SEAT BELT FORCE SENSOR SYSTEM

Abstract: A system for measuring seatbelt forces is used to control deployment of vehicle airbags. The system includes a seatbelt anchor assembly having a bracket mounted to a vehicle structure adjacent to a vehicle seat. A seatbelt mechanism has a belt portion that is looped through the bracket. The seatbelt is used to secure passengers or an infant car seat to the vehicle seat. A sensor is engaged with the anchor assembly and is used to measure the magnitude of forces exerted on the seatbelt by the passenger or car seat. The sensor generates a signal representative of the seatbelt forces, which is used to control deployment of the airbag.

Description: SEAT BELT FORCE SENSOR SYSTEM BACKGROUND OF THE INVENTION 1. Field of the Invention. This invention relates to a method and apparatus for measuring the force applied to a seat belt. Specifically, a sensor arrangement is mounted within a seatbelt anchor assembly to provide accurate seatbelt force measurements. 2. Related Art. Most vehicles include airbags and seatbelt restraint systems that work together to protect the driver and passengers from experiencing serious injuries due to a high speed collision. It is important to control the deployment force of the airbags based on the size of the driver or the passenger. When an adult is seated on the vehicle seat, the airbag should be deployed in a normal manner. If there is an infant seat secured to the vehicle seat then the airbag should not be deployed or should be deployed at a significantly lower deployment force. One way to control the airbag deployment is to monitor the weight of the seat occupant. Current systems for measuring the weight of a seat occupant are complex and expensive. One type of system uses pressure sensitive foil mats mounted within the seat bottom foam. Another system uses sensors placed at a plurality of locations within the seat bottom. The combined output from the mats or the sensors is used to determine the weight of the seat occupant. If the sensors become damaged or fail to operate for some reason, the system will not provide accurate seat weight measurements and airbag deployment could occur under undesirable conditions. Also mounting sensor systems within the seat can be difficult and time consuming. It is difficult to find mounting locations for each the sensors that will accommodate all of the various positions of a seated occupant while still providing accurate measurements. Further, shifting of the occupant on the seat can dislodge or move the sensors out of their proper location. Because the sensors are mounted within the seat bottom, it is difficult to reposition the sensors after the seat is installed in the vehicle. Current sensor systems also can have difficulty determining whether an adult is belted to the seat or whether a child car seat is belted to the seat. When a child seat is in place, an excess acts on the sensors mounted within the rear portion of the seat, which interferes with accurate sensing of the weight of an occupant. Overtightening of the seatbelt, which makes it pull down on the rear of the seat, causes this force. Due to this effect, the current weight sensing systems have difficulty in discerning between an adult and a child in a child seat. Thus, it is desirable to have a system for determining whether conditions are proper for deploying an airbag by determining whether a child in a child seat or an adult is belted to the seat. The system should further provide accurate measurements, be easy to install, and should overcome the above referenced deficiencies with prior art systems. SUMMARY OF THE INVENTION In a disclosed embodiment of this invention, a system for measuring seatbelt forces includes a seatbelt anchor mounted to a vehicle structure adjacent to a vehicle seat and a seatbelt for securing an occupant to the vehicle seat. The seatbelt has a belt portion supported by the anchor. A sensor is engaged with the anchor for measuring the magnitude of forces exerted on the seat belt. In a preferred embodiment, the seatbelt anchor is comprised of a bracket having a first portion with an opening for receiving the belt portion and a second portion for attaching the bracket to the vehicle structure. An airbag controller is used to control deployment of an airbag that is mounted within the vehicle near the seat. The sensor generates a signal representative of the seatbelt forces and transmits the signal to the controller. The airbag is prevented from deploying if the signal exceeds a predetermined limit. The system includes at least one fastener that secures the anchor to the vehicle structure. Preferably, the sensor has a portion mounted between the fastener and the anchor. A method for controlling airbag deployment includes the following steps. A seatbelt assembly is mounted adjacent to a vehicle seat with a seatbelt anchor. A force signal representative of forces applied to the seatbelt is generated via a sensor mounted to the seatbelt anchor. Deployment of an airbag is controlled based on the force signal. Preferably, deployment of the airbag is prevented if the signal exceeds a predetermined limit. These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic view showing a vehicle with an airbag system and an occupant sitting in a seat with the airbag in an active state shown in dashed lines. Figure 2 is a side view of a seat assembly with an infant car seat secured to the vehicle seat. Figure 3 is a perspective view of a seatbelt anchor assembly of the subject invention. Figure 4 is an alternate embodiment of the anchor of Figure 3. Figure 5 is an alternate embodiment of a seatbelt anchor assembly of the subject invention.. Figure 6 is a schematic view of the airbag control system. Figure 7 is graph representing seat weight added vs. seatbelt tension. DETAILED DESCRIPTION OF AN EXEMPLARY EMBODIMENT A vehicle includes a vehicle seat assembly, shown generally at 12 in Figure 1, and an airbag system 14. The seat assembly 12 is preferably a passenger seat and includes a seat back 16 and a seat bottom 18. A vehicle occupant 20 is secured to the seat 12 with a seatbelt 22. A tension force FT is exerted on the seatbelt 22. The tension force FT represents the force that the seat occupant 20 exerts against the seatbelt 22. The airbag system 14 deploys an airbag 24 under certain collision conditions. The deployment force for the airbag 24, shown in dashed lines in Figure 1, varies depending upon the type of occupant that is belted to the seat 12. When an adult 20 is belted to the vehicle seat 12, the airbag 24 should be deployed in a normal manner shown in Figure 1. If there is an infant or child seat 26 secured to the vehicle seat 12, see Figure 2, then the airbag 24 should not be deployed. Thus, it is important to be able to determine whether there is an adult 20 belted to the seat 12 or whether an infant seat 26 is belted to the seat 12. One way to determine this is by monitoring the tension exerted on the seatbelt 22. When an adult 20 is belted to the seat, normal seatbelt forces are exerted against the seatbelt 22. When an infant or child seat 26 is belted to the seat 12 high forces are exerted against the seatbelt 22 because the seatbelt 22 is overtightened to securely hold the child seat 26 in place. The subject invention provides a seatbelt force sensing system that is incorporated into a seatbelt anchor 28. The seatbelt anchor 28 is mounted to a vehicle structure adjacent to the vehicle seat 12. As shown in Figure 3, the seatbelt 22 has a belt portion 30 that is supported by the anchor 28. A sensor 32 is engaged with the anchor 28 for measuring the magnitude of forces FT exerted on the seatbelt 22. The sensor 32 is preferably a load cell sensor with at least one strain gage however, other sensors known in the art could also be used. The seatbelt anchor 28 is a bracket that has a first portion 34 with an opening 36 for receiving the belt portion 30 and a second portion 38 for attaching the bracket 28 to the vehicle structure. The first portion 34 can be orientated at a non- perpendicular angle with respect to the second portion 38 as shown in Figure 3 or can be mounted at a perpendicular angle with respect to the second portion 38 as shown in Figure 4. The tension force FT that is exerted on the seatbelt 22 by the adult occupant 20 or the child seat 26 is directly translated to the anchor 28. The sensor 32 measures the tension force FT and deployment of the airbag 24 is controlled based on this measurement. At least one fastener 40 is used to fasten the second portion 38 to the vehicle structure. The vehicle structure can be a vehicle floor 42 as shown in Figure 3 or can be a vehicle side pillar 44 as shown in Figure 5. Preferably, some portion of the sensor 32 is mounted between the fastener 40 and the anchor 28. The sensing system communicates with an airbag controller 46 and central processor 50, shown in Figure 6, which controls the deployment of the airbag 24. The sensor 32 generates a signal 48 representative of the forces FT and transmits the signal 48 to the controller 46. As discussed above, the sensor 32 is preferably a load cell sensor with at least one strain gage 52. The operation of such sensors and gages are well known in the art. The processor 50 and controller 46 can be separate units or can be incorporated into a single unit. The airbag 24 is prevented from deploying if the signal 48 exceeds a predetermined limit. Thus, when the sensor 32 measures a high tension force FT on the seatbelt 22 it is determined that a child seat 26 is belted to the vehicle seat 12 and the airbag 24 will not be deployed. The measurement of the tension force FT from the seat belt 22 can be utilized in various ways. One way is to set a predetermined limit for FT such that when FT exceeds the predetermined limit it is known that a child seat 26 and not an adult 20 is belted to the seat 12. Another way is to measure both the weight applied to the vehicle seat 12 and the tension force FT on the seatbelt 22 to determine whether an adult 20 or child seat 26 is belted to the seat 12. These are only examples of how the FT measurement can be used, it should be understood that FT could be used in other ways depending on various control parameters. As shown in Figure 7, there is a generally linear relationship between the seat weight added to the vehicle seat 12 and the belt tension. The method for controlling airbag deployment includes the following steps. A seatbelt 22 is mounted adjacent to a vehicle seat 12 with a seatbelt anchor 28. A force signal 48 representative of forces FT applied to the seatbelt 22 is generated via a sensor 32 mounted to the seatbelt anchor 28. Deployment of the airbag 24 is controlled based on the force signal 48. Preferably, deployment of the airbag 24 is prevented if the signal 48 exceeds a predetermined limit. The subject sensing system provides simplified and efficient apparatus and method for determining whether conditions are proper for deploying an airbag 24 by measuring seatbelt forces to discern whether a child in a child seat 26 or an adult is belted to the seat 12. The system provides accurate measurements and is easy to install. Although a preferred embodiment of this invention has been disclosed, it should be understood that a worker of ordinary skill in the art would recognize many modifications come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.

Claims: CLAIMS I claim: 1. A system for measuring seatbelt forces comprising: a seatbelt anchor mounted to a vehicle structure adjacent to a vehicle seat; a seatbelt for securing an occupant to the vehicle seat, said seatbelt having a belt portion supported by said anchor; and a sensor engaged with said anchor for measuring the magnitude of forces exerted on said seat belt. 2. A system according to claim 1 wherein said seatbelt anchor is comprised of a bracket having a first portion with an opening for receiving said belt portion and a second portion for attaching said bracket to the vehicle structure. 3. A system according to claim 2 including at least one fastener for fastening said second portion to the vehicle structure comprised of a vehicle floor. 4. A system according to claim2 including at least one fastener for fastening said second portion to the vehicle structure comprised of a vehicle side pillar. 5. A system according to claim 1 wherein said sensor is a load cell sensor with at least one strain gage. 6. A system according to claim 1 including an airbag controller for deploying an airbag wherein said sensor generates a signal representative of said forces and transmits said signal to said controller. 7. A system according to claim 6 wherein said airbag is prevented from deploying if said signal exceeds a predetermined limit. 8. A system according to claim 1 including at least one fastener for securing said anchor to the vehicle structure. 9. A system according to claim 8 wherein said sensor has a portion mounted between said fastener and said anchor. 10. A system for controlling airbag deployment comprising: a seatbelt anchor bracket mounted to a vehicle structure adjacent to a vehicle seat; a seatbelt for securing an object to the vehicle seat, said seatbelt having a belt portion attached to said bracket; a sensor mounted to said bracket for measuring forces exerted on said seatbelt by the object and generating a force signal representative of the magnitude of said forces; and an airbag mounted adjacent to the vehicle seat wherein said airbag does not deploy when said force signal exceeds a predetermined limit. 11. A system according to claim 10 including an airbag control module that receives said force signal to control deployment of said airbag. 12. A system according to claim 11 including at least one fastener for securing said anchor to the vehicle structure. 13. A system according to claim 12 wherein said sensor has a portion mounted between said fastener and said anchor. 14. A system according to claim 13 wherein said seatbelt anchor is comprised of a bracket having a first portion with an opening for receiving said belt portion and a second portion for attaching said bracket to the vehicle structure. 15. A method for controlling airbag deployment comprising the steps of providing a seatbelt assembly mounted adjacent to a vehicle seat with a seatbelt anchor; generating a force signal representative of forces applied to the seatbelt with a sensor mounted to the seatbelt anchor; and controlling deployment of an airbag based on the force signal. 16. A method according to claim 17 including the step of preventing deployment of the airbag if the signal exceeds a predetermined limit.

Inventors: BAKER MICHAEL, CURTIS BRIAN M, MORELL SCOTT M, REICH DANIEL A, BAKER, MICHAEL, CURTIS, BRIAN, M., MORELL, SCOTT, M., REICH, DANIEL, A.
Applicants: SIEMENS AUTOMOTIVE CORP LP, SIEMENS AUTOMOTIVE CORPORATION
Application year: 2000
Main classification: B60R21
IPC codes: B60R21, B60R22