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Siemens Safety Experts Developing Reliable Occupant Sensing System

7 March 2000

Siemens Safety Experts Thrive on the 'Strain' Of Developing the Most Reliable Occupant Sensing System

    DETROIT, March 7 The process of innovating and testing
every available technology for the improvement of occupant safety systems can
put even the best engineers under tremendous strain.  The safety experts at
Siemens Automotive, on the other hand, are using "strain" to develop the most
reliable method of classifying an occupant's weight for government-mandated
passive restraint systems, or "smart airbags."
    During the past three years, Siemens engineers from the company's Safety
Electronics and Restraint Systems division have been developing and fine-
tuning a Weight Classification System (WCS) that employs strain gage based
sensors, a technology that has been widely proven for nearly a century in
commercial/trade scale applications.
    Siemens' WCS system performs to the requirements of the recent
Supplemental Notice of Proposed Rule Making (SNPRM) regulation specified by
the National Highway Traffic Safety Association for installation in 25 percent
vehicles by model year 2003.  The SNPRM requirement represents the first step
toward implementing "smart airbags" in vehicles sold in the United States.
    Siemens' WCS technology has performed so reliably in customer testing that
the company has been awarded a large-volume contract to begin producing the
occupant sensing system in calendar year 2002 for vehicles sold in North
America.
    The key to the system's reliability is the proven strain gage technology,
which is employed by the Siemens WCS in two distinct ways:

    (1)  located in the seat track, at the four corners of the seat, strain
         gage sensors classify the occupant's weight and center of gravity in
         the seat; and,

    (2)  a single strain gage sensor is uniquely integrated into the seat belt
         within 20 millimeters of the seat belt anchor, typically behind the
         b-pillar.  This sensor measures the amount of belt force applied to
         the seat belt when a infant or baby seat is cinched tightly into the
         car seat.

    The seat track sensors and belt force sensor work in tandem to precisely
classify an occupant's weight in order to tailor the airbag system to the
specific needs of the occupant.  The belt force sensor calculates and
compensates for the added strain (weight) pressed into the car seat by an
infant/child carrier when excessively cinched into the car seat.  The belt
force sensor factors out the false weight caused by excessive tightening of
the seat belt, and ensures that the system recognizes the true weight of the
infant/child carrier.
    The WCS electronic control module gathers data from the strain gage
sensors in the track and in the seat belt and processes the sensor inputs in
order to classify an occupant as infant, small child, small adult, medium or
large adult.  The WCS control module interfaces frequently -- at a rate of
once every 250 milliseconds -- with the central airbag control module which,
in turn, determines and controls the deployment of an optimal restraint
system.
    Strain gage technology widely has been used for years in applications
ranging from industrial to highway truck and train scales. "We wanted to begin
with a proven, reliable technology, such as the strain gage, for measuring
force and uniquely package it with our electronics," explained Harald
Lichtinger, Project Leader WCS, Siemens Automotive Safety Electronics and
Restraint Systems division.
    The WCS differs from other sensors in that it can account for that portion
of the occupant's weight that is transferred to the vehicle floor through the
occupant's legs.  From the real weight, the WCS system classifies the occupant
into one of four weight classes:

    1.  "empty" less than 8 Kg;
    2.  "child class," based on the weight of an average six-year old child
        (30 Kg);
    3.  "small adult" class, based on the fifth percentile female (48 Kg);
        and,
    4.  "large adult" class, based on the 50th percentile male.

    Siemens Automotive is a tier-one supplier of automotive and electrical-
electronic systems and components with applications covering gasoline and
diesel powertrain systems, safety and chassis systems, body electronics,
electric motor drives, and driver information systems.  Worldwide sales in
fiscal year 1998/99 totaled $3.6 billion.