Gas generator for an airbag and air bag apparatus

0001The present invention relates to a gas generator for an air bag and an air bag apparatus according to the preamble of claims 1 and 15.

0002An 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.

0003It 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 <patcit id="pcit0001" dnum="JP8207696A"><text>JP-A 8-207696</text></patcit>, <patcit id="pcit0002" dnum="US4998751A"><text>US-A 4,998,751</text></patcit> and <patcit id="pcit0003" dnum="US4950458A"><text>4,950,458</text></patcit>. <patcit id="pcit0004" dnum="JP8207696A"><text>JP-A 8-207696</text></patcit> 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. <patcit id="pcit0005" dnum="US4998751A"><text>US-A 4,998,751</text></patcit> and <patcit id="pcit0006" dnum="US4950458A"><text>4,950,458</text></patcit> 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.

0004However, these gas generators have drawbacks such that an internal structure thereof is complicated, a size of a container becomes great, and a cost therefor becomes expensive.

0005Further, in <patcit id="pcit0007" dnum="JP9183359A"><text>JP-A 9-183359</text></patcit>, and <patcit id="pcit0008" dnum="DE19620758B"><text>DE-B 19620758</text></patcit>, 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, in any of the gas generators, since the igniters arranged in the respective combustion chambers are independently arranged, it becomes hard to assemble (manufacture), the structure itself of the gas generator becomes complicated and a volume thereof becomes large.

0006Furthermore, a gas generator according to the preamble of claim 1 is known from <patcit id="pcit0009" dnum="DE29801477U"><text>DE 298 01 477 U</text></patcit>.

0007It is the object of the present invention to provide a gas generator which actuates, applying as small an impact as possible to an occupant at the initial stage of an actuation and can widely and optionally adjust an output and timing of an output increase of the gas generator so as to 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, as well as restricting the total size of a container, having a simple structure and being easily manufactured.

0008The object is solved by a gas generator according to claim 1 and an air bag apparatus according to claim 15. Preferred embodiments are claimed by the subclaims.

0009It is possible to structure such that two combustion chambers concentrically provided so as to be adjacent to each other in the axial direction and/or the radial direction of the housing are formed as a cylindrical combustion chamber and an annular combustion chamber.

0010As mentioned above, by forming two combustion chambers in the housing, it is possible to make an inner structure of the gas generator simple and independently burn the gas generating agents in the respective combustion chambers.

0011The gas generating means mentioned above is provided to inflate the air bag for restraining the occupant by the combustion gas generated by the combustion thereof. Accordingly, when the ignition means includes a transfer charge which is to be ignited and burnt by the igniter so as to burn the gas generating means, the combustion gas generated by the combustion of the transfer charge is used for burning the gas generating means and is not directly used for inflating the air bag. In this respect, both can be definitely distinguished from each other. Further, two combustion chambers provided in the housing is exclusively used for storing the gas generating means In this respect, even when the ignition means is composed to include the transfer charge and the transfer charge is installed in a defined space (hereinafter, refer to as "a accommodating chamber"), this accommodating chamber of the transfer charge and the combustion chamber storing the gas generating means can be definitely distinguished from each other.

0012When the ignition means for igniting and burning the gas generating means includes two or more igniters to be actuated on an impact, it is preferable that, in order to make the mounting thereof easy, the igniters are provided in one initiator collar aligned to each other in the axial direction. Further, when the ignition means also includes the transfer charge which is to be ignited and burn in response to an activation of the igniters, it is preferable that the transfer charge is partitioned for each igniter, and independently ignited and burns by each igniter, and therefore is formed so that a flame of the transfer charge for one of the igniters does not directly ignite the transfer charge for any other igniters. As this type of structure, for example, it is possible to arrange the igniters in the respectively independent igniter accommodating chambers and then arrange the transfer charges in the igniter accommodating chambers, or to arrange the transfer charges in a place inside the independent combustion chambers where the transfer charges can be ignited and burnt in response to the activation of the igniter.

0013As mentioned above, in the case of dividing the transfer charge for each igniter, the gas generating means stored in two combustion chambers are ignited and burnt by the flame generated by burning the transfer charges arranged separately in the respective sections. That is, since the transfer charge in each section burns in response to the activation timing of the igniter, and the gas generating means in each combustion chamber can separately burn, an actuation performance of the gas generator can be optionally controlled.

0014Therefore, by adopting the structure of the gas generator according to the present invention, the transfer charge partitioned for each igniter can be independently burnt by changing the respective ignition timing of each igniter and accordingly, the ignition and combustion timing of the gas generating means in each combustion chamber can be staggered, therefore, the output of the gas generator can be optionally adjusted.

0015With respect to two combustion chambers provided in the housing, either of the combustion chambers may be provided in the axial direction of the igniter and the other combustion chamber may be provided in the radial direction of the ignition means. Further, in the case of characteristically adjusting the actuation performance of the gas generator, particularly a change with the passage of time in the gas discharge amount, two combustion chambers are charged with the gas generating means which are different in at least one of a burning rate, a composition, a composition ratio and an amount from each other, respectively, and the respective gas generating means can be independently ignited and burnt at an optional timing. Further, at each combustion chamber, the gas generating means having a different gas amount generated at a unit time may be stored.

0016As the gas generating means, in addition to an azide gas generating agent based on an inorganic azide which has been widely used, for example, a sodium azide, a non-azide gas generating agent not based on an inorganic azide may be used. However, from the view of safety, the non-azide gas generating agent is preferable, and as the non-azide gas generating composition, for example, a composition containing a nitrogen containing organic compound such as a tetrazole, a triazole or a metallic salt thereof and an oxygen containing oxidant such as an alkali metal nitrate, a composition using a triaminoguanidine nitrate, a carbohydroazide, a nitroguanidine and the like as a fuel and nitrogen source and using a nitrate, chlorate, a perchlorate or the like of an alkali metal or an alkaline earth metal as an oxidant, and the like may be employed. In addition, the gas generating means can be suitably selected according to requirements such as a burning rate, a non-toxicity, a combustion temperature, a decomposition starting temperature. In the case of using the gas generating means having different burning rates in the respective combustion chambers, may be used the gas generating means having the different composition or composition ratio itself, such that, for example, the inorganic azide such as the sodium azide or the non-azide such as the nitroguanidine is used as the fuel and the nitrogen source. Alternatively, the gas generating means obtained by changing a shape of the composition to a pellet shape, a wafer shape, a hollow cylindrical shape, a disc shape, a single hole body shape or a porous body shape, or the gas generating means obtained by changing a surface area according to a size of a formed body may be used. In particular, when the gas generating means is formed into the porous body with a plurality of through holes, an arrangement of the holes is not particularly limited, however, in order to stabilize a performance of the gas generator, an arrangement structure such that a distance between an outer end portion of the formed body and a center of the hole and a distance between each center of the holes are substantially equal to each other is preferable. Concretely, in the cylindrical body having a circular cross section, for example, 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, in the same manner, an arrangement such that eighteen holes are formed around one hole at the center may be also suggested. However, the number of the holes and the arrangement structure are determined in connection with an easiness for manufacturing the gas generating agent, a manufacture cost and a performance, and are not particularly limited.

0017Among two combustion chambers mentioned above, the combustion chamber provided outside in the radial direction may contain a coolant means for cooling the combustion gas generated due to combustion of the gas generating means on the side of a peripheral wall of the housing thereof. The coolant means is provided in the housing for the purpose of cooling and/or purifying the combustion gas generated due to the combustion of the gas generating means. For example, in addition to a filter for purifying the combustion gas and/or a coolant for cooling the generated combustion gas which have been conventionally used, a layered wire mesh filter obtained by forming a wire mesh made of a suitable material into an annular layered body and compress-molding, and the like can be used. The layered wire mesh coolant can be preferably obtained by forming a plain stitch stainless steel wire mesh in a cylindrical body, folding one end portion of the cylindrical body repeatedly and outwardly so as to form an annular layered body and then compress-molding the layered body in a die, or by forming a plain stitch stainless steel wire mesh in a cylindrical body, pressing the cylindrical body in the radial direction so as to form a plate body, rolling the plate body in a cylindrical shape at many times so as to form the layered body and then compress-molding it in the die. Further, the coolant with a double structure with different layered wire mesh bodies at an inner side and an outer side thereof, which has a function for protecting the coolant means in the inner side and a function for suppressing expansion of the coolant means in the outer side, may be used. In this case, it is possible to restrict the expansion by supporting an outer periphery of the coolant means with an outer layer such as the layered wire mesh body, the porous cylindrical body, the annular belt body.

0018And in the case of the gas generator in which the combustion gas generated due to the combustion of the gas generating means stored in two combustion chamber reaches the gas discharge port via a different flow paths in each combustion chamber so that the gas generating means stored in one combustion chamber is not directly ignited due to the combustion gas generated in the other combustion chambers, the gas generating means in the combustion chambers burns in each chamber in a completely independent manner, and therefore, the gas generating means in each combustion chamber is ignited and burnt in more secure manner. As a result, even when activation timings of two igniters are staggered significantly, the flame of the gas generating means in the first combustion chamber ignited by the firstly actuated igniter does not burn the gas generating means in the other combustion chambers, so that a stable output can be obtained. This kind of gas generator can be achieved, for example, by arranging a flow passage forming member in the housing so as to form the flow passage and introducing the combustion gas generated in the first combustion chamber to the coolant means directly.

0019The housing mentioned above can be obtained by forming a diffuser shell having a gas discharge port or gas discharge ports and a closure shell, which forms a storing space together with the diffuser shell, with a casting, a forging, a press-molding or the like, and joining both shells. The joining of both shells can be performed by various kinds of welding methods, for example, an electronic beam welding, a laser welding, a TIG arc welding, a projection welding, or the like. Forming the diffuser shell and the closure shell by press-molding various kinds of steel plates such as the stainless steel plate makes manufacture easy and reduces a manufacturing cost. Further, forming both shells into a simple shape as cylindrical shape makes the press-molding of the shells easy. With respect to the material of the diffuser shell and the closure shell, the stainless steel is preferable, and the material obtained by applying a nickel plating to the steel plate may be also acceptable.

0020In the housing mentioned above, the ignition means to be actuated by detecting the impact and ignite and burn the gas generating means is further installed. In the gas generator according to present invention, as the ignition means, an electric ignition type ignition means to be activated by an electric signal (or an activating signal) transmitted from an impact sensor or the like which detects the impact is used. The electric ignition type ignition means comprises an igniter to be activated by the electric signal transmitted from the electric sensor which exclusively detects the impact by means of an electric mechanism such as a semiconductor type acceleration sensor or the like, and a transfer charge to be ignited and burnt by the activation of the igniter as required.

0021The gas generator for the air bag mentioned above is accommodated in a module case together with the air bag (the bag body) to introduce the gas generated in the gas generator and inflate, so as to form the air bag apparatus. In this air bag apparatus, the gas generator is actuated when reacting on the impact detected by the impact sensor, and the combustion gas is discharged from the gas discharge port in the housing. The combustion gas is flowed into the air bag, by whereby the air bag breaks the module cover to inflate, and forms a cushion for absorbing the impact between the hard member in the vehicle and the occupant.

0022The other aspects of the present invention will be described below. The parts and the combination mentioned above can be utilized in the respective aspects. Only features of the respective aspects will be described below.

0023Next, a description will be given below of a gas generator including two or more combustion chambers.

0024There is provided a gas generator for an air bag which can burn the gas generating means in each combustion chamber at a different timing and/or power, in addition to igniting and burning the gas generating means stored in each combustion chamber at a different timing.

0025Namely, according to the present invention, a gas generator for an air bag which installs, in a housing with a gas discharge port, an ignition means to be activated on an impact, and gas generating means to be ignited and burnt by the ignition means and generate combustion gas for inflating an air bag, is characterized in that in the housing, two or more combustion chambers for storing the gas generating means are defined, the gas generating means stored in each combustion chamber is independently ignited and burnt by the ignition means provided at each combustion chamber, and the gas generating mean stored in each combustion chamber is different from the ones in the other chambers in at least one of a burning rate, a shape, a composition, a composition ratio and an amount.

0026The combustion chambers provided in the housing, for example, in the case of two chambers, can be arranged such that they are concentrically provided so as to be adjacent to each other in the radial direction of the housing and a communication hole which allows communication between the combustion chambers is provided.

0027As mentioned above, the gas generating means which is different from the ones in the other chambers in at least one of the burning rate, the shape, the composition, the composition ratio and the amount are stored in a plurality of combustion chambers defined in the housing, and therefore the actuation performance of the gas generator, in particular, the change in the volume of the discharged gas with the passage of time can be characteristically adjusted by independently igniting and burning the gas generating means at an optional timing. The combustion chambers are charged by the gas generating means to provide different gas amounts generated at a unit time from each other, respectively. That is, in the case of the gas generator for the air bag using the same kind of gas generating means for the respective combustion chambers, the actuation performance thereof is definitely determined according to the actuation timing of the ignition means provided in each combustion chamber. However, when the combustion chambers are charged with the gas generating means to provide the different combustion characteristics (for example, the burning rate, the shape, the composition, the composition ratio and the amount)from each other, respectively, according to the present invention, the actuation performance of the gas generator can be adjusted freely even though the actuation timings of the ignition means are the same. Accordingly, when adjusting the actuation timing of the igniter as well as the gas generating means stored in each combustion chamber, it is possible to adjust widely and finely the actuation performance of the gas generator. In particular, in case of changing the shape of the gas generating means at each combustion chamber, it can be performed by changing a thickness or a surface area of the gas generating agent, and in the case of change the amount of the gas generating means at each combustion chambers, the weight of the gas generating means stored in each chamber can be differed form the others.

0028In the gas generator mentioned above, in the case that a plurality of combustion chambers are defined in the housing and charged with the gas generating means to provide different burning rates from each other in the respective combustion chambers, with respect to a burning rate (Vs) of the gas generating means with a small burning rate stored in any combustion chamber, a value (Vl/Vs) of a burning rate (Vl) of the gas generating means with a large burning rate stored in another combustion chamber can be adjusted to a range between larger than 1 and smaller than 14. For example, in the case of partitioning the housing into two chambers (that is, first and second combustion chambers) and respectively arranging a first gas generating means and a second gas generating means in the first combustion chamber and the second combustion chamber, it is possible to adjust a burning rate of the first gas generating means to a burning rate of the second gas generating means (mm/sec) in a range between 3:40 and 40:3.

0029Further, when a plurality of combustion chambers are charged with the gas generating means to provide different shapes from each other, respectively, the gas generating means stored in one combustion chamber and the gas generating means stored in another combustion chamber can be different from each other in thickness and/or surface area thereof. For example, if the gas generating means having the different thickness for each combustion chamber are used, with respect to a thickness (Ts) of the gas generating means with a small thickness stored in one combustion chamber, a value (Tl/Ts) of a thickness (Tl) of the gas generating means with a large thickness stored in another combustion chamber is adjusted in a range between larger than 1 and not larger than 100. More concretely, in the case of defining first and second combustion chambers in the housing and respectively arranging the first gas generating means and the second gas generating means in the first combustion chamber and the second combustion chamber, a thickness of the first gas generating means to a thickness of the second gas generating means (mm) is adjusted to a range between 0.1:10 and 10:0.1. In the porous cylindrical gas generating means, the thickness of the gas generating means can be measured by a method shown in an embodiment mentioned below.

0030When a plurality of combustion chambers are charged with the gas generating means to provide different surface areas per a unit weight from each other respectively, with respect to a surface area (Ss) of the gas generating means with a small surface area stored in one combustion chamber, a value (Sl/Ss) of a surface area (Sl) of the gas generating means with a large surface area stored in another combustion chamber can be suitably selected in a range between larger than 1 and smaller than 50.

0031As mentioned above, in the gas generator storing the gas generating means being different in the shape and/or the amount in each of a plurality of combustion chambers, a ratio (TS1:TS2) of a total surface area (TS1) of the gas generating means stored in one combustion chamber to a total surface area (TS2) of the gas generating means stored in another combustion chamber can be adjusted in a range between 1:50 and 50:1 in the case of a gas generator which is shorter in the axial direction than in the radial direction (for example, a gas generator for a driver side), and can be adjusted to a range between 1:300 and 300 : 1 in the case of a gas generator which is longer in the axial direction than the radial direction (for example, a gas generator for passenger sides).

0032when changing an amount of the gas generating means at each combustion chamber, a ratio (TW1:TW2) of a total weight (g) (TW1) of the gas generating means stored in one combustion chamber to a total weight (g) (TW2) of the gas generating means stored in another combustion chamber can be adjusted in a range between 1:50 and 50:1 with a gas generator which is shorter in the axial direction than in the radial direction (for example, a gas generator for a driver side), and can be adjusted to a range between 1:300 and 300:1 with a gas generator which is longer in the axial direction rather than the radial direction (for example, a gas generator for passenger sides).

0033In the gas generating means formed in the porous body, when using different one at each combustion chamber, it is possible to store gas generating means formed in a porous cylindrical shape (for example, a seven-hole cylindrical body) in one combustion chamber and store gas generating means formed in a single-hole cylindrical shape in another combustion chamber.

0034In the gas generating generator having the gas generating means stored in a plurality of combustion chambers, one of which is never ignited directly by combustion gas generated in the other combustion chambers, the gas generating means in each combustion chamber can be completely independently burnt at each combustion chamber. Accordingly, in this case, it is possible to independently ignite and burn the gas generating means stored in each combustion chamber in a more secure manner. As a result, even in the case of significantly staggering the activation timings of the ignition means provided in the respective combustion chambers, the flame of the gas generating means in one combustion chamber ignited by the firstly actuated ignition means does not burn the gas generating means in the rest of the combustion chambers, therefore, a stable operating output can be obtained.

0035And the present invention also provides a gas generator for an air bag comprising, in the housing with the gas discharge port, the ignition means to be activated on an impact and the gas generating means to be ignited and burnt by the ignition means and generate a combustion gas for inflating the air bag, wherein, in the housing, the combustion chambers for storing the gas generating means are defined by partitioning into two or more chambers, and the gas generating means stored in each chamber is ignited and burnt independently by the igniter provided in each chamber and then generates a different amount of a gas per a unit time from each other in each chambers.

0036As mentioned above, when a plurality of combustion chambers are provided in the housing and charged with the different gas generating means form each other, respectively, the gas generating means stored in each combustion chamber is independently ignited and burnt by the different ignition means at the same time or at intervals. And by controlling an opening diameter (an opening area) of the gas discharge port and/or the thickness of the seal tape for closing the gas discharge port, the pressure (hereinafter, refer to as "a combustion internal pressure") in the housing at the time when the gas generating means burns can be unified and the combustion performance can be stabilized. In this gas generator, each of two or more combustion chambers is charged with the gas generating means to provide different amounts of the generated gas at a unit time from each other respectively. The adjustment of the breaking pressure mentioned above can be performed by arranging two or more kinds of the opening diameters and/or the opening areas of the gas discharge ports. Accordingly, with respect to two kinds of openings being next to each other in respect to diameters thereof among two or more kinds of gas discharge ports formed in the housing, it is preferable that a ratio between the large diameter gas discharge port and the small diameter gas discharge port is 4/1 to 1.1/1, and an opening area ratio is 97/3 to 3/97. Further, the adjustment of the breaking pressure is performed by arranging two or more kinds of the thickness of the sealing means. Accordingly, with respect to two kinds of the sealing means being next to each other in respect to thickness thereof, among two or more kinds of the sealing means, it is preferable that a ratio between them is 1.1/1 and 12/1.

0037Further, in the gas generator, according to the present invention, where a plurality of the combustion chambers are charged with the different gas generating means from each other, respectively, the opening diameter and/or the opening area of the gas discharge port may be arranged to have two kinds or more and the thickness of the sealing means may be arranged to have two kinds of more. Further, it is preferable that the sealing means is a seal tape comprising a seal layer having a thickness of 20 to 200 µm and a bonding layer or an adhesive layer having a thickness of 5 to 100 µm. In the present invention, the thickness of the seal tape means a thickness comprising the seal layer and the bonding layer or the adhesive layer. In the sealing means such as the seal tape, the breaking pressure is adjusted by a size of the gas discharge port and/or a thickness thereof, but the maximum internal pressure in the housing at the time of combustion of the gas generating means (hereinafter, refer to as "a combustion maximum internal pressure") and the combustion performance of the gas generating means are not adjusted.

0038Next, a description will be given of a gas generator including two igniters.

0039According to the present invention, as one solution, there is provided a gas generator for an air bag having, in the housing with the gas discharge port, the ignition means to be actuated on an impact, and the gas generating means which is to be ignited and burnt by the ignition means and generate a combustion gas for inflating the air bag, wherein the ignition means includes two or more igniters to be activated on an impact and the igniters are provided so as to be aligned to each other in the axial direction. Namely, the present invention provides a gas generator for an air bag comprising, in the housing with the gas discharge port, the ignition means to be activated on an impact, and the gas generating means to be ignited and burnt by the ignition means and generate a combustion gas for inflating the air bag, wherein the ignition means has two igniters to be activated on an impact and the igniters are provided integrally by resin.

0040Further, according to the present invention, there can be provided a gas generator for an air bag, wherein two or more igniters contained in the ignition means of the gas generator for the air bag mentioned above are installed being fitted in one initiator collar so as to be aligned to each other in the axial direction.

0041Still further, in a preferred embodyment, there can be provided a gas generator for an air bag, wherein two or more igniters contained in the ignition means of the gas generator for the air bag mentioned above are structured such that the igniters are integrated by a resin so as to be aligned to each other in the axial direction.

0042As mentioned above, in the air bag gas generator according to the present invention, since two or more igniters are provided so as to be aligned to each other in the axial direction, it is possible to draw out a lead wire for connection on the same plane in the same direction at a time of connecting the igniter to a control unit for the air bag apparatus.

0043Further, when two or more igniters are fitted into one initiator collar and/or are integrated by a resin, a mounting operation to assemble the gas generator becomes easy.

0044Further, when two or more igniters are integrated by a resin in one initiator collar, it is unnecessary to previously coincide an inner shape of the initiator collar with the outer shape of the igniter, and it is sufficient that an inner space of the initiator collar is at least larger than a size of the igniter. Further, when the igniters are integrated by the resin, a fixing member for the igniter is not required without regard to any mode of the gas generator.

0045In the gas generator according to the present invention, as the ignition means, an electric ignition type ignition means may be provided to be activated by an electric signal (or an activating signal) transmitted from an impact sensor or the like detecting an impact. The electric ignition type ignition means comprises an igniter to be activated on the basis of the electric signal transmitted from the electric type sensor which detects the impact exclusively by means of the electric mechanism such as a semiconductor type acceleration sensor , and a transfer charge to be ignited and burnt on activation of the igniter.

0046In the gas generator for the air bag according to the present invention, the elements other than the above solutions are not particularly limited, the same elements as those of the known gas generator for the air bag can be adopted, and any modification generally performed by those skilled in the art to the elements will be included.

0047Accordingly, the gas generator for the air bag according to the present invention can be structured such as to comprise two or more ignition means and two or more gas generating means (two or more combustion chambers and gas generating agents) which are independently ignited and burnt by the respective ignition means so as to generate a combustion gas for inflating the air bag.

0048Further, according to a preferred embodyment of the present invention, in the above gas generator for the air bag, there can be provided a gas generator for an air bag, wherein one of the two combustion chambers is provided outside the inner cylindrical member disposed in the housing, an inner space of the inner cylindrical member is defined into the other combustion chamber and an ignition means accommodating chamber in which the ignition means including the igniters is stored, by a partitioned circular member and a seal cup member engaged with the partitioned circular member. Further, there can be provided a gas generator for an air bag, wherein the partitioned circular member is engaged with a stepped notch portion provided on an inner peripheral surface of the inner cylindrical member. Still further, there can be provided a gas generator for an air bag, wherein a peripheral edge of the seal cup member is bent, and the bent portion of the peripheral edge is fitted into a groove provided on the inner peripheral surface of the inner cylindrical member.

0049Further, according to a preferred embodyment of the present invention, in the above gas generator for the air bag, there can be provided a gas generator for an air bag, wherein the igniter contained in the ignition means is supported by the igniter fixing member which covers the upper surface of the initiator collar and fixed to the initiator collar, the seal cup member has an igniter receiving port extending to the igniter fixing member, an O-ring is arranged in a space constituted by the igniter fixing member, the igniter receiving port and the igniter, and the O-ring seals between the igniter fixing member and the igniter receiving port, between the igniter fixing member and the igniter, and between the igniter receiving port and the igniter.

0050Further, according to a preferred embodyment of the present invention, in the above gas generator for the air bag, there can be provided a gas generator for an air bag, wherein an O-ring is interposed between the bent portion of the peripheral edge in the seal cup portion and the inner wall surface of the inner cylindrical member to which the bent portion is fitted.

0051As mentioned above, by using the seal cup member having a specific structure, it is unnecessary to interpose the O-ring in the fitting portion of the seal cup and the inner cylindrical member, and therefore, the diameter of the gas generator can be smaller. Further, since it is possible to maintain the ignition means in an airtight manner, a combustion of the transfer charge is uniformly performed in response to the activation of the igniter, and the internal pressure is increased by the combustion of the transfer charge, thereby expanding in the radial direction to press the inner wall surface of the inner cylindrical member to which the bent portion of the seal cup member is fitted, so that an airtightness is further improved and a combustion of the transfer charge can be also uniformly performed.

0052Further, as mentioned above, by commonly using the igniter fixing member and the seal cup member together with the O-ring, it is possible to completely separate two or more igniters form each other.

Brief Description of the Drawing

0053<ul id="ul0001" list-style="none" compact="compact"><li><figref idref="f0001">Fig. 1</figref> is a vertical cross sectional view which shows an embodiment of a gas generator which does not form part of the present invention;</li><li><figref idref="f0002">Fig. 2</figref> is a back view of a gas generator according to the present embodiment;</li><li><figref idref="f0002">Fig. 3</figref> is a partly enlarged view of a gas generator according to the present embodiment;</li><li><figref idref="f0003">Fig. 4</figref> is a vertical cross sectional view which shows another embodiment of a gas generator for an air bag according to the present invention;</li><li><figref idref="f0003">Fig. 5</figref> is a graph which shows an operating output of a gas generator for an air bag according to the present invention.</li></ul>

0054Reference numerals in the drawings will be described below. <dl id="dl0001" compact="compact"><dt>3</dt><dd>Housing</dd><dt>5a</dt><dd>First combustion chamber</dd><dt>5b</dt><dd>Second combustion chamber</dd><dt>7</dt><dd>Partition wall</dd><dt>9a</dt><dd>First gas generating agent</dd><dt>9b</dt><dd>Second gas generating agent</dd><dt>12a</dt><dd>First igniter</dd><dt>12b</dt><dd>Second igniter</dd><dt>13</dt><dd>Initiator collar</dd><dt>22</dt><dd>Coolant/filter</dd><dt>40</dt><dd>Resin</dd></dl>

0055At first an embodyment will be discribed which does not form part of the invention but is helpful for understanding the invention.

0056<figref idref="f0001">Fig. 1</figref> is a vertical coss sectional view of an embodiment of a gas generator for an air bag, which shows a structure particularly suitable for being arranged in a driver side.

0057The gas generator comprises a housing 3 which is formed by joining a diffuser shell 1 with gas discharge ports and a closure shell 2 forming a inner accommodating space with the diffuser shell, and an inner cylindrical member 4 formed in a substantially cylindrical shape arranged in the housing 3, thereby forming a first combustion chamber by an outer side of the inner cylindrical member 4. Further, a stepped notch portion 6 is provided inside the inner cylindrical member, a partition wall 7 formed in a substantially flat circular shape is arranged in the stepped notch portion, the partition wall further partitions an inner portion of the inner cylinder into two chambers so as to form a second combustion chamber 5b in the diffuser shell side (in the upper space side) and an ignition means accommodating chamber 8 in the closure shell side (in the lower space side), respectively. As a result, in this gas generator, the first combustion chamber 5a and the second combustion chamber 5b are concentrically provided in the housing 3 and arranged in adjacent to each other in the radial direction of the housing. Gas generating agents (9a, 9b) which is to be burnt by ignition means activated on an impact so as to generate combustion gas are stored in the first and second combustion chambers, and the ignition means to be actuated on an impact is stored in the ignition means accommodating chamber 8. A through hole 10 is provided in the inner cylindrical member 4 which defines the first combustion chamber 5a and the second combustion chamber 5b, and the through hole is closed by a seal tape 11. And, the seal tape 11 is ruptured when the gas generating agent is burnt, both combustion chambers can be communicated with each other by the through hole 10. This seal tape 11 needs to be adjusted on its material and a thickness so that the seal tape is not broken due to the combustion of the gas generating agent 9a in the first combustion chamber 5a but is broken when the gas generating agent 9b in the second combustion chamber 5b is burnt. In the present embodiment, a stainless seal tape having a thickness of 40 µm is used. Further, the through hole 10 does not function to control an internal pressure in the combustion chamber 5b since an opening area thereof is formed larger than a gas discharge port 26b.

0058The ignition means comprises two electric ignition type igniters 12a and 12b to be activated by an activating signal outputted on a basis of detection by the sensor, and the igniters are provided in parallel to each other in one initiator collar 13 so as to exposing head portions thereof. As mentioned above, two igniters are fixed to the initiator collar 13 so as to form a single member by providing two igniters 12a and 12b in one initiator collar 13, thereby facilitating an assembly to the gas generator. In particular, in the gas generator illustrated in this drawing, since the initiator collar 13 is formed in a size capable of being inserted into the inner cylindrical member 4, the igniters are easily and securely fixed by crimpig the lower end of the inner cylindrical member 4 so as to fix the initiator collar after inserting the initiator collar 13 provided with two igniters 12a and 12b into the inner cylinder 4. Further, when arranging two igniters (12a, 12b) in the initiator collar 13, a direction of each igniter can be easily controlled. As illustrated, two igniters are arranged eccentrically with respect to the center axis of the housing. In case of arranging so as to align the direction of the igniters 12a and 12b, as shown in a back view of the gas generator according to the present embodiment in <figref idref="f0002">Fig. 2</figref>, a lead wire 50 connecting the igniters (12a and 12b) to a control unit (not shown) can be drawn out in the same direction on the same plane. In <figref idref="f0002">Fig. 2</figref>, the lead wire 50 is connected to each igniter (12a, 12b) via a connector 50a and the connectors are provided in parallel on the same plane. By forming the connector in L-letter, the lead wire for transmitting an electric signal (an activating signal) to the igniter in a direction perpendicular in the axial direction of the housing (that is, in the radial direction of the housing), and at that time, the lead wire connected to each igniter is drawn out in the same direction.

0059In this embodiment, a substantially cylindrical separating cylinder 14 is arranged in a space between the initiator collar 13 and the partition wall 7 so as to surround one igniter 12b (hereinafter, refer to as "a second igniter"), a first transfer charge accommodating chamber 15a defined in the outer side of thereof and a second transfer charge accommodating chamber 15b are defined in the inner side thereof respectively, and the igniter and the transfer charge constituting the ignition means together with the igniters are stored in each accommodating chambers. As a result, transfer charges (16a, 16b) constituting the ignition means together with the igniters are securely partitioned into the respective igniters (12a, 12b), when the transfer charge 16a in the first transfer charge accommodating chamber 15a is burnt, the seal tape closing the flame-transferring hole 17 provided on the cylindrical member 4 is ruptured, by whereby the first transfer charge accommodating chamber 15a communicates the first combustion chamber 5a. And when the transfer charge 16b in the second transfer charge accommodating chamber 15b is burnt, the seal tape closing the flame-transferring hole 19 provided on the partition wall 7 is ruptured, by whereby the second transfer charge accommodating chamber 15b communicates the second combustion chamber 5b. Accordingly, in this gas generator, at activation, a flame - generated, when the first igniter 12a is ignited (activated), ignites and burns the transfer charge 16a in the accommodating chamber 15a and then, the flame thereof passes through the flame-transferring hole 17 formed in the inner cylindrical member 4 and ignites and burns a gas generating agent 9a with seven holes stored in the first combustion chamber 5a positioned in the radial direction of the chamber 15a. And the second igniter 12b ignites and burns the second transfer charge 16b stored in the accommodating chamber 15b and the flame thereof passes through the flame-transferring hole 19 provided in the axial direction of the accommodating chamber 15b and ignites and burns a gas generating agent 9b with a single hole stored in the second combustion chamber 5b disposed on an extension thereof. The combustion gas generated in the seconde combustion chamber 9b passes through the through hole 10 provided in the diffuser shell side 1 of the inner cylindrical member 4 and flows into the first combustion chamber 5a.

0060Particularly, in the gas generator shown - in <figref idref="f0001">Fig. 1</figref>, in order to stabilize an actuation performance, there is a case that the second igniter 12b and the first igniter 12a are simultaneously ignited, however, the former 12b is not activated prior to the latter 12a. That is, the gas generating agent 9b stored in the second combustion chamber 5b is burnt at the same time or at a delayed timing of the combustion of the gas generating agent 9a stored in the first combustion chamber 5a. When the gas generating agent 9a of the first combustion chamber 5a is burnt prior to the second gas generating agent 9b, as mentioned above, the seal tape 11 is not ruptured by the combustion of the first gas generating agent 9a but is ruptured only by the combustion of the second gas generating agent 9b. Further, in the gas generator shown in this drawing, the separating cylinder 14 arranged between the initiator collar and the partition wall is, as shown in a main portion enlarged view in <figref idref="f0002">Fig. 3</figref>, arranged so that a hole portions 21 corresponding to an outer shape of the separating cylinder 14 are provided on the lower surface of the partition wall 7 and the upper surface of the initiator collar 13, and the upper end and the lower end of the separating cylinder 14 are fitted into the respective hole portions. By arranging the separating cylinder 14 in this manner, a flame of the transfer charge generated in one of the transfer charge combustion chambers does not directly burn the transfer charge in the other transfer charge accommodating chamber, and the gas generating agents stored in two combustion chambers are respectively ignited and burnt by the flame generated by the combustion of the transfer charges in the different sections. Namely, in general, when the transfer charge burns in the separating cylinder 14 (that is, in the second transfer charge accommodating chamber), a pressure of the gas generated by the combustion serves so as to expand the separating cylinder in the radial direction, however, by arranging the separating cylinder as shown in <figref idref="f0002">Fig. 3</figref>, the upper and lower end portions of the separating cylinder are securely supported to peripheral walls of the _- hole portions where the respective portions are fitted, so that, in comparison with the case of simply interposing the separating cylinder between the partition wall and the initiator collar, leaking of the combustion gas and the flame of the transfer charge can be prevented securely.

0061Further, a common coolant/filter 22 for purifying and cooling the combustion gas generated by the combustion of the gas generating agents (9a, 9b) is disposed in the housing 3, an inner peripheral surface in the diffuser shell 1 side thereof is covered with a short pass preventing member 23 so that the combustion gas does not pass between an end surface of the coolant/filter 22 and a ceiling portion inner surface 28 of the diffuser shell 1. An outer layer 24 for preventing the filter 22 from expanding outwardly due to passing of the combustion gas or the like is arranged on the outer side the coolant/filter 22. The outer layer 24 is, for example, formed by using a layered wire mesh body, and in addition, may be formed by using a porous cylindrical member having a plurality of through holes on a peripheral wall surface or a belt-like suppressing layer obtained by forming a belt-like member with a predetermined width into an annular shape. A gap 25 is further formed on the outer side of the outer layer 24 so that the combustion gas can pass through the entire surface of the filter 22. A gas discharge port 26 formed in the diffuser shell is closed by a seal tape 27 so as to stop entering an ambient air. The seal tape 27 is ruptured at a time of discharging the gas The seal tape 27 aims to protect the gas generating agent from a moisture in the outer portion, and does not have any influence on controlling the performances such as the combustion internal pressure.

0062In the gas generator constituted in the above manner, when the first igniter 12a disposed in the ignition means accommodating chamber 8 and in the outer side the separating cylinder 14 is activated, the transfer charge 16a stored in the first transfer charge accommodating chamber 15a is ignited and burnt, and the flame thereof passes through the flame-transferring hole 17 in the inner cylindrical member 4 and burns the porous cylindrical first gas generating agent 9a with seven holes and stored in the first combustion chamber 5a. And when the second igniter 12b surrounded by the separating cylinder 14 is activated at the same time or at a delayed timing of the activation of the first igniter 12a, the transfer charge 16b stored in the second transfer charge accommodating chamber 15b is ignited and burnt, and the flame thereof ignites and burns the single-hole cylindrical second gas generating agent 9b stored in the second combustion chamber 5b. As a result, the ignition timings of two igniters 12a and 12b are adjusted. That is, an output's forms (an actuation performance) of the gas generator can be optionally adjusted by activating the second igniter after the activation of the first igniter or simultaneously activating the first igniter and the second igniter. And therefore, under various kinds of circumstances such as a speed of a vehicle and an environmental temperature at a time of collision, it is possible to make a inflation of the air bag in the air bag apparatus mentioned below most suitable. Particularly, in the gas generator shown in this drawing, the respective combustion chambers (5a. 5b) adopt the gas generating agents (9a, 9b) to provide different shapes from each other, respectively, and the porous cylindrical first gas generating agent 9a and the single-hole cylindrical second gas generating agent 9b are respectively stored in the first combustion chamber 5a and the second combustion chamber 5b. Further, the amount of the gas venerating agent stored in each combustion chamber (5a, 5b) is different, and the gas generating agents (9a, 9b) at an amount of 35 g and 6 g are stored respectively in the first combustion chamber 5a and the second combustion chamber 5b. Consequently, in this gas generator, the output's forms can be adjusted more precisely. Naturally, a shape, a composition, a composition ratio, an amount, etc. of the gas generating agent may be changed to obtain the desired output's forms.

0063The actuation performance of the gas generator mentioned above can be al so confirmed, for example, according to a tank combustion test mentioned below.

<Tank combustion test>

0064A gas generator for the air bag is fixed in a SUS (stainless steel) tank with an inner volume of 60 liter and is connected to an outer ignition electric circuit after sealing the tank at a room temperature. With setting a time when an ignition electric circuit switch is turned on (an ignition electric current is applied) to 0, a pressure increase change inside the tank is measured by a pressure transducer independently placed in the tank for a time between 0 and 200 milliseconds. Each of the measured data is finally set to a tank pressure/time curve by a computer process, and a curve estimating a performance of a gas generating molded article (hereinafter, refer to as "a tank curve") is obtained. After finishing the combustion, the gas in the tank is partly taken out and may be applied to a gas analysis for CO, NOx, etc..

0065Next an embodyment according to the invention is discribed.

0066<figref idref="f0003">Fig. 4</figref> is a vertical cross sectional view which shows an embodiment of a gas generator for an air bag according to the present invention. The gas generator shown in this drawing is also structured to be particularly suitable for being arranged in a driver side as same as the gas generator shown in <figref idref="f0001">Fig.1</figref>. However, the gas generator shown in this drawing is different from the gas generator shown in <figref idref="f0001">Fig. 1</figref>, in a way that a flow passage forming member 51 is arranged in the first combustion chamber 5a, and a flow passage 52 through which the combustion gas generated in the second combustion chamber 5b passes is formed between the flow passage forming member 51 and the ceiling portion inner surface 28 of the diffuser shell.

0067The flow passage forming member 51 is formed into an annular shape obtained by bending an inner periphery and an outer periphery of a circular member so as to form an inner peripheral wall 53 and an outer - peripheral wall 54, and a supporting wall 56 for forming a space with the ceiling portion inner surface 28 of the diffuser shell is integrally formed on a circular portion 55 connecting the both peripheral wall surfaces. Then, the flow passage forming member 51 holds the inner cylindrical member 4 with the inner peripheral wall 53 thereof and brings a supporting wall 56 in contact with the ceiling portion inner surface 28 of the diffuser shell, by whereby a fixed space is obtained between the circular portion 55 and the ceiling portion inner surface 28 of the diffuser shell. And since multiple through holes 57 are formed on the supporting wall, the space can function as a gas flow passage 52. The gas flow passage 52 is communicated with the second combustion chamber 5b by the through hole 10 of the inner cylindrical member 4 due to the combustion of the gas generating agent 9b in the second combustion chamber 5b. Therefore, the combustion gas generated in the second combustion chamber 5b is discharged to the gas flow passage 52 from the through hole 10, passes - through the coolant/filter 22 and is discharged from the gas discharge port 26.

0068In the gas generator constituted in the above manner, the first combustion chamber 5a and the second combustion chamber 5b can be communicated with each other via the net space of the coolant/filter 22, however, the combustion gas generated by the combustion of the gas generating agent stored in either combustion chamber passes through the coolant/filter 22 and is discharged from the gas discharge port 26 as it is. Consequently, a flame generated by the gas generating agent which is firstly ignited and burnt does not ignite the gas generating agent stored in the other combustion chamber. And the single-hole gas generating agent 9a' stored in the first combustion chamber 5a is ignited and burnt only by the activation of the first igniter 12a, and the gas generating agent 9b in the second combustion chamber 5b is ignited and burnt only by the activation of the second igniter 12b.

0069Accordingly, in the gas generator shown in this drawing, even in the case of significantly staggering the activation timing of two igniters 12a and 12b, the flame of the gas generating agent ignited by the firstly activated igniter does not burn the gas generating agent in the other combustion chamber, and thereby a stable tank curve can be obtained in the tank combustion test. This becomes further advantageous particularly in the case of activating the second igniter 12b at a predetermined time after activating the first igniter 12a. Namely, in the gas generator shown in <figref idref="f0003">Fig. 4</figref>, since the through hole 10 is not closed by the seal tape, in the case of not using the flow passage forming member, there is a possibility that the combustion gas generated in the first combustion chamber 5a passes through the through hole 10 of the inner cylindrical member 4 so as to ignite and burn the gas generating agent 9b in the second combustion chamber 5b. However, when forming the different flow passage at each combustion chamber (5a, 5b) as the present embodiment, the combustion gas generated in the first combustion chamber 5a passes through the coolant/filter 22 and is discharged as it is without igniting the gas generating agent 9b in the second combustion chamber 5b. As a result, the gas generating agent 9b stored in the second combustion chamber 5a can be optionally ignited and burnt only by activating the second igniter 12a. In the gas generator according to the present embodiment, the through hole 10 is not closed by the seal tape. But even in the case that the hole 10 is closed by the seal tape, the gas generating agent can be further independently ignited and burnt in each combustion chamber. Accordingly, it is possible to make an output performance of the gas generator most suitable in accordance with a circumstance at a time of collision of the vehicle.

0070Here, in the gas generator shown in <figref idref="f0003">Fig. 4</figref>, the transfer charge 16b to be ignited by the second igniter 12b is arranged in the second combustion chamber 5b, but not in the separating cylinder 14. By arranging the transfer charge 16b in this manner, the flame can uniformly burn the gas generating agent 9b - in the second combustion chamber 5b when the transfer charge 16b is ignited and burnt by the activation of the second igniter 12b. And further, the transfer charge 16b cannot be directly burnt by the flame of the transfer charge 16a in the first transfer charge accommodating chamber 15a. In <figref idref="f0003">Fig. 4</figref>, with respect to the same elements as those in <figref idref="f0001">Fig. 1</figref>, the same reference numerals are attached thereto and a description thereof will be omitted.

0071Next, a description will be given of an actuation performance in the case of performing the above tank combustion test using the gas generator having the structure shown, in <figref idref="f0003">Fig. 4</figref>, with reference to <figref idref="f0003">Fig. 5</figref>. In this test, the gas generating agents having different shapes are charged in the respective combustion chambers at different amounts. In the tank curve shown in <figref idref="f0003">Fig. 5</figref>, the gas generating agent 9a in the first combustion chamber 5a has a surface area at a unit weight of a gas generating agent smaller than that of the gas generating agent 9b in the second combustion - chamber 5b, and a proportions of the charging amount between the gas generating agents, i.e. a rate of the first gas generating agent to the second gas generating agent is 35/6.

0072In <figref idref="f0003">Fig. 5</figref>, "A ignition" means a tank curve obtained when only the gas generating agent 9a in the first combustion chamber 5a is burnt by the activation of the first igniter 12a of the gas generator shown in <figref idref="f0003">Fig. 4</figref>. This tank curve moves upward, drawing a gentle curve. This is because the gas generating agent 9a in the first combustion chamber 5a has a surface area at a unit weight of the gas generating agent smaller than that of the gas generating agent 9b in the second combustion chamber 5b, and does not burn at a time after ignition.

0073Further, "A + B (simultaneous) ignition" means a tank curve obtained when the first and second igniters (12a, 12b) are simultaneously activated so as to simultaneously burn the gas generating agents (9a, 9b) in the first and second combustion chambers 5a and 5b. In this tank curve, the tank pressure rapidly increases simultaneously when the activating signal is - transmitted to both igniters (12a, 12b). This is because the second gas generating agent 9b in the second combustion chamber 5b having a larger surface area per a unit weight burns at a time at the same time of the ignition so as to discharge the combustion gas. And thereafter the combustion gas generated by the gas generating agent 9a in the first combustion chamber 5a is continuously generated, so that the increased output curve (the tank curve) is maintained for a while.

0074Further, "A + B (T milliseconds delayed) ignition" means a tank curve obtained when the second igniter 12b is activated to burn the gas generating agent 9b in the second combustion chamber 5b at T milliseconds after the first igniter 12a to burn the first gas generating agent 9a in the first combustion chamber 5a is firstly activated. This tank curve is substantially the same as the tank curve of "A ignition" before T milliseconds, however, after the second igniter 12b is activated (i.e. after T milliseconds), the tank curve goes upward at a time. This is because an amount of the gas rapidly generated by the combustion of the gas generating agent 9b in the second combustion chamber 5b is added. Here, in the tank curve of "A + B (T millisecond delayed) ignition", the maximum output (X kPa) thereof is more than the maximum output (Y kPa) of the tank curve of "A + B (simultaneous) ignition". This is because the gas generating agents (9a, 9b) in both the combustion chambers (5a, 5b) are burnt at a time in the case of "A + B (simultaneous) ignition", however, on the other hand, the second gas generating agent 9b in the second combustion chamber 5b is ignited and burnt at a T milliseconds after the first gas generating agent 9b charged in the first combustion chamber 5a, so that the generated heat is continuously maintained at that degree.

0075As mentioned above, in "A + B (T millisecond delayed) ignition" in <figref idref="f0003">Fig. 5</figref>, the second igniter 12b is activated at an internal of T milliseconds after the first igniter 12a is activated. The delay timing can be set to an optional interval by adjusting the ignition circuit. Accordingly, a judging circuit - judges a speed at a time of the collision of the vehicle or an attitude of an occupant (for examples, a person with a sitting height is long or short or a person with an attitude of holding to the steering wheel), or the like at a moment so as to set a suitable delay time and actuate the ignition means, by whereby it is possible to inflate the air bag in an optimum inflating mode under various circumstances. Embodiment 3