Abstract:
A gas generator which has an initiator and a gas generating agent for use in airbag deployment systems. An initiator includes a reaction agent, a casing formed by a cup and header, an electrode and a plasma generating agent. The plasma generating agent generates a plasma in response to the energization of the electrode that makes the reaction agent initiate a reaction.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to an initiator suitable for being built in a gas generator for an airbag system or a seatbelt pretensioner, or the like, and the gas generator having the initiator.  
           [0002]    An airbag system provided on a high-speed mobile body such as a vehicle is constructed to deploy a bag-shaped airbag by a gas generator, which is called an inflator. The gas generator includes a gas generating agent and an initiator for initiating a gas generating reaction of the gas generating agent. Conventionally, the initiator includes a reaction agent, and a filament (bridge wire) as a resistance heat generating element for initiating a reaction of the reaction agent (for example, U.S. Pat. No. 5,404,263) (incorporated by reference).  
           [0003]    An example of the initiator in the related art will be described in conjunction with FIG. 8.  
           [0004]    An initiator  10  has a substantially cup-shaped casing  12  opening at the rear (the bottom in FIG. 8). A reaction agent  14  is stored in the casing  12 . The rear portion of the casing  12  is closed by an insulating material  16  formed of sintered glass or the like. Extremities of a pair of electrodes  18 ,  20  passing through the insulating material  16  are exposed in the casing  12 .  
           [0005]    A filament  22  extends between the extremities of the electrodes  18 ,  20 . The both ends of the filament  22  are welded to the extremity surfaces of the respective electrodes  18 ,  20 . The filament  22  is in contact with the reaction agent  14  in the casing  12 .  
           [0006]    The electrodes  18 ,  20 , and the casing  12  are disposed away from each other so as not to be brought into electrical contact.  
           [0007]    In the initiator  10  so constructed, one of the electrodes  18  is connected to a positive pole of a battery  26  of a motor vehicle via a control circuit  24  having a voltage boosting circuit or the like, and the other electrode  20  is connected to a vehicle body of the motor vehicle (earth connection). The negative pole of the battery  26  is connected to the vehicle body of the motor vehicle.  
           [0008]    In case or emergency such as a vehicle collision or the like, a switch element in the control circuit  24  is turned ON, and a voltage is applied on the filament  22  from the battery  26 . Accordingly, the filament  22  generates heat, and the reaction agent  14  is ignited and initiates a reaction. The reaction of the reaction agent  14  generates high pressure gas or heat, whereby the gas generating agent in the gas generator causes a gas generating reaction.  
           [0009]    The reaction agent used here includes a first reaction agent that is a mixture of lead styphnate and aluminum powder disposed so as to surround the filament  22 , and a second reaction agent formed of BKNO 3  or blasting powder disposed so as to surround the first reaction agent. The first reaction agent quickly reacts exothermally and the second reaction agent starts a reaction upon reception of heat from the first reaction agent, thereby generating a high-pressure and high-temperature gas and minute particles.  
           [0010]    Referring now to FIG. 9, an example of the gas generator provided with the initiator  10  will be described. A gas generator  30  includes a container including an outer shell having an upper housing  32  and a lower housing  34 , and a cylindrical partitioning member  36  disposed in the outer shell. One end of the partitioning member  36  passes through an opening on the bottom of the lower housing  34  and projects downward. The inner peripheral surface of the opening and the outer peripheral surface of the partitioning member  36  are welded by laser beam welding or the like. An igniting agent (booster propellant)  40  is stored inside the partitioning member  36 , and a gas generating agent (main propellant)  42  is stored outer circumferentially of the partitioning member  36 .  
           [0011]    The partitioning member  36  is provided with the initiator  10  at the above-described end thereof. When the igniting agent  40  is ignited by the initiator  10 , gas is injected from an opening  44  of the partitioning member  36  to ignite the gas generating agent  42 , whereby a large amount of gas is quickly generated and is injected through a filter  46  formed of a mesh or the like and through an opening  48  out of the gas generator  30 , so that the airbag is deployed. FIG. 9 shows only an example of the gas generator, and various gas generators of the shape other than the one shown in the drawing are used as well.] 
           [0012]    In the conventional initiator shown in FIG. 8, in order to fix an electric resistance of the filament  22 , the length or welding conditions of the filament  22  have to be controlled strictly, which takes a lot of trouble in manufacture and causes increase in costs.  
           [0013]    In addition, it is necessary that the reaction agent  14  is sensitive so as to be ignited even with a small amount of energy generated by the filament  22 , and handling of such sensitive reaction agent  14  requires a special care.  
         SUMMARY OF THE INVENTION  
         [0014]    An object of the present invention is to provide an initiator which does not use a resistance heat generating element such as a filament or the like, and is able to use a reaction agent which is easy to manufacture and is safe in the handling thereof. Another object of the present invention is to provide a gas generator provided with the initiator.  
           [0015]    An initiator of the present invention includes a casing, a reaction agent disposed in the casing, an electrode, and a plasma generating agent for generating a plasma by being energized and initiating a reaction of the reaction agent.  
           [0016]    The initiator of the present invention may include a casing, an electrode, and a mixture of a reaction agent and a plasma generating agent disposed in the casing are provided, and may be characterized in that the plasma generating agent generates a plasma in response to energization of the electrode and thus a reaction of the reaction agent is initiated.  
           [0017]    In the initiator according to the present invention, when a voltage is applied to the electrode, the plasma generating agent is turned to a high-temperature plasma state. Heat generated by the plasma generating agent causes the reaction agent to initiate a reaction, and high-pressure gas or heat generated by the reaction ignites the gas generating agent in the gas generator. Since this initiator is provided with the plasma generating agent instead of providing a filament, it may easily be manufactured and may be manufactured at a high yield ratio at a low cost without variations in quality.  
           [0018]    Since heat generating energy of the plasma generating agent is larger than heat generating energy of the filament, a reaction agent which is safer in the handling than the sensitive reaction agent that has been used when using the filament.  
           [0019]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only, and are not restrictive of the invention as claimed. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]    These and other features, aspects, and advantages of the present invention will become apparent from the following description, appended claims, and the accompanying exemplary embodiments shown in the drawings, which are briefly described below.  
         [0021]    [0021]FIG. 1 is a cross-sectional view of an initiator according to an embodiment of the present invention.  
         [0022]    [0022]FIG. 2 is a cross-sectional view of an initiator according to another embodiment of the present invention.  
         [0023]    [0023]FIG. 3 is a cross-sectional view of an initiator according to still another embodiment of the present invention.  
         [0024]    [0024]FIG. 4 is a cross-sectional view of an initiator according to an embodiment of the present invention.  
         [0025]    [0025]FIG. 5 is a cross-sectional view of an initiator according to an embodiment of the present invention.  
         [0026]    [0026]FIG. 6 is a cross-sectional view of an initiator according to an embodiment of the present invention.  
         [0027]    [0027]FIG. 7 is a cross sectional view of an initiator according to an embodiment of the present invention.  
         [0028]    [0028]FIG. 8 is a cross-sectional view of an initiator according to the related art.  
         [0029]    [0029]FIG. 9 is a cross-sectional view showing an example of a construction of a gas generator. 
     
    
     DETAILED DESCRIPTION  
       [0030]    Referring now to the drawings, embodiments will be described. FIG. 1 to FIG. 7 are cross-sectional views of an initiator according to an embodiment of the present invention.  
         [0031]    According to an initiator  50  shown in FIG. 1, a casing  56  is constructed of a cup  52  and a header  54  inserted through an entrance of the cup  52 , and a reaction agent  58  is filled in the casing  56 . In this embodiment, the cup  52  is a circular container formed of a SUS 304 or the like. The header  54  is a substantially disk-shaped member formed of SUS 304 or the like, and an outer peripheral surface thereof is secured to an inner peripheral surface of the cup  52  by welding or the like.  
         [0032]    The header  54  is provided with a through hole  60  extending in the direction of the thickness of the header at the center thereof. Electrode pins  62 ,  64  are inserted into the hole  60  at a distance from each other, and these pins  62 ,  64  are fixed to the header  54  by an insulative fixing material  66  such as glass or the like so as to keep away from the header  54 . Extremity surfaces of the pins  62 ,  64  are flush with an extremity surface of the header  54 . A thin plate shaped molding of a plasma generating agent  72  is disposed at the extremity surface (the upper end surface in the drawing) of the header  54  on the inner side of the cup.  
         [0033]    The plasma generating agent  72  is formed, for example, of water glass (Na 2 O/SiO 2 , K 2 O/SiO 2 ), KClO 3 , KClO 4 , KCl and the like, and powder, such as KClO 3 , KClO 4 , KCl and the like, is formed into a thin plate shape by being pressed. The extremities of the pins  62 ,  64  are in contact with the plasma generating agent  72 .  
         [0034]    There is a gap between an extremity surface of the plasma generating agent  72  and a ceiling surface of the cup  52  and a reaction agent  58  is stored therein.  
         [0035]    The outer surface of the cup  52  is covered with a resin cover  68  formed of nylon, polypropylene or the like. The rear side of the cup  52  and the rear end surface of the header  54  are covered with a resin cover  70  formed of nylon, polybutylene terephtalate, or the like. The pins  62 ,  64  projects outward through the resin cover  70 .  
         [0036]    The reaction agent  58  may be formed only of a first reaction agent (igniting agent), and may be formed of a mixture of the first reaction agent and a second reaction agent (particles of an oxidizing agent). Though the kind of the first reaction agent is not specifically limited, a single metal, such as Mg, Zr, Ti, W, B, Si, C, Be, Li, Al, V, CaC 2 , Ca, Ce, La or the like, or an alloy thereof, or a compound thereof are used. Though the kind of the second reaction agent is not specifically limited, KClO 4 , KClO 3 , KIO 4 , NH 4 ClO 4 , NH 4 NO 3 , KNO 3 , Fe 2 O 3 , Fe 3 O 4 , Sr (NO 3 ) 2 , CuO, NiO, and the like are used.  
         [0037]    In the initiator  50  so constructed, when a voltage is applied between the pins  62 ,  64 , a high-temperature plasma is generated from the plasma generating agent  72  provided between these two pins  62 ,  64 . Then, the reaction agent  58  initiates a reaction by heat from the plasma, and then gas containing a high pressure and high-temperature minute particles is generated. When the reaction agent  58  contains particles of an oxidizing agent, the metallic particles are quickly oxidized and thus generate heat due to oxidizing action of the particles of the oxidizing agent, thereby promoting the reaction.  
         [0038]    In this embodiment, a filament (wire bridge) is not used, and thus a lot of trouble during manufacturing may be significantly reduced.  
         [0039]    In this embodiment, a high-temperature plasma is stably generated by the plasma generating agent  72 . Therefore, a reaction agent that is less sensitive than the reaction agent (igniting agent) which is used when using the filament may be used, whereby the handling of the reaction agent is facilitated.  
         [0040]    In an initiator  50 A shown in FIG. 2, material of a header  54 A is changed into plastic (synthetic resin).  
         [0041]    The initiator  50 A in FIG. 2, a casing  56 A is constructed of a metallic cup  52 A and the plastic header  54 A inserted through the entrance of the cup  52 A. The electrode pins  62 ,  64  are inserted into the header  54 A. An extremity surface of the header  54 A is flush with the extremity surfaces of the pins  62 ,  64 . The plasma generating agent  72  is disposed so as to be superimposed on the extremity surface of the header  54 . The cup  52 A is covered by a resin cover, not shown. Other constructions are the same as the initiator  50  shown in FIG. 1, and the same parts are represented by the same reference numerals.  
         [0042]    In this initiator  50 A, when the portion between the pins  62 ,  64  is energized, a high-temperature plasma is generated from the plasma generating agent  72 , and the reaction agent  58  initiates a reaction by heat therefrom.  
         [0043]    An initiator  50 B shown in FIG. 3 includes a plasma generating agent formed by mixing a plasma generating agent and a reaction agent. A mixture  72 B is fixed to the extremities of the pins  62 ,  64  in a ball shape or in a small block shape by using a binder such as water glass or the like.  
         [0044]    In this embodiment, the extremities of the electrode pins  62 ,  64  projects from the extremity surface of the header  54 A, and a mixture  72 B is attached to the pins  62 ,  64  so as to cover the extremities thereof. The mixture  72 B is attached to the extremities of the pins  62 ,  64  so as to straddle therebetween. Other constructions are the same as the initiator  50 A in FIG. 2, and the same parts are represented by the same reference numerals.  
         [0045]    In the initiator  50 B thus constructed, when a voltage is applied between the pins  62 ,  64 , a high-temperature plasma is generated from the plasma generating agent contained in the mixture  72 B provided between the two pins  62 ,  64 . Then, the reaction agent contained in the mixture  72 B initiates a reaction by heat from the high-temperature plasma, and then the reaction agent  58  provided outside the mixture  72 B initiates a reaction by reaction heat therefrom.  
         [0046]    [0046]FIG. 4 shows an initiator  50 C of a single-pin structure. A header  54 C is constructed of a column portion  54   a , and a flange portion  54   b  projecting from the lower peripheral surface of the column portion  54   a . A casing  56 C is constructed of the header  54 C and a cup  52 C fitted on the column potion  54   a  of the header  54 C. The header  54 C and the cup  52 C are both formed of metal.  
         [0047]    The header  54 C is provided with a hole  60 C extending in the direction of thickness of the header at the center thereof. A single electrode pin  62 C is inserted into the hole  60 C, and fixed to the head  54 C by an insulative fixing material  66  such as glass or the like. An extremity of the pin  62 C is flush with an extremity of the header  54 C, and the plasma generating agent  72  is disposed on the extremity surface of the header  54 C.  
         [0048]    The flange portion  54   b  of the header  54 C is provided with a plurality of bolt holes  54   c.    
         [0049]    In the initiator  50 C of a single pin structure thus constructed, the header  54 C serves as a positive electrode. In other words, when a voltage is applied between the header  54 C and the pin  62 C, a high-temperature plasma is generated from the plasma generating agent  72 , and the reaction agent  58  initiates a reaction by the heat therefrom.  
         [0050]    In an initiator  50 D in FIG. 5, a casing  56 D is constructed of a metallic cup  52 D and a metallic header  54 D inserted through the entrance of the cup  52 D. An outer peripheral surface of an insulative sleeve  80  formed of an insulating material abuts against the inner peripheral surface of the cup  52 D. One end (upper end in the drawing) of the insulative sleeve  80  is in contact with a ceiling surface of the cup  52 D, and the other end (lower end) thereof is fitted into a recess  54   a  curved around the outer peripheral surface of the header  54 D. A plate shaped molding of a mixture  58 D of MgPP (magnesium parchlorate (reaction agent)) and a plasma generating agent is disposed at the ceiling portion of the inner surface of the cup  52 D. The mixture is formed into a plate shape by using a binder or by being pressed. The mixture  58 D is held by the ceiling surface of the cup  52 D by using the binder or by being pressed. A gap  82  formed between the mixture  58 D and the header  54 D is filled with air or oxygen in a tightly sealed manner.  
         [0051]    The header  54 D is formed with a through hole  60 D in the direction of the thickness of the header at the center thereof. An electrode pin  62 D is inserted into the hole  60 D, and is fixed to the header  54 D by an insulative fixing material  66 D such as glass or the like. An extremity of the pin  62 D is pointed, and the pointed extremity is disposed away from the mixture  58 D so as to be brought into contact therewith. An electrode pin  64 D is fixed to the rear surface of the header  54 D by welding or the like.  
         [0052]    Though it is not shown, the outer surface of the cup  52 D is covered with a resin cover, and the rear side of the cup  52 D and the rear end surface of the header  54 D are covered by a resin cover (similar to the resin cover  70  shown in FIG. 1 and FIG. 2). The pins  62 D,  64 D project through the resin cover outward.  
         [0053]    In the initiator  50 D so constructed, when a voltage is applied between the pins  62 D,  64 D, arc discharge toward the ceiling of the cup  52 D occurs from the tip of the pin  62 D. In this case, since the insulative sleeve  80  is provided on the inner peripheral surface of the cup  52 D, arc discharge occurs only between the pin  62 D and the ceiling surface of the cup  52 . When the arc passes trough the mixture  58 D, a plasma generating agent contained in the mixture  58 D reacts and generates a high-temperature plasma, and MgPP in the layer of mixture  58 D initiates a reaction.  
         [0054]    In an initiator  50 E in FIG. 6, an extremity of a pin  62 E is covered by a mixture  88 . The mixture  88  is fixed to the extremity of the pin  62 E by soaking the extremity of the pin  62 E in a slurry mixture of MgPP and a plasma generating agent, then taking out the pin  62 E therefrom, and dip drying the same.  
         [0055]    A reaction agent  86  of MgPP formed by press forming is attached to the extremity surface of the header  54 D. A gap  82  formed between the reaction agent  86  and the ceiling surface of the cup  52 D is filled with a metallic sleeve (metallic wool) formed of metal such as Zr, Mg, Ti, W, Al and the like. Other constructions of the initiator  50 E shown in FIG. 6 are the completely same as the initiator  50 D shown in FIG. 5, and the same parts are represented by the same reference numerals.  
         [0056]    In the initiator  50 E so constructed, when a voltage is applied between the pin  62 E and  64 D, ark discharge occurs between the pin  62 E and the ceiling surface of the cup  52 D, and a high-temperature plasma is generated from a plasma generating agent in the mixture  88 . MgPP in the mixture initiates reaction by heat therefrom. Heat generated in the mixture  88  is transmitted to the reaction agent  86  via the metallic sleeve  84 , and heat generated in the mixture  88  causes combustion of the metallic sleeve  84 , combustion heat of which is also transmitted to the reaction agent  86 . Transmitted heat as such initiates a reaction of the reaction agent  86 .  
         [0057]    An initiator  50 F in FIG. 7 includes the metallic cup  52 D, and a resin cover  70 F provided at the rear end (opening) of the cup  52 D. The reaction agent  86  formed of MgPP by press molding is provided on the ceiling surface of the cup  52 D. A gap  82 F is formed between the reaction agent  86  and the resin cover  70 F.  
         [0058]    Two electrode pins  62 F,  64 F are passed through the resin cover  70 F in the fore-and-aft direction (vertical direction in FIG. 7). The portions of the pins  62 F,  64 F located in the gap  82 F are covered by mixtures  90   a ,  90   b , respectively.  
         [0059]    The mixtures  90   a ,  90   b  are fixed to the pins  62 F,  64 F by soaking the extremities of the pins  62 F,  64 F into a slurry mixtures of MgPP and a plasma generating agent, taking them out and dried.  
         [0060]    The metallic sleeve  84  is filled in the space  82 F, and the outer surface of the cup  52 D is covered by a resin cover, not shown.  
         [0061]    In the initiator  50 F thus constructed, when a voltage is applied between the pin  62 F and the pin  64 F, a current is flown between the pin  62 F,  64 F via the metallic sleeve  84 , and a plasma generating agent in the mixture  90   a ,  90   b  generates a high-temperature plasma, and MgPP in the mixtures  90   a ,  90   b  initiate a reaction. Heat generated from the mixtures  90   a ,  90   b  are transmitted to the reaction agent  86  via the metallic sleeve  84 , and causes combustion of the metallic sleeve  84  to generates heat. Heat thus generated heat causes initiation of reaction of the reaction agent  86 .  
         [0062]    The initiator of the present invention maybe applied to various gas generators. The gas generators may be built in various airbag systems for a driver&#39;s seat, for a front seat, for a rear seat, for a side, for protecting a head, and for protecting a pedestrian, or in a seat belt tensioner, including, for example, the gas generator shown in FIG. 9.  
         [0063]    As described above, according to the present invention, since a bridge wire is not used, an initiator in which a trouble of welding may be omitted, and a reaction agent that can easily be manufactured and is safe in the handling, and a gas generator using such initiator are provided.  
         [0064]    The priority application, Japanese Patent Application No. 2002-380188, filed on Dec. 27, 2002, including the specification, drawings, claims and abstract, is incorporated herein by reference in its entirety.  
         [0065]    Given the disclosure of the present invention, one versed in the art would appreciate that there may be other embodiments and modifications within the scope and spirit of the invention. Accordingly, all modifications attainable by one versed in the art from the present disclosure within the scope and spirit of the present invention are to be included as further embodiments of the present invention. The scope of the present invention is to be defined as set forth in the following claims.