Initiator and gas generator

Abstract

An initiator includes a casing, a reactant disposed in the casing, and electrodes arranged to contact the reactant. The reactant contains an electrically conductive substance in a manner such that once a voltage is applied to the electrodes, an electric current flows through the electrically conductive substance, thereby initiating a reaction of the reactant. The initiator is easily manufactured with low manufacturing cost.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001] The present invention relates to an initiator suitable for installing in a gas generator of an airbag apparatus and a seat belt pre-tensioner. This invention also relates to a gas generator equipped with such an initiator.

[0002] An airbag apparatus provided in a fast moving vehicle such as an automobile is usually constructed in a manner such that a gas generator called an inflator quickly inflates a bag-shape airbag. Such a gas generator comprises a gas generating agent and an initiator for initiating a reaction of the gas generating agent. Conventionally, such an initiator comprises a reactant and a filament (a bridge wire) serving as a resistive heating element for initiating the reaction of the reactant.

[0003] An example of a conventional initiator will be described below with reference to FIG. 8.

[0004] An initiator 10 includes a substantially cap-shape casing 12 having an opening at a rear portion (a lower portion in FIG. 8). A reactant 14 is stored in the casing 12. An insulator 16 such as a sintered glass and the like seals the rear portion of the casing 12. A pair of electrodes 18, 20 is penetrating through the insulator 16 so that end portions thereof are exposed in the interior of the casing 12.

[0005] A filament 22 is bridged between the end portions of the two electrodes 18 and 20. Both ends of the filament 22 are welded to surfaces of the end portions of the respective electrodes 18 and 20. Further, the filament 22 is in contact with the reactant 14 in the casing 12.

[0006] The two electrodes 18, 20 and the casing 12 are arranged separately from each other so that they are not electrically connected with each other.

[0007] In the initiator 10 constructed in the above-described manner, the electrode 18 is connected to a positive electrode of an automobile battery 26 through a control circuit 24 equipped with a voltage step-up circuit and the like, while the other electrode 20 is connected (earth connection) to a main body of an automobile. A negative electrode of the battery 26 is connected to the main body of an automobile.

[0008] In a case of an accident such as a collision between automobiles and the like, a switching element within the control circuit 24 turns on, so that a voltage from the battery 26 is applied to the filament 22 through the respective electrodes 18 and 20. As a result, the filament 22 generates heat to ignite the reactant 14, thereby initiating the reaction of the reactant. The reaction of the reactant 14 generates a high-pressure gas and a large amount of heat, so that the gas generating agent in the gas generator initiates a gas generating reaction.

[0009] The reactant includes, for example, the first reactant and the second reactant. The first reactant is arranged around the filament 22 and is a mixture of a lead styphnate and an aluminum powder. The second reactant is arranged around the first reactant and consists of BKNO3 or a black powder. The first reactant quickly undergoes a heat generating reaction, while the second reactant starts its reaction by virtue of heat produced by the first reactant, thereby generating a high-pressure hot gas as well as fine particles.

[0010] An example of a conventional gas generator equipped with the initiator 10 is described as follows with reference to FIG. 9. A conventional gas generator 30 includes a container having an outer case consisting of an upper housing 32 and a lower housing 34, and having a cylindrical partition member 36 disposed within the outer case. One end of the cylindrical partition member 36 protrudes downwardly through an opening formed at the bottom of the lower housing 34. An internal circumferential surface of the opening and an external circumferential surface of the cylindrical partition member 36 are welded together by means of laser beam welding and the like. An igniting agent (booster propellant) 40 is stored in the cylindrical partition member 36, while a gas generating agent (main propellant) 42 is arranged at an outside of the cylindrical partition member 36.

[0011] As shown in the drawing, the initiator 10 is disposed at one end of the cylindrical partition member 36. When the igniting agent 40 is ignited by the initiator 10, a gas erupts through openings 44 of the cylindrical partition member 36, thus igniting the gas generating agent 42. As a result, a large amount of gas is generated rapidly, passing through filters 46 consisting of meshes and the like, and further passing through openings 48. Consequently, the gas erupts out of the gas generator 30, thereby inflating an airbag. Note that FIG. 9 shows only one example of the conventional gas generators, and there are many types of gas generators having shapes different from that shown in the drawing.

[0012] In the conventional initiator shown in FIG. 8, in order to ensure a predetermined constant electric resistance of the filament 22, a manufacturing process is required to perform a strict control on a length of the filament 22 as well as a welding condition when connecting the same. As a result, it is difficult to reduce time and labor in the manufacturing process, hence making it difficult to reduce a production cost.

[0013] Accordingly, it is an object of the present invention to provide an improved initiator without using a resistive heat generator such as a filament and the like, and can be manufactured easily and thus at a reduced cost.

[0014] It is another object of the invention to provide an improved gas generator equipped with such an improved initiator.

[0015] Further objects and advantages of the invention will be apparent from the following description of the invention.

SUMMARY OF THE INVENTION

[0016] An initiator of the present invention comprises a casing, a reactant disposed in the casing, and electrodes arranged to contact the reactant. The reactant contains an electrically conductive substance in a manner such that once a voltage is applied to the electrodes, an electric current flows through the electrically conductive substance, thereby initiating a reaction of the reactant.

[0017] In the initiator of the present invention, once a voltage is applied to the electrodes, an electric current will flow between the electrodes through the electrically conductive substance contained within the reactant, thereby causing the electrically conductive substance to produce heat. This heat initiates the reaction of the reactant, thereby generating a high-pressure gas and heat to ignite a gas generating agent in a gas generator. The initiator contains the electrically conductive substance instead of using a filament, thus it is possible to simplify a manufacturing process, resulting in a uniform quality, a higher yield and a lower cost.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIGS. 1(a) and 1(b) are cross sectional views showing an initiator according to an embodiment of the present invention;

[0019] FIG. 2 is a cross sectional view showing an initiator according to an embodiment of the present invention;

[0020] FIG. 3 is a cross sectional view showing an initiator according to an embodiment of the present invention;

[0021] FIG. 4 is a cross sectional view showing an initiator according to an embodiment of the present invention;

[0022] FIG. 5 is a cross sectional view showing an initiator according to an embodiment of the present invention;

[0023] FIG. 6 is a cross sectional view showing an initiator according to an embodiment of the present invention;

[0024] FIG. 7 is a cross sectional view showing an initiator according to an embodiment of the present invention;

[0025] FIG. 8 is a cross sectional view showing a conventional initiator;

[0026] FIG. 9 is a cross sectional view showing an example of a conventional gas generator;

[0027] FIG. 10 is a cross sectional view showing an initiator according to an embodiment of the present invention; and

[0028] FIG. 11 is a cross sectional view showing an initiator according to an embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0029] Hereunder, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 to FIG. 7 are cross sectional views showing initiators according to the embodiments of the present invention.

[0030] In FIG. 1(a), an initiator 50 has a casing 56 including a cup 52 and a head 54 inserted in the cup 52 through its opening. The casing 56 is filled with a reactant 58. In the present embodiment, the cup 52 is a circular container formed of SUS 304 or the like. The head 54 is a substantially circular member also formed of SUS 304 or the like. An outer circumference surface of the head 54 is secured onto the inner circumference surface of the cup 52 by welding and the like.

[0031] An internal space is formed between a front surface of the head 54 and a bottom surface of the cup 52, while the reactant 58 is received in the internal space.

[0032] A through hole 60 is formed through a central portion of the head 54 in a thickness direction thereof. An electrode pin 62 is inserted in the through hole 60 and is secured in the head 54 by means of an insulating securing material 64 such as a glass and the like. Further, in the present embodiment, the front-end surface of the pin 62 is at the same height as that of the front-end surface of the head 54. Moreover, another electrode pin 66 is secured by welding and the like on the rear end surface of the head 54.

[0033] The outer surface of the cup 52 is covered by a resin cover 68 formed of nylon, polypropylene or the like. The rear portion of the cup 52 as well as the rear end surface of the head 54 are covered by a resin cover 70 formed of nylon, polybutylene terephthalate or the like. Both pins 62 and 66 are arranged to protrude outwardly through the resin cover 70.

[0034] The reactant 58 contains a reactive component such as a valve metal like Al, Ti and the like having a rectifying function, and electrically conductive particles 58a. The electrically conductive particles 58a include metal particles and/or metal oxide particles. The metal particles include aluminum particles, magnesium particles, tantalum particles, zirconium particles, copper particles, or the like.

[0035] The metal oxide particles include oxide particles such as Ti2O3 particles, MoO2 particles, MnO2 particles or the like, each of which has an electrical conductivity and can also function as an oxidant. Preferably, the specific resistance of the electrically conductive metal oxide particles is equal to or less than 0.1 &OHgr;m. The reactant may contain both metal particles and electrically conductive oxide particles.

[0036] Further, the reactant may contain non-conductive oxidant particles. For example, it is possible for the reactant to contain both metal particles and non-conductive oxidant particles.

[0037] In the initiator 50 having the above-described structure, once a voltage is applied between the pins 62 and 66, an electric current will flow between the pin 62 and the head 54 through the electrically conductive particles 58a contained in the reactant 58. Then, due to Joule heat generated by the electric current flowing therethrough, the reactant 58 starts to react, thus producing a high-pressure gas containing hot particles. At this time, in the case that the reactant 58 contains the oxidant particles, the reaction may be accelerated due to an oxidization action produced by the oxidant particles. In the case that the electrically conductive particles 58a contains both the electrically conductive oxidant particles and metal particles, the electrically conductive oxidant shows the oxidation activity during the exothermic process, thereby causing the metal particles to be quickly oxidized and thus producing the heat.

[0038] In the present embodiment, since a filament (wire bridge) is not used, it is possible to greatly reduce a manufacturing cost.

[0039] In FIG. 1(a), the front-end surface of the pin 62 is located at the same height as that of the front-end surface of the head 54. However, it is also possible that the front end of a pin 62′ projects beyond the head 54 so as to extend into the reactant 58, as in another initiator 50′ shown in FIG. 1(b). In this way, it is possible to increase a contact area between the pin 62′ and the electrically conductive particles 58a dispersed in the reactant 58. Since other portions and elements of the initiator 50′ shown in FIG. 1(b) are the same as those of the initiator 50 shown in FIG. 1(a), the same portions and elements are represented by the same reference numerals.

[0040] An initiator 50A shown in FIG. 2 has a pin 62A formed of a front portion 62a and a rear portion 62b connected with each other by means of welding. The front portion 62a of the pin is integrally connected in advance with a solid electrically conductive oxidant 72. The front portion 62a of the pin is inserted through the hole 60 of the head 54 and welded to the rear portion 62b of the pin. A reference number 62w represents a welded position. The solid electrically conductive oxidant 72 is surrounded by a surrounding material 74. The surrounding material 74 is formed of a metal. Since other portions and elements of this initiator are the same as those of the initiator 50 shown in FIG. 1(a), the same portions and elements are represented by the same reference numerals.

[0041] An initiator 50B shown in FIG. 3 employs a casing including a cup 76 formed of a synthetic resin and a plug 78 formed of a synthetic resin. The casing is filled with the reactant 58 containing metal particles 80 and electrically conductive oxide particles 82. The pins 62 and 66 pass through a resin cover 70 and a plug 78, and protrude into the reactant 58. It is also possible to use non-conductive oxide particles instead of the electrically conductive oxide particles 82.

[0042] In an initiator 50C shown in FIG. 4, a metal block 84 is fixed to the front end of the pin 66 of the initiator 50B shown in FIG. 3. The reactant 58 contains the electrically conductive oxide particles 82, and does not contain metal particles.

[0043] In an initiator 50D shown in FIG. 5, a box-like casing 86 made of a synthetic resin contains the reactant 58. As shown in the drawing, a metal cup 88 is provided along a side surface as well as a bottom face of the casing 86. The metal cup 88 electrically contacts the pin 66. The reactant 58 contains only the electrically conductive oxide particles 82, and does not contain metal particles.

[0044] In initiators 50C′ and 50D′ shown respectively in FIG. 6 and FIG. 7, the metal block 84 and the metal cup 88 of the initiators 50C and 50D shown in FIG. 4 and FIG. 5 are covered by oxidized films 90 and 92, respectively, thereby adjusting an electric resistance between the pins 62 and 66. Here, although the oxidized film 92 is provided on an inner surface of the metal cup 88 and an outer surface of the pin 66, the oxidized film 92 is not provided on an interface between the metal cup 88 and the pin 66.

[0045] When a voltage is applied between the pins 62 and 66, the oxidized films 90 and 92 is broken, thereby generating additional heat.

[0046] In initiators 5OC″ and 50C′″ shown respectively in FIG. 10 and FIG. 11, an electrically conductive oxide block 96 is used instead of the reactant 58 and the electrically conductive particles 58a of the initiators 50C and 50C′ shown in FIG. 4 and FIG. 6, thereby simplifying handling and a manufacturing process.

[0047] In the present invention, the aforementioned metal block, metal cup as well as the electrically conductive oxides may have a porous surface. By virtue of such a porous surface, it is possible to improve reaction sensitivity.

[0048] The reactant containing the metal particles and electrically conductive oxidant particles is preferable to have a composition not listed in the powder list of Active Carbon Regulation.

[0049] Each of the above-described embodiments is only an example of the present invention. The present invention is also allowed to have an embodiment other than those illustrated in the accompanying drawings. For example, the casing is allowed to have a shape other than those illustrated in the drawings. Similarly, the shape and the number of the electrodes are not limited to those shown in the accompanying drawings. The casing may have a long and narrow cylindrical shape so that it can be used in a gas generator of an airbag apparatus for a passenger seat.

[0050] The initiator of the present invention can be applied to various types of gas generator. The initiator can be incorporated into various types of an airbag apparatus and a seat belt tensioner for a driver seat, a passenger seat, a rear seat, a side portion and a head portion of a person's body, as well as for protecting pedestrians.

[0051] As described above, in the initiator according to the present invention, since a bridge wire is not used, it is possible to eliminate a welding step during the manufacturing process, thereby making it possible to provide an improved initiator easy to be manufactured and low in the manufacturing cost, as well as an improved gas generator equipped with such an improved initiator.

[0052] While the invention has been explained with reference to the specific embodiments of the invention, the explanation is illustrative and the invention is limited only to the appended claims.

Claims

1. An initiator, comprising:

a casing,

a reactant disposed in the casing and containing an electrically conductive substance, and

electrodes situated inside the casing to contact the reactant such that when a voltage is applied to the electrodes, an electric current flows through the electrically conductive substances, thereby initiating a reaction of the reactant.

2. An initiator according to claim 1, wherein said electrically conductive substance includes at least ones of metal particles and metal oxide particles.

3. An initiator according to claim 1, wherein said reactant contains metal oxide particles having oxidization activity and metal particles having electrical conductivity.

4. An initiator according to claim 1, wherein said electrodes are pin members having front-end portions extending into the reactant.

5. An initiator according to claim 1, further comprising a metal member electrically connected to one of the electrodes and contacting the reactant.

6. An initiator according to claim 5, further comprising an oxidized film covering the metal member.

7. An initiator according to claim 5, wherein said metal member has a porous surface to improve reaction response.

8. An initiator according to claim 5, further comprising a pre-assembled block formed of the reactant connected to the other of the electrodes.

9. An initiator according to claim 8, wherein said pre-assembled block further includes a surrounding material covering the reactant, said metal member contacting the surrounding material.

10. A gas generator comprising the initiator according to claim 1, and a gas generating agent to be ignited by the initiator for generating a gas.