Abstract:
A flexible inflator provides enhanced features to an inflatable airbag restraint such as flexibility to facilitate installation in the tight spaces along the sides of a vehicle. The flexible inflator may include a housing with first and second ends made of corrugated metal. End caps are attached to each end of the cylindrical housing to form a pressure vessel. Combustible material, capable of generating inflation fluid, is positioned within a membrane inside the housing. An initiator is in communication with the combustible material, for initiating a combustible reaction within the housing. The housing is surrounded by a steel wire over-braid. The corrugated steel housing can be readily pierced without leaving a burr to damage the environmental seal. The corrugation also provides a plenum allowing gasses to readily flow from around the inflation fluid generant.

Description:
BACKGROUND OF THE INVENTION 
   1. The Field of the Invention 
   The present invention relates to a flexible airbag inflator. More specifically, the present invention relates to an airbag inflator with a corrugated metal housing that can be perforated to create inflation fluid exit ports, and bended without adversely affected the membrane-enclosed combustible material within the housing. 
   2. The Relevant Technology 
   Inflatable safety restraint devices, or “airbag restraints,” are mandatory on most new vehicles. Airbag restraints commonly contain a collision sensor, inflator, and an airbag or inflatable curtain. In the event of an accident, the collision sensor within the vehicle, such as an accelerometer, measures abnormal deceleration and triggers the inflator. The inflator is connected to the airbag which is typically housed in the steering wheel on the driver&#39;s side of a vehicle and in the dashboard on the passenger side of a vehicle. Airbags are normally housed in an inflated and folded condition to minimize space requirements. Upon receipt of the signal from the collision sensor, the inflator rapidly produces a quantity of inflation fluid or gas which fills the airbag and protects the passenger from harmful impact with the interior of the car. 
   Airbags have also been developed in response to the need for passenger protection from lateral impacts with the side of a vehicle&#39;s interior. This situation might occur when another vehicle collides with the side of the car, or when the car loses control and rolls over causing the side of car to repeatedly impact the ground. Side impact inflatable curtains are designed to prevent the head of a vehicle occupant from emerging through the window opening or from colliding with a collision surface at the side of the vehicle. The shape of the curtain generally conforms to the shape of the window area or side of the car adjacent the passenger&#39;s torso. Side inflatable curtains are typically housed in an uninflated and folded condition and attached to, or within, the roof rail of the vehicle behind a vehicle headliner. 
   With the ultimate premium on vehicle interior space, vehicle manufacturers are always seeking for new and creative ways to secure and house the curtain and the inflator within the vehicle. In certain circumstances, it is desirable to have the inflator conform to a curved portion of the vehicle frame. The problem with most inflators, however, is that they are not flexible. Thus, they cannot be mass produced for different vehicle applications. Accordingly, additional tooling and manufacturing is required which drives up costs. Further, with fixed and rigid inflator configurations, installation into the specific vehicle for which a known inflator is manufactured must be exact and precise. Thus, installation becomes more time consuming which drives up installation costs. 
   Some attempts have been made to provide a flexible inflator, but these inflators also suffer significant disadvantages. One known inflator includes a rubber housing. Often times, however, the exit ports in the rubber through which the hot inflation fluid must pass will deform, expand, or crack, under the high inflation pressure and hot expanding gasses. This can negatively affect the rate at which the inflation fluid inflates the curtain, and thus, inflation performance. Many known flexible inflators do not provide controlled diffusion of combustion pressures. Other inflators, while flexible, are not rigid enough to protect the gas generating material, which, if damaged, can also negatively affect the rate of evolving gas. Yet another problem with many flexible inflators is that they do not provide for high pressure containment for safe use in automotive applications. For example, in certain situations, it is desirable to use stored pressurized gas to create inflation fluid. Some inflators that provide flexibility, do so at the expense of being a pressure vessel. 
   Another problem with known inflators is that they do not account for the hot inflation gasses which could burn a passenger, even through the fabric of the curtain, during or immediately after inflation. Some known inflators may provide a heat sink, but again, these inflators sacrifice flexibility because the heat sink employed is rigid metal. Other flexible heat sinks can cause damage to the combustible materials or material seals because of burrs or exposed wires in the heat sink materials after inflation gas exits ports are pierced through the head sinks. 
   Thus, it would be an advancement over the prior art to provide a flexible inflator that can conform to the shape of the headliner or interior frame of a vehicle, yet won&#39;t damage the gas generating material or compromise inflation performance. It would be another advancement to provide such an inflator which has discrete exit ports that can withstand the heat and pressure of the expanding inflation fluid and not deform, thus preserving the rate of evolving gas. It would yet be another advancement to provide such an inflator that provides high pressure containment for safe use in automotive applications. It would yet be another advance to provide such an inflator with a heat sink for the inflation exiting fluid and ports that will not allow damage to the combustible material or the seal containing the combustible material. 
   Such an inflator is disclosed and claimed herein. 
   BRIEF SUMMARY OF THE INVENTION 
   The apparatus of the present invention has been developed in response to the present state of the art, and in particular, in response to the problems and needs in the art that have not yet been fully solved by currently available airbag curtain inflators. Thus, it is an overall objective of the present invention to provide an airbag/curtain inflator that is flexible without comprising inflation properties. 
   To achieve the foregoing advantages and objectives, and in accordance with the invention as embodied and broadly described herein in the preferred embodiment, a novel airbag/curtain inflator is provided. The inflator may include a housing having a first and second end. In one preferred embodiment, the housing is made of corrugated metal and is substantially cylindrical. A pair of end caps are attached to each end of the housing. 
   Combustible material may be positioned within the housing. The material is capable of generating inflation fluid upon ignition which fills an attached curtain. In one preferred embodiment, the combustible material is combustible solid fuel tablets coated with an ignition enhancer. The combustible material may be substantially enclosed by a membrane which defines a combustion chamber. The membrane may act as an environmental seal protecting the combustible material. The membrane in one embodiment is configured to expand and burst at a predetermined breakout pressure created by the inflation fluid. When the membrane bursts, inflation gas may escaped through exit ports perforated or bored in the housing. Because the housing is metal, the exit ports are discrete and resist deformation under the heat and pressure of the expanding inflation fluid. 
   A mesh covering may be positioned about the housing, assists in maintaining the inflator as a pressure vessel by limiting the axial expansion of the housing. The covering may also act as a heat sink for inflation fluid escaping through the covering. In one embodiment, the mesh covering is braided metal, preferably steel, wire which can stretch as the housing is flexed. Not only does the corrugated metal housing allow for flexing and expansion so that it can conform to a variety of configurations within a vehicle interior, but the corrugated housing also defines distal peak portions and proximal valley portions. The distal peak portions provide a surface for perforating the housing such that any perforation burrs are separated from the interior combustible material and the membrane. The peak portions also provide a series of points over which the wire braid can be placed which separates any potentially damaging wire ends from the membrane and combustible material. The housing may be detached from the membrane such that flexing of the housing does not directly translate to stretching or deformation of the membrane or internal combustible material. This configuration prevents damage which could adversely alter the rate at which the inflation fluid escapes the housing, or other inflation properties. The housing, end caps, and covering, may also comprise a pressure vessel to allow pressurized gas to be used as the inflation fluid generant. 
   An initiator may be positioned in communication with the combustible material for initiating a combustible reaction within the housing. The initiator may include a squib and may be integral with one of the end caps. 
   Accordingly, the inflator of the present invention provides a flexible inflator that can conform to the shape of a vehicle interior without damaging the combustible material with the housing. This inflator is advantageous because it provides discrete exit ports that can withstand the heat and pressure of the expanding inflation fluid and not deform, which preserves the inflation properties of the inflator. Another advantage of the inflator of the present invention is that it provides high pressure containment for safe use in automotive applications and includes a heat sink that will not damage the combustible material or a seal containing the combustible material. 
   These and other objects, features, and advantages of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In order that the manner in which the above-recited and other advantages and objects of the invention are obtained will be readily understood, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered to be limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: 
       FIG. 1  is a side cross sectional view of one embodiment of an airbag/curtain inflator according to the present invention; 
       FIG. 2  is side cross sectional view of a center portion of the airbag/curtain inflator of  FIG. 1 ; 
       FIG. 3  is a side cross sectional view of yet another embodiment of an airbag/curtain inflator according to the present invention; and 
       FIG. 4  is a side cross sectional view of another embodiment of an airbag/curtain inflator according to the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The presently preferred embodiments of the present invention will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout. It will be readily understood that the components of the present invention, as generally described and illustrated in the figures herein, could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of the embodiments of the apparatus, system, and method of the present invention, as represented in  FIGS. 1 through 4 , is not intended to limit the scope of the invention, as claimed, but is merely representative of presently preferred embodiments of the invention. 
   With particular reference to  FIG. 1 , an airbag inflator according to the present invention is generally designated at  10 . The inflator  10  includes a housing  12  having a first end  14  and a second end  16 . In one preferred embodiment, the housing  12  comprises corrugated steel. The housing  12  may be cylindrical with openings  18  defined by each end  14 ,  16  of the housing. In one embodiment, as discussed in greater detail below, the openings  18  are configured to received a first end cap  20  adjacent the first end  14  of the housing  12 , and a second end cap  22  adjacent the second end  16  of the housing  12 . The housing  12  may include a mesh covering  24  positioned about the housing  12 . The covering  24  has a first end  26  and a second end  28  and consists of braided metal wire. In one embodiment, the metal is steel. The braided nature of the covering  24  allows it to flex and expand as the housing  12  flexes and expands. Thus, the present invention allows for flexibility and expandability which facilitates attachment of the inflator to irregularly shaped vehicle interiors. The housing  12  should be of sufficient strength in combination with the covering  24 , to withstand the pressure and heat of expanding inflation fluid, yet should allow the corrugate to flex and expand. 
   The first end cap  20  is attached to the first end  14  of the housing  12 . A second end cap  22  is attached to the second end  16  of the housing  12 . In the embodiment of  FIG. 1 , the end caps  20 ,  22  each contain a stop portion  32  positioned within each end  14 ,  16  of the housing  12 . An inner end  34  of each stop portion  32  defines the space in which combustible material  36  is positioned. The stop portion  32  of each end cap  20 ,  22  could be integral with the end caps  20 ,  22  or a separate stud attached to each end cap  20 ,  22 . 
   As discussed in conjunction with  FIGS. 3 and 4  below, the end cap can be configured in a variety of ways to practice the teachings of this invention, including threaded caps that can be secured to an exterior or interior of the housing  12 . Additionally, each end cap  20 ,  22  may be secured to a respective end  14 ,  16  of the corrugated metal housing  12 , or to a respective end  26 ,  28  of the covering  24  positioned about the housing  12 . In the embodiment illustrated in  FIG. 1 , the stop portion  32  of each end cap  20 ,  22  is snugly positioned within the openings  18  of each end  14 ,  16  of the housing  12  with an outer end  38  of each end cap  20 ,  22  extending beyond respective ends  14 ,  16  of the housing  12 . The outer end  38  of each end cap  20 ,  22  is secured to the covering  24  by a crimped sleeve  40 . The sleeve  40  is preferably annular with a first end  42  fixed within a slot  44  within each end cap  20 ,  22 . A second end  46  of the sleeve is positioned about a portion of the covering  24 . The second end  46  is crimped to force a respective end  26 ,  28  of the covering  24  into an indentation  48  within each end cap  20 ,  22 , thus securing the covering  24  to the end caps  20 ,  22 . Because the corrugate housing  12  elongates when internal pressure is applied, it does not need to be directly attached by other means. However, in one alternative embodiment, the corrugate housing  12  may be sealed to the end caps  20 ,  22  by an o-ring placed between the corrugate housing  12  and the initiator  52  or the first end cap  20 . 
   The first end cap  20 ,  22  includes an opening  50  through which an initiator  52  is attached in sealing communication with the combustible material  36 . This sealing communication can be accomplished by laser welding, crimping, threading, O-ring, or other suitable hermetic seal. The housing  12 , first end cap  20 , second end cap  22 , and covering  24  are configured to form a pressure vessel suitable for containing pressurized gas. The housing has sufficient hoop strength to limit radial expansion of the gas and the covering  24  limits the axial expansion of the corregated housing  12  under the force of expanding gas. Accordingly, the present invention provides for high pressure retention of combustion gases. 
   It will be appreciated that the end caps  20 ,  22  can be configured in a variety of ways and attached to the housing  12  and/or covering  24  in a variety of ways to practice the teachings of this invention. For example the crimped sleeve  40  maybe part of an integrated sub-assembly of each end cap  20 ,  22 . The end caps  20 ,  22  may be attached to the housing  12  or covering  24  by threaded engagement, welding, epoxy, or other known methods. Additionally, either or both end caps  20 ,  22  may be configured to receive the initiator  52 . In a presently preferred embodiment, the end caps  20 ,  22  are made of steel. 
   The combustible material  36  is capable of generating inflation fluid when heated, ignited or when a combustible reaction is otherwise started. In the present invention, the combustible material  36  includes combustible solid fuel tablets coated with an ignition enhancer. In alternative embodiments, the combustible material  36  may include stored inert gas. One suitable stored gas is Argon. Other suitable combustible materials  36  may include any number of pyrotechnic ignitable materials, including, but not limited to powder, pellets, unitary masses, other gases with a heating device such as a pyrotechnic or heater. The combustible material  36  or generant is preferably compressed to maximize space. 
   The combustible material  36  is substantially enclosed by a membrane  60 . The membrane  60  is positioned within the housing  12  and defines a combustion chamber  62  in which the combustible material  36  reacts to form inflation fluid. In one preferred embodiment, is attached to the membrane  60 . It will be appreciated by those of skill in the art that there are different ways to attach combustible materials  36  to a membrane  60 , including, but not limited to adhesive bonding and friction. The membrane is constructed of a metalized film. One suitable film is Mylar®. In one embodiment, the membrane  60  forms an environmental seal around the combustible material  36  to protect it. The membrane  60  is configured to expand and burst at a predetermined breakout pressure created by the inflation fluid, after the combustible material  36  is ignited. 
   The initiator  52  is in communication with the combustible material  36 , for initiating a combustible reaction within the housing  12  and combustion chamber  62 . In the embodiment illustrated in  FIG. 1 , the initiator  52  is part of the subassembly of the first end cap  20 . A back end  66  of the initiator  52  includes an electrical connector  68  for connection to a collision sensor (not shown) which provides a signal to activate the initiator  52  and thus the inflator  10 . A front end  70  of the initiator  52  may be spaced from and adjacent to the combustible material  36 , but suitable for bursting through a bulkhead or membrane  60  to ignite the combustible material  36 . In one alternative embodiment, the front end  70  of the initiator  52  extends into the combustion chamber  62 . 
   The initiator  52  can be of any of a suitable type initiators  52  capable of starting a reaction in the combustion chamber  62 . In one preferred embodiment, the initiator  52  is a squib that is integrated within the end cap  20  subassembly. Other initiators  52  may include a bridgewire, spark discharge, heating or exploding element including wire or foil, pyrotechnic charge, or gas or heat generating devices. Initiator  52  material may take the form of pellets or powder, or these materials may simply surround the initiator  52 . 
   Referring now to  FIG. 2 , the corrugated housing  12  defines distal peak portions  76  and proximal valley portions  78 . The housing  12  defines exit ports  80 , through which inflation fluid or gas can escape into an airbag curtain. It will be appreciated by those of skill in the art the size and number of the exit ports  80 , together with the combustion properties of the combustible material  36 , allows the inflation fluid to escape from the housing  12  at a substantially predetermined rate. The metal housing  12  allows for discrete and predictable exit port  80  orifices which will not erode or split under the heat or pressure of expanding inflation fluids. Thus, the present invention significantly reduces undesirable gas flow variability. 
   The exit ports  80  may be created within the housing  12  by piercing or perforation. The housing  12  may be perforated in any location where any burrs  84  left by the creation of the exit ports  80  are separated from the protective membrane  60 . For example, as shown in  FIG. 2 , the housing  12  may be perforated adjacent the distal peak portions  76  to create an exit port  80  having burrs  84 . Alternatively, as shown in  FIG. 2A , the housing  12  may be perforated at a point between the distal peak portions  76  and the proximal valley portions  78  to create an exit port  80 A having burrs  84 A. In either embodiment, the housing  12  may be readily pierced without damaging the environmental seal or membrane  60 . 
   The corrugated housing  12  also provides a plenum  82  which allows inflation gasses to readily flow out from around the combustible material  36 . In one embodiment, the housing  12  is detached from and at least partially spaced apart from the membrane  60 . In this configuration, the housing  12  can be flexed or expanded without stretching the membrane  60  and adversely affecting the combustible material  36 . Thus, the present invention preserves the integrity of the combustible material  36  so that the rate of evolving inflation fluid is preserved. 
   In a preferred embodiment, exit ports  80  are pierced through the housing  12  prior to the application of the covering  24 . This eliminates damage to the covering  24  and prevents damage to the airbag curtain from exposed wire ends. It will be appreciated by those of skill in the art that the wire braid covering  24  acts as a heat sink to cool the inflation fluid as it exits the inflator  10 . Thus, the present invention reduces possible burn damage to vehicle passengers who come into contact with the inflated airbag. Other known materials with heat sink properties may be used for the covering  24 , including ceramics, graphite, and other composite materials. The wire braid covering  24  also functions to filter out particulates that may be by-products of the combustion reaction. These particulates may cause damage to the airbag curtain being inflated by the inflator  10 , if allowed to pass out of the inflator  10 . 
   The initiator  52  ruptures the membrane  60  and directly lights the gas generating or combustible material  36 . Inflation fluid forces the membrane  60  over the exit ports  80  in the corrugated housing  12 , and the inflation fluid bursts through the membrane  60  at a predetermined breakout pressure. The breakout pressure is determined in part by the thickness and tensile strength of the membrane  60  selected, and the type of combustible material  36  used. 
   Referring now to  FIG. 3 , an alternative inflator embodiment of the present invention is generally designated as  110 . The inflator  110  includes a corrugated cylindrical housing  112  having a first end  114  and a second end  116 . The housing  112  defines openings  118  defined by each end  114 ,  116 . The openings  118  are configured to received a first end cap  120  adjacent the first end  114  of the housing  112 , and a second end cap  122  adjacent the second end  116  of the housing  112 . The housing  112  may includes a suitable covering  124  positioned about the housing  112  which assists in maintaining the inflator as a pressure vessel and may also act as a heat sink. In the embodiment illustrated, the covering  124  is wire mesh. The covering  124  has a first end  126  and a second end  128 . 
   The end caps  120 ,  122  are each attached to the housing  112  and covering  124  with a weld ring  140 . The end caps  120 ,  122  each contain a stop portion  132  positioned within each end  114 ,  116  of the housing  112 . An outer end  138  of each end cap  120 ,  122  includes an annular extension  154 . The respective ends  114 ,  116  of the housing  112 , the respective ends  126 ,  128  of the covering  124 , and each weld ring  140 , are positioned adjacent the extension  154  of each end cap  120 ,  122  and welded together at a weld point  156 . In one embodiment, the weld ring  140 , housing  112 , and covering  124  are welded together for a first weld. The end caps  120 ,  122 , one of which may contain an initiator  152  for igniting combustible material  136 , are then welded to the first weld in a subsequent step. 
   The combustible material  136  is capable of generating inflation fluid when heated, ignited or when a combustible reaction is otherwise started. In the embodiment illustrated, the combustible material  136  includes combustible solid fuel tablets coated with an ignition enhancer. The combustible material  136  or generant is preferably compressed to maximize space. The combustible material  136  is substantially enclosed by a membrane  160 . The membrane  160  is positioned within the housing  112  and defines a combustion chamber  162  in which the combustible material  136  reacts to form inflation fluid. The membrane  160  is configured to expand and burst at a predetermined breakout pressure created by the inflation fluid, after the combustible material  136  is ignited. 
   The initiator  152  is in communication with the combustible material  136 , for initiating a combustible reaction within the housing  112  and combustion chamber  162 . The initiator  152  includes an electrical connector  168  for connection to a collision sensor (not shown) which provides a signal to activate the initiator  152  and thus the inflator  110 . The initiator  152  is suitable for bursting through a bulkhead or membrane  160  to ignite the combustible material  136 . Exit ports (not shown) are configured within the housing  112  to allow inflation fluid to exit the combustion chamber  162  and enter an airbag curtain (not shown). 
   Referring now to  FIG. 4 , another alternative inflator embodiment of the present invention is generally designated as  210 . The inflator  210  includes a corrugated cylindrical housing  212  having a first end  214  and a second end  216 . The housing  212  defines openings  218  defined by each end  214 ,  216 . The housing  212  may include a suitable covering  224  positioned about the housing  212  which assists in maintaining the inflator as a pressure vessel and may also act as a heat sink. In the embodiment illustrated, the covering  224  is braided steel. The covering  224  has a first end  226  and a second end  228 . A first end cap  220  is positioned adjacent the first end  214  of the housing  212 , and a second end cap  222  is positioned adjacent the second end  216  of the housing  212 . 
   In this embodiment, a stop  232  is positioned within the openings  218  of each end  214 ,  216  of the housing  212 . The stops  232  each have a tapered exterior portion  233  and exterior threads  235  configured within an outer end  238  of each stop  232 . The first and second end caps  220 ,  222  each have interior threads  237  configured to engage the exterior threads  235  of the stops  232 . The end caps  220 ,  220  are positioned about respective ends  226 ,  228  of the covering  224  which acts as an extension of the housing  212 . With the exterior threads  235  of the stop  232  in mating engagement with the interior threads  237  of the end caps  220 ,  222 , the ends  226 ,  228  of the covering  224  are clamped between the end caps  220 ,  222  and the stops  232  at the tapered exterior portion  233  of each stop  232 . With the end caps  220 ,  222  screwed to the stops  232  about the covering  224 , the tapered exterior portion  233  of each stop  232  prevents the stops  232  from exiting the housing  212 . In other embodiments, the stops  232  may be secured within the housing  212  by bonding, welding, latching, or other known attaching methods. The first end cap  220  is configured with external threads  239  for receiving a threaded initiator assembly  252 . 
   As with embodiments described above, the combustible material  236  is capable of generating inflation fluid when heated, ignited or when a combustible reaction is otherwise started. In the present invention, the combustible material  236  includes combustible solid fuel tablets coated with an ignition enhancer. The combustible material  236  is substantially enclosed by a membrane  260 . The membrane  260  is positioned within the housing  212  and defines a combustion chamber  262  in which the combustible material  236  reacts to form inflation fluid. The membrane  260  is configured to expand and burst at a predetermined breakout pressure created by the inflation fluid, after the combustible material  236  is ignited. 
   The initiator  252  assembly is in communication with the combustible material  236 , for initiating a combustible reaction within the housing  212  and combustion chamber  262 . The initiator  252  includes an electrical connector  268  for connection to a collision sensor (not shown) which provides a signal to activate the initiator  252  and thus the inflator  210 . The initiator  252  is configured to burst through a bulkhead or membrane  260  to ignite the combustible material  236 . Exit ports (not shown) are configured within the housing  112  to allow inflation fluid to exit the combustion chamber  162  and enter an airbag curtain (not shown). 
   The present invention may be embodied in other specific forms without departing from its structures, methods, or other essential characteristics as broadly described herein and claimed hereinafter. The described embodiments are to be considered in all respects only as illustrative, and not restrictive. The scope of the invention is, therefore, indicated by the appended claims, rather than by the foregoing description. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.