Abstract:
An automotive air bag assembly including a tethering element providing shape definition across the air bag. The tethering element may be seamed to itself or to other tethering elements by an attachment seam to reduce the effective operative length of the tethering element and to move the axis of rotation for the air bag rearward. The attachment seam is adapted to separate upon development of adequate pressures within the air bag.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from Provisional Application No. 60/293,022 having a filing date of May 23, 2001 the contents of which are incorporated by reference herein in their entirety. 
    
    
     TECHNICAL FIELD 
     This invention relates to an air bag assembly, and more particularly to an inflatable air bag cushion including tethering restraints of variable operative length. The tethering restraints are normally held in a shortened operative condition by break-away seams which are released upon tension exceeding a certain level such that the tethering elements are extended to an increased operative length as inflation of the air bag cushion proceeds. 
     BACKGROUND OF THE INVENTION 
     It is well known to provide an air bag assembly including an inflatable air bag cushion for protecting the occupant 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 vehicle 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. It is also known to utilize inflatable curtain-like structures for deployment from the structural pillars or roofline of the motor vehicle so as to promote restraint and protection of the vehicle occupant during a roll-over event. 
     Air bag assemblies typically include an inflatable cushion in fluid communication with a gas emitting inflator. Upon sensing 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 inflation gas enters the air bag cushion the pressure within the cushion is increased. As the occupant comes into contact with the expanded air bag cushion, the inflator gas is forced out of the cushion thereby dissipating the kinetic energy of the occupant achieving a so-called “ride down” effect. 
     Traditional air bag cushions tend to project outwardly away from their storage positions in a substantially straight line during the initial stages of inflation. In a so called “top mount” or “mid mount” design, this directional projection may cause the cushion to first travel in a generally upward direction away from the air bag exit opening and against the windshield. After this initial outward projection during the latter stages of inflation such cushions assume their final inflated design profile causing them to rotate downwardly in covering relation to portions of the instrument panel below the air bag exit opening. 
     In order to provide additional control over the inflation characteristics of the air bag cushion it has been suggested to utilize tethering elements in the form of straps or webs extending between surfaces of the air bag cushion. These straps or webs may be released from a first restrained operative length to a second extended operative length as the depth of the air bag cushion is increased. A system incorporating such extensible tethering straps is illustrated and described in U.S. Pat. No. 5,489,119 to Prescaro et al. the contents of which are incorporated by reference as is fully set forth herein. 
     SUMMARY OF THE INVENTION 
     The present invention provides advantages and alternatives over the prior art by providing an air bag assembly incorporating adjustable tethering elements which are releasable from a first restrained condition to a second condition of extended operative length and which further facilitate the movement of the cushion in a downward direction during the early stages of inflation. 
     According to one aspect of the present invention, an air bag assembly is provided including at least two elongate tethering elements which are adjoined to one another by a break-away seam such that the tethering elements at least partially disengage from attachment to one another as pressure increases within the air bag cushion causing tension to increase across the break-away seam during the latter states of inflation. The attachment of the tethers to one another provides an enhanced degree of control over the deployment characteristics of the cushion during the early stages of inflation. 
     According to another aspect of the present invention an air bag assembly is provided including at least one tether in the form of a panel and at least one gas transmission opening across the interior of that panel. The panel is folded upon itself and seamed so as to close off the opening. Upon the application of tension within the panel exceeding a certain level, the seam holding the panel in folded condition undergoes at least partial disengagement such that the panel is extended to an increased operative length and the opening across the panel is at least partially exposed to facilitate the transmission of inflation gas into a lower portion of the cushion. 
    
    
     
       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. 2  is a cut-away side view of an air bag cushion incorporating two elongate tethers adjoined to one another by a break-away seam assembly; 
         FIG. 3  is a view taken generally along line  3 — 3  in  FIG. 2  illustrating a “V” shaped break-away seam arrangement for adjoining tethers to one another; 
         FIG. 4  is a view similar to  FIG. 2  upon full inflation of the air bag cushion and disengagement of the break-away seam holding the tethers to one another. 
         FIG. 5  is a cut-away side view of an air bag cushion including a panel tether held in a shortened folded condition by a break-away seam arrangement; 
         FIG. 6  is a view similar to  FIG. 5  illustrating the air bag cushion in a fully deployed condition following rupture of the break-away seaming arrangement and extension of the panel tether showing gas passage through an opening at the interior of the panel tether. 
         FIG. 7  is a plan view of an exemplary panel tether within an air bag cushion having an opening therein and showing seam lines for introduction of a break-away seam when the tether is in a folded condition; 
         FIG. 8  is an enlarged side view of a panel tether folded and seamed to close off an opening within the panel tether; and 
         FIG. 9  is a view taken generally along line  9 — 9  in  FIG. 8  illustrating the folded seamed arrangement. 
     
    
    
     While the invention has been illustrated and will hereinafter be described in connection with certain exemplary 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 EMBODIMENT 
     Reference will now be made to the drawings, wherein to the extent possible, like reference numerals are utilized to designate like components through the various views. In  FIG. 1  it is seen that a vehicle  10  may include a seating structure  12  which supports an occupant  14  in generally opposing relation to a dash panel  16 . An inflatable air bag cushion  20  is housed within the dash panel  16  in fluid communication with a gas emitting inflator  21 . Upon the emission of an inflation gas from the inflator  21 , the air bag cushion  20  expands outwardly through an opening in the surface of the dash panel  16 . As will be appreciated, in an unrestricted state the air bag cushion  20  will tend to inflate in a path generally away from the inflator  21  and along windshield  18  during the initial states of inflation. As inflation proceeds, the air bag cushion  20  fills out to its desired geometry and undergoes a degree of rotation downwardly so as to provide coverage between the dash panel  16  and the torso of the occupant  14 . 
     In  FIG. 2  a tethering arrangement for use at the interior of the air bag cushion  20  is illustrated. The exemplary tethering arrangement illustrated in  FIG. 2  is believed to be useful in facilitating the downward rotation of the air bag cushion  20  at an early stage of inflation. In particular, the tethering arrangement illustrated is believed to move the axis of rotation for the air bag cushion  20  outwardly to a more rearward location relative to the vehicle  10  (i.e. towards the occupant  14 ) thereby causing a face portion  22  of the air bag cushion  20  to move downwardly at an early stage of inflation. As illustrated, the tethering arrangement incorporates a first shape defining tether  24  and at least a second shape defining tether  26 . The tethers  24 ,  26  may be of any suitable construction and material including straps or webs of pliable materials such as textile fabrics, polymer films, and the like. Elongate straps of woven textile material such as nylon  6  and nylon  6 ,  6  may be preferred. 
     As best illustrated in  FIG. 4 , in the absence of attachment between the tethers, the first shape defining tether  24  is normally disposed across the air bag cushion  20  in a path above the second shape defining tether  26 . Thus, while the tethers  24 ,  26  may originate from the same point or closely adjacent points near the mouth portion  30  they extend to substantially divergent attachment points at different elevations near the face portion  22 . 
     As illustrated, the tethers are connected to one another at a position rearward of a gas accepting mouth portion  30  which is held in position within the dash panel  16 . This attachment position moves the axis of rotation for the air bag cushion  20  rearward away from the mouth portion  30 . The attachment between the tethers  24 ,  26  is maintained by a break-away seam structure which separates as pressure is increased within the air bag cushion  20  resulting in increased tensioning forces being applied to the tethers  24 ,  26  as inflation proceeds. It is contemplated that the break-away seam structure holding the tethers  24 ,  26  together may be of various constructions including frangible sewn seams, adhesive seams, patterned welded seams, seams formed by the engagement of mateable fabrics such as VELCRO and the like. Thus, it is to be understood that by the term “break-away attachment seam” is meant any attachment which may initially hold the tethers  24 ,  26  to one another but which separates upon the achievement of adequate tensioning forces. Tear-away sewn seams may be particularly preferred. 
     In  FIG. 3  an exemplary seam structure in the form of a tear-away sewn seam  32  is illustrated. At shown, in this arrangement the tethers  24 ,  26  are formed into a multi-layer pleat structure  34 . The pleat structure  34  has a closed end  36  with the tear-away sewn seam  32  projecting away from the closed end  36  towards the location of divergence  38  at which the tethers  24 ,  26  enter and leave the pleat structure. That is, the apex of the “V” shaped sewn seam  32  points away from the closed end  36  of the pleat structure  34  and towards the position where the tethers  24 ,  26  enter and leave the pleat structure  34 . 
     During operation, as inflation gas is expelled from the inflator  20  and into the air bag cushion  20  through the mouth portion  30 , inflation will proceed with expansion being initially limited by the tethers  24 ,  26  in the manner as illustrated in  FIG. 2 . As pressure builds, the system attempts to relieve stress by first rotating downwardly around a pivot point established by the pleat structure  34 . As tension is increased still further during the latter stages of inflation, the tethers  24 ,  26  separate from one another within the pleat structure  34  with such separation commencing at the apex of the sewn seam  32 . The separation then progresses towards the closed end of the pleat structure  34  until being completed. Full expansion is thereafter completed as illustrated in  FIG. 4  with the tethers  24 ,  26  being maintained in tension across the interior of the air bag cushion  20 . That is, the extended operative length of the tethers  24 ,  26  is preferably such that they provide a restraining force across the air bag cushion even after being extended. 
     As will be appreciated, while an arrangement of only two tethers  24 ,  26  has been illustrated for exemplary and explanatory purposes, it is likewise contemplated that any number of additional tethers or sets of tethers normally disposed along various paths at different elevations within the air bag cushion may be utilized if desired. As will be further appreciated, while the tethers  24 ,  26  have been illustrated as being formed into a multi-layer pleat structure so as to reduce the operative length prior to seam separation, it is also contemplated that the tethers  24 ,  26  may be attached to one another without being folded into a pleat structure. In such an arrangement an operative shortening will still be effected by pulling one or both tethers away from a straight line orientation in order to achieve the attachment. 
     An alternative exemplary embodiment of an air bag cushion incorporating a break-away seam structure within a tethering element is illustrated in  FIGS. 5–9 . In these figures, like components to those previously illustrated and described are designated by like reference numerals increased by 100. As best illustrated through simultaneous reference to  FIGS. 5–7 , the assembly includes a panel tether  140  extending between surface portions of the air bag cushion  120  so as to substantially restrain the face portion  122  during the early stages of inflation. The panel tether which may be formed of any suitable material including polymeric films, textile fabrics, and the like extends partially across the width of the air bag cushion  120  at an elevation below the mouth portion  130  ( FIG. 7 ) so as to permit the restricted passage of inflation gas from an upper chamber  144  into a lower chamber  146  around the lateral sides of the panel tether  140  during the early stages of inflation. The panel tether  140  also includes at least one interior gas transmission opening  150  which is closed off during the initial stages of inflation ( FIG. 5 ) and which is open during the latter stages of inflation ( FIG. 6 ) so as to increase the flow-through area between the upper chamber  144  and the lower chamber  146  during such latter stages. 
     As best illustrated by simultaneous reference to  FIGS. 5 ,  7  and  8 , in practice, the panel tether  140  is folded upon itself so as to form a multi-layer gas blocking pleat structure  134  closing off the interior gas transmission opening  150 . In addition, the pleating reduces the operative length of the panel tether  140  so as to restrain the outward projection of the face portion  122 . Thus, during the early stages of inflation when the panel tether  140  is held in the restrained condition blocking the interior gas transmission opening  150 , the flow of inflation gas from the upper chamber  144  into the lower chamber  146  is reduced. 
     The gas blocking pleat structure  134  is maintained by a break-away attachment seam which separates upon the introduction of an adequate tensioning force across the panel tether  140 . By way of example only, and not limitation, one contemplated seaming arrangement is illustrated in  FIGS. 7 and 9 . As illustrated, in this arrangement a tear-away sewn seam  132  is introduced through the pleat structure  134  in a substantially “V” shaped pattern having an apex projecting towards the interior gas transmission opening  150 . Upon the application of a tensioning force across the panel tether  140 , the seam  132  is caused to gradually separate beginning at the apex of the tear-away sewn seam thereby extending the operative length of the panel tether  140  and opening the interior gas transmission opening  150  to a configuration as illustrated in  FIGS. 6 and 7 . 
     While the panel tether  140  has been illustrated as incorporating a single gas transmission opening  150 , it is, of course, anticipated that the panel tether  140  may incorporate a plurality of such openings if desired. Likewise, it is to be understood that a number of such panel tethers which are maintained either independently or which are seamed together may likewise be utilized if desired. 
     The introduction of break-away attachment seam structures at locations substantially rearward of the mouth opening  130  in the air bag cushion  120  provides a mechanism for the controlled manipulation of cushion kinematics during deployment. In particular, such break-away seam structures permit the early and controlled rotation of the air bag cushion into a downward position and away from the windshield so as to provide early stage coverage across lower portions of the instrument panel. 
     It is contemplated that the concepts of the present invention are adaptable to virtually any tethering arrangement including the use of tethers which are secured in place within an inflator housing as well as those which are secured to portions of the air bag cushion itself. Accordingly, it is to be understood that while the invention has been illustrated and described in relation to certain exemplary embodiments, constructions, and procedures, that such embodiments, constructions, and procedures are illustrative only and that the present invention is in no event to be limited thereto. In particular, it is to be understood that the present invention is in no way limited to any particular arrangement of tethering elements within the cushion and that all illustrations and/or descriptions of such arrangements are explanatory and exemplary only. It is therefore contemplated and intended that the present invention shall extend to all such configurations as may incorporate the broad principles of the present invention within the full spirit and scope thereof.