Abstract:
The present invention provides a gas generator comprising:
       a housing including a diffuser shell provided with a gas discharge port and a closure shell, a cylindrical filter disposed inside the housing, a first combustion chamber defined inside the cylindrical filter and a second combustion chamber defined inside the first combustion chamber;   the first combustion chamber having an enhancer chamber and a first gas generating agent stored outside the enhancer chamber,   the enhancer chamber, being defined by an enhancer chamber cup member and accommodating therein a first ignition device for igniting and combusting the first gas generating agent,   an enhancer cup member having, in the peripheral surface thereof, an enhancer hole for communicating the enhancer chamber with the first combustion chamber during activation;   the second combustion chamber having a through-hole for communicating the second combustion chamber with the first combustion chamber during activation,   the second combustion chamber being surrounded by a combustion chamber cup member disposed eccentrically to a central axis of the housing,   the second combustion chamber accommodating a second ignition device and a second gas generating agent therein; and   a top plate of the enhancer chamber cup member being positioned higher than a top plate of the combustion chamber cup member, the enhancer hole being positioned higher than the top plate of the combustion chamber cup member.

Description:
[0001]    This nonprovisional application claims priority under 35 U. S. C. §119(a) on Patent Application No. 2007-108813 filed in Japan on 18 Apr. 2007 and 35 U. S. C. §119(e) on U.S. Provisional Application No. 60/912877 filed on 19 Apr. 2007, which are incorporated by reference. 
       BACKGROUND OF INVENTION 
       [0002]    1. Field of Invention 
         [0003]    The present invention relates to a gas generator, for example, for a restraining device of a vehicle that is used for an airbag device or the like. 
         [0004]    2. Description of Related Art 
         [0005]    It is desirable that an output of a gas generator for a restraining device of an automobile could be adjusted to a certain degree according to a collision impact. A dual-type gas generator that is made to meet such a requirement is known, this gas generator having a structure in which a plurality of independent combustion chambers are formed inside the gas generator, a gas generating agent is accommodated in each of the combustion chambers, and the ignition and combustion timing of each gas generating agent is adjusted with a separate igniter. 
         [0006]      FIG. 4  of U.S. Pat. No. 6,189,927 shows an airbag inflator in which a first chamber  234  contains therein a second chamber  282 . The ceiling portion of the second chamber  282  is open, a shoulder portion  302  is formed on the peripheral edge thereof, and a lid  285  is attached to the shoulder portion  302 . When a gas generating agent located inside the second chamber  282  is combusted, the lid  285  is removed, the combustion gas flows into the first chamber  234 , passes through a filter  240 , and is discharged to the outside from a gas discharge port  224 . 
       SUMMARY OF INVENTION 
       [0007]    The present invention provides a gas generator including:
       a housing including a diffuser shell provided with a gas discharge port and a closure shell, a cylindrical filter disposed inside the housing, a first combustion chamber defined inside the cylindrical filter and a second combustion chamber defined inside the first combustion chamber;   the first combustion chamber having an enhancer chamber and a first gas generating agent stored outside the enhancer chamber,   the enhancer chamber, being defined by an enhancer chamber cup member and accommodating therein a first ignition device for igniting and combusting the first gas generating agent,   an enhancer cup member having, in the peripheral surface thereof, an enhancer hole for communicating the enhancer chamber with the first combustion chamber during activation;   the second combustion chamber having a through-hole for communicating the second combustion chamber with the first combustion chamber during activation,   the second combustion chamber being surrounded by a combustion chamber cup member disposed eccentrically to a central axis of the housing,   the second combustion chamber accommodating a second ignition device and a second gas generating agent therein; and   a top plate of the enhancer chamber cup member being positioned higher than a top plate of the combustion chamber cup member, the enhancer hole being positioned higher than the top plate of the combustion chamber cup member.       
 
         [0016]    The present invention provides a gas generator, including: 
         [0017]    a housing including a diffuser shell provided with a gas discharge port and a closure shell; 
         [0018]    a cylindrical filter disposed within the housing and defining a first combustion chamber including therein a first gas generating agent; 
         [0019]    an enhancer cup member provided within the first combustion chamber and defining an enhancer chamber accommodating therein a first ignition device for igniting and combusting the first gas generating agent, the enhancer cup member being provided with an enhancer hole formed in a peripheral surface thereof for communicating the enhancer chamber with the first combustion chamber during activation; 
         [0020]    a combustion chamber cup member provided eccentrically to a central axis of the housing within the first combustion chamber, the combustion chamber cup member defining a second combustion chamber including therein a second ignition device and a second gas generating agent, and having a top plate and a through-hole for communicating the second combustion chamber with the first combustion chamber during activation, the combustion chamber cup member being provided such that the enhancer hole is positioned higher than the top plate. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0021]    The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention and wherein; 
           [0022]      FIG. 1  shows a vertical sectional view of the gas generator in accordance with the present invention; 
           [0023]      FIG. 2  shows a transverse sectional view of the gas generator shown in  FIG. 1 ; 
           [0024]      FIG. 3  shows a transverse sectional view of the gas generator of another embodiment; and 
           [0025]      FIG. 4  shows a vertical sectional view of the gas generator of another embodiment. 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0026]    In the structure described in U.S. Pat. No. 6,189,927, a first igniter assembly  254  (or a cap  270 ) and the second chamber  282  (or a cup  284 ) are disposed inside a housing  212  eccentrically to a central axis of the housing, and the height of lid  285  is almost equal (or the lid  285  is slightly lower) to that of the top plate surface of the first igniter  254  (or cap  270 ). 
         [0027]    Therefore, when the gas generating agent is to be loaded into the first chamber  234 , the gas generating agent has to be loaded from a gap between the cap  270  and cup  284 , and the loading operation itself is difficult. Further, a limitation is placed on the portion for forming an orifice  276  of the cap  270  and also on the ejection direction of the ignition products that are ejected from the orifice  276 . 
         [0028]    The present invention provides a dual-type gas generator that is easy to assemble and ensures reliable ignition of a gas generating agent. 
         [0029]    In the gas generator in accordance with the present invention, the enhancer chamber cup member with the inside thereof serving as an enhancer chamber and a combustion chamber cup member that is less in height than the enhancer chamber cup member are disposed in a space on the inside of the filter within the housing, the space formed thereby serves as a first combustion chamber and the inside of the combustion chamber cup member serves as a second combustion chamber. The first ignition device and second ignition device both include only a well-known electric igniter or a combination of an electric igniter and an enhancer agent. The height of the filter is equal to, or larger than the height of the enhancer chamber cup member, and a space for loading the first gas generating agent is formed inside the filter. 
         [0030]    When the gas generator in accordance with the present invention is assembled, first, the combustion chamber cup member having the second gas generating agent accommodated therein, the ignition devices, and the enhancer chamber cup member are mounted inside the closure shell. Then, the cylindrical filter is disposed, and the predetermined amount of the first gas generating agent can be loaded into the space (the first combustion chamber) representing the inside of the housing excluding the second combustion chamber by loading the first gas generating agent toward the top plate of the combustion chamber cup member positioned on the inside of the cylindrical filter. 
         [0031]    Further, because at least part of the enhancer holes is positioned higher than the top plate of the combustion chamber cup member, the first gas generating agent is necessarily present in a position directly opposite the enhancer hole. As a result, when the ignition device is actuated and combustion products (ignition energy such as flame and high-temperature gases) is ejected from the enhancer hole, the combustion products and the first gas generating agent easily come into contact with each other. Therefore, such a configuration is effective in terms of reliability of actuation. 
         [0032]    As for a plurality of enhancer holes located in positions higher than the top plate of the combustion chamber cup member, the opening direction is preferably provided as if the enhancer holes opposite or directly opposite the circumferential wall portion of the combustion chamber cup member, when viewed from above. 
         [0033]    The present invention preferably provides 
         [0034]    the gas generator for a restraining device of a vehicle, wherein 
         [0035]    the second ignition device includes only an electric igniter, and 
         [0036]    the combustion chamber cup member includes a cylindrical member and a cover, an opening portion at one end of the cylindrical member is in contact with a bottom surface of the housing, the cover is placed on an opening portion on the other end side, and a protruding portion is provided in the center of the cover. 
         [0037]    The inside of the combustion chamber cup member serves as the second combustion chamber, and the second gas generating agent and an electric igniter having a protruding actuation portion in the central portion thereof are accommodated inside the combustion chamber cup member. Therefore, where a cover is used that has a protruding portion in the center and a small height of a circumference thereof, the actuation portion and the cover do not contact with each other even when the electric igniter is accommodated, the second gas generating agent can be introduced between the actuation portion and the protruding portion of the cover, and therefore the ignition ability of the second gas generating agent is improved. Furthermore, because the surface of the cover, except the protruding portion thereof, can be decreased in height, the capacity of the first combustion chamber can be increased accordingly. The protruding portion may be also provided close to the central portion, rather than in the central portion itself, provided that the protruding portion is directly opposite the actuation portion of the electric igniter. 
         [0038]    The present invention preferably provides 
         [0039]    the gas generator for a restraining device of a vehicle, wherein 
         [0040]    a ratio (H 2 /H 1 ) of a height (H 2 ) of the combustion chamber cup member to a height (H 1 ) of the enhancer chamber cup member is within a range of 0.3 to 0.9, and the height of the enhancer chamber cup member is equal to a height from a bottom surface to a ceiling surface of the housing. 
         [0041]    As described above, by associating the height of the enhancer chamber cup member with the height of the combustion chamber cup member, the operation of loading the first gas generating agent into the first combustion chamber is facilitated. The top plate of the enhancer chamber cup member may be in contact with the ceiling surface of the housing, or a gap that is sufficiently small to prevent the presence of gas generating agent may be provided between the top plate of the enhancer chamber cup member and the ceiling surface of the housing. 
         [0042]    The present invention preferably provides 
         [0043]    the gas generator for a restraining device of a vehicle, wherein 
         [0044]    the housing has a round planar shape, the filter has a round planar shape, the enhancer chamber cup member has a round planar shape, and the combustion chamber cup member has a circular arc planar shape, and 
         [0045]    the combustion chamber cup member is disposed so that a curved portion thereof is positioned on the inner wall surface side of the filter, and a flat portion thereof is positioned on the side of the enhancer chamber cup member. 
         [0046]    The circular arc shape is a shape of a segment between optional two points on a circle. When a circumference is divided into two portions by two points located on the circumference, an arc that has a length more than half that of the entire circumference becomes a major arc, and an arc that has a smaller length becomes a minor arc, both arcs having a shape similar to that of letter “D”. The “circular arc” as referred to in the description of the present invention also includes a semicircular shape. 
         [0047]    Thus, the combustion chamber cup member that has a planar shape (or cross-sectional shape in the width direction) in the form of a circular arc has a curved surface and a flat surface as side surfaces. Therefore, the curved portion can be abutted against, or brought close via a very small gap to the inner wall surface of the filter that has a round planar shape, and the flat portion can be brought close to the enhancer chamber cup member that has a round planar shape (or a round cross-sectional shape in the width direction), thereby making it possible to increase the capacity of the second combustion chamber. 
         [0048]    The present invention preferably provides 
         [0049]    the gas generator for a restraining device of a vehicle, wherein 
         [0050]    the housing has a round planar shape, the filter has a round planar shape, the enhancer chamber cup member has a round planar shape, and the combustion chamber cup member has a planar shape similar to a circular arc including a circumference and a concave curve, and 
         [0051]    the combustion chamber cup member is disposed so that a curved portion thereof is positioned on the inner wall surface side of the filter, and a concave curved portion thereof is positioned on the side of the enhancer chamber cup member. 
         [0052]    The circular arc shape is defined in the invention set forth in the foregoing The shape similar to a circular arc in the present invention means a shape in which a straight line facing the circumference in a circular arc shape is a concave curve. 
         [0053]    Thus, the combustion chamber cup member that has a planar shape (or cross-sectional shape in the width direction) in the form similar to a circular arc has a curved surface and a concave curved surface (that is, a convex curved surface and a concave curved surface) as side surfaces. Therefore, the curved portion can be abutted against, or brought close via a very small gap to the inner wall surface of the filter that has a round planar shape (or a round cross-sectional shape in the width direction), and the concave curved portion can be brought close to the enhancer chamber cup member that has a round planar shape (or a round cross-sectional shape in the width direction), thereby making it possible to increase the capacity of the second combustion chamber. 
         [0054]    In the gas generator in accordance with the present invention, the operation of loading the first gas generating agent into the first combustion chamber is facilitated. Further, in the gas generator in accordance with the present invention, the capacity of the second combustion chamber can be increased without changing the size of the entire housing, and the ignition ability of the gas generating agent can be improved. 
       EMBODIMENT OF INVENTION 
     (1) Gas Generator Shown in FIG. 1 and FIG. 2 
       [0055]      FIG. 1  is a vertical sectional view of the gas generator in accordance with the present invention.  FIG. 2  is a transverse sectional view of the gas generator shown in  FIG. 1 . In  FIG. 2 , only the actuation portions of the igniters are shown. 
         [0056]    In a gas generator  10 , an outer shell is formed by a housing  11  in which a diffuser shell  12  and a closure shell  13  are integrated by welding in a joint portion  11   a.  The housing  11  has a round planar shape (in the radial cross-section). 
         [0057]    A plurality of gas discharge ports  14  are provided in a peripheral surface of the diffuser shell  12  and the ports are closed on the inside with a seal tape  15  made from aluminum or stainless steel to prevent the penetration of moisture from the gas discharge ports  14 . 
         [0058]    A cylindrical filter  45  having a function of filtering and cooling the combustion gas is disposed inside the housing  11 , and a gap  55  is provided between an outer peripheral surface of the filter  45  and the gas discharge ports  14  and the seal tape  15 . 
         [0059]    A first combustion chamber  31  is formed on the inside of the cylindrical filter  45  within the housing  11 . An enhancer chamber cup member  32  and a combustion chamber cup member  41  are disposed on the inside of the cylindrical filter  45 , and the first combustion chamber  31  is a space surrounded by an inner wall surface of the housing  11 , an inner peripheral surface of the cylindrical filter  45 , an outer wall surface of the enhancer chamber cup member  32 , and an outer wall surface of the combustion chamber cup member  41 . The inside of the first combustion chamber  31  is filled with a first gas generating agent  50 . 
         [0060]    An opening portion of the enhancer chamber cup member  32  forming an enhancer chamber  33  is press-fitted onto a first igniter  21  (an igniter collar into which the first igniter  21  is fitted) that has been fitted via an orifice formed in a bottom surface  13   a  of the closure shell  13 , and the peripheral edge of the opening portion is abutted against the bottom surface  13   a  of the closure shell  13 . Therefore, the enhancer chamber cup member  32  cannot move in the axial direction or the radial direction. 
         [0061]    A top plate  32   a  and a ceiling surface  12   a  of the diffuser shell  12  face each other via a very small gap, and a first gas generating agent  50  cannot be present in this gap. The height of the enhancer chamber cup member  32  is almost equal to a height from a bottom surface (bottom surface  13   a  of the closure shell  13 ) to the ceiling surface (ceiling surface  12   a  of the diffuser shell  12 ) of the housing  11 . 
         [0062]    The enhancer chamber cup member  32  has a round planar shape (in the radial cross-section), and a plurality of enhancer holes  56  are provided in the peripheral surface thereof. The plurality of enhancer holes  56  are closed from the outside with a sealing tape  57 , but the closing method is not limited to the sealing tape. The enhancer holes  56  are formed in a position (in the diffuser ceiling surface  12   a  side) higher than the top plate  41   a  of the combustion chamber cup member  41 . Part of the enhancer holes  56  may be formed in a portion that faces the peripheral surface  41   b  of the combustion chamber cup member  41 . Further, the enhancer holes may be also formed in a portion that does not face the peripheral surface  41   b  in a position lower than the diffuser ceiling surface  12   a.    
         [0063]    An enhancer agent  53  is accommodated inside the enhancer chamber  33 , and the enhancer agent  53  and the first igniter  21  form a first ignition device. As to the first igniter  21 , an electric igniter that is actuated by an ignition current is retained by and fixed to a metal igniter collar. For example, an igniter obtained by appropriately deforming the shape of the igniter collar shown in  FIG. 1  of JP-A No. 2003-161599 can be used. In the first igniter  21 , an actuation portion  21   a  including an ignition agent for actuation is provided in a protruding condition. The igniter collar of the first igniter  21  is fixed by welding to the bottom surface  13   a,  and there is no gap in the boundary portion (welded portion) of the igniter collar and the bottom surface  13   a.  Therefore, the penetration of moisture is prevented. 
         [0064]    A second combustion chamber  35  is formed by the combustion chamber cup member  41  disposed within the first combustion chamber  31  and the bottom surface  13   a  of the closure shell, and the second combustion chamber  35  is completely enclosed in the first combustion chamber  31 . 
         [0065]    An opening portion of the combustion chamber cup member  41  is press-fitted onto, or welded to a second igniter  25  (an igniter collar into which the second igniter  25  is fitted) that has been fitted via an orifice formed in the bottom surface  13   a  of the closure shell  13 , and the peripheral edge of the opening portion is abutted against the bottom surface  13   a  of the closure shell  13 . Therefore, the combustion chamber cup member  41  cannot move in the axial direction or the radial direction. An igniter similar to the first igniter  21  can be used as the second igniter  25 . In the second igniter  25 , an actuation portion  25   a  including an ignition agent for actuation is provided in a protruding condition. The igniter collar of the second igniter  25  is fixed by welding to the bottom surface  13   a,  and there is no gap in the boundary portion (welded portion) of the igniter collar and the bottom surface  13   a.  Therefore, the penetration of moisture is prevented. 
         [0066]    The top plate  41   a  of the combustion chamber cup member  41  is positioned lower than the top plate  32   a  of the enhancer chamber cup member  32 . The ratio H 2 /H 1  of the height (H 2 ) of the top plate  41   a  to the height (H 1 ) of the top plate  32   a  is preferably within a range of 0.3 to 0.9, more preferably within a range of 0.5 to 0.8. 
         [0067]    A plurality of gas communication holes  42  are provided in the peripheral surface  41   b  of the combustion chamber cup member  41 . Prior to actuation, the gas communication holes are closed from the outside with a stainless steel tape  43 . The stainless steel tape  43  has a thickness of 100 μm, and when the tape is fractured and ruptured by the pressure applied by the combustion of the second gas generating agent  51 , the first combustion chamber  31  communicates with the second combustion chamber  35 . The stainless steel tape is not affected in any way by the combustion of the first gas generating agent  50 . A method other than that using the stainless steel tape may be used for closing the gas communication holes  42 . 
         [0068]    As shown in  FIG. 2 , the combustion chamber cup member  41  has a planar shape (a cross-sectional shape in the width direction) in the form of circular arc (shape similar to that of letter “D”) and has a curved portion  41   c  and a flat portion  41   d  as the side surfaces. The combustion chamber cup member  41  is disposed so that the curved portion  41   c  thereof is close to the inner peripheral surface of the cylindrical filter  45 , and the flat portion  41   d  is close to the peripheral wall  32   b  of the enhancer chamber cup member  32 . The gap between the curved portion  41   c  and the inner peripheral surface of the cylindrical filter  45  and the gap between the flat portion  41   d  and the peripheral wall  32   b  of the enhancer chamber cup member  32  are made small at least to a degree sufficient to prevent the presence of the first gas generating agent  50 . The curved portion  41   c  may abut against the inner peripheral surface of the cylindrical filter  45 . 
         [0069]    Because the combustion chamber cup member  41  has the above-described shape, as shown in  FIG. 1  and  FIG. 2 , the distance between the central axis C 1  of the housing  11  and the central axis C 2  of the first igniter  21  is longer than the distance between C 1  and the central axis C 3  of the second igniter  25 . As a result, the capacity of the second combustion chamber  35  can be further increased. 
         [0070]    The gas communication holes  42  can be formed in the desired position of the curved portion  41   c  and flat portion  41   d  of the combustion chamber cup member  41 . The number and location sites of enhancer holes  56  are not particularly limited, but it is preferred that the opening directions of the plurality of enhancer holes  56  located in positions higher than the top plate  41   a  of the combustion chamber cup member  41  face a side of the flat portion  41   d  of the combustion chamber cup member  41 . 
         [0071]    The enhancer holes  56  ( 56   a  to  56   d ) formed in the peripheral wall  32   b  of the enhancer chamber cup member  32  are formed in the right half (region of 180° on the side of the combustion chamber cup member  41 ) of the enhancer chamber cup member  32 . The enhancer holes  56   a,    56   d  do not face the combustion chamber cup member  41 , and are formed by four (a total of eight) holes in the axial direction. The enhancer holes  56   b,    56   c  face the side of the combustion chamber cup member  41  and are formed, by two (a total of four) holes in positions higher than the top plate  41   a  of the combustion chamber cup member  41 , as shown in  FIG. 1 . 
         [0072]    Further, the operation in the case where the gas generator shown in  FIG. 1  and  FIG. 2  is applied to an airbag system of an automobile will be explained below. When an automobile receives a small impact during collision, only the first igniter  21  is actuated, and when the impact is large, the first igniter  21  and the second igniter  25  are actuated at the same time. When the impact is of medium strength, initially the first igniter  21  is actuated and then the second igniter  25  is actuated with a delay. This case will be explained below. 
         [0073]    The first igniter  21  and the second igniter  25  are connected to a control unit (not shown in the drawings) installed on a vehicle. When the automobile collides and receives the impact, an actuation signal is received from the control unit, the first igniter  21  is actuated and ignited, and the enhancer agent  53  is ignited and combusted. Then, because the pressure inside the enhancer chamber  33  rises, the sealing tape  57 , which closes the enhancer holes  56 , is ruptured and combustion products (ignition energy) are ejected from the enhancer chamber into the first combustion chamber  31 . 
         [0074]    Due to the ejection of the combustion products, the first gas generating agent  50  is ignited and combusted and a high-temperature combustion gas is generated. In particular, because a comparatively large amount of the first gas generating agent  50  is present on the extension lines of the enhancer holes  56   b,    56   c,  the ignition ability is improved. The combustion gas is filtered and cooled, while passing through the filter  45 , and then ruptures the sealing tape  15 . As a result, the combustion gas is discharged form the gas discharge ports  14  and inflates the airbag. At this time, the second combustion chamber  35  is defined by the cup member  41 , and the gas communication hole  42  is closed by the stainless steel tape  43  and, therefore, the stainless steel tape is not ruptured by the external pressure. Accordingly, the combustion products generated in the first combustion chamber  31  do not flow into the second combustion chamber  35 . 
         [0075]    The second igniter  25  is actuated and ignited with a slight delay, the second gas generating agent  51  is ignited and combusted, and a combustion gas is generated. The combustion gas ruptures the stainless steel tape  43 , which closes the gas communication holes  42 , and creates communication between the first combustion chamber  31  and the second combustion chamber  35 . Then, the combustion gas flows out into the first combustion chamber  31  via the gas communication holes  42  and is filtered and cooled when passes through the filter  45 . Then, the combustion gas is discharged from the gas discharge ports  14  and further inflates the airbag. 
         [0076]    A method of assembling the gas generator shown in  FIG. 1  and  FIG. 2  will be explained below. The enhancer chamber cup member  32  (the enhancer holes  56  are closed with the tape  57 ) filled with the enhancer agent  53  and the combustion chamber cup member  41  (the communication holes  42  are closed with the tape  43 ) filled with the second gas generating agent  51  are attached to the closure shell  13  having the first igniter  21  and the second igniter  25  attached thereto. The filter  45  is then disposed in the closure shell  13 . 
         [0077]    Then, the first gas generating agent  50  is loaded into a space (first combustion chamber  31 ) formed by the filter  45 . At this time, where the first gas generating agent  50  is loaded toward the top plate  41   a  of the combustion chamber cup member  41 , the gas generating agent spreads naturally in the space of the first combustion chamber  31 . Therefore, the loading operation is facilitated. If necessary, vibrations can be applied to enhance the loading of the first gas generating agent  50 . The first gas generating agent  50  does not enter the gaps between the curved portion  41   c  of the combustion chamber cup member  41  and the inner peripheral surface of the cylindrical filter  45  and between the flat portion  41   d  of the combustion chamber cup member  41  and the peripheral wall  32   b  of the enhancer chamber cup member  32 . 
         [0078]    Finally, a diffuser shell (the gas discharge ports are closed with the seal tape  15 ) is attached and the flange portion is welded to obtain a weld  11   a.    
       (2) Gas Generator Shown in FIG. 3 
       [0079]      FIG. 3  is a transverse sectional view of the gas generator  10  that is another embodiment of the present invention. The difference between the gas generator shown in  FIG. 3  and the gas generator  10  shown in  FIG. 1  and  FIG. 2  is only in the partial shape of the combustion chamber cup member  41 .  FIG. 3  shows only the actuation portions of the igniters. 
         [0080]    As shown in  FIG. 3 , the combustion chamber cup member  41 ′ has a planar shape (cross-sectional shape in the width direction) similar to a circular arc and has a curved portion  41   c ′ and a concave curved portion  41   d ′ as side surfaces. The combustion chamber cup member  41 ′ is disposed so that the curved portion  41   c ′ thereof is close to the inner peripheral surface of the cylindrical filter  45 , and the concave curve portion  41   d ′ is close to the peripheral wall  32   b  of the enhancer chamber cup member  32 . The gap between the curved portion  41   c ′ and the inner peripheral surface of the cylindrical filter  45  and the gap between the concave curved portion  41   d ′ and the peripheral wall  32   b  of the enhancer chamber cup member  32  are made small at least to a degree sufficient to prevent the presence of the first gas generating agent  50 . The curved portion  41   c ′ may be brought into contact with the inner peripheral surface of the cylindrical filter  45 . 
       (3) Gas Generator Shown in FIG. 4 
       [0081]      FIG. 4  is a vertical sectional view of a gas generator  100  that is another embodiment of the present invention. The components identical to those of the gas generator  10  shown in  FIG. 1  are denoted by identical reference numerals. 
         [0082]    A combustion chamber cup member  141  has a tubular member  150  and a cover  170 . The planar shape of the tubular member  150  and the cover  170  is similar to that of the combustion chamber cup member  41  shown in  FIG. 2  or  FIG. 3 . A plurality of holes (or concave portions)  160  are formed in the peripheral surface of the tubular member  150 . An opening at one end side of the tubular member  150  is in contact with a closure shell bottom surface  13   a,  and an opening at the other end side is covered with the cover  170 . 
         [0083]    The cover  170  has a shallow cup shape with a bottom having a flat portion  170   a  and a peripheral surface portion  170   b.  A protruding portion  170   c  is provided in the center of the flat portion  170   a,  and an annular inclined portion  170   d  is provided between the flat portion  170   a  and the protruding portion  170   c.  A plurality of hooks  171  that are bent inward in the direction of the flat portion  170   a  are provided at the peripheral edge of the opening of the peripheral surface portion  170   b.  The cover  170  has a thickness less than that of the tubular portion  150  and is formed from an elastic material. 
         [0084]    The cover  170  is fixed to the tubular member  150  by securing the plurality of hooks  171  in the plurality of holes (or concave portions)  160  of the tubular member  150 . 
         [0085]    The cover  170  can be fixed in the following manner. The hooks  171  are brought close to the holes  160 , while applying a force so as to expand outwardly the peripheral edge of the opening of the peripheral surface portion  170   b  of the cover  170 . Where the force is then released in this state, the peripheral edge of the opening of the peripheral surface portion  170   b  will close inwardly (that is, will restore the shape before the expansion), and the hooks  171  will be pressed against the peripheral surface portion  170   b  and inserted into the holes  160 . 
         [0086]    A second igniter  25  is accommodated inside the combustion chamber cup member  141  (an assembly of the tubular member  150  and cover  170 ). Because the actuation portion  25   a  of the second igniter  25  is positioned directly below the protruding portion  170   c  of the cover  170 , although the flat portion  170   a  is lower than the protruding portion  170   c,  it produces no adverse effect on the accommodation of the second igniter  25 . Further, because the flat portion  170   a  can be positioned lower than the protruding portion  170   c,  the capacity of the first combustion chamber  31  can be enlarged accordingly. 
         [0087]    The protruding portion  170   c  of the combustion chamber cup member  141  is positioned lower than a top plate  32   a  of an enhancer chamber cup member  32 . The ratio H 2 /H 1  of the height (H 2 ) of the protruding portion  170   c  to the height (H 1 ) of the top plate  32   a  is preferably within a range of 0.3 to 0.9, more preferably within a range of 0.5 to 0.8. 
         [0088]    In the gas generator  100  shown in  FIG. 4 , when the second igniter  25  is actuated and the second gas generating agent  51  is combusted, the entire cover  170  or part thereof is fractured and the combustion gas flows into the first combustion chamber  31 . 
         [0089]    A method for assembling the gas generator  100  shown in  FIG. 4  will be explained below. The enhancer chamber cup member  32  (enhancer holes  56  are closed with a tape  57 ) filled with an enhancer agent  53  is attached to a closure shell  13  having the first igniter  21  and the second igniter  25  attached thereto. The tubular member  150  is then attached around the second igniter  25 , and the accommodation space of the second gas generating agent  51  is formed. Then, the second gas generating agent  51  is loaded from an opening in the upper end of the tubular member  150 , and because the loading can thus be performed from the opening at the upper end, the operation is facilitated. The cover  170  is then attached to the opening after the second gas generating agent  51  has been loaded. 
         [0090]    Then a filter  45  is disposed in a closure shell  13 , and a first gas generating agent  50  is loaded toward the top of the cover  170  located within the space surrounded by the filter  45  in the same manner as in the gas generator  10  shown in  FIG. 1 . 
         [0091]    The invention thus described, it will be obvious that the same may be varied in many ways. Such Variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.