Abstract:
A gas generator contains a housing containing an end closure assembly. An annular end closure is fixed within an annular igniter retainer thereby forming an annular wall for retention of an associated igniter. A first base portion of the annular end closure, and a second base portion of the annular igniter retainer are fixed together, by projection-welding for example, thereby facilitating a cost-effective seal about the igniter when assembled therewith.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application Ser. No. 61/268,423 filed on Jun. 12, 2009. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to gas generating systems and, more particularly, to end closure assemblies and elements thereof usable for closing and/or sealing a housing of a gas generating system, such as an inflator or gas generator. 
     When manufacturing an inflator or gas generator, an igniter or initiator is typically sealed to the gas generator by machining a body bore seal, and structurally welding the body bore seal to the base of the associated inflator. The igniter is then subsequently sealed within the inflator by forming a sealing interface with the body bore seal. The process is not only relatively expensive, but is time-consuming as well. 
     When manufacturing an inflator or gas generator, yet another consideration is the strength and robustness of the housing or pressure vessel. Oftentimes, special considerations must be taken to fortify the structural design of the pressure vessel, increasing the manufacturing complexity and cost of the inflator. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings illustrating embodiments of the present invention: 
         FIG. 1  is an exploded view of an end closure sub-assembly in accordance with an embodiment of the present invention. 
         FIG. 2  is an assembled view of the end closure sub-assembly shown in  FIG. 1 . 
         FIG. 3  is an exploded view of another end closure sub-assembly in accordance with an embodiment of the present invention, incorporating the sub-assembly shown in  FIG. 2 . 
         FIG. 4  is an exploded view of an end closure assembly in accordance with an embodiment of the present invention, incorporating the sub-assembly shown in  FIG. 3 . 
         FIG. 5  is a cross-sectional side view of an exemplary gas generating system incorporating the end closure assembly shown in  FIG. 4 . 
         FIG. 6  is a schematic view of an airbag system and a vehicle occupant protection system incorporating a gas generating system including an end closure assembly in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is an exploded view of an end closure sub-assembly  10  in accordance with an embodiment of the present invention.  FIG. 2  is an assembled view of the end closure sub-assembly shown in  FIG. 1 . Sub-assembly  10  includes an end closure  12  configured for attachment to a housing  52  (see  FIG. 5 ) of a gas generating system for closing and/or sealing the housing, and an initiator retainer  14  attached to end closure  12 . In the embodiment shown in  FIGS. 1 &amp; 2 , end closure  12  has a first base portion  12   a  and a first wall  12   b  extending along a periphery of the first base portion  12   a . In the particular embodiment shown in  FIGS. 1 &amp; 2 , a flange  12   c  extends outwardly from wall  12   b . In other embodiments, flange  12   c  is not included. End closure base portion  12   a  includes an opening  12   d  for receiving a portion of an associated initiator  18  therein. Base portion  12   a  may alternatively include multiple openings  12   d  for receiving multiple associated initiators therein; it will be appreciated that the openings  14   d  in the second base portion  14   a  (described below) will correspond to the number of openings  12   d.    
     In the particular embodiment shown in  FIGS. 1 &amp; 2 , opening  12   d  is provided in an initiator-receiving portion  12   e  of base portion  12   a . Initiator-receiving portion  12   e  is connected to base portion  12   a  by a wall  12   f  and extends from base portion  12   a  in a direction toward an interior of the gas generating system when the end closure is attached to the system housing. This enables the terminals or contacts  28  of the initiator  18  to be recessed within the end closure as shown in  FIG. 5  for protection. 
     In the embodiment shown, initiator-receiving portion  12   e  and a first annular wall  12   f  extend from a central portion of the end closure  12 . However, any initiator-receiving portion and its associated wall may be spaced apart from the center of the end closure, depending on the design considerations and geometry of a particular gas generating system. 
     Initiator-receiving portion  12   e  may be fabricated using any suitable technique, depending on such factors as the materials from which the end closure is formed, the shape of the initiator-receiving portion, and other requirements of a particular application. In one embodiment, end closure  12  is formed from a metallic material and initiator-receiving portion  12   e  and wall  12   f  are drawn in the material. In another embodiment, end closure  12  is formed from a polymer material and initiator-receiving portion  12   e  and wall  12   f  are molded into the base portion  12   a.    
     End closure  12  may be formed form any suitable material (for example, a metal, metal alloy, or polymer) suitable for the requirements of a particular application. 
     Referring again to  FIGS. 1 &amp; 2 , initiator retainer  14  has a base portion  14   a  including a formed portion or second annular wall  14   b  extending in a direction toward an interior of the gas generating system when the end closure is attached to the system housing. Formed portion  14   b  defines an opening  14   d  configured for receiving a portion of initiator  18  therein. As shown in  FIGS. 1 &amp; 2 , when retainer  14  is joined to end closure  12 , the second annular wall  14   b  is joined in nested relationship over first annular wall  12   f , respectively. Stated another way, as shown in the embodiment of  FIGS. 1 &amp; 2 , the shape of metallic initiator retainer  14  substantially conforms to the shape of metallic end closure  12 , thereby facilitating nested relationship of retainer  14  over end closure  12 . When joined in this manner, the juxtaposed annular walls  14   b  and  12   f  form an annular wall  15  for containment, seating, and sealing of an initiator  18 , as described below. 
     However, in alternative embodiments, the initiator retainer  14  may have any shape suitable for the requirements of a particular application. Embodiments of the initiator retainer  14  include features which facilitate attachment of the initiator retainer  14  to the end closure  12 . In the examples shown in  FIGS. 1 &amp; 2 , retainer  14  is secured to end closure  12  by projection welding together abutting sections of their respective base portions  14   a  and  12   a . In one embodiment, the overall wall thickness of the housing may be substantially reduced by 35 to 40% of its original thickness, by virtue of the reinforced area of the welded base portions  12   a  and  14   a . For example, it has been found in one embodiment that the wall thickness may be reduced from a typical thickness of about 2.2 millimeters to about 1.4 millimeters. As a result, the pressure vessel strength is substantially enhanced, by essentially doubling the base material thickness, while minimizing the overall housing thickness required. Other base and housing thicknesses may be iteratively determined, depending on the type of inflator, and depending on the ignition and gas generation chemistry employed. Other modes of attachment are also contemplated depending on the geometries of the end closure  12  and the initiator retainer  14 , and other design, materials, and operational factors. 
     In one embodiment, shown in  FIGS. 1 &amp; 2 , initiator retainer  14  is made from a metallic material and formed portion or second annular wall  14   b  is fabricated by drawing a portion of the initiator retainer material in the direction shown. However, it will be realized that alternative configurations suitable for receiving the initiator  18  therein may be utilized, and that other suitable fabrication methods may be used to produce such alternative configurations. In addition, retainer  14  can be made from any other suitable material (for example, a polymer). 
     In the embodiment shown, formed portion or second annular wall  14   b  is provided in a central portion of the initiator retainer  14 . However, any formed portion(s)  14   b  of the initiator retainer may alternatively be spaced apart from the center of the initiator retainer, depending on the design considerations and geometry of a particular gas generating system. 
     Formed portion or second annular wall  14   b  may be stepped as shown in  FIGS. 1 &amp; 2  to meet processing requirements of the initiator retainer material (for example, in the case of a metallic retainer), to facilitate recessed mounting of the initiator as shown in  FIG. 5 , or to meet other design requirements of a particular gas generating system. 
     In the embodiment shown in  FIGS. 1&amp;2 , a wall  14   c  extends along a periphery of the base portion  14   a , for engaging or helping to contain another element of the gas generating system. However, in alternative embodiments, wall  14   c  may be omitted if desired. 
     Initiator retainer  14  may be formed from any suitable material, for example a metallic material or a polymer material. Initiator  18  may be any suitable initiator known in the art. One exemplary initiator construction is described in U.S. Pat. No. 6,009,809, incorporated herein by reference. In the embodiment shown in  FIGS. 1-4 , a third annular wall  14   g  contiguous with formed portion or second annular wall  14   b  is structured to enable crimping of the wall  14   g  over a portion of initiator  18 , to retain the initiator in the retainer  14 . Other methods (for example, press-fitting or adhesive application) of securing the initiator to the retainer are also contemplated. 
     If desired, a resilient seal  90  (such as an o-ring seal) or other type of seal may be positioned between the initiator  18  and the retainer  14  to prevent the escape of generated gases through the initiator-retainer interface. 
     Referring to  FIG. 4 , if desired, a connector retainer  30  may be incorporated into the end closure assembly for retaining a connector (not shown) coupled to the initiator terminals  28  when the gas generating system is installed in a vehicle or other device. The connector operatively couples the initiator  18  to a device or mechanism for actuating the initiator when the need for generated gases arises. 
     Referring now to  FIG. 5 , an end closure assembly  11  as shown in  FIG. 4  is shown incorporated into a gas generating system  50 . System  50  has a housing  52 , wherein the housing  52  is formed from a first housing portion or cap  54  and an end closure assembly or base  11  secured to the first housing portion  54 , so as to form a substantially hermetic seal between the first housing portion  54  and the end closure assembly  11 . Housing  52  has one or more gas exit apertures  57  formed therein to enable fluid communication between an interior of the housing and an exterior of the housing upon activation of the gas generating system. 
     A tube  26  may be positioned within the gas generating system to enclose a portion of initiator  18  and for receiving a booster material  60  in an interior thereof. Tube  26  is generally cylindrical and may be secured within housing  52  by welding or any other suitable method. Tube  26  has at least one opening  91  formed therein to enable fluid communication between the interior of the tube and an exterior of the tube upon activation of the gas generating system. Tube  26  may be extruded, roll formed, or otherwise metal formed and may be made from carbon steel, stainless steel, or any other suitable material. In a particular embodiment, tube  26  is formed from a thermally-conductive material to facilitate heat transfer between a heat-activated auto-ignition material (not shown) and a portion of the gas generating system housing in thermal contact with tube  26  and exposed to elevated temperatures occurring on the exterior of the housing, due to a fire for example. Ignition of the auto-ignition material produces ignition of booster material  60  or gas generant material in thermal communication with the auto-ignition material, in a manner known in the art. 
     A plurality of annular gas generant wafers  62  are stacked around and adjacent tube  26 . In the embodiment shown in the drawings, wafers  62  are annular in shape and each wafer  62  has substantially the same dimensions. However, the wafers may have any of a variety of alternative shapes positionable within cavity  28 . In addition, other, alternative forms of gas generant (for example, tablets) may be used. Examples of gas generant compositions suitable for use in the embodiments of the present invention are disclosed in U.S. Pat. Nos. 5,035,757, 6,210,505, and 5,872,329, incorporated herein by reference. However, the range of suitable gas generants is not limited to that described in the cited patents. 
     Referring again to  FIG. 5 , appropriately shaped pads or cushions  64  may be provided at one or more ends of the stack of gas generant wafers  62  for holding the gas generant wafers in place and/or for cushioning the gas generant wafers against vibration and impact. Cushions  64  may be formed from a ceramic fiber material, for example. 
     Booster material  60  may be positioned in tube  26  to facilitate combustion of gas generant  62 . Activation of initiator  18  produces combustion of the booster material, thereby effecting ignition of gas generant material  62  in a manner known in the art. 
     A quantity of a known heat-activated auto-ignition material (not shown) may be positioned within the gas generating system so as to enable fluid communication between the auto-ignition material and any associated gas generant material and/or any associated booster material upon activation of the gas generating system. The auto-ignition material is a pyrotechnic material which is ignited by exposure to a temperature lower than the ignition temperature of the associated gas generant. As is known in the art, the auto-ignition material is ignited by heat transmitted from an exterior of the system housing to the interior of the housing due to an elevated external temperature condition (produced, for example, by a fire). Combustion of the auto-ignition material results in combustion of the associated gas generant, either directly or through intervening combustion of the booster material. Suitable auto ignition materials are known to those skilled in the art. Examples of suitable auto-ignition materials are nitro-cellulose based compositions and gun powder. 
     A filter  78  may be incorporated into the inflator design for filtering particulates from gases generated by combustion of gas generant material  62 . In general, filter  78  is positioned between any gas generant material in the housing and any gas exit apertures  57  formed in housing  52 . In the embodiment shown in the drawings, filter  78  is positioned between initiator retainer wall  14   c  and a similar wall  80   b  formed along a periphery of a filter retainer  80  and aligned with wall  14   c . Filter retainer  80  is secured within housing  52  using any suitable method. The filter may be formed from one of a variety of materials (for example, a carbon fiber mesh or sheet) known in the art for filtering gas generant combustion products. 
     In operation, the gas generant material  62  is ignited by activation of first initiator assembly  18  and the resulting ignition of booster material  30 . Gases resulting from the combustion of the gas generant flow through filter  78 , exiting the gas generating system through gas exit openings  57 . 
     In yet another aspect of the invention, and as inherently shown in the Figures, a method of manufacturing an inflator, or more specifically, a method of sealing a gas generant igniter within an inflator, is described by the following steps:
         1. Providing an annular end closure plate  12  having a predetermined first annular wall shape;   2. Providing an annular igniter retainer  14  having a second annular wall shape substantially congruent to and conforming to the shape of the annular end closure plate  12 ;   3. Overlaying the end closure plate  12  with the annular igniter retainer  14  to juxtapose the second annular wall shape and the first annular wall shape;   4. Welding or otherwise fixing the annular igniter retainer to the end closure plate;   5. Providing an annular seal for seating within the second annular wall shape;   6. Inserting an igniter through the juxtaposed first and second annular walls; And   7. Crimping or otherwise sealing the igniter within the annular igniter retainer.
 
It will be appreciated that the inflator is otherwise manufactured as known in the art and may for example, incorporate known gas generant, booster, and ignition compositions. Other structural features of the inflator may be made as known to one of ordinary skill in the art.
       

     It will be appreciated that inflators or gas generators manufactured in accordance with the present invention enjoy at least one or more of the following benefits. The present method of sealing an igniter within a gas generator, inherent within the end closure assembly described  11  herein, provides a relatively low-cost method of sealing the inflator. Furthermore, the relatively-expensive body bore seal is eliminated as is the relatively expensive and time-consuming structural weld necessitated when employing the body bore seal. The present end closure assembly  11  may be adapted to various initiator and connector retainers, and therefore presents a broad solution to many types of inflators. Additionally, the present end closure assembly presents a relatively strong pressure vessel given the increased relative thickness of the base, a doubling of the base wall thickness for example. 
     Referring to  FIG. 6 , in a particular application, an embodiment of a gas generating system  50  incorporating the features described above is incorporated into an airbag system  100 . Airbag system  100  comprises a housing  102  having a rupturable frontal closure  114 , an airbag  116 , and a gas generating system  50  in accordance with an embodiment of the present invention. Airbag system  100  may include (or be in communication with) a crash event sensor  210  (for example, an inertia sensor or an accelerometer) including a known crash sensor algorithm that signals actuation of one or more of initiators  18   c  and  20   c  previously described. 
     Referring again to  FIG. 6 , any embodiment of a gas generating system  50  incorporating the features described above (or an airbag system including such a gas generating system) may be incorporated into a broader, more comprehensive vehicle occupant protection system  180  including additional elements such as, for example, a safety belt assembly  150 .  FIG. 6  shows a schematic diagram of one exemplary embodiment of such a protection system. 
     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 refractor 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 with which the safety belt embodiments of the present invention may be combined are described in U.S. Pat. Nos. 6,505,790 and 6,419,177, each incorporated herein by reference. 
     Safety belt system  150  may include (or 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, previously incorporated herein by reference, provide illustrative examples of pretensioners actuated in such a manner. 
     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.