Patent Publication Number: US-2010109295-A1

Title: Gas generating system

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of provisional application Ser. No. 60/686,906, filed on Jun. 2, 2005. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to gas generating systems and, more particularly, to filterless gas generating systems for use in applications such as inflatable occupant restraint systems in motor vehicles. 
     Installation of inflatable occupant protection systems as standard equipment in all new vehicles has intensified the search for smaller, lighter and less expensive protection systems. Accordingly, since the inflation gas generator used in such protection systems tends to be the heaviest and most expensive component, there is a need for a lighter, more compact, and less expensive gas generating system. 
     A typical gas generating system includes cylindrical steel or aluminum housing having a diameter and length related to the vehicle application and characteristics of a gas generant composition contained therein. Because inhalation by a vehicle occupant of particulates generated by gas generant combustion during airbag activation can be hazardous, it is desirable to remove particulate material, or slag, produced during combustion of the gas generant. Thus, the gas generating system is generally provided with an internal or external filter comprising one or more layers of steel screen of varying mesh and wire diameter. Gas produced upon combustion of the gas generant passes through the filter before exiting the gas generating system. In a conventional system, the particulates are substantially removed as the gas passes through the filter. In addition, heat from combustion gases is transferred to the material of the filter as the gases flow through the filter. Thus, as well as filtering particulates from the gases, the filter acts to cool the combustion gases prior to dispersal into an associated airbag. However, inclusion of the filter in the gas generating system increases the complexity, weight, and expense of the gas generating system. Thus, a gas generating system construction which removes particulates and cools the generated gases without the need for a filter is desirable. 
     Variations in the filter components and in the arrangement of the filter material can also unpredictably and adversely affect gas flow through the filter, thereby contributing to ballistic variability of the gas generating system and making the system response less predictable. 
     Yet another concern involves reducing the size of the inflator thereby reducing the packaging size and providing greater design flexibility in various applications or uses. Furthermore, reducing the size of the inflator reduces the raw material requirements, and may also advantageously reduce the manufacturing complexity, thereby reducing overall manufacturing costs. 
     Other ongoing concerns with gas generating systems include the ability to achieve any one of a variety of ballistic profiles by varying as few of the physical parameters of the gas generating system as possible and/or by varying these physical parameters as economically as possible. 
     SUMMARY OF THE INVENTION 
     The above-referenced concerns may be mitigated or obviated by providing a gas generating system for use in an inflatable vehicle occupant protection system, a system that may if desired be filterless. In one aspect, the gas generating system includes a baffle system having a plurality of flow orifices defining a flow path for generated gases through an interior of the gas generating system, and a plurality of particulate aggregation surfaces positioned along the flow path of the gases for changing a flow direction of gases impinging on the aggregation surfaces. Each aggregation surface is oriented such that a difference between a flow direction of the gases prior to impinging on the aggregation surface and a flow direction of the gases after impinging on the aggregation surface is at least approximately 90°, wherein particulates in gases impinging on the aggregation surfaces aggregate or collect on the surfaces. 
     In another aspect of the invention, the gas generating system includes an outer housing including a combustion chamber, a baffle system, and may also include a high gas-yield, low solids-producing gas generant composition positioned in the combustion chamber. The baffle system includes a plurality of flow orifices defining a flow path for gases generated by combustion of the gas generant composition, the flow path extending between the combustion chamber and an exterior of the gas generating system, and a plurality of particulate aggregation surfaces positioned along the flow path of the gases for changing a flow direction of gases impinging on the aggregation surfaces, wherein particulates in gases impinging on the aggregation surfaces aggregate on the surfaces. 
     In yet another aspect of the present invention, the present inflator includes an end closure that is cold-worked or otherwise compressed within an outer housing, the end closure containing a body bore groove, and the housing or outer tube containing a flange pressed within the groove, thereby providing a body bore seal in a metal to metal contact. Stated another way, the present invention includes an inflator housing having a first end and a second end, the housing coupled to an end closure at the first end in a metal-to-metal seal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings illustrating embodiments of the present invention: 
         FIG. 1  is a cross-sectional side view of a first embodiment of a gas generating system in accordance with the present invention; 
         FIG. 1A  is an enlarged view of a portion of  FIG. 1  showing projected gas flow paths and projected particulate aggregation surfaces therealong; 
         FIG. 2  is a cross-sectional side view of a second embodiment of a gas generating system in accordance with the present invention; 
         FIG. 2A  is an enlarged view of a portion of  FIG. 2  showing projected gas flow paths and projected particulate aggregation surfaces therealong; and 
         FIG. 3  is a schematic view of an exemplary gas generating system as employed in a vehicle occupant protection system, in accordance with the present invention. 
         FIG. 4  is a cross-sectional side view of a first embodiment of a gas generating system in accordance with the present invention, wherein an annular flange or flare is shown as formed about the periphery of the outer housing prior to compressing within a recessed portion or groove formed within an end closure within the outer housing. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention broadly comprises a gas generating system that is fabricated without the wire mesh filter required in earlier designs for removing particulate materials from a stream of inflation gas. The design utilizes a tortuous path gas flow concept to cool the gas and to retain solids in the device in order to minimize flame and particulates from exiting the device. Selection of suitable gas generant compositions capable of combusting to produce inflation gas without an undue quantity of particulates further obviates the need for a filter. Obviating the need for a filter enables the gas generating system to be simpler, lighter, less expensive, and easier to manufacture. 
       FIG. 1  shows one embodiment of a gas generating system  10  in accordance with the present invention. Gas generating system  10  is generally constructed of components made from a durable metal such as carbon steel or iron, but may also include components made from tough and impact-resistant polymers, for example. One of ordinary skill in the art will appreciate various methods of construction for the various components of the inflator. U.S. Pat. Nos. 5,035,757, 6,062,143, 6,347,566, U.S. Patent Application Serial No. 2001/0045735, WO 01/08936, and WO 01/08937 exemplify typical designs for the various inflator components, and are incorporated herein by reference in their entirety, but not by way of limitation. 
     Referring to  FIG. 1 , gas generating system  10  includes a substantially cylindrical outer housing  12  having a first end  12   a , a second end  12   b  opposite the first end, and a wall  12   c  extending between the ends to define a housing interior cavity. Outer housing  12  is made from a metal or metal alloy and may be a cast, stamped, deep-drawn, extruded, or otherwise metal-formed. A nozzle  12   d  is formed at housing second end  12   b  containing one or more gas exit orifices  12   e  for enabling fluid communication between an interior of the housing and an associated inflatable device (for example, an airbag or a safety belt pretensioner incorporated into a vehicle occupant protection system.) In the embodiment shown in  FIG. 1 , outer housing  12  and nozzle  12   d  are deep drawn as a single piece. Gas exit orifice(s)  12   e  are then provided in outer housing second end  12   b  by drilling, punching, or other suitable means. 
     In a particular embodiment, the gas generating system is a micro gas generator with outer housing  12  having an outer diameter of approximately 20 mm, usable in, for example, a side seat inflator or a safety belt pretensioner. However, the characteristics of the embodiments described herein may be incorporated into gas generating systems of many alternative sizes, usable for a variety of different applications. 
     In an alternative embodiment (not shown), the gas exit orifices may be incorporated into a gas exit manifold which is formed separately from the outer housing and then welded or otherwise suitably fixed to the outer housing during assembly of the gas generating system. 
     In another alternative embodiment (not shown), a small quantity of a filter material may be incorporated into the outer housing second end proximate the gas exit orifices to filter combustion products from the inflation fluid prior to gas distribution. Any suitable metallic mesh filter or woven wire cloth may be used, many examples of which are known and obtainable from commercially available sources (for example, Wayne Wire Cloth Products, Inc. of Bloomfield Hills, Mich.) 
     In accordance with the present invention, and as exemplified in  FIG. 4 , an end closure  14  is cold-worked or otherwise metal-formed within outer housing first end  12   a . End closure  14  has formed therealong a peripheral shoulder  14   a , a central orifice  14   b , and a peripheral cavity or recessed portion  14   c . In accordance with the present invention, an annular flange or protrusion  14   d  of housing first end  12   a  (shown as a dotted line in a pre-cold-worked state in  FIG. 4 , and also shown as compressed within the groove  14   c ), is drawn through a die to cold-work and thereby compress the flange within the groove  14   c . Other known metal-forming methods may also be employed. The diameter of the inflator may be effectively reduced by eliminating the need for a typical seal such as an o-ring at the end closure and outer housing interface within groove  14   c , and also by compressing the annular flange  14   d  within groove  14   c . It will be appreciated that the volume of the annular flange or protruding portion  14   d  is at least approximately or substantially equal to the volume defined by the groove  12   c . Accordingly, a flush metal-to-metal contact is formed at the interface of groove  14   c  and flange  14   d  once the substantially assembled inflator is drawn and compressed through a die having a smaller diameter than the outer diameter of the annular flange  14   d  prior to cold-working. By cold-working the outer tube or housing  12  to fit within groove  14   c , the housing  12  is compressed to provide sufficient strength in accordance with customer specifications while simplifying the manufacturing process by reducing surface treatment or assembly of additional parts such as an o-ring. As shown in the embodiment shown in  FIG. 1 , the portion  14   d  of outer housing first end  12   a  is pressed into peripheral cavity  14   c  to secure the end closure to outer housing  12  and at the same time provide hermetic sealing of the inflator. 
     The cold-work technique of fitting and sealing the end closure  14  within the housing end  12   a  results in the ability to substantially reduce the diameter of the inflator to less than one inch outer diameter, while yet retaining the structural and other design requirements surrounding the shorting clip or ignition assembly, as determined by the customer. One embodiment exhibits an outer diameter of approximately 20 millimeters, thereby decreasing the packaging size and also increasing the design flexibility with regard to the particular application, as a side inflator within a seat for example. 
     Peripheral shoulder  14   a  is configured so that an end portion a wall  16   b  of an ignition cup  16  (described in greater detail below) having a predetermined outer diameter may be positioned to abut shoulder  14   a . End closure  14  may be stamped, extruded, die cast, or otherwise metal formed and may be made from carbon steel or stainless steel, for example. Although not required, if desired, an O-ring or seal (not shown) may be seated along an outer edge of end closure  14  to seal the interface between the end closure  14  and housing wall  12   c.    
     Referring again to  FIG. 1 , an ignition cup  16  is positioned adjacent end closure  14 , and is nested within outer housing  12  for a portion of the housing length. Ignition cup  16  has a base portion  16   a  and an annular wall  16   b  extending from the base portion to abut end closure  14 . Base portion  16   a  and wall  16   b  define a cavity  16   c  for containing a pyrotechnic compound  18  (for example, a known booster composition) therein. At least one ignition gas exit orifice  16   e  is formed in ignition cup  16  for release of ignition compound combustion products when ignition compound  18  is ignited. An annular recess is formed in base portion  16   a  and is dimensioned so that an end portion of an annular inner housing  22  (described below) having a predetermined inner diameter may be positioned within the recess to aid in locating and securing inner housing  22  within outer housing  12 . Ignition cup  16  may be stamped, extruded, die cast, or otherwise metal formed and may be made from carbon steel or stainless steel, for example. 
     In the embodiment shown in  FIG. 1 , a rupturable, fluid-tight seal (not shown) is positioned across ignition cup orifice  16   e  to fluidly isolate cavity  16   c  from a main combustion chamber  22   a  formed downstream of ignition cup  16 , prior to activation of the gas generating system. The seal is secured to a face of ignition cup base portion  16   a  and forms a fluid-tight barrier between cavity  16   c  and main combustion chamber  22   a . Various known disks, foils, films, tapes, or other suitable materials may be used to form the seal. 
     Referring again to  FIG. 1 , a quantity of a pyrotechnic compound  18  is contained within cavity  16   c . In the embodiment shown in  FIG. 1 , pyrotechnic compound  18  is a known or suitable ignition or booster compound, whose combustion ignites a second, main gas generant charge  28  positioned in combustion chamber  22   a . In an alternative embodiment, pyrotechnic compound  18  in cavity  16   c  comprises the main gas generant charge for the gas generating system. This alternative embodiment may be used in applications in which a relatively small amount of inflation gas (and, therefore, a correspondingly smaller amount of gas generant) is needed. One or more autoignition tablets (not shown) may be placed in cavity  16   c , allowing ignition of pyrotechnic compound  18  upon external heating in a manner well-known in the art. 
     Referring again to  FIG. 1 , an igniter assembly  20  is positioned and secured within end closure central orifice  14   b  so as to enable operative communication between cavity  16   c  containing ignition compound  18  and an igniter  20   a  incorporated into the igniter assembly, for igniting ignition compound  18  upon activation of the gas generating system. Igniter assembly  20  may be secured in central orifice  14   b  using any one of several known methods, for example, by welding, crimping, using an interference fit, or by adhesive application. An igniter assembly suitable for the application described herein may be obtained from any of a variety of known sources, for example Primex Technologies, Inc. of Redmond, Wash. or Aerospace Propulsion Products by, of The Netherlands. 
     The recess in ignition cup  16  is adapted to accommodate a first end portion of an inner housing  22  therealong. In the embodiment of the gas generating system shown in  FIG. 1 , inner housing  22 , in combination with center plate  26  and bulkhead  30  (described below) define a main combustion chamber  22   a  containing a main gas generant composition  28  (described in greater detail below.) Inner housing  22  is spaced apart from outer housing wall  12   c  to form an annular gas flow passage  23  extending between inner housing  22  and outer housing  12 . Inner housing  22  includes at least one and preferably a plurality of gas exit apertures  22   b  formed therealong to enable fluid communication between combustion chamber  22   a  and gas flow passage  23 . Upon activation of the gas generating system, combustion chamber  22   a  fluidly communicates with ignition cup cavity  16   c  by way of ignition cup orifice  16   e.    
     In the embodiment shown in  FIG. 1 , inner housing  22  telescopes or tapers down from a first, relatively larger inner diameter enclosing center plate  26  (described below) and combustion chamber  22   a , to a second, relatively narrower inner diameter proximate outer housing second end  12   b . Thus, the width of gas flow passage  23  (defined as half of the difference between an inner diameter of outer housing  12  and an outer diameter of inner housing  22 , where inner housing is positioned coaxially with outer housing  12 ) may vary along the length of inner housing  22 . In a particular embodiment, the width of gas flow passage  23  varies along the length of inner housing  22  from between a low-end value of approximately 0.5 mm. to a high-end value of approximately 3 mm. A second end of inner housing  22  includes an end portion which is rolled inwardly to form an annular orifice. 
     Inner housing  22  also has at least one second orifice  30   d  formed along the relatively narrow diameter portion of the inner housing to enable fluid communication between gas flow passage  23  and an interior of a baffle member  34  (described in greater detail below). 
     In an alternative embodiment  110  of the gas generating system (shown in  FIG. 2 ), a second end portion of inner housing  122  is formed without the reduction in diameter and is seated along a recess formed in a baffle element  40  (described below), thereby positioning and securing inner housing  122  radially inwardly from outer housing  12 . Thus, in this embodiment, the width of gas flow passage  23  is substantially constant along the length of inner housing  122 . In a particular embodiment, the width of gas flow passage  23  is approximately 1 mm. along the length of inner housing  22 . 
     Inner housings  22  and  122  may be extruded, deep drawn, or otherwise metal-formed from a metal or metal alloy. 
     Referring to  FIG. 1 , a perforate center plate  26  is press fit or otherwise suitably secured within housing  12 . In the embodiment shown in  FIG. 1 , center plate  26  is dimensioned so as to form an interference fit with inner housing  22  and is positioned to abut base portion  16   a  of ignition cup  16 . At least one orifice  26   a  is provided in center plate  26  to enable fluid communication between gas exit orifice  16   e  in ignition cup  16  and gas generant combustion chamber  22   a  formed in inner housing  22 . Center plate  26  is made from a metal or metal alloy and may be a cast, stamped, drawn, extruded, or otherwise metal-formed. A rupturable, fluid-tight seal (not shown) may be positioned across orifice(s)  26   a  to fluidly isolate booster cavity  16   c  from combustion chamber  22   a  prior to activation of the gas generating system. The seal is secured to a face of center plate  26  and forms a fluid-tight barrier between ignition cup cavity  16   c  and combustion chamber  22   a . Various known disks, foils, films, tapes, or other suitable materials may be used to form the seal. 
     Referring again to  FIG. 1 , gas generant composition  28  is positioned within combustion chambers  22   a . It has been found that the gas generator embodiments described herein operate most favorably with a high gas-yield, low solids-producing gas generant composition, such as a “smokeless” gas generant composition. Such gas generant compositions are exemplified by, but not limited to, compositions and processes described in U.S. Pat. Nos. 6,210,505, and 5,872,329, each incorporated by reference herein. As used herein, the term “smokeless” should be generally understood to mean such propellants as are capable of combustion yielding at least about 85% gaseous products, and preferably about 90% gaseous products, based on a total product mass; and, as a corollary, no more than about 15% solid products and, preferably, about 10% solid products, based on a total product mass. U.S. Pat. No. 6,210,505 discloses various high nitrogen nonazide gas compositions comprising a nonmetal salt of triazole or tetrazole fuel, phase stabilized ammonium nitrate (PSAN) as a primary oxidizer, a metallic second oxidizer, and an inert component such as clay or mica. U.S. Pat. No. 5,872,329 discloses various high nitrogen nonazide gas compositions comprising an amine salt of triazole or tetrazole fuel, and phase stabilized ammonium nitrate (PSAN) as an oxidizer. 
     In the embodiment shown in  FIG. 1 , a bulkhead or divider  30  is press-fit, roll-crimped, or otherwise suitably secured within inner housing  12  along the reduced-diameter portion of the inner housing, so as to maintain the divider in position within the housing when the divider is subjected to gas pressures acting on either side of the divider. Bulkhead  30  partitions inner housing  22  to define a chamber  30   a  within inner housing proximate the outer housing second end. The portion of inner housing enclosing chamber  30   a  includes apertures  30   d  formed therein to enable fluid communication between gas flow passage  23  and chamber  30   a . A gas tight seal is effected between divider  30  and inner housing  22 , thereby preventing leakage of gas from combustion chamber  22   a  toward gas exit nozzle  12   d  without transiting annular gas flow passage  23 , as described below. Divider  30  may be formed by stamping, casting, or any other suitable process from a metal or metal alloy. 
     Referring again to  FIG. 1 , a baffle member  34  is provided for channeling a flow of gas entering inner housing  22  from gas flow passage  23  into gas exit nozzle  12   d . Baffle member  34  includes an annular base portion  34   a  and an annular sleeve  34   b  extending from the base portion into inner housing  22  to define a baffle member interior in fluid communication with the gas flow passage  23 . The baffle member interior is also in fluid communication with an interior of nozzle  12   d . Base portion  34   a  is positioned and secured between a second end portion of inner housing  22  and outer housing gas exit nozzle  12   d  to secure the baffle member within housing  12 . A rupturable, fluid-tight seal (not shown) may be positioned across an end portion of annular sleeve portion  34   b  to fluidly isolate inner housing end chamber  30   a  from outer housing gas exit nozzle  16   d . Various known disks, foils, films, tapes, or other suitable materials may be used to form the seal. 
     In an alternative embodiment (shown in  FIG. 2 ), a baffle member  40  includes a substantially circular base portion  40   a  abutting inner housing  22 , and a substantially cylindrical wall  40   b  extending from base portion  40   a . Wall  40   b  is in fluid communication with gas flow passage  23 . Base portion  40   a  and wall  40   b  combine to define a baffle chamber  40   c  for receiving therein combustion products from combustion of inflation gas generant  28  in combustion chamber  22   a , in a manner described below. Baffle chamber  40   c  is also in fluid communication with nozzle  12 . A gas-tight seal is effected between baffle member base portion  40   a  and inner housing  22 , thereby preventing leakage of gas from combustion chamber  22   a  toward gas exit nozzle  12   d  without transiting annular gas flow passage  23 . A recess is formed in baffle member base portion  40   a  for receiving therealong the second end portion of inner housing  22 , for positioning and securing the inner housing second end within the gas generating system. At least one (and preferably a plurality) of orifices  40   d  is formed in wall  40   b  for enabling flow of combustion products received from gas flow passage  23 . In the embodiment shown in  FIG. 2 , several orifices  40   d  are spaced apart approximately 90° along a periphery of wall  40   b . A rupturable, fluid-tight seal (not shown) may positioned across an entrance to gas exit nozzle  12   d  to fluidly isolate baffle chamber  40   c  from outer housing gas exit nozzle  12   d . Various known disks, foils, films, tapes, or other suitable materials may be used to form the seal. 
     Particulates (especially the heavier particulates) suspended in the generated gases will have greater momentum and dynamic inertia than the gases in which they are suspended, and do not change direction as readily as the gases. Thus, the particulates will tend to collide with and aggregate upon surfaces along the gas flow path. It is also desirable to provide sufficient aggregation surface area at or near the portions of the gas generator interior where the particulates are likely to aggregate, in order to accommodate the aggregation of particulates. In addition, the more numerous the changes in direction in the gas flow, the more opportunities are provided for aggregation of the particulates. 
     It is believed that the particulates are most likely to aggregate upon surfaces on which they impinge with a relatively high velocity and/or on surfaces which produce a relatively severe change in direction of the gas flow. In one embodiment, this is achieved by providing aggregation surfaces oriented such that a difference between a flow direction of the gases prior to impinging on an aggregation surface and a flow direction of the gases after impinging on the aggregation surface is at least approximately 90°. In a particular embodiment of the present invention, each aggregation surfaces of the plurality of aggregation surfaces is substantially perpendicular to the flow direction of the gases impinging on the respective aggregation surface. Thus, at least a portion of the particulates striking the aggregation surfaces adhere to the surfaces, or aggregate on the surfaces, rather than changing direction with the remainder of the gas flow. 
     To maximize the probability of aggregating the particulates along the internal surfaces of the gas generator, it is desirable to maximize the number of collisions with the internal surfaces (and thus, the number of changes in direction of the gases), the velocity at which the particulates impact the internal surfaces, and the severity of changes of direction (more severe changes in gas flow direction of making it more likely that the particulates will temporarily stop, or that their velocity will be drastically reduced when they impinge upon an aggregation surface). 
       FIG. 1A  shows a projected gas flow path (indicated by arrows A) through the gas generating system when combustion of the gas generant begins. Referring to  FIG. 1 , it may be seen that orifices  22   b ,  30   d , and the opening into annular sleeve  34   b  define a flow path for generated gases through an interior of the gas generating system to nozzle gas exit orifices  12   e . In addition, the arrangement of the various gas generating system components described above provides a plurality of particulate aggregation surfaces positioned along the flow path of the gases for changing a flow direction of gases impinging on the surfaces, so that particulates in gases impinging on the aggregation surfaces will collect or aggregate on the surfaces. 
     In operation of the embodiment shown in  FIGS. 1 and 1A , upon receipt of a signal from a crash sensor, an electrical activation signal is sent to igniter  20   a . Combustion products from the igniter expand into ignition cup cavity  16   c , igniting booster compound  18  positioned in cavity  16   c . Products from the combustion of booster compound  18  proceed out of cavity  16   c  through ignition cup orifice  16   e  and into combustion chamber  22   a , igniting main gas generant  28 . When the main gas generant  28  has been fully ignited by the booster composition, the main gas generant begins to change phase from a solid to a liquid, then to a gas. 
     Gases and other combustion products generated by combustion of gas generant  28  are forced radially outward at a relatively high velocity toward gas exit apertures  22   b  by the internal pressure in inner housing  22 . Gases then flow through multiple orifices  22   b  in inner housing  22  into gas flow passage  23 , charging the gas flow passage with a pressure which is slightly lower than the pressure within the inner housing  22 . As the main gas generant burns, both P 1  (internal housing pressure) and P 2  (gas flow passage pressure) increase at the same rate and gases flow through the gas flow passage  23 . Products from combustion of gas generant  28  proceed through inner housing gas exit apertures  22   b  into annular gas flow passage  23  and along passage  23  toward the downstream end of inner housing  22 . While a portion of the combustion products exit inner housing  22  via exit apertures  22   b , a portion of the combustion products also impinge on inner surfaces of inner housing  22 , forcing the flow direction of the gases to change abruptly as they flow along the inner surfaces of the inner housing toward one of exit apertures  22   b . Impinging of the gases upon the inner surfaces of inner housing  22  at a relatively high velocity causes the particulates to stick to or aggregate on the inner surfaces of inner housing  22 . 
     Similarly, particulates passing through orifices  22   b  impact along inner surfaces of outer housing  12  prior to the gases changing direction as they flow along passage  23  toward orifices  30   d . Impinging of the gases upon the inner surfaces of outer housing  12  at a relatively high velocity causes the particulates to stick to or aggregate on the inner surfaces of outer housing  12 . 
     While a portion of the combustion products proceed through inner housing second end apertures  30   d  into chamber  30   a , a portion of the combustion products also enter a portion  70  of the gas flow passage defined by an intersection or abutment of end portions of inner housing  22  and outer housing  12 , forcing the flow direction of the gases to change abruptly as the gases flow back toward inner housing second end apertures  30   d . Movement of the gases into passage portion  70  at a relatively high velocity causes the particulates to stick to or aggregate on surfaces with passage portion  70 . 
     Gases proceed through inner housing second end apertures  30   d  into chamber  30   a . Particulates remaining in the gas stream upon entering apertures  30   d  may impact along an exterior surface of annular sleeve  34   b  located substantially opposite orifice(s)  30   d  formed along inner housing  22 , causing the particulates to stick to or aggregate on the exterior surface of the annular sleeve. 
     As seen in  FIG. 1A , gases deflecting off of annular sleeve  34   b  are forced toward divider  30  in order to reach the hollow center portion of the sleeve leading to nozzle gas exit orifices  12   e . Thus, particulates in the gases may also impact divider  30  and adhere thereto. Finally, gases proceeding toward nozzle orifices  12   e  may impact an inner end surface  12   f  of the nozzle, causing particulates to adhere thereto prior to exiting of the generated gas from orifices  12   e.    
     As seen from the above description, a series of aggregation surfaces is positioned between the combustion chamber and exit apertures of the gas generating system to impart abrupt changes in velocity to the gas stream, thereby causing particulates suspended in the gas stream to impact the aggregation surfaces so as to adhere thereto. It is believed that a system of aggregation surfaces as described herein acts to trap most of the particulates produced during combustion of the gas generant, without the filter needed in other designs. 
     When the internal pressure in chamber  30   a  reaches a predetermined value, any burst seals positioned therein rupture, permitting gases to flow into the sleeve portion  34   b , proceeding out of the gas generating system through nozzle  12   d.    
     Operation of the embodiment shown in  FIGS. 2 and 2A  is substantially identical to that described for the embodiment shown in  FIGS. 1 and 1A , with gases from gas flow passage  23  proceeding along the path defined by arrows B, flowing through openings  40   b  into baffle chamber  40   c , then into nozzle  12   d , exiting the gas generating system through gas exit orifices  12   e . While a portion of the combustion products proceed through inner housing second end apertures  30   d  into chamber  30   a , a portion of the combustion products also enter a portion  170  of the gas flow passage defined by an intersection or abutment of end portions of inner baffle member  40  and outer housing  12 , forcing the flow direction of the gases to change abruptly as the gases flow back toward baffle member apertures  40   d . Movement of the gases into passage portion  170  at a relatively high velocity causes the particulates to stick to or aggregate on surfaces with passage portion  170 . 
     In the process of the gases flowing out of the propellant body, into the gas flow passage  23 , into the baffle member, then out of the gas exit nozzle  12   d , all of the metal parts contacted by the gases and the tortuous path that the gases flow through provide cooling of the gases. This provides sufficient cooling of the gases so that no additional components (such as a heat sink device or a filter) are required. In addition, because additional cooling devices are not required, the gases provided by the consumed gas generant have an efficiency greater than those produced by existing gas generator system designs. 
     Referring now to  FIG. 3 , an embodiment of the gas generating system  10  described above may also be incorporated into any of a variety of vehicle occupant protection system elements. In one example, the 20 mm diameter version of the gas generating system previously described is incorporated into a safety belt assembly  150  for pretensioning the safety belt. 
       FIG. 3  shows a schematic diagram of one exemplary embodiment of an exemplary safety belt assembly  150 . Safety belt assembly  150  includes a safety belt housing  152  and a safety belt  100  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 gas-actuated 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, incorporated herein by reference. 
     Safety belt assembly  150  may also include (or be in communication with) a crash event sensor  158  (for example, an inertia sensor or an accelerometer) operates in conjunction with a crash sensor algorithm that signals actuation of belt pretensioner  156  via, for example, activation of igniter  20   a  (not shown in  FIG. 3 ) incorporated into the gas generating system. 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. 
     Referring again to  FIG. 3 , safety belt assembly  150  may also be incorporated into a broader, more comprehensive vehicle occupant restraint system  180  including additional elements such as an airbag system  200 . Airbag system  200  includes at least one airbag  202  and a gas generating system  201  coupled to airbag  202  so as to enable fluid communication with an interior of the airbag. Airbag system  200  may also include (or be in communication with) a crash event sensor  210 . Crash event sensor  210  operates in conjunction with a known crash sensor algorithm that signals actuation of airbag system  200  via, for example, activation of airbag gas generating system  10  in the event of a collision. 
     It should be appreciated that safety belt assembly  150 , airbag system  200 , and more broadly, vehicle occupant protection system  180  exemplify but do not limit uses of gas generating systems contemplated in accordance with the present invention. In addition, it should be appreciated that a gas generating system incorporating a plurality of particulate aggregation surfaces and a high gas-yield, low solids-producing gas generant composition as described herein may be used in the airbag system or in other vehicle occupant protection system elements requiring a gas generating system for operation. 
     In yet another aspect of the invention, a method of manufacturing an inflator may be described as follows:
         1. Providing an outer housing having a first end and a second end, and a periphery.   2. Forming an outer protrusion, or annular flange, about the periphery at the first end.   3. Providing an end closure having a recessed portion, or a groove.   4. Inserting the end closure within the outer housing at the first end, thereby laterally aligning the outer protrusion and the recessed portion; and   5. Compressing the outer protrusion within the recessed portion. Compressing includes cold-working or otherwise metal-forming the coupling of the protrusion and recessed portion.       

     An inflator and a vehicle occupant protection system containing an inflator formed by the method described above are also included. The text describing the end closure  14  coupled to the first end  12   a  of housing  12 , given above, is incorporated herein by reference, to fully inform the reader of the details of this method. 
     It will be understood that the foregoing description of the present invention is for illustrative purposes only, and that the various structural and operational features herein disclosed are susceptible to a number of modifications, none of which departs from the spirit and scope of the present invention. The preceding description, therefore, is not meant to limit the scope of the invention. Rather, the scope of the invention is to be determined only by the appended claims and their equivalents.