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`USOOS612876A
`
`United States Patent
`
`[19]
`
`[11] Patent Number:
`
`5,612,876
`
`Zeidler et a].
`[45] Date of Patent:
`Mar. 18, 1997
`
`5/1995 Steffens, Jr. et all
`10/1995 Mazur et a1.
`........
`11/1995 Gotomyo et a1.
`12/1995 Schousek
`2/1996 Blackburn et a1.
`
`..
`
`................... 280/735
`280/7301
`
`.. 280/7301
`280/7301
`.. 280/7301
`
`
`
`5,413,378
`5,454,591
`5,466,001
`5,474,327
`5,494,311
`
`[54] DEVICE FOR DETECTING SEAT
`OCCUPANCY IN A MOTOR VEHICLE
`
`[75]
`
`Inventors: Folk Zeidler, Sindelfingen; Volker
`Petri, Aidlingen; Reinhold Mickeler,
`Altdorf; Michael Meyer, Sindelfingen,
`all of Germany
`
`[73] Assignee: Mercedes-Benz AG, Stuttgart, Germany
`
`[21] Appl. No.: 399,714
`
`[22]
`
`Filed:
`
`Mar. 3, 1995
`
`[30]
`
`Foreign Application Priority Data
`
`Mar. 3, 1994
`
`[DE]
`
`Germany .......................... 44 06 897.2
`
`Int. Cl.6 ..................................................... B60R 21/32
`[51]
`[52] U.S. Cl.
`................................ 364/424.055; 280/7301;
`280/735; 340/667; 180/273
`[58] Field of Search ....................... 364/424.05; 340/436,
`340/438, 669, 667; 307/101; 180/273,
`274, 282; 280/7301, 734, 735
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`5,010,774
`5,074,583
`5,161,820
`
`4/1991 Kikuo et a1.
`......................... 73/862.04
`
`12/1991 Fujita et a1.
`.
`.. 280/735
`11/1992 Vollmer ................................... 340/667
`
`FOREIGN PATENT DOCUMENTS
`
`3/1990 European Fat. 011.
`0357225
`11/1972 Germany .
`2125198
`4237072 12/1993 Germany .
`
`.
`
`Primary Examiner—Gary Chin
`Attorney, Agent, or FinnwEvenson, McKeown, Edwards &
`Lenahan, P.L.L.C.
`
`[57]
`
`ABSTRACT
`
`A device for detecting seat occupancy in a motor vehicle,
`especially for inhibiting airbag release when a seat is unoc-
`cupied, is provided. A seat occupancy sensor has a front
`sensing region and a rear sensing region, which can be
`evaluated separately. In this way, it is possible to determine
`whether the front seat passenger is in a sitting position close
`to the front seat edge of the seat cushion, which reduces the
`protective effect of the airbag. This can possibly be indicated
`visually or audibly. As a further measure, the inhibiting of an
`airbag release can be provided in the case of an incorrect
`sitting position. The seat occupancy sensor can be a resistive
`membrane pressure sensor.
`
`15 Claims, 2 Drawing Sheets
`
`
`
`HN-1006
`
`1
`
`HN-1006
`
`

`

`US. Patent
`
`Mar. 13, 1997
`
`Sheet 1 of 2
`
`5,612,876
`
`
`
`I
`
`EVALUATION
`CIRCUIT
`
`
`
`
`2
`
`

`

`US. Patent
`
`Mar. 18, 1997
`
`Sheet 2 of 2
`
`5,612,876
`
`10.1
`
`11.1
`
`
`INITIAL
`EVALUATION
`
`CKT.
`
`
`
`
`
`3
`
`

`

`5,612,876
`
`1
`DEVICE FOR DETECTING SEAT
`OCCUPANCY IN A MOTOR VEHICLE
`
`BACKGROUND AND SUMMARY OF THE
`INVENTION
`
`The invention relates to a device for detectin occupancy
`for a motor vehicle and, more particularly, to a device for
`detecting seat occupancy for a motor vehicle, especially for
`inhibiting airbag release when the seat is unoccupied. The
`device has a seat occupancy sensor, which is integrated in a
`seat cushion, and an associated evaluation circuit.
`In order to protect vehicle occupants more eifectively,
`motor vehicles, inter alia, are being equipped to an increas-
`ing extent with a front seat passenger’s airbag. In doing so,
`no unnecessary damage occurs provided it is possible to
`release the front seat passenger’s airbag in the case of an
`accident only when the front seat passenger’s seat is occu-
`pied.
`A number of systems for seat occupancy detection are
`known. Thus, in German Patent document DE-AS 21 25
`198, a contact band is integrated into the seat cushion of the
`motor vehicle seat. Two contact strips of the contact band
`come into contact when loaded. This contact making is
`evaluated as a signal for the loading of the seat cushion. The
`seat occupancy detection can be carried out using contact
`bands of various patterns, as a result of which locally
`different sensitivities are achieved.
`
`An embodiment for seat occupancy detection, which
`furthermore allows locally resolved evaluation of the load,
`is known from US. 5,010,774. In this reference, a matrix of
`pressure-sensitive contact points is evaluated in order to
`detect the load on the backrest of a seat by a trial person as
`a function of difi'erent designs of the seat. Furthermore a trial
`shoe is known from the document, having a pressure-
`sensitive bottom, in the case of which the pressure load on
`the running sole and the step can be separately evaluated.
`In German Patent document DE 42 37 072 C1, a sensor
`mat is described for installation in the seat cushion of a
`motor vehicle seat. The sensor mat is constructed as a
`resistive membrane pressure sensor and,
`in addition to
`interrogation of the seat occupancy status, also allows
`simple interrogation of the functional status,
`i.e., a self
`check.
`
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`The known systems for detecting seat occupancy signal
`the seat occupancy independently of the sitting position of
`the occupant. As a result, airbag release is also allowed
`independently of the sitting position. However, it is advan‘
`tageous for an optimum impact»damping effect of the airbag ’
`if a minimum distance is ensured between the occupant and
`the airbag at the start of the airbag release, in order for there
`to be sufficient time for the airbag to unfold in the case of an
`accident.
`
`There is therefore needed a system for detecting seat
`occupancy such that an incorrect sitting position (out of
`position) close to the front seat edge, in the case of which the
`minimum distance mentioned above is not maintained, can
`be detected and the occupant warned.
`This need is met by a device for detecting seat occupancy
`for a motor vehicle and, more particularly, to a device for
`detecting seat occupancy for a motor vehicle, especially for
`inhibiting airbag release when the seat is unoccupied. The
`device has a seat occupancy sensor, which is integrated in a
`seat cushion, and an associated evaluation circuit. The seat
`occupancy sensor is divided into a front sensing region and
`a rear sensing region. The front sensing region responds to
`
`50
`
`55
`
`65
`
`2
`seat occupancy in the from region of the seat cushion and the
`rear sensing region responds to seat occupancy in the rear
`region of the seat cushion. It is possible to evaluate the
`occupancy state of both sensing regions separately. By
`splitting the sensitive region of the seat occupancy sensor
`into a front sensing region and a rear sensing region, a sitting
`position close to the front seat edge can be detected and an
`appropriate warning signal emitted.
`This measure makes particular sense if, despite the wam-
`ings in the operating instructions from the vehicle manufac-
`turer, children are seated on the front seat without there
`being a suitable child restraint system. Because of their
`shorter thighs, small children prefer to sit on the front seat
`surface for added comfort. Using the device according to the
`invention for seat occupancy detection, in conjunction with
`an audible or visual warning device,
`the driver can be
`emphatically advised to ensure that the front seat passenger
`is in a correct sitting position.
`Other objects, advantages and novel. features of the
`present invention will become apparent from the following
`detailed description of the invention when considered in
`conjunction with the accompanying drawings.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a diagram of the seat occupancy sensor accord—
`ing to the present invention;
`FIG. 2 is a schematic block diagram of the evaluation
`circuit according to the present invention; and
`FIG. 3 is schematic diagram of a preferred embodiment of
`the seat occupancy sensor formed as a resistive membrane
`pressure sensor.
`
`DETAILED DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 shows a top plan view of a driver’s seat having a
`seat cushion 1 and a backrest 2. Furthermore, a seat occu-
`pancy sensor 3 and an arrangement of two sensing regions
`3.], 3.2 over the seat cushion 1 are illustrated. It is possible
`to combine the two sensing regions 3.1, 3.2 in one mechani-
`cal structural unit (sensor mat). The front sensing region 3.1
`detects seat occupancy on the front region of the seat, close
`to the seat edge, and emits a corresponding signal V'. In an
`analogous manner, the rear sensing region 3.2 detects seat
`occupancy in the rear region, close to the backrest 2, and
`emits a corresponding signal H'. It is, of course, easily
`possible also to provide a further sensing region in the
`backrest 2, which would be included for evaluation.
`The precise geometry of the sensing regions 3.1, 3.2 and
`their delineation from one another must be optimized indi-
`vidually in a trial for each vehicle type and seat type. It also
`is necessary to reliably detect seat occupancy by a child. The
`seat occupancy sensor 3 can be implemented as a resistive
`membrane pressure sensor, or can be based on the principles
`on which other known seat occupancy sensors are based.
`In one embodiment,
`it is possible to provide that an
`adjustable longitudinal sitting position “x” of a seat is also
`detected and interrogated, for absolute determination of the
`center of gravity position of the occupant with respect to the
`vehicle and thus with respect to the airbag. The longitudinal
`sitting position x can be detected by a position sensor or
`switch as is known, for example, from seat memory circuits.
`FIG. 2 shows the evaluation circuit 4 according to the
`invention, having an input 4.1 for a first seat occupancy
`signal V which is assigned to the front sensing region, and
`an input 4.2 for a second seat occupancy signal H which is
`
`4
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`

`

`5,612,876
`
`3
`assigned to the rear sensing region. The seat occupancy
`signals V and H are provided, for example, by the signals V'
`and H' respectively from FIG. 1. In a development, an input
`4.3 for the longitudinal sitting position x can also be
`provided. The evaluation circuit determines from the input
`signals a control signal 4.5 by means of which a release
`controller 5 for an airbag 8 is driven in such a manner that
`release is allowed when the sitting position is correct.
`Furthermore, the evaluation circuit 4 determines from the
`input signals a warning signal 4.6 which drives a warning
`device 6 and is emitted when an incorrect sitting position
`(out of position) has been assumed. The warning device 6
`may comprise an audible or visual indication. The evalua-
`tion circuit can be implemented via a hardwired circuit or a
`suitably programmed microprocessor.
`In a preferred embodiment, it can be provided that the
`evaluation circuit 4 enters data via an interface 4.7 into a
`non-volatile memory 7 (MEM). This data can be, for
`example, the input signals 4.1-4.3 or the output signals 4.5,
`4.6. In this way,
`it is intended to make it possible to
`reconstruct the sitting position of the occupant and the
`measures derived from the evaluation circuit 4 therefrom,
`for example the emission of a warning signal 4.6, after an
`accident has occurred. It is thus suflicient to use a stacking
`memory (stack) for the memory 7, in which case relatively
`old data are cyclically overwritten by relatively new data, so
`that less memory space is required overall. An inhibiting
`signal 5.1, which is passed to the memory from the release
`controller 5 at the time of airbag release, ensures that the
`memory 7 can no longer be overwritten after a crash and that
`therefore the data can still be read out only by a suitable
`person. Further overwriting of the data is thus impossible
`after airbag release.
`The evaluation which is carried out in the evaluation
`circuit 4 is described in the following text with reference to
`a simple algorithm that can be performed on a micropro-
`cessor. For simplicity, it is assumed that the seat occupancy
`signals V and H are logic signals having the occupancy
`status “1” for an occupied sensing region and “0" for an
`unoccupied sensing region. A total of four occupancy com-
`binations are thus. possible for the front sensing region and
`the rear sensing region overall, which combinations are
`illustrated in the following table:
`
`
`4
`
`signal 4.6 to an audible or visual warning device 6. In
`addition, inhibition of airbag release can be provided in
`accordance with measure A, it then being possible to provide
`explicit advice by means of a display or warning symbol that
`the airbag is not ready to release.
`This supplementary measure can be provided as an alert-
`ing measure if a differentiated evaluation of the sitting
`position is possible and it is clearly evident that an infringe-
`ment of the minimum distance between the airbag and the
`occupant has been recorded.
`In one embodiment, a diflerentiated determination of the
`sitting position can be achieved in that the center of gravity
`position of the occupant with respect to the seat is detected
`and evaluated more precisely andlor the longitudinal sitting
`position x is also included, in order to precisely determine
`the position of the occupant with respect to the airbag.
`Subject to these preconditions, it can also be provided for
`measure C to be split into two levels, so that if the distance
`between the airbag and the occupant is slightly less than the
`minimum distance, only a warning signal 4.6 is emitted, and
`the inhibition of airbag release in addition does not take
`place until the minimum distance has been consider ably
`infringed. Alternatively,
`the determined absolute sitting
`position can be passed as a control signal 4.5 to the release
`controller 5, in order to influence the switching threshold for
`airbag release. It can thus be provided that the switching
`threshold for airbag release is increased the shorter the
`detemrined distance between the occupant and the airbag is.
`FIG. 3 illustrates a possible embodiment of the seat
`occupancy sensor according to the invention formed of a
`resistive membrane pressure sensor. The design is based on
`the principle described in German Patent document DE 42
`37 072 C1. The membrane pressure sensor includes two
`polymer layers which are laminated together, one polymer
`layer being coated with a semiconductor material and the
`other with meandering double cables, which fill the pres-
`sure-sensitive region. When a pressure load is applied to the
`membrane pressure sensor, the semiconductor material con-
`nects closely adjacent conductor tracks of a double cable
`more or less in parallel, so that the electrical resistance
`between the conductor track reduce as the contact pressure
`increases. As a result of the conductor tracks being designed
`without branches, complete continuity testing of the con-
`ductor tracks is also possible, by means of which it is
`possible to check the serviceability of the sensor in a simple
`manner. If the double cable is terminated by a diode at its
`end, it is possible to use the polarity of the measurement
`voltage to determine whether a pressure load measurement
`or a continuity test of the conductor tracks is carried out For
`a continuity test,
`the measurement current flows in the
`forward direction through the diode, as a result of which a
`circuit composed of the conductor tracks forming the double
`cable is closed. In the event of an interruption in a conductor
`track, the circuit for the measurement current is thus also
`interrupted.
`FIG. 3 shows a plan view of the membrane pressure
`sensor according to the invention, having a first pressure
`sensor 10.1 for the front sensing region and a second
`pressure sensor 10.2 for the rear sensing region. The two
`pressure sensors 10.1, 10.2 are each formed by a meandering
`double cable, each double cable having a first conductor
`track and a second conductor track which runs predomi-
`nantly parallel
`thereto. The respectively first conductor
`tracks of the two double cables are each connected at one of
`their ends to a connecting contact 9.1 or 9.3 respectively, and
`at their other end, in each case via a diode 11.1 or 11.2
`respectively, to a junction point 12, the two diodes 11.1, 11.2
`
`10
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` V H Occupancy situation Measure
`
`
`
`
`
`
`
`0
`0
`l
`
`0
`1
`0
`
`A
`B
`C
`
`Seat unoccupied
`Seat correctly occupied
`Seat incorrectly occupied
`(out of position)
`
`Seat correctly occupied11 E
`
`
`
`
`
`The first column always shows the occupancy status of
`the seat occupancy signal V for the front sensing region, and
`the second column the seat occupancy signal H for the rear
`sensing region. The third colunm explains the corresponding
`occupancy situation, and the fourth column shows the mea-
`sures derived therefrom.
`
`Measure A accordingly occurs when the seat is unoccu-
`pied. In this measure, the control signal 4.5 inhibits the
`release controller 5, so that it is not possible for the airbag
`8 to be released.
`
`Measure B occurs when the seat is correctly occupied. In
`this measure,
`the control signal 4.5 causes the release
`controller 5 to be ready to release the airbag.
`Measure C occurs in the casein which a seat is incorrectly
`occupied and includes at least the emission of a warning
`
`5
`
`

`

`5,612,876
`
`5
`having opposite polarity. The respective second conductor
`tracks of the two double cables are connected in series and
`form a common cable 13, which is connected at one of its
`ends to a connecting contact 9.2 and at its other end to the
`junction point 12.
`The interconnection according to the present invention of
`the total of four conductor tracks of the two pressure sensors
`10.1, 10.2 in the manner illustrated in FIG. 3 offers the
`advantage that, using only three connecting contacts
`9.1~9.3,
`it
`is possible to separately carry out both an
`interrogation of the occupancy states and a functional test of
`the two pressure sensors 10.1, 10.2. An initial evaluation
`circuit 9 is provided for this purpose, whose three inputs are
`connected to the connecting contacts 9.1~9.3 and which
`emits, via a first output 9.4, the seat occupancy signal V" for
`the front sensing region and, via a second output, the scat
`occupancy signal H" for the rear sensing region. Both seat
`occupancy signals V" and H" can drive, for example, the two
`inputs 4.1, 4.2 of the evaluation circuit 4 in FIG. 2. A third
`output 9.6 emits an error signal (ERROR), which emits the
`result of the continuity test. This error signal can be used, for
`example, to drive an indicating unit, which possibly advises
`the driver of a defect in the seat occupancy detection.
`The following table illustrates how a pressure load mea-_
`surement or a continuity test is in each case carried out as a
`function of the polarity of the measurement voltage on the
`connecting contacts 9.1—9.3, related to the from pressure
`sensor 10.1 (from) and the rear pressure sensor 10.2 (rear):
`
`Polarity on
`9.1
`9.2
`9.3
`Measurement carried out
`
`
`+
`
`-—
`
`—
`
`+
`+
`
`A
`
`Front pressure load
`measurement
`Front continuity test
`Rear pressure load
`measurement
`Rear continuity test
`
`-
`
`+
`
`In this way, it is possible to intrinsically check each of the
`two pressure sensors 10.1, 10.2 with respect to pressure load
`and serviceability.
`Although the invention has been described and illustrated
`in detail, it is to be clearly understood that the same is by
`way of illustration and example, and is not to be taken by
`way of limitation. The spirit and scope of the present
`invention are to be limited only by the terms of the appended
`claims.
`What is claimed is:
`1. A device for detecting seat occupancy states in a motor
`vehicle, the device comprising:
`a seat occupancy sensor integrated in a seat cushion of the
`seat;
`
`an evaluation circuit‘coupled to the seat occupancy sen-
`sor;
`
`wherein said seat occupancy sensor is divided into a front
`sensing region and a rear sensing region, said front
`sensing region responding to seat occupancy in a from
`region of the seat cushion and the rear sensing region
`responding to seat occupancy in a rear region of the seat
`cushion; and
`wherein an occupancy state of both said front and rear
`regions is separately evaluated by said evaluation cir-
`cuit to control an airbag.
`2. A device according to claim 1, wherein when the seat
`occupancy is detected primarily in the front sensing region,
`
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`6
`
`the evaluation circuit emits a warning signal to at least one
`of an audible and visual Warning device.
`3. A device according to claim 1, wherein when the seat
`occupancy is detected primarily in the front sensing region,
`the evaluation circuit emits a control signal to a release
`controller for the airbag, said control signal making the
`release of the airbag more difiicult.
`4. A device according to claim 1, wherein when the seat
`occupancy is detected primarily in the rear sensing region,
`the evaluation circuit emits a control signal which makes a
`release controller for an airbag ready to release.
`5. A device according to claim 1, wherein the evaluation
`circuit uses signals from the seat occupancy sensor and a
`longitudinal seat position of the vehicle seat to determine an
`absolute distance between an occupant and the airbag, and
`emits a warning signal if said absolute distance is less than
`a minimum distance.
`6. A device according to claim 1, further comprising a
`non-volatile storage medium coupled to the evaluation cir~
`cuit, said storage medium storing data which is input, output,
`or used internally in the evaluation circuit.
`7. A device according to claim 6, wherein the storage
`medium is carried out in accordance with a stacking prin-
`ciple,
`in which case relatively old data in the storage
`medium are overwritten cyclically by relatively new data
`received in the storage medium.
`8. A device according to claim 1, wherein the seat
`occupancy sensor is constructed as a resistive membrane
`pressure sensor.
`9. A device according to claim 8, wherein the membrane
`pressure sensor is formed from a front pressure sensor and
`a rear pressure sensor, each of which has a meandering
`double cable, each double cable being formed from a first
`conductor track and a second conductor track which runs
`predominantly parallel thereto.
`10. A device according to claim 9, further comprising
`three connecting contacts, wherein one end of said first
`conductor track of each of said double cables is connected
`to respective ones of said three connecting contacts, and
`another end is connected via respective diodes to a common
`junction point, wherein said second conductor tracks of said
`double cables are connected together to form a common
`cable having one end connected to another one of said three
`connecting contacts, and another end connected to said
`common junction point.
`11. A device according to claim 1, wherein in addition to
`an interrogation of the occupancy state, a functional test for
`both sensing regions is separately carried out by said evalu—
`ation circuit.
`12. A device according to claim 10, wherein an initial
`evaluation circuit
`is connected to the three connecting
`contacts, and wherein a measurement voltage having alter—
`nating polarity is in each case applied to two of said three
`connecting contacts, and further wherein seat occupancy
`signals for the front sensing region and for the rear sensing
`region are determined from the respective measurement
`currents, and still further wherein an error signal with
`respect to the operation of the seat occupancy sensor is
`determined from the respective measurement currents.
`13. A device according to claim 1, wherein when the seat .
`occupancy is detected primarily in the front sensing region,
`the evaluation circuit emits a control signal to a release
`controller for the airbag, said control signal inhibiting the
`release of the airbag.
`14. A device for detecting seat occupancy states in a motor
`vehicle, the device comprising:
`a seat occupancy sensor integrated in a seat cushion of the
`seat;
`
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`

`5,612,876
`
`7
`
`an evaluation circuit coupled to the seat occupancy sen—
`sor;
`
`wherein said seat occupancy sensor is divided into a front
`sensing region and a rear sensing region, said front
`sensing region responding to seat occupancy in a front
`region of the seat cushion close to a front seat edge, and
`the rear sensing region responding to seat occupancy in
`a rear region of the seat cushion; and
`wherein an occupancy state of both said front and rear
`regions is separately evaluated by said evaluation cir-
`cuit.
`
`15. A device for detecting seat occupancy states in a motor
`vehicle, the device comprising:
`a seat occupancy sensor integrated in a seat cushion of the
`seat;
`
`an evaluation circuit coupled to the seat occupancy sen-
`sor;
`
`5
`
`10
`
`15
`
`8
`wherein said seat occupancy sensor is divided into a front
`sensing region and a rear sensing region. said front
`sensing region responding to seat occupancy in a front
`region of the seat cushion close to a front seat edge, and
`the rear sensing region responding to seat occupancy in
`a rear region of the seat cushion;
`
`wherein an occupancy state of both said front and rear
`regions is separately evaluated by said evaluation cir—
`cuit; and
`
`whereby a response from only said front sensing region
`indicates an incorrect seat occupancy state for an airbag
`release.
`
`7
`
`