JP2021015711A - Spark plug - Google Patents

Abstract

To provide a spark plug which prevents heat in a sub-combustion chamber from being drawn from a plug cover when a spark plug is in a low temperature environment, and can promote heat in the sub-combustion chamber to be drawn from the plug cover when the spark plug is in a high temperature environment.SOLUTION: A spark plug 1 includes a housing 2, an insulator 3, a center electrode 4, a ground electrode 5, a plug cover 6, and a facing member 7. The housing 2 has a tubular shape. The insulator 3 is held inside the housing 2, and has a tubular shape. The center electrode 4 is held inside the insulator 3. The ground electrode 5 and the center electrode 4 form a discharge gap G therebetween. The plug cover 6 constitutes a sub-combustion chamber 10 having a discharge gap G arranged therein together with the housing 2. The plug cover 6 includes a jet hole 611 penetrating therethrough from the inside to the outside of the plug cover 6. The facing member 7 is arranged to face the inner surface 60 of the plug cover 6. The facing member 7 has a larger coefficient of thermal expansion than the plug cover 6.SELECTED DRAWING: Figure 1

Description

The present invention relates to a spark plug.

Spark plugs are used as ignition means in internal combustion engines such as vehicle engines and cogeneration. Patent Document 1 discloses a spark plug in which a discharge gap that generates a spark discharge is covered with a plug cover and an auxiliary combustion chamber is formed inside the plug cover.

In such a spark plug, the air-fuel mixture in the combustion chamber of the internal combustion engine is introduced into the sub-combustion chamber through the injection hole formed in the plug cover, and the air-fuel mixture is ignited by performing spark discharge in the discharge gap to ignite the sub-combustion engine. Generate a flame in the combustion chamber. Then, a flame jet is ejected from the injection hole into the combustion chamber outside the auxiliary combustion chamber, and the flame is spread over the entire combustion chamber. As a result, an internal combustion engine having a high combustion rate can be obtained.

Here, in the spark plug described in Patent Document 1, the plug cover is composed of an inner layer and an outer layer, and a core layer having a higher thermal conductivity than these. As a result, the spark plug of Patent Document 1 is trying to improve the heat drawing of the plug cover.

Japanese Unexamined Patent Publication No. 2012-199236

However, when the spark plug provided with the sub-combustion chamber as described above is in a low temperature environment at the time of cold start, for example, the heat of the flame generated in the sub-combustion chamber is taken away by the plug cover, so that the growth of the flame is hindered. It is easy, and there is a concern that the ignitability of the air-fuel mixture may decrease. On the other hand, in a high temperature environment, there is a concern that pre-ignition may occur and the life of the spark plug may be shortened. Therefore, when the spark plug is in a low temperature environment, the heat in the sub-combustion chamber is suppressed from being drawn from the plug cover, while when the spark plug is in a high temperature environment, the heat in the sub-combustion chamber is removed from the plug cover. It is preferable to promote heat drawing.

The present invention has been made in view of the above problems, and when the spark plug is in a high temperature environment while suppressing heat from being drawn from the plug cover in the sub-combustion chamber when the spark plug is in a low temperature environment. It seeks to provide a spark plug that can facilitate the heat drawn from the plug cover in the sub-combustion chamber.

One aspect of the present invention includes a tubular housing (2) and
A tubular insulator (3) held inside the housing and
The center electrode (4) held inside the insulator and
A ground electrode (5) forming a discharge gap (G) with the center electrode,
A plug cover (6) having a sub-combustion chamber (10) in which the discharge gap is arranged is formed together with the housing and has injection holes (611) penetrating inside and outside.
The spark plug (1) is arranged so as to face the inner surface (60) of the plug cover and includes a facing member (7) having a coefficient of thermal expansion larger than that of the plug cover.

The spark plug of the above aspect is arranged to face the inner surface of the plug cover, and includes a facing member having a larger coefficient of thermal expansion than the plug cover. Therefore, when the environment around the spark plug changes from low temperature to high temperature, the facing member thermally expands more than the plug cover, and the facing member and the plug cover generally approach each other, and between the facing member and the plug cover. Heat transfer is easily promoted.

Therefore, when the environment around the spark plug is a low temperature environment, heat transfer from the auxiliary combustion chamber to the plug cover via the opposing member is suppressed, and when the environment around the spark plug is a high temperature environment, Heat transfer from the sub-combustion chamber to the plug cover can be promoted via the facing member. Therefore, when the environment around the spark plug is in a low temperature environment, it is possible to prevent the growth of the flame generated in the sub-combustion chamber from being hindered and improve the ignitability, and the surroundings of the spark plug When the environment is in a high temperature environment, it is possible to prevent the occurrence of pre-ignition and shortening the life of the spark plug.

As described above, according to the above aspect, when the spark plug is in a high temperature environment, the heat in the sub-combustion chamber is suppressed from being drawn from the plug cover when the spark plug is in a high temperature environment. A spark plug can be provided that can facilitate the heat being drawn from the plug cover.
The reference numerals in parentheses described in the scope of claims and the means for solving the problem indicate the correspondence with the specific means described in the embodiments described later, and limit the technical scope of the present invention. It's not a thing.

The cross-sectional view which includes the plug central axis of the spark plug in Embodiment 1. FIG. The exploded sectional view of the facing member, the plug cover and the ground electrode in Embodiment 1. FIG. In the first embodiment, (a) a cross section orthogonal to the axial direction of the facing member and the plug cover in a normal temperature field, and (b) a cross section orthogonal to the axial direction of the facing member and the plug cover in a high temperature field. In the first embodiment, (a) an enlarged cross-sectional view between the spark plug housing and the plug cover in a normal temperature field, and (b) an enlarged cross-sectional view between the spark plug housing and the plug cover in a high temperature field. .. FIG. 5 is a cross-sectional view of a spark plug for explaining a state of flame growth in a sub-combustion chamber according to the first embodiment. In the modified form of the first embodiment, (a) a cross section orthogonal to the axial direction of the facing member and the plug cover in a normal temperature field, and (b) a cross section orthogonal to the axial direction of the facing member and the plug cover in a high temperature field. In the second embodiment, (a) a cross section orthogonal to the axial direction of the facing member and the plug cover in a normal temperature field, and (b) a cross section orthogonal to the axial direction of the facing member and the plug cover in a high temperature field. In the third embodiment, (a) a cross section orthogonal to the axial direction of the facing member and the plug cover in a normal temperature field, and (b) a cross section orthogonal to the axial direction of the facing member and the plug cover in a high temperature field.

(Embodiment 1)
An embodiment of the spark plug will be described with reference to FIGS. 1 to 5.
As shown in FIG. 1, the spark plug 1 of this embodiment includes a housing 2, an insulator 3, a center electrode 4, a ground electrode 5, a plug cover 6, and a facing member 7.

As shown in FIG. 1, the housing 2 has a tubular shape. The insulating insulator 3 is held inside the housing 2 and has a tubular shape. The center electrode 4 is held inside the insulating insulator 3. The ground electrode 5 forms a discharge gap G with the center electrode 4.

As shown in FIG. 1, the plug cover 6 constitutes an auxiliary combustion chamber 10 in which the discharge gap G is arranged together with the housing 2. The plug cover 6 includes a jet hole 611 that penetrates inside and outside. The facing member 7 is arranged to face the inner surface 60 of the plug cover 6. The facing member 7 has a larger coefficient of thermal expansion than the plug cover 6.
Hereinafter, this form will be described in detail.

Hereinafter, the central axis of the spark plug 1 will be referred to as a plug central axis C. The direction in which the plug central axis C extends is referred to as the axial direction Z. The side where the sub-combustion chamber 10 of the spark plug 1 is located in the axial direction Z (for example, the lower side of FIGS. 1 and 2) is the tip side, and the opposite side (for example, the upper side of FIGS. 1 and 2) is the base end side. That is. Further, when the term "diameter direction" is simply used, it means the radial direction of the spark plug 1. The term "circumferential direction" simply means the circumferential direction of the spark plug 1.

The spark plug 1 can be used as an ignition means in an internal combustion engine such as an automobile or cogeneration engine, for example. The base end portion of the spark plug 1 is connected to an ignition coil (not shown), and the tip end portion of the spark plug 1 is arranged in the combustion chamber of the internal combustion engine.

The housing 2 is formed of a heat-resistant metal material such as iron, nickel, iron-nickel alloy, or stainless steel in a tubular shape. As shown in FIG. 1, a mounting screw portion 21 is formed on the outer peripheral portion of the housing 2. The spark plug 1 is screwed into a female screw hole provided in a cylinder head (not shown) at the mounting screw portion 21, and is mounted on the cylinder head. When the spark plug 1 is attached to the cylinder head, a portion of the spark plug 1 on the tip side of the mounting screw portion 21 is exposed to the combustion chamber. A plug cover 6 is attached to the tip of the housing 2.

As shown in FIGS. 1 and 2, the plug cover 6 has a cup shape with the base end side open. Further, the plug cover 6 has a rotating body shape with the plug central axis C as the rotating axis. The plug cover 6 includes a cover bottom wall 61 and a cover peripheral wall 62 extending from the entire peripheral edge of the cover bottom wall 61 toward the base end side. The cover bottom wall 61 is formed in a disk shape. The cover peripheral wall 62 is formed in a cylindrical shape. The cover peripheral wall 62 is joined to the tip end portion of the housing 2 on the entire circumference of the base end portion thereof. The auxiliary combustion chamber 10 is formed by the plug cover 6 and the housing 2.

As shown in FIGS. 1 and 2, the cover bottom wall 61 is formed with a plurality of injection holes 611 that penetrate the cover bottom wall 61 and communicate the auxiliary combustion chamber 10 with the space outside the spark plug 1. The plurality of injection holes 611 are arranged on the outer peripheral side in the radial direction with respect to the plug central axis C. The plurality of injection holes 611 are formed at equal intervals in the circumferential direction. Each injection hole 611 is formed so as to be inclined toward the outer peripheral side in the radial direction toward the tip end side in the axial direction Z. The number, shape, arrangement location, etc. of the injection holes 611 are appropriately determined upon request.

As shown in FIGS. 1 and 2, the cover peripheral wall 62 is formed with a recess 621 for arranging the facing member 7. The recess 621 is formed on the inner surface 60 of the plug cover 6 so as to be recessed toward the outside of the cover rather than the portion adjacent to the recess 621. In this embodiment, the recess 621 is formed in substantially the entire cover peripheral wall 62.

As shown in FIGS. 1 and 2, the base end side of the recess 621 is open. As a result, as shown in FIG. 2, the facing member 7 can be inserted into the recess 621 from the opening 621b on the base end side of the recess 621. As shown in FIG. 1, in a state where the plug cover 6 is attached to the tip end portion of the housing 2, the opening 621b of the recess 621 is closed by the tip end surface 22 of the housing 2. The facing member 7 is inserted and arranged in the recess 621.

The facing member 7 is made of a material having a higher coefficient of thermal expansion than the plug cover 6. Further, the facing member 7 is made of a material having a higher thermal conductivity than the plug cover 6. For example, the plug cover 6 can be made of nickel and the opposing member 7 can be made of copper or naval brass. For example, nickel has a coefficient of linear expansion of 13.3 × 10 ^-6 / ° C and a thermal conductivity of 90 W / mK, and copper has a coefficient of linear expansion of 17.7 × 10 ^-6 / ° C and a thermal conductivity of 90 W / mK. It is 372 W / mK, and Naval brass has a coefficient of linear expansion of 17.7 × 10 ^-6 / ° C. and a thermal conductivity of 372 W / mK. The opposing member 7 is inserted into the recess 621. Further, the heat capacity of the facing member 7 is smaller than the heat capacity of the plug cover 6.

As shown in FIGS. 1 and 2, the opposing member 7 has a cylindrical shape with both sides open in the axial direction Z. The facing member 7 is arranged so as to face the inner peripheral surface of the recess 621 of the cover peripheral wall 62 in the radial direction. The tip of the facing member 7 faces the tip end surface 621a of the recess 621.

As shown in FIGS. 3A and 4A, when the spark plug 1 is arranged in a room temperature environment (for example, 5 ° C. to 35 ° C.) (hereinafter referred to as a room temperature field), the outside of the facing member 7 The diameter is formed so as to be smaller than the inner diameter of the recess 621. That is, in a normal temperature field, a gap 101 is formed between the facing member 7 and the recess 621 in the radial direction. As shown in FIG. 3A, in a normal temperature field, the facing member 7 has an annular cross-sectional shape orthogonal to the axial direction Z, and a gap 101 is formed between the facing member 7 and the recess 621 on the entire circumference.

Further, as shown in FIG. 4A, the length of the facing member 7 in the axial direction Z is slightly smaller than the length of the recess 621 of the plug cover 6 in the axial direction Z in the normal temperature field. The facing member 7 is arranged so as to be able to move slightly in the recess 621 in a normal temperature field, and is not fixed in the recess 621. The spark plug 1 is attached to the internal combustion engine in a posture in which the tip side is on the lower side in the direction of gravity, whereby the tip of the opposing member 7 abuts on the tip side end surface 621a of the recess 621 due to gravity in a normal temperature field. There is. Further, in a state where the spark plug 1 is attached to the internal combustion engine, a gap 102 is formed between the facing member 7 and the tip surface 22 of the housing 2 in the axial direction Z in a normal temperature field.

As shown in FIG. 3B, in a state where the spark plug 1 is arranged in a high temperature environment (for example, 400 ° C. or higher) (hereinafter referred to as a high temperature field), the outer diameter of the facing member 7 is the inner diameter of the recess 621. It is formed to be equivalent. That is, in the high temperature field, the gap 101 formed between the facing member 7 and the inner peripheral surface of the recess 621 in the radial direction disappears in the normal temperature field, and the facing member 7 and the inner peripheral surface of the recess 621 are in the radial direction. Is in contact with.

Further, in a high temperature field, the length of the facing member 7 in the axial direction Z is equivalent to the length of the recess 621 of the plug cover 6 in the axial direction Z. That is, in a high temperature field, the gap 102 formed between the facing member 7 and the tip end surface 22 of the housing 2 in the normal temperature field disappears, and the tip end portion of the facing member 7 comes into contact with the tip end surface 621a of the recess 621. The base end portion of the facing member 7 is in contact with the tip surface 22 of the housing 2.

When the spark plug 1 is attached to the internal combustion engine and shifts from a normal temperature field to a high temperature field, both the plug cover 6 and the facing member 7 thermally expand toward the outer peripheral side in the plug radial direction. Here, since the facing member 7 has a higher coefficient of thermal expansion than the plug cover 6, the facing member 7 expands more than the plug cover 6 when shifting from the normal temperature field to the high temperature field. Therefore, when shifting from the normal temperature field to the high temperature field, the contact area between the outer peripheral surface of the facing member 7 and the inner peripheral surface of the recess 621 of the plug cover 6 gradually increases. Therefore, as the temperature of the facing member 7 and the plug cover 6 becomes higher, heat transfer to each other in the radial direction becomes easier. The state of this heat transfer is shown by an arrow along the axial direction Z in FIG. 4B.

Further, in the state where the spark plug 1 is attached to the internal combustion engine, when shifting from the normal temperature field to the high temperature field, the tip of the facing member 7 is in contact with the tip end surface 621a of the recess 621, so that the facing member 7 is abutted. It thermally expands so as to extend toward the base end side, and eventually the base end portion of the opposing member 7 comes into contact with the tip surface 22 of the housing 2. As a result, in a high temperature field, the tip of the facing member 7 comes into contact with the tip end surface 621a of the recess 621, and the base end of the facing member 7 comes into contact with the tip surface 22 of the housing 2. Therefore, as the temperature of the facing member 7 and the housing 2 becomes higher, heat transfer to each other in the axial direction Z becomes easier. The state of this heat transfer is shown by an arrow orthogonal to the axial direction Z in FIG. 4B. As described above, the facing member 7 is configured so that the contact area with the plug cover 6 increases as the temperature of the spark plug 1 rises.

As shown in FIG. 1, a ground electrode 5 is provided at the center of the cover bottom wall 61 of the plug cover 6 when viewed from the axial direction Z. The ground electrode 5 can be integrated with the plug cover 6, for example, by joining an electrode separate from the plug cover 6 to the plug cover 6. The ground electrode 5 is arranged so that its central axis coincides with the plug central axis C.

As shown in FIG. 1, the ground electrode 5 extends from the cover bottom wall 61 to the proximal end side. The base end side end portion of the ground electrode 5 is arranged at a position where it overlaps with the facing member 7 in the radial direction. The end surface of the ground electrode 5 on the proximal end side faces the tip surface of the center electrode 4 in the axial direction Z, and forms a discharge gap G between the tip surface of the center electrode 4 and the tip surface of the center electrode 4.

As shown in FIG. 1, the center electrode 4 is formed so that its central axis coincides with the plug central axis C. The tip of the center electrode 4 is located closer to the tip than the housing 2. Further, the tip portion of the center electrode 4 is arranged at a position where it overlaps with the facing member 7 in the radial direction.

As shown in FIG. 1, the discharge gap G is formed at a position where it overlaps with the facing member 7 in the radial direction as a whole. That is, the entire discharge gap G is surrounded by the facing member 7 from the outer peripheral side. In other words, the opposing member 7 is arranged at least in the region where the discharge gap G is formed in the axial direction Z. The discharge gap G is arranged slightly closer to the proximal end side than the central position of the opposing member 7 in the axial direction Z. The center electrode 4 is inserted and held inside the insulating insulator 3, and the tip portion thereof protrudes from the insulating insulator 3.

The insulating insulator 3 is formed by forming alumina or the like in a tubular shape. As shown in FIG. 1, the insulating insulator 3 is held inside the housing 2. The tip of the insulating insulator 3 projects toward the tip side of the tip surface of the tip of the housing 2.

Next, the action and effect of this embodiment will be described.
The spark plug 1 of the present embodiment is arranged to face the inner surface 60 of the plug cover 6 and includes a facing member 7 having a larger coefficient of thermal expansion than the plug cover 6. Therefore, when the environment around the spark plug 1 shifts from a low temperature to a high temperature, the facing member 7 thermally expands more than the plug cover 6, and the facing member 7 and the plug cover 6 come closer to each other as a whole, and the facing member 7 approaches. Heat transfer between the plug cover 6 and the plug cover 6 is likely to be promoted.

Therefore, when the environment around the spark plug 1 is in a low temperature environment (for example, normal temperature), the spark plug 1 is in a high temperature environment while suppressing heat transfer from the auxiliary combustion chamber 10 to the plug cover 6 via the facing member 7. When the temperature is (for example, 400 ° C. or higher), heat transfer from the auxiliary combustion chamber 10 to the plug cover 6 can be promoted via the facing member 7. Therefore, when the spark plug 1 is in a low temperature environment, the heat of the flame generated in the sub-combustion chamber 10 is taken away by the plug cover 6 to prevent the growth of the flame from being hindered and the ignitability is improved. In addition to being able to achieve this, when the spark plug 1 is in a high temperature environment, it is possible to prevent the occurrence of pre-ignition and shortening the life of the spark plug 1.

Further, at room temperature, the outer diameter of the facing member 7 is smaller than the inner diameter of the portion of the plug cover 6 facing the facing member 7, and a gap 101 is formed between the facing member 7 and the plug cover 6 in the radial direction. There is. Therefore, when the environment around the spark plug 1 is in a low temperature environment, it is possible to further prevent the heat in the sub-combustion chamber 10 from being easily transferred to the plug cover 6 via the facing member 7. Therefore, when the spark plug 1 is in a low temperature environment, it is possible to prevent the growth of the flame generated in the sub-combustion chamber 10 from being hindered and to improve the ignitability.

Further, the facing member 7 is configured so that the contact area with the plug cover 6 increases as the temperature of the spark plug 1 rises. Therefore, the higher the temperature of the environment around the spark plug 1, the easier it is to promote heat transfer from the auxiliary combustion chamber 10 to the plug cover 6 via the facing member 7. Therefore, when the environment around the spark plug 1 is in a high temperature environment, it is easier to prevent the occurrence of pre-ignition and the shortening of the life of the spark plug 1.

Further, the thermal conductivity of the facing member 7 is larger than the thermal conductivity of the plug cover 6. Therefore, when the environment around the spark plug 1 is a high temperature environment, the heat in the sub-combustion chamber 10 is easily transferred to the plug cover 6 via the facing member 7, causing pre-ignition and the life of the spark plug 1. It is easier to prevent the shortening of.

Further, the heat capacity of the facing member 7 is smaller than the heat capacity of the plug cover 6. Therefore, the temperature of the opposed member 7 tends to decrease in the intake stroke after the temperature in the auxiliary combustion chamber 10 rises in the combustion stroke in the combustion cycle of the 4-stroke engine to which the spark plug 1 is attached. Therefore, it is possible to prevent the combustion chamber from being kept at a high temperature. This makes it easier to prevent the occurrence of pre-ignition and shortening the life of the spark plug 1.

Further, the facing member 7 is arranged at least in the region where the discharge gap G is formed in the axial direction Z of the spark plug 1. As a result, when the spark plug 1 is in a low temperature environment, it is easier to promote the growth of the flame in the sub-combustion chamber 10. This will be described below.

As shown in FIG. 5, by performing the spark discharge S in the discharge gap G, the air-fuel mixture introduced into the sub-combustion chamber 10 is ignited through the injection hole 611, and the flame F is generated in the sub-combustion chamber 10. The flame F spreads substantially concentrically. Therefore, by arranging the facing member 7 in the region where the discharge gap G in the axial direction Z is formed, it is possible to prevent the flame F from colliding with the plug cover 6 at an early stage. As a result, it is possible to prevent the heat of the flame F from being taken away by the plug cover 6 at an early stage and hinder the growth of the flame F, and it is easier to further promote the growth of the flame F in the sub-combustion chamber 10. In FIG. 5, the state of flame growth is represented by reference numerals F1 to F5. Reference numerals F1 to F5 indicate the outer position of the flame by time, and the time advances in the order of reference numerals F1 to F5. Further, in FIG. 5, the outline of the flame F is schematically shown by a line, but in reality, the air-fuel mixture around the flame is compressed as the flame propagates, so that the temperature of the air-fuel mixture that the flame has not reached also rises. To do.

Further, the plug cover 6 has a recess 621 in which the facing member 7 is arranged. Therefore, the positioning of the facing member 7 with respect to the plug cover 6 can be facilitated. Further, it is easy to prevent a step from being formed between the facing member 7 and the plug cover 6. As a result, when the environment around the spark plug 1 is in a low temperature environment, the heat of the flame in the combustion chamber is taken away due to the formation of the step and the increase in the area of the wall surface surrounding the auxiliary combustion chamber 10. It is possible to prevent unburned air-fuel mixture from remaining around the step.

Further, the base end side of the recess 621 is open. Therefore, when the facing member 7 is arranged in the recess 621, the facing member 7 can be inserted into the recess 621 from the base end side of the recess 621, and the productivity of the spark plug 1 can be easily improved.

As described above, according to this embodiment, when the spark plug is in a high temperature environment, the heat in the sub-combustion chamber is suppressed from being drawn from the plug cover when the spark plug is in a high temperature environment. A spark plug can be provided that can facilitate the heat being drawn from the plug cover.

In this example, a gap 101 is formed on the entire circumference between the facing member 7 and the recess 621 in a normal temperature field, but the present invention is not limited to this. For example, as shown in FIG. 6A, the facing member 7 may be eccentrically attached to the plug cover 6 in a normal temperature field, and a part of the facing member 7 may be in radial contact with the recess 621. In manufacturing, it is assumed that the facing member 7 and the recess 621 are in contact with each other in a room temperature field in this way. In this case, the facing member 7 expands as the temperature of the spark plug 1 rises, with the contact portion with the plug cover 6 as a fulcrum, and as shown in FIG. 6B, the plug cover 6 covers the entire circumference in a high temperature field. To abut.

(Embodiment 2)
As shown in FIG. 7, this embodiment has an elliptical annular cross section (hereinafter, also referred to as an orthogonal cross section) perpendicular to the axial direction Z of the opposing member 7 in a normal temperature field.

As shown in FIG. 7A, in a normal temperature field, both ends of the orthogonal cross-sectional shape of the opposing member 7 in the longitudinal direction DL are in contact with the inner surface 60 of the plug cover 6, and the other parts and the plug cover are in contact with each other. A gap 101 is formed between the six and the radial direction.

Then, as the temperature around the spark plug 1 becomes higher, the opposing member 7 thermally expands so as to spread toward both outer sides of the lateral DS of the orthogonal cross-sectional shape, and as shown in FIG. 7B, In a high temperature field, the facing member 7 and the plug cover 6 come into contact with each other all around.

Others are the same as in the first embodiment.
In addition, among the codes used in the second and subsequent embodiments, the same codes as those used in the above-described embodiments represent the same components and the like as those in the above-mentioned embodiments, unless otherwise specified.

Also in this embodiment, it has the same effect as that of the first embodiment.

(Embodiment 3)
In this embodiment, as shown in FIG. 8, in a normal temperature field, both the cross-sectional shape orthogonal to the axial direction Z of the opposing member 7 and the cross-sectional shape orthogonal to the axial direction Z of the plug cover 6 are elliptical annular. is there.

As shown in FIG. 8A, when viewed in an orthogonal cross section, the facing member 7 and the plug cover 6 are formed in an elliptical ring with the same direction as the longitudinal direction DL in the normal temperature field. Then, in a normal temperature field, both ends of the orthogonal cross-sectional shape of the opposing member 7 in the longitudinal direction DL are in contact with the inner surface 60 of the plug cover 6, and between the other portions and the plug cover 6 in the radial direction. Is formed with a gap 101.

Then, as the temperature around the spark plug 1 becomes higher, the opposing member 7 thermally expands so as to expand toward both outer sides of the lateral DS of the orthogonal cross-sectional shape, and as shown in FIG. 8B, In a high temperature field, the facing member 7 and the plug cover 6 come into contact with each other all around.
Others are the same as in the first embodiment.

Also in this embodiment, it has the same effect as that of the first embodiment.

The present invention is not limited to each of the above-described embodiments, and can be applied to various embodiments without departing from the gist thereof.

For example, in the first embodiment, the outer diameter of the facing member 7 and the inner diameter of the recess 621 may be substantially the same in a normal temperature field. Even in this case, the degree of adhesion between the facing member 7 and the plug cover 6 increases as the temperature rises, and the heat transfer property between the facing member 7 and the plug cover 6 improves as the temperature rises.

Further, in each embodiment, the facing member 7 may be configured to be smaller than the inner diameter of the recess 621 of the plug cover 6 in both the normal temperature field and the high temperature field. Even in this case, the gap 101 between the facing member 7 and the plug cover 6 becomes smaller as the temperature rises, and the heat transfer between the facing member 7 and the plug cover 6 becomes easier to promote as the temperature rises.

Further, the facing member 7 may include a portion facing the cover bottom wall 61. For example, the facing member 7 is provided with a member bottom wall facing the cover bottom wall 61 from the base end side and a cover peripheral wall 62 facing the cover peripheral wall 62 from the inner peripheral side, and the cup opens to the base end side as a whole. It may be configured to have a shape. In this case, the injection hole 611 is communicated with the inside of the auxiliary combustion chamber 10 and the external space of the spark plug 1 by forming a communication hole communicating with the injection hole 611 of the cover bottom wall 61 on the peripheral wall of the member.

1 Spark plug 10 Sub-combustion chamber 2 Housing 3 Insulator 4 Center electrode 5 Ground electrode 6 Plug cover 60 Inner surface of plug cover 611 Injection hole 7 Opposing member G Discharge gap

Claims (8)

Cylindrical housing (2) and
A tubular insulator (3) held inside the housing and
The center electrode (4) held inside the insulator and
A ground electrode (5) forming a discharge gap (G) with the center electrode,
A plug cover (6) having a sub-combustion chamber (10) in which the discharge gap is arranged is formed together with the housing and has injection holes (611) penetrating inside and outside.
A spark plug (1) provided with an opposing member (7) that is arranged to face the inner surface (60) of the plug cover and has a larger coefficient of thermal expansion than the plug cover. In a state where the spark plug is arranged in a room temperature environment, the outer diameter of the facing member is smaller than the inner diameter of the portion of the plug cover facing the facing member, and the facing member and the plug cover in the radial direction The spark plug according to claim 1, wherein a gap (101) is formed between the spark plugs. The spark plug according to claim 1 or 2, wherein the facing member is configured so that the contact area with the plug cover increases as the temperature of the spark plug rises. The spark plug according to any one of claims 1 to 3, wherein the thermal conductivity of the facing member is larger than the thermal conductivity of the plug cover. The spark plug according to any one of claims 1 to 4, wherein the heat capacity of the facing member is smaller than the heat capacity of the plug cover. The spark plug according to any one of claims 1 to 5, wherein the facing member is arranged at least in a region where the discharge gap is formed in the axial direction (Z) of the spark plug. The spark plug according to any one of claims 1 to 6, wherein the plug cover has a recess (621) for arranging the facing member. The spark plug according to claim 7, wherein the concave portion has an open base end side.

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