Abstract:
A bore seal is includes a polymeric interface portion adapted for coupling to an initiator activation signal transmission medium, and an initiator-receiving portion adapted for receiving an initiator therein. The bore seal generally houses a pyrotechnic initiator or igniter therein, for incorporation into a gas generating system or other system having a pyrotechnically actuatable element.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application Ser. No. 60/774,576 filed on Feb. 17, 2006. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates generally to gas generating systems and, more particularly, to gas generators used in vehicle occupant protection systems and related components, such as seatbelt pretensioners. 
         [0003]    Gas generators used in seatbelt pretensioners are known as micro gas generators (MGG&#39;s) due to the relatively small size of the gas generator. Exemplary pretensioners using such micro gas generators include those described in U.S. Pat. Nos. 6,460,794, 6,505,790, 6,520,443, and 6,419,177, incorporated herein by reference. Micro gas generators generally include a bore seal for receiving and securing an initiator therein, an initiator including an initiator charge, and a gas generant composition which ignites and burns in response to activation of the initiator to produce gases for actuating the seatbelt pretensioner. 
         [0004]    A portion of the bore seal is configured to mate with a mating connector element formed on a portion of a vehicle to which the initiator assembly is attached. Typically, the bore seal is formed from a metal, such as steel or aluminum. Mating features (such as slots and undercuts) and other desired features are machined into appropriate surfaces of the metal bore seal. However, machining these features into the bore seal is relatively expensive. Some existing micro gas generator designs incorporate an initiator assembly in which the initiator is molded into a bore seal formed from a plastic material to include the desired mating features. However, limitations on molding process temperatures and pressures imposed by the structure of the initiator tend to limit the range of plastics suitable for insert molding. This results in a bore seal having insufficient strength for micro gas generator operation. 
       SUMMARY OF THE INVENTION 
       [0005]    In accordance with the present invention, a bore seal is provided which includes a polymeric interface portion adapted for coupling to an initiator activation signal transmission medium, and an initiator-receiving portion adapted for receiving an initiator therein. The bore seal generally houses a pyrotechnic initiator or igniter therein, for incorporation into a gas generating system or other system having a pyrotechnically actuatable element. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIGS. 1   a - 1   c  are cross-sectional side views showing one embodiment of a conventional bore seal and a micro gas generator incorporating the bore seal; 
           [0007]      FIGS. 2   a - 2   c ,  3   a - 3   c , and  7   a - 7   f  are cross-sectional side views showing various embodiments of a bore seal in accordance with the present invention incorporated into micro gas generators; 
           [0008]      FIGS. 4   a - 4   c ,  5   a - 5   c , and  6   a - 6   b  are cross-sectional side views showing various additional embodiments of a bore seal in accordance with the present invention; 
           [0009]      FIG. 8  is an end perspective view of yet another embodiment of a bore seal in accordance with the present invention; and 
           [0010]      FIG. 9  is a schematic representation of an exemplary vehicle occupant protection system incorporating a micro gas generator utilizing a bore seal in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]      FIGS. 1   a - 1   c  show one embodiment of a conventional bore seal  930  as adapted for incorporation into a micro gas generator. Referring to  FIGS. 1   a - 1   c , an initiator or initiator assembly  932  is secured within a bore seal  930  for mounting within an associated element of a vehicle occupant protection system, for example. In the embodiment shown in  FIGS. 1   a - 1   c , bore seal  930  includes a body  934  and an annular wall  936  extending in a first direction from body  934  to define a cylindrical cavity for receiving an initiator or initiator assembly  932  therein. Another annular wall  940  extends from body  934  in a second direction, opposite the first direction, to define another cylindrical cavity adapted for housing the initiator electrodes  942 . A rear portion of bore seal  930  is configured to provide an interface mateable with a complementary connector of a wiring harness or other suitable initiator activation signal transmission medium.  FIG. 1   c  shows the bore seal  930  of  FIGS. 1   a  and  1   b  incorporated into a micro-gas generator (MGG) assembly. A casing  944  for containing a gas generant composition  945  therein is secured to bore seal  930  using adhesive application, ultrasonic welding, or other suitable methods. Bore seal  930  is typically formed from a metal or metal alloy using a suitable manufacturing process, such as die casting or machining. 
         [0012]      FIGS. 1   a - 1   c  also show features typically included in the mating portion of a conventional bore seal. As seen in  FIGS. 1   a  and  1   b , the bore seal incorporates a connector interface including an undercut  946  provided for connector and shorting clip retention, and a pair of radial slots  948  adapted to accommodate bumps formed on the shorting clip (not shown), to provide orientation for the clips and to prevent rotation of the clips. Bore seal  930  has one or more axially extending holes  950  through which initiator electrodes  942  extend. Other features may also be included in the bore seal depending upon a particular application. 
         [0013]    In conventional all-metal bore seals, the above-mentioned features are typically machined, a relatively expensive process. In the present invention, the connector mating features and other desired features normally machined into metal surfaces of the bore seal are instead molded into the bore seal, either as part of a completely molded bore seal formed from a relatively high-strength plastic material separate from the initiator, or as a polymeric bore seal element affixed to an associated metal bore seal element to form a bore seal including a polymeric interface portion adapted for coupling to the initiator activation signal transmission medium, and an initiator-receiving portion adapted for receiving the initiator therein. In general, the bore seal also incorporates features which enable mounting and sealing of the bore seal within a device, such as a seat belt pretensioner, which utilizes an initiator. 
         [0014]      FIGS. 2   a - 2   c  show a particular embodiment of a bore seal  230  in accordance with the present invention. In all of the embodiments described herein, polymer and/or metal portions of the bore seal may be joined together using suitable methods. Non-exclusive examples of such methods include ultrasonic welding, interference fits, snap fits, adhesive application, and heat crimping. An initiator assembly is affixed to the bore seal for use in a gas generating system or other suitable application. In the embodiment shown in  FIGS. 2   a - 2   c , an interface portion  229  of bore seal  230  is formed from a relatively high-strength polymer material, for example Polybutylene Terephthalate (PBT) or polycarbonate. An initiator  32  is then molded separately into initiator-receiving portion  236  of the bore seal. If required, initiator-receiving portion  236  may be formed from a polymer material (for example, a nylon) different from that of interface portion  230 , to accommodate processing requirements relating to the initiator or the interface portion. A casing  44  for containing gas generant material  45  therein is then attached to a shoulder or other suitable feature formed on bore seal  230 , as shown in  FIG. 2   c . All initiator assemblies referred to herein may be formed as known in the art. One exemplary initiator assembly construction is described in U.S. Pat. No. 6,009,809, herein incorporated by reference. 
         [0015]      FIGS. 3   a - 3   c  and  4   a - 4   c  show other embodiments of a bore seal in accordance with the present invention. In  FIGS. 3   a - 3   c  and  4   a - 4   c , the interface portions  329 ,  429  and the initiator-receiving portions  336 ,  436  of bore seals  330  and  430 , respectively, are incorporated unitarily into a piece of polymer material. Referring to  FIG. 3   a , bore seal  330  as molded includes a cavity  340  formed in the initiator receiving portion and adapted for receiving an initiator assembly  32  therein. The initiator assembly is then secured within cavity  340  using any suitable method. For example, in  FIG. 3   b  an insulator cup  142  is positioned over the initiator assembly and attached to bore seal  330 . Cup  142  may be used thusly to secure the initiator within cavity  340 . Cup  142  may be secured to the bore seal using any of a variety of methods, including adhesive attachment, heat-staking, or heat-crimping, for example.  FIG. 3   c  shows the bore seal of  FIGS. 3   a  and  3   b  incorporated into a micro gas generator. 
         [0016]    In  FIG. 4   a , an insulating material  152  is positioned between initiator assembly  32  and an annular wall  441  or similar structure formed in the initiator-receiving portion  436  of bore seal  430 , thereby creating an interference fit for retaining initiator assembly  32  within a cavity  440 . In a particular embodiment, insulator  152  is melt-pressed between initiator assembly  32  and a wall  441  or other portion of bore seal  430  to form a bond therebetween. In  FIG. 4   b , a retaining member  190  formed from a metal, polymer, or other suitable material engages both a portion of the initiator assembly and walls formed in cavity  440 , to retain initiator assembly  32  within cavity  140 . In  FIG. 4   c , initiator assembly  32  is secured in cavity  440  by portions  195  of bore seal  430  which are heat-crimped over portions of initiator  32 , over portions of an insulator cup (not shown), or over portions of another feature formed on or attached to the initiator. 
         [0017]      FIGS. 5   a - 5   c  show additional embodiments of a bore seal in accordance with the present invention. In  FIGS. 5   a - 5   c , a cavity  540  is formed in an initiator-receiving portion  536  of bore seal  599  to accommodate an initiator assembly  33  therein. In the embodiment shown in  FIGS. 5   a - 5   c , initiator assembly  33  has an integral insulating housing  33   a  already molded or otherwise formed thereon. Initiator assembly  33  may be secured within cavity  540  using one or more of the methods described herein. In the embodiment shown in  FIG. 5   a , initiator assembly  33  is secured within cavity  540  of bore seal  599  using a snap-fit. In the embodiment shown in  FIG. 5   b , initiator assembly  33  is secured within cavity  540  of bore seal  598  by crimping a portion of the bore seal over initiator assembly  33 . In the embodiment shown in  FIG. 5   c , initiator assembly  33  is secured within cavity  540  of bore seal  597  using adhesive application to bond housing  33   a  to bore seal  530 , snap-fitting, or other methods. Other securement methods are also contemplated. 
         [0018]    In  FIGS. 6   a  and  6   b , a cavity  640  is formed in the initiator receiving portion  636  of bore seal  630 . One or more snap-fit features (in  FIGS. 6   a  and  6   b , shown as resiliently deflectable peripheral tabs or wall portions  642  extending from bore seal  630  adjacent cavity  640 ) are provided for engaging the initiator assembly in a snap-fit to secure the initiator assembly within the initiator receiving portion. Wall portions  642  may include one or more retention features  644  formed therealong. An initiator or initiator assembly  33  is inserted axially into cavity  640 , causing resilient tabs  642  to deflect radially outward. Tabs  642  snap back to undeflected or substantially undeflected states when initiator assembly  33  has been fully inserted into cavity  640 . In particular embodiments, a reinforcing member in the form of a sleeve (of which various embodiments  650 ,  651  are shown in  FIGS. 6   a  and  6   b , respectively) is applied to the exterior of the support tabs  642  after positioning of the initiator within cavity  640 , thereby substantially preventing deflection of the tabs after insertion of the initiator into the cavity. This retains the initiator within the bore seal. 
         [0019]      FIGS. 7   a - 7   f  show yet another embodiment of a bore seal in accordance with the present invention. In the embodiment shown in  FIG. 7 , the initiator-receiving portion  736  of a bore seal  730  is formed from a metal or metal alloy, while the interface portion  729  of the bore seal incorporating the connector mating features is formed from a high-strength polymer material. Polymer portion  729  may be molded as a separate part and attached to metal portion  736  using one of the methods previously discussed, or other methods. Alternatively, polymer portion  729  may be molded directly onto metal portion  736 . In the embodiment shown in  FIG. 7   e , a portion of the initiator receiving portion  736  is crimped over a portion of the initiator assembly to secure the initiator assembly within the initiator receiving portion.  FIG. 7   f  shows a casing  44  secured to bore seal  730  of  FIG. 7   e . Casing  44  encloses a gas generant material  45  positioned in fluid communication with initiator  33 . In embodiments where the initiator receiving portion is formed from a metallic material, an insulating member (not shown) may be is positioned between each initiator electrode and the initiator receiving portion to insulate the electrode from the initiator receiving portion. 
         [0020]      FIG. 8  shows yet another embodiment  530  of a bore seal in accordance with the present invention. In  FIG. 8 , a grounding clip  510  is insert-molded into the polymeric portion of the bore seal, thereby eliminating the step of separately installing the ground clip in the bore seal. 
         [0021]    By separately molding the bore seal (or the portion of the bore seal that includes the connector mating features), the connector portion of the bore seal including slots, undercuts, and other features can be readily incorporated into the bore seal at a comparatively low cost. In addition, the range of materials usable for forming the connector features is greatly expanded, enabling the connector features to be molded using a relatively high-strength polymer material processed at relatively high molding temperatures and pressures and enabling other desirable aspects (for example, low moisture permeability) of various materials to be utilized. This reduces the manufacturing cost of the bore seal and increases the number of design options available with respect to the bore seal. 
         [0022]    Referring to  FIG. 9 , in a particular application, a micro gas generator  100  incorporating a bore seal as described herein is incorporated into a safety belt pretensioner  112  employed in a safety belt assembly  150  used in a vehicle occupant protection system  180 . Safety belt assembly  150  includes a safety belt housing  152  and a safety belt  160  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. Safety belt pretensioner  112  may be coupled to belt retractor mechanism  154  to actuate the retractor mechanism in the event of a collision. Gas generator  100  is adapted to actuate seat belt retractor mechanism  154  to pretension safety belt  160 . Typical seat belt retractor mechanisms which may be used in conjunction with safety belt  160  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. Safety belt assembly  150  may be in operative communication with (or may include) a crash event sensor  158  (for example, an inertia sensor or an accelerometer) that is in operative communication with a crash sensor algorithm (not shown) which signals actuation of belt pretensioner  112  via, for example, activation of an initiator (not shown in  FIG. 9 ) in micro gas generator  100 . U.S. Pat. Nos. 6,505,790 and 6,419,177 provide illustrative examples of pretensioners actuated in such a manner. Unless otherwise noted, elements of the pretensioner may be fabricated using methods known in the art. In addition, a gas generator incorporating a bore seal as described herein may be incorporated into any of a wide variety of alternative pretensioner designs. 
         [0023]    It will be understood that the foregoing descriptions of embodiments of the present invention are for illustrative purposes only. As such, the various structural and operational features herein disclosed are susceptible to a number of modifications commensurate with the abilities of one of ordinary skill in the art, none of which departs from the scope of the present invention as defined in the appended claims.