System functions

When the seat belt is fastened (door closed), the control unit for the electrically motorized reel on the left (EMALI control unit) or the control unit for the electrically motorized reel on the right (EMARE control unit) activates the drive once over a certain period of time. With the help of the electric motor, the seatbelt strap is rolled up, thus removing the belt slack.

In critical driving situations or in the event of a possible accident, the control unit also activates the drive. The duration is set in such a way that the drive is activated by the control unit until a collision occurs or until a critical driving situation ends.

To calculate whether there is a critical driving situation (e.g. vehicle oversteering), the two control units (EMALI control unit and EMARE control unit) use the data from the following systems:

• Integrated Chassis Management (ICM)

  The ICM control unit provides the systems in the entire vehicle with the dynamic driving state in the form of signals (e.g. data such as lateral and longitudinal acceleration, yaw velocity).

• Dynamic Stability Control (DSC)

  The DSC control unit delivers information such as the speed and brake pressure.

• Crash safety module (ACSM stands for "Advanced Crash Safety Module")

  The crash safety module sends a message with the status of the seat belt buckle contacts.

Fig 1: Crash Safety Module - Circuit Diagram

Courtesy of BMW OF NORTH AMERICA, INC.