Gas generator

A gas generator includes an igniter, a cup-shaped member, and a fixing member. The cup-shaped member accommodating an enhancer agent bursts or melts at the time of activation. The fixing member fixing a filter does not burst and melt even at the time of activation. Ra and Ha satisfy a condition of Ra/Ha 1.00 where Ra represents an inner diameter of a sidewall portion of the cup-shaped member and Ha represents a distance between a top wall portion of the cup-shaped member and the igniter. The sidewall portion includes a first region surrounded by a partition wall portion of the fixing member and a second region not surrounded by the partition wall portion. The partition wall portion has an end portion arranged closer to a top plate portion than the igniter. A gas generating agent is arranged to face the top wall portion, the second region, and the partition wall portion.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a United States national stage application of International Application No. PCT/JP2018/009748, filed Mar. 13, 2018, which designates the United States, and claims priority to Japanese Patent Application No. 2017-090623, filed Apr. 28, 2017, and the entire contents of each of the above applications are hereby incorporated herein by reference in entirety.

TECHNICAL FIELD

The present invention relates to a gas generator incorporated in a passenger protection apparatus which protects a driver and/or a passenger at the time of collision of a vehicle or the like, and particularly to a gas generator incorporated in an air bag apparatus equipped in a car.

BACKGROUND ART

From a point of view of protection of a driver and/or a passenger in a car, an air bag apparatus which is a passenger protection apparatus has conventionally widely been used. The air bag apparatus is equipped for the purpose of protecting a driver and/or a passenger against shock caused at the time of collision of a vehicle, and it receives a body of a driver or a passenger with an air bag serving as a cushion, as the air bag is expanded and developed instantaneously at the time of collision of the vehicle.

The gas generator is equipment which is incorporated in this air bag apparatus, an igniter therein being ignited in response to power feed through a control unit at the time of collision of a vehicle to thereby burn a gas generating agent with flame caused by the igniter and instantaneously generate a large amount of gas, and thus expands and develops an air bag.

Gas generators of various structures are available. A disc-type gas generator in a short substantially columnar shape relatively great in outer diameter is available as a gas generator particularly suitably used for an air bag apparatus on a driver's seat side or an air bag apparatus on a passenger's seat side.

A disc-type gas generator includes a short substantially cylindrical housing having opposing axial ends closed, a plurality of gas discharge openings being provided in a circumferential wall portion of the housing, the housing accommodating an enhancer agent such that the enhancer agent faces an igniter assembled to the housing, the housing being further filled with a gas generating agent to surround the enhancer agent, and a filter being accommodated in the housing to further surround the gas generating agent.

For example, Japanese Patent Laying-Open No. 2008-183939 (PTL 1) discloses a specific construction of the disc-type gas generator.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

Depending on specifications of an air bag apparatus which incorporates a gas generator, there are various types of disc-type gas generators ranging from those relatively small in amount of generation of gas at the time of activation to those relatively large in that amount.

Among such disc-type gas generators, a disc-type gas generator of which amount of generation of gas at the time of activation is set to be relatively large is more disadvantageous in delay in start of discharge of gas to the outside through a gas discharge opening after a time point of activation of an igniter than a disc-type gas generator of which amount of generation of gas at the time of activation is set to be relatively small. This is exclusively due to a relatively large amount of gas generating agent and enhancer agent filled in the disc-type gas generator of which amount of generation of gas at the time of activation is set to be relatively large.

With increase in amount of gas generating agent and enhancer agent to be loaded, a housing is inevitably increased in size, and consequently a distance from the igniter to the gas discharge opening is also increased. Therefore, gas generated immediately after start of activation should pass through a longer path until it reaches the gas discharge opening, which causes the delay.

With increase in amount of gas generating agent and enhancer agent to be loaded, an amount of unburned gas generating agent and enhancer agent immediately after start of activation is also inevitably increased. This increase brings about a flow resistance against gas generated immediately after start of activation, which causes the delay.

Furthermore, with increase in amount of enhancer agent to be loaded, the enhancer agent arranged at a position distant from the igniter cannot quickly be ignited. Consequently, smooth combustion of the gas generating agent is impeded, which also causes the delay.

Such a phenomenon of delay in start of discharge of gas to the outside through a gas discharge opening after the time point of activation of the igniter leads also to delay in development of an air bag. Therefore, how to prevent the delay is an important issue.

In a disc-type gas generator disclosed in Japanese Patent Laying-Open No. 2008-183939, a cup-shaped member which accommodates an enhancer agent is formed from a weak member which bursts or melts by combustion of the enhancer agent with activation of the igniter, and a partition wall portion which does not burst or melt even by combustion of the enhancer agent with activation of the igniter is provided as surrounding the cup-shaped member to reach a position intermediate in the combustion chamber which accommodates the gas generating agent.

In the disc-type gas generator thus constructed, spread of combustion of the gas generating agent at the time of activation of the igniter is restricted by the partition wall portion. Therefore, combustion of the gas generating agent spreads to bypass the partition wall portion so that the gas generating agent can be prevented from burning out in a short period of time.

Thus, the technique disclosed in Japanese Patent Laying-Open No. 2008-183939 aims to avoid burnout of the gas generating agent in a short period of time in a disc-type gas generator of which amount of generation of gas at the time of activation is set to relatively be small, and it is not assumed to be applied to a disc-type gas generator of which amount of generation of gas at the time of activation is set to relatively be large.

The present invention was made in view of the problem described above, and one of objects thereof is to provide a gas generator set to relatively be large in amount of generation of gas at the time of activation that is capable of effectively preventing delay in start of discharge of gas to the outside through a gas discharge opening after a time point of activation of an igniter.

Solution to Problem

A gas generator based on a first aspect of the present invention includes a housing, an igniter, a cup-shaped member, a filter, and a fixing member. The housing includes a cylindrical circumferential wall portion provided with a gas discharge opening and a top plate portion and a bottom plate portion which close one and the other axial ends of the circumferential wall portion, and contains a combustion chamber which accommodates a gas generating agent. The igniter is assembled to the bottom plate portion and includes an ignition portion which accommodates an ignition agent ignited at the time of activation. The cup-shaped member contains an enhancer chamber which accommodates an enhancer agent, and is arranged to protrude toward the combustion chamber such that the enhancer chamber faces the ignition portion. A whole portion of the cup-shaped member which defines the enhancer chamber bursts or melts by combustion of the enhancer agent with activation of the igniter. The filter is located in the housing and made from a cylindrical member arranged along an inner circumferential surface of the circumferential wall portion to surround the combustion chamber. The fixing member fixes the filter to the housing, and does not burst or melt even by combustion of the enhancer agent with activation of the igniter. The cup-shaped member includes a cylindrical sidewall portion which defines the enhancer chamber and a top wall portion which defines the enhancer chamber and closes an axial end portion of the sidewall portion located on a side of the top plate portion. The fixing member includes a base portion applied to the bottom plate portion along an inner bottom surface of the bottom plate portion, an abutment portion which abuts on an inner circumferential surface of the filter close to the bottom plate portion, and a cylindrical partition wall portion erected from the base portion toward the top plate portion. Ra and Ha satisfy a condition of Ra/Ha≤1.00 where Ra represents an inner diameter of the sidewall portion and Ha represents a distance between the top wall portion and the ignition portion along an axial direction of the circumferential wall portion. The sidewall portion includes a first region located on a side of the bottom plate portion and surrounded by the partition wall portion and a second region located on a side of the top plate portion and not surrounded by the partition wall portion, by arranging the partition wall portion to reach a position in the combustion chamber intermediate along the axial direction of the circumferential wall portion. An end portion of the partition wall portion on the side of the top plate portion is arranged closer to the top plate portion than the ignition portion along the axial direction of the circumferential wall portion. The gas generating agent is arranged to face at least the top wall portion, the second region of the sidewall portion, and an outer circumferential surface of the partition wall portion.

In the gas generator based on the first aspect of the present invention, preferably, Ra and Ha further satisfy a condition of Ra/Ha≤0.80.

In the gas generator based on the first aspect of the present invention, preferably, Hb satisfies a condition of Hb≤13.5 [mm] where Hb represents a distance between the end portion of the partition wall portion on the side of the top plate portion and the ignition portion along the axial direction of the circumferential wall portion.

In the gas generator based on the first aspect of the present invention, preferably, the gas discharge opening is provided at a position closer to the top plate portion than the partition wall portion in the axial direction of the circumferential wall portion.

In the gas generator based on the first aspect of the present invention, preferably, the gas discharge opening is provided at a position opposed to the second region of the sidewall portion in a radial direction of the circumferential wall portion.

In the gas generator based on the first aspect of the present invention, the base portion may be in a shape of an annular plate, and in that case, preferably, the abutment portion is provided to extend from an outer edge of the base portion and the partition wall portion is provided to extend from an inner edge of the base portion.

In the gas generator based on the first aspect of the present invention, preferably, the gas generating agent is not arranged in a space between the first region of the sidewall portion and the partition wall portion.

In the gas generator based on the first aspect of the present invention, the partition wall portion may include a tapered portion tapered toward the top plate portion.

A gas generator based on a second aspect of the present invention includes a housing, an igniter, and a holding portion. The housing includes a cylindrical circumferential wall portion provided with a gas discharge opening and a top plate portion and a bottom plate portion which close one and the other axial ends of the circumferential wall portion, and contains a combustion chamber which accommodates a gas generating agent. The igniter serves to burn the gas generating agent. The holding portion is provided in the bottom plate portion and holds the igniter. The bottom plate portion includes a protruding cylindrical portion provided to protrude toward the top plate portion. An opening in which the igniter is inserted and arranged is provided in an axial end portion of the protruding cylindrical portion located on a side of the top plate portion. The holding portion is made of a resin molded portion at least partly secured to the bottom plate portion by being formed by attaching a fluid resin material to the bottom plate portion so as to reach a part of an outer surface of the bottom plate portion from a part of an inner surface of the bottom plate portion through the opening and solidifying the fluid resin material. The bottom plate portion in a portion except for the protruding cylindrical portion is in such an inclined shape as being inclined toward the top plate portion, in a direction toward a radially outer side of the circumferential wall portion. An inclination angle θ1of the bottom plate portion in the portion except for the protruding cylindrical portion satisfies a condition of 0[°]<θ1≤2[°].

Advantageous Effects of Invention

According to one aspect of the present invention, in a gas generator of which amount of generation of gas at the time of activation is set to relatively be large, delay in start of discharge of gas to the outside through a gas discharge opening after a time point of activation of an igniter can effectively be prevented.

DESCRIPTION OF EMBODIMENTS

An embodiment of the present invention will be described hereinafter in detail with reference to the drawings. An embodiment shown below represents application of the present invention to a disc-type gas generator suitably incorporated in an air bag apparatus equipped in a steering wheel or the like of a car. The same or common elements in the embodiment shown below have the same reference characters allotted in the drawings and description thereof will not be repeated.

First Embodiment

FIG. 1is a schematic diagram of a disc-type gas generator in a first embodiment of the present invention. A construction of a disc-type gas generator1A in the present embodiment will initially be described with reference toFIG. 1. Disc-type gas generator1A in the present embodiment is set to relatively be large in amount of generation of gas at the time of activation, and the amount of generation of gas thereof is set to approximately 3.0 [mol].

As shown inFIG. 1, disc-type gas generator1A in the present embodiment has a short substantially cylindrical housing having axial one and the other ends closed, and is constructed to accommodate as internal construction components in an accommodation space provided in the housing, a holding portion30, an igniter40, a cup-shaped member50, an enhancer agent56, a gas generating agent61, a lower supporting member70as a fixing member, an upper supporting member80, a cushion material85, a filter90, and the like. In the accommodation space provided in the housing, a combustion chamber60mainly accommodating gas generating agent61among the internal construction components described above is located.

The housing includes a lower shell10and an upper shell20. Each of lower shell10and upper shell20is made, for example, of a press-formed product formed by press-working a plate-shaped member made of a rolled metal. A metal plate composed, for example, of stainless steel, iron steel, an aluminum alloy, a stainless alloy, or the like is made use of as the plate-shaped member made of metal which forms lower shell10and upper shell20, and what is called a high tensile steel plate which is free from such a failure as fracture even at the time of application of tensile stress not lower than 440 [MPa] and not higher than 780 [MPa] is suitably made use of.

Lower shell10and upper shell20are each formed in a substantially cylindrical shape with bottom, and the housing is constructed by combining and joining the shells such that open surfaces thereof face each other. Lower shell10has a bottom plate portion11and a cylindrical portion12and upper shell20has a top plate portion21and a cylindrical portion22.

Cylindrical portion12of lower shell10has an upper end press-fitted as being inserted in a lower end of cylindrical portion22of upper shell20. Cylindrical portion12of lower shell10and cylindrical portion22of upper shell20are joined at a portion of abutment therebetween or in the vicinity thereof so that lower shell10and upper shell20are fixed. Electron-beam welding, laser welding, friction welding, or the like can suitably be made use of for joining lower shell10and upper shell20to each other.

A portion of a circumferential wall portion of the housing close to bottom plate portion11is thus formed by cylindrical portion12of lower shell10, and a portion of the circumferential wall portion of the housing close to top plate portion21is formed by cylindrical portion22of upper shell20. One and the other axial ends of the housing are closed by bottom plate portion11of lower shell10and top plate portion21of upper shell20, respectively.

A protruding cylindrical portion13protruding toward top plate portion21is provided in a central portion of bottom plate portion11of lower shell10, so that a depression portion14is formed in the central portion of bottom plate portion11of lower shell10. Protruding cylindrical portion13is a site to which igniter40is fixed with holding portion30being interposed, and depression portion14is a site serving as a space for providing a female connector portion34in holding portion30.

Protruding cylindrical portion13is formed to be in a substantially cylindrical shape with bottom, and an opening15in a non-point-symmetrical shape (for example, in a D shape, a barrel shape, or an elliptical shape) when viewed two-dimensionally is provided at an axial end portion located on a side of top plate portion21. Opening15is a site through which a pair of terminal pins42of igniter40passes.

Igniter40serves to produce flames and includes an ignition portion41and a pair of terminal pins42described above. Ignition portion41contains an ignition agent producing flames by being ignited to burn at the time of activation and a resistor for igniting this ignition agent. The pair of terminal pins42is connected to ignition portion41for igniting the ignition agent.

More specifically, ignition portion41includes a squib cup formed like a cup and a plug closing an opening end of the squib cup and holding a pair of terminal pins42as being inserted therein. The resistor (bridge wire) is attached to couple tip ends of the pair of terminal pins42inserted in the squib cup, and the ignition agent is loaded in the squib cup so as to surround the resistor or to be in proximity to the resistor.

Here, a Nichrome wire or the like is generally made use of as a resistor, and ZPP (zirconium potassium perchlorate), ZWPP (zirconium tungsten potassium perchlorate), lead tricinate, or the like is generally made use of as the ignition agent. The squib cup and the plug described above are generally made of a metal or plastic.

Upon sensing collision, a prescribed amount of current flows in a resistor through terminal pin42. As the prescribed amount of current flows in the resistor, Joule heat is generated in the resistor and the ignition agent starts burning. Flame at a high temperature caused by being burnt bursts the squib cup accommodating the ignition agent. A time period from flow of a current in the resistor until activation of igniter40is generally not longer than 2 [ms] in a case that the Nichrome wire is employed as the resistor.

Igniter40is attached to bottom plate portion11in such a manner that terminal pin42is introduced from the inside of lower shell10to pass through opening15provided in protruding cylindrical portion13. Specifically, holding portion30formed from a resin molded portion is provided around protruding cylindrical portion13provided in bottom plate portion11, and igniter40is fixed to bottom plate portion11as being held by holding portion30.

Holding portion30is formed through injection molding (more specifically, insert molding) with the use of a mold, and formed by attaching an insulating fluid resin material to bottom plate portion11so as to reach a part of an outer surface from a part of an inner surface of bottom plate portion11through opening15provided in bottom plate portion11of lower shell10and solidifying the fluid resin material.

For a source material for holding portion30formed by injection molding, a resin material excellent in heat resistance, durability, corrosion resistance, and the like after curing is suitably selected and made use of. In that case, without being limited to a thermosetting resin represented by an epoxy resin and the like, a thermoplastic resin represented by a polybutylene terephthalate resin, a polyethylene terephthalate resin, a polyamide resin (such as nylon 6 or nylon 66), a polypropylene sulfide resin, a polypropylene oxide resin, and the like can also be made use of. In a case where these thermoplastic resins are selected as a source material, in order to ensure mechanical strength of holding portion30after molding, glass fibers or the like are preferably contained as fillers in these resin materials. In a case where sufficient mechanical strength can be ensured only by a thermoplastic resin, however, a filler as described above does not have to be added.

Holding portion30has an inner cover portion31covering a part of an inner surface of bottom plate portion11of lower shell10, an outer cover portion32covering a part of an outer surface of bottom plate portion11of lower shell10, and a coupling portion33located within opening15provided in bottom plate portion11of lower shell10and continuing to each of inner cover portion31and outer cover portion32.

Holding portion30is secured to bottom plate portion11at a surface on a side of bottom plate portion11, of each of inner cover portion31, outer cover portion32, and coupling portion33. Holding portion30is secured at each of a side surface and a lower surface of igniter40which is closer to a lower end of ignition portion41, as well as a surface of a portion of igniter40which is closer to an upper end of terminal pin42.

Thus, opening15is completely buried by terminal pin42and holding portion30, so that hermeticity of the space in the housing is ensured by sealability ensured in that portion. Since opening15is in a non-point-symmetrical shape in a plan view as described above, opening15and coupling portion33function also as a turning prevention mechanism which prevents holding portion30from turning with respect to bottom plate portion11by burying opening15with coupling portion33.

In a portion of outer cover portion32of holding portion30, which faces the outside, female connector portion34is formed. This female connector portion34is a site for receiving a male connector (not shown) of a harness for connecting igniter40and a control unit (not shown) to each other, and it is located in depression portion14provided in bottom plate portion11of lower shell10.

In this female connector portion34, a portion of igniter40closer to the lower end of terminal pin42is arranged as being exposed. The male connector is inserted in female connector portion34, so that electrical conduction between a core wire of the harness and terminal pin42is established.

Injection molding described above may be carried out with the use of lower shell10obtained by providing an adhesive layer in advance at a prescribed position on a surface of bottom plate portion11in a portion to be covered with holding portion30. The adhesive layer can be formed by applying an adhesive in advance to a prescribed position of bottom plate portion11and curing the adhesive.

By doing so, the cured adhesive layer is located between bottom plate portion11and holding portion30, so that holding portion30formed from a resin molded portion can more firmly be secured to bottom plate portion11. Therefore, by providing the adhesive layer annularly along a circumferential direction so as to surround opening15provided in bottom plate portion11, higher sealability can be ensured in that portion.

For the adhesive applied in advance to bottom plate portion11, an adhesive containing as a source material, a resin material excellent in heat resistance, durability, corrosion resistance, and the like after curing is suitably made use of, and for example, an adhesive containing a cyanoacrylate-based resin or a silicone-based resin as a source material is particularly suitably made use of. An adhesive containing as a source material other than the resin materials described above, a phenol-based resin, an epoxy-based resin, a melamine-based resin, a urea-based resin, a polyester-based resin, an alkyd-based resin, a polyurethane-based resin, a polyimide-based resin, a polyethylene-based resin, a polypropylene-based resin, a polyvinyl chloride-based resin, a polystyrene-based resin, a polyvinyl acetate-based resin, a polytetrafluoroethylene-based resin, an acrylonitrile butadiene styrene-based resin, an acrylonitrile styrene-based resin, an acrylic resin, a polyamide-based resin, a polyacetal-based resin, a polycarbonate-based resin, a polyphenylene ether-based resin, a polybutylene terephthalate-based resin, a polyethylene terephthalate-based resin, a polyolefin-based resin, a polyphenylene sulfide-based resin, a polysulfone-based resin, a polyether sulfone-based resin, a polyarylate-based resin, a polyether ether ketone-based resin, a polyamide imide-based resin, a liquid crystal polymer, styrene-based rubber, olefin-based rubber, and the like can be made use of as the adhesive described above.

Though such a construction example that igniter40can be fixed to lower shell10by injection molding holding portion30formed from the resin molded portion is exemplified, other alternative means can also be used for fixing igniter40to lower shell10.

Cup-shaped member50is assembled to bottom plate portion11so as to cover protruding cylindrical portion13, holding portion30, and igniter40. Cup-shaped member50has a substantially cylindrical shape with bottom having an open end portion on the side of bottom plate portion11, and contains an enhancer chamber55accommodating enhancer agent56. Cup-shaped member50is arranged to protrude into combustion chamber60accommodating gas generating agent61, such that enhancer chamber55provided therein faces ignition portion41of igniter40.

Cup-shaped member50has a cylindrical sidewall portion51which defines enhancer chamber55described above, a top wall portion52which defines enhancer chamber55and closes an axial end portion of sidewall portion51located on the side of top plate portion21, and an extension portion53provided to extend radially outward from a portion of sidewall portion51on a side of an open end. Extension portion53is formed to extend along an inner surface of bottom plate portion11of lower shell10. Specifically, extension portion53is in a shape curved along a shape of an inner bottom surface of bottom plate portion11in a portion where protruding cylindrical portion13is provided and in the vicinity thereof and includes a tip end portion54extending like a flange in a radially outer portion thereof.

Tip end portion54in extension portion53is arranged between bottom plate portion11and lower supporting member70along the axial direction of the housing and sandwiched between bottom plate portion11and lower supporting member70along the axial direction of the housing. Since lower supporting member70is pressed toward bottom plate portion11by gas generating agent61, cushion material85, upper supporting member80, and top plate portion21arranged above, cup-shaped member50is in such a state that tip end portion54of extension portion53is pressed toward bottom plate portion11by lower supporting member70and fixed to bottom plate portion11. Thus, cup-shaped member50is prevented from falling from bottom plate portion11without using swaging or press-fitting for fixing cup-shaped member50.

Cup-shaped member50has an opening in neither of sidewall portion51and top wall portion52and surrounds enhancer chamber55provided therein. This cup-shaped member50bursts or melts with increase in pressure in enhancer chamber55or conduction of heat generated therein when enhancer agent56is ignited as a result of activation of igniter40, and mechanical strength thereof is relatively low.

Therefore, a member made of metal such as aluminum or an aluminum alloy or a member made of a resin such as a thermosetting resin represented by an epoxy resin and the like and a thermoplastic resin represented by a polybutylene terephthalate resin, a polyethylene terephthalate resin, a polyamide resin (such as nylon 6 or nylon 66), a polypropylene sulfide resin, a polypropylene oxide resin, and the like is suitably made use of for cup-shaped member50.

A method of fixing cup-shaped member50is not limited to a fixing method using lower supporting member70described above, and other fixing methods may be made use of.

Enhancer agent56charged into enhancer chamber55generates thermal particles as it is ignited to burn by flames produced as a result of activation of igniter40. Enhancer agent56should be able to reliably start burning gas generating agent61, and generally, a composition composed of metal powders/oxidizing agent represented by B/KNO3, B/NaNO3, or Sr(NO3)2, a composition composed of titanium hydride/potassium perchlorate, or a composition composed of B/5-aminotetrazole/potassium nitrate/molybdenum trioxide is employed.

For enhancer agent56, a powdery enhancer agent, an enhancer agent formed in a prescribed shape by a binder, or the like is made use of. A shape of enhancer agent56formed by a binder includes, for example, various shapes such as a granule, a column, a sheet, a sphere, a cylinder with a single hole, a cylinder with multiple holes, a tablet, and the like.

In a space surrounding a portion where cup-shaped member50described above is arranged in a space inside the housing, combustion chamber60accommodating gas generating agent61is located. Specifically, as described above, cup-shaped member50is arranged to protrude into combustion chamber60formed in the housing, and a space provided in a portion of this cup-shaped member50facing the outer surface of sidewall portion51and a space provided in a portion thereof facing an outer surface of top wall portion52are provided as combustion chamber60.

In a space surrounding combustion chamber60accommodating gas generating agent61in a radial direction of the housing, filter90is arranged along an inner circumference of the housing. Filter90has a cylindrical shape and is arranged such that a central axis thereof substantially matches with the axial direction of the housing.

Gas generating agent61is an agent which is ignited by thermal particles generated as a result of activation of igniter40and produces gas as it burns. A non-azide-based gas generating agent is preferably employed as gas generating agent61, and gas generating agent61is formed as a molding generally containing a fuel, an oxidizing agent, and an additive.

For the fuel, for example, a triazole derivative, a tetrazole derivative, a guanidine derivative, an azodicarbonamide derivative, a hydrazine derivative, or the like, or combination thereof is made use of. Specifically, for example, nitroguanidine, guanidine nitrate, cyanoguanidine, 5-aminotetrazole, and the like are suitably made use of.

As the oxidizing agent, for example, basic nitrate such as basic copper nitrate, perchlorate such as ammonium perchlorate or potassium perchlorate, nitrate containing cations selected from an alkali metal, an alkali earth metal, a transition metal, and ammonia, or the like is made use of. As the nitrate, for example, sodium nitrate, potassium nitrate, or the like is suitably made use of.

As the additive, a binder, a slag formation agent, a combustion modifier, or the like is exemplified. As the binder, for example, an organic binder such as polyvinyl alcohol, metal salt of carboxymethyl cellulose, and stearate, or an inorganic binder such as synthetic hydrotalcite and Japanese acid clay can suitably be made use of. In addition, as the binder, polysaccharide derivatives such as hydroxyethyl cellulose, hydroxypropyl methylcellulose, cellulose acetate, cellulose propionate, cellulose acetate butyrate, nitrocellulose, microcrystalline cellulose, guar gum, polyvinyl pyrrolidone, polyacrylamide, and starch and inorganic binders such as molybdenum disulfide, talc, bentonite, diatomite, kaolin, and alumina can also suitably be made use of. As the slag formation agent, silicon nitride, silica, Japanese acid clay, or the like can suitably be made use of. As the combustion modifier, a metal oxide, ferrosilicon, activated carbon, graphite, or the like can suitably be made use of.

A shape of a molding of gas generating agent61includes various shapes such as a particulate shape including a granule, a pellet, and a column, and a disc shape. In addition, among columnar moldings, a molding with holes having through holes in the molding (such as a cylindrical shape with a single hole or a cylindrical shape with multiple holes) is also made use of. These shapes are preferably selected as appropriate depending on specifications of an air bag apparatus in which disc-type gas generator1A is incorporated, and for example, a shape optimal for the specifications is preferably selected by selecting a shape allowing change over time of a rate of generation of gas during burning of gas generating agent61. Furthermore, in addition to a shape of gas generating agent61, a size of a molding or an amount thereof for filling is preferably selected as appropriate, in consideration of a linear burning velocity, a pressure exponent, or the like of gas generating agent61.

For example, a filter obtained by winding and sintering a metal wire rod of stainless steel or iron steel, a filter formed by press-working a mesh material into which metal wire rods are knitted to thereby pack the same, or the like can be made use of as filter90. As the mesh material, specifically, a wire gauze of stocking stitch, a plain-woven wire gauze, an aggregate of crimped metal wire rods, or the like can be made use of.

In addition, a filter obtained by winding a perforated metal plate can also be made use of as filter90. In this case, as the perforated metal plate, for example, expanded metal obtained by making staggered cuts in a metal plate and providing holes by widening the cuts to thereby work the metal plate in a mesh, hook metal obtained by perforating a metal plate and collapsing burrs caused around a periphery of the hole for flattening, or the like is made use of. In this case, a size or a shape of a hole to be provided can be changed as appropriate as required, and holes different in size or shape may be included in the same metal plate. It is noted that, for example, a steel plate (mild steel) or a stainless steel plate can suitably be made use of as a metal plate, and a nonferrous metal plate of aluminum, copper, titanium, nickel, or an alloy thereof, or the like can also be made use of.

Filter90functions as cooling means for cooling gas by removing heat at a high temperature of the gas when the gas produced in combustion chamber60passes through this filter90and also functions as removal means for removing residues (slug) or the like contained in the gas. Therefore, in order to sufficiently cool the gas and to prevent emission of residues to the outside, the gas generated in combustion chamber60should reliably pass through filter90. Filter90is arranged to be distant from cylindrical portions12and22so as to provide a gap28of a prescribed size between cylindrical portion12of lower shell10and cylindrical portion22of upper shell20which form the circumferential wall portion of the housing.

A plurality of gas discharge openings23are provided in cylindrical portion22of upper shell20in a portion facing filter90. The plurality of gas discharge openings23serve for guiding gas which has passed through filter90to the outside of the housing.

To an inner circumferential surface of cylindrical portion22of upper shell20, a sealing tape24made of a metal as a sealing member is attached to close the plurality of gas discharge openings23. An aluminum foil or the like having a tacky member applied to its one surface is suitably made use of as this sealing tape24and hermeticity of combustion chamber60is ensured by sealing tape24.

In the vicinity of the end portion of combustion chamber60located on the side of bottom plate portion11, lower supporting member70is arranged. Lower supporting member70has an annular shape and is arranged as substantially being applied to filter90and bottom plate portion11so as to cover a boundary portion between filter90and bottom plate portion11. Thus, lower supporting member70is located between bottom plate portion11and gas generating agent61in the vicinity of the end portion of combustion chamber60.

Lower supporting member70includes a base portion71in a shape of an annular plate applied to bottom plate portion11along the inner bottom surface of bottom plate portion11, an abutment portion72which abuts on an inner circumferential surface of filter90close to bottom plate portion11, and a cylindrical partition wall portion73erected from base portion71toward top plate portion21. Abutment portion72is provided to extend from an outer edge of base portion71and partition wall portion73is provided to extend from an inner edge of base portion71.

Lower supporting member70serves as a member for fixing filter90to the housing and also functions as flow-out prevention means for preventing gas generated in combustion chamber60at the time of activation from flowing out through a gap between the lower end of filter90and bottom plate portion11without passing through filter90. Partition wall portion73of lower supporting member70functions also as means for preventing, at the time of activation of disc-type gas generator1A, delay in start of discharge of gas to the outside through gas discharge opening23after a time point of activation of igniter40, which will be described later.

Lower supporting member70is made from a member which does not burst or melt even by combustion of enhancer agent56with activation of igniter40. Lower supporting member70is formed, for example, by press-working a plate-shaped member made of metal, and suitably made of a member formed from a steel plate of common steel, special steel, or the like (such as a cold rolled steel plate or a stainless steel plate).

Tip end portion54of extension portion53of cup-shaped member50described above is arranged between bottom plate portion11and base portion71of lower supporting member70along the axial direction of the housing. Thus, tip end portion54is held as being sandwiched between bottom plate portion11and base portion71along the axial direction of the housing. According to the construction as such, cup-shaped member50is in such a state that tip end portion54of extension portion53is pressed toward bottom plate portion11by base portion71of lower supporting member70and fixed to bottom plate portion11.

Upper supporting member80is arranged at the end portion of combustion chamber60located on the side of top plate portion21. Upper supporting member80is substantially in a shape of a disc and is arranged as being applied to filter90and top plate portion21so as to cover the boundary portion between filter90and top plate portion21. Thus, upper supporting member80is located between top plate portion21and gas generating agent61in the vicinity of the end portion of combustion chamber60.

Upper supporting member80has a base portion81abutting on top plate portion21and an abutment portion82erected from a peripheral edge of base portion81. Abutment portion82abuts on the inner circumferential surface of an axial end portion of filter90located on the side of top plate portion21.

Upper supporting member80serves as a member for fixing filter90to the housing and also functions as flow-out prevention means for preventing gas generated in combustion chamber60at the time of activation from flowing out through a gap between the upper end of filter90and top plate portion21without passing through filter90.

Upper supporting member80is made from a member which does not burst or melt even by combustion of enhancer agent56with activation of igniter40. Similarly to lower supporting member70, upper supporting member80is formed, for example, by press-working a plate-shaped member made of metal, and suitably made of a member formed from a steel plate of common steel, special steel, or the like (such as a cold rolled steel plate or a stainless steel plate).

In this upper supporting member80, annular cushion material85is arranged to be in contact with gas generating agent61accommodated in combustion chamber60. Cushion material85is thus located between top plate portion21and gas generating agent61in a portion of combustion chamber60on the side of top plate portion21and presses gas generating agent61toward bottom plate portion11.

Cushion material85is provided for the purpose of preventing gas generating agent61made of a molding from being crushed by vibration or the like, and made of a member suitably formed of a molding of ceramic fibers, rock wool, or a foamed resin (such as foamed silicone, foamed polypropylene, or foamed polyethylene), or rubber represented by chloroprene and EPDM.

An operation of disc-type gas generator1A in the present embodiment described above will now be described with reference toFIG. 1.

When a vehicle on which disc-type gas generator1A in the present embodiment is mounted collides, collision sensing means separately provided in the vehicle senses collision, and based thereon, igniter40is activated in response to power feed through a control unit separately provided in the vehicle. Enhancer agent56accommodated in enhancer chamber55is ignited to burn by flames produced as a result of activation of igniter40, to thereby generate a large amount of thermal particles. Burning of this enhancer agent56bursts or melts cup-shaped member50and the thermal particles described above flow into combustion chamber60.

The thermal particles which have flowed in ignite and burn gas generating agent61accommodated in combustion chamber60and a large amount of gas is produced. The gas produced in combustion chamber60passes through filter90. At that time, heat is removed from the gas through filter90and the gas is cooled, slug contained in the gas is removed by filter90, and the gas flows into gap28.

As a pressure in the space in the housing increases, sealing tape24which has closed gas discharge opening23provided in upper shell20is cleaved and the gas is discharged to the outside of the housing through gas discharge opening23. The discharged gas is introduced in the air bag provided adjacent to disc-type gas generator1A and it expands and develops the air bag.

As described above, disc-type gas generator1A in the present embodiment is set to relatively be large in amount of generation of gas at the time of activation. Accordingly, the housing is made larger mainly along the axial direction to be larger in inner volume than a common housing. Thus, combustion chamber60constructed to be larger is filled with gas generating agent61in an amount larger than in a common gas generator.

With a relatively larger amount of gas generating agent61that is loaded, disc-type gas generator1A is also constructed to relatively be larger in amount of enhancer agent56that is loaded. Specifically, cup-shaped member50is constructed to be larger in inner volume of enhancer chamber55by being constructed to relatively be longer in the axial direction of the circumferential wall portion of the housing, and enhancer chamber55constructed to be larger is filled with enhancer agent56in an amount larger than in a common gas generator.

Enhancer chamber55constructed to be larger is quantitatively defined by Ra and Ha satisfying a condition of Ra/Ha≤1.00 where Ra represents an inner diameter of sidewall portion51of cup-shaped member50and Ha represents a distance between top wall portion52of cup-shaped member50and ignition portion41of igniter40along the axial direction of the circumferential wall portion of the housing with reference toFIG. 1. In disc-type gas generator1A in the present embodiment, Ra is set to approximately 14.0 [mm] and Ha is set to approximately 27.0 [mm]. A value of Ra/Ha is approximately 0.52. A disc-type gas generator set to relatively be small in amount of generation of gas at the time of activation generally satisfies a condition of Ra/Ha>1.00.

The disc-type gas generator thus constructed to satisfy the condition of Ra/Ha≤1.00 suffers from the problem of delay in start of discharge of gas to the outside through the gas discharge opening after the time point of activation of the igniter. In this regard, disc-type gas generator1A in the present embodiment solves this problem by providing partition wall portion73to surround a part of sidewall portion51of cup-shaped member50.

FIG. 2is a diagram schematically showing directivity of combustion of the enhancer agent immediately after start of activation of the disc-type gas generator shown inFIG. 1. A reason why there is no delay in start of discharge of gas to the outside through gas discharge opening23after the time point of activation of igniter40in disc-type gas generator1A in the present embodiment will now be described with reference toFIG. 2andFIG. 1described previously.

As shown inFIG. 1, cylindrical partition wall portion73erected from the inner edge of base portion71of lower supporting member70is arranged to reach a position in combustion chamber60intermediate along the axial direction of the circumferential wall portion of the housing so that sidewall portion51of cup-shaped member50includes a first region R1located on the side of bottom plate portion11and surrounded by partition wall portion73and a second region R2located on the side of top plate portion21and not surrounded by partition wall portion73.

First region R1and second region R2of sidewall portion51both correspond to a portion which defines enhancer chamber55of cup-shaped member50and they are portions which burst or melt by combustion of enhancer agent56with activation of igniter40.

An end portion of partition wall portion73on the side of top plate portion21is arranged closer to top plate portion21than an upper surface of ignition portion41of igniter40along the axial direction of the circumferential wall portion of the housing. Ignition portion41of igniter40is thus surrounded by partition wall portion73in the radial direction of the circumferential wall portion of the housing.

A space S of a prescribed size is provided between partition wall portion73and first region R1of sidewall portion51, and space S is not filled with gas generating agent61. Gas generating agent61is thus arranged to face top wall portion52of cup-shaped member50, second region R2of sidewall portion51of cup-shaped member50, and an outer circumferential surface of partition wall portion73of lower supporting member70.

According to such a construction, as shown inFIG. 2, at the time of activation of disc-type gas generator1A, prescribed directivity can be given to a direction of scattering of thermal particles generated by combustion of some enhancer agent56arranged adjacently to igniter40(FIG. 2schematically showing directivity with an arrow).

In general, combustion of an enhancer agent ignited by an igniter basically radially spreads, and accordingly thermal particles generated by combustion of the enhancer agent are also radially scattered and do not have directivity as described above.

In disc-type gas generator1A in the present embodiment, however, partition wall portion73relatively high in mechanical strength is provided to surround ignition portion41of igniter40and a space thereabove in the radial direction of the circumferential wall portion of the housing. Accordingly, a direction of travel of thermal particles scattered toward partition wall portion73is changed by partition wall portion73to scatter toward top plate portion21(in other words, the direction of travel is narrowed). Therefore, combustion of enhancer agent56efficiently spreads toward top plate portion21.

Thus, not only enhancer agent56arranged at a position close to igniter40but also enhancer agent56arranged at a position distant from igniter40can be ignited without delay after the time point of start of activation of igniter40, and consequently gas generating agent61can smoothly burn. Therefore, gas generating agent61also quickly starts to burn, and delay in start of discharge of gas to the outside through gas discharge opening23after the time point of activation of igniter40can be prevented.

Therefore, with disc-type gas generator1A as in the present embodiment described above, even though an amount of generation of gas at the time of activation is set to relatively be large, delay in start of discharge of gas to the outside through gas discharge opening23after the time point of activation of igniter40can effectively be prevented and a disc-type gas generator high in performance such as being free from delay in development of an air bag can be obtained.

Referring toFIG. 1, disc-type gas generator1A in the present embodiment is constructed such that Hb satisfies a condition of Hb≤13.5 [mm] where Hb represents a distance between the end portion of partition wall portion73on the side of top plate portion21and ignition portion41of igniter40along the axial direction of the circumferential wall portion of the housing. In disc-type gas generator1A in the present embodiment, Hb is set to approximately 4.0 [mm] and a ratio of Hb to Ha described above is approximately 0.15. Thus, distance Hb does not necessarily have to be set to be large, and a considerable effect can be obtained by satisfying at least a condition of Hb≤0 [mm].

This is because setting of extremely large Hb results in interference by partition wall portion73of combustion of gas generating agent61and even in failure in obtaining sufficient gas output (an amount of discharge of gas per unit time) in a stage of activation of the disc-type gas generator. Therefore, from a point of view of prevention of delay in discharge of gas and obtaining sufficiently large gas output without delay, the disc-type gas generator is preferably constructed to satisfy the condition of Hb≤13.5 [mm] as described above.

Referring toFIGS. 1 and 2, in disc-type gas generator1A in the present embodiment, a plurality of gas discharge openings23provided in the circumferential wall portion of the housing are all provided at a position closer to top plate portion21than partition wall portion73in the axial direction of the circumferential wall portion of the housing.

According to such a construction, a distance from gas generating agent61ignited by combustion of some enhancer agent56immediately after start of activation of igniter40to gas discharge opening23is substantially shortest. Therefore, delay in start of discharge of gas to the outside through gas discharge opening23after the time point of activation of igniter40can further effectively be prevented.

According to such a construction, an amount of unburned gas generating agent61and enhancer agent56immediately after start of activation which are located between burned gas generating agent61ignited by combustion of enhancer agent56immediately after start of activation of igniter40and gas discharge opening23can be minimized. In this regard as well, delay in start of discharge of gas to the outside through gas discharge opening23after the time point of activation of igniter40can further effectively be prevented.

In order to reliably achieve these effects, as in disc-type gas generator1A in the present embodiment, a plurality of gas discharge openings23are further preferably provided at a position opposed to second region R2of sidewall portion51of cup-shaped member50in the radial direction of the circumferential wall portion of the housing. Specifically, disc-type gas generator1A in the present embodiment is constructed such that a distance Hc along the axial direction of the circumferential wall portion of the housing between a position where the plurality of gas discharge openings23are provided and ignition portion41of igniter40is set to approximately 21.0 [mm], so that the plurality of gas discharge openings23are provided at a position opposed to second region R2of sidewall portion51of cup-shaped member50in the radial direction of the circumferential wall portion of the housing.

Referring further toFIGS. 1 and 2, in disc-type gas generator1A in the present embodiment, partition wall portion73of lower supporting member70includes a tapered portion73atapered toward top plate portion21. By thus providing tapered portion73ain a tapered shape in partition wall portion73, stronger directivity can be provided to a direction of scattering of thermal particles generated by combustion of some enhancer agent56arranged adjacently to igniter40. Therefore, enhancer agent56arranged at a position distant from igniter40can be ignited earlier after the time point of start of activation of igniter40, and delay in start of discharge of gas to the outside through gas discharge opening23after the time point of activation of igniter40can further effectively be prevented.

The effect described above is achieved by applying the present invention to the disc-type gas generator constructed to satisfy the condition of Ra/Ha≤1.00 as described previously. The present invention achieves a noticeable effect by being applied to a disc-type gas generator constructed to satisfy in particular a condition of Ra/Ha≤0.80, and furthermore achieves a particularly noticeable effect by being applied to a disc-type gas generator constructed to satisfy a condition of Ra/Ha≤0.60.

FIG. 3is a schematic cross-sectional view of a sub assembly including the lower shell, the igniter, and the holding portion of the disc-type gas generator shown inFIG. 1.FIG. 4is a schematic cross-sectional view showing a state that the lower shell is placed in a lower mold in a process of manufacturing the disc-type gas generator shown inFIG. 1andFIG. 5is a schematic cross-sectional view showing a state in a stage before forming the holding portion by injection molding. Other characteristic features of disc-type gas generator1A in the present embodiment and a method of manufacturing the same (in particular, a method of forming holding portion30by injection molding) will be described below with reference toFIGS. 3 to 5.

As shown inFIG. 3, disc-type gas generator1A in the present embodiment is constructed such that bottom plate portion11in a portion except for protruding cylindrical portion13of lower shell10is in such an inclined shape as being inclined inward (that is, toward top plate portion21), in a direction toward a radially outer side of the circumferential wall portion of the housing. An inclination angle θ1of bottom plate portion11in the portion except for protruding cylindrical portion13preferably satisfies a condition of 0[°]<θ1≤2[°].

This is a feature for preventing spring-back of lower shell10, which may occur in setting lower shell10into a mold in injection molding of holding portion30. Spring-back will be described later in detail with reference to a disc-type gas generator1X according to a comparative example which will be described later.

As shown inFIG. 4, in manufacturing disc-type gas generator1A in the present embodiment, lower shell10is placed on a lower mold100in a prescribed shape and thereafter an upper mold200is lowered in a direction shown with an arrow AR1in the figure so as to sandwich lower shell10between upper mold200and lower mold100as shown inFIG. 5. A cavity C for forming holding portion30by injection molding is provided between lower mold100and upper mold200around protruding cylindrical portion13of lower shell10. Upper mold200abuts on an outer circumferential portion of an axial end portion of protruding cylindrical portion13of lower shell10located on the side of top plate portion21such that cavity C is provided as a closed space.

As described above, in disc-type gas generator1A in the present embodiment, bottom plate portion11in the portion except for protruding cylindrical portion13of lower shell10is in such an inclined shape as being inclined inward, in the direction toward the radially outer side of the circumferential wall portion of the housing. Therefore, lower shell10abuts on lower mold100only in an inner circumferential portion of bottom plate portion11in the portion except for protruding cylindrical portion13while it is placed on lower mold100as shown inFIG. 4, and abuts on lower mold100only in the inner circumferential portion of bottom plate portion11in the portion except for protruding cylindrical portion13also in a state after the lower shell is sandwiched between lower mold100and upper mold200as shown inFIG. 5.

In the portion of bottom plate portion11of lower shell10except for the inner circumferential portion described above, lower shell10does not abut on lower mold100, and the inclined shape of bottom plate portion11in the portion except for protruding cylindrical portion13of lower shell10is maintained also while the lower shell is sandwiched between lower mold100and upper mold200.

FIG. 6is a schematic cross-sectional view of a sub assembly including a lower shell, an igniter, and a holding portion of a disc-type gas generator according to a comparative example.FIG. 7is a schematic cross-sectional view showing a state that the lower shell is placed in a lower mold in a process of manufacturing the disc-type gas generator shown inFIG. 6andFIG. 8is a schematic cross-sectional view showing a state in a stage before forming the holding portion by injection molding. A construction of disc-type gas generator1X according to the comparative example and a method of manufacturing the same (in particular, a method of forming holding portion30by injection molding) will be described below with reference toFIGS. 6 to 8.

As shown inFIG. 6, disc-type gas generator1X according to the comparative example is constructed such that bottom plate portion11in the portion except for protruding cylindrical portion13of lower shell10is at a prescribed inclination angle θ2so as to be in such an inclined shape as being inclined outward (that is, toward the outside), in a direction toward the radially outer side of the circumferential wall portion of the housing.

As shown inFIG. 7, in manufacturing disc-type gas generator1X according to the comparative example, similarly to disc-type gas generator1A in the present embodiment described above, lower shell10is placed on lower mold100in a prescribed shape and thereafter upper mold200is lowered in the direction shown with arrow AR1in the figure so as to sandwich lower shell10between upper mold200and lower mold100as shown inFIG. 8. Cavity C for forming holding portion30by injection molding is provided between lower mold100and upper mold200around protruding cylindrical portion13of lower shell10. Upper mold200abuts on the outer circumferential portion of the axial end portion of protruding cylindrical portion13of lower shell10located on the side of top plate portion21such that cavity C is provided as a closed space.

As described above, in disc-type gas generator1X according to the comparative example, bottom plate portion11in the portion except for protruding cylindrical portion13of lower shell10is in such an inclined shape as being inclined outward, in the direction toward the radially outer side of the circumferential wall portion of the housing. Therefore, lower shell10abuts on lower mold100only in the outer circumferential portion of bottom plate portion11in the portion except for protruding cylindrical portion13while it is placed on lower mold100as shown inFIG. 7, and in a state after the lower shell is sandwiched between lower mold100and upper mold200as shown inFIG. 8, the entire bottom plate portion11in the portion except for protruding cylindrical portion13abuts on lower mold100.

While lower shell10is placed on lower mold100, the inclined shape of bottom plate portion11in the portion except for protruding cylindrical portion13of lower shell10is maintained. As lower shell10is sandwiched between lower mold100and upper mold200, however, the portion of lower shell10except for the outer circumferential portion of bottom plate portion11described above is displaced by being pressed in a direction shown with an arrow AR2in the figure, and consequently lower shell10is elastically deformed. Bottom plate portion11in the portion except for protruding cylindrical portion13of lower shell10thus comes in intimate contact with lower mold100.

When disc-type gas generator1A in the present embodiment described above is compared with disc-type gas generator1X according to the comparative example, a difference below is produced in forming holding portion30.

As shown inFIG. 5, in disc-type gas generator1A in the present embodiment, the inclined shape of bottom plate portion11in the portion except for protruding cylindrical portion13of lower shell10is maintained also while lower shell10is sandwiched between lower mold100and upper mold200. Therefore, even though an insulating fluid resin material is injected into cavity C and solidified therein, the inclined shape of bottom plate portion11is maintained. When pressing of lower shell10by upper mold200is thereafter canceled, the inclined shape of bottom plate portion11is maintained. In mold release, no significant change in shape of lower shell10is caused.

Therefore, in mold release performed after formation of holding portion30as well, application of stress to holding portion30by mold release can be prevented, and disc-type gas generator1A can be manufactured at a high yield without impairing intimate contact between lower shell10and holding portion30.

On the other hand, in disc-type gas generator1X according to the comparative example as shown inFIG. 8, while lower shell10is sandwiched between lower mold100and upper mold200, lower shell10is elastically deformed. Therefore, when pressing of lower shell10by upper mold200is canceled while an insulating fluid resin material is injected into cavity C and solidified therein, bottom plate portion11tends to return to the original shape based on elastic force and the portion of bottom plate portion11described above of lower shell10except for the outer circumferential portion is displaced in a direction shown with an arrow AR3in the figure. This phenomenon is what is called spring-back, which apples large stress to holding portion30formed by injection molding.

Generation of this stress leads to the possibility of separation between lower shell10and holding portion30. When such separation occurs, intimate contact between lower shell10and holding portion30is consequently impaired. Therefore, disc-type gas generator1X according to the comparative example may not be able to maintain hermeticity in that portion, and consequently it becomes difficult to manufacture disc-type gas generator1X at a high yield.

Lower shell10is made, for example, of a press-formed product formed by press-working a plate-shaped member made of a rolled metal as described above. Therefore, a shape of the shell suffers from prescribed variation during press-working. Therefore, even though press-working is performed with such an aim that bottom plate portion11in the portion except for protruding cylindrical portion13of lower shell10is not in the inclined shape (that is, flat), the shape is naturally varied. Consequently, press-worked workpieces include a workpiece of which bottom plate portion11in the portion except for protruding cylindrical portion13of lower shell10is flat, a workpiece of which bottom plate portion11in the above-described portion of lower shell10is inclined inward in the direction toward the radially outer side of the circumferential wall portion of the housing, and a workpiece of which bottom plate portion11in the above-described portion of lower shell10is inclined outward in the direction toward the radially outer side of the circumferential wall portion of the housing.

Therefore, by performing press-working in advance with such an aim that bottom plate portion11in the portion except for protruding cylindrical portion13of lower shell10is inclined inward in the direction toward the radially outer side of the circumferential wall portion of the housing in consideration of occurrence of variation, press-worked workpieces do not include a workpiece of which bottom plate portion11in the above-described portion of lower shell10is inclined outward in the direction toward the radially outer side of the circumferential wall portion of the housing, and occurrence of a defect due to spring-back described above can be prevented.

When inclination angle θ1described above is larger than necessary, stability in placement of lower shell10with respect to lower mold100is impaired or a volume of combustion chamber60where gas generating agent61is accommodated is decreased. Therefore, inclination angle θ1preferably satisfies a condition of 0[°]<θ1≤2[°].

Other characteristic features of disc-type gas generator1A in the present embodiment described above are summarized as below.

A disc-type gas generator in the present embodiment includes a housing, an igniter, and a holding portion. The housing includes a cylindrical circumferential wall portion provided with a gas discharge opening and a top plate portion and a bottom plate portion which close one and the other axial ends of the circumferential wall portion, and contains a combustion chamber which accommodates a gas generating agent. The igniter serves to burn the gas generating agent. The holding portion is provided in the bottom plate portion and holds the igniter. The bottom plate portion includes a protruding cylindrical portion provided to protrude toward the top plate portion. An opening in which the igniter is inserted and arranged is provided in an axial end portion of the protruding cylindrical portion located on a side of the top plate portion. The holding portion is made of a resin molded portion at least partly secured to the bottom plate portion by being formed by attaching a fluid resin material to the bottom plate portion so as to reach a part of an outer surface of the bottom plate portion from a part of an inner surface of the bottom plate portion through the opening and solidifying the fluid resin material. The bottom plate portion in a portion except for the protruding cylindrical portion is in such an inclined shape as being inclined toward the top plate portion, in a direction toward a radially outer side of the circumferential wall portion. An inclination angle θ1of the bottom plate portion in the portion except for the protruding cylindrical portion satisfies a condition of 0[°]<θ1≤2 [°].

The method of manufacturing disc-type gas generator1A in the present embodiment described above is summarized as below.

The method of manufacturing a disc-type gas generator in the present embodiment is a method of manufacturing the disc-type gas generator in the present embodiment described above, and it includes placing a lower shell including the bottom plate portion provided with the protruding cylindrical portion on a lower mold, setting the igniter into the lower mold as being inserted in the opening, sandwiching the lower shell between the upper mold and the lower mold by lowering the upper mold toward the lower mold, forming the holding portion by injecting the fluid resin material into a cavity defined by the lower mold, the upper mold, the lower shell, and the igniter and solidifying the fluid resin material, and releasing the upper mold and the lower mold from the lower shell in which the holding portion is formed. In the sandwiching the lower shell between the upper mold and the lower mold, the upper mold is lowered to abut on the outer circumferential portion of the protruding cylindrical portion.

Second Embodiment

FIG. 9is a schematic diagram of a disc-type gas generator in a second embodiment of the present invention. A disc-type gas generator1B in the present embodiment will be described below with reference toFIG. 9. Though disc-type gas generator1B in the present embodiment is set to relatively be large in amount of generation of gas at the time of activation similarly to disc-type gas generator1A in the first embodiment described above, an amount of generation of gas thereof is set to approximately 2.0 [mol].

As shown inFIG. 9, disc-type gas generator1B in the present embodiment is constructed to be smaller in amount of loaded gas generating agent61and also amount of loaded enhancer agent56than disc-type gas generator1A in the first embodiment described above by an amount comparable to decrease in amount of generation of gas at the time of activation. Accordingly, a length of cup-shaped member50along the axial direction of the circumferential wall portion of the housing is also shorter. Ra is set to approximately 14.0 [mm] whereas Ha is set to approximately 14.2 [mm], and a value of Ra/Ha is approximately 0.99.

Therefore, disc-type gas generator1B in the present embodiment also satisfies the condition of Ra/Ha≤1.00 and may suffer from the problem of delay in start of discharge of gas to the outside through gas discharge opening23after the time point of activation of igniter40. Therefore, disc-type gas generator1B in the present embodiment solves the problem also by providing partition wall portion73to surround a part of sidewall portion51of cup-shaped member50similarly to disc-type gas generator1A in the first embodiment described above.

Disc-type gas generator1B in the present embodiment is also constructed to satisfy the condition of Hb≤13.5 [mm]. Specifically, Hb is set to approximately 4.0 [mm]. Therefore, a ratio of Hb to Ha described above is approximately 0.28.

Disc-type gas generator1B in the present embodiment is constructed such that Hc is set to approximately 16.0 [mm]. Thus, a part on the side of bottom plate portion11of each of the plurality of gas discharge openings23is provided to be opposed to second region R2of sidewall portion51of cup-shaped member50in the radial direction of the circumferential wall portion of the housing.

Disc-type gas generator1B thus constructed also obtains an effect the same as the effect described in the first embodiment above. Delay in start of discharge of gas to the outside through gas discharge opening23after the time point of activation of igniter40can effectively be prevented, and consequently a disc-type gas generator high in such performance as being free from delay in development of an air bag can be obtained.

Though an example in which the upper shell and the lower shell are made of press-formed products formed by press-working of a member made of a metal is shown by way of example in the first and second embodiments of the present invention described above, limitation thereto is not necessarily intended. An upper shell and a lower shell formed by combination of press-working and another type of working (forging, drawing, or cutting) may be employed, or an upper shell and a lower shell formed only by another type of working may be employed.

Though an example in which a protruding cylindrical portion is provided in the lower shell is shown by way of example in the first and second embodiments of the present invention described above, the present invention is also naturally applicable to a gas generator without a protruding cylindrical portion.

The embodiments disclosed herein are thus illustrative and non-restrictive in every respect. The technical scope of the present invention is delimited by the terms of the claims and includes any modifications within the scope and meaning equivalent to the description in the terms of the claims.

REFERENCE SIGNS LIST