JP3536873B2 - Spark plug for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spark plug for an internal combustion engine having a terminal electrode fitted into a shaft hole of an insulator, and more particularly, to a hermetic seal between the terminal electrode and the insulator, and to a connection between the terminal electrode and the insulator. The present invention relates to a terminal electrode structure of a spark plug for an internal combustion engine in which a glass seal which simultaneously joins with a center electrode is filled in a shaft hole of an insulator.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 9, a cylindrical insulator 102 having an axial hole 101 in an axial direction,
01 and the center electrode 104 held on the leg 103 side of the insulator 102 via the step 109, and the leg 10 of the insulator 102 fitted in the shaft hole 101.
The spark plug 100 for an internal combustion engine includes a terminal electrode 105 held on a side different from the side 3 and a metal shell (not shown) fitted on the outer periphery of the insulator 102 and holding an outer electrode (not shown). Are known. The airtightness between the terminal electrode 105 and the shaft hole 101 of the insulator 102 is as follows.
In general, a conductive glass seal layer 106 made of a mixture of a metal powder and a glass powder is filled in the shaft hole 101 to perform an electrical connection between the center electrode 104 and the terminal electrode 105 at the same time by a glass sealing method.

[0003] In the middle of the conductive glass seal layer 106, a resistor glass powder 10 for preventing radio noise is provided.
8 are filled. It should be noted that as the electrical resistance of the electrical resistor 108 increases, the loss of spark energy increases. Therefore, the electrical resistance is preferably smaller, but without a certain electrical resistance, the effect of suppressing radio noise is reduced. Therefore, it is known that an electric resistance value of about 3 kΩ to 7.5 kΩ is necessary in consideration of the loss of spark energy and the effect of suppressing radio noise.

[0004] Conventionally, resistor glass powder 10
The glass sealing material 107 containing the center electrode 104
Is inserted into the shaft hole 101 of the insulator 102, and the step 10
9 and a conductive glass seal layer 106 in which glass powder and metal powder are mixed, and a resistor glass powder 108 in which ceramic powder, carbon black, an organic carbonaceous substance and glass powder are mixed and adjusted, and a shaft of the insulator 102. Hole 10
1 and further filled with a conductive glass seal layer 106 , and then the entire insulator 102 is heated to a high temperature (for example, 800 ° C.).
(To about 1000 ° C.), and the terminal electrode 105 is hot-pressed into the shaft hole 101 of the insulator 102 in a state where the glass sealing material 107 is softened, thereby sealing between the center electrode 104 and the terminal electrode 105. Was being worn.

[0005]

However, in the conventional spark plug 100 for an internal combustion engine, the terminal electrode 10
5 has a flat disk shape, the conductive glass seal existing immediately below the terminal electrode 105 during the pressing step in which the tip of the terminal electrode 105 is hot-pressed with the glass sealing material 107. The layer 106 goes around the gap between the tip of the terminal electrode 105 and the insulator 102. As a result, the propagation of pressure from the terminal electrode 105 to the glass sealing material 107 is weakened, and the density of the glass sealing material 107 is reduced.

That is, since the contact state between the carbon black forming the resistor and the glass powder as the filler becomes unstable, the spark plug 1 for the internal combustion engine becomes unstable.
The electric resistance value of 00 becomes unstable. Due to such a problem, there is a problem that spark durability is deteriorated in addition to a problem such as an increase in spark energy loss and a reduction in a suppression effect of radio noise.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a spark plug for an internal combustion engine capable of stabilizing a plug resistance value, in particular, by sufficiently applying pressure from a tip end surface of a terminal electrode to a glass sealing material located immediately below a terminal electrode. To provide a plug. Another object of the present invention is to provide a spark plug for an internal combustion engine that can solve problems such as loss of spark energy, reduction of the effect of suppressing radio noise, and deterioration of spark durability.

[0008]

According to a first aspect of the present invention, there is provided an insulator having an axial hole therein,
A central electrode held on the leg long side of the shaft hole of the element, and a glass which is sealed on the center electrode in the shaft hole and held by the insulator, and is a mixture of at least a resistor powder and a glass powder and the sealing material, with between said insulator by said glass sealing member is inserted into the shaft hole is airtight, and a terminal electrode having a recessed recess than the surrounding the end surface, said pin The recess of the electrode is at the end
The outer diameter of the daughter electrode is A (mm), and the depth of the recess is D (m).
m), the relationship of A / 10 ≦ D ≦ A / 2 is satisfied.
It is characterized by that .

[0009] According to a second aspect of the invention, Oite the spark plug for an internal combustion engine according to claim 1, wherein the recess is
When the outer diameter of the terminal electrode is A (mm) and the depth of the recess is D (mm), the relationship of A / 5 ≦ D ≦ A / 2 is satisfied.

[0010]

[0011]

According to the first aspect of the present invention, the terminal electrode is provided with a depression on the tip end surface, and the depression is
The outer diameter of the terminal electrode is A (mm), and the depth of the recess is D (m).
m), by forming the relationship of A / 10 ≦ D ≦ A / 2 , a sufficient pressure is applied to the glass sealing material from the tip end surface of the terminal electrode when the terminal electrode is inserted into the shaft hole. The density of the glass sealing material increases. That is, the resistor
When the contact state between the resistor powder (for example, carbon powder) and the glass powder that form the glass powder is stabilized, the electric resistance value of the glass sealing material is further stabilized. As a result, it is possible to further prevent an increase in the loss of spark energy, a reduction in the effect of suppressing radio wave noise, and a deterioration in spark durability.

According to the second aspect of the present invention, the recess
By further limiting the size, the electrical resistance value becomes more stable
Accordingly, an increase in spark energy loss, a reduction in the effect of suppressing radio wave noise, and a deterioration in spark durability can be further suppressed as compared with the first aspect of the present invention.

[0013]

[0014]

Next, a spark plug for an internal combustion engine according to the present invention will be described with reference to an embodiment shown in the drawings.

FIGS. 1 to 4 show a first embodiment of the present invention. FIG. 1 shows a spark plug for an internal combustion engine, and FIG. 2 shows a spark plug for an internal combustion engine. It is a figure showing the principal part of a spark plug.

A spark plug 1 for an internal combustion engine is attached to each cylinder of an internal combustion engine (gasoline engine) mounted on an automobile, and a metal shell 3 holding an outer electrode 2, and an insulator held in the metal shell 3 4, a center electrode 6 held on the leg 5 side of the insulator 4, a glass sealing material 7 sealed in an intermediate portion of the insulator 4, and a terminal electrode 9 held on the corrugation portion 8 side of the insulator 4. And so on.

The outer electrode 2 is formed in a substantially L-shape so that the discharge end face formed on the tip side is opposed to the tip face of the center electrode 6, and a spark discharge gap G is formed between the outer electrode 2 and the center electrode 6. This is the ground electrode to be formed. The outer electrode 2 is obtained by encapsulating a core material made of a conductive metal having excellent heat conductivity in an electrode base material made of a nickel alloy having excellent heat resistance and corrosion resistance. A noble metal tip made of a noble metal such as platinum or iridium or a noble metal alloy mainly containing this noble metal may be joined to the discharge end face of the outer electrode 2 using joining means such as laser welding, electron beam welding, or resistance welding. good.

The metal shell 3 is a housing made of a steel material that serves to support the insulator 4 and attach it to an internal combustion engine (gasoline engine). An outer electrode is joined to the distal end surface of the metallic shell 3 by using joining means such as resistance welding. On the outer periphery of the metal shell 3, a hexagonal portion 1 for engaging a tool such as a male screw portion 11 and a tightening wrench for attaching to each cylinder head of the internal combustion engine is provided.
2 are formed. The metal shell 3 holds and fixes the insulator 4 inside by caulking the rear end.

The insulator 4 is made of aluminum oxide (Al ₂
O ₃ : alumina) or yttrium oxide (Y) on aluminum nitride (AlN).
_This is a ceramic sintered body obtained by adding and sintering at least one sintering aid selected from oxides such as ₂ O ₃ ) and calcium oxide (CaO). This insulator 4 is an insulator that electrically insulates the metal shell 3 from the center electrode 6 and the terminal electrode 9.

The insulator 4 has an axial hole 13 in the axial direction.
(For example, the inner diameter at the front end is φ2.5 mm and the inner diameter at the rear end is φ
4.7 mm), and the leg 5 is exposed to the atmosphere in the combustion chamber of the internal combustion engine. Further, the corrugation portion 8 of the insulator 4 protrudes from the rear end of the metal shell 3. And
Between the leg portion 5 and the corrugation portion 8 of the insulator 4, a flange portion 14 bulging outward is integrally formed.

Further, between the flange portion 14 and the leg long portion 5, a step portion which is locked via an annular ridge portion (locking portion) 15 formed on the inner periphery of the metal shell 3 via packing. (Locked portion) 16 is formed. A tapered step (locking portion) 17 for locking the center electrode 6 is provided on the inner periphery of the insulator 4.
Is formed. In this embodiment, the insulator 4
The sealing between the metal shell 3 and the metal shell 3 is performed by caulking through powder filling.

The center electrode 6 is obtained by encapsulating a core material made of a conductive metal having excellent heat conductivity in an electrode base material made of a nickel alloy having excellent heat resistance and corrosion resistance. The center electrode 6 is connected to the shaft hole 1 with its tip protruding from the shaft hole 13.
3 is inserted into the inside of the insulator 4 so that the leg 5
And a flange portion 19 provided at the rear end side of the rod portion 18 and having a larger outer diameter than the rod portion 18. These are formed by cold extrusion. Are formed integrally.

The flange 19 is formed by the step 1 of the insulator 4.
7 is a locked portion to be locked. A noble metal tip made of a noble metal such as platinum or iridium or a noble metal alloy mainly composed of this noble metal may be joined to the tip end surface of the center electrode 6 using joining means such as laser welding, electron beam welding, or resistance welding. good.

The glass sealing material 7 electrically connects the center electrode 6 and the terminal electrode 9, seals the center electrode 6 and the insulator 4, and seals the terminal electrode 9 and the insulator 4. It is a glass seal. The glass sealing material 7 solidifies in the shaft hole 13 of the insulator 4 in the order of the conductive glass sealing layer 21, the monolithic resistor layer 22 and the conductive glass sealing layer 23 from the center electrode 6 to the terminal electrode 9. It is filled in a state of conversion.

The conductive glass seal layers 21 and 23 are made of a conductive glass powder obtained by adding an organic binder to a glass powder as a filler and a conductive metal powder such as copper.

The monolithic resistor layer 22 is made of, for example, 5
It has an electrical resistance value of kΩ, glass powder as filler, carbon powder to form resistor, metal powder such as aluminum, magnesium and titanium, load life stabilizer such as titanium dioxide and titanium carbide, silica, alumina It is made of an electric resistive glass powder (resistor powder) containing a ceramic aggregate such as silicon or silicon nitride and an organic binder similar to that used for the conductive glass seal layers 21 and 23.

The terminal electrode 9 is made of a conductive metal (for example, mild steel).
A terminal portion 31 integrally formed with the plug cap (not shown), an annular plate-shaped flange portion 32 locked to the rear end face (locking portion) of the corrugation portion 8 of the insulator 4,
And a round bar-shaped shaft portion 33 fitted into the shaft hole 13 of the insulator 4.

The terminal portion 31 is a terminal that is electrically connected to a secondary coil of an ignition coil (not shown) and protrudes from the rear end surface of the corrugation portion 8 of the insulator 4. The flange portion 32 has an outer diameter larger than that of the terminal portion 31 and the shaft portion 33 and is larger than an inner diameter of the shaft hole 13 on the corrugation portion 8 side of the insulator 4.

The shaft portion 33 is, for example, 0.2 mm to 0.6 mm larger than the inner diameter (for example, φ4.7 mm) of the shaft hole 13 of the insulator 4.
An outer peripheral thread portion 34 is formed on the outer periphery on the distal end side to improve the fixing strength with the glass sealing material 7. In addition, a concave portion 35 is provided on the distal end surface of the shaft portion 33.
Is formed.

As shown in FIG. 3, the depression 35
A mortar-shaped concave portion having a curvature surface, the depth of the concave portion 35 from the distal end of the annular side wall portion 36 formed on the outer periphery of the distal end surface to the bottom portion 37 of the axial center is D, and the axial portion 33 of the terminal electrode 9 is D. Are formed so as to have a relationship of A / 5, where A is the outer diameter of

Next, a method of manufacturing the spark plug 1 for an internal combustion engine according to this embodiment will be briefly described with reference to FIGS. Here, FIG. 4 is a view showing a method of manufacturing the spark plug 1 for an internal combustion engine.

First, the insulator 4 is integrally formed into a predetermined cylindrical shape, and the center electrode 6 is integrally formed into a predetermined rod shape. Then, the terminal electrode 9 having the terminal portion 31, the flange portion 32, and the shaft portion 33 is integrally formed, and a recess 35 is formed on the distal end surface of the shaft portion 33 by cutting, plastic working, or the like (forming step).

Next, the center electrode 6 is inserted into the shaft hole 13 from the rear end face of the corrugation portion 8 of the insulator 4. At this time, the stepped portion 1 formed on the inner periphery of the insulator 4
7 (see FIG. 4 (a): center electrode insertion step).

Next, the conductive glass powder 41, the electric resistance glass powder 42, and the conductive glass powder 43 are inserted into the shaft hole 13 in this order from the rear end face of the corrugation portion 8 of the insulator 4 (FIG. 4B). Reference: glass sealing material filling step].

Here, the conductive glass powders 41 and 43 are:
50% by weight of glass powder, 40% by weight to 47% by weight of conductive metal powder such as copper, and an appropriate amount of organic binder such as PEG (polyethylene glycol), PEO (polyethylene oxide), dextrin (3% by weight to 10% by weight) %), Water, and mixed, granulated, and dried (containing 1% water).

The electric resistance glass powder 42 is obtained by adding carbon powder, metal powder such as aluminum, or the like to glass powder.
Load life stabilizers such as titanium dioxide and titanium carbide, ceramic aggregates such as alumina and silicon nitride, and organic binders similar to those used for the conductive glass powders 41 and 43 and water are added, mixed, granulated, and dried. Powder.

Next, the entire insulator 4 is heated at 850.degree.
The terminal electrode 9 is inserted into the shaft hole 13 from the rear end face of the corrugation portion 8 of the insulator 4 in a state where the conductive glass powders 41 and 43 and the electric resistance glass powder 42 have been softened by heating to a high temperature of about ° C. I do. At this time, the conductive glass powders 41 and 43 and the electric resistance glass powder 42 are pressed by hot pressing the terminal electrode 9 with a press molding machine.
Is hot pressed (see FIG. 4 (c): pressing step).

Here, since the concave portion 35 is formed on the tip end surface of the shaft portion 33, the shaft portion 33 is made of the conductive glass powder 4.
1, 43 and the conductive glass powder 42 existing just below the shaft 33 when the electric resistance glass powder 42 is pressed.
1 does not enter the gap between the outer periphery of the shaft portion 33 and the inner periphery of the insulator 4 so much that the pressing force of the press molding machine causes the conductive glass powders 41 and 43 and the electric resistance glass powder 42 Propagates well to Thereby, the insulator 4
The density of the glass sealing material 7 in the shaft hole 13 is increased. That is, in the electric resistance glass powder 42, the contact state between the carbon powder forming the resistor and the glass powder as the filler is improved.

Next, by cooling the insulator 4 at normal temperature, the softened glass sealing material 7 is solidified,
As shown in FIG. 4D, the conductive glass seal layer 21 and the monolithic resistor layer 2 are provided in the shaft hole 13 of the insulator 4.
2 and a conductive glass seal layer 23 are formed. Thereby, the airtightness between the terminal electrode 9 and the insulator 4 and the electrical connection between the terminal electrode 9 and the center electrode 6 are simultaneously performed by the glass sealing material 7.

[Effects of the First Embodiment] As described above, the spark plug 1 for an internal combustion engine can be used when the glass sealing material 7 is pressed on the tip end surface of the terminal electrode 9 in the third pressing step. The side wall portion 36 of the recess 35 can prevent the conductive glass powder 41 existing directly below the shaft portion 33 from going around the gap between the outer periphery of the shaft portion 33 and the inner periphery of the insulator 4. Thereby, the propagation of the pressure from the tip end surface of the shaft portion 33 to the glass sealing material 7 becomes strong, so that the density of the glass sealing material 7 can be increased.

That is, since the state of contact between the resistor powder of the electric resistance glass powder 42 and the glass powder is stabilized, the electric resistance value of the monolithic resistor layer 22 is stabilized. As a result, an increase in the electric resistance value (plug resistance value) of the monolithic resistor layer 22 can be suppressed.
It is possible to prevent an increase in spark energy loss and a deterioration in spark durability. In addition, since a decrease in the electric resistance value (plug resistance value) of the monolithic resistor layer 22 can be suppressed, a decrease in the effect of suppressing radio noise can be prevented.

[Second Embodiment] FIG. 5 shows a second embodiment of the present invention, and is a diagram showing a tip shape of a terminal electrode of a spark plug for an internal combustion engine.

In this embodiment, a recess 51 having a trapezoidal opening cross section is formed at the tip of the shaft 33 of the terminal electrode 9. The recess 51 is formed by the side wall 36 of the first embodiment.
It has a cylindrical side wall 52 having a greater thickness and a flat circular bottom 53 deeper than the bottom 37 of the first embodiment. The inner peripheral surface of the side wall portion 52 is, for example, 60 °.
The inclined surface is inclined by an inclination angle smaller than that. The depth of the depression 51 from the tip end surface of the side wall 52 to the bottom 53 is D (mm).
When the outer diameter of the shaft portion 33 is A (mm), the relationship is D = A / 2.

[Third Embodiment] FIG. 6 shows a third embodiment of the present invention, and is a view showing a tip shape of a terminal electrode of a spark plug for an internal combustion engine.

In this embodiment, a thin dish-shaped recess 54 is formed at the tip of the shaft 33 of the terminal electrode 9. The recess 54 has an annular side wall 55 having a smaller thickness than the side wall 52, and a circular bottom 56 wider than the bottom 53 and shallower than the bottom 53. The side wall 52
Is an inclined surface inclined by an inclination angle smaller than 60 °, for example. When the depth of the concave portion 54 from the distal end surface of the side wall portion 55 to the bottom portion 56 is D (mm), and the outer diameter of the shaft portion 33 of the terminal electrode 9 is A (mm), the concave portion 54 is D = A / 5.

[Fourth Embodiment] FIG. 7 shows a fourth embodiment of the present invention, and is a diagram showing a tip shape of a terminal electrode of a spark plug for an internal combustion engine.

In this embodiment, a dish-shaped recess 57 thinner than the recess 54 is formed at the tip of the shaft 33 of the terminal electrode 9. The concave portion 57 is wider than the annular convex portion 58 having a smaller thickness than the side wall portion 55 and the bottom portion 56,
It has a circular bottom 59 that is shallower than the bottom 56. Note that the inner peripheral surface of the convex portion 58 is an inclined surface inclined by an inclination angle smaller than 60 °, for example. The depression 57 is formed by a depression 5 from the tip of the projection 58 to the bottom 59.
7 is D (mm), and the outer diameter of the shaft 33 of the terminal electrode 9 is A
(Mm), it is formed so that D = A / 10.

[First to Fourth Embodiments, First and Second Conventional Examples,
Experimental Results of Comparative Example] Next, a terminal electrode in which the shape of the tip of the shaft of the terminal electrode was variously changed as shown in FIGS.
Attach to the insulator together with the center electrode and glass sealing material,
After that, we describe the experimental results of investigating each plug resistance value of a spark plug for an internal combustion engine, in which a metal shell is attached to the outer periphery of the insulator, and an outer electrode is joined to the tip surface of the metal shell. In addition, the graph of FIG. 8 shows the results of investigation of 100 samples each having the tip end of the shaft portion of each terminal electrode inserted into the insulator by the above-described manufacturing method.

Here, FIG. 8A is a comparative example having a flat mortar-shaped shaft tip shape, FIG. 8B is a first embodiment of the present invention, and FIG. FIG. 8 (d) shows a third embodiment of the present invention, FIG. 8 (e) shows a fourth embodiment of the present invention, and FIG. 8 (f) shows a circular and flat shaft portion. FIG. 8 (g) shows a first conventional example having a tip end shape, and FIG. 8 (g) shows a second conventional example having a shaft end tip shape chamfered in a circular shape.

As can be seen from the graph of FIG. 8, the plug resistance values of the first and second conventional examples are 3.3 kΩ to 7.4 kΩ.
The variation is large, such as Ω, and the variation is somewhat large, such as the plug resistance value of the comparative example of 4.0 kΩ to 6.7 kΩ. Further, the plug resistance value of the fourth embodiment is 4.0 kΩ or more.
The variation is slightly small, such as 6.5 kΩ, and the variation is small, such as the plug resistance value of the first embodiment of 4.0 kΩ to 6.0 kΩ. Then, the variation is further reduced as in the case of the plug resistance value of the third embodiment being 4.0 kΩ to 5.7 kΩ, and the plug resistance value of the second embodiment is 4.1 kΩ to 5.4.
The variation becomes the smallest like kΩ.

Therefore, in the spark plug 1 for an internal combustion engine of the first to fourth embodiments, the shaft portion of the glass sealing material 7 is formed by the side walls 36, 52, 55 and the projection 58 formed on the outer periphery of the tip of the shaft portion 33. Into the gap between the outer periphery of the insulator 33 and the inner periphery of the insulator 4 is prevented, and the bottom portions 37, 53, 56, 5
9 applies pressure to the glass sealing material 7 located immediately below. For this reason, the fluctuation range of the plug resistance value becomes extremely small as compared with the first and second conventional examples and the comparative example, so that the spark energy loss increases, the radio noise suppressing effect decreases, and the spark durability deteriorates. It can be said that the effect of preventing this is excellent.

[Modification] In this embodiment, the terminal portion 31 and the shaft portion 33 of the terminal electrode 9 are integrally formed of a conductive metal. However, the terminal portion 31 and the shaft portion 33 of the terminal electrode 9 are the same or different. It may be formed separately from a conductive metal. In this embodiment, the insulator 4 is formed integrally, but a split insulator may be used as the insulator. Also, the outer electrode 2,
The shape and material of the metal shell 3 or the center electrode 6 can be freely changed.

In this embodiment, the glass sealing material 7 is formed into three layers like the conductive glass sealing layer 21, the monolithic resistor layer 22, and the conductive glass sealing layer 23.
The glass sealing material may be composed of only a monolithic resistor, or may be further multilayered if a resistor layer is included. The material and particle size of the glass powder and the resistor powder of the glass sealing material 7 may be freely changed.

In this embodiment, the outer peripheral thread 34 at the tip of the shaft 33 of the terminal electrode 9 is formed. However, the fixing strength of the glass sealing material 7 to the outer periphery of the tip of the shaft 33 of the terminal electrode 9 is improved. A convex portion, a concave portion, a flange portion, or the like for improvement may be provided.

[Brief description of the drawings]

FIG. 1 is a half sectional view showing a first embodiment of the present invention.

FIG. 2 is a sectional view showing a main part of the first embodiment of the present invention.

FIG. 3 is a cross-sectional view showing a tip shape of the terminal electrode according to the first embodiment of the present invention.

FIGS. 4A to 4D are process diagrams showing a manufacturing method according to the first embodiment of the present invention.

FIG. 5 is a cross-sectional view showing a tip shape of a terminal electrode according to a second embodiment of the present invention.

FIG. 6 is a cross-sectional view showing a tip shape of a terminal electrode according to a third embodiment of the present invention.

FIG. 7 is a cross-sectional view showing a tip shape of a terminal electrode according to a fourth embodiment of the present invention.

FIG. 8 is a graph showing the relationship between the tip shape of the terminal electrode and the plug resistance value of the first and second conventional examples, the comparative example, and the first to fourth examples.

FIG. 9 is a half sectional view showing a main part of a conventional spark plug for an internal combustion engine.

[Explanation of symbols]

1 Spark plug for internal combustion engine 4 Insulator 6 center electrode 7 Glass sealing material 9 Terminal electrode 13 Shaft hole 17 steps 21 conductive glass seal layer 22 Monolithic resistor layer 23 Conductive glass seal layer 33 Shaft 35 hollow 41 conductive glass powder 42 Electric Resistive Glass Powder 43 conductive glass powder 51 hollow 54 hollow 57 hollow

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01T 13/20 H01T 13/34 H01T 13/41 H01T 21/02

Claims (2)

(57) [Claims] (A) An insulator having an axial hole in an axial direction inside the insulator and the insulator held on the leg side of the shaft hole of the insulator.
A core electrode, (b) a glass sealing material sealed on the center electrode in the shaft hole and held by the insulator, and at least a mixture of a resistor powder and a glass powder; and (c) the shaft hole. And a terminal electrode having a recess recessed from the periphery at the tip end surface thereof, wherein the terminal seal is airtightly sealed between the insulator and the insulator by the glass seal material , and (d) the recess of the terminal electrode. The part is outside the terminal electrode
The diameter was A (mm), and the depth of the depression was D (mm).
When the spark plug for an internal combustion engine, characterized by satisfying the relation of A / 10 ≦ D ≦ A / 2. 2. The spark plug for an internal combustion engine according to claim 1, wherein the depression has an outer diameter of the terminal electrode of A (mm) and a depth of the depression is D (mm). A spark plug for an internal combustion engine, wherein a relationship of A / 5 ≦ D ≦ A / 2 is satisfied.