JP2007172866A - Spark plug - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spark plug having both good ignition property and good durability. <P>SOLUTION: A ground electrode 4 is located at outside in diameter direction than the axial line which does not cover the tip face of a noble metal chip 32 when viewed from the tip side in axial direction, and the noble metal chip 32 has a shape in which the area of the rear end part 33 on the welded part 36 side to which the noble metal chip 32 is welded to a center electrode base material 30 is larger than the area of the tip part 34, and has a flange part 35 to form a corner part at least on the ground electrode 4 side between the rear end part 33 and the tip part 34. When the initial discharge gap between the ground electrode 4 and the tip part 34 of the noble metal chip 32 is made G1, and the initial discharge gap between the ground electrode 4 and the flange part 35 of the noble metal chip 32 is made G2, 0.1 mm≤G2-G1≤0.2 mm is satisfied. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a spark plug used for an internal combustion engine such as an automobile engine.

  Conventionally, a spark discharge is generated between the center electrode and a ground electrode provided with a discharge gap with respect to the tip of the center electrode, and is attached to the air-fuel mixture supplied to the combustion chamber of the internal combustion engine. Spark plugs used as fire sources are known.

  In recent years, the protection of the global environment has been sought, and energy conservation, emission regulations for carbon dioxide, and suppression of emission of unburned gas (hydrocarbon compounds) have been further demanded. In order to meet these demands, in the internal combustion engine, a lean burn engine, a direct injection gasoline engine, a low exhaust gas engine, and the like have been actively developed. Furthermore, in lean burn engines, exhaust gas recirculation (which recycles part of the exhaust gas into the combustion chamber reduces the negative work of the engine that occurs during the intake process and purifies it into cleaner exhaust gas ( EGR) system has been actively introduced. In such a situation, the spark plug has to be ignited to a gas mixture which is lean and contains a large amount of exhaust gas which is an inert gas, and a spark plug with higher ignitability is required.

  As a spark plug with improved ignitability, the ground electrode is removed from the tip of the center electrode, that is, when the ground electrode is viewed from the tip of the spark plug in the axial direction, the tip of the center electrode is not covered from the axis. The thing located in the radial direction outer side is known (for example, refer patent document 1). According to such a spark plug, since the ground electrode is not directly over the center electrode, the flame easily spreads in the direction of the combustion chamber, thereby improving the ignitability. However, with such a spark plug, the ignitability is improved, but the spark direction is slanted, the tip of the center electrode is biased and consumed, and the spark gap spreads quickly, resulting in poor durability. There is. It is also known to improve the ignitability by reducing the diameter of the tip of the noble metal tip (see, for example, Patent Document 2). However, in such a spark plug, although the ignitability is improved, there is a problem that the portion of the noble metal tip having a reduced diameter is easily consumed and inferior in durability.

In addition, a noble metal tip is welded to the tip of a center electrode base material made of a Ni-based alloy, and a noble metal tip is also welded to the ground electrode side so as to face directly above the noble metal tip, and discharge occurs at these noble metal tips. There is also known a spark plug that has improved durability by suppressing uneven wear (see, for example, Patent Document 3). Such a spark plug is more durable than the spark plug described above. However, since the ground electrode is present immediately above the center electrode, there is a problem that it is inferior in terms of ignitability as compared with the spark plug described above.
JP 2004-55142 A Japanese Patent Laid-Open No. 11-54240 JP 2004-127916 A

  As described above, in the prior art, ignitability and durability are in a trade-off relationship, and it has been desired to develop a spark plug having both good ignitability and good durability.

  The present invention has been made to solve the above problems. An object of this invention is to provide the spark plug which has favorable ignitability and favorable durability.

  The spark plug of the present invention includes a cylindrical metal shell, a cylindrical insulator supported in the metal shell, a center electrode supported in the insulator and extending in the axial direction, In a spark plug having a center electrode and a ground electrode spaced apart on the tip side, the center electrode is welded to a columnar center electrode base material made of a Ni-based alloy and a tip of the center electrode base material. The noble metal tip, the ground electrode does not cover the tip end surface of the noble metal tip when viewed from the tip end side in the axial direction, and is located radially outside the axis, and the noble metal tip is the center electrode An area of the rear end portion of the welded portion side welded to the base material is larger than an area of the tip end portion, and a flange portion that forms a corner portion at least on the ground electrode side between the rear end portion and the tip end portion. The ground electrode and the shape When the initial discharge gap at the tip of the metal tip is G1, and the initial discharge gap between the ground electrode and the collar portion of the noble metal tip is G2, 0.1 mm ≦ G2-G1 ≦ 0.2 mm. It is characterized by.

  In the spark plug of the present invention, the center electrode has a columnar center electrode base material made of a Ni-based alloy and a noble metal tip welded to the tip of the center electrode base material, and the ground electrode is on the tip side in the axial direction. When viewed from above, the tip end surface of the noble metal tip is not covered, and the configuration is located radially outward from the axis. Therefore, since the ground electrode is not directly over the center electrode, the flame easily spreads in the direction of the combustion chamber, thereby improving the ignitability.

  In addition, the area of the rear end portion of the welded portion side where the noble metal tip is welded to the center electrode base material is larger than the area of the front end portion, and at least a corner portion on the ground electrode side is provided between the rear end portion and the front end portion. It has the shape which has the collar part to form. When the initial discharge gap between the ground electrode and the tip of the noble metal tip is G1, and the initial discharge gap between the ground electrode and the nose metal tip is G2, 0.1 mm ≦ G2−G1 ≦ 0.2 mm. ing. As a result, in the initial stage, a discharge occurs between the ground electrode and the tip of the noble metal tip, and when the tip of the noble metal tip is consumed and G1 increases, a discharge occurs between the ground electrode and the flange of the noble metal tip. Comes to occur. Therefore, even if the tip of the noble metal tip is biased and consumed, the spread of the discharge gap can be suppressed, and the durability can be improved. Here, if G2-G1 is made smaller than 0.1 mm, for example, 0.0 mm, the ignitability deteriorates. On the other hand, if G2-G1 is larger than 0.2 mm and is set to 0.3 mm, for example, the discharge in the gap G1 increases, so the amount of increase in the discharge gap due to wear increases and the durability deteriorates. For this reason, the spark plug which has both favorable ignitability and favorable durability can be provided by setting it as 0.1 mm <= G2-G1 <= 0.2mm.

  In the spark plug of the present invention, it is preferable that the noble metal tip and the center electrode base material made of a nickel-base alloy are laser-welded by irradiating a laser beam from the radial direction. As a result, the noble metal tip and the center electrode base material having different melting temperatures can be joined in a good state.

  In the above spark plug, when the diameter of the tip of the noble metal tip is d1, the diameter of the flange of the noble metal tip is d2, and the initial axial distance between the tip of the noble metal tip and the flange is h, 0.4 mm It is preferable that ≦ d1 ≦ 1.2 mm, 0.6 mm ≦ d2−d1 ≦ 1.0 mm, 0.3 mm ≦ h ≦ 0.6 mm.

  When d1 is reduced in diameter, the ignitability is improved but the durability is lowered, and when the diameter is increased, the ignitability is lowered but the durability is improved. For this reason, it is preferable to set it as 0.4 mm <= d1 <= 1.2mm. Further, when the diameter difference d2-d1 is smaller than 0.6, the durability improvement effect is almost lost, and when the diameter difference d2-d1 is larger than 1.0, the degree of decrease in ignitability when flying to the buttocks increases, and the output fluctuates. Invite. For this reason, it is preferable to set it as 0.6 mm <= d2-d1 <= 1.0mm. Further, the initial axial distance (protrusion amount) h between the tip portion and the collar portion of the noble metal tip is 0.3 or less, the ignitability is lowered, and if it is larger than 0.6, the durability improvement effect cannot be expected. . For this reason, it is preferable to set it as 0.3 mm <= h <= 0.6mm.

  When the shape of the tip of the noble metal tip is not cylindrical, the horizontal distance perpendicular to the axial direction in the initial discharge gap between the ground electrode and the tip of the noble metal tip is g1, and the initial distance between the ground electrode and the collar of the noble metal tip is When the horizontal distance perpendicular to the axial direction in the discharge gap is g2, and the axial distance between the tip of the noble metal tip and the flange of the noble metal tip is h, 0.3 mm ≦ g1−g2 ≦ 0.5 mm, 0. 3 mm ≦ h ≦ 0.6 mm. That is, in this case, by making g1−g2 to be a half value of the diameter difference d2−d1 described above, the same effect as in the case of 0.6 mm ≦ d2−d1 ≦ 1.0 mm described above is obtained. Is obtained.

  Further, in the spark plug of the present invention, the axial length (straight length) between the front end side end portion of the collar portion of the noble metal tip and the rear end side end portion of the noble metal tip excluding the welded portion after welding. Is preferably set to L ≧ 0.3 mm. If the straight length L is less than 0.3, the projections are consumed, and when the discharge at the collar starts, it is easy for the weld to fly. If a spark is generated at the welded portion, the welded portion is rapidly consumed, the precious metal tip itself is deteriorated in heat, the temperature of the tip is increased, and the tip is exhausted and the durability is lowered.

  According to the present invention, it is possible to provide a spark plug having both good ignitability and good durability.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view in a cross section including an axis showing the overall configuration of a spark plug 100 according to an embodiment of the present invention.

  As shown in FIG. 1, the spark plug 100 includes a cylindrical metal shell 1 made of a metal such as low carbon steel. On the inside of the metal shell 1, an insulator 2 is supported which is made of a ceramic sintered body such as alumina or aluminum nitride and has a tip portion protruding from the end surface of the metal shell 1.

  In addition, a center electrode 3 is disposed inside the insulator 2 so that the tip portion protrudes from the end face of the insulator 2. The center electrode 3 includes a center electrode base material 30 that forms the surface layer portion thereof, and a noble metal tip 32 welded to the tip of the center electrode base material 30.

  The center electrode base material 30 is formed in a columnar shape from a Ni-based alloy. Specific materials include Inconel 600 (trade name) (Ni: 76 mass%, Cr: 15.5 mass%, Fe: 8 mass% (remaining trace added elements or impurities), Inconel 601 (trade name) (Ni 60.5 mass%, Cr: 23 mass%, Fe: 14 mass% (remaining trace added elements or impurities)) The electrode base material 30 of the center electrode 3 is made of Cu or a Cu alloy. A heat conduction promoting portion 31 is embedded.

  The noble metal tip 32 is, for example, one or two selected from Pt, Rh, Ru, and Re as a subcomponent for containing Ir as a main component and suppressing oxidation volatilization of Ir or improving workability. It can be composed of an Ir alloy containing 3 to 50% by mass of seeds or more in total, and its outer shape is formed in a cylindrical shape.

  The center electrode 3 is disposed on the distal end side (lower side in the drawing) of the through hole 6 formed in the direction of the axis O of the insulator 2. A terminal fitting 23 is disposed on the rear end side of the through hole 6 and is electrically connected to the center electrode 3 through the conductive glass seal layers 24 and 26 and the resistor 25 for reducing radio noise. Further, a threaded portion 7 for attaching the spark plug 100 to an engine block (not shown) is formed on the outer peripheral surface of the metal shell 1.

  The ground electrode 4 is disposed at the tip of the metal shell 1 such that one end is joined to the end surface of the metal shell 1 and the other end faces the tip of the noble metal tip 32 of the center electrode 3. As shown in FIG. 2, the ground electrode 4 is radially outward from the axis O so as not to cover the front end surface of the noble metal tip 32 when viewed from the front end side in the axial direction (lower side in the figure). It is located on the left side. Here, “not to cover the tip surface of the noble metal tip 32” means that the ground electrode 4 is not applied to at least the tip surface protruding in a convex shape in the case of the convex noble metal tip 32 as shown in FIG. More desirably, the ground electrode 4 is not applied to the entire noble metal tip 32.

  As shown in FIG. 3, in the noble metal tip 32, the area (diameter d2) of the rear end portion 33 on the welded portion 36 side welded to the center electrode base material 30 is larger than the area (diameter d1) of the front end portion 34. Between the rear end portion 33 and the front end portion 34, a shape having a flange portion 35 forming a corner portion at least on the ground electrode 4 side is provided. That is, the noble metal tip 32 has a shape in which a thin cylindrical tip portion 34 having a diameter d1 and a large cylindrical flange portion 35 having a diameter d2 are coaxially overlapped.

Then, assuming that the initial discharge gap between the ground electrode 4 and the tip portion 34 of the noble metal tip 32 is G1, and the initial discharge gap between the ground electrode 4 and the flange portion 35 of the noble metal tip 32 is G2.
0.1mm ≦ G2-G1 ≦ 0.2mm
It is said that. This is due to the following reasons.

  That is, the graph of FIG. 4 shows the results of measuring these relationships, where the vertical axis is the increase amount of the discharge gap and the horizontal axis is the endurance time. The measurement is performed by actually measuring the discharge gap after accelerating the spark plug under a predetermined condition every predetermined time. The durability of 100 hours shown in the graph indicates that an actual automobile is traveling 100,000 km. The degree of spark consumption corresponding to running the distance is shown (the same applies to the graphs of FIGS. 8 and 10 described later). In the case of a columnar noble metal tip (straight (diameter 0.6 mm)) having no flange in order from the top of the durability time 100 hours, the curve shown in this graph is G2-G1 = 0.3 mm. In the case of G2-G1 = 0.2 mm, the case of G2-G1 = 0.1 mm, and the case of G2-G1 = 0.0 mm are shown. As shown in this graph, it is necessary to satisfy G2−G1 ≦ 0.2 mm in order to suppress the increase amount of the discharge gap and ensure good durability.

  Moreover, the graph of FIG. 5 shows the result of measuring the relationship between the value of G2-G1 and the ignitability, and the horizontal axis in this graph shows the air-fuel ratio (A / F). As shown in this graph, when G2-G1 is made smaller than 0.1 mm, for example, G2-G1 = 0.0 mm, the ignitability is deteriorated. For this reason, in order to ensure favorable ignitability, it is necessary to satisfy 0.1 mm ≦ G2-G1.

  From the above, by making 0.1 mm ≦ G2-G1 ≦ 0.2 mm, it is possible to provide the spark plug 100 having both good ignitability and good durability. The above-mentioned “initial discharge gap” refers to a discharge gap in the unused spark plug 100. Actually, when the spark plug 100 is used, the noble metal tip 32 is consumed, and the discharge gap gradually widens. In the spark plug 100 of this embodiment, immediately after the start of use, discharge occurs at the ground electrode 4 and the tip portion 34 of the noble metal tip 32. When the distal end portion 34 is consumed and the discharge gap G1 is widened, a discharge is generated between the ground electrode 4 and the flange portion 35, thereby suppressing the discharge gap as a whole.

  When the noble metal tip 32 is welded to the center electrode base material 30 in the spark plug 100 described above, it is preferable to perform laser welding by irradiating a laser beam from the side. As a result, the noble metal tip 32 made of a material having a different melting point and the center electrode base material (made of a nickel-based alloy) 30 can be firmly joined. In this way, when the noble metal tip 32 and the center electrode base material 30 are welded by laser welding or the like, the noble metal tip material and the center electrode base material are melted and solidified on the rear end side of the noble metal tip 32 and solidified. A portion (weld bead) 36 (see FIG. 3) is formed.

  Due to the work function, such a welded part 36 is more likely to be discharged between the ground electrode 4 than the noble metal tip 32 itself. For this reason, the axial length (L shown in FIG. 3) between the rear end portion 33 of the precious metal tip 32 after welding (the rear end portion of the pure precious metal portion excluding the weld portion 36) and the front end side of the flange portion 35. ) Has a certain length, and it is preferable to prevent discharge from occurring in the welded portion 36.

  The graph of FIG. 6 shows the above-mentioned length (straight length) L and the remaining rate of the noble metal tip after the endurance test of 200 hours (how much volume remains with respect to the original volume in%) ) Is measured. As shown in FIG. 6, when L is 0.3 mm or more, the remaining ratio of the noble metal tip becomes constant. For this reason, it is preferable that L ≧ 0.3 mm.

  Further, the length (protrusion amount) h of the small diameter portion of the tip portion 34 of the noble metal tip 32 shown in FIG. 3 also affects the ignitability and durability. Further, the diameter difference (d2−d1) between the diameter d2 of the flange portion 35 of the noble metal tip 32 and the diameter d1 of the tip end portion 34 shown in FIG. 3 also affects the ignitability and durability.

  The graph of FIG. 7 shows the result of examining the relationship between the protrusion amount h and the ignitability. Moreover, the graph of FIG. 8 shows the result of investigating the relationship between the protrusion amount h and durability (discharge gap increase amount). The curve shown in the graph of FIG. 8 indicates that in the case of a columnar noble metal tip (diameter 0.6 mm) having no flange in order from the top at the endurance time of 100 hours, h = 0. 0.7 mm, h = 0.6 mm, h = 0.5 mm, h = 0.4 mm, h = 0.3 mm, h = 0.2 mm, h = 0.1 mm Shows the case. These measurements were performed under the conditions of d1 = 0.6 mm, d2 = 1.6 mm, and d2-d1 = 1.0 mm.

  As shown in FIG. 7, from the viewpoint of ignitability, the protrusion amount h is set to 0.3 mm or more because the inflection point is reached and the A / F is improved by setting it from 0.2 mm to 0.3 mm. Is preferred. Further, as shown in FIG. 8, from the viewpoint of durability, since the gap increase amount is suppressed to 0.3 mm in 100 hours, the protrusion amount h is preferably 0.6 mm or less. When the gap increases by 0.3 mm, the required voltage increases remarkably, and there is a demand to suppress it to 0.3 mm or less. Therefore, it is preferable that 0.3 mm ≦ h ≦ 0.6 mm.

  The graph of FIG. 9 shows the result of examining the relationship between the diameter difference d2-d1 and the ignitability. Moreover, the graph of FIG. 10 shows the result of investigating the relationship between the diameter difference d2−d1 and durability (discharge gap increase). The curve shown in the graph of FIG. 10 indicates that in the case of a columnar noble metal tip (diameter of 0.6 mm) having no flange in order from the top at the endurance time of 100 hours, d2 = d1 = 0.2 mm, d2 -D1 = 0.4 mm, d2-d1 = 0.6 mm, d2-d1 = 0.8 mm, d2-d1 = 1.0 mm. These measurements were performed under the condition of h = 0.3 mm.

  As shown in FIG. 9, from the viewpoint of ignitability, the diameter difference d2-d1 is preferably 1.0 mm or less. Further, as shown in FIG. 10, from the viewpoint of durability, the diameter difference d2-d1 is preferably 0.6 mm or more. Therefore, it is preferable that 0.6 mm ≦ d2-d1 ≦ 1.0 mm.

  Further, when the diameter d1 of the tip portion 34 of the noble metal tip 32 is reduced, the ignitability is improved but the durability is lowered. When the diameter is increased, the ignitability is lowered but the durability is improved. For this reason, it is preferable to set it as about 0.4 mm <= d1 <= 1.2mm.

  By satisfying all the above conditions of 0.4 mm ≦ d1 ≦ 1.2 mm, 0.6 mm ≦ d2−d1 ≦ 1.0 mm, and 0.3 mm ≦ h ≦ 0.6 mm, further excellent ignitability and good A spark plug 100 having durability can be obtained.

  In the above embodiment, the noble metal tip 32 has a columnar shape, the tip portion 34 having a small diameter (diameter d1) is formed on the tip side, and the flange portion 35 having a large diameter (diameter d2) is coaxially formed on the rear end side. Although the case of the formed shape has been described, the present invention is not limited to such an embodiment. For example, noble metal tips 132, 232, and 332 having shapes as shown in FIGS. In these drawings, (a) shows a longitudinal sectional shape, and (b) shows a planar shape viewed from the tip side.

  The noble metal tip 132 shown in FIG. 11 has a shape that has a large diameter in a curve from the tip end portion 134 to the flange portion 135 so as to gradually widen. In FIG. 11, reference numeral 133 denotes a rear end portion. Also, as shown in FIG. 12, a noble metal tip 232 having a shape in which the ground electrode 4 side is cut out so that the tip end portion 234 has a semi-cylindrical shape can be used. In FIG. 12, reference numeral 233 denotes a rear end portion and a 235 collar portion. Furthermore, as shown in FIG. 13, a noble metal tip 332 having a shape in which the shape of the notch portion in FIG. 12 is a curved surface can be used. In FIG. 13, 333 indicates a rear end portion, 334 indicates a front end portion, and a 335 collar portion.

Like the noble metal tip 232 shown in FIG. 12 and the noble metal tip 332 shown in FIG.
When the tip portions 234 and 334 are not cylindrical, the value of the diameter difference d2−d1 cannot be applied as it is. In this case, the horizontal distance perpendicular to the axial direction in the discharge gap G1 at the initial stage between the ground electrode 4 and the tip portions 234, 334 of the noble metal tips 232, 332 is g1, and the flanges 235 of the ground electrode 4 and the noble metal tips 232, 332 are When the horizontal distance perpendicular to the axial direction in the discharge gap G2 in the initial stage with respect to 335 is g2, 0.3 mm ≦ g1-g2 ≦ 0.5 mm is satisfied, so that the above-described 0.6 mm ≦ d2-d1 ≦. The same effect as when 1.0 mm is obtained can be obtained. That is, the positional relationship between the ground electrode 4 and the discharge part on the noble metal tip 232, 332 side is adjusted by adjusting the value of d2-d1 by adjusting the value of g1-g2 within the range of 1/2 of the value of d2-d1. In this case, the same effect can be obtained. In this case, with respect to the protrusion amount h, the same effect as in the above case can be obtained by setting 0.3 mm ≦ h ≦ 0.6 mm as in the case described above.

  In the above, the present invention has been described with reference to the embodiment. However, the present invention is not limited to the above-described embodiment and the like, and it is needless to say that the present invention can be appropriately modified and applied without departing from the gist thereof.

Sectional drawing which shows the whole structure of the spark plug which concerns on embodiment of this invention. The figure which expands and shows the principal part structure of the spark plug of FIG. The figure for demonstrating the dimension of the principal part of the spark plug of FIG. The graph which shows the result of having measured the relationship between a gap difference and durability. The graph which shows the result of having measured the relationship between gap difference and ignitability. The graph which shows the result of having measured the relationship between straight length and chip | tip residual rate. The graph which shows the result of having measured the relationship between protrusion amount and ignitability. The graph which shows the result of having measured the relationship between protrusion amount and durability. The graph which shows the result of having measured the relationship between a diameter difference and ignitability. The graph which shows the result of having measured the relationship between a diameter difference and durability. The figure which expands and shows the principal part structure of other embodiment. The figure which expands and shows the principal part structure of other embodiment. The figure which expands and shows the principal part structure of other embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Metal fitting, 2 ... Insulator, 3 ... Center electrode, 4 ... Ground electrode, 30 ... Center electrode base material, 32 ... Precious metal tip, 100 ... Spark plug.

Claims (5)

A cylindrical metal shell, a cylindrical insulator supported in the metal shell, a center electrode supported in the insulator and extending in the axial direction, and the center electrode on the tip side of the center electrode In a spark plug having a ground electrode arranged at intervals,
The center electrode has a columnar center electrode base material made of a Ni-based alloy, and a noble metal tip welded to the tip of the center electrode base material,
The ground electrode does not cover the tip end surface of the noble metal tip when viewed from the tip end side in the axial direction, and is located radially outside the axis line,
In the noble metal tip, the area of the rear end portion of the welded portion side welded to the central electrode base material is larger than the area of the front end portion, and at least on the ground electrode side between the rear end portion and the front end portion. It has a shape with a flange that forms a corner,
When an initial discharge gap between the ground electrode and the tip of the noble metal tip is G1, and an initial discharge gap between the ground electrode and the nose of the noble metal tip is G2,
0.1mm ≦ G2-G1 ≦ 0.2mm
Spark plug characterized by being said. The spark plug according to claim 1, wherein
The spark plug, wherein the noble metal tip and the center electrode base material are laser-welded by irradiating a laser beam from a radial direction. The spark plug according to claim 1 or 2,
When the diameter of the tip of the noble metal tip is d1, the diameter of the collar of the noble metal tip is d2, and the initial axial distance between the tip of the noble metal tip and the collar of the noble metal tip is h,
0.4 mm ≦ d1 ≦ 1.2 mm,
0.6 mm ≦ d2-d1 ≦ 1.0 mm,
0.3 mm ≦ h ≦ 0.6 mm,
Spark plug characterized by being said. The spark plug according to claim 1 or 2,
The horizontal distance perpendicular to the axial direction in the initial discharge gap between the ground electrode and the tip of the noble metal tip is g1, and the horizontal distance perpendicular to the axial direction in the initial discharge gap between the ground electrode and the flange portion of the noble metal tip. When the directional distance is g2, and the axial distance between the tip of the noble metal tip and the flange of the noble metal tip is h,
0.3 mm ≦ g1-g2 ≦ 0.5 mm,
0.3 mm ≦ h ≦ 0.6 mm,
Spark plug characterized by being said. In the spark plug according to any one of claims 1 to 4,
The length in the axial direction between the front end side end portion of the flange portion of the noble metal tip and the rear end side end portion of the noble metal tip excluding the welded portion after welding is defined as L,
L ≧ 0.3mm
Spark plug characterized by being said.

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