BMW 5 Series Owners & Service Manuals

BMW 5 Series: Automatic tensioner with linear mechanical force limiter

BMW 5 Series G30 2016-2024 Training Manual / Passive Safety Systems / System Components / Automatic tensioner with linear mechanical force limiter

In the event of a front-end or rear-end crash or rollover, the automatic reel blocks the extension of the seat belt in order to restrain the occupants. The belt force limiter limits the load exerted by the belt on the occupants during the accident and the airbags provide the remaining restraining effect.

With the linear system, the belt force is limited after the locking pins have been sheared off by the twisting motion of a torsion bar spring in the seat belt inertia reel.

Reel pretensioners with linear mechanical force limiters are installed in the G30 in the front and in the rear passenger compartment on the left and right.

System Components
G30 Belt tensioner with linear mechanical force limiter

  1. Connection of ignition module, belt tensioner

Automatic tensioner with adaptive force limiter

For the driver and front passenger, an automatic reel with adaptive force limitation is installed. With the aid of a gas generator, there is a changeover from a high to a low power level during the crash, in order to reduce the seat belt restraining forces.

When optimally harmonised with the airbag, it ensures the kinetic energy acting on the occupants is more evenly dissipated for the duration of the crash. Thus lower occupant stress values are achieved.

System Components
G30 Belt tensioner with adaptive force limiter

  1. Connection of ignition module, belt tensioner
  2. Connection of ignition module, adaptive force limiter

Active head restraints, front

The active head restraint is used in the G30 in conjunction with the multifunction seat (OE 456). This is a head restraint with a pyrotechnic actuator that optimizes the distance and height of the headrest in relation to the head if a rear-end collision of sufficient force occurs. This reduces the load on the cervical vertebrae in the event of a rear-end collision. The head restraint is activated early, even prior to backwards displacement of the occupant's head.

The active head restraint reduces the load in the cervical vertebrae in the event of a rear-end collision.

For the vehicle occupants therefore, correct adjustment of the head restraint and the distance of the head from the head restraint is of crucial importance.

In the event of a rear-end collision, the active head restraint reduces the distance between the head and the head restraint before the occupants are displaced backwards. This reduces the danger of injury to the cervical vertebrae, even if a minor accident occurs.

System Components
G30 connection active head restraint, front

  1. Connection active head restraint

Seat or head restraint covers and/or accessories that could impair the protective effect must not be mounted on the head restraints.

Safety battery terminal

If the ACSM detects a crash of sufficient force, the safety battery terminal is activated.

Even though the safety battery terminal has been disconnected, a voltage supply to all safety-relevant consumers such as hazard warning lights, interior light, airbag and telephone (including emergency call) is still ensured.

System Components
G30 Safety battery terminal (SBK)


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