (ACSM) determines whether activation is required and which gas generators (belt tensioner, airbags, etc.) should be ignited.

On vehicles with an internal-combustion engine, the Crash Safety Module (ACSM) also deactivates the electric fuel pump. On electric vehicles the Crash Safety Module (ACSM) also switches off the high-voltage electrical system.

The restraint systems are triggered only when 2 independent sensors detect the corresponding threshold. The Crash Safety Module (ACSM) transmits 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 instance, the Body Domain Controller (BDC) switches on the interior lamps and the hazard warning flashers. The Crash Safety Module (ACSM) transmits a signal to the Telematic Communication Box (TCB) through a direct line. The TCB then automatically transmits an emergency call that includes the location of the vehicle. When the restraint systems are activated, certain data is written to a read-only data memory in the Crash Safety Module (ACSM). 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 (ACSM) must be replaced.

For the seat belt warning, the signals of the belt buckle switch are picked up separately. The signals of the seat occupancy mat are registered for seat occupancy detection via the local interconnect network bus in the US version.

The Crash Safety Module (ACSM) contains an ignition capacitor. If the voltage supply is interrupted in the event of a crash, the ignition capacitor acts as an energy reserve for the Crash Safety Module (ACSM).

The following illustration shows an example of a Crash Safety Module (ACSM) of the 4th generation with integrated sensor system.

Courtesy of BMW OF NORTH AMERICA, INC.