Abstract:
A vehicle seat weight sensor for sensing the weight of an occupant in a vehicle seat. The sensor has a substrate that is attached between the ends of a seat bracket such that a portion of the forces applied to the seat are transferred from a seat pan to an upper slide rail through the substrate. Strain gage resistors are located on the substrate to generate an electrical signal in response to the substrate being stressed. The electrical signal changes magnitude as a function of the weight of the seat occupant. The substrate has a pair of step sections for concentrating the forces onto the strain gage resistor.

Description:
CROSS REFERENCE TO RELATED AND CO-PENDING APPLICATIONS 
     This application 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”. 
     U.S. patent application Ser. No. 09/422,382, filed Oct. 21, 1999 and titled, “Vehicle Seat Weight Sensor”. 
     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 applicant&#39;s 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 gauge resistors. 
     An additional feature of the invention is to provide a vehicle seat weight sensor for connecting to an external electrical circuit. The sensor includes a substrate that has a center section and a step section attached to the center section. The center section is located adjacent to the step section. An outer section is attached to the step section. One or more strain gage resistors are mounted on the center section of the substrate to generating an electrical signal in response to the substrate being stressed. A seat bracket has a first and second end. The seat bracket is located between a seat pan and an upper slide rail. The substrate is mounted between the first and second ends of the seat bracket such that a portion of the forces applied to the seat pan are transferred from the seat pan to the upper slide rail through the substrate. The outer sections are attached to the first and the second ends of the bracket. 
     Another feature of the invention is to provide a vehicle seat weight sensor for sensing the weight of an occupant in a vehicle seat. The seat has a seat back, a seat bottom attached to a seat pan, a seat bracket having a first end attached to the seat pan, an upper slide rail coupled to a second end of the seat bracket and a lower slide rail coupled to the upper slide rail. The sensor includes a substrate that has a first and second outer section. The first outer section is attached to the first end of the seat bracket and the second outer section is attached to the second end of the seat bracket such that a portion of the forces applied to the seat bottom are transferred from the seat pan to the upper slide rail through the substrate. One or more strain gage resistors are located on the substrate to generate an electrical signal in response to the substrate being stressed. The electrical signal changes magnitude as a function of the weight of the seat occupant. The substrate has a center section that has the stain gage resistor mounted on it. A pair of step sections are attached to the center section. The center section is located between the step sections for concentrating the forces onto the strain gage resistor. The first and second outer sections are attached to the step sections. The substrate has a fastener that is connected between the first end of the seat bracket and the first outer section and a second fastener that is connected between the second end of the seat bracket and the second outer section. The electrical signal is used to control activation of an airbag. 
     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. 
    
    
     BRIEF 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 side view of the sensor of FIG. 1 taken along lines  2 — 2 . 
     FIG. 3 is an enlarged perspective view of the automobile seat weight sensor and seat bracket. 
     FIG. 4 is a perspective view of an alternative embodiment of a seat weight sensor. 
     FIG. 5 is a top view of FIG.  4 . 
     FIG. 6 is a side view of FIG.  4 . 
    
    
     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 an rectangular tube like upper slide rail  25  and seat bottom  13 . 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 . A channel shaped 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 base  28  by a fastener  30  such as a bolt or rivet. The base  28  is attached to a vehicle floor  29  by a fastener  31  such as a bolt or rivet. 
     Four generally right angle shaped seat brackets  34  are shown mounted at the four corners of seat assembly  10  between seat pan  16  and upper slide rail  25 . Seat bracket  34  has an upper end  35  and a lower end  36 . Fasteners  27 A and  27 B attach lower end  36  to upper slide rail  25 . Fastener  27 C attaches upper end  35  to seat pan bottom  17 . Fasteners  27 A,  27 B and  27 C are conventional fasteners such as hex headed bolts and nuts or tapped Allen head screws or tapped shoulder screws or rivets. 
     Four weight sensor assemblies  40  are shown mounted to brackets  34 . Sensors  40  are attached diagonally between upper end  35  and lower end  36 . Since the bracket is generally shaped like a right angle the sensor  40  would be positioned generally along the hypotenuse of a triangle formed by the bracket and the sensor  40 . Sensors  40  are attached to upper end  35  and lower end  36  by fasteners  27 C and  27 B, respectively. Sensor  40  has a metal substrate  41  with two outer sections, a first outer section  42  and a second outer section  43 . A cover coating  45  is located in the middle of sensor  40 . 
     When an occupant sits on seat bottom  12 , the seat occupants weight is transferred from seat bottom  12 , to seat pan  16 , partially through bracket  34  and partially through sensor  40 , to upper slide rail  25 , then to lower slide rail  26 , then to seat base  28  and then to floor  29 . A portion of the 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  can be connected together at a junction box (not shown) in the center of the seat if desired. The junction box would allow 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  with the cover coat  45  removed are shown. Sensor assembly  40  has a metal substrate  41  with an upper surface  41 A and a bottom surface  41 B. Metal substrate  41  is preferably formed from  430  stainless steel. Substrate  41  has step sections  53  that extend away generally perpendicularly on both sides of a center section  55 . Outer sections  42  and  43  connect with and extend away from step sections  53 . Additionally, a third outer section  56  is connected to first outer section  42  and a fourth outer section  57  is connected to second outer section  43 . Aperture  58  extends through outer section  56 . Aperture  59  extends through outer section  57 . Aperture  60  extends through outer seat bracket lower end  36 . Fasteners  27 B and  27 A pass through apertures  59  and  60 , respectively. Fastener  27 C passes through aperture  58 . Fasteners  27 B and  27 C hold substrate  41  to bracket  34 . Substrate  41  including center section  55 , step sections  53 , outer sections  42 ,  43  and  56 ,  57  and apertures  58 ,  59 ,  60  are formed by stamping or bending of metal substrate  41 . 
     Several strain gage resistors  62 A and  62 B are arranged on surface  41 A within center section  55 . Resistors  62 A and  62 B are made up of two smaller rectangles of resistive material that are interconnected. Similarly, resistors  62 C and  62 D (not shown) are located on the bottom surface  41 B. An insulative dielectric layer  64  is shown disposed on top surface  41 A. Similarly, layer  64  would be disposed on bottom surface  41 B. On top of the dielectric layer  64 , the strain gage resistors  62 A-D are formed. Resistors  62 A-D are strain sensitive and will change resistance based on the amount of strain in substrate  41 . Output pads  65  are connected to resistors  62 A-D. The output pads  65  are used to solder (not shown) to the individual wires in wiring harness  50 . Cover coat  45  is placed over resistors  62 A-D and output pads  65 . The cover coat protects the resistors from damage and acts as a solder mask. Dielectric layer  64 , Resistors  62 A-D and output pads  65  can be formed from conventional thick film materials using conventional thick film screening and processing techniques. Dielectric layer  64 , Resistors  62 A-D and output pads  65  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  62 A and  62 C would be connected to form a half bridge circuit (not shown) and resistors  62 B and  62 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 full bridge circuit. 
     Referring to FIGS. 4,  5  and  6  an alternative embodiment of a seat weight sensor  70  is shown. Sensor  70  is designed to be piggyback mounted to a weight carrying member (not shown) in a vehicle seat. Sensor  70  is identical to sensor  40  except that the third and fourth outer sections  56  and  57  have been omitted and a pair of apertures  71  and  72  have been placed in the first and second outers sections  42  and  43 . Apertures  71  and  72  would have fasteners (not shown) placed through them in order to attach sensor  70  to a weight carrying member in a car seat. Sensor  70  can be attached by bolts, rivets or welding. A portion of the seat occupants weight is transferred though sensor  70  when it is mounted to a weight carrying member in a car seat. This weight causes strain in sensor  70  and is measured by the strain gage resistors  62 A-D. An electrical output signal is generated and transmitted to a conventional air bag controller (not shown). The electrical output signal is proportional to the weight of the seat occupant. 
     Remarks About the Preferred Embodiment 
     When an occupant sits in a vehicle seat, a portion of the occupant&#39;s weight is transferred to substrate  41  as a force through bracket  34 . Step sections  53  cause the center section  55  of substrate  41  to bend. As the center section  55  bends, the resistors  62 A,  62 B on the upper surface  41 A will be in tension and the resistors  62 C,  62 D on the bottom surface  41  B will be in compression. A voltage is applied to the resistors  62 A-D. The strain on resistors  62 A-D causes the voltage or electrical output signal across the resistors to change as a function of the weight of the seat occupant. The electrical signal is transmitted over wire harness  50  to a conventional air bag controller. The air bag controller then can control deployment of the airbag based upon the occupant&#39;s 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  62 A-D on the top and bottom surfaces of substrate  41 , more or fewer resistors could be used. If desired, resistors  62 A-D 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 a portion of 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 other than a wire harness  50 . For example, a connector or terminal. 
     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 weight sensor shown was mounted to a seat bracket, one skilled in the art will realize that the preferred embodiment could be mounted to other seat members in other locations in the seat. For example, the weight sensor could be placed on the slide rails or on the seat pan or on a part of the base. 
     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 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.