Abstract:
Apparatus for suppressing the operation of a vehicle restraint system when a child&#39;s seat is mounted in a vehicle car seat. The seat belt is connected by two plates to a vehicle anchor. One plate is stretchable, the other non-stretchable. A low seat belt load does not stretch either plate. A higher load stretches the stretchable plate until the belt load is transferred to the non-stretchable plate.

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
     This invention is related to a child seat sensing means in a motor vehicle, and more particularly to apparatus disabling the airbag system for a car seat supporting a child&#39;s seat. 
     Recent government regulations for child restraint&#39;s and airbag suppression necessitate a low cost integral load sensor. 
     A load sensor can be used with automobile onboard electronic logic to store seat belt forces for accident investigations, and for the development of load limiting devices to reduce injury to the vehicle occupants. 
     A load transducer can also be used to determine if the load is high enough to warrant the replacement of the seat belt. Visual inspection of the seat belt is the only means used by manufacturers today to replace the belt. 
     A load transducer can also be used with electronically controlled seat belt load limiters to control the maximum seat belt force a particular sized person should receive before the restraint system, such as an airbag system, is deployed or energized. 
     Typically, seat belts strapped around an adult have a small retraction force when the adult is buckled up. However, a properly secured child seat mounted on the same car seat will provide a relatively high tensile load upon the lap belt. 
     Some prior art devices related to these problems include: U.S. Pat. No. 5,996,421 issued Dec. 7, 1999, to Harald Snorre Husby for “Seat Belt Tension Sensor Employing Flexible Potentiometer”; U.S. Pat. No. 5,991,676 issued Nov. 23, 1999, to Robert Michael Podoloff and Ronald Anthony Vallette, Jr. for “Seat Occupant Sensing System”; U.S. Pat. No. 5,865,463 issued Feb. 2, 1999, to Gagnon et al. for “Airbag Deployment Controller”; U.S. Pat. No. 5,851,026 issued Dec. 22, 1998, to Aloyse Schoos and Michael White for “Method and Installation for Detecting Certain Parameters Concerning an Auxiliary Child Seat with a View to Controlling the Operation of the Airbags of a Vehicle”; U.S. Pat. No. 5,785,347 issued Jul. 28, 1998, to Adolph et al. for “Occupant Sensing and Crash Behavior System”; and U.S. Pat. No. 3,817,093 issued Jun. 18, 1974, to Charles W. Williams for “Seat Belt Webbing Tension Measuring Device”. 
     Anticipated laws require that passenger side seat airbags be suppressed when a child seat is present. 
     The preferred embodiment of the invention comprises a seat belt transducer, which compensates for the tensile force applied by the belt to a properly fastened child seat. The seat belt tension information is sent to the electronic control module (ECM). The ECM then disables the airbag system if a child&#39;s seat is strapped on a car seat. 
     The preferred embodiment of the invention comprises a transducer having a transducer plate mounted and secured parallel to a steel structural plate. Both plates are connected to an anchor device attached to the vehicle frame. Both plates have a belt opening for receiving a belt loop. However, the belt openings are offset so that a light load on the seat belt is applied only to the transducer plate. 
     The transducer plate is elongated within its elastic limits under a tensile load. Thus an initial tensile load applied by the belt, such as caused by a strapped down child&#39;s seat, will be connected through the transducer plate to the anchor device. 
     Tension in the transducer plate is converted to an electrical signal by a strain gage. This reading is sent to the ECM, which determines from the tension on the seat belt whether or not the airbag system is to be inflated. 
     In the event of a high-speed accident, the transducer plate stretches until the belt-receiving openings in the two plates are aligned, at which time the primary belt load passes through the structural plate instead of the transducer plate. A strain gage is mounted on the transducer plate to transmit a signal that is proportional to the strain, to the ECM. 
     The transducer plate also has an integral web protector that prevents tearing of the seat belt. The wire to the strain gage is routed from the strain gage around the belt opening and up the belt webbing. The seat belt webbing protects the strain gage wire and presents a clean appearance. 
     Still further objects and advantages of the invention will become readily apparent to those skilled in the art to which the invention pertains, upon reference to the following detailed description. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     The description refers to the accompanying drawings in which like reference characters refer to like parts throughout the several views, and in which: 
     FIG. 1 is a view of a child seat anchored to a car seat structure, with an airbag restraint means and electronic control means illustrated schematically; 
     FIG. 2 is an enlarged sectional view showing the two plates; 
     FIG. 3 is a view of the stretchable transducer plate; 
     FIG. 4 shows the manner in which the two plates are mounted, illustrating the transducer plate under load; 
     FIG. 5 is another view of the transducer plate; 
     FIG. 6 illustrates the transducer plate mounted on the structural plate; 
     FIG. 7 is a view of an option for mounting the wiring in the seat belt webbing; 
     FIG. 8 is a view as seen along FIGS.  8 — 8  of FIG. 7; 
     FIG. 9 is a view of another option for mounting the transducer wiring; 
     FIG. 10 is a view of the transducer anchored to the vehicle by a cable; and 
     FIG. 11 is a view of a transducer plate having a bold neck area for supporting the strain gage. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 illustrates a preferred transducer  10  connected to a seat belt  12  employed for strapping a child&#39;s seat  14  on a car seat  16 . The seat belt employs buckle apparatus  18  for connecting the two halves of the seat belt together. 
     The transducer is electrically connected by wire connector means  20  to an electronic control unit  22  which, in turn, is connected by wire connector means  24  to a electrically actuated restraint  26 . Restraint  26 , for illustrative purposes, is an inflatable airbag intended to be inflated during the course of a collision unless the child&#39;s seat is sensed as being mounted on car seat  16 . 
     Seat belt  12  is connected by transducer  10  to anchor bolt  28 , which is rigidly connected to the vehicle frame, not shown. The transducer comprises an elastically elongated transducer plate  30 , which is a juxtaposed with respect to a rigid structural metal plate  32 . 
     The transducer plate  30 , as can be seen in FIGS. 3,  5 , and  6 , has a bottom opening  34  for receiving anchor bolt  28 . Structural plate  32  also has an opening  36  which is aligned with opening  34  of the transducer plate and mounted on anchor bolt  28 . 
     Referring to FIG. 3, the transducer plate is relatively wide but has a reduced width forming a neck  38  which forms a relatively weak, stretchable part of the plate between the seat belt and the anchor. The upper end of the transducer plate also has a belt-receiving opening  40 . The transducer plate is preferably formed of a lightweight, deformable sheet metal material, or perhaps a plastic material, which tends to elongate under a tensile force in a predictable manner. The transducer plate is adapted to be elongated by a tensile force applied by the belt, which passes through the plate, pulling against anchor bolt  28 . 
     A tongue  42  is mounted in the mid section of the transducer plate beneath neck  38 . 
     Referring to FIG. 5, a strain gage  44  is attached to the transducer plate and connected by electrically conductive wires  46  which are mounted around belt-receiving opening  40 , preferably in a plastic container  48 . Wires  46  then pass upwardly to electronic control unit  22 . 
     The strain gage transmits an electrical signal to electronic control unit  22  to disable the airbag if the initial preload on the belt is consistent with the strapping load on the child&#39;s seat. 
     Structural plate  32  has a belt-receiving slot  50 , which is slightly offset from the belt-receiving opening  40  of the transducer plate. When the two plates are mounted on the anchor bolt, the transducer belt-receiving opening is closer to the anchor bolt than slot  50  in the structural plate. 
     The transducer plate also has a second tongue  52  that is received through opening  50 . Tongue  42  is received through a lower opening  54  in the structural plate so that the two plates snap together to form an assembly. 
     The arrangement is such that when an initial load is applied on the belt by fastening the belt around a child&#39;s seat, the belt load is applied to the transducer plate. This arrangement also functions if the child&#39;s seat is not mounted on the car seat, but the seat belt is strapped to an adult, not shown. If the belt is strapped around a child&#39;s seat to apply a belt initial tension, for example  50  pounds, the electronic control unit will then sense that the child&#39;s seat is strapped by the seat belt, and therefore suppress the operation of the restraint  26  or airbag system. 
     On the other hand, if an adult is sitting in the seat so that initially there is a very small, predetermined tensile load on the belt, the preliminary load will also be applied to the transducer plate. In the event of a collision, the tensile force of the belt applied by a moving adult will cause the transducer plate to elongate until the two belt-receiving openings  40  and  50  are aligned. At this point, the belt will apply the tensile load on the structural plate, which is rigid and non-yielding. Restraint  26  will then be energized by the strain gage to provide a safety device for the adult. 
     FIG. 7 illustrates an option for attaching strain gage wires  46  to the seat belt  12 . In this case the wires are routed around web slot  40  and then through the belt loop, formed by stitching  56 . 
     Another option is illustrated in FIG. 9 in which belt  12  is connected to a modified transducer plate  32 ′. The wires pass from the strain gage  44  down and around anchor bolt  28  and then into a molded wire track  60  to electronic control unit  22 . 
     Other options are possible. 
     It is to be understood that I have described an improved transducer for detecting whether a child&#39;s seat is mounted on a car seat. In the event, the tension on the belt indicates that a child&#39;s seat is mounted on the car seat, then the strain gage will send a signal to the electronic control unit, suppressing activation of the airbag system. 
     A second option of the use of the transducer may be to sense a sufficiently high tensile force on the belt consistent with the presence of a large adult. The air bag system will then be activated to provide a maximum or higher level of protection in the event of an accident above a set threshold. 
     FIG. 10 illustrates another embodiment of the invention in which the structural plate  32 ′ is connected by a cable  28 ″ rather than a bolt  28 . The transducer plate has its lower edge wrapped around the lower edge of the structural plate by lip means  100 . Similarly, a seat belt buckle  102  is connected by a plate  104  to a bolt  106 . Bolt  106  connects plate  104  to both structural plate and the transducer plate in such a manner that when the transducer plate is stretched by the buckle, that is by an upward load, the load of the buckle will be transmitted to the transducer plate when it is raised to the top of a slot  108 . 
     FIG. 11 illustrates another variation of the invention in which the transducer plate  32 ′″ is connected to the transducer plate so as to form a bow  110  at the neck portion of the transducer plate. Thus as the transducer plate is elongated by a tensile force applied by the seat belt, the load of the seat belt will then be applied to the structural plate when the transducer plate has been elongated. The strain gage  44 ′″ is mounted at the weak point, that is at the bowed neck of the transducer plate.