JP2013041753A - Spark plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a sufficient radio wave noise performance and a sufficient load life performance by restraining eccentricity and sealing failure of a terminal electrode in a spark plug having a comparatively short leg part and a comparatively small-diameter shaft hole.SOLUTION: A spark plug 1 comprises an electric insulator 2 having a shaft hole 4, a center electrode 5, a terminal electrode 6 having a leg part 61 and a head part 62, glass sealing parts 8, 9, and a resistor 7. When length from a rear end of the electric insulator 2 to a tip of the terminal electrode 6 is designated as L1 (mm), L1≤30 is satisfied. When an inside diameter of the shaft hole 4 at a predetermined position is designated as A (mm), A≤3.50 is satisfied. The leg part 61 is provided with a small-diameter part 611 satisfying 0.10≤A-D≤0.50 when its own outside diameter is designated as D (mm). When the length of the small diameter part 611 is designated as L3 (mm), 1.0≤L3≤12.0 is satisfied. Also, a large-diameter part 612 having an outside diameter larger than the outside diameter of the small-diameter part 611 by 0.05 mm or more is provided nearer to a rear end of the leg part 61 than the small-diameter part 611.

Description

  The present invention relates to 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 the air-fuel mixture in the combustion chamber. In general, a spark plug is exposed from an insulator having a shaft hole, a center electrode inserted through the front end side of the shaft hole, a leg portion inserted through the rear end side of the shaft hole, and a rear end of the insulator. A terminal electrode having a head portion, a metal shell provided on the outer periphery of the insulator, and a ground electrode joined to the tip of the metal shell. In addition, a spark discharge gap is provided between the tip of the ground electrode and the tip of the center electrode. When a high voltage is applied to the center electrode, a spark discharge is generated in the spark discharge gap and the mixture is ignited. Is done.

  In addition, a resistor for suppressing radio noise and a glass seal part for fixing the terminal electrode and the center electrode to the insulator between the center electrode and the terminal electrode in the shaft hole of the insulator Is provided. Generally, a resistor and a glass seal part are formed through a so-called hot press process. That is, after the center electrode is inserted into the tip end side of the shaft hole, the shaft hole is filled with a resistor composition containing a conductive material or ceramic powder and a glass powder mixture containing glass powder. Then, after inserting the terminal electrode into the shaft hole, the resistor composition and the glass powder mixture are compressed and fired by pressing the terminal electrode toward the center electrode while hot. As a result, the resistor and A glass seal portion is formed (see, for example, Patent Document 1). In order to improve the load life characteristics of the resistor, during hot pressing, the press length of the resistor composition etc. (the gap formed between the head of the terminal electrode and the rear end of the insulator before pressing) To a certain extent).

JP 2009-245908 A

  By the way, in recent years, there has been a demand for reducing the diameter of the spark plug, and in order to meet the demand, the insulator and thus the shaft hole can be reduced in diameter. Here, when the shaft hole has a small diameter, the portion (leg part) inserted through the shaft hole in the terminal electrode also has a small diameter. Therefore, when the terminal electrode is pressed, the central axis of the insulator ( The terminal electrode easily falls (tilts) with respect to the axis. For this reason, the terminal electrode is bent during pressing, the center axis of the terminal electrode is deviated from the axis (eccentric), and the compression of the resistor composition becomes insufficient due to the eccentricity of the terminal electrode. This may cause the load life characteristics of the resistor to deteriorate.

  Here, if the length of the leg portion is sufficiently large, even if the central axis of the terminal electrode is inclined with respect to the axis, the inclination is small. For this reason, it is difficult to cause a situation such as eccentricity of the terminal electrode and deterioration of load life characteristics of the resistor.

  However, in order to obtain excellent radio noise performance, it is necessary to secure a sufficient length of the resistor. In a spark plug having a relatively short overall length used for a general-purpose engine or the like, the resistor is lengthened. For this reason, the legs must be shortened. When the leg portion is shortened, the length of the portion of the leg portion disposed in the shaft hole is relatively small with respect to the total length of the leg portion with the terminal electrode disposed in the shaft hole. turn into. For this reason, when the center axis of the terminal electrode is tilted with respect to the axis during pressing, the tilt may be larger. That is, when the shaft hole has a small diameter and the leg portion is short, the occurrence of a situation such as eccentricity of the terminal electrode or deterioration of load life characteristics of the resistor is particularly a concern.

  Therefore, in order to suppress such problems, by thickening the leg portion, the diameter difference between the outer diameter of the leg portion and the inner diameter of the shaft hole is reduced, and the terminal electrode is made difficult to tilt. Even if it exists, it is possible to make small the inclination of the central axis of a terminal electrode with respect to an axis. However, simply making the legs thick may cause problems in the following aspects.

  That is, in consideration of convenience in manufacturing, the press length is set within a predetermined range, and a slight variation is allowed within this range. And, when the press length is relatively small within the above range, the terminal electrode head is in contact with the rear end of the insulator without any gap, with almost no deformation of the leg portion of the terminal electrode during pressing. Thus, the terminal electrode is fixed (sealed) to the insulator. On the other hand, when the press length is relatively large within the range, the leg portion is bent and deformed during pressing, so that the terminal electrode is fixed with the head in contact with the rear end of the insulator without any gap. (Sealed). That is, the variation in the press length is absorbed by bending and deforming the leg portion. However, if the leg portion is short and the leg portion is thickened, bending deformation of the leg portion is extremely difficult to occur. Therefore, in the hot press process, a product in which the head of the terminal electrode is lifted from the rear end of the insulator, that is, a product in which a sealing failure has occurred is likely to be manufactured, resulting in a decrease in productivity. There is a risk that.

  The present invention has been made in view of the above circumstances, and an object thereof is to generate eccentricity of terminal electrodes and poor sealing in a spark plug having a relatively short leg and a relatively small shaft hole. Is to achieve good radio noise performance and load life performance, and to improve productivity.

  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 of this configuration includes an insulator having an axial hole extending in the axial direction;
A center electrode inserted on the tip side of the shaft hole;
A rod-like leg portion inserted into the rear end side of the shaft hole, and a terminal electrode having a head portion exposed from the rear end of the insulator;
A glass seal portion for fixing the terminal electrode and the center electrode to the insulator in the shaft hole;
A spark plug including a resistor provided between the terminal electrode and the center electrode in the shaft hole,
When the length from the rear end of the insulator along the axis to the front end of the terminal electrode is L1 (mm), L1 ≦ 30.
When the inner diameter of the shaft hole at a position of 5 mm from the rear end of the insulator to the front end in the axial direction is A (mm), A ≦ 3.50,
The leg portion is provided with a small-diameter portion that includes 0.10 ≦ A−D ≦ 0.50 and includes a portion having the smallest outer diameter, when the outer diameter of the leg is D (mm).
When the length of the small diameter portion along the axis is L3 (mm), 1.0 ≦ L3 ≦ 12.0,
A large-diameter portion whose outer diameter is 0.05 mm or more larger than the outer diameter of the small-diameter portion is provided on the rear end side in the axial direction from the small-diameter portion of the leg portion.

  According to the configuration 1, since the length L1 is set to 30 mm or less, the length of the resistor can be sufficiently ensured, and good radio noise performance can be realized.

  On the other hand, when the length L1 is set to 30 mm or less (when the leg portion is short), as described above, there is a concern about the eccentricity of the terminal electrode, the deterioration of the load life characteristics, and the occurrence of poor sealing.

  In this regard, according to the above-described configuration 1, the leg portion is provided with the small-diameter portion, the inner diameter of the small-diameter portion is D (mm), the length is L3 (mm), and the inner diameter of the shaft hole at the predetermined portion is A. (Mm), 0.10 ≦ A−D and 1.0 ≦ L3 are satisfied. That is, the small diameter portion has a relatively small diameter and is relatively long. Accordingly, the small diameter portion is easily bent and deformed during pressing, and the occurrence of poor sealing can be effectively suppressed.

  Further, on the rear end side with respect to the small diameter portion, a large diameter portion whose own outer diameter is 0.05 mm or more larger than the outer diameter of the small diameter portion is provided. Therefore, it is difficult to cause a situation in which the terminal electrode is largely inclined during pressing, and the eccentricity of the terminal electrode can be more reliably prevented. Moreover, since the eccentricity of the terminal electrode is suppressed, the resistor composition can be sufficiently compressed, and excellent load life characteristics can be realized. As a result, good ignitability can be maintained over a long period of time.

  If the small diameter portion is excessively small or long, the small diameter portion may be excessively bent and deformed. If the small-diameter portion is excessively bent and deformed, the terminal electrode is likely to be eccentric, and the deformed portion is caught in the shaft hole, resulting in poor sealing, or the press pressure is a resistor composition. There is a risk that the load life characteristics may be deteriorated without being sufficiently transmitted to the above. In view of this point, according to the above-described configuration 1, it is configured to satisfy AD ≦ 0.50 and L3 ≦ 12.0, and an excessively small diameter and a long length of the small diameter portion are prevented. Yes. Therefore, excessive bending deformation in the small diameter portion can be suppressed, and the above-described effects can be more reliably exhibited.

  Configuration 2. The spark plug of this configuration is the above-described configuration 1, wherein the outer diameter of the leg portion is larger than the small diameter portion on the rear end side in the axial direction than the small diameter portion, and the outer diameter thereof is B (mm). In this case, a guide portion satisfying 0.02 ≦ A−B ≦ 0.13 is provided.

  According to the above configuration 2, the guide portion having a larger diameter is provided on the rear end side of the small diameter portion, and the outer diameter B (mm) of the guide portion satisfies AB ≦ 0.13. It is configured as follows. Therefore, during pressing, the terminal electrode is more difficult to tilt, and the occurrence of eccentricity in the terminal electrode can be prevented more reliably.

  Further, by setting 0.02 ≦ A−B, it is possible to reduce the frictional force that can be generated between the leg portion (guide portion) and the insulator during pressing. As a result, it becomes easier to insert the terminal electrode into the shaft hole, and the sealing failure can be more effectively suppressed.

  Configuration 3. The spark plug of this configuration is the above-mentioned configuration 2, wherein the outer diameter of the leg portion between the small diameter portion and the guide portion is larger than the outer diameter of the small diameter portion. An intermediate portion smaller than the outer diameter is provided.

  According to the configuration 3, by providing the intermediate portion, the press pressure applied to the leg portion is dispersed to some extent, and it is difficult to cause a situation in which an excessively large press pressure is applied to the small diameter portion. Therefore, excessive bending deformation in the small diameter portion can be more reliably prevented, and the effect of suppressing the eccentricity of the terminal electrode can be further enhanced.

  Configuration 4. The spark plug of this configuration satisfies any of the above configurations 1 to 3, and satisfies 0.11 ≦ A−D ≦ 0.40.

  According to the above configuration 4, the operational effects of the above configuration 1 and the like are more remarkably exhibited, and the eccentricity and poor sealing of the terminal electrode can be further effectively prevented.

  Configuration 5. The spark plug of this configuration is L2 ≧ 12 in any one of the above configurations 1 to 4, where the distance from the tip of the terminal electrode along the axis to the rear end of the center electrode is L2 (mm). It is characterized by that.

  According to the configuration 5, it is possible to secure a larger space in which the resistor is disposed, and it is possible to make the resistor longer. As a result, the effect of suppressing radio noise can be further improved.

  In addition, it is necessary to shorten the leg portion as the length L2 is larger. If the leg portion is shortened, the terminal electrode is likely to be eccentric as described above. However, by adopting the above configuration 1 or the like, the terminal electrode Can be more reliably prevented. In other words, the configuration 1 or the like is particularly significant when L2 ≧ 12 mm and there is a particular concern about the eccentricity of the terminal electrode.

  Configuration 6. The spark plug of this configuration is characterized in that 3.0 ≦ L3 ≦ 7.0 in any one of the above configurations 1 to 5.

  According to the configuration 6, the amount of deformation of the small diameter portion during pressing falls within a more appropriate range. Therefore, the occurrence of eccentricity of the terminal electrode and poor sealing can be suppressed extremely effectively.

  Configuration 7. The spark plug according to any one of claims 1 to 6, wherein the spark plug of this configuration satisfies L1 ≤ 25 in any of the above configurations 1 to 6.

  The configuration 1 and the like are particularly significant when the length L1 is 25 mm or less and the eccentricity of the terminal electrode is very likely to occur as in the configuration 7.

  Configuration 8. The spark plug of this configuration is characterized in that, in any one of the above configurations 1 to 7, the terminal electrode has a Vickers hardness of 100 Hv to 380 Hv.

  According to the configuration 8, since the hardness of the terminal electrode is 100 Hv or more, excessive deformation of the terminal electrode (particularly, the small diameter portion) during pressing can be more reliably prevented. On the other hand, since the hardness of the terminal electrode is 380 Hv or less, the terminal electrode (particularly the small diameter portion) can be appropriately deformed (to the extent that no poor sealing occurs) during pressing. That is, according to the said structure 8, the deformation amount of the small diameter part at the time of a press will be settled in a more suitable range, and generation | occurrence | production of the eccentricity of a terminal electrode and the sealing defect can be prevented more reliably.

  Configuration 9 The spark plug of this configuration is characterized in that, in any of the above configurations 1 to 8, the terminal electrode has a Vickers hardness of 220 Hv or more and 315 Hv or less.

  According to the above-described configuration 9, the deformation amount of the small-diameter portion falls within a more appropriate range, and the eccentricity of the terminal electrode can be more reliably prevented.

  Configuration 10 The spark plug of this configuration is characterized in that 0.4 ≦ L3 / D ≦ 4.5 in any one of the above configurations 1 to 9.

  According to the configuration 10, the ratio (L3 / D) of the length L3 of the small diameter portion to the outer diameter D of the small diameter portion is 0.4 or more and 4.5 or less, and the small diameter portion has its own outer diameter. It is configured so that its own length relative to is not excessively large or small. Therefore, the small diameter portion can be appropriately deformed during pressing, and the effect of suppressing the eccentricity of the terminal electrode can be further improved.

  In addition, it is more preferable to satisfy 1.1 ≦ L3 / D ≦ 4.2, and 1.1 ≦ L3 / D ≦ 2.6 from the viewpoint of further improving the eccentricity suppressing effect and the like. Even more preferred.

It is a partially broken front view which shows the structure of a spark plug. It is a partial expanded sectional view which shows the structure of the rear-end part of a spark plug. It is a front view which shows the structure of a terminal electrode. (A), (b) is sectional drawing which shows one process of a hot press process. It is a cross-sectional schematic diagram for demonstrating the amount of terminal eccentricity.

  Hereinafter, an embodiment will be described with reference to the drawings. 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. In the present embodiment, the spark plug 1 has a relatively small total length L4 along the axis CL1 (for example, 70 mm or less).

  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 bulging portion 11 projecting outward in the radial direction on the side, a middle barrel portion 12 having a smaller diameter on the distal end side than the bulging portion 11, and a distal end than the middle barrel portion 12 The leg length part 13 formed in diameter smaller than this on the side is provided. Of the insulator 2, the bulging portion 11, the middle body portion 12, and most of the leg length 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 middle trunk portion 12 and the long leg portion 13, 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 front end side of the shaft hole 4 is formed with a relatively small diameter, while the rear end side of the shaft hole 4 is formed with a larger diameter than the front end side thereof. Further, in the shaft hole 4, a tapered step portion 4 </ b> A is formed between the small diameter portion on the front end side and the large diameter portion on the rear end side.

  In addition, a center electrode 5 is inserted and fixed on the tip side of the shaft hole 4. More specifically, a flange portion 5E that bulges toward the outer peripheral side is formed on the rear end side of the center electrode 5, and the flange portion 5E is locked to the stepped portion 4A. The center electrode 5 is fixed. The center electrode 5 is composed of an inner layer 5A made of a metal having excellent thermal conductivity [for example, copper, copper alloy, pure nickel (Ni)] and an outer layer 5B made of a Ni alloy containing Ni as a main component. Yes. 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.

  Further, a rod-like terminal electrode 6 is inserted and fixed to the rear end side of the shaft hole 4 in a state of protruding from the rear end of the insulator 2 (the configuration of the terminal electrode 6 will be described in detail later). .

  Further, a conductive resistor 7 having a cylindrical shape is disposed between the center electrode 5 and the terminal electrode 6 of the shaft hole 4. The resistor 7 has a resistance value of a predetermined value (for example, 100Ω) or more in order to suppress radio noise, and a resistor composition made of a conductive material or glass powder is heated and fired. It is formed with. In addition, both ends of the resistor 7 are provided with glass seal portions 8 and 9 having conductivity (for example, a resistance value of about several hundred mΩ), and the glass seal portions 8 and 9 provide the center electrode 5. And the terminal electrode 6 are fixed to the insulator 2.

  In addition, the metal shell 3 is formed in a cylindrical shape from a metal such as low carbon steel, and a spark plug 1 is attached to the outer peripheral surface of the metal shell 3 in a mounting hole for a combustion device (for example, an internal combustion engine or a fuel cell reformer). A threaded portion (male threaded portion) 15 is formed for attachment. Further, a seat portion 16 protruding radially outward is formed on the outer peripheral surface on the rear end side of the screw portion 15, and a ring-shaped gasket 18 is fitted on the screw neck 17 on the rear end of the screw portion 15. . Furthermore, a tool engagement portion 19 having a hexagonal cross section for engaging a tool such as a wrench when the metal shell 3 is attached to the combustion device is provided on the rear end side of the metal shell 3. A caulking portion 20 for holding the insulator 2 is provided.

  Further, a tapered step portion 21 for locking the insulator 2 is provided on the distal end side of the inner peripheral surface of the metal shell 3. The insulator 2 is inserted from the rear end side to the front end side with respect to the metal shell 3, and the rear end of the metal shell 3 with its own stepped portion 14 locked to the stepped portion 21 of the metal shell 3. It is fixed to the metal shell 3 by caulking the opening on the side inward in the radial direction, that is, by forming the caulking portion 20. An annular plate packing 22 is interposed between the step portion 14 of the insulator 2 and the step portion 21 of the metal shell 3. Thereby, the airtightness in the combustion chamber is maintained, and the fuel gas 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 the sealing by caulking more complete, annular ring members 23 and 24 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 23 , 24 is filled with powder of talc (talc) 25. That is, the metal shell 3 holds the insulator 2 via the plate packing 22, the ring members 23 and 24, and the talc 25.

  Further, a substantially intermediate portion of the metal shell 3 is bent back, and a ground electrode 27 having a side surface facing the tip portion of the center electrode 5 is joined to the tip portion 26 of the metal shell 3. The ground electrode 27 is formed of an outer layer 27A formed of a Ni alloy [for example, Inconel 600 or Inconel 601 (both are registered trademarks)], a copper alloy, pure copper, or the like, which is a better heat conductive metal than the Ni alloy. And an inner layer 27B.

  Further, a spark discharge gap 28 is formed between the tip of the center electrode 5 and the tip of the ground electrode 27, and spark discharge is performed in the spark discharge gap 28 in a direction substantially along the axis CL1. It has come to be.

  Next, the configuration of the shaft hole 4 and the configuration of the terminal electrode 6 inserted through the shaft hole 4 will be described in detail.

  In this embodiment, the shaft hole 4 has a relatively small diameter. As shown in FIG. 2, the inner diameter of the shaft hole 4 at a position 5 mm from the rear end of the insulator 2 to the front end side in the axis CL1 direction is A ( mm), A ≦ 3.50 is satisfied. In the present embodiment, the inner diameter of the portion of the shaft hole 4 where the terminal electrode 6, the resistor 7, etc. are disposed is made equal to the inner diameter A. The inner diameter A is defined as described above in order to obtain the inner diameter of a portion of the shaft hole 4 through which the terminal electrode 6 is inserted and having a substantially constant inner diameter along the direction of the axis CL1. In consideration of the case where the rear end portion of the shaft hole 4 can be gradually enlarged toward the rear end side in the direction of the axis CL1 as in the present embodiment, the inner diameter of the portion having the substantially constant inner diameter. It is for obtaining more easily.

  In addition, the terminal electrode 6 is made of low carbon steel or the like, and includes a leg portion 61 and a head portion 62 as shown in FIG.

  The leg portion 61 is inserted into the rear end side of the shaft hole 4 and has a circular cross section. The head 62 is adjacent to the leg 61 on the rear end side and exposed from the rear end of the insulator 2. Furthermore, the front end surface of the head 62 is in contact with the rear end surface of the insulator 2.

  In addition, in the present embodiment, from the rear end of the insulator 2 along the axis CL1 to the tip of the terminal electrode 6 (leg portion 61) in order to sufficiently secure the length of the resistor 7 along the axis CL1. The length of the is relatively short. Specifically, when the length from the rear end of the insulator 2 along the axis CL1 to the front end of the terminal electrode 6 (leg portion 61) is L1 (mm), the length L1 ≦ 30 is satisfied. Yes. Note that it is preferable that L1 ≦ 25 be satisfied in terms of securing a longer length of the resistor 7 and improving radio noise performance.

  As shown in FIG. 3, the leg 61 has 0.10 ≦ A−D ≦ 0.50 (more preferably, 0.11 ≦ A− when the outer diameter of the leg 61 is D (mm). A small diameter portion 611 that satisfies D ≦ 0.40) is provided. The small diameter portion 611 includes a portion of the leg portion 61 having the smallest outer diameter, and in the present embodiment, the inner diameter is constant throughout the small diameter portion 611 along the axis CL1. In the case where the outer diameter of the small diameter portion 611 changes along the axis CL1, 0.10 ≦ A−D ≦ in the substantially entire region (at least 60% or more) along the axis CL1 direction of the small diameter portion 611. It is configured to satisfy 0.50.

  In addition, when the length of the small diameter portion 611 along the axis CL1 is L3 (mm), 1.0 ≦ L3 ≦ 12.0 (more preferably, 3.0 ≦ L3 ≦ 7.0) is satisfied. It is configured. The small-diameter portion 611 has 0.4 ≦ L3 / D ≦ 4.5 (more preferably, 1.1 ≦ L3 / D ≦ 4.2. More preferably, 1.1 ≦ L3 / D ≦ 2.6. ) So that the ratio of the length L3 of the small diameter portion 611 to the outer diameter D of the small diameter portion 611 is not extremely large or small.

  Further, a large-diameter portion 612 whose outer diameter is larger by 0.05 mm or more than the outer diameter of the small-diameter portion 611 is provided on the rear end side of the leg portion 61 in the axis CL1 direction with respect to the small-diameter portion 611. The large diameter part 612 includes a guide part 612A and an intermediate part 612B.

  The guide portion 612A is provided at a position adjacent to the head portion 62 on the rear end side of the large diameter portion 612. Further, the guide portion 612A is configured to satisfy 0.02 ≦ A−B ≦ 0.13 when the outer diameter of the guide portion 612A is B (mm).

  The intermediate part 612B is provided between the small diameter part 611 and the guide part 612A, and has a constant outer diameter along the direction of the axis CL1. The outer diameter of the intermediate part 612B is larger than the outer diameter of the small diameter part 611 and smaller than the outer diameter of the guide part 612A.

  In the present embodiment, as described above, the length L1 is relatively shortened, so that the resistor 7 has a sufficient length along the axis CL1. Therefore, as shown in FIG. 1, when the distance along the axis CL1 between the tip of the terminal electrode 6 and the rear end of the center electrode 5 (space where the resistor 7 is disposed) is L2 (mm), L2 ≧ 12 is satisfied. In the present embodiment, the thickness of the glass seal portion 8 (distance along the axis CL1 from the tip of the terminal electrode 6 to the rear end of the resistor 7) and the thickness of the glass seal portion 9 (resistor 7). The distance along the axis CL1 from the front end of the central electrode 5 to the rear end of the center electrode 5) is relatively small (for example, 3 mm or less).

  Furthermore, the terminal electrode 6 has a Vickers hardness of 100 Hv or more and 380 Hv or less (more preferably, 220 Hv or more and 315 Hv or less). Note that the hardness of the terminal electrode 6 is, for example, that the terminal electrode 6 is manufactured using a material having a high hardness, and then the obtained terminal electrode 6 is subjected to a heat treatment (annealing process) to obtain the hardness of the terminal electrode 6. It can be adjusted by lowering. However, the heat treatment time and the heating temperature are adjusted so that the hardness of the terminal electrode 6 is 100 Hv or more even after the heat treatment.

  In addition, in the present embodiment, as shown in FIG. 3, a foot portion 613 having a plurality of grooves (knurls) formed on the outer peripheral surface is provided at the distal end portion of the terminal electrode 6 (leg portion 61). . At least the tip portion of the foot portion 613 is embedded in the glass seal portion 8, and as a result, the terminal electrode 6 is firmly fixed to the insulator 2.

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

  First, the metal shell 3 is processed in advance. That is, a rough shape is formed on a cylindrical metal material (for example, an iron-based material or a stainless steel material) by cold forging or the like, and a through hole is formed. Thereafter, the outer shape is adjusted by cutting to obtain a metal shell intermediate.

  Next, a straight bar-like (needle-like) ground electrode 27 made of Ni alloy or the like is resistance-welded to the front end surface of the metal shell intermediate. When the welding is performed, so-called “sag” is generated. After the “sag” is removed, the threaded portion 15 is formed by rolling at a predetermined portion of the metal shell intermediate body. Thereby, the metal shell 3 to which the ground electrode 27 is welded is obtained.

  Next, the metal shell 3 to which the ground electrode 27 is welded is subjected to galvanization or Ni plating. 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 compact for molding is prepared, and a rubber-molded product is used to form a cylindrical molded body. Is obtained. The obtained molded body is ground and shaped, and the shaped product is fired in a firing furnace, whereby the insulator 2 is obtained.

  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 or the like for improving heat dissipation is arranged at the center.

  Furthermore, a powdery resistor composition for forming the resistor 7 is prepared. More specifically, first, a conductive material (for example, carbon black), ceramic particles, and a predetermined binder are blended, and mixed using water as a medium. And the resistor composition is obtained by drying the slurry obtained by mixing and mixing and stirring glass powder to this.

  Next, in the hot pressing process, the resistor 7 is provided in the shaft hole 4, and the center electrode 5 and the terminal electrode 6 are sealed and fixed to the insulator 2 by the glass seal portions 8 and 9. More specifically, first, as shown in FIG. 4A, the center electrode 5 is inserted into the tip end side of the shaft hole 4. At this time, the flange portion 5E of the center electrode 5 is locked to the step portion 4A of the shaft hole 4.

  Next, a glass powder mixture 41 generally prepared by mixing borosilicate glass and metal powder is filled into the shaft hole 4, and the filled glass powder mixture 41 is pre-compressed. Next, the resistor composition 42 is filled into the shaft hole 4 and preliminarily compressed in the same manner. Further, the glass powder mixture 43 is filled into the shaft hole 4 and preliminarily compressed. Next, the leg portion 61 of the terminal electrode 6 is inserted into the shaft hole 4, and the terminal electrode 6 is placed on the glass powder mixture 43. At this time, in order to improve the load life characteristics of the resistor 7, the press length of the resistor composition 42 and the like (the size of the gap formed between the head 62 and the rear end of the insulator 2) is sufficient. Size is secured. The press length is not strictly constant, and some variation is allowed within a predetermined range.

  In this state, the terminal electrode 6 is pressed into the shaft hole 4 from the opposite side of the center electrode 5 and heated at a predetermined target temperature (for example, 900 ° C.) above the glass softening point in the firing furnace. By heating, as shown in FIG. 4B, the resistor composition 42 and the glass powder mixtures 41 and 43 in the laminated state are heated and compressed to become the resistor 7 and the glass seal portions 8 and 9, and the glass. The center electrode 5 and the terminal electrode 6 are sealed and fixed to the insulator 2 by the seal portions 8 and 9. In addition, at the time of the heating in a baking furnace, it is good also as baking a glaze layer simultaneously on the surface of the rear end side trunk | drum 10 of the insulator 2, and it is good also as forming a glaze layer in advance.

  Thereafter, the insulator 2 provided with the center electrode 5 and the resistor 7 and the like manufactured as described above and the metal shell 3 provided with the ground electrode 27 are fixed. More specifically, after the insulator 2 is inserted through the metal shell 3, the opening on the rear end side of the metal shell 3 formed relatively thin is caulked radially inward, that is, the caulking portion 20 is By forming, the insulator 2 and the metal shell 3 are fixed.

  Finally, a substantially intermediate portion of the ground electrode 27 is bent toward the center electrode 5 side, and the size of the spark discharge gap 28 formed between the center electrode 5 and the ground electrode 27 is adjusted, whereby the above-described spark plug. 1 is obtained.

  As described above in detail, according to the present embodiment, since the length L1 is 30 mm or less, the length of the resistor 7 can be sufficiently secured, and good radio noise performance can be realized. Can do. On the other hand, when the length L1 is set to 30 mm or less, there is a concern about the eccentricity of the terminal electrode 6, the deterioration of the load life characteristics, and the occurrence of poor sealing during the hot pressing process.

  In this regard, in the present embodiment, the leg portion 61 is provided with a small diameter portion 611, the inner diameter of the small diameter portion 611 is D (mm), the length is L3 (mm), and the inner diameter of the shaft hole 4 at a predetermined site is set. When A (mm) is set, 0.10 ≦ A−D and 1.0 ≦ L3 are satisfied. That is, the small diameter portion 611 is relatively small in diameter and relatively long. Therefore, the small diameter portion 611 is easily bent and deformed during pressing, and the occurrence of poor sealing can be effectively suppressed.

  Further, on the rear end side of the small diameter portion 611, a large diameter portion 612 whose own outer diameter is larger by 0.05 mm or more than the outer diameter of the small diameter portion 611 is provided. Therefore, it is difficult for the terminal electrode 6 to be greatly inclined during pressing, and the eccentricity of the terminal electrode 6 can be more reliably prevented. Moreover, by suppressing the eccentricity of the terminal electrode 6, the resistor composition 42 can be sufficiently compressed, and excellent load life characteristics can be realized. As a result, good ignitability can be maintained over a long period of time.

  In addition, in this embodiment, it is configured to satisfy AD ≦ 0.50 and L3 ≦ 12.0, and excessively small diameter and long length of the small diameter portion 611 are prevented. Therefore, excessive bending deformation in the small diameter portion 611 can be suppressed, and the above-described effects can be more reliably exhibited.

  Further, a guide portion 612A having a larger diameter than that of the small diameter portion 611 is provided on the rear end side so that the outer diameter B (mm) of the guide portion 612A satisfies AB ≦ 0.13. It is configured. Therefore, during pressing, the terminal electrode 6 becomes more difficult to tilt, and the occurrence of eccentricity in the terminal electrode 6 can be more reliably prevented.

  Furthermore, by setting 0.02 ≦ A−B, it is possible to reduce the frictional force that can be generated between the leg portion 61 (guide portion 612A) and the insulator 2 during pressing. As a result, it becomes easier to insert the terminal electrode 6 into the shaft hole 4, and the sealing failure can be more effectively suppressed.

  In addition, an intermediate portion 612B is provided between the small diameter portion 611 and the guide portion 612A. By providing the intermediate portion 612B, the press pressure applied to the leg portion 61 is dispersed to some extent, and a situation in which an excessively large press pressure is applied to the small diameter portion 611 is less likely to occur. Therefore, excessive bending deformation in the small diameter portion 611 can be more reliably prevented, and the eccentricity suppressing effect of the terminal electrode 6 can be further enhanced.

  In addition, in this embodiment, since L2 ≧ 12 mm, a larger space for placing the resistor 7 can be secured. As a result, the resistor 7 can be made longer, and the effect of suppressing radio noise can be further improved.

  In addition, since the hardness of the terminal electrode 6 is 100 Hv or more, excessive deformation of the terminal electrode 6 (particularly, the small diameter portion 611) during pressing can be more reliably prevented. On the other hand, since the hardness of the terminal electrode 6 is 380 Hv or less, the terminal electrode 6 (particularly the small diameter portion 611) can be sufficiently deformed during pressing. That is, by setting the hardness of the terminal electrode 6 to 100 Hv or more and 380 Hv or less, the deformation amount of the small diameter portion 611 at the time of pressing falls within a more appropriate range. Therefore, the eccentricity of the terminal electrode 6 and the occurrence of poor sealing can be prevented more reliably.

  Furthermore, since the ratio (L3 / D) of the length L3 of the small diameter portion 611 to the outer diameter D of the small diameter portion 611 is 0.4 or more and 4.5 or less, the small diameter portion 611 is appropriately deformed during pressing. The effect of suppressing the eccentricity of the terminal electrode 6 can be further improved.

  Next, in order to confirm the operational effects achieved by the above-described embodiment, an insulator having an inner diameter A (mm) of the shaft hole of 3.00 mm, 3.50 mm, or 4.00 mm, and a leg, a guide When the outer diameter B (mm) of the part corresponding to the part, the presence or absence of a small diameter part, a small diameter part is provided, the outer diameter D (mm) and its length L3, the presence or absence of an intermediate part, the case of providing an intermediate part Were prepared with terminal electrodes in which the outer diameter C (mm) and the length L1 were variously changed, and the above hot pressing process was performed using these insulators and terminal electrodes. And the eccentricity and productivity of the terminal electrode were evaluated after the hot press process.

  Here, the eccentricity of the terminal electrode was evaluated as follows. First, after the insulator with the terminal electrode inserted is horizontally disposed, the insulator and the terminal electrode are rotated while rotating the insulator by 30 degrees around the axis line as the rotation axis from above using a predetermined imaging device. A total of 6 images were taken. In each of the obtained six captured images, as shown in FIG. 5, a distance X between an intersection P between an axis CL1 and a straight line DL1 described later, and an intersection Q between the straight line DL and a straight line DL2 described later. Asked. Next, the largest of the distances X in each captured image is the terminal eccentricity amount. When the terminal eccentricity amount is 0.0 mm or more and 0.10 mm or less, 10 points are obtained, and the terminal eccentricity amount is more than 0.10 mm and 0. 9 points when the terminal eccentricity is 15 mm or less, and deducted by 1 point each time the terminal eccentricity increases by 0.05 mm (for example, 7 points when the terminal eccentricity is more than 0.20 mm and less than 0.25 mm, 4 points when the amount of eccentricity is more than 0.35 mm and less than 0.40 mm).

  The “straight line DL” refers to a straight line passing through the intersection of the rear end surface of the terminal electrode and the axis line CL1 and orthogonal to the axis line CL1. Further, the “straight line DL2” draws straight lines AL1 to AL4 orthogonal to the axis CL1 every 1 mm along the axis CL1 direction from the rear end (intersection point P) of the terminal electrode. The approximate straight lines of the midpoints MP1 to MP4 when the midpoints MP1 to MP4 of the two intersections with the side surface are taken.

  The productivity was evaluated as follows. That is, 1000 samples are obtained through a hot pressing process, and the contact state of the head of the terminal electrode with respect to the rear end surface of the insulator is confirmed for each sample, and the head contacts the rear end surface of the insulator. In the case where the head is separated from the rear end surface of the insulator, the sealing is poor. Then, the occurrence ratio (defective rate) of the sealing failure in 1000 pieces is calculated, and when the defective rate is 0.0%, 10 points, when the defective rate is 0.1%, the defective rate is 0. 8 points when 2% or more and 0.3% or less, 7 points when defective rate is 0.4% or more and 1.0% or less, and when defective rate is 1.1% or more and 1.5% or less From this point onwards, 1 point was deducted every time the defect rate increased by 0.5% (for example, 4 points when the defect rate was 2.1% or more and 2.5% or less).

  Table 1 shows the inner diameter A, the outer diameter B, the presence or absence of a small diameter portion, and the evaluation of eccentricity and productivity of the terminal electrode in each sample. In each sample, the length L2 was set to 13 mm. Moreover, the sample which did not provide a small diameter part made constant the outer diameter of the leg part except the said foot part and the last end part of a leg part, and made the outer diameter the same as the outer diameter of a large diameter part. In addition, in the sample provided with the small diameter portion but not provided with the intermediate portion, the outer diameter of the portion corresponding to the intermediate portion was made the same as the outer diameter of the small diameter portion. In the sample provided with the intermediate portion, the outer diameter B of the large diameter portion corresponds to the outer diameter of the guide portion.

  Moreover, if it becomes 7 points | pieces or more in both evaluation of eccentricity in a terminal electrode and evaluation of productivity, it can be said that it is favorable in both sides of eccentricity suppression and productivity.

  As shown in Table 1, in the samples (samples 1 to 5) having an inner diameter A of 4.00 mm, when the legs are relatively thick (when the outer diameter is 3.90 mm or more), The legs are difficult to bend and deform, and the productivity is insufficient, but by reducing the outer diameter of the legs, excellent productivity can be realized, and even if A-D exceeds 0.50 mm, the terminal It was found that the electrode is not easily eccentric. That is, when the inner diameter A is more than 3.50 mm, it has been confirmed that an excellent eccentricity suppressing effect and productivity can be realized by simply narrowing the leg portion.

  On the other hand, when attention is paid to a sample (samples 6 to 33) having an inner diameter A of 3.50 mm or less, a sample having a length L1 exceeding 30 mm (sample 6) suppresses the eccentricity of the terminal electrode and the productivity. The samples (samples 7 to 12) in which the length L1 was 30 mm or less, the outer diameter of the leg portion was reduced, and AD was more than 0.50 mm (samples 7 to 12) are terminals. It became clear that eccentricity of electrodes and poor sealing are likely to occur. This is because when the length L1 is 30 mm or less, the central axis of the terminal electrode is easily inclined with respect to the axis, and the outer diameter D is small, so that the small diameter portion is easily bent and deformed locally. (Eccentricity is likely to occur), and it is considered that the terminal electrode is hindered from further movement due to the bent deformation portion being caught in the shaft hole.

  Moreover, it turns out that the sample (samples 13 and 14) which made the leg part thick and AD was less than 0.10 mm, and the sample (sample 15) which made length L3 less than 1.0 mm are inferior in productivity. It was. This is because the legs are difficult to bend and deform during pressing, and it is difficult to absorb variations in the press length (the distance between the rear end of the insulator and the head of the terminal electrode before pressing). Conceivable.

  Furthermore, it was revealed that the sample (sample 16) having the length L3 exceeding 12.0 mm is also inferior in productivity. This is considered to be because the leg portion (small diameter portion) was excessively bent and deformed during pressing.

  On the other hand, while providing a small-diameter portion whose outer diameter D is smaller by 0.05 mm or more (satisfy BD ≧ 0.05) than the outer diameter B of the large-diameter portion, 0.10 ≦ AD It was revealed that samples satisfying ≦ 0.50 (samples 18 to 33) were excellent in both the eccentricity suppressing effect and productivity even when the length L1 was set to 30 mm or less. This is because the provision of the large-diameter portion reduces the inclination of the terminal electrode with respect to the axis during pressing, and the provision of the small-diameter portion causes the small-diameter portion to bend and deform appropriately at the time of pressing. This is thought to be because the variation was sufficiently absorbed. In addition, although the small diameter portion is provided, when the diameter difference (BD) of the small diameter portion with respect to the large diameter portion is less than 0.05 mm (sample 17), the effect due to the provision of the small diameter portion is not sufficiently exhibited. I understood that.

  Moreover, when comparing the samples 21 and 22 in which the presence / absence of the intermediate portion was changed, it was confirmed that the sample 21 provided with the intermediate portion can more effectively suppress the eccentricity of the terminal electrode. This is because the press pressure is dispersed to some extent by the intermediate portion, so that an excessively large press pressure is prevented from being applied to the small diameter portion, and the situation where the small diameter portion is excessively deformed can be prevented more reliably. It is thought that.

  Furthermore, when attention is paid to samples (samples 25 to 29) in which only the length L3 of the small diameter portion is changed, the length L3 is set to 3.0 mm or more and 7.0 mm or less, thereby suppressing the eccentricity of the terminal electrode. It has been found that productivity can be further improved. This is considered to be because the amount of deformation of the small diameter portion is within a more appropriate range by setting the length L3 to 3.0 mm or more and 7.0 mm or less.

  From the test results of the above test, in the spark plug in which L1 ≦ 30 mm and A ≦ 3.50 mm, the occurrence of eccentricity in the terminal electrode is more reliably prevented, and the occurrence of poor sealing is suppressed. In order to realize high productivity, a small diameter portion satisfying 0.10 ≦ AD ≦ 0.50, and its outer diameter on the rear end side of the small diameter portion is 0.05 mm from the outer diameter of the small diameter portion. It can be said that it is preferable to provide a large diameter portion as described above and to configure the length L3 (mm) of the small diameter portion to satisfy 1.0 ≦ L3 ≦ 12.0.

  Also, from the viewpoint of more effectively preventing the eccentricity of the terminal electrode, the outer diameter of the terminal portion is larger than the outer diameter of the small diameter portion at the portion between the small diameter portion and the guide portion. It is more preferable to provide a small intermediate portion.

  Furthermore, it can be said that the length L3 is more preferably 3.0 mm or more and 7.0 mm or less in order to further improve the eccentricity suppressing effect and productivity of the terminal electrode.

  When attention is paid to Samples 9 to 12, it can be said that when the length L1 is set to 25 mm or less, the terminal electrode is more likely to be decentered or poorly sealed. In addition, with the above configuration (0.10 ≦ A ≦ D ≦ 0.50, etc.), as shown in the test results of Samples 31 to 33, it is possible to achieve a good eccentricity suppressing effect and productivity. it can. In other words, the above-described configuration is particularly significant in a spark plug that satisfies L1 ≦ 25.

  Next, an insulator having an inner diameter A of the shaft hole of 3.00 mm and a leg portion are provided with a small diameter portion, an intermediate portion, and a guide portion, and the outer diameter B (mm) of the guide portion is changed, so that A Using the terminal electrodes having different values of -B, the hot pressing process described above is performed, and after the hot pressing process, the eccentricity evaluation and productivity evaluation of the terminal electrodes are performed. It was. Table 2 shows the values of the inner diameter A, the outer diameter B, and AB of each sample, and evaluation of eccentricity and productivity of the terminal electrode. In each sample, the length L1 was 21 mm, the length L2 was 13 mm, and the length L3 was 5.0 mm.

  As shown in Table 2, it was found that the samples satisfying 0.02 mm ≦ A−B ≦ 0.13 mm (samples 41 and 42) were further excellent in both the suppression of the eccentricity of the terminal electrode and the productivity. This is because 0.02 mm ≦ A−B, the frictional force that can be generated between the guide portion and the insulator during pressing can be reduced, and the insertion of the terminal electrode into the shaft hole becomes easier. This is considered to be due to the fact that the central axis of the terminal electrode becomes more difficult to tilt with respect to the axis by setting A−B ≦ 0.13 mm.

  As a result of the above test, in order to further improve the eccentricity suppressing effect and productivity of the terminal electrode, a guide portion having an outer diameter larger than the small diameter portion is provided on the rear end side in the axial direction rather than the small diameter portion. It can be said that the outer diameter B (mm) is more preferably configured to satisfy 0.02 ≦ A−B ≦ 0.13.

  Next, after providing the insulator with the inner diameter A of the shaft hole of 3.00 mm or 3.05 mm and the leg portion with the small diameter portion and the large diameter portion, the outer diameter D (mm) of the small diameter portion is set. The above-described hot pressing process was performed using the terminal electrodes having different values of A-D by changing, and after the hot pressing process, the eccentricity of the terminal electrodes was evaluated. . Table 3 shows the values of the inner diameter A, the outer diameter D, AD, and the evaluation of the eccentricity of the terminal electrode. In each sample, the length L1 was 21 mm, the length L2 was 13 mm, and the length L3 was 5.0 mm. Moreover, the outer diameter of the site | part corresponded to an intermediate part was made the same with the outer diameter of a small diameter part, without providing an intermediate part with each sample.

  As shown in Table 3, it was confirmed that the eccentricity of the terminal electrode can be more effectively suppressed by satisfying 0.11 mm ≦ AD ≦ 0.40 mm.

  From the results of the above test, it can be said that it is more preferable to configure so as to satisfy 0.11 mm ≦ AD ≦ 0.40 mm from the viewpoint of more reliably preventing the eccentricity of the terminal electrode.

  Next, three spark plug samples having various lengths L1 and L2 were prepared, and a radio noise performance evaluation test was performed on each sample. The outline of the radio noise performance evaluation test is as follows. In other words, among various standards established by the International Radio Interference Special Committee (CISPR), it is described in “Tolerances and Measurement Methods of Interference Waves from Vehicles, Motorboats, and Spark Ignition Engine Drives” defined as CISPR12. Based on the measured measurement method (CISPR box method), the level of electric noise generated in the sample was measured. Here, on the basis of the level of the noise generated in the sample 65 having the length L2 of 13 mm, 9 points when the level of the noise is larger than the reference level by 0.3 db or more and less than 0.6 db, If it is larger by 0.6 db or more and less than 0.9 db, 8 points are given, and thereafter, every time 0.3 db is increased, one point is deducted (for example, the level of the noise level is 0.9 db from the reference level). If it is greater than 1.2 db, it is 7 points).

  In each sample, the length L3 was 5.0 mm, and the resistance difference between the resistors was 0.1 kΩ or less. Moreover, the level of the electric noise was obtained by the average value of the three.

  As shown in Table 4, it was found that by setting L2 ≧ 12 mm, radio noise can be more effectively suppressed. This is considered due to the fact that the resistor is longer.

  From the results of the above test, it can be said that it is more preferable to satisfy L2 ≧ 12 mm in order to suppress radio noise more effectively.

  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 outer diameter of the intermediate portion 612B is constant along the axis CL1, but the configuration of the intermediate portion 612B is not limited to this. Therefore, for example, the outer diameter of the intermediate portion 612B may be configured to decrease stepwise toward the tip end side in the axis CL1 direction, and a plurality of steps may be formed on the outer periphery of the intermediate portion 612B. .

  (B) In the above embodiment, the large-diameter portion 612 includes the guide portion 612A and the intermediate portion 612B having different outer diameters, but the large-diameter portion 612 is configured to have a constant outer diameter along the axis CL1. (That is, the intermediate portion 612B may not be provided).

  (C) In the above-described embodiment, the rear end portion of the shaft hole 4 has a shape that gradually increases in diameter toward the rear end side in the direction of the axis CL1. Also good. Accordingly, for example, the inner peripheral surface of the rear end portion of the shaft hole 4 is configured to be parallel to the axis CL1, and the inner peripheral surface of the rear end portion of the shaft hole 4 and the rear end surface of the insulator 2 are configured to be orthogonal to each other. Also good.

  (D) In the above embodiment, the overall length L4 of the spark plug 1 is relatively small. However, the technical idea of the present invention may be applied to a spark plug having a relatively large overall length L4.

  (E) In the above embodiment, the spark discharge gap 28 is formed between the center electrode 5 and the ground electrode 27, but noble metal alloy (for example, platinum alloy or iridium alloy) is provided on one or both of the electrodes 5 and 27. Etc.) and a spark discharge gap 28 is formed between the tip provided on one electrode 5 (27) and the other electrode 27 (5), or on both electrodes 5, 27. It may be formed between both provided chips.

  (F) In the above embodiment, the tool engaging portion 19 has a hexagonal cross section, but the shape of the tool engaging portion 19 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 ... Terminal electrode 7 ... Resistor 8, 9 ... Glass seal part 61 ... Leg part 62 ... Head 611 ... Small diameter part 612 ... Large diameter part 612A ... Guide part 612B ... Intermediate part CL1 ... Axis

Claims (10)

An insulator having an axial hole extending in the axial direction;
A center electrode inserted on the tip side of the shaft hole;
A rod-like leg portion inserted into the rear end side of the shaft hole, and a terminal electrode having a head portion exposed from the rear end of the insulator;
A glass seal portion for fixing the terminal electrode and the center electrode to the insulator in the shaft hole;
A spark plug including a resistor provided between the terminal electrode and the center electrode in the shaft hole,
When the length from the rear end of the insulator along the axis to the front end of the terminal electrode is L1 (mm), L1 ≦ 30.
When the inner diameter of the shaft hole at a position of 5 mm from the rear end of the insulator to the front end in the axial direction is A (mm), A ≦ 3.50,
The leg portion is provided with a small-diameter portion that includes 0.10 ≦ A−D ≦ 0.50 and includes a portion having the smallest outer diameter, when the outer diameter of the leg is D (mm).
When the length of the small diameter portion along the axis is L3 (mm), 1.0 ≦ L3 ≦ 12.0,
A spark plug characterized in that a large-diameter portion whose outer diameter is 0.05 mm or more larger than the outer diameter of the small-diameter portion is provided on the rear end side in the axial direction with respect to the small-diameter portion of the leg portion. .   The outer diameter of the leg portion is larger than the small diameter portion on the rear end side in the axial direction than the small diameter portion. When the outer diameter of the leg portion is B (mm), 0.02 ≦ A−B ≦ The spark plug according to claim 1, wherein a guide portion satisfying 0.13 is provided.   A portion of the leg portion between the small diameter portion and the guide portion is provided with an intermediate portion having an outer diameter larger than the outer diameter of the small diameter portion and smaller than the outer diameter of the guide portion. The spark plug according to claim 2.   The ignition plug according to claim 1, wherein 0.11 ≦ A−D ≦ 0.40 is satisfied.   5. The relationship according to claim 1, wherein L2 ≧ 12 when the distance from the front end of the terminal electrode along the axis to the rear end of the center electrode is L2 (mm). The spark plug described.   The spark plug according to any one of claims 1 to 5, wherein 3.0≤L3≤7.0.   The spark plug according to any one of claims 1 to 6, wherein L1≤25.   The spark plug according to any one of claims 1 to 7, wherein the terminal electrode has a Vickers hardness of 100 Hv or more and 380 Hv or less.   9. The spark plug according to claim 1, wherein the terminal electrode has a Vickers hardness of 220 Hv or more and 315 Hv or less.   The spark plug according to claim 1, wherein 0.4 ≦ L3 / D ≦ 4.5.

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