Spark plug

Abstract

To stabilize combustion even when a combustion temperature in a cylinder is increased.SOLUTION: A ground electrode chip 60 and a tip portion 52 are fused together by laser welding to form a fusion portion 7, and a recess 71 is formed in the fusion portion 7, which curves and retreats toward the center of the ground electrode tip 60. An intersection angle θ between a line LNa along a surface 72 of the fusion portion 7 and a line LNb passing through an opening end 712 of the recess 71, circumscribing the curved surface 711 of the recess 71, and along an extension direction of the tip portion 52 is θ>90°, and a relation between a width L of the opening end 712 of the recess 71 and a depth H of the recess 71 is H / L<0.5.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to spark plugs. [Background technology]

[0002] In the spark plug described in Patent Document 1 below, a part of a precious metal tip is embedded in a hole provided in a ground electrode. A side surface of the embedded part is laser-welded so as to penetrate from the outer side surface of the ground electrode, forming a wedge-shaped fusion zone where the precious metal tip and the ground electrode are fused together, and the precious metal tip and the ground electrode are joined by this fusion zone. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2005-183167 A Summary of the Invention [Problem to be solved by the invention]

[0004] In order to improve the thermal efficiency of engines that use spark plugs, the combustion temperature inside the cylinders is increased. When the combustion temperature inside the cylinders is increased, the combustion fluctuation increases, which can lead to a loss of stability or pre-ignition.

[0005] The present disclosure aims to stabilize combustion even when the combustion temperature in a cylinder is increased. [Means for solving the problem]

[0006] The present disclosure relates to a spark plug, comprising an insulator (12) that houses a center electrode (13), a housing (11) that houses the insulator, a ground electrode base material (50) including a tip end (52) that is spaced apart from the center electrode by a predetermined distance and a base end (51) that extends along the center electrode and is joined to the housing, and a ground electrode tip (60) that is provided at the tip end to face the center electrode, and a fusion zone (7, 7B, 7C, 7E) is formed by fusion-joining the ground electrode tip and the tip end by laser welding. A recess (71, 71E) that curves back toward the center of the ground electrode tip is formed in the fusion zone. The intersection angle θ between a line (LNa) along the surface (72, 72E) of the molten portion and a line (LNb) that passes through the opening end (712) of the recess, circumscribes the curved surface (711, 711E) of the recess, and is along the direction in which the tip portion extends is θ>90°, and the width L of the opening end of the recess and the depth H of the recess are H / L<0.5. Effect of the Invention

[0007] According to the present disclosure, combustion is stable even when the combustion temperature in the cylinder is increased. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a partial cross-sectional view of a spark plug according to the present embodiment. [Diagram 2] FIG. 2 is a cross-sectional view showing an xy cross section in the vicinity of the ground electrode tip in FIG. [Diagram 3] FIG. 3 is a cross-sectional view showing an Xy cross section in the vicinity of the ground electrode tip in FIG. 1, and shows an example different from that in FIG. [Figure 4] FIG. 4 is a graph illustrating the relationship between the crank angle and the in-cylinder pressure. [Diagram 5] FIG. 5 is a graph illustrating the relationship between the crossing angle and the in-cylinder pressure. [Figure 6] FIG. 6 is a diagram illustrating a comparative example to the state in the vicinity of the ground electrode tip illustrated in FIGS. [Figure 7]FIG. 7 is a graph illustrating the relationship between H / L and the in-cylinder pressure. [Figure 8] FIG. 8 is a perspective view of the vicinity of the ground electrode tip. [Figure 9] FIG. 9 is a diagram illustrating a modification of the state in the vicinity of the ground electrode tip illustrated in FIG. [Figure 10] FIG. 10 is a diagram illustrating a modification of the state in the vicinity of the ground electrode tip illustrated in FIG. [Figure 11] FIG. 11 is a diagram illustrating a modified example of the state in the vicinity of the ground electrode tip illustrated in FIGS. [Figure 12] FIG. 12 is a diagram illustrating a modified example of the state in the vicinity of the ground electrode tip illustrated in FIGS. [Figure 13] FIG. 13 is a diagram illustrating a modification of the state in the vicinity of the ground electrode tip illustrated in FIG. [Figure 14] FIG. 14 is a diagram illustrating a modification of the state in the vicinity of the ground electrode tip illustrated in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, the present embodiment will be described with reference to the accompanying drawings. In order to facilitate understanding of the description, the same components in each drawing are denoted by the same reference numerals as much as possible, and duplicated description will be omitted.

[0010] A schematic configuration of a spark plug 10 in this embodiment will be described with reference to Fig. 1. The spark plug 10 is attached to, for example, an engine head block. The spark plug 10 generates a spark discharge based on application of a voltage, and ignites the air-fuel mixture in the cylinder of the engine. The spark plug 10 includes a housing 11, an insulator 12, a center electrode 13, and a ground electrode 14.

[0011] The housing 11 is formed in a cylindrical shape centered on a plug central axis m10, which is the central axis of the spark plug 10. The housing 11 is formed of a metal material such as carbon steel. The lower end of the insulator 12 is inserted into the inside of the housing 11. A threaded portion 114 is formed on the outer circumferential surface of the lower part of the housing 11. The spark plug 10 can be fastened and fixed to the engine head block by screwing the threaded portion 114 into a screw hole formed in the engine head block. In the following, the direction along the plug central axis m10 is also referred to as the "plug axial direction Da". The circumferential direction centered on the plug central axis m10 is also referred to as the "plug circumferential direction Dc". The ground electrode 14 side is also referred to as the tip side, and the opposite side is also referred to as the base side.

[0012] The insulator 12 is formed in a cylindrical shape centered on the plug central axis m10. The insulator 12 is made of an insulating material such as alumina. The housing 11 is integrally assembled to the outer periphery of the insulator 12. An axial hole 120 is formed inside the insulator 12. The axial hole 120 is formed so as to penetrate the insulator 12 from the tip end side to the base end side along the plug central axis m10. The center electrode 13, the first seal body 15, the resistor 16, the second seal body 17, and the terminal fitting 18 are inserted in this order from the tip end side into the axial hole 120. The center electrode 13 is inserted into the insulator 12 so as to be exposed from the tip end of the insulator 12.

[0013] The center electrode 13 has a center electrode base material 30 and a center electrode tip 40. The center electrode base material 30 is formed in a cylindrical shape centered on the plug central axis m10. The center electrode base material 30 is made of a nickel (Ni) alloy or the like having excellent heat resistance. The center electrode tip 40 is joined to the tip of the center electrode base material 30. The center electrode tip 40 is formed in a cylindrical shape centered on the plug central axis m10. The center electrode tip 40 is made of an iridium alloy or the like. A first seal body 15, a resistor 16, and a second seal body 17 are sandwiched between the base end side of the center electrode 13 and the tip side of the terminal fitting 18.

[0014] The terminal fitting 18 is formed in a substantially cylindrical shape centered on the plug central axis m10. The terminal fitting 18 is formed of a steel material or the like. A terminal portion 180 is provided on the base end side of the terminal fitting 18. The terminal portion 180 is exposed to the outside from the base end side of the insulator 12.

[0015] The ground electrode 14 has a ground electrode base material 50 and a ground electrode tip 60. The ground electrode base material 50 is formed of a nickel (Ni) alloy or the like. The ground electrode base material 50 is joined to a front end surface 110 of the housing 11. The ground electrode base material 50 is formed so as to extend from the front end surface 110 of the housing 11 to a position facing the center electrode tip 40.

[0016] The ground electrode base material 50 has a base end 51 and a tip end 52. The base end 51 is joined to the tip end surface 110 of the housing 11. The base end 51 is formed to extend from the tip end surface 110 of the housing 11 in the plug axial direction Da. The tip end 52 is formed to extend from the tip of the base end 51 to a position facing the center electrode tip 40 of the center electrode 13. The ground electrode base material 50 is formed into a substantially L-shape as a whole by being composed of the base end 51 and the tip end 52.

[0017] The ground electrode tip 60 is joined to the tip portion 52 of the ground electrode base material 50. The ground electrode tip 60 is made of a precious metal alloy such as an iridium alloy or a platinum alloy. The ground electrode tip 60 is disposed so as to face the center electrode tip 40. A gap formed between the center electrode tip 40 and the ground electrode tip 60 is called a spark gap 19.

[0018] In the spark plug 10, an external circuit capable of applying a high voltage is connected to the terminal portion 180 of the terminal fitting 18. When a high voltage is applied to the terminal portion 180 by the external circuit, a spark discharge is generated between the center electrode tip 40 of the center electrode 13 and the ground electrode tip 60 of the ground electrode 14. This spark discharge ignites the air-fuel mixture in the cylinder of the engine, forming a flame, and the mixture is burned.

[0019] In FIG. 1, an x-axis, a y-axis, and a z-axis are set, which are perpendicular to each other. The z-axis is set to be along the plug central axis m10. The x-axis and the y-axis are set along a plane perpendicular to the z-axis. The y-axis is set to be along the paper surface of FIG. 1. The x-axis is set to be perpendicular to the paper surface of FIG. 1.

[0020] The x-axis is set to have a positive direction from the back to the front in Fig. 1. The y-axis is set to have a positive direction from the left to the right in Fig. 1. The z-axis is set to have a positive direction from the tip end to the base end of the spark plug 10.

[0021] Next, the joining state of the ground electrode tip 60 to the tip portion 52 will be described with reference to Fig. 2. Fig. 2 is a cross-sectional view taken along the yz plane of the tip portion 52 and the ground electrode tip 60 of the spark plug 10 shown in Fig. 1. The cross-sectional view shown in Fig. 2 shows a cross section taken along the yz plane passing through the plug central axis m10 of Fig. 1.

[0022] As shown in FIG. 2, the ground electrode tip 60 is partially embedded in the tip portion 52. After the ground electrode tip 60 is embedded in the tip portion 52, laser welding is performed from the side surface of the tip portion 52. The laser welding is performed from the side surface of the tip side of the tip portion 52 in the negative y-axis direction. When the laser welding is performed, a molten portion 7 is formed from the tip portion 52 to the ground electrode tip 60. A recess 71 is formed on a surface 72, which is the surface of the molten portion 7 exposed to the outside. Although one molten portion 7 is illustrated in FIG. 2, a plurality of molten portions 7 may be formed along the outer periphery of the ground electrode tip 60.

[0023] The recess 71 has a curved surface 711 that curves back from the surface 72. The recess 71 is provided so that the intersection angle θ between a line LNa along the surface 72 of the fusion zone 7 and a line LNb that passes through the opening end 712 of the recess 71, circumscribes the curved surface 711 of the recess 71, and is along the y direction in which the tip portion 52 extends, is θ>90°. The opening end 712 of the recess 71 is the portion where the curved surface 711 of the recess 71 and the surface 72 contact each other.

[0024] By setting the crossing angle θ to an obtuse angle, a localized rapid temperature rise at the end of the recess 71 is suppressed, thereby suppressing the occurrence of pre-ignition. The crossing angle θ is an obtuse angle when the width L of the opening end 712 is the maximum width of the recess 71. A comparative example in which the crossing angle θ is an acute angle will be described with reference to FIG.

[0025] As shown in FIG. 6, an opening end 712A is formed at the portion where the curved surface 711A and the surface 72A of the recess 71A, which is a comparative example, come into contact. When the intersection angle θ is an acute angle, the width L at the opening end 712A of the recess 71A is smaller than the maximum width M of the recess 71A. As shown in FIG. 6, when the vicinity of the opening end 712A is an acute angle, the volume of this portion becomes relatively small, and the temperature rise due to the heat received from the fuel gas becomes steep. If this situation is repeated, only the fuel gas around the opening end 712A reaches the expected temperature earlier than the expected time, and pre-ignition due to early ignition may occur.

[0026] On the other hand, as described with reference to Fig. 2, when the intersection angle θ is an obtuse angle, the volume near the opening end 712 becomes relatively large, and it is possible to mitigate the local temperature rise caused by the heat received from the fuel gas. By mitigating the local temperature rise, it is possible to suppress the occurrence of pre-ignition. In addition, it is possible to delay the rise time of the ground electrode temperature beyond the time required for the pre-ignition prevention measures to be completed by control by the engine ECU, for example.

[0027] In order to confirm the effect of making the crossing angle θ obtuse, spark plugs with crossing angles θ changed from 45° to 160° were created and mounted on an engine to monitor the change in cylinder pressure. The engine evaluation was performed at a constant speed of 3000 rpm, the change in cylinder pressure was monitored, and the relationship between the crossing angle θ and the cylinder pressure at the time of maximum pressure was investigated.

[0028] FIG. 4 is a graph showing the results of monitoring the in-cylinder pressure waveform when an engine is evaluated. FIG. 5 is a graph plotting the relationship between the maximum in-cylinder pressure and the crossing angle θ. In FIG. 4, when the maximum in-cylinder pressure occurs before the crank angle is 30°, pre-ignition occurs. The maximum in-cylinder pressure at which pre-ignition occurs is 6200 [kPa]. In FIG. 5, when the crossing angle θ is 90° or more, the maximum in-cylinder pressure is 6 [MPa] or less, which is significantly lower than when the crossing angle θ is an acute angle. In particular, it is more preferable if the crossing angle θ is greater than 120°.

[0029] Fig. 7 is a graph showing the relationship between H / L, which is the ratio of the width L of the opening end 712 of the recess 71 to the depth H of the recess 71, and the maximum in-cylinder pressure. The data shown in Fig. 7 is the result of an engine evaluation of spark plugs having different H / Ls with a cross angle θ of 90°. The engine evaluation was performed at a constant speed of 3000 rpm, and the change in the in-cylinder pressure was monitored to investigate the relationship between the in-cylinder pressure and H / L when the maximum pressure was indicated. As shown in Fig. 7, it was found that the maximum in-cylinder pressure could be suppressed when H / L was 0.5 or less.

[0030] As shown in FIG. 3, the ground electrode tip 60 does not have to be embedded in the tip portion 52. In the example shown in FIG. 3, the ground electrode tip 60 is placed on the tip portion 52. After the ground electrode tip 60 is placed on the tip portion 52, laser welding is performed from the side of the tip portion 52 and the ground electrode tip 60. The laser welding is performed from the side of the tip side of the tip portion 52 and the ground electrode tip 60 in the negative y-axis direction. When the laser welding is performed, a molten portion 7 is formed that extends from the tip portion 52 to the ground electrode tip 60. A recess 71 is formed on a surface 72 that is the surface of the molten portion 7 exposed to the outside.

[0031] The configurations of the ground electrode tip and the tip portion are not limited to those described with reference to Figures 2 and 3. As shown in Figure 8, the tip side of the tip portion 52 may be curved and shaped to fit the outer periphery of the ground electrode tip 60. In the example shown in Figure 8, a fusion zone 7 is formed along the outer periphery of the ground electrode tip 60.

[0032] Also, as shown in FIG. 9, a rectangular ground electrode tip 60B may be formed along the tip side of the tip portion 52B, and a fusion zone 7B may be formed and joined.

[0033] Also, as shown in FIG. 10, a ground electrode tip 60C may be placed on the front end portion 62C, and the abutting portion between the ground electrode tip 60C and the front end portion 62C may be obliquely laser-welded to form a fusion zone 7C.

[0034] In some cases, no recess 71 is formed on surface 72 of fusion zone 7, and in such cases, adjustment of crossing angle θ as described above is not necessary. However, there are cases where the recess is confined inside the fusion zone, forming a cavity within the fusion zone. In such cases, adjustment of the position of the cavity is required, which will be described with reference to FIG. 11.

[0035] 11, the ground electrode tip 60 is partially embedded in the tip portion 52. After the ground electrode tip 60 is embedded in the tip portion 52, laser welding is performed from the side surface of the tip portion 52. The laser welding is performed from the side surface of the tip side of the tip portion 52 in the negative y-axis direction. When the laser welding is performed, a molten portion 7 is formed that extends from the tip portion 52 to the ground electrode tip 60. A cavity 71D is formed at a position away from a surface 72 that is the surface where the molten portion 7 is exposed to the outside.

[0036] 12, a discharge in the gap occurs between the center electrode tip 40 and the ground electrode tip 60 when a discharge is formed. After that, the discharge origin on the ground electrode tip 60 side moves according to the direction of the airflow inside the cylinder, and finally a discharge occurs between the center electrode tip 40 and the tip portion 52. As the discharge origin moves, the tip portion 52 through which the discharge origin passes and the molten portion 7 are consumed. If the molten portion 7 is consumed, and the cavity 71D is close to the surface 72, the cavity 71D will be exposed, and there is a concern that a state similar to the state in which the intersection angle θ is an acute angle described with reference to FIG. 6 will occur.

[0037] Therefore, it is necessary to set the formation position D so that the cavity 71D is not exposed even if the fusion zone 7 is consumed. The formation position D is related to the life setting of the spark plug 10. That is, the spark gap, which is the distance between the center electrode tip 40 and the ground electrode tip 60, is generally designed so that when the gap is expanded by about 0.3 mm, the required voltage applied between the gap exceeds the limit at which a discharge can be formed. Therefore, it is preferable that the formation position D of the cavity 71D is also 0.3 mm or more. However, since Inconel, which is a Ni-based alloy often used as a ground electrode material, is consumed about twice as fast as a precious metal tip, it is preferable that the formation position D is 0.6 mm or more. The formation position D of the cavity 71D may be selected by controlling laser welding so that the cavity 71D is formed at a target position, or may be selected by measuring the cavity 71D with an X-ray or the like after welding.

[0038] As shown in FIG. 12, the base end 51 is preferably a three-layer structure including a core material 512 and a pair of highly heat-conductive materials 511. The core material 512 is sandwiched between a pair of highly heat-conductive materials 511. The highly heat-conductive material 511 includes, for example, Cu. The core material 512 includes, for example, Ni as a high-strength material. This structure improves the heat dissipation of the tip of the ground electrode, and can raise the limit leading to pre-ignition. The three-layer structure shown in FIG. 12 can be applied to all of the base ends 51 of the present embodiment described with reference to FIGS. 2 and 3.

[0039] The depth of the recess can be reduced by further performing laser welding from the state shown in Fig. 6. Fig. 13 is a cross-sectional view showing an example in which further laser welding is performed from the state shown in Fig. 6. This further laser welding has a weaker laser strength than the laser welding in the state shown in Fig. 6.

[0040] A new molten portion 7E is formed by further laser welding. The new molten portion 7E melts a portion including the recess 71A shown in Fig. 6, and a new recess 71E is formed. The recess 71E has a curved surface 711E that recedes from the surface 72E of the molten portion 7E.

[0041] [Note] Notes 1 to 7 below can be combined in any way as long as there is no technical contradiction.

[0042] [Appendix 1] an insulator 12 that houses a center electrode 13; A housing 11 that accommodates an insulator 12; a ground electrode base material 50 including a front end portion 52 arranged at a predetermined distance from the center electrode 13 and a base end portion 51 extending along the center electrode 13 and joined to the housing 11; and a ground electrode tip 60 provided at the front end portion 52 so as to face the center electrode 13, The ground electrode tip 60 and the front end 52 are fused and joined by laser welding to form fusion zones 7, 7B, 7C, and 7E. The fusion zones 7, 7B, 7C, and 7E are formed with recesses 71, 71E or recesses (not shown) that curve and retreat toward the center of the ground electrode tip 60. The intersection angle θ between a line LNa along the surface 72, 72E of the fusion portion 7, 7B, 7C, 7E and a line LNb passing through the opening end 712 of the recess 71, 71E, circumscribing the curved surface 711, 711E of the recess 71, 71E, and along the direction in which the tip portion 52 extends is θ>90°, The spark plug 10 has a width L of the opening end 712 of the recess 71, 71E and a depth H of the recess 71, 71E satisfying H / L<0.5.

[0043] In Supplementary Note 1, the line LNa is along the surfaces 72, 72E and also along the plug central axis m10. Since the line LNa is along the surface of the fusion zone 7C illustrated in FIG. 10, for example, the line LNa is provided in a direction intersecting with the plug central axis m10.

[0044] According to Supplementary Note 1, as described with reference to Figures 5 and 7, the increase in cylinder pressure can be suppressed and premature ignition is suppressed, so that combustion is stable even if the combustion temperature in the cylinder is increased.

[0045] [Appendix 2] A ground electrode tip 60 is embedded in the distal end 52; 2. The spark plug (10) according to claim 1, wherein the fusion zone (7) penetrates through the side surface of the front end portion (52) and reaches the ground electrode tip (60).

[0046] [Appendix 3] The ground electrode tip 60 is placed on the tip portion 52, and the side surface of the ground electrode tip 60 is arranged along the side surface of the tip portion 52. 2. The spark plug (10) according to claim 1, wherein the fusion zone (7) is formed so as to extend from the side surfaces of the ground electrode tip (60) and the front end portion (52).

[0047] [Appendix 4] 4. The spark plug 10 of any one of claims 1 to 3, wherein the crossing angle θ is θ>120°.

[0048] According to Supplementary Note 4, as described with reference to Figures 5 and 7, the increase in the cylinder pressure can be further suppressed, and premature ignition is suppressed, so that combustion is stable even if the combustion temperature in the cylinder is increased.

[0049] [Appendix 5] 5. The spark plug according to claim 1, wherein the base end portion includes a core material and a pair of highly thermally conductive materials sandwiching the core material.

[0050] [Appendix 6] 6. The spark plug according to claim 1, wherein one recess 71, 71E is formed in one fusion portion 7, 7B, 7C, 7E.

[0051] [Appendix 7] an insulator 12 that houses a center electrode 13; A housing 11 that accommodates an insulator 12; a ground electrode base material 50 including a front end portion 52 arranged at a predetermined distance from the center electrode 13 and a base end portion 51 extending along the center electrode 13 and joined to the housing 11; and a ground electrode tip 60 provided at the front end portion 52 so as to face the center electrode 13, The ground electrode tip 60 and the front end 52 are fused together by laser welding to form a fusion zone 7. A cavity 71D is formed in the fusion zone 7, The spark plug 10 is provided at a distance of 0.6 mm or more from the surface 72 of the fusion portion 7.

[0052] The present embodiment has been described above with reference to specific examples. However, the present disclosure is not limited to these specific examples. Any design modifications made by a person skilled in the art to these specific examples are also included within the scope of the present disclosure as long as they have the features of the present disclosure. The elements of each of the above-mentioned specific examples and their arrangements, conditions, shapes, etc. are not limited to those exemplified and can be changed as appropriate. The combination of each of the elements of each of the above-mentioned specific examples can be changed as appropriate as long as no technical contradiction occurs. [Explanation of symbols]

[0053] 10: Spark plug 11: Housing 12: Insulator 13: Center electrode 14: Ground electrode 50: Ground electrode base material 51: Proximal end 52:Tip 60: Ground electrode tip 7: Welding part 71: Recess 72: Surface 711: Curved surface 712: Open end

Claims

1. an insulator (12) that houses a center electrode (13); A housing (11) for accommodating the insulator; a ground electrode (14) having a ground electrode base material (50) including a front end portion (52) arranged at a predetermined distance from the center electrode and a base end portion (51) extending along the center electrode and joined to the housing, and a ground electrode tip (60) provided at the front end portion so as to face the center electrode, The ground electrode tip and the front end are fused and joined by laser welding to form a fused portion (7, 7B, 7C, 7E), A recess (71, 71E) is formed in the fusion zone, the recess being curved toward the center of the ground electrode tip, A crossing angle θ between a line (LNa) along the surface (72, 72E) of the fusion portion and a line (LNb) passing through the opening end (712) of the recess, circumscribing the curved surface (711, 711E) of the recess, and along the direction in which the tip portion extends is θ>90°, A spark plug, wherein a width L of an opening end of the recess and a depth H of the recess satisfy H / L<0.

5.

2. the ground electrode tip is embedded in the tip; 2. The spark plug of claim 1, wherein said fusion zone penetrates a side surface of said leading end portion and reaches said ground electrode tip.

3. the ground electrode tip is placed on the tip portion and a side surface of the ground electrode tip is disposed along a side surface of the tip portion; 2. The spark plug according to claim 1, wherein the fusion zone is formed so as to extend from the side surfaces of the ground electrode tip and the front end portion.

4. 4. The spark plug according to claim 1, wherein the crossing angle θ is greater than 120°.

5. 4. The spark plug according to claim 1, wherein the base end portion includes a core material (512) and a pair of highly thermally conductive materials (511) provided with the core material sandwiched therebetween.

6. 4. The spark plug according to claim 1, wherein one of the recesses is formed in one of the fusion portions.

7. an insulator (12) that houses a center electrode (13); A housing (11) for accommodating the insulator; a ground electrode base material (50) including a front end portion (52) arranged at a predetermined distance from the center electrode and a base end portion (51) extending along the center electrode and joined to the housing, and a ground electrode tip (60) provided at the front end portion so as to face the center electrode, A fusion zone (7) is formed by fusion-joining the ground electrode tip and the front end portion by laser welding, A cavity (71D) is formed in the fusion zone, The spark plug is provided at a distance of 0.6 mm or more from the surface (72) of the fusion zone.

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