Abstract:
An airbag module utilizes tape dispensing cartridges. A tape end extends from each cartridge to the inside surface of an airbag. As the airbag inflates, tape is drawn from the tape cartridges as the tapes are drawn along with the deploying airbag. The rate at which tape is withdrawn from the cartridges is measured by sensible indicia of a magnetic or optical nature positioned on the tape and drawn past a sensor contained within the tape cartridge. The markings on the tape can be nonuniform along the length of the tape. The tape storage area outlet and the cartridge outlet are each formed by two relatively large radius corners. The tape is sealed to the cartridge to prevent the ingress of contaminants. As the airbag withdraws tape from the cartridges, the seals are unseated.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to airbags and sensors used to control air bag deployment in general, and to sensors that monitor the actual deployment sequence in particular. 
     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 the occupants of a motor vehicle, they can present a danger to an occupant who is positioned too close to an airbag when it deploys. This condition, where the vehicle 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” 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 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. Constant monitoring of sensors, which may have high data rates, requires the design of algorithms that can reduce sensor data to a single condition or a limited number of data conditions that are used in an airbag deployment decision to prevent airbag deployment or for a dual 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 vehicle occupant 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 vehicle occupant is approaching the airbag, the vehicle 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 vehicle 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 airbag is more likely to harm than to benefit the occupant. Successfully creating a sensor and algorithm system is complicated inasmuch as there is usually very little delay between the decision to deploy and the 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 that employs vehicle 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. 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 can detect airbag impact with a vehicle occupant by a decrease in airbag velocity as measured by the rate of tape withdrawal from the cartridge. Improvements are needed to the known tape cartridges to improve the functionality and reliability of the tape type airbag deployment monitoring sensors. 
     SUMMARY OF THE INVENTION 
     The airbag module of this invention utilizes several tape dispensing cartridges mounted on an airbag housing. A quantity of tape is stored within each cartridge. A tape end extends from each cartridge, and is mounted to the inside surface of an airbag that is attached to the airbag housing. A gas generant cartridge positioned within the airbag housing is used to inflate the airbag. As the airbag inflates, tape is drawn from the tape cartridges as the free ends of the tapes are drawn along with the airbag as it deploys. The rate at which tapes are withdrawn from the cartridges is measured by sensible indicia of a magnetic or optical nature positioned on the tape and drawn past a sensor contained within the tape cartridge. The markings on the tape can be nonuniform along the length of the tape; e.g., the first portion of the tape has no markings so that a photo diode and light sensor will function during a self-test. 
     The tape cartridge has a storage area for tape where the tape is stored folded or wound. The outlet of the storage area has an opening surrounded by relatively large radius corners approximately one-quarter inch or six millimeters in radius to facilitate the smooth withdrawal of tape from the storage area. In a similar manner, the outlet of the cartridge is formed by two relatively large radius corners of approximately one quarter inch, or six millimeters, in radius to prevent the tape from breaking, because especially as the airbag is first deployed, the airbag and the attached tape may pull from a wide range of directions. Between the stored tape and the tape outlet a brake is positioned. The brake comprises a spring-loaded plunger that pushes a smooth brake surface against the tape as it traverses a brake surface parallel to the path of the tape. The brake allows tape to be withdrawn from the cartridge as long as a relatively strong force is applied to the tape by the expanding airbag. When the airbag collides with an object so that the portion of the airbag stops moving forward the tape attached to that portion of the airbag is no longer pulled from the cartridge, and the brake is sufficient to overcome the inertia of the already deployed tape within a few millimeters or centimeters of tape travel. 
     The tape may be constructed of cloth that is woven or marked with a pattern of transverse lines extending perpendicular to the direction in which the tape is extracted. A light source such as a light emitting diode is mounted to the cartridge on one side of the tape and a light sensitive sensor is mounted to the cartridge on the side of the tape opposite the light source. Movement of the tape causes the light sensor output to change depending on whether or not a line is positioned between the light source and a light sensor. By counting or otherwise tracking the number of times or the rate at which the light is alternatively blocked or transmitted, the rate at which tape is being withdrawn from the cartridge can be determined. When a portion of the airbag collides with an object or vehicle occupant, that portion at the airbag ceases its forward movement and that causes the tape to no longer be extracted from the cartridge, or to be extracted at a substantially lower rate. The transverse markings may be nonuniformly spaced along the tape. For instance, the markings may not exist at all at the very beginning of the tape so that nondestructive testing can be performed by turning on the light source and detecting it with the light sensor. Alternatively a special marking with different transmissivity or reflectivity at the beginning of the tape could be used to produce a recognizable signal that would verify the functionality of the sensor, and that the tape has not been inadvertently pulled out e.g. during the airbag module assembly. 
     Airbags and their components must function years after they are manufactured. For this reason, to prevent the tape cartridge and the components within the tape cartridge from deteriorating, the tape cartridge is sealed. More particularly, an elastomeric grommet is mounted on the tape and positioned at the outlet of the cartridge. The grommet snaps to the cartridge to prevent the ingress of moisture and dust or other contaminants. The relatively strong pull of the deploying airbag unseats the grommet, allowing the tape to be withdrawn from the cartridge. Alternatively, a wax or elastomeric seal may be formed between the tape and the inside surfaces of the tape cartridge outlet. 
     It is a feature of the present invention to provide a means for detecting an out of position vehicle occupant when an airbag deployment is occurring. 
     It is another feature of the present invention to provide a tape cartridge that provides a tape withdrawal signal which facilitates processing of the withdrawal signal. 
     It is further feature of the present invention to provide a tape cartridge wherein the tape can be withdrawn reliably over a range of angles. 
     It is yet another feature of the present invention to provide a tape cartridge that can be sealed against the environment to increase service life. 
     It is a still further feature of the present invention to provide a tape cartridge that can provide a built-in test function. 
     It is still another feature of the present invention to provide a more reliable tape cartridge with simplified construction. 
     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 
         FIG. 1  is an isometric view, partially cut away in section, of the airbag module of this invention as the airbag is deployed. 
         FIG. 2  is a partially exploded isometric view of the tape cartridge of this invention. 
         FIG. 3  is a partially exploded isometric view of an alternative embodiment tape cartridge of this invention. 
         FIG. 4  is an enlarged detail cross-sectional view of the tape outlet of the tape cartridge of  FIG. 2  showing a grommet seal. 
         FIG. 5  is an enlarged detail cross-sectional view of the tape outlet of the cartridge of  FIG. 2  showing an elastomeric seal. 
         FIG. 6  is an enlarged detail view of the tape outlet of the cartridge of  FIG. 2  showing an alternative embodiment grommet seal. 
         FIG. 7  is an enlarged detail view of tape being withdrawn at a plurality of angles from the outlet of the cartridge of FIG.  2 . 
         FIG. 8   a  is an enlarged fragmentary view of the ultrasonic joint used to seal the tape cartridge of  FIG. 2  before assembly. 
         FIG. 8   b  is an enlarged fragmentary view of the ultrasonic joint used to seal the tape cartridge of  FIG. 2  after assembly. 
         FIG. 9  is a top plan view of an alternative embodiment brake mechanism used with the tape cartridge of FIG.  2 . 
         FIG. 10  is an isometric view of an alternative embodiment bottom portion of the tape cartridge of  FIG. 2  having an integral molded braking spring. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring more particularly to  FIGS. 1-10 , wherein like numbers refer to similar parts, an airbag module  20  deploying an airbag  22  is shown in FIG.  1 . An airbag housing  24  contains an igniter  26  and a quantity of gas generant  28  such as 5-aminotetrazole and is mounted behind an instrument panel  30 . A vehicle occupant  32  is seated on a vehicle seat  34  facing the airbag  22 . Cloth tapes  36  are fastened to the inside surface  38  of the airbag  22 , and are retained within tape dispensing cartridges  40  mounted to or behind the airbag housing  24 . The cartridges  40  are mounted fixed with respect to the airbag housing so the relative movement of the airbag  22  can be measured. When the airbag module  20  is activated, the airbag  22  deploys towards the vehicle occupant  32 , and the tapes  36  are withdrawn from the cartridges  40 . The purpose of the cartridges  40  and the tapes  36  that are withdrawn from the cartridges is to allow the detection of an “out of position” vehicle occupant and adjust or stop the deployment of the airbag in response to detecting the “out of position” vehicle occupant. 
     As shown in  FIG. 2 , withdrawal of a tape  36  from a dispenser cartridge  40  is monitored by a light emitting diode  42  mounted within the cartridge  40 . The light emitting diode  42  passes light through the tape  36  to a light sensor  44  mounted opposite the diode  42 . The sensor detects the changing light intensity as the tape  36  passes between the light emitting diode  42  and the light sensor  44 . The tape  36  has bands of dark coloring  46  that may be printed on the tape or woven into the tape. As a tape  36  is withdrawn from a cartridge  40 , the light sensor  44  alternatively receives or does not receive light from the diode  42 . By monitoring the rate (frequency) at which the light sensor  44  transitions from receiving light to not receiving light, the number of bands  46  that have passed between the light emitting diode and the light sensor can be determined. When correlated with time, the distance, velocity, and acceleration of an airbag portion  38  to which a tape  36  is attached can be determined from the signal derived from the tape cartridges  40 . 
     When the portion  38  of the airbag to which the tape  36  is attached comes into contact with an object, the bag portion decreases in velocity or comes to a stop. As shown in  FIG. 2 , the withdrawal of the tape  36  is continuously being retarded by a brake  50  comprising a plunger  52  biased from a cartridge housing by a spring  54 . The plunger  52  constantly urges the tape  36  against an opposed brake surface  56 . The brake  50  overcomes the momentum of the tape  36  so that once the bag portion  48  is no longer drawing the tape  36  from the tape dispenser cartridge  40 , the tape comes to a stop within a few millimeters to about one centimeter. 
     As shown in  FIG. 2 , the tape  36  is stored folded in a tape compartment  58  that stores about three feet (about one meter) of tape. The outlet  60  of the tape compartment  58  is formed between two radiused corners  62 , each having a radius of approximately six millimeters. The radiused outlet  60  allows the tape  36  to be drawn without binding through the tape cartridge  40 . The tape  36  travels from the tape compartment  58  past the brake  50  and the sensor  44  and then out of the cartridge at a cartridge outlet  64 . The cartridge outlet  64  is also formed by two radiused corners  66  to prevent jamming of the tape  36  as it is drawn at high speed from the cartridge  40 . The outlet  60  of the tape compartment  58  and the cartridge outlet  64  form radiused tapers, i.e. a taper where the angle of the taper increases in the direction the tape leaves the cartridge  40 . As shown in  FIG. 7 , during the initial deployment of the airbag  22 , the tape  36  may be pulled back and forth at an angle with respect to the cartridge outlet  64 . The smooth radiused corners  66  are essential to allow functioning of the high-speed withdrawal of the tape that is simultaneously moving from side to side due to bag flutter. 
     Because of the long life expected from airbag components, it is important that the airbag module  20  be resistant to aging. In particular, the tape cartridge  40  is sealed to prevent moisture and other contaminants from migrating into the interior  68  of the cartridge  40 . As shown in  FIG. 2 , a cover  70  may be ultrasonically welded to a cover bottom portion  74 , as shown in detail in  FIGS. 8   a  and  8   b . An ultrasonic joint  72  is formed between the cover  70  and the bottom portion  74  of the cartridge. The weld is formed between a beveled edge  76  and an overhanging lip  78 . The cover  70  is vibrated at high frequency and brought into engagement with the bottom portion  74 , thereby forming a hermetic seal. The tape  38  may be sealed to the cartridge outlet in one of a number of approaches as shown in  FIGS. 4-6 . A rubber grommet  80 , as shown in  FIG. 4 , may be fixed to the end of the tape that has fingers  82  that fit into grooves  84  in the outlet  64  of the cartridge  40 . Alternatively, as shown in  FIG. 6 , a grommet  86  that is bonded to the tape  36  may be attached by grooves  88  that fit over flanges  90  that protrude from both sides of the outlet. When the tape is extracted from the cartridge, the grommet  86  moves with the tape and pulls away from the outlet  64  that it had previously sealed. Another alternative construction, as shown in  FIG. 5 , has a sealing material such as a wax or an elastomer such as rubber that forms a seal  92  which likewise pulls away with the tape  36  upon airbag deployment. 
     An alternative embodiment tape cartridge  94  is shown in  FIG. 3  in which the tape cartridge stores tape  36  wound into a roll  96  that is positioned about but not attached to a spindle  98  positioned in a tape storage compartment  100 . The tape cartridge  94  has the advantage that the tape approaches the storage compartment outlet  102  from a more consistent angle. In prior art devices a brake was applied to a spool on which the tape was wound to overcome the momentum of the spinning spool as tape was withdrawn. The tape cartridge  94  employs a brake  104  only on the tape itself, because testing has shown it is not necessary to brake the roll  96 . The brake  104  is sufficient to prevent the tape from continuing to leave the cartridge and passing between the sensor  106  and the cartridge outlet  108  when the airbag  22  is no longer pulling on the tape  36 . A spool (not shown) could be used with the tape roll  96  and the tape end  110  can be attached to the spool, or to the spindle  98 . 
     The cover  112  of the tape cartridge  94  may be attached by interfitting posts  114  on the bottom portion  116  that fit into holes (not shown) in the cover  112 , and posts (not shown) on the cover that fit within holes  118  on the bottom portion  116  of the cartridge  94 . A groove  120  surrounds the periphery of the bottom portion  116  and is filled with a gasket, or a dispensed elastomer or adhesive to form the seal with the cover  112 . 
     An alternative design brake  122  within the tape cartridge is shown in the  FIG. 9. A  first leaf spring  124  is mounted to a first post  126  and positioned by a flange  128 . The first leaf spring  124  is biased towards a second leaf spring  130  that is mounted to a second post  132  and positioned by a second flange  134 . 
     Yet another design of a brake  136  within the cartridge  138 , as shown in  FIG. 10 , is to co-form a plastic spring member  140  that is mounted by living hinges  142  to the cartridge  138 . The spring member  140  is molded in a first position  144  and pushed over center to a second position  146  shown in  FIG. 10 , where it is biased against a braking surface  148 . In order to allow free movement of the plastic spring member  140 , the spring may need to be cut free of the cartridge lower portion  150  or could be molded with a hole beneath the spring that is then sealed by a plug (not shown). A side action mold, while increasing the complexity of the mold, could be used to allow the spring to move freely with respect to the cartridge lower portion  150 . 
     Referring to  FIGS. 1 and 2 , the tape  36  functions as a scan medium that is scanned past a sensor, and can be constructed of woven cloth such as cotton, flax, fiberglass, nylon, and similar materials. The tape  36  can also be of polymer-based film, or a fibrous mat or thin metal. Where light is used in either transmission or reflection to detect the encoding, the tape may be encoded by a variety of techniques. For example, a cloth tape can be dyed, painted or woven with a high contrast pattern. Films may be metallized and subsequently etched to produce a contrast pattern. Physical holes may also be used particularly in a polymer film or metal tape. 
     The scan medium, or tape  36 , can be encoded with a magnetic pattern, by using a magnetizable metal coating on a film, or a magnetizable magnetic strip, or magnetizable fibers within a fibrous tape, or by using a magnetizable ink or the like. The magnetizable material can be selectively positioned or selectively magnetizable to create a detectable pattern when the tape is moved past a magnetic sensor such as a Hall affect sensor or GMR sensor. A conductive film, conductive particles, or threads can also be detected with an inductive sensor. 
     It should be understood that the scan medium may consist of woven tape, a string or a cord. The width, thickness, length and material from which the scan medium is made, may be varied. Other approaches include a wire, a plastic film, a metal tape, or other elongated member that can be packaged within the cartridge and can be encoded so as to produce a signal when moved past a sensor that is proportional to the length or velocity of the scan medium. 
     The encoded tape may be designed with uniformly spaced markings that are read optically or magnetically. The spacing may also be nonuniform; for example the first portion of the tape may not have any markings so as to pass or reflect light to a sensor. In this way the presence of the tape and the functioning of light and the light sensor can be tested. In addition, the pattern may be varied, for instance with a logarithmic arrangement, or a change in the spacing of the marks to provide varying resolution during different portions of the airbag deployment. For simplicity in signal processing, the objective may be to generate an alternating signal that can be processed and amplified and filtered in a way which may have benefits in terms of overcoming sources of noise, simplicity of processing, and reliability of algorithms. 
     Given an expected acceleration profile the markings on the tape could be arranged to produce a single frequency throughout deployment until the cushion forward motion stops. Such an arrangement may simplify the electronics used to detect and monitor airbag deployment. 
     The information from the sensors that detect the markings on the tape is sent to an electronic control unit that can be used to control vents  152  that may be squib activated, or otherwise activated to let gases out of the airbag module housing  24  to slow or stop inflation. Opening a vent almost instantaneously reduces the pressure in the airbag  22 . 
     It should be understood that where the sensor affecting attributes are described as not being evenly distributed along the elongated scan medium, reference is not being made to the manner in which information is encoded (such as by dark lines, holes, magnetic field reversals etc.) but rather to the fact that the encoding such as the dark lines, holes, magnetic field reversals, is not evenly distributed. In other words, if the tape were withdrawn at a constant rate, the frequency or other aspect of the signal produced by the tape would not remain constant. 
     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.