Spark plugs for internal combustion engines

Abstract

To provide a spark plug for an internal combustion engine capable of suppressing preignition.SOLUTION: A spark plug 1 for an internal combustion engine has an insulator, a center electrode 4, a housing 2, a ground electrode 6, and a plug cover 5. The ground electrode 6 is protruded from a fixed end part 61 fixed to the housing 2 or the plug cover 5 at an outer peripheral side of a sub combustion chamber 50 to the inside of the sub combustion chamber 50. The plug cover 5 is formed with three or more injection holes 51. When seen from a plug axial direction, injection hole axes 51L of the injection holes are inclined to a plug radial direction. A projection edge 62 of the ground electrode 6 is arranged inside a polygon P1 formed by the injection hole axes 51L of the three or more injection holes 51 when seen from the plug axial direction. The injection hole axes 51L pass on a base end side of the plug axial direction from the projection edge 62 of the ground electrode 6 when seen from a direction orthogonal to both the injection hole axes 51L and the plug axial direction.SELECTED DRAWING: Figure 2

Description

[Technical field]

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

[0002] For example, as disclosed in Patent Document 1, a spark plug for an internal combustion engine having an auxiliary combustion chamber at its tip is known. In this spark plug, a nozzle hole is formed in a plug cover covering the auxiliary combustion chamber. This allows a flame to be ejected from the auxiliary combustion chamber through the nozzle hole into the main combustion chamber, thereby combusting the air-fuel mixture in the main combustion chamber. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-184435 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, the spark plug described in Patent Document 1 has room for improvement in terms of suppressing pre-ignition. That is, in the spark plug described in the above Patent Document 1, the nozzle hole is formed at an angle so as to face the vicinity of the protruding end edge of the ground electrode. Therefore, the air-fuel mixture that flows into the auxiliary combustion chamber from the nozzle hole reaches the vicinity of the protruding end edge of the ground electrode early with respect to the ignition timing. In addition, the protruding end edge of the ground electrode is a portion that is likely to become hot. Therefore, if the air-fuel mixture reaches the vicinity of the protruding end edge of the ground electrode, which is likely to become hot, early with respect to the ignition timing, pre-ignition is likely to occur. In other words, there is a problem that ignition is likely to occur earlier than the ignition timing.

[0005] The present invention has been made in view of the above problems, and has an object to provide a spark plug for an internal combustion engine that is capable of suppressing pre-ignition. [Means for solving the problem]

[0006] One aspect of the present invention is a cylindrical insulator (3), a center electrode (4) held on the inner circumferential side of the insulator and protruding from the insulator toward the tip side; a cylindrical housing (2) that holds the insulator on its inner periphery; a ground electrode (6) forming a discharge gap (G) between itself and the center electrode; a plug cover (5) provided at the tip of the housing so as to cover a sub-combustion chamber (50) in which the discharge gap is disposed, The ground electrode protrudes into the auxiliary combustion chamber from a fixed end portion (61) fixed to the housing or the plug cover on the outer circumferential side of the auxiliary combustion chamber, The plug cover is formed with three or more nozzle holes (51) that communicate the auxiliary combustion chamber with the outside, When viewed from the plug axial direction (Z), the nozzle hole axis (51L) of the nozzle hole is inclined with respect to the plug radial direction, a projecting end edge (62) of the ground electrode is disposed inside a polygon (P1) formed by the nozzle hole axes of the three or more nozzle holes as viewed from the plug axial direction, the injection hole is formed on a tip side in the plug axial direction relative to a projecting end edge of the ground electrode, The nozzle hole axis is located in a spark plug (1) for an internal combustion engine, and passes through a base end side in the plug axial direction relative to the protruding end edge of the ground electrode when viewed from a direction perpendicular to both the nozzle hole axis and the plug axial direction. Effect of the Invention

[0007] In the above spark plug for an internal combustion engine, the protruding edge of the ground electrode is disposed inside a polygon formed by the nozzle hole axes of three or more nozzle holes when viewed from the plug axial direction. Also, when viewed from a direction perpendicular to both the nozzle hole axis and the plug axial direction, the nozzle hole axis passes closer to the base end side in the plug axial direction than the protruding edge of the ground electrode. This makes it possible to prevent the mixture flowing in from the nozzle hole from reaching the vicinity of the protruding edge of the ground electrode prematurely. Therefore, it is possible to prevent the fuel mass ratio from becoming high at the protruding edge of the ground electrode earlier than the ignition timing. As a result, pre-ignition can be suppressed.

[0008] As described above, according to the above aspect, it is possible to provide a spark plug for an internal combustion engine that is capable of suppressing pre-ignition. In addition, the symbols in parentheses described in the claims and the means for solving the problems indicate a correspondence with the specific means described in the embodiments described below, and do not limit the technical scope of the present invention. [Brief description of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view taken along the central axis of a tip portion of a spark plug for an internal combustion engine according to a first embodiment. [Diagram 2] Cross-sectional view taken along line II-II in FIG. [Diagram 3] FIG. 3 is a view taken along the line III in FIG. 2 . [Figure 4] IV arrow view of FIG. 2. [Diagram 5] FIG. 4 is an explanatory diagram of an air flow in an auxiliary combustion chamber in the first embodiment. [Figure 6] FIG. 11 is an explanatory diagram showing the relationship between the injection hole and the ground electrode as viewed from the plug axial direction in a second embodiment. [Figure 7] FIG. 11 is an explanatory diagram showing the relationship between the injection hole and the ground electrode as viewed in the plug radial direction in a third embodiment. [Figure 8] FIG. 11 is an explanatory diagram showing the relationship between the injection hole and the ground electrode as viewed from another radial direction of the plug in the third embodiment. [Figure 9]11 is an explanatory cross-sectional view taken along the line IX-IX in FIG. 10, as viewed from the plug axial direction in the fourth embodiment; FIG. [Figure 10] FIG. 11 is a cross-sectional view taken along the central axis of a tip portion of a spark plug for an internal combustion engine according to a fourth embodiment. [Figure 11] FIG. 11 is a cross-sectional view taken along the central axis of a tip portion of a spark plug for an internal combustion engine according to a fifth embodiment. [Figure 12] 13 is a cross-sectional view taken along the central axis of a tip portion of a spark plug for an internal combustion engine according to a sixth embodiment. FIG. [Figure 13] FIG. 13 is a cross-sectional view taken along the central axis of a tip portion of a spark plug for an internal combustion engine according to a seventh embodiment. [Figure 14] 13 is a cross-sectional view taken along the central axis of a tip portion of a spark plug for an internal combustion engine according to an eighth embodiment. FIG. [Figure 15] 15 is a cross-sectional view taken along line XV-XV in FIG. 14 . [Figure 16] 13 is a diagram showing test results in Experimental Example 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

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

[0012] The ground electrode 6 is fixed to the housing 2 or the plug cover 5 on the outer periphery side of the auxiliary combustion chamber 50. The ground electrode 6 protrudes into the auxiliary combustion chamber 50 from this fixed end portion 61. The plug cover 5 has three or more injection holes 51 formed therein, which connect the auxiliary combustion chamber 50 with the outside.

[0013] As shown in FIG. 2, when viewed from the plug axial direction Z, the injection hole axis 51L of the injection hole 51 is inclined with respect to the plug radial direction. The projecting edge 62 of the ground electrode 6 is disposed inside a polygon P1 formed by the nozzle hole axes 51L of the three or more nozzle holes 51 when viewed from the plug axial direction Z.

[0014] When viewed from a direction perpendicular to both the injection hole axis 51L and the plug axial direction Z, the injection hole axis 51L passes on the base end side in the plug axial direction Z beyond the protruding end edge 62 of the ground electrode 6, as shown in Figures 3 and 4.

[0015] That is, when viewed from the direction of arrow III in Fig. 2, the nozzle hole axis 51L of the nozzle hole 51 arranged on the right side in Fig. 2 passes further toward the base end in the plug axial direction Z than the protruding edge 62 of the ground electrode 6, as shown in Fig. 3. Also, when viewed from the direction of arrow IV in Fig. 2, the nozzle hole axis 51L of the nozzle hole 51 arranged on the lower side in Fig. 2 passes further toward the base end in the plug axial direction Z than the protruding edge 62 of the ground electrode 6, as shown in Fig. 4.

[0016] The spark plug 1 of this embodiment can be used as an ignition means in an internal combustion engine of an automobile, a cogeneration system, or the like. One end of the spark plug 1 in the plug axial direction Z is disposed in the main combustion chamber of the internal combustion engine. In the plug axial direction Z, the side exposed to the main combustion chamber is referred to as the tip side, and the opposite side is referred to as the base side. The direction perpendicular to the central axis PC of the spark plug 1 is referred to as the plug radial direction. The direction along the circumference centered on the plug central axis PC is referred to as the plug circumferential direction.

[0017] In this embodiment, four injection holes 51 are formed. As shown in FIG. 2, the four injection holes 51 are disposed at equal intervals in the plug circumferential direction. The injection hole axes 51L of the four injection holes 51 are inclined with respect to the plug radial direction when viewed from the plug axial direction Z. That is, when viewed from the plug axial direction Z, the injection hole axis 51L of each injection hole 51 is inclined at an acute angle α with respect to a virtual line VL that passes through the injection hole 51 and the plug central axis PC and extends in the plug radial direction. The injection holes 51 have the same inclination direction of the injection hole axis 51L with respect to the virtual line VL in each injection hole 51 in the plug circumferential direction. In this embodiment, the injection holes 51 have the same angle α.

[0018] Due to such a configuration of the nozzle hole 51, the airflow introduced from the nozzle hole 51 into the auxiliary combustion chamber 50 forms a swirl flow Fs in the auxiliary combustion chamber 50 as shown in Fig. 5. In this embodiment, the swirl flow Fs is generated in a clockwise spiral shape in Fig. 5 around the plug central axis PC.

[0019] As shown in Fig. 2, the nozzle hole axes 51L of the four nozzle holes 51 are perpendicular to each other when viewed from the plug axis direction Z. Therefore, a polygon P1 formed by the four nozzle hole axes 51L is a square. The protruding edge 62 of the ground electrode 6 is disposed inside this square. That is, the entire protruding edge 62 is contained inside the polygon P1. In this embodiment, the entire protruding edge 62 is contained inside the inscribed circle C1 of the polygon P1.

[0020] 1, a fixed end 61 of the ground electrode 6 is fixed to the housing 2 or the plug cover 5. In this embodiment, the fixed end 61 is joined to the front end of the housing 2 by welding or the like. The ground electrode 6 has a bent portion 611 at the fixed end 61. The ground electrode 6 extends in the plug radial direction from the bent portion 611 toward the protruding end edge 62. A portion of the ground electrode 6 near the protruding end edge 62 faces the front end of the center electrode 4 in the plug axial direction Z, with a discharge gap G between them.

[0021] Next, the effects of this embodiment will be described. In the above spark plug 1 for an internal combustion engine, the protruding edge 62 of the ground electrode 6 is disposed inside a polygon P1 formed by the nozzle hole axes 51L of the four nozzle holes 51 as viewed from the plug axial direction Z. The nozzle hole axis 51L passes closer to the base end side in the plug axial direction Z than the protruding edge 62 of the ground electrode 6 as viewed from a direction perpendicular to both the nozzle hole axis 51L and the plug axial direction Z. This makes it possible to prevent the mixture flowing in from the nozzle hole 51 from reaching the vicinity of the protruding edge 62 of the ground electrode 6 prematurely. Therefore, it is possible to suppress the fuel mass ratio from becoming high near the protruding edge 62 of the ground electrode 6 earlier than the ignition timing. As a result, it is possible to suppress pre-ignition.

[0022] The protruding edge 62 of the ground electrode 6 is a portion that is relatively difficult to cool and is easily overheated. Therefore, if the fuel mass ratio in the vicinity of the protruding edge 62 becomes high during the compression stroke of the internal combustion engine, there is a concern that ignition may occur earlier than the ignition timing. In particular, during high-load operation, the temperature of the protruding edge 62 is likely to become high, increasing the concern of pre-ignition.

[0023] In this embodiment, as described above, the air-fuel mixture introduced into the auxiliary combustion chamber 50 can be prevented from reaching the vicinity of the protruding edge 62 early. In other words, the air-fuel mixture introduced into the auxiliary combustion chamber 50 from the injection hole 51 is unlikely to reach the inside of the polygon P1 early. The air-fuel mixture gradually spreads throughout the entire auxiliary combustion chamber 50 while swirling on the swirl flow Fs. Therefore, it is possible to prevent the fuel mass ratio near the protruding edge 62 from becoming high earlier than the ignition timing. As a result, it is possible to prevent ignition starting from the protruding edge 62 of the ground electrode 6 earlier than the ignition timing. In other words, pre-ignition can be suppressed.

[0024] As described above, according to this embodiment, it is possible to provide a spark plug for an internal combustion engine that is capable of suppressing pre-ignition.

[0025] (Embodiment 2) 6, in this embodiment, the projecting edge 62 of the ground electrode 6 is disposed inside a polygon P2 formed by the contour lines 51M on the side closer to the plug central axis PC in the three or more extension regions 51E as viewed from the plug axial direction Z. The three or more extension regions 51E are regions obtained by extending the three or more injection holes 51 in parallel to their respective injection hole axes 51L.

[0026] That is, in this embodiment, the protruding edge 62 of the ground electrode 6 is disposed within a more limited range compared to embodiment 1. In this embodiment, the protruding edge 62 of the ground electrode 6 is disposed inside the inscribed circle C2 of the polygon P2.

[0027] The rest is the same as in embodiment 1. Note that, among the symbols used in embodiment 2 and onwards, the same symbols used in the previous embodiments represent the same components, etc. as in the previous embodiments, unless otherwise specified.

[0028] In this embodiment, it is possible to more effectively prevent the air-fuel mixture flowing in from the injection hole 51 from reaching the vicinity of the protruding end edge 62 of the ground electrode 6 prematurely. Therefore, it is possible to further prevent the fuel mass ratio from becoming high near the protruding end edge 62 of the ground electrode 6 earlier than the ignition timing. As a result, it is possible to further suppress pre-ignition. In addition, the same effects as those of the first embodiment are achieved.

[0029] (Embodiment 3) In this embodiment, as shown in Figures 7 and 8, an extension region 51E obtained by extending the nozzle hole 51 parallel to the nozzle hole axis 52 passes on the base end side in the plug axial direction Z of the protruding edge 62 of the ground electrode 6 when viewed from a direction perpendicular to both the nozzle hole axis 51L and the plug axial direction Z.

[0030] That is, in FIGS. 7 and 8, the dashed line 51N passes through the protruding end edge 62 of the ground electrode 6 on the base end side. Other than that, it is the same as in embodiment 1. However, the arrangement of the projecting edge 62 of the ground electrode 6 as viewed from the plug axial direction Z may be the same as in embodiment 2 (see FIG. 6).

[0031] In this embodiment, it is possible to more effectively prevent the air-fuel mixture introduced into the auxiliary combustion chamber 50 from the injection hole 51 from prematurely reaching the vicinity of the protruding end edge 62 of the ground electrode 6. Therefore, it is possible to further suppress pre-ignition. In addition, the same effects as those of the first and second embodiments are obtained.

[0032] (Embodiment 4) In this embodiment, as shown in Figs. 9 and 10, at least a part of the projecting edge 62 of the ground electrode 6 is disposed at a position overlapping the center electrode 4 when viewed from the axial direction Z of the plug.

[0033] 10, in the present embodiment, the center electrode 4 has a smaller profile in a cross section perpendicular to the axial direction Z at its tip end than at a portion held by the insulator 3. The tip end of the center electrode 4 and at least a part of the protruding edge 62 of the ground electrode 6 overlap with each other when viewed from the axial direction Z.

[0034] In particular, in this embodiment, the protruding edge 62 of the ground electrode 6 passes through the plug central axis PC when viewed from the plug axial direction Z. The protruding edge 62 of the ground electrode 6 is disposed in approximately the center of the auxiliary combustion chamber 50 when viewed from the plug axial direction Z. The rest is the same as in the first embodiment.

[0035] In this embodiment, the protruding edge 62 of the ground electrode 6 can be easily disposed at a position where the air-fuel mixture introduced from the injection hole 51 into the auxiliary combustion chamber 50 is unlikely to arrive early. In addition, the same effects as those of the first embodiment are achieved.

[0036] (Embodiment 5) As shown in FIG. 11, in the spark plug 1 of this embodiment, the ground electrode 6 is inclined from the fixed end portion 61 toward the protruding end edge 62 toward the tip side in the plug axial direction Z. In this embodiment, the fixed end 61 of the ground electrode 6 is fixed to the housing 2 on the base end side relative to the tip end of the housing 2 . The rest is the same as in the first embodiment.

[0037] In this embodiment, the fixed end 61 of the ground electrode 6 can be connected to a position closer to the base end of the housing 2. This makes it easier to improve the heat dissipation of the ground electrode 6, and prevents overheating of the ground electrode 6. As a result, pre-ignition can be further prevented. In addition, the same effects as those of the first embodiment are achieved.

[0038] (Embodiment 6) In this embodiment, as shown in FIG. 12, the ground electrode 6 is formed in a substantially linear shape from the fixed end portion 61 to the protruding end edge 62. In the embodiment shown in FIG. That is, in the spark plug 1 of this embodiment, the ground electrode 6 does not have a bent portion 611 (see FIGS. 1, 11, etc.). The ground electrode 6 is inclined at a substantially constant angle with respect to the plug axial direction Z from the fixed end portion 61 to the protruding end edge 62. The rest is the same as in the fifth embodiment.

[0039] In this embodiment, the distance from the protruding edge 62 of the ground electrode 6 to the fixed end 61 can be made shorter. This makes it easier to improve the heat dissipation of the protruding edge 62. As a result, overheating of the protruding edge 62 can be further suppressed. In addition, the same effects as those of the fifth embodiment are achieved.

[0040] (Embodiment 7) In this embodiment, as shown in FIG. 13, the ground electrode 6 is formed in a substantially straight line from a fixed end portion 61 to a protruding end edge 62 and protrudes in a direction perpendicular to the plug axial direction Z.

[0041] That is, the spark plug 1 of this embodiment corresponds to the spark plug 1 of the first embodiment in which the shape of the ground electrode 6 is substantially straight rod-shaped. The rest is the same as in the first embodiment. In this embodiment, the same effects as those of the first embodiment are achieved.

[0042] (Embodiment 8) In this embodiment, as shown in FIGS. 14 and 15, a discharge gap G is formed between the side surface of the center electrode 4 and the protruding edge 62 of the ground electrode 6. In the embodiment shown in FIG. The rest is the same as in the first embodiment. In this embodiment, the same effects as those of the first embodiment are achieved.

[0043] (Experimental Example 1) In this example, the pre-ignition resistance (hereinafter referred to as "plague resistance") of the spark plug 1 according to the first embodiment was evaluated. As sample 1, the spark plug 1 of embodiment 1 was prepared, in which the angle α shown in Fig. 2 was set to 30°. This angle α will hereinafter also be referred to as "injection hole axis inclination α". Also, a spark plug was prepared as sample 2, in which the direction of the nozzle hole when viewed from the plug axial direction Z was the plug radial direction. This spark plug of sample 2 corresponds to one in which the nozzle hole axis inclination α is 0°. The inclination of the nozzle hole axis with respect to the plug axial direction Z is the same for sample 1 and sample 2.

[0044] These samples 1 and 2 were attached to an internal combustion engine and evaluated by operating it at 6500 rpm with the throttle fully open. The evaluation of plague resistance was based on how far the ignition timing had to be advanced before plague began to occur. In other words, generally, the more the ignition timing is advanced, the easier plague will occur, so the greater the advance amount at which plague begins to occur, the better the plague resistance.

[0045] The advance amount here is the amount of advance from MBT (Minimum advance for the Best Torque), which is the optimal ignition timing. If the advance amount at which plague begins to occur is 5° or less, it is rated as poor. If the advance amount at which plague begins to occur is 6 to 19°, it is rated as good. If the advance amount at which plague begins to occur is 20° or more, it is rated as excellent.

[0046] As a result of the test, sample 2 was evaluated as "good," whereas sample 1 was evaluated as "excellent." This result shows that the spark plug 1 of embodiment 1 can improve the plague resistance.

[0047] (Experimental Example 2) In this example, as shown in FIG. 16, a change in the fuel thinning near the protruding end edge 62 of the ground electrode 6 during the compression stroke of an internal combustion engine was examined by simulation. A similar simulation was performed for each of Sample 1 and Sample 2 prepared in the above Experimental Example 1. The operating conditions were the same as those in Experimental Example 1.

[0048] The fuel leanness was evaluated as (total gas mass) / (fuel mass) at the evaluation position. Hereinafter, this will be referred to as G / F where appropriate. A larger G / F indicates a lower fuel ratio at the evaluation position. The evaluation position was a position between the protruding end edge 62 of the ground electrode 6 and the plug cover 5 in the plug axial direction Z. The evaluation results are shown in FIG. 16.

[0049] In the figure, the horizontal axis represents time and crank angle, and the vertical axis represents G / F at the evaluation position. The solid curve S1 represents the data for sample 1, and the dashed curve S2 represents the data for sample 2.

[0050] As can be seen from the figure, the G / F at the evaluation position is higher for Sample 1 than for Sample 2, and the difference is particularly noticeable at -90° to -60° ATDC. Therefore, it can be said that Sample 1 prevents the air-fuel mixture from reaching the vicinity of the protruding edge of the ground electrode early. This result is consistent with the mechanism discussed so far.

[0051] In addition to the above-described embodiment, various other configurations are possible. For example, the number of nozzle holes may be three or five or more. In these cases, the polygons P1 and P2 described above are triangular or have pentagons or more.

[0052] The present invention is not limited to the above-described embodiments, and can be applied to various embodiments without departing from the gist of the present invention. [Explanation of symbols]

[0053] 1. Spark plugs for internal combustion engines 2. Housing 3. Insulators 4 Center electrode 5 Plug cover 50 Auxiliary combustion chamber 51 Spray hole 6 Ground electrode 61 Fixed end 62 Protruding edge

Claims

1. A cylindrical insulator (3); a center electrode (4) held on the inner circumferential side of the insulator and protruding from the insulator toward the tip side; a cylindrical housing (2) that holds the insulator on its inner periphery; a ground electrode (6) forming a discharge gap (G) between itself and the center electrode; a plug cover (5) provided at the tip of the housing so as to cover a sub-combustion chamber (50) in which the discharge gap is disposed, The ground electrode protrudes into the auxiliary combustion chamber from a fixed end portion (61) fixed to the housing or the plug cover on the outer circumferential side of the auxiliary combustion chamber, The plug cover is formed with three or more nozzle holes (51) that communicate the auxiliary combustion chamber with the outside, When viewed from the plug axial direction (Z), the injection hole axis (51L) of the injection hole is inclined with respect to the plug radial direction, a projecting end edge (62) of the ground electrode is disposed inside a polygon (P1) formed by the nozzle hole axes of the three or more nozzle holes as viewed in the plug axial direction, the injection hole is formed on a tip side in the plug axial direction relative to a projecting end edge of the ground electrode, A spark plug for an internal combustion engine (1), wherein the nozzle hole axis passes further toward the base end in the plug axial direction than the protruding end edge of the ground electrode when viewed in a direction perpendicular to both the nozzle hole axis and the plug axial direction.

2. 2. A spark plug for an internal combustion engine according to claim 1, wherein a protruding end edge of said ground electrode is disposed inside a polygon (P2) formed by contour lines on a side closer to a central axis of the plug in an extension region (51E) obtained by extending said three or more nozzle holes in parallel to their respective nozzle hole axes, as viewed in a plug axial direction.

3. 3. A spark plug for an internal combustion engine according to claim 1, wherein an extension region (51E) obtained by extending the nozzle hole parallel to a nozzle hole axis passes on a base end side in the plug axial direction relative to a protruding end edge of the ground electrode when viewed in a direction perpendicular to both the nozzle hole axis and the plug axial direction.

4. 4. The spark plug for an internal combustion engine according to claim 1, wherein at least a part of a projecting edge of said ground electrode is disposed at a position overlapping said center electrode when viewed in the plug axial direction.

5. 5. The spark plug for an internal combustion engine according to claim 1, wherein the ground electrode is inclined from the fixed end portion toward the protruding end edge toward a tip side in the plug axial direction.

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