JPH0963745A - Spark plug for internal combustion engine and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize an electric resistance value for a monolithic resistor layer and restrain the sparking durability of a spark plug for an internal combustion engine. SOLUTION: A bowl-shaped recess 35 with a face of curvature is formed at the end of a terminals electrode 9. After the process of filling glass seal material 7 containing electric resistant glass powder 42 into an axial hole 13 in an insulator 4, the whole insulator 4 is heated to a high temperature to melt the glass seal material 7 and, in such a condition, the terminal electrode 9 is inserted into the axial hole 13 in the insulator 4 to perform the process of hot-pressing the glass seal material 7. At this time, the glass seal material 7 which exists right under the terminal electrode 9 is prevented from turning around in a gap between the outer periphery of the terminal electrode 9 and the inner periphery of the insulator 4, so that sufficient pressure is applied from the end of the terminal electrode 9 to the glass seal material 7, contact between resistor powder and glass powder in the electric resistant glass powder 42 is in a good condition and a resistance value for a plug is stabilized.

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 provided with a terminal electrode fitted in a shaft hole of an insulator, and more particularly to an airtightness between the terminal electrode and the insulator and a terminal electrode. The present invention relates to a terminal electrode structure of a spark plug for an internal combustion engine in which a glass seal for simultaneously joining 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 a shaft hole 101 in the axial direction, and a shaft hole 1 are provided.
01 and the central electrode 104 which is held on the leg long portion 103 side of the insulator 102 via the step portion 109, and the long leg portion 10 of the insulator 102 which is fitted in the shaft hole 101.
A spark plug 100 for an internal combustion engine including a terminal electrode 105 held on a side different from 3 and a metal shell (not shown) fitted to the outer circumference of the insulator 102 and holding an outer electrode (not shown) is provided. Are known. The airtightness between the terminal electrode 105 and the shaft hole 101 of the insulator 102 is
Generally, the conductive glass seal layer 106 made of a mixture of metal powder and glass powder is filled in the shaft hole 101 to electrically connect the center electrode 104 and the terminal electrode 105 at the same time by the glass seal method.

A resistor glass powder 10 for preventing radio noise is provided in the middle of the conductive glass seal layer 106.
8 is filled. Note that the larger the electric resistance value of the electric resistor 108, the more the spark energy loss increases, so the smaller the electric resistance value, the better. However, if there is no electric resistance value to some extent, the effect of suppressing radio noise becomes less. Therefore, it is known that an electric resistance value of about 3 kΩ to 7.5 kΩ is required in consideration of the loss of spark energy and the effect of suppressing radio noise.

And, conventionally, resistor glass powder 10 has been used.
The glass sealing material 107 including
Is inserted into the shaft hole 101 of the insulator 102, and the step 10
9, 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 or organic carbonaceous substance and glass powder are mixed and adjusted are attached to the shaft of the insulator 102. Hole 10
1 and then further filled with the glass sealing material 107, the entire insulator 102 is heated to a high temperature (eg, 800 ° C. to 10 ° C.).
(00 ° C.) to soften the glass sealing material 107, and the terminal electrode 105 is attached to the shaft hole 101 of the insulator 102.
It was sealed between the center electrode 104 and the terminal electrode 105 by hot pressing.

[0005]

However, in the conventional spark plug 100 for an internal combustion engine, the terminal electrode 10 is used.
Since the tip end shape of 5 is a flat disk shape, the conductive glass seal present immediately below the terminal electrode 105 during the pressurizing step in which the tip end portion of the terminal electrode 105 is hot pressed by the glass sealant 107. The layer 106 wraps around in 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, so that the density of the glass sealing material 107 is reduced.

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

An object of the present invention is to make a spark resistance for an internal combustion engine capable of stabilizing a plug resistance value by making a sufficient pressure from a tip surface of the terminal electrode on a glass sealing material existing immediately below the terminal electrode. To provide a plug. Another object of the present invention is to provide a spark plug for an internal combustion engine capable of solving problems such as loss of spark energy, reduction of radio noise suppression effect, and deterioration of spark durability.

[0008]

According to a first aspect of the present invention, there is provided an insulator having an axial shaft hole therein, and an insulator sealed in the shaft hole and held by the insulator, and at least a resistor powder. And a glass sealing material that is a mixture of glass powder, and the airtight between the insulator is inserted into the shaft hole by the glass sealing material, the recessed portion recessed from the surroundings on the tip surface. The technical means provided with the terminal electrode which has was adopted.

According to a second aspect of the present invention, in addition to the spark plug for an internal combustion engine according to the first aspect, the outer diameter of the terminal electrode is A (mm) and the depth of the recess is D (mm). Then, the relationship of A / 10 ≦ D ≦ A / 2 is satisfied. According to a third aspect of the present invention, in addition to the spark plug for an internal combustion engine according to the first aspect, the outer diameter of the terminal electrode is A (mm) and the depth of the recess is D (mm). ,
It is characterized in that the relationship of A / 5 ≦ D ≦ A / 2 is satisfied.

According to a fourth aspect of the present invention, the center electrode is inserted into the shaft hole of the insulator and locked to the step portion, and the glass is a mixture of at least the resistor powder and the glass powder in the shaft hole. A filling step of filling a sealing material, and a state in which the entire glass insulator is heated to melt the glass sealing material, and in the shaft hole of the ceramic insulator, a tip surface in which a recessed portion that is recessed from the surrounding is formed The first step is to insert the terminal electrode and pressurize the glass sealing material.

[0011]

According to the invention described in claim 1, by forming the recessed portion on the tip end surface of the terminal electrode,
When the terminal electrode is inserted into the shaft hole, sufficient pressure is applied to the glass sealing material from the tip end surface of the terminal electrode, so that the density of the glass sealing material increases. That is, the electrical resistance value of the glass sealing material is stabilized by stabilizing the contact state between the resistor powder (for example, carbon powder) and the glass powder. As a result, it is possible to prevent an increase in spark energy loss, a decrease in radio noise suppression effect, and a decrease in spark durability.

According to the second aspect of the invention, the electrical resistance value is further stabilized by further stabilizing the contact state between the carbon forming the resistor and the glass powder as the filler. As a result, increased spark energy loss,
It is possible to further suppress the deterioration of the suppression effect of radio noise and the deterioration of spark durability. According to the invention described in claim 3, it is possible to further suppress the increase in the loss of spark energy, the decrease in the effect of suppressing radio noise, and the deterioration in the spark durability, as compared with the invention described in claim 2.

According to the fourth aspect of the present invention, by forming the recessed portion on the tip end surface of the terminal electrode, when the glass sealing material is pressed by the tip end surface of the terminal electrode in the pressing step, the terminal electrode It is possible to prevent the glass sealing material existing immediately below the electrode from going around the gap between the terminal electrode and the insulator. As a result, the pressure is strongly propagated from the tip end surface of the terminal electrode to the glass sealing material, so that the density of the glass sealing material can be prevented from lowering. That is,
By stabilizing the contact state between the resistor powder (for example, carbon powder) and the glass powder, the electric resistance value of the glass sealing material is stabilized. As a result, it is possible to prevent an increase in spark energy loss, a decrease in radio noise suppression effect, and a decrease in spark durability.

[0014]

Next, a spark plug for an internal combustion engine of the present invention will be described based on the embodiment shown in the drawings.

[Structure of First Embodiment] FIGS. 1 to 4 show a first embodiment of the present invention. FIG. 1 is a view showing a spark plug for an internal combustion engine, and FIG. 2 is for an internal combustion engine. It is the figure which showed 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, a metal shell 3 holding an outer electrode 2, and an insulator held in the metal shell 3. 4, center electrode 6 held on the long leg 5 side of the insulator 4, glass sealing material 7 sealed in the middle part of the insulator 4, and terminal electrode 9 held on the corrugation part 8 side of the insulator 4. Etc.

The outer electrode 2 is formed in a substantially L shape so that the discharge end face formed on the tip side is arranged to face 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. It is a ground electrode to be formed. The outer electrode 2 is obtained by encapsulating a core material made of a conductive metal having excellent thermal conductivity in an electrode base material made of a nickel alloy having excellent heat resistance and corrosion resistance. Even if 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 is joined to the discharge end surface of the outer electrode 2 by using joining means such as laser welding, electron beam welding, or resistance welding. good.

The metal shell 3 is a housing made of steel which plays a role of supporting the insulator 4 and mounting it on an internal combustion engine (gasoline engine). The outer electrode is joined to the front end surface of the metal shell 3 by using a joining means such as resistance welding. Then, on the outer periphery of the metal shell 3, a hexagonal portion 1 for engaging a male thread portion 11 for attaching to each cylinder head of the internal combustion engine and a tool such as a tightening wrench.
2 is formed. Further, the metallic shell 3 holds the insulator 4 inside by crimping the rear end portion.

The insulator 4 is made of aluminum oxide (Al ₂
O ₃ : alumina) as a main component, or aluminum nitride (AlN) with yttrium oxide (Y
It is a ceramics sintered body obtained by adding and sintering a sintering aid selected from one or more kinds of oxides such as ₂ O ₃ ) and calcium oxide (CaO). The 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 axial hole 13 inside.
(For example, the inner diameter on the front end side is φ2.5 mm and the inner diameter on the rear end side is φ
The length of 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 projects beyond the rear end of the metal shell 3. And
A brim-shaped portion 14 that bulges outward is integrally formed between the long leg portion 5 of the insulator 4 and the corrugated portion 8.

Further, between the brim-shaped portion 14 and the long leg portion 5, a step portion which is engaged with an annular protrusion (locking portion) 15 formed on the inner circumference of the metal shell 3 through packing. (Locked portion) 16 is formed. Further, on the inner circumference of the insulator 4, a tapered step portion (locking portion) 17 for locking the center electrode 6 is formed.
Are formed. In this embodiment, the insulator 4
The metal shell 3 and the metal shell 3 are sealed by caulking via powder filling.

The center electrode 6 is obtained by encapsulating a core material made of a conductive metal having excellent thermal conductivity in an electrode base material made of a nickel alloy having excellent heat resistance and corrosion resistance. The center electrode 6 has a tip portion projecting from the shaft hole 13 and the shaft hole 1
By being fitted inside 3, the long leg portion 5 of the insulator 4
It has a circular rod-shaped portion 18 held inside, and a collar-shaped portion 19 provided on the rear end side of the rod-shaped portion 18 and having a larger outer diameter than the rod-shaped portion 18, and these are cold-extruded. Are integrally formed by.

The collar-shaped portion 19 is the step portion 1 of the insulator 4.
7 is a locked portion that is locked by 7. Even if 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 is joined to the tip surface of the center electrode 6 by 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. This glass sealing material 7 is solid 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 toward the terminal electrode 9. It is filled in the liquefied state.

The conductive glass seal layers 21 and 23 are made of conductive glass powder in which an organic binder is added to glass powder as a filler and conductive metal powder such as copper.

The monolithic resistor layer 22 has, for example, 5
It has an electric resistance of kΩ, and glass powder as a filler, carbon powder forming a resistor, metal powder such as aluminum, magnesium and titanium, load life stabilizer such as titanium dioxide and titanium carbide, silica and alumina. And an electrically resistant glass powder (resistor powder) containing a ceramic aggregate such as silicon nitride and the same organic binder as 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 molded by a plug cap (not shown), and an annular plate-shaped brim portion 32 locked to the rear end surface (locking portion) of the corrugation portion 8 of the insulator 4.
And a round bar-shaped shaft portion 33 and the like fitted in the shaft hole 13 of the insulator 4.

The terminal portion 31 is a terminal electrically connected to a secondary coil of an ignition coil (not shown) and protruding from the rear end face of the corrugation portion 8 of the insulator 4. The flange portion 32 has a larger outer diameter than the terminal portion 31 and the shaft portion 33, and is larger than the 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.
The outer peripheral threaded portion 34 is formed on the outer periphery of the tip end side for improving the fixing strength with the glass sealing material 7. In addition, a dent 35 is formed on the tip surface of the shaft 33.
Are formed.

As shown in FIG. 3, this recess 35 has
It is a mortar-shaped recess having a curved surface, and the depth of the recess 35 from the tip of the annular side wall 36 formed on the outer periphery of the tip surface to the bottom 37 of the shaft center is D, and the shaft 33 of the terminal electrode 9 is formed. The outer diameter of A is A, and the outer diameter is A / 5.

[Manufacturing Method of First Embodiment] Next, a manufacturing method of the spark plug 1 for an internal combustion engine of this embodiment will be briefly described with reference to FIGS. 1 to 4. Here, FIG. 4 is a diagram 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 collar portion 32, and the shaft portion 33 is integrally molded, and the recessed portion 35 is formed on the tip end surface of the shaft portion 33 by cutting or plastic working [molding step].

Next, the center electrode 6 is inserted into the shaft hole 13 from the rear end surface of the corrugation portion 8 of the insulator 4. At this time, the stepped portion 1 in which the collar-shaped portion 19 is formed on the inner circumference of the insulator 4
7 (see FIG. 4A: center electrode insertion step).

Next, the conductive glass powder 41, the electrically resistive glass powder 42, and the conductive glass powder 43 are inserted in this order from the rear end face of the corrugation portion 8 of the insulator 4 into the shaft hole 13 [FIG. 4 (b)]. 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 (3% by weight to 10% by weight) of organic binder such as PEG (polyethylene glycol), PEO (polyethylene oxide) and dextrin. %) And water, mixed, granulated, and dried (containing 1% of water content).

The electrically resistive glass powder 42 is made of glass powder, carbon powder, metal powder such as aluminum,
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 to mix, granulate, and dry. It is a powdered grain.

Next, the entire insulator 4 is heated at 850 ° C. to 950 ° C.
Insert the terminal electrode 9 into the shaft hole 13 from the rear end face of the corrugation portion 8 of the insulator 4 while heating the conductive glass powders 41 and 43 and the electrically resistive glass powder 42 by heating to a high temperature of around ℃. To do. At this time, the conductive glass powders 41 and 43 and the electrically resistive glass powder 42 are obtained by hot pressing the terminal electrode 9 with a press molding machine.
Is hot-pressed [see FIG. 4 (c): pressurizing step].

Here, since the hollow portion 35 is formed on the tip surface of the shaft portion 33, the shaft portion 33 is formed into the conductive glass powder 4.
1 and 43 and the electrically resistive glass powder 42 are being pressed, the electrically conductive glass powder 4 present immediately below the shaft portion 33
1 does not go too far into the gap between the outer circumference of the shaft portion 33 and the inner circumference of the insulator 4, and the pressing force of the press molding machine causes the conductive glass powders 41, 43 and the electrically resistive glass powder 42 from the tip surface of the shaft portion 33. Propagate to enough. As a result, the insulator 4
The density of the glass sealing material 7 in the shaft hole 13 is increased. That is, in the electrically resistive glass powder 42, the contact state between the carbon powder forming the resistor and the glass powder as the filler becomes good.

Next, by cooling the insulator 4 at room 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 the conductive glass seal layer 23 are formed. As a result, the glass sealing material 7 simultaneously hermetically seals the terminal electrode 9 and the insulator 4 and electrically connects the terminal electrode 9 and the center electrode 6.

[Effects of First Embodiment] As described above, in the spark plug 1 for an internal combustion engine, when the glass sealing material 7 is pressed by the tip surface of the terminal electrode 9 in the pressing step which is the third step. The side wall portion 36 of the hollow portion 35 can prevent the conductive glass powder 41 existing immediately below the shaft portion 33 from wrapping around in the gap between the outer circumference of the shaft portion 33 and the inner circumference of the insulator 4. As a result, the pressure transmission 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, the contact state between the resistor powder of the electrically resistive glass powder 42 and the glass powder is stabilized, so that the electrical resistance value of the monolithic resistor layer 22 is stabilized. As a result, the increase in the electric resistance value (plug resistance value) of the monolithic resistance layer 22 can be suppressed,
It is possible to prevent an increase in spark energy loss and a deterioration in spark durability. Further, since it is possible to suppress a decrease in the electric resistance value (plug resistance value) of the monolithic resistance layer 22, it is possible to prevent a decrease in the effect of suppressing radio noise.

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

In this embodiment, a hollow portion 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 the side wall portion 36 of the first embodiment.
It has a thicker cylindrical side wall portion 52 and a flat circular bottom portion 53 deeper than the bottom portion 37 of the first embodiment. The inner peripheral surface of the side wall portion 52 has, for example, 60 °.
The inclined surface is inclined by a smaller inclination angle. The recessed portion 51 has a depth of D (mm) from the tip surface of the side wall portion 52 to the bottom portion 53 of the terminal electrode 9
When the outer diameter of the shaft portion 33 is A (mm), the relationship of D = A / 2 is formed.

[Third Embodiment] FIG. 6 shows a third embodiment of the present invention and is a view showing the tip shape of the terminal electrode of the 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 that is thinner than the side wall 52, and a circular bottom 56 that is wider than the bottom 53 and is shallower than the bottom 53. The side wall portion 52
The inner peripheral surface of is an inclined surface inclined by an inclination angle smaller than 60 °, for example. When the depth of the recess 54 from the tip surface of the side wall 55 to the bottom 56 is D (mm) and the outer diameter of the shaft 33 of the terminal electrode 9 is A (mm), the recess 54 is D. = A / 5.

[Fourth Embodiment] FIG. 7 shows a fourth embodiment of the present invention and is a view showing the tip shape of the terminal electrode of the 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 recess 57 is wider than the annular protrusion 58 and the bottom 56, which are thinner than the side wall 55,
It has a circular bottom 59 that is shallower than the bottom 56. The inner peripheral surface of the convex portion 58 is an inclined surface inclined by an inclination angle smaller than 60 °, for example. The recessed portion 57 is the recessed portion 5 from the tip of the protrusion 58 to the bottom 59.
7 is D (mm) and the outer diameter of the shaft portion 33 of the terminal electrode 9 is A
(Mm), the relationship is D = A / 10.

[First to Fourth Examples, First and Second Conventional Examples,
Experimental Results of Comparative Example] Next, the terminal electrode in which the tip shape of the shaft portion of the terminal electrode was variously changed as shown in FIGS.
Assemble with the center electrode and glass sealant to the insulator,
After that, the experimental results of investigating the respective plug resistance values of the spark plug for the internal combustion engine in which the metallic shell is assembled on the outer circumference of the insulator and the outer electrode is joined to the tip surface of the metallic shell will be described. In addition, as a sample, 100 pieces of the tip shape of the shaft portion of each terminal electrode were inserted into the insulator by the above-described manufacturing method, and the examination results are shown in the graph of FIG.

Here, FIG. 8A is a comparative example having a flat mortar-shaped shaft tip shape, FIG. 8B is the first embodiment of the present invention, and FIG. 8C is the present invention. 8 (d) is a third embodiment of the present invention, FIG. 8 (e) is a fourth embodiment of the present invention, and FIG. 8 (f) is a circular flat shaft portion. FIG. 8 (g) is a second conventional example having a tip shape, and FIG. 8 (g) is a second conventional example having a chamfered shaft tip 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 k.
And the plug resistance value of the comparative example is slightly large, such as 4.0 kΩ to 6.7 kΩ. Further, the plug resistance value of the fourth embodiment is 4.0 kΩ to
The variation is slightly small like 6.5 kΩ, and the variation is small like the plug resistance value of the first embodiment is 4.0 kΩ to 6.0 kΩ. Then, the variation in the plug resistance value of the third embodiment is further reduced to 4.0 kΩ to 5.7 kΩ, and the plug resistance value of the second embodiment is 4.1 kΩ to 5.4 kΩ.
The variation is the smallest like kΩ.

Therefore, in the spark plugs 1 for internal combustion engines of the first to fourth embodiments, the shaft portion of the glass sealing material 7 is formed by the side wall portions 36, 52, 55 and the convex portion 58 formed on the outer periphery of the tip of the shaft portion 33. The wraparound of the outer periphery of 33 and the inner periphery of the insulator 4 is prevented, and the bottom portions 37, 53, 56, 5
By 9, the pressure is concentrated on the glass sealing material 7 existing 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 increase of the spark energy loss, the reduction of the radio noise suppression effect, and the deterioration of the spark durability are suppressed. It can be said that the effect of prevention is excellent.

[Modification] In this embodiment, the terminal portion 31 of the terminal electrode 9 and the shaft portion 33 are integrally formed of conductive metal, but the terminal portion 31 and the shaft portion 33 of the terminal electrode 9 are the same or different. It may be separately formed of a conductive metal. In this embodiment, the insulator 4 is integrally formed, but a split type 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 has three layers such as 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 multi-layered if it includes a resistor layer. The material and particle size of the glass powder or the resistor powder of the glass sealing material 7 may be freely changed.

In this embodiment, the outer peripheral threaded portion 34 of the tip portion of the shaft portion 33 of the terminal electrode 9 is formed, but the fixing strength with the glass seal material 7 is secured to the outer periphery of the tip portion of the shaft portion 33 of the terminal electrode 9. You may provide a convex part, a concave part, a collar part, etc. for improvement.

[Brief description of 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 the tip shape of the terminal electrode according to the first embodiment of the present invention.

4 (a) to 4 (d) are process drawings showing the manufacturing method of the first embodiment of the present invention.

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

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

FIG. 7 is a sectional view showing the tip shape of the terminal electrode of the 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 in 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 Step Part 21 Conductive Glass Seal Layer 22 Monolithic Resistor Layer 23 Conductive Glass Seal Layer 33 Shaft Part 35 Recess 41 Conductive glass powder 42 Electric resistance glass powder 43 Conductive glass powder 51 Recessed portion 54 Recessed portion 57 Recessed portion

Claims (4)

[Claims] 1. A mixture of at least a resistor powder and a glass powder, which is (a) an insulator having a shaft hole in an axial direction inside thereof, and (b) which is enclosed in the shaft hole and held by the insulator. A certain glass seal material, and (c) a terminal electrode which is inserted into the shaft hole and hermetically seals the gap between the insulator and the glass seal material, and which has a recessed portion at the tip surface which is recessed from the surroundings. Spark plug for internal combustion engine. 2. The spark plug for an internal combustion engine according to claim 1, wherein the outer diameter of the terminal electrode is A (mm) and the depth of the recess is D.
(Mm), a spark plug for an internal combustion engine, which satisfies the relationship of A / 10 ≦ D ≦ A / 2. 3. The spark plug for an internal combustion engine according to claim 1, wherein the outer diameter of the terminal electrode is A (mm) and the depth of the recess is D.
(Mm), a spark plug for an internal combustion engine, which satisfies the relationship of A / 5 ≦ D ≦ A / 2. 4. (a) Inserting a center electrode into the shaft hole of an insulator and locking it to a step, and filling the shaft hole with a glass sealing material which is a mixture of at least resistor powder and glass powder. And (b) in a state where the entire glass-ceramic material is melted by heating the entire insulator, a tip surface in which a recessed portion that is recessed from the surroundings is formed is formed in the shaft hole of the insulator. A method of manufacturing a spark plug for an internal combustion engine, comprising the step of first inserting the terminal electrode and pressurizing the glass sealing material.