Abstract:
A squib includes a heat-generating portion that has an energizing portion and a fuel portion, and that is formed such that heat that is generated by supplying current to the energizing portion can be transmitted to the fuel portion to ignite same. The squib includes a noise removal device that is connected in parallel with the heat generating portion, and a circuit element that temporally scatters noise such that the noise is more completely removed by the noise removal device. In this manner, the heat-generating portion is protected from all typed of noise, including momentary noise, increasing reliability of the squib.

Description:
[0001]     Priority is claimed on Japanese Patent Application No. 2003-419478, filed Dec. 17, 2003, the contents of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates to a squib (i.e., an ignition apparatus) that is used in an explosive-actuated system for driving, for example, a seat belt pretensioner apparatus or an airbag apparatus for an automobile, and, in particular, to a squib that is provided with a heat generating portion capable of generating heat by means of a small amount of energy.  
         [0003]     In recent years squibs are used with the aim of igniting a gas generating agent in order to operate systems inclusive of, for instance, a seat belt pretensioner apparatus and an airbag apparatus. Generally, the squib is attached to an inflator that contains a gas generating agent in an explosive-actuated system. The squib is structured such that a heat generating portion is attached to a header to which pins are fixed, and an explosive is inserted under pressure using a cup so as to be in contact with the heat generating portion. The squib pins are electrically connected to a master control unit.  
         [0004]     Moreover, low energy squibs that can operate on only a tiny amount of energy have been proposed as squibs suitable for use in and for mounting on vehicle safety systems (whose number has tended to increase in recent years). This type of low energy squib is constructed with the power generating portion including an energizing portion and a fuel portion, and generates heat efficiently in comparison with a normal squib. When current is supplied to the energizing portion, it causes a violent chemical reaction and a large quantity of heat is generated.  
         [0005]     Because the low energy squib having this type of structure is extremely sensitive to electrical noise, the heat generating portion needs to be protected from noise. Therefore, conventionally, a two-way zener diode is connected in parallel with the heat generating portion. By employing this type of structure, excess voltage that is applied to the squib caused by the noise is made to bypass via the zener diode so as to protect the heat generating portion from the noise as described in U.S. Pat. Nos. 5,847,309; 5,905,266; and 6,192,802.  
         [0006]     However, if the zener diode is simply connected to the heat generating portion of the low energy squib, a certain period of time, i.e., a delay time is needed until the zener diode operates against the applied noise. Therefore, the zener diode does not operate effectively against momentary noise such as static electricity and, therefore, there is a possibility that the noise will intrude into the heat generating portion. This creates the problem that there is a possibility that the reliability thereof will deteriorate.  
         [0007]     The present invention was conceived in view of the above circumstances, and it is an object thereof to provide a squib that enables a heat generating portion to be protected from noise even when the momentary noise is applied thereto, and that enables reliability to be increased.  
       SUMMARY OF THE INVENTION  
       [0008]     With the first aspect of the present invention, a squib (for example, the squib  1  in a preferred embodiment) having a heat generating portion (for example, the heat generating portion  3  in the embodiment) that has an energizing portion (for example, the energizing portion  11  in the embodiment) and a fuel portion (for example, the fuel portion  12  in the embodiment), wherein the heat generating portion operates such that heat generated by supplying current to the energizing portion can be transmitted to the fuel portion, comprises: a noise removal device (for example, a two-way zener diode  15  in the embodiment) that is connected in parallel with the heat generating portion; and a circuit element (for example, the capacitor  13  in the embodiment) that temporally scatters noise to the noise removal device.  
         [0009]     According to the present invention, even when the noise is generated due to, for example, static electricity that is generated by the momentary supply of a large amount of power, it is possible to scatter the noise over a sufficient time period by means of the circuit element. As a result, the momentary noise thus scattered can be removed by the noise removal device. Accordingly, the heat generating portion can be protected from the noise even if the momentary noise is applied thereto, and reliability can thereby be increased.  
         [0010]     With the second aspect of the present invention, the squib according to the first aspect of the invention has a two-way zener diode as the noise removal device.  
         [0011]     According to this aspect, the two-way zener diode can be operated irrespective of the direction of the noise that is applied to the two-way zener diode. As a result, the reliability can be further improved.  
         [0012]     With the third aspect of the present invention, the squib according to the first or second aspects of the invention has a capacitor as the circuit elementcapacitor for temporally scattering the noise.  
         [0013]     According to this aspect, when the noise is being scattered temporally, the influence of the scattering on the ignition current can be reduced to a minimum. As a result, the heat generating portion can be protected from noise without losing the characteristics of the low energy squib that achieves an ignition using a small amount of energy being impaired.  
         [0014]     In consequence, the first aspect of the present invention enables the heat generating portion to be protected from noise even if the momentary noise is applied thereto, and enables reliability to thereby be increased.  
         [0015]     The second aspect of the present invention enables the two-way zener diode to be operated irrespective of the direction of the noise, thereby enabling the reliability to be further improved.  
         [0016]     The third aspect of the present invention enables the influence of the scattering on the ignition current to be practically reduced to a minimum when the noise is being scattered temporally, thereby enabling the heat generating portion to be protected from noise without deteriorating the characteristics of the low energy squib that achieves an ignition using a small amount of energy being impaired. 
     
    
     BRIEF DESCRIPTION THE DRAWINGS  
       [0017]      FIG. 1  is a vertical cross-sectional view of a squib according to an embodiment of the present invention.  
         [0018]      FIG. 2  is a cross-sectional view taken along a line A-A of the squib shown in  FIG. 1 .  
         [0019]      FIG. 3  is a perspective view of the heat generating portion shown in  FIG. 1   
         [0020]      FIG. 4  is a circuit structure diagram of the squib shown in  FIG. 1 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]     While preferred embodiments of the invention have been described and illustrated above, it should be understood that these are exemplary of the invention and are not to be considered as limiting. Additions, omissions, substitutions, and other modifications can be made without departing from the spirit or scope of the present invention. Accordingly, the invention is not to be considered as limited by the foregoing description and is only limited by the scope of the appended claims.  
         [0022]     The squib according to an embodiment of the present invention will now be described in reference to drawings.  FIG. 1  is a vertical cross-sectional view of a squib (i.e., an ignition apparatus) according to an embodiment of the present invention, while  FIG. 2  is a cross-sectional view taken along a line A-A in  FIG. 1 .  
         [0023]     As is shown in  FIGS. 1 and 2 , a squib  1  has a capacitor  13 , a two-way zener diode  15 , and a heat generating portion  3 , which is an igniting element, which are placed on a flat top surface of a header portion  4 . The header portion  4  is provided with a pin  8  and a pin  7 , which are connecting terminals that are provided in order to make a connection with a two-line type of bus wire (not shown), which is an external signal wire. An igniting agent  5  that ignites a gas generating agent of a supplemental restraint system is further placed on top (leftward direction in  FIG. 1 ) of the heat generating portion  3 . Note that the pin  7  and the header  4  are connected by welding. In addition, although in the vertical cross-sectional view shown in  FIG. 1 , the header  4  appears to be in two different locations, in actual fact, the header  4  is positioned so as to surround the pin  8  as shown in  FIG. 2 . Moreover, the space between the pin  8  and the header  4  is filled with a insulating material  9  such as glass in order to fix the pin  8  in position.  
         [0024]     The igniting agent  5 , the heat generating portion  3 , the capacitor  13 , the zener diode  15  and the header  4  are covered by a circular cylinder shaped cap  2  whose top portion is closed off. Furthermore, the igniting agent  5 , the heat generating portion  3 , the header  4 , and the pin  8  that are covered by the cap  2  are formed integrally by being covered by a resin mold  6  that is made to extend across the portions of the pins  8  and  7  using a molding process. Note that, in the above description, the materials used for each portion are merely examples thereof and a variety of modifications can be employed such as, for example, using a cap  2  formed from metal.  
         [0025]     As is shown in  FIG. 3 , the heat generating portion  3  is provided with an energizing portion  11  and a fuel portion  12 . If current is supplied to the energizing portion  11 , it generates heat and activates the adjacent fuel portion  12 . When the fuel portion  12  is activated, it generates a violent chemical reaction and a large quantity of heat is generated. By forming the heat generating portion  3  from the energizing portion  11  and the fuel portion  12  in this manner, it becomes possible to perform an ignition using less energy than in a normal squib.  
         [0026]     Moreover, as is shown in  FIG. 4 , the zener diode  15 , the capacitor  13  and the heat generating portion  3  (i.e., with the energizing portion  11  and the fuel portion  12 ) are connected in parallel with a control unit  16 . As a result, when an ignition command signal is input into the control unit  16  via a bus  17 , power that is stored in a rechargeable battery (capacitor) in the control unit  16  is supplied to the energizing portion  11 .  
         [0027]     The squib  1  is connected to an acceleration rate sensor (not shown) that detects a frontal collision or side collision of the vehicle, and that is connected to the respective control circuits. A plurality of squibs  1  are mounted at positions adjacent to propellant of inflators (i.e., gas generating apparatuses) of airbag systems that inflate in appropriate locations such as in a steering wheel, in a dashboard, in left and right seats, and in left and right side portions of a roof. The pins  7  and  8  of each of the squibs  1  are connected via the common bus  17 .  
         [0028]     A squib  1  having the above described structure is operated in the manner described below. Firstly, when the acceleration rate sensor detects a rate of acceleration exceeding a predetermined value, a superior control unit (not shown) that operates a predetermined airbag system outputs an inflate command signal to the bus  17 . When the superior control unit supplies power to the bus  17  and sends a charge command, electric power required for a supplemental restraint system to be operated is stored in the rechargeable battery (not shown) such as a capacitor which is provided in the control unit  16 . The supplemental restraint system is designed to be operated in response to the ignition of the heat generating portion  3  of the squib  1  to the igniting agent  5 . In this state, if the superior control unit sends an ignition execute signal (i.e., an ignition execute command) to the squib  1 , the control unit  16  of the squib  1  conducts the electric power that is stored in the rechargeable battery (not shown) to the heat generating portion  3  of the squib  1 , and the igniting agent  5  incorporated in the squib  1  is exploded so that the supplemental restraint system can be operated.  
         [0029]     As described above, in the present embodiment, the two-way zener diode  15  and capacitor  13  are connected in parallel with the heat generating portion  3 . Therefore, even when the noise is generated by the momentary supply of a large amount of power caused by static electricity or such, it is possible to temporally scatter this noise over a longer or sufficient time period using the capacitor  13 . As a result, the noise thus scattered can be removed by the two-way zener diode  15 . Accordingly, the heat generating portion  3  can be protected from noise even if the momentary noise is applied thereto, and reliability can thereby be increased.  
         [0030]     Furthermore, because the two-way zener diode  15  is used as the noise removing device, the two-way zener diode  15  can be operated irrespective of the direction of flow of the noise that is applied to the two-way zener diode  15 . As a result, the reliability can be further improved.  
         [0031]     In addition, because the capacitor  13  is used as the circuit element for scattering noise, when the noise is being scattered temporally, the influence thereof on the ignition current can be reduced to a minimum. Accordingly, the heat generating portion  3  can be protected from noise without deteriorating the characteristics of the low energy squib that achieves an ignition using a small amount of energy being impaired.  
         [0032]     Note that the content of the present invention is not limited to solely the above described embodiment. For example, in the present embodiment, the capacitor  13  is placed above the header  4 , however, the capacitor  13  can also be placed between the pins  7  and  8  or inside a squib connector (not shown).  
         [0033]     Furthermore, in the present embodiment, the squib and control circuit are connected by the bus, however, it is also possible to employ a conventional connection manner in which the two are connected one to one (i.e., point to point).