spark plug

Abstract

One spark plug (100), with: a center electrode (20) extending in a direction of an axis (AX) and having a first discharge surface (20S); an insulating member (10) having an axial bore (12) extending in the direction of the axis (AX) and having a front end portion at which the center electrode (20) is arranged; a metal sleeve (2, 2B) having a cylindrical shape and arranged radially outside the insulating element (10); a ground electrode (30, 30B) having a second discharge surface (30S) opposite the first discharge surface (20S) in the direction of the axis (AX) and forming a gap (G) between the first discharge surface (20S) and the second discharge surface (30S), wherein the metal sleeve (2, 2B) and the ground electrode (30, 30B) are electrically and mechanically connected to each other; and a cover (90, 90B) connected to a front end portion (61) of the metal sleeve (2, 2B) and covering an opening of the metal sleeve (2, 2B) on the front end side for defining an additional combustion chamber (BS) in which the gap (G) is arranged, wherein the cover (90, 90B) has at least one through-hole (95a-95d) connecting the additional combustion chamber (BS) to the outside area, wherein a first line (L1), a special point (SP), a first tangent line (C1a-C1d), a second tangent line (C2a-C2d) and a second line (L2a-L2d) are defined in a section (CF1, CF2) containing a center of gravity of an opening of a special through-hole (95a-95d) of the at least one through-hole (95a-95d) on the side of the additional combustion chamber (BS) and the axis (AX), wherein the first line (L1) passes through a center point (MP) of a region which is perpendicular to the axis (AX) and in which the first discharge surface (20S) and the second discharge surface (30S) are present, and is parallel to the axis (AX), the special point (SP) is a midpoint of a line (LS) connecting an intersection point (XP1) between the first line (L1) and the first discharge surface (20S) with an intersection point (XP2) between the first line (L1) and the second discharge surface (30S), the first tangent line (C1a-C1d) is a half-line extending from the special point (SP) and is tangent to the center electrode (20) on the side of the special through-hole (95a-95d) of the first line (L1), the second tangent line (C2a-C2d) is a half-line extending from the special point (SP) and is tangent to the ground electrode (30, 30B) on the side of the special through-hole (95a-95d) of the first line (L1), the second line (L2a-L2d) is a half-line extending to the side of the special through-hole (95a-95d) of the first line (L1) and perpendicular to the axis (AX), a first angle (Aa-Ad) is formed by the second line (L2a-L2d) and the first tangent line (C1a-C1d), a second angle (Ba-Bd) is formed by the second line (L2a-L2d) and the second tangent line (C2a-C2d), where the second angle (Ba-Bd) is greater than the first angle (Aa-Ad), and at least one area of ​​the opening (95ao-95do) of the special through-bore (95a-95d) on the side of the additional combustion chamber (BS) lies within the second angle (Ba-Bd).

Description

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a spark plug.

[0002] Conventionally, a spark plug is used in an internal combustion engine, such as a gasoline engine or a gas engine. For example, Japanese Patent Application Laid-Open No. 2015-130302 (corresponding to US Patent Application Laid-Open No. US 2015-0194793 A1) discloses a spark plug with an auxiliary combustion chamber. In this spark plug, the auxiliary combustion chamber is formed in a cover attached to a front end portion of a metal shell. The cover includes a hole connecting the auxiliary combustion chamber to the outside. Fuel gas is introduced into the auxiliary combustion chamber through the hole of the cover. Further, a center electrode and a ground electrode are arranged in the auxiliary combustion chamber. A spark generated in a gap between the center electrode and the ground electrode ignites the fuel gas introduced into the auxiliary combustion chamber.The flame is then guided outwards through the hole in the cover, i.e. into the combustion chamber of the internal combustion engine, so that the fuel gas is burned in the combustion chamber.

[0003] Further relevant prior art is disclosed in the following document: WO 2011 / 008 115 A2. OVERVIEW OF THE INVENTION

[0004] However, the described prior art is not sufficiently designed with regard to the pressure loss and heat loss caused in the auxiliary combustion chamber. Therefore, the pressure loss and heat loss caused in the auxiliary combustion chamber are excessively increased, so that it may not be possible to achieve sufficient ignition behavior (e.g., combustion stability).

[0005] It is therefore an object of the present invention to provide a spark plug having an additional combustion chamber and designed to solve the aforementioned problems in order to improve the ignition behavior. To solve the above-described problem, a spark plug having the feature of claim 1 is provided. Further advantageous embodiments are defined in the subclaims.

[0006] According to one aspect of the present invention, a spark plug comprises: a center electrode extending in an axis direction and having a first discharge surface; an insulating member having an axial bore, extending in the axis direction and having a front end portion at which the center electrode is disposed; a metal shell having a cylindrical shape and disposed radially outside the insulating member; a ground electrode having a second discharge surface opposite to the first discharge surface in the axis direction and forming a gap between the first discharge surface and the second discharge surface, wherein the metal shell and the ground electrode are electrically and mechanically connected to each other; and a cover connected to a front end portion of the metal shell and covering an opening of the metal shell on the front end side,that an additional combustion chamber is delimited in which the gap is arranged, wherein the cover has at least one through-hole, wherein a first line, a specific point, a first tangent line, a second tangent line, and a second line are defined in a section that has a center of gravity of an opening of a specific through-hole of the at least one through-hole on the side of the additional combustion chamber and contains the first axis, wherein the first line passes through the center of a region that is perpendicular to the axis and in which the first discharge surface and the second discharge surface are present, and which is parallel to the axis, wherein the specific point is a center of a line that connects a center between the first line and the first discharge surface with an intersection point between the first line and the second discharge surface,wherein the first tangent line is a half-line extending from the specific point and being a tangent to the center electrode on the specific through-hole side of the first line, wherein the second tangent line is a half-line extending from the specific point and being a tangent to the ground electrode on the specific through-hole side of the first line, wherein the second line is a half-line extending to the specific through-hole side of the first line and being perpendicular to the axis, wherein a first angle is formed by the second line and the first tangent line, a second angle is formed by the second line and the second tangent line, and wherein the second angle is greater than the first angle,and wherein at least a portion of the opening of the special through-hole on the auxiliary combustion chamber side is arranged within a range or within the second angle. Therefore, it is possible to improve the ignition behavior of the spark plug.

[0007] A spark plug of the present invention includes: a center electrode (20) extending in the direction of an axis (AX) and including a first discharge surface (20S); an insulating member (10) having an axial bore (12), extending in the direction of the axis (AX) and having a front end portion at which the center electrode (20) is arranged; a metal shell (2, 2B) having a cylindrical shape and arranged radially outside the insulating member (10); a ground electrode (30, 30B) having a second discharge surface (30S) opposite the first discharge surface (20S) in the direction of the axis (AX) and forming a gap (G) between the first discharge surface (20S) and the second discharge surface (30S), wherein the metal shell (2, 2B) and the ground electrode (30, 30B) are electrically and mechanically connected to each other; and a cover (90, 90B) connected to a front end portion (61) of the metal sleeve (2,2B) and covers an opening of the metal sleeve (2, 2B) on the front end side for defining an additional combustion chamber (BS) in which the gap (G) is arranged, wherein the cover (90, 90B) has at least one through-hole (95a-95d) connecting the additional combustion chamber (BS) to the outside, wherein a first line (L1), a special point (SP), a first tangent line (C1a-C1d), a second tangent line (C2a-C2d) and a second line (L2a-L2d) are defined in a section (CF1, CF2) containing a center of gravity of an opening of a special through-hole (95a-95d) of the at least one through-hole (95a-95d) on the side of the additional combustion chamber (BS) and the axis AX, wherein the first line (L1) passes through a center point (MP) of a region perpendicular to the axis (AX), and in which the first discharge surface (20S) and the second discharge surface (30S) are present, and is parallel to the axis (AX),the special point (SP) is a midpoint of a line (LS) connecting an intersection point (XP1) between the first line (L1) and the first discharge surface (20S) with an intersection point (XP2) between the first line (L1) and the second discharge surface (30S), the first tangent line (C1a-C1d) is a half-line extending from the special point (SP) and being tangent to the center electrode (20) on the side of the special through-hole (95a-95d) of the first line (L1), the second tangent line (C2a-C2d) is a half-line extending from the special point (SP) and being tangent to the ground electrode (30, 30B) on the side of the special through-hole (95a-95d) of the first line (L1), the second line (L2a-L2d) is a half-line extending to the side of the special through hole (95a-95d) of the first line (L1) and is perpendicular to the axis (AX),wherein a first angle (Aa-Ad) is formed by the second line (L2a-L2d) and the first tangent line (C1a-C1d), a second angle (Ba-Bd) is formed by the second line (L2a-L2d) and the second tangent line (C2a-C2d), the second angle (Ba-Bd) is greater than the first angle (Aa-Ad), and at least a region of the opening (95ao-95do) of the special through-bore (95a-95d) on the side of the additional combustion chamber (BS) lies in a region of the second angle or within the angle (Ba-Bd).

[0008] With the above-described structure, the second angle is larger than the first angle. Therefore, the flame can be efficiently guided beyond the spark plug to the front end side. Furthermore, at least a portion of the opening of the specific through-hole on the auxiliary combustion chamber side is located in the second angle region. Therefore, it is possible to reduce the interruption of the flame, which is enlarged by the spark generated in the gap and discharged from the specific through-hole, by the ground electrode. Therefore, it is possible to reduce the heat loss and pressure loss caused by contact of the flame with the ground electrode. Therefore, it is possible to improve the ignition performance of the spark plug.

[0009] In an advantageous development of the spark plug of the present invention, the entire special through-bore (95a-95d) lies in the range of a sum of the first angle (Aa-Ad) and the second angle (Ba-Bd).

[0010] The structure described above makes it possible to reduce the interruption of the flame emitted from the special through-hole, which would otherwise be caused by the ground electrode.

[0011] In an advantageous development of the spark plug of the present invention, the entire special through-bore (95a-95d) lies in the region of the second angle (Ba-Bd).

[0012] The previously described design allows the flame to be guided even more efficiently beyond the spark plug toward the front end. This makes it possible to further improve the ignition behavior of the spark plug.

[0013] In an advantageous development of the spark plug of the present invention, the cover (90, 90B) contains a plurality of special through holes (95a-95d).

[0014] The previously described design allows the flame to be emitted from several special through-holes. This makes it possible to further improve the ignition behavior of the spark plug.

[0015] The present invention is applicable to various devices. For example, the present invention can be applied to a spark plug, an ignition device using the spark plug, an internal combustion engine using the spark plug, and the like. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a sectional view showing a spark plug 100 according to an embodiment of the present invention. Fig. 2 is a view showing a front end portion of the spark plug 100 when viewed along an axial line AX from a front end side toward a rear end BD. Fig. Figure 3 is a view showing a section CF1 along a surface defined by a dashed line AA of the Fig. 2, and wherein the section is obtained by cutting the front end portion of the spark plug 100. Fig. 4 is a view obtained by enlarging a rectangular area SA shown in Fig. 3 is shown. Fig. Figure 5 is a view showing a section CF2 taken along a surface defined by a dashed line BB of the Fig. 2, and wherein the section of the front end portion of the spark plug 100 is obtained. Fig. Fig. 6 is an explanatory view showing a variant of the embodiment. DETAILED DESCRIPTION OF THE INVENTION 1. First Embodiment: 1-1. [Structure of the Spark Plug]

[0016] Fig. Fig. 1 is a sectional view showing a spark plug 100 according to a first embodiment. One direction (up-and-down directions of the Fig. 1) parallel to an axis AX is called an axial direction. A radial direction of a circle for the axis AX on a surface that is perpendicular to the axis AX is called a radial direction only. A downward direction in Fig. 1 is referred to as a front-end direction FD. An upward direction in Fig. 1 is referred to as a rear end direction BD. A lower side in Fig. 1 is referred to as a front (tip) end face of the spark plug 100. An upper face in Fig. 1 is referred to as a rear end side of the spark plug 100.

[0017] The spark plug 100 is mounted in an internal combustion engine as described above. The spark plug 100 is used to ignite fuel gas in a combustion chamber of the internal combustion engine. The spark plug 100 includes an insulating member 10; a center electrode 20; a ground electrode 30; a terminal electrode 40; a metal shell 2 having an inner metal shell 50 and an outer metal shell 60; a resistance element 70; conductive sealing elements 80A and 80B; and a cover 90.

[0018] The insulating member 10 extends along the axis AX. The insulating member 10 is essentially a cylindrical member with an axial bore 12, which is a through-hole penetrating the insulating member 10. The insulating member 10 is made of, for example, a ceramic, such as alumina. The insulating member 10 includes a collar or protruding portion 19; a cylindrical rear end portion 18; a cylindrical front end portion 17; a decreasing outer diameter portion 15; and a long base portion 13.

[0019] The collar portion 19 is a portion of the insulating member 10 located substantially at a central position of the insulating member 10 in the axial direction. The rear end side cylindrical portion 18 is located on the rear end side of the collar portion 19. The rear end side cylindrical portion 18 has an outer diameter smaller than an outer diameter of the collar portion 19. The front end side cylindrical portion 17 is located on the front end side of the collar portion 19. The front end side cylindrical portion 17 has an outer diameter smaller than the outer diameter of the rear end side cylindrical portion 18. The long root portion 13 is located on the front end side of the front end side cylindrical portion 17. The long root portion 13 has an outer diameter smaller than the outer diameter of the front end side cylindrical portion.The diameter of the long root portion 13 becomes smaller (decreases) toward the front end side. The long root portion 13 includes a front end portion protruding beyond a front end surface of the inner metal shell 50 toward the front end side. The outer diameter decreasing portion 15 is formed between the long root portion 13 and the front end side cylinder portion 17. The outer diameter decreasing portion 15 has an outer diameter that becomes smaller (decreases) from the rear end side toward the front end side.

[0020] On an inner circumference side of the insulating member 10, the insulating member 10 includes a large inner diameter portion 12L located on a rear end side; a small inner diameter portion 12S located on the front end side of the large inner diameter portion 12L and having an inner diameter smaller than an inner diameter of the large inner diameter portion 12L; and a decreasing inner diameter portion 16. The decreasing inner diameter portion 16 is formed between the large inner diameter portion 12L and the small inner diameter portion 12S. The decreasing inner diameter portion 16 has inner diameters decreasing from the rear end side toward the front end side.In this embodiment, the inner diameter decreasing portion 16 is arranged at an axial position corresponding to the front end portion of the cylinder portion of the front end side 17.

[0021] The inner metal shell 50 is made of a conductive metal (e.g., low-carbon steel). The inner metal shell 50 has a cylindrical shape. The inner metal shell 50 includes a through-hole 59 extending through the inner metal shell 50 in the axial direction AX. The inner metal shell 50 is disposed radially outside the insulating member 10. That is, the insulating member 10 is inserted into and held in the through-hole 59 of the inner metal shell 50. A front end of the insulating member 10 protrudes beyond the front end of the inner metal shell 50 toward the front end side. A rear end of the insulating member 10 protrudes beyond the rear end of the inner metal shell 50 toward the rear end side.

[0022] The inner metal sleeve 50 includes a tool engagement portion 51 having a hexagonal cylindrical shape and to which a spark plug wrench is engaged; a fastening screw portion 52 on which an external screw for fastening the inner metal sleeve 50 to the outer metal sleeve 60 is formed; and a support portion 54 having a collar shape (protruding shape) formed between the tool engagement portion 51 and the fastening screw portion 52. A nominal diameter of the fastening screw portion 52 is, for example, M8 to M14.

[0023] An inner seal 5A is inserted and secured between the fastening screw portion 52 and the support portion 54 of the inner metal sleeve 50. The inner seal 5A is made of metal. The inner seal 5A has an annular structure. The inner seal 5A seals a gap between a support portion 64 (described below) of the outer metal sleeve 60 and the support portion 54 of the inner metal sleeve 50.

[0024] Furthermore, the inner metal shell 50 includes a crimping portion 53 having a thin shape and provided on the rear end side of the tool engagement portion 51; and a compression deformation portion 58 having a thin shape and provided between the bearing portion 54 and the tool engagement portion 51. Annular line seals 6 and 7 are arranged in an annular region formed between an inner peripheral surface of the inner metal shell 50 from the tool engagement portion 51 to the crimping portion 53 and an outer periphery of the cylindrical portion of the rear end side 18 of the insulating member 10. Powder of talc 9 is filled between the line seals 6 and 7 in the above-described region. A rear end of the crimping portion 53 is bent in a radially inward direction and fixed to the outer peripheral surface of the insulating member 10.During the manufacturing process, the crimping portion 53 fixed to the outer peripheral surface of the insulating member 10 is crimped toward the front end side, so that the compression deformation portion 58 of the inner metal shell 50 is compressed and deformed. The insulating member 10 is crimped inside the inner metal shell 58 by the line seals 6 and 7 and the talc 9 toward the front end side by the compression and deformation of the compression deformation portion 58. The outer diameter decreasing portion 15 (the insulating member side stepped portion) of the insulating member 10 is crimped via an annular plate seal 8 by a stepped portion 56 (metal shell side stepped portion) formed on the inner periphery of the inner metal shell 50 at the position of the fastening screw portion 52.Thereby, the plate seal 8 prevents leakage of the gas within the combustion chamber of the internal combustion engine from the gap between the inner metal sleeve 50 and the insulating element 10 to the outside.

[0025] The outer metal sleeve 60 has a cylindrical shape. The outer metal sleeve 60 is made of a conductive metal identical to that of the inner metal sleeve 50. The outer metal sleeve 50 includes a through hole 69 extending through the outer metal sleeve 50 along the axis AX. The outer metal sleeve 60 is disposed radially outside the inner metal sleeve 50 on the front end side of the support portion 54 of the inner metal sleeve 50. The outer metal sleeve 60 includes an inner screw 66 formed in an inner peripheral surface of the outer metal sleeve 60. The outer screw formed on the fastening screw portion 52 of the inner metal sleeve 50 is engaged with the inner screw 66. Thereby, a part of the inner metal sleeve 50 disposed on the front end side of the support portion 54 is inserted into the through hole 69 of the outer metal sleeve 60 and held therein.

[0026] The outer metal shell 60 includes a fastening screw portion 62; a support portion 64 disposed on the rear end side of the fastening screw portion 62. A nominal diameter of the fastening screw portion 62 is, for example, M10 to M18. The fastening screw portion 62 includes an outer screw formed on an outer peripheral surface of the fastening screw portion 62 and used to fasten the spark plug 100 to an engine head (not shown) of the internal combustion engine.

[0027] An outer seal 5B is inserted and secured between the fastening screw portion 62 and the support portion 64 of the outer metal sleeve 60. The outer seal 5B is made of metal. The outer seal 5B has a ring shape. The outer seal 5B seals a gap between the spark plug 100 and the internal combustion engine (the engine head) when the spark plug 100 is attached to the internal combustion engine.

[0028] A cover 90 is formed on the front end portion 61 of the outer metal shell 60. The cover 90 covers openings 60o and 50o of the outer metal shell 60 and the inner metal shell 50, which are located on the front end side. The structure of the cover 90 will be described later. The cover 90 defines and forms a supplementary combustion region BS in which a gap G (described later) is disposed.

[0029] The cover 90 is made of a metal with high corrosion resistance and high thermal resistance, for example, nickel (Ni) or a nickel-based alloy (e.g., NCF600, NCF601), tungsten. In this embodiment, the outer metal sleeve 60 is made of the Ni alloy. The cover 90 is formed as a unit with the outer metal sleeve 60. Alternatively, the cover 90 may be made of a member separate from the outer metal sleeve 60. The cover 90 is connected to the front end of the outer metal sleeve 60 by welding.

[0030] The center electrode 20 is a rod-shaped member extending along the axis AX. The center electrode 20 is made of a metal having high corrosion resistance and high thermal resistance, such as nickel (Ni) or a nickel-based alloy (e.g., NCF600, NCF601). The center electrode 20 has a two-layer structure with a base metal made of Ni or a Ni alloy and a core portion embedded in the base metal. In this case, the core portion is made of copper with a thermal conductivity higher than that of the base metal and higher than that of a copper-based alloy. The center electrode is held at a portion on the front end side of the inside of the axial bore 12. That is, the rear end side of the center electrode 20 is disposed within the axial bore 12.A surface of a leg portion 25 on the front end side is a first discharge surface 20S. A gap G is formed between the first discharge surface 20S and a second discharge surface 30S of the ground electrode 30, which will be described later.

[0031] As in Fig. 1, the center electrode 20 includes a flange portion 24 provided at a predetermined axial position; a head portion 23 (electrode head portion) located on the rear end side of the flange portion 24; and the foot portion 25 (electrode foot portion) located on the front end side of the flange portion 24. The flange portion 24 is supported from the front end side by the inner diameter decreasing portion 16 of the insulating member 10. That is, the center electrode 20 is supported on the inner diameter decreasing portion 16. In this way, the rear end side of the center electrode 20 is located within the axial bore 12 (the small inner diameter portion 12S).

[0032] The terminal electrode 40 is a rod-shaped member extending in the axial direction. The terminal electrode 40 is inserted into the axial bore 12 of the insulating member 10 from the rear end side. The terminal electrode 40 is arranged in the axial bore 12 on the rear end side of the center electrode 20. The terminal electrode 40 is made of a conductive metal (e.g., a low-carbon metal). For example, Ni plating is formed on the surface of the terminal electrode 40 for corrosion protection.

[0033] The terminal electrode 40 includes a flange portion 42 (terminal jaw portion) formed at a predetermined axial position; a cover attachment portion 41 located on the rear end side of the flange portion 42; and a leg portion 43 (terminal leg portion) located on the front end side of the flange portion 42. The cover attachment portion 41 of the terminal electrode 40 is exposed with respect to the insulating member 10 up to the rear end side. The leg portion 43 of the terminal electrode 40 is inserted into the axial bore 12 of the insulating member 10. A connector cover is attached to the cover attachment portion 41. The connector cover is a high-voltage cable (not shown). High voltage is applied to the cover attachment portion 41 to generate electric discharge.

[0034] The resistance element 70 is arranged in the axial bore 12 of the insulating member 10 between the front end of the terminal electrode 40 and the rear end of the center electrode 20. The resistance element 70 has a resistance value of, for example, 1 kΩ or greater (for example, 5 kΩ). The resistance element 70 functions to reduce high-frequency noise during spark generation. The resistance element 70 is made of, for example, a composite material comprising glass particles as the main components, non-glass ceramic particles, and the conductive material.

[0035] A conductive sealing element 80A is embedded in a gap between the resistance element 70 and the center electrode 20 in the axial bore 12. A conductive sealing element 80B is embedded in a gap between the resistance element 70 and the terminal electrode 40. That is, the sealing element 80A abuts the center electrode 20 and the resistance element 70. The sealing element 80A separates the center electrode 20 from the resistance element 70. The sealing element 80B abuts the resistance element 70 and the terminal electrode 40. The sealing element 80B separates the resistance element 70 from the terminal electrode 40. In this way, the sealing elements 80A and 80B electrically and mechanically connect the center electrode 20 and the terminal electrode 40 via the resistance element 70. The sealing elements 80A and 80B are made of conductive material, for example, a composition (composite material) containing glass particles, such as B2O3-SiO2 and metal particles (Cu, Fe, etc.).) are manufactured.

[0036] The ground electrode 30 is a rod-shaped element with a rectangular cross section, as shown in Fig. 1. The ground electrode 30 includes a connection end portion 32 located on a first end side; and a free end portion 31 located on a second end side opposite to the first end side. The connection end portion 32 is connected to the front end portion 50s of the inner metal shell 50 by, for example, resistance welding. Thereby, the metal shell 2 (the inner metal shell 50 and the outer metal shell 60) and the ground electrode 30 are electrically and mechanically connected to each other. A portion near the connection terminal 32 of the ground electrode 30 extends in the direction of the axis AX. A portion near the free end portion 31 extends perpendicular to the direction of the axis AX. The rod-shaped ground electrode 30 is bent at a central portion by substantially 90 degrees.

[0037] The ground electrode 30 is made of a metal having high corrosion resistance and high thermal resistance, such as nickel (Ni) or a nickel-based alloy (e.g., NCF600, NCF601). Similar to the center electrode 20, the ground electrode 30 may be of a two-layer structure having a base material and a core portion made of a metal (e.g., copper) having a higher thermal conductivity than that of the base metal, and embedded in the base metal. A side surface facing the rear end side of the free end portion 31 is the second discharge surface 30S. The gap G is formed between the second discharge surface 30S and the first discharge surface 20S of the center electrode 20. The first discharge surface 20S and the second discharge surface 30S are opposed to each other in the axis AX direction. The gap G is an ignition gap in which the electric discharge is generated.

[0038] Fig. Fig. 2 is a view showing a portion near the spark plug 100 when viewed in the direction of the axis AX from the front end side to the rear end BD. The cover 90 includes a plurality of through holes 95a to 95d (in the example of Fig. 2, four through holes) that connect the auxiliary combustion chamber BS with the outside. The four through holes 95a to 95d are arranged at intervals in the circumferential direction. Fig. 2 shows centers of gravity CPa to CPd of openings 95ao to 95do of the four through holes 95a to 95d on the side of the additional combustion chamber BS.

[0039] A first direction D1 is in Fig. 2 is defined by a direction in which the free end portion 31 of the ground electrode 30 extends to pass through the axis AX. Furthermore, a second direction D1 is defined in Fig. 2 through one direction (in Fig. 2, the upward direction) which is perpendicular to the first direction D1. The four through holes 95a to 95d are arranged at positions in the circumferential direction such that 45 degrees are formed with respect to the first direction D1 and the second direction D2. Therefore, the four through holes 95a to 95d are in Fig. 1 not shown.

[0040] Fig. 3 shows a section CF1 along a dashed line AA of the Fig. 2, wherein the section is obtained by cutting a region near the front end of the spark plug 100. The section indicated by the dashed line AA of the Fig. 2 is a surface including the axis AX, the center of gravity CPa of the opening 95ao of the through hole 95a on the side of the auxiliary combustion chamber BS, and the center of gravity CPb of the opening 95bo of the through hole 95b on the side of the auxiliary combustion chamber BS.

[0041] As in Fig. 3, the cover 90 is a hollow member substantially in the shape of a hemisphere. Therefore, the auxiliary combustion chamber BS has a substantially hemisphere shape. The front end side portion of the long root portion 13, the ground electrode 30, and the front end side portion of the center electrode 20 are disposed within the auxiliary combustion chamber BS. The gap G is disposed in the auxiliary combustion chamber BS.

[0042] In this embodiment, as in Fig. 2 and Fig. 3, the through-hole is not formed at a position intersecting the axis AX in the cover 90. The axial positions of the four through-holes 95a to 95d are substantially identical to the axial positions where the free end portion 31 of the ground electrode 30 and the gap G are located.

[0043] Fig. 4 is a view obtained by enlarging a rectangular area SA shown in Fig. 3. A lateral region in which the first discharge surface 20S of the center electrode 20 and the second discharge surface 30S of the ground electrode 30 are arranged in the section CF as shown in Fig. 4 is referred to as a discharge region GR. The lateral region in Fig. 4 is a region perpendicular to the axis AX. A region centerline L1 is defined as a line passing through a center point MP of the discharge region GR and oriented parallel to the axis AX. In this embodiment, the region centerline L1 is aligned with the axis AX in the section CF1, as shown in Fig. 1. A specific point SP is defined as a midpoint of a line LS connecting an intersection point XP1 between the area center line L1 and the first discharge surface CF1 with an intersection point XP2 between the area center line L1 and the second discharge surface 30S.

[0044] As the position of the through hole 95a, half-lines indicated by dashed lines in Fig. 3 and Fig. 4. That is, a tangent line on the side of the central electrode C1a, a tangent line on the side of the ground electrode C2a and a gap center line L2a are defined as shown in Fig. 3 and Fig. 4. The tangent line on the side of the center electrode C1a is a half-line extending from the specific point SP and having a tangent to the center electrode 20 on the side of the through-hole 95a (the right side of the Fig. 3 and Fig. 4) of the area center line L1. The tangent line on the ground electrode C2a side is a half-line extending from the special point SP and forming a tangent to the ground electrode 30 on the through-hole 95a side (the right side of the Fig. 3 and Fig. 4) of the area center line L1. The gap center line L2a is a half-line extending from the special point SP toward the through-hole 95a side (the right side of the Fig. 3 and Fig. 4) and which is perpendicular to the axis AX. In Fig. 4, a point CP1a is a contact point between the tangent line on the side of the center electrode C1a and the center electrode 20. A point CP2a is a contact point between the tangent line on the side of the ground electrode C2a and the ground electrode 30.

[0045] As in Fig. 3, a first angle Aa is formed by the tangent line on the center electrode C1a side and the gap center line L2a in the section CF1. A second angle Ba is formed by the tangent line on the ground electrode C2a side and the gap center line L2a in the section CF1. The second angle Ba is larger than the first angle Aa. The opening 95ao of the through hole 95a on the auxiliary combustion chamber BS side is in the range of the second angle Ba. Furthermore, the entire through hole 95a is arranged in the range of the second angle Ba in the section CF1.

[0046] Similar to the position of the through hole 95b, three half-lines are indicated by solid lines in Fig. 3 and Fig. 4, wherein, in particular, a tangent line on the side of the center electrode C1b, a tangent line on the side of the ground electrode C2b, and a gap center line L2b are defined. The tangent line on the side of the center electrode C1b is a half-line extending from the specific point SP and having a tangent to the center electrode 20 on the side of the through-hole 95b (the left side of the Fig. 3 and Fig. 4) of the area center line L1. The tangent line on the ground electrode C2b side is a half-line extending from the special point SP and forming a tangent to the ground electrode 30 on the through-hole 95b side (the left side of the Fig. 3 and Fig. 4) the area centerline L1. The gap centerline L2b is a half-line extending from the special point SP to the through-hole 95b and oriented perpendicular to the axis AX. In Fig. 4, a point CP1b is a contact point between the tangent line on the side of the center electrode C1b and the center electrode 20. A point CP2 is a contact point between the tangent line on the side of the ground electrode C2b and the ground electrode 30.

[0047] As in Fig. 3, a first angle Ab is formed by the tangent line on the center electrode C1b side and the gap center line L2b in the section CF1. A second angle Bb is formed by the tangent line on the ground electrode C2b side and the gap center line L2b in the section CF1. The second angle Bb is larger than the first angle Ab. The opening 95bo of the through hole 95b on the auxiliary combustion chamber BS side lies within the range of the second angle Bb. Further, the entire through hole 95b lies within the range of the second angle Bb in the section CF1.

[0048] Fig. 5 shows a section along a dashed line BB of the Fig. 2, which is obtained by cutting an area near the front end of the spark plug 100. The area indicated by the dashed line BB of the Fig. 2 is a surface including the axis AX, the center of gravity CPc of the opening 95co of the through hole 95c on the auxiliary combustion chamber BS side; and the center of gravity CPd of the opening 95do of the through hole 95d on the auxiliary combustion chamber BS side.

[0049] As in Fig. 5, the section CF2 satisfies a relationship identical to that in the section CF1 ( Fig. 3). In particular, as the position of the through hole 95c, three half-lines, which are indicated by dashed lines in Fig. 5, that is, a tangent line on the side of the center electrode C1c, a tangent line on the side of the ground electrode C2c, and a gap center line L2c. The tangent line on the side of the center electrode C1c is a half-line extending from a specific point SP2 and having a tangent to the center electrode 20 on the side of the through-hole 95c (the right side in Fig. 5) of the area center line L12. The tangent line on the ground electrode C2c side is a half-line extending from the special point SP2 and forming a tangent to the ground electrode 30 on the through-hole 95c side (in Fig. 5 the right side) of the area centerline L12. The gap centerline L2c is a half-line extending from the special point SP2 to the through hole 95c (in Fig. 5 the right side) and which is oriented perpendicular to the axis AX. In this case, the area centerline L12 and the special point SP2 in the section CF2 are similar to the special point SP and the area centerline L1 in the section CF1 ( Fig. 4). That is, the region center line L12 is a line passing through a center point of a lateral region in which the first discharge surface 20S and the second discharge surface 30S are present in the section CF2 and which is parallel to the axis AX. In Fig. 5, the area centerline L12 and the axis AX are aligned with each other. The special point SP2 is a midpoint of a line connecting an intersection point between the area centerline L12 and the first discharge surface 20S with an intersection point between the area centerline L12 and the second discharge surface 30S.

[0050] As in Fig. 5, a first angle Ac is formed by the center electrode C1c side tangent line and the gap center line L2c in the section CF2. A second angle Bc is formed by the ground electrode C2c side tangent line and the gap center line L2c in the section CF2. The second angle Bc is larger than the first angle Ac. The opening 95co of the auxiliary combustion chamber BS side through-hole 95c lies in the range of the second angle Bc. Furthermore, the entire through-hole 95c lies in the range of the second angle Bc in the section CF.

[0051] Similar to the position of the through hole 95d, three half-lines, which are indicated by solid lines in Fig. 5, specifically, a tangent line on the side of the center electrode C1d, a tangent line on the side of the ground electrode C2d, and a gap center line L2d. The tangent line on the side of the center electrode C1d is a half-line extending from the specific point SP2 and having a tangent to the center electrode 20 on the side of the through-hole 95d (in Fig. 5 the left side) of the area center line L12. The tangent line on the ground electrode C2d side is a half-line extending from the special point SP2 and is tangent to the ground electrode 30 on the through-hole 95d side (in Fig. 5 (the left side) of the area centerline L12. The gap centerline L2d is a half-line extending from the specific point SP2 toward the through-hole 95d and oriented perpendicular to the axis AX.

[0052] As in Fig. 5, a first angle Ad is formed in the section CF2 by the tangent line on the center electrode C1d side and the gap center line L2d. A second angle Bd is formed in the section CF2 by the tangent line on the ground electrode C2d side and the gap center line L2d. The second angle Bd is larger than the first angle Ad. The opening 95d of the through hole 95d on the auxiliary combustion chamber BS side lies within the range of the second angle Bd. Furthermore, the entire through hole 95d lies within the range of the second angle Bd in the section CF2.

[0053] The above-described spark plug 100 according to the embodiment operates as follows. The spark plug 100 is mounted and used in an internal combustion engine, such as a gasoline engine. An ignition device (for example, a full-transistor ignition device) with a predetermined power source applies the voltage between the ground electrode 30 and the center electrode 20 of the spark plug 100. This generates an ignition discharge in the gap G between the ground electrode 30 and the center electrode 20. The fuel gas in the combustion chamber of the internal combustion engine flows into the auxiliary combustion chamber BS through the through-holes 95a to 95d of the cover 90. The fuel gas is ignited by the spark generated in the auxiliary combustion chamber BS. The flame generated by the combustion of the ignited fuel gas is guided to the outside (to the combustion chamber of the internal combustion engine) through the through-holes 95a to 95d of the cover 90.The fuel gas in the combustion chamber of the internal combustion engine is ignited by the emitted flame. Consequently, it is possible to burn all the fuel gas in the combustion chamber even in an internal combustion engine with a large-volume combustion chamber.

[0054] In the above-described spark plug 100 according to the embodiment, the second angle Ba is larger than the first angle Aa in the section CF1 containing the center of gravity CPa of the opening 95ao of the through-hole 95a and the axis AX. Furthermore, the through-hole 95a and the opening 95ao are in the range of the second angle Ba (see Fig. 3). Therefore, the flame in the auxiliary combustion chamber BS can be efficiently guided through the opening 95ao of the through-hole 95a beyond the spark plug 100 toward the front end side. Furthermore, the opening 95ao of the through-hole 95a is arranged in the range of the second angle Ba. This makes it possible to suppress the interruption of the flame, which is enlarged from the spark generated in the gap G and is given from the through-hole 95a through the ground electrode 30. Therefore, it is possible to reduce the heat loss and pressure loss caused by the contact of the flame with the ground electrode 30. Therefore, it is possible to improve the ignition performance.

[0055] Furthermore, in the spark plug 100 according to the embodiment, the entire through-hole 95a is located in the range of the sum of the first angle Aa and the second angle Ba in the section CF1. That is, in the section CF1, the rear end of the through-hole 95a is located on the front end side of the tangent line on the center electrode C1a side. The front end of the through-hole 95a is located on the rear end side of the tangent line on the ground electrode C2a side (see Fig. 3). Therefore, it is possible to suppress the interruption of the flame emitted from the through hole 95a by the ground electrode 30. Therefore, it is possible to further improve the ignition performance of the spark plug 100.

[0056] Furthermore, in the spark plug 100 according to the embodiment, the entire through-hole 95a in the section CF1 is located within the range of the second angle Ba. That is, in the section CF1, the rear end of the through-hole 95a is located on the front end side of the gap center line L2a. The front end of the through-hole 95a is located on the rear end side of the tangent line on the ground electrode C2a side (see Fig. 3). Therefore, the flame within the auxiliary combustion chamber BS can be guided even more easily toward the front end side via the through hole 95a beyond the spark plug 100. Therefore, it is possible to further improve the ignition performance of the spark plug 100.

[0057] Furthermore, in the spark plug 100 according to the embodiment, the other through holes 95b to 95d satisfy the requirements identical to those of the through hole 95a. That is, in the section CF1, the second angle Bb is larger than the first angle Ab. The opening 95bo of the through hole 95b is in the range of the second angle Bb (see Fig. 3). Furthermore, in the section CF2, the second angles Bc and Bd are correspondingly larger than the respective first angles Ac and Ad. The openings 95co and 95do of the through holes 95c and 95d are correspondingly in the ranges of the respective second angles Bc and Bd (see Fig. 5). Therefore, the flame inside the auxiliary combustion chamber BS can be efficiently guided beyond the spark plug 100 toward the front end side via the plurality of through holes 95a to 95d. Therefore, it is possible to reduce the heat loss and pressure loss caused by the contact of the flame passing through the plurality of through holes 95a to 95d with the ground electrode 30. Therefore, it is possible to improve the ignition performance of the spark plug 100.

[0058] Furthermore, in sections CF1 and CF2, the entire through holes 95b to 95d are arranged at the sum of the first angles Ab, Ac, and Ad and the second angles Bb, Bc, and Bd, respectively. Therefore, it is possible to suppress the interruption of the flame emitted from the through holes 95b, 95c, and 95d by the ground electrode 30.

[0059] Furthermore, in sections CF1 and CF2, the entire through holes 95b, 95c, and 95d are arranged in the ranges of the respective second angles Bb, Bc, and Bd, respectively. Therefore, the flame in the auxiliary combustion chamber BS can be guided more efficiently through the through holes 95b, 95c, and 95d beyond the spark plug 100 toward the front end side.

[0060] As apparent from the foregoing explanations, the center electrode side tangent lines C1a to C1d according to the embodiment are examples of a first tangent line. The ground electrode side tangent lines C2a to C2d are examples of a second tangent line. The area center lines L1 and L12 are examples of a first line. The gap center lines L2a to L2d are examples of a second line. 2. Variants

[0061] (1) In the above-described embodiment, the entire through-hole 95a is arranged within the range of the second angle Ba. Instead, a part of the through-hole 95a may be arranged outside the range of the second angle Ba. For example, the front end of the through-hole 95a may be arranged on the front end side of the tangent line on the ground electrode C2a side. The rear end of the through-hole 95a may be arranged on the rear end side of the tangent line on the center electrode C1a side. However, it is preferable that at least a portion of the opening 95ao of the through-hole 95a be within the range of the second angle Ba. This makes it possible to suppress the interruption of the flame emitted from the through-hole 95a due to the ground electrode 30. This also applies to the other through-holes 95b to 95d.

[0062] (2) The cover 90 may have additional through holes in addition to the through holes 95a to 95d. For example, in sections CF1 and CF2, the cover 90 may have the through hole whose entire structure lies outside the second angles Ba to Bd. In particular, the cover 90 may have a through hole that is open along the axis AX.

[0063] (3) In the cover 90 of the above-described embodiment, the plurality of through-holes 95a to 95d have different circumferential positions, the same axial position, the same radial position, the same shape, and the same size. Instead, all or some of the plurality of through-holes 95a to 95d may have a different axial position, a different radial position, a different shape, and / or a different size.

[0064] (4) The detailed structure of the spark plug 100 according to the embodiment is only an example. The present invention is not limited thereto. Fig. 6 is an explanatory view showing a variant. Fig. Figure 6 shows a region corresponding to the section CF2 according to the first embodiment of the Fig. 1 corresponds.

[0065] In this variant, a metal shell 2B is not divided into two elements. The metal shell 2B is formed by a single element. Further, in this variant, a cover 90B is fixed to a front end surface of the metal shell 2B by welding. Furthermore, in this variant, a ground electrode 30B is a cylindrical rod extending in the direction of the axis AX. A surface of the ground electrode 30B on the rear end side is a second discharge surface 30S. A surface of the ground electrode 30B on the front end side is connected to an inner surface of the cover 90B by welding. Thereby, the ground electrode 30B is electrically connected to the metal shell 2B via the cover 90B. The other structures of the spark plug in Fig. 6 are identical to those of the spark plug 100 according to the first embodiment.

[0066] In the embodiment, materials, shapes, sizes, and the like for the center electrode 20, the terminal electrode 40, the ground electrode 30, etc. can be varied. For example, in the above-described embodiment, the center electrode 20 and the ground electrode 30 are each made of one material. Instead, the center electrode may include a center electrode main body and a center electrode tip welded to a front end of the center electrode main body and having a discharge surface. Furthermore, the ground electrode 30 may include a ground electrode main body and a ground electrode tip welded to a free end portion of the ground electrode main body and having a discharge surface.The center electrode tip and the ground electrode tip are made of materials (for example, a noble metal such as iridium (Ir), platinum (Pt), and tungsten (W), and an alloy containing at least one of these metals), which results in resistance to electric discharge higher than that of the electrode main body (for example, Ni alloy).

[0067] Although the invention has been described above with reference to certain embodiments of the invention, the invention is not limited to the above-described embodiments. Modifications and variations of the above-described embodiments will become apparent to those skilled in the art in light of the above teachings. The scope of the invention is defined with reference to the following claims.

Claims

[1] A spark plug (100), with: a center electrode (20) extending in a direction of an axis (AX) and having a first discharge surface (20S); an insulating member (10) having an axial bore (12) extending in the direction of the axis (AX) and having a front end portion at which the center electrode (20) is arranged; a metal sleeve (2, 2B) having a cylindrical shape and arranged radially outside the insulating element (10); a ground electrode (30, 30B) having a second discharge surface (30S) opposite the first discharge surface (20S) in the direction of the axis (AX) and forming a gap (G) between the first discharge surface (20S) and the second discharge surface (30S), wherein the metal sleeve (2, 2B) and the ground electrode (30, 30B) are electrically and mechanically connected to each other; and a cover (90, 90B) connected to a front end portion (61) of the metal sleeve (2, 2B) and covering an opening of the metal sleeve (2, 2B) on the front end side for defining an additional combustion chamber (BS) in which the gap (G) is arranged, wherein the cover (90, 90B) has at least one through-hole (95a-95d) connecting the additional combustion chamber (BS) to the outside area, wherein a first line (L1), a special point (SP), a first tangent line (C1a-C1d), a second tangent line (C2a-C2d) and a second line (L2a-L2d) are defined in a section (CF1, CF2) containing a center of gravity of an opening of a special through-hole (95a-95d) of the at least one through-hole (95a-95d) on the side of the additional combustion chamber (BS) and the axis (AX), wherein the first line (L1) passes through a center point (MP) of a region which is perpendicular to the axis (AX) and in which the first discharge surface (20S) and the second discharge surface (30S) are present, and is parallel to the axis (AX), the special point (SP) is a midpoint of a line (LS) connecting an intersection point (XP1) between the first line (L1) and the first discharge surface (20S) with an intersection point (XP2) between the first line (L1) and the second discharge surface (30S), the first tangent line (C1a-C1d) is a half-line extending from the special point (SP) and is tangent to the center electrode (20) on the side of the special through-hole (95a-95d) of the first line (L1), the second tangent line (C2a-C2d) is a half-line extending from the special point (SP) and is tangent to the ground electrode (30, 30B) on the side of the special through-hole (95a-95d) of the first line (L1), the second line (L2a-L2d) is a half-line extending to the side of the special through-hole (95a-95d) of the first line (L1) and perpendicular to the axis (AX), a first angle (Aa-Ad) is formed by the second line (L2a-L2d) and the first tangent line (C1a-C1d), a second angle (Ba-Bd) is formed by the second line (L2a-L2d) and the second tangent line (C2a-C2d), where the second angle (Ba-Bd) is greater than the first angle (Aa-Ad), and at least one area of ​​the opening (95ao-95do) of the special through-bore (95a-95d) on the side of the additional combustion chamber (BS) lies within the second angle (Ba-Bd). [2] The spark plug according to claim 1, wherein in the section (CF1, CF2), the entire special through hole (95a-95d) is arranged in a range of a sum of the first angle (Aa-Ad) and the second angle (Ba-Bd). [3] The spark plug according to claim 2, wherein in the section (CF1, CF2) the entire special through hole (95a-95d) lies within the second angle (Ba-Bd). [4] The spark plug according to any one of claims 1 to 3, wherein the cover (90, 90B) has a plurality of the special through holes (95a-95d).

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