Abstract:
The present invention is best described as a gas generator including an inflator housing  12  containing an initiator assembly  18  and a propellant bed  44  in ignitable communication with the initiator assembly  18.  The gas generator  10  further contains a filter body  14  fixed to the inflator housing  12  and coaxially aligned therewith, wherein the filter body  14  at least contains a first filter  56  and a second filter  62  such that the second filter  62  is in coaxial and linear relation with the first filter  56.  If desired, the filter body  14  may additionally contain at least one perforated disc  50,  at least one spacer member  54,  and at least one additional filter member  62.  Design requirements or specific applications determine the arrangement and addition of these components in the filter body  14.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    The present application claims the benefit of U.S. Provisional Application No. 60/359,686 filed on Feb. 26, 2002. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates to vehicle occupant protection systems, and specifically to a gas generator or inflator that provides an adjustable gas output rate and tailored thrust for inflators associated with airbelts or side impact airbags, for example.  
         BACKGROUND  
         [0003]    Ongoing improvements in vehicle occupant protection systems include the advent of sub systems such as a side impact airbag and an airbelt system. To facilitate such systems in a variety of vehicles, a gas generator featuring an adjustable gas output rate and a tailored thrust is desired. Although many of the state-of-the-art gas generators are useful in these contexts, ready tailoring of the gas output and the attendant inflator thrust presents certain advantages over known inflators.  
         SUMMARY OF THE INVENTION  
         [0004]    An airbelt inflator ( 10 ) is provided for supplying and directing gas from the combustion of pyrotechnic materials into an inflatable safety belt or airbag. The inflator ( 10 ) preferably includes a substantially cylindrical inflator body ( 12 ) as well as a substantially cylindrical filter body ( 14 ). An initiator assembly ( 22 ) including an initiator body ( 24 ), an igniter ( 26 ), and if desired, a booster charge ( 40 ), is fixed to a first end ( 18 ) of the gas generator ( 10 ) and ignites a gas generant bed ( 44 ) upon inflator ( 10 ) operation. The bodies  12  and  14  are joined at a central circumferential weld ( 16 ) having a perforated disc  50  radially extending within the filter body  14  for separation of bodies  12  and  14 .  
           [0005]    If desired, a substantially cylindrical elongate spacer member ( 30 ) rests upon a ledge ( 34 ) within the inflator body ( 12 ), and includes a quantity of booster propellant ( 40 ). A plurality of apertures fluidly connect a first booster chamber ( 38 ) of the elongate spacer member ( 30 ) with a second propellant chamber ( 42 ) containing a quantity of main propellant ( 44 ). The second chamber ( 42 ) is separated by a perforated cushion ( 46 ) and burst shim ( 48 ) from a third chamber formed by the interior of a cylindrical spacer member ( 54 ).  
           [0006]    Spacers having different dimensions, and thus creating spaces having different volumes can be positioned in the inflator to vary the reduction of gas output rate. A filter ( 56 ) and second perforated disc ( 58 ) separate the third chamber from a fourth chamber, also an interior of a second cylindrical spacer member ( 60 ). An output enhancer or second filter ( 62 ) is positioned adjacent the fourth chamber, and attenuates or increases the rate of gas output through a nozzle ( 64 ) positioned at an end of the inflator ( 10 ) by reducing or increasing the available flow area for gas to exit the inflator. Output enhancers having different interstitial densities may be positioned in the inflator ( 10 ) to tune the gas output for varying rates of inflation. Stated another way, output enhancers having relatively more or less metal mesh per cubic centimeter than the first filter ( 28 ) facilitate an increase or decrease in the gas pressure over time.  
           [0007]    In sum, the present invention is best described as a gas generator including an inflator housing containing an initiator assembly and a propellant bed in ignitable communication with the initiator assembly. The gas generator further contains a filter body fixed to the inflator housing and coaxially aligned therewith, wherein the filter body at least contains a first filter and a second filter such that the second filter is in coaxial and linear relation with the first filter. If desired, the filter body may additionally contain at least one perforated disc, at least one spacer member, and at least one additional filter member. Design requirements or specific applications determine the arrangement and addition of these components in the filter body.  
           [0008]    The interstitial volume of the first filter is equal to, greater than, or less than the interstitial volume of the second filter. Stated another way, the metallic mesh density, that is the total grams per cubic centimeter of metal in the first filter is either greater than, less than, or equal to the metallic mesh density for the second filter. It will be appreciated that “density” as used herein refers to the total volume of metal rather than the density inherent to the type of metal as a physical property. A preferred embodiment actually contains first and second filters made from the same metal but having different metal volumes as described above. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0009]    [0009]FIG. 1 is a cross-sectioned view of a gas generator in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0010]    Referring to FIG. 1, there is shown a sectioned side view of an airbelt inflator  10  according to a preferred embodiment of the present invention. Inflator  10  is designed primarily for supplying and directing gas from the combustion of pyrotechnic materials into an inflatable vehicle safety airbelt or a side impact airbag, but is not limited thereto. Exemplary, but not limiting airbelts are described in U.S. Pat. Nos. 6,439,601, 6,116,137, 6,170,863, 6,145,873, and 6,142,512, the teachings of which are herein incorporated by reference.  
         [0011]    Inflator  10  includes a substantially cylindrical inflator body  12 , preferably metallic, as well as a substantially cylindrical filter body  14 , also preferably metallic. Inflator body  12  is preferably slightly smaller in diameter than filter body  14 , however, they might be of similar dimensions or inflator body  12  might even be larger than filter body  14  without departing from the scope of the present invention. In a preferred embodiment, the component body parts  12  and  14  are welded together along a circumferential weld  16 , however, some other attachment method such as threads, crimping, or even an adhesive might be used without departing from the scope of the present invention. Inflator  10  preferably has a first end  18  and a second end  20 . An initiator assembly  22 , preferably metallic, is positioned within first end  18 , and secured by crimping inflator body  12  in a conventional manner. Initiator assembly  22  includes an initiator body  24  with an attached igniter  26 . It should be appreciated that some other attachment method such as mating threads or a snap-fit or press-fit connection could be used rather than crimping to hold initiator assembly  22  in place. An O-ring  28 , that can be a conventional elastomeric material, preferably encircles initiator body  24 , and fluidly seals first end  18  of inflator body  12 . The igniter  26  or squib has a set of electrical contacts  28 , preferably accessible from first end  18 . Igniter  26  may be any suitable known igniter, for instance, the igniter taught in U.S. Pat. No. 5,934,705, herein incorporated by reference, and is preferably communicates with a known crash sensor algorithm typically used in a vehicle occupant protection system, whereby it can be activated in a conventional manner.  
         [0012]    In a first embodiment, initiator body  24  rests upon a substantially cylindrical spacer member  30  having a perforated end plate  32 , the spacer member  30  abutting an interior ledge  34  integral to an inner wall of inflator body  12 . As such, when first end  18  is crimped, initiator assembly  22  and spacer member  30  are held securely in place between first end  18  and ledge  34 . In an embodiment having mating threads on initiator body  24  and inflator body  12 , twisting of initiator body  24  relative to inflator body  12  could similarly secure the components rather than crimping the inflator body  12 .  
         [0013]    Spacer member  30  preferably includes an elongate sidewall  36  that spaces initiator assembly  22  from end plate  32 , creating a first chamber  38 . In a preferred embodiment, a booster charge  40  as well as an autoignition material are placed in cavity  38 , and are ignited by igniter  26  in a conventional manner. A second chamber  42 , is formed opposite perforate end plate  32  and contains the main propellant charge  44 . As shown in FIG. 1, end plate  32  separates the first chamber  38  from the second chamber  42 . The charge or gas generant composition may be any suitable propellant known in the art, and preferably consists of a nonazide propellant in tablet form. Exemplary, but not limiting compositions are described in U.S. Pat. Nos. 5,872,329, 5,756,929, and 5,386,775, herein incorporated by reference. A cushion  46  is preferably placed adjacent the main propellant charge  44 , and assists in cushioning the propellant tablets against abrasion and degradation during normal vehicular operation. A burst shim  48  is positioned adjacent cushion  46 , and is ruptured shortly after ignition of propellant charge  44  in a conventional manner. Inflator  10  is preferably assembled by first welding the body components  12  and  14 , then serially positioning the interior components in coaxial alignment and in an innermost to outermost fashion, i.e. inserting those components adjacent weld union  16  first, and inserting the components adjacent first end  18  or second end  20  last.  
         [0014]    In a preferred embodiment, the components situated within filter housing  14  include a perforated disc member  50  is preferably positioned to abut a cylindrical end surface  52  of inflator body  12 , and is adjacent weld union  16 . An open-ended substantially cylindrical spacer  54  is preferably positioned adjacent disc member  50  on a first side, and is adjacent a filter  56  on a second side. Filter  56  is preferably a well-known conventional metallic mesh filter provided by Wayne Wire Cloth of Hillman, Mich. or by Expan Metal of Saginaw, Mich. however, some other suitable type of filter might be substituted. Filter  56  removes combustion slag from the inflation gas in a conventional manner, and also serves as a heat sink to lower the temperature of the inflation gas leaving inflator  10 .  
         [0015]    In a preferred embodiment, a second perforated disc  58  is positioned adjacent filter  56 , outwardly toward second end  20  and abuts a second substantially cylindrical spacer  60 . Next to spacer  60  is an output enhancer or second filter  62 , preferably a metallic mesh filter similar to filter  56  accordingly, the metal used in filters  56  and  62  is preferably the same, however, the density of the metal, or gm/cm 3  may differ to facilitate either attenuated or increased flow through filter body  14 . A nozzle  64 , preferably a single metallic piece, is positioned adjacent output enhancer  62  and preferably includes a circumferential O-ring  66  similar to O-ring  28 , creating a fluid-tight seal at second end  20 . In a preferred embodiment, second end  20  is crimped to secure the various components therein, however, mating threads on nozzle  64  and filter body  14  might be used instead.  
         [0016]    Inflator  10  is relatively small, lightweight, and easy to manufacture. In addition, the various components positioned in inflator body  12 , and in particular in filter housing  14 , can be positioned and organized in a wide variety of ways. Because each combination of filters, discs, enhancers, spacers, and a nozzle produces different gas output characteristics, the present invention allows the inflator&#39;s output to be tuned for different applications. For example, one embodiment of the present invention includes a first perforated disc  50  having a plurality of apertures  68 , and a second perforated disc  58  having a single central aperture  70 . An alternative embodiment could include the same discs, but with switched positions, resulting in differing gas flows. Numerous other arrangements are possible and additional discs or filters might even be positioned in filter body  14  for other applications.  
         [0017]    In the event of an impact, sudden vehicle deceleration, or other desired condition, an electrical signal is sent to igniter  26  from an onboard electronic controller (not shown) in a conventional manner. Igniter  26  subsequently ignites the gas generant booster tablets located in first cavity  38 . Ignition of booster tablets  40  results in a relatively rapid ignition of the main charge tablets  44  in second cavity  42 . Ignition of main charge  44  results in the very rapid creation of combustion gases in inflator body  12 , and a consequent very rapid rise in the internal gas pressure in inflator body  12 . When the internal gas pressure has risen to a sufficient level, it ruptures burst shim  48  in a conventional manner. Thenceforth, the gas flows into filter body  14 , through the various components, and out nozzle  64  into an associated airbelt or airbag (not shown). In a preferred embodiment, inflator  10  is positioned in a vehicle B-pillar, and is operable to direct inflation gas into an inflatable safety restraint belt when activated by a vehicle sensing system. However, inflator  10  might also be positioned in a vehicle C-pillar, or even elsewhere in the vehicle. Furthermore, inflator  10 , although especially useful in vehicle airbelts, may also be applicable in other vehicle occupant protection airbags.  
         [0018]    In a second embodiment, the filter body  14  may contain fewer components than those described above. The components that are included, however, are still all coaxially aligned with a longitudinal axis  72  extending through the inflator body  12  and the filter body  14 . For example, the filter body  14  might simply contain the following components arranged serially in an axially outward fashion from the weld union  16  to the second end  20 : the first perforated disc  50 , the first filter  56 , the second filter  62 , and the nozzle  64 . Upon inflator operation, gas produced from combustion of the propellant  44  is first routed through perforated disc  50  from inflator housing  12 . The gas then proceeds through filter  56  for filtration and cooling thereof. Next, the gas passes through filter  56  for filtration and cooling thereof. Next, the gas passes through filter  62  for the desired modification of the attendant gas flow and/or thrust. Finally, the gas passes through the nozzle  64  now characteristic of the various thrust, temperature and flow properties imparted by passage through filter housing  14 .  
         [0019]    Several situations illustrate how the filters are believed to work together to modify the gas pressure over time:  
         [0020]    1) First, if the metal mesh density, or gm/cm 3  of metal in filter  56  is greater than -that of filter  62  (all other things being equal, e.g. volume and type of metal used) than the chamber pressure would exhibit a relatively gradual increase over time.  
         [0021]    2) Secondly, if the metal mesh density, or gm/cm 3  of metal in filter  56  is less than that of filter  62  (all other things being equal, e.g. volume and type of metal used) than the chamber pressure would exhibit a sharp increase over a relatively shorter period of time (i.e. exhibit a much steeper slope).  
         [0022]    3) Thirdly, if the metal mesh density, or gm/cm 3  of metal in filter  56  equaled that of filter  62  (all other things being equal, e.g. volume and type of metal used) than the chamber pressure would exhibit an increase intermediate of situations (1) and (2) over time.  
         [0023]    It should be noted that the metal mesh filters  56  and  62  will preferably contain from 35-60% by volume of metal mesh with respect to the total interstitial volume represented in each filter. In general, the interstitial volume is inversely related to the metallic mesh volume in each filter. Stated another way, the greater the density of metal mesh, the lesser the interstitial volume within the same filter.  
         [0024]    Finally, as noted above, the other components may also be optimized to facilitate various gas flow and temperature regimes based on design requirements. For example, gas thrust can be modified by combining perforated discs and spacers to create either a throttling or venturi type of effect. As such, altering the number of perforations or gas orifices in a respective disc, for example, will necessarily alter the gas flow rate. The use of a spacer following a perforated disc, therefore, could facilitate the cooling and expansion of gases as determined by customer requirements.  
         [0025]    In essence, the present invention permits tailoring of gases flowing out of the inflator body  12  by fluid communication with a filter body  14  specifically designed for various applications such as a side-impact or an airbelt, for example. Stated another way, the filter body  14  taken as a whole could be viewed as a gas flow modifier by virtue of the many permutations or combinations of components as described above.  
         [0026]    The present description is intended for illustrative purposes only, and should not be construed to limit the breadth of the present invention in any way. Thus, those skilled in the art will appreciate that various modifications, additions, and alterations to the presently disclosed embodiments might be made without departing from the intended scope as determined by the appended claims.