JP4965422B2 - Spark plug - Google Patents

Description

  The present invention relates to a spark plug for an internal combustion engine comprising a center electrode welded to a center electrode tip and an outer electrode welded to an outer electrode tip.

  Conventionally, in order to improve both ignitability and durability, a spark plug having an outer electrode in which a cylindrical outer electrode tip is welded to an outer electrode base material is known. However, since the outer electrode tip is welded to the outer electrode in such a form, the entire length of the outer electrode tends to be longer, the heat load during use is increased, and the breaking strength against vibration is also reduced. For this reason, as in the spark plug disclosed in Patent Document 1, a copper core is sealed in the outer electrode, or as in the spark plug disclosed in Patent Document 2, the distal end portion of the metal shell is extended to the distal end side. It has been considered to improve the heat extraction and strength of the outer electrode by adopting a different form or increasing the cross-sectional area of the outer electrode.

Japanese Patent No. 1918156 JP 60-235379 A

  Recent internal combustion engines are required to have high ignition performance and high output for low fuel consumption and low emissions, and high compression ratio internal combustion engines, etc. have been developed, and the amount of heat received by spark plugs further increases. Tend to. Further, since the size of the outer electrode needs to be reduced due to the demand for reducing the diameter of the spark plug, the heat resistance and breakage resistance of the outer electrode tend to become increasingly severe. In order to solve this problem, it is most effective to shorten the length of the outer electrode. However, it has been found that conventional multipolar electrode type spark plugs and semi-creeping type spark plugs that can shorten the outer electrode are less ignitable than parallel electrode type spark plugs that have a longer outer electrode. .

  In order to improve the ignitability, it is conceivable to form a center electrode and an outer electrode by welding a noble metal tip having a smaller diameter to the center electrode substrate and the outer electrode substrate. By setting it as such a form, while being able to suppress the flame-extinguishing effect | action to the flame nucleus of each electrode, a spark position can be stabilized to some extent at the front-end | tip part (noble metal tip) of each electrode. However, the sparks with the outer electrode in the center electrode may occur not only in the noble metal tip forming the tip portion but also in the welded portion formed by welding the noble metal tip to the center electrode base material, and the ignitability is May decrease.

  This invention is made | formed in view of this present condition, Comprising: It aims at providing the spark plug which can improve ignitability, ensuring the heat resistance and breakage resistance of an outer electrode.

The solution includes a cylindrical metal shell having an axis, a cylindrical insulator inserted radially inward of the metal shell, and a center electrode inserted radially inward of the insulator, The insulator has a center electrode protrusion that protrudes from the insulator front end surface toward the axial front end, and the center electrode protrusion includes a central electrode base material protrusion positioned on the axial base end side, and the center A center electrode, which is located on the front end side in the axial direction of the electrode base protrusion, is thinner than the center electrode base protrusion, and includes a columnar center electrode tip welded to the center electrode base protrusion, and the main body An outer electrode formed by welding a columnar outer electrode tip thinner than the outer electrode base to the base end of the outer electrode base extending from the metal fitting, wherein the tip end surface of the outer electrode tip is the outer periphery of the center electrode tip The surface and the spark discharge gap A spark plug including one or a plurality of outer electrodes, wherein the shortest distance from the outer electrode to a welded portion between the central electrode base protrusion and the central electrode tip is a shortest distance F (mm), when the length of the spark discharge gap and gap length AD (mm), Ri Do as a form satisfying F ≧ AD × 1.05, it includes a central point of the axis of the weld, perpendicular to the axis In the transverse cross section of the welded portion, the centroid of the welded portion in the transverse cross section is obtained, and for each range of every 15 degrees of the central angle centered on the centroid, A difference D (= Rmax−Rmin) between the radius Rmax of the largest circle in contact with the outer periphery and the radius Rmin of the smallest circle in contact with the outer periphery of the welded portion with the centroid as the center is obtained. The circumferential step of the weld When the difference is Da (μm), the spark plug is configured to satisfy Da ≦ 9 .

  In the spark plug of the present invention, the outer electrode has a shape in which the tip end surface of the outer electrode tip is separated from the outer peripheral surface of the center electrode tip with a spark discharge gap, and the spark discharge path is from a general axial direction. The radial direction. That is, it is a transverse discharge type spark plug. By doing in this way, since the length of an outer side electrode can be shortened both in an axial direction and a radial direction, while being able to reduce the temperature of the outer side electrode at the time of use, breakage strength can be improved. Therefore, the heat resistance and breakage resistance of the outer electrode can be improved.

  Further, an outer electrode is formed by welding an outer electrode tip thinner than this to the outer electrode substrate, and a center electrode tip (center electrode protruding portion) is welded to the center electrode substrate protruding portion by welding a thinner center electrode tip. Therefore, while it is a transverse discharge type spark plug, it is possible to reduce the extinguishing action on the flame nuclei and to hardly inhibit the growth of the flame nuclei, thereby improving the ignitability. The reason for this is that the outer electrode and the center electrode, which have a lower temperature than the flame kernel, are less likely to become obstacles when the flame kernel spreads because the tip portion of the outer electrode and the tip portion of the center electrode become thinner. It is done.

Furthermore, in the spark plug of the present invention, the shortest distance F (mm) from the outer electrode to the welded portion of the center electrode and the gap length AD (mm) of the spark discharge gap satisfy F ≧ AD × 1.05. It is said. Thereby, since the distance from the outer electrode to the welded portion of the center electrode becomes longer, it is possible to suppress flying from the outer electrode to the welded portion of the center electrode. Therefore, the ignitability of the spark plug can be further improved.
Furthermore, in the spark plug of the present invention, the circumferential step Da (μm) of the welded portion of the center electrode is Da ≦ 9. By reducing the circumferential step Da of the welded portion in this way, the electric field strength at the welded portion becomes lower than that of the conventional welded portion, and therefore, a higher voltage than before is required for sparks at the welded portion. As a result, it is difficult for sparks to occur at the weld. Therefore, flying to the welded portion can be further suppressed, and the ignitability can be further improved.

The “shortest distance F” is the shortest distance from the outer electrode to the welded portion of the center electrode as described above. Therefore, the “shortest distance F” may be measured from the outer electrode tip of the outer electrode as a starting point, or may be measured from the outer electrode substrate of the outer electrode as a starting point.
The “center electrode tip” and the “outer electrode tip” may be columnar, and examples thereof include a columnar shape, a rectangular column shape such as a quadrangular column, and an elliptical column shape.
In addition, the materials of the “center electrode tip” and the “outer electrode tip” can be appropriately changed in consideration of durability, ignitability, and the like. In particular, when formed from a Pt alloy containing 70% by weight or more of Pt or an Ir alloy to which Rh is added, the amount of chip wear that occurs with use can be suppressed, and the durability can be particularly improved.

  Further, as described above, the “outer electrode” is formed by welding a columnar outer electrode tip that is thinner than the outer electrode base to the base end portion of the outer electrode base. As such a form, for example, a columnar outer electrode tip protrudes toward the center electrode at a predetermined position on the front end surface of the base electrode of the ground electrode base material. A bonded ground electrode may be mentioned. In addition, for example, the columnar outer electrode tip protrudes beyond the base end surface at a predetermined position on the side surface (side surface connected to the base end surface) of the base end portion of the ground electrode base material. A ground electrode joined in such a form.

  Furthermore, the spark plug is preferably a spark plug satisfying F ≧ AD × 1.25.

  In the spark plug of the present invention, since F ≧ AD × 1.25 is further satisfied, the distance from the outer electrode to the weld of the center electrode is further increased. Can be more effectively suppressed. Therefore, the ignitability of the spark plug can be further improved.

  Furthermore, the spark plug is preferably a spark plug configured to satisfy Da ≦ 7.

  In the spark plug of the present invention, Da ≦ 7 is further satisfied. In this way, by further reducing the circumferential step Da, it is possible to further suppress the sparks to the welded portion, so that the ignitability can be further improved.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a spark plug 100 according to this embodiment. FIG. 2 shows a side view of the vicinity of the center electrode 130 and the ground electrode (outer electrode) 140 of the spark plug 100, and FIG. 3 shows the axis of the center electrode 130, the ground electrode 140, etc. The figure which looked at the base end side from the AX direction front end side (henceforth only a front end side) is shown. FIG. 4 shows a view of the ground electrode 140 as seen from the radially inner side to the radially outer side. The spark plug 100 is a spark plug for an internal combustion engine that is attached to a cylinder head of an engine for use.

As shown in FIG. 1, the spark plug 100 includes a cylindrical metal shell 110, a cylindrical insulator 120, a center electrode 130, and a ground electrode 140.
Among these, the metal shell 110 is made of low carbon steel and has a cylindrical shape extending in the direction of the axis AX. The metal shell 110 is located on the flange portion 110f having a large diameter and on the base end side in the axis AX direction (hereinafter also simply referred to as the base end side, upward in FIG. 1), and the spark plug 100 is used as a cylinder head. A tool engaging portion 110h having a hexagonal cross section for engaging a tool when attaching, and a caulking portion 110j that is located on the base end side thereof and for caulking and fixing the insulator 120 to the metal shell 110 are provided. . Further, the front end of the flange portion 110f (downward in FIG. 1) has a diameter smaller than that of the flange portion 110f and has a mounting screw portion 110g for screwing the spark plug 100 to the cylinder head on the outer periphery. Part 110s.

The insulator 120 is made of alumina ceramic and has a cylindrical shape extending in the direction of the axis AX. The insulator 120 is inserted inward of the metal shell 110 in the radial direction, and an insulator protrusion 120s located on the distal end side projects from the metal tip end surface 110sc of the metal shell 110 to the distal end side and is positioned on the proximal end side. The insulator base end portion 120k to be held is held by the metal shell 110 in a state of protruding from the crimping portion 110j of the metal shell 110 to the base end side. The protruding length Z (refer to FIG. 2) of the metal shell 110 of the insulator protrusion 120s located on the tip side from the metal tip surface 110sc is 1.0 mm or more (specifically, 2.0 mm).
A center electrode 130 is inserted inside the insulator 120 on the radially inner side on the distal end side. A terminal fitting 150 for guiding a high voltage to the center electrode 130 is inserted on the radially inner side of the insulator 120 on the proximal end side.

  The center electrode 130 is inserted inside the insulator 120 in the radial direction, and is held by the insulator 120 in a state where the center electrode protrusion 130s located on the tip side protrudes from the insulator tip surface 120sc of the insulator 120 to the tip side. Has been. The protruding length T (see FIG. 2) of the central electrode protruding portion 130s from the metal tip 110sc of the metal shell 110 is 3.5 mm or more (specifically, 5.0 mm).

  As shown in FIGS. 2 and 3, the center electrode 130 is obtained by coaxially welding a central electrode tip 133 having a cylindrical shape with a diameter smaller than that of a rod-shaped center electrode base material 131 as a base material. is there. The center electrode protrusion 130 s forms a part of the center electrode base material 131, and the center electrode base material protrusion 131 t constituting the base end side portion (downward in FIG. 2) of the center electrode protrusion 130 s and the center The center electrode tip 133 is located on the distal end side (FIG. 2, upper side) of the electrode base material protrusion 131t and is coaxially welded to the center electrode base material protrusion 131t.

Among these, the center electrode base material protruding portion 131t is a first columnar portion 131p that is located on the proximal end side and has a large cylindrical shape, and a truncated cone that is located on the distal end side and has a truncated cone shape that is smaller in diameter toward the distal end side. Part 131q. The center electrode substrate 131 is made of a Ni alloy containing Ni as a main component.
On the other hand, the center electrode tip 133 protrudes from the center electrode base material 131 (center electrode base material protruding portion 131t) toward the front end side (upward in FIG. 2), and forms a front end portion of the cylindrical center electrode that forms the front end portion of the center electrode 130. A portion 130ss is formed. The center electrode tip 133 is made of a Pt alloy containing 70% by weight or more of Pt. The center electrode tip 133 may be formed of an Ir alloy to which Rh is added.
Since the center electrode tip 133 and the center electrode base material 131 (center electrode base material protruding portion 131t) are laser-welded, the center electrode tip 133 and the central electrode base material protruding portion 131t have a center electrode between them. A frustum-shaped welded portion 135 is formed in which the tip 133 and the center electrode base material protruding portion 131t are melted and mixed with each other and solidified.

As shown in FIGS. 2 to 4, the ground electrode 140 is formed on a ground electrode base material (outer electrode base material) 141, which is a base material obtained by bending a quadrangular prism, and has a smaller diameter and a cylindrical shape. A tip (outside electrode tip) 143 is welded.
Among these, the ground electrode substrate 141 is made of a Ni alloy containing Ni as a main component. The ground electrode base material 141 has a base material base end portion 141k joined to the metal fitting front end surface 110sc of the metal shell 110, and the base material front end portion 141s is bent inward in the radial direction. 141sc is directed radially inward.

  The ground electrode tip 143 has a cylindrical shape having a central axis BX, is joined to the center of the base end surface 141sc of the ground electrode base 141 by laser welding, and protrudes radially inward. The tip end surface 143sc of the ground electrode tip 143 is separated from the outer peripheral surface 130ssn of the center electrode tip end portion 130ss (center electrode tip 133) with a spark discharge gap G that causes spark discharge. When the tip length of the ground electrode tip 143 from the base end surface 141sc to the tip end surface 143sc is a length C (mm), 0.3 ≦ C ≦ 1.6 is satisfied (specifically, C = 0.9 mm). The ground electrode tip 143 is made of a Pt alloy containing 70% by weight or more of Pt. The ground electrode tip 143 may be formed of an Ir alloy to which Rh is added.

  Here, in the spark plug 100, as shown in FIG. 5, the length of the spark discharge gap G is defined as a gap length AD (mm). Further, the shortest distance from the ground electrode 140 (specifically, the ground electrode tip 143 in the present embodiment) to the welded portion 135 of the center electrode 130 is defined as the shortest distance F (mm). For such a gap length AD (mm) and shortest distance F (mm), the spark plug 100 of the present embodiment satisfies F ≧ AD × 1.05, and further satisfies F ≧ AD × 1.25. It is said. Note that specific numerical values of the length AD (mm) and the shortest distance F (mm) will be described later.

Next, a cross section of the welded portion 135 including the center point W on the axis AX of the welded portion 135 and perpendicular to the axis AX is viewed. FIG. 6 shows this transverse section (HH section in FIG. 5). FIG. 7 is an enlarged view including a J portion indicated by a broken line in FIG.
Next, the centroid P (the center of gravity of the cross section) of the welded portion 135 in this cross section is obtained.
Then, for each range of the central angle 15 degrees around the centroid P, the radius Rmax of the maximum circle ET1 that is in contact with the outer periphery 135n of the welded part 135 and centered on the centroid P is centered on the centroid P. And the radius Rmin of the minimum circle ET2 in contact with the outer periphery 135n of the welded portion 135 is obtained. Then, the difference D (= Rmax−Rmin) is obtained.
Furthermore, the average of each difference D of 24 pieces (360 degrees / 15 degrees = 24) in total is obtained and set as a circumferential step Da (μm) of the welded part 135.
With respect to such a circumferential step Da (μm), the spark plug 100 of the present embodiment satisfies Da ≦ 9 and further satisfies Da ≦ 7. The specific numerical value of the circumferential step Da (μm) will be described later.

  As described above, in the spark plug 100, the ground electrode 140 is connected to the spark discharge gap G between the outer peripheral surface 130ssn of the center electrode front end portion 130ss and the tip end surface 143sc of the ground electrode tip 143 facing radially inward. The spark discharge type is a transverse discharge type spark plug in which a spark discharge path is formed in the radial direction. By doing in this way, since the length of the ground electrode 140 can be shortened both in the axis AX direction and in the radial direction, the temperature during use of the ground electrode 140 can be reduced and the breakage strength can be improved. Therefore, the heat resistance and breakage resistance of the ground electrode 140 can be improved.

  Further, a ground electrode 140 is formed by welding a ground electrode tip 143 having a smaller diameter to the ground electrode substrate 141, and a center electrode 130 is formed by welding the center electrode tip 133 to the center electrode substrate 131. ing. For this reason, although it is a horizontal discharge type spark plug, the extinguishing action on the flame kernel can be reduced and the growth of the flame kernel is hardly inhibited, so that the ignitability can be improved. Since the tip portions of the ground electrode 140 and the center electrode 130 are the small-diameter ground electrode tip 143 and the center electrode tip 133, the ground electrode 140 (the ground electrode tip 143) and the center electrode 130 (the center are lower in temperature than the flame kernel). This is probably because the electrode tip 133) is less likely to become an obstacle when the flame kernel spreads.

  Furthermore, in the spark plug 100 of the present embodiment, the shortest distance F (mm) from the ground electrode 140 to the welded portion 135 of the center electrode 130 and the gap length AD (mm) of the spark discharge gap G are F ≧ AD ×. 1.05 is satisfied, and further, F ≧ AD × 1.25 is satisfied. As a result, the distance from the ground electrode 140 to the welded portion 135 of the center electrode 130 becomes longer, so that the sparks from the ground electrode 140 to the welded portion 135 of the center electrode 130 can be effectively suppressed. Therefore, the ignitability of the spark plug 100 can be greatly improved.

  Further, the circumferential step Da (μm) of the welded portion 135 of the center electrode 130 is Da ≦ 9, and further Da ≦ 7. For this reason, since the electric field strength in the welded portion 135 is lower than that in the conventional welded portion, a higher voltage is required for the spark in the welded portion 135 than in the conventional case, and therefore a spark in the welded portion 135 occurs. It becomes difficult. Accordingly, it is possible to more effectively suppress the sparks to the welded portion 135 and further improve the ignitability.

The spark plug 100 can be manufactured by the following method. That is, the center electrode tip 133 is formed by laser welding the center electrode tip 133 to the center electrode substrate 131. Then, the center electrode 130 is assembled to the separately prepared insulator 120, and the terminal fitting 150 and the like are also assembled to the insulator 120, and glass sealing is performed.
Next, the metallic shell 110 is prepared, and the rod-shaped ground electrode base material 141 (the ground electrode base material 141 in a state where the ground electrode tip 143 is not joined and is not bent) is joined to the metallic shell 110. . Thereafter, the insulator 120 with the center electrode 130 and the like assembled to the metal shell 110 to which the ground electrode base material 141 is joined, and caulking or the like is performed.
Next, the ground electrode tip 143 is laser-welded to the ground electrode base material 141 joined to the metal shell 110 to form the ground electrode 140. Thereafter, the spark plug 100 is completed by bending the ground electrode 140 radially inward to have a predetermined shape and forming a spark discharge gap G with the center electrode 130.

Next, the results of various tests performed to verify the effect of the spark plug 100 of the present embodiment will be described.
(Test 1)
In Test 1, the gap length AD (mm) of the spark discharge gap G is set to 0.3 mm, 0.6 mm, 0.9 mm, and 1.2 mm, and the shortest distance F from the ground electrode to the welded portion of the center electrode. A number of spark plugs with different (mm) were prepared. And about each spark plug, the ignition rate to a welding part was investigated, and ignitability was evaluated. The result is shown in the graph of FIG.

  The ratio of fire to the weld was determined as follows. In other words, a spark plug was attached to the pressurized chamber, and the situation of the fire was photographed with a high-speed camera, and the position of the fire was examined. This was performed for 1000 samples for each spark plug. The test conditions were a pressure of 0.4 MPa, a repetition frequency of 15 Hz, and an air atmosphere.

  According to this result, regardless of the size of the gap length AD of the spark discharge gap G, when the F / AD ratio is smaller than 1.05, the spark rate at the welded portion 135 increases rapidly, and the spark rate is increased. It will exceed 20%. On the other hand, when the F / AD ratio is 1.05 or more, the spark ratio at the welded portion is sufficiently small. Furthermore, when the F / AD ratio is 1.25 or more, sparks at the welded portion are not observed. For this reason, by setting F / AD ≧ 1.05, and further by setting F / AD ≧ 1.25, stable firing can be performed at the center electrode tip, and the ignitability is greatly improved. I know that

(Test 2)
In this test 2, many spark plugs were prepared in which the F / AD ratio was 1.025, 1.05, 1.1, and 1.2, and the above-described circumferential step Da (μm) was changed. . And about each spark plug, the ignition rate in a welding part was investigated, and ignitability was evaluated. The flying ratio at the welded portion was investigated in the same manner as in Test 1 above. The result is shown in the graph of FIG.

According to this result, in the spark plug having an F / AD ratio of 1.025, the spark ratio at the welded portion decreases as the circumferential step Da decreases, but the spark ratio exceeds 10%. .
On the other hand, in each spark plug having F / AD ratios of 1.05, 1.1 and 1.2, by setting the circumferential step Da to 9 μm or less, the rate of fire to the welded portion is 5% or less. The ignitability is improved. Furthermore, in these spark plugs, by setting the circumferential step Da to 7 μm or less, no sparks are seen at the welded portion, and the ignitability is greatly improved.
From this, it can be said that by setting the circumferential step Da (μm) to Da ≦ 9 and further Da ≦ 7, it is possible to more effectively suppress the sparks to the welded part 135 and to greatly improve the ignitability.

(Deformation)
Next, modifications of the above embodiment will be described. Note that description of the same parts as those in the above embodiment is omitted or simplified. In this modification, the form of the ground electrode 240 is different from the form of the ground electrode 140 of the above embodiment. The rest is basically the same as the above embodiment. FIG. 10 shows a side view of the vicinity of the center electrode 130 and the ground electrode 240 in the spark plug 200 according to this modification. FIG. 11A shows a cross-sectional view (YY cross section in FIG. 10) of the ground electrode base material 241 in the ground electrode 240, and FIG. 11B shows a radially outer side from the radially inner side. A front view of the vicinity of the tip of the ground electrode 240 seen in FIG. In FIG. 11A, the upper side is the radially outer side and the lower side is the radial inner side in the figure. In FIG. 11B, the upper side in the figure is the distal end side, and the lower side in the figure is the proximal side.

The ground electrode 240 of the spark plug 200 according to this modified embodiment includes a ground electrode base material 241 that is a base material, and a ground electrode tip 243 welded thereto.
Of these, the ground electrode base material 241 has a base material base end portion 241k joined to the metal fitting front end surface 110sc of the metal shell 110, and the base material front end portion 241s is bent inward in the radial direction. The surface 241sc faces inward in the radial direction. As shown in FIG. 11A, the ground electrode substrate 241 has a substantially semicircular (kamaboko) cross section.

  The ground electrode tip 243 has a rectangular column shape that is thinner (having a smaller cross-sectional area) than the ground electrode substrate 241. The ground electrode tip 243 is joined by resistance welding to the base end surface 241sc and the base end side surface 241sd of the base end portion 241s of the ground electrode base 241. The ground electrode tip 243 protrudes radially inward beyond the base end surface 241sc of the ground electrode base 241. The tip end surface 243sc of the ground electrode tip 243 is separated from the outer peripheral surface 130ssn of the center electrode tip portion 130ss by a spark discharge gap G that causes spark discharge.

  In the spark plug 200 having the ground electrode 240 having such a configuration, the ignitability can be improved while ensuring the heat resistance and breakage resistance of the ground electrode 240 as in the spark plug 100 of the above embodiment. . In addition, the same parts as in the above embodiment have the same operations and effects as in the above embodiment.

In the above, the present invention has been described with reference to the embodiments and modifications. However, the present invention is not limited to the above-described embodiments and the like, and can be appropriately modified and applied without departing from the gist thereof. Needless to say.
For example, in the above-described embodiment and the like, the spark plug 100 or the like provided with one ground electrode 140 or 240 is exemplified, but a plurality of ground electrodes 140 and 240 may be provided.

It is a side view of the spark plug which concerns on embodiment. It is a side view of the vicinity of a center electrode and a ground electrode in the spark plug according to the embodiment. It is the top view which looked at the center electrode, the ground electrode, etc. from the front end side among the spark plugs concerning embodiment. It is explanatory drawing which looked at the ground electrode of the spark plug which concerns on embodiment from the radial inside to the radial outside. It is the figure which looked at the center electrode and the ground electrode from the side among the spark plugs according to the embodiment, and is an explanatory view for explaining the gap length AD and the shortest distance F of the spark discharge gap. FIG. 6 is a transverse cross-sectional view (HH cross-sectional view in FIG. 5) at the center in the axial direction of the welded portion of the center electrode in the spark plug according to the embodiment. It is an enlarged view including J part shown with the broken line in FIG. 6 among the spark plugs which concern on embodiment. It is the graph which showed the relationship between F / AD and the spark rate to a welding part about the spark plug from which the length of a spark discharge discharge gap differs. It is the graph which showed the relationship between the circumferential direction level | step difference and the flying rate to a welding part about the spark plug from which F / AD differs. It is a side view near a center electrode and a ground electrode among spark plugs concerning a modification. It is a figure which shows the ground electrode of the spark plug which concerns on a deformation | transformation form, (a) is a cross-sectional view (YY cross section in FIG. 10) of a ground electrode base material, (b) is a diameter from radial inside. It is a front view near the front-end | tip of the ground electrode seen to the direction outer side.

DESCRIPTION OF SYMBOLS 100 Spark plug 110 Main metal fitting 110sc Metal fitting front end surface 120 Insulator 120s Insulator protrusion part 120sc Insulator front end surface 130 Center electrode 130s Center electrode protrusion part 130ss Center electrode front end part 130ssn Outer peripheral surface 131 Center electrode base material 131t Center electrode base material protrusion Part 133 Center electrode tip 135 Welded part 135n Outer circumference 140 Ground electrode (outer electrode)
141 Ground electrode substrate (outer electrode substrate)
143 Ground electrode tip (outer electrode tip)
143sc Tip end surface 150 Terminal fitting AX Axis line BX Center axis G Spark discharge gap AD Gap length F Shortest distance P Centroid ET1 Maximum circle ET2 Minimum circle Rmax (maximum circle) radius Rmin (minimum circle) radius

Claims (3)

A cylindrical metal shell having an axis,
A cylindrical insulator inserted inside the metal shell in the radial direction;
A central electrode inserted radially inward of the insulator,
A center electrode protrusion protruding from the insulator front end surface of the insulator toward the front end in the axial direction;
The central electrode protrusion is positioned on the axial base end side of the central electrode base material, and the axial end of the central electrode base material protrusion is narrower than the central electrode base protrusion. A center electrode including a columnar center electrode tip welded to the center electrode base material protrusion, and
An outer electrode formed by welding a columnar outer electrode tip that is thinner than a base end of an outer electrode base extending from the metal shell, wherein the tip end surface of the outer electrode tip is the center electrode tip One or a plurality of outer electrodes spaced apart from each other with a spark discharge gap therebetween,
A spark plug comprising:
The shortest distance F (mm) is the shortest distance from the outer electrode to the welded portion of the central electrode base material protrusion and the central electrode tip,
When the length of the spark discharge gap is the gap length AD (mm),
Ri Do a form satisfying F ≧ AD × 1.05,
In the cross section of the weld that includes a center point on the axis of the weld and is orthogonal to the axis,
Find the centroid of the weld in this cross section,
For each range of 15 degrees centered on this centroid, the radius Rmax of the largest circle that touches the outer periphery of the welded portion centered on the centroid and the welded portion centered on the centroid A difference D (= Rmax−Rmin) from the radius Rmin of the smallest circle in contact with the outer periphery of
When the average of each difference D is the circumferential step Da (μm) of the weld,
A spark plug configured to satisfy Da ≦ 9 . The spark plug according to claim 1,
A spark plug configured to satisfy F ≧ AD × 1.25. The spark plug according to claim 1 or 2 , wherein
A spark plug configured to satisfy Da ≦ 7.

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