Patent Publication Number: US-6669230-B1

Title: Multistage gas generator for air bag and air bag apparatus

Description:
This application is a divisional of application Ser. No. 09/601,238, filed on Sep. 25, 2000. application Ser. No. 09/601,238 is the national phase of PCT International Application No. PCT/JP00/00800 filed on Feb. 15, 2000 under 35 U.S.C. §371. The entire contents of each of the above-identified applications are hereby incorporated by reference. 
    
    
     TECHNICAL FIELD OF THE INVENTION 
     The present invention relates to a multistage gas generator for an air bag and an air bag apparatus using the gas generator. 
     PRIOR ART 
     An air bag system which is mounted on various kinds of vehicles and the like including automobiles, aims to hold an occupant by means of an air bag (a bag body) rapidly inflated by a gas when the vehicle collides at a high speed so as to prevent the occupant from crashing into a hard portion inside the vehicle such as a steering wheel, a windscreen due to an inertia and being injured. This kind of air bag system generally comprises a gas generator to be actuated according to a collision of the vehicle and discharge a gas, and an air bag to introduce the gas to inflate. 
     It is desired that the air bag system of this type can safely restrain the occupant even when frame of the occupant (for example, whether a sitting height is long or short, whether an adult or a child, and the like), a sitting attitude (for example, an attitude of holding on the steering wheel) and the like are different. Then, there has been conventionally suggested an air bag system which actuates, applying an impact to the occupant as small as possible at the initial stage of the actuation. Gas generators in such a system are disclosed in JP-A 8-207696, U.S. Pat. Nos. 4,998,751 and 4,950,458. JP-A 8-207696 suggests a gas generator in which one igniter ignites two kinds of gas generating agent capsules so as to generate the gas at two stages. U.S. Pat. Nos. 4,998,751 and 4,950,458 suggest a gas generator in which two combustion chambers are provided for controlling actuation of the gas generator so as to generate the gas at two stages due to a expanded flame of the gas generating agent. 
     Further, in JP-A 9-183359, and DE-B 19620758, there is disclosed a gas generator in which two combustion chambers storing a gas generating agent are provided in a housing and an igniter is arranged in each combustion chamber, so as to adjust an activation timing of each of the igniters, thereby adjusting an output of the gas generator. 
     However, these above conventional gas generators are not a multistage gas generator for an air bag with a simple structure which can be manufactured easily, suppressing the entire size of the container (housing). 
     DISCLOSURE OF THE INVENTION 
     The present invention provides a multistage gas generator for an air bag, wherein, at the initial stage of actuation, the gas generator is actuated to give a passenger as a small impact as possible, and according to variation of passengers&#39; physiques (such that a sitting height is tall or low, adult or child) and sitting postures (such as clinging to a steering wheel), actuation output of the gas generator and timing of increase of output can be arbitrarily adjusted in order to restrain the passenger safely, and the gas generator can be manufactured easily with a simple structure, the entire size of the container (housing) can be suppressed, and finally the volume ratio of each combustion chamber can be arbitrarily be adjusted. 
     The present invention is characterized in an inner structure, specially a layout structure of the combustion chambers capable of suppressing the entire size of the gas generator and adjusting the volume ratio of each of the combustion chambers arbitrarily in a multistage gas generator for an air bag provided with a plural combustion chambers inside the housing thereof. 
     In other words, the multistage gas generator of the present invention having a cylindrical housing comprising a diffuser shell with a plurality of gas discharge ports formed in a cylindrical side wall and a closure shell forming a inner space with the diffuser shell, a plurality of combustion chambers for accommodating gas generating means provided in a cylindrical housing, and ignition means disposed in the respective combustion chambers to ignite and burn the gas generating means, wherein, in the housing, at least one of the combustion chambers is disposed in the inner side of an inner shell provided eccentrically with respect to a center axis of the housing, the ignition means provided for the respective combustion chambers are disposed eccentrically with respect to the center axis of the housing. 
     Further, in the gas generator of the present invention, a communication hole which allows mutual communication between the combustion chambers can be provided. 
     An automatic ignition material (AIM) which is to be ignited and burnt by transmitted heat may be disposed in either one of the combustion chambers. 
     The present invention further provides a multistage air bag apparatus which comprises the above-described gas generator, an ignition signal-outputting means provided with as many outputting portions, which outputs activation signals to the igniters on impact, as the igniters of the ignition means, and a plurality of lead wires having connectors, the igniters and the outputting portions are connected to each other through the lead wires having the connectors, and the connectors include defining means for deciding the unique connection between one of the connectors and one of the outputting portions. 
     The above gas generator may further comprise a cylindrical filter means for purifying and/or cooling an activation gas, one or both of axial end surfaces of the filter means may be formed as inclining end surfaces which get narrower in the axial extending direction and the interior angle with respect to the inner peripheral surface is an acute angle, and a supporting portion which is opposed to the inclining end surface of the filter may be provided in the housing (a self-contracting type filter). 
     In the present invention, most of an outer surface of the inner shell can be in direct contact with gas generating agent existing outside of the inner shell without interposing a heat insulator. The gas generating agent comes into contact with the outer surface of the inner shell where the communication hole is provided. A wall of the inner shell exists between a first gas generating agent which burns first and the other second gas generating agent. Even if the first gas generating burns, the second gas generating agent will never start burning before actuation of a second igniter, and the second gas generating agent is burnt by actuation of the second igniter before a temperature of the second gas generating agent reaches an ignition temperature by heat transfer. 
     After the first gas generating is ignited, if the gas generator is left standing without igniting the second gas generating agent, the second gas generating agent is ignited after about 10 seconds. 
     In the present invention, it is generally preferable that the inner shell is of cylindrical shape whose upper end is closed and its horizontal cross sectional shape is circular. The horizontal cross sectional shape of the inner shell may be formed into various shapes such as rectangular shape and elliptic shape. However, it is desirable to form the horizontal cross sectional shape of the inner shell into circular in view of easiness of connection. The inner shell is disposed in the housing eccentrically with respect to the center axis of the housing. That is, the inner shell is disposed in the housing such that a center of the inner shell does not coincide with a center of the housing, and the inner shell is disposed in the housing eccentrically with respect to the cylindrical housing. Therefore, even if the plane shape of the housing is substantially elliptic, in case that the center of the plane shape and the center of the inner shell are deviated from each other, the inner shell and the housing are deviated from each other. Besides, the center axis of the housing is specified exclusively based on the plane shape of the cylindrical body, and even if the housing has a flange for mounting the housing to the module, the flange is not taken into consideration when the center axis of the housing is specified. 
     The ignition means disposed in the respective combustion chambers include an igniter which is actuated by electric signal. The igniters can be provided aligned in the axial direction of the housing. The closure shell constituting the housing can include a collar portion for fixing the igniter, and the igniter can be fixed to the collar portion. In this case, it is preferable that all igniters included in the respective ignition means are fixed to a single collar portion. This is because when the closure shell is formed including the collar portion, by fixing the plurality of igniters to the collar portion beforehand, the plurality of igniters can be fixed in the housing with a single operation for forming the closure shell, which is advantageous in manufacture. 
     The inner shell disposed in the housing eccentrically is of cylindrical shape and the inner shell includes an opening portion which opens by combustion of the gas generating means in one of the combustion chambers. The inner shell can be formed into another shape as described above. However, in view of easiness in connecting to the closure shell, it is preferable that the plane cross sectional shape is circle. The inner shell enable the gas to flow through the combustion chambers which are defined inside and outside of the inner shell by opening the opening portion. Such opening portion may be formed by forming a plurality of holes in the peripheral wall of the inner shell, and by closing the holes using breaking members. The holes closed by the breaking members can be opened exclusively by burning the gas generating means in the combustion chambers provided inside the inner shell. The hole is opened by combustion of the gas generating means, e.g., by rupturing, peeling, burning or detaching the breaking member due to a pressure caused by combustion of the gas generating means. Alternatively, this can be realized by providing the inner shell with a notch or by reducing the thickness of a portion of the inner shell. A shielding plate can be disposed outside of the opening portion, and the shielding plate can prevent flame generated in the combustion chamber provided outside the inner shell from coming into direct contact with the opening portion. The opening portion may be formed such as to be opened only by combustion of the gas generating means in one of the combustion chambers. 
     As described above, the inner shell is disposed in the housing eccentrically with respect to the center axis of the housing, and the ignition means disposed in each of the combustion chambers is disposed eccentrically with respect to the center axis of the housing. With this structure, it is possible to suppress the size of the housing to the minimum, and flexibility in volume, layout and the like of the combustion chamber can be maximized. That is, when two combustion chambers are defined in the housing, by disposing the inner shell eccentrically in the housing and defining a first combustion chamber on the outer side thereof and defining a second combustion chamber on the inner side, the volume ratio of the first and second combustion chambers can be freely changed by changing the volume of the inner shell. At that time, if the igniter of the ignition means disposed in each of the combustion chambers is also disposed eccentrically with respect to the center axis of the housing, the igniter disposed in the first combustion chamber will not be an obstacle to increase the volume of the second combustion chamber. Therefore, in the present invention, it is possible to maximize the flexibility in volume and the like of the first and second combustion chambers. 
     Further, the present invention provides a multistage gas generator for an air bag which is provided, in the combustion chamber inside the inner shell, with an automatic ignition material (AIM), to be ignited and burnt by heat generated by combustion of the gas generating means disposed in the combustion chamber outside the inner shell, and also provides a multistage gas generator for an air bag in which the automatic ignition material (AIM) is included in the ignition means disposed in the combustion chamber inside the inner shell. That is, in most cases, when the multistage type gas generator is actuated, all the ignition means are actuated and the gas generating means in all the combustion chambers are burnt. However, under a certain actuating condition, there is a case in which only one of the ignition means is actuated intentionally to burn the gas generating means in a selected combustion chamber. In this case, remaining ignition means and gas generating means which were not actuated cause inconvenience at the time of later disposal or damping. Therefore, it is preferable to ignite and burn them after actuation of the gas generator. Thereupon, by disposing the automatic ignition material (AIM) in the combustion chamber and/or ignition means, even when the gas generating means and/or ignition means in either of the combustion chambers were not burnt and remained, it is possible to ignite and burn the gas generating and/or ignition means at a delayed timing by heat (transmitted heat) caused by combustion of the gas generating means in the other combustion chamber. Therefore, in the present invention also, in the combustion chamber and/or the ignition means provided inside the inner shell, it is preferable to dispose the automatic ignition material (AIM) which is to be ignited and burnt by heat generated by combustion of the gas generating means in the combustion chamber provided outside the inner shell. As the automatic ignition material (AIM), material which is ignited with a lower temperature compared with the gas generating means or transfer charge is preferably used. The gas generating means is ignited by the automatic ignition material (AIM) after activation of the gas generating means. That is, the ignition of the gas generating means by the automatic ignition material is different from the ignition of the gas generating agent delaying intentionally the actuation timing of the ignition means for the purpose of adjusting the actuation performance of the gas generator. The ignition by AIM is performed when a sufficient period of time has passed after actuations at intentional intervals of the igniters to adjust the actuation performance of the gas generator. Therefore, after one ignition means is actuated first, the remaining gas generating means will not be ignited by the automatic ignition material before the other ignition means is actuated with intentionally delayed timing. 
     The housing can be formed by joining the diffuser shell and the closure shell by various welding methods such as friction welding, electron beam welding, laser welding, TIG welding and projection welding. Among these welding methods, when both the shells are joined by friction welding to form the housing, it is preferable to carry out the friction welding while fixing the closure shell. Generally, both the shells are joined at the final stage. And by performing the friction welding while fixing the closure shell in this manner, even when the center of gravity of the closure shell side is deviated such that the ignition means is disposed eccentrically, both the shells can be stably be joined. In other words, the friction welding is carried out in a state where one object is fixed and the other object is rotated. If the center of gravity of the object to be rotated is deviated, it is difficult to stably carry out the friction welding. Thereupon, in the present invention, stable friction welding is realized by carrying out the friction welding while fixing the closure shell side. 
     When the friction welding is carried out while fixing the closure shell, it is preferable that the flange portion for mounting the gas generator to the module case is provided on the closure shell, and the flange portion is formed with a positioning portion for specifying a direction and/or a position of the closure shell which is fixed at the time of friction welding. When the flange portion has a plurality radially projections for fixing the gas generator to the module case, the positioning portion is realized by forming the projections asymmetrically with respect to each other. Only one projecting is provided, the projection itself can be the positioning portion. By forming the flange portion with the positioning portion in this manner, when the inner shell is fixed in the housing by the friction welding, the joining position of the housing is always determined constantly with respect to the inner shell which is rotated. Therefore, it is possible to reliably fix the inner shell in a predetermined direction and/or position. By forming the positioning portion on the flange portion, the flange portion is used both for positioning and mounting of the gas generator. In the present invention, in order to fix the closure shell in the predetermined direction and/or a position at the time of friction welding, it is of course possible to form the positioning portion on another portion such as a peripheral wall and bottom surface instead of the flange. 
     Further, the igniting means disposed in the combustion chamber can include injecting-direction restricting means for restricting an injecting direction of flame which is generated by the actuation of the ignition means. The injecting-direction restricting means is used for restricting the injecting direction of flame generated by actuation of the ignition means, i.e., the injecting direction of flame to ignite and burn the gas generating means. 
     The injecting-direction restricting means can envelop at least a portion of the ignition means which generates the flame, and includes a hollow container having two or more flame-transferring holes for restricting the injecting direction of the flame into a desired direction. Examples of such injecting-direction restricting means are deflector plates, a cylindrical member capable of enveloping the entire ignition means, and a cup-like container or the like capable of enveloping a portion of the ignition means where the flame is generated. 
     By using such injecting-direction restricting means, it is possible to restrict the injecting direction of flame of the ignition means to a direction along the inner wall surface of the combustion chamber. The “direction along the inner wall surface of the combustion chamber” means that the flame is ejected, moving in a direction which coincides with a shape of the inner wall surface. By restricting the injecting direction of the flame of the ignition means in this manner, it is possible to preferably burn the gas generating means in the combustion chamber even when the ignition means is not disposed at center of the combustion chamber or when the combustion chamber is not circular in shape and a distance between the gas generating means and the ignition means disposed at corners of the combustion chamber is remarkably fair. 
     As the injecting-direction restricting means, the gas discharge ports may be distributed so that the number of the gas discharge ports formed further from the first igniter may be greater or the total opening area thereof may be greater than otherwise. It is preferable to combine these to form the injecting-direction restricting means. 
     The outputs of the ignition means disposed in the respective combustion chambers can be changed from one another. When the ignition means include a transfer charge in addition to the igniters having different outputs, it is possible to adjust the material, shape or amount of the transfer charge, thereby adjusting the output of the ignition means. 
     A retainer can be disposed inside the inner shell in order to perform the connection with the closure shell stably and smoothly. The retainer may be a gas generating agent fixing member shown in the embodiment. When fixing the inner shell to the closure shell by friction welding, crimping, resistance welding, convex-concave joint or the like, the retainer keeps the gas generating agent in the inner shell so that the gas generating agent does not come into direct contact with the closure shell, and also obtains a space for accommodating the ignition means in the inner shell. By using this retainer, the assembling operation can be facilitated. Especially when charging directions of two or more gas generating means are different at the time of assembling as in the present invention, it is effective to use the retainer. The retainer may have a canister-like shape made of aluminum or iron, or may be a porous material made of wire mesh or the like. 
     The igniter included in the ignition means is activated upon reception of activation signal of the gas generator which is outputted from a control unit or the like. Therefore, a cable for transmitting the activation signal from the control unit or the like is connected to each of the igniters. Since the gas generator of the present invention includes two or more ignition means, two or more igniters are included. By pulling out the cables connected to the igniters in the same direction, the gas generator can be mounted to the module easily afterwards. 
     In the multistage gas generator for the air bag of the present invention, when the ignition means disposed in each of the combustion chambers comprises an igniter which is to be activated by an electric signal and a cable for transmitting the electric signal is connected to each igniter through a connector, it is preferable that the connector has a positioning means capable of connecting the cable to only one of the igniters. That is, in the cables which are connected to the respective igniters to transmit different activation signals with the aim of adjusting activation timing, if a wrong cable is connected to one of the igniters, a desired activation output can never be obtained. Thereupon, the respective igniters are provided with the respective positioning means to be connected to exclusively one of the cables, which can prevent the connection error. Such positioning means can be realized by forming the engaging portions, which is between the igniter and the connector and for connecting the igniter and the cable, into different shapes for the respective igniters, or by forming the connectors with groove and/or projections having different positions and/or shapes. Additionally, plural cables of the respective igniters can be collected to one connector and the connector can be formed with the positioning means. The positioning means provided in the connector of the invention also includes all cases in which any elements determining whether a plug and a jack can be connected such as a case in which shape and size of a portion (blade or current-carrying plug) which connects and energize the connector) or shape and size of the case of the connector are different. That is, any means which uniquely defines combination of connection between the cable and the ignition is included. 
     With a gas generator comprising a housing having a plurality of combustion chambers therein and gas generating means which are different from each other in an amount of a generated gas per unit time in the respective combustion chambers such as gas generating means which are different from each other in at least one of burning rate, composition, composition ratio, shape and amount, activation performance of the gas generator, particularly the change with time of the gas discharging amount can be adjusted distinctively and arbitrarily. When the gas generating means in each of the combustion chambers is independently ignited and burnt with arbitrary timing, ignition means which is independently ignited and burnt is disposed in each of the combustion chambers. As the gas generating means, it is possible to use inorganic azide which is conventionally and widely used such as azide-based gas generating agent based on sodium azide or non-azide-based gas generating agent not based on inorganic azide. If safety is taken into consideration, non-azide-based gas generating agent is desirable. The gas generating means is appropriately selected in accordance with requirements such as burning rate, non-toxicity, combustion temperature, decomposition-starting temperature. When gas generating means having different burning rate for each combustion chamber, it is possible to use gas generating means having different composition or composition ratio itself by using inorganic non-azide such as sodium azide, non-azide such as nitroguanidine or the like as fuel and nitrogen source, or gas generating means in which the shape of composition can be changed such as pellet-like, wafer-like, hollow columnar, disk-like, body having a single hole, porous body or the surface area is changed by size of the molded article. Especially when the gas generating means is formed into a porous body having a plurality of through-holes, although layout of the holes is not limited, it is preferable to a distance between an outer end of the molded article and a center of the hole and a distance between the centers of the respective holes are substantially equal to each other so that performance of the gas generator is stabilized. More specifically, in a cylindrical molded article whose cross section is circular, a preferred structure is such that one hole is arranged at the center and six holes are formed around the hole so that the center of each hole is the apex of regular triangles of the equal distances between the holes. Further, it is conceived to dispose one hole at a center and 18 holes around the central hole. The number of holes and layout of the holes are determined based on combination of easiness of manufacture of the gas generating agent, manufacturing cost and performance, and accordingly, the number of holes and layout of the holes are not limited. 
     In a gas generator (pyrotechnic gas generator) using solid gas generating means for obtaining gas for expanding the air bag, a filter or a coolant is usually preferably used for purifying or cooling combustion gas generated by combustion of the gas generating means. Therefore, in the gas generator of the present invention, when a combustion gas generated by combustion of the gas generating means is purified and/or cooled, filter means formed by compressing laminated wire mesh can be used. If such filter means is formed into self-contracting structure in which the filter means can be pushed radially outward by the pressure of the combustion gas and its upper and lower ends are pressed by the inner surface of the housing, a short pass of the combustion gas between the end surface of the filter means and the inner surface of the housing can be avoided without providing any special member. Such a self-contracting structure can be realized by inclining upper and lower inner surfaces of the housing such as to narrow the inner surfaces, and by inclining upper and lower end surfaces of the filter means such as to be aligned with the upper and lower inner surfaces of the housing. Inside and outside of the filter means can be formed into different laminated wire mesh bodies to provide a triple structure, so that the inner side of the filter means can exhibit protection function of the filter means and the outer side of the filter can exhibit suppressing expansion function of the filter means. The suppressing expansion function can be exhibited by supporting an outer periphery of the filter means with an outer layer made of laminated wire mesh body, porous cylindrical body, annular belt body or the like such as to suppress the expansion. 
     When the plurality of combustion chambers are provided in the housing and combustion gas is generated by combustion of the gas generating means in the respective combustion chambers as described above, it is preferable that the combustion gas discharged from each combustion chamber passes through a common filter. If all combustion gas passes through the common filter means, it is enough to dispose one filter means in the housing and as a result, the entire volume can be reduced, and the manufacturing cost can be reduced. Further, the combustion gas passing through the common filter means can be discharged from a common gas discharge port(s) formed in the housing. 
     The above-described gas generator for the air bag is accommodated in a module case together with an air bag (bag) into which gas generated by the gas generator is introduced for expansion, thereby constituting the air bag apparatus. In this air bag apparatus, the gas generator is actuated when an impact sensor senses an impact, thereby discharging the combustion gas from the gas discharge port of the housing. The combustion gas flows into the air bag so that the air bag breaks a module cover and expands, thereby forming a cushion between a passenger and a hard structural member of the vehicle for absorbing the impact. 
     According to the present invention, there is provided a multistage gas generator for an air bag in which the entire size of the container can be suppressed, the structure is simple and the gas generator can be manufactured easily, the gas generator is actuated, at the initial stage of actuation, to give a passenger as a small impact as possible, and, according to variation of passengers&#39; physiques (such that a sitting height is tall or low, adult or child) and sitting postures (such as clinging to a steering wheel), actuation output of the gas generator and timing of increase of output can be arbitrarily adjusted in order to restrain the passenger safely. 
     Further in the gas generator of the invention, at least one of the combustion chambers is disposed eccentrically with respect to the housing, the ignition means provided for each of the combustion chambers is disposed in the housing eccentrically with respect to the housing. With this feature, it is possible to maximize the flexibility of the combustion chamber while suppressing the size of the housing in its radial direction. 
     The gas generator of the eccentric structure can be realized by including AIM, a connector, a self-contracting type filer which will be explained later, or combination thereof. The gas generator can also be realized by combining other parts described in the present specification. 
     According to the present invention, the gas generator for the air bag includes a plurality of igniters, activation signals are outputted from the ignition signal-outputting means to the igniters respectively, connection error between each igniter and the ignition signal outputting apparatus outputting section is eliminated, and the multistage type gas generator can always actuate with desired output. Therefore, in the multistage type air bag apparatus capable of adjusting actuation output and timing of output increase, desired actuation performance can always be obtained. 
     Further, also when the filter means radially expands by passage of the activation gas, since the inclining end surface of the filter means is in contact with the supporting portion in the housing and the surface contact between both the members can be maintained, and thereby, short pass of the activation gas can be effectively avoided. Since the filter means is a member capable of expanding, high assembling accuracy is not required, and assembling operation into the hosing can be easily carried out. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a vertical cross sectional view showing one embodiment of a gas generator of the present invention; 
     FIG. 2 is a plan view of the embodiment; 
     FIGS.  3 ( a ) and ( b ) are cross sectional views of the gas generator of the invention; 
     FIG. 4 is a rear view of the gas generator of the invention; 
     FIGS.  5 ( a )-( d ) are partial perspective views showing positioning means; 
     FIG. 6 is a partial cross sectional view showing a filter of self-contracting structure; 
     FIG. 7 is a rear view of the gas generator showing a positioning portion; 
     FIG. 8 is a vertical cross sectional view showing another embodiment of the gas generator of the invention; 
     FIG. 9 is a view showing a structure of an air bag apparatus of the invention; 
     FIG. 10 is a schematic vertical cross sectional view showing one embodiment of the air bag apparatus of the invention; 
     FIG. 11 is a schematic perspective view showing another embodiment of the air bag apparatus; 
     FIGS.  12 ( a )-( d ) are schematic perspective views showing an embodiment of defining means; 
     FIGS.  13 ( a )-( c ) are schematic perspective views showing another embodiment of defining means; 
     FIG. 14 is a schematic perspective view showing another embodiment of the air bag apparatus; 
     FIG. 15 is a schematic perspective view showing still another embodiment of the air bag apparatus; 
     FIGS.  16 ( a )-( c ) are schematic perspective views showing still another embodiment of defining means; 
     FIG. 17 is a schematic perspective view showing another embodiment of the air bag apparatus; 
     FIG. 18 is a vertical cross sectional view showing another embodiment of the gas generator of the present invention; 
     FIG. 19 is a vertical cross sectional view showing the embodiment of a gas generator of the present invention; 
     FIG. 20 is a vertical cross sectional view showing an embodiment of filter means of the invention; 
     FIG. 21 is a vertical cross sectional view showing another embodiment of the filter means; 
     FIG. 22 is a vertical cross sectional view showing another embodiment of the gas generator; 
     FIG. 23 is a vertical cross sectional view showing still another embodiment of the gas generator; 
     FIG. 24 is a vertical cross sectional view showing another embodiment of the gas generator; 
     FIG. 25 is a vertical cross sectional view showing another embodiment of the gas generator; 
     FIG. 26 is a phantom view of the gas generator shown in FIG. 25; 
     FIG. 27 is a vertical cross sectional view showing another embodiment of the gas generator; 
     FIG. 28 is a vertical cross sectional view showing one embodiment of the gas generator of the invention; 
     FIG. 29 is a exploded perspective view of an essential portion showing a partition wall; 
     FIGS.  30 ( a )-( d ) are exploded perspective views of an essential portion showing the positioning means; 
     FIG. 31 is a vertical cross sectional view showing another embodiment of the gas generator for an air bag; 
     FIG. 32 is a vertical cross sectional view showing still another embodiment of the gas generator for the air bag; and 
     FIG. 33 is a phantom view of the gas generator shown in FIG.  31 . 
     FIG. 34 is a plain view of the present embodiment having a deflector plate. 
    
    
     EXPLANATION OF SYMBOLS 
       1  diffuser shell 
       2  closure shell 
       3  housing 
       4  inner shell 
       5  opening portion 
       8  transfer charge 
       10  gas discharge port 
       25  coolant/filter 
       32  flange 
       50  first combustion chamber 
       51  first igniter 
       52  first gas generating agent 
       60  second combustion chamber 
       61  second igniter 
       62  second gas generating agent 
       101  gas generator for air bag 
       102  activation signal outputting means 
       103  air bag 
       107  activation signal outputting portion 
       108  igniter 
       109  lead wire 
       110  connector 
       301  diffuser shell 
       302  closure shell 
       303  housing 
       305  filter means 
       309  gas generating agent 
       311  igniter 
       351  inclining end surface of filter means 
       352 ,  452 ,  552 ,  652 ,  752  inclining surface (supporting portion) 
       353  filter means supporting means 
       453 ,  553 ,  653 ,  753  inclining portion of housing 
       803  housing 
       822  coolant/filter 
       1105   a  first combustion chamber 
       1105   b  second combustion chamber 
       1107  partition wall 
       1109   a  first gas generating agent 
       1109   b  second gas generating agent 
       1112   a  first igniter 
       1112   b  second igniter 
       1113  initiator collar 
       1185  automatic ignition material (AIM) 
     BEST MODE FOR CARRYING OUT THE INVENTION 
     A multistage gas generator for an air bag of the present invention will be explained below based on embodiments shown in the drawings. 
     Embodiment of Eccentric Structure 
     FIG. 1 is a vertical cross sectional view showing one embodiment of the gas generator of the present invention. The gas generator shown in FIG. 1 has a structure suitable to be disposed on a driver side. 
     In FIG. 1, the gas generator includes a cylindrical. housing  3  which is formed by joining, using friction welding, a diffuser shell  1  having a gas discharge port  10  and a closure shell  2  forming an interior accommodating space with the diffuser shell. A capsule-like inner shell  4  whose horizontal cross section is circular and upper end thereof is closed is disposed and fixed in the housing  3  eccentrically with respect to a center axis of the housing. An eccentric degree of the inner shell with respect to the housing can be appropriately changed in accordance with a desired volume ratio of the combustion chambers. The eccentric degree might be changed depending upon a structure inside the housing, e.g., whether or not there exists a coolant/filter  25 . For example, when the coolant/filter  25  is placed such as to be opposed to a peripheral wall surface as in the gas generator shown in FIG. 1, the eccentric degree can be appropriately selected within a range of 10 to 75%. However, since this numeral range might be changed depending upon a size of the igniter and the like, the numeric value range is shown as an index of eccentricity of the inner shell  4  in the gas generator shown in FIG.  1 . 
     The horizontal cross sectional shape of the inner shell can be formed into various shapes such as rectangular shape and elliptic shape. In view of facilitating joint to the closure shell  2  and the like, the horizontal cross sectional shape of the inner shell is preferably formed into circular. In other words, the horizontal plane cross sectional shape of the inner shell  4  needs to be circular, when the inner shell  4  is joined to the closure shell  2  by the friction welding. Further, when these members are joined by laser welding, it is necessary to keep the laser irradiation distance constant. 
     The inner shell  4  is disposed while securing a slight gap between the inner shell  4  and the coolant/filter  25 . This gap is secured to form a gas flow between the coolant/filter  25  and the inner shell  4  and to effectively use the entire surface of the filter  25 . And when an opening portion of the inner shell  4  is opened as will be described later, the coolant/filter  25  will not hinder because of the gap. Therefore, this gap is appropriately selected in a range of the above purpose. 
     The inner shell  4  defines a first combustion chamber  50  and a second combustion chamber  60 . That is, the first combustion chamber  50  is provided outside the inner shell, and the second combustion chamber  60  is provided inside the inner shell  4 . A volume ratio of the first combustion chamber  50  and the second combustion chamber  60  (a volume of the first combustion chamber: a volume of the second combustion chamber) is set to 3.3:1 in the present embodiment, but this ratio can be appropriately selected within a rage of 97:1 to 1:1. This volume ratio also might be changed depending upon a size of the igniter, a shape of the gas generating agent and the like. Therefore, the numeric value range is shown as a range which can be selected in the structure of the gas generator shown in FIG.  1 . 
     Gas generating agent ( 52 ,  62 ) are respectively accommodated in the second combustion chamber  60  and the first combustion chamber  50  which are isolated form each other by the inner shell  4 . The first gas generating agent  52  is accommodated in the first combustion chamber  50 , and the second gas generating agent  62  is accommodated in the second combustion chamber  60 . In the present embodiment, the first gas generating agent  52  and the second gas generating agent  62  are the same in shape and the like, the respective combustion chambers can accommodate gas generating means which are different from each other in at least one of burning rate, composition, composition ratio and amount. 
     The inner shell  4  defining the first combustion chamber  50  and the second combustion chamber  60  is disposed eccentrically with respect to the center axis of the housing  3 . The second combustion chamber  60  provided inside the inner shell  4  is also eccentric with respect to the housing  3 . Igniters are respectively disposed in the first combustion chamber  50  and the second combustion chamber  60 , and among them, the second igniter  61  disposed in the second combustion chamber is disposed at a center of the second combustion chamber  60  which is eccentric with respect to the center axis of the housing  3 . As a result, flame generated due to the actuation of the igniter  61  can uniformly burn the second gas generating agent  62 . Further, the second igniter  61  and the first igniter  51  which is disposed in the first combustion chamber  50  are both disposed eccentrically with respect to the center axis of the housing  3 . By disposing the first and second igniters as well as the inner shell eccentrically with respect to the center axis of the housing  3 , variation in volume ratio of the first and second combustion chambers can be expanded, and a size of the housing  3  in its radial direction can be suppressed to the minimum. 
     Among the igniters disposed in the respective combustion chambers, the igniter  51  disposed in the first combustion chamber  50  has transfer charge  8  around and above the igniter  51 . The transfer charge  8  is accommodated in a transfer charge container  26  in order to facilitate assembly of the gas generator, and to prevent the transfer charge  8  from being dispersed in the first combustion chamber  50  due to impacts or vibrations caused while the transfer charge is mounted in a vehicle so that the ignition performance with respect to the first gas generating agent  52  is deteriorated. The transfer charge container  26  is made of aluminum having such a thickness (e.g., about 200 μm) that the container  26  is easily broken by combustion of the transfer charge  8  in the transfer charge container  26  to transfer flame to its surroundings. A transfer charge such as that disposed in the first combustion chamber  50  is not necessarily needed for the second combustion chamber  60 . This is because the second gas generating agent  62  is ignited more easily, than the first gas generating agent  52 , and the pressure of the second combustion chamber is increasing in a sealed state until the breaking member  7  for sealing a hole  6  of the below-described inner shell  4  is ruptured. The breaking member  7  is not ruptured even when the internal pressure of the first combustion chamber  50  increases due to the combustion of the first gas generating agent  52  but it is ruptured when the internal pressure of the second combustion chamber  60  increases more than that of the first combustion chamber  50 . However, the transfer charge can be used as required. 
     A cylindrical member  36  is disposed in the first combustion chamber  50  so as to surround the first igniter  51  and a radially outer side of the transfer charge  8  disposed above the first igniter  51 . The cylindrical member  36  is formed into a cylindrical shape whose upper and lower ends are opened, one end thereof is fitted over an outer periphery of a portion to which the igniter  51  is fixed without gap, and the other end is interposed by the retainer  11  provided in the vicinity of an inner surface of a ceiling portion of the diffuser shell  1  and fixed to a predetermined location. The cylindrical member  36  is formed at its peripheral wall with a plurality of flame-transferring holes  37 . Flame generated by combustion of the transfer charge  8  ejects from the flame-transferring holes  37 , and then ignites and burns the first gas generating agent provided outside the cylindrical member. It is preferable that the cylindrical member is made of the same material as that of the housing  3 . 
     Especially in the gas generator shown in this embodiment, the first combustion chamber  50  is formed, as shown in FIG. 2, into annular shape similar to falcate shape whose circular inner side thereof is punched out circularly, and the first gas generating agent  52  is disposed in this. Therefore, unlike the second combustion chamber  60 , in the first combustion chamber  50 , a distance between the gas generating agent  52  and the ignition  51  is varied depending upon a location where the gas generating agent  52  is accommodated. Accordingly, when the igniter  51  is ignited, the first gas generating agents  52  is ignited and burnt unevenly. For this reason, the directions of the flame-transferring holes  37  formed in the peripheral wall of the inner cylindrical member  36  are restricted such that the flame of the transfer charge  8  is ejected in the direction along an inner wall surface  50   a  of the first combustion chamber  50  (the direction shown with the arrows in FIG.  2 ). With this arrangement, the gas generating agent  52  located behind the second combustion chamber  60  (i.e., the inner shell  4 ) can also be burnt uniformly. In this embodiment, the inner wall surface  50   a  coincides with a surface of the coolant/filter  25 . 
     As another example of the injecting-direction restricting means, instead of the inner cylindrical member  36 , it is possible to use a cup-like container having a nozzle on the peripheral wall thereof for ejecting flame of the first ignition means (the igniter  51  and the transfer charge  8  in FIG. 1) in a direction along an inner wall surface  50   a  of the first combustion chamber  50  (direction shown with the arrows in FIG.  2 ). Therefore, the cup-like container as the injecting-direction restricting means can envelop at least the ignition  51  and the transfer charge  8  to restrict the injecting direction of the flame, and is used being mounted (put on) around the first ignition means. Even when such an injecting-direction restricting means is used, it is preferable that the first ignition means disposed inside thereof includes a transfer charge which is to be ignited and burnt by the igniter and actuation of the igniter. 
     Another example of the injecting-direction restricting means is a deflector plate  99  shown in FIG. 34 which reflect the flame in direction shown with arrows to restrict the direction. For example, a concave plate is placed between the combustion chamber and the housing. The deflector plate may be inside the filter or outside the filter. The deflector plate functions to control the direction of flame from the first igniter and also functions to control a flow of gas generated by combustion of the gas generating agent. 
     The inner shell  4  defining the first combustion chamber  50  and the second combustion chamber  60  is of capsule-like shape as described above, and a plurality of opening portion  5  are formed on the peripheral wall thereof. The opening portion  5  formed such that they are opened only by combustion of the second gas generating agent  62  disposed in the second combustion chamber  60 , and such that they are not opened by combustion of the first gas generating agent  52  disposed in the first combustion chamber  50 . In the present embodiment, the opening portions  5  comprise a plurality of holes  6  formed in the peripheral wall of the inner shell  4  and a breaking member  7  for closing these holes. As for the breaking member  7 , a stainless seal tape is used. The breaking member  7  is formed such that it opens the holes  6  by being broken, peeled, burnt or detached exclusively due to the combustion of the second gas generating agent  62 , and such that the breaking member  7  is not broken by combustion of the first gas generating agent  52 . Alternatively, as another way to prevent the opening portions of the inner shell  4  from opening by the first gas generating agent  52 , it is also possible to cover the opening portions  5  of the inner shell  4  with a shielding plate or the like which is obtained by forming a shielding plate having appropriate shape, for example, by forming a band-like member into annular shape, so that the flame caused by combustion of the first gas generating agent  52  does not come into direct contact with the opening portion  5 . 
     Alternatively, the opening portions  5  can also be realized by forming a notch  12  in the peripheral wall of the inner shell  4  as shown in FIG. 3 a , or by partially reducing the thickness of the peripheral wall of the inner shell as shown in FIG. 3 b . When the opening portions are opened, the first combustion chamber  50  and the second combustion chamber  60  communicate with each other, and the combustion gas generated in the second combustion chamber  60  passes through the first combustion chamber  50  and then, is discharged outside the housing  1 . 
     The inner shell  4  is fixed by connecting an opened lower portion  13  thereof to the closure shell  2 . When the closure shell  2  includes a collar portion  2   a  for fixing the igniter, the inner shell  4  can be mounted to the collar portion  2   a . In the gas generator shown in FIG. 1, the closure shell  2  is formed such that a circular collar portion having a size capable of fixing two igniters is integrally connected to a bottom surface of the cylindrical shell portion  2   b  which is connected to the diffuser shell  1 . The inner shell  4  is connected the collar portion  2   a . The collar portion  2   a  can be formed integrally on the bottom surface of the circular cylindrical shell portion  2   b  as a circle having a size capable of fixing for each igniter. Further, the collar portion  2   a  can be formed integrally on the bottom surface of the cylindrical shell portion  2   b . In such a case, the inner shell  4  can directly be mounted to the bottom surface of the cylindrical shell portion  2   b  other than the collar portion  2   a  of the closure shell. 
     The joint of the inner shell  4  and the closure shell  2  can be performed by friction welding, crimping, resistance welding, or convex-concave joint. When both members are joined by the friction welding, it is preferable to join the members while fixing the closure shell  2 . With this arrangement, even if axes of the inner shell  4  and the closure shell  2  are not aligned with each other, the friction welding can be carried out stably. If the friction welding is carried out while the inner shell  4  is fixed and the closure shell  2  is rotated, since the center of gravity of the closure shell  2  is deviated from the rotation center, the friction welding can not be carried out stably. Thereupon, in the present invention, the friction welding is carried out while the closure shell  2  is fixed, the inner shell  4  is rotated. At the time of the friction welding, in order to dispose the inner shell  4  into the predetermined position constantly, it is desirable that the closure shell  2  is positioned and fixed. Therefore, it is desirable that the closure shell  2  is appropriately provided with a positioning means. 
     A gas generating agent fixing member  14  is disposed in the inner shell  4  for safely and smoothly connect the closure shell  2 . When the inner shell  4  is friction-welded to the closure shell  2 , the gas generating agent fixing member  14  is used for preventing the gas generating agent  62  from coming into direct contact with the closure shell  2  and for securing the installation space of the igniter  61  in a space formed by the inner shell  4 . When the inner shell  4  is mounted to the closure shell  2 , it can be mounted not only by the above-described friction welding, but also by resistance welding, crimping, convex-concave joint or the like. In that case also, by using the gas generating agent fixing member  14 , the assembling operation is facilitated. As the gas generating agent fixing member  14 , a canister made of aluminum having such a thickness that it is easily broken by combustion of the gas generating agent  62 . Rather than this, it is possible to use appropriate members to achieve the above object such as porous member using wire mesh (a material, a shape and the like are not limited). When the gas generating agent fixing member  14  is not used, a single-hole cylindrical gas generating agent  62  is formed into a gas generating agent solid having the same shape as that of the inner space of the inner shell  4 , and this solid can be disposed in the inner shell  4 . In this case, the gas generating agent fixing member  14  may be omitted. 
     In the present embodiment, the collar portion  2   a  of the closure shell  2  is formed into a size capable fixing the two igniters  51  and  61  side by side. With this arrangement, if the two igniters  51  and  61  are previously fixed to the collar portion  2   a  by crimping or the like, and the collar portion  2   a  is integrally formed with the cylindrical shell portion  2   b  to form the closure shell  2 , the two igniters  51  and  61  can be fixed to the closure shell  2 . Although the first igniter  51  and the second igniter  61  are shown with the same size in the drawing, they can have different outputs for the respective combustion chamber. 
     In this embodiment, as shown in a bottom view of FIG. 4, cables  15  which are respectively connected to the igniters  51  and  61  for transmitting actuation signals are pulled out in the same direction. Positioning means are formed on locations where the igniters  51  and  61  are disposed so that the respective cables  15  can be specified to be connected to the respective igniters. As shown in the enlarged views of essential portion of FIGS. 5 a  to  5   d , such positioning means can be realized by using connectors  16  having different shapes for the respective igniters. In the positioning means shown in FIG. 5 a , the connectors  16  are formed with positioning grooves (or projections)  17 , and projections (or grooves)  18  corresponding to the positioning grooves (or projections)  17  are different from each other for the respective igniters. That is, positions of the grooves (or projections)  17  of the respective connectors are changed so that, at the time of mounting the connectors  16  to the gas generator, if the connectors  16  are not mounted in a right direction, the connectors interfere with each other and can not be mounted correctly. In the positioning means shown in FIG. 5 b , only one of connectors  21  is provided with a positioning groove (or projection)  19 . That is, a connector  21 A having the groove (or projection)  19  can be connected to an igniter  22   b  which does not have a projection (or groove)  20 , but a connector  21 B which does not have the grove (or projection)  19  can not be connected to an igniter  22   a  having the projection (or groove)  20 . As a result, connection error of the connectors  21  can be easily found at the time of assembling. In FIG. 5 c , connecting portions  23  themselves of the connectors are different from each other. In FIG. 5 d , two connectors are formed into one connector, and a positioning groove (or projection)  24  is formed. As the positioning means, other means for eliminating connection error of connector can be appropriately employed. 
     A coolant/filter  25  as filter means for purifying/cooling the combustion gas generated by combustion of the gas generating agent is disposed in the housing  3 . Gases generated by combustion of the first and second gas generating agents commonly pass through the coolant/filter  25 . In order to prevent the short pass such that the combustion gas passes through a space between the end surface of the coolant/filter  25  and the inner surface of the ceiling of the diffuser shell  1 , the upper and lower inner peripheral surfaces of the coolant/filter  25  and the inner surface of the housing can be covered with an inwardly-bending flange-like short pass preventing member. 
     An outer layer  27  for preventing the coolant/filter  25  from expanding due to passage of combustion gas. This outer layer  27  can be formed using not only a laminated wire mesh body, but also a porous cylindrical member provided at its peripheral wall surface with a plurality of through-holes, or a belt-like suppressing layer comprising an annular band-like member having a predetermined width. The outer layer is provided at its outer side with a gap  28  having a predetermined width so that the combustion gas can pass through the entire surface of the filter. The gas discharge port  10  formed in the diffuser shell  1  is closed by a seal tape  29  for preventing outside air from entering. This seal tape  29  is ruptured when the gas is discharged. The purpose of the seal tape  29  is to protect the gas generating agent from outside moisture, and the seal tape  29  does not affect any performance adjustment such as combustion internal pressure at all. The gas caused by combustion of the first gas generating agent  52  and the gas caused by combustion of the second gas generating agent  62  both pass through the gas discharge port  10 . 
     As shown in FIG. 6 or other drawing, as the filter means for purifying and/or cooling the combustion gas, self-contracting type filter means  30  whose upper and lower end surfaces are inclined in the outer peripheral direction. When the self-contracting type filter means  30  is used, it is preferable that the upper and inner surfaces  31  of the housing are inclined so as to be narrowed. As a result, the upper and lower end surfaces of the filter means  30 , when pushed radially outward by combustion gas, abuts against the inner surface  31  of the housing, and it is possible to prevent the short pass of the combustion gas therebetween. 
     As described above, in the gas generator shown in FIG. 1, the igniters  51 ,  61  and the inner shell  4  are disposed eccentrically with respect to the housing  3 . In such a gas generator, when the diffuser shell  1  and the closure shell  2  are joined by the friction welding, by fixing the closure shell  2  while the friction welding is carried out, both the shells can be joined stably. Especially when the inner shell  4  is directly mounted to the closure shell  2  by the friction welding, as shown in FIG. 7, it is preferable that the closure shell  2  is provided with a flange portion  32  for mounting the gas generator to the module case and a positioning portion  34  which has their peripheries notched is formed on a portion constituting the flange portion  32  such as a projection  33 . If the positioning portion  34  is formed in this manner, since the closure shell  2  is fixed at any time in the constant direction according to the positioning portion  34 , the inner shell  4  can reliably be mounted to the predetermined position. 
     In the gas generator formed in the above-described manner, when the first igniter  51  which is disposed inside the first combustion chamber  50  provided outside the inner shell  4  is actuated, the first gas generating agent  52  in the combustion chamber  50  is ignited and burnt to generate the combustion gas. Since a gap through which the gas can pass is secured between the inner shell  4  and the coolant/filter  25 , the combustion gas can pass through the entire coolant/filter  25 . While the combustion gas passes through the coolant/filter  25 , the gas is purified and cooled and then, is discharged from the gas discharge port  10 . 
     On the other hand, when the second igniter  61  disposed in the inner shell  4  is actuated, the second gas generating agent  62  is ignited and burnt to generate the combustion gas. This combustion gas opens the opening portion  5  of the inner shell  4 , and flows into the first combustion chamber  50  from the opening portion  5 . Thereafter, the combustion gas passes through the coolant/filter  25  and is discharged from the gas discharge port  10  like the combustion gas of the first gas generating agent  52 . The seal tape  29  closing the gas discharge port  10  is ruptured by passage of the combustion gas generated in the housing  3 . The second gas generating agent  62  is ignited and burnt by the actuation of the second igniter  61 , and is not directly burnt by combustion of the first gas generating agent  52 . This is because that the opening portion  5  of the inner shell  4  is opened exclusively by combustion of the second gas generating agent  62 , and is not opened by combustion of the first gas generating agent  52 . However, as shown in FIG. 8, when the automatic ignition material (AIM)  35  which is to be ignited by combustion heat of the first gas generating agent  52  transmitted from the housing  1  and the like is accommodated in the second combustion chamber  60 , the second gas generating agent  62  can be burnt indirectly through the combustion of the first gas generating agent  52 . 
     That is, in the above-described multistage gas generator for an air bag, the first and second gas generating agents  52  and  62  are respectively ignited and burnt by the first and second igniters independently, However, there is a case that electric current is allowed to flow only to the first. igniter  51  to ignite and burn exclusively the gas generating agent  52  in the first combustion chamber  50  intentionally. That is, the second gas generating agent  62  and the second igniter  61  are left unburnt intentionally. In such a case, inconvenience is caused at the time of later disposal or damping. Therefore, it is preferable that, after the actuation of the gas generator (only the first igniter), the gas generating agent  62  of the second combustion chamber  60  is burnt at further delayed timing (e.g., 100 milliseconds or more) than the normal delay ignition timing (e.g., 10 to 40 milliseconds) for actuating the second igniter  61 . Thereupon, the automatic ignition material  35  which is to be ignited and burnt by transmission of the combustion heat of the first gas generating agent  52  is provided in the gas generator shown in FIG.  8 . The second gas generating agent  62  is ignited by the automatic ignition material  35  when a sufficient period of time longer than the delayed timing (i.e., actuation interval between the igniters) when the second igniter  61  is actuated after a predetermined time lag is elapsed since the first igniter  51  is actuated. That is, this is different from the case that combustion of the second gas generating agent  62  is delayed (in other words, ignition of the second igniter is delayed) in order to adjust the actuation performance of the gas generator. Further, the gas generating agent  62  is never be ignited and burnt by the automatic ignition material  35  during the period when the actuation current to the second igniter  61  is delayed arbitrarily in order to adjust actuation performance of the gas generator. The automatic ignition material  35  can be combined with the second igniter  61 . 
     According to the gas generator formed in the above-described manner, the output mode (actuation performance) of the gas generator can be adjusted arbitrarily by adjusting the igniting timing of the two igniters  51  and  61 , e.g., by actuating either of the first and second igniters  51  and  61  at first or by actuating both the igniters simultaneously. Therefore, in various conditions such as speed of the vehicle and environment temperature at the time of collision, development of the air bag in the air bag apparatus described later can be made most suitably. Especially in the gas generator shown in FIG. 1, since the two combustion chambers are arranged in the radial direction, the height of the gas generator can be suppressed to the minimum. 
     Also, shapes, composition, composition ratio and amount and the like of the gas generating agent can be appropriately changed for obtaining desired output mode. 
     Embodiment of an Air Bag Apparatus 
     FIG. 9 shows an embodiment of an air bag apparatus according to the present invention in the case of constructing the air bag apparatus in such a manner as to include a gas generator using the electric ignition type ignition means. 
     The air bag apparatus comprises a gas generator  200 , an impact sensor  201 , a control unit  202 , a module case  203  and an air bag  204 . In the gas generator  200 , the gas generator described with reference to FIG. 1 is used and the actuation performance thereof is adjusted so as to apply as a small impact as possible to the occupant at the initial stage of the actuation of the gas generator. 
     The impact sensor  201  can comprises, for example, a semiconductor type acceleration sensor. This semiconductor type acceleration sensor is structured such that four semiconductor strain gauges are formed on a silicone base plate to be bent when the acceleration is applied, and these semiconductor strain gauges are bridge-connected. When the acceleration is applied, the beam defects and a strain is produced on the surface. Due to the strain, a resistance of the semiconductor strain gauge is changed, and the structure is made such that the resistance change can be detected as a voltage signal in proportion to the acceleration. 
     The control unit  202  is provided with an ignition decision circuit, and the structure is made such that the signals from the semiconductor type acceleration sensor is inputted to the ignition decision circuit. The control unit  202  starts calculation at a time when the impact signal from the sensor  201  exceeds a certain value, and when the calculated result exceeds a certain value, it outputs an activating signal to the igniter  51 ,  61  of the gas generator  200 . 
     The module case  203  is formed, for example, by a polyurethane, and includes a module cover  205 . The air bag  204  and the gas generator  200  are stored in the module case  203  so as to be constituted as a pad module. This pad module is generally mounted to a steering wheel  207  when being mounted to a driver side of an automobile. 
     The air bag  204  is formed by a nylon (for example, a nylon  66 ), a polyester or the like, is structured such that a bag port  206  thereof surrounds the gas discharge port of the gas generator and is fixed to a flange portion of the gas generator in a folded state. 
     When the semiconductor type acceleration sensor  201  detects the impact at a time of collision of the automobile, the signal is transmitted to the control unit  202 , and the control unit  202  starts calculation at a time when the impact signal from the sensor exceeds a certain value. When the calculated result exceeds a certain value, it outputs the activating signal to the igniter  51 ,  61  of the gas generator  200 . Accordingly, the igniter  51 ,  61  is activated so as to ignite the gas generating agent, and the gas generating agent burns and generates the gas. The gas is discharged into the air bag  204 , by whereby the air bag breaks the module cover  205  so as to inflate, thereby forming a cushion absorbing an impact between the steering wheel  207  and the occupant. 
     The gas generator of eccentric structure can be realized by the AIM, the communication hole, the connector, the self-contracting type filter or a combination thereof. The gas generator can also be realized by combining other parts described in the present specification. 
     The present invention includes a gas generator or an air bag apparatus including AIM, the communication hole, the connector, the self-contracting type filter. The AIM, the communication hole, the connector, the self-contracting type filter disclosed here are suitable for the eccentric structure and can be used in combination. 
     (AIM) 
     Namely, a gas generator for an air bag of the present invention comprises a housing including a gas discharge port, igniting means which is accommodated in the housing and to be actuated on an impact, and gas generating means which is accommodated in the housing and to be ignited and burnt by the ignition means and generate combustion gas for expanding the air bag, wherein two or more combustion chambers for accommodating gas generating means are provided being partitioned in the housing, and the automatic ignition material (AIM) to be ignited and burnt by transmitted heat is disposed in either of the combustion chambers. 
     A communication hole which allows mutual communication between the combustion chambers can also be provided. 
     For example, if the gas generating means accommodated in the plurality of combustion chambers are burnt at different timing in the respective combustion chambers, it is preferable that the automatic ignition material (AIM) is disposed in the combustion chamber in which the gas generating means to be burnt at delayed timing is accommodated. In this case, the automatic ignition material (AIM) can be ignited and burnt by transmitted heat generated by combustion of gas generating agent which has been burnt first. It is preferable that the automatic ignition material burns the gas generating agent to burn at delayed timing after 100 milliseconds or longer from the point when the ignition means for igniting the gas generating means which is burnt first is actuated. Further, the automatic ignition material can be disposed in combination with the igniter included in the ignition means which ignites and burns the gas generating means which is burnt at a delayed timing (or which may still remain after the actuation of the gas generator). 
     The gas generator which burns the gas generating means in the respective combustion chambers at different timing can be realized by a gas generator in which an ignition means includes a transfer charge to be ignited and burnt by the actuation of a igniter, and the transfer charge is divided for each igniter and to be independently ignited and burnt at each igniter, and gas generating means accommodated in the plurality of combustion chambers are to be ignited and burnt by flame caused by combustion of the transfer charges in different sections. 
     For example, in the gas generator in which two combustion chamber for accommodating the gas generating means are provided in the housing, the first gas generating means which burns first and the second gas generating means which burns at delayed timing are respectively disposed in the combustion chambers, and the first ignition means for igniting the first gas generating means and the second ignition means for igniting the second gas generating means are provided, the automatic ignition material (AIM) is provided in the igniter included in the second combustion chamber or the second ignition means. As the automatic ignition material (AIM), the material, which is ignited and burnt by the heat transmitted through the housing which is generated by combustion of the first gas generating means, is used. 
     Two combustion chambers for accommodating the gas generating means can be provided in the housing concentrically adjacent to one another in the radial direction of the housing, and a communication hole which allows communication between the combustion chambers can be provided. 
     As the automatic ignition material (AIM) which can be used in the present invention, the material which can be ignited and burnt at least by combustion heat (i.e. transmitted heat) of the gas generating means (which has been burnt first) transmitted from the housing and the like. An example of such material is nitrocellulose. 
     However, since these may be changed, naturally, by kinds of gas generating means to be used, a heat transfer member (e.g., housing) for transmitting the combustion heat, a distance from a position where the gas generating means to be burnt first is accommodated, it is necessary to appropriately employ these at the stage of design. 
     The above-described gas generator for the air bag is accommodated in a module case together with an air bag (bag) which introduces a gas generated by the gas generator to expand, thereby constituting the air bag apparatus. In this air bag apparatus, the gas generator is actuated in reaction that an impact sensor senses an impact, thereby discharging the combustion gas from the gas discharge port of the housing. The combustion gas flows into the air bag so that the air bag breaks a module cover and expands, thereby forming a cushion between a passenger and a hard structural member of the vehicle for absorbing the impact. 
     Embodiment of AIM 1 
     FIG. 28 is a vertical cross sectional view showing another embodiment of the gas generator for an air bag of the present invention. The gas generator shown in this figure has a structure suitable to be disposed on a driver side. 
     In the gas generator shown in this figure, a first combustion chamber  1105   a  and a second combustion chamber  1105   b  are defined by an inner cylindrical member  1104 , and are disposed adjacent to each other concentrically in a housing  803 . The inner cylindrical member  1104  is provided at its inner peripheral surface with a step notch  1106  at a predetermined height. A partition wall  1107  for defining the second combustion chamber  1105   b  and an ignition means accommodating chamber  1108  is disposed in the step notch  1106 . In the present embodiment, as shown in an exploded perspective view in FIG. 29, the partition wall  1107  comprises a sectioning circular member  1150  which engages the step notch  1106  of the inner cylindrical member  1104  and a seal cup member  1160  which engages the sectioning circular member  1150 . The sectioning circular member  1150  is of substantially flat circular shape, and includes an opening portion  1151  into which a transfer charge accommodating portion  1161  of the seal cup member  1160  is fitted inwardly, a circular hole  1152  having a bottom surface with a circular hollow for accommodating an upper portion of an igniter  1112   b , and a second flame-transferring hole  1119  which pierces through the substantial center of the circular hole  1152 . The seal cup member  1160  includes the cylindrical transfer charge accommodating portion  1161  fitting into the opening portion  1151  of the sectioning circular member  1150  and projecting into the second combustion chamber  1105   b , and a cylindrical igniter receiving port  1162  formed at a location opposed to the circular hole  1152  of the sectioning circular member  1150  and extending to the opposite side from the transfer charge accommodating portion  1161 . A first transfer charge  1116   a  is accommodated in the transfer charge accommodating portion  1161 , and a second igniter  1112   b  is fitted into the igniter receiving portion  1162 . The sectioning circular member  1150  and the seal cup member  1160  are engaged with each other such that the transfer charge accommodating portion  1161  of the seal cup member  1160  is fitted into the opening portion  1151  of the sectioning circular member  1150 . An upper portion of the second igniter  1112   b  fitted through the igniter receiving port  1162  projects into the circular hole  1152  of the sectioning circular member  1150 . 
     The partition wall  1107  comprising the sectioning circular member  1150  and the seal cup member  1160  are engaged with the step notch  1106  formed in the inner peripheral surface of the inner cylindrical member  1104  as shown in FIG.  28 . That is, a peripheral edge of the sectioning circular member  1150  is supported by the step notch  1106 , and the seal cup member  1160  is abutted against and supported by the sectioning circular member  1150 . A peripheral edge of the seal cup member  1160  is formed such as to bend in the same direction as that of the igniter receiving port  1162 , and a bent portion  1163  is fitted to the groove  1164  formed in the inner peripheral surface of the inner cylindrical member  1104 . With this arrangement, the sectioning circular member  1150  is supported by the seal cup member  1160  so that movement thereof in the axial direction of the housing  803  is inhibited. Further, by fitting the bent portion  1163  of the peripheral edge of the seal cup member  1160  into the groove  1164  of the inner peripheral surface of the inner cylindrical member  1104 , the partition wall  1107  (i.e., seal cup member  1160 ) and the inner cylindrical member  1104  are engaged with each other without a gap. Therefore, in the inner cylindrical member  1104 , the ignition means accommodating chamber  1108  provided on the side of the closure shell  802  and the second combustion chamber  1105   b  provided on the side of the diffuser shell  802  are reliably sectioned by the ignition means seal structure comprising the seal cup member  1160  and the groove  1164 . 
     The igniter receiving port  1162  formed in the seal cup member  1160  has a skirt portion which spreads like a fan, and its inner side, i.e., between the igniter receiving port  1162  and the-second igniter  1112   b  accommodated in the igniter receiving port  1162 , an O-ring  1181  is disposed for sealing a space between the igniter receiving port  1162  and the second igniter  1112   b . Further, since the O-ring  1181  is also pressed on an under-mentioned igniter fixing member  1182 , the second igniter  1112   b  is disposed in a space defined by the circular hole  1152  of the sectioning circular member, the igniter receiving port  1162  of the seal cup member, the O-ring  1181  and the igniter fixing member  1182 . When, on the actuation of the second igniter  1112   b , the seal tape  1120  closing the second flame-transferring hole  1119  formed in the circular hole  1152  of the sectioning circular member  1150  is ruptured, and the defined space communicates with the second combustion chamber  1105   b . The first igniter  1112   a  and the second igniter  1112   b  are reliably separated from each other by the seal structure (hereinafter referred as “the igniter seal structure”) comprising the skirt of the igniter receiving port  1162 , the O-ring  1181  and the igniter fixing member  1182 . With this arrangement, flame generated by actuation of any of the igniters will not directly flow into the space where another igniter is accommodated. 
     In the present embodiment also, the two igniters  1112   a  and  1112   b  are fixed to a single initiator collar  1113  such that the igniters can easily be disposed into the housing. Especially in the present embodiment, the two igniters  1112   a  and  1112   b  are supported by the igniter fixing member  1182  which engages the initiator collar  1113  and are fixed to the initiator collar  1113 . The igniter fixing member  1182  is formed into a shape which covers the upper surface of the initiator collar  1113 , and has holes  1184  into which into the upper portions of the igniters are inserted, that support the shoulders  1183 . The two igniters  1112   a  and  1112   b  disposed in the initiator collar  1113  are fixed to the igniter fixing member  1182  which fits over the initiator collar  1113 . By using such an igniter fixing member  1182 , the two igniters  1112   a  and  1112   b  can easily assembled into the initiator collar  1113 . In the gas generator shown in this embodiment, the first igniter  1112   a  and the second igniter  1112   b  are different from each other in the shapes and the actuation output, but igniters having the same actuation output can also be used. 
     When the gas generator shown in the present embodiment is actuated, flame generated by the actuation of the first igniter  1112   a  ignites and burns the first transfer charge  1116   a  disposed above the igniter. Flame generated by combustion of the first transfer charge  1116   a  never flows into a space where the second igniter  1112   b  is accommodated because of the igniter sealing structure, nor flows into the second combustion chamber  1105   b  because of the ignition means sealing structure comprising the bent portion  1163  of the seal cup member  1160  and the groove  1164  of the inner cylindrical member  1104 . Therefore, the flame generated by combustion of the first transfer charge  1116   a  passes through a first flame-transferring hole  1117  formed in the peripheral wall of the inner cylindrical member  1104  and flows exclusively into the first combustion chamber  1105   a , and ignites and burns the first gas generating agent  1109   a  to generate a combustion gas. Flame generated on actuation of the second igniter  1112   b  passes through the second flame-transferring hole  1119  formed in the circular hole of the dividing circular member  1150  and flows exclusively into the second combustion chamber  1105   b , and ignites and burns the second gas generating agent  1109   b  to generate a combustion gas. Especially in the gas generator of this embodiment, the second transfer charge is not provided, and the second gas generating agent  1109   a  directly ignited and burnt by the flame generated on actuation of the second igniter  1112   b.    
     Combustion gases generated by combustion of the first gas generating agent  1109   a  and the second gas generating agent  1109   b  then pass through a common coolant/filter  822  and during which, the combustion gas is purified and cooled, and is discharged from the gas discharge port  826  after passing through a gap  825 . Seal tapes  1118  and  1120  closing the first and second flame-transferring holes are ruptured when the flame of the igniter and the combustion gas of the transfer charge pass through, and the seal tape  827  closing the gas discharge port  826  is ruptured when the combustion gas passes through. 
     In this manner, when the actuation timing of the igniters  1112   a  and  1112   b  are staggered, and igniting timing of the gas generating agents  1109   a  and  1109   b , i.e., actuation performance of the gas generator is adjusted, positioning means is formed to decide the specified lead wires  815 ′ for the respective igniters  1112   a  and  1112   b . As shown in exploded perspective views of essential portions in FIGS. 30 a  to  30   d  for example, the positioning means can be realized by using connector  816 ′ having different shape for each igniter. In the case of the positioning means shown in FIG. 30 a , connectors are formed with positioning grooves (or projections)  817 ′, and position of projections (or grooves)  818 ′ corresponding to the positioning grooves (or projections)  817 ′ are different for each igniter. That is, positions of the grooves (or projections)  817 ′ of the connectors are changed so that, if the connectors  816 ′ are not mounted in a right direction at the time of mounting the connectors  816 ′ to the gas generator, the connectors interfere with each other and can not be mounted correctly. In the positioning means shown in FIG. 30 b , only one of connectors  821 ′ is provided with a positioning groove (or projection)  819 ′. That is, a connector  821 A′ having the groove (or projection)  819 ′ can be connected to an igniter  822   b ′ which does not have a projection (or groove)  820 ′, but a connector  821 B′ not having the grove (or projection)  819 ′ can not be connected to an igniter  822   a  ′ which has the projection (or groove)  820 ′. As a result, connection error of the connectors  821 ′ can easily be found at the time of assembling. In FIG. 30 c , connecting portions  823 ′ themselves of the connectors are different from each other. In FIG. 30 d , two connectors are formed into one connector, and a positioning groove (or projection)  824 ′ is formed. As the positioning means, other means for eliminating connection error of connector can be appropriately employed. 
     That is, in the gas generator of the present embodiment also, the first and second gas generating agents  1109   a  and  1109   b  are respectively ignited and burnt by the first and second igniters  1112   a  and  1112   b  independently. In some cases, an electric current is applied only to the first igniter  1112   a  to ignite and burn only the gas generating agent  1109   a  in the first combustion chamber  1105   a . In other words, the second gas generating agent  1109   b  and the second igniter  1112   b  are left unburnt . This case causes inconvenience at the time of later disposal or damping. Therefore, it is preferable that the gas generating agent  1109   b  in the second combustion chamber  1105   b  is burnt after at further delayed timing (e.g., 100 milliseconds or more) than the normal delay ignition timing (e.g., 10 to 40 milliseconds) of actuating the second igniter  1112   b  after actuation of the gas generator (the first igniter  1112   a  only). Thereupon, the automatic ignition material  1185  which is ignited and burnt by transmission of combustion heat of the first gas generating agent  1109   a  is disposed in the present invention. In such case, the second gas generating agent  1109   b  is ignited by the automatic ignition material  1185  after further sufficient time passes, which is longer than the normal predetermined delayed timing (i.e., the actuation interval between the igniters) for actuating the second igniter  1112   b  following actuation of the first igniter  1112   a . That is, it is different from the case that the second gas generating agent  1109   b  is burnt at the delayed timing (i.e., the second igniter is ignited at delayed timing) in order to adjust the actuation performance of the gas generator. While the actuation current to the second igniter  1112   b  is delayed arbitrarily to adjust the actuation performance of the gas generator, the second gas generating agent  1109   b  is never ignited and burnt by the automatic ignition material  1185 . Besides, the automatic ignition material  1185  can be provided, being combined with the second igniter  1112   b.    
     The ignition timing of the automatic ignition material is determined by thermal conductivity of heat transmitting material (e.g., housing) which transmits the combustion heat of the first gas generating agent, a distance and the like. In this embodiment, non-azide based gas generating agent is used as the gas generating agent. The heat transmitting material for transmitting the combustion heat of the gas generating agent which burns first is the housing and/or the inner cylindrical member. It is preferable that the automatic ignition material is disposed in a position near each shell in the second combustion chamber and more preferably, the automatic ignition material is in contact with the shell. 
     The automatic ignition material may be disposed in the second combustion chamber by adhesion, or only the automatic ignition material may be put into another container and the container may be placed in the second combustion chamber. It is preferable that the automatic ignition material is in contact with the heat transmitting material. 
     In the gas generator in which the automatic ignition material is disposed as described above, even when only the first gas generating agent  1109   a  is burnt and the second gas generating agent  1109   b  disposed in the second combustion chamber  1105   b  left unburnt after the activation of the gas generator, it is possible to burn the second gas generating agent indirectly resulting from the combustion of the first gas generating agent  1109   a , and after the actuation of the gas generator, disposal or damping can be carried out without any problem. 
     The first combustion chamber  1105   a  and the second combustion chamber  1105   b  are defined by the inner cylindrical member  1104 . The inner cylindrical member  1104  is provided with a through-hole  1110  which is closed by a stainless plate  1111 . The stainless plate  1111  is adhered to the inner cylindrical member  1104  by adhesion member such as adhesion, and the through-hole  1110  is opened only by combustion of the second gas generating agent  1109   b , and is never opened by combustion of the first gas generating agent  1109   a . The reason why the through-hole  1110  is closed by the stainless plate  1111  is to prevent a flame caused by combustion of the first gas generating agent  1109   a  from flowing into the second combustion chamber  1105   b  through the through-hole  1110  to burn the second gas generating agent  1109   b . Therefore, if such a function can be ensured, instead of closing the through-hole  1110  by the stainless plate  1111 , a breaking plate which is broken, peeled, burnt or detached by pressure or the like due to the combustion of the second gas generating agent may be welded, adhered or heat-sealed to close the through-hole  1110 , or the peripheral wall of the inner cylindrical member  1104  may be provided with a notch, or the thickness of the peripheral wall of the inner cylindrical member  1104  maybe formed partially thin. Further, as shown in FIG. 31, a substantially ring-like shielding plate  1186  can be disposed such as to cover the through-hole  1110  formed in the inner cylindrical member  1104 . Especially in the gas generator shown in FIG. 31, even if the combustion gas is generated by combustion of the first gas generating agent  1109   a , since the seal tape which closes the through-hole  1110  is protected by the shielding plate  1186 , it is not broken by combustion of the first gas generating agent  1109   a . As described above, in the present embodiment, the through-hole  1110  of the inner cylindrical member  1104  is opened exclusively by combustion of the second gas generating agent  1109   b , and is never opened by combustion of the first gas generating agent  1109   a . Therefore, even if the combustion gas is generated in the first combustion chamber  1105   a  first, this never flows into the second combustion chamber  1105   b , and the gas generating agent  1109   b  in the second combustion chamber  1105   b  is ignited and burnt by the actuation of the second igniter  1112   b  (combustion of the automatic ignition material  1185  in some cases) The combustion gas generated by the second gas generating agent  1112   b  passes through the through-hole  1110  which is opened by combustion of the second gas generating agent  1112   b  and passes through the first combustion chamber  1105   a  and then, purified and cooled by the coolant/filter  822  and discharged from the gas discharge port  826 . 
     In FIG. 28, the numeral  823  represents a short-pass preventing member for preventing the combustion gas from passing between the end surface of the coolant/filter and the ceiling inner surface of the diffuser shell. 
     Connector 
     The present invention provides a multistage type gas generating device, wherein, in an air bag apparatus which includes a gas generator for an air bag comprising a plurality of igniters, and in which actuation signals are outputted from a ignition signal-outputting means to each of the igniters, connection error between the igniters and the ignition signal outputting apparatus is eliminated, and the air bag apparatus can always actuate with a desired output. 
     The present invention provides a multistage type air bag apparatus wherein, in a gas generating device which comprises a multistage type gas generator for an air bag including a plurality of igniters and in which actuation signals are outputted from ignition signal-outputting means to each of the igniters by a lead wire having the connector, the connector is provided with defining means, and, when the ignition signal-outputting means and the igniters are connected through the lead wires, the respective connections are specified as a unique combination. 
     In other words, the air bag apparatus of the present invention is a multistage type air bag apparatus comprising a multistage gas generator storing a plurality of electrical ignition type igniters in a housing thereof, an ignition outputting means provided with the equal numbers of the igniters and outputting portions for outputting an actuation signal to the igniters on an impact, and a plurality of lead wires having connectors, wherein the igniters and the outputting portions are connected by the lead wires having the connectors, and said connectors have a defining means which specifies a unique connection of the respective igniters and the respective outputting portions. 
     The defining means may be formed on the connector provided on at least one end of the lead wire connecting the igniter and the outputting portion, or the defining means may be formed on a way-connector provided at least one on the lead wire which connects the igniter and the outputting portion. 
     The lead wire may be provided in the same numbers as the electrical ignition type igniter provided n the gas generator. The ignition timing of each of a plurality of the igniters is individually adjusted in accordance with environmental condition at the time of actuation of the air bag apparatus. 
     When the igniter includes a connecting portion for connecting the igniter to the connector, and the defining means may be formed on the connecting portion of each of the igniters and the connector which connects the lead wire extending from the outputting portion to each of the igniters. When the outputting portion includes a connecting portion to be connected to the connector, the defining means may be formed on the connecting portion of the outputting portions and the connector which connects the lead wire extending from the gas generator to the outputting portion. The way-connector may comprise a plug portion and a jack portion, these portions includes connecting portions, the defining means may be formed on the connecting portions of the plug portion and the jack portion of the way-connector which connects the lead wire extending from the gas generator and the lead wire extending from the outputting portion. 
     Conductive portions exist on the connector and the connecting portion, the respective conductive portions are brought into contact with each other by connecting the connector and the connecting portion so that ignition signal outputted from the ignition signal-outputting means can be transferred to each of the igniters. In this case, the defining means can be realized by changing at least one of a shape, the number and a position of the conductive portion existing on the connector. For example, the conductive portion of the connector is of convex shape or concave shape, and is connected to the conductive portion of the connecting portion which is formed into a concave shape or convex shape. When the connector provided in each lead wire is made of plastic member, the plastic member maybe provided with a defining means, and the a plurality of connectors can be connected to one another by the defining means. The plurality of lead wires are converged into one connector, and the connector can be provided with a defining means. 
     As described above, in the multistage air bag apparatus, if the connector having the defining means is used for the lead wire for connecting the ignition signal-outputting means and the igniter and for transmitting the actuation signal, it is possible to specify a unique connection of the respective igniters, the respective connectors and the respective actuation outputting means. 
     In this multistage type air bag apparatus, it is possible to use a gas generator having a cylindrical housing comprising a diffuser shell including a gas discharge port and a closure shell forming an internal space in cooperation with the diffuser shell. A plurality of igniters may be arranged in the same direction as the axis of the housing, and provided in the closure shell. 
     Further, the present invention also provides a multistage gas generator for an air bag, comprising a housing with a gas discharge port, a plurality of igniters which is accommodated in the housing and to be actuated by electric signals, and gas generating means which is accommodated in the housing and to be burnt and/or expanded by actuation of the igniter for generating an activation gas, wherein each of the igniters includes a connecting portion for connecting to connectors disposed on tip ends of lead wires which transmit an activation signal outputted from an outputting portion of ignition signal-outputting means, and the connecting portion is provided with defining means which allows only one connection of the respective connectors. Especially, this multistage type gas generator for an air bag can be preferably used for the multistage type air bag apparatus. 
     In other words, this gas generator has, when the gas generator is assembled into the air bag apparatus, the connecting portion for connecting to connectors disposed on tip ends of lead wires which transmit an activation signal outputted from an ignition signal-outputting means, and the connecting portion is provided with a defining means which enables to connect only one of the connectors. As an example of the defining means, the conductive portions in the igniters, which receives the actuation signal from the ignition signal-outputting means, are different from each other in a shape, the number and/or a position of for the respective igniters. With this arrangement, only the corresponding specific connector can be connected. Alternatively, the shape of the connecting portion of the igniter can be formed into a shape which is complementarily fitted only to the specific connector. In the latter case, a groove and/or a projection can be formed on the connecting portion so that positions and/or shapes thereof are different from each other at the respective igniters. 
     This gas generator is good enough as long as it includes two or more igniters, and the gas generating means for generating the actuation gas for expanding the air bag (bag) may be solid gas generating agent or pressurized gas. And the gas generator may be formed into either shape suitable to be disposed on a driver side or suitable to be disposed on a passenger side. This gas generator preferably has a structure such that combustion chambers as many as igniters are provided in the housing, and gas generating means in each combustion chamber is burnt and expanded at each igniter. 
     Further, the present invention provides a connecting method for connecting the ignition signal-outputting means (outputting portion) and the igniter preferably used in the above-described multistage type air bag apparatus. 
     That is, the present invention provides a connecting method of connecting a ignition signal-outputting means which includes a control unit for sending an ignition signal to a plurality of igniters included in a gas generator, and a plurality of ignition means included in the gas generator, wherein each of the igniters is connected to an ignition means outputting apparatus through a lead wire having a connector, and connections of the respective igniter and the respective output portion are specified by defining means. 
     As for the defining means, the conductive portions provided on the respective igniters are formed differently from each other in a shape, the number and/or a position at the respective igniters. Alternatively, the defining means can be realized by forming the connector and the connecting portion so as to be fitted to each other complementarily, and thereby the combination thereof is unique. Especially, the latter case can be realized by forming a groove and/or a projection on the connecting portion which is different from each other in a position and/or a shape thereof at each igniter. 
     Usually, modules comprising the gas generator and the air bag (bag) are different in size and shape in accordance with a disposed position such as a driver side or a passenger side, but the multistage type air bag apparatus of the invention can be used irrespective of the shape and size of the module. Similarly, the gas generator for the multistage type air bag of the invention can be employed to any apparatus such as for a drive side, a passenger side and a backseat regardless of variation of shape and size. 
     In the multistage type air bag apparatus, any actuation signal outputting apparatus can be used as long as it includes a plurality of actuation signal outputting portions, the outputting timing of the actuation signal outputted from the outputting portions can be adjusted and it senses an impact and outputs the actuation signal. Therefore, the actuation signal outputting apparatus can be used as long as it includes a portion sensing the impact, and a portion for judging a degree of the impact and controlling the output signal, without regard to a structure whether the two portions are integrally formed or separately formed. 
     In the above-described multistage type air bag apparatus, for optimizing the developing pattern of the air bag (bag), when the actuation signal outputting means senses an impact, the outputting timing of the actuation signal is adjusted, and actuation timing of each igniter included in the gas generator is adjusted. At that time, since the connectors of the lead wires connecting the ignition signal-outputting means and the ignitions are provided with defining means respectively, the actuation signal outputted from the actuation signal outputting means is reliably sent to the specific igniter, i.e., the igniter which is initially planned to be actuated, no variation of actuation performance of the air bag apparatus is caused due to connection error of the ignition signal-outputting means and the igniter. Therefore, in this multistage type air bag apparatus, it is possible to optimize the developing pattern of the air bag more reliably. 
     Embodiment of Connector 
     The multistage gas generator for an air bag apparatus of the present invention will be explained based on the embodiment shown in the drawing below. FIG. 10 is a vertical cross sectional view showing one embodiment of the multistage type air bag apparatus of the invention. 
     The multistage type air bag apparatus shown in FIG. 10 comprises a gas generator  101  for a multistage type air bag including two igniters  108   a  and  108   b , and an actuation signal outputting means  102  for outputting actuation signal to each igniter in accordance with an impact. Among them, the gas generator  101  for the multistage type air bag is accommodated in a module case  104  together with an air bag  103  which is to be expanded by introducing an actuation gas generated by actuation of the gas generator. 
     The actuation signal outputting means  102  comprises an impact sensor  105  which senses an impact and a control unit  106  for inputting a signal from the impact sensor and outputting the ignition actuation signal. 
     The impact sensor  105  is for sensing the impact, and can be formed using a semiconductor acceleration sensor for example. In the semiconductor acceleration sensor, four semiconductor strain gauges are formed on a beam of a silicon substrate which deflects if acceleration is applied, and the semiconductor strain gauges are bridge-connected. When acceleration is applied, the beam is bent, and strain is generated on the surface. With this strain, resistance of the semiconductor strain gauge is changed, and the resistance change is detected as a voltage signal in proportion with the acceleration. 
     The control unit  106  includes an ignition judging circuit. A signal from the semiconductor strain gauges is inputted to the ignition judging circuit. When an impact signal from the sensor  105  exceeds a certain value, the control unit  106  starts calculation, and when the calculated result exceeds a certain value, an actuation signal is outputted to the igniters  108   a  and  108   b  of the gas generator  101 . 
     The module case  104  is made of polyurethane, for example, and includes a module cover  129 . The air bag  103  and the gas generator  101  are accommodated in the module case  104  to constitute a pad module. When the pad module is mounted to the driver side of an automobile, it is usually mounted in a steering wheel  130 . 
     The air bag  103  is made of nylon (e.g., nylon 66) or polyester and the like, its bag port  131  surrounds a gas discharge port of the gas generator, and the air bag is fixed to the flange portion of the gas generator in a folded state. 
     In the multistage type air bag apparatus having the above-described structure, when the semiconductor acceleration sensor  105  senses an impact at the time of collision of the automobile, its signal is sent to the control unit  106 , and when the impact signal from the sensor exceeds the certain value, the control unit  106  starts calculation. If the calculated result exceeds the certain value, the actuation timing is adjusted, and the actuation signal is outputted to the igniters  108   a  and  108   b . With this, the igniters  108   a  and  108   b  are actuated to ignite and burn the gas generating agents for generating a combustion gas. The gas is ejected into the air bag  103 , and the air bag breaks the In module cover  129  and expands, and then forms a cushion between the steering wheel  130  and the passenger for absorbing the impact. 
     The actuation signal outputted from the control unit  106  is outputted from an outputting portion  107  provided in the respective igniters  108   a  and  108   b  in the control unit  106 . The number of the outputting portions  107  should be more than the number of igniters  108  included in the gas generator  101 , i.e., two or more in the present embodiment. For adjusting the actuation timing of the igniters, the actuation signals from the outputting portions  107   a  and  107   b  can be outputted at different timings. The actuation signals outputted from the outputting portions  107   a  and  107   b  transmitted to the igniters  108   a  and  108   b  included in the gas generator  101  by the lead wires  109   a  and  109   b  provided in the same numbers as the igniters  108   a  and  108   b . In this case, if wrong lead wire  109  is erroneously connected to any of the igniter, desired actuation output can not be obtained. Thereupon, the lead wires  109   a  and  109   b  for connecting the outputting portions  107   a  and  107   b  and the igniters  108   a  and  108   b  are provided with connectors  110   a  and  110   b , and connectors  110   a  and  110   b  are provided with defining means. with this arrangement, actuation signal outputted from the first outputting portion  107   a  is reliably sent to the first igniter  108   a , and actuation signal outputted from the second outputting portion  107   b  is reliably sent to the second-igniter  108   b . The defining means can be formed differently in accordance with a structure of the igniter  108  and the control unit  106  or a shape of the lead wire  109  for connecting the igniter  108  and the outputting portion  107 . 
     In the multistage type air bag apparatus of FIG. 10, as shown in FIG. 11, when the connectors  110   a  and  110   b  are mounted to tip ends of the lead wires  109   a  and  109   b  respectively extending from the outputting portions  107   a  and  107   b , and the respective connectors  110   a  and  110   b  are connected to connecting portions  111   a  and  111   b  of the igniter  108   a  and  108   b , connectors  110   a  and  10   b  and the connecting portions  111   a  and  111   b  can be provided with defining means as shown in FIGS. 12 and 13. When the connector  110  of the lead wire  109  is connected to the igniter in this manner, a conductive portion i.e., a conductive pin  112 , which receives the actuation output from the control unit  106 , is used. 
     In the defining means shown in FIG. 12, shapes of the connecting portion are different from each other at the respective igniters, or a groove and/or a projection are formed so that positions and/or shapes thereof are different from each other at the respective igniters. In the case of the defining means shown in FIG. 12 a , positioning grooves (or projections)  117  are formed on the connectors  110   a  and  110   b , and positions where projections (or grooves)  118  corresponding to the positioning grooves (or projections)  117  are different from each other at each igniter. In the case of the defining means shown in this drawing, positions of the grooves (or projections)  117  of the connectors are different from each other so that, at the time of mounting the connectors  110   a  and  110   b  to the gas generator, if the connectors are not mounted in the right direction, the connectors interfere with each other and they can not be mounted right. In the defining means shown in FIG. 12 b , only one connector  110   b  is provided with a positioning groove (or projection)  119 . That is, a connector  110   b  having the groove (or projection)  119  can be connected to an igniter  108   a  which does not have a projection (or groove)  120 , but a connector  110   a  which does not have the grove (or projection)  119  can not be connected to an igniter  108   b  having the projection (or groove)  120 . As a result, connection error of the connectors can easily be found at the time of assembling. In FIG. 12 c , the shapes of connecting portions  116  of the connectors  110   a  and  110   b  are different from each other. In FIG. 12 d , two connectors are formed into one connector, and a positioning groove (or projection)  124  is formed. 
     As the gas generator shown in FIG. 11, when the conductive pin  112  is provided as the conductive portion on the connecting portion to which the connector is connected and the conductive portion (the conductive pin  112 ) of the connecting portion  111  is connected to the conductive portion of the connector  110  so that current can flow, the shape, the number or the position of the conductive pin  112  can be changed in each igniter, and in accordance with this, the shape, the number or the position of the conductive portion of the connector  110  can be changed. 
     FIG. 13 shows a mode of the conductive pins different from each other at the respective igniters. FIG. 13 a  shows that the shapes of the conductive pins  112  of the igniters  108   a  and  108   b  are different, and FIG. 13 b  shows that the conductive pins  112  of the igniters  108   a  and  108   b  are formed at the different positions. Such mode of conductive pins can be appropriately employed as long as the respective igniters have different conductive pins form each other. In this case, the shape, the position or the number of the conductive portions of the connectors  110   a  and  110   b  are adjusted in accordance with a mode of the conductive pins  112  of the igniters  108   a  and  108   b . When the conductive pins  112  of the igniters  108   a  and  108   b  are formed at the different positions as shown in FIG. 13 b , the connectors  110   a  and  110   b  can also be connected as shown in FIG. 13 c.    
     When the defining means are provided to connect the igniters and the connectors  110   a  and  110   b  as described above, the connectors  110   a  and  110   b  are preferably designed so that the lead wires  109   a  and  109   b  which are connected to the respective connectors  110   a  and  10   b  are pulled out in the same direction and further, that direction is perpendicular to the center axis of the housing. 
     Further, in the multistage type air bag apparatus shown in FIG. 10, when the ends of the lead wires  109   a  and  109   b  are provided with connectors  113   a  and  113   b , and the connectors  113   a  and  113   b  are respectively connected to connecting portions  114   a  and  114   b  of the outputting portions  107   a  and  107   b  as shown in FIG. 14, the connectors  113   a  and  113   b  and the connecting portions  114   a  and  114   b  can be respectively provided with defining means similar to those of the igniters shown in FIG.  12 . Namely, shapes of the connecting portions  114   a  and  114   b  of the outputting portions  107   a  and  107   b  are different at the respective connectors  113   a  and  113   b , or grooves and/or projections which are different in position and/or shape are formed. In accordance with the connecting portions  114   a  and  114   b  of the outputting portions  107   a  and  107   b , in this case, the connectors  113   a  and  113   b  are formed in shape to have positions and/or into shapes of the grooves and/or the projections respectively. Further, when the connecting portions  114   a  and  114   b  of the outputting portions  107   a  and  107   b  have conductive pins  115   a  and  115   b  which functions as the conductive portions, the conductive pins  115   a  and  115   b  can be formed into the mode shown in FIG.  13 . In this manner, in the case of the multistage type air bag apparatus in which the connector  113  of the lead wire  109  is connected to the ignition signal-outputting means (the control unit  106  in the present embodiment), by providing the connecting portions  114   a  and  114   b  of the outputting portions  107   a  and  107   b  and the connectors  113   a  and  113   b  with the defining means, the lead wire  109   a  is connected to the first outputting portion  107   a  through the connector  113   a , and the lead wire  109   b  is connected to the second outputting portion  107   b  through the connector  113   b . Therefore, when the igniters  108   a  and  108   b  are connected to the lead wires  109   a  and  109   b  respectively, by providing the defining means shown in FIGS. 12 and 13, the actuation signal outputted from the first outputting portion  107   a  is inputted to the first igniter  108   a  without mistake, and the actuation signal outputted from the second outputting portion  107   b  is inputted to the second igniter  108   b  without mistake. With this arrangement, in the multistage type air bag apparatus, a desired actuation performance can be obtained reliably. 
     Further, in the multistage type air bag apparatus shown in FIG. 10, as shown in FIG. 15, when way-connectors  125   a  and  125   b  are connected to the intermediate portions of the lead wires which connect the outputting portions  107   a  and  107   b  of the ignition signal-outputting means (the control unit  106  in the present embodiment) and the gas generator for the multistage type air bag (the igniter  108  in the present embodiment), the way-connectors  125   a  and  125   b  can also be provided with defining means. That is, the defining means as explained in FIGS. 12 and 13 are provided in a plug  125   a   1  and a jack  125   a   2  of the way-connector  125   a , and in a plug  125   b   1  and a jack  125   b   2  of the way-connector  125   b . Such defining means can be realized by adjusting the shape of the connector itself or by providing or not providing concave and convex, or adjusting the position, shape and the like of the conductive pin so that the plug  125   a   1  can be connected only to the jack  125   a   2 , and the plug  125   b   1  can be connected only to the jack  125   b   2 . More specifically, as shown in FIG.  16 ( a ), the locations where the conductive pins  121  of the plugs  125   a   1  and  125   b   1  can be set different from each other at the respective way-connectors  125   a  and  125   b . Alternatively, as shown in FIG.  16 ( b ), shapes of the conductive pins  121  of the plugs  125   a   1  and  125   b   1  can be made different from each other at the respective way-connectors  125   a  and  125   b . Or as shown in FIG.  16 ( c ), the shapes of the connectors  125   a  and  125   b  can be made different from each other. For example, as shown in FIG. 17, the method of providing the defining means to such way-connectors can be employed also when the igniters  126   a  and  126   b  provided in the gas generator do not directly connect the connectors. In other words, when the igniters include a connecting portion for connecting the connector, the defining means can be provided by the method as shown in FIGS. 12 and 13, but when the lead wires  127   a  and  127   b  are connected directly to the igniters  126   a  and  126   b  as shown in FIG. 17, it is difficult to connect the connectors directly to the igniters  126   a  and  126   b . Thereupon, the lead wires  127   a  and  127   b  extending from the igniters  126   a  and  126   b  are provided at their tip ends with the connectors  128   a  and  128   b , and the way-connectors  125   a  and  125   b  are connected to the connectors. If the connectors are respectively provided with the defining means and the way-connector  125   a  is connected to the connector  128   a  and the way-connector  125   b  is connected to the connector  128   b , the actuation signal sent from the first lead wire  126   a  is reliably transmitted to the first igniter  126   a , and the actuation signal sent from the second lead wire  126   b  is reliably transmitted to the second igniter  126   b.    
     By the above-described structure and method, in this multistage type air bag apparatus, connection error of the outputting portion and the ignition is eliminated, and the actuation signals of the igniters outputted from the outputting portions  107   a  and  107   b  of the control unit  106  in the ignition signal-outputting means can be transmitted to the desired igniters. Therefore, according to this multistage type air bag apparatus, a desired actuation performance can reliably be obtained. 
     FIG. 18 is a vertical cross sectional view showing an embodiment of a multistage type air bag apparatus preferably used for the above-described multistage type air bag apparatus. Namely in this gas generator, the multistage type air bag is provided with defining means which can specify the connectors  110   a  and  110   b  mounted to tip ends of the lead wires connected to the ignition signal-outputting means and can connect the connectors, as explained in the above. 
     In this gas generator, two combustion chambers  133   a, b  for accommodating gas generating agents are provided in a housing  132 , and two igniters  135   a, b  for burning gas generating agents  134   a, b  disposed in the respective combustion chambers are accommodated. The igniters disposed in the housing can be actuated independently, and when one of the igniters is actuated, the gas generating agent in one of the combustion chambers is ignited and burnt. That is, this gas generator is adapted such that the gas generating agents  134   a, b  in the combustion chambers  133   a, b  are ignited and burnt only by either one of the igniters  135 . Therefore, if the actuation timings of the igniters  135   a, b  are adjusted, the burning timings of the gas generating agents  134   a, b  in the combustion chambers can be adjusted, and with this feature, the actuation performance of the gas generator and the air bag apparatus can be adjusted. More specifically, when the first igniter  135   a  is actuated, the transfer charge  136  is burnt, the flame is ejected from first flame-transferring hole  150  into the first combustion chamber  133   a  to ignite and burn the first gas generating agent  134   a  accommodated in the first combustion chamber. The second igniter  135   b  is actuated simultaneously with or slightly later than the first igniter, and the flame passes through the second flame-transferring hole  150   b  and ejected into-the second combustion chamber. The second gas generating agent is ignited and burnt by this flame to generate the actuation gas, and the gas passes through the through-hole  152  of the inner cylindrical member  151  and is ejected into the first combustion chamber  133   a . The actuation gas generated by combustion of the first gas generating agent  134   a  and the second gas generating agent  134   b  is purified and cooled while the gas passes through the coolant/filter  137  and discharged from the gas discharge port  153 . 
     In this gas generator, the transfer charge  136  capable of being ignited and burnt by the actuation of the igniter  135  to efficiently burn the gas generating agent can be combined in the igniter  135 . When the gas generating agent  134  is burnt and combustion residue is also generated, a filter for purifying the combustion residue can be disposed, and a coolant for cooling the combustion gas can be disposed. In the present embodiment, the coolant/filter  137  for purifying and cooling the combustion gas is used. 
     In this gas generator, the two igniters are respectively accommodated in igniter collars  138  and disposed in the housing  132 . In the igniter collar, the position where the igniter  135  is accommodated is provided with a connecting portion  139 . Connectors  110  of tip ends of the lead wires  109  extending from the ignition signal-outputting means are respectively connected to the connecting portions when the air bag apparatus is formed using the gas generator. 
     In the gas generator of the present invention, the connecting portion  139  is provided with a defining means  140  so that among the plurality of connectors  110   a, b  for transmitting the actuation signals from the ignition signal-outputting means to the igniters  135   a, b , the connector  110   a  capable of being connected to the connecting portion  140  can be specified. That is, the defining means  140  of the igniter  110   a, b  are formed differently at the respective igniters  110   a, b . For example, as shown in FIG. 12, the shapes of the connecting portions  139   a, b  of the igniters  125   a, b  can be formed differently from each other, or grooves and/or projections having different positions and/or shapes can be formed. Further, as shown in FIG. 13, shapes, positions or the like of the conductive pins  141  of the igniters projecting into the connections  139   a , b can be set different from each other at the respective igniters  135   a, b.    
     Although the gas generator suitable to be disposed on a driver side has been described in the present embodiment, a gas generator which is long in the axial direction suitable to be disposed on a passenger side, or a gas generator using pressurized gas instead of solid gas generating agent can be used as long as the gas generator includes two or more igniters. 
     The two igniters may not be always disposed on the same plane as shown in FIG. 18, and the igniters can also be disposed on different planes, e.g., on the upper surface and the lower surface of the gas generator. 
     Self-contracting Type Filter 
     Filter means of a gas generator for an air bag of the present invention is substantially cylindrical shape as a whole, and at least any of axially end surface is formed such as to be inclined and narrowed outwardly in the radial direction. This filter means expands radially outward by the actuation gas generated by the actuation of the gas generator. By this expansion, the filter means abuts against the supporting portion and/or supporting member in the housing, and the filter means is contracted in the axial direction by the inclination of the end surface, and at the time of actuation of the gas generator, the short pass of the actuation gas at the end surface of the filter means can be prevented. 
     That is, the filter means of the gas generator for the air bag of the present invention is disposed in the housing of the gas generator for the air bag, and the cylindrical filter means is for purifying and/or a cooling an activation gas, one or both of axial end surfaces of the filter means are formed as inclining end surfaces which get narrower in an axial extending direction and the interior angle with respect to the inner peripheral surface is an acute angle. Especially, since this filter means expands outwardly in the radial direction by the actuation gas generated on the actuation of the gas generator, it is preferable that the filter means is made of wore rods, and formed so as to expand and contract in the radial direction. 
     Such filter means includes any filter means, having a opening through which the actuation gas passes, such as the filter used for cooling the actuation gas when a temperature of the gas is high and, in addition, a filter for purifying the combustion residue included in the actuation gas, and a coolant/filter having both the functions. The filter means is substantially cylindrical shape as a whole, and one or both of axial end surfaces of the filter means are formed as inclining end surfaces. The inclining end surfaces are inclined so as to be narrowed in the axial extending direction of the filter means. More specifically, if the upper end surface is inclined, it is inclined so as to descend outwardly in the radial direction, and if the lower end surface is inclined, it is inclined so as to ascent outwardly in the radial direction. That is, the filter means comprises an inclining portion formed with an inclined end surface, and a straight body portion axially connected to the inclining portion to form a peripheral surface. The inclining portion can be provided on the both sides of the straight body portion in the axial direction, or on either side of straight body portion. 
     This filter means can be formed by laminating cylindrically a wire mesh made of various wire rods to form a laminated wire mesh filter, and then compress-molding the filter. An example of the wire mesh made of wire rods is preferably a stainless steel wire mesh, and as the stainless steel of the wire mesh material, SUS 304 , SUS 310 S, SUS 316  (in the Japanese Industrial Standards codes) and the like can be used. SUS 304  (18Cr-8Ni-0.06C) exhibits excellent corrosion resistance as an austenitic stainless steel. If such a filter means made of wire rods is formed to expand and contract at least in the radial direction, further remarkable effects can be obtained. 
     Further, the present invention provides, a gas generator for air bag for effectively preventing the short pass of the actuation gas using the above-described filter means. 
     That is, a gas generator for an air bag of the present invention comprises, in a housing with a gas discharge port, a igniting means to be actuated on an impact, a gas generating means for generating an activation gas to expand the air bag due to actuation of the ignition means and a cylindrical filter means for purifying and/or cooling the activation gas, wherein in said filter means, one or both of axial end surfaces are formed as inclining end surfaces which get narrower in an axial extending direction and the interior angle with respect to the inner peripheral surface is an acute angle, and a supporting portion which is opposed to the inclining end surface of the filter exists in the housing. 
     As the supporting portion provided in this housing, for example, the inner surface of the housing opposed to the inclining end surface of the filter means, i.e., the inner surface where the inclining end surface of the filter means are provided as well as in the axial direction of the position where the filter means are provided, an inclining surface having substantially the same inclination as the inclining end surface of the filter means are formed as the supporting portion of the housing. Alternatively, a filter means supporting member which has a inclining side opposed to the inclining end surface of the filter means is disposed in the housing in the axial direction of the filter means end surface and on the side where the inclining end surface of the filter means is formed, and thereby, the inclining surface of the filter means supporting member can be the above supporting portion. 
     As the filter means, the one whose end surfaces of the axially opposite sides are formed as inclining end surfaces can be used. Alternatively, the filter means whose either of end surfaces of axially opposite sides formed into the inclining end surface. In other words, the filter means comprises a straight body portion forming the peripheral surface and an inclining portion formed with an inclining end surface. The inclining portion is provided on either or both sides of the straight portion in the axial direction. When the filter means formed at its axially both end surfaces with the inclining end surfaces (inclining portions) is used, the supporting portions provided in the housing are provided on axially both sides where the filter means is disposed. When the filter means formed at its axially one end surface with the inclining surface (inclining portion), the supporting portion provided in the housing is provided in the axial direction of the filter means as well as on the side of the inclining surface (inclining portion) of the filter means. In this case, it is preferable that a retainer having an annular portion and an outer peripheral wall is disposed in the housing on the axially opposite side of the supporting portion, i.e., the opposite side of the inclining end surface, with respect to the filter means end surface, and an inner surface of the outer peripheral wall of the retainer is opposed to an outer peripheral surface of the filter means end. Instead of disposing the retainer, the outer diameter on the end surface where the inclining end surface of the filter means is not formed can be formed larger so that the end surface abuts against the inner surface of the peripheral wall of the housing. 
     When it is not desired that the straight portion of the filter means is expanded and deformed, e.g. , when it is desired to ensure a space between the inner surface of the housing and an outer surface of the filter means, the straight portion may be provided at its outer peripheral surface with expansion-suppressing means comprising a punching metal or a winding of a porous cylindrical shape to prohibit expansion thereof. In this case, only the inclining portion of the filter means expands and then abuts against and is supported by the supporting portion (material). 
     The gas generator of the present invention is not limited by the entire shape thereof. Therefore, for example, the gas generator having a cylindrical shape which is long in the axial direction or the gas generator having a cylindrical shape which is wide in the radial direction can be used. As the ignition means disposed in the housing, as long as it is actuated on an impact, an igniter which is actuated electric signal output by an impact, any known igniter, which is used to make the gas generating means generate an actuation gas, such as an igniter to be activated by an electrical signal outputted on an impact, or a combination of said igniter and a transfer charge to be ignited and burnt by actuation of the igniter, can be used. 
     Examples of the gas generating means which is accommodated in the housing for generating the actuation gas to expand the air bag on the actuation of the ignition means are a solid gas generating agent which is to be ignited and burnt by the actuated ignition means to generate an actuation gas, a pressurized gas which is heated to expand and generate an actuation gas, and a combination. As the gas generating agent, a conventionally and widely used azide-based gas generating agent based on inorganic azide such as sodium azide, or a non-azide-based gas generating agent not based on inorganic azide can be used. Further, as the pressurized gas, a known gas such as a mixture of oxygen and inert gas can be used. That is, the gas generator of the present invention can be realized by both of a pyrotechnic gas generator using a solid gas generating agent, and a hybrid gas generator using pressurized gas as well as solid gas generating agent. 
     The gas generator of the present invention is actuated so that, after the ignition means is actuated, the actuation gas is generated form the gas generating means, the actuation gas is purified and cooled while it passes through the filter means and then, the gas is discharged form the gas discharge port. When the actuation gas passes through the filter means, the filter means expands in the radial direction due to the pressure of the actuation gas, but in the gas generator, the axially one or both end surfaces of the filter means is formed as the inclining surface which is inclined so as to be narrowed outwardly in the radial direction, and the supporting portion having the inclining surface which is opposed to the inclining surface of the filter means is provided in the housing. Therefore, the inclining surface of the filter means which expands in the radial direction abuts against the supporting portion in the housing, and the filter means is slightly contracted in the axial direction by this inclination. With this, the end surface of the filter means is strongly brought into contact with the supporting portion with pressure, and the short-pass of the actuation gas between the inclining surface (i.e., end surface) of the filter means and the supporting portion can be prevented. 
     As realized also in the gas generator having the above-described structure, manufacturing cost can be reduced by employing the method of a purifying and/or cooling an actuation gas wherein a supporting portion which is inclined so as to be narrowed in the axial extending direction of the housing is provided in the housing, the cylindrical filter means expanded radially by passage of the actuation gas is contracted in the axial direction by inclination of the supporting portion and is abutted against the supporting portion, and thereby preventing the activation gas from passing between the filter means and the supporting portion. 
     The above-described gas generator is accommodated in the module case together with the air bag (bag) to expand by a gas generated by the gas generator, and combined with the impact sensor for sensing at least an impact to actuate the gas generator, thereby constituting the air bag apparatus. In this air bag apparatus, the gas generator is actuated as an impact sensor senses an impact, thereby discharging the combustion gas from the gas discharge port of the housing. The combustion gas flows into the air bag so that the air bag breaks a module cover and expands to form a cushion between a passenger and a hard structural member in the vehicle for absorbing the impact. 
     Embodiment of Self-contracting Type Filter  1   
     FIG. 19 is a vertical cross sectional view showing one embodiment of a gas generator for an air bag of the present invention. Especially, the gas generator shown in this drawing is a pyrotechnic type gas generator for generating the actuation gas by combustion, and has a structure which is longer in its diametrical direction than in the axial direction. 
     In the gas generator shown in the present embodiment, a diffuser shell  301  having a gas discharge port  310  and a closure shell  302  forming an internal space in cooperation of the diffuser shell are joined to each other to form a substantially cylindrical housing  303 . An inner cylindrical member provided at its peripheral wall with a plurality of through-holes  320  is disposed in the housing  303  concentrically. The outside of the inner cylindrical member  304  is formed as a first combustion chamber  305   a . Inside of the inner cylindrical member is divided into two chambers by a partition wall  321  comprising a seal cup member  106  and a dividing circular member  307 , and the two chambers are adjacent to each other in the axial direction. One of the chambers closer to the diffuser shell  301  is a second combustion chamber  305   b , and the other chamber closer to the closure shell  302  is an ignition means accommodating chamber  308 . Gas generating agents  309  are disposed in the first and second combustion chambers, and the gas generating agents disposed in the combustion chambers are independently ignited and burnt by the actuation of two igniters  311   a, b  disposed in the ignition means accommodating chambers. 
     A filter means  350  of one embodiment of the present invention is used in the housing  303 . FIG. 20 shows a partial sectional view of the filter means  350 . In the filter means having substantially cylindrical shape as a whole, axially opposite end surfaces thereof are inclined, being narrowed in the axial extending direction, to form an inclining end surface  351  whose interior angle θ with respect to the inner peripheral surface is acute angle. More specifically, the upper end surface thereof is inclined so as to descend outwardly in the radial direction, and the lower end surface thereof is inclined so as to ascend outwardly in the radial direction. This filter means  350  can be made by laminating cylindrically wire mesh made of various wire rods to form a laminated wire mesh filter, and then compress-molding the filter. As shown in FIG. 19, the filter means  350  is disposed in the housing so as to be opposed to an inner peripheral surface of the housing  301 . A supporting member  353  having an inclining surface  352  opposed to an inclining end surface  351  of the filter means is disposed in the housing in the axial direction of the end surface of the filter. The inclining surface  352  of the supporting member  353  functions as a supporting portion of the filter means  350 . That is, in this embodiment, the filter means  350  whose both axially opposite ends are formed as the inclining end surfaces  351  is used, and the filter means supporting members  353  are provided on axially opposite sides of the filter means in the housing. The inclining surface  352  of the filter means supporting member  353  abuts and supports the inclining end surface  351  of the filter means  350  which expands in the radial direction. 
     A partition wall  321  defining an interior of the inner cylindrical member into the second combustion chamber  305   b  and the ignition means accommodating chamber  308  comprises a seal cup member  306  and a substantially flat plate-like dividing circular member  307 . A transfer charge accommodating portion  312  provided in the seal cup member  306  is combined so as to project from an opening portion  313  of the dividing circular. member. The partition wall  321  is engaged with and fixed to a step notch  314  of the inner cylindrical member. The seal cup member  306  includes a cylindrical igniter receiving port  315  extending into the opposite side of the transfer charge accommodating portion  312 , and a second igniter  311   b  is accommodated in the igniter receiving port  315 . 
     The first igniter  311   a  and the second igniter  311   b  are accommodated in an initiator collar  316 , and supported by and fixed to an igniter fixing member  317  which covers the collar  316 . The igniter receiving port  315  of the seal cup member  306  is located in the vicinity of the igniter fixing member  317 , and an O-ring  325  is disposed therebetween. With this arrangement, sealing between the first igniter  311   a  and the second ii  311   b , as well as between the second combustion chamber  305   b  and the housing are realized. 
     This gas generator is actuated in such a manner that, on actuation of the first igniter  311   a , the first transfer charge  318  accommodated in the transfer charge accommodating portion  312  of the seal cup member  306   a  is ignited and burnt, the flame is discharged from the first flame-transferring hole  319   a  provided in the inner cylindrical member  304  into the first combustion chamber  305   a  to ignite and burn the first gas generating agent  309   a . The second igniter  311   b  accommodated in the igniting means accommodating chamber  308  is actuated simultaneously with or slightly later than the first igniter  311   a , the flame is discharged into the second combustion chamber  305   b  from the second flame transferring hole  319   b  formed in the dividing circular member  307 , thereby burning the second gas generating agent  309   b . The actuation gas generated by combustion of the second gas generating agent is discharged into the first combustion chamber  305   a  from the through-hole  320  provided in the inner cylindrical member  304 . 
     The actuation gas generated by combustion of the first gas generating agent  309   a  and the second gas generating agent  309   b  passes through the filter means  350  disposed so as to surround radially the outer side of the first combustion chamber  305   a , and during that period, a combustion residue is collected and the gas is cooled. At that time, the filter means  350  slightly expands outwardly in the radial direction due to the pressure and the like of the actuation gas. The expanded filter means is abutted against and supported by the filter means supporting member  353  which is disposed in the axial direction of the filter, and the short pass of the actuation gas such that the actuation gas passes through the gap between the filter means end surface and the filter means supporting member  353  can be prevented. Namely, the filter means  350  is a self-contracting type filter which is contracted by itself due to passage of the actuation gas. The actuation gas which has passed through the filter means  350  breaks the seal tape  322  which closes the gas discharge port  310 , and is discharged out from the housing through the discharge port  310 . 
     In the gas generator of the present embodiment, known gas generating agents  309   a, b , transfer charge  318 , igniters  311   a, b  and the like can be used. 
     In the present embodiment, it is possible to use filter means provided at its only one side with the inclining surface as shown in FIG. 21, i.e., a filter means  355  which is substantially cylindrical shape as a whole, and axially one end surface thereof adjusted to be inclined, being narrowed in the axial extending direction, to form an inclining end surface  351  whose interior angle θ with respect to the inner peripheral surface is an acute angle. However, in this case, as shown in FIG. 22, the filter means supporting member  353  disposed in the housing  303  is disposed only on the side where the inclining end surface  351  of the filter means is formed, and a retainer  324  comprising an annular portion  323   b  and a wall surface portion  323   a  having the inner and outer peripheries is disposed on the opposite side (i.e., on the closure shell  302  side). A outer peripheral skirt portion  354  of the filter means is abutted against and supported by an inner surface of an outer peripheral wall  323   a  of the retainer. 
     In the gas generator shown in FIG. 22, if the actuation gas is generated by the burning of the first and second gas generating agents, the actuation gas expands the filter means  355  outwardly in the radial direction when the gas passes through the filter means as the gas generator shown in FIG.  19 . The radially expanded filter means  355  is abutted at its inclining end surface  351  against the inclining surface  352  of the filter means supporting member  353 , the outer peripheral skirt portion  354  is abutted against the inner surface of the outer peripheral wall of the retainer  324 . Therefore, this filter means  355  also becomes a self-contracting type filter which is contracted by itself by passage of the actuation gas due to the inclining end surface  352  formed on the upper end surface. 
     Embodiment of Self-contracting Type Filter  2   
     A gas generator shown in FIG. 23 is characterized in that an inclining surface  452  which is inclined so as to be narrowed outwardly in the radial direction is formed on the inner surface of the housing  403 . This inclining surface  452  is formed inside the housing axially on the side where the inclining surface of the filter means is formed. In the present embodiment, the inclining surface functions as a supporting portion of the filter means, and this is provided by forming an inclining portion which inclines in a chamfering shape on a peripheral edge of a circular portion  461  of the housing  403 . 
     In the gas generator shown in this embodiment, the housing  403  comprises a diffuser shell  401  having a gas discharge port  410  and a closure shell  402  forming an interior space in cooperation with the diffuser shell. A substantially cylindrical inner cylindrical member  404  provided at its peripheral wall with a plurality of through-holes  420  is disposed in the housing  403 , and outside of the cylindrical member is defined as a combustion chamber  405  and inside thereof is defined as an ignition means accommodating chamber  408 . A gas generating agent  409  for generating the actuation gas by combustion is accommodated in the combustion chamber  405 . An ignition means comprises an igniter  411  and a transfer charge  418  is disposed in the ignition means accommodating chamber  408 . Disposed radially outside of the combustion chamber  405  is filter means  355  provided at its only one side with the inclining surface as shown in FIG. 21, i.e., filter means  355  which is substantially cylindrical shape as a whole, and axially one end surface thereof is inclined, being narrowed in the axial extending direction, to form an inclining end surface  351  whose interior angle θ with respect to the inner peripheral surface is an acute angle. 
     Especially in this embodiment, a filter means supporting member as shown in Embodiment 1 is not disposed in the axial direction of the inclining end surface  351  of the filter means  355 . This is because that the inclining surface  452  against which the inclining end surface of the filter means abuts is formed in the housing  403  at a location where the filter means  355  is disposed and the inclining end surface  351  is formed. Therefore, in this embodiment, the inclining surface  452  functions as the supporting portion of the filter means  355 . 
     The housing  403  having such an inclining surface can be realized by press-molding various metal plates such as a stainless steel plate, a nickel plated steel plate and an aluminum alloy plate to form the diffuser shell and the closure shell, and forming the inclining portion  453  on the shell (diffuser shell  401  in the present embodiment) on the side of which the inclining surface  351  of the filter means  355  is provided. 
     In the present embodiment, the diffuser shell  401  constituting the housing comprises a circular portion  461  forming a ceiling surface, an inclining portion  453  which is inclined so as to spread like a fan outwardly in the radial direction from the outer periphery of the circular portion, a peripheral wall  462  bent from a tip end of the inclining portion and extended downward, and a flange portion  463  bending from the lower end of the peripheral wall and spreading radially outward of the housing. The closure shell  402  comprises an annular portion  465  provided at its central portion with a hole  464  in which the inner cylindrical member  404  is included, a peripheral wall  466  rising from the outer peripheral edge of the annular portion in the axial direction of the housing, and a flange portion  467  bending from the upper end of the outer peripheral wall and spreading radially outward of the housing. The flange portions of both the shells are joined to each other by various welding methods to form the housing. The diffuser shell  401  is formed at its peripheral wall surface with a plurality of gas discharge ports  410  for discharging the actuation gas, and the gas discharge ports are closed by moisture-proof seal tape  422 . A tape which is ruptured by the actuation gas is used as the seal tape  422 . 
     In the housing formed in this manner, an inner surface of the inclining portion  453  of the diffuser shell  401  is also formed as an inclining surface spreading downward like a fan, and more specifically, as the inclining surface  452  inclining downward radially outward. The filter means  355  is disposed in the housing  403  so that its inclining end surface  351  is opposed to the inclining surface  452 . The inclining surface  452  formed on the inner surface of the housing functions as a supporting member of the filter means like the inclining surface of the filter means supporting member of Embodiment 1, and abuts and supports the inclining end surface  351  of the filter means which expands outwardly in the radial direction due to passage of the actuation gas. 
     In the present embodiment also, like the gas generator shown in FIG. 22, a retainer  424  comprising a flat plate annular portion  422  and a wall surface  423  provided at its inner periphery and outer periphery is disposed on an end surface of the filter means  355  on the side where the inclining end surface is not formed. The outer peripheral skirt portion of the filter means is abutted against and supported by an inner surface of the outer peripheral wall  423  of the retainer  424 . 
     According to the gas generator shown in this drawing, when the igniter  411  is actuated, the transfer charge  418  disposed above the igniter  411  is ignited and burnt, and the flame is ejected from the through-hole  420  of the inner cylindrical member  404  into the combustion chamber  405  in which the gas generating agent  409  is accommodated. The flame of the transfer charge  418  ejected into the combustion chamber ignites and burns the gas generating agent  409 , thereby generating the actuation gas for expanding the air bag. This actuation gas is purified and cooled while it passes through the filter means  355 , and breaks the seal tape  422  and is discharged from the gas discharge port  410 . 
     While the actuation gas passes through the filter means  355 , the filter means is expanded radially outward due to the pressure. If the filter means  355  is expanded radially outward, its inclining end surface  351  abuts against the inclining surface  452  of the housing inner surface, and it is possible to prevent the short pass of the actuation gas between the filter means end surface (the inclining end surface  351 ) and the housing inner surface. 
     Therefore, in the gas generator shown in this embodiment, since the inclining end surface  351  of the filter means are pressed to the inclining surface  452  of the inner surface of the housing, it is possible to prevent the short pass of the actuation gas in the end surface of the filter means  355  without disposing a special member for supporting the filter means  355 . 
     In this gas generator also, a known gas generating agent  409 , transfer charge  418 , igniter  411  and the like can be used. 
     Embodiment of Self-contracting Type Filter  3   
     FIG. 24 shows a gas generator for an air bag of the present invention of another embodiment. The gas generator shown in FIG. 24, like the gas generator shown in FIG. 23, an inner surface of a housing  503  is formed with inclining surfaces  552   a, b , and inclining end surfaces  551   a, b  provided on an end surface of the filter means  550  are supported by the inclining surfaces  552   a, b.    
     Unlike the gas generator shown in Embodiment 2, the gas generator shown in the present embodiment uses the filter means  550  which is provided at its axially end surfaces with inclining end surfaces  551 . The inclining surfaces  551  formed on the opposite sides of the axial end surfaces of the filter means are inclined so as to be narrowed radially outward, the upper end surface  551   a  is inclined so as to descend outwardly in the radial direction, and the lower end surface  551   b  is inclined so as to ascend outwardly in the radial direction. A lower portion of the filter means of the present embodiment is formed so as to expand radially outward. 
     The inclining surfaces  552   a, b  capable of supporting the filter means  550  are formed on an inner surface of the housing  503  so as to be opposed to the inclining end surfaces  551   a, b  of the filter means. Especially in this embodiment, since the filter means is provided at its opposite sides of axial end surfaces with inclining end surfaces  551 , the inclining surfaces  552   a, b  opposed to the inclining end surfaces  551   a, b  of the filter means  550  are formed on both the inner surface of the diffuser shell  501  and the inner surface of the closure shell  502 . More specifically, the diffuser shell  501  and the closure shell  502  are formed by press-molding using various metal plates as in Embodiment 2, and the inclining portions  553  are formed on the shell on the side of which the inclining surfaces of the filter means  550  are provided, i.e., the diffuser shell  501  and the closure shell  502  in this embodiment. In FIG. 24, the inclining portions  553   a, b  are formed between a circular portion  561  and a peripheral wall  562  in the diffuser shell  501 , and between an annular portion  565  and a peripheral wall  566  in the closure shell  502 . 
     Both the upper and lower end surfaces of the filter means  550  are formed into the inclining end surfaces  551 . The filter means  550  is disposed in the housing so that the upper end inclining end surface  551   a  is opposed to the inclining surface  552   a  of the inner surface of the diffuser shell  501 , and the lower end inclining end surface  551   b  is opposed to the inclining surface  552  of the closure shell. An expanding portion  556  of a lower portion of the filter means expanding in the radial direction is disposed so that the outer periphery of the expanding portion abuts against the inner surface of a peripheral wall  566  of the closure shell. 
     According to the gas generator of the present embodiment formed in this manner, when the transfer charge  518  is ignited and burnt by the actuation of the igniter  511 , the flame is ejected into the combustion chamber  505  from the through-hole  520  of the inner member  504 , thereby igniting and burning the gas generating agent  509 . The actuation gas generated by combustion of the gas generating agent  509  is purified and cooled while the gas passes through the filter means  550 , and the gas breaks the seal tape  522  and is discharged from the gas discharge port  510 . The filter means  550  is expanded radially due to passage of the actuation gas, and the inclining surfaces  551   a, b  provided on the upper and lower ends of the filter means  550  abut against the inclining surfaces  552   a, b  provided on the inner surfaces of both the shells, and it is possible to prevent the short pass of the actuation gas between the end surface of the filter means  550  and the inner surface of the housing  503 . 
     Especially in the gas generator shown in FIG. 24, the outer periphery of the expanding portion of the lower portion of the filter means  550  is in contact with the inner surface of the peripheral wall  566  of the housing. Therefore, when the filter means  550  is expanded due to passage of the actuation gas, a portion thereof comes into contact with the inner surface of the peripheral wall of the housing, and it is possible to suppress further deformation and control the expanding amount. With this arrangement, it is possible to stably secure the contact state between the filter means  550  and the inclining surface  552 . 
     In relation with the present embodiment, the gas generator in which the upper and lower inner surfaces of the housing are provided with inclining surfaces which incline so as to be narrowed in the radial direction can employ a structure shown in FIG.  25 . 
     In addition to the internal structure such as layout and the number of combustion chambers and the igniters, the gas generator shown in FIG. 25 is different from the one shown in FIG. 24 in that a diffuser shell  601  and a closure shell  602  are joined by friction welding, and filter means (FIG. 20) which is not provided at its lower portion with an expanding portion is used as filter means  650 . FIG. 26 is a schematic plan view of the gas generator for an air bag shown in FIG.  25 . 
     In the gas generator of this embodiment, the diffuser shell  601  having a gas discharge port  610  and the closure shell  602  having a flange portion  667  are joined to each other by friction welding, thereby forming a housing  603 . A cylindrical inner shell  625  whose upper opening is closed is disposed in the housing  603  eccentrically with respect to the center axis of the housing. The outside of the inner shell  625  is defined as a first combustion chamber  605   a , and the inside of the shell  625  is defined as a second combustion chamber  605   b . Electrical ignition type igniters  611  to be actuated by an electric signal and gas generating agents  609   a, b  which are to be ignited and burnt by actuation of the igniters are accommodated in the combustion chambers  605   a, b , respectively. Especially, as shown in FIG. 26, the igniter  611   a  in the first combustion chamber  605   a  is disposed inside of the inner cylindrical member  604  in which a flame-transferring hole  619  is provided eccentrically with respect to the peripheral wall. A transfer charge  618  which is to be ignited and burnt by the igniter  611   a  is disposed above the igniter  611   a . Although the transfer charge is not disposed in the second combustion chamber  605   b  in the drawing, it can be disposed if required. 
     The inner shell  625  defines the first combustion chamber  605   a  and the second combustion chamber  605   b , and a peripheral wall thereof provided with an opening portion  660 . The opening portion is closed by a seal tape  662  or the like. The seal tape  622  or the like for closing the opening portion  660  is formed so as to be burst, peeled, burnt or detached by combustion of the second gas generating agent  609   b  accommodated in the second combustion chamber  605   b . The opening portion  660  is formed so that it does not open by combustion of the gas generating agent  609   a  in the first combustion chamber  605   a.    
     In the gas generator shown in FIG. 25, the housing  603  is formed by joining the diffuser shell  601  and the closure shell  602  by the friction welding. The diffuser shell  601  is formed with an inclining portion  653   a  which is inclined so as to be narrowed toward the ceiling surface  661  from the peripheral wall  662 . The closure shell  602  is also formed with an inclining portion  653   b  which is inclined so as to be narrowed toward the bottom surface  665  from the peripheral wall  666 . The inner surfaces of the inclining portions  653   a, b  of both the shells are the inclining surfaces  652  which is opposed to inclining end surfaces  651  of the filter means  650 , and these inclining surface  652  functions as a supporting portion of the filter means  650 . In the drawing, the inclining portions  653   a, b  are formed by bending the shells, but it is also possible to form the inclining portions by curving the shells. 
     Filter means  350  as shown in FIG. 20 whose upper and lower ends are formed with inclining end surfaces  651  is disposed in the housing  603 . In the drawing, the filter means  350  is disposed so that its upper inclining end surface  351  is opposed to the inclining surface  652   a  of the diffuser shell, and its lower inclining end surface  351  is opposed to the inclining surface  652   b  of the closure shell  602 . 
     In this gas generator, when the first igniter  611   a  is actuated, the first transfer charge  618  is ignited and burnt. The flame of the transfer charge  618  is discharged in the direction shown with the arrow in FIG. 26 so that the flame surrounds the inner shell  625  from the flame-transferring hole  619  provided eccentrically with respect to the inner cylindrical member  604 . The flame discharged from the flame-transferring hole  619  ignites and burns the gas generating agent  609   a  in the first combustion chamber  605   a . The second igniter  611   b  is actuated simultaneously with or slightly later than the first igniter  611   a . The second gas generating agent  609   b  in the second combustion chamber  605   b  is ignited and burnt by the actuation of the igniter  611   b , thereby generating the actuation gas. The opening portion  620  provided in the peripheral wall of the inner shell  625  is opened due to the pressure of the actuation gas. With this opening, the actuation gas generated by combustion of the second gas generating agent  609   b  flows into the first combustion chamber  605   a.    
     The actuation gas generated by combustion of the first gas generating agent  609   a  and the second gas generating agent  609   b  is purified and cooled while the gas passes through the filter means  350 , and the gas breaks the seal tape  622  and is discharged from the gas discharge port  610 . In the gas generator shown in this drawing also, the filter means  350  expands radially outward by passage of the actuation gas, the inclining end surfaces  351  formed on the upper and lower end surfaces are pressed to the inclining surfaces  652   a, b  in the housing, i.e., the supporting portion, and it is possible to prevent the short pass of the actuation gas between the end surface of the filter means  350  and the inner surface of the housing  603 . 
     Embodiment of Self-contracting Type Filter  4   
     FIG. 27 is a vertical cross sectional view showing another embodiment of the gas generator using filter means of the present invention. The gas generator shown in this embodiment is longer in the axial direction than the inner diameter thereof. 
     In the gas generator shown in FIG. 27, a filter means accommodating container  702  (hereinafter referred to “a filter container”) in which filter means  750  is accommodated is connected to axially one end opening  730  of a cylindrical member  701 , thereby forming a housing  703 . The other end opening  731  is closed by an annular member  732  in which an ignition means container  704 . 
     In the housing, a gas generating agent  709  which is to burnt to generate the actuation gas is accommodated in the cylindrical member  701 . The interior space of the cylindrical member  701  functions as the combustion chamber  705  in which the gas generating agent burns. A circular porous plate  733  spreading in the diametrical direction is disposed on the end on the side of the filter container  702  in the combustion chamber  705 . The gas generating agent  709  in the combustion chamber  705  is supported by the porous plate  733 . 
     The igniting means container  704  fitted in the annular member  732  closes an end surface projecting into the combustion chamber  705 . An ignition means accommodating chamber  708  separated from the combustion chamber  705  is provided inside the end surface. The ignition means comprising an igniter  711  and a transfer charge  718  is accommodated in the ignition means accommodating chamber  708 . A plurality of flame-transferring holes  719  are formed in the peripheral wall of the ignition means container  704 , and the flame generated by actuation of the ignition means is ejected from the flame-transferring holes  719  into the combustion chamber  705 , thereby igniting and burning the gas generating agent  709 . 
     The filter container  702  is substantially cylindrical shape as a whole, and peripheral edges of axially opposite end surfaces thereof are formed with inclining portions  753  which is formed like the chamfering shape and inclined so as to be narrowed in the axial direction of the container. A through-hole  734  is formed in the end surface of the filter container  702  on the side of the housing, and the other end surface is provided with a stud bolt  735  for mounting the gas generator to the module. A plurality of gas discharge ports  710  are formed in the peripheral wall. The interior space of the filter container  702  is in communication with the combustion chamber  705  through the through-hole  734  formed in the end surface of the housing. In the drawing, the filter container  702  is formed by closing the opened end of the cup-like member comprising a peripheral wall surface  736 , an inclining portion  753  and a housing side end surface  737  by a lid member comprising an inclining portion  753  and an end surface  739  including the stud bolt  735 . 
     The filter means  350  of the present invention shown in FIG. 20., i.e., a filter means which is substantially cylindrical shape as a whole and the inclining end surfaces  351  which is inclined so as to be narrowed in the axial extending direction are formed on axially opposite end surfaces thereof is accommodated in the filter container  702 . The filter means  350  is disposed so that its inclining end surface  351  is opposed to the inner surface of the inclining portion  753  of the filter container  702 , i.e., the inclining surface  752 . A gap  741  having a predetermined width is secured between the outer peripheral surface of the filter means and the inner wall surface of the filter container  702 . 
     At the time of actuation of this gas generator, when the igniter  711  is actuated, the transfer charge  718  is ignited and burnt, and the flame thereof is ejected from the flame-transferring hole  719  of the ignition means container  704  into the combustion chamber  705 . The gas generating agent  709  is ignited and burnt by the flame of the transfer charge  718  ejected into the combustion chamber, thereby generating the actuation gas. The actuation gas flows into the filter container  702 , and is purified and cooled while the gas passes through the filter means  350 , and discharged from the gas discharge port  710 . With passage of the actuation gas through the filter means  350 , the filter-means  350  expands in the diametric direction, its inclining end surface  351  abuts against the supporting portion (i.e., the inclining surface  752 ) on the inner surface of the inclining portion  753  of the filter container  702 , and contracted in the axial direction. As a result, the filter means  350  is strongly pressed to the inner surface of the filter container  702 , and it is possible to prevent the short pass of the actuation gas passing between both the members. A gas generator having a plurality of igniters 
     Further, the present invention includes a gas generator for an air bag, comprising a housing with a plurality of gas discharge ports which forms an outer shell container and accommodates two or more ignition means to ignite on an impact and a gas generating means which are to be independently ignited and burnt by the ignition means so as to generate a combustion gas for inflating an air bag, wherein the gas discharge ports are closed by sealing means for maintaining an internal pressure of the housing to the given pressure, and by controlling the gas discharge ports and/or the sealing means, a breaking pressure for breaking the sealing means is adjusted at multiple stages and thereby a difference of the housing maximum internal pressures at the time when each ignition means is activated can be suppressed. 
     FIG. 32 is a vertical cross sectional view which shows a gas generator for an air bag according to the other embodiment of the present invention. The gas generator shown in this embodiment also has a structure being particularly suitable for being arranged in a driver side. 
     In particular, the gas generator shown in this embodiment is characterized by an arrangement of two combustion chambers provided in the housing and a forming method. 
     Also in the present embodiment, a gas discharge port  1210  formed in a diffuser shell  1201  has two kinds of gas discharge ports  1210   a  and  1210   b  having different diameters, and these are closed by a seal tape  1229  for protecting a gas generating agent  1252  from an influence of an environment such as a humidity outside the housing. By providing two kinds of gas discharge ports  1210   a  and  1210   b  having different inner diameters (and opening areas), a combustion internal pressure in the housing  1203  at an actuation can be equalized (stabilizing of a combustion performance). 
     That is, in the gas generator shown in this embodiment, in a cylindrical housing  1203  obtained by joining a diffuser shell  1201  having a plurality of gas discharge ports  1210  and a closure shell  1202  for forming an inner storing space together with the diffuser shell  1201  and applying a friction welding to these shells, a cylindrical inner shell  1204  in a capsule-like shape having a circle in the horizontal cross section and a closed upper end is arranged and fixed eccentrically with respect to the center axis of the housing, thereby forming a first combustion chamber  1250  is formed in an outer side thereof and forming a second combustion chamber  1260  in an inner side thereof. 
     A eccentric degree of the inner shell  1204  arranged in the housing  1203  with respect to the housing  1203  can be suitably changed according to a desired volume ratio of a combustion chamber and the like, and may be changed according to a structure inside the housing  1203 , for example, whether or not a coolant/filter  1225  exists. As an example, like the gas generator shown in this drawing, when the coolant/filter  1225  is arranged opposite to a peripheral wall surface of the housing  1203 , it is possible to suitably select the eccentric degree in a range between 10 and 75%. However, since this range can be changed due to a size of the igniters  1251  and  1261  and the like, the range is only a measure of eccentricity of the inner shell  1204  in the gas generator shown in FIG.  32 . 
     The inner shell  1204  may be formed in various kinds of shapes such as a rectangular shape, an oval shape and the like in a horizontal cross section, in order to join easily to the closure shell  1202 , etc., it is preferable to be formed in a circular shape. In other wards, the horizontal cross sectional shape of the inner shell  1204  has to be a circular shape when joining the inner shell  1204  and the closure shell  1202  by a friction welding, and also when joining by a laser welding, it is necessary to keep an emitting distance of the laser constant. 
     As mentioned above, in this embodiment, the first combustion chamber  1250  and the second combustion chamber  1260  are defined by the inner shell  1204 . That is, the first combustion chamber  1250  is provided on the outer side of the inner shell  1204 , and the second combustion chamber  1260  is provided on the inner side of the inner shell  1204 . A volume ratio between the first combustion chamber  1250  and the second combustion chamber  1260  (a volume of the first combustion chamber:a volume of the second combustion chamber) is set to 3.3:1 in the present embodiment, and it can also be suitably selected in a range of 97:1 to 1:1.1. However, also with respect to the volume ratio, the selected range can be suitably changed due to a size of the igniters ( 1251 ,  1261 ) and a shape of the gas generating agents ( 1252 ,  1262 ). Accordingly, the above range shows a range which can be selected in the structure of the gas generator shown in this drawing. 
     As mentioned above, the gas generating agents ( 1252 ,  1262 ) are respectively stored in the second combustion chamber  1260  and the first combustion chamber  1250  which are partitioned by the inner shell  1204 . The first gas generating agent  1252  is stored in the first combustion chamber  1250  and the second gas generating agent  1262  is stored in the second combustion chamber  1260 , respectively. In the present embodiment, the first gas generating agent  1252  and the second gas generating agent  1262  have the same shape or the like. The gas generating agents different from each other in at least one of a burning rate, a composition, a composition ratio and an amount can be stored in the respective combustion chambers. 
     The inner shell  1204  which defines the first combustion chamber  1250  and the second combustion chamber  1260  is arranged eccentrically with respect to the center axis of the housing  1203 , and the second combustion chamber  1260  provided inside the inner shell  1204  is eccentric with respect to the housing  1203 . The igniters are respectively arranged in the first combustion chamber  1250  and the second combustion chamber  1260 , the second igniter  1261  arranged in the second combustion chamber  1260  is disposed in the center of the second combustion chamber  1260  which is eccentric with respect to the center axis of the housing  1203 . Therefore, a flame generated by an activation of the igniter  1261  can uniformly burns the second gas generating agent  1262 . And the second igniter  1261  and the first igniter  1251  disposed in the first combustion chamber  1250  are both arranged eccentrically with respect to the center axis of the housing  1203 . As mentioned above, by arranging eccentrically the first and second igniters as well as the inner shell  1204  with respect to the center axis of the housing  1203 , a range of a difference in the volume ratio of the first and second combustion chambers can be made larger, and the size of the housing  1203  in a diametrical direction can be restricted as much as possible. 
     Among the igniters arranged in the respective combustion chambers, the igniter  1251  arranged in the first combustion chamber  1250  has a transfer charge  1208  arranged in a peripheral and upper directions thereof. For convenience at assembling the gas generator, or in order to prevent the transfer charge  1208  from being scattered in the first combustion chamber  1250  due to the impact and the vibration applied at mounting on the vehicle, and to prevent an ignition performance to the first gas generating agent  1252  form being slipped, the transfer charge  1208  is stored in a transfer charge container  1226 . The transfer charge container  1226  is easily broken due to the combustion of the transfer charge  1208  arranged therein and formed by an aluminum having a thickness (for example, about 200 μm) so as to transfer the flame to the periphery thereof. On the other hand, a transfer charge like the one arranged in the first combustion chamber  1250  is not necessarily required in the second combustion chamber  1260 . This is because the second gas generating agent  1262  is ignited more easily, than the first gas generating agent  1252 , and the pressure of the second combustion chamber is increasing in a sealed state until the breaking member  1207  for sealing a hole  1206  of the below-described inner shell  1204  is ruptured. The breaking member  1207  is not ruptured even when the internal pressure of the combustion chamber  1250  increases due to the combustion of the first gas generating agent  1252  but it is ruptured when the internal pressure of the second combustion chamber  1260  increases more than that of the first combustion chamber  1250 . However, the transfer charge can be used as required. 
     A cylindrical member  1236  is placed in the first combustion chamber  1250  so as to surround an outer side in the radial direction of the first igniter  1251  and the transfer charge  1208  disposed above the igniter. The cylindrical member  1236  is formed into a cylindrical shape open at both upper and lower ends, one end portion thereof is outwardly fitted to an outer periphery of a portion fixed with the igniter  1251  so that no gap is formed. And the other end portion is inserted to be supported by a retainer  1211  disposed near an inner surface of a ceiling portion of the diffuser shell  1201  so as to be fixed to a predetermined portion. A plurality of flame-transferring holes  1237  are formed on a peripheral wall of the cylindrical member  1236 , and the flame generated by the combustion of the transfer charge  1208  is injected from the flame-transferring hole  1237  so as to ignite and burn the first gas generating agent  1252  disposed in the outer side of the cylindrical member. It is preferable that the cylindrical member  1236  is made of the same material as that of the housing  1203 . 
     In particular, in the gas generator shown in this embodiment, the first combustion chamber  1250  is formed into an annular shape similar to a crescent shape obtained by stamping an inner side of a circle roundly, as shown in a perspective plan view in FIG. 33, and the first gas generating agent  1252  is placed therein. Accordingly, in the first combustion chamber  1250 , as is different from the second combustion chamber  1260 , a distance between the gas generating agent  1252  and the igniter  1251  is varied with a place for storing the gas generating agent  1252 . Therefore, at a time of ignition of the igniter  1251 , the ignition and the combustion of the first gas generating agent  1252  are performed unevenly. Then, the flame-transferring hole  1237  provided in a peripheral wall of the inner cylindrical member  1236  restricts a direction thereof so as to lead the flame of the transfer charge  1208  in a direction shown by an arrow in FIG.  33 . Accordingly, it is possible to burn the gas generating agent  1252  in a portion shaded by the second combustion chamber  1260  (i.e. the inner shell  1204 ) evenly. Further, in place of the inner cylindrical member  1236 , a injecting-direction restricting means (not shown) having holes formed in a direction shown by an arrow in FIG. 33 can be used. The injecting-direction restricting means restricts the direction of the injecting flame which is generated by the activation of the first ignition means (the igniter  1251  and the transfer charge  1208  in FIG. 32) for igniting the first gas generating agent  1252 , in order to effectively burn the first gas generating agent  1252 . As the injecting-direction restricting means, for example, a cup-like container having one end portion closed by a cylinder member and in which a nozzle for leading the flame of the ignition means in a desired direction (a direction shown by an arrow in FIG. 33) is provided on a peripheral wall portion. In this case, the injecting-direction restricting means is used in a state of being mounted (covered) around the first ignition means. Also in the case of using the above injecting-direction restricting means, it is preferable that the first ignition means arranged inside it comprises the igniter and the transfer charge which is to be ignited and burnt by the activation of the igniter. 
     The inner shell  1204  which defines the first combustion chamber  1250  and the second combustion chamber  1260  is formed into a capsule shape as mentioned above, and a plurality of opening portions  1205  are formed on a peripheral wall thereof. The opening portion  1205  is designed such as to be opened only by the combustion of the second gas generating agent  1262  stored in the second combustion chamber  1260  and is not opened by the combustion of the first gas generating agent  1252  stored in the first combustion chamber  1250 . In the present embodiment, the opening portion  1205  comprises a plurality of holes  1206  provided on the peripheral wall of the inner shell  1204  and the breaking member  1207  for closing the hole, and a stainless seal tape is used as the breaking member  1207 . The breaking member  1207  is designed such as to be broken, peeled, burnt or removed only by the combustion of the second gas generating agent  1262  so as to open the hole  1206  but not to be broken by the combustion of the first gas generating agent  1252 . 
     The above inner shell  1204  is fixed by connecting an open lower portion  1213  thereof to the closure shell  1202 . When the closure shell  1202  comprises the collar portion  1202   a  for fixing the igniter, the inner shell  1204  can be mounted to the collar portion  1202   a . In the gas generator shown in FIG. 32, the closure shell  1202  is formed such as to integrally joint a circular collar portion having a size capable of fixing two igniters on a bottom surface of the cylindrical shell portion  1202   b  jointed to the diffuser shell  1201 , and the inner shell  1204  is jointed to the collar portion  1202   a . The collar portion  1202   a  can be integrally formed on the bottom surface of the cylindrical shell portion  1202   b  in a circular shape capable of being fixed at each igniter, and can be integrally formed on the bottom surface of the cylindrical shell portion  1202   b . In such a case, the inner shell  1204  can be directly mounted on the bottom surface of the cylindrical shell portion  1202   b  in addition to the collar portion  1202   a  of the closure shell. 
     In the present embodiment, a joint of the inner shell  1204  and the closure shell  1202  can be performed by an convex-concave joint in addition to a friction welding, a cramping, a resistance welding and the like. In particular, in the case of joining the both by friction welding, preferably, it is performed in a state of fixing the closure shell  1202 . Accordingly, even when the axial cores of the inner shell  1204  and the closure shell  1202  are not aligned to each other, a friction welding can be performed stably. In other words, when friction welding is performed in a state of fixing the inner shell  1204  and rotating the closure shell  1202 , a center of gravity of the closure shell  1202  is shifted from a center of rotation and thereby a stable friction welding cannot be performed. Therefore, in the present invention, friction welding is performed in a state of fixing the closure shell  1202  and rotating the inner shell  1204 . Further, at friction welding, it is preferable that the closure shell  1202  is positioned and fixed so as to always mount the inner shell  1204  to a determined position. Accordingly, it is preferable that a positioning means is suitably provided in the closure shell  1202 . A gas generating agent fixing member  1214  is arranged in the inner shell  1204  in order to safely and smoothly perform a connection to the closure shell  1202 . The gas generating agent fixing member  1214  is used in order to prevent the gas generating agent  1262  from directly contacting with the inner shell  1204  at a time of friction welding the inner shell  1204  to the closure shell  1202  and to obtain a placing space for the igniter  1261  inside the space formed by the inner shell  1204 . When mounting the inner shell  1204  to the closure shell  1202 , in addition to the above friction welding, it is possible to mount by an convex-concave joint as well as a crimping, a resistance welding and the like. Also in this case, an assembly performance is improved by using the gas generating agent fixing member  1214 . The gas generating agent fixing member  1214  adopts here a canister made of aluminum and having a thickness which can be easily broken by the combustion of the gas generating agent  1262 , as one example, and further, a suitable member capable of achieving the object mentioned above (regardless a material, shape and the like) such as a porous member made of a wire mesh. Besides, when the above gas generating agent fixing member  1214  is not used, it is possible to form a lump of the gas generating agent obtained by forming a lump of the single-hole cylindrical gas generating agent  1262  into the same shape as the inner space of the inner shell  1204  and place it in the inner shell  1204 . In this case, the gas generating agent fixing member  1214  may be omitted. 
     In the present embodiment, the collar portion  1202   a  of the closure shell  1202  is formed in a size capable of fixing two igniters  1251  and  1261  horizontally. Accordingly, two igniters  1251  and  1261  are previously fixed to the collar portion  1202   a  by crimping, etc., and then, this collar portion  1202  is integrally formed with the cylindrical shell portion  1202   b  so as to form the closure shell  1202 , and thereby, two igniters  1251  and  1261  can be fixed to the closure shell  1202 . In the drawing, the first igniter  1251  and the second igniter  1261  are described in the same size, however, they may be structured such as to have a different output at each combustion chamber. Further, in this embodiment, a cable  1215  connected to each igniter  1251  and  1261  so as to transmit an activating signal is drawn out in the same direction. 
     A coolant/filter  1225  is arranged in the housing  1203  as filter means for purifying and cooling the combustion gas generated by the combustion of the gas generating agent. The gases generated by the combustion of the first and second gas generating agents both pass through the coolant/filter  1225 . In order to prevent a short pass, that is, to prevent the combustion gas from passing between an end surface of the coolant/filter  1225  and an inner surface of the ceiling portion of the diffuser shell  1201 , the upper and lower inner peripheral surfaces of the coolant/filter  1225  and the inner surface of the housing may be covered with a cylindrical short-pass preventing member having an inward flange. In particular, in the gas generator shown in FIG. 32, a self-contracting type coolant/filter  1225  tapers at both upper and lower ends outwardly in the radial direction. A gap  1228  which is a flow path for the combustion gas is formed on the outer side the coolant/filter  1225 . 
     For example, in the gas generator shown in FIG. 32, the igniter ( 1251 ,  1261 ) and the inner shell  1204  are arranged eccentrically with respect to the housing  1203 . In the above gas generator, when the diffuser shell  1201  and the closure shell  1202  are joined by friction welding, joining the both the shells can be performed stably by fixing the side of the closure shell  1202  at the time of friction welding. Particularly, when inner shell  1204  is directly mounted to the closure shell  1202  by friction welding, as shown in FIG. 32, it is preferable that a flange portion  1232  for mounting the gas generator to the module case is provided in the side of the closure shell  1202 , and a positioning portion is formed in a portion constituting the flange portion  1232 , for example, a protruding portion  1233  or the like by notching the peripheral edge thereof. In case of forming in this manner, since the closure shell  1202  is always fixed in a definite direction on the positioning portion, the inner shell  1204  can be securely mounted at a determined position. 
     In the gas generator formed in the above manner, when the first igniter  1251  arranged in the first combustion chamber  1250  provided on the outer side the inner shell  1204  is activated, the first gas generating agent  1252  in the combustion chamber  1250  is ignited and burnt so as to generate the combustion gas. And a little gap is obtained between the inner shell  1204  and the coolant/filter  1225  and this gap allows a gas flow between the coolant/filter  1225  and the inner shell  1204 , and thereby, the combustion gas can effectively use all the surface of the filter  1225 . The combustion gas is purified and cooled while passing through the coolant/filter  1225 , and thereafter is discharged from the gas discharge port  1210 . 
     On the other hand, when the second igniter  1261  arranged in the inner shell  1204  is activated, the second gas generating agent  1262  is ignited and burnt so as to generate the combustion gas. The combustion gas opens the opening portion  1205  of the inner shell  1204  and flows into the first combustion chamber  1250  from the opening portion  1205 . Thereafter, it passes through the coolant/filter  1225  as the combustion gas of the first gas generating agent  1252  does, and is discharged from the gas discharge port  1210 . The seal tape  1229  which closes the gas discharge port  1210  is ruptured by passage of the combustion gas generated in the housing  1203 . The second gas generating agent  1262  is ignited and burnt due to the activated second igniter  1261 , and is never directly burnt on the combustion of the first gas generating agent  1252 . This is because the opening portion  1205  of the inner shell  1204  is opened only by the combustion of the second gas generating agent  1262  but is not opened by the combustion of the first gas generating agent  1252 . 
     In the gas generator formed in the above manner, the ignition timings of two igniters is adjusted such as to activate the second igniter  1261  after activating the first igniter  1251 , or to simultaneously activate the first igniter  1251  and the second igniter  1261 , and thereby an output&#39;s forms (an operating performance) of the gas generator can be optionally adjusted so that, under various conditions such as a vehicle speed at a time of collision, an environmental temperature, inflation of the air bag can be made most suitable in the air bag apparatus mentioned below. Particularly, in the gas generator shown in FIG. 32, two combustion chambers are arranged in the radial direction, by whereby a height of the gas generator can be restricted as much as possible. 
     Also in the gas generator shown in this drawing, a plurality of gas discharge ports  1210  formed in the housing  1203  are structured such that the opening diameter and/or the opening area thereof are controlled in two or more kinds. Therefore, a difference of the housing maximum internal pressure at the time when each ignition means is activated is suppressed, the internal pressure at the time when the gas generator is actuated is equalized, which provides a gas generator for an air bag having a stable combustion performance. Further, also in the gas generator according to this embodiment, by setting the opening area of each gas discharge port  1210  constant but by changing the thickness of the sealing means  1229  such as a seal tape so as to adjust the breaking pressure, a difference of the housing maximum internal pressure at the time when each ignition means is activated can be suppressed. Further, it is naturally possible to control both of the opening diameter and/or the opening surface in the gas discharge port  410  and the thickness of the sealing means  1229 .