Abstract:
A tensioning system which provides continuous tensioning to an inflatable curtain air bag during deployment of the curtain air bag. A dynamic tethering element is utilized which travels in conjunction with the downward deployment of the inflatable curtain air bag so as to both tension the curtain air bag while at the same time providing a guiding action so as to bring the curtain air bag into the proper position at which it is thereafter maintained.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims priority from U.S. Provisional application 60/252,844 filed Nov. 22, 2000, the contents of which are incorporated by reference herein. 
     
    
     
       TECHNICAL FIELD  
         [0002]    The present invention relates to an assembly for tensioning an inflatable curtain-type restraint across a side portion of a vehicle during a collision event.  
         BACKGROUND OF THE INVENTION  
         [0003]    It is well known in motor vehicles to provide air bag cushions for protecting a vehicle occupant during a collision event wherein such air bag cushions are in fluid communication with gas generating inflators so as to inflate the cushions upon sensing predetermined vehicle conditions such as deceleration exceeding a certain level. It is further known to provide air bag systems including inflatable restraint cushions which are deployed from positions of attachment along the roof rail portion of the vehicle frame above the doors of the vehicle such that the inflatable cushion extends downwardly in substantially curtain-like fashion between the occupant to be protected and the side portions of the vehicle adjacent to such occupants. Such coverage provides a cushioning restraint to the occupant during a side impact or extended roll-over collision event thereby aiding in the protection of the occupant during such events.  
           [0004]    It is generally desirable for a curtain-like side air bag cushion to be held in a substantially tensioned condition across the surface being covered so as to provide a well defined extended barrier between the occupant and the side portion of the vehicle. Such a condition may be useful in holding the vehicle occupant within the protective frame of the vehicle during an extended roll-over event.  
           [0005]    A typical prior tethering arrangement for maintaining tension across the lower edge of a curtain-like cushion is illustrated in FIGS. 1A and 1B. As illustrated, in such prior embodiments an inflatable curtain  10  is stored in packed relation generally along the roof rail  12  of a vehicle  14  generally above the doors  16 . The length of the inflatable curtain  10  is such that upon inflation coverage is provided over at least a portion of the distance extending along the side of the vehicle interior between two or more structural pillars  20  extending away from the roof rail  12 .  
           [0006]    In the illustrated embodiment, the inflatable curtain  10  is shown to be attached at the forward “A” pillar and at the rearward “C” pillar so as to cover the intermediate “B” pillar. As shown, in prior constructions the inflatable curtain  10  is inflated by a gas generating inflator  22  thereby causing the lower edge of the inflatable curtain  10  to move downwardly away from the roof rail  12 . As the inflatable curtain  10  undergoes inflation, it tends to shorten as cushioning depth is developed (FIG. 1B). This shortening may be restricted by the presence of tethering straps  24  of fixed length extending between the lower edge of the inflatable curtain  10  and the forward and rearward pillars  20  bordering the area to be covered.  
           [0007]    Utilizing the prior design of fixed length tethers  24  is useful in providing tension across the lower edge once the designed inflation of the inflatable curtain  10  is complete. In particular, once the curtain is in the fully inflated condition, a balanced tension is established and may thereafter be maintained between the shortened inflatable curtain  10  and the fully extended tethering straps  24 . Thus prior curtain constructions which utilize a combination of inflation induced shortening and fixed length tethering straps  24  are typically dependent upon the cushion shape being substantially fully established before the final tension is generated. Accordingly, tensioning may be absent during the preliminary stages of deployment prior to the bottom edge becoming positioned and fully tensioned.  
         SUMMARY OF THE INVENTION  
         [0008]    This invention provides advantages and alternatives over the prior art by providing a tensioning system which provides continuous tensioning to an inflatable curtain structure during inflation and which is not dependent upon the achievement of any particular deployed position to provide tensioning support to the cushion.  
           [0009]    In the invention, a dynamic tethering element is utilized which travels in conjunction with the downward deployment of the inflatable curtain structure so as to both tension the curtain structure while at the same time providing a guiding action so as to bring the curtain structure into the proper position at which it is thereafter maintained. The dynamic tethering element avoids total reliance upon curtain shortening to provides a tensioning force across the inflatable curtain structure. In addition, the dynamic tethering element may be useful in pulling the inflating curtain into a desired position at an early stage of deployment. Accordingly, a number of new and useful advantages are provided over the prior art. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    The accompanying drawings which are incorporated in and which constitute a part of this specification illustrate several potentially preferred embodiments of the present invention and, together with a general description of the invention given above and the detail description set forth below, serve to explain the principles of the invention wherein:  
         [0011]    [0011]FIGS. 1A and 1B are cut-away side views of a vehicle incorporating a prior-art tethering system;  
         [0012]    [0012]FIG. 2A is a cut-away view of a dynamic tensioning device for moving a tethering strap in conjunction with the deployment of an inflatable curtain;  
         [0013]    [0013]FIG. 2B is a cut-away view of a vehicle side interior incorporating the assembly of FIG. 2A following deployment of a tensioned air bag curtain;  
         [0014]    [0014]FIG. 3A illustrates a dynamic tensioning device for use in the controlled movement of a tensioning strap in conjunction with deployment of an associated inflatable curtain;  
         [0015]    [0015]FIG. 3B is a cut-away view of a vehicle side interior incorporating the assembly of FIG. 3A following deployment of a tensioned air bag curtain;  
         [0016]    [0016]FIG. 4A illustrates a dynamic tensioning device for use in the controlled movement of a tensioning strap in conjunction with deployment of an associated inflatable curtain;  
         [0017]    [0017]FIG. 4B is a cut-away view of a vehicle side interior incorporating the assembly of FIG. 4A following deployment of a tensioned air bag curtain;  
         [0018]    [0018]FIG. 5A is a cut-away view of a tensioning device for use in both moving the tether in conjunction with the deployment of an inflatable curtain structure and in simultaneously adjusting the length of the tether such that tension is continuously maintained;  
         [0019]    [0019]FIG. 5B is a side view of a vehicle interior illustrating an inflatable curtain deployed in conjunction with the tensioning assembly illustrated in FIG. 5A;  
         [0020]    [0020]FIG. 5C is a view taken along line  5 C- 5 C of a spring biased locking pin assembly for use in conjunction with the tensioning assembly of FIG. 5A;  
         [0021]    [0021]FIG. 6A is an exploded assembly view of a tether tensioning device utilizing a stroking piston movement;  
         [0022]    [0022]FIG. 6B is an assembled view of the tether tensioning device of FIG. 6A including an adjustable tethering strap;  
         [0023]    [0023]FIG. 7 is a plan view of a locking element for use in maintaining the tensioned condition of the tethering element following deployment of the inflatable curtain;  
         [0024]    [0024]FIG. 8 is a cut-away view of an extended side portion of a vehicle interior illustrating a first placement position for the tensioning device illustrated in FIGS. 6A and 6B wherein tensioning and cushion inflation are driven by a common gas-generating device;  
         [0025]    [0025]FIG. 9 is a view similar to FIG. 8 showing an alternative placement location for the tensioning device;  
         [0026]    [0026]FIG. 10 is a view taken generally along line  10 - 10  in FIG. 9 illustrating a gas conveyance path for use in directing inflation gas from a common inflator to an inflatable curtain and to the tensioning device;  
         [0027]    [0027]FIG. 11 is a cut-away view of a self actuating tether tensioning assembly;  
         [0028]    [0028]FIG. 12 illustrates operation of a tether tensioning assembly as illustrated in FIG. 11; and  
         [0029]    [0029]FIG. 13 illustrates a tensioning arrangement for use in tensioning the sides of an air bag curtain of split construction so as to provide accommodation for passage around a seat belt web. 
     
    
       [0030]    While the invention has been illustrated and generally described above and will hereinafter be described in connection with certain potentially preferred embodiments and procedures, it is to be understood and appreciated that in no event is the invention to be limited to such illustrated and described embodiments and procedures. On the contrary, it is intended that the present invention shall extend to all alternatives and modifications as may embrace the broad principles of this invention within the true spirit and scope thereof.  
       DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0031]    In FIGS. 2A and 2B, a first illustrative embodiment is illustrated. In FIG. 2A, there is illustrated a first tether tensioning device  125 . As shown, in this embodiment a gas generating inflator  126  is disposed in fluid communication with the neck  127  of an inflatable curtain  110  (FIG. 2B) which is normally disposed in folded condition along the roof rail  112  of the vehicle prior to deployment. As shown, it is contemplated that the inflatable curtain  110  may include noninflating regions  128  at pre-established locations across the inflatable curtain  110 . Of course, the presence of such non-inflating regions  128  is fully discretionary.  
         [0032]    As will be appreciated, upon the receipt of an activating signal through leads  129  the inflator  126  emits a pressurized volume of inflation gas through gas emitting openings arranged at a discharge end  131  of the inflator  126 . A directional cap element  132  may be held in place over the discharged end  131  so as to convey the emitted discharge gas in a desired direction. By way of example only, and not limitation, one such arrangement of inflator and directional cap element is illustrated and described in U.S. Pat. No. 5,803,486 to Spencer et al, the contents of which are incorporated by reference in their entirety as if fully set forth herein.  
         [0033]    As shown, a sliding cylinder  134  extends between the inflator  126  and the neck  127  of the inflatable curtain  110  so as to define a gas transmission conduit between the inflator  126  and the inflatable curtain  110 . As shown, the sliding cylinder  134  is carried on a bearing seal  135  so as to permit movement of the sliding cylinder  134  along the body of the inflator  126  without substantial gas leakage. Sufficient material is present within the neck portion  127  of the inflatable curtain to permit such movement. A bumper guard  136  of hard rubber or like material limits the axial movement of the sliding cylinder  134  as it moves downwardly along the inflator  126 .  
         [0034]    In the illustrated embodiment, the sliding cylinder  134  is attached to a tensioning tether element  137  which extends to the inflatable curtain  110 . It is contemplated that the tensioning tether element  137  may be attached at a lower edge of the inflatable curtain  11 O or may extend through a sleeve  138  or other carrying structure for attachment to an opposing structural pillar  120  in the manner as illustrated in FIG. 2B. It is also contemplated that any number of other attachment arrangements between the tensioning tether element  137  and the inflatable curtain  110  as may be known to those of skill in the art may likewise be utilized if desired.  
         [0035]    Regardless of the attachment arrangement which is utilized between the tensioning tether element  137  and the inflatable curtain  110 , the operation of the tether tensioning device  125  is the same. In operation, upon the discharge of inflation gas from the gas emitting openings  130 , the inflation gas is transmitted through the sliding cylinder  134  and into the neck portion  127  of the inflatable curtain  110 . Upon the introduction of the inflation gas, the inflatable curtain  110  expands downwardly and away from the roof rail  112 . During this expansion, the upper edge of the inflatable curtain  110  is held in place along the roof rail  112  at connection points  139  in the manner as will be well known to those of skill in the art.  
         [0036]    As the lower edge of the inflatable curtain  110  moves downwardly away from roof rail  112 , a downward force is likewise applied to the tensioning tether element  137 . The application of this downward force pulls the tensioning tether element  137  and the attached sliding cylinder  134  in a downward direction moving along the length of the inflator  126  until contacting the bumper guard  136 . The sliding cylinder  134  and attached tensioning tether element  137  are thereby moved from the position illustrated in FIG. 2A to the orientation illustrated in FIG. 2B.  
         [0037]    Simultaneous with the downward movement of the inflatable curtain  110  and the accompanying vertical force component applied to the tensioning tether element  137 , the inflatable curtain  110  also undergoes a degree of shortening as inflation takes place. This shortening gives rise to the application of a substantially horizontal force component to the tensioning tether element  137 . It is believed that the ability of the tensioning tether element  137  to move downwardly in conjunction with the inflatable curtain  110  as both vertical and horizontal tensioning forces are applied permits the tensioning tether element  137  to be maintained in a state of tensioned dynamic equilibrium during the inflation event while nonetheless using a tether which is of substantially fixed length.  
         [0038]    In FIGS. 3A and 3B, there is illustrated a variant to the assembly illustrated and described in relation to FIGS. 2A and 2B. In FIGS. 3A and 3B, elements corresponding to those previously illustrated and described are designated by like reference numerals increased by  200 . As best seen by simultaneous reference to FIGS. 3A and 3B, in this embodiment the tether tensioning device  225  is arranged such that the inflator  226  projects downwardly at an angle extending away from the inflation path of the inflatable curtain  210 . In this embodiment, inflation gas is projected outwardly from the discharge end  231  of the inflator  226  and into contact with a reverse bend  240  within the sliding cylinder  234  extending between the inflator  226  and the neck portion  227  of the inflatable curtain.  
         [0039]    In operation, upon the application of pressure at the interior of the reverse bend  240 , the U-shaped sliding cylinder  234  is biased in a downward direction and may slide over the inflator  226  along bearing seals  235  to the extent permitted by the tensioning tether element  237 . The distance of possible movement by the U-shaped sliding cylinder  234  is limited by a bumper guard  236  held at a predetermined position along the length of the inflator. During an inflation event, the discharge of inflation gas initially pushes against the reverse bend  240  thereby establishing an initial tension within the tensioning tether element  237  as the U-shaped sliding cylinder attempts to move downwardly in response to the applied force. This downward movement is permitted only as the inflatable curtain  210  moves downwardly. Thus, a state of tensioned dynamic equilibrium is established across the tensioning tether element  237  from initial activation of the inflator  226  until deployment of the inflatable curtain  210  is completed.  
         [0040]    As will be appreciated, the introduction of tension within the tensioning tether element  137 ,  237  in the tensioning assemblies illustrated in FIGS. 2A and 3A is in each case augmented by the fact that the tensioning tether element is moved along a path extending downwardly and angled away from the air bag curtain. The movement of the tensioning tether elements in such an angled path results in the introduction of both horizontal and vertical force components. As the tensioning tether element  137 ,  237  is moved along the path, the horizontal force component within the tether element is increased thereby requiring an increasing vertical force component to effect continued movement thereby establishing a continuing state of dynamic tension during the entire process.  
         [0041]    It is contemplated that in both of the embodiments illustrated in FIGS. 2A and 3A, the tensioning tether element  137 ,  237  may undergo an initial rapid downward movement as pressure is expelled from the inflator and any available slack in the tensioning tether elements is taken up. In some instances, it may be beneficial to dampen the initial pressure surge by locating the inflator at a location remote from the tensioning tether elements  137 ,  237 . In such arrangements it is contemplated that a extension conduit such as a dimensionally stable straight or angled metal tubing structure may extend away from the inflator in which case the sliding cylinder  134 ,  234  may slide along the extension conduit rather than along the inflator.  
         [0042]    In FIGS. 4A and 4B, there is illustrated another embodiment for a tether tensioning device  325  which may find applicability at a remote storage location away from the inflatable curtain  310 . In FIGS. 4A and 4B, elements corresponding to structures previously described are designated by corresponding reference numerals increased by  300 . As shown, in the tether tensioning assembly  325  of FIG. 4A and inflator  326  is mounted in substantially parallel relation to a gas accepting cylinder  341 . A piston element  342  is carried in sliding relation within the gas accepting cylinder  341 . The piston element  342  includes a head portion  343  having dimensions substantially mated to the interior of the gas accepting chamber so as to establish a substantially gas tight sliding relation. An attachment arm  344  projects away from the piston element  342  through a slot within the gas accepting chamber  341  and is adjoined to a tensioning tether element  337  as previously described. As will be appreciated, in such an arrangement gas pressure is maintained by the bearing seal  335  located below the head portion  343 .  
         [0043]    The inflator  326  expels inflation gas into a dual outlet chamber  345  so as to convey a portion of the inflation gas into the gas accepting cylinder  341  as well as into a transmission conduit  346  extending to the inflatable curtain  310  (FIG. 4B). As illustrated, the transmission conduit  346  may include a flow restricting orifice  347  so as to aid in the establishment of a pressure within the dual outlet chamber  345 .  
         [0044]    In operation, upon the discharge of inflation gas into the dual outlet chamber  345 , a driving force is established across the head portion  343  of the piston element  342  thereby biasing the piston element  342  to move downwardly through the gas accepting cylinder  341  in angled relation away from the inflatable curtain  310 . However, due to the attachment between the tensioning tether element  337  and the inflatable curtain  310  movement of the piston element  342  is permitted only as relaxation is introduced into the tensioning tether element  337  as the inflatable curtain  310  moves downwardly. Thus, as the inflatable curtain  310  moves away from the roof rail  312  a system of dynamic tension is established and maintained across the tensioning tether element  337  such that the tensioning tether element  337  is in a state of substantially continuous tension during the deployment event.  
         [0045]    In FIGS. 5A and 5B, there is illustrated a tether tensioning assembly  425  which utilizes inflation gas to dynamically reposition a tensioning tether element  437  while nonetheless being stored at a location remote from the gas generating inflator  426  used to inflate the curtain  410 . In this embodiment, the tether tensioning assembly  425  includes a gas accepting cylinder  441  which is attached in fluid communication with the inflatable curtain  410  such that the inflatable curtain  410  is disposed between a gas generating inflator  426  and the gas accepting cylinder  441  of the tether tensioning assembly  425 . The gas accepting cylinder  441  is preferably an extension of the gas diffuser normally extending away from the inflatable curtain  410 . A gas containment bearing  448  is disposed behind the head portion  443  so as to define a possible length of movement for the piston element  442 .  
         [0046]    As shown, the tensioning tether element  437  extends through a ring element  449  which rides in attached relation with the piston element  442  at a position behind the gas containment bearing  448 . The ring element  449  rides along a path above a channel  450 . A plurality of teeth  451  extend away from the side of the channel  450  so as to form projections extending at least partially across the channel  450 . During operation, upon inflation of the inflatable curtain  410  a quantity of inflation gas is directed into the gas accepting cylinder  441  thereby depressing the piston element  442  and carrying the tensioning tether element  437  downwardly to the extent permitted by its attachment to the inflating curtain  410 .  
         [0047]    As illustrated in FIG. 5C, the ring element  449  rides above a spring loaded pin element  452  which is normally biased to a downward position. As movement of the ring element  449  progresses, the spring loaded pin element  452  passes progressively over the projection forming teeth  451  in a ratcheting manner. Upon termination of movement, the spring loaded pin element  452  projects downwardly between adjacent teeth  451  such that the teeth  451  act to block retreat of the piston element  442  back through the gas accepting cylinder  441 . The tensioning tether element  437  is thus held in tension both during and after deployment of the inflatable curtain  410 .  
         [0048]    In FIGS. 6A and 6B, there is illustrated a tether tensioning device  525  which may be operated by use of cushion inflating gas to drive a tether conveying piston element. As best illustrated in FIG. 6A, the components of the tether tensioning device  525  include an elongate tubular housing  555  having a pair of diametrically opposed slots  556  having a width sufficient to accept in sliding relation the tensioning tether element  537 . Disposed at the interior of the housing  555  is an elongate piston unit  557  which is preferably made of a plastic material. A groove-fitted O-ring  558  is seated around the piston  557  adjacent a proximal end of the piston  557  so as to ensure retention of gas introduced into the housing  555  in a manner as will be described hereinafter. The piston includes a body portion  559  extending to a tether holding portion  560  of enhanced diameter. The tether holding portion  560  includes a tether acceptance opening  562  extending therethrough. The dimensions of the tether acceptance opening  562  are such that the tensioning tether element  537  may be passed in sliding relation through the tether acceptance opening  562 . A nipple  563  extends away from the tether holding portion  560 . As illustrated, the nipple  563  is preferably tapered to a reduced diameter at its terminal end so as to facilitate sliding insertion into a retaining disk  565  and towards a retaining cap  566 .  
         [0049]    During assembly, the retaining disk  565  is seated at the interior base of the retaining cap  566 . The retaining cap  566  is preferably of an open ended construction so as to establish a passageway through both the retaining disk  565  and the retaining cap  566 . The retaining cap with seated retaining disk  565  is thereafter secured over a distal end  567  of the housing  555 . The piston  557  may be dropped into the housing  555  through a proximal end  568  and rotated such that the tether acceptance openings  562  are aligned with the slots  556  within the housing  555 . If desired, a male connection element  569  may thereafter be threaded over the proximal end  568 . The tensioning tether element  537  may thereafter be threaded through the slots  556  and tether acceptance opening  562  for attachment at either end to locations exterior to the tether tensioning device  525 .  
         [0050]    The tensioning tether element  537  normally supports the light weight piston  557  such that the nipple  563  is held away from the distal end  567  of the housing. However, upon the introduction of a pressurizing medium into the housing through the proximal end  568 , the piston  557  is forced to move towards the distal end  567  of the housing such that the nipple  563  penetrates and extends at least partially through the retaining disk  565  and the corresponding retaining cap  566  in the manner as shown in FIG. 6B. Upon the achievement of this position, the piston  557  is thereafter held in place by inwardly extending teeth  570  projecting into the interior of the retaining disk  565 . The retaining disk  565  is preferably formed of a spring steel material such that the teeth  570  are of highly resilient character.  
         [0051]    To enhance the retention of the nipple within the retaining disk  565 , the teeth  570  are preferably angled slightly away from the plane of the perimeter of the disk so as to extend in the direction of movement of the nipple  563 . Such an orientation facilitates insertion of the nipple  563  through the interior of the retaining disk  565  while at the same time establishing a locking relationship wherein the resilient teeth  570  tend to bite into the surface of the nipple  563  upon attempted withdrawal.  
         [0052]    The tether tensioning device  525  as describe in relation to FIGS. 6A and 6B is believed to be useful in a number of applications wherein a common inflator may be used to both pressurize the housing  555  and to simultaneously inflate a cushion operatively connected to one end of the tensioning tether element  537 . In FIG. 8, there is illustrated a first exemplary arrangement for a tether tensioning assembly  525  in disposition along an intermediate structural pillar  520  such as a “C” pillar in a vehicle having a four pillar frame structure. In the illustrated arrangement, an inflator  526  is arranged adjacent the roof rail of the vehicle to transmit inflation gas through a gas conduit  572  into the inflatable curtain  510 . As shown, the gas conduit  572  is of a branched construction having a first leg  573  which channels gas into the inflatable cushion  510  and a second leg  574  which channels inflation gas into the housing  555  of the tether tensioning device  525 .  
         [0053]    As shown in broken lines, the tensioning tether element  537  initially extends in looped relation between a lower edge of the stored inflatable curtain  510  through the housing  555  and to a fixed point of attachment  575  along the structural pillar  520 . Of course, prior to deployment the tensioning tether element  537  is hidden from view by overlying trim extending in covering relation to the vehicle frame components. As shown in solid lines in FIG. 8, upon activation of the inflator  526  a portion of inflation gas is directed into the housing  555  thereby applying a driving force to the internal piston and biasing the tensioning tether element  537  downward. As with previously described embodiments, this movement of the tensioning tether element establishes an internal tension within the tensioning tether element  537  between the tether tensioning device  525  and the inflatable curtain  510 . Thus, a dynamic equilibrium is established during the downward movement of the inflatable cushion  510  until such time as the inflatable curtain  510  is fully deployed and the piston within the housing  555  has been stroked to its full extension and locked in place by engagement between the nipple  563  and the internal retaining disk  565  held at the retaining cap  566 . Thereafter, retreat of the tensioning tether element is prevented by the engagement between the nipple  563  and the teeth  570  of the retaining disk  565 .  
         [0054]    By way of further example, in FIGS. 9 and 10, there is illustrated another arrangement for the inflation gas activated tether tensioning device illustrated and described in relation to FIGS. 6A and 6B. In the arrangement illustrated in FIGS. 9 and 10, components corresponding to those previously illustrated and described are designated by corresponding reference numerals with a prime. In the illustrated arrangement, a tether tensioning device  525 ′ is housed along the roof rail of the vehicle adjacent to a gas generating inflator  526 ′. As shown in the break-out section of FIG. 10, the inflator directs inflation gas along a first leg  573 ′ but also diverts a portion of gas back through a second leg  574 ′ and into the housing  555 ′. As illustrated in broken lines, prior to activation, the tensioning tether element  537 ′ extends away from the inflatable curtain  510 ′, around a series of guide pulleys  576 ′ arranged at the structural pillar  520 ′ and through the tether tensioning device  525 ′ to a point of attachment  575 ′. In this arrangement, as the air bag cushion  510 ′ is deployed downwardly away from the roof rail the pressure from the inflation gas which enters the housing  555 ′ causes the slack which would otherwise occur in the tensioning tether element  537 ′ to be taken up by movement of the interior piston thereby pulling the tensioning tether  537 ′ around the guide pulleys and maintaining the tensioning tether element in a substantially taut state during and after deployment of the inflatable curtain  510 ′.  
         [0055]    It is contemplated that the arrangement of elements as illustrated and described in relation to FIGS. 6A and 6B may also be used in conjunction with a dedicated initiating device such as a gas generating squib element or micro-gas generator which releases a relatively small quantity of pressurized gas on demand so as to drive the tether holding piston from a first position to a second position at a given time without reliance upon gas produced by the inflator for the cushion. Of course other members such as a small servomotor or the like may also be utilized to move the piston.  
         [0056]    One illustrative arrangement for a self-actuating tether tensioning device  625  is illustrated in FIG. 11. As shown, this assembly is substantially identical to that as illustrated and described in relation to FIGS. 6A and 6B with the exception that a selectively activatable micro-gas generator or squib  680  is affixed at the proximal end  668  of the housing  655 . As will be appreciated, the micro-gas generator  680  is simply a small inflator which may be selectively activated upon the receipt of an activating signal through leads  681 . Upon activation, a pulse of pressurized gas is developed thereby causing the sliding relocation of the piston within the housing  655  in the manner as previously described.  
         [0057]    One possible arrangement for the tether tensioning device  625  within a vehicle is illustrated in FIG. 12. As shown in dotted lines, in this arrangement the tensioning tether element  637  extends directly from a lower portion of the inflatable curtain  610  to the tether tensioning device  625  along a guide path defined by a properly placed guide pulley element  676 . Upon activation of the curtain inflator  626 , the lower portion of the inflatable curtain  610  expands downwardly away from roof rail and across a side portion of the vehicle interior. At a desired time relative to the activation of the cushion inflator  626 , the micro-gas generator  680  may also be activated thereby applying a biasing tension to the tensioning tether element  637 . It is contemplated that the activation of the micro-gas generator  680  may substantially coincide with the activation of the curtain inflator  626 . However, it is also contemplated that such activation may take place either before or after the activation of the curtain inflator  626  as may be desired to achieve a given tensioning effect.  
         [0058]    As will be appreciated, the ability to selectively activate the tether tensioning assembly  625  may be beneficial in permitting a wider range of placement options for the tether tensioning assembly  625  within the vehicle since gas communication with the curtain inflator  626  is no longer required. In addition, it is contemplated that the ability to selectively actuate the tether tensioning assembly  625  may provide enhanced operational benefits by permitting tensioning to be adjusted based upon the actual conditions occurring during a collision event.  
         [0059]    It is contemplated the elongate tether tensioning assembly geometry of the configurations as illustrated in FIGS. 6A, 6B and  11  may be particularly useful in the development and retention of tension between adjacent portions of a split cushion geometry such as may be used to effect deployment around seat belt structures. One such arrangement is illustrated in FIG. 13. As shown, the inflatable curtain  710  in FIG. 13 is of a split construction having a forward section  784  and a rear section  785  in fluid communication with one another along a common inflated header  786 . The forward section  784  is arranged to cover a region between the “A” pillar and the intermediate “B” pillar, while the rear section  785  is arranged to cover a region between the intermediate “B” pillar and the rearward “C” pillar.  
         [0060]    In the illustrated arrangement, the forward section  784  and the rear section  785  are separated by a gap disposed in overlying relation to a portion of the “B” pillar so as to avoid interference between the inflated curtain  710  and a seat belt web guide ring  788  located at the “B” pillar. If desired, an optional bridging element  789  such as a piece of fabric or the like may extend between the forward and rearward sections. As shown in broken lines, prior to deployment a tensioning tether element  737  extends in hanging relation between opposing edges of the forward and rearward sections. As illustrated, the orientation of the tensioning tether element  737  is such that it hangs below the seat belt web guide ring  788  and is hidden by the overlying trim. Upon activation of the curtain inflator  726 , the tensioning tether element is pulled downwardly with the curtain  710 . Simultaneously, any relaxation within the tensioning tether element  737  is taken up by the tether tensioning device  725  such that the tensioning tether element  737  pulls the attached portions of the inflatable curtain  710  inwardly towards the tether tensioning device  725  in the manner shown.  
         [0061]    In the illustrated embodiment, the tether tensioning device  725  is operated by fluid communication with the cushion inflator  726 . However, it is to be appreciated that the tether tensioning device  725  may also utilize a microgas generator if desired. It is to be understood that in actual practice, the length of the tether tensioning device  725  may be required to be fairly extensive so as to extend a substantial distance below the region to be covered by the inflatable curtain  710 . However, it is believed that the requisite distance is generally readily available.  
         [0062]    It is to be understood that while the present invention has been illustrated and described in relation to certain potentially preferred embodiments, constructions and procedures the presentation of such embodiments, constructions and procedures is intended to be illustrative only and the present invention is in no event to be limited thereto. Accordingly, it is to be understood that the present invention is intended to extend to all modifications and variations as may incorporate the broad aspects of the invention which fall within the full spirit and scope of the appended claims and all equivalents thereto.