Abstract:
A vehicle seat weight sensor for sensing the weight of an occupant in a vehicle seat. The sensor has a housing. A substrate is located in the housing and has a first and second end. Strain gauge resistors are located on the substrate to generate an electrical signal in response to the substrate being stressed by the occupants weight. The electrical signal is 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.

Description:
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 sensing the weight of an occupant in a vehicle seat. The sensor includes a housing. The housing has a connector shroud. A substrate is located in the housing and has a first and second end. A strain gauge resistor is located on the substrate to generate 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. 
     Another feature of the invention is to provide a method for controlling deployment of an air bag. The method includes providing a seat weight sensor that is connected between a seat spring and a seat basket of the vehicle seat. An occupant is seated into the seat. An electrical signal changes as a function of the weight of the seat occupant. The electrical signal is provided to an airbag controller. The deployment of the airbag is controlled in response to the electrical signal. 
     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 perspective view of the automobile seat weight sensor of FIG.  1 . 
     FIG. 3 is a top view of FIG.  2 . 
     FIG. 4 is a cross-sectional view of FIG. 2 when the sensor is attached to a seat. 
     FIG. 5 is a top view of FIG. 2 with the housing removed. 
     FIG. 6 is an enlarged side view of FIG. 5 along lines  6 — 6 . 
     FIG. 7 is a cross-sectional view of an alternative embodiment. 
     FIG. 8 is a perspective view of an alternative embodiment. 
    
    
     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 EMBODIMENT 
     The present invention provides a vehicle weight sensor for detecting the weight of a seat occupant. Referring to FIG. 1, there is a seat assembly  12  shown. Seat assembly  12  has a seat back  14 , seat bottom  16 , side rail  18 , seat basket  20 , seat spring  22  and a connector or wire harness  24 . Weight sensor assembly  30  is shown mounted in the seat between spring  22  and seat basket  20 . When an occupant sits on seat bottom  16 , the occupants weight causes the tension force in spring  22  to increase. This force is measured by sensor  30  and an electrical signal output is generated and transmitted over wire harness  24  to a conventional air bag controller. The air bag controller then can control deployment of the airbag based upon the occupants weight. 
     Referring to FIGS. 2,  3 , and  4  details of sensor assembly  30  are shown. Sensor assembly  30  has a metal substrate  31  with an upper surface  32 A and a bottom surface  32 B. Metal substrate  31  is preferably formed from steel. Substrate  31  has step sections  33  that extends downwardly on both sides of a center section  35 . A pair of outer flat sections  34 A and  34 B connect with and extend away from step sections  33 . A spring aperture  36  is located in section  34 A and has spring end  23  of seat spring  22  passing therethrough. A hook aperture  37  and hook  38  are formed in section  34 B. Seat basket  20  attaches over hook  38  to connect sensor  30  to seat assembly  10 . Step sections  33 , apertures  36  and  37  and hook  38  are formed by stamping substrate  31 . Housing  40  is insert molded using plastic injection molding around metal substrate  31 . Housing  40  has a connector shroud  42 , a connector cavity  43  and a latch tab  44 . Wire harness  24  connects onto connector shroud  42  and locks in place with latch tab  44 . Inside housing  40 , on center section  35  on surfaces  32 A and  32 B, conductors  56  are located. Terminals  60  are electrically and mechanically attached to conductors  56  using a conventional solder  59 . Terminals  60  extend into housing cavity  43 , where they mate with the wiring harness  24 . 
     Referring to FIGS. 5 and 6, details of the sensor inside the housing are shown. FIG. 5 is a top view with the housing removed and FIG. 6 is an enlarged side view of FIG. 5 along lines  6 — 6 . A dielectric  51  layer is shown disposed on top surface  32 A in center section  35 . Similarly, layer  51  would be disposed on bottom surface  32 B. On top of dielectric layer  51 , a strain gauge resistor  55  is formed. Resistors  55  are strain sensitive and will change resistance based on the amount of flex or bend in substrate  31 . Conductors  56  connect to resistors  55 . A cover coat  57  is placed over resistors  55  and conductors  56 . The cover coat protects the resistors from damage and acts as a solder mask. Terminals  60  are soldered to conductors  56  using a solder  59 . Dielectric  51 , Resistors  55 , and conductors  56  are formed from conventional thick film materials using conventional thick film processing techniques or 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, two resistors  55  would be placed on top surface  32 A and two resistors  55  would be placed on bottom surface  32 B to form a bridge circuit (not shown) that is well known in the art. Alternatively, the resistors could be placed only on the top or the bottom surface. 
     Referring to FIG. 7, an alternative embodiment is shown. If desired, the seat sensor  30  may be connected between two seat springs  22 , omitting the seat basket  20  connection. In this case, the hook  38  is eliminated and another aperture  36  is formed in section  34 B. 
     Referring to FIG. 8, another alternative embodiment is shown. In some applications, it may be desired, to sense tension on the seat springs in two directions. Sensor assembly  80  pairs together two of sensor assembly  30  in a common housing  82  to give electrical output signals representative of seat tension in two directions. Sensor assembly  80  can be mounted in the center of a seat or can be mounted in a corner of the seat. Housing  82  is insert molded using plastic injection molding around two metal substrates  31 . 
     Remarks About the Preferred Embodiment 
     When an occupant sits in a vehicle seat, weight is transferred to substrate  31  as a force through seat spring  22  and seat basket  20 . Step sections  33  cause the center section  35  of substrate  31  to bend. As the center section  35  bends, the resistors on the top surface will be in compression and the resistors on the bottom surface will be in tension. A voltage is applied to the resistors  55 . The strain on resistors  55  causes the voltage or electrical output signal across resistors  55  to change as a function of the weight of the seat occupant. The electrical signal is transmitted over wire harness  24  to a conventional air bag controller. The air bag controller then can control deployment of the airbag based upon the 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 a resistor  55  on the top and bottom surface of substrate  31 , more or fewer resistors could be used. If desired, resistors  55  could be placed on only one surface of substrate  31 . 
     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  31  or thin film resistors could be used. Furthermore, the shape of substrate  31  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  30  was shown with a housing  40 , it is contemplated to omit housing  40 . 
     Another variation of the weight sensor would be to utilize other electrical connections other than terminals  60 . For example, other types of connectors or discrete wires could be used in place of terminals  60 . 
     Yet, a further variation, would be to place signal conditioning circuitry on substrate  31  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.