Abstract:
A primary gas flow aperture communicates between upstream and the downstream sides of a bulkhead securable across an inflator discharge passageway, accommodating some inflation gas flow through the passageway. A deformable flow control panel peripherally secured on the downstream side of the bulkhead has a closure portion obscuring some inflation gas flow past the bulkhead. Pressure of the inflation gas on the closure portion deforms the control panel away from the bulkhead. A primary gas flow window through the flow control panel overlies all or some of the primary gas flow aperture. When the primary gas flow window is larger than or equal to the primary gas flow aperture, supplemental gas flow apertures are formed through the bulkhead separated from the primary gas flow aperture. Otherwise, supplemental gas flow windows are formed through the flow control panel separated from the primary gas flow window.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to vehicle passenger safety modules that use pressurized gas from an inflator to deploy an airbag between passengers and the interior of a vehicle in the event of a collision. The present invention pertains to such an inflator and, with more particularity, to the discharge orifice for pressurized inflation gas produced in the gas generation chamber of that inflator. 
         [0003]    2. Background 
         [0004]    An airbag for a vehicle passenger safety module includes an inflation portion that captures pressurized gas from an inflator, thereby becoming a gas-filled cushion interposed between a vehicle occupant and the interior vehicle surfaces surrounding that occupant. 
         [0005]    Typically, the inflator is ignited electrically in response to a momentum monitor carried in the vehicle. The inflator is a structure having walls sufficiently sturdy to safely retain inflation gas at high pressures and to direct the pressurized inflation gas therefrom in directions and in quantities that are optimally suited to nondestructively, but efficiently, inflate an airbag cushion. The pressurized inflation gas is produced in an internal gas generation chamber of the inflator as a result of a single or a series of extremely rapid reactions. The pressurized inflation gas flows from the gas generation chamber through a discharge passageway to the exterior of the inflator. 
         [0006]    The temperatures and the combustion pressures arising in the gas generation chamber depend on the properties of the various materials employed inside the gas generation chamber to produce pressurized inflation gas. Singular chemical reactions of modest quantities of medium energy materials give rise to modest combustion pressures and low temperatures in the gas generation chamber, which in turn generally result in a low volume production of inflation gas. Low volume inflation gas production may be appropriate in view of the location and the intended function of the airbag into which the inflation gas is to be directed. 
         [0007]    On the other hand, conditions may exist in which the production of a high volume of pressurized inflation gas is a necessity to fully implement intended passenger safety measures through the inflation of, for example, larger airbags. In such circumstances, a plurality of reactions may be conducted in the inflator involving major quantities of high energy materials. Then the temperatures and combustion pressures produced in the gas generation chamber of the inflator can become extreme. 
         [0008]    Pressurized inflation gas from the gas generation chamber of an inflator flows through a discharge passageway to the exterior of the inflator. A discharge orifice is located in the discharge passageway in order to establish, for pressurized inflation gas leaving the gas generation chamber, an effective outflow cross section that is suited to conditions anticipated in the gas generation chamber. 
       BRIEF SUMMARY OF THE INVENTION 
       [0009]    A discharge orifice having fixed dimensions is unable to adapt to changes in the flow of pressurized inflation gas in the discharge passageway, thereby to compensate for increases in the temperatures and the combustion pressures produced in the gas generation chamber. This is the case even during a single-stage reaction in the gas generation chamber. In a multiple-stage series of reactions, the variation in the temperature and combustion pressure arising in a gas generation chamber can be quite substantial. 
         [0010]    Thus, in an inflator, when a discharge orifice of fixed dimension is tuned with the intention of maintaining a desired combustion pressure under specified temperature conditions during the high volume inflation gas production that occurs in a multiple-stage series of reactions, the discharge orifice will be too large to maintain the desired combustion pressure when the inflator is used under lower temperature conditions in, for example, a single-stage reaction or an initial period of a multiple-stage series of reactions. On the other hand, if a discharge orifice of fixed dimension is sized to maintain a desired combustion pressure for a single-stage reaction under lower temperature conditions, the discharge orifice will be insufficient in size to permit sufficiently rapid pressurized inflation gas outflow during conditions of high volume inflation gas production and higher temperatures. This could cause combustion pressures in the gas generation chamber to exceed the structural limits of the inflator. 
         [0011]    Accordingly, it is an object of the present invention to decrease the difference arising in a gas generation chamber between the lower temperature, single-stage reactions associated with low volume inflation gas production and the higher temperature, multiple-stage reactions required for high volume inflation gas production. The inventive gas discharge orifice and the methods associated therewith address the temperatures and output-induced pressure differentials arising in the gas generation chamber of an inflator of a vehicle passenger safety module. These differentials are particularly challenging in the case of multiple-stage reaction, high volume pressurized inflation gas production. 
         [0012]    Each embodiment of the inventive discharge orifice disclosed herein controls combustion pressures arising upstream therefrom by deforming a control surface and thereby exposing additional cross-sectional flow areas through the discharge orifice. The control surface is carried on a deformable flow control panel. Under normal temperatures or in single-stage reactions, the control panel remains in a disposition that limits the flow of pressurized inflation gas through the discharge orifice to a single low-flow effective outflow cross section. When the combustion pressure upstream of the discharge orifice increases due, either to temperature, pressure, or inflation gas output, the flow control panel is deformed in such a manner as to open to the flow of pressurized inflation gas additional amounts of effective outflow cross section. 
         [0013]    Accordingly, a gas discharge orifice incorporating teachings of the present invention includes a continuous open frame securable within the discharge passageway circumscribing the flow of inflation gas therethrough and an inflation gas flow control valve filling the frame. The flow control valve operates from an open first condition thereof into an open second condition thereof responsive to the development of combustion pressure in the gas generation chamber greater than a predetermined threshold combustion pressure. The first condition of the flow control valve presents to the flow of inflation gas through the discharge passageway a first effective outflow cross section that is tuned to low volume inflation gas production in the gas generation chamber, while the second condition of the flow control valve presents to the flow of inflation gas in the discharge passageway a second effective outflow cross section that is greater than the first effective outflow cross section and that is tuned to high volume inflation gas production in the gas generation chamber. In this manner, the flow control valve moderates the difference between the combustion pressure arising in the gas generation chamber during low volume inflation gas production and the combustion pressure arising in the gas generation chamber during high volume inflation gas production. Operation of the flow control valve from the first condition thereof into the second condition thereof may be configured to be irreversible. 
         [0014]    In one aspect of the present invention, an embodiment of the flow control valve includes a rigid bulkhead that is peripherally secured to the frame and that has an upstream side directed toward the gas generation chamber when the frame of the gas discharge orifice is secured in the discharge passageway, and a downstream side opposite therefrom. A primary gas flow aperture is formed through the bulkhead communicating between the upstream side and the down stream side thereof. A portion of the primary gas flow aperture accommodates a flow of inflation gas through the flow control valve in both the first condition and the second condition thereof. A deformable flow control panel is peripherally secured to the frame adjacent to and on the downstream side of the bulkhead. In the first condition of the flow control valve the control panel contacts the bulkhead with a closure portion of the control panel obscuring a portion of the primary gas flow aperture. The control panel is urged out of contact with the bulkhead into the second condition of the flow control valve by pressure exerted by inflation gas through the through the primary gas flow aperture against the closure portion of the control panel. The primary gas flow aperture defines the second effective outflow cross section presented to the flow of inflation gas in the second condition of the flow control valve. 
         [0015]    A primary gas flow window is formed through the flow control panel. In the first condition of the flow control valve, the primary gas flow window overlies a portion of the primary gas flow aperture in the bulkhead. The primary gas flow window is smaller in cross section than the primary gas flow aperture. A plurality of supplemental gas flow windows are formed through the flow control panel at locations radially separated from the primary gas flow window. In the second condition of the flow control valve the supplemental gas flow windows contribute to defining the second effective outflow cross section presented to the flow of inflation gas. 
         [0016]    In an alternative embodiment of the flow control valve, the entire primary gas flow aperture accommodates a flow of inflation gas through the flow control valve in both the first condition and the second condition thereof, and a relief aperture is formed through the bulkhead at a location separated from the primary gas flow aperture. A deformable flow control panel is peripherally secured to the frame adjacent to and on the downstream side of the bulkhead. In the first condition of the flow control valve the control panel contacts the bulkhead with a closure portion of the control panel obscuring the relief aperture. The control panel is urged out of contact with the bulkhead into the second condition of the flow control valve by pressure exerted by inflation gas through the relief aperture against the closure portion of the control panel. The primary gas flow aperture defines the first effective outflow cross section presented to the flow of inflation gas in the first condition of the flow control valve. In the second condition of the flow control valve the relief aperture contributes to defining the second effective outflow cross section presented to the flow of inflation gas. A primary gas flow window is formed through the flow control panel. The gas flow window is larger in cross section than the primary gas flow aperture in the bulkhead. In the first condition of the flow control valve a portion of the primary gas flow window is overlapped by the primary gas flow aperture. 
         [0017]    In yet another embodiment of the flow control valve, a deformable flow control panel is peripherally secured to the frame. The flow control panel has an upstream side directed toward the gas generation chamber, when the frame is secured in the discharge passageway, and a downstream side opposite therefrom. In the first condition of the flow control valve the upstream side of the flow control panel is crimped into engagement with itself in a folded region of the flow control panel. The folded region is concentric with the primary gas flow window. A primary gas flow window is formed through the flow control panel at a central location. The primary gas flow window defines the first effective outflow cross section presented to the flow of inflation gas in the first condition of the flow control valve. A plurality of supplemental gas flow windows are formed through the folded region of the flow control panel. In the first condition of the flow control valve the supplemental gas flow windows are obscured by the crimping of the flow control panel upon itself, while in the second condition of the flow control valve the control panel is urged by the pressure of inflation gas against the upstream side of the flow control panel to uncrimp the folded region of the flow control panel and open the supplemental gas flow windows. 
         [0018]    According to another aspect of the present invention, a gas discharge orifice for a vehicle safety airbag inflator includes a rigid bulkhead that is peripherally securable across the discharge passageway and that has an upstream side directed toward the gas generation chamber, when the bulkhead is secured in the discharge passageway, and a downstream side opposite therefrom. A primary gas flow aperture is formed through the bulkhead communicating between the upstream side and the down stream side thereof. At least a portion of the primary gas flow aperture accommodates a flow of inflation gas through the gas discharge orifice on all occasions. A deformable flow control panel is peripherally secured to the bulkhead on the downstream side thereof. The control panel contacts the bulkhead with a closure portion of the control panel obscuring inflation gas flow past the bulkhead, but the control panel is urged out of contact with the bulkhead by pressure exerted by inflation gas through the bulkhead against the closure portion of the control panel. 
         [0019]    A primary gas flow window is formed through the flow control panel overlying at least a portion of the primary gas flow aperture in the bulkhead, and a plurality of supplemental gas flow windows are formed through the flow control panel at locations radially separated from the primary gas flow window. The primary gas flow window may be smaller in cross section than the primary gas flow aperture in the bulkhead. 
         [0020]    Alternatively, the primary gas flow window in the flow control panel is larger in cross section than the primary gas flow aperture in the bulkhead, and a plurality of relief apertures is formed through the bulkhead at a locations radially separated from the primary gas flow aperture. 
         [0021]    The present invention also includes methods for moderating the difference between the combustion pressure in the gas generation chamber of a vehicle safety airbag inflator during low volume inflation gas production and the combustion pressure in the gas generation chamber during high volume inflation gas production. 
         [0022]    One embodiment of such a method includes determining a predetermined threshold combustion pressure above which the combustion pressure arising in the gas generation chamber ceases to correspond to low volume inflation gas production and sensing the combustion pressure in the gas generation chamber from a location in the discharge passageway. The effective gas outflow cross section of the discharge passageway is then sized in the following manner. When the combustion pressure is less than the predetermined threshold combustion pressure, the flow of inflation gas through the discharge passageway is presented with a first effective gas outflow cross section that is tuned to low volume inflation gas production; and when the combustion pressure is greater than or equal to the predetermined threshold combustion pressure, the flow of inflation gas in the discharge passageway is presented with a second effective gas outflow cross section that is greater than the first effective gas outflow cross section and that is tuned to high volume inflation gas production. 
         [0023]    Sensing the existing combustion pressure in the gas generation chamber from a location in the discharge passageway involves forming centrally through a deformable, substantially planar flow control panel a primary gas flow window, and securing the flow control panel across the discharge passageway. The flow control panel is deformable downstream within the flow of inflation gas in the discharge passageway during high volume inflation gas production. Sizing effective gas outflow cross section of the discharge passageway involves producing a primary gas flow aperture centrally through a rigid bulkhead, disposing the bulkhead in the discharge passageway upstream of and in parallel face-to-face abutment with the flow control panel with the primary gas flow aperture in fluid-flow alignment with the primary gas flow window, and rendering the primary gas flow aperture unequal in size to the primary gas flow window. The cross-sectional area of the smaller of the primary gas flow aperture and the primary gas flow window corresponds to the first effective gas outflow cross section. The step of sensing concludes by creating a plurality of relief openings through the one of the bulkhead and the flow control panel associated with the smaller of the primary gas flow aperture and the primary gas flow window, doing so in such a manner that the total of the cross-sectional areas of the relief openings combine with the cross-sectional area of the smaller of the primary gas flow aperture and the primary gas flow window to correspond to the second effective gas outflow cross section. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0024]    In order that the manner in which the above-recited and other features and advantages of the present invention are obtained will be readily understood, a more particular description of the present invention briefly described above will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the present invention and are not therefore to be considered to be limiting of the scope thereof, the present invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: 
           [0025]      FIG. 1  is an elevation view, superimposed against a profile in phantom of a side window of a typical passenger vehicle, of an inflated curtain airbag for a vehicle passenger safety module that is attached to the discharge end of an inflator incorporating teachings of the present invention; 
           [0026]      FIG. 2  is an enlarged view in partial cross section of the inflator of  FIG. 1  showing the combustion chamber and the discharge passageway thereof and depicting in diagrammatic manner the relationship to those structures of a first embodiment of a discharge orifice incorporating teachings of the present invention; 
           [0027]      FIG. 3  is a perspective view of a second embodiment of a discharge orifice incorporating teachings of the present invention; 
           [0028]      FIG. 4  is a disassembled perspective view of the discharge orifice of  FIG. 3 ; 
           [0029]      FIG. 5A  is a elevation cross-sectional view of the discharge orifice of  FIG. 3  taken along section line  5 A- 5 A therein, thereby to depict the discharge orifice in an open first condition thereof wherein the discharge orifice presents to the flow of inflation gas through the discharge passageway a first effective outflow cross section tuned to low volume inflation gas production; 
           [0030]      FIG. 5B  is a elevation cross-sectional view of the discharge orifice of  FIG. 5A  in an open second condition thereof wherein the discharge orifice presents to the flow of inflation gas through the discharge passageway a second effective outflow cross section tuned to low volume inflation gas production; 
           [0031]      FIG. 6  is a perspective view of a third embodiment of a discharge orifice incorporating teachings of the present invention; 
           [0032]      FIG. 7  is a disassembled perspective view of the discharge orifice of  FIG. 6 ; 
           [0033]      FIG. 8A  is a elevation cross-sectional view of the discharge orifice of  FIG. 6  taken along section line  8 A- 8 A therein, thereby to depict the discharge orifice in an open first condition thereof wherein the discharge orifice presents to the flow of inflation gas through the discharge passageway a first effective outflow cross section tuned to low volume inflation gas production; 
           [0034]      FIG. 8B  is a elevation cross-sectional view of the discharge orifice of  FIG. 8A  in an open second condition thereof wherein the discharge orifice presents to the flow of inflation gas through the discharge passageway a second effective outflow cross section tuned to low volume inflation gas production; 
           [0035]      FIG. 9  is a perspective view of a fourth embodiment of a discharge orifice incorporating teachings of the present invention; 
           [0036]      FIG. 10A  is a elevation cross-sectional view of the discharge orifice of  FIG. 9  taken along section line  10 A- 10 A therein, thereby to depict the discharge orifice in an open first condition thereof wherein the discharge orifice presents to the flow of inflation gas through the discharge passageway a first effective outflow cross section tuned to low volume inflation gas production; 
           [0037]      FIG. 10B  is a elevation cross-sectional view of the discharge orifice of  FIG. 10A  in an open second condition thereof wherein the discharge orifice presents to the flow of inflation gas through the discharge passageway a second effective outflow cross section tuned to low volume inflation gas production; and 
           [0038]      FIG. 11  is a flowchart of steps in a method incorporating teachings of the present invention by which to moderate the difference between the combustion pressure in the gas generation chamber of a vehicle safety airbag inflator during low volume inflation gas production and the combustion pressure in the gas generation chamber during high volume inflation gas production. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0039]    The presently preferred embodiments of the present invention will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout. It will be readily understood that the components of the apparatus of present invention, as generally described and illustrated in the figures herein, could be arranged and designed in a wide variety of different configurations, and that the steps of the methods of the present invention could be performed in diverse manners and in various orders. Thus, the following more detailed description of the embodiments of the present invention, as represented in  FIGS. 1-11 , is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. 
         [0040]      FIG. 1  is an elevation view of a vehicle passenger safety module  10  that includes a curtain airbag  12  communicating with a discharge end  14  of an inflator  16 . Although for illustrative purposes,  FIG. 1  shows a curtain airbag, persons of skill in the art will understand that the advantages of the present invention can also be adapted and used with other types of airbags. Pressurized inflation gas with which to deploy airbag  12  is produced in a gas generation chamber within inflator  16  and flows therefrom through a discharge passageway to discharge end  14  of inflator  16 . While neither the gas generation chamber nor the discharge passageway of inflator  16  is visible in  FIG. 1 , these structures do appear in subsequent drawings. 
         [0041]    Inflator  16  incorporates teachings of the present invention by including a discharge orifice that is also not visible in  FIG. 1 . The inventive discharge orifice moderates the difference between the combustion pressure in the gas generation chamber of inflator  16  during low volume inflation gas production and the combustion pressure in the gas generation chamber during high volume inflation gas production. Pressurized inflation gas from the gas generation chamber flows through the discharge passageway to the exterior of inflator  16  and is released from discharge end  14  of inflator  16  for passage into airbag  12 . For perspective, these elements of safety module  10  are superimposed against a profile in phantom of a side of a typical passenger vehicle  18 . Airbag  12  includes an inflation portion  20  that becomes a protective cushion by capturing pressurized inflation gas from inflator  14 , and a sleeve-like inlet portion  22  that communicates inflation gas into inflation portion  20 . The open end  24  of inlet portion  22  of inflator  12  has been advanced over discharge end  14  of inflator  16  and secured thereabout by an attachment bracket  26 . 
         [0042]      FIG. 2  is an enlarged view in partial cross section of inflator  16  in  FIG. 1 . Discharge end  14  of inflator  16  is inserted into inlet portion  22  of airbag  12 , which is drawn in phantom. Attachment bracket  26  has been omitted to improve comprehension. Pressurized inflation gas I can be seen to be entering airbag  12  through a plurality of egress apertures  28  radially disposed about the distal tip  30  of discharge end  14  of inflator  16 . 
         [0043]    Pressurized inflation gas I is produced in a gas generation chamber  32  interior of inflator  16  and communicated therefrom to egress apertures  28  through a discharge passageway  34 . Mounted within and across discharge passageway  34  is a discharge orifice  40  for inflator  16  that incorporates teachings of the present invention. Accordingly, discharge orifice  40  moderates the difference between the combustion pressure in gas generation chamber  32  during low volume inflation gas production and the combustion pressure in gas generation chamber  32  during high volume inflation gas production. By so doing, discharge orifice  40  serves to raise the combustion pressure in gas generation chamber  32  during low volume inflation gas production and lower the combustion pressure in gas generation chamber  32  during high volume inflation gas production. 
         [0044]    The attainment of this advantageous result will be explored, initially in general terms by reference to discharge orifice  40  in the enlarged inset associated with  FIG. 2 . Thereafter, that achievement will be discussed with more specificity in relation to a plurality of embodiments of discharge orifices incorporating teachings of the present invention that are depicted in subsequent figures. 
         [0045]    The flow of pressurized inflation gas I within discharge passageway  34  establishes a directional frame of reference within inflator  16 . Thus, gas generation chamber  32  is upstream in the flow of pressurized inflation gas I from discharge passageway  34 , upstream direction U being indicated by an arrow directed to the left adjacent to the inset of  FIG. 2 . On the other hand, egress apertures  28  are located downstream in the flow of pressurized inflation gas I from discharge passageway  34  and gas generation chamber  32 , downstream direction D being indicated by an arrow directed to the right adjacent to the inset of  FIG. 2 . Discharge orifice  40  is depicted in the inset associated with  FIG. 2  as being positioned along the course of discharge passageway  34 . Thus, discharge orifice  40  has an upstream side  42  oriented toward gas generation chamber  32  and a downstream side  44  oriented oppositely therefrom. 
         [0046]    Broadly, discharge orifice  40  includes a continuous open frame  46  that is securable within discharge passageway  34  circumscribing the flow of pressurized inflation gas I therethrough. An inflation gas flow control valve  48  fills frame  46  between upstream side  42  and downstream side  44  of discharge orifice  40 . Flow control valve  48  operates irreversibly from an open first condition thereof into an open second condition thereof in response to the development of a combustion pressure P 32  in gas generation chamber  32  that is greater than predetermined threshold combustion pressure P T . The development of a combustion pressure P 32  that is greater than a predetermined threshold combustion pressure P T  is detected within discharge passageway  34  by the structures of flow control valve  48 , rather than within gas generation chamber  32 . 
         [0047]    In the first condition of flow control valve  48 , pressurized inflation gas I passing through discharge passageway  34  is presented with a first effective outflow cross section that is tuned to low volume inflation gas production in gas generation chamber  32 . The effective outflow cross section in discharge passageway  34  is restricted by flow control valve  48  to a relatively small effective outflow cross section. This in turn increases the back pressure maintained in upstream direction U toward and inside gas generation chamber  32 , increasing the speed of the development of higher combustion pressures there. 
         [0048]    In the second condition of control valve  48 , the flow of inflation gas I in discharge passageway  34  is presented with a second effective outflow cross section that is greater than the first effective outflow cross section and is tuned to high volume inflation gas production in gas generation chamber  32 . Both the first condition and the second condition of flow control valve  48  are open to the passage of some pressurized inflation gas I therethrough on all occasions, but in the first condition the effective outflow cross section presented to the passage of pressurized inflation gas I is less than the effective outflow cross section presented to the passage of pressurized inflation gas I in the second condition. 
         [0049]    Flow control valve  40  may accordingly be viewed as an ever-open relief valve that increases the effective outflow cross section presented to the passage of pressurized inflation gas I, and correspondingly reduces the back pressure maintained upstream toward and inside gas generation chamber  32 , when the combustion pressure P 32  in gas generation chamber  32  begins to surpass predetermined threshold combustion pressure P T . The reduction of back pressure is suited to increasing the outflow volume of pressurized inflation gas I through discharge passageway  34 , a condition appropriate to high volume inflation gas production. In this light, predetermined threshold combustion pressure P T  is chosen to equal a combustion pressure above which conditions in gas generation chamber  32  cease to correspond to those associated with low volume inflation gas production. 
         [0050]      FIG. 3  is a perspective view of a second embodiment of a discharge orifice  50  incorporating teachings of the present invention, while  FIG. 4  is a disassembled perspective view of the elements of discharge orifice  50 . Upstream direction U and downstream direction D are shown by arrows. In  FIGS. 3 and 4  only the downstream sides of the depicted structures are visible. The upstream sides of those structures are presented subsequently in discussing the operation of discharge orifice  50 . 
         [0051]    Discharge orifice  50  includes a continuous open frame  52  that is intended to be secured within discharge passageway  34  circumscribing the flow of pressurized inflation gas I therethrough. A rigid, plate-like bulkhead  54  is secured about the periphery  56  thereof within frame  52 . Bulkhead  54  has an upstream side that is directed toward gas generation chamber  32  when frame  52  with bulkhead  54  carried therein is secured in discharge passageway  34  in the manner of discharge orifice  40  in  FIG. 2 . Opposite therefrom bulkhead  54  has a downstream side  58  that is visible in  FIGS. 3 and 4 . 
         [0052]    A primary gas flow aperture  60  is formed through bulkhead  54  communicating between downstream side  58  and the upstream side thereof Primary gas flow aperture  60  as seen to best advantage in  FIG. 4  is a circular opening centrally located within bulkhead  54 . Nonetheless, alternative configurations are possible of a primary gas flow aperture through a bulkhead, such as bulkhead  54 . As will be borne out subsequently in an exploration of the operation of discharge orifice  50 , a portion of primary gas flow aperture  60  accommodates some flow of pressurized inflation gas I through discharge orifice  50  on all occasions. 
         [0053]    Discharge orifice  50  also includes a relatively thin, deformable flow control panel  62  that is secured by the periphery  64  thereof within frame  52 . Flow control panel  62  has an upstream side that is directed toward gas generation chamber  32  when frame  52  carrying flow control panel  62  is secured in discharge passageway  34  in the manner of discharge orifice  40  in  FIG. 2 . Oppositely therefrom, flow control panel  62  has a downstream side  66 . As suggested by the assembly arrows A in  FIG. 4 , when flow control panel  62  is carried in frame  52 , the upstream side of flow control panel  62  is adjacent to and in contact with downstream side  58  of bulkhead  54 . A primary gas flow window  68  is formed through flow control panel  62  communicating between downstream side  66  and the upstream side thereof. As illustrated in  FIGS. 3 and 4 , primary gas flow window  68  is a circular opening centrally formed through flow control panel  62 . Nonetheless, alternative configurations are possible of a primary gas flow window through a flow control panel, such as control panel  62 . 
         [0054]    Primary gas flow window  68  in flow control panel  62  is smaller in cross-sectional area than is primary gas flow aperture  60  in bulkhead  54 . When frame  52 , bulkhead  54 , and flow control panel  62  are assembled as shown in  FIG. 3 , primary gas flow aperture  60  of bulkhead  54  and primary gas flow window  68  of flow control panel  62  are concentrically aligned. In that condition, a closure portion  70  of flow control panel  62  adjacent to and circumscribing primary gas flow window  68  obscures a portion of primary gas flow aperture  60  in bulkhead  54 . The location of primary gas flow aperture  60  behind and in abutment with flow control panel  62  is indicated in  FIGS. 3 and 4  on downstream side  66  of flow control panel  62  in the form of a phantom primary flow aperture  60 ′, which accordingly defines the radially outermost terminus of closure portion  70  of flow control panel  62 . 
         [0055]    A plurality of relatively small supplemental gas flow windows  72  are formed through flow control panel  62  uniformly circumferentially spaced about gas flow window  68  at equal radial distances therefrom. Nonetheless, alternative configurations are possible of supplemental gas flow windows  72  through a flow control panel, such as flow control panel  62 . When flow control panel  62  and bulkhead  54  are assembled within frame  52 , supplemental gas flow windows  72  are blocked by bulkhead  54 . It is, for example, only through supplemental gas flow windows  72  that downstream side  58  of bulkhead  54  is visible in  FIG. 3 . 
         [0056]      FIG. 5A  is a cross-sectional elevation view of discharge orifice  50  from  FIG. 3  disposed in discharge passageway  34  within discharge end  14  of inflator  16  in the manner of discharge orifice  40  in  FIG. 2 . Accordingly,  FIG. 5A  depicts discharge orifice  50  in an open first condition thereof in which discharge orifice  50  presents to the flow of pressurized inflation gas I through discharge passageway  34  a first effective outflow cross section that is tuned to low volume inflation gas production. Frame  52  is lodged in discharge passageway  34 . Periphery  56  of bulkhead  54  and periphery  64  of flow control panel  62  are secured within frame  52  traversing the flow of pressurized inflation gas I through discharge passageway  34 . Downstream side  58  of bulkhead  54  is presented through supplemental gas flow window  72  in flow control panel  62 , while the upstream side  74  of bulkhead  54  is oriented in upstream direction U, toward gas generation chamber  32 . 
         [0057]    Bulkhead  54  is disposed upstream of and in parallel face-to-face abutment with the upstream side  76  of flow control panel  62 . Primary gas flow aperture  60  in bulkhead  54  is in fluid-flow alignment with primary gas flow window in flow control panel  62 , but closure portion  70  of flow control panel  62  partially blocks the passage of pressurized inflation gas I through primary flow aperture  60 . Accordingly, in the open first condition of discharge orifice  50 , primary gas flow window  68  in flow control panel  62  defines the first effective outflow cross section presented to the flow of pressurized inflation gas I. As combustion pressure P 32  increases, the pressure exerted on upstream side  76  of closure portion  70  of flow control panel  62  also increases. 
         [0058]    Eventually, when combustion pressure P 32  reaches a predetermined combustion pressure P T  at and above which low volume inflation gas production in gas generation chamber  32  is no longer evidenced, discharge orifice  50  is driven irreversibly into the open second condition thereof depicted in  FIG. 5B . The development of predetermined combustion pressure P T  in gas generation chamber  32  increases the pressure against upstream side  76  of closure portion  70  of flow control panel  62  sufficiently to urge flow control panel  62  to deform in downstream direction D in the flow of pressurized inflation gas I. This separates upstream side  76  of flow control panel  62  from downstream side  58  of bulkhead  54 . 
         [0059]    Once upstream side  76  of flow control panel  62  ceases to be in contact with downstream side  58  of bulkhead  54 , closure portion  70  of flow control panel  62  no longer restricts the flow of pressurized inflation gas I through primary gas flow aperture  60  in bulkhead  54 . Supplemental gas flow windows  72  in flow control panel  62  simultaneously become opened, affording passage for additional pressurized inflation gas I through control panel  62 . In the open second condition of discharge orifice  50 , bulkhead  54  and flow control panel  62  together present to the flow of pressurized inflation gas I in discharge passageway  34  a second effective outflow cross section that is greater than the first effective outflow cross section presented in the open first condition of discharge orifice  50 . 
         [0060]    The increase in effective outflow cross section arising in the open second condition of discharge orifice  50  reduces the back pressure communicated from discharge orifice  50  in upstream direction U through discharge passageway  34  into gas generation chamber  32 . In this manner, discharge orifice  50  moderates the difference between combustion pressure P 32  arising during low volume inflation gas production and combustion pressure P 32  arising during high volume inflation gas production. 
         [0061]      FIG. 6  is a perspective view of a third embodiment of a discharge orifice  80  incorporating teachings of the present invention, while  FIG. 7  is a disassembled perspective view of the elements of discharge orifice  80 . Upstream direction U and downstream direction D are shown by arrows. In  FIGS. 6 and 7  only the downstream sides of the depicted structures are visible. The upstream sides of those structures are presented subsequently in discussing the operation of discharge orifice  80 . 
         [0062]    Discharge orifice  80  includes a continuous open frame  82  that is intended to be secured within discharge passageway  34  circumscribing the flow of pressurized inflation gas I therethrough. A rigid bulkhead  84  is secured about the periphery  86  thereof within frame  82 . Bulkhead  84  has an upstream side that is directed toward gas generation chamber  32  when frame  82  with bulkhead  84  carried therein is secured in discharge passageway  34  in the manner of discharge orifice  40  in  FIG. 2 . Opposite therefrom, bulkhead  84  has a downstream side  88  that is visible in  FIGS. 3 and 4 . 
         [0063]    A primary gas flow aperture  90  is formed through bulkhead  84  communicating between downstream side  88  and the upstream side thereof. Primary gas flow aperture as seen to best advantage in  FIG. 7  is a circular opening centrally located within bulkhead  84 . Nonetheless, alternative configurations are possible of a primary gas flow aperture through a bulkhead, such as bulkhead  84 . As will be borne out subsequently in an exploration of the operation of discharge orifice  80 , gas flow aperture  90  accommodates some flow of pressurized inflation gas I through discharge orifice  80  on all occasions. 
         [0064]    A plurality of relatively small supplemental gas flow apertures  92  are formed through bulkhead  84  uniformly circumferentially spaced about primary gas flow aperture  90  at equal radial distances therefrom. Nonetheless, alternative configurations are possible of supplemental gas flow apertures through a bulkhead, such as bulkhead  84 . 
         [0065]    Discharge orifice  80  also includes a relatively thin, deformable flow control panel  94  that is secured by the periphery  96  thereof within frame  82 . Flow control panel  94  has an upstream side that is directed toward gas generation chamber  32  when frame  82  carrying flow control panel  94  is secured in discharge passageway  34  in the manner of discharge orifice  40  in  FIG. 2 . Oppositely therefrom, flow control panel  94  has a downstream side  98 . As suggested by assembly arrows A in  FIG. 7 , when flow control panel  94  is carried in frame  82 , the upstream side of flow control panel  94  is adjacent to and in contact with downstream side  88  of bulkhead  84 . 
         [0066]    A primary gas flow window  100  is formed through flow control panel  94  communicating between downstream side  98  and the upstream side thereof. As illustrated in  FIGS. 6 and 7 , primary gas flow window  100  is a circular opening centrally formed through flow control panel  94 . Nonetheless, alternative configurations are possible of a primary gas flow window through a flow control panel, such as flow control panel  94 . 
         [0067]    Primary gas flow window  100  in flow control panel  94  is larger in cross-sectional area than is primary gas flow aperture  90  in bulkhead  84 . When frame  82 , bulkhead  84 , and flow control panel  94  are assembled as shown in  FIG. 6 , primary gas flow aperture  90  in bulkhead  84  and primary gas flow window  100  in flow control panel  94  are concentrically aligned. Thus, it is only through primary gas flow window  100  that downstream side  88  of bulkhead  84  is visible in  FIG. 6 . When flow control panel  94  and bulkhead  84  are assembled within frame  82 , supplemental gas flow apertures  92  in bulkhead  84  are blocked by flow control panel  94 . In that condition, flow control panel  94  includes a plurality of closure portions  102  that obscure respective of supplemental gas flow apertures  92  in bulkhead  84 . The location of supplemental gas flow apertures  92  behind and in abutment with flow control panel  94  is indicated in  FIGS. 6 and 7  on downstream side  98  of flow control panel as phantom primary flow control apertures  92 ′, which accordingly define the radially outermost terminus of each respective closure portion  102  of flow control panel  94 . 
         [0068]      FIG. 8A  is a cross-sectional elevation view of discharge orifice  80  from  FIG. 6  disposed in discharge passageway  34  within discharge end  14  of inflator  16  in the manner of discharge orifice  40  in  FIG. 2 . Accordingly,  FIG. 8A  depicts discharge orifice  80  in an open first condition thereof in which discharge orifice  80  presents to the flow of pressurized inflation gas I through discharge passageway  34  a first effective outflow cross section that is tuned to low volume inflation gas production. Frame  82  is lodged in discharge passageway  34 . Periphery  86  of bulkhead  84  and periphery  96  of flow control panel  94  are secured within frame  82  traversing the flow of pressurized inflation gas I through discharge passageway  34 . Downstream side  88  of bulkhead  84  is presented through primary gas flow window  100  in flow control panel  94 , while upstream side  104  of bulkhead  84  is oriented in upstream direction U, toward gas generation chamber  32 . 
         [0069]    Bulkhead  84  is disposed upstream of and in parallel face-to-face abutment with upstream side  106  of flow control panel  94 . Primary gas flow window  100  in flow control panel  94  is in fluid-flow alignment with primary gas flow aperture  90  in bulkhead  84 , but closure portions  102  of flow control panel  94  block the passage of pressurized inflation gas I through supplemental gas flow apertures  92  in bulkhead  84 . Accordingly, in the open first condition of discharge orifice  80 , primary gas flow aperture  90  in bulkhead  84  defines the first effective outflow cross section presented to the flow of pressurized inflation gas I. As combustion pressure P 32  increases, the pressure exerted on upstream side  106  of closure portions  102  of flow control panel  94  also increases. 
         [0070]    Eventually, when combustion pressure P 32  reaches a predetermined combustion pressure P T  at and above which low volume inflation gas production in gas generation chamber  32  is no longer evidenced, discharge orifice  80  is driven irreversibly into the open second condition thereof depicted in  FIG. 8B . The development of predetermined combustion pressure P T  in gas generation chamber  32  increases the pressure against upstream side  106  of closure portions  102  of flow control panel  94  sufficiently to urge flow control panel  94  to deform in downstream direction D in the flow of pressurized inflation gas I. This separates upstream side  106  of flow control panel  94  from downstream side  88  of bulkhead  84 . 
         [0071]    Once upstream side  106  of flow control panel  94  ceases to be in contact with downstream side  88  of bulkhead  54 , closure portions  102  of flow control panel  94  no longer restrict the flow of pressurized inflation gas I through supplemental gas flow apertures  92  in bulkhead  84 . Supplemental gas flow apertures  92  in bulkhead  84  then become opened, affording passage for additional pressurized inflation gas I through bulkhead  84 . In the open condition of discharge orifice  80 , bulkhead  84  and flow control panel  94  together present to the flow of pressurized inflation gas I in discharge passageway  34  a second effective outflow cross section that is greater than the first effective outflow cross section presented in the open first condition of discharge orifice  80 . 
         [0072]    The increase in effective outflow cross section arising in the open second condition of discharge orifice  80  reduces the back pressure communicated from discharge orifice  80  in upstream direction U through discharged passageway  34  into gas generation chamber  32 . In this manner, discharge orifice  80  moderates the difference between combustion pressure P 32  arising during low volume inflation gas production and combustion pressure P 32  arising during high volume inflation gas production. 
         [0073]      FIG. 9  is a perspective view of a fourth embodiment of a discharge orifice  110  incorporating teachings of the present invention. Upstream direction U and downstream direction D are shown by arrows, and only the downstream sides of the depicted structures are visible. The upstream sides of those structures are presented subsequently in discussing the operation of discharge orifice  110 . 
         [0074]    Discharge orifice  110  includes a continuous open frame  112  that is intended to be secured within discharge passageway  34  circumscribing the flow of pressurized inflation gas I therethrough. A deformable flow control panel  114  is secured by the periphery  116  thereof within frame  112 . Flow control panel  114  has an upstream side that is directed toward gas generation chamber  32  when frame  112  carrying flow control panel  114  is secured in discharge passageway  34  in the manner of discharge orifice  40  in  FIG. 2 . Oppositely therefrom, flow control panel  114  has a downstream side  118 . 
         [0075]    A primary gas flow window  120  is formed through flow control panel  114  communicating between downstream side  118  and the upstream side thereof. As illustrated in  FIG. 9 , primary gas flow window  120  is a circular opening centrally formed through flow control panel  114 . Nonetheless alternative configurations are possible of a primary gas flow window through a flow control panel, such as flow control panel  114 . 
         [0076]    Flow control panel  114  includes a folded region  122  wherein the upstream side of flow control panel is crimped into engagement with itself, causing folded region  122  to project in downstream direction D from downstream side  118  of flow control panel  114 . A plurality of supplemental gas flow windows  124  are formed through folded region  122  of flow control panel  114 . Supplemental gas flow windows  124  are so positioned within flow control panel  114  as to be obscured by the upstream side of flow control panel  114  when folded region  122  is crimped as shown in  FIG. 9 . There, folded region  122  of flow control panel  114  assumes the form of a continuous circular structure upstanding from downstream side  118  of flow control panel  114  that is concentrically disposed relative to primary gas flow window  120 . Primary gas flow window  120  affords passage of some pressurized inflation gas I through discharge orifice  110  in all circumstances. 
         [0077]      FIG. 10A  is a cross-sectional elevation view of discharge orifice  110  of  FIG. 9  disposed in discharge passageway  34  within discharge end  14  of inflator  16  in the manner of discharge orifice  40  in  FIG. 2 . Accordingly,  FIG. 10A  depicts discharge orifice  110  in an open first condition thereof in which discharge orifice  110  presents to the flow of pressurized inflation gas I through discharge passageway  34  a first effective outflow cross section that is tuned to low volume inflation gas production. Frame  112  is lodged in discharge passageway  34 , and periphery  116  of flow control panel  114  is secured within the frame  112  traversing the flow of pressurized inflation gas I through discharge passageway  34 . Accordingly, in the open first condition of discharge orifice  110 , primary gas flow window  120  in flow control panel  114  defines the first effective outflow cross section presented to the flow of pressurized inflation gas I. As combustion pressure P 32  increases, the pressure exerted on the upstream side  126  of flow control panel  114  also increases. 
         [0078]    Eventually, when combustion pressure P 32  reaches a predetermined combustion pressure P T  at and above which low volume inflation gas production is no longer evidenced in combustion chamber  32 , discharge orifice  110  is driven irreversibly into the open second condition thereof depicted in  FIG. 10B . The development of predetermined combustion pressure P T  in gas generation chamber  32  increases the pressure against upstream side  126  of flow control panel  114  sufficiently to urge flow control panel  114  to deform in downstream direction D in the flow of pressurized inflation gas I. This uncrimps folded region  122  and opens supplemental gas flow windows  124  to the downstream flow of additional pressurized inflation gas I. In the open second condition of discharge orifice  110 , primary gas flow window  120  and supplemental gas flow windows  124  together present to the flow of pressurized inflation gas I in discharge passageway  34  a second effective outflow cross section that is greater than the first effective outflow cross section presented in the open first condition of discharge orifice  110 . 
         [0079]    The increase in effective outflow cross section arising in the open second condition of discharge orifice  110  reduces the back pressure communicated from discharge orifice  110  in upstream direction U through discharge passageway  34  into gas generation chamber  32 . In this manner discharge orifice  110  moderates the difference between combustion pressure P 32  arising during low volume inflation gas production and combustion pressure P 32  arising during high volume inflation gas production. Although  FIG. 10A  shows gas flow windows  124  extending through just one side of the crimped folded region  122 , in yet other embodiments, the gas flow windows  124  may be configured differently such as extending fully through the crimped folded region  122  so that additional effective outflow can be provided. 
         [0080]    The subject invention also includes methods for moderating the difference between the combustion pressure in the gas generation chamber of a vehicle safety air bag inflator during low volume inflation gas production and the combustion pressure in the gas generation chamber during high volume inflation gas production. 
         [0081]    A first embodiment of such a method  130  is illustrated in  FIG. 11 . From an initiation oval  132 , method  130  proceeds to the step indicated in instruction rectangle  134  of determining a predetermined threshold combustion pressure P T  above which combustion pressure P 32  arising in a gas generation chamber ceases to correspond to low volume inflation gas production. Broadly thereafter, method  130  involves sensing the combustion pressure P 32  in the gas generation chamber from a location in the discharge passageway, as indicated in subroutine rectangle  136 , and, as indicated in subroutine rectangle  138 , sizing the effective gas outflow cross section of the discharge passageway in a manner that is adaptive to a specific threshold change in combustion pressure P 32 . When combustion pressure P 32  is less than predetermined threshold combustion pressure P T , the flow of inflation gas I through the discharge passageway is presented with a first effective gas outflow cross section that is tuned to low volume inflation gas I production in the gas generation chamber. On the other hand, when combustion pressure P 32  is greater than or equal to predetermined threshold combustion pressure P T , the flow of inflation gas I in the discharge passageway is presented with a second effective outflow cross section that is greater than the first effective outflow cross section and that is tuned to high volume inflation gas production in the gas generation chamber. Method  30  concludes at termination oval  140 . 
         [0082]    Sensing combustion pressure P 32  as called for in subroutine rectangle  136  is conducted from a location in the discharge passageway, first by forming centrally through a deformable, substantially planar flow control panel a primary gas flow window, as indicated in instruction rectangle  142 , and then by securing the flow control panel across the discharge passageway, as indicated in instruction rectangle  144 . The flow control panel employed in subroutine rectangle  136  is so constructed as to be deformable downstream within the flow of the pressurized inflation gas I in the discharge passageway during high volume inflation gas production in the gas generation chamber. 
         [0083]    Sizing the effective gas outflow cross section of the discharge passageway in the manner called for in subroutine rectangle  138  is performed, first by producing centrally through a rigid bulkhead a primary gas flow aperture, as indicated in instruction rectangle  146 . Thereafter, as indicated in instruction rectangle  148 , the bulkhead is disposed in a discharge passageway upstream of and in parallel face-to-face abutment with the flow control panel utilized in subroutine rectangle  136 . The primary gas flow aperture in the bulkhead is in this step placed in fluid-flow alignment with the primary gas flow window of the flow control panel. As indicated in instruction rectangle  150 , the primary gas flow aperture is rendered unequal in size to the primary gas flow window. The cross-sectional area of the smaller of either, the primary gas flow aperture, or the primary gas flow window, corresponds to the first effective gas outflow cross section that is tuned to low volume inflation gas production. Finally, a plurality of supplemental gas flow openings are created through the one of the bulkhead or the flow control panel that is associated with the smaller of the primary gas flow aperture or the primary gas flow window, as indicated in instruction rectangle  152 . The total of the cross-sectional areas of the plurality of supplemental gas flow openings combined with the cross-sectional area of the smaller of the primary gas flow aperture or the primary gas flow window corresponds to the second effective gas flow cross section that is tuned to high volume inflation gas production in the gas generation chamber. The method concludes at stop oval  140 . 
         [0084]    The present invention may be embodied in other specific forms without departing from its structures, methods, or other essential characteristics as broadly described herein and claimed hereinafter. The described embodiments are to be considered in all respects only as illustrative, and not restrictive. The scope of the invention is, therefore, indicated by the appended claims, rather than by the foregoing description. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.