Abstract:
The present invention provides a hybrid inflator capable of adjusting an amount of a pressurized medium and a material of a gas generating agent to meet the requirements. 
     An outer shell of a first gas generating chamber  130  is formed by an inflator housing  101  and a second gas generating chamber housing  146 , and an outer shell of a second gas generating chamber  140  is formed by the second gas generating chamber housing  146 . For this reason, even when the requirement for downsizing and reducing weight is met, an amount of a gas generating agent does not have to be reduced.

Description:
This application claims priority on provisional Application No. 60/360,008 filed on Feb. 28, 2002, the entire contents of which are hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a hybrid inflator suitable for an inflating-type safety system of motor vehicles, and an air bag system using the same inflator. 
     PRIOR ART 
     With the development of an inflator for an inflating-type safety system of motor vehicles, a hybrid inflator using both a pressurized gas and a solid gas generating agent is attracting attention. A main design requirement for a hybrid inflator is that the inflator inflates an air bag by a predetermined amount in a predetermined time so that the air bag is effectively activated. Various proposals concerning a structure to meet the requirement have heretofore been made (for example, as referred in JP-A 08-282427). From the viewpoint of weight reduction of a vehicle, such a hybrid inflator is required to be small in size and light in weight. Further, from the viewpoint of securing safety of a passenger, it is required to inflate and develop an air bag up to a predetermined volume rapidly and unfailingly. For this reason, while meeting the requirement for downsizing and reducing weight, it is demanded to secure necessary charged amounts of a pressurized medium and a gas generating agent in accordance with the requirements such as a kind of an automobile or the like. 
     BRIEF SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a hybrid inflator in which the requirement for downsizing and reducing weight is met and an amount of a pressurized medium and an amount of a gas generating agent can properly be adjusted without deteriorating a function of an inflator, and an air bag system using the same inflator. 
     The present invention provides, as a means for solving the above problem, a multistage inflating-type hybrid inflator comprising an inflator housing, at least two gas generating chambers provided with a gas generating agent which is stored in the inflator housing, and an ignition chamber provided with an igniter connected to at least two gas generating chambers, wherein 
     a pressurized medium is charged in a space portion except for the ignition chamber inside the inflator housing, 
     a diffuser portion having a gas discharging port is provided at one end of the inflator housing, and a principal rupturable plate closing an outflow passage of the pressurized medium between the diffuser portion and the inflator housing is provided, and 
     the at least two gas generating chambers are formed by axially dividing the interior of the inflator housing into at least two sections with a partition wall or a gas generating chamber housing provided inside the inflator housing. 
     In the present invention, the at least two gas generating chambers can occupy the whole space in a radial sectional view of the inflator housing. In the present invention, an inner wall surface of the inflator housing can be utilized as a wall (an outer shell) of the gas generating chamber. 
     Also, as another means for solving the above-described problem, in the present invention, the at least two gas generating chambers may be formed by at least two gas generating chamber housings provided in the inflator housing independently. 
     In the present invention, the at least two gas generating chambers occupy part of the space in a radial sectional view of the inflator housing. 
     Further, as another means for solving the above-described problem, in the above invention, the at least two gas generating chambers are defined by the inflator housing and at least one gas generating chamber housing provided inside the inflator housing. 
     In this invention, at least two gas generating chambers may occupy the whole space in a radial sectional view of the inflator housing. In this invention, an inner wall surface of the inflator housing can be utilized as a wall (an outer shell) of the gas generating chamber. 
     By forming at least two gas generating chambers as described in the above respective inventions, charge amounts of the pressurized medium and the gas generating agent can easily be adjusted to desired ranges. Further, the volume which is occupied by the at least two gas generating chambers in the axial direction in the inflator housing can be reduced or the axial length of the inflator housing can be shortened, so that, the hybrid inflator can be downsized correspondingly. 
     The present invention provides, as another means for solving the above-described problem, a multistage inflating-type hybrid inflator comprising an inflator housing, at least two gas generating chambers provided with a gas generating agent which is stored in the inflator housing, and an ignition chamber provided with an igniter connected to the at least two gas generating chambers, wherein 
     a pressurized medium is charged in a space portion except for the ignition chamber inside the inflator housing, 
     the at least two gas generating chambers provided with the gas generating agent and the ignition chamber provided with the igniter connected to the at least two gas generating chambers are arranged in both or one of the spaces formed by radially dividing the inflator housing into two sections with a partition plate, 
     the at least two gas generating chambers are formed by axially dividing the interior of the inflator housing into at least two sections with a partition wall or a gas generating chamber housing provided inside the inflator housing, and 
     one or at least two gas passages connecting the two spaces, one or at least two gas discharging holes connecting to the outflow passage of the pressurized medium, and a principal rupturable plate closing the outflow passage of the pressurized medium are provided in the partition plate. 
     In this invention, the at least two gas generating chambers may occupy the whole space in a radial sectional view of the inflator housing. In this invention, an inner wall surface of the inflator housing can be utilized as a wall (an outer shell) of the gas generating chamber. 
     Also, as another means for solving the above-described problem, in the above invention, the at least two gas generating chambers are formed by at least two gas generating chamber housings provided inside the inflator housing independently. 
     In this invention, the at least two gas generating chambers may occupy part of the space in a radial sectional view of the inflator housing. 
     Also, as another means for solving the above-described problem, in this invention, the at least two gas generating chambers are defined by the inflator housing and at least one gas generating chamber housing provided inside the inflator housing. 
     In this invention, the at least two gas generating chambers may occupy the whole space in a radial sectional view of the inflator housing. In this invention, an inner wall surface of the inflator housing can be utilized as a wall (an outer shell) of the gas generating chamber. 
     By forming at least two gas generating chambers as described in the above respective inventions, charged amounts of a pressurized medium and a gas generating agent can easily be adjusted to desired ranges. Further, the volume which is occupied by the at least two gas generating chambers in the axial direction in the inflator housing can be reduced or the axial length of the inflator housing can be shortened, and therefore, the hybrid inflator can be downsized correspondingly. As described above, particularly, in a structure in which the inflator housing is partitioned and divided into first and second chambers by a partition wall, if the partition wall exists at a central portion of the inflator housing, the length of the gas generating chamber in the axial direction is restricted so that the length of the gas generating chamber in the axial direction can be advantageously shortened. Further, if the partition wall exists in the central portion of the inflator housing, the length of the inflator housing in the axial direction is made longer by the thickness of the partition wall, but the diameter (or width) of the inflator housing is made smaller to improve pressure resisting performance. Therefore, the thickness of the inflator housing can be thinner and weight-reduction can be achieved correspondingly. 
     When the pressurized medium used in the present invention has a composition comprising oxygen and an inert gas such as argon or helium (nitrogen is also included in the inert gas in the present invention), the oxygen works to convert carbon monoxide and hydrogen generated due to combustion of a gas generating agent as a gas generating means into carbon dioxide and water vapor, and the argon works to promote the thermal expansion of the pressurized medium. Helium is preferably included in the pressurized medium since the leakage of the pressurized medium can be detected easily, and consequently distribution of imperfect products can be prevented. A charging pressure of the pressurized medium (=pressure inside the inflator housing) is preferably 10,000 to 70,000 kPa and more preferably, 20,000 to 50,000 kPa. The pressurized medium may, or may not include oxygen, and when oxygen is included, it is preferable that the maximum amount is 30 mol %. 
     As the gas generating agent stored in the gas generating chamber and used in the present invention, for example, a gun propellant can be used. As the gun propellant, a single-base gun propellant, a double-base gun propellant and a triple-base gun propellant can be used. In addition to these propellants, it is possible to use a gun propellant obtained by mixing a secondary explosive, a binder, a plasticizer, a stabilizer and the like, and molding the resultant mixture in a desired shape. 
     The secondary explosive can include hexahydrotrinitrotriazine (RDX), cyclotetramethylene tetranitramine (HMX), pentaerithritol tetranitrate (PETN), and triaminoguanidine nitrate (TAGN) and the like. For example, when a gas generating agent using RDX as a secondary explosive is burnt in an oxygen-absent atmosphere under a pressure of 20,670 kPa and at a combustion temperature of 3348 K, formed gas in a combustion gas comprises 33 mol % of nitrogen, 25 mol % of carbon monoxide, 23 mol % of water vapor, 8 mol % of carbon dioxide and other gas components. 
     The bonding agent can include cellulose acetate, cellulose acetate butylate, cellulose acetate propiolate, ethyl cellulose, polyvinyl acetate, azide polymer, polybutadiene, hydrogenated polybutadiene and polyurethane and the like; the plasticizer can include trimethylolethane trinitrate, butantriol trinitrate, nitroglycerine, bis (2,2-dinitropropyl) acetal/formal, glycidyl azide and acetyltriethyl citrate and the like; and the stabilizer can include ethlcentralite, diphenylamine and resocinol and the like. 
     In a preferable ratio of the secondary explosive to the binding agent, plasticizer and stabilizer, secondary explosive is about 50 to 90 wt. % and the binder, plasticizer and stabilizer in all are about 10 to 50 wt. %. 
     It is difficult in some cases to burn the gas generating agent of the above-described composition under normal pressure. However, in the hybrid inflator according to the present invention, the interior thereof is maintained at a high pressure in advance, the gas generating agents can be burnt stably and smoothly. 
     In addition, as the gas generating agent, for example, it is possible to use a material including the fuel and the oxidizing agent, or the fuel, the oxidizing agent and the slag-forming agent, being mixed with the binding agent if required, and formed into a desired shape. If such a gas generating agent is used, a gas generated by combustion of the agent can be used for developing the air bag together with the pressurized medium. Especially when the gas generating agent including the slag-forming agent is used, an amount of mist discharged from the inflator can be largely reduced. 
     Preferably, the fuel can be one or at least two selected from guanidine derivatives such as nitroguanidine (NQ), guanidine nitrite (GN), guanidine carbonate, amino nitroguanidine, amino guanidine nitrite, amino guanidine carbonate, diamino guanidine nitrite, diamino guanidine carbonate, or triamino guanidine nitrite. As a fuel, one or at least two materials selected from the group comprising tetrazole and tetrazole derivative can be used. 
     As the oxidizing agent, one or more materials selected from the group comprising strontium perchlorate, potassium nitrate, ammoniumnitrate, potassiumperchlorate, copper oxide, ferrous oxide, a basic copper nitrate are preferably used. A preferable compounding amount of the oxidizing agent is 10 to 80 parts by weight, and more preferably, 20 to 50 parts by weight with respect to 100 parts by weight of the fuel. 
     As the slag-forming agent, one or at least two materials selected from the group comprising acid clay, talc, bentonite, diatomaceous earth, kaolin, silica, alumina, sodium silicate, silicon nitride, silicon carbide, hydrotalsite, and a mixture thereof are preferably used. A preferable amount of the slag-forming agent is 0 to 50 parts by weight, and more preferably, 1 to 10 parts by weight with respect to 100 parts by weight of the fuel. 
     As the binding agent, one or more materials selected from the group comprising sodium salt of carboxymethylcellulose, hydroxyethyl cellulose, starch, polyvinyl alcohol, guar gum, microcrystal cellulose, polyacrylamide and calcium stearate are preferably used. A preferable amount of the binding agent is 0 to 30 parts by weight, and more preferably, 3 to 10 parts by weight with respect to 100 parts by weight of the fuel. 
     The present invention further provides an air bag system comprising an activation signal-outputting means including an impact sensor and a control unit, and a module case in which the above-described multistage inflating-type hybrid inflator and an air bag are accommodated. 
     In the present invention, the term “a gas generator” means a unit having a gas generating function of generating a high temperature combustion gas due to combustion of the gas generating means (gas generating agent) stored in the gas generator housing (gas generating chamber), thereby allowing the high temperature combustion gas to flow into the inflator housing. And the hybrid inflator includes the gas generator inside a inflator housing thereof. 
     The hybrid inflator of the present invention can meet the requirement of downsizing and reducing weight, and can adjust an amount of the pressurized medium and an amount of the gas generating agent properly according to the requirements without deteriorating the function for an inflator. 
    
    
     
       BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is an axial sectional view of a hybrid inflator of the present invention. 
         FIG. 2  is an axial sectional view of a hybrid inflator according to another embodiment of the present invention. 
         FIG. 3  is an axial sectional view of a hybrid inflator according to another embodiment of the present invention. 
         FIG. 4  is an axial sectional view of a hybrid inflator according to another embodiment of the present invention. 
         FIG. 5  is an axial sectional view of a hybrid inflator according to another embodiment of the present invention. 
         FIG. 6  is an axial sectional view of a hybrid inflator according to another embodiment of the present invention. 
         FIG. 7  is a conceptual diagram for explaining an air bag system of the present invention. 
         FIG. 8  explains a conceptual diagram in the plain view direction of another air bag system of the present invention. 
         FIG. 9  is a conceptual diagram in a side direction of the air bag system in FIG.  8 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     One embodiment of the present invention will be explained with reference to the drawings. FIG.  1 ( a ) is an axial sectional view of a hybrid inflator  100  of the present invention, and FIG.  1 ( b ) is a sectional view cut along A—A in the direction shown by the arrows in FIG.  1 ( a ). In this case, FIG.  1 ( b ) is used only for explaining an arrangement of gas generating chambers. 
     An inflator housing  101  comprises a cylindrical pressure-resisting container, and an inner space  150  is charged with a pressurized medium and maintained at a high pressure. The pressurized medium is usually charged from a thin hole formed in a boss  109  or the like joined to the inflator housing  101  or one end portion of the inflator housing  101 , and the thin hole is closed with a sealing pin after the inflator housing is filled with the pressurized medium. 
     The boss  109  is provided with a first ignition chamber  110  and a second ignition chamber  120 , a first igniter  112  is accommodated and fixed in the first ignition chamber  110  and a second igniter  122  is accommodated and fixed in the second ignition chamber  120 . The numerals  114  and  124  denote connectors, and the numerals  116  and  126  denote conductive pins. 
     A first gas generating chamber  130 , whose outer shell is formed by the inflator housing  101 , part of a wall of a second gas generating chamber housing  146  and a partition wall  135 , is disposed in the axial extension line of the first ignition chamber  110 , and a required amount of a first gas generating agent  132  is stored in the first gas generating chamber  130 . 
     A first rupturable plate  118  closes between the first ignition chamber  110  and the first gas generating chamber  130 , and a flame-transferring means  119  is disposed at a position where the first gas generating chamber  130  contacts the first rupturable plate  118 . The flame-transferring means  119  comprises a cup made of aluminum and a transfer charge charged therein. 
     The partition wall  135  is provided with a required number of first communication holes  137  for discharging a combustion gas generated by combustion of the first gas generating agent  132 , and the holes are opened in the axial direction of the inflator housing  101 . The diameter of the first communication hole  137  is adjusted to such a size that the first gas generating agent  132  cannot leak out, and a screen comprising a wire mesh or the like may be disposed inside or outside the first communication hole  137 . 
     In FIG.  1 ( a ), one partition wall  135  is used for the first gas generating chamber  130  and the second gas generating chamber  140 . Instead, two partition walls may be used, and a retainer having a structure shown in  FIGS. 4  to  6  may be used. 
     A second gas generating chamber  140 , whose outer shell is formed by the inflator housing  101 , the second gas generating chamber housing  146  and the partition wall  135 , is disposed in the axial extension line of the second ignition chamber  120 , and a required amount of a second gas generating agent  142  is stored in the second gas generating chamber  140 . 
     The first gas generating chamber  130  and the second gas generating chamber  140  are separated along the axial direction as shown in FIG.  1 ( a ), and they are adjacent radially to each other. Further, as shown in FIG.  1 ( b ), the chambers occupy the whole space in the radial sectional view of the inflator housing  101 . 
     A second rupturable plate  128  closes between the second ignition chamber  120  and the second gas generating chamber  140 , and a flame-transferring means  129  is disposed at a position where the second gas generating chamber  140  contacts the second rupturable plate  128 . The flame-transferring means  129  comprises a cup made of aluminum or the like and a transfer charge charged therein. 
     A required number of second communication holes  147  for discharging a combustion gas generated by combustion of the second gas generating agent  142  are provided in the partition wall  135 , and the holes are opened in the axial direction of the inflator housing  101 . The diameter of the second communication hole  147  is adjusted to such a size that the second gas generating agent  142  cannot leak out, and a screen comprising a wire mesh or the like may be disposed inside or outside the second communication hole  147 . 
     A diffuser portion  160  having a required number of gas discharging ports  163  for discharging a pressurized medium and a combustion gas is provided at the other end portion of the inflator housing  101 . The diffuser portion  160  is welded and fixed to the inflator housing  101  by a laser welding, a resistance welding, an electron beam welding or the like. 
     Since an inner space  161  of the diffuser portion  160  and an inner space  150  of the inflator housing  101  are separated from each other by a principal rupturable plate  162 , the inner space  161  is maintained in a normal pressure. The principal rupturable plate  162  is welded and fixed to the diffuser portion  160  at a brim (a peripheral edge portion of an opening portion)  158  by a laser welding, a resistance welding, an electron beam welding or the like. In this case, a filter member for removing mist or the like can be arranged to contact the gas discharging ports  163  inside the diffuser portion  160 . As the filter member, a wire mesh, a punching metal or the like can be used. 
     Incidentally, in the hybrid inflator  100  shown in FIGS.  1 ( a ) and  1 ( b ), the first gas generating chamber  130  and a second gas generating chamber  140  are defined axially by the inflator housing  101  and the second gas generating chamber housing  146 . Alternatively, two gas generating chambers can be defined by disposing one rectangular partition member (partition wall) in the axial direction. Further, three or four or more gas generating chambers can be defined by combining at least two partition members (partition walls) and a gas generating chamber housing and disposing them axially. 
     In the hybrid inflator  100  shown in FIGS.  1 ( a ) and  1 ( b ), the operational effects such as the following (1) to (3) can be obtained on the basis of its structure. 
     (1) A volume of the gas generating chamber inside the inflator housing  101  can be made large, and thereby, even when the axial length of the inflator housing  101  and the diameter thereof are made small, a sufficient volume for charging the gas generating agent and the pressurized medium can be secured, so that it is unnecessary to reduce a charged amount of the gas generating agent or the pressurized medium accompanying with downsizing the hybrid inflator. 
     (2) The volume of at least two gas generating chambers occupying the inflator housing axially can be made small, or the axial length thereof can be shortened, so that the inflator housing can be smaller correspondingly. 
     (3) When the inner wall of the inflator housing  101  is utilized as the outer shell of the gas generating chamber, a weight of the inflator housing can be reduced as compared with a case that a gas generating chamber housing is provided independently from the inflator housing. 
     Another embodiment which is a modification of the hybrid inflator  100  in  FIG. 1  will be explained below with reference to  FIG. 2. A  hybrid inflator in  FIG. 2  is different from that in  FIG. 1  only in the arrangements of gas generating chambers, so that the same portions other than the above are denoted by the same numerals as these in FIG.  1 . FIG.  2 ( a ) is an axial sectional view of a hybrid inflator of the present invention, and FIG.  2 ( b ) is a sectional view cut along A—A in the direction shown by the arrows in FIG.  2 ( a ). In this case, FIG.  2 ( b ) is used only for explaining the arrangement of gas generating chambers. 
     The first gas generating chamber  130  and the second gas generating chamber  140  are separated along the axial direction as shown in FIG.  2 ( a ), and they are adjacent radially to each other. Further, as shown in FIG.  2 ( b ), the chambers occupy the whole space in the radial sectional view of the inflator housing  101 . 
     An outer shell of the first gas generating chamber  130  is formed by a first gas generating chamber housing  136  and a second gas generating chamber housing  146 , and an outer shell of the second gas generating chamber  140  is formed by the second gas generating chamber housing  146 . Respective end surfaces of the first gas generating chamber housing  136  and the second gas generating chamber housing  146  which face the inner space  150  contact with each other. 
     A required number of first communication holes  137  for discharging a combustion gas generated by combustion of the first gas generating agent  132  are provided in an end surface facing the inner space  150  of the first gas generating chamber housing  136  and the first gas generating chamber  130 , and the holes are opened in the axial direction of the inflator housing  101 . The diameter of the first communication hole  137  is adjusted to such a size that the first gas generating agent  132  cannot leak out, and a screen comprising a wire mesh or the like may be disposed inside or outside the first communication hole  137 . 
     A required number of second communication holes  170  for discharging a combustion gas generated by combustion of the second gas generating agent  142  are provided at an end surface of the second gas generating chamber housing  146  facing the inner space  150 , and the holes are opened in the axial direction of the inflator housing  101 . The diameter of the second communication hole  170  is adjusted to such a size that the second gas generating agent  142  cannot leak out. Further, a third communication hole  148  which allows communication between all of a plurality of second communication holes  170  and the inner space  150  is provided in an end surface of the first gas generating chamber housing  136  facing the second communication holes  147 . The second communication holes  170  and the third communication hole  148  contact each other, and a screen comprising a wire mesh or the like can be disposed inside or outside these communication holes. 
     Incidentally, the hybrid inflator  100  shown in FIGS.  2 ( a ) and  2 ( b ) can be partitioned to three or four or more gas generating chambers by arranging one or at least two independent gas generating chamber housings separately. 
     In the hybrid inflator  100  shown in FIGS.  2 ( a ) and  2 ( b ), the operational effect such as the above-described (1) and (2) can be obtained on the basis of its structure. 
     Another embodiment of the hybrid inflator  100  which is a modification of that in  FIG. 1  will be explained below with reference to FIG.  3 . Since a hybrid inflator in  FIG. 3  is different from that in  FIG. 1  only in the arrangement of gas generating chambers, the same portions other than the above as these in  FIG. 1  are denoted by the same numerals. FIG.  3 ( a ) is an axial sectional view of a hybrid inflator of the present invention, and FIG.  3 ( b ) is a sectional view cut along A—A in the direction shown by the arrows in FIG.  3 ( a ). In this case, FIG.  3 ( b ) is used only for explaining the arrangement of gas generating chambers. 
     A first gas generating chamber  130  and a second gas generating chamber  140  are separated along the axial direction as shown in FIG.  3 ( a ), and they are adjacent radially to each other. Further, as shown in FIG.  3 ( b ), the second gas generating chamber  140  is disposed to be enclosed by the first gas generating chamber  130 , and the chambers occupy the whole space in the radial sectional view of the inflator housing  101 . 
     An outer shell of the first gas generating chamber  130  is formed by the inflator housing  101 , the entire wall of a second gas generating chamber housing  146  and a first partition wall  135 , and an outer shell of a second gas generating chamber  140  is formed by the second gas generating chamber housing  146  and a second retainer  145 . 
     Incidentally, the hybrid inflator  100  shown in FIGS.  3 ( a ) and  3 ( b ) can be partitioned into three or four or more gas generating chambers by disposing one or at least two independent gas generating chamber housings separately. 
     In the hybrid inflator  100  shown in FIGS.  3 ( a ) and  3 ( b ), the operational effect such as the above-described (1) to (3) can be obtained on the basis of its structure. 
     Next, the operations of the hybrid inflators  100  shown in  FIG. 1  to  FIG. 3  will be explained. Although the first igniter  112  and the second igniter  122  can be activated simultaneously, in the following, a case such that the first igniter  112  is first activated and the second igniter  122  is activated with a delay therefrom will be explained. 
     When a vehicle collides, after the first igniter  112  is activated and ignited by an activation signal-outputting means to rupture the first rupturable plate  118 , the transfer charge  119  is ignited and burnt to generate a high-temperature gas (flame), and the first gas generating agent  132  in the first gas generating chamber  130  is ignited and burnt by the flame, thereby generating a high-temperature gas. The high-temperature gas flows out of the first communication holes  137  to form a mixed gas together with the pressurized medium so that the mixed gas is filled in the inner space  150 . 
     Thereafter, the pressure inside the inner space  150  is increased by the mixed gas to rupture the principal rupturable plate  162  rapidly. Consequently, the mixed gas is instantaneously ejected from the gas discharging ports  163  via the ruptured principal rupturable plate  162  to inflate the air bag. 
     The second igniter  122  is activated and ignited with a slight delay from the activation and ignition of the first igniter  112  and the second rupturable plate  128  is ruptured, so that the second gas generating agent  142  in the second gas generating chamber  140  is ignited and burnt to generate a high-temperature gas. The high-temperature gas flows out of the second communication holes  171  (the second communication holes  171  and the third communication hole  148  in  FIG. 3 ) to form a mixed gas together with the remaining pressurized medium, so that the mixed gas is ejected from the gas discharging ports  163  via the ruptured principal rupturable plate  162  to further inflate the air bag. 
     Next, another embodiment of the present invention will be explained with reference to the drawings. FIG.  4 ( a ) is an axial sectional view of a hybrid inflator of the present invention, FIG.  4 ( b ) is a sectional view cut along A—A in the direction shown by the arrows in FIG.  4 ( a ), and FIG.  4 ( c ) is a sectional view cut along B—B in the direction shown by the arrows in FIG.  4 ( a ). FIG.  4 ( c ) is used only for explaining the arrangement of gas generating chambers. 
     In a hybrid inflator  200  shown in FIGS.  4 ( a ) to  4 ( c ), a cylindrical inflator housing  201  is partitioned into two sections ( 201   a  and  201   b ) by a partition plate  202  provided at the axial center of the inflator housing  201  or in the vicinity thereof, so that a first chamber  250  and a second chamber  260 , which are two spaces arranged axially in series, are provided. 
     The partition plate  202  is fixed to the inflator housing  201  ( 201   a ,  201   b ) by welding (or a screw), and it has four gas discharging holes  203  provided in the radial direction of the partition wall and four gas passages  204  which are provided in a thickness direction thereof to communicate the first chamber  250  and the second chamber  260 . 
     The gas discharging holes  203  are in communication with the second chamber  260  via the principal rupturable plate  205 , and the gas discharging holes  203  and the gas passages  204  do not intersect each other. Since the total opening area of the gas discharging holes  203  is set to be smaller than the total opening area of the gas passages  204 , the ejection pressure of the mixed gas comprising a pressurized medium and a combustion gas is controlled by the gas discharging holes  203 . 
     The kinds of materials constituting the inflator housing  201  and the partition plate  202  are not particularly limited. In view of welding easiness, however, it is desirable that the materials are the same. For example, stainless steel can be used as the material. 
     A screen such as a wire mesh for removing foreign matters (for example, fragments of the principal rupturable plate  205 ) contained in the mixed gas can be arranged at a desired position in the outflow passage for the mixed gas extending from the principal rupturable plate  205  to the gas discharging holes  203 . A plurality of the gas discharging holes  203  can be provided at equal intervals or at different intervals over the entire peripheral surface of the partition plate  202 . 
     A first gas generating chamber  230 , whose outer shell is formed by the inflator housing  201   a , part of a wall of the second gas generating chamber housing  246  and a first retainer  235 , is disposed in a first chamber  250  which is one of the spaces formed by partitioning the inflator housing  201  with the partition plate  202 , and a required amount of a first gas generating agent  232  is stored in the first gas generating chamber  230 . The volume of the first gas generating chamber  230  can be adjusted by axially moving the second retainer  235  in both directions in accordance with an amount of the first gas generating agent  232  to be used. 
     A required number of first communication holes  237  for discharging a combustion gas generated by combustion of the first gas generating agent  232  are provided in the first retainer  235 , and they are opened in the axial direction of the inflator housing  201 . The diameter of the first communication hole  237  is adjusted to such a size that the first gas generating agent  232  cannot leak out, and a screen comprising a wire mesh or the like can be disposed inside or outside the first communication holes  237 . 
     A first ignition chamber  210  is formed in a boss  209  mounted to one end of the inflator housing  201 , and a first igniter  212  is fitted therein. The numeral  214  denotes a connector and the numeral  216  denotes a conductive pin. 
     A transfer charge  219  charged into an aluminum container or the like is disposed and fixed in the first gas generating chamber  230  to be correctly opposite to the distal end of the first igniter  212  via a first rupturable plate  218  provided to separate the first gas generating chamber  230  from the first ignition chamber  210 . 
     Further, a second gas generating chamber  240  whose outer shell is formed by the second gas generating chamber housing  246  and the second retainer  245  is disposed in the first chamber  250 , and a required amount of a second gas generating agent  242  is stored in the second gas generating chamber  240 . The volume of the second gas generating chamber  240  can be adjusted by axially moving the second retainer  245  in both directions in accordance with an amount of the second gas generating agent  242  to be used. 
     The first gas generating chamber  230  and the second gas generating chamber  240  are separated along the axial direction as shown in FIG.  4 ( a ), and they are radially adjacent to each other. Further, as shown in FIG.  4 ( b ), the chambers occupy the whole space in a radial sectional view of the inflator housing  201 . 
     A required number of second communication holes  247  for discharging a combustion gas generated by combustion of the second gas generating agent  242  are provided in the second retainer  245 , and the holes are opened in an axial direction of the inflator housing  201 . The diameter of the second communication hole  247  is adjusted to such a size that the second gas generating agent  242  cannot leak out, and a screen comprising a wire mesh or the like can be disposed inside or outside the second communication holes  247 . 
     A second ignition chamber  220  is formed by the boss  209  mounted to the one end of the inflator housing  201 , and a second igniter  222  is fitted therein. The numeral  224  denotes a connector and the numeral  226  denotes a conductive pin. A second rupturable plate  228  is provided in the second gas generating chamber  240  to separate the second gas generating chamber  240  from the second ignition chamber  220 . 
     In the first chamber  250 , the pressurized medium is charged with a high pressure in a space including the first gas generating chamber  230  and the second gas generating chamber  240 , and the space is maintained in a high and equal pressure. 
     A pressurized medium is charged with a high pressure in a second chamber  260  which is the other of the spaces formed by partitioning the inflator housing  201  with the partition plate  202 . However, a gas outflow passage extending from the principal rupturable plate  205  to the gas discharging holes  203  is maintained in a normal pressure. The numeral  208  denotes a sealing pin used for closing the charging hole for the pressurized medium. 
     In this case, the hybrid inflator  200  shown in FIGS.  4 ( a ) to  4 ( c ) is partitioned axially into the first gas generating chamber  230  and the second gas generating chamber  240  by the inflator housing  201   a  and the second gas generating chamber housing  246 . Alternatively, it may be partitioned into two gas generating chambers by disposing a partitioning member (partition wall) such as a rectangular plate in the axial direction. Further, the hybrid inflator can be partitioned into three or four or more gas generating chambers by disposing at least two partitioning members (partition walls) or gas generating chamber housings. 
     In the hybrid inflator  200  shown in FIGS.  4 ( a ) to  4 ( c ), in addition to the operational effects such as the above-described (1) to (3), the operational effects of the following (4) to (6) can be obtained on the basis of its structure. 
     (4) In the hybrid inflator  200 , since a mixed gas can be discharged from a central portion, a rectifying plate required, at the time of being mounted the air bag system, in a hybrid inflator of a type which discharges the gas from an end portion can be omitted. 
     (5) In the hybrid inflator  200 , the first chamber  250  and the second chamber  260  are in communication with each other via the gas passage  204 . Therefore, when the pressurized medium is charged from a pressurized medium charging hole in a manufacturing process, the pressurized medium flows in both of the second chamber  260  and the first chamber  250  via the gas passage  204 , so that the pressurized medium can be charged by a single charging work. 
     (6) Since the mixed gas in the first chamber  250  is discharged always after it flows into the second chamber  260  via the gas passage  204 , the mixed gas is properly cooled in a course of such an outflow, so that the temperature of the mixed gas is not only lowered but also a mist contained in the mixed gas is easily solidified. 
     An embodiment which is a modification of the hybrid inflator  200  in  FIG. 4  will be explained below with reference to FIG.  5 . Since a hybrid inflator in  FIG. 5  is different from that in  FIG. 4  only in the arrangement of gas generating chambers, the same portions other than the above as these in  FIG. 5  are denoted by the same numerals. FIG.  5 ( a ) is an axial sectional view of a hybrid inflator of the present invention, FIG.  5 ( b ) is a sectional view cut along A—A in the direction shown by the arrows in FIG.  5 ( a ), and FIG.  5 ( c ) is a sectional view cut along B—B in the direction shown by the in FIG.  5 ( a ). In this case, FIG.  5 ( c ) is used only for explaining the arrangement of the gas generating chambers. 
     A first gas generating chamber  230  and a second gas generating chamber  240  are provided inside a first chamber  250  which is one of the spaces formed by partitioning an inflator housing  201  with a partition plate  202 . 
     An outer shell of the first gas generating chamber  230  is formed by a first gas generating chamber housing  236  and a first retainer  235 , and an outer shell of the second gas generating chamber  240  is formed by a second gas generating chamber housing  246  and a second retainer  245 . 
     As shown in FIG.  4 ( a ), the first gas generating chamber  230  and the second gas generating chamber  240  are separated along the axial direction and they are disposed to have a small gap therebetween in the radial direction. Further, as shown in FIG.  5 ( c ), these chambers occupy only part of the space in a radial sectional view of the inflator housing  201 . 
     In this case, the hybrid inflator  200  shown in FIGS.  5 ( a ) to  5 ( c ) can be partitioned into three or four or more gas generating chambers by disposing three or four or more independent gas generating chamber housings. 
     In the hybrid inflator  200  shown in FIGS.  5 ( a ) to  5 ( c ), in addition to the operational effects such as the following (1′), the operational effects such as the above-described (4) to (6) can be obtained on the basis of its structure. 
     (1′) Since a volume occupied by the gas generating chambers in the inflator housing  101  is small, the embodiment is suitable for a hybrid inflator in which an amount of the gas generating agent is small and an amount of the pressurized medium is increased. 
     Further, as another embodiment of the hybrid inflator  200  shown in  FIG. 5 , two gas generating chamber housings in the shape shown in FIG.  4 ( c ) (the second gas generating chamber housing  246  in a semi-circular shape) can be used in combination to form a first gas generating chamber and a second gas generating chamber in a halved circle shape. In this case, two gas generating chambers occupy the whole space in a radial sectional view of the inflator housing. 
     Another embodiment which is a modification of the hybrid inflator  200  in  FIG. 4  will be explained below with reference to FIG.  6 . Since a hybrid inflator in  FIG. 6  is different from that in  FIG. 4  only in the arrangement of gas generating chambers, the same portions as these in  FIG. 6  are denoted by the same numerals. FIG.  6 ( a ) is an axial sectional view of a hybrid inflator of the present invention, FIG.  6 ( b ) is a sectional view cut along A—A in the direction shown by the arrows in FIG.  6 ( a ), and FIG.  6 ( c ) is a sectional view cut along B—B in the direction shown by the arrows in FIG.  6 ( a ). In this case, FIG.  6 ( c ) is used only for explaining the arrangement of the gas generating chambers. 
     A first gas generating chamber  230  and a second gas generating chamber  240  are provided in a first chamber  250  which is one of the spaces formed by partitioning an inflator housing  201  with a partition plate  202 . 
     An outer shell of the first gas generating chamber  230  is formed by an inflator housing  201 a, the entire wall of the second gas generating chamber housing  246  and a first retainer  235 , and an outer shell of the second gas generating chamber  240  is formed by a second gas generating chamber housing  246  and a second retainer  245 . 
     As shown in FIG.  6 ( a ), the first gas generating chamber  230  and the second gas generating chamber  240  are separated along the axial direction, and the second gas generating chamber  240  is disposed to be enclosed by the first gas generating chamber  230 . Further, as shown in FIG.  6 ( b ), the chambers occupy the whole space in radial sectional view of the inflator housing  201 . 
     In this case, the hybrid inflator  200  shown in FIGS.  6 ( a ) to  6 ( c ) can be partitioned to three or four or more gas generating chambers by disposing one or at least two independent gas generating chamber housings separately. 
     In the hybrid inflator  200  shown in FIGS.  6 ( a ) to  6 ( c ), the operational effects such as the above-described (1) to (6) can be obtained on the basis of its structure. 
     Next, the operation of the hybrid inflators  200  shown in  FIG. 4  to  FIG. 6  will be explained. Although the first igniter  212  and the second igniter  222  can be activated simultaneously, in this case, a case such that the first igniter  212  is first activated and the second igniter  222  is activated with a delay from the activation of the first igniter will be explained. 
     When a vehicle collides, the first igniter  212  is activated and ignited by an activation signal-outputting means to rupture the first rupturable plate  218 , and then, the flame-transferring means  219  is ignited and burnt to generate a high-temperature gas (flame). And the first gas generating agent  232  in the first gas generating chamber  230  is ignited and burnt by the flame, thereby generating a high-temperature gas. The high-temperature gas flows out of the first communication holes  172  to form a mixed gas together with the pressurized medium so that the mixed gas is filled in the first chamber  250 . 
     Thereafter, since the mixed gas flows in the second chamber  260  through the gas passage  204  provided in the partition plate  202  to increase the internal pressure in the second chamber, the principal rupturable plate  205  is ruptured rapidly. Consequently, the mixed gas from the first chamber  250  and the pressurized medium in the second chamber are instantaneously ejected from the gas discharging holes  203  through the ruptured principal rupturable plate  205  to inflate an air bag. 
     The second igniter  222  is activated and ignited with a slight delay from the activation and ignition of the first igniter  212 , the second rupturable plate  228  is ruptured, so that the second gas generating agent  242  in the second gas generating chamber  240  is ignited and burnt to generate a high-temperature gas. The high-temperature gas flows out from the second communication hole  247  to form a mixed gas together with the remaining pressurized medium. After the mixed gas flows in the second chamber  260  through the gas passage  204 , the mixed gas together with the remaining pressurized medium in the second chamber  260  is ejected from the gas discharging holes  203  via the ruptured principal rupturable plate  205  to further inflate the air bag. 
     Next, an air bag system of the present invention will be explained. Any one of the hybrid inflators of  FIG. 1  to  FIG. 6  can be applied to the air bag system of the present invention. However, the following is a description of a case such that the hybrid inflator  200  shown in  FIG. 4  to  FIG. 6  is used. 
     First, one embodiment of the air bag system will be explained with reference to FIG.  7 .  FIG. 7  is a conceptual diagram of an air bag system in a widthwise direction (a direction corresponding to the radial direction of the hybrid inflator  200  assembled in the system). The white arrow in  FIG. 7  shows a developing direction of an air bag, namely a direction where a passenger exists, and the arrows shows ejecting directions of a mixed gas. 
     An air bag system  400  comprises an activation signal-outputting means including an impact sensor and a control unit, and a module in which the hybrid inflator  200  and an air bag  404  are accommodated in a module case  402 . The hybrid inflator  200  is connected to the activation signal outputting means (the impact sensor and the control unit) in the first igniter  212  and second igniter  222  side to be fixed inside the module case  402  mounted with the air bag  404 . At this time, the gas discharging holes  203  of the hybrid inflator  200  do not face the air bag  404 , preferably the holes are arranged in the opposite side of the air bag  404  to face an inner wall  406  of the module case  402 . In the air bag system  400  having such a structure, an amount of a generated gas can be adjusted in accordance with the magnitude of the impact by appropriately setting an activation-signal outputting condition of the activation signal-outputting means, and therefore, the inflating speed of the air bag  404  can be adjusted. 
     In the air bag system  400 , since the mixed gas is ejected from the central portion of the hybrid inflator  200 , it is unnecessary to dispose a rectifying plate inside the module case  402 . Also, a common specification can be employed regardless of whether a vehicle is a right steering wheel vehicle or a left steering wheel vehicle. 
     Further, in the air bag system  400 , by a certain arrangement of the gas discharging holes  204 , as illustrated, by mounting the hybrid inflator  200  to make the orientation of the gas discharging holes  203  face the inner wall  406 , the ejected mixed gas can strike the inner wall before flowing into the air bag  404 . With this, the temperature of the mixed gas can be lowered correspondingly. 
       FIG. 8  shows an air bag module including a module case  450  and a hybrid inflator  200 . The hybrid inflator  200  is the inflator disclosed in  FIGS. 4 ,  5  and  6 , which includes a partition plate  202  provided in an intermediate portion between both ends of an inflator housing  201 . The module case  450  has a container  452  for accommodating therein an air bag  454 . The container  452  further includes a port  456 , which is a center portion of a backplate in the container  452 . 
     The hybrid inflator  200  is provided in an outside of the module case  450 , which is different from an arrangement of the inflator  200  and the module case  402  of FIG.  7 . The hybrid inflator  200  in  FIG. 8  is attached to the module case  450  by an attaching member  457  such that the attaching member  457  surrounds a gas discharging hole  203  and a space defined by the attaching member  457  and inflator  200  becomes a gas passage to communicate with the air bag  454 , as shown in FIG.  9 . When the hybrid inflator  200  operates, an inflation gas generated from the gas discharging hole  203  of the hybrid inflator  200  enters the space, and then, as shown in  FIG. 9 , passes through the port  456  into the module case  450 . Because of the location of the port  456 , the inflation gas is provided in the air bag  454  uniformly, the airbag is inflated evenly.