Abstract:
The present invention relates to a combination heater and occupant sensor device that may be used in an automobile seat. The device will heat a seat and sense the mass of an occupant in the seat. The device provides the ability to combine occupant sensors with a seat heater without damaging the sensors or obtaining incorrect sensor readings. The sensor results may be processed and used to control air bag deployment, for example, or to indicate if the seat belt of an occupied seat is not being employed. To provide flexibility of the device during use, the device may be formed on a polymer substrate and configured to include apertures throughout. In addition, in the heating portion of the device, conductive material may be blended in a polymer and the device may be configured to limit conductor cracking after repeated flexing of the device thus extending the life of the device.

Description:
FIELD OF THE INVENTION 
   The present invention relates generally to seat heaters for automobiles and more particularly to seat heaters that incorporate an occupant sensor. 
   BACKGROUND OF THE INVENTION 
   Various heating devices are known and are used in the automotive industry. Examples of such heating devices include seat heaters that are used in many vehicles to improve the comfort of passengers riding in the vehicle. Some of these known seat heaters include a flexible heating device that is used to maintain the flexural characteristics of the seat. Examples of such heaters can be found in U.S. Pat. Nos. 6,884,965 and 7,053,344, both commonly owned by the applicant and incorporated herein by reference. These heaters have proven satisfactory and provide additional benefits including increased heating capacity, uniformity of heating, and protection against contact with liquid spills, among other benefits. 
   Recently, occupant sensors have been incorporated into automobile seats. These occupant sensors have been used to provide a reminder signal that if a seat is occupied but the associated seatbelt is not being employed, the occupant is alerted to fasten the seatbelt. Occupant sensors have also been used with vehicle air bags. In these applications, depending on the data collected by the occupant sensor, the air bag may be activated so that it is ready for deployment if needed. More specifically, as the occupant sensor detects the weight of the passenger sitting on the seat, a processor calculates the weight or other parameters and sends a signal to a controller to perform a certain action, such as activation of the air bag for deployment. In another embodiment, depending on the weight of the occupant, the signal to the controller may be to reduce the amount of force in which the air bag will release. In North America, for example, federal regulations require occupant sensor to have the ability to detect size and weight of an occupant. 
   Presently, automotive seat heaters and occupant sensors exist as separate components within a seat and utilize different technologies. For example, seat heaters typically include fabric based, wire wound elements, or carbon fiber elements. Occupant sensors on the other hand are often plastic sheet based, screen printed, polymer thick film (PTF). Each of the two technologies works well alone but when combined each can cause difficulties to the operation of the other&#39;s systems. For example, the heater wires and carbon fiber can interfere with the sensing capabilities of the occupant sensors, causing false or incorrect readings due to heat and varying pressure points. As a result, many known vehicle seats having an occupant sensor do not include the seat heater option, or the seat heater is installed below the occupant sensor which severely limits the seat heater&#39;s performance. Consequently, there exists a need in the automotive industry for a combination seat heater and occupant sensor device. The present invention addresses these and other known drawbacks with existing seat heater and occupant sensor devices. 
   SUMMARY OF THE INVENTION 
   The present invention relates to a combination heater and occupant sensor device that may be used in an automobile seat. With the invention, the high temperatures generated by the heater will not affect the operation of the occupant sensor. In addition, false readings experienced with existing occupant sensors are reduced, if not eliminated. Advantages of incorporating both a heater and sensor into a single device include decreased costs and assembly time, as well as the elimination of unsafe static buildup, wear, and friction between two rubbing parts. 
   Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims and drawings in which like numerals are used to designate like features. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1   a  is a top plan view of the heater/occupant sensor device of an embodiment of the present invention, illustrating the heater portion. 
       FIG. 1   b  is a bottom plan view of the heater/occupant sensor device of  FIG. 1   a , illustrating the occupant sensor portion. 
       FIG. 2  is an exploded view of the heater/sensor device of  FIG. 1   a , illustrating the layers of the heater/occupant sensor device. 
       FIG. 3  is an exploded view of the occupant sensor portion of an embodiment of the present invention. 
       FIG. 4  is a schematic of an alternative embodiment of a seat heater portion in accordance with the present invention. 
       FIG. 5   a  is a cross-sectional view of a membrane switch of an occupant sensor portion of an embodiment of the invention, illustrating actuation of the switch. 
       FIG. 5   b  is a cross-sectional view of a membrane switch of an occupant sensor portion of an embodiment of the invention, illustrating release of the switch. 
   

   DETAILED DESCRIPTION OF THE EMBODIMENTS 
   The present invention may be embodied in many forms, some of which are illustrated by the Figures. Referring to  FIGS. 1   a  and  1   b , in one aspect of the invention, a combination heater and occupant sensor device  20  is illustrated showing both sides of the device  20 . The device  20  may include a polymer sheet substrate  10 , for example a polyester sheet such as Mylar®, on which a heater portion  12  ( FIG. 1   a ) may be screen printed on one side, and an occupant sensor portion  14  ( FIG. 1   b ) may be screen-printed on the opposite side of the substrate  10 . The substrate  10  may be made of an electrically insulative material in the form of a thin film, for example having a thickness generally within the range of 0.004 to 0.010 inches though other film thicknesses are possible. 
   Alternatively, the heater portion  12  and occupant sensor portion  14  may both be screen-printed on the same side of the substrate  10 . In aspects of the invention providing the heater and sensor on the same side of the substrate  10 , the heater portion  12  is adapted to accommodate the occupant sensors  16  of the sensor portion  14  by including a conductive layer forming at least one buss  13 . As shown in  FIGS. 1   a  and  2 , two busses  13  may be used and may extend from one end of the substrate  10  to the opposing end. It should be understood that still other numbers and configurations of busses are possible and may be used with various aspects of the invention. In an exemplary embodiment, the busses  13  are configured to form a plurality of substantially isolated nonconductive areas  15  on the substrate surface  10  in which the sensors  16  will be located. Positioning the sensors  16  within the isolated nonconductive areas on the same side of the substrate as the heater may protect the sensors  16  from heat generated during operation of the heater portion  12 . In embodiments in which the sensor portion  14  and heater portion  12  are on opposite sides of the substrate  10 , the sensors  16  may be protected from interference from the heater by the substrate  10 , and thus the sensors  16  may be located in any positions on the sensor portion  14  suitable for the particular application. Similarly, the busses  13  may be configured in any appropriate design on the heater portion  12 , for example without providing any isolated nonconductive areas. 
   To provide even heating across the heater portion  12 , numerous traces  17  may extend outwardly from the busses  13  to distribute the heat across the heater portion. In an alternative aspect of the invention, at least some of the traces  17  may include spurs (similar to spurs  103  depicted in  FIG. 4 ) extending toward the next adjacent trace. Additionally, at least some of these spurs may include branches extending in a variety of directions to more fully cover the substrate  10  and distribute heat, except over the isolated areas  15 . 
   Referring back to  FIG. 1   b , the occupant sensor portion  14  may include a plurality of sensors  16 , such as membrane switches provided as dielectric honeycombs or other suitable configurations that are spaced across the sensor portion  14 . The sensors  16  may be in electrical communication with conductive traces  18 , which extend from each sensor to an electrical lead that will in turn deliver the sensor signal to a processor. The conductive traces  18  may be made of polymer silver or other suitable materials. 
   Referring to  FIG. 2 , which illustrates an exploded view of the device  20 , the occupant sensor portion  14  may include two sensor layers  24  and  26  that may be attached through the use of a dielectric adhesive. The plurality of sensors  16  may be positioned on one substrate  10  and a second electrically insulative substrate  10  may be positioned over these sensors  16 . In one aspect of the invention, when the device  20  is assembled and the heater portion  12  is applied to the substrate  10 , the sensors  16  are positioned such they are located over the isolated nonconductive areas  15 . 
   One skilled in the art will understand that known heaters may include electrical conductors that are typically made from a conductive metal such as copper, silver, gold, aluminum, carbon, or graphitic materials. It is further known that the conductive material used as the electrical conductor may be made of very small flakes of material in a polymer matrix. If this material is caused to be over-stretched or subject to repeated stretching, the conductive layer may crack, thereby resulting in undesirable arcing. 
   To overcome these known problems, in an alternative aspect of the invention illustrated in  FIG. 4 , a heater portion  80  may be configured to limit elongation of the conductive layer when the device is subjected to a flexing action. This is accomplished by the incorporation of apertures  101  in the substrate. Providing apertures  101  in the form of intersecting elongated slots substantially normal to each other, such as in a cross-shaped pattern shown in  FIG. 4 , will permit the desired flexing of the heater portion  80  without the undesirable cracking of the conductive layer used on the heater. As illustrated in  FIG. 4 , a possible configuration of apertures includes cross-shaped apertures  101  arranged in aligned rows and ranks offset with respect to each other, so that apertures  101  in adjacent rows and ranks overlap. In an alternative, the apertures  101  may be configured with rounded ends as shown, providing stress relief and reducing any potential tearing from the bending and flexing of the heater portion during use. 
   Returning back to  FIG. 1   a , a resistive layer  19  may be disposed on the conductive layer forming at least one buss  13  such that when an electrical power source is connected to the buss structure of the device  20 , heat is generated. The resistive layer  19  may include a positive temperature coefficient (PTC) material to provide an increasing resistance in response to an increasing temperature, known as a self-regulating heater, or it may include a fixed resistance element which requires an electronic controller to regulate the heat level. The resistive layer  19  may be comprised of a polymer thick film. 
   In an alternative aspect of the invention, a dielectric film may be applied between the substrate  10  and the conductive layer forming the at least one buss  13  to improve chemical resistance and durability of the device  20 . For example, the dielectric film may be a polyester film with a polyester adhesive. Additionally, other types of films, such as nylon polyolefin and polyimide, may be used as well as other types of adhesives such as epoxy and acrylics. The dielectric film, which effectively functions as a laminate, protects the surface of the heating portion  12  by preventing the conductive materials, for example silver and carbon black, from being removed by contact and abrasion during use. The laminate can further help reduce or eliminate cracking of the conductive layer forming at least one buss  13 , thereby extending the life of the heating portion  12 . 
   Referring again to  FIG. 4 , the heater  80  may be configured to be employed with vehicle seats having tie-down channels commonly used in automotive seat construction. Various open areas  102  may be provided adjacent to heating zones  104 ,  106 , and  108 . This will permit the heater  80  to be folded at these areas and into tie-down channels of the seat construction. Depending on the application, the size, number and shape of individual heating zones  104 ,  106  and  108  may vary to provide proper heating for the seat. As illustrated in  FIG. 4 , the heating zones may include conductive traces  105  that further define spurs  103  that extend toward adjacent conductive traces. As shown, the traces and spurs extend in numerous directions to substantially cover the individual heating zones to provide uniform heating over these areas. 
   The occupant sensor  16  may comprise any suitable sensing device, such as a device capable of sensing mass. In one embodiment of the invention, the sensor  16  may be a membrane switch. Referring to  FIGS. 5   a  and  5   b , cross-section views of an exemplary membrane switch are depicted. A membrane switch  16   a  may have first and second substantially flexible electrical contacts  120  facing each other that when come into contact with each other ( FIG. 5   a ) will send an electrical signal to a processor indicating this contact. The membrane switch  16   a  may also have a layer of dielectric material  122  deposited between, and on the surface of, one of the first and second contacts  120 . The layer of dielectric material  122  may be deposited in a predetermined geometric pattern including a plurality of cells  130  defined by cell walls  132 . The cell walls are broken in predetermined positions about the perimeter of each cell so that, during and after actuation of the switch, air within any cell can vent to one or more adjoining cells. This venting enables activation and prevents a vacuum from forming between the first and second contacts thereby enabling the switch to break contact after being depressed. 
   The dielectric spacer  122  is deposited with a uniform thickness on top of the conductive layer  120  such as by deposition, silk screening or any similar process where the thickness can vary. In one embodiment, the predetermined pattern of the dielectric spacer layer  122  is in the form of a series of hexagons forming a plurality of substantially identical cells  130  across the surface of the conductive layer  120 . Each cell  130  is defined by six cell walls  132  which are shared with adjacent cells in the pattern. It has been found that the hexagonal pattern provides the most conductive surface areas with the least amount of dead space at the wall junctions. While not as preferred, other patterns and shapes such as in the form of rectangles, circles or similar patterns may be used. Each cell wall  132  is broken proximate its midpoint to provide channels  134  between adjacent cells  130 . Such channels  134  enable air between the first and second assemblies  12  and  14  to move between one or more adjacent cells  130  when depressed to activate the switch  16 . Additionally, when the switch  16  is released, the channels  134  enable air to re-enter the depressed cell or cells  130 . 
   In an embodiment having a dielectric spacer layer  122  on the surface of each conductive layer  120 , the channels  134  of each cell  130  preferably align with the channels  134  on the opposite side of the cells  130  so that three continuous sets of parallel lines or air channels are formed across the membrane switch  16 . These lines or air channels assist in the free flow of air between one or more cells  130 , which in turn provides better actuation and release of the switch. In order to vary the force required to activate the switch  16 , the size of the hexagons may be adjusted. 
   Variations and modifications of the foregoing are within the scope of the present invention. It should be understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text and/or drawings. All of these different combinations constitute various alternative aspects of the present invention. The embodiments described herein explain the best modes known for practicing the invention and will enable others skilled in the art to utilize the invention. The claims are to be construed to include alternative embodiments to the extent permitted by the prior art. 
   Various features of the invention are set forth in the following claims.