JP2011150875A - Method of manufacturing spark plug - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a spark plug capable of adding substantially large pressure on a resistive composition, and furthermore, capable of forming a resistive element superior in load life characteristics. <P>SOLUTION: The spark plug 1 includes an insulator 2 with an axis hole 4, a center electrode 5 as well as a terminal electrode 6, and a resistive element 7 made by baking the resistive composition 52. A maximum inner diameter of the axis hole 4 at a part where the resistive element 7 is arranged is to be ≤2.9 mm. The steps of manufacturing of the spark plug 1 include an arrangement step of arranging the center electrode 5 in the axis hole 4, a glass-filling step of filling glass powder mixture 51, a resistive element filling step of filling the resistive element composition 52, a press-pin insertion step of inserting a press pin 53, a hot press-fitting step of hot-pressing the press pin 53 and compressing the resistive composition 52 or the like, and a terminal electrode arrangement step of fitting a terminal electrode 6 in the axis hole 4. At least a site inserted into the axis hole 4 out of the press pin 53 is to be structured of ceramics. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a spark plug used for an internal combustion engine or the like.

  The spark plug is attached to an internal combustion engine (engine) or the like, and is used to ignite an air-fuel mixture in a combustion chamber. Generally, a spark plug is provided on the outer periphery of an insulator having an axial hole, a center electrode inserted through the front end of the axial hole, a terminal electrode inserted through the rear end of the axial hole, and the insulator. A metal shell and a ground electrode that is joined to the tip of the metal shell and forms a spark discharge gap with the center electrode. In addition, a resistor is provided in the shaft hole between the center electrode and the terminal electrode for suppressing radio noise generated by the operation of the engine, and both electrodes are electrically connected via the resistor. Connected. In addition, the center electrode is sealed and fixed to the insulator by a glass sealing layer formed by baking a glass powder mixture containing glass powder.

  The resistor is formed by performing so-called hot pressing. That is, after arranging the center electrode in the shaft hole, the resistor composition containing the conductive material and the ceramic powder is filled in the shaft hole, and the terminal electrode is press-fitted into the shaft hole in the hot state. The resistor composition is compressed and fired, and as a result, a resistor is formed (see, for example, Patent Document 1).

  Recently, in order to improve the degree of freedom of engine layout, etc., it is required to reduce the diameter of the spark plug. Here, the diameter of the insulator can be reduced in order to reduce the diameter of the spark plug, but there is a limit to reducing the diameter of the insulator by reducing the thickness due to the necessity of maintaining the withstand voltage performance and mechanical strength. Therefore, the diameter of the shaft hole of the insulator is reduced in order to reduce the diameter of the insulator while ensuring the necessary thickness. In this case, a relatively thin terminal electrode is used as a terminal electrode inserted into the shaft hole so as to correspond to the shaft hole having a reduced diameter.

Japanese Patent No. 3813708

  However, reducing the diameter of the terminal electrode leads to a decrease in strength of the terminal electrode. That is, when the terminal electrode is pressed into the shaft hole to pressurize the resistor composition, the terminal electrode may be deformed and a desired pressure may not be applied to the resistor composition. If the pressure applied to the resistor composition is reduced, a relatively large gap is formed between the conductive materials in the resistor, and there is a possibility that discharge occurs in the gap. As a result, the resistance value of the resistor rapidly increases / decreases (the load life characteristic deteriorates), which may cause a problem in spark discharge.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to allow a sufficiently large pressure to be applied to a resistor composition in an insulator with a reduced diameter of a shaft hole, and thus a load life. An object of the present invention is to provide a spark plug manufacturing method capable of forming a resistor having excellent characteristics.

  Hereinafter, each configuration suitable for solving the above-described object will be described in terms of items. In addition, the effect specific to the corresponding structure is added as needed.

Configuration 1. The spark plug manufacturing method of the present configuration includes an insulator having an axial hole penetrating in the axial direction;
A center electrode provided on the tip side of the shaft hole;
A terminal electrode provided on the rear end side of the shaft hole;
In the shaft hole, formed by firing a resistor composition containing a conductive material and ceramic powder, comprising a resistor that electrically connects the center electrode and the terminal electrode,
A method of manufacturing a spark plug having a maximum inner diameter of 2.9 mm or less at a position where the resistor is disposed in the shaft hole,
An arrangement step of arranging the center electrode in the shaft hole;
A glass filling step of filling a glass powder mixture comprising glass powder in the shaft hole;
A resistor filling step of filling the shaft hole with the resistor composition;
A press pin inserting step of inserting a rod-shaped press pin into the shaft hole;
Hot press-fitting the press pin, hot press-fitting step of compressing the glass powder mixture and the resistor composition,
After the hot press-fitting step, including a terminal electrode arrangement step of providing the terminal electrode on the rear end side of the shaft hole,
Of the press pin, at least a portion inserted into the shaft hole is made of ceramics.

  As described above, the smaller the inner diameter of the shaft hole, the smaller the diameter of the terminal electrode is required. As a result, there is a concern that the terminal electrode is deformed when the terminal electrode is press-fitted. In particular, when the maximum inner diameter of the portion where the resistor is disposed in the shaft hole is reduced to 2.9 mm or less as in the configuration 1, the terminal electrode may be further deformed.

  In this regard, according to the above-described configuration 1, in the hot press-fitting process for firing the resistor, the terminal electrode made of metal (for example, low carbon steel) is not press-fitted as before, and at least in the shaft hole. The resistor composition or the like is compressed by press-fitting a press pin in which the portion to be inserted is made of ceramics. Here, since ceramics are generally superior in hardness (deformation resistance) compared to metals, the press pin is not easily deformed when the resistor composition or the like is pressed. Therefore, the resistor composition and the like can be more reliably compressed, and the formation of gaps in the fired resistor can be more reliably suppressed. As a result, even in a spark plug having a reduced diameter shaft hole, the load life characteristics of the resistor can be made sufficiently excellent.

Configuration 2. The spark plug manufacturing method of the present configuration is the above-described configuration 1, wherein the terminal electrode arrangement step includes:
In the shaft hole, a rear end side glass filling step of filling the rear end side of the resistor with the glass powder mixture;
A terminal electrode insertion step of inserting the terminal electrode into the shaft hole;
And a secondary hot press-fitting step of press-fitting the terminal electrode and compressing the glass powder mixture filled on the rear end side of the resistor.

  According to the above-described configuration 2, in the manufacture of a spark plug of a method (so-called glass seal method) in which the terminal electrode is fixed to an insulator by a glass seal layer formed by baking a glass powder mixture, The same effect is exhibited.

Configuration 3. The spark plug manufacturing method of this configuration is the metal member arrangement in which the cylindrical metal member is arranged in the shaft hole in the configuration 1 after the resistor filling step and before the press pin insertion step. Including steps,
In the hot press-fitting step, the metal member is pressed by the press pin, the glass powder mixture and the resistor composition are compressed,
In the terminal electrode arrangement step, the metal member and the terminal electrode are electrically connected.

  According to the above-described configuration 3, a metal member is provided on the rear end side of the resistor, and in manufacturing a spark plug in which the metal member and the terminal electrode are electrically connected, the same function and effect as those of the configuration 1 are provided. Will be played.

  Configuration 4. The spark plug manufacturing method of this configuration is characterized in that, in the above configuration 3, the length of the metal member along the axis is 10 mm or less.

  According to the said structure 4, about the metal member pressed by a press pin in a hot press-fit process, the length along an axis line is comparatively short with 10 mm or less. Therefore, the deformation of the metal member when pressed by the press pin can be prevented more reliably, and as a result, the resistor composition and the like can be more reliably compressed via the metal member. As a result, the load life characteristics of the resistor can be further improved.

Configuration 5. The method for manufacturing a spark plug of this configuration is the above configuration 3 or 4, wherein after the hot press-fitting step and before the terminal electrode arrangement step,
A conductive member disposing step of disposing a conductive member elastically deformable along the axial direction between the metal member and the terminal electrode;
The metal member and the terminal electrode are electrically connected by the conductive member.

  According to the configuration 5, the conducting member that can be elastically deformed along the axis is provided between the metal member and the terminal electrode. Therefore, even if there is some variation in the sizes of the terminal electrode, the metal member, and the resistor, the metal member and the terminal electrode can be more reliably electrically connected.

It is a partially broken front view which shows the structure of the spark plug in 1st Embodiment. (A), (b) is sectional drawing, such as an insulator for demonstrating the manufacturing method of the spark plug in 1st Embodiment. (A), (b) is sectional drawing, such as an insulator for demonstrating the manufacturing method of the spark plug in 1st Embodiment. It is a partially broken front view which shows the structure of the spark plug in 2nd Embodiment. (A)-(c) is sectional drawing, such as an insulator for demonstrating the manufacturing method of the spark plug in 2nd Embodiment. It is a partially broken front view which shows the structure of the press pin in another embodiment.

Embodiments will be described below with reference to the drawings.
[First Embodiment]
FIG. 1 is a partially cutaway front view showing a spark plug 1. In FIG. 1, the direction of the axis CL <b> 1 of the spark plug 1 is the vertical direction in the drawing, the lower side is the front end side of the spark plug 1, and the upper side is the rear end side.

  The spark plug 1 includes an insulator 2 as a cylindrical insulator, a cylindrical metal shell 3 that holds the insulator 2, and the like.

  As is well known, the insulator 2 is formed by firing alumina or the like, and in its outer portion, a rear end side body portion 10 formed on the rear end side, and a front end than the rear end side body portion 10. A large-diameter portion 11 that protrudes radially outward on the side, a middle body portion 12 that is smaller in diameter than the large-diameter portion 11, and a tip portion that is more distal than the middle body portion 12. On the side, a leg length part 13 formed with a smaller diameter than this is provided. Of the insulator 2, the large-diameter portion 11, the middle trunk portion 12, and most of the leg long portions 13 are accommodated inside the metal shell 3. A tapered step portion 14 tapering toward the distal end side is formed at the connecting portion between the leg length portion 13 and the middle trunk portion 12, and the insulator 2 is attached to the metal shell 3 at the step portion 14. It is locked.

  Further, a shaft hole 4 is formed through the insulator 2 along the axis CL1. The shaft hole 4 has a small diameter portion 15 formed on the tip side thereof, and a large diameter portion 16 having a diameter larger than that of the small diameter portion 15 on the rear end side of the small diameter portion 15. Further, a tapered shaft hole step portion 17 is formed between the small diameter portion 15 and the large diameter portion 16. In this embodiment, the diameter of the insulator 2 is reduced in order to reduce the diameter of the spark plug 1. Therefore, the inner diameter of the large diameter portion 16 in the shaft hole 4 is 2.9 mm or less (for example, 2.5 mm or less).

  In addition, the center electrode 5 is inserted and fixed to the tip end side (small diameter portion 15) of the shaft hole 4. More specifically, a bulging portion 18 bulging outward in the radial direction is formed at the rear end portion of the center electrode 5, and the bulging portion 18 is locked to the shaft hole step portion 17. In this state, the center electrode 5 is fixed. The center electrode 5 is composed of an inner layer 5A made of copper or a copper alloy and an outer layer 5B made of a Ni alloy containing nickel (Ni) as a main component. Further, the center electrode 5 has a rod shape (cylindrical shape) as a whole, and a tip portion thereof protrudes from the tip of the insulator 2. In addition, a columnar noble metal tip 32 made of a noble metal alloy (for example, a platinum alloy or an iridium alloy) is joined to the front end surface of the center electrode 5.

  In addition, on the rear end portion side (large diameter portion 16) of the shaft hole 4, a front end side portion of the terminal electrode 6 formed of a predetermined metal material is inserted. More specifically, the terminal electrode 6 includes a mounted portion 6A to which a power supply plug cap (not shown) and the like are mounted, and extends from the mounted portion 6A to the distal end side, and has a smaller diameter than the mounted portion 6A. And an extending portion 6B formed on the surface. The extending portion 6B is inserted into and fixed to the shaft hole 4 in a state where the mounted portion 6A is in contact with the rear end surface of the insulator 2.

  Furthermore, a cylindrical resistor 7 is disposed between the center electrode 5 and the terminal electrode 6 of the shaft hole 4 (large diameter portion 16). Both ends of the resistor 7 are electrically connected to the center electrode 5 and the terminal electrode 6 through conductive glass seal layers 8 and 9, respectively. In addition, with the diameter reduction of the shaft hole 4 mentioned above, the outer diameter of the resistor 7 provided in the large diameter part 16 is also reduced to 2.9 mm or less.

  In addition, the metal shell 3 is formed in a cylindrical shape from a metal such as low carbon steel, and a screw portion (male screw portion) 19 for attaching the spark plug 1 to an engine head or the like is formed on the outer peripheral surface thereof. ing. Further, a seat portion 20 is formed on the outer peripheral surface on the rear end side of the screw portion 19, and a ring-shaped gasket 22 is fitted on the screw neck 21 on the rear end of the screw portion 19. Further, on the rear end side of the metal shell 3, a tool engaging portion 23 having a hexagonal cross section for engaging a tool such as a wrench when the metal shell 3 is attached to an engine head or the like is provided. A crimping portion 24 for holding the insulator 2 is provided.

  Further, a tapered step portion 25 for locking the insulator 2 is provided on the inner peripheral surface of the metal shell 3. The insulator 2 is inserted from the rear end side to the front end side of the metal shell 3, and the rear end of the metal shell 3 is engaged with the step 14 of the metal shell 3. It is fixed by caulking the opening on the side radially inward, that is, by forming the caulking portion 24. An annular plate packing 26 is interposed between the step portion 14 and the step portion 25. Thereby, the air tightness in the combustion chamber is maintained, and the fuel air entering the gap between the leg long portion 13 of the insulator 2 exposed to the combustion chamber and the inner peripheral surface of the metal shell 3 is prevented from leaking outside.

  Further, in order to make sealing by caulking more complete, annular ring members 27 and 28 are interposed between the metal shell 3 and the insulator 2 on the rear end side of the metal shell 3, and the ring member 27. , 28 is filled with talc 29 powder. That is, the metal shell 3 holds the insulator 2 via the plate packing 26, the ring members 27 and 28, and the talc 29.

  Further, a ground electrode 31 made of a nickel (Ni) alloy or the like is joined to the distal end portion 30 of the metal shell 3. The ground electrode 31 is welded at its rear end to the front end 30 of the metal shell 3 and is bent back toward the center electrode 5 so that its side faces the front end of the center electrode 5. . The ground electrode 31 has a two-layer structure including an outer layer 31A and an inner layer 31B. In the present embodiment, the outer layer 31A is made of a Ni alloy [for example, Inconel 600 and Inconel 601 (both are registered trademarks)]. On the other hand, the inner layer 31B is made of a copper alloy or pure copper, which is a better heat conductive metal than the Ni alloy.

  In addition, a noble metal tip 33 made of a noble metal alloy (for example, a platinum alloy) is joined to a portion of the ground electrode 31 facing the tip surface of the noble metal tip 32. A spark discharge gap 34 is formed between the noble metal tips 32 and 33, and spark discharge is performed in the spark discharge gap 34 in a direction substantially along the axis CL1.

  Next, the manufacturing method of the spark plug 1 comprised as mentioned above is demonstrated. First, the metal shell 3 is processed in advance. That is, a cylindrical metal material (for example, an iron-based material such as S17C or S25C or a stainless steel material) is formed by forming a through-hole by cold forging to produce a rough shape. Thereafter, the outer shape is adjusted by cutting to obtain a metal shell intermediate.

  Subsequently, the ground electrode 31 made of Ni alloy or the like is resistance-welded to the front end surface of the metal shell intermediate. During the welding, so-called “sag” is generated, and after the “sag” is removed, the threaded portion 19 is formed by rolling at a predetermined portion of the metal shell intermediate body. Thereby, the metal shell 3 to which the ground electrode 31 is welded is obtained. Further, the metal shell 3 to which the ground electrode 31 is welded is galvanized or nickel plated. In order to improve the corrosion resistance, the surface may be further subjected to chromate treatment.

  On the other hand, the insulator 2 is formed separately from the metal shell 3. For example, by using a raw material powder mainly composed of alumina and containing a binder or the like, a green granulated material for molding is prepared, and rubber press molding is used to obtain a cylindrical molded body. Then, the insulator 2 is obtained by grinding and shaping the obtained molded body and putting the shaped article into a firing furnace and firing.

  Separately from the metal shell 3 and the insulator 2, the center electrode 5 is manufactured. That is, the center electrode 5 is produced by forging a Ni alloy in which a copper alloy for improving heat dissipation is arranged at the center. In addition, the noble metal tip 32 is joined to the tip of the center electrode 5 by laser welding or the like.

  Furthermore, the insulator 2 and the center electrode 5, the resistor 7, and the terminal electrode 6 obtained as described above are sealed and fixed by the glass seal layers 8 and 9.

  First, as shown in FIG. 2 (a), the stepped portion formed between the large diameter portion 11 and the middle barrel portion 12 of the insulator 2 is supported by the tip surface of a support tube 41 made of metal and having a cylindrical shape. To do. In the arranging step, the center electrode 5 is inserted into the small diameter portion 15 of the shaft hole 4 so that the bulging portion 18 of the center electrode 5 is locked to the shaft hole step portion 17.

Next, in the glass filling step, as shown in FIG. 2B, glass powder (for example, powder made of SiO ₂ —B ₂ O ₃ —Na ₂ O-based ceramic material), metal powder, and the like are mixed. The conductive glass powder mixture 51 prepared in this manner is compressed and filled into the shaft hole 4.

In the resistor filling step, the resistor composition 52 is filled on the glass powder mixture 51 filled in the shaft hole 4. The resistor composition 52 is prepared by, for example, blending conductive carbon black, ceramic particles, and a predetermined binder, mixing them with water as a medium, and drying a slurry obtained by mixing them. It is obtained by mixing and stirring glass powder (for example, made of B ₂ O ₃ —SiO ₂ glass material).

  Next, in the press pin insertion step, the press pin 53 is inserted into the shaft hole 4. The press pin 53 is made of a ceramic (for example, silicon nitride, alumina, silicon carbide, or the like) material having excellent strength at high temperatures, and a portion (tip portion) inserted into the large-diameter portion 16 of the press pin 53. ) Has an outer diameter substantially equal to the inner diameter of the large diameter portion 16 of the shaft hole 4. More specifically, the diameter difference between the outer diameter of the portion of the press pin 53 to be inserted into the large diameter portion 16 and the inner diameter of the large diameter portion 16 is set to a predetermined numerical value or less (for example, 0.1 mm or less). Further, a release agent (for example, dried alcohol in which boron nitride is dissolved) is attached to the tip of the press pin 53.

  After the press pin 53 is inserted, in the hot press-fitting process, the press pin 53 is press-fitted into the shaft hole 4 from the opposite side of the center electrode 5 and a predetermined temperature above the glass softening point in the firing furnace (this embodiment) Then, the resistor composition 52 and the like are heated at 800 ° C. to 950 ° C. for a predetermined time (for example, about 20 minutes). At this time, the press-fitting distance L1 of the press pin 53 (the distance along the axial direction from the hook-shaped portion of the plus pin 53 in a state where the tip is in contact with the resistor composition 52 to the rear end surface of the insulator 2) is predetermined. Set to distance. Next, the heated glass powder mixture 51, the resistor composition 52, and the like are naturally cooled while the press pin 53 is being pressed in, so that the glass seal layer 8 and the resistance can be obtained as shown in FIG. A body 7 is formed.

  In the hot press-fitting step, the press pin 53 may be press-fitted after heating the resistor composition 52 and the like. Alternatively, after the resistor composition 52 or the like is heated, the press pin 53 may be inserted and the press pin 53 may be press-fitted, or after the resistor composition 52 or the like is heated, the press pin 53 is inserted, Next, the press pin 6 may be press-fitted while the resistor composition 52 and the like are further heated. That is, the press-fitting of the press pin 53 may be performed while heating the resistor composition 52 or the like, or may be performed after heating the resistor composition 52 or the like. Further, the insertion of the press pin 53 may be performed before the resistor composition 52 or the like is heated, may be performed during the heating, or may be performed after the heating.

  Further, after the press pin 53 is pulled out from the shaft hole 4, the terminal electrode 6 is inserted and fixed to the rear end side of the shaft hole 4 in the terminal electrode arrangement step. That is, as shown in FIG. 3A, in the rear end side glass powder filling step, the glass powder mixture 54 is compressed and filled on the rear end side of the resistor 7. Then, in the terminal electrode insertion step, the extension 6B of the terminal electrode 6 is inserted into the shaft hole 4, and in the secondary hot press-fitting step, the terminal electrode 6 is inserted into the shaft hole 4 by a predetermined distance L2 (the tip is made of glass). A predetermined temperature (for example, 800 ° C. to 800 ° C.) in the firing furnace in a state in which only a distance along the axial direction from the bowl-shaped portion of the terminal electrode 6 in contact with the powder mixture 54 to the rear end face of the insulator 2 At 950 ° C., the glass powder mixture 54 and the like are heated for a predetermined time (for example, about 20 minutes). After heating, the glass powder mixture 54 is naturally cooled, so that the softened glass powder is solidified and the glass seal layer 9 is formed as shown in FIG. As a result, the terminal electrode 6 is sealed and fixed to the insulator 2. In addition, at the time of the heating in a baking furnace, it is good also as baking a glaze layer simultaneously on the rear-end side trunk | drum 10 surface of the insulator 2, and it is good also as forming a glaze layer in advance. The press-fitting of the terminal electrode 6 may be performed while heating the glass powder mixture 54 or the like, or may be performed after heating the glass powder mixture 54 or the like. Furthermore, the insertion of the terminal electrode 6 may be performed before the glass powder mixture 54 or the like is heated, may be performed during the heating, or may be performed after the heating.

  Thereafter, the insulator 2 provided with the center electrode 5 and the like respectively prepared as described above and the metal shell 3 provided with the ground electrode 31 are assembled. More specifically, it is assembled by caulking the opening on the rear end side of the metal shell 3 formed relatively thin inward in the radial direction, that is, by forming the caulking portion 24.

  Next, the noble metal tip 33 is joined to the tip of the ground electrode 31 from which plating has been removed by resistance welding.

  Finally, the process of bending the ground electrode 31 toward the center electrode 5 and adjusting the spark discharge gap 34 formed between the noble metal tips 32 and 33 is performed, so that the spark plug 1 described above is formed. can get.

  As described in detail above, according to the present embodiment, in the hot press-fitting process for firing the resistor, the metal (for example, low carbon steel or the like) terminal electrode 6 is not press-fitted as before. The resistor composition etc. 52 is compressed by press-fitting the ceramic press pin 53. Here, since ceramics are generally excellent in hardness (deformation resistance) compared to metals, the press pin 53 is not easily deformed when the resistor composition 52 or the like is pressed. Therefore, the resistor composition 52 and the like can be more reliably compressed, and the formation of gaps in the fired resistor 7 can be more reliably suppressed. As a result, even if the spark plug 1 has a reduced diameter, the load life characteristics of the resistor 7 can be made sufficiently excellent.

A release agent is attached to the tip of the press pin 53. Therefore, it is possible to more reliably prevent the glass powder of the resistor composition 52 from adhering to the press pin 53 when the press pin 53 is pulled out from the shaft hole 4.
[Second Embodiment]
Next, the second embodiment will be described focusing on the differences from the first embodiment. The spark plug 1A according to the second embodiment is different from the spark plug 1 according to the first embodiment, particularly in the configuration of the rear end side from the resistor 7 in the shaft hole 4.

  That is, as shown in FIG. 4, a glass seal layer 61 is disposed on the rear end side of the resistor 7, and a metal member 62 sealed and fixed to the insulator 2 by the glass seal layer 61 is provided. Provided. The metal member 62 is formed of a predetermined metal material (for example, low carbon steel or the like) and is substantially equal to the inner diameter of the shaft hole 4 (large diameter portion 16) (for example, the inner diameter of the large diameter portion 16). It has a cylindrical shape with an outer diameter (diameter difference of 1.0 mm or less). Further, the length of the metal member 62 along the axis CL1 is set to 10 mm or less. In addition, the metal member 62 is plated with Ni or zinc on its surface in order to improve the corrosion resistance.

  Further, a conduction member 64 is provided between the metal member 62 and the terminal electrode 63. The conducting member 64 has a spring shape, is configured to be elastically deformable along the axis CL1, and is in contact with both the metal member 62 and the terminal electrode 63 in a state of being slightly compressed and deformed along the axis CL1. . Thereby, electrical conduction between the metal member 62 and the terminal electrode 63 is ensured.

  In addition, a screw portion 63C is formed on the base side of the extending portion 63B inserted into the shaft hole 4 in the terminal electrode 63, and the screw portion 63C is formed in the rear end opening of the shaft hole 4. The terminal electrode 63 is fixed to the insulator 2 by being screwed into the female thread portion 65 formed. Instead of fixing by screwing, for example, the terminal electrode 63 may be fixed to the insulator 2 by using cement or adhesive.

  Next, a method for manufacturing the above-described spark plug 1A will be described.

  First, as shown in FIG. 5A, the center electrode 5 is placed in the shaft hole 4 in the placement step. And as shown in FIG.5 (b), the glass powder mixture 51, the resistor composition 52, and the glass powder mixture 66 are compressed and filled in the shaft hole 4 in this order.

  Next, in the metal member arranging step, the metal member 62 is inserted and arranged in the shaft hole 4. In the hot press-fitting step, the resistor composition 52 and the glass powder mixture are placed in the firing furnace at a predetermined temperature for a predetermined time in a state where the ceramic press pin 53 is press-fitted into the shaft hole 4. 66 etc. are heated. And the resistor composition 52 etc. are cooled in the state which pressed the metal member 62 grade | etc., With the press pin 53. FIG. Thereby, the glass seal layer 61 and the resistor 7 are formed, and the metal member 62 is sealed and fixed to the insulator 2 by the glass seal layer 61.

  Thereafter, in the conducting member arranging step, the conducting member 64 is inserted and arranged in the shaft hole. Then, in the terminal electrode arrangement step, the extension part 63B of the terminal electrode 63 is inserted into the shaft hole 4, and the screw part 63C is screwed into the female screw part 65 of the insulator 2. As a result, as shown in FIG. 5C, the terminal electrode 63 and the metal member 62 are electrically connected by the conductive member 64 in a state where the conductive member 64 is slightly compressed along the axis CL <b> 1.

  As described above in detail, according to the second embodiment, the metal member 62 is provided on the rear end side of the resistor 7 and the metal member 62 and the terminal electrode 63 are electrically connected to each other. In manufacturing the plug 1A, the same effects as those of the first embodiment are exhibited.

  Furthermore, the metal member 62 pressed by the press pin 53 in the hot press-fitting step is used with a relatively short length of 10 mm or less along the axis CL1. Therefore, the deformation of the metal member 62 when pressed by the press pin 53 can be prevented more reliably, and as a result, the resistor composition 52 and the like can be more reliably compressed. As a result, the load life characteristics of the resistor 7 can be further improved.

  In addition, a conductive member 64 that is elastically deformable along the axis CL <b> 1 is provided between the metal member 62 and the terminal electrode 63. Therefore, even if there is some variation in the sizes of the terminal electrode 63 and the metal member 62, the metal member 62 and the terminal electrode 63 can be more reliably electrically connected.

  Next, in order to confirm the effects achieved by the above embodiment, a spark plug sample (corresponding to a comparative example) in which a terminal electrode is press-fitted and an insulator composition is compressed and fired, and a ceramic press A sample of a spark plug (corresponding to an example) in which a pin was press-fitted and the insulator composition was compressed and fired was produced, and a desktop load life test was performed on each sample. The desktop load life test is a test based on JIS B8031, and the outline is as follows. That is, after measuring the initial resistance value of the resistor in each sample, at a high temperature (350 ° C.), the discharge voltage was 20 kV, the number of discharges per minute was 3600 times, and over 200 hours. Each sample was discharged. Next, for each sample resistor, the resistance value when 56 hours passed, the resistance value after 100 hours, and the resistance value after 200 hours were measured, respectively. The rate of change in resistance value was calculated. Here, if the rate of change is within ± 15%, please evaluate “◎” because there is almost no change in resistance value of the resistor. If the rate of change is within ± 30% Since the resistance value fluctuation of the resistor is small, the evaluation of “◯” is made. On the other hand, when the rate of change exceeds ± 30%, the resistance value fluctuation of the resistor is large, and “x” is evaluated. Table 1 shows the results of the evaluation test for each sample. In the sample corresponding to the example, the metal member is disposed in each sample, while the length along the axis of the metal member is variously changed. Moreover, about the sample corresponded to the comparative example, the terminal electrode was sealed and fixed by the glass sealing layer, without providing a metal member. In addition, regarding the shaft hole of each sample, the maximum inner diameter of the large diameter portion (the portion where the resistor is disposed) was set to 2.9 mm.

  As shown in Table 1, in the sample (sample 8) in which the terminal electrode was press-fitted and the insulator composition was compressed and fired, the change rate of the resistance value exceeded ± 30% after 56 hours, and the load It became clear that the life characteristics were inferior. This is because the terminal electrode is deformed by press-fitting a relatively small-sized terminal electrode that can be inserted into the reduced-diameter shaft hole, and the compression of the resistor composition becomes insufficient. It is thought to be caused by this.

  On the other hand, the sample (samples 1 to 7) obtained by press-fitting a ceramic press pin and compressing and firing the insulator composition has a change rate of resistance value within ± 30% after 56 hours. It was found that the load life characteristics were excellent. This is because the press pin is made of ceramics having excellent strength (deformation resistance), so that even a relatively small diameter that can be inserted into a small-diameter shaft hole has sufficient strength. This is probably because the composition was compressed with sufficient pressure.

  Further, in view of the fluctuation of the load life characteristics due to the length of the metal member, the shorter the metal member, the better the load life characteristics. In particular, a sample (sample 1 to 1) having a length along the axis of the metal member of 12 mm or less. In 6), even when 100 hours have elapsed, the change rate of the resistance value is within ± 30%, and it was revealed that extremely excellent load life characteristics are realized. Furthermore, the samples (samples 1 to 5) whose length along the axis of the metal member is 10 mm or less have a change rate of resistance value within ± 30% even after 200 hours, and even more excellent load life characteristics. It was found that can be realized. This is because by shortening the length of the metal member, deformation of the metal member when pressed with a press pin was more reliably prevented, and as a result, greater pressure could be applied to the resistor composition. It is believed that there is.

  As mentioned above, it can be said that it is significant to compress and fire the resistor composition using a ceramic press pin in order to improve the load life characteristics in consideration of the results of the above test. In particular, when a metal member is provided in the shaft hole, it is desirable to use a relatively short metal member, the length along the axis of the metal member is preferably 12 mm or less, and the length along the axis is It can be said that it is more preferable to set it to 10 mm or less.

  In addition, it is not limited to the description content of the said embodiment, For example, you may implement as follows. Of course, other application examples and modification examples not illustrated below are also possible.

  (A) In the above embodiment, the press pin 53 has a rod shape, but the shape of the press pin 53 is not limited to this. Therefore, for example, as shown in FIG. 6, the press pin 73 may have a T-shaped cross section.

  (B) In the embodiment described above, the entire press pin 53 is formed of ceramics, but at least a portion of the press pin 53 to be inserted into the shaft hole 4 may be formed of ceramics.

  (C) In the second embodiment, the conductive member 64 is provided between the terminal electrode 63 and the metal member 62. However, the terminal electrode 63 and the metal member 62 are directly connected without providing the conductive member 64. It is good also as connecting to. When the conductive member 64 is omitted, the metal member 62 is made of a relatively soft material (for example, aluminum) in order to prevent a gap from being generated between the terminal electrode 63 and the metal member 62. Etc.), the terminal electrode 6 may be configured to be embedded in the metal member 62.

  (D) In the above embodiment, when the press pin 53 is press-fitted, the step portion between the large-diameter portion 11 and the middle barrel portion 12 of the insulator 2 is supported by the support cylinder 41, but the middle barrel portion 12 and It is good also as supporting the step part 14 formed between the leg long parts 13 with a support cylinder. In this case, when the press pin 53 is press-fitted or when the glass powder mixture 51 or the like is compressed and filled, it is possible to prevent the stress along the axis CL1 from being applied to the middle body portion 12. When manufacturing a spark plug with a reduced diameter, which is likely to cause a decrease in strength of the insulator 2, the insulator 2 can be effectively prevented from being damaged. Moreover, since the breakage of the insulator 2 can be prevented, the pressing force by the press pin 53 can be further increased, and the resistor composition 52 can be more reliably compressed.

  (E) In the above embodiment, the case where the ground electrode 31 is joined to the distal end portion 30 of the metal shell 3 is embodied. However, a part of the metal shell (or the tip metal fitting previously welded to the metal shell) The present invention can also be applied to the case where the ground electrode is formed so as to cut out a part of (see Japanese Patent Laid-Open No. 2006-236906, etc.).

  (F) In the above embodiment, the tool engaging portion 23 has a hexagonal cross section, but the shape of the tool engaging portion 23 is not limited to such a shape. For example, it may be a Bi-HEX (deformed 12-angle) shape [ISO 22777: 2005 (E)].

1 ... Spark plug 2 ... Insulator (insulator)
DESCRIPTION OF SYMBOLS 4 ... Shaft hole 5 ... Center electrode 6, 63 ... Terminal electrode 7 ... Resistor 51, 54, 66 ... Glass powder mixture 52 ... Resistor composition 53, 73 ... Press pin 62 ... Metal member 64 ... Conductive member CL1 ... Axis line

Claims (5)

An insulator having an axial hole penetrating in the axial direction;
A center electrode provided on the tip side of the shaft hole;
A terminal electrode provided on the rear end side of the shaft hole;
In the shaft hole, formed by firing a resistor composition containing a conductive material and ceramic powder, comprising a resistor that electrically connects the center electrode and the terminal electrode,
A method of manufacturing a spark plug having a maximum inner diameter of 2.9 mm or less at a position where the resistor is disposed in the shaft hole,
An arrangement step of arranging the center electrode in the shaft hole;
A glass filling step of filling a glass powder mixture comprising glass powder in the shaft hole;
A resistor filling step of filling the shaft hole with the resistor composition;
A press pin inserting step of inserting a rod-shaped press pin into the shaft hole;
Hot press-fitting the press pin, hot press-fitting step of compressing the glass powder mixture and the resistor composition,
After the hot press-fitting step, including a terminal electrode arrangement step of providing the terminal electrode on the rear end side of the shaft hole,
A method for manufacturing a spark plug, wherein at least a portion of the press pin that is inserted into the shaft hole is made of ceramics. The terminal electrode arrangement step includes
In the shaft hole, a rear end side glass filling step of filling the rear end side of the resistor with the glass powder mixture;
A terminal electrode insertion step of inserting the terminal electrode into the shaft hole;
2. The spark plug according to claim 1, further comprising a second hot press-fitting step of press-fitting the terminal electrode and compressing a glass powder mixture filled on a rear end side of the resistor. Manufacturing method. After the resistor filling step and before the press pin insertion step, including a metal member arrangement step of arranging a columnar metal member in the shaft hole,
In the hot press-fitting step, the metal member is pressed by the press pin, the glass powder mixture and the resistor composition are compressed,
The spark plug manufacturing method according to claim 1, wherein the metal member and the terminal electrode are electrically connected in the terminal electrode arranging step.   The length of the said metal member along the said axis line is 10 mm or less, The manufacturing method of the spark plug of Claim 3 characterized by the above-mentioned. After the hot press-fitting step, before the terminal electrode arrangement step,
A conductive member disposing step of disposing a conductive member elastically deformable along the axial direction between the metal member and the terminal electrode;
The spark plug manufacturing method according to claim 3, wherein the metal member and the terminal electrode are electrically connected by the conductive member.

Images