Spark plugs for internal combustion engines

Abstract

To provide a spark plug for an internal combustion engine that can facilitate suppression of overheat of a plug cover.SOLUTION: Provided is a spark plug 1 for an internal combustion engine that has an insulator 3, a center electrode 4, a housing 2, a ground electrode 6, and a plug cover 5. A base end part of the plug cover 5 is bonded with a front-end part of the housing 2. At the front-end part of the housing 2 at an inner peripheral side of the base end part of the plug cover 5, a front-end taper surface 21 inclined toward an outer peripheral side as it goes toward the front-end side is formed. The ground electrode 6 has: a fixed end part 61 fixed to the front-end taper surface 21; an extension part 62 extended from the fixed end part 61 in a normal line direction of the front-end taper surface 21; and an opposed part 63 that forms a discharge gap G with the center electrode 4. The discharge gap G is formed at a portion where the opposed part 63 of the ground electrode 6 and a front-end part of the center electrode 4 are opposed to each other in a plug axis direction Z.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a spark plug for an internal combustion engine. [Background technology]

[0002] A spark plug equipped with a sub-combustion chamber is disclosed, for example, in Patent Document 1. In the spark plug disclosed in Patent Document 1, a ground electrode is joined to the tip of a housing. A plug cover is fixed to the housing on the outer periphery of the joint between the housing and the ground electrode. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-103179 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the spark plug described in Patent Document 1, the thickness of the base end of the plug cover that is joined to the housing is thin. Therefore, the cross-sectional area of ​​the heat dissipation path from the plug cover to the housing is small, which makes the plug cover prone to overheating. In addition, the joint between the housing and the ground electrode is disposed on the inner periphery of the plug cover. This makes it difficult to increase the thickness of the base end of the plug cover. Therefore, the problem of difficulty in preventing overheating of the plug cover remains.

[0005] The present invention has been made in view of the above-mentioned problems, and aims to provide a spark plug for an internal combustion engine that can easily prevent overheating of the plug cover. [Means for solving the problem]

[0006] One aspect of the present invention is a cylindrical insulator (3), a center electrode (4) held on the inner circumferential side of the insulator and exposed from the insulator to the tip side; a cylindrical housing (2) that holds the insulator on its inner periphery; a ground electrode (6) forming a discharge gap (G) between itself and the center electrode; a plug cover (5) provided at a tip end of the housing so as to cover a sub-combustion chamber (50) in which the discharge gap is disposed, A base end of the plug cover is joined to a front end of the housing, A tip end tapered surface (21) is formed on the tip end of the housing on the inner peripheral side of the base end of the plug cover, the tip end tapered surface (21) being inclined toward the outer peripheral side as it approaches the tip end side, The ground electrode is in a spark plug for an internal combustion engine and has a fixed end (61) fixed to the tip tapered surface, an extension portion (62) extending from the fixed end in a normal direction to the tip tapered surface, and an opposing portion (63) forming a discharge gap between the center electrode and the ground electrode. Effect of the Invention

[0007] In the spark plug for an internal combustion engine, the housing has the tip tapered surface, and the ground electrode is joined to the tip tapered surface. This allows the dimension of the joint in the plug radial direction to be reduced without reducing the joint area between the housing and the ground electrode. This makes it easier to ensure a large space in the plug radial direction for arranging the base end of the plug cover. This makes it easier to ensure the thickness of the base end of the plug cover. As a result, overheating of the plug cover is easily suppressed.

[0008] As described above, according to the above aspect, it is possible to provide a spark plug for an internal combustion engine in which overheating of the plug cover can be easily suppressed. In addition, the symbols in parentheses described in the claims and the means for solving the problems indicate a correspondence with the specific means described in the embodiments described below, and do not limit the technical scope of the present invention. [Brief description of the drawings]

[0009] [Figure 1] 2. FIG. 3 is an explanatory cross-sectional view of the vicinity of the tip portion of the spark plug for an internal combustion engine in the first embodiment, the cross-sectional view being taken along line II in FIG. [Diagram 2] FIG. 2 is a cross-sectional view taken along line II-II in FIG. [Diagram 3] FIG. 2 is a cross-sectional view illustrating the vicinity of a tip portion of the spark plug according to the first embodiment. [Figure 4] FIG. 4 is an explanatory cross-sectional view showing a state immediately before joining a ground electrode to a housing in the first embodiment. [Diagram 5] FIG. 4 is a plan view of the state before the ground electrode is joined to the housing in the first embodiment, as viewed from the tip side. [Figure 6] FIG. 4 is a plan view of the state in which the ground electrode is joined to the housing in the first embodiment, as viewed from the tip side. [Figure 7] FIG. 4 is an explanatory cross-sectional view showing a state in which a ground electrode is joined to a housing in the first embodiment. [Figure 8] FIG. 4 is a cross-sectional view illustrating an air flow in an auxiliary combustion chamber in the first embodiment. [Figure 9] FIG. 3 is an explanatory diagram of a cross section perpendicular to the longitudinal direction of the ground electrode in the first embodiment. [Figure 10] FIG. 11 is an explanatory diagram of a cross section perpendicular to the longitudinal direction of the ground electrode in a modified embodiment. [Figure 11] FIG. 13 is an explanatory diagram of a cross section perpendicular to the longitudinal direction of the ground electrode in another modified embodiment. [Figure 12] FIG. 13 is an explanatory diagram of a cross section perpendicular to the longitudinal direction of a ground electrode in yet another modified embodiment. [Figure 13] FIG. 11 is a cross-sectional view illustrating the vicinity of a tip portion of a spark plug according to a second embodiment. [Figure 14] FIG. 11 is a plan view of a spark plug according to a second embodiment, viewed from the tip side, with a plug cover removed. [Figure 15] FIG. 11 is a plan view of the state before the ground electrode is joined to the housing in the second embodiment, as viewed from the tip side. [Figure 16] 10A to 10C are explanatory views of an example of a method for manufacturing a ground electrode in the second embodiment. [Figure 17] FIG. 10 is an explanatory view of another example of the method for manufacturing the ground electrode in the second embodiment. [Figure 18] FIG. 11 is a plan view of a state before a ground electrode is joined to a housing in a third embodiment, as viewed from the tip side. [Figure 19] FIG. 11 is an explanatory cross-sectional view of the vicinity of a tip portion of a spark plug according to a fourth embodiment. [Figure 20] FIG. 13 is an explanatory cross-sectional view of the vicinity of the tip portion of a spark plug according to a fifth embodiment. [Figure 21] FIG. 13 is an explanatory cross-sectional view of the vicinity of the tip portion of a spark plug according to a sixth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] (Embodiment 1) An embodiment of a spark plug for an internal combustion engine and a manufacturing method thereof will be described with reference to Figs. A spark plug 1 of this embodiment includes a cylindrical insulator 3, a center electrode 4, a cylindrical housing 2, a ground electrode 6, and a plug cover 5, as shown in FIGS.

[0011] The center electrode 4 is held on the inner periphery of the insulator 3 and is exposed from the tip side of the insulator 3. The cylindrical housing 2 holds the insulator 3 on the inner periphery. The ground electrode 6 forms a discharge gap G between the center electrode 4 and the ground electrode 6. The plug cover 5 is provided at the tip of the housing 2 to cover the auxiliary combustion chamber 50 in which the discharge gap G is located.

[0012] The base end of the plug cover 5 is joined to the front end of the housing 2 . A tip tapered surface 21 is formed at the tip of the housing 2 on the inner peripheral side of the base end of the plug cover 5. The tip tapered surface 21 is inclined so as to approach the outer periphery as it approaches the tip side.

[0013] The ground electrode 6 has a fixed end 61, an extension portion 62, and a facing portion 63. The fixed end 61 is an end portion that is fixed to the tip tapered surface 21. The extension portion 62 is a portion that is extended from the fixed end 61 in the normal direction of the tip tapered surface 21. The facing portion 63 is a portion that forms a discharge gap G between itself and the center electrode 4.

[0014] The tip of the center electrode 4 is disposed further forward than the tip of the housing 2. The discharge gap G is formed at a portion where the opposing portion 63 of the ground electrode 6 and the tip of the center electrode 4 face each other in the plug axial direction Z.

[0015] The spark plug 1 can be used as an ignition means in an internal combustion engine of an automobile, a cogeneration system, or the like. One end of the spark plug 1 in the plug axial direction Z is disposed in the main combustion chamber of the internal combustion engine. In the plug axial direction Z, the side exposed to the main combustion chamber is referred to as the tip side, and the opposite side is referred to as the base side. A direction perpendicular to the central axis of the spark plug 1 (i.e., the plug central axis) is referred to as the plug radial direction. A direction along a circumference centered on the plug central axis is referred to as the plug circumferential direction. The housing 2 has a mounting thread portion 23 on its outer circumferential surface. The spark plug 1 is mounted to the internal combustion engine by screwing the mounting thread portion 23 into a female thread portion formed in a plug hole of the internal combustion engine.

[0016] 2, in this embodiment, the tip tapered surface 21 is formed only on a portion of the plug circumferential direction. The tip tapered surface 21 is a flat surface. The width D of the tip tapered surface 21 is equal to or greater than the width w of the ground electrode 6. Here, the width D of the tip tapered surface 21 is the width in the tangential direction of the plug circumferential direction. Moreover, the width w of the ground electrode 6 is the width in the direction perpendicular to the extension direction of the ground electrode 6 when viewed from the plug axial direction Z.

[0017] 3, the length L of the tip tapered surface 21 is equal to or greater than the thickness t of the ground electrode 6. Here, the length L of the tip tapered surface 21 is the length of the tip tapered surface 21 as seen in a cross section taken along a plane including both the plug central axis C and the central axis of the ground electrode 6. The thickness t of the ground electrode 6 refers to the dimension in a direction perpendicular to both the extension direction and width direction of the ground electrode 6. In this embodiment, the angle θ between the plug axial direction Z and the tip tapered surface 21 can be, for example, about 15° to 45°.

[0018] Further, the facing portion 63 of the ground electrode 6 is formed along the extending direction of the extension portion 62. That is, in this embodiment, the ground electrode 6 has a straight rod shape. Particularly, in this embodiment, the cross section of the ground electrode 6 perpendicular to the extending direction has a substantially rectangular shape as shown in FIG.

[0019] 1 and 2, the plug cover 5 is formed with injection holes 51 that communicate the auxiliary combustion chamber 50 with the outside. In this embodiment, four injection holes 51 are formed. When viewed from the plug axial direction Z, the injection hole axis of the injection hole 51 faces in the plug radial direction. The plug cover 5 is substantially cup-shaped, and its open end side is joined to the tip portion of the housing 2.

[0020] The plug cover 5 is made of, for example, a nickel alloy. The housing 2 is made of, for example, low carbon steel. The ground electrode 6 is made of, for example, a nickel alloy.

[0021] Next, a method for manufacturing the spark plug 1 of this embodiment will be described. First, as shown in Figures 4 and 5, a sub-assembly is prepared in which the center electrode 4 and the insulator 3 are assembled inside the housing 2. Here, as shown in Figures 4 and 5, a tip tapered surface 21 is formed at the tip of the housing 2. This tip tapered surface 21 can be formed in advance by performing cutting work or the like on the housing 2. Note that Figure 5 is a view of the sub-assembly as viewed from the tip side.

[0022] Next, as shown in Fig. 4, Fig. 6, and Fig. 7, the ground electrode 6 is joined to the tip tapered surface 21 of the housing 2. At this time, first, the end face of the ground electrode 6 on the fixed end portion 61 side is brought into surface contact with the tip tapered surface 21. Then, as shown in Fig. 7, the extension direction of the ground electrode 6 is set to be the normal direction of the tip tapered surface 21. In this state, the abutting portion between the ground electrode 6 and the tip tapered surface 21 is welded. This welding can be performed by resistance welding. When performing resistance welding, for example, it is considered to perform welding while holding a part of the ground electrode 6 with an electrode of a welding machine and pressing the ground electrode 6 against the tip tapered surface 21.

[0023] The ground electrode 6 can also be welded to the housing 2 by laser welding. The ground electrode 6 can also be welded to the housing 2 by both resistance welding and laser welding.

[0024] Next, the plug cover 5 is joined to the front end of the housing 2. The base end of the plug cover 5 is brought into contact with the outer periphery of the front end tapered surface 21 of the housing 2 and welded by laser welding or the like. In this way, the spark plug 1 shown in FIG. 1 is obtained.

[0025] Next, the effects of this embodiment will be described. In the spark plug 1 for an internal combustion engine, the housing 2 has a tip tapered surface 21, and the ground electrode 6 is joined to the tip tapered surface 21. This allows the dimension of the joint in the plug radial direction to be reduced without reducing the joint area between the housing 2 and the ground electrode 6. This makes it easier to ensure a large arrangement space in the plug radial direction for the base end of the plug cover 5. This makes it easier to ensure the thickness of the base end of the plug cover 5. As a result, overheating of the plug cover 5 can be easily suppressed. This makes it easier to suppress pre-ignition starting from the plug cover 5.

[0026] Furthermore, the opposing portion 63 of the ground electrode 6 is formed along the extending direction of the extension portion 62. This makes it easy to press the ground electrode 6 in the normal direction of the tip tapered surface 21 when joining the ground electrode 6 to the housing 2. This makes it possible to easily and reliably weld the ground electrode 6 to the tip tapered surface 21. It also makes it possible to join the ground electrode 6 to the housing 2 by resistance welding without using laser welding. This further simplifies the manufacture of the spark plug 1.

[0027] In addition, the tip of the center electrode 4 is disposed further tip than the tip of the housing 2. The discharge gap G is formed at a portion where the opposing portion 63 of the ground electrode 6 and the tip of the center electrode 4 face each other in the plug axial direction Z. This makes it easy to visually check the discharge gap G before assembling the plug cover 5 to the housing 2. It also makes it easy to fine-tune the discharge gap G as needed.

[0028] Moreover, the ground electrode 6 is inclined so as to move toward the tip side in the plug axial direction Z as it moves from the fixed end 61 side toward the opposing portion 63 side. Therefore, as shown in FIG. 8, it is easy to guide the airflow to the discharge gap G, and it is easy to extend the discharge S. This point will be explained below. First, the mounting attitude of the spark plug 1 to the internal combustion engine is controlled so that the airflow F flows into the auxiliary combustion chamber 50 from the nozzle hole 51 on the side closer to the fixed end 61. Then, a tumble flow that rotates around an axis perpendicular to the plug axial direction Z is formed in the auxiliary combustion chamber 50 by this airflow F. This tumble flow hits the ground electrode 6 on the fixed end 61 side rather than the discharge gap G. As a result, the ground electrode 6 makes it easy to guide the airflow F to the discharge gap G. Therefore, the discharge S formed in the discharge gap G is extended by the airflow F. As a result, it is possible to improve the ignition performance. Thus, the spark plug 1 of this embodiment has an effect of suppressing overheating of the plug cover 5, as well as an effect of improving the ignition performance.

[0029] In this embodiment, it is considered that the shape of the cross section perpendicular to the longitudinal direction of the ground electrode 6 is rectangular, as shown in Fig. 9, and the surface 64 facing the discharge gap G is a flat surface. However, from the viewpoint of guiding the airflow F, it is also considered that the surface 64 facing the discharge gap G is a concave surface as shown in Figs. 10 to 12. The surface 64 of the ground electrode 6 shown in Fig. 10 is a concave surface made up of two flat surfaces, the surface 64 of the ground electrode 6 shown in Fig. 11 is a concave surface made up of three flat surfaces, and the surface 64 of the ground electrode 6 shown in Fig. 12 is a concave curved surface.

[0030] As described above, according to the present embodiment, it is possible to provide a spark plug for an internal combustion engine in which overheating of the plug cover can be easily prevented.

[0031] (Embodiment 2) As shown in Figs. 13 to 15, this embodiment is a spark plug 1 in which a leading end tapered surface 21 is formed over the entire circumference in the plug circumferential direction.

[0032] That is, as shown in Fig. 15, before the ground electrode 6 is joined, a tip tapered surface 21 is provided in an annular shape over the entire circumference at the tip of the housing 2. And, as shown in Fig. 14, the ground electrode 6 is joined to a part of the plug circumferential direction of this annular tip tapered surface 21.

[0033] In this embodiment, the tip tapered surface 21 is a concave curved surface, as shown in Fig. 14. Therefore, the end face of the ground electrode 6 on the fixed end 61 side is a convex curved surface that follows the tip tapered surface 21 that is a concave curved surface.

[0034] In producing the ground electrode 6 having such a shape, for example, a long metal member 60 may be cut into a curved shape as shown in Fig. 16. The cut ground electrode 6 may then be formed so that the end face on the fixed end portion 61 side is a convex curved surface and the end face on the opposing portion 63 side is a concave curved surface.

[0035] 17, when cutting the long metal member 60 to obtain the ground electrode 6, both end faces can be curved in a convex shape. In this case, either end face in the longitudinal direction can be the fixed end 61 side. This improves the production efficiency of the spark plug 1. In addition, the end face of the ground electrode 6 shown in FIG. 14 on the opposing portion 63 side is made flat.

[0036] The rest is the same as in embodiment 1. Note that, among the symbols used in embodiment 2 and onwards, the same symbols used in the previous embodiments represent the same components, etc. as in the previous embodiments, unless otherwise specified.

[0037] In this embodiment, the tip tapered surface 21 is present at any position in the circumferential direction of the plug. Therefore, when joining the ground electrode 6 to the housing 2, it is not necessary to particularly determine the position of the ground electrode 6 relative to the housing 2 in the circumferential direction of the plug. Therefore, joining of the ground electrode 6 to the housing 2 can be carried out with high production efficiency. In addition, since the shape of the housing 2 can be made into the shape of a body of revolution about the central axis of the plug, the manufacturing of the housing 2 can be facilitated. In addition, the same effects as those of the first embodiment are achieved.

[0038] (Embodiment 3) 18, this embodiment has a polygonal tip tapered surface 21 when viewed from the plug axial direction Z. Note that this figure shows the state before the ground electrode 6 is joined.

[0039] In this embodiment, a plurality of tapered surfaces 21 at the ends of flat surfaces are formed. In this embodiment, a plurality of tip tapered surfaces 21 are formed in an octagonal shape when viewed from the plug axial direction Z. That is, flat tip tapered surfaces 21 are provided at eight positions in the plug circumferential direction. The rest is the same as in the first embodiment.

[0040] In this embodiment, even if the end face of the ground electrode 6 on the fixed end 61 side is flat, it can be brought into surface contact with the tip tapered surface 21. In addition, since the tip tapered surfaces 21 are formed at multiple locations all around the plug circumferential direction, the ground electrode 6 can be joined to the housing 2 at a selected position in the plug circumferential direction. This makes it possible to improve both the production efficiency of the ground electrode 6 and the efficiency of assembling the ground electrode 6 to the housing 2. In addition, the same effects as those of the first embodiment are achieved.

[0041] (Embodiment 4) In this embodiment, as shown in FIG. 19, the surface of the front end of the housing 2 to which the plug cover 5 is joined is set back from the front end of the front end tapered surface 21 toward the base end. That is, a step portion 22 is provided on the tip portion of the housing 2 on the outer circumferential side of the tip tapered surface 21, and the plug cover 5 is joined to the step portion 22. The rest is the same as in the first embodiment.

[0042] In the case of this embodiment, when joining the plug cover 5 to the housing 2, the housing 2 and the plug cover 5 can be accurately positioned in the plug radial direction. It has the same effects as the first embodiment.

[0043] (Embodiment 5) In this embodiment, as shown in FIG. 20, the surface of the tip end of the housing 2 to which the plug cover 5 is joined is formed into an outer circumferential tapered surface 24. The outer circumferential tapered surface 24 is inclined toward the base end side in the plug axial direction Z as it approaches the outer circumferential side in the plug radial direction. The rest is the same as in the first embodiment.

[0044] In the case of this embodiment, when joining the plug cover 5 to the housing 2, the housing 2 and the plug cover 5 can be easily positioned in the plug radial direction. It has the same effects as the first embodiment.

[0045] (Embodiment 6) In this embodiment, as shown in FIG. 21, the facing portion 63 of the ground electrode 6 is bent with respect to the extension portion 62. In the embodiment shown in FIG. The opposing portion 63 extends in a direction perpendicular to the plug axial direction Z. A base end side surface of the opposing portion 63 is substantially perpendicular to the plug axial direction Z and faces the base end. The base end side surface of the opposing portion 63 and the tip surface of the center electrode 4 face each other substantially in parallel with each other across the discharge gap G. The rest is the same as in the first embodiment.

[0046] In this embodiment, the increase in the discharge gap G due to electrode wear is relatively suppressed, and the life of the spark plug 1 is easily extended. In addition, the same effects as those of the first embodiment are achieved.

[0047] The present invention is not limited to the above-described embodiments, and can be applied to various embodiments without departing from the gist of the present invention. [Explanation of symbols]

[0048] 1...spark plug for internal combustion engine, 2...housing, 21...tip tapered surface, 3...insulator, 4...center electrode, 5...plug cover, 50...auxiliary combustion chamber, 6...ground electrode, 61...fixed end, 62...extension, 63...opposing portion, Z...plug axial direction

Claims

1. A cylindrical insulator (3); a center electrode (4) held on the inner circumferential side of the insulator and exposed on the tip side from the insulator; a cylindrical housing (2) that holds the insulator on its inner periphery; a ground electrode (6) forming a discharge gap (G) between itself and the center electrode; a plug cover (5) provided at a tip end of the housing so as to cover a sub-combustion chamber (50) in which the discharge gap is disposed, A base end of the plug cover is joined to a front end of the housing, A tip end tapered surface (21) is formed on the tip end of the housing on the inner peripheral side of the base end of the plug cover, the tip end tapered surface (21) being inclined toward the outer peripheral side as it approaches the tip end side, the ground electrode has a fixed end (61) fixed to the tip tapered surface, an extension portion (62) extending from the fixed end in a normal direction to the tip tapered surface, and an opposing portion (63) forming a discharge gap between the center electrode and the ground electrode.

2. 2. A spark plug for an internal combustion engine according to claim 1, wherein a tip of the center electrode is disposed further tip than a tip of the housing, and the discharge gap is formed in a portion where the opposing portion of the ground electrode and the tip portion of the center electrode face each other in an axial direction (Z).

3. 2. The spark plug for an internal combustion engine according to claim 1, wherein said tip tapered surface is formed over an entire circumference of the plug in a circumferential direction.

4. 3. The spark plug for an internal combustion engine according to claim 1, wherein the facing portion is formed along an extending direction of the extended portion.

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