Abstract:
An airbag deployment sensor stores a quantity of tape which is drawn out of a cartridge during airbag deployment by one end of the tape which is attached to the inside surface of an airbag. To facilitate assembly of an airbag system, the cartridge is designed with a key for locking the tape against premature extraction from the cartridge during the assembly process. The cartridge is used in combination with a mounting bracket which assures that the tape is free to be extracted from the cartridge once the cartridge is mounted to the bracket because, either the cartridge cannot be mounted to the bracket with the key in place, or the mounting bracket causes the key to move to a non-locking position.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to airbag sensors which monitor the deployment sequence of an airbag with a tape which is pulled out of the cartridge by an end of the tape which is attached to the inside surface of the airbag.  
         BACKGROUND OF THE INVENTION  
         [0002]    Airbags, originally developed as a passive restraint system, work best in combination with seatbelts and other safety systems. Various systems have been developed to detect an “out of position” vehicle occupant. Sensor systems designed to detect the vehicle occupant&#39;s position often require constant monitoring so that in the event of a crash the vehicle occupant&#39;s position is known. Sensor systems designed to detect the position of the vehicle occupant have been proposed based on ultrasound, optical, or capacitance sensors.  
           [0003]    A simpler type of sensor such as shown in European Patent application EP 0990567A1, employs a plurality of tapes which extend between the front of an 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 Tape extraction sensors within the cartridge monitor the rate at which tape is withdrawn from the cartridge and thus can detect airbag impact with a vehicle occupant by a decrease in airbag velocity. Improvements are needed to the known tape cartridges to facilitate installing the cartridges in an airbag module without allowing the tape to be prematurely drawn out of the cartridge.  
         SUMMARY OF THE INVENTION  
         [0004]    The airbag deployment sensor of this invention has a cartridge which stores a quantity of tape that is drawn out of the cartridge during airbag deployment by one end of the tape which is attached to the inside surface of the airbag. In order to facilitate assembly of the cartridge into an airbag system, the cartridge is designed with a means for preventing tape from being prematurely extracted from the cartridge during the assembly process. The cartridge is used in combination with a mounting bracket designed to assure that the tape is free to be extracted from the cartridge once the cartridge is mounted to the bracket. A first embodiment employs a screw or key, which biases a brake member within the cartridge against the tape to prevent it from being extracted. The first embodiment can be used with a mounting bracket that will not allow the cartridge to be mounted so long as the screw or key, which functions to lock the tape within the cartridge, is in its locking position. A second approach is to use a spring biased locking member that biases a brake member within the cartridge against the tape to prevent the tape from being extracted. The second embodiment is used in conjunction with a mounting structure which engages the locking member so as to release the locking member, rendering it inoperative when the cartridge is installed to the mounting structure. A third approach employs the same principle as the first approach but is used with a cartridge that contains a spool on which the tape is wound. A key locks the spool against rotation so preventing tape from being prematurely drawn from the cartridge. Again the cartridge can be used with a mounting structure or bracket which prevents the cartridge from being mounted if the key is in the locking position. A fourth approach, which is similar to the second approach, uses a spring biased member that is biased to a position which prevents a spool from rotating. When the cartridge is installed the mounting structure compresses the biasing spring so that the spring no longer prevents rotation of the spool.  
           [0005]    It is a feature of the present invention to provide a cartridge from which a tape is drawn during airbag deployment to measure the rate at which the airbag is deployed, wherein the tape is locked against withdrawal during airbag assembly, but when installed in the airbag module housing the tape can be withdrawn.  
           [0006]    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 DRAWING  
       [0007]    [0007]FIG. 1 is a schematic cross sectional view of an undeployed airbag showing the arrangement of a tape cartridge according to the present invention and its mounting bracket.  
         [0008]    [0008]FIG. 2 is an exploded isometric view of the tape dispensing cartridge.  
         [0009]    [0009]FIG. 3 is a cross-sectional view of a locking mechanism of an alternative embodiment tape dispensing cartridge according to the present invention, shown with the tape locked in position.  
         [0010]    [0010]FIG. 4 is a cross sectional view of the locking mechanism of FIG. 3 mounted to a bracket such that tape can be withdrawn from the tape dispensing cartridge.  
         [0011]    [0011]FIG. 5 is an exploded isometric view of tape dispensing cartridge of FIG. 3  
         [0012]    [0012]FIG. 6 is a top plan view, partially cut away in section of a further alternative embodiment of the tape dispensing cartridge of this invention.  
         [0013]    [0013]FIG. 7 is a side elevational cross-sectional view of the tape dispensing cartridge of FIG. 6 taken along section line  7 - 7   
         [0014]    [0014]FIG. 7A is a side elevational cross-sectional view of the tape dispensing cartridge of FIG. 7 shown installed on a bracket.  
         [0015]    [0015]FIG. 8 is an exploded isometric cross-sectional view, partially cut away in section of yet another tape dispensing cartridge of this invention, wherein a tape spool is locked against rotation.  
         [0016]    [0016]FIG. 9 is an isometric cross-sectional view of the tape dispensing cartridge of FIG. 8 wherein the tape spool is free to rotate.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]    Referring to FIGS. 1-9 wherein like numbers refer to similar parts, an airbag module  20  is shown in FIG. 1. The airbag module  20  has a folded airbag  22  mounted to the airbag housing  24 , and an inflator  26  for causing inflation of the airbag. The inflator  26  incorporates a pressure relief valve formed by an actuator  28  and a connected flap  29  which allows the inflation of the airbag  22  to be terminated in response to information provided by airbag deployment sensor cartridges  30 . Each deployment cartridge  30  contains a quantity of tape  32 . A first end  34  of the tape  32  is attached to the inside surface  36  of the airbag  22  during assembly of the airbag module  20 . The tape cartridge  30  is then mounted to a bracket  38 , as shown in FIG. 2.  
         [0018]    To prevent the tape  32  from being pulled out of the cartridge  30  during assembly, a threaded key  40  which forms a selectively engageable structure, extends through a first wall  41  of the body  42  of the cartridge  30  to bias a braking member  44  against a braking surface  46 , to thereby clamp the tape  32  against movement. The bracket  38  has a protruding flange  48  which projects perpendicularly to the mounting plate  39  of the bracket. The flange  48  extends generally parallel to the cartridge first wall  41 . The first wall  41  lies adjacent the flange  48 , mounting holes  50  in the bracket mounting plate  39  are in alignment with mounting holes  52  in the cartridge  30 . The presence of the key  40 , protruding from the first wall towards the bracket flange  48 , prevents the cartridge  30  from being positioned so that mounting holes  50  on the bracket  38  line up with the mounting holes  52  of the cartridge  30 . Thus the key  40  prevents tape from being extracted during the assembly process and the bracket  38  and attached flange  48  prevent the key  40  from being inadvertently left in place after assembly. If the key were to remain in place in the assembled the cartridge would not allow tape  32  to be extracted from the cartridge when the airbag  22  is deployed. With the key  40  removed, the first wall  41  may be brought up against the flange  48 , and the cartridge properly mounted to the bracket  38 . For clarity in illustration the cover of the cartridge  30  is not shown.  
         [0019]    An alternative tape cartridge  54 , shown in FIGS. 3-5, is similar to the cartridge  30 , except that a different mechanism is employed to prevent inadvertent locking of the tape when installed in an airbag system. The cartridge  54  has a braking member  56  that travels within a slot  57  and in use is urged by a spring  76  towards the tape  32  to engage the tape against a braking surface  58  of the cartridge. The braking member  56  has a central opening  59  that receives a cam  60  therethrough.  
         [0020]    Prior to assembly, the braking member  56  is held biased against the tape  32  and the braking surface  58  by the cam  60 . The cam  60  that forms a selectively engageable structure, may be a plastic element that travels perpendicular to the motion of the braking member within a recess  61  formed in the slot  57 . The cam  60  is biased upwardly towards the braking member  56  by a spring  62  positioned within the recess  61 . The cam  60  has an upwardly facing inclined cam surface  64  which engages a complementary downwardly facing inclined surface  66  on the braking member  56 . When the cam  60  is urged upwardly by the spring  62 , the tape  32  is clamped between the braking member  56  and the braking surface  58 .  
         [0021]    The cam  60  has an upwardly extending post  68  that protrudes through the opening  59  in the braking member  56 . The cartridge  54  has a cover  72  with a small opening  70  therein which overlies the cam  60  and through which the cam post  68  protrudes. As shown in FIG. 4, when the cartridge  54  is assembled to a mounting bracket  74 , the post  68  is depressed downwardly which causes the cam surface  64  to disengage from the complementary surface  66  on the braking member.  
         [0022]    When the cam  60  is disengaged, the braking member  56  may then move within the slot  57 , with only the force of the brake spring  76  urging the braking member  56  against the tape  32 . In accordance with the principal of an inclined plane, the angle of the cam surface  64  with respect to the direction of the locking force supplied by the spring  62  is such as to provide mechanical advantage providing several times the locking force against the tape  32  compared to the strength of the spring  62 .  
         [0023]    When the tape cartridge  54  is mounted to the mounting bracket  74 , the mounting bracket depresses the cam post  68  and causes the cam  60 , which serves as a locking means during transit, to disengage without removing the cam from the tape cartridge  54 . With the cam  60  disengaged, the tape  32  can be withdrawn from the cartridge  54  when the airbag  22  is deployed. The tape  32  may be marked with dark bands  78  so a sensor  80  and a light source  82  can be used to detect the rate at which tape  32  is withdrawn from the cartridge  54 .  
         [0024]    Another alternative tape cartridge  84  configuration is shown in FIGS. 6-7A. The tape cartridge  84  has a body  86  and a cover  88 . A spool  90  is located within the body  86 , and a quantity of tape  32  is wound around the spool. A shaft  92  protrudes from the spool  90 , and the spool rotates about the shaft. The shaft  92  is held for rotation in a first bearing  94  formed by portions of the body  86  and a second bearing  96  formed by portions of the cover  88 . Portions  98  of the shaft  92  extend upwardly through an opening  100  in the cover  88 . The upwardly extending portions  98  form a hexagonal socket  102 . A wrench (not shown) can be placed in the socket  102  to rewind tape  32  onto the spool  90 . A locking key  104  that forms a selectively engageable structure has portion  106  which engage the hexagonal socket  102 . The locking key has a square flange  108  that sits in a complementary square depression  110  on an outer portion of the cover  88 . The locking key  104  interfits with the square depression  110  and the hexagonal slot  102  which locks the spool  90  against rotation with respect to the square depression  110  and thus the cover  88  and the body  86  of the tape cartridge  84 . A mounting flange  112  to which the cartridge  84  is mounted by screws  114  interferes with a protruding portion  116  of the key  104  as shown in FIG. 7 and thus the cartridge  84  cannot be mounted to the flange  112 , as shown in FIG. 7A, while the key  104  is in place.  
         [0025]    A further alternative tape cartridge  118  is shown in FIGS. 8 and 9. The tape cartridge  118  contains a spool  120  about which a quantity of tape  32  is wrapped. The spool  120  has a central shaft  122  which has lower bearing portions  124  which engage lower bearing portions  126  on the housing  128  of the cartridge  118 . The spool  120  has upper bearing portions  130  that engage upper bearing portions  132  of the housing  128 .  
         [0026]    A stub shaft extends from the upper bearing portions  130  that terminates in a square key  136 . A wave spring  138  with a complementary square hole  140  is positioned so that in its relaxed position the square hole  140  in the spring is positioned about the square key  136  of the stub shaft  134 . The spring  138  is held in a depression  139  in the upper surface of the housing  128  by tabs  141  that allow some movement of the spring  138  in the depression  139 .  
         [0027]    The complementary square hole  140  in the spring  138  prevents the rotation of the square key  136  and thereby prevents the rotation of the central shaft  122  and the spool  120  on which the tape  32  is wrapped. When the tape cartridge  118  is mounted to a mounting bracket  142 , however, a central hole  144  in the mounting bracket sits over the square key  136  which terminates the stub shaft  134 . The central hole  144  is sufficiently large so that the square key  136  may freely rotate within the central hole  144 . When the bracket  142  is in place, portions  146  of the bracket, spaced from the central hole  144 , compress the wave spring  138  and thereby push the complementary hole  140  in the spring downwardly away from the square key  136  to be positioned about the smaller circular stub shaft  134 . Thus, when the tape cartridge  118  is installed on the bracket  142 , the wave spring  138  that forms a selectively engageable structure is compressed so as to allow free rotation of the spool  120  about the central shaft  122 .  
         [0028]    It should be understood that the invention is not limited to the particular mechanisms illustrated and described, but is directed broadly to the use of a removable key which, when the key is installed, blocks the extraction of tape from the tape cartridge. Additional advantage is achieved if the removable key is used with a bracket which prevents the key from being inadvertently left installed when the tape cartridge is in its final installed position on the bracket. Alternatively the invention is directed to a key which locks a tape cartridge against the withdrawal of tape, but is not removable but rather can be moved to a non-blocking position. Again, a mounting bracket may be used with the tape cartridge to assure that the key is in the non-blocking position when the tape cartridge is installed in its final location.  
         [0029]    It should be understood that when a tape is described, the tape could be a plastic film, a metal strip, a woven material, a monofilament line, or a string composed of several fibers or filaments. Generally, tape should be understood to refer to any material connection between the inside surface of the airbag and a cartridge containing a sensor for detecting the rate at which the tape is withdrawn from the cartridge.  
         [0030]    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.