WO2004067330A1

WO2004067330A1 - Conductive liner with integrated occupant sensor

Info

Publication number: WO2004067330A1
Application number: PCT/US2004/001262
Authority: WO
Inventors: Clarence P. Lipke; Victor Claude Evjen
Original assignee: Intier Automotive Inc.
Priority date: 2003-01-21
Filing date: 2004-01-20
Publication date: 2004-08-12

Abstract

A conductive liner with integrated occupant sensor (10) for a vehicle comprising a core layer (12) having a top surface and a bottom surface. A first conductive layer (14) is attached to the top surface of the core layer and a second conductive layer (14) is attached to the bottom surface of the core layer. The first conductive layer acts as an oscillator input loop (15). The second conductive layer acts a s a detector output loop (17). The first and second conductive layers (14) act together as a capacitance-based sensor to determine a location of an occupant.

Description

CONDUCTIVE LINER WITH INTEGRATED OCCUPANT SENSOR

Technical Field

[0001] The present invention relates to an airbag occupant sensor. In particular, the invention relates to a conductive liner with an integrated occupant sensor for a vehicle.

Background of the Invention

[0002] Automobile occupant airbag systems are well known means of attempting to reduce the likelihood of serious injury to occupants in collisions. Even if a vehicle is equipped with an occupant airbag restraint system, it is not always desirable to inflate the airbag every time a crash condition occurs. Crash conditions are classified as either non- deployment crash conditions or deployment crash conditions. Non-deployment crash conditions are those for which the occupant seat belt alone provides adequate protection of the occupant. Most cars are now equipped with more than one airbag. For example, airbags are present for the both the driver and the occupant. However, typically only one occupant airbag sensor is placed withm the vehicle. Thus, if the vehicle is in a deployment crash condition, both airbags are deployed, irrespective of whether how many occupants are in the vehicle.

[0003] In deployment crash conditions, the deployment of the occupant airbag may critically depend on the initial position and subsequent movement of the occupant. Those skilled in the art are aware that overhead occupant sensors can determine occupant position and subsequent movement within the vehicle. There are many advantages to using an overhead occupant sensor, especially regarding deployment of the occupant airbag, in terms of its success in preventing occupant injury. However, current overhead occupant sensors must be assembled into the vehicle separately from the headliner.

Summary of the Invention

[0004] The inventor of the present invention has recognized these and other problems associated with conventional overhead occupant sensors. To this end, the inventor has developed a conductive liner with integrated occupant sensor for a vehicle compπsing a core layer having a top surface and a bottom surface. A first conductive layer is attached to the top surface of the core layer and a second conductive layer is attached to the bottom surface of the core layer. The first conductive layer acts as an oscillator input loop. The second conductive layer acts as a detector output loop. The first and second conductive layers act together as a capacitance-based sensor to determine a location of an occupant within the vehicle.

Brief Description of the Drawings

[0005] Figure 1 is a partial cut-away view of the passenger compartment of a vehicle according to an embodiment of the invention.

[0006] Figure 2 is a partial cross-sectional view of the conductive liner according to an embodiment of the invention taken along line 2-2 of Figure 1.

[0007] Figure 3 is a top plan view showing a plurality of discrete sensor zones according to an embodiment of the invention.

[0008] Figure 4 is a top plan view showing one discrete sensor zone according to an embodiment of the invention.

[0009] Figure 5 illustrates a capacitive-based sensor circuit used in conjunction with the conductive liner according to an embodiment of the invention.

Description of the Preferred Embodiment

[0010] Referring now to Figure 1, a conductive liner 10 with an integrated occupant sensor is shown according to an embodiment of the invention. In the illustrated embodiment of the invention, the conductive liner 10 is used as a headliner of a vehicle.

[0011] Figure 2 illustrates a cut-away view of one embodiment of the conductive liner 10 of the present invention. Conductive liner 10 comprises a core layer 12 between two conductive layers 14. The conductive layers 14 include conductive particles, such as carbon fibers or the like, that replace the fiberglass content of a conventional headliner- One purpose of the combination of the core layer 12 and two conductive layers 14 is tσ provide a structure that has sufficient thickness and strength to prevent bending of the conductive liner 10, and which provides a structure with a suitable moment of inertia. In a preferred embodiment, the core layer 12 is made from an electrically non-conductive mateπal that provides acoustical absorbance. Examples of mateπals for the core layeϊ 12 include, but are not limited to, polyurethane and polyester fiber.

[0012] The conductive liner 10 can further include a top and bottom scrim/adhesive layer (not shown), as well as a decorative, cover mateπal layer (not shown.) The scrim/adhesive layers are preferably layers that contain or encapsulate the fibers in the conductive layers 14. More particularly, the fibers are maintained in place in the conductive layers 14 by the scπm/adhesive layers An example of a mateπal for the adhesive used for the scrim/adhesive layer is polyethylene. The scπm mateπal used preferably helps release the adhesive mateπal from the tooling. An example of the scnm material for the scnm/adhesive layer is a lightweight polyester. It will be appreciated that the scnm/adhesive layer can be omitted and that the decorative cover mateπal can be attached directly to one conductive layer 14 using an adhesive.

[0013] Another purpose of the two conductive layers 14 is to act as an occupant airbag sensor to determine the initial position and subsequent movement of the occupant. Specifically, the two conductive layers 14 act as a capacitance-based sensor that responds to the different conductivity of the occupant versus that of air and the surrounding mateπals of the passenger compartment. The airbag or airbags will only be deployed if an occupant, such as a dπver or occupant, is sensed by the two conductive layers 14 On the other hand, if an occupant is not sensed by the two conductive layers 14, the associated airbag or airbags will not be deployed, theieby preventing unnecessary deployment of the airbag oi an bags

[0014] As shown in Figure 5, the two conductive layers 14 form an oscillator input loop 15, and a detector output loop 17. The two conductive layers 14 function as an occupant aπbag sensor by creating an electrostatic field (not shown) between oscillator input loop 15 and detector output loop 17 The electrostatic field is affected by the presence of a person, as a result of capacitive coupling, due to the fact that the human body has a conductivity and a dielectric constant different from those of air. Thus, the piesence of a person near the two conductive layers 14, or occupant airbag sensor, causes a change in the capacitance between the oscillator input loop 15 and the detector output loop 17. As is well known in the electronic arts, such a capacitive coupling effect will be dependent on the distance of the person from the occupant airbag sensor. The measured capacitance change may be used to determine the distance of the person from the occupant airbag sensor.

[0015] Figure 3 illustrates one embodiment of the present invention in which the conductive liner 10 is divided into a plurality of discrete sensor zones, for example, four discrete sensor zones 20a, 20b, 20c, and 20d. Occupant positioning is determined by using discrete sensor zones providing voltage output to the microprocessor 28, representing the capacitive coupling effect of the occupant's position relative to each discrete sensor zone. The microprocessor 28 can compare these voltages against known values indicating occupant zone position, without referring to a voltage-distance translation function. The zones, voltages, and airbag system response can be varied to suit the requirements of the vehicle dimensions and airbag system parameters. Each discrete sensor zone 20a, 20b, 20c, and 20d is electrically insulated from adjacent discrete sensor zones.

[0016] It will be appreciated that the invention is not limited by the number of discrete sensor zones. For example, a large number of discrete sensor zones enables a more accurate position of the occupant than a smaller number of discrete sensor zones. On the other hand, the present invention can be practiced with only one discrete sensor zone 20 encompassing a substantial portion of the conductive liner 10, as shown in Figure 4.

[0017] The zoning concepts are feasible for a variety of sensor geometries, including round, rectangular, and polygon-shaped sensors. By use of non-round sensors, the sensing fields can be tailored in shape to match the dimensions of most positions of a seated occupant, including upright or fully reclined seatback, seat positioned full forward or aft, and occupant resting against the door or window. The invention is not to be regarded as being limited to any particular choices of the spacing dimensions of the discrete sensor zones or the geometry of the discrete sensor zone.

[0018] Referring back to Figure 5, a signal processing circuit 22, an oscillator 24, charge-sensitive amplifier 26 and microprocessor 28, are connected to the conductive liner 10. The signal processing circuit 22, along with the oscillator 24 and the charge-sensitive amplifier 26 continuously monitor the capacitive coupling effect, and changes in the magnitude of the effect, so that the microprocessor 28 will continuously receive signals from each of the discrete sensor zones 20, indicative of occupant location. The signals will be particularly sensitive to the occupant's head position and head motion, because the head is closest to the conductive liner 10, and the each of the discrete sensor zones 20. The sampling rate for the signal processing circuit 22 may be determined by means contained within the microprocessor 28, such as a conventional analog-to-digital converter circui t if the microprocessor operates digitally, or the like. The signal processing circuit 22 may consist of a conventional full wave rectifier and a conventional peak detector, connected in series. The invention is not to be regarded as being limited to any particular sensor operating rate or sampling rate.

[0019] In certain vehicles, it may be preferable to employ analog circuitry to geometrically determine head position, allowing virtually instantaneous derivations of head velocity and acceleration. Because digital microprocessors are relatively slow for complex trigonometric functions, a data throughout of approximately one millisecond may be insufficient for airbag deployment in high speed crashes. By using analog computing circuitry, the data throughput is much greater, providing thousands of data points per millisecond. This data rate is comparable to the operating rates of micromachined accelerometers, yet relies on actual measurements of the occupant rather than a remote sensing device to activate the airbag. This can improve reliability and airbag deployment timing. Use of analog circuitry makes analog/digital conversion unnecessary, and eliminates the need for a digital microprocessor to perform the geometric algorithm and reconvert the results back to analog form.

[0020] The microprocessor continuously monitors the distance of the effective electronic center of a occupant from each of the discrete sensor zones 20, by comparing the capacitive coupling effect produced in each of the discrete sensor zones 20, with a lookup table containing capacitive coupling effect correlations to distance, stored in the memory of the microprocessor. The memory of microprocessor 28 is of a size sufficient to contain at least the most recent 50,000 occupant positions, corresponding to about 5 seconds of sensing, after which newer data overwrites previously recorded data. Thus, the microprocessor 28 will contain a detailed record of occupant position during the last fi-ve seconds before a crash, and will continue to record data for five seconds after the crash, which will be quite useful for later crash analysis purposes. Airbag deployment will stop the erasure of old data. The microprocessor 28 memory also contains occupant head motion lookup tables of threshold acceleration values which may be used to distinguish lesser acceleration motions which often occur in non-collision conditions, i.e., head motion from a sneeze

[0021] Either the first or second conductive layer 14 can be electπcally connected to a positive terminal of a power source (not shown). The other conductive layer 14 can be electπcally connected to a negative terminal of a power source. Thus, an electπcal circuit is formed between the power source and the conductive layers 14.

[0022] The presence of sensing devices withm the conductive layers 14 of the conductive liner 10, as in the present invention, is advantageous over the prior art. Each discrete sensor zone 20 only activates the airbag associated with that particular discrete sensor zone 20 and only if the discrete sensor zone senses the presence of an occupant. For example, if only a dπvei is present in the vehicle, only the discrete sensor zone 20 associated with the dπver will activate an airbag if the vehicle is in a deployment crash. If there are no occupants in the vehicle when the vehicle is hit, for instance in a parked vehicle, no airbags will deploy because the discrete sensor zones 20 do not detect any occupants. Accordingly, the conductive liner 10 of the present invention prevents unnecessaiy deployment of airbags

[0023] Moreover, in the present invention, the occupant airbag sensor is integral to the conductive layers 14 of the conductive liner 10, thereby eliminating the need for additional assembly steps of mounting the occupant sensor to the headliner as in the prior art In addition, because the conductive liner 10 and the occupant sensor are integrated into one assembly, there may also be a cost and weight reduction in the manufacturing of the vehicle

[0024] Further, the use of carbon fibers in the conductive layers 10 in accordance with the present invention provides many advantages over the prior art Because the conductive layers 14 act as reinforcement for the conductive liner 10, the present invention also eliminates the need to use non-conductive reinforcing material, such as fiberglass reinforcing layers. Thus, the conductive liner 10 of the present invention can be thinner and/or weigh less and still provide sufficient structural reinforcement as in conventional lmers.

[0025] While the invention has been descπbed with respect to specific examples including preferred modes of carrying out the invention, those skilled in the art will appreciate that there are numerous variation and permutation of the above described systems and techniques that fall within the spirit and scope of the invention as set forth in the appended claims.

Claims

What is claimed is

1 A conductive liner with integrated occupant sensor for a vehicle, compπsing a core layer having a top surface and a bottom surface, a first conductive layer attached to said top surface of said core layer, a second conductive layer attached to said bottom surface of said core layer, and wherein said first conductive layer acts as an oscillator input loop, said second conductive layers acts as a detector output loop, and said first and second conductive layers act together as a capacitance-based sensor to determine a location of an occupant within the vehicle

2 A conductive liner with integrated occupant sensor for a vehicle as in claim

1, further comprising an oscillator, a microprocessor, a signal piocessor and a charge- sensitive amplifier, wherein said oscillator, said microprocessor, said signal piocessor and said charge-sensitive amplifier provide means for detecting presence or absence of said occupant using said capacitive-based sensor

3 A conductive liner with integrated occupant sensor for a vehicle as in claim

2, wherein said microprocessor contains a detailed record of said occupant position for at least five seconds and an occupant head motion lookup table of threshold acceleration values

4 A conductive liner with integrated occupant sensor for a vehicle as in claim

1, wherein said first conductive layer and said second conductive layer are separated into at least two electπcally insulated disci ete sensoi zones

5. A conductive liner with integrated occupant sensor for a vehicle as in claim

1, wherein said first and second conductive layers include carbon fibers.

6 A conductive liner with integrated occupant sensor, compnsing: a core layer having a top and bottom surface; a first conductive layer attached to said top surface of said core layer, said first conductive layer acts as an oscillator input loop, a second conductive layer attached to said bottom surface of said core layer, said second conductive layer acts as a detector output loop, an oscillator, a microprocessor, a signal processor, and a charge-sensitive amplifier; wherein said first and second conductive layers act together as a capacitance-based sensor to determine a location of an occupant and wherein said oscillator, said microprocessor, said signal processor and said charge-sensitive amplifier provide means for detecting presence or absence of said occupant using said capacitive-based sensor.

7 A conductive liner with integrated occupant sensor as in claim 6, wherein said first conductive layer and said second conductive layer are separated into at least two electncally insulated discrete sensor zones.

8 A conductive liner with integrated occupant sensor as in claim 6, wherein said microprocessor contains a detailed record of said occupant position for at least five seconds and an occupant head motion lookup table of threshold acceleration values.

9 A conductive lmer with integrated occupant sensor as in claim 6, wherein said first and second conductive layers include carbon fibers.