Spark plug

Abstract

A spark plug (1) includes: a fitting member (30a) having a cylindrical portion (30a); a center electrode (21) disposed in the cylindrical portion (30a); and a ground electrode (11) inserted into an opening portion (40) provided in the cylindrical portion (30a) and forming a gap between a front end portion in an extension direction of the ground electrode and the center electrode (21). A thread (37a) is provided on an outer peripheral surface of the cylindrical portion (30a). In a cross section of the cylindrical portion (30a), the opening portion (40) has an inclined portion (41) that gradually narrows from the outer peripheral surface of the cylindrical portion (30a) toward an inner peripheral surface side.

Description

Technical Field

[0001] This disclosure relates to spark plugs for internal combustion engines. Background Technology

[0002] Spark plugs are used as ignition units in internal combustion engines such as automobile engines. A spark plug, as a structure for generating a spark discharge, includes a center electrode and a ground electrode. The center electrode is mounted on the front end side inside a cylindrical body fitting that extends along the axis. The ground electrode is positioned close to the front end of the center electrode.

[0003] In such spark plugs, there is a spark plug in which an opening is formed in a cylindrical body fitting, and a ground electrode is installed in the body fitting by inserting a rod-shaped ground electrode relative to the opening (for example, see Patent Document 1).

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2019-46660 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] For example, in patent document 1 Figure 5 In the spark plug shown, a hole 34c is formed at the front end of the mounting thread 52c of the main body part 50c, in a direction perpendicular to the spark plug's axis AX, through the mounting thread 52c. A grounding electrode tip 39c is pressed into this hole 34c.

[0009] This hole (opening) in the mounting thread of the main component is formed by machining the outer peripheral surface of the main component. Typically, the shape of the cutting surface in the opening of the main component is, for example, like the spark plug in Patent Document 1, perpendicular to the central axis of the main component.

[0010] However, if the cutting surface of the opening is perpendicular to the inner diameter center axis of the main component, then when the spark plug is threaded into the threaded hole of the internal combustion engine, the thread teeth at the boundary between the spark plug and the opening will be tilted forward relative to the direction of rotation of the thread. Therefore, for example, when tightening the spark plug into the internal combustion engine, the thread teeth of the spark plug may bite into the threaded hole of the internal combustion engine.

[0011] Therefore, one aspect of this disclosure is to provide a spark plug that can suppress the biting of the thread teeth during installation in an internal combustion engine.

[0012] Technical solutions for solving the problem

[0013] One aspect of this disclosure relates to a spark plug comprising: a fitting member having a cylindrical portion extending along an axis; a center electrode disposed within the cylindrical portion and extending along the axis; and a ground electrode inserted into an opening provided in the cylindrical portion, forming a gap between its front end in its extending direction and the center electrode. In this spark plug, the outer peripheral surface of the cylindrical portion is provided with threads. In a cross-section of the cylindrical portion in a direction orthogonal to the axis, at a position where the apex of the threads intersects the edge of the opening, the opening has an inclined portion that gradually tapers from the outer peripheral surface of the cylindrical portion toward the inner peripheral surface. The angle between the tangent of the outer peripheral surface at the boundary position between the apex of the threads and the opening and the inclined portion of the opening is 90 degrees or more.

[0014] According to the above structure, when the spark plug is threaded into the threaded hole of the internal combustion engine, the thread teeth on the outer peripheral surface of the cylindrical portion are shaped so as not to tilt forward relative to the direction of thread travel. Therefore, the possibility of the thread teeth biting into the threaded hole of the internal combustion engine can be reduced when the spark plug is tightened into or removed from the internal combustion engine.

[0015] In the spark plugs described in one aspect of the present disclosure, the inclined portion may extend at least from the apex of the thread to the groove of the thread.

[0016] According to the above structure, since the cutting surface of the opening is sloping throughout the thread tooth (i.e., from the apex of the thread tooth to the bottom of the thread groove), the edge portion of the opening can be more reliably suppressed when the spark plug is installed into and removed from the internal combustion engine.

[0017] In the spark plugs disclosed in one aspect above, the inclined portion may be disposed on both sides of the opening in the cross section of the opening at the position where the apex of the thread tooth intersects with the edge of the opening.

[0018] Based on the above structure, when the spark plug rotates clockwise or counterclockwise around its axis, it becomes an inclined portion with an opening in the direction of thread travel. Therefore, it can prevent the thread teeth from biting in when installing the spark plug relative to or removing it from the internal combustion engine.

[0019] In the spark plugs described in one aspect of the present disclosure, the inclined portion may also be provided in a region covering two or more of the aforementioned thread teeth.

[0020] The diameter of the opening is set according to the size of the grounding electrode, and is usually larger than the thread width (the distance between two adjacent thread teeth in the axial direction) of the thread teeth provided on the outer peripheral surface of the cylindrical portion. Therefore, the opening is formed covering the forming area of ​​two or more adjacent thread teeth in the axial direction. Therefore, it is preferable that the inclined portion provided in the opening is also formed covering the forming area of ​​two or more adjacent thread teeth in the axial direction. This prevents the thread teeth present at the edge of the opening from biting in.

[0021] Invention Effects

[0022] As described above, the spark plug according to one aspect of this disclosure can suppress the biting of the thread teeth formed on the outer peripheral surface of the fitting component when it is installed in an internal combustion engine, etc. Attached Figure Description

[0023] Figure 1 This is a partial cross-sectional view showing the appearance and internal structure of a spark plug according to one embodiment.

[0024] Figure 2 This is a side view diagram showing an enlarged view of the mounting portion of the center electrode and ground electrode in the spark plug according to the first embodiment.

[0025] Figure 3 This is a side view showing the appearance of the spark plug according to the first embodiment.

[0026] Figure 4 This is a perspective view showing the appearance of the spark plug according to the first embodiment.

[0027] Figure 5 It means Figure 3 A cross-sectional view of the structure of the AA line portion of the main component shown.

[0028] Figure 6 This is a schematic diagram showing the shape of the cross-section of the opening formed in the main body component of the spark plug according to the first embodiment.

[0029] Figure 7 This is a schematic diagram showing the shape of the cross-section of the opening formed in the main body of a conventional spark plug.

[0030] Figure 8 This is a schematic diagram showing the shape of the cross-section of the opening formed in the main body fitting of the spark plug, which is being compared.

[0031] Figure 9 This is a side view showing an enlarged view of the mounting portion of the center electrode and ground electrode in the spark plug according to the second embodiment.

[0032] Figure 10This is a cross-sectional view showing the structure of the main components of a conventional spark plug. Detailed Implementation

[0033] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Figure 1 The schematic structure of a spark plug 1 according to one embodiment of the present invention is shown.

[0034] [First Implementation Method]

[0035] In the first embodiment, a lateral discharge type spark plug will be used as an example for explanation.

[0036] (The overall structure of a spark plug)

[0037] First, refer to Figure 1 The overall structure of spark plug 1 is described below. Spark plug 1 includes an insulator 50 and a main component (component) 30.

[0038] The insulator 50 is a generally cylindrical component extending along the length of the spark plug 1. A bore extending along axis O is formed within the insulator 50. The insulator 50 is made of a material with excellent insulation, heat resistance, and thermal conductivity. For example, the insulator 50 is made of alumina-based ceramic. A center electrode 21 is provided at the front end 51 of the insulator 50. In the spark plug 1, the side with the center electrode 21 is designated as the front end side of the spark plug 1, and the other end side is designated as the rear end side. A terminal fitting 52 is installed at the rear end of the insulator 50.

[0039] The center electrode 21 protrudes from the front end 51 of the insulator 50 and is held in the axial hole of the insulator 50. The center electrode 21 is mounted on the axis O of the generally cylindrical insulator 50. The center electrode 21 has a generally cylindrical shape, slightly tapering towards its front end. A cylindrical noble metal end (not shown) is joined to the front end of the center electrode 21, for example by welding.

[0040] The center electrode 21 is formed, for example, of a metallic material such as a Ni-based alloy containing Ni (nickel) as the main component. Examples of alloying elements added to the Ni-based alloy include Al (aluminum). A core material (not shown) may also be embedded inside the center electrode 21. The core material can be formed of a metallic material (e.g., Cu (copper) or a Cu alloy) that has superior thermal conductivity compared to the electrode substrate forming the center electrode 21. Alternatively, in other embodiments, a core material may not be provided inside the center electrode 21. That is, the center electrode may be formed solely of the electrode substrate.

[0041] The main body component 30 is a generally cylindrical component that is fixed to a threaded hole in an internal combustion engine. The main body component 30 is configured to partially cover the outer periphery of the insulator 50. With a portion of the insulator 50 inserted into the generally cylindrical main body component 30, the gap between the main body component 30 and the insulator 50 at the rear end is filled with talcum powder 61.

[0042] The main body component 30 is formed of a conductive metallic material. Examples of such a metallic material include low-carbon steel or a metal material with iron as its main component. The main body component 30 mainly includes a riveting part 31, a tool engaging part 32, a bending part 33, a seat part 34, and a main body 36. The above-mentioned parts are arranged along the axis O and form the cylindrical part 30a of the main body component 30 as a whole.

[0043] The riveting portion 31 and the bending portion 33 are for mounting the main body fitting 30 to the insulator 50. The tool engaging portion 32 is the portion where tools such as wrenches are engaged when mounting the main body fitting 30 to the threaded hole of the internal combustion engine. The seat portion 34 is located between the tool engaging portion 32 and the main body 36. With the spark plug 1 installed in the internal combustion engine, an annular washer is placed on the seat portion 34. The main body 36 is located on the front end portion 51 side of the insulator 50. When the spark plug 1 is installed in the internal combustion engine, the thread shape 37 (i.e., thread teeth 37a and thread grooves 37b) formed on the outer periphery of the main body 36 (see reference) Figure 2 (etc.) and threadedly engaged with the threaded hole of the internal combustion engine.

[0044] Additionally, a grounding electrode 11 is provided at the front end of the main body component 30 (the side where the main stem 36 is located). The grounding electrode 11 is a rod-shaped member that penetrates the generally cylindrical main stem 36 and extends toward the center electrode 21 in a direction approximately orthogonal to the axis O. The grounding electrode 11 is inserted into the cylindrical portion 30a from the opening 40 provided in the main stem 36.

[0045] The grounding electrode 11 is formed, for example, using a Ni-based alloy or other metallic material as the base material. Examples of alloying elements added to the Ni-based alloy include Al (aluminum). The grounding electrode 11 may also contain at least one element selected from Mn (manganese), Cr (chromium), Al (aluminum), and Ti (titanium) as a component other than Ni. Furthermore, in addition to Ni-based alloys, metallic materials with precious metals such as Pt (platinum) and Ir (iridium) as the main component may also be used.

[0046] Figure 2 This shows a state where a grounding electrode 11 is installed relative to the opening 40 of the main component 30. (Example) Figure 2 As shown, the spark plug 1 involved in this embodiment is a so-called lateral discharge type spark plug, which is configured such that the front end face 11a of the ground electrode 11 faces the side of the center electrode 21.

[0047] In the spark plug 1 of this embodiment, a discharge gap G (see reference) is formed between the side portion of the center electrode 21 extending along the axis O and the front end face 11a of the ground electrode 11 extending toward the center electrode 21 in a direction substantially orthogonal to the axis O. Figure 2 ).

[0048] In addition, in this embodiment, the base material of the ground electrode 11 has a front end surface 11a that is opposite to the side of the center electrode 21. However, in other embodiments, a structure in which a precious metal end is provided on the front end surface of the base material of the ground electrode 11 may also be adopted.

[0049] (Structure of the opening in the main component)

[0050] Next, the detailed structure of the opening 40 of the cylindrical part 30a (specifically the main body 36) provided in the main body part 30 will be described. Figure 3 and Figure 4 The appearance of the spark plug 1 according to the first embodiment is shown. Figure 3 and Figure 4 The image shows the spark plug 1 in its state before the grounding electrode 11 is installed. Figure 3 This is a side view of the spark plug 1 with the opening 40 on one side. Figure 4 This is a perspective view of spark plug 1 showing the shape of the opening 40.

[0051] Figure 5 The structure of the cross-section of the main component 30 is shown. Figure 5 yes Figure 3 The diagram shows a cross-sectional view of the AA line portion. The AA line is orthogonal to the axis O and passes through a vertex of the thread tooth 37a, intersecting the edge of the opening 40.

[0052] like Figure 3 As shown, the opening 40 is provided on the front end side of the main body 36 of the main body accessory 30. More specifically, the opening 40 is formed at a position approximately the same as the front end of the center electrode 21 provided at the front end of the insulator 50 in the axial direction O. Thus, when the ground electrode 11 is installed relative to the opening 40, the front end face 11a of the ground electrode 11 is configured to face the side near the front end of the center electrode 21.

[0053] The opening 40 is sized to allow insertion of a rod-shaped electrode base material forming the grounding electrode 11. Typically, the diameter of the opening 40 is set to be larger than the thread width (the size between two adjacent thread teeth 37a, 37a in the axial direction) of the thread shape 37 provided on the surface of the main body 36. Therefore, the opening 40 is formed over the forming area of ​​two or more adjacent thread teeth 37a in the axial direction.

[0054] A tapered portion 41 is provided on the outer peripheral surface of the opening 40. This tapered portion 41 is inclined in a manner that gradually tapers from the outer peripheral surface of the cylindrical portion 30a toward the inner peripheral surface (i.e., in a manner that narrows the opening diameter of the opening 40). Such a tapered portion 41 is formed at least on the outer peripheral surface of the cylindrical portion 30a into which the electrode base material into which the ground electrode 11 is inserted. The opening 40 on the outer peripheral surface of the cylindrical portion 30a has such a shape that it reduces the possibility of the thread teeth 37a getting caught in the threaded hole of the internal combustion engine when the spark plug 1 is threaded into the threaded hole of the internal combustion engine.

[0055] Figure 5 This is a cross-sectional view of the main body 36 of the main body fitting 30 cut off at a position where it is orthogonal to the axis O and one vertex of the thread 37a intersects the edge of the opening 40. In such a cross-section of the main body fitting 30, the opening 40 has a tapered portion 41 that gradually tapers from the outer peripheral surface of the cylindrical portion 30a toward the inner peripheral surface.

[0056] The tapered portion 41 is provided at least in the forming region of the thread shape 37. In this embodiment, the tapered portion 41 extends from the forming region of the thread shape 37 to a position slightly deeper than the inner circumferential surface. That is, the tapered portion 41 is provided at a position slightly deeper than the depth of the groove in the thread shape 37. Figure 5 As shown, the inner cutting surface 42 of the opening 40 on the inner circumferential side of the region where the thread shape 37 is formed is not formed into a tapered shape, and the opening diameter of the opening 40 is constant. The opening diameter of the opening 40 in the region where the inner cutting surface 42 is formed is set according to the size of the electrode base material of the inserted ground electrode 11.

[0057] For comparison, the structure of the opening in the main component of a conventional spark plug will be explained here. Figure 10 The diagram shows the cross-sectional structure of a conventional spark plug body assembly 930. This figure illustrates the conventional spark plug body assembly 930 in a configuration equivalent to... Figure 3 This is a cross-sectional view showing the cut at the location of the AA line. An opening 940 for inserting the grounding electrode 11 is provided in the cylindrical portion 30a (specifically, the main body 36) of the main body fitting 930. Furthermore, the basic structure of the main body fitting 930, except for the opening 940, is the same as that of the main body fitting 30.

[0058] like Figure 10 As shown, in conventional spark plugs, the opening diameter of the opening 940 is approximately constant from the outer circumferential surface of the cylindrical portion 30a to the inner circumferential surface. That is, in conventional spark plugs, the opening 940 of the main body fitting 930 does not have a tapered portion 41, and the cutting surface 942 of the opening 940 is perpendicular to the central axis of the inner diameter of the main body fitting 930. If the opening 940 has this shape, when the spark plug is threaded into the threaded hole of the internal combustion engine, the thread teeth at the boundary between the opening 940 and the threaded portion become forward-leaning relative to the rotation direction of the thread (i.e., the direction of travel of the spark plug) (see reference). Figure 7 Therefore, when tightening or removing spark plugs from an internal combustion engine, the threads may bite into the engine's threaded holes.

[0059] In contrast, in the spark plug 1 according to this embodiment, a tapered portion 41 is provided in the opening 40 of the main body fitting 30. As a result, when the spark plug 1 is threaded into the threaded hole of the internal combustion engine, the possibility of the thread teeth 37a getting into the threaded hole of the internal combustion engine can be reduced.

[0060] Such a tapered portion 41 is preferably provided at least in the forming region of the thread shape 37 (i.e., from the thread tooth 37a to the thread groove 37b) in the depth direction of the opening 40. As a result, since the entire forming region of the thread shape 37 covering the outer peripheral surface of the main body 36 is tapered, the biting of the edge portion of the opening can be more reliably suppressed when the spark plug 1 is installed into and removed from the internal combustion engine.

[0061] In addition, such as Figure 5 As shown, the cone 41 is preferably provided on both sides of the opening 40 in the cross section of the opening 40 at the position where the apex of the thread 37a intersects with the edge of the opening 40. Thus, in both cases when installing or removing the spark plug 1 relative to the internal combustion engine (i.e., in...) Figure 6 In both cases (R1 and R2 shown), thread bite can be prevented.

[0062] Furthermore, in this embodiment, a tapered portion 41, as described above, is provided over approximately the entire area covering the edge of the opening 40. This makes machining the cutting surface with the tapered portion 41 easier when the opening 40 is formed by countersinking using a cutting tool.

[0063] Here, refer to Figures 6 to 8 The tilt angle of the cone 41 is explained. Figures 6 to 8 The cross-sections of the main body fitting 30, which have various different cross-sectional shapes for the openings, are schematically shown. Figures 6 to 8In the diagram, R1 represents the direction of thread travel when the spark plug 1 is tightened into the internal combustion engine, and R2 represents the direction of thread travel when the spark plug 1 is removed from the internal combustion engine.

[0064] Figure 6 This refers to the cross-section of the opening 40 of the spark plug 1 according to this embodiment (e.g., Figure 3 A schematic diagram of the shape of the cross-section of the AA line portion. Figure 6 Only the shape of the outer peripheral surface of the opening 40 is shown in the diagram. That is, in Figure 6 The inner cutting surface 42, which is located on the inner circumferential side of the cone 41, is omitted from the illustration.

[0065] exist Figure 6 In the spark plug 1 shown, the angle θ1 formed by the tangent T of the outer peripheral surface at the boundary position between the vertex of the thread tooth 37a on the outer peripheral surface of the cylindrical part 30a of the main body fitting 30 and the opening 40 and the cone part 41 of the opening 40 is 90 degrees or more.

[0066] Figure 7 This refers to the cross-section of the opening 940 of the conventional spark plug body fitting 930 (e.g., equivalent to...). Figure 3 A schematic diagram showing the shape of the cross-section at the location of line AA. (See reference...) Figure 10 As described above, the cutting surface 942 of the opening 940 of the main body part 930 is perpendicular to the inner diameter center axis of the main body part 930.

[0067] exist Figure 7 In the conventional spark plug shown, the angle θ2 formed by the tangent T of the outer peripheral surface at the boundary position between the vertex of the thread tooth 37a on the outer peripheral surface of the cylindrical portion 30a of the main body fitting 930 and the cutting surface 942 of the opening 940 is an acute angle (less than 90 degrees).

[0068] In this structure, the thread teeth at the boundary between the spark plug and the opening 940 are shaped to be forward-leaning relative to the direction of rotation of the thread (i.e., the spark plug's direction of travel R1 or R2). Therefore, when the spark plug is tightened into or removed from the internal combustion engine, the thread teeth may bite into the internal combustion engine's threaded hole.

[0069] Figure 8 This refers to the cross-section of the opening 840 of the spark plug body fitting 830, which is being compared (e.g., equivalent to...). Figure 3 A schematic diagram of the shape of the cross-section at the location of the AA line portion. Figure 8 The opening 840 shown has a tapered portion 841 that gradually tapers from the outer peripheral surface of the cylindrical portion 30a toward the inner peripheral surface. The angle of inclination of this tapered portion 841 relative to the tangent T is different from that of the tapered portion 41. Figure 8In the spark plug shown, the angle θ3 formed by the tangent T of the outer peripheral surface at the boundary position between the vertex of the thread tooth 37a on the outer peripheral surface of the cylindrical portion 30a of the main body fitting 830 and the opening portion 840 and the cone portion 841 of the opening portion 840 is an acute angle (less than 90 degrees). That is, θ3 < 90 degrees ≤ θ1.

[0070] In this structure, the thread teeth at the boundary between the opening 840 and the threaded portion are slightly inclined forward relative to the direction of rotation of the thread (i.e., the spark plug's direction of travel R1 or R2). Therefore, with Figure 7 Compared to existing spark plugs, the possibility of thread teeth biting in during thread rotation is reduced. However, when installing or removing spark plugs from an internal combustion engine, the thread teeth may still bite into the internal combustion engine's threaded holes.

[0071] As described above, in the spark plug 1 according to this embodiment, the angle θ1 formed by the tangent T of the outer peripheral surface of the main body fitting 30 and the cone 41 of the opening 40 is 90 degrees or more. Therefore, when the spark plug 1 is threaded into the threaded hole of the internal combustion engine, the thread teeth 37a are shaped to not tilt forward relative to the direction of thread travel. Thus, the possibility of the thread teeth 37a getting caught in the threaded hole of the internal combustion engine can be reduced when the spark plug 1 is tightened into or removed from the internal combustion engine.

[0072] Furthermore, by providing the tapered portion 41 as described above in the opening 40, interference between the electrode base material inserted into the opening 40 and the thread 37a can be reduced when installing the ground electrode 11 into the opening 40 of the main body fitting 30. Therefore, the insertion and fixing of the ground electrode during the manufacturing of the spark plug 1 can be performed more easily.

[0073] Furthermore, when forming the opening 40 in the main body component 30, conventional machining methods such as cutting and countersinking can be used. Then, a rod-shaped electrode base material, serving as the ground electrode 11, is inserted into and fixed to the formed opening 40. The ground electrode 11 is fixed to the main body component 30, for example, by pressing or welding. Thus, a ground electrode 11 extending from the cylindrical portion 30a of the main body component 30 in a direction intersecting the axis O is obtained. In the spark plug 1 manufacturing method, for manufacturing processes other than the forming step of the opening 40, the same manufacturing methods as conventional spark plug manufacturing methods can be applied.

[0074] In this embodiment, the cross-sectional shape of the opening 40 is described as an example when the main body 36 of the main body accessory 30 is cut along the thread 37a perpendicular to the axis O and intersecting with one thread 37a. Furthermore, in the spark plug 1 according to this embodiment, when the main body 36 of the main body accessory 30 is cut along the thread 37a in a manner intersecting the axis O, the same tapered portion 41 (inclined portion) may also be provided on the cut surface of the opening 40.

[0075] (Summary of the first implementation method)

[0076] As described above, the spark plug 1 includes: a main body fitting (fitting component) 30 having a cylindrical portion 30a; a center electrode 21 disposed within the cylindrical portion 30a; and a ground electrode 11 inserted into an opening 40 provided in the cylindrical portion 30a, forming a gap between its front end in its extending direction and the center electrode 21. The outer peripheral surface of the cylindrical portion 30a has a thread shape 37 (thread teeth 37a and thread grooves 37b). In a cross-section of the cylindrical portion 30a in a direction orthogonal to the axis O, at the position where the apex of the thread teeth 37a intersects the edge of the opening 40, the opening 40 has a tapered portion (inclined portion) 41 that gradually tapers from the outer peripheral surface of the cylindrical portion 30a toward the inner peripheral surface.

[0077] Furthermore, the inclination angle θ1 of the cone 41 is 90 degrees or more relative to the tangent T of the outer peripheral surface of the cylindrical portion 30a at the boundary position between the apex of the thread tooth (i.e., the thread shape 37) and the opening 40 (see reference). Figure 6 Therefore, when the spark plug 1 is threaded into the threaded hole of the internal combustion engine, the thread tooth 37a is shaped so as not to tilt forward relative to the direction of thread travel. Thus, the possibility of the thread tooth 37a getting into the threaded hole of the internal combustion engine can be reduced when the spark plug 1 is tightened into or removed from the internal combustion engine.

[0078] Furthermore, the angle between the tangent T and the inclined portion 41 (i.e., the inclination angle θ1 of the cone 41) is preferably greater than 90 degrees (i.e., it becomes an obtuse angle). According to this structure, the thread teeth at the boundary between the tangent T and the opening 40 become a shape that is further inclined backward relative to the direction of thread rotation, thus further reducing engagement during thread rotation. Furthermore, the angle between the tangent T and the inclined portion 41 (i.e., the inclination angle θ1 of the cone 41) is more preferably 110 degrees or more, and even more preferably 120 degrees or more.

[0079] [Second Implementation]

[0080] Next, the spark plug 1 according to the second embodiment will be described. In the first embodiment described above, a lateral discharge type spark plug was used as an example. The present invention can also be applied to spark plugs other than lateral discharge type. Therefore, in the second embodiment, a longitudinal discharge type spark plug will be used as an example for description.

[0081] Figure 9 The structure of a portion of the spark plug 1 according to the second embodiment is shown. Figure 9This is an enlarged side view showing the mounting portion of the center electrode 21 and the ground electrode 11 in the spark plug 1 according to this embodiment. Regarding the overall structure of the spark plug 1, the same structure as in the first embodiment can be applied.

[0082] like Figure 9 As shown, in the spark plug 1 of this embodiment, a discharge gap G is formed between the front end face 21a of the center electrode 21 extending along the axis O and the side near the front end of the ground electrode 11 extending toward the center electrode 21 in a direction substantially orthogonal to the axis O.

[0083] The grounding electrode 11 is a rod-shaped component that passes through the generally cylindrical main body 36 and extends toward the center electrode 21 in a direction approximately orthogonal to the axis O. The grounding electrode 11 is inserted into the cylindrical portion 30a from the opening 40 provided in the main body 36.

[0084] Similar to the first embodiment, a tapered portion 41 is provided on the outer peripheral surface of the opening 40. This tapered portion 41 is inclined in a manner that gradually tapers from the outer peripheral surface of the cylindrical portion 30a toward the inner peripheral surface (i.e., in a manner that narrows the opening diameter of the opening 40). Such a tapered portion 41 is formed at least on the outer peripheral surface of the cylindrical portion 30a into which the grounding electrode 11 is inserted (see reference). Figure 5 Similar to the first embodiment, the opening 40 may also have an inner cutting surface 42 on the inner circumferential side of the area where the thread shape 37 is formed, and the inner cutting surface 42 has a constant opening diameter throughout the cutting direction.

[0085] The opening 40 on the outer peripheral side of the cylindrical portion 30a has such a shape that when the spark plug 1 is threaded into the threaded hole of the internal combustion engine, the possibility of the thread teeth 37a getting into the threaded hole of the internal combustion engine can be reduced.

[0086] Furthermore, similar to the first embodiment, the angle θ1 formed by the tangent T of the outer peripheral surface at the boundary position between the apex of the thread tooth 37a on the outer peripheral surface of the cylindrical portion 30a of the main body fitting 30 and the cone portion 41 of the opening 40 is 90 degrees or more. Therefore, when the spark plug 1 is threaded into the threaded hole of the internal combustion engine, the thread tooth 37a is shaped to not tilt forward relative to the direction of thread travel. Thus, the possibility of the thread tooth 37a biting into the threaded hole of the internal combustion engine can be reduced when the spark plug 1 is tightened into or removed from the internal combustion engine.

[0087] It should be considered that the embodiments disclosed herein are illustrative in all respects and not restrictive. The scope of the invention is not limited to the foregoing description, but is indicated by the scope of the claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of the claims. Furthermore, structures obtained by combining the structures of the different embodiments described in this specification are also included within the scope of the invention.

[0088] For example, in the embodiment disclosed herein, the structure is an opening at the front end of the main component 30. However, in other embodiments, it may be a structure in which a cover member is provided on the front end side of the main component 30 to form a sub-chamber that covers the front end side of the center electrode 21 and the ground electrode 11.

[0089] Additionally, for example, in the embodiments disclosed herein, the cone 41 is a structure that is inclined in a straight line in cross-section, but in other embodiments, the cone 41 may also be a structure that is inclined in a curved shape in cross-section (i.e., a structure in which the inclined portion is curved).

[0090] Label Explanation

[0091] 1: Spark plugs

[0092] 11: Grounding electrode

[0093] 21: Central electrode

[0094] 30: Main components (accessory parts)

[0095] 30a: Cylindrical part

[0096] 37: Thread shape (thread teeth)

[0097] 37a: Thread tooth (the apex of the thread tooth)

[0098] 37b: Threaded groove

[0099] 40: Opening

[0100] 41: Conical part (sloping part)

[0101] 50: Insulator

[0102] G: Discharge gap (gap)

[0103] O: Axis

[0104] T: (Tangent line on the outer circumference of the cylindrical part)

Claims

1. A spark plug comprising: a fitting member having a cylindrical portion extending along an axis; a center electrode disposed within the cylindrical portion and extending along the axis; and a ground electrode inserted into an opening portion provided to the cylindrical portion and forming a gap between a front end portion thereof in an extending direction thereof and the center electrode, wherein a thread is provided to an outer peripheral surface of the cylindrical portion, wherein the opening portion has a tapered portion gradually tapered from the outer peripheral surface of the cylindrical portion toward an inner peripheral surface side in a cross section of the opening portion at a position where an apex of the thread and an edge of the opening portion intersect in a direction orthogonal to the axis, and wherein an angle formed by a tangent line of the outer peripheral surface at a boundary position between the apex of the thread and the opening portion and the tapered portion of the opening portion is 90 degrees or more.

2. The spark plug according to claim 1, wherein the tapered portion is provided at least from the apex of the thread to a groove of the thread.

3. The spark plug according to claim 1 or 2, wherein the tapered portion is provided to both sides of the opening portion in the cross section of the opening portion at the position where the apex of the thread and the edge of the opening portion intersect.

4. The spark plug according to any one of claims 1 to 3, wherein the tapered portion is provided to a region including two or more of the threads. ​ ​ ​ ​ ​ ​ ​ ​ ​

Images