Abstract:
A gas generator is formed of a container having an outer-shell member, and a partition member disposed at least partly inside the outer-shell member to thereby form a plurality of chambers inside the container and fixed to the outer-shell member, a fixation area increasing portion formed at at least one of the partition member and the outer-shell member, a gas generating agent disposed inside the plurality of chambers of the container, and an igniter for igniting the gas generating agent. The gas generator reliably prevents the gas leak from a portion of fixation of the outer-shell member and the partition member.

Description:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT  
         [0001]    The present invention relates to a gas generator suitable for incorporation in an airbag device, and to the airbag device incorporating the gas generator.  
           [0002]    An airbag device installed in an automobile includes an airbag, a gas generator commonly called an inflator, and a module cover for covering the airbag. In an emergency of the automobile, such as when the automobile collides, the gas generator operates, causing the airbag to expand and to catch an occupant in the automobile.  
           [0003]    [0003]FIG. 6 is a side view of an example of a conventional steering wheel; FIG. 7 is a front view of the conventional steering wheel; FIG. 8 is an enlarged sectional view taken along line  8 - 8  of FIG. 7; and FIG. 9 is a sectional view of a gas generator incorporated in an airbag device of this steering wheel.  
           [0004]    As shown in FIGS. 6 and 7, an airbag device  14  is installed in an area situated at the inner side of a steering wheel  10 . Reference numerals  12  denote spokes.  
           [0005]    As shown in FIG. 8, the airbag device  14  comprises a retainer  20  fixed on the steering wheel by a bracket  18 , an airbag  22  including a gas-introducing-opening edge portion mounted to the retainer  20 , a gas generator or inflator  24  mounted to the retainer  20  for ejecting gas into the airbag  22 , and a module cover  26  for covering the airbag  22 . The base end side of the module cover  26  is connected to the retainer  20 .  
           [0006]    As shown in FIG. 9, the gas generator  24  is formed of a container which comprises an outer-shell member and a cylindrical partition member  29 , wherein the outer-shell member is formed by an upper housing  27  and a lower housing  28 , and the cylindrical partition member  29  is installed inside the outer-shell member. One end of the partition member  29  passes through and protrudes downward from an opening in the bottom surface of the lower housing  28 . The inner peripheral surface defining the opening and the outer peripheral surface of the partition member  29  are welded together by, for example, laser beam welding. An igniting agent or booster propellant  30  is held at the inner side of the partition member  29 , whereas a gas generating agent or main propellant  32  is held at the outer peripheral side of the partition member  29 .  
           [0007]    A squib  34  is installed at the aforementioned one end of the partition member  29 , and is constructed so that the igniting agent  30  is ignited when the squib  34  is energized through a squib connector  36  and a squib lead wire  38 . When the igniting agent  30  is ignited, gas is ejected from openings  40  of the partition member  29 , so that the gas generating agent  32  is ignited. As a result, a large amount of gas is generated rapidly. The gas passes through a filter  42  formed by mesh or the like, and is ejected outward from the gas generator  24  through openings  44 , causing the airbag  22  to expand. When the airbag  22  expands, the module cover  26  cleaves along a tear line, causing the airbag  22  to expand greatly inside the vehicle. The steering wheel is secured by a nut  48  and an externally threaded portion  46  at the top end of a steering shaft.  
           [0008]    In the above-described gas generator, when the gas generating agent is ignited, the internal pressure in the container increases, so that a large stress is exerted on a connection portion of the lower housing  28  and the partition member  29 .  
           [0009]    An object of the present invention is to provide a gas generator including a structure for fixing a partition member and a container, which can sufficiently resist a large stress when a gas generating agent is ignited as mentioned above, and to provide an airbag device including the gas generator.  
           [0010]    Further objects and advantages of the invention will be apparent from the following description.  
         SUMMARY OF THE INVENTION  
         [0011]    A gas generator of the present invention includes a container; a gas generating agent inside the container; and an igniter for igniting the gas generating agent. The container includes an outer-shell member and a partition member fixed to the outer-shell member, and at least a portion of the partition member is disposed inside the outer-shell member. A plurality of chambers for containing the gas generating agent is formed by the partition member. A fixation area increasing portion is provided at at least one of the partition member and the outer-shell member.  
           [0012]    In such a gas generator, since the fixation area of the partition member and the container is large, it is possible to sufficiently resist a large stress even when it is exerted on a connection portion of the partition member and the container when the gas generating agent is ignited.  
           [0013]    In the gas generator of the present invention, it is preferable that the partition member has a cylindrical shape, with one end thereof being fixed to an inside surface of the outer-shell member at one side of the outer-shell member, and the other end thereof passing through and extending outward from an opening provided at the other side of the outer-shell member. In addition, it is preferable that an inner peripheral surface defining the opening and an outer peripheral surface of the tubular partition member are fixed together. Further, it is preferable that the fixation area increasing portion is used to increase a fixation area of the inner peripheral surface defining the opening and the outer peripheral surface of the partition member. When the gas generator is constructed in this way, since the fixation area of the partition member and the opening of the outer-shell member is large, gas leakage does not occur even when a large gas pressure is exerted on the fixation portion.  
           [0014]    In this case, it is preferable that the fixation area increasing portion is an annular portion provided at the outer-shell member and protruding inside the outer-shell member. When the gas generator is constructed in this way, the annular portion is pushed against the outer peripheral surface of the partition member when the outer-shell member expands outward by the gas pressure as a result of ignition of the gas generating agent. Therefore, the connection between the outer-shell member and the partition member is made stronger, and gas leaks from a portion between these members is more reliably prevented.  
           [0015]    In the present invention, it is preferable to fix the opening of the outer-shell member and the partition member by welding. In such a case, it is possible to considerably increase the weld strength between the partition member and the outer-shell member by increasing the welding depth, and to considerably reliably prevent gas leak from the portion between the partition member and the outer-shell member.  
           [0016]    An airbag device of the present invention includes an airbag; any one of the above-described gas generators for generating gas to expand the airbag; and a module cover for covering the airbag. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    [0017]FIG. 1 is a sectional view of a gas generator of an embodiment of the present invention;  
         [0018]    [0018]FIG. 2 is an enlarged view of the main portion of the gas generator shown in FIG. 1;  
         [0019]    [0019]FIG. 3 is a sectional view showing the same portion as that shown in FIG. 2 when the gas generator ejects gas;  
         [0020]    [0020]FIG. 4 is an enlarged sectional view of the main portion of a lower housing;  
         [0021]    [0021]FIG. 5 is a bottom view of the gas generator;  
         [0022]    [0022]FIG. 6 is a side view of a conventional steering wheel;  
         [0023]    [0023]FIG. 7 is a front view of the conventional steering wheel;  
         [0024]    [0024]FIG. 8 is a sectional view taken along line  8 - 8  of FIG. 7; and  
         [0025]    [0025]FIG. 9 is a sectional view of the conventional gas generator of the airbag device shown in FIG. 8. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0026]    Hereunder, a description of an embodiment of the present invention will be made with reference to FIGS.  1  to  5 . FIG. 1 is a sectional view of an embodiment of a gas generator in accordance with the present invention, i.e. enlarged sectional view taken along line  1 - 1  of FIG. 5; FIG. 2 is an enlarged view of the main portion shown in FIG. 1; FIG. 3 is a sectional view showing the same portion as that shown in FIG. 2 when the gas generator is ejecting gas; FIG. 4 is an enlarged sectional view of the main portion of a lower housing; and FIG. 5 is a bottom view of the gas generator.  
         [0027]    A gas generator  50  includes a container  60  which comprises an outer-shell member  56  formed by an upper housing  52  and a lower housing  54 , and a cylindrical partition member  58 . A large portion of the partition member  58  is located inside the outer-shell member  56  and a portion of the partition member  58  protrudes from the outer-shell member  56 .  
         [0028]    The upper housing  52  includes a substantially disk-shaped top plate  52   a  and a peripheral wall  52   b  inclining downward from the peripheral edge of the top plate  52   a . A plurality of gas ports  52   c  is provided in the peripheral wall  52   b.    
         [0029]    The partition member  58  is disposed coaxially with the peripheral wall  52   b  of the upper housing  52 . The top end surface of the partition member  58  is affixed to the top plate  52   a  by welding, such as projection welding. However, the method of affixation is not limited to welding. A plurality of gas ports  58   a  is provided in the upper portion of the partition member  58 .  
         [0030]    The lower housing  54  comprises a substantially disk-shaped bottom plate  54   a  and a peripheral wall  54   b  extending upward from the peripheral edge of the bottom plate  54   a . The top edge of the peripheral wall  54   b  gradually widens outward, and continues to a flange  54   c . As shown in FIG. 5, the flange  54   c  is a substantially square flange protruding at the outer periphery of the outer-shell member  56 , and has insertion holes  54   d  at four corners thereof for, for example, bolts or rivets.  
         [0031]    A circular opening  54   e  is provided at the center of the bottom plate  54   a , and the partition member  58  is inserted in the opening  54   e . An annular portion  62  is provided so as to protrude upward from the end portion defining the opening  54   e . In the embodiment, as shown in FIG. 4, the annular portion  62  is formed by burring the bottom plate  54   a , but the method of forming the annular portion  62  is not limited to the burring process.  
         [0032]    A large portion of the partition member  58  is disposed inside the outer-shell member  56 , with the portion near the lower end thereof alone passing through and protruding downward from the opening  54   e . A squib  64  is inserted in the lower portion inside the partition member  58 . The squib  64  comprises a squib body  64   a  and a substantially tubular squib holder  64   b  externally fitted onto the squib body  64   a . A gasket mounting groove is provided in the outer peripheral surface of the squib holder  64   b  in order to dispose a gasket  64   c  in the gasket mounting groove. An O-ring, formed of heat-resistant rubber or the like, may be used as the gasket  64   c . The gasket  64   c  contacts the inner peripheral surface of the partition member  58  to make them airtight.  
         [0033]    An inwardly facing flange  58   b  is formed at the bottom end of the partition member  58  by, for example, pressing. The bottom end of the squib holder  64   b  is held by the flange  58   b . Although not shown, a squib connector is connected to a terminal  64   d  at the bottom end of the squib  64 .  
         [0034]    An enhancer cup  66 , formed of, for example, a low-melting metal such as aluminum, is disposed inside the partition member  58 . An igniting agent (booster propellant)  68  is provided inside the enhancer cup  66 . When the squib  64  is energized, the booster propellant starts to react. When the temperature and the gas pressure inside the enhancer cup  66  become sufficiently high, the enhancer cup  66  tears, so that gas is ejected via the gas ports  58   a  onto a gas generating agent (main propellant)  70 , which starts reacting to generate gas. Although sodium azide or the like may be used for the igniting agent and the gas generating agent, the substances which may be used for these agents are not limited thereto.  
         [0035]    The gas generating agent  70  is filled in the portion between the partition member  58  and a filter  72 . The filter  72  is formed by hardening a metallic wire net or mesh into an annular shape by press molding or the like. An annular filter holder  74 , using a perforated plate formed of, for example, a punching metal, is disposed along the outer peripheral surface of the filter  72 .  
         [0036]    A substantially disk-shaped filter positioning member  76  with a center hole is disposed between the inner peripheral surface of the top portion of the filter  72  and the top portion of the partition member  58 .  
         [0037]    A substantially disk-shaped spatter shield  78  with a center hole is externally fitted to the lower portion of the partition member  58 . A cushion  80  is disposed on the top side of the spatter shield  78 . The gas generating agent  70  is provided between the filter positioning member  76  and the cushion  80 .  
         [0038]    In forming the gas generator  50 , the upper housing  52  and the partition member  58  are fixed to each other by, for example, projection welding. The enhancer cup  66 , the squib  64 , and the igniting agent  68  are put into the partition member  58 , and the bottom end of the partition member  58  is pressed in order to form the flange  58   b.    
         [0039]    The upper housing  52  is set in a posture with the top and bottom sides reversed with respect to those shown in FIG. 1. First, the filter positioning member  76  and the filter  72  with the filter holder  74  are installed in the upper housing  52 . Then, the upper housing  52  is filled with the gas generator  70 , and the cushion  80  and the spatter shield  78  are disposed so as to hold the gas generating agent  70 .  
         [0040]    The lower housing  54  is mounted to the upper housing  52 . The inside diameters of the opening  54 e and the annular portion  62  are set slightly smaller than the outside diameter of the partition member  58 . The partition member  58  is press-fitted to the annular portion  62  and the opening  54   e . The peripheral wall  52   b  of the upper housing  52  is press-fitted to the peripheral wall  54   b  of the lower housing  54 . Thereafter, the contact portion of the partition member  58  and the opening  54   e  and the contact portion of the peripheral walls  52   b  and  54   b  are respectively subjected to laser beam welding. In the welding, since the inner peripheral surface of the annular portion  62  contacts the outer peripheral surface of the partition member  58 , the weld penetration depth (depth of welding in a direction parallel to an axial line of the partition member  58 ) can be made sufficiently large. The spatter shield  78  prevents the gas generator  70  from being irradiated with laser light which leaks during the laser beam welding of the partition member  58  and the edge of the opening  54   e , and welding pieces or spatter from contacting the gas generator  70 .  
         [0041]    The gas generator  50  constructed in this way is incorporated in an airbag device, such as that shown in FIG. 8. Although the gas generator  50  is incorporated in the airbag device shown in FIG. 8 for the driver&#39;s seat, the gas generator  50  may be applied to various airbag devices, such as a passenger airbag device, a back-seat airbag device, a side airbag device, and an airbag device for protecting the head of an occupant.  
         [0042]    By energizing the squib  64  of the gas generator  50 , the igniting agent  68  is ignited, and generated gas is ejected by passing through the gas ports  58   a  of the partition member  58 , causing the gas generator  70  to react to generate gas. By this, a large amount of gas is generated. This gas is ejected through the filter  72  and the gas ports  52   c  of the upper housing  52 , causing the airbag to expand.  
         [0043]    As mentioned above, since the weld penetration depth at the welded portion of the partition member  58  and the opening  54   e  of the lower housing  54  is large, the partition member  58  and the lower housing  54  are firmly connected together, thereby reliably preventing the gas leak from the welded interface. In the embodiment, when the gas generator  50  is used to generate gas, the bottom plate  54   a  of the lower housing  54  tries to expand downward in FIG. 1 by the pressure of the gas. However, the annular portion  62  is provided in an upstanding manner so as to extend upward from the bottom plate  54   a , so that, as shown in FIG. 3, when the bottom plate  54   a  starts expanding outward (in the direction of arrows A), the annular portion  62  tries to tilt towards the center of the opening  54   e  (in the directions of arrows B) and to bite the outer peripheral surface of the partition member  58 . Therefore, the bottom plate  54   a  and the partition member  58  are more firmly connected together, and the gas leak from the portion between the partition member  58  and the opening  54   e  is more reliably prevented.  
         [0044]    In this embodiment, as shown in FIG. 4, the annular portion  62  is formed by burring, and the outer corner edge defining the opening  54   e  is rounded. Therefore, a groove-like beveled portion is formed between the outer peripheral surface of the tubular partition member  58  inserted in the opening, and the outer corner edge defining the opening  54   e , so that the area of fusion by the laser beam welding becomes large, thereby causing the weld strength to be high. The surface defining the opening formed by burring is smooth as compared to that formed by punching, so that it is not necessary to finish the surface by cutting.  
         [0045]    As described above, the present invention provides a gas generator which reliably prevents the gas leak from the portion of fixation of the outer-shell member and the partition member as a result of a high fixing strength between the outer-shell member and the partition member; and an airbag device using the gas generator.  
         [0046]    While the invention has been explained with reference to the specific embodiments of the invention, the explanation is illustrative, and the invention is limited only by the appended claims.