Abstract:
A vehicle seat belt tension sensor for detecting the magnitude of tension in a seat belt when an occupant is in the seat. A limit structure is attached between a vehicle member and the seat belt. A sensor is attached to the limit structure to generate an electrical signal in response to the sensor being placed in tension. The electrical signal changes as a function of tension on the seat belt. The limit structure moves between a first position in which the sensor carries all of the seat belt tension and a second position in which the limit structure carries all of the seat belt tension.

Description:
CROSS REFERENCE TO RELATED AND CO-PENDING APPLICATIONS 
     This application is a continuation in part of U.S. patent application Ser. No. 09/441,350, filed Nov. 15, 1999 and titled, “Automobile Seat Having Seat Supporting Brackets with a Stepped Weight Sensor”. 
     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 sensor for detecting the magnitude of a tensile force in a seat belt used in a car seat, and in particular to a sensor that can detect the magnitude of tension in a seat belt and provide an electrical signal that is representative of the magnitude of tensile force. 
     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. 
     Unfortunately there are several problems with detecting seat occupant weight. For example, when a seat occupant puts on a seat belt, the force of cinching down the seat belt on the occupant can cause a seat weight sensor to have false and erroneous readings. In another example, if a child&#39;s car seat is cinched down tightly in the car seat, it can appear to the weight sensor that a heavy person is in the seat, which is the wrong reading. 
     A current unmet need exists for a reliable, low cost, simple and robust seat belt tension sensor that can be used to input additional seat occupant information to an airbag controller to control airbag deployment. 
     SUMMARY OF THE INVENTION 
     It is a feature of the invention to provide a reliable and cost-effective vehicle seat belt tension sensor for detecting the magnitude of tension in a seat belt when an occupant is in the seat. 
     An additional feature of the invention is to provide a seat belt tension sensor for attachment to a seat belt in a vehicle. The seat belt tension sensor includes a limit structure that is attached between a vehicle member and the seat belt. A sensor is attached to the limit structure to generate an electrical signal in response to the sensor being placed in tension. The electrical signal changes as a function of tension on the seat belt. The limit structure moves between a first position in which the sensor carries all of the seat belt tension and a second position in which the limit structure carries all of the seat belt tension. 
     Another feature of the invention is to provide a seat belt tension sensor for attachment to a seat belt in a vehicle. A stationary slide is attached to a vehicle member and has a pair of rails extending outwardly from the stationary slide. A movable slide is located adjacent the stationary slide and is in engagement with the rails. A sensor is attached to the stationary slide and the moveable slide for generating an electrical signal in response to the sensor being placed in tension. The electrical signal changes as a function of tension on the seat belt. A collar is located in the travel limit aperture. A fastener extends through the sensor, the collar and is threadably engaged with the moveable slide. The moveable slide moves between a first position in which the sensor carries all of the seat belt tension and a second position in which the slides carry all of the seat belt tension. 
     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 exploded view of the preferred embodiment of a seat belt tension sensor. 
     FIG. 2 is a cross-sectional view of FIG. 1 in an assembled state. 
     FIG. 3 is an enlarged view of FIG. 2 showing details around the collar. 
     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 is a seat belt tension sensor. Referring to FIGS. 1,  2  and  3  there is a seat belt tension sensor assembly  10  shown. Assembly  10  has a limit structure  12  and a sensor  14 . Limit structure  12  is fastened between seat belt components. For example, structure  12  can be attached on one end to seat belt buckle  16  and on the other end to a vehicle seat or floor (not shown). Buckle  16  has a buckle plate  18  extending from one end. Buckle  16  typically is the receiving end of the seat belt. The belt webbing is extended and a metal end (not shown) clicks into buckle  16 . Buckle  16  is attached to moveable slide  22  by fasteners  20  passing through holes  19  and  23 . Fasteners  20  can be screws, bolts or rivets. If fastener  20  is a screw or bolt, then holes  23  could be threaded. 
     Moveable slide  22  is generally planar and has a sensor slot  25  extending therethrough. A threaded travel limit hole  28  is located between holes  23  and slot  25 . A clearance hole  24  is located at the other end of slide  22 . A pair of tabs  26  extend away from the moveable slide on each side. 
     A stationary slide  30  is also generally planar and has a sensor slot  32  extending therethrough. A pair of rails  34  are located on sides of slide  30  and each have a groove  35  therein. Moveable slide  22  fits into and is slidably engaged with rails  34 . A travel limit aperture  36  is located at one end of slide  30 . A mounting hole  39  is located at the other end of slide  30 . Mounting hole  39  is used to attach slide  30  to a vehicle member such as a car floor or a car seat. A threaded aperture  38  is located between hole  39  and slot  32 . 
     A circular stepped collar  42  fits into travel limit aperture  36 . Stepped collar  42  has a flange  44  with a smaller outside diameter than collar  42 . Flange  44  fits into one of sensor holes  60 . Collar  42  has a passage  43  passing therethrough. A circumferencial gap  45  is formed between collar  42  and stationary slide  30 . 
     A circular straight collar  46  fits into the other sensor hole  60 . Collar  43  has a passage  47  passing therethrough. 
     After assembly, threaded fastener  50  extends through sensor hole  60 , passage  43 , travel limit aperture  36 , and mates with threads in travel limit hole  28 . 
     After assembly, threaded fastener  51  extends through sensor hole  60 , passage  47  and mates with threads in threaded hole  38 . Fasteners  50  and  51  are conventional fasteners such as hex headed bolts, Allen head screws, shoulder screws or rivets. 
     Strain gauge sensor  14  has a metal substrate  61 . Metal substrate  61  is preferably formed from  430  stainless steel. Substrate  61  has an offset section  62 . Several strain gage resistors  64  are arranged on substrate  61  within section  62 . Details of the construction and operation of resistors  64  are shown U.S. patent application Ser. No. 09/441,350, filed Nov. 15, 1999 and titled, “Automobile Seat Having Seat Supporting Brackets with a Stepped Weight Sensor”. 
     Resistors  64  would typically be connected in a conventional bridge configuration. Resistors  64  are strain sensitive and will change resistance based on the amount of strain in substrate  61 . A wiring harness (not shown) would typically connect resistors  64  to an external electrical circuit. 
     When an occupant sits in a vehicle seat and buckles a seat belt, the tension placed in the seat belt is transferred from buckle plate  18  to moveable slide  22 , sensor  14 , stationary slide  34  and then to the vehicle floor or seat frame. An electrical output signal is generated by the resistors  64  in sensor  14  that is proportional to the magnitude of the tension in the seat belt and is transmitted over a wire harness (not shown) to a conventional air bag controller (not shown). The air bag controller then can use the seat belt tension information to compute a more accurate profile of the seat occupant and use that information to control deployment of the airbag. This is the normal operational state of the seat belt tension sensor in which all of the seat belt tension is carried through the sensor  14 . 
     In a situation where the vehicle is involved in a crash, the seat belt tension sensor operates in a different mode called a high load or crash state. In the high load state, the slides carry all of the tension placed on the seat belt. The amount of tension in the seat belt in a crash situation is much larger than in normal operation. If the substrate  61  of the sensor was designed to carry all of this tension, it would not flex enough to properly function as a strain gage sensor. Therefore, in a crash situation, the slides engage and carry the tension through the much stronger limit structure  12 . As the tension in the seat belt increases, the sensor  14  flexes until moveable slide  22  engages collar  42  eliminating one side of gap  45  providing a positive stop. The seat belt tension is then transferred through buckle plate  18  to moveable slide  22 , collar  42 , fastener  50 , stationary slide  34  and then to the vehicle floor or seat frame. The limit structure  12  is designed so as not to deform under the load placed on it by the seat occupant during a crash situation. Tabs  26  are designed as a secondary stop mechanism and provide extra strength to the limit structure  12 . Tabs  26  engage the end of rails  34  providing a secondary positive stop. 
     Remarks About the Preferred Embodiment 
     The seat belt tension sensor has several advantages. It allows accurate sensing of seat belt tension, while at the same time providing the structural strength needed for occupant restraint in a crash situation. The seat belt tension sensor allows an airbag controller to make better decisions as to when and how to deploy and airbag based upon more accurate seat occupant information. In the case of a child&#39;s car seat being strapped into a car seat, the seat belt tension sensor in conjunction with a seat weight sensor allows the airbag controller to properly compute that the seat occupant has a low weight and to prevent deployment of the airbag. 
     Variations of the Preferred Embodiment 
     The sensor  14  shown was several strain gage resistors, one skilled in the art will realize that the preferred embodiment would work with other types of sensors. For example, discrete chip resistors could be attached to substrate  61  or foil type strain gages. Furthermore, the shape of substrate  61  could be varied to any configuration that would transfer the weight from the seat belt. 
     Although sensor assembly  10  was shown without a housing, it is contemplated to add a housing. 
     Another variation of the seat belt tension sensor would be to utilize other electrical connections other than a wire harness. For example, a connector or terminals could be added. 
     Yet, a further variation, would be to place signal conditioning circuitry on substrate  61  or on limit structure  12  to amplify and filter the electrical signal before it is transmitted to the airbag controller. 
     The seat belt tension sensor shown was mounted between a seat belt and a vehicle member. One skilled in the art will realize that the preferred embodiment could be mounted to various locations on the seat or vehicle interior. For example, the seat belt tension sensor could be attached to the vehicle roof. 
     The illustrated embodiment showed the use of the seat belt tension sensor in an automobile seat. It is contemplated to utilize the seat belt tension sensor in other occupant sensing applications such as chairs, sofas, scales, beds and mattresses, hospital equipment, cribs, airplane seats, train seats, boat seats, amusement rides, and theater seats, 
     The illustrated embodiment showed the use of tabs  26  as a secondary positive stop. It is contemplated to omit tabs  26  and utilize the collar  42  and fastener  50  as the only stop. Alternatively, it is contemplated to omit collar  42  and fastener  50  and use tabs  26  as the only stop. 
     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.