X Series E83 X3 2.0i (N46) OFFRD
Mechanical components in the multiple restraint system (MRS):
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Seat belts
The seat belts are the primary restraint system for all occupants. A lap and diagonal automatic belt is fitted on
each seat.
If there is a very severe impact, the seat belt strap may cause injuries to the chest of the person it is securing. To
minimise this risk, the front seat belts are fitted with belt force limiters as standard. The belt force limiters allow
the seat belt to be unrolled in a controlled fashion if the belt force exceeds a critical value. The risk of injury due
to the belt force acting on the body is therefore reduced.
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Passive knee protection (US version)
Not every state in the USA has a requirement for seat belts to be worn. Therefore, the E83 also has additional
plastic impact protection on the driver and passenger sides. In the event of an impact, the passive knee
protection provides a flat support for the lower leg, especially if the front passengers are not wearing their seat
belts. This causes the forwards movement of the upper body to be controlled towards the relevant airbag (driver
or passenger airbag).
System functions
The following system functions of the multiple restraint system (MRS) are described:
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Triggering the multiple restraint system
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Emergency call (EURO version)
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Emergency call (US version)
Triggering the multiple restraint system
Extensive testing has allowed the triggering thresholds to be determined for all possible types of accidents.
Various triggering thresholds were set for activating the different restraint systems:
The multiple restraint system comprises:
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Belt tensioners
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Front airbags
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Side airbags
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Head airbags
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Safety battery terminal
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Electric fuel pump
The following examples illustrate how the various restraint systems are triggered:
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Head-on collision
The belt tensioners, the front airbags and the safety battery terminal are triggered if the head-on collision is
so severe that the triggering threshold of the MRS control unit is exceeded.
The belt tensioners have a lower triggering threshold than the front airbags. The belt tensioners are
therefore triggered earlier.
If the seat-belt-lock switch is faulty, the triggering threshold for the front airbag on this side is lowered. Even
though there is a fault message, the MRS control unit will try to trigger the belt tensioners.
If the seat-occupancy detector is faulty, the control unit assumes that the passenger seat is occupied. The
restraint systems are activated.
The electric fuel pump is switched off. An automatic emergency call is initiated (only in vehicles with the
relevant equipment fitted).
SBT Multiple restraint system 4 E83
BMW AG - TIS
09.02.2013 04:27
Issue status (12/2007) Valid only until next DVD is issued
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