Abstract:
The present invention incorporates a tether release system within a conventional airbag system or a conventional vehicle occupant protection system. Release of an associated tether may simultaneously open a vent on an associated airbag. A housing contains an actuator contained within the housing for actuation of the tether release system upon receipt of a crash detection signal, for example. A first moving member is configured for receipt of a propulsive force emanating from the actuator upon actuation of the tether release system. A movable tether release member is contained within the housing wherein the movable tether release member operably communicates with the first moving member upon actuation of the tether release system, for release of an associated tether.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Application Ser. Nos. 61,351,237, 61,357,808, and 61/351,615, having filing dates of Jun. 3, 2010, Jun. 23, 2010, and Jun. 4, 2010, respectively. 
    
    
     BACKGROUND OF THE INVENTION 
     Airbags and other pliable and inflatable restraints are being designed using releasable tethers to selectively modify the shape of the restraint, to provide the restraint with enhanced rigidity, and to control venting of the restraint during deployment. In certain embodiments, tension in the tether maintains a valve controlling an airbag vent in a closed position. At some point during or after deployment of the inflatable device, tension in the tether may be relieved to permit actuation of the vent valve and subsequent release of airbag gases. 
     The embodiments of the present invention provide a releasable tether retention system and if desired, an airbag vent valve actuation mechanism designed to retain at least one end of an extensible tether and to release the tether upon application of an activation signal to an actuator. 
     SUMMARY OF THE PRESENT INVENTION 
     The present invention incorporates a tether release system within a conventional airbag system or a conventional vehicle occupant protection system. Release of an associated tether may simultaneously open a vent on an associated airbag designed to deflate or depressurize the airbag once actuated. As described below, the tether is operably supported by the tether release system, prior to actuation of the system. 
     A housing having a first end and a second end is secured to a base, wherein the base may be integrated within a vehicle component such as a dash board structure, for example. A pyrotechnic, pneumatic, hydraulic, or other functionable actuator is fixed or sealed within the first end of the housing for actuation of the tether release system upon receipt of an electronic or mechanical crash detection signal, from a vehicle algorithm, for example. A first moving member such as a piston or plunger, for example, may be juxtaposed to the actuator within the housing, for receipt of a propulsive force emanating from the actuator upon actuation of the tether release system. A second moving member or a movable tether release member is contained within the housing and juxtaposed to the second end of the housing; the movable tether release member operably communicates and/or cooperates with the first moving member upon actuation of the tether release system, thereby releasing the tether supported by and/or associated with the movable tether release member prior to actuation thereof. 
     Stated another way, the present invention may be described as a releasable tether retention system including a housing; a retention mechanism operably coupled to the housing; and an element movably mounted within the housing and operatively coupled to the retention mechanism such that the retention mechanism is actuatable by movement of the member from a first position to a second position. It will be appreciated that the retention mechanism is configured to secure a tether thereto when the element is in the first position, and is further configured to release the tether upon movement of the element from the first position to the second position. 
     It will be appreciated that the aforementioned tether may be released in a variety of methods in accordance with the inventive principles of the present invention, and as exemplified by, but not limited by, the illustrative embodiments described below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A-6C  show various views of a releasable tether retention system and associated components thereof in accordance with one embodiment of the present invention. 
         FIGS. 7-11  show various views of a releasable tether retention system and associated components thereof in accordance with a second embodiment of the present invention. 
         FIGS. 12-16  show various views of a releasable tether retention system and associated components thereof in accordance with a second embodiment of the present invention. 
         FIG. 17  is a schematic representation of an exemplary vehicle occupant protection system incorporating a releasable tether retention system in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIGS. 1A-6C , a releasable tether retention system  10  in accordance with one embodiment of the present invention includes a housing  12 , a support element  14 , a first movable member  15  slidably mounted in housing  12 , a second movable member or sliding element  16  coupled to the first movable member  15 , and an actuator  18  operatively coupled to housing  12  for producing a motion of first movable member or piston  15  after receipt of an actuation signal. 
     Housing  12  has a first end  30  with a first opening  30   a  and a second end  32  opposite first end  30 . The second end  32  includes a second opening  32   a . In the embodiment shown, openings  30   a  and  32   a  are substantially coaxial along an axis A of the housing. An axial bore  24  extends through housing  12  between first end  30  and second end  32 . In a particular embodiment, first end  30  of the housing  12  is configured so as to be crimpable or otherwise deformable to aid in retaining actuator  18  within (or to) housing  12 . Housing  12  may include features such as shoulder  12   a  configured to limit the travel of movable member  15  (described below) within bore  24  during operation of the tether retention system. Housing  12  may be formed using any suitable method from a metallic material or any other suitable material. 
     A base  20  is provided for mounting of housing  12  thereto. In one embodiment, base  20  comprises an integral portion of a vehicle or other device to which tether retention system  10  is to be attached. In another embodiment, base  20  is formed separately from the vehicle or other element and is attached by welding or any other suitable method to a portion of the vehicle or other device to which the tether retention system is to be secured. Base  20  includes an opening  20   b  formed therein to permit tether  22  to extend therethrough. Housing  12  is mounted to the base  20  proximate opening  20   b . In an alternative embodiment, housing  12  is secured to another portion of the vehicle or device to which the tether retention system is mounted, but is still positioned and secured proximate opening  20   b.    
     A support element  14  is provided for engaging and supporting a portion of a tether  22  prior to release of the tether. Support element  14  is positioned and secured spaced apart from base  20  and the opening  20   b  formed therein. In the embodiment shown in the drawings, opening  20   b  is punched or otherwise formed in base  20 , and a portion of the base material that occupied opening  20   b  is formed or otherwise shaped to provide support element  14 . In this embodiment, support element  14  is spaced apart from both base  20  and its opening  20   b  by forming part of the material of support element  14  into a connecting section  14   a  which joins support element  14  to the remainder of base  20 . 
     In alternative embodiments, support element  14  may be formed separately from base  20  and suitably attached to the base, or the support element may be positioned spaced apart from the base  20  and opening  20   b  and coupled to an element separate from the base. In a particular embodiment, base  20  and/or support element  14  incorporate a feature or features (not shown) configured to limit the travel of second movable member or sliding element  16  (described below) or first movable member or element  15  (described below). Base  20  may be formed using any suitable method from a metallic material or any other suitable material. Support element  14  may be formed using any suitable method from a metallic material or any other suitable material. As described below, taken together, support element  14  and second movable member or sliding element  16  constitute a releasable tether retention mechanism  14 / 16  that that when coupled to the housing  12  and first movable member  15 , facilitates the retention and subsequent release of an associated tether upon actuation of the system  10 . 
     An actuator  18  is secured to housing first end  30  and extends into bore  24  so as to enable fluid communication between the actuator and bore  24  containing first movable member  15 , after activation of the system to release the tether. In one embodiment, actuator  18  is in the form of an electrically-actuated pyrotechnic initiator, or squib, secured within a bore seal  36 . Actuator  18  may be formed as known in the art. One exemplary actuator construction is described in U.S. Pat. No. 6,009,809, herein incorporated by reference. Bore seal  36  may be stamped, extruded, cast, machined, or otherwise metal formed and may be made from carbon steel or stainless steel, for example. 
     Actuator  18  may be secured within bore seal using any of a variety of known methods including, but not limited to, an interference fit, adhesive application, or crimping. Similarly, bore seal  36  may be secured to housing  12  using any of a variety of known methods including, but not limited to, crimping, welding, or adhesive application. In addition, features may be provided for engaging the actuator and/or bore seal with base  20  or a portion of the vehicle or device to which system  10  is mounted, to aid in preventing rotation or other movement of the actuator relative to housing  12  and/or base  20 . 
     In alternative embodiments, actuator  18  may be in the form of a pneumatically or hydraulically actuated valve coupled to an end of housing  12  so as to enable fluid communication between an outlet of the valve and bore  24  upon receipt by the retention system of a suitable activation signal. In these embodiments, activation of the system to release the tether results in opening of the valve to admit a high-pressure fluid into bore  24 , resulting in movement of the first movable member  15  as described below. Alternatively, actuator  18  may be positioned remotely from housing  12  but so as to enable fluid communication between the actuator and bore  24  upon receipt by the retention system of a suitable activation signal. 
     First movable member  15  is configured to slidably move along and within bore  24 . In one embodiment, a detent feature (not shown) is provided for ensuring sufficient engagement or interference between the movable member and housing  12  such that movement of the first movable member  15  within bore  24  is prevented prior to activation of the system to release the tether. In the embodiment shown in the drawings, movable member portion  15   a  has a groove  15   b  formed therein for engaging a portion of the second movable member or sliding element  16 . 
     In one particular embodiment, the detent feature is in the formed of a knurl, stake, or other deformation (not shown) in a surface of the movable member which engages a wall of the housing defining the bore  24 . 
     In another particular embodiment, the detent feature is formed in the housing, rather than in the movable member  15 . 
     In another particular embodiment, the detent effect is provided by dimensioning the bore diameter and an outer diameter or dimension of the movable member  15  such that a slight interference between the movable member and the housing is provided when the movable member is in a pre-activation position. 
     In another particular embodiment, the movable member  15  and/or the housing  12  include one or more features configured to produce a slowing of movable member  15  as it approaches housing second end  32  after activation of the system to release the tether. This slowing effect may be provided by dimensioning the bore diameter and an outer diameter or dimension of the movable member  15  such that an interference fit between the movable member and the housing is provided as the movable member approaches housing second end  32 . In one example, a diameter of the bore  24  is tapered from a relatively larger dimension to a relatively smaller dimension along the direction of movement of movable member  15 , so that slowing of the movable member is relatively gradual. The rate of deceleration of the movable member along bore  24  may be controlled to some degree by the severity of the taper. A portion  15   a  of movable member  15  extends out of housing  12  to enable coupling of sliding element  16  thereto. 
     The dimensions of the movable member may also be specified so as to affect the rate of deceleration of the movable member within the housing  12 . 
     First movable member/piston  15  may be formed from a metallic material or any other suitable material. 
     Second movable member/sliding element  16  has a first portion  16   a  and a second portion  16   b  extending from first portion  16   a . Portion  16   a  has an opening  16   c  formed therein to permit a portion of tether  22  to extend therethrough. Prior to activation of the system  10  to release the tether, first portion  16   a  is positioned between base  20  and support element  14  such that opening  16   c  resides between base opening  20   b  and the support element. 
     In the embodiment shown in the drawings, second portion  16   b  has a slot  16   d  for receiving therein a grooved portion  15   a  of movable member  15 . In this manner, the sliding element  16  is engaged with the movable member  15  so that the sliding element moves in conjunction with the movable member. In one particular embodiment, slot  16   d  is open-ended to permit the movable member grooved portion  15   a  to be inserted into the open end. 
     In another particular embodiment (shown in  FIG. 3 ), the slot has a keyhole-shape, with first section  16   d   1  configured to permit insertion of an end  15   e  of the movable member therein, and a second section  16   d   2  adjoining the first section, for engaging movable member grooved portion  15   a . Slot second section is sized to receive movable member grooved portion  15   a  therein, but also to prevent withdrawal of end  15   a  therethrough. Thus, end  15   a  is inserted into first section  16   d   1  until grooved portion  15   a  is aligned with second section  16   d   2 . Then grooved portion  15   a  is inserted into second portion  16   d   2  to couple the sliding element  16  to movable member  15 . 
     Sliding element or second movable element  16  may be formed from a metallic material or any other suitable material. 
     As shown in  FIG. 1 , prior to activation of the system to release tether  22 , a looped end  22   a  of the tether passes through base opening  20   b  and through sliding element opening  16   c  and is looped over support element  14 . Sliding element second portion  16   b  and an edge  16   a   1  of first portion  16   a  bracket the tether, preventing motion of the tether parallel to axis A and preventing the tether end  22   a  from sliding off of support element  14 . This configuration also ensures that the tether end  22   a  will move in conjunction with sliding element  16 . Referring to  FIG. 1D , sliding element opening  16   c  may also be configured such that forces acting on tether  22  in the direction indicated by arrow “B” in  FIG. 1A  are transmitted to parts  16   e ,  16   f  of first portion  16   a  on either side of opening  16   c , via the portions of the tether squeezed between the support element  14  and parts  16   e ,  16   f . In this manner, parts  16   e ,  16   f  act to reinforce support element  14  against tension forces acting on the tether, to aid in preventing bending of the support element. 
     A securement member  50  (for example, a conventional hold-down strap) may be used to secure the housing  12  to base  20  or to another portion of the vehicle or device to which the system  10  is attached. However, housing  12  may be secured to base  20  by welding or by any other suitable method. 
     Referring to  FIGS. 5A-5F , system  10  may be assembled as follows. Sliding element  16  is positioned in its pre-activation position in relation to base  20 . Tether end  22   a  is then slid through base opening  20   b  and sliding element opening  16   c . Tether portion  22   a  is then slid over support element  14  and sliding element  16  is slid between the support element and base  20  such that the support element extends into the loop of tether end  22   a . Housing  12  with movable member  15  residing therein is then positioned such that the exposed end of the first movable member  15  engages the second movable element or sliding element  16  as previously described. Housing  12  is then secured to base  20  using securement member  50 . 
     Referring to  FIGS. 1A-6C , in operation, upon receipt of a signal from a crash sensor or other system activation mechanism, an activation signal is sent to actuator  18 . In an embodiment where the actuator is a squib, combustion products from the squib impinge on an end face of movable member  15  in fluid communication with the actuator, forcing the movable member in the direction indicated by arrow “C” in  FIG. 2 . Sliding element or second movable member  16  moves in conjunction with first movable member  15 , forcing the tether looped end  22   a  (which is trapped between sliding element edge  16   a   1  and second portion  16   b ) to move in direction “C”. This motion forces the lopped end  22   a  to slide off of the free end of support element  14 . When looped end  22   a  is disengaged from support element  14 , the looped end is free to pass through opening  16   c  in sliding element  16  and through base opening  20   b , thereby freeing the tether. 
       FIG. 17  shows a particular application of a releasable tether retention system  10  in accordance with the present invention. Referring to  FIG. 17 , the releasable tether retention system  10  is incorporated into a vehicle occupant protection system  180  including additional elements such as, for example, a safety belt assembly  150  and/or an airbag module.  FIG. 17  shows a schematic diagram of one exemplary embodiment of such a protection system. Tether retention system  10  may be in operable communication with a crash event sensor  210  which is in communication with a known crash sensor algorithm that signals actuation of the tether release mechanism via activation of actuator  18  based on any desired criteria, for example, the occurrence of a collision event, deployment of a vehicle airbag, the occurrence of a predetermined occupant condition, or any other desired criteria. 
     Safety belt assembly  150  includes a safety belt housing  152  and a safety belt  225  in accordance with the present invention extending from housing  152 . A safety belt retractor mechanism  154  (for example, a spring-loaded mechanism) may be coupled to an end portion of the belt. In addition, a safety belt pretensioner  156  may be coupled to belt retractor mechanism  154  to actuate the retractor mechanism in the event of a collision. Typical seat belt retractor mechanisms which may be used in conjunction with the safety belt embodiments of the present invention are described in U.S. Pat. Nos. 5,743,480, 5,553,803, 5,667,161, 5,451,008, 4,558,832 and 4,597,546, incorporated herein by reference. Illustrative examples of typical pretensioners in system  150  are described in U.S. Pat. Nos. 6,505,790 and 6,419,177, incorporated herein by reference. 
     Safety belt system  150  may be in communication with a crash event sensor  158  (for example, an inertia sensor or an accelerometer) including a known crash sensor algorithm that signals actuation of belt pretensioner  156  via, for example, activation of a pyrotechnic igniter (not shown) incorporated into the pretensioner. U.S. Pat. Nos. 6,505,790 and 6,419,177, incorporated herein by reference, provide illustrative examples of pretensioners actuated in such a manner. 
     If desired, one or more of sensors  210  and/or  158  may be operatively coupled to valve release mechanism actuator  18  to provide one or more associated inputs prompting activation of the valve release mechanism, depending on such factors as vehicle occupant weight, elapsed time since the occurrence of a collision event, or any other pertinent factors. 
     In yet other embodiments illustrating the present invention, and referring to  FIGS. 7-11 , an airbag vent valve actuation mechanism or tether release system  310  in accordance with one embodiment of the present invention includes a housing  312 , a first movable member or element  315  slidably mounted in housing  312 , an actuator  318  operatively coupled to housing  312  for producing a motion of movable member  315  after receipt of an actuation signal, a link  316  coupled to the first movable member  315 , and a second movable member or rotatable element  319  coupled to the link  316  for supporting a tether  322  prior to activation of the valve actuation mechanism. As described below, taken together, the link  316  and second movable member or rotatable element  319  when coupled to the housing  312  and the first movable member or element  315  constitute a releasable tether retention mechanism  316 / 319  that facilitates the retention and subsequent release of an associated tether upon actuation of the system  310 . 
     Housing  312  has a first end  330  with a first opening  330   a  and a second end  332  opposite first end  330 . The second end  332  includes a second opening  332   a . In the embodiment shown, openings  330   a  and  332   a  are substantially coaxial along an axis A of the housing. An axial bore  324  extends through housing  312  between first end  330  and second end  332 . In a particular embodiment, first end  330  of the housing  312  is configured so as to be crimpable or otherwise deformable to aid in retaining actuator  318  within (or to) housing  312 . Housing  312  may include features such a shoulder (not shown) configured to limit the travel of movable member  315  (described below) within bore  324  during operation of the airbag vent valve actuation mechanism. 
     In another particular embodiment (shown in  FIGS. 7-11 ), a portion of an actuator  318  (described below) extends into and is secured within housing first end  330 , and a portion of the actuator extends outside of the housing first end. Housing first end  330  is then secured within a bore seal  336  so as to enclose the portion of the actuator extending from housing end  330 . Bore seal may then provide an interface permitting mating of a connector or other suitable signal transmission medium (not shown) with the actuator  318 . 
     Housing  312  may be mounted to any suitable surface, for example, to a portion of a vehicle or device to which the valve actuation mechanism is operatively coupled. In a particular embodiment, the housing is mounted to a base  320  (described below) to which rotatable element  319  (described below) is also mounted. In another embodiment, the mounting surface for housing  312  is formed separately from the vehicle or device and is attached by welding or any other suitable method to a portion of the vehicle or device. Housing  312  is mounted to its mounting surface so as to remain fixed or stationary with respect to base  320 . Housing  312  may be formed using any suitable method from a metallic material or any other suitable material. 
     First movable member or piston  315  is configured to slidably move along and within bore  324 . First movable member  315  is positioned either in fluid communication with actuator  318  (described below) or so as to enable fluid communication with the actuator after activation of the valve actuation mechanism. Activation of first movable member  315  in the manner described below produces motion of the movable member within bore  324 . 
     In one embodiment, a detent feature (not shown) is provided for preventing movement of the first movable member  315  within bore  324  prior to activation of the valve actuation mechanism. In one particular embodiment, the detent feature is in the form of a knurl, stake, or other deformation (not shown) in a surface of the movable member which engages a wall of the housing defining the bore  324 . In another particular embodiment, the detent feature is formed in the housing, rather than in the first movable member  315 . 
     First movable member  315  may be formed from a metallic material or any other suitable material. 
     An actuator  318  is secured in housing first end  330  and extends into bore  324  so as to enable fluid communication between the actuator and bore  324  containing piston or first movable member  315 , after activation of the valve actuation mechanism. In one embodiment, actuator  318  is in the form of an electrically-actuated pyrotechnic initiator, or squib, secured within bore seal  336  or housing  312 . Actuator  318  may be formed as known in the art. One exemplary actuator construction is described in U.S. Pat. No. 6,009,809, herein incorporated by reference. Bore seal  36  may be stamped, extruded, cast, machined, or otherwise metal formed and may be made from carbon steel or stainless steel, for example. 
     Actuator  318  may be secured within bore seal using any of a variety of known methods including, but not limited to, an interference fit, adhesive application, or crimping. Similarly, bore seal  336  may be secured to housing  312  using any of a variety of known methods including, but not limited to, crimping, welding, or adhesive application. In addition, features may be provided for engaging the actuator and/or bore seal with base  320  or a portion of the vehicle or device to which system  310  is mounted, to aid in preventing rotation or other movement of the actuator relative to housing  312  and/or base  320 . 
     In alternative embodiments, actuator  318  may be in the form of a pneumatically or hydraulically actuated valve coupled to an end of housing  312  so as to enable fluid communication between an outlet of the valve and bore  324  upon receipt by the retention system of a suitable activation signal. In these embodiments, activation of the system to actuation the tether results in opening of the valve to admit a high-pressure fluid into bore  324 , resulting in movement of the movable member  315  as described below. Alternatively, actuator  318  may be positioned remotely from housing  312  but so as to enable fluid communication between the actuator and bore  324  upon receipt of a suitable activation signal by the valve actuation mechanism. 
     A link  316  is coupled to movable member  315  so as to move in conjunction with the movable member. Link  316  is also coupled to a second movable member or rotatable element  319  (using a bolt, rivet, or other suitable mechanism) so as to produce rotation of the rotatable element with respect to the link responsive to motion of the link within housing  312  after activation of the valve actuation mechanism. In the embodiment shown in  FIGS. 7-11 , a portion of the link  316  is positioned and secured within a complementary cavity formed in movable member  315 . Link  316  may be formed from a metallic material or any other suitable material. 
     Base  320  may be any suitable mounting surface, for example, to a portion of a vehicle or device to which the valve actuation mechanism is operatively coupled. In a particular embodiment, the base  320  is the same surface to which housing  312  is mounted. In another embodiment, base  320  is formed separately from the vehicle or other device and is attached by welding or any other suitable method to a portion of the vehicle or device to which the valve actuation mechanism is to be secured. 
     Base  320  includes an opening  320   b  formed therein to permit tether  322  to extend therethrough for engaging rotatable element third portion  319   c  (described below). In the embodiment shown in the drawings, the second movable member or rotatable element  319  (described below) is rotatably mounted to the base  320  proximate opening  320   b . Opening  320   b  has a first portion  320   c  over which rotatable member third portion  319   c  extends prior to system activation and a second portion  320   e  adjacent first portion  320   c  and configured for permitting deflection of third portion  319   c  therein and sliding of tether end  322   a  from third portion  319   c.    
     One or more features may be provided for restricting rotation of rotatable element  319 . In the embodiment shown in  FIGS. 7-11 , opening  320   b  is punched or otherwise formed in base  320 , and a portion of the base material that occupied opening  320   b  is formed or otherwise shaped to provide a hard stop  320   h  for restricting the rotation of rotatable element  319 . However, the rotation-restricting feature may be located on rotatable member  319  and configured to engage a portion of base  320 , or the rotation-restricting feature may have any of a variety of alternative forms. 
     Base  320  may be formed using any suitable method from a metallic material or any other suitable material. 
     Rotatable element  319  is rotatably coupled to link  316 , as previously described. Rotatable element  319  is also rotatably mounted to base  320  at using a bolt, rivet, or other suitable rotatable coupling  319   r . In the embodiment shown in the drawings, rotatable element  319  has a first portion  319   a  rotatably coupled to base  320  at rotatable coupling  319   r . A second portion  319   b  extends from first portion  319   a  and is rotatably coupled to link  316 , and a third portion  319   c  extends from first portion  319   a  to span base opening first portion  320   c  for engaging and supporting a portion of a tether  322  prior to release of the tether. Rotatable coupling  319   r  may comprise a bolt, a rivet, or any other suitable connection configured for rotatably securing the rotatable member  319  to base  320 . In an alternative embodiment, rotatable element  319  is rotatably mounted to another portion of the vehicle or device to which the valve actuation mechanism is mounted, but is still located proximate opening  320   b.    
     Third portion  319   c  extends across opening first portion  320   c  as shown in  FIG. 8  such that an end of third portion  319   c  rests slidably on, or resides slightly spaced apart from, base  320  prior to placement of tether  322  on third portion  319   c . This permits the base  320  to support third portion  319   c  against forces exerted by the tether prior to system activation. 
     Rotatable element third portion  319   c  may also have a cross-section that is relatively weaker or less resistant to deformation due to forces exerted on the third portion by the attached tether. This cross-section is configured and positioned for facilitating bending or deformation of the third portion responsive to forces exerted on the third portion by the tether after activation of the valve actuation mechanism and sufficient rotation of rotatable element  319 . In the embodiment shown in  FIGS. 7-11 , the relatively weaker cross-section is provided by a notch  319   n  (see  FIG. 8 ) formed along a surface of third portion  319   c  to reduce the cross-sectional area of the third portion in a location where it desired to facilitate bending of the third portion. 
     Rotatable element  319  may be formed using any suitable method from a metallic material or any other suitable material. 
     A securement member  350  (for example, a conventional hold-down strap) may be used to secure the housing  312  to base  320  or to another portion of the vehicle or device to which the system  310  is attached. Alternatively, the housing  312  may be welded or otherwise suitably secured to its mounting surface. 
     As shown in  FIGS. 7 ,  8 , and  9 , prior to activation of the system to release tether  322 , a looped end  322   a  of the tether passes through base opening  320   b  and is looped over rotatable element third portion  319   c . In addition, as stated previously, rotatable element third portion  319   c  rests slidably on, or resides slightly spaced apart from, base portion  320 . This permits base portion  320  to support third portion  319   c  against forces exerted by the tether prior to system activation. Movement of tether end  322   a  along third portion  319   c  is constrained by rotatable member first portion  319   a  and by an edge of base opening first portion  320   c.    
     Referring to  FIGS. 10 and 11 , in operation, upon receipt of a signal from a crash sensor or other system activation mechanism, an activation signal is sent to actuator  318 . In an embodiment where the actuator is a squib, combustion products from the squib impinge on an end face of first movable member  315  in fluid communication with the actuator, forcing the first movable member  315  in the direction indicated by arrow “C” in  FIG. 10 . Movement of the movable member  315  in direction “C” causes the second movable and rotatable member  319  connected to the first movable member  315  to rotate in direction “E” shown in  FIG. 10 . When third portion  319   c  has rotated to a position over opening second portion  320   e , the third portion  319   c  is no longer supported by the base  320 . The third portion  319   c  is thus permitted to deflect into opening second portion  320   e  responsive to forces exerted by the tether, allowing tether end  322   a  to slide off a free end of the third portion as shown in  FIG. 11 . 
     In one embodiment, the tether  322  is operatively coupled to a valve (not shown) controlling a flow of inflation gases from a vent of an airbag (also not shown). The mechanism is structured so that the valve remains closed while the tether end  322   a  is engaged with rotatable member third portion as shown in  FIGS. 7 and 8 . Activation of any of the valve actuation mechanism embodiments described herein produces rotation of the rotatable member and release of tether end  322   a  as just described. As tether end  322   a  begins to slide off of rotatable member third portion  319   c , tension in the tether starts to relax, permitting the valve to open and allowing release of inflation gases from the airbag. 
     Embodiments of the valve actuation mechanism disclosed herein may be activated to permit release of gases from the airbag in situations where a smaller or lighter vehicle occupant is present during a crash situation. Release of a portion of the gases from the inflated airbag provides a relatively softer, less rigid cushion for the lighter vehicle occupant. 
       FIG. 17  shows a particular application of a valve actuation mechanism  310  in accordance with the present invention. Referring to  FIG. 17 , the valve actuation mechanism may be incorporated into a vehicle occupant protection system  180  including additional elements such as, for example, a safety belt assembly  150  and/or an airbag module.  FIG. 17  shows a schematic diagram of one exemplary embodiment of such a protection system. valve actuation mechanism  310  may be in operable communication with a crash event sensor  210  which is in communication with a known crash sensor algorithm that signals actuation of the valve actuation mechanism via activation of actuator  18  based on any desired criteria, for example, the occurrence of a collision event, deployment of a vehicle airbag, the occurrence of a predetermined occupant condition, or any other desired criteria. 
     In yet another embodiment of the invention,  FIGS. 12-16  show an airbag vent valve actuation mechanism or tether release system  497  in accordance with the present invention 
     An actuator housing  412  has a first end  430  with a first opening  430   a  and a second end  432  opposite first end  430 . In one embodiment, the housing  412  is generally cylindrical, although a housing having any of a variety of alternative cross-sectional shapes may be used. An axial bore  424  extends through housing  412  between first end  430  and second end  432 . Bore  424  is configured for slidably receiving an actuator  418  therein, as described below. A wall (or walls) of housing  412  includes opposed, elongated slots  412   v  formed therein. Slots  412   v  are configured for receiving therein a portion of a locking pin  405  (described below) to enable the received portions of the pin to sliding within the slots  412   v  or along edges of the slots. After activation of the valve actuation mechanism, one or more end portions  412   w  of the slots  412   v  may serve as hard stops, limiting travel of pin  405  in the direction indicated by arrow A. 
     In a particular embodiment, first end  430  of the housing  412  is configured so as to be crimpable or otherwise deformable to aid in retaining actuator  418  within (or to) housing  412 . In another particular embodiment, an end of the housing is shaped so as to receive the actuator therein or so as to facilitate retention of the actuator therein. 
     Housing  412  may include features such a shoulder (not shown) configured to limit the travel of a movable member  415  (described below) within bore  424  during operation of the airbag vent valve actuation mechanism. Housing  412  may be mounted to any suitable surface, for example, to a portion of a vehicle or device to which the valve actuation mechanism is operatively coupled. Housing  412  is mounted to its mounting surface so as to remain fixed or stationary with respect to the mounting surface. Housing  412  may be formed using any suitable method from a metallic material or any other suitable material. 
     A base  411  may be provided for mounting of housing  412  and other elements of the system  410  thereon. Base  411  may be formed by a portion of a vehicle or other device on which the mechanism  410  is mounted. Alternatively, base  411  may be in the form of a stand-alone bracket or other structure which may be welded or otherwise suitably attached to a portion of the vehicle or device. In one embodiment, base  411  is configured so as to provide a clearance between the base and locking pin  405  (described below) when the locking pin is mounted in first movable member  415 . Base  411  may be formed using any suitable method from a metallic material or any other suitable material. 
     In the embodiment shown in  FIGS. 12-16 , housing  412  is secured to base  411  using a clamp  499  coupled to base  411 . However, the housing  412  may be secured to the base  411  or to the vehicle or other device using any other suitable method. 
     Clamp  499  may be secured to base  411  using welding, riveting, or any other suitable method. Clamp  499  has a base portion  499   a  and a pair of opposed aims  499   b  extending from the clamp base portion to form a cavity therebetween. Arms  499   b  are configured to facilitate gripping or engagement of actuator housing  412  when the housing is positioned between the arms  499   b , thereby securing the housing  412  within the cavity. 
     The housing may be clamped or secured between the arms  499   b  by forcing end portions of arms toward each other after housing  412  is inserted into the cavity between the arms, until a desired engagement force is achieved. Then the arms  499   b  are secured in the engagement position using a bolt  402  or other suitable means. 
     Clamp  499  may be formed using any suitable method from a metallic material or any other suitable material. 
     An actuator  418  is secured in housing first end  430  and extends into bore  424  so as to enable fluid communication between the actuator and bore  424  containing movable member  415 , after activation of the valve actuation mechanism. In one embodiment, actuator  418  is in the form of an electrically-actuated pyrotechnic initiator, or squib, secured within a bore seal (not shown) or housing  412 . Actuator  418  may be formed as known in the art. One exemplary actuator construction is described in U.S. Pat. No. 6,009,809, herein incorporated by reference. 
     In the embodiment shown in  FIGS. 12-16 , a portion of actuator  418  extends into and is secured within housing first end  430 , and a portion of the actuator extends outside of the housing first end to enable mating of a connector  403  or other suitable signal transmission medium with the actuator  418 . 
     The actuator  418  may be secured within a bore seal (not shown) mountable within housing  412  so as to provide a substantially gas-tight seal between the housing  412  and the bore seal, and also between the bore seal and the actuator  418 . Actuator  418  may be secured within the bore seal using any of a variety of known methods including, but not limited to, an interference fit, adhesive application, or crimping. Similarly, the bore seal may be secured to housing  412  using any of a variety of known methods including, but not limited to, crimping, welding, or adhesive application. Alternatively, the actuator  418  may be secured within housing  412  using an adhesive suitable for providing the desired seal. Other methods of mounting the actuator  418  in or to housing  412  and for providing the desired seal are also contemplated. 
     In addition, features may be provided for engaging the actuator and/or bore seal with base  420  or a portion of the vehicle or device to which system  497  is mounted, to aid in preventing rotation or other movement of the actuator relative to housing  412  and/or base  420 . 
     In alternative embodiments, actuator  418  may be in the form of a pneumatically or hydraulically actuated valve coupled to an end of housing  412  so as to enable fluid communication between an outlet of the valve and bore  424  upon receipt by the valve actuation mechanism of a suitable activation signal. In these embodiments, activation of the mechanism to release the tether results in opening of the valve to admit a high-pressure fluid into bore  424 , resulting in movement of the movable member  415  as described below. Alternatively, actuator  418  may be positioned remotely from housing  412  but so as to enable fluid communication between the actuator and bore  424  upon receipt of a suitable activation signal by the valve actuation mechanism. 
     A first movable member  415  is configured to slidably move along and within bore  424 . In the embodiment shown in  FIGS. 12-16 , member  415  has a cavity  415   a  configured for receiving a portion of actuator  418  therein when the valve actuation mechanism is in a pre-activation state. Member  415  also includes a through hole  415   b  formed therein for receiving a locking pin  405  therethrough. Pin  405  forms an interference fit with edges of hole  415   b  or is otherwise secured within hole  415   b  so as to ensure motion of the pin  405  in correspondence with movable member  415 . 
     Movable member is positioned either in fluid communication with actuator  418  (described below) or so as to enable fluid communication with the actuator after activation of the valve actuation mechanism. Activation of movable member  415  in the manner described below produces motion of the movable member within bore  424 . 
     In one embodiment, a detent feature (not shown) is provided for preventing movement of the movable member  415  within bore  424  prior to activation of the valve actuation mechanism. In one particular embodiment, the detent feature is in the form of a knurl, stake, or other deformation (not shown) in a surface of the movable member which engages a wall of the housing defining the bore  424 . In another particular embodiment, the detent feature is formed in the housing, rather than in the movable member  415 . 
     Movable member  415  may be formed from a metallic material or any other suitable material. 
     Locking pin  405  extends through movable member opening  415   b  and also through housing  412  to project from both of opposed housing slots  12   v . Pin  405  is dimensioned so as to extend from housing  12  a sufficient amount to engage portions of arms  408  and  410  when the valve actuation mechanism is in a pre-activation state, as described below. Pin  405  may be formed from a metallic material or any other suitable material. 
     A mounting member  406  is coupled to housing  412  to enable a pair of actuating arms  408  and  410  to be rotatably mounted thereon. Arms  408  and  410 , may when taken together be considered as a second movable member  408 / 410 . In one embodiment, the mounting member is in the form of a stud or shaft portion secured to a side  411   a  of base  411  opposite the side  411   b  along which clamp  499  is mounted. In another embodiment, the mounting member is secured directly to the housing  412 . However, the mounting member may be secured to any other suitable surface. 
     Arms  408  and  410  are mounted in a stacked fashion on mounting member  406  so as to enable free rotation of the arms about the mounting member when the arms are not constrained in positions securing tether  422 , as described below. If desired, pads or spacers (for example, in the form of washers such as a washer  413 ) may be positioned along mounting member  406  between arm  408  and base  411  and/or between arm  408  and arm  410 , to facilitate smooth, low-friction motion of arm  408  relative to base  411  and of arms  408  and  410  relative to each other. The spacers may be formed from any suitable material having a low coefficient of friction relative to the material (or materials) from which arms  408  and  410  and base  411  are formed. 
     In the embodiment shown in  FIGS. 12-16 , arm  408  has a notch  408   a  formed proximate an end thereof and configured for receiving therein a portion of locking pin  405  when the valve actuation mechanism is in a pre-activation state. A through hole  408   e  is formed through a body of the arm  408  to enable rotatable mounting of the arm on mounting member  406 . Arm  408  also includes a pair of sloped surfaces  408   b ,  408   c  which converge to define a well  408   d  configured for receiving therein a looped portion of a tether  422  when the valve actuation mechanism is in a pre-activation state. The portion of arm  408  including surfaces  408   b  and  408   c  terminates in a rounded end  408   g  and defines a “claw”  408   m  which extends in a first direction across an axis X passing through a center of mounting hole  408   e.    
     Arm  410  has a notch  410   a  formed proximate an end thereof and configured for receiving therein a portion of locking pin  405  when the valve actuation mechanism is in a pre-activation state. A through hole  410   e  is formed through a body of the arm  410  to enable rotatable mounting of the arm on mounting member  406 . Arm  410  also includes a pair of sloped surfaces  410   b ,  410   c  which converge to define a well  410   d  configured for receiving therein a looped portion of a tether  422  when the valve actuation mechanism is in a pre-activation state. The portion of min  410  including surfaces  410   b  and  410   c  terminates in a rounded end  410   g  and defines a “claw”  410   m  which extends across axis X passing through a center of mounting hole  410   e . Claw  410   m  extends across axis X in a second direction substantially opposite the first direction. 
     As seen in  FIG. 13 , well  410   d  formed by surfaces  410   b  and  410   c  opens in a direction opposite to that in which the well  408   d  opens. In addition, claws  408   m  and  410   m  are configured so as to overlap across axis X when the valve actuation mechanism is in a pre-activation state. In this configuration, the looped portion  422   a  of tether  422  is wrapped over the overlapping claws of the arms  408 ,  410  and extends into wells  408   d  and  410   d . The overlapping claws thus secure the tether  422  to the valve actuation mechanism prior to system activation. 
     Arms  408  and  410  are configured so that claws  408   m  and  410   m  are in an overlapping state when the arms are rotated such that notches  408   a  and  410   a  are aligned with each other so as to permit insertion of locking pin  405  into both notches. Positioning of pin  405  within notches  408   a  and  410   a  maintains the claws in an overlapping state by preventing rotation of the arms. Arms  408  and  410  may be secured to mounting member  406  using a nut or other fastener, or by any other suitable method. Arms  408  and  410  may be formed using any suitable method from a metallic material or any other suitable material. 
     As described above, and when taken together, the arms  408  and  410  and the associated features when coupled to the housing  412  through mounting member  406  and the first movable member or element  415  constitute a releasable tether retention mechanism  408 / 410  that facilitates the retention and subsequent release of an associated tether upon actuation of the system  497 . 
     As shown in  FIGS. 12 and 13 , prior to activation of the system to release tether  422 , a looped end  422   a  of the tether passes through the mechanism as shown in  FIGS. 12-16 , with locking pin  405  residing in notches  408   a  and  410   a  of arms  408  and  410 . In addition, a certain amount of tension force is present in the tether which tends to pull the tether away from the mechanism  497 , in the general direction indicated by arrow “E”. 
     Referring to  FIGS. 14-16 , upon receipt of a signal from a crash sensor or other system activation mechanism (not shown), an activation signal is sent to actuator  418 . In an embodiment where the actuator is a squib, combustion products from the squib impinge on an end face of first movable member  415  in fluid communication with the actuator  418 , forcing the movable member  415  in the direction indicated by arrow “A” in  FIG. 13 . Movement of the first movable member  415  in direction “A” causes the locking pin  405  to be extracted from notches  408   a  and  410   a . This releases the rotational constraints on arms  408  and  410 . The tether tension force in direction pulls on the arm ends  408   g  and  410   g  along surfaces  408   c  and  410   c , causing them to rotate outwardly about mounting member  406 , in the directions indicated by arrows “G” and “H”. As rotation of the arms continues and the ends of the arms continue to separate, the tether looped portion  422   a  eventually slides down surfaces  4108   c  and  410   c  and over the curved ends of arms  408  and  410 , slipping free of the mechanism. 
     In one embodiment, the tether  422  is operatively coupled to a valve (not shown) controlling a flow of inflation gases from a vent of an airbag (also not shown). The system is structured so that the valve remains closed while the tether end  422   a  is engaged with mechanism  410 . Activation of any of the valve actuation mechanism embodiments described herein produces rotation of the arms  408  and  410  and release of tether end  422   a  as just described. As tether end  422   a  begins to slide off of arms  408  and  410 , tension in the tether starts to relax, permitting the valve to open and allowing release of inflation gases from the airbag. 
     Embodiments of the valve actuation mechanism disclosed herein may be activated to permit release of gases from the airbag in situations where a smaller or lighter vehicle occupant is present during a crash situation. Release of a portion of the gases from the inflated airbag provides a relatively softer, less rigid cushion for the lighter vehicle occupant. 
       FIG. 17  shows a particular application of a valve actuation mechanism  410  in accordance with the present invention. Referring to  FIG. 17 , the valve actuation mechanism may be incorporated into a vehicle occupant protection system  180  including additional elements such as, for example, a safety belt assembly  150  and/or an airbag module.  FIG. 17  shows a schematic diagram of one exemplary embodiment of such a protection system. valve actuation mechanism  10  may be in operable communication with a crash event sensor  210  which is in communication with a known crash sensor algorithm that signals actuation of the valve actuation mechanism via activation of actuator  18  based on any desired criteria, for example, the occurrence of a collision event, deployment of a vehicle airbag, the occurrence of a predetermined occupant condition, or any other desired criteria. 
     Safety belt assembly  150  includes a safety belt housing  152  and a safety belt  225  in accordance with the present invention extending from housing  152 . A safety belt retractor mechanism  154  (for example, a spring-loaded mechanism) may be coupled to an end portion of the belt. In addition, a safety belt pretensioner  156  may be coupled to belt retractor mechanism  154  to actuate the retractor mechanism in the event of a collision. Typical seat belt retractor mechanisms which may be used in conjunction with the safety belt embodiments of the present invention are described in U.S. Pat. Nos. 5,743,480, 5,553,803, 5,667,161, 5,451,008, 4,558,832 and 4,597,546, incorporated herein by reference. Illustrative examples of typical pretensioners in system  150  are described in U.S. Pat. Nos. 6,505,790 and 6,419,177, incorporated herein by reference. 
     Safety belt system  150  may be in communication with a crash event sensor  158  (for example, an inertia sensor or an accelerometer) including a known crash sensor algorithm that signals actuation of belt pretensioner  156  via, for example, activation of a pyrotechnic igniter (not shown) incorporated into the pretensioner. U.S. Pat. Nos. 6,505,790 and 6,419,177, incorporated herein by reference, provide illustrative examples of pretensioners actuated in such a manner. 
     If desired, one or more of sensors  210  and/or  158  may be operatively coupled to valve actuation mechanism actuator  18  to provide one or more associated inputs prompting activation of the valve actuation mechanism, depending on such factors as vehicle occupant weight, elapsed time since the occurrence of a collision event, or any other pertinent factors. 
     It should be understood that the preceding is merely a detailed description of various embodiments of this invention and that numerous changes to the disclosed embodiments can be made in accordance with the disclosure herein without departing from the spirit or scope of the invention. The preceding description, therefore, is not meant to limit the scope of the invention, but should be interpreted to encompass the full range of literal and equivalent embodiments with regard to the appended claims.