Vehicle occupant sensor system

The present invention is a sensor element, particularly a sensor element useful in a vehicle occupant detection system. The sensor element comprises a first conductor and a second conductor disposed transversely with respect to one another to define a junction. In use, when a constant voltage is applied to the conductors, a first conductance is produced in the absence of applied weight to sensor element and a second conductance is produced in the presence of applied weight to the sensor element wherein the second conductance being greater than the first conductance. By incorporating a number of such junctions into matrix arrangement, the present sensor can be advantageously employed in a vehicle occupant detection system. This allows for the creation of a spreadsheet-like environment where interrogation of each matrix cell provides information about the acting force. Since it is possible to identify the location of the given cell in an overall matrix, it is possible to pinpoint the position of the acting force or pressure. The combination of information on each cell can be recognized as one or more patterns. A centroid for such patterns can be readily calculated (i.e., based on interrogating the matrix for the conductance difference referred to above) and the prediction of the position of the occupant in the vehicle seat can be deduced.

BACKGROUND OF THE INVENTION

1. Field of the Invention

In one of its aspects, the present invention relates to a sensor element, particularly for use of vehicular occupant detection system. In another of its aspects, the invention relates to a vehicular occupant detection system.

2. Description of the Prior Art

In recent years, the use of supplementary restraint systems (SRS) such as airbags has become widespread in the automotive industry.

Thus, it is now conventional (and in some jurisdictions mandated) to utilize an airbag-based SRS. Indeed, such systems now utilize airbags which may be deployed from one or more of the dashboard, the A-pillar, the headliner and the like.

While the advent of SRS has, to some degree, revolutionized the automotive industry, there is still room for improvement.

Specifically, as has been widely reported, there can be situations where it is not appropriate for the airbag to fully deploy or deploy at all. Thus, if the occupant in the vehicle seat is a small child, a pregnant woman or a “regular” occupant who is leaning forward, full deployment of the airbag can sometimes lead to unintended (and potential fatal) consequences.

Thus, in recent years, much work has centered on the development on so-called vehicle occupant detection systems which operate generally by providing more information about the occupant in the vehicle seat (e.g., occupant weight, occupant position and the like) and utilize this information to control deployment of the airbag and, in some cases, to disengage deployment of the airbag entirely.

One body of this work relates to the use of strain gauges and the like incorporated in the frame and/or seat pan of the vehicle seat to measure a change in weight when an occupant is seated. While determining the weight of the occupant is useful information, this measurement alone, in most cases, does not provide sufficient information for optimal control of the airbag deployment system.

A second body of work relates to the use of capacitance sensors to map position of the occupant. In some cases, the capacitance sensors can be combined with weight sensors such that the weight and the position of the occupant can be determined. While the use of capacitance sensors in the vehicle occupant detection system is an advance in the art, the long term effects of such a system are unknown. Specifically, it is known that, in order for a capacitance sensor to operate properly, the sensor emit a frequency field which, when interrupted by an occupant, can be detected by the sensor. In other words, whenever the occupant is seated in the vehicle under operation, that occupant will be subjected to the frequency field. Unfortunately, the long term health effects on the occupant of residing in such a field while seated in the vehicle are currently unknown and, at the very least, raises uncertainty as to the overall usefulness of such systems.

Thus, despite advances made in the art, it would be desirable to have a vehicle occupant detection system which provides the advantages of capacitance sensing system (i.e., the ability to map the position of the occupant) while avoiding the requirement for using a frequency field and any long-term health effects on a vehicle occupant residing in that field for an extend period of time.

SUMMARY OF THE INVENTION

It is an object of the present invention to obviate or mitigate at least one of the above-mentioned disadvantages of the prior art.

Accordingly, in one of its aspects, the present invention provides a sensor element comprising a first conductor and a second conductor disposed transversely with respect to the first conductor to define a first junction, wherein at a constant voltage, a first conductance is produced in the absence of applied weight to sensor element and a second conductance is produced in the presence of applied weight to the sensor element, the second conductance being greater than the first conductance.

Thus, the present inventor has discovered a novel approach for a sensor element, particularly a sensor element useful in a vehicle occupant detection system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The sensor element comprises a first conductor and a second conductor which are disposed transversely with respect to one another.FIG. 1illustrates an enlarged cross-sectional view of an example of such an arrangement where each conductor is a round, bare electrically conductive material such as wire.FIG. 2illustrates a wiring diagram for the arrangement ofFIG. 1.

With reference toFIGS. 1 and 2, when no pressure or force is applied on the conductors, there is “zero” force (no contact)—junction1—indicating no physical contact area but closeness between the conductors. If one accounts for the effective gravity, (e.g., the weight exerted on the area of the conductors by the physical properties), the result is shown a junction to where there is minimal contact between the two conductors.

When force or pressure (e.g., weight of an occupant) is applied to the conductors the area of contact at the junction is increased—see junction3inFIG. 1.

If one considers the application of an applied voltage (e.g., one volt) the current at junction1is zero because the area of contact between the two conductors is zero.

With regard to junction2, the current is not zero since the two conductors are contacting each other allowing for electrons to cross from one conductor to the other conductor. This “crossing” area defined as the junction and the size of this area allows some electrons to flow across it as a function of the “driving force” of the applied voltage (e.g., one volt) and the total resistance in the circuit.

As is known to those of skill in the art, the law of electrical conductance states that the current is directly proportional to the size of the area and some material constant, and indirectly proportional to the length of the conductor. In mathematical terms:
conductance=area of the conductor*material constant/length of the conductor

The electrical unit for conductance is given in “Siemens”.

Thus, for a fixed length of conductor with a constant cross-sectional area the relationship can be rewritten as follows:
conductance=area of contact*material constant

The present sensor employs this concept, and is particularly advantageous when applied to a vehicle occupant detection system.

With reference to junction 3, the current is higher at this junction than junction2since the added weight on the conductors presses the conductors together thereby increasing the effective area. Since the area of contact increases, the current increases, thus, there is more “conductive area” and therefore more conductance.

The foregoing discussion is illustrative of one of the concepts employed by the present sensor. If the above circuit is modified such that the bare conductor has a higher conductivity with respect to the junction area (e.g., if a lower conductivity material of a approximately 10 mm length is inserted at the junction locations, it is possible to create a sensor with an improved sensing range.

It is possible to determine the current at various junctions if conductors are “lifted”, in various arrangements.

For example, no current will flow through any of the junctions if all conductors are lifted off their respective junctions (i.e., applying “zero” force or pressure). The current will only flow through junction2if the conductor is lifted from junction3. The current will only flow through junction3if the conductor is lifted off junction2. Currents can flow through both junction2and junction3providing “joint venture” current. This “cross talk” means that there are two junctions engaged and facilitates prediction where the forces are applied—i.e., it is possible to model where the forces are acting by modeling where the particular junctions are located in space.

Thus, summarizing the above in tabular form, it is possible to determine junction activity and the geometry of forces as follows:

Thus, if one were to include junction1and cycle all junctions through three different states (e.g., “0”, Eigengravity and Eigengravity+applied force), it is possible to increase the number of combinations.

By considering all three junctions to alternate through three different states the combinations increase and the joint venture current becomes more complex. If a hundred junctions are created and allow for many pressure states for each junction, the combinations and joint venture current become more complex. It is apparent that this complexity should be managed by separating the area of interest in collecting the information in a spreadsheet like format by re-establishing proper force/pressure measurements and their respective positions in space.

In a particularly preferred embodiment of the present sensor, many junctions are combined together in a small confined space—e.g., approximately a hundred junctions in a 10 mm square. This 10 mm square area can be considered as the effective contact area which maybe referred to as the “Matrix cell area”. The combinations of the individual junction areas can be thought of as a “Matrix contact area” where the resulting current provides information about what happens in each discreet junction. Pressure applied to this Matrix area (e.g., by an occupant sitting on the seat incorporating the sensor) produces a current, which is proportional to the sum of all minimal area changes. The benefit of this approach is the sensor is able to sense occupant weight/pressure and position.

By connecting sub-matrices into an overall matrix the present sensor can be advantageously employed in a vehicle occupant detection system. This allows for the creation of a spreadsheet like environment where interrogation of each matrix cell provides information about the acting force. Since it is possible to identify the location of the given cell in an overall matrix, it is possible to pinpoint the position of the acting force or pressure. The combination of information on each cell can be recognized as one or more patterns. A centroid for such patterns can be readily calculated and the prediction of the occupant's position in the vehicle seat can be deduced.

The conductors used in the present sensor may be derived from a number of sources. Non-limiting examples of suitable materials include metal, carbon, semi-conductors, spray-on films and other materials which are known to be electrically conducting. A particularly preferred material for use in the present sensor is conventionally known as Electro Conductive Textile (ECT). It is also possible to use metal-based textiles and carbonized textiles to produce the present sensor. A particularly preferred material is a carbonized fabric in which all conductors are weaved in a single direction alternating with non-conductors in a different direction for separation. This construction is believed to minimize hysteresis, i.e., the fabric regains its original geometric shape more quickly after removal of the applied force (i.e., after the occupant leaves the vehicle seat or the occupant shifts his/her weight).

In one embodiment of the present sensor, a so-called in-line sandwich construction is utilized. The physical construction and wiring diagram for this embodiment are shown inFIGS. 3 and 4, respectively.

In this embodiment, the conductor material is contained in a carbonized fabric in which all conductors are weaved in a single direction alternating with non-conductors weaved in a transverse direction. If one refers to the conductor material as A and the conductive matrix material as B, the junction area would be similar to a laminate structure having the form A-B-A relative to the contact area for each junction. This construction is referred to as “in-line” since the force/pressure is passed through both contacts simultaneously.

Conductor1touches the bottom of the matrix and conductor2touches the top of the matrix at junctions2and3, respectively. Thus, the conductivity of the circuit is influenced by two area changes for each force change and also depends on the conductivity of the matrix itself and the individual junction areas (approximately one hundred in this embodiment as discussed above).

Even though this embodiment relates to area changes produced by pressure changes, it shows similar behaviour as load cells, where the current is proportional to any force rather than a pressure. Thus, the configuration is relatively insensitive to side loads and provides a measurement of point forces governed by the area of the conductor (in many embodiments this will be about 0.1 mm wide wire or fabric material).

In a modified version of the in-line sandwich construction discussed above, it is possible to increase the area of the two conductors to the same size as the matrix area—for example, 10 mm square. This modification creates two physically equal areas between two dissimilar conductors—seeFIG. 5. The effective area is thus governed by the applied forces over the area—i.e., the pressure. Again, this embodiment provides a laminate structure of A-B-A as discussed above for the first embodiment of the in-line sandwich construction—seeFIG. 5.

Thus, as above junction1has no conduction, junction2has some conduction caused by its Eigengravity and junction3has even more conduction than junction2due to the extra applied force acting on its area. Again, it is possible to measure the current proportional to the area changes between the conductors and the matrix. However, in this embodiment, the geometric area change of the conductors due to gravity and applied forces has been removed from the measurement method. Therefore, the pressure affects only the individual junction areas allowing current to flow over the small crossing areas.

In a further embodiment, it is possible to employ a so-called bridge sandwich construction—this is illustrated inFIG. 6. In this embodiment, the matrix bridges the current from conductor1to conductor2. This embodiment is similar to the above-discussed embodiments insofar as the contact area relationship is A-B-A.

An alternate bridge sandwich construction is shown inFIG. 7where the shape of the conductors is flat as is the conductive matrix. Again, the configuration of contacts is A-B-A but the forces are not in-line—A might have a different force than B. A further modification of the sandwich construction is illustrated inFIG. 8wherein two matrices (or more) are arranged adjacent one another in order to provide different ranges of measurement and other characteristics. In this embodiment, the contact are relationship is: A-B-B-A in the line of applied force. It is possible to build sensors with say, ten or more matrix layers to decrease sensitivity.

As described above, the present sensor is particularly useful in a vehicle occupant detection system. The present sensor may be employed in such a system as a discreet sensor or a plurality of discreet sensors or it may be contained in a single sheet along with other sensors as will be described in more detail below.

With reference toFIG. 9, there is illustrated a vehicular seat10. Vehicular seat10comprises a seat bottom15having a primary seating surface20. Vehicular seat10further comprises a seat back25having a primary seating surface30.

Disposed in primary seating surface20are nine sensors22which are arranged generally in a 3×3 matrix pattern. Disposed in primary seating surface30are six sensors32arranged in a 2×3 matrix pattern.

Sensors22are individually connected to a bus24. Sensors32are individually connected to a connection bus (not shown).

In the illustrated embodiment, sensors22and32have an identical construction which will be described in more detail with reference toFIGS. 10–14. As further shown inFIG. 1, vehicle seat10is disposed in proximity to a spot where an airbag50would be deployed during collision of the vehicle.

With reference toFIGS. 10–14, sensor22comprises a first conductive foil24and a second conductive foil26. First conductive foil24is connected to an electrical lead27and second conductive foil26is connected to an electrical lead28. Interposed between conductive foils24and26are a pair of electrically insulating layers29. Also interposed between conductive foils24and26is a carbonized fabric material60which will be described in more detail below. Conductive foils24and26may be constructed from copper, aluminum or any other electrical conductive material. Further, the electrical conductive material may made wire, foil, solid and/or woven conductive materials.

Insulating layers29may be constructed from any suitable electrically non-conductive material—e.g., plastic and the like. Alternatively, insulating layers29may omitted if a larger portion of carbon fabric material60is utilized to cover, preferable over-cover, substantially the entire surface of foils24and26.

With continued reference toFIGS. 10–14, carbonized fabric material60will be described in more detail.

As shown, carbonized fabric material60comprises a matrix of electrically non-conductive fibers62. Disposed in this matrix are a number of electrically conductive fibers64. As shown, electrically conductive fibers64run in a single direction through fabric60. As can be seen, particularly with reference toFIG. 13, fabric60has an elastic modulus or resiliency such that it may be compressed and, once the compression force is removed, it will return to its precompressed state.

As shown, particularly inFIG. 12, sensor22is affixed to a surface of a foam element17of seat bottom. The nature of how this is accomplished does not particularly restrict it. For example, sensor22may be glued to the surface of foam element17. Alternatively, sensor22may be molded into the surface of foam element17in a conventional manner. A trim cover19is applied over foam element17to produce seat bottom15. When a weight or force is applied to the surface of seat bottom15in the direction of arrow A, the compressive force is transmitted to fabric16which compresses. This compression results in partial contact between foil24, electrically conducting strands64of fabric60and foil26. This results in a change in conductivity of sensor22which can be detected as discussed below. Once the applied weight or force is removed (e.g., the occupant leaves vehicle seat bottom15or the occupant shifts his/her weight).

With reference toFIGS. 15–18, there is illustrated an alternate embodiment of sensor22. Thus,FIG. 15illustrates a sensor100comprising a first layer110and a second layer130.

First layer110comprises a pair of opposed conductive strips112which are interconnected by a lead114. Disposed between and in contact with strips112is a carbonized fabric116of the same construction as fabric60described above with reference toFIGS. 10–14. In the illustrated embodiment, the electrically conductive fibers in fabric116run in the direction of arrow B.

First layer110further comprises an electrical lead118connected to one strip112and a connection bus (not shown).

Second layer130comprises the same element as first layer110and, for clarity, is labelled such that last digit in the element numbers corresponds to the same last digit of the elements of first layer110(for example, in second layer130, the carbonized fabric is element136which is constructed from the same material as fabric116of first layer110).

In the illustrated embodiment, the electrically conducting fibers of fabric136run in the direction of arrow C. Thus, the electrically conducting fibers in first layer110are disposed transverse, preferably substantially perpendicular, to the electrically conducting fibers in the fabric of second layer130.

With particular reference toFIGS. 16 and 17, the operation of sensor100will now be described. It will be seen thatFIGS. 16 and 17do not illustrate the other components of the vehicle seat (e.g., the foam element, the trim cover, the electrical connections and the like—this is for clarity only).

Thus,FIG. 16illustrates sensor100in the so-called resting state where there is no contact between first layer110and second layer130(in practice, the weight of these layers may result in there being minimal contact between the layers).

InFIGS. 16 and 17, suffix “a” is to denote an electrically conductive fiber whereas suffix “b” denotes an electrically non-conductive fiber.

InFIG. 17, a weight or force is applied in the direction of arrows D resulting in more surface area contacts at the junction between first layer110and second layer130. This results in an increase in the conductance of sensor100at a constant applied voltage as described above.

With reference toFIG. 19, there is illustrated yet a further embodiment of the present sensor. Thus, there is illustrated a sensor200comprising a single mat fabric210which is carbonized having the carbon fibers running in the directions of both arrows E and F. Individual fibers215are disposed in the direction of arrow E whereas individual fibers220are disposed in the direction of arrow F.

In the illustrated embodiment, there are nine crossover regions G where a trio of fibers215transverses a trio of fibers220. This creates a 3×3 matrix of individual sensors on a single fabric mat210. A series of electrical connections230is disposed at the edge of fabric mat210.

In operation, fabric mat210is compressed when a weight or force is applied thereto resulting in increased contact area and increased conductance as discussed above with the previous embodiments.

As discussed above, the present sensor allows for detection of a change of conductance between a resting state and an applied force or weight state (e.g., an occupant sitting on the vehicle seat). It is believed that the electronic circuitry to monitor the change in conduction is within the purview of a person of ordinary skill in the art. However, for clarity and illustrative purposes only, a number of embodiments of circuit diagrams for interrogating a 3×3 matrix of sensor elements (any of the embodiments discussed above) are provided inFIGS. 20–23. The circuit shown inFIG. 20is particularly well suited for use in a backrest. The circuit illustrated inFIG. 21is particularly well suited for use in a seat bottom. The circuits illustrated inFIGS. 22 and 23are alternate embodiments which are also useful. Of course, of those of ordinary skill in the art will be able to develop other circuits for interrogating the matrix to detect when a change of conductance has occurred.

By modeling various types and sizes of occupants of vehicle seats, it is possible to generate a database which can be used for comparison with actual conductance measurements taken while the vehicle is in operation to provide information on the nature of the occupant of the vehicle seat. This can then be used to control how or if the airbag should be fired in the event of a collision of the vehicle. Such control measures are conventional in the art.