Abstract:
A vehicle seat weight sensor for sensing the weight of an occupant in a vehicle seat. The sensor includes a substrate that has a first and second end. The substrate is located between the seat bottom and the vehicle floor. Strain gauge resistors are located on the substrate for generating an electrical signal in response to the substrate being stressed by the weight of the seat occupant. The electrical signal changes as a function of the weight of the seat occupant. Several mounting configurations to the vehicle seat are shown.

Description:
CROSS REFERENCE TO RELATED AND CO-PENDING APPLICATIONS 
     This application is a division of U.S. Ser. No. 09/422,382 filed Oct. 21, 1999 and is related to the following U.S. patent applications: 
     U.S. patent application Ser. No. 09/374,874, filed Aug. 16, 1999 and titled, “Automobile seat weight Sensor”. 
     U.S. patent application Ser. No. 09/374,870, filed Aug. 16, 1999 and titled, “Vehicle Occupant Position Detector and Airbag Control System”. 
     The foregoing patents have the same assignee as the instant application and are herein incorporated by reference in their entirety for related and supportive teachings. 
    
    
     BACKGROUND OF THE INVENTION 
     1 . Field of the Invention 
     This invention relates to an automobile weight sensor for detecting the presence of a person having a weight in a car seat, and in particular to a sensor that can detect the presence of an occupant using strain sensitive resistors and provide an electrical signal to control activation of an airbag. 
     2 . Description of the Related Art 
     Various devices are well known for their ability to measure force, pressure, acceleration, temperature, position, etc. by using a sensing structure combined with signal processing electronics. One general type of sensor or transducer for such applications is a resistive strain gauge sensor in which force or pressure is sensed or measured based on strain placed on the resistors. Resistive strain gauges function by exhibiting changes in resistance proportional to force which causes dimensional changes of the resistor. 
     Many types of strain gauge sensors have been designed and made commercially available. Various strain gauge sensors have proven to be generally satisfactory. Prior art sensors, however, have tended to be rather expensive and not suitable in certain applications such as sensing the presence of an occupant in an automobile seat. A sensor suitable for such an application must be compact, robust, impervious to shock and vibration and yet inexpensive. 
     Automobile seats can use sensors to activate air bags, which would be deployed during an accident. Injury to infants or small children from air bag deployment with excessive force is a current industry problem. A weight sensor in the seat can be used to control the deployment force during air bag activation. If a heavy person is in the seat, the airbag is deployed at full force. If a light person is in the seat, such as a child, the airbag is deployed at a slower, less forceful rate or not at all. A current unmet need exists for a reliable, low cost, simple and robust automobile seat weight sensor that is used to control airbag deployment. 
     3 . Related Art 
     Examples of patents that are related to the present invention are as follows, and each patent is herein incorporated by reference for the supporting teachings: 
     U.S. Pat. No. 5,573,269 is a apparatus for sensing and restraining an occupant of a vehicle seat. 
     U.S. Pat. No. 4,556,598 is a porcelain tape for producing porcelainized metal substrates. 
     The foregoing patents reflect the state of the art of which the applicant is aware and are tendered with the view toward discharging the applicants acknowledged duty of candor in disclosing information which may be pertinent in the examination of this application. It is respectfully stipulated, however, that none of these patents teach or render obvious, singly or when considered in combination, the applicants claimed invention. 
     SUMMARY OF THE INVENTION 
     It is a feature of the invention to provide a reliable and cost-effective vehicle seat weight sensor for detecting the weight of a seat occupant. The sensor uses strain sensitive resistors. 
     An additional feature of the invention is to provide a vehicle seat weight sensor for sensing the weight of an occupant in a vehicle seat for use by an airbag control system. The seat has a seat back, a seat bottom and a seat bracket connected to a vehicle floor. A lower slide rail and an upper slide rail are coupled to the bracket and a seat pan is attached to the upper rail. The sensor includes a horizontally elongated substrate that is located between the seat bottom and the vehicle floor such that a portion of the weight of the seat occupant on the seat bottom is transferred from the seat bottom to the vehicle floor through the substrate. The substrate has a first and a second end. A neckdown region is formed in the substrate between the first and second ends for concentrating the weight of the vehicle occupant. Several strain gauge resistors are located on the neckdown region for generating an electrical signal in response to the substrate being stressed by the weight of the seat occupant. The electrical signal changes magnitude as a function of the weight of the seat occupant. The sensor can be located in several locations within the car seat. The substrate can be located between the upper slide rail and the seat pan. The substrate can be located between the lower slide rail and the seat bracket. The substrate can also be located between the lower seat rail and the vehicle floor. An additional feature of the invention is to provide a vehicle seat weight sensor for sensing the weight of an occupant in a vehicle seat. The sensor includes a substrate that has a first and second end. At least one strain gauge resistor is located on the substrate for generating an electrical signal in response to the substrate being stressed. The electrical signal changes as a function of the weight of the seat occupant. A connection mechanism is located at the first and second ends of the substrate to connect the substrate to the vehicle seat. 
     The invention resides not in any one of these features per se, but rather in the particular combination of all of them herein disclosed and claimed and it is distinguished from the prior art in this particular combination of all of its structures for the functions specified. Other features of the present invention will become more clear from the following detailed description of the invention, taken in conjunction with the accompanying drawings and claims, or may be learned by the practice of the invention. 
     There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject matter of the claims appended hereto. Those skilled in the art will appreciate that the conception, upon which this disclosure is based, may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of the preferred embodiment of an automobile seat weight sensor in an automobile seat. 
     FIG. 2 is a partial cross-sectional side view of a FIG. 1 looking at the sensor from the inside of the seat along line  2 — 2 . 
     FIG. 3 is a perspective view of the sensor. 
     FIG. 4 is a perspective view of an alternative embodiment of an automobile seat weight sensor in an automobile seat. 
     FIG. 5 is a partial cross sectional side view of FIG. 4 looking at the sensor from the inside of the seat along line  5 — 5 . 
    
    
     It is noted that the drawings of the invention are not to scale. The drawings are merely schematic representations, not intended to portray specific parameters of the invention. The drawings are intended to depict only typical embodiments of the invention, and therefore should not be considered as limiting the scope of the invention. The invention will be described with additional specificity and detail through the use of the accompanying drawings. In the drawings like numbering represents like elements between the drawings. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention provides a vehicle weight sensor for detecting the weight of a seat occupant. Referring to FIGS. 1 and 2, there is a seat assembly  10  shown. Seat assembly  10  has a seat  12  with a seat back  14 , and a seat bottom  13 . A seat pan  16  is located between the an upper slide rail  25  and seat bottom  12 . Seat pan  16  has seat pan bottom  17  that has a seat pan clearance aperture  18  formed therein. A seat pan outer rim  19  runs around the outside perimeter of seat pan  16 . A seat lip  21  extends inwardly from outer rim  19 . Seat pan fasteners  20  are used to attach seat bottom  13  to seat pan  16 . A lower slide rail  26  is slidably attached to upper slide rail  25  by roller bearings (not shown). The slide rails  25  and  26  allow seat assembly  10  to slide forward and backwards in a vehicle. The lower slide rail  26  is attached to seat bracket  28  by a fastener  30  such as a bolt or rivet. The seat bracket  28  is attached to a vehicle floor  29  by a fastener  31  such as a bolt or rivet. 
     Four weight sensor assemblies  40  are shown mounted at the four corners of seat assembly  10  between seat pan  16  and upper slide rail  25 . Sensor  40  has a metal substrate  41  with two ends, a first end  42  and a second end  43 . A cover coating  45  is located in the middle of sensor  40 . A substrate to seat pan fastener  46  is used to attach the substrate first end  42  to the seat pan  16 . Fastener  46  can be a bolt and nut or a bolt and a threaded hole or can be a rivet. A spacer  47  is located between first end  42  and seat pan bottom  17 . A substrate to upper slide rail threaded fastener  48 A is used to attach the substrate to the upper slide rail. Fastener  48 A passes through clearance aperture  18 . A nut  48 B is located above substrate  41  and another nut  48 C is located below substrate  41 . Nuts  48 B and  48 C are tightened to securely hold fastener  48  to substrate  41 . Fastener  48 A has a standoff  48 D located above the upper slide rail  25  between the upper slide rail  25  and the seat pan  16 . A swaged head  48 E is shown in phantom inside slide rail  25 . Swaged head  48 E and standoff  48 D securely attach fastener  48 A to upper slide rail  25 . Fastener  48 A could also use threaded holes in substrate  41  or slide rail  25  instead of nuts if desired. 
     When an occupant sits on seat bottom  12 , the seat occupants weight is transferred from seat bottom  12  to seat pan  16 , through sensor  40 , to upper slide rail  25 , then to lower slide rail  26 , then to seat bracket  28  and then to floor  29 . The entire weight of the seat occupant is transferred as a force through the four sensors  40 . This weight causes strain in sensor  40  and is measured by sensor  40 . An electrical output signal is generated and transmitted over a wire harness  50  to a conventional air bag controller (not shown). The air bag controller then can control deployment of the airbag based upon the seat occupants weight. The wiring harnesses  50  from four sensors  40  are connected together at a junction box  52  in the center of the seat. The junction box  52  would be connected by another wiring harness (not shown) to a conventional airbag controller. Junction box  52  allows for convenient attachment of a single connector to connect with all four sensors  40 . 
     Referring additionally to FIG. 3, more details of the sensor assembly  40  are shown. Sensor assembly  40  has a metal substrate  41  with an upper surface  41 A and a bottom surface  41 B. Substrate  41  is generally elongated and dog boned shaped. Substrate  41  is preferably formed from 430 stainless steel. Substrate  41  has a first end  42 , a second end  43  and a neckdown region  44  located between first end  42  and second end  43 . A first end aperture  56  is located in the first end  42  and a second end aperture  57  are located in the second end  43 . Fasteners  46  and  48 A pass through apertures  56  and  57 , respectively. Several strain gauge resistors  53 A and  53 B are arranged on surface  41 A at the junction of the neckdown region and the first and second end, respectively. Similarly, resistors  53 C and  53 D (not shown) are located on the bottom surface  41 B. A insulative dielectric layer  59  is shown disposed on top surface  41 A. Similarly, layer  59  would be disposed on bottom surface  41 B. On top of the dielectric layer  59 , the strain gauge resistors  53 A-D are formed. Resistors  53 A-D are strain sensitive and will change resistance based on the amount of strain in substrate  41 . Output pads  54  are connected to resistors  53 A-D. The output pads  54  are used to solder to the individual wires in wiring harness  50 . Cover coat  45  is placed over resistors  53 A-D and pads  54 . The cover coat protects the resistors from damage and acts as a solder mask. Dielectric layer  59 , Resistors  53 A-D and pads  54  can be formed from conventional thick film materials using conventional thick film screening and processing techniques. Dielectric layer  59 , Resistors  53 A-D and pads  54  can also be formed from a ceramic green tape. Such methods of forming resistors on metal substrates are detailed in U.S. Pat. No. 4,556,598 titled, “A porcelain tape for producing porcelainized metal substrates”, the contents of which are specifically herein incorporated by reference. 
     In a typical configuration, Resistors  53 A and  53 C would be connected to form a half bridge circuit (not shown) that is well known in the art and resistors  53 B and  53 D would be connected to form another half of a bridge circuit that is well known in the art. The two half bridges would be connected to form a conventional full bridge circuit. 
     Referring to FIGS. 4 and 5, there is a perspective view of an alternative embodiment of an automobile seat assembly  100  shown. Seat assembly  100  has a seat  12  with a seat back  14 , and a seat bottom  13 . A seat pan  16  is located between the an upper slide rail  25  and seat bottom  12  (omitted for clarity from FIG.  4 ). Seat pan  16  has seat pan bottom  17 . A seat pan outer rim  19  runs around the outside perimeter of seat pan  16 . A seat lip  21  extends inwardly from outer rim  19 . Seat pan fasteners  20  are used to attach seat pan  16  to upper rail  25 . A lower slide rail  26  is slidably attached to upper slide rail  25  by roller bearings (not shown). The slide rails  25  and  26  allow seat assembly  10  to slide forward and backwards in a vehicle. Seat brackets  28  on each side of the seat are attached to a vehicle floor  29  by a fastener  31  such as a bolt or rivet. A seat bracket clearance aperture  28 A is located in bracket  28 . 
     Four weight sensor assemblies  40  are shown mounted at the four corners of seat assembly  100  between lower slide rail  26  and bracket  28 . The sensor  40  of FIGS. 4 and 5 is the same as was detailed for FIGS. 1 and 2. Sensor  40  has a metal substrate  41  with two ends, a first end  42  and a second end  43 . A cover coating  45  is located in the middle of sensor  40 . An angled support  102  has a lower section  106  and an upper section  104 . Fasteners  108  are used to attach support  102  to seat bracket  28 . First end  42  of substrate  41  rests on upper section  104 . A substrate to support fastener  46 A and nut  46 B is used to attach the substrate first end  42  to the support  102 . Fastener  46  can be a bolt and nut or a bolt and a threaded hole or can be a rivet. A substrate to lower slide rail threaded fastener  48 A is used to attach the substrate second end  43  to the lower slide rail  26 . Fastener  48 A passes through clearance aperture  28 A. A nut  48 B is located below substrate  41  and another nut  48 C is located above substrate  41 . Nuts  48 B and  48 C are tightened to securely hold fastener  48 A to substrate  41 . Fastener  48 A has a standoff  48 D located below the lower slide rail  26  between the lower slide rail  26  and the bracket  28 . A swaged head  48 E is shown in phantom inside slide rail  26 . Swaged head  48 E and standoff  48 D securely attach fastener  48 A to slide rail  26 . Fastener  48 A could also use threaded holes in substrate  41  or slide rail  26  instead of nuts if desired. 
     When an occupant sits on seat bottom  12 , the seat occupants weight is transferred from seat bottom  12  to seat pan  16  and upper slide rail  25 , then to lower slide rail  26 , through sensor  40 , to support  102 , then to seat bracket  28  and then to floor  29 . The entire weight of the seat occupant is transferred as a force through the four sensors  40  at each corner of the seat. This weight causes strain in sensor  40  and is measured by the strain gauge resistors  53 A-D. An electrical output signal is generated and transmitted over a wire harness  50  to a conventional air bag controller (not shown). The air bag controller then can control deployment of the airbag based upon the seat occupants weight. The wiring harnesses  50  from four sensors  40  are connected together at a junction box  52  in the center of the seat. The junction box  52  would be connected by another wiring harness (not shown) to a conventional airbag controller. Junction box  52  allows for convenient attachment of a single connector to connect with all four sensors  40 . 
     Remarks About the Preferred Embodiment 
     When an occupant sits on seat bottom  12 , the seat occupants weight is transferred from seat bottom  12  to seat pan  16 , through sensor  40 , to upper slide rail  25 , then to lower slide rail  26 , then to seat bracket  28  and then to floor  29 . The entire weight of the seat occupant is transferred as a force through the four sensors  40 . This weight causes strain and flex in sensor  40 . A voltage is applied to the resistors. The strain on the resistors causes the voltage or electrical output signal across the resistors to change as a function of the weight of the seat occupant. The resistors are connected together in a bridge configuration. The output of the bridge is transmitted over wire harness  50  to a conventional air bag controller (not shown). The air bag controller then can control deployment of the airbag based upon the seat occupants weight. Typically, the air bag is disengaged or turned off below a minimum weight. The air bag deploys with less force for a lighter person and more force for a heavier person. 
     Variations of the Preferred Embodiment 
     Although the illustrated embodiment shows resistors  53 A-D on the top and bottom surface of substrate  41 , more or fewer resistors could be used. If desired, the resistors could be placed on only one surface of substrate  41 . 
     The weight sensor shown used a thick film resistor, one skilled in the art will realize that the preferred embodiment would work with other types of resistors. For example, discrete chip resistors could be attached to substrate  41  or thin film resistors could be used. Furthermore, the shape of substrate  41  could be varied to any configuration that would transfer the weight from the seat and concentrate it in the desired location on the substrate. 
     Although sensor assembly  40  was shown without a housing, it is contemplated to add a housing. 
     Another variation of the weight sensor would be to utilize other electrical connections. For example, other types of connectors or terminals could be used in place of wire harness  50 . 
     Yet, a further variation, would be to place signal conditioning circuitry on substrate  41  to amplify and filter the electrical signal before it is transmitted to the airbag controller. 
     The illustrated embodiment showed the use of the weight sensor in an automobile seat. It is contemplated to utilize the weight sensor in other occupant weight sensing applications such as chairs, sofas, scales, beds and mattresses, hospital equipment, cribs, airplane seats, train seats, boat seats, amusement rides, and theater seats, 
     While the invention has been taught with specific reference to these embodiments, someone skilled in the art will recognize that changes can be made in form and detail without departing from the spirit and the scope of the invention. The invention should therefore be limited only by the scope of the human imagination. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.