JP7600897B2 - Spark plug - Google Patents

Description

This disclosure relates to spark plugs.

A conventional spark plug is described in the following Patent Document 1. The spark plug described in Patent Document 1 includes a metal shell, an insulator, a center electrode, and a ground electrode. The ground electrode includes a base portion joined to the tip surface of the metal shell, a narrow portion located on the tip side of the base portion, and a tapered portion located between the base portion and the narrow portion. The base portion is formed in a substantially rectangular cross section having a constant width. The narrow portion is formed in a circular cross section. The tapered portion is formed so that the cross section changes gradually along the longitudinal direction. In this spark plug, even in a situation where the air-fuel mixture hits the back surface of the ground electrode, the narrow portion formed in a circular cross section makes it easier for the air-fuel mixture to flow around the inside of the ground electrode, thereby improving ignition performance. In addition, heat dissipation can be ensured in the base portion having a constant width.

Patent No. 4676912

In recent engines, which have been designed to improve thermal efficiency, the temperature of the combustion gas is higher than before, and the ground electrode is exposed to the high-temperature combustion gas. Therefore, even if a structure that ensures heat dissipation, such as the spark plug described in Patent Document 1, is adopted, the temperature of the ground electrode may not drop sufficiently. This is undesirable because it may lead to the air-fuel mixture self-igniting at an unintended timing, known as pre-ignition.

This disclosure was made in light of these circumstances, and its purpose is to provide a spark plug that can improve the heat dissipation properties of the ground electrode.

A spark plug (10) that solves the above problem includes an insulator (12) formed in a cylindrical shape around a predetermined central axis, a center electrode (13) inserted into the insulator so as to be exposed from the tip of the insulator, a cylindrical housing (11) provided on the outer periphery of the center electrode, and a ground electrode (14) joined to the housing. The ground electrode has an erected portion (51) formed to extend from the tip surface of the housing in the direction of the central axis, and an extension portion (52) formed to extend from the tip of the erected portion to a position facing the center electrode. When the circumferential direction centered on the central axis is defined as the plug circumferential direction and the outer surface of the erected portion in the plug circumferential direction is defined as the side surface, the spark plug further includes an outer wall (71, 72, 80) that is disposed with a predetermined gap in the plug circumferential direction from the side surface of the erected portion. The outer wall has opposing surfaces (710, 720, 811, 812) that are formed to face the central axis and are spaced farther away from the side surface of the erected portion as they approach the central axis.

With this configuration, when an airflow is generated from the center electrode toward the erected portion of the ground electrode, this airflow flows along the opposing surface of the outer wall. The gap formed between the opposing surface of the outer wall and the side surface of the erected portion narrows as it moves radially outward from the plug, so the airflow flowing along the opposing surface of the outer wall is first narrowed and then passes through the open space. This increases the flow rate of the airflow, so that new gas with a lower temperature is sequentially sent to the ground electrode. As a result, more heat can be removed from the ground electrode compared to when the outer wall is not provided, making it possible to improve the heat dissipation of the ground electrode.

Note that the symbols in parentheses in the above means and claims are examples showing the correspondence with the specific means described in the embodiments described below.

The spark plug disclosed herein can improve the heat dissipation of the ground electrode.

FIG. 1 is a cross-sectional view showing a broken cross-sectional structure of a spark plug according to a first embodiment. FIG. 2 is a perspective view showing a perspective structure of the ground electrode and its periphery of the spark plug of the first embodiment. FIG. 3 is a cross-sectional view showing a cutaway cross-sectional structure of the ground electrode of the first embodiment. FIG. 4 is a bottom view showing the bottom structure of the spark plug of the first embodiment. FIG. 5 is a cross-sectional view showing a cross-sectional structure around the ground electrode of the spark plug of the first embodiment. FIG. 6 is a bottom view showing the bottom structure of the spark plug of the first embodiment. FIG. 7 is a graph showing the relationship between the width of the narrowed portion and the temperature of the ground electrode, which was obtained through an experiment by the inventor. FIG. 8 is a cross-sectional view showing a cross-sectional structure around a ground electrode in a spark plug according to a first modified example of the first embodiment. FIG. 9 is a perspective view showing a perspective structure of the periphery of a ground electrode in a spark plug according to a second modified example of the first embodiment. FIG. 10 is a perspective view showing a perspective structure of the periphery of the ground electrode of the spark plug of the second embodiment. FIG. 11 is a cross-sectional view showing a cross-sectional structure around the ground electrode of a spark plug according to the second embodiment. FIG. 12 is a cross-sectional view showing a cross-sectional structure around a ground electrode in a spark plug according to a modification of the second embodiment.

Hereinafter, an embodiment of a spark plug will be described with reference to the drawings. In order to facilitate understanding of the description, the same components in the various drawings are denoted by the same reference numerals as much as possible, and duplicated description will be omitted.
First Embodiment
First, a schematic configuration of a spark plug 10 according to a first embodiment shown in Fig. 1 will be described. The spark plug 10 is mounted, for example, on an engine head. The spark plug 10 ignites an air-fuel mixture in a cylinder of the engine by forming a spark discharge based on application of a voltage. The spark plug 10 includes a housing 11, an insulator 12, a center electrode 13, and a ground electrode 14.

The housing 11 is formed in a cylindrical shape centered on the central axis m10 of the spark plug 10. The housing 11 is formed of a metal material such as carbon steel. The lower end of the insulator 12 is coaxially inserted inside the housing 11. A threaded portion 114 is formed on the outer peripheral surface of the lower part of the housing 11. The spark plug 10 can be fastened and fixed to the engine head block by screwing the threaded portion 114 of the housing 11 into a screw hole formed in the engine head block. In the following, the central axis m10 is referred to as the "plug central axis m10", the direction along the plug central axis m10 is referred to as the "plug axial direction Da", and the circumferential direction centered on the plug central axis m10 is referred to as the "plug circumferential direction Dc". In this embodiment, the plug central axis m10 corresponds to a predetermined central axis.

The insulator 12 is formed in a cylindrical shape centered on the plug central axis m10. The insulator 12 is made of an insulating material such as alumina. The housing 11 is integrally assembled to the outer periphery of the insulator 12. An axial hole 120 is formed inside the insulator 12. The axial hole 120 is formed so as to penetrate the insulator 12 from the tip to the base end along the plug central axis m10. The center electrode 13, the first seal body 15, the resistor 16, the second seal body 17, and the terminal metal fitting 18 are inserted into the axial hole 120 in this order from the tip side. The center electrode 13 is inserted into the insulator 12 so as to be exposed from the tip end of the insulator 12.

The center electrode 13 has an electrode base material 30 and an electrode tip 40. The center electrode base material 30 is formed in a cylindrical shape centered on the plug central axis m10. The center electrode base material 30 is formed of a nickel (Ni) alloy or the like, which has excellent heat resistance. The center electrode tip 40 is joined to the tip of the center electrode base material 30. The center electrode tip 40 is formed in a cylindrical shape centered on the plug central axis m10. The center electrode tip 40 is formed of an iridium alloy or the like. A first seal body 15, a resistor 16, and a second seal body 17 are sandwiched between the base end of the center electrode 13 and the tip of the terminal metal fitting 18.

The terminal fitting 18 is formed in a generally cylindrical shape centered on the plug central axis m10. The terminal fitting 18 is made of steel or the like. A terminal portion 180 is provided at the base end of the terminal fitting 18. The terminal portion 180 is exposed to the outside from the base end of the insulator 12.
The ground electrode 14 has an electrode base material 50 and an electrode tip 60. The ground electrode base material 50 is made of a nickel alloy or the like. The ground electrode base material 50 is joined to the front end surface of the housing 11. The ground electrode base material 50 is formed so as to extend from the front end surface of the housing 11 to a position facing the center electrode tip 40. The ground electrode tip 60 is joined to the front end of the ground electrode base material 50. The ground electrode tip 60 is made of a precious metal alloy such as an iridium alloy or a platinum alloy. The ground electrode tip 60 is disposed so as to face the center electrode tip 40 with a predetermined gap 19 therebetween. Hereinafter, the gap 19 formed between the center electrode tip 40 and the ground electrode tip 60 will be referred to as a "spark gap 19".

In this spark plug 10, an external circuit capable of applying a high voltage is connected to the terminal portion 180 of the terminal fitting 18. When a high voltage is applied to the terminal portion 180 by the external circuit, a spark discharge is generated between the electrode tip 40 of the center electrode 13 and the electrode tip 60 of the ground electrode 14. This spark discharge ignites the air-fuel mixture in the engine cylinder, forming a flame, and the mixture is burned.

Next, the structures of the housing 11 and the ground electrode 14 will be described in detail.
2, the ground electrode base material 50 has a standing portion 51 and an extension portion 52. The standing portion 51 is joined to the front end surface 110 of the housing 11. The standing portion 51 is formed to extend from the front end surface 110 of the housing 11 in the plug axial direction Da. The extension portion 52 is formed to extend from the front end of the standing portion 51 to a position facing the electrode tip 40 of the center electrode 13. The ground electrode base material 50 is formed to be substantially L-shaped overall by being composed of the standing portion 51 and the extension portion 52.

3, the ground electrode base material 50 has a two-layer structure including an outer layer 50a and an inner layer 50b. The outer layer 50a is made of a nickel alloy or the like. The inner layer 50b is made of a metal having a higher thermal conductivity than the nickel alloy, such as copper.
In the following, as shown in FIG. 2 , one outer surface of the standing portion 51 provided in the plug circumferential direction Dc will be referred to as one side surface 511 , and the other outer surface will be referred to as the other side surface 512 .

A first outer wall 71 and a second outer wall 72 are provided on the tip surface 110 of the housing 11 so as to be adjacent to the erected portion 51 of the ground electrode base material 50. As shown in FIG. 4, the first outer wall 71 is disposed with a predetermined gap in the plug circumferential direction Dc relative to one side surface 511 of the ground electrode base material 50. The second outer wall 72 is disposed with a predetermined gap in the plug circumferential direction Dc relative to the other side surface 512 of the ground electrode base material 50. The first outer wall 71 and the second outer wall 72 are separate from the housing 11 and are joined to the tip surface 110 of the housing 11.

The first outer wall 71 is made of a rectangular member having a pair of long sides 710, 711 and a pair of short sides 712, 713. Of the pair of long sides 710, 711, one long side 710 is arranged to face the plug central axis m10. In addition, the long side 710 and the short side 712, as well as the corner 714 located between them, are arranged to face one side 511 of the standing portion 51. The long side 710 is formed so that the closer it is to the plug central axis m10, the more separated it is from the one side 511 of the standing portion 51. The short side 712 is formed so that the farther it is from the plug central axis m10, the more separated it is from the one side 511 of the standing portion 51. As a result, as shown in FIG. 5, if the radial direction centered on the plug central axis m10 is the "plug radial direction Dr", the gap W11 formed between the one side surface 511 of the standing portion 51 and the first outer wall 71 narrows from the inner surface 513 of the standing portion 51 toward the outside in the plug radial direction Dr, is narrowest at the corner 714 of the first outer wall 71, and widens from the corner 714 toward the outside in the plug radial direction Dr. Therefore, in the gap W11, a narrowed portion P11 is formed in the portion where the one side surface 511 of the standing portion 51 and the corner 714 of the first outer wall 71 face each other. The width H30 of the narrowed portion P11 is narrower than the width H10 of the longitudinal side surfaces 710, 711 of the first outer wall 71. Hereinafter, the gap W11 is referred to as the "flow path W11".

The second outer wall 72, like the first outer wall 71, is made of a rectangular member having a pair of long sides 720, 721 and a pair of short sides 722, 723. Of the pair of long sides 720, 721, the long side 720 arranged to face the plug central axis m10 is formed so that the closer it is to the plug central axis m10, the further away it is from the other side 512 of the standing portion 51. In the flow path W12 formed between the other side 512 of the standing portion 51 and the second outer wall 72, a constriction portion P12 is also formed in the portion where the other side 512 of the standing portion 51 and the corner portion 724 of the second outer wall 72 face each other.

The first outer wall 71 and the second outer wall 72 are arranged relative to the erected portion 51 of the ground electrode 14 as shown in Figures 4 and 5, so that when the tip of the spark plug 10 is viewed from outside the housing 11, the first outer wall 71 and the second outer wall 72 are arranged to form a roughly V-shape.

As shown in FIG. 6, when the line connecting the center C10 of the width of the erected portion 51 of the ground electrode 14 in the plug circumferential direction Dc and the plug central axis m10 is taken as the reference line m20, when the insulator 12 and the outer walls 71, 72 are projected parallel to a line parallel to the reference line m20, the projection areas D21, D22 of the outer walls 71, 72 are located outside the projection area D11 of the insulator 12 on the projection plane D.

Next, an example of the operation of the spark plug 10 of this embodiment will be described.
In the spark plug 10, an airflow as shown by the arrow in Fig. 5, i.e., an airflow in a direction from the center electrode 13 to the ground electrode 14, may be formed. At this time, the airflow flows along the outer periphery of the insulator 12, then flows toward the first outer wall 71 and the second outer wall 72, and collides with the first outer wall 71 and the second outer wall 72, respectively. As a result, the airflow that collides with the first outer wall 71 flows into a flow path W11 formed between one side surface 511 of the ground electrode 14 and the first outer wall 71. Meanwhile, the airflow that collides with the second outer wall 72 flows into a flow path W12 formed between the other side surface 512 of the ground electrode 14 and the second outer wall 72.

The airflow that flows into each flow path W11, W12 is first narrowed by the narrowing section P11, P12, and then exits into the open space S11, S12, respectively. When the airflow exits from the narrowing section P11, P12 to the open space S11, S12, the flow rate of the airflow increases. Therefore, new gas with a lower temperature is sequentially sent to the side surfaces 511, 512 of the ground electrode 14. As a result, more heat can be removed from the ground electrode 14 compared to when the outer walls 71, 72 are not provided, and the heat dissipation properties of the ground electrode 14 can be improved.

Next, the relationship between the width of the narrowed portions P11, P12 and the temperature of the tip portion of the ground electrode 14 will be described.
The inventors created a temperature plug in which a thermocouple was embedded in the tip of the ground electrode 14, more specifically, in the tip of the extension portion 52 of the ground electrode 14, and then conducted an experiment in which they measured the temperature of the thermocouple while changing the width H30 of the narrowing portions P11 and P12.

In this experiment, the width H10 of the long sides 710, 711, 720, and 721 of the outer walls 71 and 72 shown in FIG. 5 was set to 2.2 mm, and the width H11 of the short sides 712, 713, 722, and 723 was set to 1.1 mm. The width H20 of the standing portion 51 of the ground electrode 14 in the long direction was set to 1.2 mm, and the width H21 of the standing portion 51 in the short direction was set to 1.0 mm.

Furthermore, as shown in FIG. 6, when the lines passing through the centers of the outer walls 71, 72 are defined as center lines m31, m32, the intersection angles θ11, θ12, which are the angles that the center lines m31, m32 respectively form with respect to the reference line m20 of the ground electrode 14, were set to "45°". In addition, the shape of the threaded portion 114 of the housing 11 shown in FIG. 1 was set to "M12". Furthermore, the engine operating conditions were set to a constant condition of a rotation speed of "6000 rpm" in a WOT (Wide Open Throttle) state, i.e., when the throttle valve is fully open, so that the basic flow velocity and flow rate were set to be equal.

Figure 7 is a graph showing the results of an experiment conducted under the above conditions. As shown in Figure 7, when the width H30 of the narrowed portions P11, P12 satisfies "0.2 [mm] ≦ H30 < 0.5 [mm]", the wider the width H30 of the narrowed portions P11, P12, the lower the temperature of the tip of the ground electrode 14. When the width H30 of the narrowed portions P11, P12 is "0.5 [mm]", the temperature of the tip of the ground electrode 14 is at its minimum. When the width H30 of the narrowed portions P11, P12 satisfies "0.5 [mm] < H30", the wider the width H30 of the narrowed portions P11, P12, the higher the temperature of the tip of the ground electrode 14 becomes, and the temperature converges to a constant value.

In general, when air flows through a flow path in which a throttling portion is provided, the flow path area at any two points of the flow path is "A1" and "A2", and the flow speed of the air flow at each of these points is "V1" and "V2", and the relationship "A1 x V1 = A2 x V2" is established. Considering the experimental results of FIG. 7 based on this relationship, it is considered that when the width H30 of the throttling portions P11 and P12 exceeds "1.5 [mm]", the flow speed of the air flow flowing between the standing portion 51 of the ground electrode 14 and the outer walls 71 and 72 is difficult to increase, making it difficult to reduce the temperature of the tip of the ground electrode 14. On the other hand, when the width H30 of the throttling portions P11 and P12 is narrower than "0.5 [mm]", the flow rate of the air flow flowing between the standing portion 51 of the ground electrode 14 and the outer walls 71 and 72 is reduced, and as a result, a phenomenon in which the temperature of the tip of the ground electrode 14 rises is generated.

According to the spark plug 10 of the present embodiment described above, the following actions and effects (1) to (7) can be obtained.
(1) As shown in Fig. 5, when the airflow passes from the constricted portions P11, P12 to the open spaces S11, S12, the flow velocity of the airflow increases. Therefore, new gas with a lower temperature is sequentially sent to the side surfaces 511, 512 of the ground electrode 14. As a result, compared to a case in which the outer walls 71, 72 are not provided, more heat can be removed from the ground electrode 14, and the heat dissipation property of the ground electrode 14 can be improved.

(2) Of the pair of longitudinal sides 710, 711 of the first outer wall 71, one longitudinal side 710 that is arranged to face the plug central axis m10 is formed so that the closer it is to the plug central axis m10, the further away it is from one side 511 of the ground electrode 14. The same is true for the second outer wall 72. With this configuration, it is easy to form the flow paths W11, W12 having the narrowed portions P11, P12 as shown in FIG. 5.

(3) The width H30 of each of the narrowed portions P11, P12 of the flow paths W11, W12 is narrower than the width H10 of the longitudinal side surfaces 710, 711, 720, 721 of the outer walls 71, 72. This configuration allows the flow paths W11, W12 to be formed in a way that can increase the flow rate of the airflow, thereby further improving the heat dissipation of the ground electrode 14.

(4) The corners 714, 724 of the outer walls 71, 72 are arranged to face the side surfaces 511, 512 of the erected portion 51 of the ground electrode 14 in the plug circumferential direction Dc. This configuration makes it easy to form the flow paths W11, W12 having the constricted portions P11, P12 as shown in FIG. 5.

(5) As shown in FIG. 6, when the insulator 12 and the outer walls 71, 72 are parallel projected onto a line parallel to the reference line m20, the projection area of the outer walls 71, 72 is located outside the projection area D11 of the insulator 12 on the projection plane D. With this configuration, the airflow that flows along the outer circumference of the insulator 12 can be more easily received by the outer walls 71, 72, and the airflow can be more accurately guided to the ground electrode 14. This further improves the heat dissipation of the ground electrode 14.

(6) As shown in FIG. 2, the tip portions 715, 725 of the outer walls 71, 72 are located closer to the tip surface 110 of the housing 11 than the surface 520 of the extension portion 52 of the ground electrode 14 that faces the center electrode. This configuration makes it possible to prevent the outer walls 71, 72 from becoming too long, which makes it difficult for heat to build up in the outer walls 71, 72. As a result, the occurrence of pre-ignition, etc. can be suppressed.

(7) A copper core is provided inside the ground electrode 14. With this configuration, the heat dissipation performance of the ground electrode 14 can be improved, and the heat dissipation performance of the ground electrode 14 can be further improved.
(First Modification)
Next, a first modification of the spark plug 10 of the first embodiment will be described.

As shown in FIG. 8, in the spark plug 10 of this modified example, the outer walls 71, 72 are disposed closer to the plug center axis m10 than the erected portion 51 of the ground electrode 14. Specifically, the corners 714, 724 of the outer walls 71, 72 are disposed closer to the plug center axis m10 in the plug circumferential direction Dc than the side surfaces 511, 512 of the erected portion 51 of the ground electrode 14. Even with this configuration, it is possible to obtain actions and effects similar to those of the spark plug 10 of the first embodiment.

(Second Modification)
Next, a second modification of the spark plug 10 of the first embodiment will be described.
9, in the spark plug 10 of this modified example, the outer walls 71, 72 are formed integrally with the ground electrode base material 50. Even with this configuration, it is possible to obtain actions and effects similar to those of the spark plug 10 of the first embodiment.

Second Embodiment
Next, a second embodiment of the spark plug 10 will be described. The following description will focus on the differences from the spark plug 10 of the first embodiment.
10 , in the spark plug 10 of this embodiment, an arc portion 80 is formed integrally with the tip surface 110 of the housing 11 in place of the outer walls 71, 72. The arc portion 80 is formed in a semicircular arc shape along the tip surface 110 of the housing 11. A notch 81 is formed in the approximate center of the arc portion 80. The erected portion 51 of the ground electrode 14 is disposed in the notch 81.

As shown in FIG. 11, the first inner surface 811 facing the one side surface 511 of the standing portion 51 of the ground electrode 14 in the cutout portion 81 is formed to face the plug central axis m10, and is formed so as to be spaced apart from the one side surface 511 of the standing portion 51 as it approaches the plug central axis m10. The second inner surface 812 facing the other side surface 512 of the standing portion 51 of the ground electrode 14 in the cutout portion 81 is formed to face the plug central axis m10, and is formed so as to be spaced apart from the other side surface 512 of the standing portion 51 as it approaches the plug central axis m10. A gap is formed between the first inner surface 811 of the cutout portion 81 and the one side surface 511 of the standing portion 51, and between the second inner surface 812 of the cutout portion 81 and the other side surface 512 of the standing portion 51. In this embodiment, the inner surfaces 811 and 812 of the cutout portion 81 correspond to the opposing surfaces.

Even with the spark plug 10 having such a configuration, it is possible to obtain actions and effects similar to those of the spark plug 10 of the first embodiment.
(Modification)
Next, a modification of the spark plug 10 of the second embodiment will be described.

As shown in FIG. 12, in the spark plug 10 of this modified example, an opposing surface 811a and a parallel surface 811b are formed on the first inner surface 811 of the cutout portion 81. The opposing surface 811a is formed to face the plug central axis m10, and is formed to be more distant from the one side surface 511 of the standing portion 51 the closer it is to the plug central axis m10. The parallel surface 811b is provided so as to be continuous with the opposing surface 811a on the outside in the plug radial direction Dr, and is formed parallel to the one side surface 511 of the standing portion 51.

Similarly, the second inner surface 812 of the cutout portion 81 is formed with an opposing surface 812a and a parallel surface 812b.
Even with the spark plug 10 having such a configuration, it is possible to obtain actions and effects similar to those of the spark plug 10 of the first embodiment.

<Other embodiments>
The above embodiment can also be implemented in the following manner.
In the spark plug 10 of the first embodiment, only one of the outer walls 71 and 72 may be formed.

In the spark plug 10 of the second embodiment, the arc portion 80 is not limited to a semicircular arc shape and may be formed in any arc shape. Furthermore, the arc portion 80 may be disposed adjacent to only one of the side surfaces 511, 512 of the erect portion 51 of the ground electrode 14.
The present disclosure is not limited to the above specific examples. Any design changes made by a person skilled in the art to the above specific examples are also included in the scope of the present disclosure as long as they have the features of the present disclosure. The elements of each of the above specific examples, as well as their arrangements, conditions, shapes, etc., are not limited to those exemplified and can be changed as appropriate. The elements of each of the above specific examples can be combined as appropriate as long as no technical contradictions arise.

P11, P12: throttle portion 10: spark plug 11: housing 12: insulator 13: center electrode 14: ground electrode 51: standing portion 52: extension portions 71, 72: outer wall 80: arc portion (outer wall)
81: Notch portions 511, 512: Side surfaces 710, 720: Longitudinal side surfaces (opposing surfaces)
711, 721: Long side surfaces 712, 713, 722, 723: Short side surfaces 714, 724: Corners 811, 812: Inner surfaces (opposing surfaces)
811a, 812a: Opposing surfaces 811b, 812b: Parallel surfaces

Claims (10)

An insulator (12) formed in a cylindrical shape around a predetermined central axis;
a center electrode (13) inserted into the insulator so as to be exposed from a tip end of the insulator;
A cylindrical housing (11) provided on the outer periphery of the center electrode;
a ground electrode (14) joined to the housing;
The ground electrode is
A standing portion (51) formed so as to extend in the direction of the central axis from a tip end surface of the housing;
an extension portion (52) formed to extend from a tip end of the standing portion to a position facing the center electrode,
When a circumferential direction about the central axis is defined as a plug circumferential direction, and an outer surface of the erected portion provided in the plug circumferential direction is defined as a side surface (511, 512),
an outer wall (71, 72, 80) disposed with a predetermined gap in the circumferential direction of the plug relative to a side surface of the erected portion,
The outer wall has an opposing surface (710, 720, 811, 812) formed to face the central axis and to be spaced apart from the side surface of the erected portion as it becomes closer to the central axis ,
The outer walls (71, 72) are separate from the housing, are rectangular members having a pair of long sides (710, 711, 720, 721) and a pair of short sides (712, 713, 722, 723), and are joined to a tip end surface of the housing.
Of the pair of longitudinal side surfaces, one longitudinal side surface (710, 720) that is arranged to face the central axis is formed as the facing surface such that the closer the portion is to the central axis, the further away it is from the side surface of the erected portion.
Spark plug. When the narrowest portion of the gap formed between the side surface of the erected portion and the outer wall is a narrowed portion (P11, P12),
The spark plug according to claim 1 , wherein a width of the constriction is narrower than a width of the longitudinal side surface of the outer wall. 3. The spark plug according to claim 1, wherein a corner portion (714, 724) located on the outer wall between the long side surface and the short side surface is disposed so as to face the side surface of the erected portion in the plug circumferential direction. 3. The spark plug according to claim 1, wherein a corner portion of the outer wall between the long side surface and the short side surface is disposed closer to the central axis in the circumferential direction of the plug than a side surface of the upright portion. When a line connecting the center of the width of the upright portion in the circumferential direction of the plug and the central axis is defined as a reference line,
5. The spark plug according to claim 1, wherein, when the insulator and the outer wall are parallel projected with a line parallel to the reference line as a projection line, a projection area of the opposing surface of the outer wall is located outside a projection area of the insulator on a projection plane. An insulator (12) formed in a cylindrical shape around a predetermined central axis;
a center electrode (13) inserted into the insulator so as to be exposed from a tip end of the insulator;
A cylindrical housing (11) provided on the outer periphery of the center electrode;
a ground electrode (14) joined to the housing;
The ground electrode is
A standing portion (51) formed so as to extend in the direction of the central axis from a tip end surface of the housing;
an extension portion (52) formed to extend from a tip end of the standing portion to a position facing the center electrode,
When a circumferential direction about the central axis is defined as a plug circumferential direction, and an outer surface of the erected portion provided in the plug circumferential direction is defined as a side surface (511, 512),
an outer wall (71, 72, 80) disposed with a predetermined gap in the circumferential direction of the plug relative to a side surface of the erected portion,
The outer wall has an opposing surface (710, 720, 811, 812) formed to face the central axis and to be spaced apart from the side surface of the erected portion as it becomes closer to the central axis ,
The outer wall is integrally formed with a tip surface of the housing,
The outer wall is made of an arcuate portion (80) formed in an arc shape along a tip end surface of the housing,
A cutout portion (81) in which the standing portion is disposed is formed in the arc portion,
The opposed surfaces are formed on inner surfaces (811, 812) of the cutout portions that face the side surfaces of the erected portions.
Spark plug. When the radial direction about the central axis is defined as the plug radial direction,
7. The spark plug according to claim 6, wherein the inner surface of the cutout portion is formed with the opposing surface and a parallel surface that is continuous with the opposing surface outward in the plug radial direction and is parallel to the side surface of the erected portion. The spark plug according to claim 6 or 7 , wherein the arc portion is formed in a semicircular arc shape. 9. The spark plug according to claim 1 , wherein a tip end portion of the outer wall is located closer to a tip end face of the housing than a surface of the extension of the ground electrode that faces the center electrode. 10. The spark plug according to claim 1 , wherein a copper core is provided inside the ground electrode.

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