Patent Publication Number: US-2006017269-A1

Title: Igniter assembly

Description:
This nonprovisional application claims priority under 35 U.S.C. §119(e) on U.S. Provisional Application No. 60/591,877 filed on Jul. 29, 2004 and under U.S.C. §119(a) on Patent Application No. 2004-217039 filed in Japan on Jul. 26, 2004, which are herein incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to an igniter assembly, a gas generator for an air bag which uses this igniter assembly, and a manufacturing method for the igniter assembly.  
      2. Description of the Related Art  
      When attaching an electric igniter to a gas generator for an air bag, a method of embedding the igniter into a metallic collar and then attaching the igniter to the gas generator in this state is typically employed. To provide insulation in this case, an igniter assembly, in which the periphery of the igniter is wrapped in an insulation sheet, is fitted together with the metallic collar.  
      This type of igniter assembly is manufactured by placing the igniter in a mold, injecting molten resin into the mold, and cooling/hardening the resin such that the igniter and the collar are integrated with each other. However, volume shrinkage occurs when the molten resin hardens, and this may produce gaps between the resin and the insulation sheet. When these gaps occur, moisture in the outside air may infiltrate through the gaps.  
      In U.S. Pat. No. 5,131,679, a metallic cup  158  is covered by a thin plastic film  170 , and an end portion  172  of the film  170  is provided inside a plastic material  150 .  
      In U.S. Pat. No. 5,556,132, an electrically insulating material  192  is disposed on a cup  106 , thereby preventing the cup  106  from being grounded. During manufacture, the members are assembled, and finally a plastic material  104  is poured in.  
      In all of the prior art described above, structures are disclosed in which an end portion of an insulating member (film) exists within a plastic mold, but none of the prior art refers to the possibility such that gaps occur at the contact portions between the insulating material (film) and plastic mold, or to methods for preventing these gaps.  
     SUMMARY OF THE INVENTION  
      An aspect of the present invention is to provide an igniter assembly which can prevent the infiltration of moisture in the outside air, thereby ensuring long-term operational stability, a manufacturing method for the igniter assembly, and a gas generator for an air bag which uses the igniter assembly.  
      As means of achieving this object, the present invention provides an igniter assembly comprising: an igniter having a metallic header to which at least one conductive pin is fixed, a heat generating body provided on the metallic header in electrical contact with the at least one conductive pin, an ignition charge contacting the heat generating body, which is charged into a metallic cup placed over the metallic header, and a resin sheet covering the entire outer surface of the metallic cup; and a resin molded body that is injection-molded so as to surround a part of the igniter,  
      wherein the resin molded body encloses a part of the resin sheet and surrounds the igniter such that the conductive pins are capable of electrification, and the resin sheet and resin molded body are integrated at a contact portion between the resin molded body and resin sheet.  
      The resin molded body is typically molded into a shape which matches the interior shape of a metallic collar into which the igniter assembly is embedded. However, as described in the “Description of the Related Art” section, during cooling and hardening, volume shrinkage is inevitable, and hence gaps may appear between the igniter and resin molded body. When the resin molded body is injection-molded to contact the metallic header and conductive pins, and then cooled and hardened, gaps may also appear between these components.  
      In the present invention, however, the resin molded body is in direct contact with the resin sheet, and the resin molded body and resin sheet are integrated with each other at the contact portion. Therefore, no gaps exist between the resin molded body and resin sheet. Moreover, since the resin sheet is integrated with the resin molded body, the resin sheet never becomes dislodged from the resin molded body. Here, “integrated” signifies that the resin molded body and resin sheet remain are fused at the contact portion therebetween when cooled and hardened.  
      The resin molded body and resin sheet are integrated during the manufacturing process by injecting molten resin, which is to serve as the resin molded body, into contact with the resin sheet such that the resin sheet melts at the point of contact with the molten resin. Then, when the molten resin of the resin molded body is cooled and hardened, the resin sheet that is fused thereto also cools and hardens. As a result of this manufacturing process, no gaps exist between the resin molded body and resin sheet.  
      In the igniter assembly of the present invention, the resin used as the resin sheet preferably has a melting point that is not higher than (is equal to or lower than) the melting point of the resin used as the resin molded body, and preferably has an electrical insulation property.  
      It is believed that when the melting point of the resin used as the resin sheet is not higher than the melting point of the resin used as the resin molded body (by approximately 10° C., for example), and the resin molded body is melted at a temperature that is not lower than (is equal to or higher than) melting point of the resin sheet and then injected (with the temperature of the resin during injection preferably set equal to or higher than the melting point of the resin sheet), the resin sheet and resin molded body become fused.  
      However, to integrate the resin sheet and resin molded body more reliably and prevent excessive thermal deformation of the resin sheet, the melting point of the resin used as the resin sheet is preferably equal to or lower than the melting point of the resin used as the resin molded body, and more preferably between 30° C. and 70° C. lower than the melting point of the resin used as the resin molded body.  
      By providing the resin sheet with an electric insulation property, situations in which an electric current flows from the metallic cup into another member (another member of the device to which the igniter assembly is applied) such that normal operations can no longer be performed are prevented.  
      As other means for achieving the object, the present invention provides a manufacturing method for the igniter assembly described above, comprising the steps of:. assembling an igniter having a metallic header to which at least one conductive pin is fixed, a heat generating body provided on the metallic header in electric contact with the at least one conductive pin, and an ignition charge contacting the heat generating body, which is charged into a metallic cup placed over the metallic header; covering the entire outer surface of the metallic cup of the igniter with a resin sheet; fitting the igniter covered with the resin sheet into a mold having a predetermined shape and a resin injection hole; and injecting a molten resin serving as the resin of the resin molded body through the resin injection hole such that the molten resin contacts and becomes fused to at least a part of the resin sheet, and then cooling the molten resin.  
      The present invention also provides a gas generator for an air bag, comprising the igniter assembly according to the present invention.  
      The igniter assembly of the present invention may be applied to well-known various gas generators for air bags such as an air bag gas generator for a driver side or a front passenger side. The igniter assembly may also be applied to various actuators such as a seatbelt pretensioner, an automatic flash distinguisher or suppresser, a circuit breaker, and a rocket motor.  
      In the igniter assembly of the present invention, the resin sheet and resin molded body are integrated with each other such that no gaps exist therebetween, and hence moisture infiltration is prevented. As a result, long-term operational reliability is ensured. Moreover, since the resin sheet and resin molded body are integrated, the resin sheet itself does not become dislodged from the igniter. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a schematic sectional view in an axial direction of an igniter assembly.  
       FIG. 2  is an illustrative view of a manufacturing process of the igniter assembly.  
       FIG. 3  is an illustrative view of the manufacturing process of the igniter assembly. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      (1) Igniter Assembly  
      An igniter assembly will be described using  FIG. 1 .  FIG. 1  is a schematic sectional view in the axial direction of an igniter assembly.  
      An igniter assembly  10  comprises an igniter  11  having a metallic header and so on, and a resin molded body  21  surrounding a part of the igniter  11 .  
      The metallic header  12  holds two conductive pins  13   a,    13   b.  The end portion of the conductive pin  13   a  is fixed to the metallic header  12 , and the end portion of the conductive pin  13   b  is buried within and fixed to an insulation portion (glass portion)  14  attached integrally to the metallic header  12 .  
      A heat generating body  15  is provided on the surface of the metallic header  12 . One end of the heat generating body  15  contacts the conductive pin  13   b , and, bridging the glass portion  14 , the other end contacts the surface of the metallic header  12 . A metal coil or metal wire which generates heat easily, such as a nichrome wire, for example, may be used as the heat generating body  15 .  
      A metallic cup  16  is placed over the metallic header  12 . The metallic cup  16  covers the entire peripheral surface of the metallic header  12 , and the metallic header  12  and metallic cup  16  are welded together at a welded portion  19 .  
      An ignition charge  17  is charged into the metallic cup  16 . The ignition charge  17  and heat generating body  15  contact each other tightly. Zirconium/potassium perchlorate that is used generally or the like may be used as the ignition charge.  
      The entire outer surface of the metallic cup  16  is covered by a cup-form resin sheet  18  having the same shape and the same size as (or a slightly larger size than) the metallic cup  16 .  
      The resin molded body  21  encloses the lower end side of the metallic sheet  18 , and covers the igniter  11  such that the conductive pins  13   a,    13   b  are capable of electrification. The resin molded body  21  is molded into a shape which matches the internal shape of a metallic collar so that the igniter assembly  10  can be embedded into the metallic collar.  
      The resin sheet  18  and resin molded body  21  are integrated at a contact portion therebetween such that no gaps exist between the two members. To enhance the joining strength and ensure moisture resistance between the resin sheet  18  and resin molded body  21 , the ratio of an overall height H 1  of the resin sheet  18  and a contact portion H 2  between the resin sheet  18  and resin molded body  21  is preferably within the range of 10% to 90% when the ratio is determined as (H 2 ×100)/H 1 , and more preferably within the range of 30% to 70%.  
      The material of the resin sheet  18  preferably has a lower melting point than that of the material of the resin molded body  21  and an electric insulation property. Accordingly, nylon  12  (having a melting point of 170° C.) may be used as the resin sheet  18 , and nylon  6 - 12  (having a melting point of 212° C.) may be used as the resin molded body  21 . Alternatively, nylon  6 , nylon  12 , nylon  66 , and nylon  6 - 10  may be used as the resin molded body or resin sheet.  
      In the igniter assembly  10 , the resin sheet  18  and resin molded body  21  are integrated at the contact portion, and no gaps exist in the contact portion. Hence, moisture in the outside air does not infiltrate through the contact portion between the resin sheet  18  and resin molded body  21 , ensuring long-term operational reliability.  
      Moreover, the resin sheet does not become detached from the metallic cup  16 . Even if a gap is formed between the resin molded body  21  and the metallic header  12  or conductive pins  13   a,    13   b , moisture infiltration is prevented as long as the resin sheet  18  and resin molded body  21  are in close contact (such that gas is prevented from infiltrating therebetween).  
      (2) Manufacturing Method of Igniter Assembly  
      A manufacturing method for the igniter assembly will be described using FIGS.  1  to  3 .  FIGS. 2 and 3  are illustrative views of a manufacturing method for the igniter assembly.  
      First, the igniter  11  shown in  FIG. 1  is assembled without the resin sheet (made of nylon  12  having a melting point of 170° C., for example)  18 . In this case, the igniter  11  without the resin sheet  18  is a universally known device.  
      Next, as shown in  FIG. 2 , the resin sheet  18  is placed over the entire outer surface of the metallic cup  16  of the igniter  11 . There are no particular limitations on the shape of the resin sheet  18 , but in terms of workability, the resin sheet  18  preferably has the same shape and the same size as the metallic cup  16 , or a slightly larger size than the metallic cup  16 , as shown in the drawing.  
      Next, as shown in  FIG. 3 , the igniter  11  is fitted into a lower mold  31  having a predetermined shape, whereupon an upper mold  32  having a predetermined shape is fitted onto the lower mold  31 . At this time, as shown in the drawing, a part of the resin sheet  18  (a length part corresponding to H 2  in  FIG. 1 ) does not contact the lower mold  31 , but instead is exposed within an interior space  35  surrounded by the lower mold  31  and upper mold  32 . Note that a part of the conductive pins  13   a ,  13   b  protrudes to the outside through the upper mold  32  as shown in the drawing.  
      Next, molten resin (nylon  6 - 12  having a melting point of 212° C., for example) serving as the resin for forming the resin molded body  21  is injected into the interior space  35  through a plurality of molten resin injection holes  33  formed in the upper mold  32 . At this time, the molten resin contacts a part of the resin sheet  18 , causing the contacted part of the resin sheet  18  to melt such that the molten resin and resin sheet  18  are fused at this contact portion. Further, the injection temperature of the resin during injection to the interior of the lower mold  31  and upper mold  32  is set between 30° C. and 70° C. higher than the melting point of the resin sheet  18 .  
      Heat also affects the remaining portion of the resin sheet  18  that does not contact the molten resin (the part corresponding to H 1 -H 2  in  FIG. 1 ), and also affects the metallic cup  16 . This heat softens the remaining portion of the resin sheet  18  such that the resin sheet  18  is adhered tightly to the metallic cup  16 .  
      When the igniter assembly  10  is left to cool at room temperature with the molten resin and resin sheet  18  fused together, the cooling process hardens the fused molten resin and resin sheet such that the two components are integrated at the contact portion. The lower mold  31  and upper mold  32  are then removed, whereby the igniter assembly  10  shown in  FIG. 1  is obtained.  
      (3) Gas Generator for Use in Air Bag  
      The igniter assembly  10  shown in  FIG. 1  may be incorporated as an electric igniter into a gas generator for an air bag with a part of the resin molded body  21  embedded in a metallic collar. At this time, a connector is connected to the conductive pins  13   a,    13   b , and a lead wire extending from the connector is connected to a battery.  
      During an operation, an electric current supplied from the battery flows from the conductive pin  13   b  to the conductive pin  13   a  such that the heat generating body  15  generates heat. This heat causes the ignition charge  17  contacting the heat generating body  15  to ignite and burn. The ignition energy generated through the ignition and burning of the ignition charge  17  either ignites and burns a gas generating agent, or burns a transfer charge which then causes the gas generating agent to ignite and burn. As a result, gas is generated and the air bag is inflated.  
      Note that when the resin sheet  18  is not provided, current may flow from the metallic cup  16  to the gas generator side during electrification (when the electrification sequence of the conductive pins may reverse), but when the resin sheet  18  having an electric insulation property is provided, the possibility of this situation arising is eliminated.  
      Further, if the metallic cup  16  contacts another member when the igniter assembly  10  is incorporated into the gas generator, electric conduction may occur between the metallic cup  16  and the other member, but by covering the metallic cup  16  with the resin sheet  18 , this situation is prevented.  
      There are no particular limitations on the air bag gas generator to which the igniter assembly  10  can be applied, and any well-known air bag gas generator may be used.  
      This invention thus described, it will be obvious that the same may be varied in many ways, such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modification as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.