JPH09264535A - Spark plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a firing part from being rendered to arc creepage by raising voltage of the arc creepage. SOLUTION: This spark plug A includes a main fitment 1 having a fitment shelf 11, an electrical insulator 2 fixed in the main fitment 1 for stopping a seat surface 21 in a rear slope 111 through a packing 12, and a central electrode 3 fixed in a shaft hole 20. The central electrode 3 has a diameter reduction stage 31 located by Mmm(M>=1.6mm) interioly from an insulator tip end surface 22, a diameter ϕD2 from the diameter reduction stage 31 to an electrode tip end surface 32 being smaller (0.3mm or more) than an original diameter ϕD1 .

Description

Detailed Description of the Invention

[0001]

The present invention relates to a spark plug mounted on an internal combustion engine.

[0002]

2. Description of the Related Art Generally, a spark plug has a seat surface 5 through a ring-shaped packing 501 for hermetically supporting it.
02 is locked to the rear slope 504 of the metal rack 503. Then, the metal shell 5 is inserted through the ring 505 and the talc 506.
By tightening the rear end portion 508 of 07, the shaft hole 509
An insulator 511 having the center electrode 510 fixed therein is fixed in the metal shell 507 (see FIG. 10).

[0003]

In the above-described conventional spark plug D, spark discharge does not occur in the regular spark gap 512, and the ignition portion insulator 513 as shown by the arrow 500.
May jump sideways (creeping part creeping discharge). The occurrence of this creeping discharge creeping part causes engine malfunction such as engine stall, idle instability, engine start failure at low temperature, and poor acceleration. In addition, the insulator 5
Spark plug D due to scraping of 11 or abnormal combustion
The durability is reduced. Furthermore, if the ignition part insulator 513 is broken by the creeping discharge of the ignition part and falls into the engine, the engine is damaged.

The inventors investigated the susceptibility of creeping discharge to the sparking part of various spark plugs. As a result, the spark plug having the structure and the spark plug (-) used in the gas engine particularly discharge to the sparking part. I found that it was easy to get up.

A spark plug with a short leg length. Spark plug for use in engines with high compression ratio. Spark plug that ignites gaseous fuel (requires high discharge voltage). Spark plug with a wide spark gap 512 (high discharge voltage required).

A first object of the present invention is to provide a spark plug in which the creeping discharge voltage at the ignition part is increased to prevent the creeping discharge at the ignition part. A second object of the present invention is to provide a spark plug for a gas engine, in which the creeping discharge voltage at the ignition part is increased to prevent the creeping discharge at the ignition part.

[0007]

In order to solve the above-mentioned problems,
The present invention employs the following configuration. (1) In a spark plug having a tubular metal shell, an insulator with a shaft hole fixed in the metal shell, and a center electrode fixed in the shaft hole so that the tip projects from the insulator tip surface. , The center electrode is 1.6 mm from the insulator tip surface.
As described above, there is a diameter reduction step, and the diameter from the diameter reduction step to the electrode tip surface is made 0.3 mm or more (smaller than the original diameter of the center electrode).

(2) It has a tubular metal shell, an insulator with a shaft hole fixed in the metal shell, and a center electrode fixed in the shaft hole so that the tip projects from the insulator tip surface. In the spark plug, the insulator has a diameter increase step at a depth of 2.0 mm or more from the tip end surface of the insulator, and a shaft hole diameter from the diameter increase step to the insulator tip surface is 0.3 mm or more (the diameter of the shaft hole Larger than the diameter).

(3) It has a tubular metal shell, an insulator with a shaft hole fixed in the metal shell, and a center electrode fixed in the shaft hole so that the tip projects from the insulator tip surface. In the spark plug, the center electrode has a diameter reduction step 1.6 mm or more behind the insulator tip surface, and a diameter from the diameter reduction step to the electrode tip surface is 0.3 mm or more (from the original diameter of the center electrode). In addition, the insulator has a diameter increase step 2.0 mm or more deeper than the tip surface of the insulator, and the diameter of the shaft hole from the diameter increase step to the tip surface of the insulator is 0.3 mm or more ( Larger than the original diameter).

(4) The spark plug having any one of the structures (1) to (3) is mounted on a gas engine for use.

[0011]

[Operation and effect of the invention]

[Claim 1] The center electrode has a diameter reduction step at a depth of 1.6 mm or more from the insulator tip surface of the insulator, and the diameter of the center electrode from the diameter reduction step to the electrode tip surface is the original diameter of the center electrode. Since it is smaller than 0.3 mm, the insulation path (the tip of the center electrode-the inner wall of the metal shell in the gas volume) can be earned. As a result, the creeping discharge voltage on the ignition part becomes higher than that of the conventional one, and the creeping discharge on the ignition part can be prevented.

[0012] Therefore, the engine malfunction is eliminated because the sparks fly in the regular spark gap. Further, since the engine burns normally and the insulator is not scraped by the surface discharge of the ignition part, the durability of the spark plug is improved. It should be noted that the effect of improving the discharge voltage on the surface of the ignition part is that the position where the diameter reduction step is formed is 1.6 mm or more behind the insulator tip surface, and the diameter of the center electrode from the diameter reduction step to the electrode tip surface is 0.3 than the original diameter
Remarkably appears by making it smaller than mm.

[Claim 2] The insulator has a diameter step at a depth of 2.0 mm or more from the tip surface of the insulator, and the diameter of the shaft hole from the diameter increase to the tip surface of the insulator is larger than the base diameter of the shaft hole. 0.3 m
Insulation path (tip of center electrode-
Earn the metal shell inside the gas volume). As a result, the creeping discharge voltage on the ignition part becomes higher than that of the conventional one, and the creeping discharge on the ignition part can be prevented.

[0014] Therefore, the engine malfunction is eliminated because the spark is fired at the regular spark gap. Further, since the engine burns normally and the insulator is not scraped by the surface discharge of the ignition part, the durability of the spark plug is improved. In addition, the effect of improving the discharge voltage on the surface of the ignition part is that the formation position of the diameter-increasing step is 2.0 mm or more behind the insulator tip surface of the insulator, and the shaft hole diameter from the diameter-increasing step to the insulator tip surface is 0.3m larger than the hole diameter
It becomes noticeable by making it larger than m.

[Claim 3] The center electrode has a diameter reduction step 1.6 mm or more deeper than the tip surface of the insulator, and the diameter of the center electrode from the diameter reduction step to the electrode tip surface is defined as the original diameter of the center electrode. Is 0.3 mm or more smaller than that. In addition to this, the insulator has a diameter increase step 2.0 mm or more from the tip surface of the insulator, and the diameter of the shaft hole from the diameter increase to the tip surface of the insulator is 0.3 mm or more larger than the base diameter of the shaft hole. are doing. This allows
An insulating path (tip of the center electrode-inner wall of the metal shell in the gas volume) can be earned, the discharge voltage at the ignition part becomes higher than the conventional one, and the discharge at the ignition part can be prevented.

[0016] Therefore, the engine malfunction is eliminated because the sparks fly at the regular spark gap. Further, since the engine burns normally and the insulator is not scraped by the surface discharge of the ignition part, the durability of the spark plug is improved. The effect of improving the creeping discharge voltage on the ignition part is that the diameter reduction step is formed 1.6 mm or more deeper than the insulator tip surface, and the diameter of the center electrode from the diameter reduction step to the electrode tip surface is the original diameter of the center electrode. Is 0.3 mm or more smaller than the diameter, and the diameter increasing step is 2.0 mm or more deeper than the insulator tip surface, and the diameter of the shaft hole from the diameter increasing step to the insulator tip surface is 0. It becomes noticeable when it is larger than 3 mm.

[Claim 4] In the gas engine, the compression ratio in the combustion chamber is high, and it is necessary to apply a high voltage to the spark plug of high heat value (short leg length) mounted in the combustion chamber (ignition of gaseous fuel). Therefore, a creeping discharge is likely to occur in the ignition part. However, by applying the configuration of claim 1, claim 2, or claim 3, since it is possible to raise the creeping discharge voltage of the ignition part where the creeping discharge of the ignition part occurs, it is suitable as a spark plug for a gas engine. .

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention (Claim 1,
4) will be described with reference to FIGS. Figure 1,
As shown in 2, the spark plug A for gas engine is
Cylindrical metal shell 1 having a metal shelf 11 protruding inward
And an insulator 2 with a shaft hole 20 fixed in the metal shell 1 by locking the seat surface 21 to the rear slant surface 111 of the metal fitting shelf 11 via the ring-shaped packing 12, and the tip 30 of the insulator tip surface. The center electrode 3 fixed in the shaft hole 20 so as to project from the outer hole 22, and the outer electrode 4 protruding from the tip surface 13 of the metal shell 1.
And is screwed to the combustion chamber (not shown) of the gas engine via the gasket 15.

The metal shell 1 is made of low carbon steel, has a threaded portion 16 having a metal shelf 11 formed on the inner circumference and a screw 161 formed on the outer circumference, and a body portion 17 having a gasket 15 arranged on the front side.
And a hexagonal part 18 for fitting a plug wrench. In the present embodiment, the inner diameter of the metal shell 1 surrounding the leg length 23 is φ8.7, and the minimum inner diameter of the metal rack 11 is φ7.
It is set to 0 mm.

The insulator 2 is formed of a ceramic sintered body mainly composed of alumina, and has a leg length 23 located inside the screw portion 16 and a large diameter portion 24 located from the hexagonal portion 18 to the inside of the body portion 17. , A head 25 having a corrugation 251 formed on the outer circumference. A shaft hole 20 (φJ ₁ = 2.2) is formed along the axis of the insulator 2.

This insulator 2 has a metal packing 12
The seat surface 21 is locked to the rear slanted surface 111 via the ring, and the rear end portion 181 of the metal shell 1 is swaged via the rings 241, 242 and the sealing material 243, whereby the insulator tip 23
1 is fixed in the metal shell 1 so as to project from the tip surface 13.

In this embodiment, the insulator tip surface 22 has a diameter of φ4.
9, the base diameter (insulator diameter of the base of the leg length 23) is φ6.5, the length of the leg length 23 (ignition portion insulator length) is 9 mm, and the protruding length from the tip surface 13 is set to 1.5 mm.

The center electrode 3 (Ni alloy) is filled with a good heat-conducting metal such as copper or silver and has a protrusion length of 1.5 mm from the insulator insulator tip surface 22 and an original diameter φD ₁ of 2 mm and a spark gap. Is set to 0.8 mm. Further, the center electrode 3 is far from the insulator tip surface 22 by a distance M (M = 2.5 m).
m) has a diameter reduction step 31, and the diameter φD ₂ from the diameter reduction step 31 to the electrode tip surface 32 is formed to 1.65 mm, which is 0.35 mm thinner than the original diameter φD ₁ (2 mm).

The impact ionization effect is more likely to occur when the pointed side is on the negative side (spark discharge is more likely to occur and the discharge voltage can be lowered). A high voltage of negative polarity is applied.

The outer electrode 4 (Ni alloy) has a substantially L shape. The outer electrode 4 is resistance-welded to the tip surface 13 of the metal shell 1 so that the discharge portion on the inner surface of the tip faces the electrode tip surface 32.

In order to find the preferable range of the distance M, (the original diameter φD
₁ -diameter φD ₂ ) is fixed to 0.35 mm, and the distance M from the insulator tip surface 22 to the diameter reduction step 31 is 0.5 mm,
1.0 mm, 1.5 mm, 3.0 mm, and 6.0 mm
Other configurations include five types of spark plugs that are the same as the spark plug A, and (the original diameter φD ₁ −the diameter φD ₂ ) is 0.35 mm, and the distance M from the insulator tip surface 22 to the diameter reduction step 31 is Ten spark plugs A each having a size of 2.5 mm were manufactured, and the creeping discharge voltage (average value) at which the sparking portion creeping discharge started was measured. The results shown in the graph of FIG. 3 were obtained. Then, the measurement of the creeping discharge voltage at the ignition part is performed by raising the outer electrode 4 vertically or without attaching it from the beginning. It should be noted that the same test was carried out even if (original diameter φD ₁ −diameter φD ₂ ) was changed to another value, and it was found that the effect of improving the creeping discharge voltage at the ignition part was remarkably exhibited when the distance M ≧ 1.6 mm. .

Further, in order to obtain a preferable range of (original diameter φD ₁ -diameter φD ₂ ), the distance M from the insulator tip surface 22 to the diameter reduction step 31 is kept constant at 2.5 mm and (original diameter φD ₁ -diameter φD ₂ φD
₂ ) is 0.2 mm, 0.3 mm, 0.55 mm, and 0.75 mm, and other configurations are the same as the spark plug A. Four types of spark plugs and the distance M is 2.5 mm.
And, each of 10 spark plugs A each having (original diameter φD ₁ −diameter φD ₂ ) of 0.35 mm was manufactured, and the creeping part discharge voltage (average value) at which the sparking part creeping discharge started was measured. The results shown in the graph of FIG. 4 were obtained. still,
The same test is performed even if the distance M is changed to another value, and the original diameter φD
It was found that if ₁ -diameter φD ₂ ) ≧ 0.3 mm, the effect of improving the creeping discharge voltage of the ignition part is remarkably exhibited.

The spark plug A of this embodiment has the following advantages. The center electrode 3 is located at a distance M from the insulator tip surface 22.
A diameter reduction step 31 is provided only at the back (M = 2.5 mm), and a diameter φD ₂ from the diameter reduction step 31 to the electrode tip surface 32 is calculated as
It is formed to be 1.65 mm thinner than D ₁ (2 mm) by 0.35 mm.

For this reason, the insulating path between the tip of the center electrode 3 and the inner wall of the metal shell in the gas volume becomes long, and as shown in "spark plug A" in FIGS. The creeping discharge voltage on the ignition part can be made higher than that of the conventional one (20 kV → 23.5 kV), and the creeping discharge on the ignition part can be prevented. Therefore, the engine malfunctions are resolved because the sparks fly in the regular spark gap. Further, since the engine burns normally and the insulator 2 is not scraped by the creeping discharge of the ignition part, the durability of the spark plug is improved.

Next, a second embodiment of the present invention will be described.
4) will be described with reference to FIGS. FIG.
The spark plug B for a gas engine shown in 6 is different from the spark plug A in the following points, and other spark plugs A
Is the same as

In this embodiment, the porcelain insulator 2 is provided with a diameter increasing step 23 at a distance N (N = 3.0 mm) from the tip surface 22 of the porcelain insulator.
2, the diameter φJ ₁ of the shaft hole from the diameter increasing step 232 to the insulator tip surface 22 is 0.35 m from the diameter φJ _{2 of the} shaft hole 20.
It is formed to be m larger (φJ ₁ = 2.55).

In order to obtain a preferable range of the distance N, (diameter increase step 2
32 to the insulator tip surface 22 of the shaft hole diameter φJ ₁ )-(diameter φJ _{2 of the} shaft hole 20) is kept constant at 0.35 mm, and the distance N from the insulator tip surface 22 to the diameter reduction step 31 is 0.5 m.
m, 1.0 mm, 2.0 mm, 2.5 mm, and 6.0
mm, and the other configurations have the same five types of spark plugs as the spark plug B, and (φJ ₁ −φJ ₂ ) is 0.3.
A spark plug B having a length N of 5 mm and a distance N from the insulator tip surface 22 to the diameter increasing step 232 of 3.0 mm is 10
The samples were manufactured one by one, and the creeping discharge voltage (average value) at which the creeping discharge started, and the results shown in the graph of FIG. 7 were obtained. It should be noted that the same test was performed even when (φJ ₁ −φJ ₂ ) was changed to another value, and it was found that the effect of improving the creeping discharge voltage at the ignition part was remarkably exhibited when the distance N ≧ 2.0 mm.

In addition, (φJ₁-ΦJ_Two) Seeking a suitable range of
Therefore, the distance N from the insulator tip surface 22 to the diameter increasing step 232 is
Keep it constant at 3.0 mm ((φJ₁-ΦJ_Two), 0.2
mm, 0.3 mm, 0.55 mm, and 0.75 mm
However, the other configurations are the same as those of the spark plug B.
The distance N from the spark plug is set to 3.0 mm, and (φJ ₁
-ΦJ_Two) With a spark plug B of 0.35 mm
10 pieces of each are manufactured, and the creeping discharge starts at the ignition part.
The creeping discharge voltage (average value) of the
The results shown in the rough were obtained. In addition, the distance N is set to another value.
The same test is performed for (φJ₁-ΦJ_Two) ≧ 0.3mm
In that case, the effect of improving the discharge voltage on the surface of the ignition part becomes remarkable.
It has been found.

The spark plug B of this embodiment has the following advantages. Insulator 2 is separated from insulator tip surface 22 by distance N
Only at the back (N = 3.0 mm), there is a diameter increasing step 232, and the diameter of the shaft hole φJ from the diameter increasing step 232 to the insulator tip surface 22.
₁ is 2.55 mm, which is 0.35 mm larger than the diameter φJ ₂ of the shaft hole 20.

As a result, the insulation path becomes long, and the insulation path shown in FIGS.
As shown in "Spark plug B", the creeping discharge voltage at the ignition part where the creeping discharge at the ignition part starts can be made higher than that of the conventional one (around 20 kV → 24 kV), and the creeping discharge at the ignition part can be prevented. Therefore, the engine malfunctions are resolved because the sparks fly in the regular spark gap. Further, since the engine burns normally and the insulator 2 is not scraped by the creeping discharge of the ignition part, the durability of the spark plug is improved.

Next, a third embodiment of the present invention (claims 1 to 3)
4) will be described with reference to FIG. The spark plug C for a gas engine shown in FIG. 9 is the same as the spark plug A except for the following points.

In this embodiment, the diameter of the center electrode 3 is reduced 31 by a distance M from the insulator tip surface 22 (M = 2.5 mm).
And the diameter φ from the diameter reduction step 31 to the electrode tip surface 32
D ₂ is 0.35 mm larger than the original diameter φD ₁ (2.0 mm)
It is formed to be thin 1.65 mm. Also, insulator 2
Has a diameter increasing step 232 in the back (N = 3.0 mm) from the insulator tip surface 22 by N, and from the diameter increasing step 232 to the insulator tip surface 22.
The diameter φJ ₁ of the shaft hole is up to 0.35 mm larger than the diameter φJ _{2 of the} shaft hole 20 (φJ ₁ = 2.55).

As a result, the insulation path becomes longer, and the creeping discharge voltage at the firing part, where the creeping discharge at the ignition part starts, can be made higher than that of the conventional one (around 20 kV → 25.5 kV).
The spark plug C can prevent the creeping discharge on the ignition part. Therefore, the engine malfunctions are resolved because the sparks fly in the regular spark gap. Further, since the engine burns normally and the insulator 2 is not scraped by the creeping discharge of the ignition part, the durability of the spark plug is improved.

[Brief description of drawings]

FIG. 1 is a partial sectional view of a spark plug according to a first embodiment of the present invention.

FIG. 2 is an enlarged sectional view of a main part of the spark plug according to the first embodiment of the present invention.

FIG. 3 is a graph showing the relationship between the distance M from the tip surface of the insulator to the diameter reduction step and the discharge voltage on the creeping part.

FIG. 4 is a graph showing the relationship between (original diameter φD ₁ −diameter φD ₂ ) and the creeping discharge voltage of the ignition part.

FIG. 5 is a partial sectional view of a spark plug according to a second embodiment of the present invention.

FIG. 6 is an enlarged sectional view of a main part of a spark plug according to a second embodiment of the present invention.

FIG. 7 is a graph showing the relationship between the distance N from the tip surface of the insulator to the diameter reduction step and the creeping discharge voltage of the ignition part.

FIG. 8 is a graph showing the relationship between (φJ ₁ −φJ ₂ ) and the creeping discharge voltage of the ignition part.

FIG. 9 is an enlarged sectional view of a main part of a spark plug according to a third embodiment of the present invention.

FIG. 10 is an enlarged sectional view of a main part of a spark plug according to a conventional technique.

[Explanation of symbols]

1 Metal shell 2 Insulator 3 Center electrode 12 Packing 20 Shaft hole 22 Insulator tip surface 31 Diameter reduction step 32 Electrode tip surface 232 Diameter increase step D ₁ Center electrode original diameter D ₂ Diameter from diameter reduction step to electrode tip surface J ₁ Shaft hole diameter from the additional diameter to the insulator tip surface J ₂ Shaft hole diameter A, B, C Spark plug

Claims (4)

[Claims] 1. A spark having a tubular metal shell, an insulator with a shaft hole fixed in the metal shell, and a center electrode fixed in the shaft hole such that the tip projects from the insulator tip surface. In the plug, the center electrode has a diameter reduction step 1.6 mm or more behind the insulator tip surface, and a diameter from the diameter reduction step to the electrode tip surface is reduced by 0.3 mm or more. . 2. A spark having a tubular metal shell, an insulator with a shaft hole fixed in the metal shell, and a center electrode fixed in the shaft hole so that the tip projects from the insulator tip surface. In the plug, the porcelain insulator has a stepped diameter 2.0 mm or more deeper than the tip surface of the porcelain insulator, and a shaft hole diameter from the stepped diametrical step to the tip surface of the porcelain insulator is increased by 0.3 mm or more. Spark plug to do. 3. A spark having a tubular metal shell, an insulator with a shaft hole fixed in the metal shell, and a center electrode fixed in the shaft hole such that the tip of the metal shell is protruded from the tip surface of the insulator. In the plug, the center electrode has a diameter reduction step at a depth of 1.6 mm or more from the insulator tip surface, and a diameter from the diameter reduction step to the electrode tip surface is reduced by 0.3 mm or more, and the insulator is A spark plug having a step diameter increased 2.0 mm or more from the tip surface of the insulator, and a shaft hole diameter from the step diameter increase to the tip surface of the insulator is increased by 0.3 mm or more. 4. The spark plug according to claim 1, wherein the spark plug is mounted on a gas engine for use.