JP2001237045A - Spark plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a spark plug which is strong to 'smoke' and superior to ignitability with a long life. SOLUTION: A main air gap (α) is formed between a parallel ground electrode 11 and an apical surface of center electrode 2, and a semi-creepage gap (β) is formed between an end face 12C of semi-creepage ground electrode 12 and side circumferential face 2A of center electrode 2, and a semi-creepage insulator gap (γ) is formed between the end face 12C and circumferential face 1E of insulator 1. Then, the main air gap (α) and semi-creepage insulator gap (β) satisfy a relation of α<β, and the main air gap (α) and the semi-creepage insulator gap (γ) satisfy a relation of α>γ, and the main air gap (α) is α=1.1 mm or less, and the semi-creepage insulator gap (γ) is 0.5 mm<=γ<=0.7 mm, and a diameter difference (δ) between that of insulator and main metal fittings, is constituted to becomes 3.6 mm or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art A conventional spark plug comprises a center electrode projecting downward from a front end face of an insulator, and a parallel ground electrode disposed opposite to the center electrode and having one end joined to a metal shell. In general, a spark discharge is caused in the air gap between the center electrode and the parallel ground electrode to ignite the fuel mixture gas.

Further, in order to improve the ignitability in the air gap, Japanese Patent Application Laid-Open Nos.
JP-A-130454 proposes an arrangement in which, in addition to a parallel ground electrode facing the end surface of the center electrode, an auxiliary ground electrode facing the side peripheral surface of the center electrode is provided. These auxiliary ground electrodes are not intended to ignite the gap between the auxiliary ground electrode and the center electrode, but the presence of the auxiliary ground electrode improves the electric field distribution between the parallel ground electrode and the center electrode, resulting in lower discharge. A voltage is applied to the gap between the parallel ground electrode and the center electrode to improve the ignitability.
For this reason, these spark plugs are structurally such that the edge of the end face of the auxiliary ground electrode is not always located near the tip face of the insulator.

Further, Japanese Patent Application Laid-Open No. Hei 9-199260 proposes an arrangement in which an auxiliary ground electrode is provided near the front end surface of an insulator in addition to a parallel ground electrode facing the end surface of a center electrode.

[0005]

However, Japanese Patent Application Laid-Open No. 5-326107 and Japanese Patent Application Laid-Open No. 7-13045 described above.
All of the conventional spark plugs described in Japanese Patent Application Laid-open No. 4 (1999) have a problem that they are vulnerable to so-called "smoldering". During a steady operation in which the internal combustion engine is rotating at a predetermined temperature at a predetermined rotation speed or more, the temperature of the leg portion, which is a lower portion of the insulator of the spark plug, rises moderately, and the tip surface of the insulator located inside the combustion chamber. The nearby surface temperature rises to about 500 ° C. When the temperature rises to this extent, the carbon adhering to the surface of the insulator is burned and cleaned, so that the surface of the insulator is kept clean. Therefore, "smoldering" does not occur. However, when the temperature of the internal combustion engine is extremely low and the engine speed is low and the load is low, the temperature of the insulator surface does not rise and carbon due to combustion adheres and accumulates on the insulator surface, resulting in a so-called "smoldering" state. become. If this progresses further, the insulation between the center electrode and the ground electrode decreases, so that spark discharge becomes impossible, leading to engine stall.

The conventional spark plug described in Japanese Patent Application Laid-Open No. Hei 9-199260 discloses a conventional spark plug having a distance from a parallel ground electrode or an auxiliary ground electrode to a center electrode (main air gap or semi-surface gap), and an auxiliary ground electrode. The relationship between the distance from the end surface to the side surface of the insulator (semi-surface insulator gap) has not been clarified.

Further, Japanese Patent Application Laid-Open No. S59-71279 discloses a semi-creep plug in which a ground electrode is provided so as to face the side peripheral surface of the insulator. In this plug, the sparks run along the surface of the insulator, so that the carbon attached to the surface of the insulator is burned off, and the problem of "smoldering" does not occur much. However, because the sparks constantly run along the surface of the insulator, the insulator surface is damaged by the spark,
The so-called "channeling" problem arises. For this reason, there was a problem that the life of the spark plug was short.

Therefore, the present invention is strong against "smoldering",
It is another object of the present invention to provide a spark plug having excellent ignition performance.

[0009]

In order to achieve the above object, a spark plug according to the present invention has the following basic structure. That is, the spark plug of the present invention
An insulator having a center through-hole, a center electrode held in the center through-hole and disposed at a tip of the insulator, and a metal shell for holding the tip of the insulator so as to protrude from its own tip surface, A parallel ground electrode having one end joined to the distal end surface of the metal shell and the other end facing the distal end surface of the center electrode, and the main air gap is formed by the parallel ground electrode and the distal end surface of the center electrode. (Α) is formed. Also, a plurality of semi-creeping ground electrodes are provided, one end of which is joined to the metal shell and the other end is disposed so as to face the side peripheral surface of the center electrode or the side peripheral surface of the insulator. A semi-creeping gap (β) is formed between the end face of the other end and the side peripheral face of the center electrode facing this end face. A semi-surface insulator gap (γ) is formed between the end surface of the semi-surface ground electrode and the side peripheral surface of the insulator facing the end surface, and the distance α between the main air gap (α) and The semi-creeping gap (β) distance β satisfies the relationship α <β. Further, the distance α of the main air gap (α) and the distance γ of the semi-surface insulator gap (γ) satisfy the relationship α> γ.

When formed in this manner, the distance α of the main air gap (α) is smaller than the distance β of the semi-creeping gap (β) (α <β). A spark discharge occurs in the main air gap (α) between the parallel ground electrode. On the other hand, the distance γ of the semi-surface insulator gap (γ) is smaller than the distance α of the main air gap (α) (γ <α). Therefore, "smoldering" in which the tip surface of the insulator is contaminated by carbon generated by combustion
In this state, a spark discharge is generated between the edge of the semi-surface ground electrode and the side peripheral surface of the center electrode via the surface of the front end surface of the insulator (hereinafter, referred to as semi-surface discharge). The spark of the semi-creeping discharge runs along the surface of the insulator after flying over the semi-creeping insulator gap (γ) (or vice versa if the voltage polarity is reversed). After several semi-surface discharges, the carbon deposited on the tip surface of the insulator is burned off and the surface of the insulator returns to a clean state. Then, the spark discharge returns from the semi-surface gap (β) to the main air gap (α). In the present specification, the distance β of the semi-surface gap (β) is defined as the direction perpendicular to the axis of the spark plug between the side peripheral surface of the center electrode and the semi-surface surface ground electrode at the position of the front end surface of the insulator. Say the minimum distance. The distance γ of the semi-creep insulator gap (γ) refers to the shortest distance between the insulator and the semi-creep ground electrode.

In the spark plug having the above basic structure, spark discharge occurs in the main air gap (α) between the spark plug and the parallel ground electrode almost all the time, and the surface of the insulator is smoldered by carbon. Only in the state of (1), a semi-surface discharge occurs in the semi-surface gap (β) between the semi-surface ground electrode and the mixed gas in the combustion chamber to ignite. Most of the time, the mixed gas is ignited by the spark discharge in the main air gap (α), so that the ignitability is excellent. In addition, since the semi-creeping discharge has a self-cleaning effect of burning off carbon deposited on the surface of the insulator, the spark plug is extremely resistant to "smoldering". Furthermore, since the semi-surface discharge does not occur frequently and the discharge time is completed in a very short time, the effect of "channeling" due to sparks is weakened, and almost no channeling occurs. Therefore, the life of the spark plug is sufficiently long.

As shown in FIG. 23, when the spark plug (100) of the present invention having two semi-creeping ground electrodes (12, 12) is attached to the direct injection type internal combustion engine (150), It is preferable that the semi-creeping ground electrodes (12, 12) are located in the middle direction between the intake valve (201) and the exhaust valve (203).

In the example shown in FIG. 23, a virtual reference plane (SP) including the center axis (O) of the spark plug (100) attached to the cylinder head (S) and a center axis (O) are also included. When a virtual auxiliary reference plane (CSP) orthogonal to the reference plane (SP) is considered, the reference plane (S
P) and intake valves (201, 20) on one side
1) has an exhaust valve (203, 20) on the other side.
3) are arranged in a positional relationship such that the distances from the reference plane (SP) are substantially equal. The intake valve (201, 201) and the exhaust valve (20
3, 203), two each for convenience are arranged on both sides of the auxiliary reference plane (CSP). In this case, the semi-creeping ground electrode (12) has a substantially reference plane (SP) so that the base position of attachment to the metal shell (5) is closer to the reference plane (SP) than to the auxiliary reference plane (CSP). ). In addition, the parallel ground electrode (11)
Is the reference plane (SP) when the base position of the attachment to the metal shell (5)
Here, it is arranged so as to be closer to the auxiliary reference plane (CSP), so that it is located substantially on the auxiliary reference plane (CSP).

The mounting direction of the spark plug (100) as described above is different from the mounting direction of a general spark plug having only a parallel ground electrode. That is, the internal combustion engine (1
The flow direction of the intake air in the combustion chamber (CR) of 50) flows from the intake valve (201) to the exhaust valve (203). According to the study by the present inventors, the cavity is formed by the piston ( The vertical flow (tumble) due to the eccentric existence on the intake valve side including the center portion of P), and the lateral flow generated in the cavity direction from the periphery of the combustion chamber (CR) wall by the rise of the piston (P). In the spark plug (100) of the present invention applied to a direct injection type internal combustion engine that needs to consider the flow in the direction (squish), the spark plug (100) can be directed in a direction that can ensure the ignitability of the semi-surface creeping ground electrode (12). It turned out to be important. Therefore, if the spark plug (100) is attached in the above positional relationship,
The spark generated by the semi-surface ground electrode (12), which is susceptible to squish because it is located close to the combustion chamber wall surface, has a shape that ignites in a direction that is almost perpendicular to the flow of the intake air.

In particular, two semi-surface creeping ground electrodes (12, 12) are located at 90 ° on both sides with respect to the parallel ground electrode (11).
In the spark plug (100) of the type having the above, it is particularly effective to direct the welded portion of the parallel ground electrode (11) to the metal shell (5) toward the intake valve (201). That is, the direction in which the parallel ground electrode (11) is not welded to the metal shell (5) may be directed toward the exhaust valve (203). Since the spark by the parallel ground electrode (11) is affected by both the tumble and the squish, the spark flows from the oblique tip end side of the spark plug. Since the flow of the intake air is a considerably large flow, if the flow is directed in the opposite direction, the spark flows to a position where the parallel ground electrode (11) does not exist during the generation of the spark, so that the flow tends to be interrupted. By arranging in this way, even if a spark is swept, the parallel ground electrode (11)
Because of the presence of, it is hard to be interrupted on the way and the ignitability is hardly reduced.

The intake valves (201, 20)
1) and the exhaust valves (203, 203) are each 2
Type internal combustion engine (ie, a four-valve internal combustion engine)
Then, the intake valves facing each other (201,
01) and the exhaust valve (203, 203) may be applied to the above idea. That is, the following can be considered. Generally, in a four-valve internal combustion engine, when viewed from the front of the internal combustion engine, one side of a pent roof type cylinder head (S) having a triangular roof shape (that is, a reference surface (S
Intake valve 2 on either side of P)
(201, 201), and two exhaust valves (203, 203) are arranged on the other side. Further, the intake valve (201) and the exhaust valve (203) on the same side with respect to the auxiliary reference plane (CSP) have a shape facing each other with the reference plane (SP) interposed therebetween. Then, with respect to the center axis (O), the spark plug ( 100) can be attached.

The inventors of the present invention have examined the spark plug having the above-described basic structure. According to the study, the spark generation position cannot be uniquely determined by the simple magnitude relationship between the electrodes. It has been found that sparks may occur even in a place where the distance is large depending on the conditions (hereinafter, this phenomenon is referred to as "reversal spark phenomenon" in the present specification). When this phenomenon occurs, "smoldering"
In the case of occurrence of a spark, a spark is generated between the front end face of the metal shell and the insulator, not a spark at the semi-surface insulator gap (γ), which should be expected (hereinafter, in this specification, Are referred to as “metal fittings / insulator sparks”). Some configurations of the spark plug according to the present invention provide specific means for solving problems such as a metal fitting / insulator spark based on a reversal spark phenomenon.

For example, the ability to prevent metal fittings / insulator sparks is very effective especially in a stratified combustion type direct injection internal combustion engine. That is, in the direct injection type internal combustion engine, the spark is easily generated between the front end face of the metal shell and the insulator, so that the ignitability tends to decrease. This is considered to be largely due to the position where the spark is generated. That is, in the stratified combustion type internal combustion engine, the layer of the rich mixture in the combustion chamber is in a very narrow range, and outside the range, the mixture becomes very thin. Whether or not a spark can be reliably blown to the rich air-fuel mixture layer is the key to the success or failure of normal ignition of the air-fuel mixture. That is, when a rich mixture layer can reliably generate a spark at this position when it reaches between the center electrode and the ground electrode, which is the regular spark discharge gap of the spark plug, the spark ignites the mixture. can do.

However, as already described, since the rich mixture layer is formed only in a very narrow range, no spark is generated in the regular spark discharge gap, and the regular spark discharge gap, such as a metal fitting / insulator spark, is generated. Other positions (ie,
If a spark is generated in the vicinity of the wall of the combustion chamber), the air-fuel mixture at this position is very thin. It is. If a spark is generated at such a position near the wall surface of the combustion chamber, a misfire occurs in the combustion cycle, so that the output of the internal combustion engine is reduced and the unburned mixture is discharged from the exhaust pipe. Therefore, emission regulations may not be satisfied. In addition, the unburned gas will not be exhausted from the exhaust pipe and will adhere to the wall of the combustion chamber, and will also adhere to the spark plug. It is even less likely to occur.

Therefore, if sparks can be reliably generated at the main air gap (α) or semi-creepage gap (β) by preventing the reversal spark phenomenon and, hence, the metal fitting / insulator spark, if "smoldering" occurs. In this case, it is possible to burn off "smoldering" by generating a spark at the semi-surface creeping ground electrode. Further, even in a direct injection type internal combustion engine, if a spark is generated at the semi-surface ground electrode, the ignition is in a rich mixture, so that a decrease in ignitability can be suppressed. However, in the prior arts such as the above-mentioned Japanese Patent Application Laid-Open No. 9-199260, there has been no specific proposal regarding improvement of the spark plug from such a viewpoint.

On the premise of the above, further detailed configurations of the spark plug of the present invention will be described below. First, in the first configuration, in addition to the basic configuration described above, the main air gap (α) is α ≦ 1.1 mm (1−); and the semi-creep insulator gap (γ) is 0.5 mm ≦ γ ≦ 0. 0.7mm
(1-); the diameter difference δ between the insulator and the metal shell at the position of the front end face of the metal shell is δ ≧ 3.6 mm (1-
) ;.

As a result of extensive studies by the present inventors, in the spark plug having the basic structure, the main air gap (α), the semi-surface insulator gap (γ), and the diameter difference between the insulator and the metal shell ( δ) is above (1-) to (1-
Satisfies the relationship, for example, even when "smoldering" occurs, the above-described reversal spark phenomenon and, consequently, metal fittings /
It has been experimentally demonstrated for the first time that an insulator spark is effectively suppressed and a spark can be reliably generated in a semi-surface insulator gap (γ), and the invention of the first configuration has been completed.

The size of the main air gap (α) can be set to various values in design according to the required level of ignitability, the air-fuel ratio of the air-fuel mixture, and the like. In addition, since the semi-creep insulator gap (γ) also needs to satisfy the relationship of α> γ,
It is set to an appropriate range according to the size of the main air gap (α). In the spark plug of the first configuration, it is assumed that the main air gap (α) and the semi-creep insulator gap (γ) are set within the range of (1-) and (1-). I do. Under this premise, the gist of the first configuration is that the diameter difference δ between the insulator and the metal shell at the position of the metal shell tip surface is in the range of (1-). That is, by setting the diameter difference (δ) in this way, even if “smoldering” occurs, if a spark is generated at the semi-surface creeping ground electrode, it is possible to burn off fouling deposits on the insulator. In addition, even in a direct injection type internal combustion engine, if a spark is generated at the semi-surface ground electrode, it is possible to suppress a decrease in ignitability since the mixture is in a rich mixture. Note that the distance α of the main air gap (α) cannot be reduced indefinitely, and may be set to, for example, 0. It is effective to secure a length of 6 mm or more (this is the same in a spark plug according to another configuration of the present invention). Also, the diameter difference (δ) cannot be increased without limit, and the metal shell
In consideration of ensuring the strength of the center electrode and ensuring the withstand voltage of the insulator, it is effective to set the thickness to, for example, 5.4 mm or less, and desirably to 5.0 mm or less (this is another configuration of the present invention). The same applies to the spark plug according to (1).

The spark plug according to the second configuration has a main air gap (α) of 0.8 m in addition to the basic configuration described above.
m ≦ α ≦ 1.0 mm (2-), and the semi-creep insulator gap (γ) is 0.5 mm ≦ γ ≦ 0.7 mm (2)
−), The main air gap (α) and the semi-surface insulator gap (γ) are 0.2 mm ≦ (α−γ) ≦ 0.4 mm (2-
). Note that the invention of the second configuration can be combined with the invention of the first configuration.

In the spark plug having the above configuration, the main air gap (α) is generated for the purpose of reducing the spark generation voltage.
Is set to a somewhat narrow range such as (2-), and the semi-creep insulator gap (γ) is set to a range of (2-) (similar to the first configuration described above). At this time, the relationship between the main air gap (α) and the semi-creep insulator gap (γ) (α−
By setting γ) in the range of the above (2-),
The inversion spark phenomenon and, consequently, the metal / insulator spark can be effectively suppressed. Further, as a new effect, particularly in a direct injection type internal combustion engine, it is possible to widen the region of the injection end timing in which misfire does not occur.

In general, in an internal combustion engine, the ignitability improves as the main air gap (α) increases. However, when the main air gap (α) is widened, the discharge voltage increases. In a direct injection internal combustion engine, "smoldering" is very likely to occur, so "smoldering" occurs even during normal operation. In a state where such “smoldering” occurs, a high discharge voltage increases the possibility of causing a misfire.
That is, in the direct injection type internal combustion engine, it is considered that the ignition timing at which a spark is generated in the spark plug at the crank angle and the end timing of the fuel injection are set such that the wider the range in which no misfire occurs, the better the ignitability.

In the direct injection type internal combustion engine, the rich mixture region immediately after the injection gradually diffuses while moving in the combustion chamber. The mixture region tends to diffuse and become thin. Therefore, it is necessary to ignite in a thin air-fuel mixture region. However, since the air-fuel mixture is thin, the discharge voltage increases even in the same gap. On the other hand, as described above, since the spark plug is normally in the state of "smoldering", the spark, that is, the metal /
Insulator sparks are more likely to occur and, as a result, misfires are more likely to occur. Conversely, the later the fuel injection end time is, the more sparks are generated in the rich mixture. In this state, stable combustion occurs, but due to the rich mixture,
Even if combustion is stable, "smoldering" is more likely to occur. As a result, a spark is generated between the metal shell and the insulator, which may cause a misfire.

That is, according to the study by the present inventors, in a general internal combustion engine, the ignitability increases as the main air gap (α) increases, but in a direct injection internal combustion engine, the gap increases. Therefore, it was found that the discharge voltage was increased, and the ignitability was rather lowered.
In the invention of the second configuration, the main air gap (α) and the semi-surface insulator are set to appropriate ranges shown in (2-), and the main air gap (α) and the semi-surface insulator are set. By appropriately setting the relationship with the gap (γ) in the range shown in (2-), generation of sparks between the tip surface of the metal shell and the insulator is suppressed, and the stable combustion region is widened. You can do it.

It is desirable to widen the stable combustion region for the following reasons. That is, in the direct injection type internal combustion engine, the ignition timing and the fuel injection timing are controlled so as to be constant with respect to the operating conditions. There is a case where the change in atmosphere does not match. In such a state, the air-fuel mixture around the spark plug may become thin or thick due to a transient phenomenon such as a shift in the fuel injection timing or a shift in the ignition timing. When the fuel injection timing and the ignition timing tend to separate from each other, the air-fuel mixture becomes thin, so that the discharge voltage increases. Further, when the injection timing and the ignition timing tend to approach each other, a spark is generated in a richer mixture, so that the smoldering is further advanced. For this reason, by using a spark plug having a characteristically wide stable combustion region, good combustion can be ensured without causing misfire even in such a transient phenomenon.

The width of the parallel ground electrode at the position of the center point of the center electrode when the front end of the insulator is planarly viewed from the front in the axial direction is 2 mm. .2 mm or less, and preferably at least twice the outer diameter of the front end surface of the center electrode. By setting such a dimensional relationship, the discharge voltage can be reduced, and the fuel is held between the center electrode and the ground electrode while ensuring ignitability.
A so-called bridge can be hardly generated.

The third configuration is, in addition to the basic configuration described above,
The main air gap (α) is α ≦ 0.9 mm (3-
), Semi-creep insulator gap (γ) is 0.5mm ≦ γ ≦
0.7 mm (3-), and the diameter difference δ between the insulator and the metal shell at the position of the front end face of the metal shell is 2.8 mm.
The above is (3-). The third configuration can be combined with at least one of the first and second configurations.

In the spark plug of the third configuration, it is assumed that the main air gap (α) and the semi-creep insulator gap (γ) are set within the ranges of (3-) and (3-). And For the same reason as in the second configuration, the main air gap (α) is (1−1) in the first configuration.
). Under this premise, by setting the diameter difference (δ) between the insulator and the metal shell at the position of the metal shell tip end surface in the range of (3-), even when “smoldering” occurs. If a spark is generated at the semi-creeping ground electrode, it is possible to burn off fouling deposits on the insulator. Further, even in a direct injection type internal combustion engine, if a spark is generated at the semi-surface ground electrode, the ignition is in a rich mixture, so that a decrease in ignitability can be suppressed.

The fourth configuration is similar to the basic configuration described above.
The main air gap (α) is α ≦ 1.1 mm (4-
), The semi-creep insulator gap (γ) is 0.5 mm ≦
γ ≦ 0.7 mm (4-), and the number of the semi-creeping ground electrodes provided is 3 or more (4-),
It is characterized by. The fourth configuration can be combined with at least one of the first to third configurations.

In the spark plug according to the fourth configuration, the setting ranges (4-) and (4-) of the main air gap (α) and the semi-surface insulator gap (γ) are determined according to the first configuration. Are the same as (1-) and (1-). The first configuration is different from the first embodiment in that the number of the semi-surface ground electrodes is three or more. The aim is to reduce the frequency of occurrence of phenomena and thus of metal / insulator sparks.

That is, an increase in the number of semi-surface ground electrodes provided means that the probability of spark generation at the semi-surface ground electrodes is increased. Therefore, even if the ambient condition around the spark plug is such that if the number of semi-creeping ground electrodes is small, metal fittings / insulators may ignite, more semi-creeping grounding electrodes are located close to the front end face of the metal shell. By doing so, even when "smoldering" occurs, sparks can be reliably generated at the semi-surface creeping ground electrode, and contaminants adhering to the "smoldering" can be burned off. Further, even in a direct injection type internal combustion engine, if a spark is generated at the semi-surface ground electrode, the ignition is in a rich mixture, so that a decrease in ignitability can be suppressed.

When the spark plug is mounted on the internal combustion engine, the distal end of the insulator is cooled by the relatively low temperature intake air drawn into the combustion chamber from the intake valve. As the number of surface ground electrodes increases, the tip of the insulator may be hidden behind the semi-surface ground electrode, making it difficult to cool. This causes pre-ignition. Therefore, it is desirable to reduce the number of semi-creeping ground electrodes to four or less in consideration of this. In the fourth configuration, it is possible to configure so as to satisfy the numerical range (1-) of the diameter difference δ in the first configuration.

In the spark plug of the fifth configuration,
In addition to the basic configuration described above, the insulator has a straight tubular portion at the front end thereof, and when the side where the front end is located in the axial direction of the insulator is the front side, the rear end position of the straight tubular portion is semi-conductive. The rear end side edge of the end surface of the creeping ground electrode coincides or is on the front side, and in the axial direction between the height position of the front end surface and the height position of the rear end side edge of the end surface of the semi-creeping ground electrode Step E
(Unit: mm) and the difference between the radius of curvature R (unit: mm) of the curved surface from the tip end surface of the insulator to the side peripheral surface is expressed as RE ≦≦
(5) which is 0.1 mm.
The fifth configuration can be combined with at least one of the first to fourth configurations. Here, step E
Is defined as a positive direction in the direction of the center axis of the insulator toward the front end. Therefore, when the height position of the front end surface of the insulator is on the front end side (front side) from the height position of the rear end side edge of the semi-creeping ground electrode end surface, the step E becomes a positive number, and Is a negative number.

According to the fifth configuration, the spark from the rear edge of the semi-surface ground electrode toward the center electrode is blocked by the front end portion of the insulator, so that the center of the spark is generated from the spark generation position of the semi-surface ground electrode. No spark is generated on the straight line toward the electrode,
It is bent in the circumferential direction of the insulator. As a result, the discharge path of the spark changes each time a spark is generated, so that the range of the spark crawling on the front end surface of the insulator can be widened, channeling can be reduced, and "smoldering" can be reduced over a wide range. it can.

In the case of a spark that is bent in the circumferential direction of the insulator, the discharge path becomes longer and the spark generation voltage becomes higher.
In an attempt to avoid such sparks, the sparks tend to increase on the front edge side where the attack on the insulator is softer than on the rear edge of the semi-surface ground electrode. Therefore, this also contributes to the suppression of channeling. In addition, the spark on the front edge side is also effective for improving the ignitability, and it is possible to effectively suppress problems such as misfire. In particular, when the above-mentioned step E, that is, the wrap length between the semi-surface ground electrode end surface and the insulator side peripheral surface in the central axis direction is small, sparks on the rear end side edge side of the semi-surface ground electrode are generated. It becomes inevitably occurs easily because the sparks distance is relatively small. However, by increasing the radius of curvature R of the curved surface from the front end surface to the side peripheral surface of the insulator so that the above-mentioned relationship (5-) is satisfied, the frequency of sparks on the front edge side can be increased. And contributes to suppression of channeling or improvement of ignitability. Specifically, in the case of a spark plug having a small wrap length, in which the length of the step E is 0.5 mm or less, this configuration has a particularly large ripple effect. The lower limit of the value of E is appropriately determined within a range in which semi-creeping discharge is not disabled. For example, when the value is a negative number as shown in FIG. 4, the absolute value is set to be smaller than the main air gap α. Is done.

In this configuration, a straight tubular portion is formed on the insulator. By making the tip of the insulator a straight tube, it has the effect of suppressing heat received at the tip during the combustion cycle in the internal combustion engine from going to the holding part of the insulator with the metal shell. The temperature of the tip of the insulator can be easily increased. Therefore, even in a direct injection type internal combustion engine in which the temperature does not easily rise during normal operation, the temperature at the tip of the insulator can be easily increased, and fouling deposits such as carbon deposited by smoldering can be burned off. It will be easier. In addition, with such a configuration, since the heat volume at the distal end of the insulator is small, the insulator is easily cooled by relatively low-temperature gas sucked from the intake pipe. For this reason, during the combustion cycle in the internal combustion engine, the temperature rise such that preignition occurs hardly occurs.

If the rear edge of the end surface of the semi-surface creeping ground electrode is on the rear side of the rear end position of the straight tubular portion, it is difficult to set the dimension of the gap. On the other hand, the positional relationship is set such that the rear end side edge of the end surface of the semi-surface creeping ground electrode coincides with this or is on the front side. On the other hand, if the length of the straight tubular portion is excessively long, sparks generated at the semi-creeping ground electrode are likely to droop greatly to the rear side along the straight tubular portion, and the ignitability is impaired. May lead to If the length of the straight tubular portion is not at least 0.5 mm or more, it is difficult to set the dimension of the gap, and the above effect may not be sufficiently obtained. The length of the straight tubular portion is desirably set in the range of 0.5 mm or more and 1.5 mm or less.

In the spark plug of the sixth configuration,
In addition to the basic configuration described above, a JIS standard (JIS: B803) for a spark plug to which this spark plug is applied.
1) Or ISO displayed corresponding to the JIS standard
Standards (ISO 1910, ISO 2704, ISO 234
6, ISO / DIS8479, ISO2705, ISO
2344, ISO2345, ISO2347, ISO3
412), the amount of protrusion F of the insulator projecting to the tip side from the dimension A is 3.0 mm ≦ F ≦ 5.0 mm
(6-). The sixth configuration includes:
It can be combined with at least one of the first to fifth configurations.

According to the sixth configuration, by setting the protrusion F of the insulator in the range of (6-), it is possible to improve the ignitability to the air-fuel mixture and to raise the temperature of the tip of the insulator. it can. Further, compared with the spark generation position, the concentration of the air-fuel mixture is extremely low at the position between the tip end surface of the metal shell and the insulator, but the protrusion amount F of the insulator is (6-).
In this range, the voltage required to generate a spark rises between the distal end surface of the metal shell and the insulator where the air-fuel mixture becomes thinner in this manner, and the generation of a spark at this position is further suppressed. be able to. As a result, it is possible to widen the range of the fuel injection end timing that does not cause misfire.

In the spark plug of the seventh configuration,
In addition to the basic configuration described above, the main air gap (α) is α
≦ 1.1 mm (7−), and the semi-creep insulator gap (γ) is 0.5 mm ≦ γ ≦ 0.7 mm (7−).
), A first extension line extending outward from a line indicating the tip surface when the insulator is represented by an orthogonal projection with respect to a virtual plane parallel to the axis of the insulator, and a semi-creep gap of the insulator. The distance between the intersections of the two lines extending from the two lines indicating the side peripheral surfaces on both sides of the axis facing the (β) portion toward the tip surface (hereinafter simply referred to as “insulator”) The difference between the tip diameter “φD (unit: mm)” and the width of the semi-surface creeping ground electrode.
(Unit: mm) is ψ ≦ 1.8 mm (7−),
It is characterized by the following. The seventh configuration can be combined with at least one of the first to sixth configurations.

By reducing the difference ψ between the insulator tip diameter φD and the width of the semi-creeping ground electrode, it is possible to prevent the spark generated at the semi-creeping ground electrode from easily drooping greatly toward the rear side of the insulator. be able to. As a result,
It is possible to widen the range of the fuel injection end timing that does not cause misfire, and it is possible to improve the ignitability in the fuel lean state. When this difference is large, when a spark is generated between the semi-surface creeping ground electrode and the center electrode, it goes around the outer periphery of the distal end portion of the insulator greatly. This is considered for the following reason. That is, when a spark is generated obliquely rearward from the rear corner of the end surface of the semi-surface creeping ground electrode, the spark reaches the center electrode after hitting the tip of the insulator. When the spark collides with the tip of the insulator, the spark crawls obliquely rearward along the outer peripheral surface, and then changes direction and crawls in the direction of the peripheral surface on the center electrode tip side. Therefore, when the difference between the diameter of the insulator tip and the width of the semi-surface creeping ground electrode is large, the amount of spark crawling obliquely rearward along the outer peripheral surface of the insulator becomes large, and it is considered that the spark droops greatly.

The difference ψ between the distance between the intersection of the first extension line and the two second extension lines and the width of the semi-creeping ground electrode is (7)
In order to satisfy the relationship of-), the first extended line and the second extended line obtained by extending the line indicating the side peripheral surface facing the semi-creep gap (β) portion of the insulator in the direction of the front end surface are required. From the intersection,
The insulator tip thickness ρ defined as the shortest distance to the intersection of the first extension and the extension of the center through hole is ρ ≦ 0.
It is preferably 9 mm (7-). When this relationship is satisfied, the thickness of the insulator tip can be reduced, so that the discharge voltage can be reduced due to the concentration of the electric field and the discharge voltage at the semi-creep gap (β) can be suppressed to reduce the channeling. Reduction is possible. Further, the temperature at the tip of the insulator is easily increased, so that the effect of improving the self-cleaning property in the direct injection type internal combustion engine in which smoldering tends to occur is great. In addition, since the insulator can be made thinner as a whole, the gap between the metal shell and the insulator can be kept wide especially in a spark plug having a small diameter. If the thickness of the insulator is too thin, the possibility of penetration of the insulator increases. Therefore, the thickness ρ of the insulator tip is preferably set to ρ ≧ 0.6 mm, and more preferably ρ ≧ 0.6 mm. It is good to be 0.7.

In the spark plug of the eighth configuration,
In addition to the basic structure described above, the amount H of the center electrode protruding from the front end surface of the insulator is H ≦ 1.25 mm (8−). The eighth configuration can be combined with at least one of the first to seventh configurations.

In particular, in a direct injection type internal combustion engine, when a spark is generated in the semi-creep gap (β) during high-speed operation, the range of the fuel injection end timing at which no misfire occurs becomes narrower. However, according to the eighth configuration, the main air gap (α), which is a regular spark discharge gap, is selected by selecting the amount H at which the center electrode projects from the front end surface of the insulator as (8−). And the spark generation position by the semi-surface ground electrode can be further reduced. Therefore, even a direct-injection internal combustion engine in which a difference in ignitability easily occurs depending on the spark generation position, has a sufficient ignitability at the spark position at the semi-surface ground electrode generated when "smoldering" occurs. The amount H of the center electrode protruding from the front end surface of the insulator is
When H ≦ 0.5 mm, the propagation path of the spark formed around the center electrode is easily dispersed, and the channeling resistance and the cleanliness against “smoldering” can be improved. H is a negative number, that is, the center electrode may be recessed from the front end surface of the insulator. In this case, H ≧ −
0.3 mm (withdrawal depth of 0.3 m
m) is desirable for further improving the channeling resistance and the “smoldering” cleaning effect.

In the ninth configuration of the spark plug,
In addition to the basic configuration described above, the main air gap (α), semi-creep gap (β), and semi-creep insulator gap (γ) have a relationship of α ≦ 0.4 × (β−γ) + γ (9−). Is satisfied. The ninth configuration can be combined with at least one of the first to eighth configurations.

As described above, when the main air gap (α), the semi-creeping gap (β) and the semi-creeping insulator gap (γ) satisfy the above-mentioned relationship (9-), the reversal spark and the metal fitting / insulator are obtained. The problem of sparks can be effectively suppressed. By satisfying the relationship of (9-), when the atmosphere gas around the gap of the spark plug has a flow as in the case where the spark plug is mounted on an actual internal combustion engine, It can be said that it is also advantageous in that sparks are more easily generated between the distal end surface of the fitting and the insulator.

In the ninth configuration, the main air gap (α) and the semi-creep insulator gap (γ) are (α−
It is desirable to satisfy γ) ≦ 0.4 mm. By satisfying such a relationship, it is possible to reduce channeling in an internal combustion engine that performs particularly strict supercharging on channeling or an internal combustion engine with a high compression ratio. However, when α-γ is smaller than 0.2 mm, the discharge frequency on the semi-creeping ground electrode side decreases, and the cleaning effect on “smoldering” may be impaired.
m or more.

In general, even when "smoldering" does not occur, sparks do not occur only in the main air gap (α) but may also occur in the semi-surface insulator gap (γ). Even if the internal combustion engine is operated under the same conditions, there is variation in the environmental atmosphere between the gaps of the spark plug, so that the voltage required to generate a spark between the gaps may also vary. Therefore, when the required voltage for spark generation is lower than the semi-surface crevice insulator gap (γ) in the main air gap (α), a spark is generated in the main air gap (α).

On the other hand, since the voltage required for generating a spark in each gap varies, when the minimum value and the maximum value of the voltage are measured, the main air gap (α) and the semi-surface insulator gap ( γ) may partially overlap each other. The overlapping width can be almost uniquely determined by the size of each gap. Then, when the discharge voltage required for spark generation rises according to the environmental atmosphere between the gaps of the spark plug, the voltage rises to the overlapping portion. In this case, it is not determined whether a spark is generated in the main air gap (α) or a spark is generated in the semi-surface crevice insulator gap (γ). Therefore, if a spark is generated in the semi-surface insulator gap (γ) when the voltage is increased in this manner, channeling is likely to occur due to the high discharge voltage.

Therefore, when the difference from the semi-surface insulator gap (γ) is reduced by narrowing the main air gap (α), the maximum value of the voltage required to generate a spark in the main air gap (α) is reduced. , The overlapping portion becomes narrow. As a result, unnecessary spark generation at the semi-surface insulator gap (γ) can be suppressed, and channeling can be reduced because the discharge voltage when a spark is generated at the semi-surface insulator gap (γ) is also reduced. Further, when the main air gap (α) is set to α ≦ 0.9 mm, the voltage required for spark generation can be kept low. Therefore, when “smoldering” occurs, the distance between the center electrode and the metal shell is reduced. This is a particularly effective method for a high heat value type plug (a plug having a short distance from the holding portion of the insulator to the metal shell to the tip of the insulator) in which the insulation resistance value tends to decrease.

In the spark plug of the tenth configuration,
In addition to the basic configuration described above, when the front end of the insulator is viewed in plan from the front side in the axial direction, the semi-creeping ground electrode is larger than the front opening diameter of the center through hole of the insulator at least at the other end face. It has a width. The tenth configuration can be combined with at least one of the first to ninth configurations.

According to the above configuration, the semi-surface creeping ground electrode has at least a tip end surface with a diameter of a tip end opening of the center through hole of the insulator (and, consequently, an outer diameter of a center electrode tip end surface or a tip end surface of a noble metal tip described later). Since it is configured as having a large width, the range of sparks crawling on the front end surface of the insulator is wider, and channeling can be reduced, and "smoldering" can be cleaned with sparks in a wide range.

In the eleventh configuration of the spark plug, in addition to the basic configuration described above, the insulator is formed with a reduced diameter straight tubular portion which is a tip portion, and the axially rearward portion of the straight tubular portion in the axial direction. A bulged portion having a diameter larger than that of the straight tubular portion is formed adjacent to the side, the length of the straight tubular portion is 1.5 mm or less, and the semi-creeping ground electrode is an insulating surface of the other end. On a virtual plane including the midpoint of the rear side edge in the axial direction of the insulator and the axis of the insulator, the midpoint of the rear side edge is defined as γ (unit: mm), where the size of the semi-creep insulator gap is γ. When a circle of (γ + 0.1) mm centered on is drawn, the entire bulge portion is located outside the circle. The eleventh configuration can be combined with at least one of the first to tenth configurations.

Also in this configuration, a straight tubular portion having a length of 1.5 mm or less (preferably 0.5 mm or more) is provided. The effect is as described in the fifth configuration. In the straight tubular portion, a bulged portion having a diameter larger than that of the straight tubular portion is formed adjacent to the rear side in the axial direction. If the position of the bulge is too close to the rear edge of the semi-creeping ground electrode, sparks from the rear edge may be directed toward the electric field concentration part (particularly, a step edge provided with a radius or the like) in the bulge. As a result, it is easy to sag to the rear side, and the ignitability is easily impaired.

Therefore, in the eleventh configuration, the midpoint of the rear side edge of the other end of the semi-creeping ground electrode (which becomes a discharge surface for the semi-creeping gap) in the axial direction of the insulator is provided. On a virtual plane including the axis of the insulator, the magnitude of the semi-surface insulator gap is defined as γ (unit: m
m) centered on the midpoint of the rear side edge (γ + 0.m).
1) When a circle of mm was drawn, the entire bulge was located outside the circle. In this way, by making the position of the bulging portion farther from the rear side edge of the other end face of the semi-creeping ground electrode, it is possible to effectively suppress the dripping of sparks from the semi-creeping ground electrode, and to reduce the ignitability Can be kept good.

The spark plug of the twelfth configuration is characterized in that, in addition to the basic configuration described above, the center through hole of the insulator is reduced in diameter at the tip end side of the insulator. The twelfth configuration can be combined with at least one of the first to eleventh configurations. Since the spark plug of the present invention includes the semi-creeping ground electrode, the heat received at the tip during the combustion cycle in the internal combustion engine has a moderate tendency to escape to the center electrode side. Thus, the temperature of the tip of the insulator can be easily increased. Therefore, even in a direct injection type internal combustion engine in which the temperature does not easily rise during normal operation, the temperature at the tip of the insulator can be easily increased, and carbon deposited by "smoldering" can be easily burned off. In addition, it is possible to prevent sparks from being generated between the distal end surface of the metal shell and the insulator, and to prevent sparks from being generated in the vicinity of the holding portion. A stable combustion area can be widened. In this configuration, it is more preferable that the additional requirement 3 described later is satisfied.

In the spark plug of the thirteenth configuration, in addition to the basic configuration described above, the side where the tip is located in the axial direction of the insulator is defined as the front side, and further, the other end of the semi-creeping ground electrode is formed. For a virtual plane that includes the midpoint and the axis of the rear side edge of the end face, a plane that includes the axis and is orthogonal to the plane is defined as a projection plane, and is represented by an orthogonal projection to the projection plane. The end face of the other end is defined as X at the intersection of the axis and the rear side edge on the projection plane, and Y at the intersection with the front side edge. Also has a shape in which the area S1 of the region located on the front side is larger than the area S2 of the region located on the rear side. The thirteenth configuration can be combined with at least one of the first to twelfth configurations.

The spark at the semi-surface creeping ground electrode is more likely to occur on the front end side where the attack on the insulator is softer than on the rear end side at the other end face serving as the discharge surface.
It is desirable from the viewpoint of suppressing channeling and improving ignitability. Therefore, as described above, the shape of the end face of the other end is defined by using a reference line located between the front edge and the rear edge as a boundary.
By setting the area S1 of the region located on the front side to be larger than the area S2 of the region located on the rear side, it is possible to increase the frequency of sparks on the front end side of the other end surface. And contributes to suppressing channeling or improving ignitability.

In the spark plug of the fourteenth configuration, the side where the front end portion is located in the axial direction of the insulator is defined as the front side, and the semi-creeping ground electrode has the rear side edge of the other end face. For a virtual plane containing points and axes,
A plane that includes the axis and is orthogonal to the plane is defined as the projection plane, and when the plane is orthogonally projected on the projection plane, the outer peripheral edge of the other end face has the axis and the rear side edge on the projection plane. X is the intersection with, and Y is the intersection with the front side edge.
At least in the region located behind the reference line orthogonal to the axis through the middle point, the corner has a tip curvature radius or chamfer width of 0.2 mm or more or forms this corner 2
The side part has an angle of more than 90 degrees. The fourteenth configuration can be combined with at least one of the first to thirteenth configurations.

The gist of the above-described structure is to suppress a spark on the rear end side at the other end surface serving as the discharge surface of the semi-creeping ground electrode. That is, the presence of a sharp corner tends to be a starting point of spark generation, but by excluding this from the region located on the rear side of the above-described reference line, the rear end side spark on the other end surface is suppressed. You. As a result, the frequency of sparks on the tip side can be increased, which contributes to suppressing channeling or improving ignitability. Also, if the above-mentioned sharp corners are formed at both ends of the rear edge,
From this point, sparks may fly in the form of drooping obliquely outward and downward, and the ignitability may be significantly impaired.However, according to the above configuration, sharp corners are naturally excluded from such positions. Therefore, the problem can be prevented or suppressed at the same time. This configuration is
When combined with the thirteenth configuration described above, it is more effective in suppressing channeling or improving ignitability.

Hereinafter, requirements that can be added in common to the above-described first to fourteenth spark plugs (including combinations) will be described. (Additional requirement 1) First, the insulator is provided with a straight tubular portion at the front end thereof, and the straight tubular portion extends from the front end surface of the metal shell to the rear end side. Can be. In this case, the diameter difference between the distal end face of the metal shell and the insulator can be easily kept larger, and the generation of sparks at this position can be easily suppressed. In this case, it is desirable that the length of the straight tubular portion is 1.5 mm at the maximum. In this case, the operation and effect of providing the straight tubular portion are the same as those described in the eleventh configuration.

(Additional requirement 2) Further, a noble metal tip formed of a noble metal or a noble metal alloy having a melting point of 1600 ° C. or more can be joined to the tip of the base material of the center electrode. In this case, it is possible to adopt a structure in which this joint is joined in the center through hole of the insulator. By joining the joint in the center through hole of the insulator in this way, not only when a spark is generated at the main air gap (α), but also when a spark is generated at the semi-surface gap (β). A spark is generated between the semi-creeping ground electrode and the noble metal tip.
Therefore, even if sparks are generated in any of the gaps, the durability is improved. The noble metal alloy, Pt, in addition to the Ir, Pt-Ir, Ir- Rh, Ir-Pt, Ir-Y 2
Pt alloys such as O ₃ and Ir alloys having a melting point of 1600 ° C. or more are preferable.

(Additional Requirement 3) Also, the insulator on the distal end side with respect to the holding portion which is locked and held by the metal shell,
It is desirable that the minimum diameter (D3) of the center through hole be D3 ≦ 2.1 mm. By thus reducing the inner diameter of the insulator, the outer diameter of the center electrode is also reduced. For this reason, since the heat received at the tip portion during the combustion cycle in the internal combustion engine is hardly released to the center electrode side, the tip temperature of the insulator can be easily increased. Therefore, even in a direct injection type internal combustion engine in which the temperature does not easily rise during normal operation, the temperature at the tip of the insulator can be easily increased, and carbon deposited by "smoldering" can be easily burned off. In addition, it is possible to prevent sparks from being generated between the distal end surface of the metal shell and the insulator, and to prevent sparks from being generated in the vicinity of the holding portion. A stable combustion area can be widened. However, from the viewpoint of preventing channeling, it is desirable that D3 ≧ 0.8 mm.

(Additional Requirement 4) When the above-mentioned noble metal tip is used, the outer diameter of the joining portion between the noble metal tip and the center electrode base material is equal to the outer diameter of the tip side where the main air gap (α) is formed. It can be configured to be larger than the outer diameter. With this configuration, it is possible to prevent the noble metal tip from falling off from the center electrode base material even when a spark occurs at the semi-surface gap (β). In other words, if sparks occur at the semi-creep gap (β),
A spark will be generated between the side surface of the noble metal tip and the semi-creeping ground electrode. If sparks occur frequently at this position, the noble metal tip near the tip surface of the insulator will be consumed and become thinner than the noble metal tip tip. When the spark generation at the semi-creep gap (β) is repeated as described above, the leading end of the noble metal tip may fall off. However, such a phenomenon can be suppressed by increasing the diameter of the joint portion as described above.

Further, since the tip of the noble metal tip has a smaller diameter than the joint side, the discharge voltage when a spark is generated in the main air gap (α) can be reduced, and the ignitability is improved. Can be done. In particular, in a direct injection internal combustion engine, the stable combustion region can be widened. The enlarged diameter portion of the noble metal tip may be located inside the tip surface of the insulator. In this case, when a spark is generated at the semi-creep gap (β), the spark crawling on the front end face of the insulator further crawls on the inner wall of the center through hole of the insulator and reaches a portion where the diameter of the noble metal tip is increased. . Therefore, even if the large-diameter portion is inside the center through hole of the insulator, the above-described effect is produced because the spark is generated between the large-diameter portion and the semi-creeping ground electrode.

(Additional requirement 5) The minimum value of the diameter difference between the outer diameter of the noble metal tip and the inner diameter of the center through hole of the insulator is 0.2.
mm or less. This makes it easier to suppress the consumption of the center electrode base material due to spark discharge. As described above, when a spark occurs in the semi-surface gap (β), the spark crawls on the inner wall of the center through hole of the insulator. At this time, if the diameter difference between the outer diameter of the noble metal tip and the inner diameter of the center through hole of the insulator becomes large, the sparks may enter deeper without jumping to the noble metal tip and reach the center electrode base material. Since the center electrode base material has a lower spark wear resistance than the noble metal tip, the center electrode base material is liable to be consumed quickly, and the tip may fall off. Therefore, by reducing the diameter difference, the phenomenon that sparks reach the center electrode base material can be suppressed, and the durability is improved. Here, the “minimum value of the diameter difference” has significance as a representative value of the following diameter difference. That is, when the outer diameter of the noble metal tip and the inner diameter of the center through hole are uniform in the axial direction, the difference in diameter is also substantially uniform in the axial direction. However, when either the outer diameter of the noble metal tip or the inner diameter of the center through hole is not uniform in the axial direction (for example, when the center through hole has a slight taper), the minimum value in the axial direction is determined by the diameter difference. Is adopted as a representative value.

[0071]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a partial sectional view of a spark plug 100 according to the first embodiment. As is well known, the insulator 1 made of alumina or the like is provided with a corrugation 1A at a rear end thereof for increasing a creepage distance, and a leg portion 1B at a front end exposed to a combustion chamber of an internal combustion engine. Has a central through hole 1C. In the center through hole 1C, if there is a noble metal tip, Inconel (trade name) is used, and if there is no noble metal tip, 95% by mass nickel (remainder such as chromium, manganese, silicon , Aluminum, iron), a center electrode 2 made of a nickel-based metal or the like having a nickel content of 85% by mass or more.

The center electrode 2 is electrically connected to an upper terminal fitting 4 via a ceramic resistor 3 provided inside the center through hole 1C. A high voltage cable (not shown) is connected to the terminal fitting 4 to apply a high voltage. The insulator 1 is surrounded by a metal shell 5 and is provided with a holding portion 51 and a caulking portion 5C.
Supported by The metal shell 5 is formed of a low-carbon steel material, and has a hexagonal portion 5A fitted with a spark plug wrench.
And a screw part 5B of M14S, for example. The metal shell 5 is caulked to the insulator 1 by the caulking portion 5C, and the metal shell 5 and the insulator 1 are integrated. In order to complete the sealing by caulking, a plate-shaped packing member 6 and wire-shaped sealing members 7, 8 are interposed between the metal shell 5 and the insulator 1, and the sealing members 7, 8 are provided.
The talc (powder) 9 is filled with the powder between 8.
Further, the rear end of the screw portion 5B, that is, the seat surface 52 of the metallic shell 5
Is fitted with a gasket 10.

A parallel ground electrode 11 made of a nickel alloy at least as a base material constituting a surface layer is joined to the distal end face 5D of the metal shell 5 by welding. The parallel ground electrode 11 is axially opposed to the tip surface of the center electrode 2, and forms a main air gap (α) between the center electrode 2 and the parallel ground electrode 11. The opposite side dimension of the hexagonal diameter portion 5A is 16 mm,
The length from the bearing surface 52 to the distal end surface 5D of the metal shell 5 is set to, for example, 19 mm. This dimension setting is based on JI
S: A standard size of a spark plug having a small hexagon of 14 mm and a dimension A of 19 mm specified in B 8031. As shown in FIG. 24, the parallel ground electrode 11
In order to reduce the temperature of the tip portion and suppress spark consumption, a good heat conductive material 11a made of a material (for example, Cu, pure Ni or a composite material thereof) having better heat conductivity than the base material 11b is provided inside. You may have. Up to this point, it is the same as the conventional spark plug.

The spark plug 10 according to this embodiment
0, a plurality of semi-creeping ground electrodes 12 are provided separately from the parallel ground electrodes 11. The semi-surface creeping ground electrode 12 has at least a base material 12b (see FIG. 2 (a)) forming a surface layer made of a nickel alloy, and one end of which is formed on the front end face 5 of the metal shell 5.
D is welded, and the other end surface 12C is disposed so as to face the side peripheral surface 2A of the center electrode 2 or the side peripheral surface 1E of the leg long portion 1B. As shown in FIG. 26, the two semi-creeping ground electrodes 12 are disposed at positions shifted by 90 ° from the parallel grounding electrodes 11, respectively.
They are arranged at positions shifted from each other by approximately 180 °. Also,
FIG. 26 shows a state in which the distal end of the insulator 1 is viewed from the front side in the direction of the axis 30 in a plan view. Has a width larger than the opening diameter of the tip. As shown in FIG. 2, each semi-creeping ground electrode 12
A semi-creeping gap (β) is formed between the end face 12C of the center electrode 2 and the side peripheral face 2A of the center electrode 2, respectively. Respectively, a semi-creep insulator gap (γ) is formed.

In FIG. 26, the end surface 12C of the semi-creeping ground electrode 12 is formed flat, but semi-creeping gaps are formed at substantially uniform intervals along the side peripheral surface of the insulator 2. As shown in FIG.
The axis of the insulator 2 (30:
It can also be formed in a cylindrical shape centered on FIG. 2).

The semi-surface creeping ground electrode 12, like the parallel ground electrode 11, may have a good heat conducting material 12a made of Cu, pure Ni, or a composite material thereof inside. In this case, the semi-creeping ground electrode 12 has a base material 12b forming the surface layer portion and a good heat conductive material 12a forming the inner layer portion and having a better heat conductivity than the base material 12b. Becomes

FIG. 2A shows the first embodiment.
FIG. 2B is an enlarged partial cross-sectional view showing the vicinity of a center electrode 2, a parallel ground electrode 11, and a semi-creeping ground electrode 12 of the spark plug according to the first embodiment, and FIG. FIG. In the figure, the distance of the main air gap (α) between the front end surface of the center electrode 2 and the parallel ground electrode 11 is α, and the distance between the side peripheral surface 2A of the center electrode 2 at the position of the front end surface 1D of the insulator 1 is End surface 12 of semi-surface ground electrode 12
The distance of the semi-creep gap (β) from C is β.
Further, when the semi-creeping ground electrode 12 and the insulator 1 are cut along the central axis 30, the tip surface 1D of the insulator 1
And a second extension obtained by extending a line indicating the side peripheral surface 1E near the semi-creep gap (β) of the insulator 1 in the direction of the tip surface 1D. Line 32
And a third extension line 33 obtained by extending a line indicating the end surface 12C of the semi-surface creeping ground electrode 12 to the distal end side. Then, the intersection P of the first extension line 31 and the second extension line 32
Assuming that the distance from No. 1 to the intersection P2 of the first extension line 31 and the third extension line 33 is the distance γ of the semi-surface insulator gap (γ), γ is the distance between the insulator 1 and the semi-surface earth electrode 12. Represents the shortest distance to And these α,
There is a relationship of α <β and γ <α between β and γ.

By setting in this way, when the insulation on the surface of the insulator 1 is normal and high, discharge can be performed in the main air gap (α) between the insulator 1 and the parallel ground electrode 11.
At the time of “smoldering” in which the insulation on the surface of the insulator 1 is reduced, the discharge can be performed in the semi-creeping gap (β) between the insulator 1 and the semi-creeping ground electrode 12. Further, the step between the front end face 1D of the insulator 1 and the rear end side edge 12B of the end face 12C of the semi-creeping ground electrode 12 is E, the protrusion amount of the insulator 1 from the front end face 5D of the metal shell 5 is F, and the center is F. Let H be the amount of protrusion of the electrode 2 from the front end face 1D of the insulator 1. In addition, the front end face 5 of the metal shell 5 of the insulator 1 in the present embodiment.
The amount of protrusion F from D is determined according to the JIS standard (JIS: B8031) to which this spark plug is applied or the J value.
This corresponds to the amount of protrusion of the insulator that protrudes to the tip side from the dimension A defined in the ISO standard corresponding to the IS standard.

At the tip of the insulator 1, a straight tubular portion 102 (portion having a straight cylindrical outer peripheral surface centered on the center axis 30) is formed.
It extends to the rear end side from D. With this configuration, the diameter difference between the distal end face 5D of the metal shell 5 and the insulator 1 can be more easily maintained, and the generation of sparks at this position can be easily suppressed. Further, since the tip of the insulator 1 is a straight tube, heat received at the tip during a combustion cycle in the internal combustion engine is slightly applied to the holder 51 of the insulator 1 with the metal shell 5. Because it has the effect of making it difficult to escape,
The temperature of the tip end of the insulator 1 can be easily increased. Therefore, even in a direct injection type internal combustion engine in which the temperature hardly rises during normal operation, the temperature at the tip end of the insulator 1 can be easily increased, and the carbon deposited by "smoldering" can be easily burned off. In addition, with such a configuration, since the heat volume of the distal end portion of the insulator 1 is small, the insulator is easily cooled by relatively low-temperature gas sucked from the intake pipe. For this reason, during a combustion cycle in the internal combustion engine, a temperature rise that causes preignition hardly occurs. Note that the rear side edge of the end surface 12C of the semi-surface creeping ground electrode 12 is located forward of the rear side edge of the straight tubular portion 102.

In this embodiment, unless otherwise specified, the protrusion F of the insulator 1 was 3.0 mm, and the original diameter D2 of the center electrode 2 was 2.0 mm. The semi-creeping ground electrode 12 has a width of 2.2 mm and a thickness of 1.0 mm.
The parallel ground electrode 11 has a width of 2.
The one having a thickness of 5 mm and a thickness of 1.4 mm is used.

A step E between the height position of the front end face 1D of the insulator 1 and the height position of the rear end side edge 12B of the end face 12C of the semi-creeping ground electrode 12 is provided with a semi-creeping ground electrode 12 There are the following three types depending on the height position. That is, first, as shown in FIG. 2A, the rear end side edge 12B and the front end side 12A of the semi-surface creeping ground electrode 12 (FIG. 2B) are larger than the front end face 1D of the insulator 1. This is the case at the rear end side.
Second, as shown in FIG. 3, of the first embodiment, the semi-surface creeping ground electrode 12 of the spark plug according to the second aspect.
In the case where only the rear end side edge 12B is located on the rear end side with respect to the front end face 1D of the insulator 1, the third is the third mode of the first embodiment as shown in FIG. In this case, the rear end side edge 12B of the semi-surface creeping ground electrode 12 of the spark plug is located on the front end side of the front end face 1D of the insulator 1.

In any case, it is preferable that one of the rear end side edge 12B and the front end side edge 12A of the end face 12C of the semi-surface creeping ground electrode 12 is located at a height near the front end face 1D of the insulator 1. That is, the step E is preferably small. This is because the semi-creeping discharge has a sharp edge and the electric field is concentrated at an acute angle.
Since sparks are considered to fly from A, the sparks flying from the rear end side edge 12B and the front end side edge 12A are brought closer to the front end face 1D of the insulator 1 to enhance the self-cleaning action of burning off carbon deposited on the surface of the insulator 1. That's why.

In the above-described spark plug 100, the dimensions or dimensional relationships of the respective parts are appropriately determined depending on which of the various configurations described in the section “Means for Solving the Problems and the Functions and Effects”. Determined. Hereinafter, the specific configuration will be described in detail along with experimental results for supporting the operation and effect.

(Experiment 1: First Configuration; α ≦ 1.1 mm,
Grounds for 0.5 mm ≦ γ ≦ 0.7 mm, δ ≧ 3.6 mm) Main air gap (α) is set to α = 1.1 mm, and two semi-creeping ground electrodes 12 are provided as shown in FIG. Provided,
Both semi-surface insulator gaps (γ) are γ = 0.6m
m, semi creepage gap (β): β = 1.6 mm
And a spark plug in which the inner diameter of the portion of the metal shell 5 closer to the tip end than the holding portion 51 was variously changed was prepared. Table 1 shows the tip surface of the metallic shell 5 when the diameter difference (δ) between the insulator 1 and the metallic shell 5 at the position of the distal end surface 5D of the metallic shell 5 is variously changed using these spark plugs. The result of examining the ratio of the phenomenon of spark discharge between the 5D and the insulator 1 (metal fitting / insulator spark) is shown. In addition,
The experiment was carried out at an idling speed of 600 rpm by using an automobile using a 1800 cc in-line four-cylinder direct injection internal combustion engine with the shift lever in the D range. The spark plug ignition timing is before top dead center (hereinafter referred to as "BTDC").
15 °, the fuel injection end timing was fixed at 30 ° BTDC. Furthermore, the results are as follows: those in which the occurrence of metal fittings / insulator sparks occurred 3 times or more per minute; x: from 1 to 2 times; and ○: those in which no metal fitting / insulator sparks occurred.
Was evaluated and evaluated.

[0085]

[Table 1]

At the position of the distal end face 5D of the metal shell 5,
When the diameter difference (δ) between the insulator 1 and the metal shell 5 was 3.4 mm or less, sparks occurred at least once at this position. Therefore, by setting the diameter difference to 3.6 mm or more, even when “smoldering” occurs, the metallic shell 5
It can be seen that a spark can be generated at the semi-surface creepage insulator gap (γ) without generating a spark between the tip surface 5D of the insulator 1 and the insulator 1. The effect of preventing a metal fitting / insulator from sparking, particularly in a stratified combustion type direct injection internal combustion engine, has already been described.

(Experiment 2: Third Configuration: α ≦ 0.9 mm,
0.5 mm ≦ γ ≦ 0.7 mm, δ ≧ 2.8 mm) Insulator 1 at the position of tip end face 5D of metal shell 5
The diameter difference (δ) between the metal shell 5 and the metal shell 5 is 2.8 mm, and
Two semi-creeping ground electrodes are provided, the semi-creeping insulator gap (γ) is set to γ = 0.6 mm, the semi-creeping gap (β) is set to β = 1.6 mm, and
Spark plugs with various main air gaps (α) were prepared. Except for using these spark plugs, a test was performed under exactly the same conditions as in Experiment 1, and evaluation and judgment were similarly performed. Table 2 shows the results.

[0088]

[Table 2]

According to this, the main air gap (α) is
In the case of α ≧ 1.0 mm, it can be seen that the metal / insulator spark has occurred at least once at the position of the tip end face 5D of the metal shell 5. Therefore, the main air gap (α)
It can be seen that by setting α to 0.9 mm, a spark can be generated in the semi-surface creepage insulator gap (γ) without causing a fitting / insulator spark even when “smoldering” occurs.

(Experiment 3: Fourth Configuration; Grounds for Using Three or More Semi-Creepage Grounding Electrodes) When the main air gap (α) is α =
1.1 mm, the diameter difference (δ) between the insulator 1 and the metal shell 5 at the position of the distal end face 5D of the metal shell 5 is 2.8 mm, the semi-surface insulator gap (γ) is γ = 0.6 mm, and the semi-surface Spark plugs were prepared in which the gap (β) was set to β = 1.6 mm and the number of semi-creeping ground electrodes 12 having the gap was varied. Except for using these spark plugs, a test was performed under exactly the same conditions as in Experiment 1, and evaluation and judgment were similarly performed. Table 3 shows the results.

[0091]

[Table 3]

According to the results, good results were not obtained in Experiment 1. The main air gap (α) was α = 1.1 m.
m and the diameter difference δ is 2.8 mm, when the number of the semi-creeping ground electrodes 12 is increased to three or more, the metal / insulator spark at the position of the distal end face 5D of the metal shell 5 is effectively reduced. It turns out that it is suppressed. Therefore, by setting the number of the semi-creeping ground electrodes 12 to three or more, even if “smoldering” occurs, a spark is generated in the semi-creeping insulator gap (γ) without causing a metal fitting / insulator spark. It can be seen that it can be done. FIG. 24 shows a third semi-creeping ground electrode 12 with respect to the spark plug 100 of FIG.
(Indicated by a dashed line) is shown. FIG. 25 is a plan view thereof, in which three semi-creeping ground electrodes 12 and parallel ground electrodes 11 are
Are arranged at an interval of about 90 ° around the central axis.

(Experiment 4: Fifth Configuration: Step E between the height of the front end surface of the insulator and the height position of the rear end side edge of the semi-surface ground electrode, and the side from the front end surface of the insulator Grounds for setting the difference between the radius of curvature R of the curved surface reaching the peripheral surface and R−E ≦ 0.1 mm) In the spark plug of FIG.
And two semi-creeping ground electrodes 12 are provided, the semi-creeping insulator gap (γ) is set to γ = 0.6 mm, the semi-creeping gap (β) is set to β = 1.6 mm, and the insulation is performed. A step E between the height position of the front end surface 1D of the insulator 1 and the height position of the rear end side edge 12B of the end surface 12C of the semi-surface creeping ground electrode 12, and the side peripheral surface 1D from the front end surface 1D of the insulator 1
A variety of curvature radii R of a curved surface reaching E was prepared. The following experiment was performed to evaluate the channeling resistance of these spark plugs. That is, a spark plug is attached to the chamber,
The operation of generating a spark 60 times a second by a full transistor power supply while applying pressure to MPa is performed for 100 hours.
Continued. Then, while measuring the channeling depth of the spark plug after the end of the operation, a spark plug having a channeling groove depth of less than 0.2 mm is slightly (○), 0.2 to
Those having a thickness of 0.4 mm were evaluated as moderate (△), and those exceeding 0.4 mm were evaluated as severe (x). The results are shown in Table 4.

[0094]

[Table 4]

From these results, the main air gap (α) and the semi-surface gap (β) satisfy α <β, and the main air gap (α) and the semi-surface creepage gap (γ)
When α> γ, by setting R−E ≦ 0.1 mm,
It can be seen that channeling can be effectively reduced. This is because the spark from the rear end side edge 12B of the semi-creeping ground electrode 12 toward the center electrode 2 is blocked by the tip of the insulator 1, so that the spark is generated from the semi-creeping ground electrode 12 to the center electrode 2. It is considered that no spark is generated on the straight line toward the insulator 1 and the insulator 1 is bent in the circumferential direction. As a result, the discharge path of the spark changes every time a spark is generated, so that the range of the spark crawling on the front end face 1D of the insulator 1 is widened, and the channeling can be reduced.
"Smoldering" sparks can be cleaned in a wide range. Although the spark plug of the present invention originally has the parallel ground electrode 11, if it is used as it is, a spark does not occur on the semi-creeping ground electrode 12 unless contamination proceeds, and Even if the fouled sediment is burned off, the spark is interrupted, so that the channeling evaluation has a very long time. Therefore, in order to accelerate and investigate the channeling behavior of the semi-creeping ground electrode 12, the evaluation was performed with the parallel ground electrode 11 removed.

Further, the value of E is selected in the range of 0.1 to 0.7 mm, and for each value of E, RE is set to 0.2.
mm when channeling groove depth δ0 (mm)
And a channeling groove depth δ1 (mm) when RE is set to 0 mm, and a channeling improvement width λ expressed by λ = δ0−δ1 (mm) is calculated.
It was estimated how much channeling could be improved by reducing E from 0.2 mm to 0 mm. Table 5 shows the results.

[0097]

[Table 5]

As can be seen from this, when the length of the step E is 0.5 mm or less, the channeling effect is particularly large.

(Experiment 5: Sixth configuration; grounds for setting protrusion amount (F) of insulator 1 to be 3.0 mm ≦ F ≦ 5.0 mm)
The main air gap (α) is set to α = 1.1 mm, the diameter difference (δ) between the insulator 1 and the metal shell 5 at the position of the distal end face 5D of the metal shell 5 is set to 2.8 mm, and the semi-surface creeping ground electrode 12 is formed. Are provided, and the semi-creep insulator gap (γ) is γ =
0.6 mm, semi-creeping gap (β) is β =
The spark plug is set to 1.6 mm and the JIS standard (JIS B
8031) or a spark plug in which the amount of protrusion (F) of the insulator 1 protruding toward the distal end side from the dimension A defined in the ISO standard corresponding to the JIS standard is prepared. Then, similarly to Experiment 1, these spark plugs were attached to an automobile using a 1800 cc in-line four-cylinder direct-injection internal combustion engine, the shift lever was put in the D range, and the engine was operated at an idling speed of 600 rpm. The spark timing of the spark plug was fixed at 15 ° BTDC. Then, in the case of the protrusion amount (F) of each of the insulators 1, the width of the injection end time at which the frequency of misfiring per minute becomes substantially zero (combustion stable region) was measured. In a direct injection internal combustion engine, this width is a measure for determining the quality of ignitability.

FIG. 5 shows the results. The protrusion amount (F) of the insulator 1 is 3.0 mm ≦ F ≦ 5.0 m.
It can be seen that by setting m, the range of the fuel injection end timing that does not cause misfire (that is, the width of the stable combustion region) can be widened. In the spark plug according to the first embodiment, as shown in FIG. 6, an extended shell type spark plug in which the tip 5E is extended from the threaded portion 5B of the metal shell 5 of the spark plug according to the fourth aspect. Have obtained similar results. However, in this case, the protrusion amount (F) of the insulator 1 is not the dimension from the front end surface 5D of the metal shell 5, but the length of the extended end portion 5E, that is, is determined in the JIS standard. The length is a length obtained by further adding the length on the distal end side to the dimension A.

(Experiment 6: Eighth Configuration; Basis for Making the Center Electrode 2 Protrude Amount (H) from the Insulator 1 as (H) ≦ 1.25 mm) Main Air Gap (α) is α = 1 .1 mm, two semi-creeping ground electrodes 12 are provided, the semi-creeping insulator gaps (γ) are both set to γ = 0.6 mm, and the semi-creeping gaps (β) are both set to β = 1.6 mm. Then, spark plugs were prepared in which the center electrode diameter was set to φ2.5 mm and the amount of protrusion (H) of the center electrode 2 projecting from the front end face 1D of the insulator 1 was variously set. And the result of having measured the stable combustion area | region using the same vehicle as the experiment 5 using these spark plugs is shown. However, the traveling condition was not idling but a constant traveling condition of 100 km / h (assuming high-speed operation). The spark plug ignition timing was fixed at BTDC 25 °. The other conditions were the same as in Experiment 5, and in the case of the protrusion amount (H) of each center electrode 2, the width of the injection end time at which the misfire occurrence frequency per minute became substantially zero was measured. Fig. 7 shows the results.
Is shown in

From these results, the main air gap (α) and the semi-surface gap (β) satisfy α <β, and the main air gap (α) and the semi-surface insulator gap (γ)
α> γ, and the amount (H) by which the center electrode projects from the front end surface of the insulator is H ≦ 1.25 mm.
Even if a spark is generated in the semi-surface gap (β) during high-speed operation, it is possible to widen the range of the fuel injection end timing at which misfire does not occur. Therefore, even in a direct-injection type internal combustion engine in which the ignitability tends to differ depending on the spark generation position, the "smoldering"
At the spark position at the semi-creeping ground electrode 12 which is generated when the occurrence of the fire occurs. Here, the value of H is shown here as a positive value as shown in FIG. 28 (a), but H becomes almost zero as shown in FIG. 28 (b) (that is, H of the center electrode 2). The tip face or the tip face of a noble metal tip described later may be substantially flush with the tip face of the insulator 1), or H may be a negative number as shown in (c). (That is, the front end surface is recessed from the front end surface of the insulator 1).
In this case, from the viewpoint of further improving the channeling resistance and the “smoldering” cleaning effect, −0.3 mm ≦
It is even better if H ≦ 0.5.

(Experiment 7: Ninth Configuration: α ≦ 0.4 × (β
Grounds for setting -γ) + γ) Semi creepage gap (β) is set to 1.
Main air gap (α) of various sizes, set at 6 mm
And a plurality of spark plugs provided with two parallel semi-surface ground electrodes 12 having the same size and various semi-surface crimp insulator gaps (γ). Then, the spark plug is attached to the chamber, and a desk test for observing the direction in which sparks are generated is performed with the interior of the chamber pressurized to 1.0 MPa.
It was examined whether a spark was generated between D and the insulator 1. The spark was generated 60 times per second by a full transistor power supply, and the measurement time was 1 minute.

FIG. 8 shows the above results. In the figure, line 1
Reference numeral 01 denotes a boundary as to whether or not a spark occurs between the distal end face 5D of the metal shell 5 and the insulator 1. In the area AA above this straight line, a spark is generated between the distal end face 5D of the metal shell 5 and the insulator 1, and in the area BB below, no spark is generated. The straight line 101 is represented by the following equation (1), and serves as a boundary line indicating whether or not a spark occurs between the distal end face 5D of the metal shell 5 and the insulator 1. α = 0.4 × (β−γ) + γ ‥‥ (1) Therefore, in order to prevent a spark from being generated between the distal end face 5D of the metal shell 5 and the insulator 1, the condition of the following equation (2) is satisfied. It turns out that it is necessary. α ≦ 0.4 × (β−γ) + γ ‥‥ (2)

From these results, the main air gap (α) and the semi-surface creepage gap (β) satisfy α <β, and the main air gap (α) and the semi-surface creepage gap (γ)
α> γ, and the main air gap (α), the semi-creeping gap (β) and the semi-creeping insulator gap (γ) satisfy α ≦
By setting 0.4 × (β−γ) + γ, it is possible to suppress the occurrence of sparks between the distal end face 5 </ b> D of the metal shell 5 and the insulator 1. Also, when the ambient gas around the gap of the spark plug has a flow, such as when mounted on an actual internal combustion engine, sparks are more likely to occur between the distal end surface of the metal shell and the insulator. It is more preferable that α ≦ 0.3 × (β−γ) + γ to facilitate the operation.

(Experiment 8: Grounds for setting (α−γ) ≦ 0.4 mm) Main air gaps (α) of various sizes
And a plurality of spark plugs provided with two parallel semi-surface ground electrodes 12 having the same size and various semi-surface crimp insulator gaps (γ). The following experiment was performed to evaluate the channeling resistance of these spark plugs. That is, the spark plug is mounted on an automobile using a 2500 cc in-line six-cylinder turbocharged internal combustion engine, and the shift lever is put into the D range.
r operation continued. Then, while measuring the channeling depth of the spark plug after the end of the operation, the spark plug having a channeling groove depth of less than 0.2 mm is slightly (（),
Those having a thickness of 0.2 to 0.4 mm were evaluated as moderate (△), and those exceeding 0.4 mm were evaluated as severe (x). The results are shown in Table 6.

[0107]

[Table 6]

From these results, the main air gap (α) and the semi-surface insulator gap (γ) are (α−γ) ≦ 0.4 m
It can be seen that channeling can be reduced by setting m. By satisfying such a relationship, it can be seen that channeling in a supercharged internal combustion engine or an internal combustion engine with a high compression ratio, which is particularly severe for channeling, can be reduced.

(Experiment 9: Second configuration; 0.2 mm ≦ (α
-Γ) ≦ 0.4 mm) The diameter of the center electrode 2 is φ
2.5 mm, the diameter difference (δ) between the insulator 1 and the metal shell 5 at the position of the distal end face 5D of the metal shell 5 is 2.8 mm, two semi-surface ground electrodes 12 are provided, and the semi-surface insulator gap ( γ) is set to γ = 0.6 mm for all, and the semi-creeping gap (β) is set to β = 1.6 mm for all, and the relationship between the main air gap (α) and the semi-creeping insulator gap (γ) is variously set. A spark plug was prepared. Then, these spark plugs were mounted on an automobile using a 1800 cc in-line four-cylinder direct-injection internal combustion engine, the shift lever was put in the D range, and operation was performed at idling at 600 rpm. The spark timing of the spark plug was fixed at 15 ° BTDC. Then, for each value of α-γ, the width (combustion stable region) of the injection end timing at which the misfire occurrence frequency per minute becomes substantially zero was measured. FIG. 9 shows the results.

From these results, the main air gap (α) is 0.8 mm ≦ α ≦ 1.0 mm, the semi-creep insulator gap (γ) is 0.5 mm ≦ γ ≦ 0.7 mm, and (α)
It can be seen that when −γ) satisfies 0.2 mm ≦ (α−γ) ≦ 0.4 mm, the region of the injection end timing can be widened.

(Experiment 10: The width of the parallel ground electrode was 2.2 m)
m, not less than twice the outer diameter of the center electrode tip surface) The diameter of the center electrode 2 inside the insulator 1 at the large diameter portion is φ2.2 mm, and the center of the main air gap (α) is formed. The outer diameter of the tip of the reduced diameter portion of the electrode 2 is φ0.6 m
m, the main air gap (α) is 1.1 mm, the diameter difference (δ) between the insulator 1 and the metal shell 5 at the position of the distal end face 5D of the metal shell 5 is 2.8 mm, and the semi-creeping ground electrode 12 Are provided, and the semi-creep insulator gap (γ) is γ =
0.6 mm, semi-creeping gap (β) is β =
It was set to 1.6 mm. Then, spark plugs were prepared in which the width W of the parallel ground electrode at the position of the center point of the center electrode when viewed from the front of the insulator 1 in the axial direction was varied. The tip of the parallel ground electrode 11 is cut in a tapered shape like the spark plug 205 of the fifth embodiment shown in FIG. 10 in the first embodiment. The width W of the electrode 11 is set in a state where the included angle θ of the tapered cut 11k is constant.
This was set by changing the width of the entire parallel ground electrode 11. The following tests were performed using these spark plugs. First, the vehicle was mounted on an automobile using a 2000 cc in-line six-cylinder internal combustion engine, the shift lever was put into the N range, and the accelerator was suddenly depressed from idling at 600 rpm until racing became 3000 rpm or more. Then, the maximum value of the discharge voltage was measured for each value of the ratio of W to the outer diameter of the front end surface of the center electrode 2. The results are shown in FIG.

From these results, the main air gap (α) is 0.8 mm ≦ α ≦ 1.0 mm, the semi-creep insulator gap (γ) is 0.5 mm ≦ γ ≦ 0.7 mm, and (α)
−γ) satisfies 0.2 mm ≦ (α−γ) ≦ 0.4 mm, and by making the width of the parallel ground electrode twice or more the outer diameter of the center electrode tip surface, the discharge voltage at the parallel ground electrode is reduced. It can be seen that it can be reduced sufficiently. Therefore, it is possible to suppress the occurrence of spark discharge at the semi-surface creeping ground electrodes 12 and 12 more than necessary.

Next, the following fuel bridge test was performed. In this experiment, water was used instead of gasoline generally used for internal combustion engines. The reason for this is that the brittleness of the bridge created in the spark discharge gap generally becomes a problem when the fuel bridge is at a very low temperature, that is, when the viscosity of the fuel is reduced. It has been found that the viscosity of water at room temperature is almost equal to the viscosity of gasoline at about -40 ° C. Material. First, each sample SP is mounted on the arm 501 of the fuel bridge tester 500 as shown in FIG.
05 ml was attached. After tilting the arm 501 by 30 °, the arm 501 was allowed to freely fall five times each time, and during that time, it was observed whether or not the bridge was broken every time the arm 501 was dropped. Then, three test samples were performed. One test sample was not supplemented with water until the end of the test.

FIG. 13 shows the test results. ○ indicates that the bridge was broken, and X indicates that the bridge was not broken. As a result of this test, the main air gap (α) was 0.8 mm ≦ α ≦ 1.0 mm, the semi-creep insulator gap (γ) was 0.5 mm ≦ γ ≦ 0.7 mm, (α
It can be seen that the occurrence of bridges can be sufficiently reduced by satisfying 0.2 mm ≦ (α−γ) ≦ 0.4 mm and setting the width of the parallel ground electrode to 2.2 mm or less.

Next, the following ignitability test was performed.
In this test, the shift lever was set to the D range using a car using a 2000 cc in-line 6-cylinder engine,
The test was performed under the constant running conditions of km / h (assuming a homogeneous lean burn combustion state). Under these engine conditions, the value of A / F when 1% misfire occurred was determined to be the ignition limit. FIG. 14 shows the results of this test. From this result, as a result of this test, the main air gap (α) was 0.8 mm ≦ α ≦ 1.0 m.
m, and the semi-creep insulator gap (γ) is 0.5 mm ≦
γ ≦ 0.7 mm, and (α−γ) is 0.2 mm ≦ (α
It can be seen that the occurrence of bridges can be sufficiently reduced by satisfying −γ) ≦ 0.4 mm and setting the width of the parallel ground electrode to 2.2 mm or less.

From the above test results, the main air gap (α) is 0.8 mm ≦ α ≦ 1.0 mm, the semi-creep insulator gap (γ) is 0.5 mm ≦ γ ≦ 0.7 mm, and α-γ) is 0.2 mm ≦ (α-γ) ≦ 0.4 mm
And the width of the parallel ground electrode is 2.2 mm or less and at least twice the outer diameter at the front end surface of the center electrode, so that the discharge voltage at the parallel ground electrode can be sufficiently increased without causing a fuel bridge. It can be seen that as a result, it has excellent ignitability.

(Experiment 11: Seventh Configuration; α ≦ 1.1 m)
m, 0.5 mm ≦ γ ≦ 0.7 mm, ψ ≦ 1.8 mm) The diameter of the large diameter portion of the center electrode 2 inside the insulator 1 is φ2.2 mm, and the main air gap (α) is The outer diameter of the center electrode 2 to be formed at the distal end face of the reduced diameter portion is φ0.6 m.
m, the main air gap (α) is 1.1 mm, the diameter difference (δ) between the insulator 1 and the metal shell 5 at the position of the tip end face 5D of the metal shell 5 is 2.8 mm, and the semi-metal is 2.2 mm wide. Two creepage ground electrodes 12 are provided, and semi-creepage insulator gap (γ)
Were set to γ = 0.6 mm and the semi-creeping gap (β) was set to β = 1.6 mm. Then, by changing the diameter φD of the insulator tip, the semi-surface creeping ground electrode 1 is changed.
Spark plugs in which the difference ψ from the width of No. 2 was set variously were prepared. FIG. 15 shows the results of measuring a stable combustion region using an automobile set under the same conditions as in Experiment 6 using these spark plugs.

From these results, α ≦ 1.1 mm, and
By setting 0.5 mm ≦ γ ≦ 0.7 mm and １ ≦ 1.8 mm, the range of the fuel injection end timing that does not cause misfire (that is, the width of the stable combustion region) can be widened, and the fuel lean It can be seen that the ignitability in the state can be improved. Such a phenomenon is considered to be due to the following reasons. In other words, if the difference between the diameter of the insulator tip and the width of the semi-creeping ground electrode 12 increases, when sparks occur between the semi-creeping ground electrode 12 and the center electrode 2, the outer periphery of the tip of the insulator 1 Will go around greatly. When a spark is generated obliquely rearward from the rear corner of the end surface of the semi-creeping ground electrode 12, the spark hits the front end of the insulator 1 and reaches the center electrode 2. When the spark collides with the front end of the insulator 1, the spark crawls obliquely rearward along the outer peripheral surface, and then changes direction and crawls in the direction of the peripheral surface on the front end side of the center electrode 1. Therefore, if the difference between the tip diameter of the insulator 1 and the width of the semi-creeping ground electrode 12 is large, the amount of spark crawls obliquely rearward along the outer peripheral surface of the insulator 1 becomes large, and the spark droops greatly. Can be

(Experiment 12: Additional requirement 3: The minimum diameter (D3) of the center through hole at the tip of the insulator is D3 ≦ 2.
Basis for 1 mm) The diameter difference (δ) between the insulator 1 and the metal shell 5 at the position of the tip end face 5D of the metal shell 5 is δ = 2.
8 mm, the main air gap (α) is α = 1.1 mm,
Two semi-creeping ground electrodes 12 are provided, the semi-creeping insulator gap (γ) is set to γ = 0.6 mm, the semi-creeping gap (β) is set to β = 1.6 mm, and
Spark plugs in which the insulator 1 had variously set minimum diameters (D3) of the center through-holes on the tip side of the holding portion 51 of the metal shell 5 were manufactured. Note that the outer diameter of the center electrode 2 is variously changed according to the diameter of the center through hole. These spark plugs were mounted on an automobile using a 1800 cc in-line four-cylinder direct injection internal combustion engine as in Experiment 1, the shift lever was put in the D range, and the engine was operated at idling at 600 rpm. The spark timing of the spark plug was fixed at 15 ° BTDC. Then, for each value of D3, the width of the injection end timing at which the misfiring occurrence frequency per minute becomes substantially zero (combustion stable region) was measured. FIG. 16 shows the results. From this result, the minimum diameter of the center through hole of the insulator 1 was φ2.1 m
It can be seen that a stable combustion region during idling operation can be widened by setting m or less.

Further, a pre-delivery fouling test was performed on the spark plug. The test conditions are as follows. That is, a spark plug is attached to an automobile using a 6-cylinder direct injection internal combustion engine having a displacement of 3000 cc. Then, the vehicle is placed in a low-temperature test room at -10 ° C.
According to the operation pattern specified in the low load compatibility test of SD1606, the number of cycles until reaching 10 MΩ was measured as one cycle of a predetermined operation pattern in which the jogging was performed several times at a low speed. Table 7 shows the above results.

[0121]

[Table 7]

According to the results, by setting the minimum diameter of the center through hole of the insulator 1 to be not more than φ2.1 mm, the number of cycles reaching 10 MΩ is extremely reduced even in the pre-delivery fouling test. 10
It can be seen that the number of cycles can be increased.

From the above two types of evaluation results, the minimum diameter (D3) of the center through-hole at the tip end side of the holding portion 51 where the insulator 1 is locked and held by the metal shell 5 is given by D3 ≦
It has been shown that by setting it to 2.1 mm, a stable combustion region can be widened even in a direct injection type internal combustion engine, and furthermore, a problem hardly occurs in a pre-delivery fouling test. By reducing the inner diameter of the insulator 1, the outer diameter of the center electrode 2 is also reduced, and the heat received at the tip of the insulator during the combustion cycle is appropriately suppressed from escaping to the center electrode 2. 1 makes it easy to raise the tip temperature. Therefore, even in a direct injection type internal combustion engine in which the temperature hardly rises during normal operation, the temperature at the tip end of the insulator 1 can be easily increased, and the carbon deposited by "smoldering" can be easily burned off. In addition, it is possible to prevent a spark from being generated between the distal end face 5D of the metal shell 5 and the insulator 1 and a spark from being generated near the holding portion. Also in the engine, it is possible to widen a stable combustion area. Similar results are obtained in the case of a spark plug 200 of the second embodiment in which only the tip of the center electrode 2 is reduced in diameter, as shown in FIG.

Next, another embodiment of the present invention will be described with reference to the drawings. In the following embodiment, the description will be omitted because there is no change other than the shapes of the insulator 1, the metal shell 5, and the center electrode 2 as compared with the above embodiment, and only different portions will be described. These explanations are given in FIG.
22 to the central electrode 2, the parallel ground electrode 11, the semi-surface creeping ground electrode 12, and the vicinity of the tip of the metal shell 5 '.

First, in the spark plug 210 according to the third embodiment shown in FIG. 18, the area of the distal end face 5D 'is increased by reducing the distal end of the metal shell 5' to the inner diameter side. By making the distal end portion of the metal shell 5 'in such a shape, it is possible to suppress the fuel from entering the inside of the metal shell 5'. In a direct injection internal combustion engine,
Since the fuel injection nozzle is directed toward the piston, the fuel that once hits the piston and rebounds approaches the diagonal tip side of the spark plug under the influence of the flow of intake air due to tumble and squish. When the fuel comes at this angle, it tends to get inside the metal shell. Therefore, by reducing the diameter of the distal end portion of the metal shell 5 ′ toward the inner diameter side as in the present embodiment, it is easy to suppress the fuel from entering the inside. In addition, since the area of the distal end face 5D 'is widened, welding can be facilitated and the thickness of the ground electrode can be increased for the spark plug having a plurality of ground electrodes as in the present invention. Furthermore, since the tip side can be wider than the holding portion 51 'of the metal shell 5',
The generation of a spark in the vicinity of the holding portion 51 'can be suppressed. As described above, the inner diameter of the reduced diameter portion when the distal end portion of the metal shell 5 ′ is reduced is such that the diameter difference δ from the insulator 1 is δ ≧ 2.6 × with respect to the main air gap (α). It is good to satisfy the relation of α.

In the spark plug 220 according to the fourth embodiment shown in FIG. 19, the tip of the electrode base material of the center electrode 2 ′ is reduced in diameter on the tip side of the tip face 1 D of the insulator 1, and a noble metal tip is attached to the tip. 21 ′ are joined by laser welding all around. The semi-creeping ground electrode 12 has a positional relationship such that a first extension line 31 extending outward from a line indicating the tip end face 1D of the insulator 1 is located on the tip end face 12C of the semi-creeping ground electrode 12. Is set. In the present embodiment, for example, the diameter of the center electrode base material is φ1.8 mm, and an Ir-5 mass% Pt tip of φ0.8 mm is joined to the tip thereof. Further, the distance β of the semi-surface gap (β) in the case of this embodiment is the outer diameter of the center electrode 2 at the position of the front end face 1D of the insulator 1, that is, the base before the center electrode base material is reduced in diameter. The distance between the diameter and the semi-creeping ground electrode 12 is the distance in the direction perpendicular to the axial direction of the spark plug.

In the spark plug 230 of the fifth embodiment shown in FIG. 20, the tip of the electrode base material of the center electrode 2 'is reduced in diameter, and the noble metal tip 21' is joined to the tip by laser welding all around. I have.

On the other hand, in the spark plug 240 of the sixth embodiment shown in FIG. 21, the tip of the electrode base material of the center electrode 2 'is not reduced in diameter, and the noble metal tip 21 having a substantially convex shape at the tip. 'Are joined by laser welding all around.
Further, the tip of the laser weld 212 is located on substantially the same plane as the tip face 1D of the insulator 1. In the present embodiment, for example, the diameter of the center electrode base material is φ1.8 mm, and the diameter of the distal end side is φ0.6 mm, and the diameter of the large diameter portion 211 ′ is Ir-20 mass% of φ1.8 mm. Rh chips are bonded. The inner diameter of the center through hole of the insulator 1 is φ
It is set to 1.9 mm. Further, the distance β of the semi-surface gap (β) in the case of the present embodiment is equal to the outer diameter of the center electrode 2 at the position of the front end face 1D of the insulator 1, that is, the semi-creep gap and the large diameter portion 211 ′ of the noble metal tip 21 ′. The distance from the creeping ground electrode 12 is perpendicular to the axial direction of the spark plug. With this configuration, it is possible to prevent the noble metal tip 21 ′ from falling off from the center electrode base material even when a spark occurs in the semi-creep gap (β). When a spark is generated in the semi-creeping gap (β), a spark is generated between the side surface of the noble metal tip 21 ′ and the semi-creeping ground electrode 12. If sparks occur frequently at this position, even if the noble metal tip 21 ′ near the distal end face 1 </ b> D of the insulator 1 is consumed, the noble metal tip 21 ′ does not become thinner than the tip of the noble metal tip 21 ′. The tip of the tip 21 'can be prevented from falling off. Furthermore, because the tip is thin,
It is possible to reduce the discharge voltage when a spark occurs in the main air gap (α). Therefore, the ignitability is improved. In particular, in a direct injection internal combustion engine, the stable combustion region can be widened.

Similarly, in the spark plug of the seventh embodiment shown in FIG. 22, the tip of the electrode base material of the center electrode 2 'is not reduced in diameter, and the noble metal tip 2 has a substantially convex shape at the tip.
1 ′ are joined by laser welding all around. In this embodiment, the large-diameter portion 211 ′ of the noble metal tip 21 ′ is located inside the distal end face 1 D of the insulator 1. In the present embodiment, for example, the diameter of the center electrode base material is φ1.8 mm.
An Ir-20 mass% Rh chip having a diameter of φ0.6 mm on the distal end side and a diameter of φ1.8 mm on the large diameter portion 211 ′ is bonded to the distal end. Since the inner diameter of the center through hole of the insulator 1 is set to φ1.9 mm, the insulator 1
Is set to 0.1 mm between the inner diameter of the center through hole and the outer diameter of the noble metal tip 21 '. Further, the distance β of the semi-surface gap (β) in the case of the present embodiment is the outer diameter of the center electrode 2 at the position of the front end face 1D of the insulator 1, that is, the small diameter of the noble metal tip 21 ′ of the noble metal tip 21 ′. It is the distance between the part and the semi-creeping ground electrode 12.

When a spark is generated at the semi-creep gap (β), the spark crawling on the front end face 1D of the insulator 1 further crawls on the inner wall of the center through hole of the insulator 1 and the noble metal tip 21 '.
Large diameter portion 211 ′. Therefore, even if the large-diameter portion 211 ′ is inside the center through hole of the insulator 1, a spark is generated between the large-diameter portion 211 ′ and the semi-surface creeping ground electrode 12, so that the tip of the noble metal tip 21 ′ Can be prevented from falling off. Further, since the tip portion has a small diameter, it is possible to reduce a discharge voltage when a spark is generated in the main air gap (α). Therefore, the ignitability is improved. Also,
Particularly in a direct injection type internal combustion engine, the stable combustion region can be widened. Then, the outer diameter of the noble metal tip 21 ′ and the insulator 1
Since the minimum value of the diameter difference from the inner diameter of the center through hole is 0.1 mm, it is easier to suppress the consumption of the base material of the center electrode 2 ′ due to spark discharge. This is considered to be due to the following reasons. That is, when a spark is generated in the semi-surface gap (β), the spark crawls on the inner wall of the center through hole of the insulator 1. At this time, the noble metal tip 21 '
If the diameter difference between the outer diameter and the inner diameter of the center through hole of the insulator 1 becomes large, the sparks may enter the precious metal tip 21 'further deeply without reaching the precious metal tip 21' and reach the base material of the center electrode 2 '. Since the base material of the center electrode 2 'has a lower spark wear resistance than the noble metal tip 21', the base material is liable to be consumed quickly and the chip may fall off. Therefore, by reducing the diameter difference, the phenomenon that sparks reach the base material of the center electrode 2 'can be suppressed, and the durability is improved.

As shown in FIG. 30, the noble metal tip 50 can be welded to a position facing the main air gap of the parallel ground electrode 11 as well. The spark plug 2
Reference numeral 70 denotes an example in which the noble metal tip 50 is also provided on the parallel ground electrode 11 in the spark plug 220 of FIG. The material of the noble metal tip 50 can be the same as the noble metal tip 21 'on the parallel ground electrode 11 side. On the other hand,
When a spark plug is used with a voltage polarity at which the center electrode 2 side is negative, spark consumption is slightly slower on the parallel ground electrode 11 side than on the center electrode 2 side, so that the melting point is slightly higher than on the center electrode 2 side. (For example, when the noble metal tip 21 ′ on the center electrode 2 side is made of an iridium alloy, the noble metal tip 50 on the parallel ground electrode 11 side can be made of platinum or a platinum alloy. ).

Parallel ground electrode 11 and semi-creeping ground electrode 12
Means that any of the base materials forming the surface layer portion can be made of nickel or a nickel alloy. In this case, it is possible to use different materials for the base materials for the electrodes 11 and 12. That is, the base material of the parallel ground electrode 11 is made of a first nickel base metal containing nickel as a main component,
The base material of the semi-creeping ground electrode 12 can be composed of a second nickel base metal containing nickel as a main component.

For example, in FIG. 30 (the form of the semi-surface creeping ground electrode 12 is the same as that of FIG. 2 or FIG. 19; The noble metal tip is not welded, and the entire end face is made of the second nickel-based base metal, while at least the surface layer portion 11b of the parallel ground electrode 11 is made of the first nickel-based base metal, A noble metal tip 50 is welded to the surface facing the electrode 2. In this case, the nickel content of the second nickel base metal can be made lower. That is, since the noble metal tip 50 is welded to the parallel ground electrode 11, the spark consumption of the base material does not matter much. On the other hand, since the semi-creeping ground electrode 12 side has a higher spark frequency than the parallel ground electrode 11 side,
The idea is to reduce the cost by omitting the noble metal tip and, in this case, to reduce the spark consumption by improving the nickel content, since the base material surface itself becomes the discharge surface. In this case, the nickel content of the second nickel base metal is desirably 85% by mass or more. For example, the first nickel base metal is Inconel 600 (trade name), and the second nickel base metal is 9
It can be composed of a 5 mass% nickel alloy (the balance is chromium, manganese, silicon, aluminum, iron, etc.).

(Other Embodiments) In each of the embodiments described above, the semi-creeping ground electrode 12 has two poles. However, the semi-creeping ground electrode 12 may be a single pole or three or more poles. It may be multipolar. However, for a single pole, the insulator 1
It is difficult to burn off carbon with sparks over the entire circumference of the end face of the electrode, and the spark cleanliness deteriorates.
2 is preferably 2 to 4 poles. In addition, the position of the semi-creeping ground electrode 12 has been described in many embodiments in the case where the entire front end surface 12C of the semi-creeping grounding electrode 12 faces the straight tubular portion 102 of the insulator 1. May be set such that a first extension line 31 obtained by extending a line indicating the front end surface 1D of the semi-surface creeping ground electrode 12 is located on the front end surface 12C of the semi-surface creeping ground electrode 12. Furthermore, the spark plug in which the diameter of the center electrode is not reduced (so-called thermo) inside the front end of the insulator 1 has been described, but the spark plug may be reduced in diameter in one or more stages.

The spark plug 260 shown in FIG.
This is an example in which a straight tubular portion 102B is formed through a stepwise reduced diameter portion. Spark plug 10 shown in FIG. 23 or FIG.
0 and 260, the straight tubular portion 102 or 102B is formed at the tip of the insulator 1. The length of the straight tubular portion 102 or 102B in the direction of the axis 30 is 0.5 to 1.5 mm. In these configurations, a tapered bulging portion 10 as shown in FIG. 31 (c) is provided behind the straight tubular portion 102 or 102B.
5, or a step-like bulging portion 102A as shown in FIG.

If the bulging portion is too close to the rear side edge 12B of the end surface 12C of the semi-surface creeping ground electrode 12, sparks from the bulging portion tend to hang down rearward.
For example, as shown in FIG. 32 (a), the electric field tends to concentrate on the rounded transition portion 102T of the step-shaped bulging portion 102A, and the rear side edge 12B of the semi-creeping ground electrode 12
As a result, the spark SP3 is discharged toward the transition portion 102T, so that the spark SP3 hangs rearward and fires around the rear portion of the side peripheral surface of the insulator 1. It is clear that such sparks deteriorate the ignitability.

Therefore, as shown in FIG. 31, the midpoint of the rear side edge 12B of the end surface 12C of the semi-creeping ground electrode 12 in the direction of the axis 30 of the insulator 2 and the axis 30 of the insulator 2 are aligned. On the imaginary plane including the surface, the size of the semi-creeping gap is defined as γ (unit: mm),
When a circle Ck of (γ + 0.1) mm centering on the middle point of A is drawn, if the entire bulging portion 102A is positioned outside the circle Ck, a spark such as SP3 in FIG. Can be effectively prevented from sagging. In addition,
As shown in FIG. 31B, if the transition portion 102T of the bulging portion 102A is formed as an inclined surface following the circle Ck, FIG.
As compared with a mode in which the transition portion 102T rises vertically from the outer peripheral surface of the straight tubular portion 102B as shown in FIG.
The length of the transition section 102 can be reduced.
Since a small-angle edge that tends to concentrate the electric field at T is less likely to be generated, it is more effective to prevent the spark from drooping.

The following experiment was conducted to confirm the above effects. (Experiment 13) In the spark plug of FIG. 3, the shape of the straight tubular portion 102 of the insulator 1 is changed to the type shown in FIG. 31 (c) (type A) and the type shown in FIG. 31 (a) (type B). Were prepared. In each of these spark plugs, the parallel ground electrode 11 is eliminated, two semi-creeping ground electrodes 12 are provided, the semi-creeping insulator gap (γ) is γ = 0.6 mm, and the semi-creeping gap (β) is both. β is set to 1.6 mm, and the height position of the end face 1D of the insulator 1 and the end face 1 of the semi-creeping ground electrode 12 are set.
The step E from the height of the rear edge 12B of the 2C is 0.9 m.
m. Then, the straight tubular portion (102 or 102
The lengths of B) were various values shown in Table 8 from 0.9 to 1.8 mm. Table 8 shows the radius (γ + 0.
1) The bulge 105 or 10 within the range of the circle of mm.
The case where 2A exists is indicated by “*”, and the case where 2A does not exist is indicated by “◎”. The following experiment was performed using these spark plugs. That is, the spark plug was attached to the chamber, the inside of the chamber was pressurized to 0.6 MPa, and the operation of generating a spark once per second by the full transistor power supply was continued for one minute. A video of the state of spark generation during that time is taken, and the image is analyzed, so that the end surface 12
C, the rear side edge 1 of the spark generated from the rear side edge 12B.
Maximum droop length L in the direction from 2B to axis 30
Were evaluated as good (○) when the length was within 2.5 mm, and as poor (x) when the length was not within 2.5 mm. Table 8 shows the above results.

[0139]

[Table 8]

That is, the length of the straight tubular portion is 1.5 mm or less, or the radius (γ + 0.1) mm
It can be seen that when there is no bulging portion in the circle, the sagging of the spark is effectively suppressed.

Next, the end surface 12C of the semi-creeping ground electrode 12
It is possible to improve the form of generation of sparks from the surface by devising the shape of the end face 12C. First, when defining the form of the end face 12C, the following geometrical definition is made. That is, in FIG. 2B, the side where the tip of the insulator 1 is located in the direction of the axis 30 is defined as the front side, and the opposite side is defined as the rear side. Furthermore, a virtual plane VP including the midpoint M1 of the rear side edge 12B of the end surface 12C and the axis 30 of the semi-surface creeping ground electrode 12
In contrast, a plane that includes the axis 30 and is orthogonal to the plane VP is defined as the projection plane PP. Then, the orthogonal projection of the end face 12C onto the projection plane PP is referred to as 12NP (hereinafter, referred to as an end face orthogonal projection 12N).
P). When the end face 12C is parallel to the projection plane PP as shown in FIG. 26, the orthographic projection 12NP is geometrically congruent with the end face 12C as shown in FIG. 2B. On the other hand, as shown in FIG. 21, when the end face 12C is formed into an arc-shaped surface instead of a plane,
Although the shape of C is a curved surface, as shown in FIG.
The shape of the end face orthographic projection 12NP is basically not different from the case shown in FIG.

When the semi-surface creeping ground electrode 12 is formed by bending a linear member having a rectangular axial cross section, for example, as shown in FIG. The shape is also rectangular. At this time, the intersection of the axis 30 and the rear side edge 12B on the projection plane PP is represented by X
Similarly, when a point of intersection with the front side edge 12A is set to Y, and a reference line RL orthogonal to the axis 30 is drawn through the midpoint Q of the line segment XY, an area located forward of the reference line RL ( Hereinafter, the area S1 of the front area FA is the same as the area located on the rear side (hereinafter, the rear area RA).
Is approximately equal to the area S2. In the discussion on the projection plane PP, it is complicated to refer to each time as “orthogonal projection of 都”.
B "," front side edge 12A "and the like.

If the end face orthographic projection 12NP is the end face 12C having such a shape, the front area FA and the rear area RA
In, the frequency of occurrence of sparks per unit time is substantially equal. For example, as shown in FIG. 32 (c), when it is assumed that spark wear is locally delayed in the area DW for some reason, the gap interval of the area DW left behind from the wear becomes smaller than other areas. , And after that area D
Conversely, spark discharge at W tends to occur. From a causal point of view based on this fact, the semi-surface ground electrode 12 is consumed uniformly over the entire end surface 12C serving as a discharge surface, in other words, in a unit, so that local gap interval abnormality is not generated as much as possible. Spark frequency per area / unit time is
It must be substantially uniform over the entire end face 12C.
Therefore, the end face orthographic projection 12 bisected with respect to the reference line RL
Since the two areas of the NP, that is, the areas S1 and S2 of the front area FA and the rear area RA are equal, each area FA
Thus, the frequency of sparks generated per unit time between and RA is also substantially equal. As a result, sparks occur at substantially the same frequency in both the front area FA and the rear area RA, so that the effects of suppressing channeling and improving ignitability cannot be expected.

Therefore, in FIG. 33, the end face orthographic projection N
The area S1 of the front area FA in P is the rear area RA
The shape of the end face 12C is selected so as to be larger than the area S2. Such a semi-creeping ground electrode 12
As the area increases, the frequency of sparks SP per unit time in the front side area FA increases, and the front side area FA with a soft attack on the insulator 1 increases, thereby suppressing channeling and improving ignitability. It can be achieved effectively. In FIG. 33, a trapezoidal shape in which the shorter side of the parallel opposite side is the rear side edge 12B is adopted. The frequency of occurrence of the spark SP is schematically represented by the length of the arrow. On the other hand, FIG. 34 shows an example in which the rear side edge 12B has an arcuate or semilunar shape coinciding with the arc, and S1> S.
It is clear that 2 holds.

Next, the semi-surface creeping ground electrode 12 is
When a rectangular end face 12C as shown in (b) is provided, if its corners, particularly the corners at both ends of the rear side edge 12B, have a pin angle as shown in the figure, the starting point is set here. As a result, the spark SP3 is easily emitted obliquely outward and downward. As shown in FIG. 32 (a), such a spark SP3 may fly in a drooping shape along the axial direction of the insulator 1, leading to a problem that the ignitability is significantly impaired. In particular, when a sharp step-like transition portion 102T is formed at the base end of the straight pipe portion 102B, the spark SP
3 has a shape in which it wraps around a ridge line portion where electric field concentration is likely to occur, so that drooping becomes even more severe, leading to a problem that ignitability is greatly impaired.

Therefore, as shown in FIG. 35, at least in the rear area RA, the radius of curvature or the chamfer width at the tip of the corner is 0.2 mm or more, or the angle between two sides forming this corner exceeds 90 degrees. By selecting the shape of the end face 12C such that no sharp corner appears in the end face orthographic projection 12NP, the rear side region R
It is possible to effectively suppress the generation of the spark accompanying the dripping from A as described above. In addition, by eliminating sharp corners that are likely to be the starting points of spark generation from the rear area RA, the spark generation frequency itself on the area side is also reduced.

FIG. 35A shows a straight rear side edge 12B.
(The angle between the two sides is approximately 90 ° C.)
In this example, C1 and RC2 are rounded portions having a radius of curvature of 0.2 mm or more (for example, up to about 1.0 mm). FIG. 35B is an example in which the corners RC1 and RC2 are chamfers having a width of 0.2 mm or more. In this case, one corner is formed at each end of the chamfered portion. However, since these two corners have obtuse angles on both sides and are unlikely to be sensitive spark generation starting portions, the radius of curvature at the tip is small. May be less than 0.2 mm.

In FIGS. 35A and 35B, the corners RC1 and RC2 formed at both ends of the rear side edge 12B are shown.
Only a round portion or a chamfered portion is formed. As a result, the area S1 of the front side area FA is slightly larger than the area S2 of the rear side area RA, and the effect of S1> S2 is somewhat generated. However, as shown in FIG. 35 (c), corners FC formed at both ends of the front side edge 12A.
It is of course possible to form rounded portions (chamfered portions) at all four corners including FC1 and FC2 so that S1 and S2 are substantially equal. The configuration in FIG.
Since the end face orthographic projection 12NP has a substantially equilateral trapezoidal shape, and the corners RC1 and RC2 formed at both ends of the rear side edge 12B are both obtuse, the effect of eliminating sharp corners is also produced. Also in the configuration of FIG. 34, the rear side edge 12B
However, since it is formed in an arc shape in which a sharp corner is essentially not generated, it can be said that the sharp corner is similarly excluded.

FIG. 36A shows the trapezoidal end face 1 of FIG.
In FIG. 2C, each corner is formed in a round shape, and the effect of S1> S2 and the effect of eliminating sharp corners are more ideally achieved. In this case, as shown in (b), when the end face 12C has a cylindrical shape as shown in FIG. 27, as will be apparent when the end face 12C is developed, the corners RC1 at both ends of the rear side edge 12B are apparent. , RC2, the angle between the two sides is further increased, and the spark generation suppressing effect can be made more remarkable.

Note that the semi-creeping ground electrode 12 of any shape shown in FIGS. 33 to 36 can be formed by bending a linear member having the same axial cross section as the desired end face orthographic shape.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view of a spark plug according to a first embodiment.

FIG. 2A is an enlarged partial cross-sectional view showing the vicinity of an electrode of a spark plug according to a first embodiment; FIG.
(C) is a diagram for explaining the projection of the semi-surface creeping ground electrode 12 onto the plane PP.

FIG. 3 is an enlarged partial sectional view showing the vicinity of an electrode of a spark plug according to a second embodiment.

FIG. 4 is an enlarged partial sectional view showing the vicinity of an electrode of a spark plug according to a third embodiment.

FIG. 5 is a JIS standard (JIS B8031) of a spark plug to which the spark plug is applied or the J
FIG. 4 is a graph showing a relationship between a protrusion amount (F) of the insulator protruding to the distal end side from a dimension A defined in the ISO standard corresponding to the IS standard and an injection end timing for stable combustion.

FIG. 6 is an enlarged partial sectional view showing the vicinity of an electrode of a spark plug according to a fourth embodiment.

FIG. 7 is a graph showing the relationship between the amount of protrusion of the center electrode 2 from the front end face 1D of the insulator 1 and the injection end timing for stable combustion.

FIG. 8 shows a spark between the distal end face 5D of the metal shell 5 and the insulator 1 with the vertical axis representing the distance α of the main air gap (α) and the horizontal axis representing the distance γ of the semi-surface creepage gap (γ). FIG. 4 is a graph in which points at which the occurrence of phenomena have started are plotted.

FIG. 9 is a graph showing a relationship between a difference (α−γ) between a main air gap (α) and a semi-surface crevice insulator gap (γ) and an injection end timing for stable combustion.

FIG. 10 is an enlarged partial sectional view showing the vicinity of an electrode of a spark plug according to a fifth embodiment.

FIG. 11 is a graph showing the relationship between the ratio of the width W of the parallel ground electrode to the center electrode tip diameter at the position of the center point of the center electrode and the discharge voltage.

FIG. 12 is a diagram showing an outline of a fuel bridge tester.

FIG. 13 is a diagram showing the results of a fuel bridge test.

FIG. 14 is a graph showing the relationship between the ratio of the width W of the parallel ground electrode to the center electrode tip diameter at the position of the center point of the center electrode, and the ignitability.

FIG. 15 is a graph showing the relationship between the difference の between the diameter of the insulator tip and the width of the semi-creeping ground electrode and the injection end timing for stable combustion.

FIG. 16 is a view showing a minimum diameter (D) of a center through hole at a tip portion of a holding portion of an insulator which is locked and held by a metal shell.
FIG. 3 is a graph showing a relationship between 3) and an injection end time at which stable combustion is performed.

FIG. 17 is an enlarged partial sectional view showing the vicinity of an electrode of a spark plug according to a second embodiment.

FIG. 18 is an enlarged partial sectional view showing the vicinity of an electrode of a spark plug according to a third embodiment.

FIG. 19 is an enlarged partial sectional view showing the vicinity of an electrode of a spark plug according to a fourth embodiment.

FIG. 20 is an enlarged partial sectional view showing the vicinity of an electrode of a spark plug according to a fifth embodiment.

FIG. 21 is an enlarged partial sectional view showing the vicinity of an electrode of a spark plug according to a sixth embodiment.

FIG. 22 is an enlarged partial cross-sectional view showing the vicinity of an electrode of a spark plug according to a seventh embodiment.

FIG. 23 is an explanatory view showing an example of a mode of attaching a spark plug to a direct injection engine.

FIG. 24 is a main part side view showing an example of a spark plug in which three semi-creeping ground electrodes are provided and a good heat conductive material is arranged in the parallel ground electrodes.

FIG. 25 is a bottom view showing an example of a spark plug provided with three semi-creeping ground electrodes.

FIG. 26 is a bottom view of the spark plug of FIG. 2;

FIG. 27 is a bottom view showing an example in which the end surface of the semi-surface creeping ground electrode in FIG. 26 is cylindrical.

FIG. 28 is a schematic view exemplarily showing various relationships between a center electrode front end surface and an insulator front end surface.

FIG. 29 is a partial front sectional view showing an example of a spark plug in which a straight tubular portion of an insulator is formed in two steps.

FIG. 30 is an essential part side view showing an example of a spark plug in which a noble metal tip is joined to a parallel ground electrode.

FIG. 31 is a schematic view illustrating various positional relationships between the straight tubular portion of the insulator and the semi-creeping gap.

FIG. 32 is an explanatory view showing the relationship between various spark generation forms and the shape of the electrode tip surface in the semi-surface creeping ground electrode.

FIGS. 33A and 33B are a side view and a front view showing a first improvement example of the end surface shape of the semi-creeping ground electrode. FIGS.

34A and 34B are a side view and a front view showing a second improvement example of the end surface shape of the semi-surface creeping ground electrode.

FIG. 35 is a side view showing third, fourth, and fifth improved examples of the end surface shape of the semi-surface creeping ground electrode.

FIG. 36 is an explanatory view showing sixth and seventh examples of improvement of the end surface shape of the semi-surface ground electrode.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Insulator 1D Insulator tip surface 1E Insulator side peripheral surface 2 Center electrode 2 'Center electrode 2A Center electrode side peripheral surface 5 Metal shell 5D Metal shell tip surface 11 Parallel ground electrode 12 Semi creeping ground electrode 12 'Semi creeping ground electrode 12A Front end side edge 12B Rear end side edge 12C End surface of semi creeping ground electrode 21, 21', 50 Noble metal tip 30 Central axis 31 First extension line 32 Second extension line 33 Third Extension line 102 Straight tubular part (α) Main air gap α Main air gap distance (β) Semi creepage gap β Semi creepage gap distance (γ) Semi creepage insulator gap γ Semi creepage insulator gap distance φD Insulator tip Diameter D2 Center electrode base diameter D3 Minimum diameter of center through hole of insulator E Step between rear end side edge of semi-creeping ground electrode and front end face of insulator F Insulation amount of insulator H Central power Pole protruding amount P1 Intersection point of first and second extension lines P2 Intersection point of first and third extension lines W Width of parallel ground electrode at position of center point of center electrode

Claims (28)

[Claims] 1. An insulator having a center through hole, a center electrode held in the center through hole and disposed at a tip of the insulator, and a tip of the insulator protruding from its tip surface. And a parallel ground electrode, one end of which is joined to the front end surface of the metal shell and the other end is disposed so as to face the front end surface of the center electrode. A main air gap (α) is formed by the front end surface of the center electrode, and one end is joined to the metallic shell and the other end is opposed to the side peripheral surface of the center electrode or the side peripheral surface of the insulator. A plurality of semi-creeping ground electrodes arranged so that the semi-creeping ground electrode has a semi-creeping ground gap between an end face of the other end of the semi-creeping ground electrode and a side peripheral face of the center electrode opposed to this end face. β) is formed,
A semi-surface insulator gap (γ) is formed between an end surface of the semi-surface ground electrode and a side peripheral surface of the insulator facing the end surface, and the main air gap (α) is formed.
Distance α (unit: mm) and the semi-creeping gap (β)
And the distance β (unit: mm) satisfies the relationship α <β,
In addition, the distance α of the main air gap (α) and the distance γ (unit: mm) of the semi-surface insulator gap (γ) are α>
A spark plug characterized by satisfying the relationship of γ. 2. The method according to claim 1, wherein the main air gap (α) is α ≦ 1.
1 mm, and the semi-surface insulator gap (γ) is:
0.5 mm ≦ γ ≦ 0.7 mm, and a diameter difference δ (unit: mm) between the insulator and the metal shell at the position of the distal end surface of the metal shell is δ ≧ 3.6 mm. The spark plug according to 1. 3. The main air gap (α) is 0.8 m.
m ≦ α ≦ 1.0 mm, and the semi-surface insulator gap (γ) is 0.5 mm ≦ γ ≦ 0.7 mm, and the main air gap (α) and the semi-surface insulator gap (γ) 3. The spark plug according to claim 1, wherein 0.2 mm ≦ (α−γ) ≦ 0.4 mm. 4. The center electrode has a tip portion reduced in diameter and a width W of the parallel ground electrode at a position of a center point of the center electrode when viewed in plan from the axial front side of the insulator. 4. The spark plug according to claim 3, wherein the spark plug is not more than 2.2 mm and at least twice as large as the outer diameter of the front end surface of the center electrode. 5. The main air gap (α) is α ≦ 0.9.
mm, and the semi-creep insulator gap (γ) is 0.
5 .ltoreq.2.8 mm, wherein 5 mm.ltoreq..gtoreq..ltoreq.0.7 mm, and the diameter difference .delta. Between the insulator and the metallic shell at the position of the distal end face of the metallic shell is .delta..gtoreq.2.8 mm. Spark plug. 6. The main air gap (α) is α ≦ 1.1.
mm, and the semi-creep insulator gap (γ) is 0.
6. The spark plug according to claim 1, wherein 5 mm ≦ γ ≦ 0.7 mm, and the number of the semi-creeping ground electrodes is three or more. 7. 7. The insulator has a straight tubular portion at the tip end thereof, and when the side where the tip end is located in the axial direction of the insulator is the front side, the straight tubular portion is located at the rear end position. On the other hand, the rear end side edge of the end surface of the semi-creeping ground electrode is coincident or located on the front side, and the height position of the front end surface and the height of the rear end side edge of the end surface of the semi-creeping ground electrode A step E (unit: mm) in the axial direction from the height position,
The spark plug according to any one of claims 1 to 6, wherein a difference between a radius of curvature R (unit: mm) of a curved surface from the distal end surface to the side peripheral surface of the insulator is RE 0.1 mm. . 8. The spark plug according to claim 7, wherein the value of the step E is 0.5 mm or less. 9. The spark plug, to which the spark plug is applied, protrudes forward from a dimension A defined in the JIS standard (JIS: B8031) or the ISO standard indicated in the JIS standard. The protrusion amount F (unit: mm) of the insulator is 3.0 mm ≦ F ≦ 5.0 m
The spark plug according to any one of claims 1 to 8, wherein m is m. 10. The parallel ground electrode has a base material forming a surface layer portion and a good heat conductive material forming an inner layer portion and made of a material having better heat conductivity than the base material. Spark plug according to 1. 11. The main air gap (α) is defined as α ≦
1.1 mm, the semi-surface insulator gap (γ)
Is 0.5 mm ≦ γ ≦ 0.7 mm, and when the insulator is represented by an orthogonal projection with respect to a virtual plane parallel to the axis of the insulator, a line indicating the tip surface is extended outward. A first extension line and the semi-creeping gap (β) of the insulator
The distance between the intersections of two lines indicating the side peripheral surfaces on both sides of the axis facing the portion and extending in the direction of the front end surface (hereinafter simply referred to as "the insulator tip"). The spark plug according to any one of claims 1 to 10, wherein a difference ψ (unit: mm) between a diameter “φD (unit: mm)” and a width of the semi-creeping ground electrode is ψ ≤ 1.8 mm. 12. An intersection point of a first extension line and a second extension line extending from a line indicating a side peripheral surface of the insulator facing the semi-surface crevice gap (β) toward the tip end surface. ,
The shortest distance (hereinafter simply referred to as “insulator tip thickness” ρ (unit: mm)) to the intersection of the first extension line and the extension line of the center through hole is ρ ≦ 0.9 mm. The spark plug according to claim 11. 13. The spark plug according to claim 1, wherein an amount H (unit: mm) of the center electrode protruding from a front end surface of the insulator satisfies H ≦ 1.25 mm. 14. The spark plug according to claim 13, wherein an amount H by which the center electrode projects from a tip end surface of the insulator satisfies H ≦ 0.5 mm. 15. The main air gap (α), the semi-creeping gap (β) and the semi-creeping insulator gap (γ) satisfy a relationship of α ≦ 0.4 × (β−γ) + γ. The spark plug according to any one of claims 1 to 14. 16. The semi-creeping ground electrode has at least an end face diameter of the center through hole of the insulator at least at an end face of the other end when the tip end of the insulator is viewed from the axial front side in a plan view. Claim 1 having a greater width than
16. The spark plug according to any one of claims 15 to 15. 17. The insulator according to claim 1, wherein said central through-hole of said insulator is reduced in diameter at a tip end side of said insulator.
7. The spark plug according to any of 6. 18. The insulator has a reduced diameter straight tubular portion forming a tip portion, and a bulge larger in diameter than the straight tubular portion adjacent to an axially rear side of the straight tubular portion in the axial direction. A length of the straight tubular portion is 1.5 mm or less; and the semi-creeping ground electrode is a midpoint of a rear side edge of the other end face in the axial direction of the insulator. And on the imaginary plane including the axis of the insulator and the distance of the semi-creeping insulator gap (γ) as γ (unit: mm), centering on the midpoint of the rear side edge (γ + 0. 1)
The spark plug according to any one of claims 1 to 17, wherein when a circle of mm is drawn, the whole of the bulging portion is located outside the circle. 19. A side where the tip portion is located in the axial direction of the insulator is defined as a front side, and further, a midpoint of a rear side edge of the other end face of the semi-surface creeping ground electrode and the axis line. With respect to a virtual plane including, the plane including the axis and orthogonal to the plane is defined as a projection plane, and when the plane is orthogonally projected on the projection plane, the other end face is the projection plane. Above, the intersection point between the axis and the rear side edge is X, and the intersection point with the front side edge is Y, which is located on the front side of a reference line orthogonal to the axis through the midpoint of the line XY. 19. The spark plug according to claim 1, wherein the area S1 of the region has a shape larger than the area S2 of the region located on the rear side. 20. A side where the tip portion is located in the axial direction of the insulator is defined as a front side, and further, a midpoint of a rear side edge of the other end face of the semi-creeping ground electrode and the axis line. For a virtual plane including, the plane including the axis and orthogonal to the plane is defined as a projection plane, and when expressed by orthographic projection on the projection plane, the outer peripheral edge of the end face of the other end is X is the intersection of the axis and the rear side edge on the projection plane.
Similarly, assuming that the intersection with the front side edge is Y, at least in the region located behind the reference line orthogonal to the axis through the midpoint of the line segment XY, at least the corner has a tip radius of curvature or chamfer width. The spark plug according to any one of claims 1 to 19, wherein two sides forming the corners have an angle larger than 90 degrees. 21. The insulator according to claim 1, further comprising a straight tubular portion at a tip end of the insulator, the straight tubular portion extending from a tip end surface of the metal shell to a rear end side. 20
The spark plug according to any one of the above. 22. The center electrode is formed by joining a noble metal tip formed of a noble metal or a noble metal alloy having a melting point of 1600 ° C. or more to a tip portion of a base material, and the joining portion is formed of the insulator. 22. The spark plug according to claim 1, wherein the spark plug is joined in the center through hole. 23. A minimum diameter D3 (unit: mm) of the center through hole at a tip end side of a holding portion where the insulator is locked and held by the metal shell is D3 ≦ 2.1 mm.
The spark plug according to any one of claims 1 to 22, wherein 24. The noble metal tip is configured such that an outer diameter on the joint side is larger than an outer diameter on a distal end side.
3. The spark plug according to 3. 25. The spark plug according to claim 23, wherein a minimum value of a difference between an outer diameter of the noble metal tip and an inner diameter of a center through hole of the insulator is 0.2 mm or less. 26. The parallel ground electrode includes a base material forming a surface layer portion and a good heat conductive material forming an inner layer portion and made of a material having better heat conductivity than the base material. Item 29. The spark plug according to any one of Items 1 to 25. 27. The semi-surface creeping ground electrode, wherein a noble metal tip is not welded to the end face of the other end, and the entire end face is made of a second nickel base metal mainly composed of nickel. On the other hand, at least the surface layer of the parallel ground electrode is made of a first nickel base metal having nickel as a main component, and a noble metal tip is welded to a surface facing the center electrode, and further, 27. The spark plug according to claim 1, wherein the nickel content of the second nickel-base metal is higher than the nickel content of the first nickel-base metal. 28. The spark plug according to claim 27, wherein the nickel content of the second nickel base metal is 85% by mass or more.