Electric Motor Driven Reel: Notes

Debuting in the F01/F02, an electric motor driven reel (EMA) is used for the seat belt. The electric motor driven reel is paired with the multifunction seat.

The electric motor driven reel reduces seat belt slack when fastening the seat belt using low retracting force as soon as the doors are closed. Removing the belt slack ensures that the seat belt fits the driver or front passenger. Thus better restraining action can be provided in the event of a crash.

Another advantage of the electric motor driven reel is the pre-tensions to the occupants before a possible accident with increased retracting force, thus also reducing the incidence of slipping out of the belt and the risk of submarining.

The dynamic driving control sensors in the ICM (Integrated Chassis Management) record data such as longitudinal acceleration and lateral acceleration, yaw rate, etc. The ICM passes on the data via the PT-CAN to the two EMA control units. The DSC also delivers information such as speed and brake pressure. The ACSM sends a message about the status of the belt contact to the two EMA control units.

From this data, the EMA control units calculate whether there is a critical driving situation, e.g. vehicle oversteer and as a result activates the electric motor, which pretensions the seat belt.

If there is now an accident with corresponding severity, the belt tensioner is also triggered and the seat belt fastened securely to the occupants.

The pre-tensions of the seat belt can reduce the force on the occupants in the event of an accident.

Fig 1: Identifying Electric Motor Driven Reel Seat Belt

Courtesy of BMW OF NORTH AMERICA, INC.