Airbag deployment system and method of determining occupant presence

Abstract: An occupant sensor system 12 is coupled to an airbag deployment system 14. Occupant sensor system 12 has an occupant sensor 24 that comprises a seat belt and a plurality of wires extending a predetermined length within seat belt 26. Wires 28 are coupled to a controller 22 that is used to sense a changing electrical characteristic of wires 28 such as capacitance or inductance to determine the presence of an occupant. Controller 22 in response to the signal from occupant sensor 24 may then adjust the deployment of an airbag 18.

Description: The present invention relates generally to a sensor for determining the presence of an occupant within an automotive vehicle and, more specifically, to an occupant sensor incorporated within the seat belt that may be used to control the deployment of an airbag. Still more specifically, the invention relates to an airbag deployment system and a method of determining occupant presence. In the first iteration of airbags for automotive vehicles, the airbags deployed upon sensing a predetermined deceleration of the vehicle. The airbags deployed at a predefined rate without regard to other input. More recently, airbags have been developed that deploy at a lesser rate than early airbags. These airbags, however, also do not take into consideration other factors. For example, both a passenger side and driver side airbag deploy simultaneously without regard to whether a passenger is present. Various methods for determining the presence of an occupant have been proposed. These sensors include infrared sensors directed to the passenger area, weight sensors that are located under the seat, and seat belt use sensors that measure the radius of the webbing spooled upon the retractor. The radius of the webbing may be determined by a mechanical type sensor that measures the thickness of the web around the spool. The drawback to retractor systems is that because the designs are mechanical, the moving parts must be assembled, adjusted and may be subject to wear. This increases the cost of the systems. US Patent No 5724024 showing the features of the preamble of the independent claims discloses an airbag deployment systems employing a sensor to detect the presence of a human being occupying a seat by monitoring the resultant change in capacitance between one or more fixed electrodes and a sensor electrode attached to or embedded in a seat belt, together with circuitry to generate signals relating to breathing and/or heart rhythm. US Patent No 4015236 discloses the use of a low frequency oscillator attached to a seat belt and co-operating with a fixed electrode to determine whether or not the seat belt is being worn around an occupant and to activate an alarm if not. US Patent No 4885566 is similar, except that it uses an electrode attached to, or woven into, the seat belt instead of the low frequency oscillator. These systems are responsive to the change in position of the sensor relative to the fixed electrode(s) brought about by the presence of an occupant. Japanese patent No 63305057 discloses a system for detecting whether a seat belt is employed correctly by detecting twisting in wires embedded in the seat belt. It would be therefore be desirable to provide a low cost sensing system for detecting the presence of a seat occupant. According to a first aspect, the invention provides an airbag deployment system for an automotive vehicle comprising an airbag, a seat belt, a retractor about which part of the seat belt is wound, an occupant sensor comprising wires extending along the seat belt and conforming to the shape of the seat belt; and an airbag controller coupled to the sensor; the wires having an inductance that varies with the shape of the wires, characterised in that the controller is operative to determine the presence of an occupant in response to a change in the inductance of the wires when the shape of the wires is changed as a result of the seat belt being worn by the occupant. In a further aspect of the invention, there is provided a method of determining the presence of an occupant in a seat in an automotive vehicle, the vehicle having a seat belt with a retractor and an airbag deployment system including an airbag controller associated with the seat, the method comprising the steps of providing wires to extend along and conforming to the shape of the seat belt, and passing an electrical signal through the wires to determine the presence of an occupant in the seat, the wires having an inductance that varies in dependence upon the shape of the seat belt, characterised in that the inductance of the wires is measured and changes in the measured inductance are evaluated to determine the presence of an occupant in the seat. One advantage of a system embodying the invention is that not only may the presence of an occupant be detected, but the size of the occupant may also be detected. Another advantage of a system embodying the invention is that the sensor may be incorporated into the seat belt without significant expense. The sensor operates electrically without moving mechanical parts. The present invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of an automotive vehicle having an occupant sensor and airbag deployment system according to the present invention; Figure 2 is an elevational view of an airbag deployment system according to the present invention; Figure 3 is a cross-sectional view of a seat belt according to the present invention; Figure 4 is a perspective view of a seat belt with occupant sensor coupled to an airbag module; and Figure 5 is a schematic view of an airbag module according to the present invention. In the following figures, the same reference numerals will be used to identify identical components in the various views. The present invention is illustrated with respect a single occupant sensor associated with a single seat within the automotive vehicle. However, the present invention may be employed with respect to the passenger, driver and a middle occupant of the front seats of the vehicle. The present invention is also equally applicable to occupant sensing in rear seating positions of the vehicle. Also, the system is illustrated with respect to a one retractor system mounted to the vehicle. Those skilled in the art would recognise that the present invention is suitable for other types of systems that are seat mounted or may have more retractors. Referring now to Figure 1, a perspective view of a portion of an automotive vehicle 10 having an occupant sensor system 12 and an airbag deployment system 14 is illustrated. Automotive vehicle 10 has a seat 16 positioned adjacent to an airbag 18. If seat 16 is a driver seat, airbag 18 may be included within a steering wheel 20. An airbag controller 22 is coupled to airbag 18 to control the deployment of the airbag 18. Occupant sensor system 12 has an occupant sensor 24 positioned within seat belt 26 and an airbag controller 26. Occupant sensor 24 is coupled to airbag controller 22 and indicates to the airbag controller 22 the presence of an occupant. Of course, a separate occupant sensor controller may be employed. Referring now to Figure 2, controller 22 is shown coupled to occupant sensor 24 within seat belt 26. Occupant sensor 24 comprises a plurality of wires 28 extending a predetermined length of seat belt 26. The length of occupant sensor 24 may extend the entire length of seat belt 26 or only a portion thereof. Of course, one skilled in the art would recognise that the length of occupant sensor 24 may vary depending on the desired needs of the particular system, the sensitivity of the system and the design of the automotive vehicle. As illustrated, the wires are parallel, however various shapes such as meandering or criss-cross or comb-shaped may be employed. A suitable shape based on the particular design can be easily determined by one skilled in the art. Seat belt 26 is mounted within automotive vehicle 10 at an anchor 30 and at a retractor 32. Both anchor 30 and retractor 32 are fixedly coupled to structure within automotive vehicle 10. Anchor 30 is a fixed anchor point whereas retractor 30 may be used to remove excess play in seat belt 26. Retractor 30 holds excess seat belt 26 when not in use. Seat belt 26 has a buckle 34 positioned thereon. Buckle 34 may be slid with respect to the length of seat belt 26 to adjust around an occupant. A buckle receiver 36 is fixedly mounted to the structure of automotive vehicle 10 and buckle 34. A buckle sensor 38 may be coupled to controller 22 to provide an indication as to whether buckle 34 has been placed within buckle receiver 36. Buckle sensor 38 may be a mechanical, electrical or magnetic position sensor. Although optional, buckle sensor 38 is used to provide additional information to controller and is an optional feature. Prior to positioning seat belt 26 around an occupant, the seat belt 26 is positioned between anchor 30 and retractor 32 with excess seat belt 26 wrapped around retractor 32. In such a position, buckle 34 is positioned between anchor 30 and retractor 32. When an occupant enters the vehicle, the seat belt 26 with occupant sensor 24 is extended around the occupant so that buckle 34 may be placed within buckle receiver 36. Thus, when seat belt 26 is installed, seat belt 26 forms a lap portion 40 and a shoulder portion 42. Referring now to Figure 3, seat belt 26 is shown having wires 28 positioned therebetween. Wires 28 may also be positioned on the outside of seat belt 26. Commonly, seat belts are formed of cloth webbing. Wires 28 may also be woven within the webbing of seat belt 26. Referring now to Figure 4, occupant sensor system 12 is illustrated in a position representing partially around an occupant. As shown, occupant sensor 24 within seat belt 26 with wires 28 contained therein is extended from retractor 32. Seat belt 26 between buckle 34 and anchor 30 has a curvature as opposed to the straight unretracted position. Seat belt 26 between buckle 34 and retractor may also have various irregular shapes such as various radius curves. The shape of seat belt causes the wires 28 to have different inductance when electrical signals are passed therethrough. Occupant sensor 24 receives an electrical signal from controller 22. Controller 22 monitors the inductance of occupant sensor 24. By monitoring the change of inductance of occupant sensor 24, the controller 22 senses when an occupant is present. The size of the occupant may also be determined. Referring now to Figure 5, controller 22 has a microprocessor 44 contained therein. Microprocessor 44 based on various inputs, controls the deployment of airbag 18. Microprocessor 44 has a memory 46 coupled thereto. As illustrated, memory 46 is positioned outside controller 22. However, memory 46 may be included within controller 22 and may be an integral part of microprocessor 44. Memory 46 is preferably a non-volatile memory such as an EEPROM. Memory 46, as will be further described below, may be used to store a lookup table that has inductance values and corresponding occupant values. Occupant sensor 24 is controlled and monitored by microprocessor 44. Occupant sensor 24 has an input 48 and an output 50. Input 48 has a constant current source 52 or a constant voltage source 54 coupled thereto. Input 48 and output 50 correspond to wires 28 shown above. A high impedance voltage follower 56 is coupled between input 48 and microprocessor 44. Because occupant sensor 24 has a low resistance, high impedance voltage follower 56 allows microprocessor 44 to control the application of voltage or current to occupant sensor 24 without an unduly large current drain therefrom. Microprocessors are typically low operating current devices. Microprocessor 44 may provide a variety of signals to occupant sensor 24. For example, a square wave, a pulsed input, or a constant voltage or current may be applied to occupant sensor 24. Microprocessor 44 may also not constantly monitor occupant sensor 24. For example, buckle sensor 38 may be used as input to initiate microprocessor 44 to control occupant sensor 24. That is, upon the insertion of buckle 34 within buckle receiver 36, buckle sensor 38 provides a signal 44 in response to the signal from buckle sensor 38. Microprocessor 44 initiates the application of a predetermined signal to occupant sensor 24. Output 50 may be coupled to a current-to-voltage converter 56. Current-to-voltage converter 56 is coupled to an input of microprocessor 44. Current-to-voltage converter 56 changes the current from occupant sensor 50 into a voltage 56 suitable for input to microprocessor 44. If, however, microprocessor 44 is capable of receiving a current, current-to-voltage converter 56 may be eliminated. In operation, an occupant within the vehicle sits in seat 16 and extends seat belt 26. Buckle 34 is placed into a buckle receiver 36. Buckle sensor 38 provides a signal to microprocessor 44. Buckle sensor 38 is an optional feature of the present invention. If the buckle sensor 38 is not used, the microprocessor may constantly monitor sensor 24 after the ignition switch of the vehicle is on. The shape including curvature of the occupant sensor 24 and wires 28 therein provide a changing inductance. Microprocessor 44 initiates the application of an electrical signal to occupant sensor 24. Microprocessor 44 receives a signal that corresponds to the inductance to be measured. Microprocessor 44 compares the received signal from occupant sensor 24 and compares it to predetermined values. The predetermined values may be stored in memory 46. Various ranges of the inductance will correspond with an occupant wearing seat belt 26. Microprocessor 44 thus indicates the presence or absence of an occupant based upon the comparison. Further, because the inductance may vary based on the curvature of wires 28, the size of the occupant may also be determined. Microprocessor 44 in response to the signal from occupant sensor 24 may control the deployment of airbag 18. For example, if occupant sensor 24 indicates no occupant is present, the airbag may not be deployed. Further, if a signal indicating a small occupant 24 is present, the airbag deployment rate may be reduced. Those skilled in the art would recognise that various airbag deployment strategies may be employed in response to occupant sensor 24.

Claims: An airbag deployment system for an automotive vehicle comprising: an airbag (18); a seat belt (26); a retractor about which part of the seat belt is wound, an occupant sensor (24) comprising wires (28) extending along the seat belt (26) and conforming to the shape of the seat belt (26); and an airbag controller (22) coupled to the sensor (24); the wires (28) having aninductance that varies with the shape of the wires, characterised in that the controller is operative to determine the presence of an occupant in response to a change in the inductance of the wires (23) when the shape of the wires is changed as a result of the seat belt being worn by the occupant. An airbag deployment system as claimed in claim 1, further comprising a memory (46) coupled to the airbag controller (22) . An airbag deployment system as claimed in claim 1 or 2, wherein the airbag controller (22) comprises a constant current source (52) coupled to the occupant sensor (24). An airbag deployment system as claimed in claim 1 or 2, wherein the airbag controller (22) comprises a constant voltage source (54) coupled to the occupant sensor (24). An airbag deployment system as claimed in any preceding claim, wherein the airbag controller (22) comprises a current to voltage converter (56) coupled to the occupant sensor (24). An airbag deployment system as claimed in any preceding claim, further comprising a buckle sensor (38) coupled to the airbag controller (24) indicating a buckled seat belt. An airbag deployment system as claimed in any preceding claim, wherein the wires (28) extend within the seat belt (26). A method of determining the presence of an occupant in a seat in an automotive vehicle, the vehicle having a seat belt (26) with a retractor (32) and an airbag deployment system including an airbag controller (22) associated with the seat, the method comprising the steps of: providing wires (28) to extend along and conforming to the shape of the seat belt, and passing an electrical signal through the wires (28) to determine the presence of an occupant in the seat, the wires (28) having an inductance that varies in dependence upon the shape of the seat belt, characterised in that the inductance of the wires is measured and changes in the measured inductance are evaluated to determine the presence of an occupant in the seat. A method as claimed in claim 8, wherein changes in the measured inductance are evaluated by comparing the measured value of the inductance with predetermined values stored in a look-up table (46).

Inventors: BROSIG RALF, HAGEN MARKUS, SCHONDORF STEVEN YELLIN, BROSIG, RALF, HAGEN, MARKUS, SCHONDORF, STEVEN YELLIN
Applicants: FORD GLOBAL TECH LLC, FORD GLOBAL TECHNOLOGIES, LLC
Application year: 2000
Main classification: B60R21
IPC codes: B60R21, B60R22