Abstract:
An assembly of efficient construction and operation to hold restraining air bag tethers to a shortened operative length under a first set of conditions and to extend such tethers under a second set of conditions. The extension of the restraining tethers is carried out in conjunction with the delivery of an increased volume of inflating gas to the air bag cushion. The air bag assembly may be operated using as few as two activatable initiators to activate inflation stages while simultaneously controlling tether length to effect delivery of a proper volume of inflation gas for a desired cushion profile.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority from Provisional Application No. 60/408,323 having a filing date of Sep. 5, 2002 the contents of which are incorporated herein by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     This invention relates generally to an air bag assembly, and more particularly to an air bag assembly capable of variable expansion by selective retention or release of restraining tether elements operatively connected to an inflatable cushion in combination with controlled conveyance of inflation gas to the inflatable cushion. 
     BACKGROUND OF THE INVENTION 
     It is well known to provide an air bag assembly including an inflatable air bag cushion for protecting the occupants of a transportation vehicle. In an automotive vehicle such air bag assemblies are typically located within the hub of the steering wheel and in a recess in the instrument panel for protection of the vehicle occupants seated in opposing relation to such assemblies. Additional air bag assemblies may be located within the seats and/or door panels for protection of the occupants during a side-impact event. 
     Air bag assemblies typically include an inflatable cushion in fluid communication with a gas emitting inflator. Upon sensing certain predetermined vehicle conditions, such as a certain level of vehicle deceleration, the inflator discharges a fixed amount of inflator gas thereby forcing the air bag into a deployed position. The inflator gas occupies the available volume within the air bag cushion thereby forcing the air bag cushion to expand outwardly to the extent permitted by its construction. As the occupant comes into contact with the expanded air bag, the inflator gas is forced out of the air bag thereby dissipating the kinetic energy of the occupant. 
     Absent restraint, an inflated body tends to assume a generally spherical profile. In order to provide control over the inflated shape of the air bag cushion, it is known to utilize tethering elements in the form of straps or webs extending between surfaces of the air bag cushion to thereby hold the surfaces in fixed orientation relative to one another upon inflation. The selection and length of such tethering elements can thus be used to establish a desired inflated profile. However, once the tethering elements are attached in fixed relation to the surface of the air bag cushion, the inflated geometry of the cushion is likewise fixed and is not subject to adjustment. 
     It has been recognized that the preferred inflated profile of the air bag cushion may vary depending upon the severity of the activating impact event and/or upon the size and position of the occupant to be protected. Thus, the ability to effectively control the inflation characteristics of the air bag cushion is potentially desirable. In order to provide a degree of control over the inflated profile of the air bag cushion it is known to use an inflator that has varied levels or stages of inflator gas output in response to the sensing of different vehicle occupant conditions. Thus, it is generally known in the prior art to utilize so-called “dual-stage” inflators that discharge predetermined amounts of gas at one or two levels. However, the use of such “dual-stage” inflators provides control over only the amount of inflator gas which is discharged and does not provide control over the expanded geometry of the inflated air bag cushion. That is, due to the compressible nature of the inflation gas, so long as the air bag has a fixed volumetric capacity, the inflator gas will tend to fill that capacity and the expanded configuration of the air bag will be generally the same although the pressure may vary. 
     In order to provide an additional level of control over the air bag performance it has been suggested to utilize air bag cushions which incorporate sewn or woven in seams within the air bag to control the expanded geometry of the inflated air bag. Such seams separate upon the introduction of pressures exceeding a certain level thereby freeing the air bag cushion from the restraint imposed by the seams at lower pressures. In order for such break-away seams to provide controlled expansion, the introduction of such seams must be carried out with substantial precision such that seam separation will occur in a highly reproducible and predictable manner. In some instances, such requisite precision and reproducibility may be difficult to achieve. Moreover, even when such break-away seams are utilized, the expansion which occurs may be in all directions. In some applications it is believed that preferential expansion in the depth of the air bag (i.e. towards the occupant to be protected) may be desirable. 
     In order to address the desire to provide enhanced control over the final inflated profile of the air bag, it has been proposed to utilize release mechanisms to hold tether straps in place under normal conditions and to release the straps in situations where an extended profile is desired. By way of example only, and not limitation, various release mechanisms are illustrated and described in U.S. Pat. No. 6,390,501 to Greib et al., U.S. Pat. No. 6,422,597 to Pinsenschaum et al. and U.S. Pat. No. 6,454,300 to Dunkle et al., the contents of all of which are incorporated by reference as if fully set forth herein. 
     SUMMARY OF THE INVENTION 
     This invention provides advantages and alternatives over the prior art by providing a release mechanism of efficient construction and operation to hold restraining air bag tethers in place under a first set of predetermined conditions and to extend such tethers under a second set of predetermined conditions. The extension of the restraining tethers is carried out in conjunction with the delivery of an increased volume of inflating gas to the air bag cushion. The air bag assembly may be operated using as few as two activatable initiators to activate inflation stages within a dual stage inflator while simultaneously controlling tether length to effect delivery of a proper volume of inflation gas for a desired cushion profile. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will now be described by way of example only, with reference to the accompanying drawings which constitute a part of the specification herein and in which: 
         FIG. 1  is a cut-away view of a vehicle interior showing an air bag cushion in a stored undeployed state in opposing relation to a vehicle occupant; 
         FIG. 2A  is a view similar to  FIG. 1  illustrating an air bag cushion in a deployed state restrained by an internal tether arrangement; 
         FIG. 2B  is a view similar to  FIG. 2A  wherein the tether arrangement is released to a second restrained state to permit enhanced expansion of the air bag cushion towards a vehicle occupant; 
         FIG. 3  is a cut-away schematic side view of a dual stage inflator having two initiators and a selectively releasable tether restraint with a tether illustrated in a restrained operatively shortened condition; 
         FIG. 4  is an end view of the inflator illustrated in  FIG. 3  taken generally along line  4 — 4  in  FIG. 3 ; 
         FIG. 5  is a view similar to  FIG. 3 , with a first stage initiator in an activated condition so as to inflate an air bag cushion to a condition as illustrated in  FIG. 2A ; 
         FIG. 6  is a view similar to  FIG. 3 , with a first stage initiator and a second stage initiator in an activated condition so as to release a restraining tether to a lengthened operative condition and inflate an air bag cushion to a condition as illustrated in  FIG. 2B ; 
         FIG. 7  is a view similar to  FIG. 5 , including a puncture device in fluid communication with the second stage initiator; 
         FIG. 8  is a view similar to  FIG. 7 , with the first stage initiator and second stage initiator activated and the puncture device pushed forward to open a conveyance path for gas from the second stage initiator; 
         FIG. 9  is a view similar to  FIG. 7 , including an alternative arrangement for a puncture device in fluid communication with the second stage initiator; and 
         FIG. 10  is a view similar to  FIG. 9 , with the first stage initiator and second stage initiator activated and the puncture device pushed forward to open a conveyance path for gas from the second stage initiator; 
     
    
    
     While the invention has been illustrated and will hereinafter be described in connection with certain potentially preferred embodiments, procedures and practices, it is to be understood that in no event is the invention to be limited to such illustrated and described embodiments, procedures and practices. On the contrary, it is intended that the present invention shall extend to all alternatives and modifications as may embrace the principles of this invention within the true spirit and scope thereof. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made to the drawings, wherein to the extent possible, like reference numerals are utilized to designate like components throughout the various views. In  FIG. 1  a vehicle  10  is shown including a seating structure  12  which supports an occupant  14  in generally opposing relation to an instrument panel  16 . An air bag assembly  18  including an air bag cushion  20  is housed within the instrument panel  16  for outward deployment towards the occupant  14  in the event of a collision. 
     While the air bag assembly  18  and corresponding air bag cushion  20  are illustrated for descriptive purposes in relation to a vehicle passenger, it is to be understood that the present invention is in no way to be limited to a passenger side configuration. On the contrary, it is contemplated that the present invention may have applicability to air bag deployment in opposing relation to the operator (not shown) of the vehicle  10  as well as in relation to air bags deployed from other regions within the vehicle interior. 
     It is contemplated that the vehicle  10  may include a seat position sensor  22  to detect the position of the occupant  14  relative to the air bag assembly  18 . It is further contemplated that the vehicle  10  may include additional position sensors such as an optical scanner  24  or the like to measure both the volume and position of the occupant to be protected. The vehicle  10  may also be provided with a scale  26  within the seating structure  12  so as to provide additional data regarding the load to which the inflatable air bag cushion  20  may be subjected upon impact by the occupant  14 . It is additionally contemplated that the seating structure  12  may be provided with sensing elements to measure the degree to which the seating structure is reclined. The vehicle  10  may also be provided with sensors to determine and communicate whether or not the occupant is utilizing the recommended seat belt structures  28 . The data so collected may be combined at an on-board computer  19  which in turn, sends an activation signal to one or more initiators upon the occurrence of a collision event to release controlled volumes of inflation gas so as to effect the desirable expanded profile characteristics for the air bag cushion  20  in a given situation. 
     It is contemplated that the air bag cushion  20  has a first restrained expanded profile which is obtained upon extension of internal tethering elements  30  held in a shortened operative length condition and at least a second restrained expanded profile which is characterized by greater depth than the first profile. As best illustrated through simultaneous reference to  FIGS. 2A and 2B , it is contemplated that one or more tethering elements  30  in the form of straps extending from locations at an interior or exterior surface of the air bag cushion  20  are utilized to control the inflated profile of the air bag cushion  20 . The tethering elements  30  are normally held to a shortened operative length between connection points  29  at the interior of the cushion and a releasable restraint assembly  36  in the vicinity of a gas generating inflator  40 . In this regard it is to be understood that the connection points  29  may be either fixed connection points or sliding connection points such as supporting sleeves or the like through which the tethering elements  30  are threaded. The releasable attachment at the restraint assembly  36  may be effected by use of an integral or supplemental sliding loop structure  25  such as a short length of cord or the like although it is contemplated that any number of other arrangements may likewise be utilized. 
     As shown in  FIG. 2A  under normal operating conditions, the tethering elements  30  restrain the profile of the expanding air bag cushion  20  to a first diminished depth. By way of example only, and not limitation, it is contemplated that such a restrained profile may be of particular use in the protection of smaller stature occupants and/or occupants seated in close proximity to the instrument panel  16 . As shown in  FIG. 2B , in instances where a deeper profile is desired, the tethering elements  30  may be released from the restraint assembly  36  thereby yielding a permissible expanded geometry of expanded depth. 
     It is contemplated that some degree of restraint may nonetheless be maintained by a length extending tether extension  23  such as a strap or the like operatively connected between the tethering elements and a secondary attachment location  27  which may be either on the surface of the air bag cushion or at an external location. The tethering elements  30  may be arranged within the air bag cushion  20  such that they are affixed at opposing ends to the surface of the cushion and are brought to a shortened operative condition by pulling an intermediate portion of the tethering elements through surface loops and towards the restraint assembly  36 . Regardless of the tethering arrangement, it is contemplated that an expanded depth may be useful in the protection of larger stature occupants and/or in the protection of occupants seated a substantial distance away from the instrument panel  16 . 
     As will be appreciated, upon the release of the tethering elements  30  from the restraint assembly  36 , the volume of the air bag is increased. According to a potentially preferred practice, the air bag assembly  18  incorporates a selectively activatable variable inflation device which causes a controlled volume of inflation gas to be delivered to the air bag cushion depending upon the desired inflation characteristics. That is, the variable inflation device will deliver a greater volume of inflation gas to the air bag cushion  20  in instances where a deep profile such as is illustrated in  FIG. 2B  is desired. Conversely, in instances where a more shallow inflated profile is desired such as illustrated in  FIG. 2A , a smaller volume of inflation gas is released into the air bag cushion  20 . 
     According to a first exemplary practice, the variable inflation device incorporates a displaceable plug element  42  which is operatively connected to a tether displacement or carrier element  44  which makes up part of the releasable restraint assembly. In a potentially preferred arrangement, the plug element  42  is adapted to undergo a sliding displacement in conjunction with the delivery of an enhanced volume of inflation gas from the inflator  40 . The sliding displacement of the plug element  42  is, in turn, translated to the tether displacement element  44  so as to carry the tethering elements  30  away from an anchoring structure  46  thereby permitting the tethering elements  30  to be pulled away from an initial anchored position and assume an extended operative length. The sliding displacement of the plug element also opens up a normally closed auxiliary gas transfer path to convey an enhanced volume of inflation gas into the air bag cushion. 
     In the exemplary embodiment illustrated schematically in  FIG. 3 , the inflator  40  includes a primary diffuser  50  including an arrangement of gas transmission openings  52  arranged so as to convey released inflation gas into an air bag cushion. In the illustrated arrangement, a stud  54  projecting away from a spacer  55  may be disposed at the surface of the primary diffuser  50  for supporting attachment through a wall of an inflator housing  56  such as by a nut  57  or other appropriate fastening device. Of course, virtually any other support arrangement as may be desired may likewise be utilized if desired. 
     As best illustrated through simultaneous reference to  FIGS. 3 and 4 , the anchoring structure  46  may be made up of one or more support pins  58  which extend away from the outer face of the primary diffuser and in sliding relation through aligned openings in the tether displacement element  44 . In the illustrated construction, the support pins  58  support the tethering elements  30  within the gap between walls of the slotted carrier element  44 . Thus, in the position illustrated in  FIG. 3 , the tethering element  30  is restrained on either side by the walls of the carrier element  44  and thus cannot move away from the support pins  58 . In the illustrated configuration, a screw  60  or other attachment device extends through the carrier element  44  and into the plug element  42  so as to establish an operative connection between the carrier element  44  and the plug element  42 . Of course, other means for effecting operative connection between the tether carrier element  44  and the plug element  42  such as welding, fusion bonding and adhesive connection may also be used if desired. 
     As illustrated, the plug element  42  is housed within a secondary diffuser  62  including an arrangement of gas transmission openings  63 . As illustrated, in this arrangement the outer diameter of the plug element  42  is such that it slides within the secondary diffuser upon the application of a sufficient force in the direction of the carrier element  44 . While the actual configuration of the plug element  42  is not critical, it is contemplated that the plug element  42  may include a relatively large diameter gas impingement portion  64  having an outer diameter which substantially fills the inner diameter of the secondary diffuser  62 . The gas impingement portion  64  of the plug element  42  thus defines a reaction surface for contacting a pressurized stream of inflation gas to cause movement of the plug element along the secondary diffuser  62  in a manner to be described further hereinafter. The plug element  42  may also have a reduced diameter portion  65  projecting in the direction of movement of the plug element. 
     If desired, it is contemplated that shear elements  66  may be disposed between the plug element  42  and the secondary diffuser  63  to prevent undesired movement of the plug element  42  prior to the introduction of an activating driving force. Of course, such shear elements may be of any arrangement as may be desired. It is likewise contemplated that shear elements may be disposed at the carrier element  44  rather than within the secondary diffuser  62 . 
     The operation of the device may be readily understood by reference to  FIGS. 5 and 6 . Referring first to  FIG. 5 , in the event that a reduced profile cushion deployment such as is illustrated in  FIG. 2A  is desired, an activating signal is sent by the on board computer  19  to a first initiator  69  such as a pyrotechnic squib or the like through leads  70 . The initiator  69  activates a primary gas generator  72  thereby causing a volume of inflation gas to be emitted from the primary gas generator  72 . Of course, it is to be understood that the primary gas generator  72  may be of any suitable type as will be known to those of skill in the art. By way of example only, suitable gas generators may include chemical reactive inflators, stored gas inflators and hybrid inflators utilizing combinations of both chemical reaction and stored gas. 
     Upon emission of inflation gas from the primary gas generator  72 , a pressure will be developed within the body of the inflator  40  thereby causing the opening of a normally sealed first gas path opening  79  which is isolated from the impingement portion  64  of the plug element  42 . Inflation gas thus passes through the first gas path opening  79  into the primary diffuser  50  and through the gas transmission openings  52  to an air bag cushion. Under the conditions illustrated in  FIG. 5 , a second initiator  81  remains inactive and the plug element  42  and carrier element  44  remain unmoved such that the tether element  30  remains secured at the support pins  58 . 
     In the arrangement illustrated in  FIG. 5  the selective expulsion of inflation gas into the primary diffuser  50  without movement of the plug element  42  is effected by the use of a first burst disk  77  disposed in covering relation to the first gas path opening  79 . A second burst disk  78  is disposed in covering relation to a second gas path opening  80  which is in fluid communication with the gas impingement portion  64  of the plug element  42 . As shown in  FIG. 5 , the first burst disk  77  is adapted to open upon exposure to pressure at a level developed within the inflator by activation of the primary gas generator. However, at this pressure the second burst disk remains intact thereby maintaining the isolation of the secondary discharge flow channel and thus avoiding pressurized displacement of the plug element  42 . 
     As shown in  FIG. 6 , when an extended depth cushion profile such as illustrated in  FIG. 2B  is desired, activating signals are communicated through leads  70 ,  71  to the first initiator  69  and to the second initiator  81  such as a pyrotechnic squib or the like. Under these conditions, the primary gas generator  72  and the secondary gas generator  75  are both activated so as to generate an enhanced volume of inflation gas. Due to this enhanced volume of inflation gas, an adequate pressure is developed to fracture the first burst disk  77  as well as the second burst disk  78 . If desired, it is contemplated that the enhanced volume of inflation gas may be produced simply providing additional heat to the volume of gas expelled by a single gas generator. In such an arrangement the second gas generator may be eliminated if desired 
     As inflation gas passes under pressure through the second gas path opening  80 , the inflation gas contacts the gas impingement portion  64  of the plug element  42  with sufficient force to overcome the shear elements  66  and thereby push the plug element  42  along the length of the secondary diffuser  62 . As the plug element  42  is displaced, gas transmission openings  63  are opened thereby directing the driving gas outwardly and into the air bag cushion. As shown, the displacement of the plug element  42  is translated to the operatively connected carrier element  44  thereby causing the carrier element  44  to push the loop structure  25  off of the support pins  58 . Once the loop structure is clear of the support pins  58 , the tether element  30  may be pulled away from the releasable restraint assembly  36  by tension introduced by the inflating air bag cushion. As will be appreciated, this device can thus simultaneously adjust gas flow and tether length. Moreover, such adjustment may be carried out using only two initiators  69 ,  81 . 
     Of course, it is to be understood that the present invention may be the subject of a wide range of alternatives. By way of example only, and not limitation, one alternative construction is illustrated in  FIGS. 7 and 8  wherein elements corresponding to those previously described are designated by like reference numerals with a prime. As will be appreciated, the variable inflation device illustrated in  FIGS. 7 and 8  operates in a substantially identical manner to the arrangement illustrated in  FIGS. 5 and 6  with the exception that the second burst disk  78 ′ is opened by a puncture element  85 ′ which is pushed into contact with the second burst disk  78 ′ upon activation of the secondary gas generator  75 ′. 
     As illustrated, the puncture element  85 ′ is normally held out of contact with the second burst disk  78 ′ such as by a support member  86 ′ spaced away from the second burst disk  78 ′. However, the puncture element is nonetheless disposed in fluid communication with the secondary gas generator  75 ′ such as by a gas conduit  87 ′. Upon activation of the secondary gas generator  75 ′, the puncture element  85 ′ is driven forward so as to puncture the second burst disk and open up the second gas path opening  80 ′ (FIG.  8 ). Of course, various arrangements may be utilized to pass inflation gas from the secondary gas generator around and/or through the puncture element  85 ′ after the puncture has taken place. By way of example only, it is contemplated that the puncture element  85 ′ may include an arrangement of grooves  88 ′ around its outer surface thereby allowing gas to pass around the puncture element. It is also contemplated that the puncture element  85 ′ may include an arrangement of internal gas openings  89 ′ through the interior. As will be appreciated, such external grooves and/or internal openings may be sized so as to allow passage of gas following puncture while nonetheless providing sufficient resistance to initiate displacement of the puncture element  85 ′. The support member  86 ′ also preferably includes an arrangement of gas passages. 
     Still another configuration is illustrated in  FIGS. 9 and 10  in which elements corresponding to those previously described are designated by like reference numerals with a double prime. As will be appreciated, the configuration in  FIGS. 9 and 10  is substantially the same as the construction illustrated in  FIGS. 7 and 8  with the exception that second gas path opening  80 ″ and covering burst disk  78 ″ are extended towards the secondary gas generator  75 ″ by an extension conduit  91 ″. Such a construction may simplify construction and provide improved activation speed due to the shortened distance between the secondary gas generator  75 ″ and the puncture element  85 ″. 
     It is to be understood that while the present invention has been illustrated and described in relation to potentially preferred embodiments, constructions and procedures, that such embodiments, constructions and procedures are illustrative only and the present invention is in no event to be limited thereto. Rather it is contemplated that modifications and variations embodying the principles of the present invention will no doubt occur to those skilled in the art. It is therefore contemplated and intended that the present invention shall extend to all such modifications and variations as may incorporate the broad aspects of the present invention within the full spirit and scope thereof.