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`[19]
`United States Patent
`5,474,327
`[11] Patent Number:
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`Dec. 12, 1995
`Schousek
`[45] Date of Patent:
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`llilllIlilllllllllllllllllllllllllllllllllIlllilllll|||||||||||||||||I|||I|
`USOOS474327A
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`[54] VEHICLE OCCUPANT RESTRAINT WITH
`SEAT PRESSURE SENSOR
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`Attorney, Agent, or Firm—Mark A. Navarre
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`[75]
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`Inventor: Theresa J. Schousek, Kokomo, Ind.
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`[57]
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`ABSTRACT
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`[73] Assignee: Delco Electronics Corporation,
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`Kokomo, Ind.
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`[21] Appl. No.: 325,718
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`Filed:
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`[22]
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`Jan. 10, 1995
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`Int. Cl.6 ..................................................... B60R 21/32
`[51]
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`280/735; 180/268; 280/730.1
`[52]
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`[58] Field of Search ................................. 280/730.1, 732,
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`280/735; 180/268
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`[56]
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`References Cited
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`U.S. PATENT DOCUMENTS
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`5,074,583 12ll991 Fujita et a1. ................ 280/735
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`5,161,820
`11/1992 Vollmer
`...........
`.. 280/730.1
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`5,172,790 12/1992 Ishikawa et a1. .......... 180/268
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`5,232,243
`8/1993 Blackburn et a1.
`..................... 280/732
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`OTHER PUBLICATIONS
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`Alps Product Brochure (publication date unknown).
`Interlink Product Brochure (publication date unknown).
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`Primary Examiner—Kenneth R. Rice
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`An air bag restraint system is equipped with seat occupant
`sensing apparatus for a passenger seat which detects both
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`infant seats and adults and distinguishes between rear and
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`forward facing infant seats. Air bag deployment is inhibited
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`when an occupied rear facing infant seat is present. The
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`sensing apparatus comprises eight variable resistance pres-
`sure sensor in the seat cushion. The response of each sensor
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`to occupant pressure is monitored by a microprocessor
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`which calculated total weight and weight distribution. The
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`weight is used to discriminate between an occupied infant
`seat, an adult and no occupant. The weight distribution is
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`used to distinguish between forward and rear facing infant
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`seats. Another embodiment uses the occupant sensing along
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`with seat belt fastening detection to indicate when a seat is
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`occupied and the belt is not fastened.
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`11 Claims, 4 Drawing Sheets
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`132
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`INDICATOR
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`A
`_I
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`*-
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`CONTROL
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`CIRCUIT
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`Page 1 of 9
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`Hyundai Exhibit 1010
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`Page 1 of 9
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`Hyundai Exhibit 1010
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`

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`US. Patent
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`Dec. 12, 1995
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`Sheet 1 of 4
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`5,474,327
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`O
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`24
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`u
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`g
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`2°
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`FAULTINDICATOR
`x
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`18
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`AIR BAG
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`DEPLOYMENT
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`10J
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`30
`28
`26
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`--»
`”M.
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`g
`8 W.
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`26'
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`E
`30
`23
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`26
`5
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`34
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`2
`IMM-
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`)m
`26
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`i' 2230 23
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`SIR MODULE i SEAT OCCUPANT \ 12
`i
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`16
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`DECISION'
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`DETECTOR
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`INDICATOR .
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`FIG - 6
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`CONTROL ._=_
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`CIRCUIT =:
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`Page 2 of 9
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`

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`US. Patent
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`Dec. 12, 1995
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`Sheet 2 of 4
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`5,474,327
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`Page 3 of 9
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`Page 3 of 9
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`

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`US. Patent
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`Dec. 12, 1995
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`Sheet 3 of 4
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`5,474,327
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`62
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`FIG — 5A
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` LESS
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`THAN ONE
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`SECOND
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`NO
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`SAMPLE EACH SENSOR
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`FORCE = CALIBRATION - SAMPLE
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`64
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`66
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`CALCULATE TOTAL WEIGHT PARAMETER
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`‘38
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`CALCULATE CENTER OF WEIGHT
`70
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`76
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`72
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`8 I
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`Page 4 of 9
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`DEPLOY DECISION
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`MAx INFANT SEAT
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`THRESHOLD
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`TOTA ISEIG
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`* SEAT EMPTY
`LW HT‘
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`NOT DEPLOY DECISION
`THRE§HOLD
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`INFANT SEAT OR
`SMALL CHILD
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`D ETECTED
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`IS
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`CENTER OF
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`‘ INFANT SEAT DETECTED
`WE'GggLngiflggD OF
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`NOT DEPLOY DECISION
`REFERENCE
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`INFANT SEAT DETECTED
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`' DEPLOY DECISION
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`Page 4 of 9
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`ARE ALL 5
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`DECISIONS THE
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`SAME
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`102
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`CURENT DECISION IS NOW
`THE PREVIOUS DECISION
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`US. Patent
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`Dec. 12, 1995
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`Sheet 4 of 4
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`5,474,327
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`90
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`FIG - 5B
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`STORE DECISION IN ARRAY
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`94
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`INCREMENT DECISION COUNTER
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`HAVE
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`LESS THAN
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`5 DECISIONS BEEN
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`STOORED
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`92
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`YES
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`CLEAR DECISION COUNTER
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`TRANSMIT DECISION TO
`SIR MODULE
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`IS
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`ER
`DECISIISNLLIHOY
`UNT
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`> MAXALLOWED UNSTABLE _READ’INGS
`‘
`TRANSMIT FAULT TO
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`SIR MODULE
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`COUNTER
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`104
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`CLEAR FAULTY DECISION
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`CENTER
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`TRANSMIT PREVIOUS DECISION
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`TO SIR MODULE
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`INCREMENT FAULTY DECISION COUNTER
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`CLEAR FAULTY DECISION
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`RETURN
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`Page 5 of 9
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`Page 5 of 9
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`

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`1
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`VEHICLE OCCUPANT RESTRAINT WITH
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`SEAT PRESSURE SENSOR
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`FIELD OF THE INVENTION
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`This invention relates to occupant restraints for vehicles
`and particularly to a restraint system having seat sensors to
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`identify adult and infant seat occupancy.
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`BACKGROUND OF THE INVENTION
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`The expanding use of supplemental inflatable restraints
`(SIRs) or air bags for occupant protection in vehicles
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`increasingly involves equipment for the front outboard pas—
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`senger seat. The driver side air bag has been deployed
`whenever an imminent crash is sensed. The position and size
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`of the driver is fairly predictable so that such deployment
`can advantageously interact with the driver upon a crash.
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`The passenger seat, however, may be occupied by a large or
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`a small occupant including a baby in an infant seat. It can not
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`be assumed that a passenger of any size is at an optimum
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`position (leaning against or near the seat back). An infant
`seat is normally used in a rear facing position for small
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`babies and in a forward facing position for larger babies and
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`small children. While the forward facing position approxi-
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`mates the preferred position for air bag interaction, the rear
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`facing position places the top portion of the infant seat close
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`to the vehicle panel which houses the passenger side air bag.
`In the latter event, it may be desirable to prevent deployment
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`of the air bag. Similarly, if a passenger in the seat is leaning
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`forward, it may be desirable to prevent air bag deployment.
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`It has been proposed to use a magnet or other special
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`attachment on an infant seat and a special sensor in the seat
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`or panelboard which detects the attachment and allows
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`determination that an infant seat is present and is positioned
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`in a particular way. Of course that arrangement is operable
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`only with the specially equipped infant seats; other infant
`seats and passengers are not serviced. A separate sensing
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`system would have to be employed to detect the position or
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`presence of small children or adults.
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`Seat belt restraint systems can also benefit by information
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`about the presence of passengers. For example, by monitor-
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`ing which belts are buckled and which seats are occupied, a
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`warning display can inform the driver that some seat or a
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`particular seat is occupied and the belt is not utilized. Where
`an infant seat is in a vehicle seat and the infant seat is
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`occupied, this seat also should be belted in and the wanting
`system employed to detect a failure to meet this condition.
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`SUMMARY OF THE INVENTION
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`It is therefore an object of the invention to detect a full
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`range of vehicle passengers including occupied infant seats
`supported on a vehicle seat. Another object is to detect such
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`passengers and to discriminate between rear facing and front
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`facing infant seats. Another object is to control a restraint
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`system in accordance with information developed by detect-
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`ing the presence of occupants and the positions of occupants.
`A SIR system, as is well known, has an acceleration
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`sensor to detect an impending crash, a micro-controller to
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`process the sensor signal and to decide whether to deploy an
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`air bag, and a deployment unit fired by the micro-controller.
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`An occupant detection system can determine if an occupant
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`or infant seat is positioned in a way to not benefit from
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`deployment,
`and then signalling the micro-controller
`whether to allow deploying the air bag.
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`A large array of many hundreds of pressure sensors in or
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`on a vehicle seat cushion can reveal a pressure profile which
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`is distinctive for each type of seat occupant and can also
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`measure the weight of the occupant. An adult has one kind
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`of profile, a front facing infant seat has another, and a rear
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`facing infant seat has still another. These profiles indicate
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`that the “center of gravity” or center of weight distribution
`is distinctive for each of these three conditions. Such an
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`array of sensors, however, is very expensive and the elec-
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`tronic equipment for servicing the array and analyzing the
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`pressure information is also expensive.
`It has been found, however, that a very small number of
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`sensors, judicially located in the seat, can garner suflicient
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`pressure and distribution information to allow determination
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`of the occupant type and infant seat position. This informa-
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`ment. Two sets of four sensors symmetrically arranged on
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`either side of a seat centerline are adequate to gather the
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`pressure data. In each set, two sensors are situated near the
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`centerline and near the back of the seat cushion, the other
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`two are further forward and outboard, one on the wing of the
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`cushion and the other just inboard of the wing. Each sensor
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`is a very thin resistive device, having lower resistance as
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`pressure increases. A microprocessor is programmed to
`sample each sensor, determine a total weight parameter by
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`summing the pressures registered by the several sensors, and
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`determine the center of weight distribution from the sum of
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`the products of each sensed pressure and its distance from
`the rear of the seat, and dividing the product by the total
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`weight.
`Based on the minimum weight of an occupied infant seat
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`(about 10 pounds) and the maximum weight of an occupied
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`infant seat (50 pounds), maximum and minimum thresholds
`are calibrated, and those are compared to the measured total
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`weight parameter to determine whether the vehicle seat is
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`holding an occupied infant seat, a larger person, or has no
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`occupant. The center of weight distribution is used to
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`determine the position of an infant seat, a rear facing seat
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`having a weight center much further forward than a forward
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`facing seat. Given the occupant information, it can then be
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`decided whether to deploy the air bag during a crash. The
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`decision depends on the desired results which may be
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`dictated by the legal requirements where the vehicle is
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`operated. Typically, the air bag deployment will be pre-
`vented at least in the case of an occupied rear facing infant
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`seat.
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`A sampling of the sensors and a deployment decision is
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`made periodically, say each second, and the system is
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`monitored for failure by testing consistency of the decisions.
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`If five consecutive decisions are the same, that decision is
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`validated and signalled to the SIR microcontroller; if the five
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`decisions are not the same, a failure is registered and the
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`previous validated decision is maintained. In any event, a
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`signal to enable or disable deployment is issued every five
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`seconds. However the failures are counted and if a large
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`number of failures occur, a failure signal is sent to the
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`micro-controller.
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`Another use of the seat pressure profile sensor in a
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`restraint system is for a seat belt warning indicator to advise
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`the vehicle operator whether any seat is occupied either by
`a baby in an infant seat or by a larger person, and the seat
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`belt for that seat is not fastened.
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`BRIEF DESCRIPTION OF THE DRAWINGS
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`The above and other advantages of the invention will
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`become more apparent from the following description taken
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`Page 6 of 9
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`

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`5,474,327
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`3
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`in conjunction with the accompanying drawings wherein
`like references refer to like parts and wherein:
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`FIG. 1 is a schematic diagram of a SIR system and an
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`associated seat sensor system according to the invention;
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`FIG. 2 is a top view of a vehicle seat cushion having
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`pressure sensors positioned on the seat, according to the
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`invention;
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`FIG. 3 is an outline elevational view of a vehicle seat
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`containing a rear facing infant seat illustrating an application
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`of the invention;
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`FIG. 4 is an outline elevational view of a vehicle seat
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`containing a forward facing infant seat illustrating an appli-
`cation of the invention;
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`FIGS. 5a, 5b and, in combination, comprise a flow chart
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`representing a computer program for seat occupant detection
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`and SIR control according to the invention; and
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`FIG. 6 is a schematic diagram of a seat pressure sensor
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`and seat belt system according to another embodiment of the
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`invention.
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`10
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`15
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`20
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`DESCRIPTION OF THE INVENTION
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`4
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`side of a seat center line and a second set 42 is symmetrically
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`disposed on the left side of the center line. In each set, a
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`sensor at position A is close to the centerline and near the
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`back of the cushion, a sensor at position B is outboard of
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`position A and further back. A third sensor 28 at position C
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`is forward of position A and near the wing 37, and a fourth
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`sensor at position D is on the wing 37 and forward of
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`position C. Although weight distribution of an occupant may
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`be assumed to be approximately balanced between left and
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`right sides of the seat, having sensors on both sides of the
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`seat allows good data collection and measurement of total
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`weight and distribution in the event of unbalance. Weight
`distribution is centered somewhere within the confines of the
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`sensor grouping and is calculated with reference to an
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`arbitrary datum line 44 extending transversely of the seat.
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`The particular center of weight distribution is determined by
`calculating the product of each measured sensor response
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`and the sensor distance SD from the datum line 44, summing
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`the products, and dividing the sum by the total of all the
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`measured weights. In practice, it is found that the center of
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`weight varies greatly depending on the type of occupant and
`whether an infant seat faces forward or rearward.
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`In FIG. 3, a vehicle seat 46 having a bottom cushion 36
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`instrumented according to the arrangement of FIG. 2, sup-
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`ports an infant seat 48 facing to the rear, which is the
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`preferred position for small babies. Seat belts for securing
`the infant seat are not shown. The top or head portion 50 of
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`the infant seat 48 extends toward the front of the passenger
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`compartment and is spaced from the vehicle instrument
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`panel 52. FIG. 4 shows the same infant seat 48 facing
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`forward and the head portion leans against the seat back. It
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`is apparent by comparison of the FIGS. 3 and 4 that the
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`center of gravity of the rear facing infant seat is much further
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`forward than the forward facing seat, and experimental data
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`supports that conclusion. Adult occupants, when seated
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`normally, have a center of gravity near the rear of the seat.
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`The seat pressure sensor locations are selected to detect
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`the difference of center of gravity of the rear and forward
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`facing infant seats. In FIG. 2 the positions A and B mainly
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`reflect the adult occupant presence and the positions C and
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`D mainly reflect the infant seat presence. While the sensors
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`are localized and do not actually weigh the whole person or
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`infant seat,
`they can measure weight parameters which
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`together represent the total weight and can be empirically
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`related to the total weight, and in the same way the center of
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`weight distribution calculations can approximate the real
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`center of gravity positions well enough to clearly distinguish
`between forward and rear facing infant seats.
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`The sensors are preferably located just beneath the seat
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`cover and some pressure is exerted on the sensors by the seat
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`cover. At the time of vehicle manufacture, the sensors are
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`calibrated by measuring each sensor voltage for an empty
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`seat condition and those calibration voltages are stored.
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`When weight measurements are made by a particular sensor,
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`the current voltage is read and subtracted from the calibra-
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`tion voltage. The difierence voltage then is a function of the
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`pressure exerted on the sensor and is empirically related to
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`actual occupant weight. That is, the sum of measured voltage
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`difierences is a weight parameter which represents occupant
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`weight and the value of that sum is empirically determined
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`for critical threshold values which are used in determining
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`the occupant type. These values are, for example, 50 pounds
`for the maximum weight of an occupied infant seat, and 10
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`pounds for the minimum weight of an occupied infant seat,
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`allowing a range of 5 to 10 pounds for seat weight and a
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`range of 5 to 40 pounds for baby weight. Thus by selecting
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`voltage values for these two thresholds a distinction can be
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`25
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`30
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`Referring to FIG. 1, a SIR system includes a SIR module
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`10 coupled to a seat occupant sensing system 12. The SIR
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`module 10 includes an accelerometer 14 mounted on the
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`vehicle body for sensing an impending crash, a micropro-
`cessor 16 for receiving a signal from the accelerometer and
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`for deciding whether to deploy an air bag. An air bag
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`deployment unit 18 is controlled by the microprocessor 16
`and fires a pyrotechnic or compressed gas device to inflate
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`an air bag when a deploy command is received. A fault
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`indicator 20, also controlled by the microprocessor 16 will
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`show a failure of the seat occupant sensing system 12.
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`35
`The seat occupant sensing system 12 comprises a micro-
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`processor 22 having a 5 volt supply and an enabling line 24
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`periodically provided with a 5 volt enabling pulse, and a
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`series of voltage dividers coupled between the enabling line
`24 and ground. Each voltage divider has a fixed resistor 26
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`in series with a pressure sensor or variable resistor 28, and
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`the junction point of each resistor 26 and variable resistor 28
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`is connected to an AID port 30 of the microprocessor 22. The
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`microprocessor 22 controls the pulse on enabling line 24 and
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`reads each sensor 28 voltage during the pulse period. The
`microprocessor 22 analyzes the sensor inputs and issues a
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`decision whether to inhibit air bag deployment and the
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`decision is coupled to the microprocessor 16 by a line 32.
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`The microprocessor 22 also monitors its decisions for con-
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`sistency and issues a fault signal on line 34 to the micro-
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`processor 16 if faults continue to occur over a long period.
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`Each fixed resistor 26 is, for example, 17.4 kohms and the
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`variable resistors vary between 2 kohms at high pressure and
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`174 kohms at low pressure. Then the voltage applied to the
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`ports 30 will vary with pressure from about 4.6 volts to 0.5
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`volts. Each sensor is mounted between polymer film sheets
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`and includes a pair of conductive electrodes about one inch
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`in diameter separated by carbon layers such that the resis-
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`tance between electrodes decreases as pressure increases.
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`Such sensors are available as UniForce (TM) sensors from
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`Force Imaging Technologies, Inc., Chicago, 111. To minimize
`any deteriorating eifects of current through the sensors, short
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`enabling pulses of 1 ms are applied once each second.
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`The mounting arrangement of sensors 28 on a bottom
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`bucket seat cushion 36 with lateral wings 37 is shown in
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`FIG. 2. A first set 38 of four sensors 28 mounted on a
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`common flexible circuit substrate 40 is located on the right
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`40
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`45
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`60
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`65
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`Page 7 of 9
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`Page 7 of 9
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`5,474,327
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`5
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`made among empty seat, occupied infant seat and a larger
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`seated occupant. The maximum and minimum threshold
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`values are stored in the microprocessor 22.
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`The calculated weight center or weight distribution
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`parameter made by summing the products of the sensor
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`outputs and their distance from a datum line, and dividing
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`the sum by the total weight parameter yields a first set of
`results for a rear facing infant seat and a second set for a
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`front facing infant seat. These two sets are on opposite sides
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`of an imaginary transverse reference line; the results for rear
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`facing seats are in front of the line and the results for forward
`facing seats are behind the reference line. The distance data
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`for each sensor is stored in the microprocessor 22 which
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`makes the calculation, and the position of the imaginary
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`reference line is also stored there for comparison with the
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`calculated weight distribution parameter.
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`The microprocessor 22 is programmed to issue enabling
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`pulses on line 24, read each sensor during each pulse, make
`a decision whether to allow deployment, monitor the deci-
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`sions for a fault, and output the decision and fault results to
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`the SIR microprocessor 16. The flow chart of FIGS. 5a, 5b
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`and represents the program. Reference numerals shown
`herein in angle brackets <nn> refer to functions described in
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`flow chart boxes bearing those numerals. At the beginning of
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`the program a timer is initialized <60> and the program is
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`delayed <62> until one second has elapsed in order to limit
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`the program execution to once per second. Then the sensors
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`are enabled and each sensor sampled <64>. The sampled
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`voltage is subtracted from the sensor calibration voltage to
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`determine a force for each sensor <66> and they are summed
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`to obtain a total force or weight parameter <68>. Then a
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`center of force or weight distribution is made <70>. If the
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`total weight parameter is greater than the maximum infant
`seat weight <72> this indicates that a larger occupant is
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`present and a decision is made to allow deployment <74>.
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`Otherwise, if the total weight parameter is less than the
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`minimum weight threshold for an occupied infant seat <76>
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`it is determined that the seat is empty and a decision is made
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`to inhibit deployment <78>. The same result could be
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`obtained if a child or larger occupant in the seat is out of
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`position, i.e., leaning forward; then it still is desirable to
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`inhibit deployment. If the total weight parameter is between
`the threshold the occupant is identified as an occupied infant
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`seat or a small child <80>. If the center of weight distribu-
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`tion is forward of the reference line <82> a rear facing infant
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`seat is detected and a decision to inhibit deployment is made
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`<84>. If the center of weight distribution is not forward of
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`the reference line, a forward facing infant seat is detected
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`and a decision is made to allow deployment of the air bag
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`<86>.
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`The portion of the flow chart shown in FIG. 5b is directed
`to detecting a fault by monitoring the consistency of the
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`decisions. The decision made in each loop execution is
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`stored in an array <90> and if less than five decisions have
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`been stored <92> a decision counter is incremented <94>. If
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`the counter reaches a count of five, the counter is cleared
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`<96> and the decisions are compared to determine if they are
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`all the same <98>. If they are the same, the current decision
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`is transmitted to the SIR module 10 <100>, the current
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`decision is labelled as the previous decision <102>, and a
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`faulty decision counter is cleared <104>. If all five decisions
`are not the same, the previous decision is retransmitted to the
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`module 10 <106> and the faulty decision counter is incre-
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`mented <108>. If a large number of consecutive faulty
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`decisions occur <110> a fault signal is transmitted to the SIR
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`module 10 <112> and the faulty decision counter is cleared
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`<ll4>. The maximum allowed number of unstable readings
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`10
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`15
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`20
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`25
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`55
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`60
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`65
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`Page 8 of 9
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`6
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`may, for example, amount to one half hour of operation.
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`With this program the decision to allow deployment is
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`updated every five seconds, and an occasional spurious
`decision, which may be due to occupant movement or other
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`instability, is filtered out. Extended instability triggers the
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`fault signal which results in energizing the fault indicator 20.
`It is thus seen that a relatively simple seat pressure sensor
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`along with a logical decision program can provide a sub-
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`stantial amount of information about the nature of a pas-
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`senger seat occupant, if any, and a reliable decision whether
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`to inhibit air bag deployment. It is expected that this system
`be limited to a passenger seat subject to SIR protection.
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`Referring to FIG. 6, a seat belt monitoring system pro-
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`vides belt usage information to the driver for each passenger
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`seat so that the driver can enforce a requirement that each
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`passenger’s seat belt be fastened. Thus it is desirable to
`determine whether a seat is occupied and to generate a
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`warning signal only if an occupied seat has an unfastened
`belt. Each passenger seat position for front and rear seats
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`120 is equipped with a seat sensor 122 of the type shown in
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`FIG. 2. Seat belts 124 for each position each have a seat belt
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`detector 126 which signals that a belt is not fastened. Signal
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`lines 128 from the sensors 122 and detectors 126 connect
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`with a control circuit 130 which can determine whether a
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`seat is occupied and the corresponding belt is unfastened,
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`and if so to activate an indicator 132 which informs the
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`driver of non-compliance. In the case of infant seats only the
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`weight measurement is needed to determine whether a seat
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`is occupied, the position of the infant seat being irrelevant.
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`The control circuit 130 then should contain a microprocessor
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`programmed with steps 60 through 80 of FIG. 5a to deter-
`mine if a seat is empty or occupied, the program being
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`separately executed for each seat sensor 122, and additional
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`logic to determined whether an occupied seat correlates with
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`an unfastened belt.
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`The embodiments of the invention in which an exclusive
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`property or privilege is claimed are defined as follows:
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`1. In a vehicle occupant restraint system sensitive to the
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`occupancy of a vehicle seat by an adult and an occupied
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`infant seat and to the position of an infant seat including
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`pressure sensors strategically located in the vehicle seat for
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`response to the adult occupants and of infant seats, the
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`method of controlling air ba