Abstract:
An airbag assembly may include an airbag and an inflator in fluid communication with the airbag. The inflator may have a first chamber containing a first gas source and a second chamber containing a second gas source. A filter module may be positioned to filter and redirect gas flows from the first and second gas sources. The filter module may be constructed by securing a baffle within an interior cavity of a filter medium having a generally tubular shape, prior to installation of the filter module the inflator. The baffle may be supported directly by the material of the filter module, by a bracket, or by a support structure formed of wire thicker than that of the filter medium. The baffle may maintain isolation between the first and second chambers, or may help gas from the first gas source initiate gas provision from the second gas source.

Description:
TECHNICAL FIELD 
     The present invention relates to automotive safety. More specifically, the present invention relates to airbag inflators that enhance the cost-effectiveness of airbag systems. 
     BACKGROUND 
     Inflatable safety restraint devices, or airbags, are mandatory on most new vehicles. Airbags are typically installed as part of a system with an airbag module in the steering wheel on the driver&#39;s side of car and in the dashboard on the passenger side of a car. In the event of an accident, a sensor within the vehicle measures abnormal deceleration and triggers the ignition of a charge contained within an inflator. Expanding gases from the charge travel through conduits and fill the airbags, which immediately inflate in front of the driver and passenger to protect them from harmful impact with the interior of the car. Typically, airbags are concealed within the vehicle trim to be invisible during normal vehicle operation. 
     The inflator is a critical part of the airbag assembly because it supplies the inflation gas needed to inflate the airbag cushion. Typically, inflators are compressed gas, pyrotechnic, or hybrid inflators. “Compressed gas” inflators contain gas under pressure, while “pyrotechnic” inflators contain a pyrotechnic gas generant that ignites to produce the gas. “Hybrid” inflators typically use both compressed gas and a pyrotechnic charge. Some inflators are “dual stage,” meaning that they can receive two independent activation signals to enable production of a selectively variable quantity of inflation gas, and others have only a single stage. However, single stage inflators can have multiple timed events, such as the ignition of multiple separate pyrotechnic charges and/or the release of distinct volumes of compressed gas, that are all triggered by a single activation signal. 
     Inflators of all types are typically made from a wide variety of parts. Each inflator may contain a selection of chambers, diffusers, filters, frangible membranes, initiators, generants, baffles, and containers, attachment hardware, and other components. Each of these parts adds significantly to the cost of the inflator. Hence, the inflator typically makes up a large portion of the cost of an airbag assembly. 
     Additionally, a series of different manufacturing steps may be needed to manufacture each inflator. The quantity of steps involved not only further increases the cost of potential inflators, it also increases the likelihood of defects in material or workmanship in the finished inflator. 
     SUMMARY OF THE INVENTION 
     The various systems and methods of the present invention have 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 systems and methods. Thus, it is advantageous to provide airbag systems and methods that provide reliable protection for vehicle occupants in a wide variety of collision situations. Further, it is advantageous to minimize manufacturing and installation costs. The present invention may have other benefits that are not specifically set forth herein. 
     To achieve the foregoing, and in accordance with the invention as embodied and broadly described herein, an airbag assembly may be provided for protecting a vehicle occupant from injury through use of an airbag. The airbag assembly may include an inflator in fluid communication with the airbag. The inflator may include an exterior wall with an aperture and a first gas source contained within a first chamber defined within the exterior wall. In response to receipt by the inflator of a first activation signal, the first gas source may provide a gas that defines a first gas flow pathway that moves through the inflator and exits the inflator via the aperture. The inflator may also include a filter module positioned in the first gas flow pathway. The filter module may include a filter medium having plurality of holes sized such that, as the gas flows through the filter medium, particulate matter entrained in the gas is trapped in the filter medium, and a baffle secured to the filter medium, the baffle having an impingement surface positioned such that the gas impinges against the impingement surface in a manner that causes redirection of the first gas flow pathway. The baffle may be positioned such that the baffle is in contact with no component of the inflator outside the filter module. 
     The inflator may further have a second gas source contained within a second chamber defined within the exterior wall. In response to receipt by the inflator of a second activation signal, the second gas source may provide gas that defines a second gas flow pathway that moves through the inflator and exits the inflator via the aperture. The filter module may be positioned in the second gas flow pathway. The impingement surface may be substantially planar and may be oriented substantially perpendicular to the first gas flow pathway where the gas impinges against the impingement surface. Redirection of the first gas flow may prevent the first gas flow from flowing directly into the second chamber through the filter module. 
     Alternatively, in response to entry of the first gas flow into the second chamber, the second gas source may provide gas that defines a second gas flow pathway that moves through the inflator and exits the inflator via the aperture. The impingement surface may define a generally frusto-conical shape having an axis oriented substantially parallel to the first gas flow pathway where the gas impinges against the impingement surface. Redirection of the first gas flow may direct the first gas flow into the second chamber to facilitate initiation of gas provision by the second gas source. 
     The filter medium may have a generally tubular shape with an interior surface that defines an interior cavity within which the baffle resides. The baffle may include a circumferential region captured directly by the interior surface. The filter module may alternatively include a bracket captured by the interior surface. the baffle may include a circumferential region that abuts the bracket such that the bracket supports the baffle. As another alternative, the filter medium may be formed of a plurality of wires woven together, and the filter module may include a support structure formed of a plurality of support wires that are significantly thicker than the plurality of wires. The baffle may include a circumferential region that abuts the support structure such that the support structure supports the baffle. As yet another alternative, the interior surface may be tapered such that the filter medium is thicker where it surrounds the baffle than at the ends of the interior surface. 
     According to one method of manufacturing an inflator, such a method may include providing an exterior wall comprising an aperture, providing a first gas source, positioning the first gas source within a first chamber defined within the exterior wall such that, in response to receipt by the inflator of a first activation signal, the first gas source provides a gas that defines a first gas flow pathway that moves through the inflator and exits the inflator via the aperture, providing a filter module comprising a filter medium having plurality of holes, and a baffle secured to the filter medium, the baffle comprising an impingement surface, and positioning the filter module in the first gas flow pathway such that, as the gas flows through the filter medium, particulate matter entrained in the gas is trapped in the filter medium and the gas impinges against the impingement surface in a manner that causes redirection of the first gas flow pathway. Providing the filter module may include securing the baffle to the filter medium prior to positioning of the filter module in the first gas flow pathway. 
     The method may further include providing a second gas source, and positioning the second gas source within a second chamber defined within the exterior wall such that, in response to receipt by the inflator of a second activation signal, the second gas source provides gas that defines a second gas flow pathway that moves through the inflator and exits the inflator via the aperture. The impingement surface may be substantially planar. Positioning the filter module in the first gas flow pathway may include positioning the filter module in the second gas flow pathway and orienting the impingement surface substantially perpendicular to the first gas flow pathway where the gas impinges against the impingement surface. Redirection of the first gas flow may prevent the first gas flow from flowing directly into the second chamber through the filter module. 
     Alternatively, the method may include providing a second gas source, and positioning the second gas source within a second chamber defined within the exterior wall such that, in response to entry of the first gas flow into the second chamber, the second gas source provides gas that defines a second gas flow pathway that moves through the inflator and exits the inflator via the aperture. The impingement surface may define a generally frusto-conical shape. Positioning the filter module in the first gas flow pathway may include orienting an axis of the frusto-conical shape substantially parallel to the first gas flow pathway where the gas impinges against the impingement surface. Redirection of the first gas flow may direct the first gas flow into the second chamber to facilitate initiation of gas provision by the second gas source. 
     The filter medium may have a generally tubular shape with an interior surface that defines an interior cavity. The baffle may have a circumferential region. Securing the baffle to the filter medium may include directly capturing the circumferential region with the interior surface. Alternatively, the filter module may further include a bracket. Securing the baffle to the filter medium may include capturing the bracket with the interior surface, and positioning the baffle such that the circumferential region abuts the bracket such that the bracket supports the baffle. As another alternative, the filter medium may be formed of a plurality of wires woven together and the filter module may further have a support structure formed of a plurality of support wires that are significantly thicker than the plurality of wires. Securing the baffle to the filter medium may include capturing the support structure with the interior surface, and positioning the baffle such that the circumferential region abuts the support structure such that the support structure supports the baffle. 
     According to another embodiment, an airbag assembly for protecting a vehicle occupant from injury may include an airbag, an inflator in fluid communication with the airbag. The inflator may include an exterior wall with an aperture, a first gas source contained within a first chamber defined within the exterior wall, wherein, in response to receipt by the inflator of a first activation signal, the first gas source provides a gas that defines a first gas flow pathway that moves through the inflator and exits the inflator via the aperture, a second gas source contained within a second chamber defined within the exterior wall, and a filter module positioned in the first gas flow pathway. The filter module may include a filter medium having plurality of holes sized such that, as the gas flows through the filter medium, particulate matter entrained in the gas is trapped in the filter medium, and a baffle secured to the filter medium. The baffle may have an impingement surface positioned such that the gas impinges against the impingement surface in a manner that causes redirection of the first gas flow pathway. The filter medium may include a generally tubular shape comprising an interior surface that defines an interior cavity within which the baffle entirely resides. 
     In response to receipt by the inflator of a second activation signal, the second gas source may provide a gas that defines a second gas flow pathway that moves through the inflator and exits the inflator via the aperture. The filter module may be positioned in the second gas flow pathway. The impingement surface may be substantially planar and may be oriented substantially perpendicular to the first gas flow pathway where the gas impinges against the impingement surface. Redirection of the first gas flow may prevent the first gas flow from flowing directly into the second chamber through the filter module. 
     Alternatively, in response to entry of the first gas flow into the second chamber, the second gas source may provide gas that defines a second gas flow pathway that moves through the inflator and exits the inflator via the aperture. The impingement surface may define a generally frusto-conical shape having an axis oriented substantially parallel to the first gas flow pathway where the gas impinges against the impingement surface. Redirection of the first gas flow may direct the first gas flow into the second chamber to facilitate initiation of gas provision by the second gas source. 
     These and other 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 
       Exemplary embodiments of the invention will become more fully apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. Understanding that these drawings depict only exemplary embodiments and are, therefore, not to be considered limiting of the invention&#39;s scope, the exemplary embodiments of the invention will be described with additional specificity and detail through use of the accompanying drawings in which: 
         FIG. 1  is a perspective view of an airbag assembly according to one embodiment of the invention; 
         FIG. 2  is a side elevation, section view of the inflator of the airbag assembly of  FIG. 1 ; 
         FIG. 3  is a side elevation, section view of an inflator according to one alternative embodiment of the invention; 
         FIG. 4  is a side elevation, section view of a filter module of an inflator according to another alternative embodiment of the invention; 
         FIG. 5  is a side elevation, section view of a filter module of an inflator according to yet another alternative embodiment of the invention; and 
         FIG. 6  is a side elevation, section view of a filter module of an inflator according to still another alternative embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Exemplary 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 6 , is not intended to limit the scope of the invention, as claimed, but is merely representative of exemplary embodiments of the invention. 
     The phrases “connected to,” “coupled to” and “in communication with” refer to any form of interaction between two or more entities, including mechanical, electrical, magnetic, electromagnetic, fluid, and thermal interaction. Two components may be coupled to each other even though they are not in direct contact with each other. The term “abutting” refers to items that are in direct physical contact with each other, although the items may not necessarily be attached together. The phrase “fluid communication” refers to two features that are connected such that a fluid that exits one feature is able to pass into or otherwise contact the other feature. 
     The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments. While the various aspects of the embodiments are presented in drawings, the drawings are not necessarily drawn to scale unless specifically indicated. 
     Inflatable airbag systems are widely used to minimize occupant injury in a collision scenario. Airbag modules have been installed at various locations within a vehicle, including, but not limited to, the steering wheel, the instrument panel, within the side doors or side seats, adjacent to the roof rail of the vehicle, in an overhead position, or at the knee or leg position. In the following disclosure, “airbag” may refer to any airbag type. 
     Referring to  FIG. 1 , a perspective view illustrates an airbag assembly  100  that may be used to protect the occupants of a vehicle during a collision. The airbag assembly  100  may be of any known type, including but not limited to driver&#39;s side airbags, passenger&#39;s side airbags, side airbags, inflatable curtain airbags, and knee airbags. The airbag assembly  100  may have a longitudinal direction  102 , a lateral direction  104 , and a transverse direction  106 , all of which are orthogonal to each other. 
     The airbag assembly  100  may include an airbag  110  and an inflator  120 . The airbag  110  may have a cushion  130  that inflates to receive and cushion impact from one or more vehicle occupants, and a mounting portion  132  securable to the vehicle. The airbag  110  may generally be formed from a first layer  134  and a second layer  136 , both of which may be formed of a flexible material such as a woven fabric, a thin polymer sheet, or the like. The first layer  134  and the second layer  136  may be attached together via one-piece weaving, ultrasonic welding, RF welding, stitching, adhesive bonding, or a variety of other methods known in the art. 
     The first layer  134  and the second layer  136  may cooperate to define a first flap  140  and a second flap  142 , which may be secured together to partially or fully enclose the inflator  120 . A pair of holes  144  may be formed in the first flap  140  to facilitate attachment of the inflator  120  and the mounting portion  132  to the vehicle. 
     The inflator  120  may have a generally cylindrical shape oriented generally along the longitudinal direction  102 . The inflator  120  may have a length along the longitudinal direction  102  that is much greater than its width along the lateral direction  104  and the transverse direction  106 . The inflator  120  may have an exterior wall  150 , a first end cap  152 , and a second end cap  154 . The exterior wall  150  may have a plurality of apertures  156  that release inflation gas into the interior of the cushion  130  in response to receipt of an activation signal indicative of a collision, impending collision, or other sudden acceleration or deceleration event. 
     The inflator  120  may also have mounting features that facilitate attachment of the inflator  120  and the mounting portion  132  to the vehicle. The mounting features may take the form of a pair of fasteners  158  that are secured to the exterior wall  150  and are spaced apart so as to be insertable through the holes  144  of the first flap  140 . After insertion through the holes  144 , the fasteners  158  may be secured to a mounting bracket or other interface on the vehicle. 
     The configuration illustrated in  FIG. 1  may be particularly suited to a side impact airbag that deploys from the seat or a part of the vehicle proximate the outboard surface of the seat. However, in use with the other airbag types set forth above, an inflator and airbag may be configured much differently from those shown in  FIG. 1 . For example, the inflator  120  may not be elongated, but may have a more disc-like shape in which the width is greater than the length. Apertures need not be located in the middle of an inflator as illustrated; rather apertures may be positioned at one or both ends of the inflator and/or at any location between them. Those of skill in the art will recognize that the inventive principles set forth herein may be used with a wide variety of inflator types. 
     Referring to  FIG. 2 , a side elevation, section view illustrates the inflator  120  of the airbag assembly  100  of  FIG. 1 . The exterior wall  150  may have a first end  160  and a second end  162  displaced from the first end  160  along the longitudinal direction  102 . As shown, the exterior wall  150  may be formed as a single piece, but in alternative embodiments, an exterior wall may be formed of multiple pieces joined together. The exterior wall  150  may be secured to the first end cap  152  and the second end cap  154  through a variety of ways including welding, brazing, chemical or adhesive bonding, fastening, or the like. 
     As illustrated, the exterior wall  150  may be secured to the first end cap  152  and the second end cap  154  via welds  164 , which may be formed via a variety of techniques. Such techniques include laser welding, in which a laser is applied to the junctions between the exterior wall  150  and the first end cap  152  and/or the second end cap  154  to directly heat the material. Such techniques also include inertial welding, in which relative rotation and pressure between the exterior wall  150  and the first end cap  152  and/or the second end cap  154  causes friction that generates the heat needed to form the welds  164 . 
     The fasteners  158  may pass through fastener holes  166  in the exterior wall  150 . The fasteners  158  may be bonded, fastened, or otherwise secured to the exterior wall  150 . Alternatively, mounting hardware need not be incorporated into the inflator  120 , but may instead be provided separately. 
     The first end cap  152  may have an initiator  170  that ignites in response to receipt of an activation signal from the vehicle, which may, in turn, be generated by a signal-generating element (not shown) such as a control system, sensor assembly, or other apparatus within the vehicle. The initiator  170  may be located within a cavity  172  defined within the interior of the first end cap  152  as shown, or may alternatively protrude into the interior of the inflator  120 . The initiator  170  may be electrically connected to the activation signal-generating element within the vehicle via a pin  174  that resides within a socket  176  defined within the exposed end of the first end cap  152  so as to receive a connector such as a plug (not shown) connected to the signal-generating element. 
     The inflator  120  may be a single stage inflator, and may thus fully activate in response to receipt of only a single activation signal. Thus, the second end cap  154  need not receive or convey an activation signal. The second end cap  154  may be a unitary block of material as shown. 
     A first chamber  180  and a second chamber  182  may be defined within the exterior wall  150 . The first chamber  180  may contain a first gas source and the second chamber  182  may contain a second gas source. The present invention encompasses all different gas sources; accordingly, gas sources including pyrotechnic generants, compressed, stored gas, or any other known gas sources may be used. 
     The inflator  120  may take the form of a hybrid inflator that utilizes both pyrotechnic generants and compressed gases. Thus, the first chamber  180  may contain a generant  184  and a gas  186 . Generally, a “generant” is a substance that produces gas through some type of reaction including combustion or other chemical reactions. A generant may be a solid, a liquid, or any combination thereof. As shown in  FIG. 2 , the generant  184  may take the form of pellets that predictably combust to produce inflation gas. 
     The gas  186  may be a compressed gas that resides under pressure within the first chamber  180 . The gas  186  may be kept separate from the generant  184  by a circumferential wall  188  and an end wall  190  that cooperate to define a generant chamber that contains the generant  184 . The circumferential wall  188  may be crimped on either side of the end wall  190  to keep the end wall  190  in place without the need for fasteners or adhesives. The end wall  190  may be designed to rupture as the generant  184  commences producing gas. 
     The second chamber  182  may also contain a generant  194  and a gas  196 , which may be similar to the generant  184  and the gas  186  within the first chamber  180 . The generant  194  and the gas  196  may be intermingled as shown, or alternatively, the generant  184  may be retained within a separate container within the second chamber  182 . Generally, the generant  194  and the gas  196  within the second chamber  182  may be ignited and/or released by gas flowing from the first chamber  180 . Thus, the generant  194  and the gas  196  may serve to augment the gas produced by the generant  184  and the gas  186 , and may provide inflation gases at a time that provides the proper inflation profile of the airbag  110  over time. 
     Each of the first chamber  180  and the second chamber  182  may contain an internal barrier  198  that helps to restrict the ejection of fast-moving particulates. Such particulates may include combusting generant and/or parts of the circumferential wall  188  and the end wall  190  after rupture thereof. The internal barriers  198  may help keep such particulates and debris within the first chamber  180  and the second chamber  182 , thereby providing an initial filtration stage that helps to keep such matter within the inflator  120  and prevents it from interfering with the operation of downstream components. The first chamber  180  and the second chamber  182  may each be sealed via a frangible membrane such as a burst disc  200 . Each of the burst discs  200  may be designed to rupture as the pressure within the first chamber  180  or the second chamber  182  exceeds a threshold level. 
     The exterior wall  150  may define the circumference of each of the first chamber  180  and the second chamber  182 . The first chamber  180  and the second chamber  182  may be further defined via an end wall  202  that is oriented generally perpendicular to the longitudinal direction  102 . Each of the end walls  202  may be secured to the interior surface of the exterior wall  150  via welding, brazing, chemical or adhesive bonding, or any other suitable attachment method. Each of the end walls  202  may have a opening  204  covered by the burst disc  200  that corresponds to it. 
     The end walls  202  may be connected together via a circumferential wall  206  with a generally cylindrical shape. The circumferential wall  206  may be secured to each of the end walls  202  via welding, brazing, chemical or adhesive bonding, or any other suitable attachment method. The circumferential walls  206  and the end walls  202  may thus cooperate to define a filter chamber  210  that is generally in the center of the airbag  110 . The circumferential wall  206  may have openings  208  positioned to permit gas to flow out of the filter chamber  210  and out of the inflator  120  through the apertures  156 . 
     A filter module  212  may be positioned to further filter the gases provided by the various gas sources within the inflator  120 , including the generant  184 , the gas  186 , the generant  194 , and the gas  196 . The filter module  212  may have a filter medium  214  and a baffle  216 . The filter medium  214  may have a generally tubular shape with an interior surface  215  that defines a generally cylindrical internal cavity within the interior of the filter medium  214 . The baffle  216  may be positioned to reside entirely within the interior cavity of the filter medium  214 , as shown. The filter medium  214  may be formed of woven, knit, expanded, or compressed metal such as wire. The filter medium  214  may be formed of a relatively thin wire that leaves narrow intervening spaces such that the filter medium  214  is effective in trapping the particulates and other impurities that may be entrained in the gas flowing through the filter chamber  210 . 
     The baffle  216  may have a generally frusto-conical shape with an axis parallel to the longitudinal direction  102  and to the axis of the inflator  120 . The baffle  216  may have an opening  218  toward the second chamber  182 , and a circumferential region  219  captured by the interior surface  215  of the filter medium  214 . The baffle  216  may further have an impingement surface  222  against which gas from the first chamber  180  impinges during deployment of the inflator  120 . 
     In the inflator  120  of  FIG. 2 , the baffle  216  may be in contact with only the filter medium  214 . The filter medium  214  and the baffle  216  may be assembled together prior to installation of the resulting filter module  212  in the inflator  120 . The integration of the filter medium  214  and the baffle  216  may help to conserve metal that may otherwise be needed to form a baffle that can be secured to the end wall  202 , the circumferential wall  206 , and/or any other part of the inflator  120 . Integration of the filter medium  214  and the baffle  216  may also facilitate assembly of the inflator  120  by omitting the attachment of the baffle  216  to the inflator interior, which may otherwise be required for the use of a baffle that is discrete from the filter medium (not shown). 
     In operation, an activation signal may be produced by the associated signal-generating element in response to detection of a collision, impending collision, or other event that requires deployment of the airbag assembly  100 . The activation signal may be conveyed to the socket  176  and to the initiator  170  through the pin  174 . The initiator  170  may then ignite to cause ignition of the generant  184  within the first chamber  180 . The generant  184  may produce gas that ruptures the circumferential wall  188  and/or the end wall  190 . The expanding gas may rupture the burst disc  200  and flow out of the opening  204  in the end wall  202  to enter the filter chamber  210 . 
     The gas provided by the first chamber  180  may define first gas flow pathways  224  that flows from the first chamber  180  to the apertures  156  that permit the gas to flow out of the inflator  120 . Some of the first gas flow pathways  224  may enter the filter medium  214  directly, or may impinge against the baffle  216  in a manner that they are redirected radially to pass through the filter medium  214 , through the openings  208  of the circumferential wall  206 , and through the apertures  156  to exit the inflator  120 . 
     Some of the first gas flow pathways  224  may also impinge against the impingement surface  222  of the baffle  216 . The impingement surface  222  may, in return, redirect the first gas flow pathways  224  such that some of the first gas flow pathways  224  are concentrated to flow through the opening  218  of the baffle  216 . The gas in these first gas flow pathways  224  may thus form a jet exiting the opening  218  to impinge against the burst disc  200 , thereby rupturing the burst disc  200  and opening the second chamber  182 . These gases may enter the second chamber  182  and may be of a sufficient temperature and pressure to ignite the generant  194  in the second chamber  182 . 
     The gas produced by the generant  194  may combine with the gas  196  to provide second gas flow pathways  226  exiting the second chamber  182 . Some of the second gas flow pathways  226  may also impinge against the baffle  216 , and may be redirected generally radially so that the second gas flow pathways  226  flow through the filter medium  214  to pass through the filter medium  214 , through the openings  208  of the circumferential wall  206 , and through the apertures  156  to exit the inflator  120 . 
     During passage of the gases in the first gas flow pathways  224  and the second gas flow pathways  226  through the filter medium  214 , particulates, debris, and any other impurities within the gas may be trapped, and the gas may be cooled. Thus, the gas may exit the inflator  120  a the desired temperature and level of purity to effectively inflate the airbag  110  without damaging it. 
     The filter module  212  may be produced in a variety of ways. According to one method, the filter medium  214  may be formed separately from the baffle  216  via methods known in the art, and the baffle  216  may be stamped, forged, rolled, or otherwise formed by any of a variety of manufacturing methods. The baffle  216  may be inserted into the interior cavity defined within the filter medium  214  after formation of the filter medium  214 . This may be accomplished, for example, by deforming the interior surface  215  of the filter medium  214  to enable the interior surface  215  to receive the baffle  216 , and then returning the filter medium  214  back to its proper configuration. 
     Alternatively, a temperature differential may be applied between the filter medium  214  and the baffle  216  to cause the filter medium  214  to expand (for example, by heating the filter medium  214 ) and/or cause the baffle  216  to contract (for example, by cooling the baffle  216 ). Once the baffle  216  is in place, the filter medium  214  and baffle  216  may return to similar temperatures so that the circumferential region  219  of the baffle  216  is captured by the interior surface  215  in the manner illustrated. 
     In the alternative to the foregoing, the filter medium  214  may not be fully formed prior to insertion of the baffle  216  into the interior cavity. For example, the filter medium  214  may be wound and/or woven form one longitudinal end to the other. The baffle  216  may be inserted into the partially-formed filter medium  214  so that the circumferential region  219  is captured by the interior surface  215  during the remainder of the process of fabricating the filter medium  214 . 
     Alternatively, the interior surface  215  of the filter medium  214  may first be formed around the baffle  216  to capture the baffle  216  in the initial stages of formation of the filter medium  214 . The remainder of the filter medium  214  may then be formed outwardly of the interior surface  215  with the baffle  216  in place. 
     As yet another alternative, if the filter medium  214  is formed of compacted wire, the filter medium  214  may simply be compacted into the tubular shape around the baffle  216 . For example, a mold (not shown) may receive the baffle  216  prior to compaction of the material of the filter medium  214  into the mold. The material of the filter medium  214  may then be compacted into the mold around the baffle  216  so that, when the compaction process is complete, the baffle  216  is in place within the interior surface  215 . 
     As mentioned, the inflator  120  is a dual-stage, hybrid inflator. The principles of the present invention may be applied to a wide variety of inflator types. One alternative inflator type will be shown and described in connection with  FIG. 3 . 
     Referring to  FIG. 3 , a side elevation, section view illustrates an inflator  220  according to one alternative embodiment of the invention. Some elements of the inflator  220  are the same or similar to those of the inflator  120 , and are thus indicated by the same reference numbers used before. The inflator  220  differs from the inflator  120  in that the inflator  220  is a dual-stage inflator. Thus, the inflator  220  may have a second end cap  254  that is configured in a manner similar to that of the first end cap  152  so that a second activation signal can be received through the second end cap  254  to ignite an initiator  170  that is separate from and independent of the initiator  170  in the first end cap  152 . The initiator  170  may be electrically connected to the signal-generating element via the pin  174  and socket  176  of the second end cap  254 , which may receive a corresponding electrical plug (not shown) or the like. 
     The inflator  220  may have a first chamber  280  similar to the first chamber  180 , except that the first chamber  280  may not contain the gas  186 . Rather, the inflator  220  may be a purely pyrotechnic inflator. The inflator  220  may also have a second chamber  282  that is substantially the same as the first chamber  280 . Thus, the second chamber  282  may also contain a generant  184  retained within a chamber defined by a circumferential wall  188  and a end wall  190  like those of the first chamber  280 . Like the first chamber  280 , the second chamber  282  may not contain a compressed gas, and may provide gas solely via the generant  184 . As in the first chamber  280 , the generant  184  in the second chamber  282  may be ignited to produce gas in response to ignition of the initiator  170  in the second end cap  254 . 
     In the inflator  220 , the end walls  202  and the circumferential wall  206  may cooperate to define a filter chamber  310 . A filter module  312  may be positioned within the filter chamber  310 . The filter module  312  may include a filter medium  314  and a baffle  316 . The filter medium  314  may have an interior surface  315  defining an interior cavity within the filter medium  314 , within which the baffle  316  resides in its entirety. 
     The baffle  316  may have a generally discoid shape with a circumferential region  319  captured by the interior surface  315  of the filter medium  314 . The baffle  316  may also have two impingement surfaces  322  that face outward toward the first chamber  280  and the second chamber  282 . The baffle  316  may generally serve to keep gases from each of the first chamber  280  and the second chamber  282  from interfering with the operation of the other chamber so that the first chamber  280  and the second chamber  282  can be operated independently. Thus, depending, for example, on the severity of the impact, only one or both of the first chamber  280  and the second chamber  282  may deploy. 
     In operation, the initiator  170  of the first end cap  152  may receive a first activation signal from the signal-generating element, and in response, may ignite to cause ignition of the generant  184 . The generant  184  may produce gas at a pressure that ruptures the circumferential wall  188  and/or the end wall  190 , and then passes through the internal barrier  198  within the first chamber  280  to rupture the burst disc  200  that seals the first chamber  280 . The gases from the first chamber  280  may define first gas flow pathways  324  that flow into the filter chamber  310  an impinge against the impingement surface  322  that faces the first chamber  280 . The impingement surface  322  may redirect the gases of the first gas flow pathways  324  radially so that these gases pass through the filter medium  314 , through the openings  208  of the circumferential wall  206 , and through the apertures  156  to exit the inflator  220 . 
     The baffle  316  may prevent the gases of the first gas flow pathways  324  from flowing with significant velocity into the opening  204  of the second chamber  282 . Thus, the baffle  316  may prevent these gases from interfering with the second chamber  282  by, for example, causing undesired deployment of the second chamber  282  or resisting the rupture of the burst disc  200  of the second chamber  282  by gases emerging from the second chamber  282 . 
     Assuming the second chamber  282  is also deployed through the use of a second activation signal to the initiator  170  of the second end cap  254 , the generant  184  within the second chamber  282  may also ignite to produce gases. These expanding gases may rupture the circumferential wall  188  and/or the end wall  190  of the second chamber  282 , and then rupture the burst disc  200  within the second chamber  282  to define second gas flow pathways  326  exiting the second chamber  282 . Like the first gas flow pathways  324 , the gases of the second gas flow pathways  326  may impinge against the impingement surface  322  facing the second chamber  282 . The gases of the second gas flow pathways  326  may be redirected by the impingement surface  322  in radial directions so that these gases pass through the filter medium  314 , through the openings  208  of the circumferential wall  206 , and through the apertures  156  to exit the inflator  220 . 
     Beneficially, the baffle  316  may also keep the gases of the second gas flow pathways  326  from interfering with the operation of the first chamber  280 . Hence, either of the first chamber  280  and the second chamber  282  may be deployed without deploying the other, and without interfering with deployment of the other. 
     The filter module  312  may be manufactured in any of a variety of ways, as disclosed in the discussion of the filter module  212 . The filter module  312  may also provide the benefits of cost savings through reduced material and streamlined assembly. A variety of different structures and methods may be used to enhance retention of a baffle within a filter module and/or facilitate manufacture of the filter module, as will be shown and described in connection with  FIGS. 4 and 5 . 
     Referring to  FIG. 4 , a side elevation, section view illustrates a filter module  412  of an inflator according to another alternative embodiment of the invention. The filter module  412  may have a filter medium  414  with an interior surface  415  defining an interior cavity within the filter medium  414 . The filter module  412  may also have a baffle  416  that resides entirely within the interior cavity defined by the interior surface  415 . The baffle  416  may be similar to the baffle  316  of the previous embodiment, and may this have a generally discoid shape with a circumferential region  419  captured by the interior surface  415  of the filter medium  414 , and two impingement surfaces  422  that face in opposite longitudinal directions. 
     The filter module  412  may differ from the filter module  312  of the previous embodiment in that the filter module  412  has a support structure  430  different from the material of which the main body of the filter medium  414  is formed. The support structure  430  may provide enhanced support for the baffle  416  to ensure that the circumferential region  419  of the baffle  416  remains retained by the interior surface  415 . As shown, the support structure  430  may have one or more support wires  432 . If the filter medium  414  is formed of metal wire, such as woven or compacted wire, the support wires  432  may be larger in diameter than the wires of which the body of the filter medium  414  is made. 
     Thus, the support wires  432  may have higher rigidity than that of the surrounding material. The support wires  432  may provide enhanced resistance to any tendency of the circumferential region  419  of the baffle  416  to shear away the abutting portion of the filter medium  414  as gases impinging against either of the impingement surfaces  422  exert force on the baffle  416  tending to move it in the longitudinal direction  102 . 
     The support wires  432  may be wound in a semi-toroidal shape to form the support structure  430 . Alternatively, the support wires  432  may be woven or otherwise grouped into the desired shape. If desired, the support wires  432  may be welded, bonded, or otherwise secured together to enhance their ability to retain the baffle  416  in spite of the action of the forces described above. 
     The filter module  412  may be made in a variety of ways. In one example, the support structure  430  may be provided first, and then the filter medium  414  may be formed around the support structure  430 . The baffle  416  may then be inserted into the support structure  430 , for example, by temporarily deflecting the support wires  432  to enable the support structure  430  to receive the baffle  416 , and then deflecting the support wires  432  back into position. Alternatively, the support structure  430  may be inserted into engagement with the interior surface  415  of an existing filter medium  414 . The baffle  416  may optionally be inserted into the support structure  430  prior to assembly of the support structure  430  and the filter medium  414 . 
     According to one embodiment, the support structure  430  may be wound into place around the circumferential region  419  of the baffle  416 . Then, the filter medium  414  may be formed around the support structure  430  and the baffle  416 . Any of these methods may be used in combination with any of the methods set forth in the description of manufacture of the filter module  212  and/or in combination with other manufacturing methods known in the art. 
     Referring to  FIG. 5 , a side elevation, section view illustrates a filter module  512  of an inflator according to yet another alternative embodiment of the invention. As shown, the filter module  512  may have a filter medium  514  with an interior surface  515  that defines an interior cavity within the filter medium  514 . The filter module  512  may also have a baffle  516  with a discoid shape similar to that of the baffle  416  of the previous embodiment. The baffle  516  may have a circumferential region  519  captured by the interior surface  515  and impingement surfaces  522  that face in opposite directions. 
     The filter module  512  may also have a bracket  530  that penetrates the interior surface  515  and is seated in the interior of the filter medium  514  to help retain the baffle  516 . Like the support structure  430  of the previous embodiment, the bracket  530  may help to keep the baffle  516  in place within the structure of the filter medium  514 , which may be relatively more pliable. The bracket  530  may have a fitted region  532  that receives the circumferential region  519  relatively snugly, and a splayed region  534  that tapers outward toward the axis of the bracket  530  to facilitate entry of baffle  516  into engagement with the fitted region  532 . 
     The filter module  512  may be manufactured in a wide variety of ways. According to one example, the baffle  516  may be provided first, and then the bracket  530  may be stamped, molded, or otherwise formed around the circumferential region  519  of the baffle  516 . Then, the filter medium  514  may be formed around the bracket  530 . 
     Alternatively, the baffle  516  may be inserted into the bracket  530  after the bracket  530  has been formed and/or seated in the interior cavity of the filter medium  514 . Any of the methods set forth in the preceding description and/or any of a variety of known manufacturing methods may be combined to effectively manufacture the filter module  512  illustrated in Figure 
     Referring to  FIG. 6 , a side elevation, section view illustrates a filter module  612  of an inflator according to still another alternative embodiment of the invention. As shown, the filter module  612  may have a filter medium  614  with an interior surface  615  that defines an interior cavity within the filter medium  614 . The filter module  612  may also have a baffle  616  with a discoid shape similar to that of the baffle  416  and the baffle  516  of the previous embodiments. The baffle  616  may have a circumferential region  619  captured by the interior surface  615  and impingement surfaces  622  that face in opposite directions. 
     The filter module  612  may be different from previous embodiments in that the interior surface  615  has an hourglass-like shape. Thus, the interior surface  615  may taper such that, from both ends of the filter module  612 , the interior surface  615  gets narrower as it approaches the baffle  616 . The filter module  612  may also have a more elongated shape in the longitudinal direction  102  than those of previous embodiments. 
     The taper may serve to thicken the portion of the filter medium  614  that surrounds the baffle  616  to permit the baffle  616  to penetrate more deeply into the material of the filter medium  614 . This may enhance retention of the baffle  616  by providing more support, in particular, to resist any tendency of the baffle  616  to shear through the capturing material of the filter medium  614  and move in the longitudinal direction  102 . 
     The tapered shape of the interior surface  615  may also help induce the gas flows impinging against the impingement surfaces  622  to deposit additional impurities proximate the baffle  616 . More precisely, as inflation gases approach the baffle  616 , they may enter the more restrictive space proximate the baffle  616 , wherein the interior surface  615  defines a narrower passageway. This may produce a flow restriction that induces the gas flows to reverse directions and travel toward the outer portions of the filter module  612 , where the interior surface  615  defines a broader passageway. In the process of reversing directions, the inflation gases may deposit impurities on the impingement surface  622 , thereby enhancing the purity of the inflation gases exiting the inflator (not shown). 
     Those of skill in the art will recognize that the filter module  212 , the filter module  312 , the filter module  412 , the filter module  512 , and the filter module  612  are only examples of how the present invention may be applied. A wide variety of filter modules may be made and used in conjunction with the various known inflator types and configurations. 
     Any methods disclosed herein comprise one or more steps or actions for performing the described method. The method steps and/or actions may be interchanged with one another. In other words, unless a specific order of steps or actions is required for proper operation of the embodiment, the order and/or use of specific steps and/or actions may be modified. 
     Reference throughout this specification to “an embodiment” or “the embodiment” means that a particular feature, structure or characteristic described in connection with that embodiment is included in at least one embodiment. Thus, the quoted phrases, or variations thereof, as recited throughout this specification are not necessarily all referring to the same embodiment. 
     Similarly, it should be appreciated that in the above description of embodiments, various features are sometimes grouped together in a single embodiment, Figure, or description thereof for the purpose of streamlining the disclosure. This method of disclosure, however, is not to be interpreted as reflecting an intention that any claim require more features than those expressly recited in that claim. Rather, as the following claims reflect, inventive aspects lie in a combination of fewer than all features of any single foregoing disclosed embodiment. Thus, the claims following this Detailed Description are hereby expressly incorporated into this Detailed Description, with each claim standing on its own as a separate embodiment. This disclosure includes all permutations of the independent claims with their dependent claims. 
     Recitation in the claims of the term “first” with respect to a feature or element does not necessarily imply the existence of a second or additional such feature or element. Elements recited in means-plus-function format are intended to be construed in accordance with 35 U.S.C. §112 Para. 6. It will be apparent to those having skill in the art that changes may be made to the details of the above-described embodiments without departing from the underlying principles of the invention. Embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows. 
     While specific embodiments and applications of the present invention have been illustrated and described, it is to be understood that the invention is not limited to the precise configuration and components disclosed herein. Various modifications, changes, and variations which will be apparent to those skilled in the art may be made in the arrangement, operation, and details of the methods and systems of the present invention disclosed herein without departing from the spirit and scope of the invention.