Abstract:
A cartridge stores a quantity of string, one end of which is attached to the inside surface of an airbag cushion. A spool which transitions to a cone is situated within the cartridge. A narrow gap around the spool forms a string storage space and a similar gap overlies the cone and leads to an outlet. Positioned within the body of the cartridge is a light source and a light detector. As string is drawn out of the cartridge, the string traverses between the light sources and a light detector generating a signal directly proportional to the rate at which string is withdrawn. The geometry of the cartridge is arranged to provide friction against the string. The friction is created between the string and the junction between the cylindrical spool and the cone and rapidly overcomes the momentum of the string when the airbag cushion comes to a stop.

Description:
FIELD OF THE INVENTION 
     The present invention relates to airbags and sensors used to control airbag deployment, and to sensors that monitor the actual deployment sequence in particular. 
     BACKGROUND OF THE INVENTION 
     While airbags were originally developed as a passive restraint system, experience has shown that airbags work best in combination with seatbelts and other safety systems. Although airbags contribute to the overall safety of occupants of an automobile, they can present a danger to an occupant who is positioned too close to an airbag when it deploys. This condition, where the occupant is positioned so that airbag deployment might be dangerous, is referred to as the occupant being “out of position.” Various systems have been developed to detect an “out of position” occupant. Sensor systems designed to detect the occupant&#39;s position often require constant monitoring so that in the event of a crash the occupant&#39;s position is known. Sensor systems designed to detect the position of the occupant have been proposed based on ultrasound, optical, or capacitance sensors. Constant monitoring of sensors, which may have high data rates, requires the design of algorithms which can reduce sensor data to a single condition or a limited number of data conditions which are used in an airbag deployment decision to prevent airbag deployment or for a duel stage airbag to select the level of deployment. Maintaining data integrity between the non-crash positional data, and positional data needed during airbag deployment is complicated by the noisy environment produced by a crash. Dealing with data integrity issues requires increased processor capabilities and algorithm development, which also requires additional testing. 
     Prior art approaches attempt to determine, based on various sensors, the distance between the airbag and the passenger before the airbag is deployed. In many instances, the vehicle occupant will not be too close to the airbag at the time the decision to deploy the airbag is made, but, because of the rate at which the occupant is approaching the airbag, the occupant will be too close when the airbag is actually deploying. To handle these situations, more sophisticated sensors and algorithms are needed to attempt to predict the occupant&#39;s position when the airbag is actually deployed or nearly completely deployed. In other words, the ideal airbag deployment system functions such that the airbag deploys fully or nearly fully before the occupant engages the airbag. Existing systems inhibit airbag deployment when, based on various sensors and algorithms, it is determined that, because of the position of the vehicle occupant, the bag is more likely to harm than to benefit the occupant. 
     Successfully creating a sensor and algorithm system is complicated because there is usually very little delay between the decision to deploy and actual deployment. This is so because the maximum benefit from an airbag is achieved by early deployment, and at the same time, more time before deployment maximizes the information available to determine whether deployment is necessary. The desire to maximize effective deployment of the airbag while minimizing unnecessary deployment creates a tension between waiting for more information and deploying immediately. Therefore, once sufficient information is available, deployment typically follows nearly immediately. 
     Therefore, a system which employs occupant position sensors and algorithms must be able to supply at all times an indication of whether airbag deployment should be inhibited so that the inhibit decision can be applied whenever the airbag deployment decision occurs. This means the sensors and algorithms used to develop the occupant position inhibit signal cannot be optimized to deal with a specific time frame in which the actual deployment decision is made. The end result is that such algorithms may be less accurate than desired because they must predict events relatively far in the future—perhaps tens of milliseconds. 
     DISCUSSION OF THE PRIOR ART 
     One known type of sensor shown in European application EP 0990567A1 employs a plurality of tapes that extend between the front of the airbag and a tape dispensing cartridge mounted on the airbag housing. Tape extraction sensors within the cartridge monitor the rate at which tape is withdrawn from the cartridge and thus can detect airbag impact with an occupant by a decrease in airbag velocity. Improvements are needed to the known tape cartridges to improve the functionality and reliability of the tape type bag deployment monitoring sensors. 
     SUMMARY OF THE INVENTION 
     The airbag deployment sensor of this invention employs a cartridge that stores a quantity of string. One end of the string stored in the cartridge is attached to the inside surface of an airbag cushion. As the string is withdrawn from the cartridge it is caused to repeatedly move in front of one or more sensors so the rate at which string is being withdrawn from the cartridge can be determined. The geometry of the cartridge is arranged to provide a controlled amount of friction on the string. The friction in the cartridge is selected so as to rapidly overcome the momentum of the string when the portion of the airbag cushion to which the string is attached comes to a stop. A preferred embodiment has an axisymmetric cylindrical spool which transitions to a cone situated within the cartridge. A narrow gap around the cylindrical spool defines a string storage space and a similar gap overlying the cone and leading to an outlet overlying the apex of the cone defines a payout structure. The cone is penetrated by a plurality of holes which cross an axis defined by the cylindrical spool and the co-joined cone. Positioned within the body of the cartridge opposite one side of each hole in the cone is a light source. Positioned within the body of the cartridge opposite a second side of each hole is a light detector. As string is drawn out of the cartridge by deployment of the airbag, the string traverses between the light sources and the light detectors so that a signal with twice the frequency of the number of holes in the cone is generated each time a loop of string is withdrawn from the cartridge. The signal frequency is directly proportional to the rate at which string is withdrawn and provides a direct measurement of the forward velocity of the portion of the airbag cushion to which the string is attached. Friction to overcome the momentum of the deployed string is created between the string and the junction between the cylindrical spool and the cone. 
     An alternative embodiment utilizes an elliptical or oval prismatic spool with or without a conical extension. A further embodiment utilizes two prismatic spools about which the string is wound in a figure-eight pattern. 
     It is a feature of the present invention to provide an airbag deployment sensor which can detect a portion of the airbag cushion impacting an object before the cushion is fully deployed. 
     It is a further feature of the present invention to provide an airbag deployment sensor which utilizes the payout of string to measure the speed of a portion of an airbag wherein the string deployment cartridge has no moving parts. 
     It is a still further feature of the present invention to provide an airbag deployment sensor which utilizes the payout of string to measure the speed of a portion of an airbag wherein the fractional resistance to drawing string from a deployment cartridge is simply controlled in design. 
     It is yet another feature of the present invention to provide an airbag deployment sensor incorporating a string deployment cartridge wherein no marks are required on the string. 
     Further features and advantages of the invention will be apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an isometric view partially cut-away in section of the airbag deployment sensor of this invention. 
         FIG. 2  is a side elevational view partly cutaway of the airbag deployment sensor of  FIG. 1  positioned to detect the rate of deployment of an airbag cushion. 
         FIG. 3  is a side elevational view, partially cut-away in section, of an alternative embodiment of the airbag deployment sensor of this invention. 
         FIG. 4  is a side elevational view, partially cut-away in section, of another alternative embodiment of the airbag deployment sensor of this invention. 
         FIG. 5  is a schematic top plan view of an alternative arrangement of the light sources and light detectors that could be used with the airbag deployment sensor of FIG.  1 . 
         FIG. 6  is a schematic top plan view of arrangement of light sources and light detectors for use with the airbag deployment sensors of  FIGS. 3 and 4 . 
         FIG. 7  is a schematic top plan view of an another alternative arrangement of the light sources and light detectors that could be used with the airbag deployment sensor of FIG.  1 . 
         FIG. 8  is a schematic top plan view of a further alternative arrangement of the light sources and light detectors which could be used with the airbag deployment sensor of FIG.  1 . 
         FIG. 9  is a schematic top plan view of a yet further alternative arrangement of the light sources and light detectors which could be used with the airbag deployment sensor of FIG.  1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring more particularly to  FIGS. 1-9 , wherein like numbers refer to similar parts, an airbag module  20  is shown in FIG.  2 . The airbag module  20  is positioned opposite a vehicle passenger  22  seated on a vehicle seat  23 . A housing  24  containing a quantity of gas generant  26  is positioned behind an instrument panel  28 . When activated by an igniter  30 , the gas generant  26  inflates an airbag cushion  32  that extends through the instrument panel  28  towards the passenger  22 . A plurality of airbag deployment sensors  34  are mounted to the housing  24 . 
     Each sensor  34 , as shown in  FIG. 1 , has a cartridge  36  that contains a quantity of string  38 . As used herein and in the claims the term “string” is understood to mean an elongated flexible member having a cross section of any suitable shape, not just circular, including for example rectangular or oblong. One end  40  of the string  38  is attached to the inside surface  42  on the airbag cushion  32 . As the airbag cushion  32  is deployed towards the passenger  22 , string  38  is drawn from the cartridge  36 . By monitoring the rate at which string  38  is withdrawn from the cartridge  36  it is possible to detect when a portion  44  of the airbag cushion  32  impacts an object because, as the portion  44  of the airbag comes to a stop, it ceases to draw string  38  from the cartridge  36 . This information can be used by a safety system controller (not shown) to control valves  46  on the housing  24  to vent the airbag cushion  32  or to otherwise limit or control the continued inflation of the cushion  32 . 
     As shown in  FIG. 1 , the airbag deployment sensor  34  has a cartridge  36  within which is contained a cylindrical spool  48  about which the string  38  is wound. A gap  50  between the spool  48  and the body  52  of the cartridge  36  forms a reservoir for the storage of the string. Typically about three feet of string will be stored within the cartridge  36  before the airbag cushion deployment begins. The cylindrical spool  48  is topped by a cone  54  that tapers towards an apex  56 . The gap  50  forming the string reservoir continues to follow the cone  54  until it reaches an opening  58  positioned over the apex  56  of the cone  54 . The gap over the cone forms a passageway  60  through which the string  38  moves in reaching the opening  58 . 
     The arrangement of the cylindrical spool  48  and the cone  54  is such that the string sweeps along the surface  62  of the cone  54  as it is pulled from the reservoir formed by the gap  50  about the cylindrical spool  48 . The cone  54  is formed with a plurality of holes  64  that are perpendicular to an axis  66  defined by the cylindrical spool  48  and the cone  54 . The holes  64  in the cone  54  are aligned to allow light from a light source  68  such as an LED to be transmitted through the cone  54  to a light sensor  70  such as a phototransistor positioned opposite the light source  68 . 
     As shown in  FIG. 1 , the light sources and light sensors are mounted within the cartridge body  52  within collimating sockets  72 . As the string  38  is withdrawn from the cartridge  36  and thus rotates, as illustrated in  FIG. 1 , along the surface  62  it twice passes between any particular light source  68  and light sensor  70  momentarily completely or partially blocking the reception of light by the light sensor  70 . If there are four pairs of light sources  68  and light sensors  70  as shown in  FIG. 1 , each time a coil  74  of string  38  is withdrawn from the cartridge  36  the string will pass once completely around the surface  62  of the cone  54  causing eight interruptions of light passing from a light source to a light sensor. Thus the movement of the string  38  creates a periodicity which is proportional to the length of string withdrawn. 
     If the cylindrical spool has a diameter, for example of 1.9 centimeters (¾ inch), one coil  74  would have a length of about 5.9 centimeters (2⅓ inches) and removal of about every 0.8 centimeters (⅓ inch) of string would be detected, if four sensors and light sources are used as shown in FIG.  1 . By increasing the number of light sources and light sensors, a more precise and higher frequency signal can be generated by the withdrawal of string  38  from the cartridge  36 . 
     The string  38  moves through the opening  58  which has a rounded outlet lip  76  to prevent binding, as the airbag cushion motion during deployment may cause the string  38  to be pulled from varying directions, especially during the early phases of airbag cushion deployment when cushion flutter may be experienced. 
     To hermetically seal the cartridge  36  during the storage life of the airbag  20 , a plug  78  attached to the string  38  may be used to seal the opening  58 . The plug  76  is pulled away from the opening  58 , as illustrated in FIG.  1 . As the string  38  is drawn from the cartridge  36 , the string rubs on the cylindrical edge  80  where the string transitions from being pulled upwardly along the cylindrical spool  48  to being pulled along the cone  54 . This rubbing will produce a frictional force, which will retard the withdrawal of the string  38 . The frictional force losses, act as a brake to overcome the momentum of the string already withdrawn so that when the portion  44  of the airbag to which the string is connected comes to a stop, the rate at which string is withdrawn from the cartridge  36  will rapidly reflect the velocity of the airbag portion  44  to which the string is attached. By adjusting the height of the cone  54 , the angle at which the string is drawn over the cylindrical edge can be adjusted, which should control the amount of friction experienced by the string  38 . 
     The string  38  may be woven of a single filament or of a twisted strand of fibers, selected from fibers such as high-strength &amp; high-modulus polyethylene fiber (HSM-PE fiber) or an aromatic (polyamide) fiber. A sizing such as wax may be applied to the string  38  to prevent tangling as the string is withdrawn from the storage reservoir, and to hold the string within the gap  50  allowing only a single coil  74  to be withdrawn at one time. The second end (not shown) of the string may be attached to the body  52  of the cartridge  36 . 
     An alternative embodiment of an airbag deployment sensor  82  is shown in FIG.  3 . The airbag deployment sensor  82  has a cartridge  84  with an elliptical or oval spool  86 . A string storage reservoir is defined by a gap between the oval spool  86  and the body  88  of the cartridge  84 . String  90  is wound about the spool  86 . Portions  92  of the cartridge  84  form the elliptical or oval conical space through which the string  90  is drawn. Light sources  94  and light sensors  96  are positioned about the conical space such that pulling the string  90  results in the string passing back and forth between the light sensors  96  and light sources  94 . 
     A further embodiment of an airbag deployment sensor  98  is shown in FIG.  4 . The deployment sensor  98  has a cartridge  100  and two elliptical- or tear-shaped right prismatic spools  102  about which a string  104  is wound in a figure eight pattern. Portions  106  of the cartridge  100  form the oval conical space through which string  108  is drawn. Light sources  110  and light sensors  112  are positioned about the conical space such that pulling string  104  from the cartridge  100  results in the string passing back and forth between light sensors  112  and light sources  110 . 
     The light sensors  70  and light sources  68  illustrated in  FIG. 1  could be arranged in various ways.  FIG. 5  illustrates three LEDs positioned opposite three photo transistors arranged in a linear array.  FIG. 7  illustrates eight separate LEDs  68  positioned in the cone  54  that passes light to eight separate phototransistors  70 .  FIG. 8  shows an arrangement opposite the one shown in  FIG. 7 , with a single photodiode  70  mounted in the cone  54  receiving light from eight LEDs mounted in the body  52  of the cartridge  36 . The arrangement of  FIG. 8  has the advantage of a single light detector which produces a single higher frequency output signal which does not need to be created by adding the output of multiple light sensors. 
       FIG. 9  illustrates the use of mirrors  114  so that a single light source  68  such as a diode laser can make multiple passes through the space  116  through which the string is drawn before reaching a light sensor  70 . The arrangement of  FIG. 9  also provides simplified electronics, because only a single sensor is used. Using a single sensor avoids the additional electronics associated with adding the output of multiple sensors together to get a single signal indicative of the speed with which string is withdrawn from the cartridge. 
       FIG. 6  shows an alternative arrangement of a single light source  110  such as a diode laser and mirrors  118  which makes multiple passes across a conical space before reaching a light detector  112  which is suitable for use with the airbag deployment sensor  98  shown in FIG.  4 . Again, the use of a single sensor simplifies the detecting electronics. 
     It should be understood that the string  38 ,  90 ,  104  can be a single filament or woven fiber or a tape, and will preferably be made of high strength lightweight material, for example high-strength &amp; high-modulus polyethylene fiber (HSM-PE fiber) or an aromatic (polyamide) fiber. The string may be coated with a size such as wax to facilitate the orderly withdrawal from the cartridge, the size holding the string in place within the string reservoir until the pulling action of the airbag cushion causes the string to peel away from the string remaining in the reservoir. The size selected may also be used to control the amount of breaking friction by selecting a size that increases or decreases withdrawal friction as necessary. It should be understood that this string can be directly attached to the airbag cushion interior surface, or could be attached indirectly by way of a string, tape or web which is attached to the airbag cushion interior surface. 
     As the string is withdrawn from the cartridge, the string emerging from the cartridge opening defines a direction of string motion toward the airbag attachment point, even though in practice due to airbag flutter the airbag string will at times be pulled in a range of directions which on average defines the string motion. 
     It is understood that the invention is not limited to the particular construction and arrangement of parts herein illustrated and described, but embraces all such modified forms thereof as come within the scope of the following claims.