JP2012164644A - Spark plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize both excellent ignitability and excellent wear resistance.SOLUTION: A spark plug 1 comprises a center electrode side chip 31 and a ground electrode side chip 32, and a spark discharge gap 33 is formed between the ground electrode side chip 32 and the center electrode side chip 31. On a virtual plane orthogonal to an axis line CL1, among a projection face formed by projecting tip faces of the ground electrode side chip 32 and the center electrode side chip 31, an area SA1 (mm) of a region surrounded by a first tangential line TL1, a second tangential line TL2, a projection line on the other end face of the ground electrode side chip 32, and a projection line on an outer periphery of the tip face of the center electrode side chip 31; an area SA2 (mm) of a region, in which projection regions of both of the chips 31, 32 when projecting the other end faces of the center electrode side chip 31 and the ground electrode side chips 32 on a virtual plane parallel to the other end face of the ground electrode side chip 32; and a size G (mm) of the spark discharge gasp 33 satisfy 0.12≤SA1×SA2/G(mm)≤0.49.

Description

  The present invention relates to a spark plug used for an internal combustion engine or the like.

  A spark plug used in a combustion apparatus such as an internal combustion engine includes, for example, a center electrode extending in the axial direction, an insulator provided on the outer periphery of the center electrode, a cylindrical metal shell provided on the outer periphery of the insulator, and one end And a bar-shaped ground electrode joined to the tip of the metal shell. The ground electrode is arranged with its substantially middle part bent back so that the other end faces the tip of the center electrode, thereby causing a spark discharge between the tip of the center electrode and the other end of the ground electrode. A gap is formed. In addition, a technique is known in which a noble metal tip is provided at a portion where the spark discharge gap is formed in the other end of the ground electrode to improve wear resistance and ignition performance.

  By the way, the ground electrode protrudes toward the center side of the combustion chamber. For this reason, the ground electrode is overheated, and there is a possibility that pre-ignition (early ignition) may occur due to the high-temperature ground electrode, or the ground electrode may be melted or broken.

  Therefore, in order to improve the heat resistance of the ground electrode while maintaining the ignitability, the ground electrode is made relatively short, and the tip surface of the ground electrode (precious metal tip) is made to face the tip portion side surface of the center electrode, There has been proposed a technique (so-called lateral discharge type spark plug) that generates a spark discharge along a substantially orthogonal direction (see, for example, Patent Document 1). According to this method, the amount of heat received by the ground electrode can be reduced, the heat of the ground electrode can be easily conducted to the metal shell, and the heat resistance can be improved. In addition, the flame kernel can be smoothly grown toward the center of the combustion chamber without being obstructed by the ground electrode, and the ignitability can be sufficiently maintained.

JP 2009-151984

  However, in recent years, an engine with a supercharger, a high compression ratio engine, and the like have been proposed in order to achieve low fuel consumption, low emission, and high output. For this reason, the voltage (discharge voltage) required to cause a spark discharge may increase or the ground electrode may become hotter than before, and the ground electrode and precious metal tip are consumed due to the spark discharge. There is concern that this will progress rapidly.

  Here, in order to improve the wear resistance of the ground electrode or the like, it is conceivable to increase the facing area between the ground electrode (noble metal tip) and the center electrode. In this case, the ground electrode (noble metal tip) Further, the growth of flame nuclei may be hindered by the center electrode or the discharge position may vary, leading to a decrease in ignitability.

  The present invention has been made in view of the above circumstances, and the purpose thereof is a spark plug in which a ground electrode and a noble metal tip are opposed to a side surface of a tip portion of a center electrode, and has excellent performance in both ignitability and wear resistance. An object of the present invention is to provide a spark plug capable of realizing the above.

  Hereinafter, each configuration suitable for solving the above-described object will be described in terms of items. In addition, the effect specific to the corresponding structure is added as needed.

Configuration 1. The spark plug of this configuration includes an insulator having an axial hole penetrating in the axial direction;
A center electrode inserted in the shaft hole;
A metal shell provided on the outer periphery of the insulator;
A ground electrode fixed to the tip of the metal shell,
A ground electrode side tip made of a metal containing a noble metal, at least one end of which is joined to the tip of the ground electrode,
The center electrode has a center electrode side tip made of a metal containing a noble metal at its tip,
A spark plug in which the other end surface of the ground electrode side chip faces the side surface of the center electrode side chip, and a gap is formed between the other end surface of the ground electrode side chip and the side surface of the center electrode side chip. ,
The center electrode from one end of the side corresponding to the other end surface of the ground electrode side chip out of the projection plane obtained by projecting the ground electrode side chip and the tip surface of the center electrode side chip in a virtual plane orthogonal to the axis. The first tangent line drawn on the projection area corresponding to the tip surface of the side tip and the other end of the side corresponding to the other end face of the ground electrode side tip are drawn to the projection area corresponding to the tip surface of the center electrode tip. The area of the region surrounded by the second tangent line, the projection line corresponding to the other end surface of the ground electrode side chip, and the projection line corresponding to the outer periphery of the tip end surface of the center electrode side chip is SA1 (mm ² ). age,
The projection region of the center electrode side chip and the ground electrode side chip when the center electrode side chip and the other end surface of the ground electrode side chip are projected onto a virtual plane parallel to the other end surface of the ground electrode side chip. The area of the area where the projection area on the other end surface overlaps is SA2 (mm ² ),
When the size of the gap is G (mm),
0.12 ≦ SA1 × SA2 / G (mm ³ ) ≦ 0.49
The filling,
A portion of the other end surface of the ground electrode side chip located closest to the rear end side in the axial direction, and an axis of the surface of the center electrode side chip facing the other end surface of the ground electrode side chip. A (mm) is the distance along the axis line between the most distal end portion and
When the length along the axis of the other end surface of the ground electrode side tip is B (mm),
0.05 ≦ A ≦ B + 0.2 and 0.3 ≦ B ≦ 0.7
The filling,
When the area of the other end surface of the ground electrode side chip is SX (mm ² ),
0.3 ≦ SX ≦ 0.6 and 0.4 ≦ G ≦ 1.0
It is characterized by satisfying.

  In the projection plane, when a tangent line is drawn from one end and the other end of the side corresponding to the other end face of the ground electrode side tip to the projection area corresponding to the tip end face of the center electrode side tip, Two tangents can be drawn, but the “first tangent” and “second tangent” are on the side corresponding to the other end face of the ground electrode side tip and the tip end face of the center electrode side tip. It means two tangents that do not intersect each other between the corresponding projection areas.

  According to the configuration 1, the relative positional relationship between the ground electrode side tip and the center electrode side tip is configured to satisfy 0.12 ≦ SA1 × SA2 / G. Therefore, an increase in the discharge voltage can be suppressed, and spark discharge is generated between only a part of the ground electrode side chip and the center electrode side chip, and the ground electrode side chip and the like are locally consumed. Can be prevented more reliably. As a result, wear resistance can be effectively improved.

  Furthermore, according to the said structure 1, it is comprised so that SA1 * SA2 / G <= 0.49 may be satisfy | filled. For this reason, it is possible to more reliably prevent flame nucleus growth inhibition due to the presence of the ground electrode side tip and the center electrode side tip, and it is possible to suppress a situation in which the discharge position varies extremely. As a result, excellent ignitability can be realized while sufficiently maintaining the above-described effect of improving wear resistance.

  In addition, according to the configuration 1, the distance B is set to 0.3 mm or more, and the ground electrode side tip is configured to be sufficiently thick. Accordingly, overheating of the ground electrode side chip can be suppressed, and a sufficient consumption volume can be secured in the ground electrode side chip.

  Further, the distance A is set to 0.05 mm or more, and the facing area between the center electrode side tip and the ground electrode side tip is not extremely reduced. For this reason, it is possible to more reliably prevent a situation in which spark discharge centering on the respective edge portions of the center electrode side tip and the ground electrode side tip is intensively generated and the edge portions are consumed unevenly.

  As described above, the function and effect of setting the distance B to 0.3 mm or more and the function and effect of setting the distance A to 0.05 mm or more act synergistically to further improve wear resistance. Can be planned.

  Furthermore, according to the said structure 1, the distance B is 0.7 mm or less, and it is comprised so that the thickness of the ground electrode side tip may not become large too much. Therefore, the situation where the growth of the flame kernel is inhibited or the heat of the flame kernel is deprived by the ground electrode side tip can be more reliably suppressed.

  In addition, the distance A is set to be “B + 0.2 mm” or less, and the protruding amount toward the tip end side in the axial direction of the center electrode side tip with respect to the other end surface of the ground electrode side tip is configured not to be excessively large. . Therefore, the flame kernel can be further grown toward the center side of the combustion chamber without being obstructed by the center electrode side tip.

  In addition, the center electrode tip is generally joined to the base electrode base material through a melted portion formed by laser welding or the like. By setting the distance A to be “B + 0.2 mm” or less. The other end surface of the ground electrode side chip can be separated from the melting part. Therefore, it is possible to more reliably suppress the occurrence of spark discharge between the ground electrode side tip and the melting part (that is, a position away from the center of the combustion chamber).

  As described above, combined with the operational effect by setting the distance B to 0.7 mm or less and the operational effect by setting the distance A to “B + 0.2 mm” or less, the ignitability can be further improved. Can do.

In addition, according to the configuration 1, since the size G of the spark discharge gap is 1.0 mm or less, an increase in the discharge voltage can be more reliably suppressed, and the area SX is 0.3 mm. ^Since it is set to ² or more, the consumption volume of the ground electrode side tip can be secured even larger. Thereby, the further improvement of wear resistance can be aimed at.

Further, according to the above configuration 1, the size G of the spark discharge gap is set to 0.4 mm or more and the area SX is set to 0.6 mm ² or less. Inhibition can be more effectively suppressed. As a result, the ignitability can be further improved.

Configuration 2. The spark plug of this configuration includes an insulator having an axial hole penetrating in the axial direction;
A center electrode inserted in the shaft hole;
A metal shell provided on the outer periphery of the insulator;
A ground electrode fixed at an end of the metal shell to one end of the metal shell;
A spark plug in which the other end surface of the ground electrode is opposed to a side surface of the tip portion of the center electrode, and a gap is formed between the other end surface of the ground electrode and a side surface of the tip portion of the center electrode;
Corresponding to the front end surface of the center electrode from one end of the side corresponding to the other end surface of the ground electrode among the projection surfaces obtained by projecting the ground electrode and the front end surface of the center electrode in a virtual plane orthogonal to the axis. A third tangent line drawn in the projection area, a fourth tangent line drawn from the other end of the side corresponding to the other end face of the ground electrode to the projection area corresponding to the front end face of the center electrode, and other ground electrodes. The area of the region surrounded by the projection line corresponding to the end surface and the projection line corresponding to the outer periphery of the front end surface of the center electrode is SB1 (mm ² ),
A region where a projection region of the center electrode and a projection region of the other end surface of the ground electrode overlap when the center electrode and the other end surface of the ground electrode are projected on a virtual plane parallel to the other end surface of the ground electrode; The area is SB2 (mm ² )
When the size of the gap is G (mm),
0.21 ≦ SB1 × SB2 / G (mm ³ ) ≦ 0.49
It is characterized by satisfying.

  The “third tangent” and the “fourth tangent” are two lines that do not intersect each other between the side corresponding to the other end face of the ground electrode and the projection area corresponding to the tip end face of the center electrode. Tangent line.

  According to the above configuration 2, in the spark plug in which the other end surface of the ground electrode is opposed to the side surface of the tip portion of the center electrode, excellent performance in both wear resistance and ignition performance can be realized.

  In the configuration 2, the center electrode tip may or may not be provided at the tip of the center electrode.

Configuration 3. The spark plug of the present configuration has an arbitrary cross section along the direction orthogonal to the central axis of the ground electrode between the longitudinal center of the ground electrode and one end of the ground electrode in the above configuration 1 or 2.
When the sectional area of the ground electrode is SY (mm ² ) and the width of the ground electrode is W (mm),
2.3 ≦ SY ≦ 3.5 and 1.8 ≦ W ≦ 2.2
It is characterized by satisfying.

According to the configuration 3, since the cross-sectional area SY on one end side (side fixed to the metal shell) of the ground electrode is 2.3 mm ² or more, the other end portion of the ground electrode is on the one end side (metal shell). Heat) can be conducted efficiently to the side). Even if the cross-sectional area is 2.3 mm ² or more, if the width of the ground electrode is extremely small, the thickness of the ground electrode becomes excessively large, so that the ground electrode protrudes toward the center of the combustion chamber. Thus, although there is a concern about overheating of the ground electrode, since the width W is set to 1.8 mm or more, the concern can be eliminated. That is, by setting the width W to 1.8 mm or more while keeping the cross-sectional area SY to 2.3 mm ² or less, it is possible to further improve heat resistance in a horizontal discharge type spark plug that is generally excellent in heat resistance. .

Furthermore, according to the configuration 3, since the cross-sectional area SY is 3.5 mm ² or less, it is possible to more reliably prevent the heat of the flame kernel from being taken away by the ground electrode. Since W is 2.2 mm or less, the inhibition of the growth of flame nuclei by the ground electrode can be effectively suppressed. As a result, the ignitability can be further improved.

Configuration 4. The spark plug of this configuration includes any one of the above configurations 1 to 3, wherein the ground electrode includes an outer layer, and an inner layer provided in the outer layer and made of a metal having higher thermal conductivity than the outer layer.
In the cross section in which the cross-sectional area of the inner layer is maximum along the direction orthogonal to the central axis of the ground electrode,
When the cross-sectional area of the inner layer is SI (mm ² ) and the cross-sectional area of the ground electrode is SZ (mm ² ),
0.2 ≦ SI / SZ ≦ 0.5
It is characterized by satisfying.

  According to the above configuration 4, the inner layer having excellent thermal conductivity is provided inside the ground electrode, and 0.2 ≦ SI / SZ is satisfied (that is, the inner layer has a sufficient volume with respect to the ground electrode). As configured). Therefore, the thermal conductivity of the ground electrode can be dramatically increased, and the heat resistance can be improved extremely effectively.

  On the other hand, if the proportion of the inner layer in the cross section of the ground electrode is excessively increased, the outer layer becomes thin as a result, and the outer layer may be damaged due to thermal expansion of the inner layer. In this respect, according to the configuration 4, since SI / SZ ≦ 0.5, the thickness of the outer layer can be sufficiently secured, and the strength of the outer layer can be sufficiently maintained. As a result, it is possible to more reliably prevent the outer layer from being damaged due to the thermal expansion of the inner layer.

Configuration 5. In the spark plug of this configuration, in any one of the above configurations 1 to 4, both side surfaces adjacent to the facing surface facing the center electrode of the ground electrode have an outwardly convex curved shape,
In a cross section orthogonal to the central axis of the ground electrode, when the radius of curvature of the outline of the both side surfaces is R (mm),
R ≦ 1.5
It is characterized by satisfying.

  When the radius of curvature is not constant, “curvature radius R” means three points of one end point and the other end point of the outline of the side surface and the midpoint of both in the cross section orthogonal to the central axis of the ground electrode. The radius of curvature of the virtual circle that passes through.

  According to the above configuration 5, the convex curved surfaces are formed on both side surfaces of the ground electrode, so that the fuel gas can easily enter the gap, and the ignitability can be further improved.

It is a partially broken front view which shows the structure of a spark plug. It is a partially broken expanded front view which shows the structure of the front-end | tip part of a spark plug. It is a partial expanded sectional view which shows the cross-sectional shape etc. of a ground electrode. It is a partial expanded side view which shows the structure of the front-end | tip part of a ground electrode. It is the projection which projected the center electrode etc. on the virtual plane orthogonal to an axis. It is the projection which projected the center electrode etc. on the virtual plane parallel to the other end surface of the ground electrode side chip. It is a partially broken enlarged front view which shows the structure of the front-end | tip part of the spark plug in 2nd Embodiment. In 2nd Embodiment, it is the projection which projected the center electrode etc. on the virtual plane orthogonal to an axis line. In 2nd Embodiment, it is the projection which projected the center electrode etc. on the virtual plane parallel to the other end surface of a ground electrode. It is a partially broken enlarged front view which shows the structure of a comparative example sample. It is a graph which shows the test result of the desktop spark endurance test in the sample which changed distance A and B variously. It is a graph which shows the test result of the ignitability evaluation test in the sample which changed distance A and B variously. It is a graph which shows the test result of the desktop spark endurance test in the sample which changed area SX and the magnitude | size G of the spark discharge gap variously. It is a graph which shows the test result of the ignitability evaluation test in the sample which changed the area SX and the magnitude | size G of the spark discharge gap variously. It is a graph which shows the test result of the ignitability evaluation test in the sample which changed the area SY and the width W of the ground electrode variously. It is a graph which shows the improvement value of a heat value in the sample which changed SI / SZ variously. It is a graph which shows the fluctuation | variation range of a limit air fuel ratio in the sample which changed the cross-sectional shape of the ground electrode variously. It is a partially broken enlarged front view which shows the structure of the spark plug in another embodiment. It is a partial enlarged plan view which shows the structure of the ground electrode in another embodiment. It is a partial enlarged plan view which shows the structure of the ground electrode in another embodiment.

Hereinafter, embodiments will be described with reference to the drawings.
[First Embodiment]
FIG. 1 is a partially cutaway front view showing a spark plug 1. In FIG. 1, the direction of the axis CL <b> 1 of the spark plug 1 is the vertical direction in the drawing, the lower side is the front end side of the spark plug 1, and the upper side is the rear end side.

  The spark plug 1 includes an insulator 2 as a cylindrical insulator, a cylindrical metal shell 3 that holds the insulator 2, and the like.

  As is well known, the insulator 2 is formed by firing alumina or the like, and in its outer portion, a rear end side body portion 10 formed on the rear end side, and a front end than the rear end side body portion 10. A large-diameter portion 11 that protrudes radially outward on the side, a middle body portion 12 that is smaller in diameter than the large-diameter portion 11, and a tip portion that is more distal than the middle body portion 12. The leg length part 13 formed in diameter smaller than this on the side is provided. In addition, of the insulator 2, the large diameter portion 11, the middle trunk portion 12, and most of the leg long portions 13 are accommodated inside the metal shell 3. A tapered step portion 14 is formed at the connecting portion between the middle body portion 12 and the long leg portion 13, and the insulator 2 is locked to the metal shell 3 at the step portion 14.

  Further, the insulator 2 is formed with a shaft hole 4 extending along the axis CL <b> 1, and a center electrode 5 is inserted and fixed to the tip side of the shaft hole 4. The center electrode 5 has a rod shape (cylindrical shape) as a whole, and its tip portion protrudes from the tip of the insulator 2. In addition, the center electrode 5 includes an inner layer 5A made of copper or a copper alloy and an outer layer 5B made of a Ni alloy containing nickel (Ni) as a main component. Furthermore, a cylindrical center made of a metal containing a noble metal (for example, platinum, iridium, etc.) joined to the outer layer 5B through a fusion part 34 formed by laser welding or the like at the tip of the center electrode 5 An electrode side tip 31 is provided.

  A terminal electrode 6 is inserted and fixed on the rear end side of the shaft hole 4 in a state of protruding from the rear end of the insulator 2.

  Further, a cylindrical resistor 7 is disposed between the center electrode 5 and the terminal electrode 6 of the shaft hole 4. Both ends of the resistor 7 are electrically connected to the center electrode 5 and the terminal electrode 6 through conductive glass seal layers 8 and 9, respectively.

  In addition, the metal shell 3 is formed in a cylindrical shape from a metal such as low carbon steel, and a screw for attaching the spark plug 1 to a combustion device such as an internal combustion engine or a fuel cell reformer on the outer peripheral surface thereof. A portion (male screw portion) 15 is formed. Further, a seat portion 16 is formed on the rear end side of the screw portion 15 so as to protrude toward the outer peripheral side, and a ring-shaped gasket 18 is fitted into the screw neck 17 at the rear end of the screw portion 15. Further, a tool engaging portion 19 having a hexagonal cross section for engaging a tool such as a wrench when the metal shell 3 is attached to the combustion device is provided on the rear end side of the metal shell 3. A caulking portion 20 that bends inward in the radial direction is provided at the rear end portion of the metal shell 3.

  In addition, a tapered step portion 21 for locking the insulator 2 is provided on the inner peripheral surface of the metal shell 3. The insulator 2 is inserted from the rear end side to the front end side of the metal shell 3, and the rear end of the metal shell 3 is engaged with the step portion 14 of the metal shell 3. It is fixed to the metal shell 3 by caulking the opening on the side inward in the radial direction, that is, by forming the caulking portion 20. An annular plate packing 22 is interposed between the step portions 14 and 21 of both the insulator 2 and the metal shell 3. Thereby, the airtightness in the combustion chamber is maintained, and the fuel gas entering the gap between the leg long portion 13 of the insulator 2 exposed to the combustion chamber and the inner peripheral surface of the metal shell 3 is prevented from leaking outside.

  Further, in order to make the sealing by caulking more complete, annular ring members 23 and 24 are interposed between the metal shell 3 and the insulator 2 on the rear end side of the metal shell 3, and the ring member 23 , 24 is filled with talc 25 powder. That is, the metal shell 3 holds the insulator 2 via the plate packing 22, the ring members 23 and 24, and the talc 25.

  In addition, as shown in FIG. 2, one end of a rod-shaped ground electrode 27 is joined to the distal end portion 26 of the metal shell 3. The ground electrode 27 is bent back substantially at an intermediate portion, and is provided with an outer layer 27Z made of a Ni alloy containing Ni as a main component, and a metal (having higher thermal conductivity than the outer layer 27Z). For example, the inner layer 27I made of copper, copper alloy, pure Ni, or the like) is provided. In the present embodiment, the distance between the tip of the inner layer 27I and the other end of the ground electrode 27 is configured to be sufficiently small (for example, 2 mm or less).

  In addition, in the present embodiment, as shown in FIG. 3, the ground electrode 27 faces the center electrode side chip 31 (in the center electrode 5 side) in an arbitrary cross section along the direction orthogonal to the center axis CL2. Both side surfaces 27S1 and 27S2 adjacent to the opposing surface 27T (located) are curved outwardly convex. And, in the cross section orthogonal to the central axis CL2 of the ground electrode 27, when the curvature radii of the outlines of the side surfaces 27S1 and 27S2 are R1 (mm) and R2 (mm), respectively, R1 ≦ 1.5 and R2 It is configured to satisfy ≦ 1.5. When the radius of curvature is not constant, “curvature radius R1, R2” means that the radius of curvature of the virtual circle passing through the three points of the one end point and the other end point of the side lines 27S1, 27S2 and the midpoint of both. Say.

Further, the ground electrode 27 is configured to have a substantially constant width and cross-sectional area along the longitudinal direction of the ground electrode 27, and in any cross section along the direction orthogonal to the central axis CL2 of the ground electrode 27, the ground electrode 27 When the cross sectional area of the electrode 27 is SY (mm ² ) and the width of the ground electrode 27 is W (mm), 2.3 ≦ SY ≦ 3.5 and 1.8 ≦ W ≦ 2.2 are satisfied. It is configured as follows. In the present embodiment, the cross-sectional area SY and the like are configured so as to satisfy the above expression in an arbitrary cross section along the direction orthogonal to the central axis CL2, but at least the ground electrode 27 is grounded from the longitudinal center. The cross-sectional area SY etc. should just be comprised so that the cross-sectional area SY etc. may satisfy | fill the said formula | equation in the arbitrary cross sections along the direction orthogonal to the said central axis CL2 to the end of the electrode 27.

In addition, in the cross section where the cross-sectional area of the inner layer 27I is maximum along the direction orthogonal to the central axis CL2 of the ground electrode 27, the cross-sectional area of the inner layer 27I is SI (mm ² ), and the cross-sectional area of the ground electrode 27 is When SZ (mm ² ) is set, 0.2 ≦ SI / SZ ≦ 0.5 is set. In the present embodiment, the cross-sectional area of the inner layer 27I along the direction orthogonal to the central axis CL2 of the ground electrode 27 is at least half of the embedded range of the inner layer 27I along the longitudinal direction of the ground electrode 27. The cross sectional area is 0.2 times or more.

  Returning to FIG. 2, a ground electrode side tip 32 made of a metal including a noble metal (for example, platinum, iridium, etc.) is projected from the other end surface 27 </ b> F of the ground electrode 27 on the tip side of the opposing surface 27 </ b> T of the ground electrode 27. It is joined. The ground electrode side chip 32 has a rectangular cross section (see FIG. 4), and is joined in a state where one end of itself is partially embedded in the ground electrode 27. In addition, the other end surface 32 </ b> F of the ground electrode side chip 32 faces the side surface of the tip of the center electrode side chip 31. A spark discharge gap 33 is formed as a gap between the side surface of the center electrode side chip 31 and the other end face 32F of the ground electrode side chip 32, and the spark discharge gap 33 is orthogonal to the axis CL1. Spark discharge is performed in a direction substantially along the direction.

  Further, in the present embodiment, a portion of the other end surface 32F of the ground electrode side chip 32 that is located on the most rear end side along the direction of the axis CL1 and the other end surface 32F of the ground electrode side chip 32 of the center electrode side chip 31 are arranged. The distance along the axis CL1 between the portion located on the most distal side along the axis CL1 of the surface opposite to the surface is A (mm), and the length along the axis CL1 of the other end surface 32F of the ground electrode side chip 32 When B is (mm), 0.05 ≦ A ≦ B + 0.2 and 0.3 ≦ B ≦ 0.7 are satisfied.

Further, when the size of the spark discharge gap 33 (the shortest distance between the two chips 31 and 32) is G (mm), the center electrode side chip 31 and the ground electrode so as to satisfy 0.4 ≦ G ≦ 1.0. A distance from the side chip 32 is set. In addition, when the area of the other end surface 32F of the ground electrode side chip 32 is SX (mm ² ), the width and thickness of the ground electrode side chip 32 are set so as to satisfy 0.3 ≦ SX ≦ 0.6, respectively. (For example, the ground electrode side chip 32 has a width of 0.75 mm to 0.85 mm and a thickness of 0.4 mm to 0.7 mm).

In addition, in the present embodiment, an area described later when the ground electrode side chip 32 and the tip surface of the center electrode side chip 31 are projected along the axis CL1 on a virtual plane orthogonal to the axis CL1 shown in FIG. Centered along a direction orthogonal to the axis CL1 on a virtual plane parallel to SA1 (mm ² ; a portion with a dotted pattern in FIG. 5) and the other end surface 32F of the ground electrode side chip 32 shown in FIG. An area SA2 (mm ² ; a portion with a dotted pattern in FIG. 6) described later when the electrode side tip 31 and the other end surface 32F of the ground electrode side tip 32 are projected, and the size G of the spark discharge gap 33 (Mm) is configured to satisfy 0.12 ≦ SA1 × SA2 / G (mm ³ ) ≦ 0.49.

  As shown in FIG. 5, the area SA <b> 1 is a first area drawn from one end of the side corresponding to the other end surface 32 </ b> F of the ground electrode side chip 32 to a projection region corresponding to the front end surface of the center electrode side chip 31. A tangent line TL1, a second tangent line TL2 drawn from the other end of the side corresponding to the other end face 32F of the ground electrode side chip 32 to a projection region corresponding to the tip end face of the center electrode side chip 31, and a ground electrode side chip 32. An area AR1 surrounded by a projection line (side) corresponding to the other end surface 32F and a projection line corresponding to the outer periphery of the tip end surface of the center electrode chip 31.

  Further, the area SA2 refers to the area of the area AR2 where the projection area of the center electrode side chip 31 and the projection area of the ground electrode side chip 32 overlap as shown in FIG.

  As described above in detail, according to the present embodiment, the relative positional relationship between the ground electrode side chip 32 and the center electrode side chip 31 is configured to satisfy 0.12 ≦ SA1 × SA2 / G. Accordingly, an increase in the discharge voltage can be suppressed, and spark discharge is generated only in a small part of the ground electrode side chip 32 and the center electrode side chip 31, and the ground electrode side chip 32 and the like are locally consumed. Can be prevented more reliably. As a result, wear resistance can be effectively improved.

  Furthermore, since it is configured to satisfy SA1 × SA2 / G ≦ 0.49, it is possible to more reliably prevent flame kernel growth inhibition due to the presence of the ground electrode side tip 32 and the center electrode side tip 31, and the discharge position. Can be prevented from extremely fluctuating. As a result, excellent ignitability can be realized while sufficiently maintaining the above-described effect of improving wear resistance.

  In addition, since the distance B is 0.3 mm or more, it is possible to suppress overheating of the ground electrode side chip 32 and the distance A is 0.05 mm or more. In addition, uneven wear at the edge portion of the ground electrode side chip 32 can be prevented more reliably. As a result, the wear resistance can be further improved.

  In addition, since the distance B is set to 0.7 mm or less, it is possible to effectively prevent the heat of the flame kernel from being taken away by the ground electrode side chip 32, and the distance A is “B + 0.2 mm. Therefore, the flame kernel can be smoothly grown toward the center of the combustion chamber. Thereby, ignitability can be further improved.

Further, since the size G of the spark discharge gap 33 is set to 1.0 mm or less, an increase in the discharge voltage can be more reliably suppressed, and the area SX is set to 0.3 mm ² or more. The consumption volume of the ground electrode side chip 32 can be further increased. Thereby, further improvement in wear resistance can be achieved.

In addition, since the size G of the spark discharge gap 33 is set to 0.4 mm or more and the area SX is set to 0.6 mm ² or less, the growth inhibition of the flame kernel by the ground electrode side chip 32 or the like is further effective. Therefore, the ignitability can be further improved.

Further, by setting the width W to 1.8 mm or more while the cross-sectional area SY is 2.3 mm ² or more, the thermal conductivity of the ground electrode 27 is sufficiently increased, and overheating of the ground electrode 27 is further suppressed. it can. As a result, the heat resistance can be further improved.

Furthermore, since the cross-sectional area SY is 3.5 mm ² or less, it is possible to more reliably prevent the heat of the flame kernel from being taken away by the ground electrode 27, and the width W is 2.2 mm or less. Therefore, it is possible to effectively suppress flame kernel growth inhibition by the ground electrode 27. As a result, the ignitability can be further improved.

  In addition, an inner layer 27I having excellent thermal conductivity is provided inside the ground electrode 27, and is configured to satisfy 0.2 ≦ SI / SZ. Therefore, the thermal conductivity of the ground electrode 27 can be dramatically increased, and the heat resistance can be improved extremely effectively.

  Further, since SI / SZ ≦ 0.5, the thickness of the outer layer 27Z can be sufficiently secured, and the outer layer 27Z can be more reliably prevented from being damaged due to the thermal expansion of the inner layer 27I.

In addition, since convex curved surfaces are formed on both side surfaces 27S1 and 27S2 of the ground electrode 27, the fuel gas can easily enter the spark discharge gap 33, and the ignitability can be further improved.
[Second Embodiment]
Next, the second embodiment will be described focusing on the differences from the first embodiment. In the first embodiment, the ground electrode side chip 32 is joined to the tip of the ground electrode 27, and the other end surface 32 </ b> F of the ground electrode side chip 32 faces the side surface of the center electrode side chip 31. On the other hand, in the second embodiment, as shown in FIG. 7, the ground electrode side tip 32 is not provided, and the other end surface 37 </ b> F of the ground electrode 37 is the side surface (center electrode side) of the tip portion of the center electrode 5. It is configured to face the side surface of the chip 31. A spark discharge gap 43 is formed between the other end surface 37 </ b> F of the ground electrode 37 and the tip side surface (side surface of the center electrode side chip 31) of the center electrode 5.

In addition, in the second embodiment, the ground electrode 37 and the tip surface of the center electrode 5 (center electrode side chip 31) are projected along the axis CL1 on a virtual plane orthogonal to the axis CL1 shown in FIG. In a direction perpendicular to the axis CL1 in an area SB1 (mm ² ; a portion with a dotted pattern in FIG. 8) and a virtual plane parallel to the other end surface 37F of the ground electrode 37 shown in FIG. Area SB2 (mm ² ; a portion with a dotted pattern in FIG. 9) to be described later when the center electrode 5 (center electrode side chip 31) and the other end surface 37F of the ground electrode 37 are projected along, and spark discharge The size G (mm) of the gap 43 is configured to satisfy 0.21 ≦ SB1 × SB2 / G (mm ³ ) ≦ 0.49.

  As shown in FIG. 8, the area SB1 is drawn from one end of the side corresponding to the other end surface 37F of the ground electrode 37 to the projection region corresponding to the front end surface of the center electrode 5 (center electrode side chip 31). A third tangent line TL3, and a fourth tangent line TL4 drawn from the other end of the side corresponding to the other end face 37F of the ground electrode 37 to the projection region corresponding to the tip end face of the center electrode 5 (center electrode side chip 31). The area AR3 surrounded by the projection line (side) corresponding to the other end surface 37F of the ground electrode 37 and the projection line corresponding to the outer periphery of the tip surface of the center electrode 5 (center electrode side chip 31).

  Further, the area SB2 refers to the area of an area AR4 where the projection area of the center electrode 5 (center electrode side chip 31) and the projection area of the other end surface 37F of the ground electrode 37 overlap as shown in FIG. .

  As described above, according to the second embodiment, the same operational effects as those of the first embodiment are basically obtained.

  In particular, in the second embodiment, the ground electrode 37 that is less consumable than the ground electrode side chip 32 by satisfying 0.21 ≦ SB1 × SB2 / G is the center electrode 5 (center electrode side chip). Even in the case of facing 31), excellent wear resistance can be realized.

Next, in order to confirm the effects achieved by the above-described embodiment, a sample of a spark plug in which the ground electrode side tip is provided on the ground electrode and the value of the formula SA1 × SA2 / G (mm ³ ) is variously changed is manufactured. Each sample was subjected to a desktop spark durability test and a flame kernel growth evaluation test. Then, the test result of each sample is provided with a ground electrode side tip (length 0.8 mm) made of an iridium alloy on the opposite surface of the other end of the ground electrode, and the other end surface of the ground electrode side tip is a center electrode side tip ( The spark plug sample (comparative example sample; see FIG. 10) facing the tip surface having a length of 0.5 mm was compared with the test results when the above tests were performed. Here, when the performance was superior to that of the comparative example sample, the evaluation of “◯” was made, and when the performance was equal to or lower than that of the comparative example sample, the evaluation of “x” was made. It was decided that

  The outline of the desktop spark durability test is as follows. That is, after attaching the sample to a predetermined chamber, the pressure in the chamber is set to 1.6 MPa, and the frequency of the applied voltage is set to 100 Hz (that is, at a rate of 6000 times per minute). It was discharged over. Then, after 300 hours, the size of the spark discharge gap was measured, and the amount of increase (gap increase amount) with respect to the size of the spark discharge gap (initial gap size G) before the test (initial state) was measured. It can be said that the smaller the gap increase, the better the wear resistance.

  Furthermore, the outline of the flame nucleus growth evaluation test is as follows. That is, after a sample was attached to a predetermined chamber, a predetermined voltage was applied to the sample to generate a spark discharge. Then, after a lapse of a predetermined time from the spark discharge, a schlieren image at the center of the spark discharge gap and the vicinity thereof is obtained, and the obtained schlieren image is binarized with a predetermined threshold to obtain an area of a high-density portion (that is, a growth area). The area of the subsequent flame kernel was measured. It can be said that the larger the area, the better the ignitability.

  Table 1 shows the test results of both tests. In Table 1, for reference, the outer diameter of the tip surface of the center electrode side tip, the width of the tip of the ground electrode side tip, the distance A, the length B, and the size G of the initial gap are shown for reference. Show. In each sample, the ground electrode had a rectangular cross section.

  As shown in Table 1, it was revealed that the sample in which SA1 × SA2 / G was larger than 0.49 was inferior in ignitability. This is presumably because the growth of flame nuclei is hindered by the ground electrode side tip (ground electrode) and the center electrode side tip, or the discharge position varies.

  It was also found that when SA1 × SA2 / G was made smaller than 0.12, the wear resistance was poor. This is considered to be because the ground electrode side tip and the center electrode side tip are locally consumed or the discharge voltage is increased.

  On the other hand, it was confirmed that the sample satisfying 0.12 ≦ SA1 × SA2 / G ≦ 0.49 has excellent performance in both ignitability and wear resistance.

  Next, from the reference when the tip end side is the plus side and the back end side is the minus side along the axial direction, the center electrode from the reference when the portion located at the most rear end side of the other end surface of the ground electrode side chip is used as a reference A plurality of spark plug samples in which the distance A (mm) along the axis to the tip surface of the side tip and the length B (mm) along the axis of the other end surface of the ground electrode side tip are variously changed, About each sample, the ignitability evaluation test and the above-mentioned desktop spark durability test were done.

  The outline of the ignitability evaluation test is as follows. That is, each sample was mounted on a 4-liter engine (N / A) with a displacement of 1.6 L, and the engine was operated at a rotational speed of 1600 rpm with an ignition timing of 60 ° BTDC. Then, while gradually increasing the air-fuel ratio (thinning the fuel), the engine torque fluctuation rate is measured for each air-fuel ratio, and the air-fuel ratio when the engine torque fluctuation rate exceeds 5% is taken as the limit air-fuel ratio. Identified. In addition, it means that it is excellent in ignitability, so that a limit air fuel ratio is large.

FIG. 11 shows the test results of the desktop spark durability test, and FIG. 12 shows the test results of the ignitability evaluation test. In FIG. 11 and FIG. 12, the test result of the sample with the distance B set to 0.1 mm is indicated by a circle, the test result of the sample with the distance B set to 0.3 mm is indicated by a triangle, and the distance B is set to 0. The test result of the sample with 5 mm is shown by a square, and the test result of a sample with a distance B of 0.7 mm is shown by a diamond. Moreover, in FIG. 12, the test result of the sample in which the distance B is 0.9 mm is indicated by cross marks. In addition to the desktop spark endurance test, the actual endurance test for each sample [with each sample assembled in a 4-cylinder engine (DOHC I / C T / C) with a displacement of 0.66 L, the throttle fully opened (= 6000 rpm) In this test, the engine was operated for 500 hours and the gap increase was measured after 500 hours.] Both tests yielded similar results. Therefore, in FIG. 11, only the test result of a desktop spark endurance test is shown. In FIG. 11, the distance A being negative means that the other end surface of the ground electrode side tip is located on the tip side in the axial direction with respect to the tip surface of the center electrode side tip. Further, in each sample, 0.12 ≦ SA1 × SA2 / G (mm ³ ) ≦ 0.49, 0.3 ≦ SX (mm) ≦ 0.6, and 0.4 ≦ G (mm) ≦ 1. 0 and the ground electrode had a rectangular cross section.

  As shown in FIG. 11, it was found that the sample with the distance B less than 0.3 mm tends to increase the size of the spark discharge gap and is slightly inferior in wear resistance. This is presumably because the ground electrode side tip was overheated or the sufficient consumption volume could not be ensured, so that the ground electrode side tip was rapidly consumed. Moreover, it was confirmed that the sample with the distance A less than 0.05 mm was slightly inferior in wear resistance. This is considered to be because the spark discharge centered on the respective edge portions of the center electrode side chip and the ground electrode side chip is concentrated.

  Furthermore, as shown in FIG. 12, it was found that the sample in which the distance B was larger than 0.7 mm and the sample in which the distance A was larger than “B + 0.2 mm” were slightly inferior in ignitability. This is considered to be due to the fact that the growth of flame nuclei is easily inhibited by the ground electrode side tip and the center electrode side tip.

  On the other hand, it is clear that the sample in which the distance A is set to 0.05 mm or more and the distance B is set to 0.3 mm or more has an increase in gap of less than 0.10 mm and has excellent wear resistance. It was. Furthermore, it was found that a sample in which the distance A was set to “B + 0.2 mm” or less and the distance B was set to 0.7 mm or less had a limit air-fuel ratio exceeding 20, and excellent ignitability.

Next, spark plug samples in which the area SX (mm ² ) of the other end surface of the ground electrode side chip and the size G (mm) of the spark discharge gap were variously changed were prepared, and the above-described desktop spark durability test was performed on each sample. And an ignitability evaluation test was conducted. FIG. 13 shows the test results of the desktop spark durability test, and FIG. 14 shows the test results of the ignitability evaluation test. In FIG. 13 and FIG. 14, the test result of the sample with the area SX of 0.1 mm ² is indicated by a circle, the test result of the sample with the area SX of 0.3 mm ² is indicated by a triangle, and the area SX is The test result of the sample with 0.6 mm ² is shown by a square, and the test result of a sample with an area SX of 0.9 mm ² is shown by a diamond. In the desk spark endurance test, the distance A is 0.05 mm and the distance B is 0.3 mm for each sample. In the ignitability evaluation test, the distance A is 0.9 mm and the distance B is 0 for each sample. 7 mm. Furthermore, in both tests, each sample was configured to satisfy 0.12 ≦ SA1 × SA2 / G (mm ³ ) ≦ 0.49, and the ground electrode had a rectangular cross section.

As shown in FIG. 13, the sample with a spark discharge gap size G greater than 1.0 mm and the sample with an area SX of less than 0.3 mm ² have a relatively large gap increase, resulting in wear resistance. It was confirmed that it was slightly inferior to sex. This is presumably because the discharge voltage increased or the consumption volume of the ground electrode side tip was not sufficiently secured.

Further, as shown in FIG. 14, it was found that the sample in which the spark discharge gap size G was less than 0.4 mm and the sample in which the area SX was larger than 0.6 mm ² were slightly inferior in ignitability. This is considered to be due to the fact that the growth of the flame kernel is easily inhibited by the ground electrode side tip or the like.

On the other hand, a sample in which the size G of the spark discharge gap is 0.4 mm or more and 1.0 mm or less and the area SX is 0.3 mm ² or more and 0.6 mm ² or less is more excellent in wear resistance and It became clear that it had ignitability.

From the above test results, in order to achieve excellent performance in both ignitability and wear resistance in a spark plug having a ground electrode side tip and having a spark discharge gap between the ground electrode side tip and the center electrode. 0.12 ≦ SA1 × SA2 / G ≦ 0.49, 0.05 ≦ A (mm) ≦ B + 0.2, 0.3 ≦ B (mm) ≦ 0.7, 0.3 ≦ SX (mm ² ) It can be said that it is preferable to satisfy ≦ 0.6 and 0.4 ≦ G (mm) ≦ 1.0.

  Next, without providing the ground electrode side tip, the other end surface of the ground electrode is configured to face the side surface of the tip of the center electrode, and samples of the spark plug in which the value of the above formula SB1 × SB2 / G is variously changed are manufactured. Then, the above-described desktop spark durability test and flame kernel growth evaluation test were performed for each sample. Table 2 shows the test results of both tests. For reference, Table 2 shows the outer diameter of the tip surface of the center electrode tip, the width of the tip of the ground electrode, the distance A, and the size G of the initial gap in each sample.

  As shown in Table 2, it was revealed that the sample in which SB1 × SB2 / G was larger than 0.49 was inferior in ignitability. This is presumably because the growth of flame nuclei is hindered by the ground electrode or the center electrode, or the discharge position varies.

  Moreover, when SB1 * SB2 / G was made smaller than 0.21, it turned out that it is inferior to wear resistance. This is presumably because the ground electrode and the center electrode are locally consumed or the discharge voltage is increased.

  On the other hand, it was confirmed that the sample satisfying 0.21 ≦ SB1 × SB2 / G ≦ 0.49 has excellent performance in both ignitability and wear resistance.

  From the test results of the above test, in order to achieve excellent performance in both ignitability and wear resistance in a spark plug that does not include a tip on the ground electrode side and has a spark discharge gap between the ground electrode and the center electrode. Therefore, it can be said that 0.21 ≦ SB1 × SB2 / G ≦ 0.49 is preferably satisfied.

Next, for the spark plug samples in which the cross-sectional area SY (mm ² ) of the ground electrode and the width W (mm) of the ground electrode were variously changed, the heat resistance evaluation test and the ignition timing were changed from 60 ° BTDC to 75 °. The above-described ignitability evaluation test was performed by changing to BTDC (that is, using a more severe condition).

  The outline of the heat resistance evaluation test is as follows. In other words, after assembling a sample with an engine set at SC 17.6 (SAE J2203) with a compression ratio of 5.6 and an ignition timing of 30 ° BTDC, the engine was run at 2700 rpm using benzol as the main fuel. While operating, a certain amount of supercharging was performed, and the fuel injection amount at which the temperature in the combustion chamber was the highest was specified. Then, it was confirmed whether or not preignition occurred when the engine was operated with the specified fuel injection amount.

Tables 3 and 4 show the test results of the heat resistance evaluation test, and FIG. 15 shows the test results of the ignitability evaluation test. Table 3 shows the test results of the sample in which the cross-sectional area SY is changed after setting the width W to 1.8 mm, and Table 4 shows the width after setting the cross-sectional area SY to 2.3 mm ^2. The test result of the sample which changed W is shown. Further, in FIG. 15, the test result of the sample having the cross-sectional area SY of 2.1 mm ² is indicated by a circle, the test result of the sample having the cross-sectional area SY of 2.3 mm ² is indicated by a triangle, and the cross-sectional area SY is The test result of the sample with 2.9 mm ² is shown by a square, the test result of a sample with a cross-sectional area SY of 3.5 mm ² is shown by a diamond, and the test result of a sample with a cross-sectional area SY of 4.0 mm ² is Shown with a mark. Each sample was configured to satisfy 0.12 ≦ SA1 × SA2 / G ≦ 0.49, and the ground electrode had a rectangular cross section.

As shown in Table 3, it was confirmed that pre-ignition occurred in the sample having a cross-sectional area SY of less than 2.3 mm ² . This is presumably because the ground electrode was relatively thin, the heat conduction efficiency from the other end of the ground electrode to one end was lowered, and the ground electrode was overheated. Moreover, as shown in Table 4, even when the cross-sectional area was 2.3 mm ² , it was found that the sample with the width W less than 1.8 mm was inferior in heat resistance. This is because the width of the ground electrode increases as a result of narrowing the width, and as a result, the ground electrode protrudes toward the center of the higher temperature combustion chamber, and the amount of heat received by the ground electrode increases. This is thought to be due to the fact that it has been closed.

In addition, as shown in FIG. 15, it was revealed that the sample with the cross-sectional area SY exceeding 3.5 mm ² and the sample with the width W exceeding 2.2 mm are slightly inferior in ignitability. This is considered to be because the heat of the flame kernel is easily taken away by the ground electrode, or the growth of the flame kernel is easily inhibited by the ground electrode.

On the other hand, a sample having a cross-sectional area SY of 2.3 mm ^{2 to} 3.5 mm ² and a width W of 1.8 mm to 2.2 mm is more excellent in both ignitability and heat resistance. I understood.

From the results of the above test, 2.3 ≦ SY (mm ² ) ≦ 3.5 and 1.8 ≦ W (mm) ≦ 2.2 are satisfied in order to further improve both ignitability and heat resistance. Is preferable.

Next, in the cross section in which the cross-sectional area of the inner layer is maximized along the direction orthogonal to the central axis of the ground electrode, the cross-sectional area SI (mm ² ) of the inner layer of the ground electrode and the cross-sectional area SZ (mm ² ) of the ground electrode By increasing or decreasing the value, spark plug samples with various SI / SZ changes were produced, and a desktop burner test and a heat resistance improvement value measurement test were performed for each sample.

  The outline of the desktop burner test is as follows. That is, the sample was subjected to 3000 cycles, with one cycle consisting of heating with a burner for 1 minute and then gradually cooling for 1 minute so that the temperature of the ground electrode was 1050 ° C. in an air atmosphere. After the end of 3000 cycles, the ground electrode was observed to confirm the presence or absence of cracks in the outer layer accompanying the expansion of the inner layer. Table 5 shows the test results of the test.

The outline of the heat resistance improvement value measurement test is as follows. That is, a spark plug sample in which the ground electrode has a cross-sectional area SY of 2.3 mm ² , 2.6 mm ² , or 2.9 mm ² and the ground electrode is formed of Ni alloy without providing an inner layer (comparison) The heat value of the target sample) was measured for each cross-sectional area SY. Then, with the cross-sectional area SY of the ground electrode set to 2.3 mm ² , 2.6 mm ² , or 2.9 mm ² , the thermal value of each spark plug sample in which SI / SZ was changed was measured. The improvement value of the heat value with respect to the heat value of the comparative sample having the same cross-sectional area SY was measured. FIG. 16 shows the test results of the test. In FIG. 16, the test results of the sample having the cross-sectional area SY of 2.3 mm ² are indicated by circles, the test results of the sample having the cross-sectional area SY of 2.6 mm ² are indicated by triangles, and the cross-sectional area SY is The test result of the sample set to 2.9 mm ² is shown by a square.

  Moreover, the heat value was measured as follows. That is, after assembling a sample with an engine set at SC 17.6 (SAE J2203) with a compression ratio of 5.6 and an ignition timing of 30 ° BTDC, the engine is rotated at 2700 rpm using fuel mainly composed of benzol. The fuel injection amount was adjusted so that the combustion chamber temperature reached the maximum with the supercharging amount. Then, the increase of the supercharging amount and the adjustment of the fuel injection amount were repeated, and the supercharging pressure immediately before the occurrence of preignition (early ignition) was specified. After that, by finely adjusting the specified supercharging pressure and adjusting the fuel injection amount, the engine output when the engine operates stably for 3 minutes is measured, and the average effective pressure (PSI) is calculated. The average effective pressure was specified as the heat value of each sample.

  As shown in Table 5 and FIG. 16, it was revealed that the samples having SI / SZ of 0.2 or more and 0.5 or less can dramatically improve the heat resistance without causing cracks in the outer layer. . This is because the SI / SZ is 0.5 or less, the outer layer has a thickness that can withstand the thermal expansion of the inner layer, and the SI / SZ is 0.2 or more. This is considered to be because the volume of the inner layer excellent in conductivity is sufficiently secured and the thermal conductivity of the ground electrode is improved.

  From the test results of the above test, it can be configured to satisfy 0.2 ≦ SI / SZ ≦ 0.5 from the viewpoint of further improving heat resistance while preventing damage to the ground electrode (outer layer). It can be said that it is preferable.

  Next, a spark plug sample in which the ground electrode has a rectangular cross section, and the side surface of the ground electrode is formed in a curved shape protruding outward, and the curvature radius R of the side surface is 1.2 mm, 1.5 mm, or 1 A spark plug sample with a thickness of 8 mm was prepared. Each sample was assembled to the engine such that the relative position of the ground electrode with respect to the engine (fuel injection port) was different, and the ignition timing test described above (the ignition timing was changed from 60 ° BTDC to 75 ° BTDC). The critical air-fuel ratio at each relative position was measured. FIG. 17 shows the fluctuation range of the limit air-fuel ratio associated with the change of the relative position in each sample.

  As shown in FIG. 17, the sample with a radius of curvature R of 1.5 mm or less has a very narrow limit air-fuel ratio variation range and a large limit air-fuel ratio as a whole, and stable excellent ignitability. It became clear that it can be realized. This is considered to be due to the fact that the fuel gas easily enters the spark discharge gap in the form of surrounding the ground electrode.

  From the results of the above test, in order to further improve the ignitability, it is preferable that the side surface of the ground electrode is formed in a convex curved shape outward and the curvature radius R of the side surface is 1.5 mm or less. It can be said.

  In addition, it is not limited to the description content of the said embodiment, For example, you may implement as follows. Of course, other application examples and modification examples not illustrated below are also possible.

  (A) In the first embodiment, the ground electrode side chip 32 is bonded to the facing surface 27T of the ground electrode 27. However, as shown in FIG. 18, the ground electrode side chip 42 is connected to the other end surface 27F of the ground electrode 27. It is good also as joining to.

  (B) In the second embodiment, the center electrode-side tip 31 is provided at the tip of the center electrode 5, but the center electrode 5 may be configured without providing the center electrode-side tip 31.

  (C) In the above embodiment, the ground electrode 27 is configured to have a substantially constant width along its longitudinal direction. However, as shown in FIGS. 19 and 20, the ground electrode 27 (37) A tapered portion 48 (49) may be provided at the front end portion of the first electrode, and the ground electrode 27 (37) may be gradually narrowed toward the other end side thereof. In this case, the flame kernel growth inhibition by the ground electrode 27 (37) is further suppressed, and the ignitability can be further improved.

  (D) In the above embodiment, the ground electrode 27 is described as having a two-layer structure. However, the ground electrode 27 may be composed of a single metal (for example, Ni alloy), or three or more layers. You may comprise so that a multilayer structure may be made. In the case of a multilayer structure, it is desirable that the inner layer of the outer layer 27Z contains a better heat conductive metal than the outer layer 27Z. For example, an intermediate layer made of copper alloy or pure copper may be provided inside the outer layer 27Z, and an innermost layer made of pure nickel may be provided inside the intermediate layer. In addition, when the ground electrode 27 has a three-layer structure or more, a plurality of layers that are located inside the outer layer 27Z and contain a better heat conductive metal than the outer layer 27Z correspond to the inner layer 27I. For example, when the above-described configuration in which the intermediate layer and the innermost layer are provided is employed, the intermediate layer and the innermost layer correspond to the inner layer 27I.

  (E) In the above embodiment, the case where the ground electrode 27 is joined to the distal end portion 26 of the metal shell 3 is embodied. However, a part of the metal shell (or the tip metal fitting previously welded to the metal shell). The present invention can also be applied to the case where the ground electrode is formed so as to cut out a part of (see Japanese Patent Laid-Open No. 2006-236906, etc.).

  (F) In the above embodiment, the tool engaging portion 19 has a hexagonal cross section, but the shape of the tool engaging portion 19 is not limited to such a shape. For example, it may be a Bi-HEX (deformed 12-angle) shape [ISO 22777: 2005 (E)].

1 ... Spark plug 2 ... Insulator (insulator)
3 ... metal shell 4 ... shaft hole 5 ... center electrode 27 ... ground electrode 27F ... other end surface 27I ... inner layer 27T ... opposing surface 27S1, 27S2 ... (ground electrode) side surface 27Z ... outer layer 31 ... Center electrode side tip 32 ... Ground electrode side tip 32F ... Other end surface (of the ground electrode side tip) 33 ... Spark discharge gap (gap)
CL1 ... axis CL2 ... central axis (of ground electrode) TL1 ... first tangent TL2 ... second tangent TL3 ... third tangent TL4 ... fourth tangent

Claims (5)

An insulator having an axial hole penetrating in the axial direction;
A center electrode inserted in the shaft hole;
A metal shell provided on the outer periphery of the insulator;
A ground electrode fixed to the tip of the metal shell,
A ground electrode side tip made of a metal containing a noble metal, at least one end of which is joined to the tip of the ground electrode,
The center electrode has a center electrode side tip made of a metal containing a noble metal at its tip,
A spark plug in which the other end surface of the ground electrode side chip faces the side surface of the center electrode side chip, and a gap is formed between the other end surface of the ground electrode side chip and the side surface of the center electrode side chip. ,
The center electrode from one end of the side corresponding to the other end surface of the ground electrode side chip out of the projection plane obtained by projecting the ground electrode side chip and the tip surface of the center electrode side chip in a virtual plane orthogonal to the axis. The first tangent line drawn on the projection area corresponding to the tip surface of the side tip and the other end of the side corresponding to the other end face of the ground electrode side tip are drawn to the projection area corresponding to the tip surface of the center electrode tip. The area of the region surrounded by the second tangent line, the projection line corresponding to the other end surface of the ground electrode side chip, and the projection line corresponding to the outer periphery of the tip end surface of the center electrode side chip is SA1 (mm ² ). age,
The projection region of the center electrode side chip and the ground electrode side chip when the center electrode side chip and the other end surface of the ground electrode side chip are projected onto a virtual plane parallel to the other end surface of the ground electrode side chip. The area of the area where the projection area on the other end surface overlaps is SA2 (mm ² ),
When the size of the gap is G (mm),
0.12 ≦ SA1 × SA2 / G (mm ³ ) ≦ 0.49
The filling,
A portion of the other end surface of the ground electrode side chip located closest to the rear end side in the axial direction, and an axis of the surface of the center electrode side chip facing the other end surface of the ground electrode side chip. A (mm) is the distance along the axis line between the most distal end portion and
When the length along the axis of the other end surface of the ground electrode side tip is B (mm),
0.05 ≦ A ≦ B + 0.2 and 0.3 ≦ B ≦ 0.7
The filling,
When the area of the other end surface of the ground electrode side chip is SX (mm ² ),
0.3 ≦ SX ≦ 0.6 and 0.4 ≦ G ≦ 1.0
A spark plug characterized by satisfying. An insulator having an axial hole penetrating in the axial direction;
A center electrode inserted in the shaft hole;
A metal shell provided on the outer periphery of the insulator;
A ground electrode fixed at an end of the metal shell to one end of the metal shell;
A spark plug in which the other end surface of the ground electrode is opposed to a side surface of the tip portion of the center electrode, and a gap is formed between the other end surface of the ground electrode and a side surface of the tip portion of the center electrode;
Corresponding to the front end surface of the center electrode from one end of the side corresponding to the other end surface of the ground electrode among the projection surfaces obtained by projecting the ground electrode and the front end surface of the center electrode in a virtual plane orthogonal to the axis. A third tangent line drawn in the projection area, a fourth tangent line drawn from the other end of the side corresponding to the other end face of the ground electrode to the projection area corresponding to the front end face of the center electrode, and other ground electrodes. The area of the region surrounded by the projection line corresponding to the end surface and the projection line corresponding to the outer periphery of the front end surface of the center electrode is SB1 (mm ² ),
A region where a projection region of the center electrode and a projection region of the other end surface of the ground electrode overlap when the center electrode and the other end surface of the ground electrode are projected on a virtual plane parallel to the other end surface of the ground electrode; The area is SB2 (mm ² )
When the size of the gap is G (mm),
0.21 ≦ SB1 × SB2 / G (mm ³ ) ≦ 0.49
A spark plug characterized by satisfying. In an arbitrary cross section along the direction orthogonal to the central axis of the ground electrode between the longitudinal center of the ground electrode and one end of the ground electrode,
When the sectional area of the ground electrode is SY (mm ² ) and the width of the ground electrode is W (mm),
2.3 ≦ SY ≦ 3.5 and 1.8 ≦ W ≦ 2.2
The spark plug according to any one of claims 1 and 2, wherein: The ground electrode includes an outer layer and an inner layer provided in the outer layer and made of a metal having higher thermal conductivity than the outer layer,
In the cross section in which the cross-sectional area of the inner layer is maximum along the direction orthogonal to the central axis of the ground electrode,
When the cross-sectional area of the inner layer is SI (mm ² ) and the cross-sectional area of the ground electrode is SZ (mm ² ),
0.2 ≦ SI / SZ ≦ 0.5
The spark plug according to any one of claims 1 to 3, wherein: Of the ground electrode, both side surfaces adjacent to the facing surface facing the center electrode have an outwardly convex curved shape,
In a cross section orthogonal to the central axis of the ground electrode, when the radius of curvature of the outline of the both side surfaces is R (mm),
R ≦ 1.5
The spark plug according to any one of claims 1 to 4, wherein:

Images