JP4377177B2 - Spark plug for internal combustion engine - Google Patents

Description

  The present invention relates to a spark plug for an internal combustion engine, in particular, in the form of creeping discharge between the creeping ground electrode and the insulator, and between the insulator and the central electrode via the tip of the insulator. The present invention relates to a spark plug for an internal combustion engine that generates a propagating spark discharge.

  In recent years, along with improvements in engine performance, spark plugs for internal combustion engines are required to have a longer life and improved antifouling property. For example, a spark plug that generates semi-surface discharge is known as a spark plug for an internal combustion engine with improved fouling resistance (see, for example, Patent Document 1). Semi-creeping discharge is a spark discharge that propagates in the form of creeping discharge between the surface of the insulator and the center electrode, and the surface of the surface of the insulator is in the air. Say. In general, when a spark plug for an internal combustion engine is used for a long time in a low temperature environment, it becomes a so-called “buzz” or “cover” state, and the surface of the tip of the insulator is covered with a conductive fouling substance such as carbon. Malfunction is likely to occur. On the other hand, as described above, the spark plug that generates a semi-surface discharge has excellent anti-fouling property because it can burn off a fouling substance such as carbon by the surface discharge along the surface of the tip of the insulator.

Japanese Unexamined Patent Publication No. 2000-68032 (FIGS. 1 and 2) Japanese National Patent Publication No. 11-510958 (FIG. 1)

  By the way, in the semi-surface discharge type spark plug of Patent Document 1, since the tip of the creeping ground electrode faces the insulator tip, the electric field strength between the creeping ground electrode and the insulator tip is excessive. There was a risk of becoming stronger. Therefore, there has been a risk that the insulator will be prematurely consumed or penetrated due to semi-surface discharge.

  On the other hand, in the semi-surface discharge type spark plug shown in FIG. 1 of Patent Document 2, the tip of the creeping ground electrode does not face the insulator tip, and further on the radially outer side of the insulator tip. The semi-creeping discharge gap (creeping ground electrode and insulator) is formed between the inner surface of the creeping ground electrode facing the center electrode and extending in the longitudinal direction of the creeping ground electrode and the tip of the insulator. The shortest distance from the tip). As a result, the electric field strength between the creeping ground electrode and the tip of the insulator is not excessively increased, and the early consumption / penetration breakdown of the insulator due to the semi-creeping discharge is suppressed.

  By the way, spark plugs that generate semi-surface discharge satisfy various conditions such as good anti-fouling property and good ignitability in addition to suppressing early consumption and penetration failure of the insulator due to semi-surface discharge. It has been demanded. In order to satisfy these conditions, it is necessary to adjust various positional relationships (dimensional relationships) between the creeping ground electrode and other portions. On the other hand, in the semi-surface discharge type spark plug shown in FIG. 1 of Patent Document 2, regarding the size and shape of the surface ground electrode, the surface ground electrode is simply the thickness of the surface ground electrode from the tip of the insulator. Alternatively, it is only necessary to project to the tip side by a length corresponding to the thickness, and various positional relationships (dimensional relationships) between the ground electrode and other parts have not been known.

  The present invention has been made in view of such a current situation, and is capable of obtaining good fouling resistance, good ignitability, and the like while suppressing early consumption / penetration breakdown of an insulator due to semi-surface discharge. An object is to provide a spark plug for an engine.

  The solution includes a cylindrical insulator having an axial hole penetrating in the axial direction, and a center electrode inserted into the axial hole, the center electrode having a center electrode tip protruding from the tip of the insulator. An electrode and a cylindrical metal shell, which surrounds the insulator and is arranged so that a part of the insulator protrudes from the tip of itself, and is joined to the tip surface of the metal shell One or a plurality of creeping ground electrodes formed on a portion of a discharge path of a spark discharge generated between the creeping ground electrode and the tip of the center electrode. An internal combustion engine comprising: a creeping ground electrode having a shape with respect to the insulator tip and the center electrode tip so as to include a creeping discharge path along a surface of the insulator tip protruding beyond the tip. Spark plug for engine The ground electrode has a smooth inner surface extending from the front end surface of the metal shell toward the center electrode side, and has an inner side surface extending from the front end of the insulator to the front end side in the axial direction. When the shortest gap among the gaps between the ground electrode and the insulator tip is defined as a semi-creeping discharge gap, the inner surface of the creeping ground electrode has the semi-creeping discharge gap between the insulator tip and the insulator. Including an electrode-side gap position, where the tip of the insulator is the starting point, the tip in the axial direction is the positive direction, and the base end in the axial direction is the negative direction. The axial distance L1 (mm) to the gap position is a spark plug for an internal combustion engine that satisfies a relationship of −0.8 ≦ L1 ≦ 0.0.

  In the spark plug for an internal combustion engine according to the present invention, the creeping ground electrode is a smooth inner surface extending from the front end surface of the metal shell toward the center electrode side, and extends from the front end of the insulator to the front end in the axial direction. It has a side. Further, the inner side surface includes an electrode side gap position that forms a semi-creeping discharge gap with the insulator tip. In other words, the semi-creeping discharge gap is formed between the smooth inner surface of the creeping ground electrode and the insulator tip. For this reason, the electric field strength is not excessively increased between the creeping ground electrode and the tip of the insulator, and semi-creeping discharge (air-discharge between the creeping ground electrode and the insulator is caused by Between the first and second insulators, which means spark discharge that creeps along the surface of the tip of the insulator), and can prevent early consumption and penetration breakdown of the insulator.

  Furthermore, in the spark plug for an internal combustion engine according to the present invention, when the tip of the insulator is the starting point, the tip in the axial direction is the positive direction, and the base end in the axial direction is the negative direction, the gap on the electrode side from the tip of the insulator The axial distance L1 (mm) to the position satisfies the relationship of −0.8 ≦ L1 ≦ 0.0. In other words, by setting L1 to 0.0 mm or less, the semi-creeping discharge gap is formed at a position closer to the base end side in the axial direction than the tip of the insulator, so that the surface of the tip of the insulator is relatively long. It is possible to cause creeping discharge over a distance. Therefore, when the spark plug is soiled due to adhesion of carbon or the like, the soiling material such as carbon can be burned out over a relatively wide area of the surface of the insulator tip, so that the soil resistance is good. On the other hand, when L1 is set to −0.8 mm or more, in other words, the semi-surface discharge gap is formed in a range not exceeding 0.8 mm on the proximal side in the axial direction from the distal end of the insulator. The ignitability can be improved. This is because, in the region sandwiched between the creeping ground electrode and the insulator, the air-fuel mixture tends to become leaner toward the proximal end in the axial direction, so the air-fuel mixture increases as the semi-creeping discharge gap is located closer to the proximal end in the axial direction. This is based on the fact that the ignitability tends to decrease.

Examples of the shape of the smooth inner surface of the creeping ground electrode include a curved surface shape that is gently bent and extended, and a smooth surface that extends straight.
Moreover, as a spark plug for internal combustion engines of this invention, the semi-surface discharge type spark plug which has only a surface ground electrode as an electrode which carries out a spark discharge between center electrodes is mentioned, for example. Moreover, it is good also as a spark plug which combined this semi-surface discharge type spark plug with the air electrode which forms an air discharge gap between the front-end | tips of a center electrode.

  Another solution is a cylindrical insulator having an axial hole penetrating in the axial direction, and a central electrode inserted into the axial hole, the central electrode having a distal end protruding from the distal end of the insulator. A central electrode and a cylindrical metal shell, which surrounds the periphery of the insulator and is disposed so that a part of the insulator protrudes from the tip of itself; and on the tip surface of the metal shell One or a plurality of creeping ground electrodes bonded to each other, and the metal shell of the insulator is part of a discharge path of a spark discharge generated between the creeping ground electrode and the tip of the center electrode. A creeping ground electrode having a shape defined with respect to the insulator tip and the center electrode tip so as to include a creeping discharge path along the surface of the insulator tip protruding beyond the tip of the insulator. A spark plug for an internal combustion engine, wherein The ground electrode has a smooth inner surface extending from the front end surface of the metal shell toward the center electrode side, and has an inner side surface extending from the front end of the insulator to the front end side in the axial direction. When the shortest gap among the gaps between the ground electrode and the insulator tip is defined as a semi-creeping discharge gap, the inner surface of the creeping ground electrode has the semi-creeping discharge gap between the insulator tip and the insulator. None, the semi-surface discharge gap dimension G2 (mm) is a spark plug for an internal combustion engine that satisfies a relationship of 0.35 ≦ G2 ≦ 0.80.

  In the spark plug for an internal combustion engine of the present invention, the semi-surface discharge gap dimension G2 (mm) satisfies the relationship of 0.35 ≦ G2 ≦ 0.80. By setting 0.35 ≦ G2 ≦ 0.80, it is possible to appropriately cause a spark discharge in the semi-creeping discharge gap. Specifically, by setting G2 to 0.35 mm or more, for example, the fuel in the air-fuel mixture enters the semi-creeping discharge gap or a carbon bridge is generated at the position of the semi-creeping discharge gap, resulting in misfire. The risk is reduced. On the other hand, by setting G2 to 0.80 mm or less, for example, even when a conductive fouling substance such as carbon adheres to the insulator surface in the cylinder of the metal shell, the inner peripheral surface of the metal shell and the insulator fouling There is little risk of spark discharge between the parts, and spark discharge can be appropriately performed in the semi-creeping discharge gap.

In addition, examples of the smooth inner surface of the creeping ground electrode include a curved surface that is gently bent and extends, a smooth surface that extends straight, and the like.
The spark plug for the internal combustion engine of the present invention includes a semi-surface discharge type spark plug, a spark plug in which an air electrode is combined with the semi-surface discharge type spark plug, and the like.

  Furthermore, in the spark plug for an internal combustion engine of the present invention, the axial direction from the tip of the insulator to the electrode-side gap position forming a semi-creeping discharge gap between the inner surface of the creeping ground electrode and the tip of the insulator When the distance to the base end side is L1 (mm), a spark plug for an internal combustion engine that satisfies the relationship of 0.0 ≦ L1 ≦ 0.8 is preferable. By doing so, as described above, the fouling resistance can be improved and the ignitability to the air-fuel mixture can also be improved.

Further, a tubular insulator having an axial hole penetrating in the axial direction, a center electrode which is inserted into the shaft hole, a center electrode having a center electrode leading end portion protruding from the tip of the insulator, A cylindrical metal shell, which surrounds the insulator and is disposed so that a part of the insulator protrudes from the tip of the metal shell, and 1 joined to the tip surface of the metal shell Or a plurality of creeping ground electrodes, and a part of a discharge path of a spark discharge generated between the creeping ground electrode and the tip of the center electrode, than the tip of the metal shell of the insulator. A spark for an internal combustion engine, comprising: a creeping ground electrode having a shape with respect to the insulator tip and the center electrode tip so as to include a creeping discharge path along a surface of the insulator tip protruding to the tip side. Plug, the creeping ground electrode is A smooth inner surface extending from the front end surface of the metal shell toward the center electrode side, the inner surface extending from the front end of the insulator to the front end side in the axial direction, and the creeping ground electrode and the When the shortest gap among the gaps with the insulator tip is the semi-creeping discharge gap, the inner surface of the creeping ground electrode forms the semi-creeping discharge gap with the insulator tip, and the center The electrode is located in the vicinity of the distal end of the insulator and has a reduced diameter portion that decreases in diameter toward the distal end side in the axial direction, and a cylindrical proximal end side portion that extends from the reduced diameter portion to the proximal side in the axial direction. Where the distal end of the insulator is the starting point, the distal end side in the axial direction is the positive direction, and the proximal end side in the axial direction is the negative direction. The axial distance to the annular ridgeline formed between the end side part (Mm) is preferably set to spark plug satisfies the relationship N ≧ -0.5.

In this spark plug for an internal combustion engine, when the front end of the insulator is the starting point, the front end side in the axial direction is the positive direction, and the base end side in the axial direction is the negative direction, the reduced diameter portion of the center electrode from the front end of the insulator The axial distance N (mm) to the annular ridge formed between the base end side portion satisfies the relationship of N ≧ −0.5. Since the annular ridge line of the center electrode is a corner, the electric field is concentrated in the vicinity thereof and tends to be an end point (start point or end point) of discharge. For this reason, if this annular ridge line is positioned larger than the distal end of the insulator on the base end side, there is a risk that the creeping discharge may occur and the electric discharge penetrate through the insulator. On the other hand, in this spark plug , the annular ridge line of the center electrode is arranged on the distal end side in the axial direction from the position 0.5 mm away from the distal end of the insulator to the proximal end side in the axial direction. As a result, even when a spark discharge occurs with the annular ridge line as an end point due to an increase in the electric field strength in the vicinity of the annular ridge line, it is possible to appropriately cause a creeping discharge without the spark discharge penetrating the insulator.

The axial distance N (mm) from the tip of the insulator to the annular ridge line of the center electrode is not limited to a negative value (when the annular ridge line is positioned closer to the proximal side in the axial direction than the tip of the insulator), It may be a positive value (when the annular ridge line is located on the tip side in the axial direction with respect to the tip of the insulator).
In addition, examples of the smooth inner surface of the creeping ground electrode include a curved surface that is gently bent and extended, a smooth surface that extends straight, and the like. As the spark plug for an internal combustion engine described above, the same as defined in Claim 1, and the semi-creeping discharge type spark plug, such as spark plugs and the like which combined aerial electrodes to the semi-creeping discharge type spark plug.

  Furthermore, any one of the above-described spark plugs for an internal combustion engine, wherein the spark plug for the internal combustion engine has an air electrode fixed to the metal shell and forming an air discharge gap with the tip of the center electrode. good.

  The present invention can also be applied to a spark plug in which a semi-surface discharge spark plug is combined with an air electrode that forms an air discharge gap with the tip of the center electrode. Also in such a spark plug, it is possible to obtain good fouling resistance, good ignition property, etc. while suppressing early consumption of the insulator due to semi-surface discharge and through breakage.

  The air discharge gap refers to the shortest gap among the gaps between the tip of the center electrode and the air electrode. In order to improve ignitability and durability, a noble metal tip may be provided at at least one of the tip of the center electrode and the air electrode facing the tip of the center electrode. When the noble metal tip is provided at the tip of the center electrode, the tip of the center electrode is the tip of the noble metal tip, and when the noble metal tip is provided on the air electrode, the air discharge gap is the shortest distance between the noble metal tips of both electrodes. Distance. As this noble metal tip, for example, an alloy containing a noble metal such as Pt, Ir, Rh or the like as a main component can be cited.

  Further, in the above-mentioned spark plug for an internal combustion engine, the tip of the creeping ground electrode may be a spark plug for an internal combustion engine that is positioned on the proximal side in the axial direction from the tip of the center electrode.

  The spark plug for an internal combustion engine according to the present invention is a spark plug in which a semi-surface discharge type spark plug is combined with an air electrode that forms an air discharge gap with the tip of the center electrode. Is positioned on the proximal side in the axial direction from the tip of the center electrode. For this reason, there is no possibility that the spread of the flame when spark discharge occurs in the air discharge gap is hindered by the creeping ground electrode. Therefore, it is possible to improve the ignitability of the air-fuel mixture when spark discharge occurs in the air discharge gap.

  Furthermore, in any of the above-described spark plugs for an internal combustion engine, the semi-surface discharge gap dimension G2 (mm) satisfies a relationship of 0.35 ≦ G2 ≦ 0.80, and the air discharge gap dimension. G1 (mm) is preferably a spark plug for an internal combustion engine that satisfies the relationship of 0.5 ≦ G1 ≦ 1.1.

  The spark plug for an internal combustion engine of the present invention is a spark plug in which a semi-surface discharge type spark plug is combined with an air electrode that forms an air discharge gap with the tip of a center electrode. When (mm) is 0.35 ≦ G2 ≦ 0.80, the air discharge gap dimension G1 (mm) satisfies the relationship of 0.5 ≦ G1 ≦ 1.1. By setting G1 to 0.5 mm or more, when spark discharge occurs in the air discharge gap, the ignitability of the air-fuel mixture can be improved. Specifically, by setting G1 to 0.5 mm or more, a sufficient air-fuel mixture can be interposed in the air discharge gap, and a sufficient spark discharge for igniting this air-fuel mixture can be generated. it can.

  On the other hand, by setting G1 to 1.1 mm or less, the discharge voltage of the discharge path passing through the air discharge gap can be prevented from becoming too high, and a spark discharge can be appropriately generated via the air discharge gap. . Specifically, for example, the discharge voltage of the discharge path through the air discharge gap is too high, so that the semi-surface discharge is not contaminated (carbon is not attached to the surface of the insulator tip). It is possible to reduce the risk that spark discharge occurs in the gap and the ignitability is lowered. Alternatively, the risk of a discharge penetrating the insulator can be reduced without causing a spark discharge in any of the air discharge gap and the semi-surface discharge gap.

  Furthermore, in any one of the above-described spark plugs for an internal combustion engine, the air electrode is fixed to the metal shell and extends to the axial front end side, and extends from the base end portion to extend the metal shell. An air electrode main body portion including a bent portion that is bent radially inward, and a distal end portion that extends from the bent portion and extends to a position facing the central electrode in the axial direction, and the air electrode main body portion. A noble metal tip fixed directly or indirectly to the tip portion and forming the air discharge gap with the tip of the center electrode, and the center of the tip portion of the air electrode body portion When a distance in a direction perpendicular to the inner surface of the tip portion from the inner surface of the tip portion facing the electrode side to the tip side gap position of the noble metal tip forming the air discharge gap in the noble metal tip is defined as H (mm), H ≧ 0.1 It may be a spark plug for an internal combustion engine that satisfies the relationship.

  In the spark plug for an internal combustion engine of the present invention, a noble metal tip that forms an air discharge gap with the tip of the center electrode is provided at the tip of the air electrode main body. For this reason, ignitability and durability (spark wear resistance) are improved. Furthermore, when the distance in the direction perpendicular to the inner surface of the tip from the inner surface of the tip of the air electrode main body to the tip side gap position is H (mm), the relationship of H ≧ 0.1 is satisfied. In other words, the air discharge gap is provided at a position separated by 0.1 mm or more from the inner surface of the distal end portion of the air electrode main body. This makes it difficult for flame spread when spark discharge occurs in the air discharge gap to be hindered by the tip of the air electrode main body. Therefore, it is possible to improve the ignitability of the air-fuel mixture when spark discharge occurs in the air discharge gap.

In addition, as a fixed form of a noble metal tip, the form fixed directly on the inner surface of the front-end | tip part of an air electrode main body part is mentioned, for example. Alternatively, the noble metal tip may be provided in a form in which another noble metal tip or the like is interposed between the inner surface of the distal end portion of the air electrode main body and the noble metal tip. Or it is good also as a form which arrange | positions a noble metal chip | tip in the recessed part provided in the air electrode main-body part, and the front-end | tip of a noble metal main body part protrudes from the inner surface of the front-end | tip part at least.
As the noble metal tip, for example, an alloy containing a noble metal such as Pt, Ir, Rh or the like as a main component can be cited.

  Furthermore, any of the above-described spark plugs for an internal combustion engine, wherein the metal shell has a tip outer diameter of 10.1 mm or less.

  In recent years, as the output of internal combustion engines has increased, the intake and exhaust valves in combustion chambers have been increased in size and four valves have been studied. In addition, because of the trend toward smaller engines, it is hoped that spark plugs for internal combustion engines will be smaller. It is rare. However, in a spark plug that performs creeping discharge, such as a semi-creeping discharge type spark plug, the thickness of the insulator tends to be thinner as the size is reduced (smaller diameter). For this reason, the problem of premature wear and penetration breakage of the insulator becomes particularly serious when the screw diameter of the metal shell is M12 or less (the outer diameter of the tip of the metal shell is 10.1 mm or less).

On the other hand, the spark plug for an internal combustion engine of the present invention has a creeping ground electrode and an outer diameter of the metal shell, even if the tip outer diameter of the metal shell is 10.1 mm or less (corresponding to the tip outer diameter of the metal shell having a screw diameter of M12 or less) The strength of the electric field between the front end of the insulator does not become excessively high, and the early consumption of the insulator due to semi-surface discharge and penetration damage can be suppressed.
Note that the outer diameter of the front end of the metal shell means the outer diameter of the front end excluding the chamfered portion formed at the front end corner of the metal shell, and the present invention has a mounting screw portion formed on the outer surface of the metal shell. It can also be applied to a so-called screwless plug.

  Furthermore, in any one of the spark plugs for an internal combustion engine, the creeping ground electrode has a base end portion that extends from a front end surface of the metal shell and approaches the center electrode toward the front end side in the axial direction. It is better to use a spark plug.

A creeping ground electrode of a conventional spark plug for an internal combustion engine (see Patent Document 2, FIG. 1) has a shape in which the base end portion extends in the axial direction from the front end surface of the metal shell. For this reason, in order to form a semi-creeping discharge gap between the inner surface of the creeping ground electrode facing the center electrode side and extending in the longitudinal direction of the creeping ground electrode and the tip of the insulator, the creeping ground electrode is temporarily Has to be bent toward the center electrode side to approach the tip of the insulator.
On the other hand, in the spark plug for an internal combustion engine of the present invention, the base end portion of the creeping ground electrode extends from the front end surface of the metal shell and approaches the center electrode toward the front end side in the axial direction. Therefore, a semi-creeping discharge gap can be formed between the inner surface of the creeping ground electrode and the tip of the insulator without bending the creeping ground electrode toward the center electrode. For this reason, it is easy to form the creeping ground electrode, and the cost is reduced.

  Furthermore, in the spark plug for an internal combustion engine of the present invention, it is not necessary to bend the base end portion of the creeping ground electrode so as to approach the center electrode as described above, so the shape of the creeping ground electrode in the vicinity of the semi-creeping discharge gap Can be made the same as the shape of Patent Document 2 (FIG. 1), the length of the creeping ground electrode can be shortened in each of the axial direction and the radial direction of the spark plug. On the other hand, if the creeping ground electrode has the same axial length as that of Patent Document 2 (FIG. 1), draw a gentler curve than the shape of Patent Document 2 (FIG. 1). The selection range for selecting an appropriate shape can be expanded so as to generate an appropriate semi-surface discharge, such as relaxation of electric field concentration.

  In particular, the spark plug for an internal combustion engine of the present invention is suitable for a small diameter plug of M12 or less. Specifically, for the following reason. As the spark plug becomes smaller (smaller in diameter), the radial distance between the fixing surface of the metal shell to which the creeping ground electrode is fixed and the tip of the insulator becomes shorter. Further, the amount of protrusion of the insulator and the center electrode from the tip of the metal shell tends to be small. For this reason, in a creeping ground electrode that is bent at two locations as in Patent Document 2 (FIG. 1), in order to reduce the length of the creeping ground electrode in the axial direction and the radial direction of the spark plug, respectively. There was a limit and it was difficult to apply to a small diameter plug of M12 or less. On the other hand, in the spark plug of the present invention, as described above, the length of the creeping ground electrode in each of the axial direction and the radial direction of the spark plug can be reduced by reducing the portion bent to the center electrode side of the creeping ground electrode. Therefore, an appropriate semi-creeping discharge gap can be formed even for a small-diameter plug of M12 or less.

  The base end portion of the creeping ground electrode only needs to extend from the distal end surface of the metal shell and have a form closer to the center electrode toward the distal end side in the axial direction. For example, the front end surface of the metal shell is a slope that is farther from the axis toward the tip in the axial direction, and a linear base end portion that extends perpendicularly from the slope can be used. Further, the distal end surface of the metal shell is a surface perpendicular to the axial direction as in Patent Document 2 (FIG. 1), but the joint end surface that joins the distal surface of the metal shell among the creeping ground electrodes is the base end portion. They may be joined obliquely with respect to the extending direction. Further, the base end portion is not limited to a linear shape, and may be a curved shape.

  Examples 1 to 4 according to the present invention will be described below.

  As shown in FIG. 1, the spark plug 100 for an internal combustion engine according to the first embodiment includes a creeping ground electrode 110, a center electrode 120, a metal shell 130, an insulator 140, and an air electrode 150. The spark plug 100 for an internal combustion engine is attached to a cylinder head of an engine (not shown) using a screw portion 130b formed on the outer surface of the metal shell 130, and is used.

  Here, an enlarged view of the front end side portion (B portion in FIG. 1) of the spark plug 100 for the internal combustion engine is shown in FIG. 2, and the spark plug 100 for the internal combustion engine will be described in detail. The insulator 140 is a cylindrical body made of alumina and having a shaft hole 140b penetrating in the direction of the axis C. The metal shell 130 is a cylindrical metal body having a screw portion 130b with a nominal size M10 formed on the outer surface, and surrounds the insulator 140 with a gap. Furthermore, the front end surface 132 of the metal shell 130 has an inclination that is farther from the axis C toward the front end side in the axis C direction (downward in FIG. 2). In the first embodiment, the outer diameter D of the front end of the metal shell 130 is 8.5 mm.

  The center electrode 120 is a shaft-shaped metal body that is inserted into the shaft hole 140 b of the insulator 140 and fixed so that the tip 121 thereof protrudes from the tip 141 b of the insulator 140 to the tip side. The center electrode 120 is located near the distal end 141b of the insulator 140 and has a diameter-reduced portion 123 that decreases in diameter toward the distal end side in the axis C direction, and a cylindrical base extending from the reduced diameter portion 123 toward the proximal end side in the axis C direction. And an end side portion 124. Here, the annular ridgeline formed between the reduced diameter portion 123 and the proximal end side portion 124 corresponds to the annular ridgeline 125 (corresponding to the boundary line between the reduced diameter portion 123 and the proximal end side portion 124, as shown in FIG. (Shown with a broken line). Further, when the tip end 141b of the insulator 140 is a starting point, the tip end side in the axis C direction (downward direction in FIG. 2) is the positive direction, and the base end side in the axis C direction (upward direction in FIG. 2) is the negative direction. The distance from the tip 141b of the insulator 140 to the annular ridge line 125 of the center electrode 120 is N (mm).

  Examples of the metal body of the electrode base material constituting the center electrode 120 include Ni heat-resistant alloys and Fe heat-resistant alloys. Further, a good heat conductive metal core made of Cu or Cu alloy may be enclosed in these electrode base materials. In the spark plug 100 for an internal combustion engine, a disc-shaped noble metal tip 122 is fixed to the tip of the center electrode 120 by laser welding. The noble metal tip 122 is formed of, for example, an alloy containing a noble metal such as Pt, Ir, or Rh as a main component. Here, the distance from the tip 141b of the insulator 140 to the tip 120b of the center electrode 120 (corresponding to the tip of the noble metal tip 122 in the first embodiment) on the tip side in the axis C direction is J (mm).

  The creeping ground electrode 110 is a metal body made of, for example, a Ni heat-resistant alloy or an Fe heat-resistant alloy, and is provided at two positions facing each other with the center electrode 120 interposed therebetween. Specifically, the creeping ground electrode 110 has a linear base end portion 111 fixed to the front end surface 132 of the metal shell 130 and a linear tip end portion 112 extending in the axis C direction. Among such creeping ground electrodes 110, the inner side surface 114 extending from the front end surface 132 of the metal shell 130 toward the center electrode 120 constitutes a smooth surface.

  Here, the shortest gap among the gaps between the creeping ground electrode 110 and the insulator tip 141 is called a semi-creeping discharge gap, and the dimension of the semi-creeping discharge gap is G2 (mm). Further, when the tip end 141b of the insulator 140 is a starting point, the tip end side in the axis C direction is a positive direction, and the base end side in the axis C direction is a negative direction, the tip of the creeping ground electrode 110 extends from the tip 141b of the insulator 140. The axial distance to 113 (in the first embodiment, the tip coincides with the tip surface) is L2 (mm). Similarly, the axial distance from the tip 141b of the insulator 140 to the electrode side gap position 110g forming a semi-creeping discharge gap with the insulator tip 141 of the creeping ground electrode 110 is defined as L1 (mm).

  The base end portion 111 of the creeping ground electrode 110 has a linear shape, and the joining end surface 116 that joins the tip end surface 132 of the metal shell 130 in the base end portion 111 extends in the extending direction of the base end portion 111. It faces (in other words, the joint end surface 116 is perpendicular to the axis of the base end portion 111). Further, the joining end face 116 of the creeping ground electrode 110 is fixed vertically to the tip end face 132 in a form in contact with the tip end face 132. As a result, the base end portion 111 of the creeping ground electrode 110 is closer to the center electrode 120 toward the tip end side in the axis C direction (downward in FIG. 2).

  By the way, the creeping ground electrode of the conventional spark plug for an internal combustion engine (see Patent Document 2, FIG. 1) has a shape in which the base end portion extends in the axial direction from the front end surface of the metal shell. For this reason, in order to form a semi-creeping gap between the inner surface of the creeping ground electrode and the tip of the insulator, the creeping ground electrode was once bent toward the center electrode and brought closer to the tip of the insulator. . On the other hand, in the spark plug 100 for the internal combustion engine of the present embodiment, as described above, the base end portion 111 of the creeping ground electrode 110 is closer to the center electrode 120 toward the front end side in the axis C direction. An appropriate semi-creeping gap dimension G2 can be ensured between the inner surface 114 of the creeping ground electrode 110 and the insulator tip 141 without bending the creeping ground electrode 110 toward the center electrode 120 side. For this reason, formation of the creeping ground electrode 110 is facilitated and the cost is reduced.

  In particular, as the spark plug is made smaller (smaller in diameter), the radial distance between the front end surface 132 of the metal shell 130 and the insulator front end 141 becomes shorter. Further, the amount of protrusion of the insulator 140 and the center electrode 120 from the tip 131 of the metal shell 130 tends to be small. For this reason, in a creeping ground electrode that is bent at two locations as in Patent Document 2 (FIG. 1), in order to reduce the length of the creeping ground electrode in the axial direction and the radial direction of the spark plug, respectively. There was a limit and it was difficult to apply to a small diameter plug of M12 or less.

On the other hand, in the spark plug 100 for the internal combustion engine according to the present embodiment, since it is not necessary to bend the creeping ground electrode 110 in order to approach the center electrode 120, compared with Patent Document 2 (FIG. 1). The length of the creeping ground electrode 110 can be shortened in each of the axial direction C and the radial direction of the plug. Accordingly, the spark plug 1 for the internal combustion engine of the present embodiment.
00 can secure an appropriate semi-creeping gap dimension G2 even if the outer diameter D of the metal shell 130 is 8.5 mm (corresponding to the outer diameter of the metal shell having a screw diameter of M10).

  As shown in FIG. 3, the air electrode 150 includes an air electrode main body 155 and a noble metal tip 152. Among these, the air electrode main body 155 is a metal body, is fixed to the distal end surface 132 of the metallic shell 130 and extends to the distal end side in the axis C direction, and extends from the proximal end 154 to extend the metallic shell. 130 has a bent portion 153 bent inward in the radial direction, and a tip portion 151 extending from the bent portion 153 to a position facing the center electrode 120 in the axis C direction. In the first embodiment, the tip 151 of the air electrode main body 155 extends in a direction orthogonal to the axis C direction.

  The noble metal tip 152 is made of, for example, an alloy containing a noble metal such as Pt, Ir, or Rh as a main component, and a resistance is provided at a position that substantially opposes the tip 120b of the center electrode 120 in the tip 151 of the air electrode body 155. It is fixed by welding or laser welding. As a result, an air discharge gap is formed between the tip 120b of the center electrode 120 and the noble metal tip 152 of the air electrode 150. The size of the air discharge gap is G1 (mm). Further, the front end portion 151 of the air electrode body portion 155 is perpendicular to the front end portion inner surface 151b from the front end portion inner side surface 151b facing the center electrode 120 to the tip side gap position 152b of the noble metal tip 152 forming the air discharge gap. The distance in the right direction (corresponding to the amount of protrusion of the noble metal tip 152 from the tip inner surface 151b in the first embodiment) is H (mm).

With respect to such a spark plug 100 for an internal combustion engine, appropriate dimension ranges of the dimension values H (mm), N (mm), L1 (mm), L2 (mm), G1 (mm), and G2 (mm) described above are set. In order to investigate, a sample was prepared and a spark discharge test was conducted.
First, in order to investigate an appropriate dimension range of the distance L2 (mm) from the tip 141b of the insulator 140 to the tip 113 of the creeping ground electrode 110, J (mm), H (mm), N (mm), L1 Four types of samples having the same values of (mm), G2 (mm), and G1 (mm) but different values of L2 (mm) were prepared. Specifically, J = 1.5 (mm), H = 0.1 (mm), N = −0.3 (mm), L1 = −0.3 (mm), G2 = 0.35 (mm) ), G1 = 2.0 (mm), and only L2 was L4 = −0.2, −0.1, 0.0, 0.1 (mm). In this test, G1 = 2.0 (mm) is set to a large value so as not to cause air discharge in the air discharge gap.

  Each of these four types of samples was attached to an engine with a displacement of 2000 cc, and continuously operated for 5 hours at an engine speed of 3500 rpm, and the relationship between L2 (mm) and the penetration failure of the insulator 140 due to spark discharge was investigated. did. The test results are shown in Table 1. In Table 1, the case where penetration failure occurred is indicated by x, and the case where no penetration failure occurred is indicated by ○. The discharge voltages of the four types of samples are about 30 kV each.

  As shown in Table 1, in two samples in which L2 (mm) is set to a negative value, specifically, L2 = −0.2, −0.1 (mm), the penetration failure of the insulator 140 occurs. I have. On the other hand, the penetration failure of the insulator 140 did not occur in the two samples in which L2 (mm) was set to a value of 0 or more, specifically, L2 = 0.0, 0.1 (mm). By the way, in the sample used in this test, as shown in FIG. 2, the axial position of the tip 113 of the creeping ground electrode 110 and the axial position of the tip of the inner surface 114 coincide with each other. It is formed smoothly. In other words, the smooth inner surface 114 of the creeping ground electrode 110 extends to the axial position of the tip 113 of the creeping ground electrode 110.

  Therefore, from this test result, L2 (mm) is a value of 0 or more, in other words, the smooth inner side surface 114 of the creeping ground electrode 110 is extended to the tip end side in the axial direction from the tip of the insulator, and this inner side surface 114 By including the electrode side gap position 110g, it can be said that the penetration breakdown of the insulator 140 can be suppressed. This is because the smooth inner surface 114 of the creeping ground electrode 110 includes the electrode-side gap position 110g, in other words, a semi-surface discharge between the smooth inner surface 114 and the insulator tip 141. It is considered that the formation of the gap prevents the electric field strength between the creeping ground electrode 110 and the insulator tip 141 from becoming excessively strong.

  Furthermore, in order to investigate an appropriate dimension range of L2 (mm), the values of J (mm), H (mm), N (mm), L1 (mm), G2 (mm), and G1 (mm) are the same. Seven types of samples differing only in the value of L2 (mm) were prepared. Specifically, J = 1.5 (mm), H = 0.1 (mm), N = −0.3 (mm), L1 = −0.3 (mm), G2 = 0.5 (mm) ), G1 = 0.9 (mm), and only L2 is L2 = 0.0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0 (mm) did.

  Each of these seven types of samples was attached to an engine with a displacement of 2000 cc, A / F (air-fuel ratio) was shifted from the lean side, and an ignitability test was performed under idling conditions (engine speed 700 rpm). In this test, the A / F value when the HC spike occurs 3 times per 2 minutes under the above engine conditions is determined as the ignition limit, and the relationship between the A / F value and L2 (mm) at this time is determined. investigated. The test results are shown in the graph of FIG.

  As shown in FIG. 4, in the four samples set to L2 (mm) = 0.0, 0.5, 1.0, 1.5 (mm), the A / F value at the ignition limit is 16. The value was as high as 8 and extremely good ignitability could be obtained. However, when L2 is larger than 1.5 mm, specifically, in the three samples set to L2 = 2.0, 2.5, 3.0 (mm), the value of A / F is 16.5, 16 It gradually decreased to 0.0, 15.0. That is, when L2 is larger than 1.5 mm, the ignitability is lowered.

  By the way, in the sample used in this test, as described above, the distance J from the tip 141b of the insulator 140 to the tip 120b of the central electrode 120 in the direction of the axis C is set to 1.5 (mm). Therefore, from this test result, if the tip 113 of the creeping ground electrode 110 is positioned closer to the tip end side in the axis C direction (downward in FIG. 2) than the tip 120b of the center electrode 120, the ignitability is reduced. I can say that. On the contrary, it can be said that the ignitability of the air-fuel mixture can be improved by positioning the tip 113 of the creeping ground electrode 110 closer to the base end side in the axis C direction than the tip 120b of the center electrode 120. This is considered to be because the spread of the flame when spark discharge occurs in the air discharge gap is not hindered by the creeping ground electrode 1110.

  Next, in order to investigate an appropriate dimension range of the distance L1 (mm) in the axis C direction from the tip 141b of the insulator 140 to the electrode side gap position 110g, J (mm), H (mm), N (mm), Four types of samples were prepared in which the values of L2 (mm), G2 (mm), and G1 (mm) were the same and only the value of L1 (mm) was different. Specifically, J = 1.5 (mm), H = 0.1 (mm), N = −0.2 (mm), L2 = 0.5 (mm), G2 = 0.5 (mm) , G1 = 1.0 (mm), and only L1 has four types of L1 = −0.2, −0.1, 0.0, 0.1 (mm).

  Each of these four types of samples was attached to an engine with a displacement of 2000 cc, and a smoldering fouling test was conducted according to JIS D 1606. In this test, a predetermined operation pattern defined in JIS D 1606 was set as one cycle, and the number of cycles until the insulation resistance reached 10 MΩ was investigated for each sample. The test results are shown in Table 2.

  As shown in Table 2, in the sample in which L1 (mm) was set to a positive value, specifically, L2 = 0.1 (mm), the insulation resistance reached 10 MΩ after 7 cycles. In contrast, in the three samples where L1 (mm) is set to 0.0 mm or less, specifically, L2 = −0.2, −0.1, 0.0 (mm), the insulation resistance reaches 10 MΩ. Until then, it was able to operate for 8 cycles. Therefore, from this test result, by setting L1 (mm) to 0.0 mm or less, in other words, the semi-creeping discharge gap G2 is formed at a position closer to the proximal end side in the axis C direction than the distal end 141b of the insulator 140. Thus, it can be said that the decrease in insulation resistance can be suppressed, that is, the stain resistance can be improved.

  The factors of this test result are considered as follows. In other words, by setting L1 to 0.0 mm or less, the semi-surface discharge gap G2 is formed at a position closer to the base end side in the direction of the axis C than the tip 141b of the insulator 140, whereby the surface of the insulator tip 141 is formed. It is possible to cause creeping discharge over a relatively long distance. Accordingly, when the spark plug is soiled due to adhesion of carbon or the like, the soiling material such as carbon can be burned out over a relatively wide area of the surface of the insulator tip portion 141, so that the soil resistance is good. .

  Further, in order to investigate an appropriate dimension range of L1 (mm), the values of J (mm), H (mm), N (mm), L2 (mm), and G2 (mm) are not changed, and L1 Only 5 samples were prepared with L1 = −1.5, −1.0, −0.5, 0.0, 0.5 (mm). In this test, G1 = 2.0 (mm) is set to a large value so as not to cause air discharge in the air discharge gap.

  Each of these five types of samples was attached to an engine with a displacement of 2000 cc, A / F (air-fuel ratio) was shifted from the lean side, and an ignitability test was performed under idling conditions (engine speed 700 rpm). In this test, the A / F value when the HC spike occurs 3 times per 2 minutes under the above engine conditions is determined as the ignition limit, and the relationship between the A / F value and L2 (mm) at this time is determined. investigated. The test results are shown in the graph of FIG.

  As shown in FIG. 5, in the sample set to L1 = −1.5, −1.0 (mm), the A / F value at the ignition limit was as low as 14.5 and 15.0, but L1 = As the value increases to -0.5, 0.0, 0.5 (mm), the A / F values at the ignition limit show high values of 16.0, 16.5, 16.8, and good ignition I was able to get sex. In this way, in this test, as the value of L1 (mm) increases, in other words, as the semi-creeping discharge gap G2 is arranged closer to the base end side in the axis C direction, the value of A / F at the ignition limit increases. It was found that the ignitability improved. In particular, from the graph of FIG. 5, it was found that when L1 = −0.8 (mm) or more, the A / F value at the ignition limit is 15.5 or more, and the ignitability is improved.

Therefore, by setting L1 to be −0.8 mm or more, in other words, the semi-surface discharge gap G2 is formed in a range not exceeding 0.8 mm on the base end side in the axis C direction from the tip 141b of the insulator 140. Thus, it can be said that the ignitability of the air-fuel mixture can be improved. This is because, in the region sandwiched between the creeping ground electrode 110 and the insulator 140, the air-fuel mixture tends to become leaner toward the base end side in the axis C direction, so that the semi-creeping discharge gap G2 is on the base end side in the axis C direction. This is probably because the ignitability of the air-fuel mixture tends to decrease as the position increases.
As explained above, the fouling resistance can be improved by setting L1 (mm) to 0.0 mm or less, and the ignitability to the air-fuel mixture can be improved by setting it to -0.8 mm or more. It was. Therefore, it can be said that by satisfying the relationship of −0.8 ≦ L1 ≦ 0.0, the fouling resistance can be improved and the ignitability can be improved.

  Next, J (mm), H (mm), N (mm), L2 (mm), L1 (mm), G1 (mm) are investigated in order to investigate an appropriate dimension range of the semi-creeping discharge gap dimension G2 (mm). ) Values were the same, and five types of samples differing only in G2 (mm) values were prepared. Specifically, J = 1.5 (mm), H = 0.1 (mm), N = −0.2 (mm), L2 = 0.5 (mm), L1 = −0.3 (mm) ), And only G2, five types of G2 = 0.30, 0.35, 0.40, 0.45, 0.50 (mm) were used. In this test, G1 = 2.0 (mm) is set to a large value so as not to cause air discharge in the air discharge gap.

  Each of these five types of samples was attached to an engine with a displacement of 2000 cc, and a smoldering fouling test was carried out based on JIS D 1606. In this test, a predetermined operation pattern defined in JIS D 1606 was set as one cycle, and each sample was operated until the insulation resistance reached 10 MΩ. Thereafter, each sample was examined for the presence of a carbon bridge at the semi-creeping discharge gap. The test results are shown in Table 3. In Table 3, the case where the carbon bridge was generated is indicated by x, and the case where the carbon bridge was not generated is indicated by ◯. In addition, this test is performed on the temperature conditions of room temperature-10 degreeC.

  As shown in Table 3, in the sample set to G2 = 0.30 (mm), a carbon bridge occurred. On the other hand, carbon bridges did not occur in the four samples in which G2 was set to 0.35 mm or more, specifically G2 = 0.35, 0.40, 0.45, 0.50 (mm). Therefore, from this test result, it can be said that by setting G2 to 0.35 mm or more, the occurrence of carbon bridges at the semi-creeping discharge gap position can be suppressed, and the risk of misfire can be reduced.

  Further, in order to investigate an appropriate dimension range of G2 (mm), the values of J (mm), H (mm), N (mm), L2 (mm), and L1 (mm) are not changed, and G2 Six types of samples with 0.5 = 0.6, 0.7, 0.8, 0.9, 1.0 (mm) were prepared. In this test, G1 is set to 0.9 (mm).

  Each of these six types of samples was mounted on a 2000 cc engine with an insulation resistance of 100 MΩ, and a spark discharge test was performed under a pressure of 0.2 MPa. In this test, the leak rate (%) at this time was investigated. In addition, the leak in this test refers to a phenomenon in which, for example, a spark discharge occurs between the inner peripheral surface of the metal shell and the insulator fouling portion without causing a spark discharge in the semi-surface discharge gap. The test results are shown in Table 4.

As shown in Table 4, in the four samples set to G2 = 0.5, 0.6, 0.7, 0.8 (mm), there is no leakage, and sparks are appropriately generated in the semi-creeping discharge gap. Discharged. On the other hand, leakage occurred in the sample in which G2 exceeded 0.80 mm, specifically, in the two samples set to G2 = 0.90 and 1.00 (mm). Specifically, the leak rate (%) was 5% and 15%, respectively, and the leak rate (%) increased as G2 increased. Therefore, from the result of this test, by setting G2 to 0.80 mm or less, the spark plug is in a state of being rolled (for example, conductive fouling substances such as carbon adhere to the insulator surface in the cylinder of the metal shell. State), the risk of leakage (for example, spark discharge between the inner peripheral surface of the metal shell and the contaminated part of the insulator) is small, and spark discharge is appropriately performed in the semi-surface discharge gap. It can be said that it is possible.
From the above, it can be said that by setting 0.35 ≦ G2 ≦ 0.80, it is possible to appropriately cause a spark discharge in the semi-creeping discharge gap.

  Next, J (mm), H (mm), and L2 (mm) are investigated in order to investigate an appropriate dimension range of the distance N (mm) in the axis C direction from the tip 141b of the insulator 140 to the annular ridgeline 125 of the center electrode 120. ), L1 (mm), G2 (mm), and G1 (mm) are the same, and four types of samples differing only in the value of N (mm) were prepared. Specifically, J = 1.5 (mm), H = 0.1 (mm), L2 = 0.0 (mm), L1 = −0.3 (mm), G2 = 0.35 (mm) , G1 = 2.0 (mm), and N is four types of N = −0.7, −0.5, −0.3, and −0.1 (mm). In this test, G1 = 2.0 (mm) is set to a large value so as not to cause air discharge in the air discharge gap.

  Each of these four types of samples was attached to an engine with a displacement of 2000 cc, and continuously operated for 5 hours at an engine speed of 3500 rpm, and the relationship between N (mm) and penetration failure of the insulator 140 was investigated. The test results are shown in Table 5. In Table 5, the case where penetration failure occurred is indicated by x, and the case where no penetration failure occurred is indicated by ◯. The discharge voltages of the four types of samples are about 30 kV each.

  As shown in Table 5, in the sample set to N = −0.7 (mm), the penetration failure of the insulator 140 occurred. This is considered due to the following reasons. Since the annular ridge line 125 of the center electrode 120 is a corner, the electric field is concentrated in the vicinity thereof, and tends to be an end point (start point or end point) of discharge. Therefore, when the annular ridge line 125 is positioned larger than the distal end 141b of the insulator 140 on the proximal side in the axial direction, a discharge penetrating the insulator 140 is more likely to occur than a creeping discharge along the surface of the insulator distal end portion 141. This is probably because of this.

  On the other hand, in three samples in which N (mm) is set to a value of −0.5 or more, specifically, N = −0.5, −0.3, and −0.1 (mm), the insulator 140 penetration failure did not occur. Therefore, from this test result, N ≧ −0.5, in other words, the annular ridge line 125 of the center electrode 120 is more axial than the position of 0.5 mm away from the distal end 141b of the insulator 140 toward the proximal side in the axial direction. It can be said that the breakthrough of the insulator 140 can be suppressed by disposing it on the tip side. This is because the position of the annular ridge line 125 is relatively close to the distal end 141b of the insulator 140 even if the position of the annular ridge line 125 is closer to the proximal end side in the axial direction than the distal end 141b of the insulator 140. Even if a spark discharge occurs at the starting point, it is considered that the spark discharge can appropriately cause a creeping discharge without penetrating the insulator 140.

  Next, when 0.35 ≦ G2 ≦ 0.80, J (mm), H (mm), L2 (mm), in order to investigate an appropriate size range of the air discharge gap G1 (mm), Five types of samples having the same values of L1 (mm), G2 (mm), and N (mm) but different values of G1 (mm) were prepared. Specifically, J = 1.5 (mm), H = 0.1 (mm), L2 = 0.0 (mm), L1 = −0.3 (mm), N = −0.2 (mm) ), And G1 has five types of G1 = 0.3, 0.5, 0.7, 0.9, 1.1 (mm). In this test, G2 = 0.5 (mm) is selected from a suitable range of 0.35 ≦ G2 ≦ 0.80.

  Each of these five types of samples was attached to an engine with a displacement of 2000 cc, A / F (air-fuel ratio) was shifted from the lean side, and an ignitability test was performed under idling conditions (engine speed 700 rpm). In this test, the A / F value when the HC spike occurs 3 times per 2 minutes under the above engine conditions is determined as the ignition limit, and the relationship between the A / F value and L2 (mm) at this time is determined. investigated. The test results are shown in the graph of FIG.

  As shown in FIG. 6, in the sample set to G1 = 0.3 (mm), the A / F value at the ignition limit was as low as 15.0, but G1 = 0.5, 0.7, 0. As the value increased to 9 (mm), the A / F value at the ignition limit increased to 15.5, 16.0, 17.0, and good ignitability could be obtained. Further, in the sample set to G1 = 1.1 (mm), the A / F value at the ignition limit was lower than that of the sample set to G1 = 0.9 (mm), but A / F = 15 .5 and the ignitability was good. From this test result, it was found that by setting 0.5 ≦ G1 ≦ 1.1, the A / F value at the ignition limit became 15.5 or more, and the ignitability could be improved.

  This is considered due to the following reasons. It is considered that by setting G1 to 0.5 mm or more, a sufficient air-fuel mixture can be interposed in the air discharge gap, and a sufficient spark discharge for igniting this air-fuel mixture can be generated. . On the other hand, by setting G1 to 1.1 mm or less, the discharge voltage of the discharge path passing through the air discharge gap can be prevented from becoming too high, and a spark discharge can be appropriately generated via the air discharge gap. This is probably because of this.

  Next, in order to investigate an appropriate dimensional range of the distance H (mm) in the direction perpendicular to the tip inner surface 151b from the tip inner surface 151b of the air electrode main body 155 to the tip-side gap position 152b, J (mm ), N (mm), L2 (mm), L1 (mm), G2 (mm), and G1 (mm) were the same, and five types of samples differing only in the value of H (mm) were prepared. Specifically, J = 1.5 (mm), N = −0.2 (mm), L2 = 0.5 (mm), L1 = −0.3 (mm), G2 = 0.5 (mm) ), G1 = 0.8 (mm), and H is five types of H = 0, 0.05, 0.10, 0.15, 0.20 (mm).

  Each of these five types of samples was attached to an engine with a displacement of 2000 cc, A / F (air-fuel ratio) was shifted from the lean side, and an ignitability test was performed under idling conditions (engine speed 700 rpm). In this test, the A / F value when the HC spike occurs 3 times per 2 minutes under the above engine conditions is determined as the ignition limit, and the relationship between the A / F value and L2 (mm) at this time is determined. investigated. The test results are shown in the graph of FIG.

  As shown in FIG. 7, in the two samples set at H = 0, 0.05 (mm), the A / F value at the ignition limit was as low as 15.3, but H = 0.10, 0. In the three samples of 15, 0.20 (mm), the A / F values at the ignition limit are as high as 16.8, 16.9, 17.0, and good ignitability can be obtained. It was. Therefore, from this test result, by setting H ≧ 0.1, in other words, the air discharge gap is provided at a position 0.1 mm or more away from the inner surface 151b of the distal end portion of the air electrode main body 155. Thus, it can be said that the ignitability of the air-fuel mixture can be improved. This is considered to be because when H ≧ 0.1, it is difficult for the tip of the air electrode main body 155 to prevent the flame from spreading when a spark discharge occurs in the air discharge gap.

The spark plug 100 for the internal combustion engine according to the first embodiment is manufactured as follows.
First, the insulator 140 is formed by using alumina as a main raw material and firing it into a predetermined shape at a high temperature. Moreover, the substantially cylindrical metal shell 130 is formed by using a steel material and plastic processing into a predetermined shape. Next, the front end side of the metal shell 130 is cut to form a front end surface 132 that is inclined farther from the axis C toward the front end side in the axis C direction (see FIG. 2).

  On the other hand, two straight rod-shaped creeping ground electrodes 110 made of Ni heat-resistant alloy and one aerial electrode 150 are prepared. In addition, the joining end surface 116 joined to the front end surface 132 of the metal shell 130 of the creeping ground electrode 110 is formed so as to face the extending direction of the straight rod-like creeping ground electrode 110 (in other words, the joining end surface 116 is And formed perpendicular to the axis of the creeping ground electrode 110) (see FIG. 8). Moreover, the joining end surface 156 joined to the front end surface 132 of the metal shell 130 in the air electrode 150 is formed obliquely with respect to the extending direction of the straight bar-shaped air electrode 150 (see FIG. 9). Specifically, when the extending direction of the air electrode 150 is made to coincide with the direction of the axis C, the inclination of the joining end face 156 is made to coincide with the inclination of the front end face 132 of the metal shell 130. Further, a noble metal tip 152 is fixed to the distal end portion 152 of the air electrode 150 by laser welding.

  Next, as shown in FIG. 8, the two creeping ground electrodes 110 are fixed to the front end surface 132 of the metal shell 130 so as to face each other with the axis C interposed therebetween by electric resistance welding. At this time, the creeping ground electrode 110 is configured to approach the center electrode 120 toward the tip end side in the axis C direction. Next, the aerial electrode 150 is fixed by electrical resistance welding at a position shifted by 90 degrees from the fixing surface 132b to which the two creeping ground electrodes 110 are fixed on the front end surface 132 of the metal shell 130 (FIG. 8B). )reference). At this time, the air electrode 150 is fixed to the front end surface 132 of the metallic shell 130 in a form extending in the direction of the axis C as shown in FIG.

Next, the creeping ground electrode 110 is bent so that the tip 112 of the creeping ground electrode 110 moves away from the axis C, and the tip 112 of the creeping ground electrode 110 extends in the direction of the axis C.
Thereafter, a screw portion 130b having a name of M10 is formed on the outer surface of the metal shell 130. Next, the metal shell 130 to which the insulator 140, the center electrode 120, the creeping ground electrode 110, and the air electrode 150 are fixed is assembled. Next, the aerial electrode 150 is bent so that the front end portion 151 of the aerial electrode 150 extends perpendicularly to the axis C direction. In this way, the spark plug 100 for the internal combustion engine as shown in FIG. 1 is completed.

  Next, the internal combustion engine spark plug 400 according to the second embodiment will be described. As shown in FIG. 10, the spark plug 400 for the internal combustion engine of the second embodiment is different from the spark plug 100 for the internal combustion engine of the first embodiment in the shapes of the creeping ground electrode and the air electrode. The same applies to the parts.

  In the spark plug 100 for the internal combustion engine of the first embodiment, the base end portion 111 of the creeping ground electrode 110 has a linear shape in such a form that it approaches the center electrode 120 toward the tip end side in the axis C direction (see FIG. 2). . On the other hand, in the spark plug 400 for the internal combustion engine of the second embodiment, the base end portion 411 of the creeping ground electrode 410 has a curved shape as shown in FIG. The tip side is closer to the center electrode 120. For this reason, even in the spark plug 400 for the internal combustion engine of the second embodiment, the creeping ground electrode 410 is not bent toward the center electrode 120 side, and the gap between the inner side surface 414 of the creeping ground electrode 410 and the insulator tip portion 141 is reduced. Thus, an appropriate semi-creeping gap G2 can be formed. As described above, the base end portion of the creeping ground electrode is formed so as to be closer to the center electrode toward the distal end side in the axial direction regardless of the shape thereof, so that the creeping ground electrode is not bent toward the center electrode side. An appropriate semi-creeping gap can be formed between the inner surface of the surface ground electrode and the insulator tip.

  Further, in the spark plug 100 for the internal combustion engine of the first embodiment, as shown in FIG. 3, the distal end portion 151 of the air electrode main body portion 155 extends in a direction orthogonal to the axis C direction. On the other hand, in the spark plug 400 for the internal combustion engine of the second embodiment, as shown in FIG. 10B, the tip portion 451 of the air electrode 450 extends obliquely with respect to the axis C direction. By doing in this way, the front-end | tip part 451 of the air electrode 450 forms an air discharge gap between the corner | angular parts of the front-end | tip 120b of the center electrode 120. FIG. For this reason, the electric field strength in the vicinity of the air discharge gap is increased, and the spark discharge in the air discharge gap is improved.

Further, in the spark plug 100 for the internal combustion engine of the first embodiment, as shown in FIG. 3, the noble metal tip 152 is provided at the tip portion 151 of the air electrode 150. In contrast, in the spark plug 400 for the internal combustion engine of the second embodiment, the noble metal tip 152 is not provided at the tip portion 451 of the air electrode 450 as shown in FIG. In this way, by reducing the expensive noble metal tip 152, the spark plug 400 for the internal combustion engine of the second embodiment is reduced in cost.
Also in the spark plug 400 for the internal combustion engine of the second embodiment, H (mm), N (mm), L1 (mm), L2 (mm), G1 (mm), and G2 (mm) are examples. By setting the size range to be the same as that of the spark plug 100 for an internal combustion engine of 1, the penetration damage of the insulator 140 can be suppressed and the ignitability can be improved.

  Next, a spark plug 300 for an internal combustion engine according to a third embodiment will be described. As shown in FIG. 11, the spark plug 300 for the internal combustion engine of the third embodiment is different in the shape of the creeping ground electrode from the spark plug 100 for the internal combustion engine of the first embodiment, and the other parts are the same. It is.

  In the spark plug 100 for an internal combustion engine according to the first embodiment, the creeping ground electrode 110 is bent at only one place, and the tip 112 of the creeping ground electrode 110 is extended in the direction of the axis C (see FIG. 2). On the other hand, in the spark plug 300 for the internal combustion engine of the third embodiment, the creeping ground electrode 310 is bent at only one place as in the spark plug 100 for the internal combustion engine of the first embodiment. The tip portion 312 of 310 has a form that approaches the center electrode 120 toward the tip end side in the axis C direction. However, like the spark plug 100 for the internal combustion engine of the first embodiment, the tip portion 312 of the creeping ground electrode 310 is positioned farther from the center electrode 120 than the virtual tip portion 312k of the virtual creeping ground electrode 310k. Therefore, an appropriate semi-creeping gap G2 can be formed (see FIG. 11). The virtual creeping ground electrode is a creeping ground electrode when it is assumed that the creeping ground electrode is linearly extended in the extending direction of the base end portion.

  Also in the spark plug 300 for the internal combustion engine of the third embodiment, H (mm), N (mm), L1 (mm), L2 (mm), G1 (mm), and G2 (mm) are examples. By setting the size range to be the same as that of the spark plug 100 for an internal combustion engine of 1, the penetration damage of the insulator 140 can be suppressed and the ignitability can be improved.

  Next, a spark plug 500 for an internal combustion engine according to a fourth embodiment will be described. As shown in FIG. 12, the spark plug 500 for the internal combustion engine of the fourth embodiment is different from the spark plug 100 for the internal combustion engine of the first embodiment in the shapes of the front end surface of the metal shell and the creeping ground electrode. The other parts are the same.

In the spark plug 100 for the internal combustion engine of the first embodiment, the distal end surface 132 of the metallic shell 130 is a slope that is farther from the axis C toward the distal end side in the axis C direction, and the proximal end 111 extends vertically from the distal end surface 132. The surface ground electrode 110 was fixed (see FIG. 2). Accordingly, the base end portion 111 of the creeping ground electrode 110 is configured to approach the center electrode 120 toward the tip end side in the axis C direction.
On the other hand, in the spark plug 500 for the internal combustion engine of the fourth embodiment, as shown in FIG. 12, the front end surface 532 of the metal shell 530 is a surface perpendicular to the axis C, but the joining end surface of the creeping ground electrode 510 is 516 is formed obliquely with respect to the direction in which the base end portion 511 extends, and the base end portion 511 of the creeping ground electrode 510 is configured to approach the center electrode 120 toward the front end side in the axis C direction.

As described above, in the spark plug 500 for the internal combustion engine of the fourth embodiment, as in the spark plug 100 for the internal combustion engine of the first embodiment, the proximal end portion of the creeping ground electrode is closer to the front end side in the axis C direction. Therefore, the semi-creeping gap G2 is formed between the inner surface 514 of the creeping ground electrode 510 and the insulator tip 141 without bending the creeping ground electrode 510 to the center electrode 120 side. Can do.
Also in the spark plug 500 for the internal combustion engine of the fourth embodiment, H (mm), N (mm), L1 (mm), L2 (mm), G1 (mm), and G2 (mm) are examples. By setting the size range to be the same as that of the spark plug 100 for an internal combustion engine of 1, the penetration damage of the insulator 140 can be suppressed and the ignitability can be improved.

In the above, the present invention has been described with reference to the first to fourth embodiments. However, the present invention is not limited to the first to fourth embodiments, and can be appropriately modified and applied without departing from the gist thereof. Needless to say.
For example, in the spark plugs 100, 300, 400, 500 for the internal combustion engine of Examples 1 to 4, a spark plug having a nominal diameter M10 of the threaded portion 130b of the metal shell 130 was used. However, the present invention is not limited to the M10 spark plug. Further, it is particularly effective for spark plugs for internal combustion engines having M12 or less, for example, M12, M8 metal shells.
The present invention can also be applied to a so-called screwless plug in which a mounting screw portion is not formed on the outer surface of the metal shell.

Further, in the spark plugs 100, 300, 400, 500 for the internal combustion engines of the first to fourth embodiments, two sparking ground electrodes 110, 310, 410, 510 are provided, and further, the spark electrodes 150, 450 are provided. Plug. However, a semi-creeping discharge type spark plug having only a creeping ground electrode without providing an air electrode may be used. Further, the creeping ground electrode may be one or more, and for example, three or four creeping ground electrodes may be provided.
Further, in the spark plugs 100, 300, 400, 500 for the internal combustion engine of Examples 1 to 4, the axial C direction distance N (mm) from the tip 141b of the insulator 140 to the annular ridge line 125 of the center electrode 120 is negative. The value (the annular ridge line 125 is arranged closer to the base end side in the axis C direction than the distal end 141b of the insulator 140). However, even if the positive value (the annular ridge 125 is arranged on the tip end side in the axis C direction with respect to the tip 141b of the insulator 140), the penetration failure of the insulator 140 can be suppressed.

1 is a front view of a spark plug 100 for an internal combustion engine according to a first embodiment. FIG. 2 is an enlarged view of the front end side of the spark plug 100 for an internal combustion engine according to the first embodiment, and corresponds to a partial cross-sectional view of FIG. FIG. 3 is an enlarged view of the front end side of the spark plug 100 for the internal combustion engine according to the first embodiment, and corresponds to a side view of FIG. 2. It is a graph which shows the result of the ignitability test of the spark plug 100 for internal combustion engines concerning Example 1, and shows the value of A / F accompanying the fluctuation | variation of L2 (mm). It is a graph which shows the result of the ignitability test of the spark plug 100 for internal combustion engines concerning Example 1, and shows the value of A / F accompanying the fluctuation | variation of L1 (mm). It is a graph which shows the result of the ignitability test of the spark plug 100 for internal combustion engines concerning Example 1, and shows the value of A / F accompanying the fluctuation | variation of G1 (mm). It is a graph which shows the result of the ignitability test of the spark plug 100 for internal combustion engines concerning Example 1, and shows the value of A / F accompanying the fluctuation | variation of H (mm). BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory diagram for explaining a method for manufacturing an internal combustion engine spark plug 100 according to a first embodiment; BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory diagram for explaining a method for manufacturing an internal combustion engine spark plug 100 according to a first embodiment; It is a figure which shows the front end side of the spark plug 400 for internal combustion engines concerning Example 2, (a) is a fragmentary sectional view, (b) is the side view. FIG. 6 is a partial cross-sectional view of a tip side of a spark plug 300 for an internal combustion engine according to a third embodiment. FIG. 6 is a partial cross-sectional view of a tip side of a spark plug 500 for an internal combustion engine according to a fourth embodiment.

100, 300, 400, 500 Spark plug for internal combustion engine 110, 310, 410, 510 Creeping ground electrode 110g, 310g, 410g, 510g Electrode side gap position 111, 311, 411, 511 Base end 112 of creeping ground electrode , 312, 412 Creeping ground electrode tip 114, 314, 414, 514 Creeping ground electrode inner surface 120 Center electrode 120 b Tip side gap position 121 Center electrode tip 122, 152 Precious metal tip 123 Reduced diameter portion of center electrode 124 Base electrode side end portion 125 Center electrode annular ridge 130, 530 Metal shell 140 Insulator 141 Insulator tip 141b Insulator tip 150, 450 Air electrode 155, 455 Air electrode main body 151b Air electrode Inner side surface C of the tip of the main body Axis D Outer diameter G1 of the metal shell Dimension G2 Semi-surface discharge gap dimension H Distance in the direction perpendicular to the inner surface of the tip from the inner surface of the tip of the aerial electrode body to the tip-side gap position J Axis C direction from the tip of the insulator to the tip of the center electrode Distance L1 to tip side Axial direction distance L2 from tip of insulator to electrode side gap position Axial direction distance N from tip of insulator to tip of creeping ground electrode Axial direction distance from tip of insulator to annular ridge line

Claims (8)

A cylindrical insulator having an axial hole penetrating in the axial direction;
A center electrode inserted into the shaft hole, the center electrode having a center electrode tip protruding from the tip of the insulator;
A cylindrical metal shell that surrounds the insulator and is arranged so that a part of the insulator protrudes from its tip;
One or a plurality of creeping ground electrodes joined to the front end surface of the metal shell, and a part of a discharge path of a spark discharge generated between the creeping ground electrode and the center electrode front end portion, Of the insulator, a shape with respect to the insulator tip and the center electrode tip is defined so as to include a creeping discharge path along the surface of the insulator tip protruding beyond the tip of the metal shell. A surface ground electrode;
A spark plug for an internal combustion engine comprising:
The creeping ground electrode is a smooth inner surface extending from the front end surface of the metal shell toward the center electrode side, and has an inner side surface extending from the front end of the insulator to the front end side in the axial direction.
When the shortest gap among the gaps between the creeping ground electrode and the insulator tip is a semi-creeping discharge gap, the inner surface of the creeping ground electrode is in contact with the insulator tip. Including the electrode side gap position forming the discharge gap,
The axial distance from the distal end of the insulator to the electrode-side gap position when the distal end of the insulator is a starting point, the distal end side in the axial direction is a positive direction, and the proximal end side in the axial direction is a negative direction. L1 (mm) is a spark plug for an internal combustion engine that satisfies a relationship of −0.8 ≦ L1 ≦ 0.0. A cylindrical insulator having an axial hole penetrating in the axial direction;
A center electrode inserted into the shaft hole, the center electrode having a center electrode tip protruding from the tip of the insulator;
A cylindrical metal shell that surrounds the insulator and is arranged so that a part of the insulator protrudes from its tip;
One or a plurality of creeping ground electrodes joined to the front end surface of the metal shell, and a part of a discharge path of a spark discharge generated between the creeping ground electrode and the center electrode front end portion, Of the insulator, a shape with respect to the insulator tip and the center electrode tip is defined so as to include a creeping discharge path along the surface of the insulator tip protruding beyond the tip of the metal shell. A surface ground electrode;
A spark plug for an internal combustion engine comprising:
The creeping ground electrode is a smooth inner surface extending from the front end surface of the metal shell toward the center electrode side, and has an inner side surface extending from the front end of the insulator to the front end side in the axial direction.
When the shortest gap among the gaps between the creeping ground electrode and the insulator tip is a semi-creeping discharge gap, the inner surface of the creeping ground electrode is in contact with the insulator tip. No discharge gap,
The spark plug for an internal combustion engine, wherein the semi-surface discharge gap dimension G2 (mm) satisfies a relationship of 0.35 ≦ G2 ≦ 0.80. A spark plug for an internal combustion engine according to claim 1 or 2 ,
A spark plug for an internal combustion engine having an air electrode fixed to the metal shell and forming an air discharge gap with a tip of the center electrode. A spark plug for an internal combustion engine according to claim 3 ,
A spark plug for an internal combustion engine, wherein a tip of the creeping ground electrode is positioned closer to a base end side in the axial direction than a tip of the center electrode. A spark plug for an internal combustion engine according to claim 3 or 4 ,
The semi-surface discharge gap dimension G2 (mm) satisfies a relationship of 0.35 ≦ G2 ≦ 0.80, and the air discharge gap dimension G1 (mm) is 0.5 ≦ G1 ≦ 1.1. A spark plug for internal combustion engines that satisfies this relationship. A spark plug for an internal combustion engine according to any one of claims 3 to 5 ,
The air electrode is
A base end portion fixed to the metal shell and extending toward the axial front end side, a bent portion extending from the base end portion and bending radially inward of the metal shell, and extending from the bent portion to the center An air electrode main body comprising a tip extending to a position facing the electrode in the axial direction;
A noble metal tip that is directly or indirectly fixed to the tip of the air electrode main body and forms the air discharge gap with the tip of the center electrode;
A direction perpendicular to the inner surface of the tip from the inner surface of the tip of the air electrode main body facing the center electrode to the tip side gap position of the noble metal tip forming the air discharge gap. A spark plug for an internal combustion engine that satisfies a relationship of H ≧ 0.1 when the distance to is H (mm). A spark plug for an internal combustion engine according to any one of claims 1 to 6 ,
A spark plug for an internal combustion engine, wherein the outer diameter of the metal shell is 10.1 mm or less. A spark plug for an internal combustion engine according to any one of claims 1 to 7 ,
The creeping ground electrode is a spark plug for an internal combustion engine that has a base end portion that extends from a front end surface of the metal shell and is closer to the center electrode toward the front end side in the axial direction.

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