Spark plug for internal combustion engine

Abstract

To provide a spark plug for an internal combustion engine that can restrain overheating of a ground electrode.SOLUTION: In a spark plug 1, a plug cover 5 is provided at the tip portion of a housing 2 so as to cover a sub-combustion chamber 50 in which a discharge gap G is arranged. A ground electrode 6 has an upright portion 62, a bent portion 63, and an extended portion 64. Further, the ground electrode 6 has an outer layer portion 65 mainly composed of nickel, and a core portion 66 which is disposed inside the outer layer portion 65 and mainly composed of copper. When the height of the ground electrode 6 in a plug axial direction Z is represented by H mm, and the mass ratio of the core portion 66 to the entire ground electrode 6 is represented by Wcu mass%, the spark plug 1 satisfies the following formula (1): H≤(2×Wcu / 17)+2.5 (1)SELECTED DRAWING: Figure 3

Description

Technical Field

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

Background Art

[0002] For example, as disclosed in Patent Document 1, a spark plug for an internal combustion engine having a sub-combustion chamber at the tip is known. In this spark plug, the plug cover covering the sub-combustion chamber has a reduced thickness at the tip portion. This is intended to suppress the tip portion from becoming hot and to suppress the ignition of the air-fuel mixture (i.e., pre-ignition) before the generation of discharge by the spark plug.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, although the spark plug described in Patent Document 1 takes into consideration suppressing overheating of the plug cover, it does not consider suppressing overheating of the ground electrode. Therefore, there is a concern about pre-ignition starting from the ground electrode, and it can be said that there is room for further improvement.

[0005] The present invention has been made in view of such problems, and aims to provide a spark plug for an internal combustion engine that can suppress overheating of the ground electrode.

Means for Solving the Problems

[0006] An aspect of the present invention is a cylindrical insulator (3), and First a A center electrode (4) that is held on the inner peripheral side of the insulator and exposed from the insulator toward the tip side, A cylindrical housing (2) that holds the insulator on the inner peripheral side, A ground electrode (6) that forms a discharge gap (G) with the center electrode, A plug cover (5) provided at the tip of the housing so as to cover a sub-combustion chamber (50) where the discharge gap is disposed, The plug cover is formed with a spray hole (51) that communicates the sub-combustion chamber with the outside, The ground electrode protrudes into the sub-combustion chamber from a fixed end portion (61) fixed to the housing tip side surface (21) at the tip of the housing, The ground electrode has the fixed end portion, an erected portion (62) erected from the housing tip side surface toward the tip side, a bent portion (63) bent from the tip of the erected portion toward the inside in the plug diameter direction, and an extended portion (64) extended from the bent portion toward the inside in the plug diameter direction, The ground electrode has an outer layer portion (65) mainly composed of nickel and a core portion (66) disposed inside the outer layer portion and mainly composed of copper, The discharge gap is formed by the tip of the center electrode and the extended portion of the ground electrode facing each other in the plug axis direction (Z), When the height of the ground electrode in the plug axis direction is Hmm and the mass ratio of the core portion to the entire ground electrode is Wcu mass%, the following formula (1) is satisfied Shi 、 The plug cover has a peripheral wall portion (52) that covers the outer peripheral side of the sub-combustion chamber, a bottom wall portion (53) that covers the tip side of the sub-combustion chamber, and a corner portion (54) that connects the tip of the peripheral wall portion and the outer periphery of the bottom wall portion in a curved surface shape. A gap (g1) is formed between the extended portion and the bottom wall portion, and the distance (D1) between the extended portion and the bottom wall portion in the plug axis direction is equal to or less than the thickness (T2) of the plug cover. It is in a spark plug (1) for an internal combustion engine. H ≦ (2 × Wcu / 17) + 2.5 ··· (1) The second aspect of the present invention is a cylindrical insulator (3), a center electrode (4) held on the inner peripheral side of the insulator and exposed from the insulator to the tip side, a cylindrical housing (2) that holds the insulator on the inner peripheral side, a ground electrode (6) that forms a discharge gap (G) between the center electrode, and a plug cover (5) provided at the tip of the housing so as to cover the sub-combustion chamber (50) where the discharge gap is arranged. The plug cover is formed with a nozzle hole (51) that communicates the sub-combustion chamber with the outside. The ground electrode projects into the sub-combustion chamber from a fixed end portion (61) fixed to the housing tip side surface (21) at the tip of the housing. The ground electrode has the fixed end portion, a standing portion (62) standing from the housing tip side surface to the tip side, a bent portion (63) bent inward in the plug diameter direction from the tip of the standing portion, and an extended portion (64) extended inward in the plug diameter direction from the bent portion. The ground electrode has an outer layer portion (65) mainly composed of nickel and a core portion (66) arranged inside the outer layer portion and mainly composed of copper. The discharge gap is formed by the tip portion of the center electrode and the extended portion of the ground electrode facing each other in the plug axis direction (Z). When the height of the ground electrode in the plug axis direction is Hmm and the mass ratio of the core portion to the entire ground electrode is Wcu mass%, the following formula (1) is satisfied. The plug cover has a peripheral wall portion (52) that covers the outer peripheral side of the sub-combustion chamber, a bottom wall portion (53) that covers the tip side of the sub-combustion chamber, and a corner portion (54) that connects the tip of the peripheral wall portion and the outer periphery of the bottom wall portion in a curved surface shape. The plug cover has a cover recess (56) formed by a part of the circumferential direction on its inner peripheral surface (55) retreating outward in the plug diameter direction. In the plug cover, the cover recess opens to the base end side. The cover recess is formed from the peripheral wall portion to the corner portion, A spark plug (1) for an internal combustion engine, wherein at least a part of the standing portion is disposed inside the cover recess. H≦(2×Wcu / 17)+2.5 ···(1)

Advantages of the Invention

[0007] The spark plug has a ground electrode having a core portion mainly composed of copper and satisfies the above formula (1). Therefore, the heat of the ground electrode is easily dissipated to the outside, and the heat reception of the ground electrode due to combustion in the main combustion chamber can be suppressed. As a result, overheating of the ground electrode 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 can suppress overheating of the ground electrode. Note that the reference numerals in parentheses described in the claims and the means for solving the problems indicate the correspondence with the specific means described in the embodiments described later, and do not limit the technical scope of the present invention.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Best Mode for Carrying Out the Invention

[0010] (Embodiment 1) An embodiment of a spark plug for an internal combustion engine will be described with reference to FIGS. 1 to 11. The spark plug 1 for an internal combustion engine of this embodiment has 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. 1 and 2. The center electrode 4 is held on the inner peripheral side of the insulator 3 and exposed from the insulator 3 to the tip side. The housing 2 holds the insulator 3 on the inner peripheral side. The ground electrode 6 forms a discharge gap G with the center electrode 4. The plug cover 5 is provided at the tip of the housing 2 so as to cover the sub-combustion chamber 50 where the discharge gap G is arranged. The plug cover 5 is formed with an injection hole 51 that communicates the sub-combustion chamber 50 with the outside.

[0011] The ground electrode 6 protrudes into the sub-combustion chamber 50 from a fixed end portion 61 fixed to the housing tip side surface 21 at the tip of the housing 2. The ground electrode 6 has an upright portion 62, a bent portion 63, and an extended portion 64. The upright portion 62 has the fixed end portion 61 and stands upright from the housing tip side surface 21 toward the tip side. The bent portion 63 bends from the tip of the upright portion 62 toward the inside in the plug diameter direction. The extended portion 64 extends from the bent portion 63 toward the inside in the plug diameter direction.

[0012] Further, the ground electrode 6 has an outer layer portion 65 mainly composed of nickel and a core portion 66 arranged inside the outer layer portion 65 and mainly composed of copper.

[0013] The discharge gap G is formed by the tip of the center electrode 4 and the extended portion 64 of the ground electrode 6 facing each other in the plug axis direction Z.

[0014] As shown in FIG. 3, let the height of the ground electrode 6 in the plug axis direction Z be Hmm, and the mass ratio of the core portion 66 to the entire ground electrode 6 be Wcu mass%. At this time, the spark plug 1 satisfies the following formula (1). H ≦ (2 × Wcu / 17) + 2.5 ···(1)

[0015] Further, it is more preferable that the spark plug 1 further satisfies the following formula (2). H ≦ (2 × Wcu / 17) + 0.5 ···(2)

[0016] The spark plug 1 of this embodiment can be used, for example, as an ignition means in an internal combustion engine such as an automobile. As shown in FIG. 5, the screw portion 22 of the housing 2 is screwed into the female screw portion of the plug hole 711 of the cylinder head 71, and the spark plug 1 is attached to the internal combustion engine 10. The housing 2 is in thermal contact with the cylinder head 71.

[0017] The internal combustion engine 10 includes a piston 74 that reciprocates within a cylinder 70. The main combustion chamber 101 changes in volume due to the reciprocating motion of the piston 74. The internal combustion engine 10 is formed with an intake port 721 and an exhaust port 731, and is provided with an intake valve 72 or an exhaust valve 73 respectively.

[0018] One end of the spark plug 1 in the axial direction Z is disposed in the main combustion chamber 101 of the internal combustion engine 10. In the axial direction Z of the spark plug 1, the side exposed to the main combustion chamber 101 is defined as the tip side, and the opposite side is defined as the base end side. Also, the axial direction Z of the spark plug 1 is appropriately referred to as the plug axial direction Z or simply the Z direction. Note that the plug central axis C means the central axis of the spark plug 1. Also, the plug radial direction means the radial direction of a circle centered on the plug central axis C on a plane orthogonal to the plug central axis C. Also, the plug central axis C is also the central axis of the center electrode 4 in the present embodiment.

[0019] In the present embodiment, the plug cover 5 is joined to the tip of the housing 2 by welding or the like. In a state where the spark plug 1 is attached to the internal combustion engine 10, the plug cover 5 partitions the sub-combustion chamber 50 from the main combustion chamber 101. Also, the injection hole 51 communicates the sub-combustion chamber 50 with the main combustion chamber 101.

[0020] As shown in FIG. 3, the plug cover 5 has a peripheral wall portion 52, a bottom wall portion 53, and a corner portion 54. The peripheral wall portion 52 is a substantially cylindrical portion that covers a part of the outer peripheral side of the sub-combustion chamber 50. The bottom wall portion 53 is a portion that covers the tip side of the sub-combustion chamber 50. The corner portion 54 is a portion that connects the tip of the peripheral wall portion 52 and the outer periphery of the bottom wall portion 53 in a curved surface shape. The base end portion of the peripheral wall portion 52 is joined to the tip of the housing 2. The plug cover 5 is in thermal contact with the housing 2.

[0021] Also, the injection hole 51 is formed in the corner portion 54 of the plug cover 5. The injection hole 51 is inclined and opens in the Z direction so as to go outward in the plug radial direction toward the tip side.

[0022] Further, as shown in FIGS. 1 and 2, the plug cover 5 has a cover recess 56 formed by a part of the circumferential direction on its inner peripheral surface 55 retreating outward in the plug radial direction. The cover recess 56 is formed from the peripheral wall portion 52 to the corner portion 54. The cover recess 56 is open at the proximal end side. Further, at least a part of the standing portion 62 of the ground electrode 6 is disposed inside the cover recess 56.

[0023] In this embodiment, the ground electrode 6 is fixed to the front end side surface 21 of the housing without contacting the plug cover 5. The ground electrode 6 is in thermal contact with the housing 2. Further, as shown in FIG. 3, a gap g1 is formed between the extending portion 64 of the ground electrode 6 and the bottom wall portion 53 of the plug cover 5. The distance D1 between the extending portion 64 and the bottom wall portion 53 in the Z direction is equal to or less than the thickness T2 of the plug cover 5. In this embodiment, the distance D1 is 0.5 to 1.0 mm. Further, the height H of the ground electrode 6 in the Z direction is 1.5 mm or more.

[0024] As shown in FIG. 4, the cross section orthogonal to the extending direction of the ground electrode 6 has a substantially rectangular parallelepiped shape. The thickness T1 of the ground electrode 6 is smaller than the width W1 of the ground electrode 6. In this embodiment, the thickness T1 is 1.0 mm or more.

[0025] Further, as shown in FIG. 3, the fixed end portion 61 of the ground electrode 6 is joined to the front end side surface 21 of the housing by welding. The outer layer portion 65 and the core portion 66 are directly fixed to the front end side surface 21 of the housing, respectively. The core portion 66 is sealed by the outer layer portion 65 and the front end side surface 21 of the housing.

[0026] The outer layer portion 65 is formed from the fixed end portion 61 to the protruding end portion 67 of the ground electrode 6. Further, the core portion 66 is formed from the fixed end portion 61 to the extending portion 64. In this embodiment, the core portion 66 is not provided at the protruding end portion 67.

[0027] In this embodiment, the mass ratio Wcu of the core portion 66 to the entire ground electrode 6 is 10% by mass or more and 25% by mass or less. Also, the core portion 66 has a higher thermal conductivity than the outer layer portion 65. In this embodiment, the copper content in the core portion 66 is 99% by mass or more. Also, the nickel content in the outer layer portion 65 is 85% by mass or more.

[0028] Also, the ground electrode 6 is disposed inside the core portion 66 and has a shaft portion 68 mainly composed of nickel. The shaft portion 68 is formed from the fixed end portion 61 to the extended portion 64. The nickel content in the shaft portion 68 is 85% by mass or more.

[0029] Also, as shown in FIGS. 1, 3, and 4, the ground electrode 6 has a multilayer structure in which the outer layer portion 65, the core portion 66, and the shaft portion 68 overlap in both the thickness direction and the width direction of the ground electrode 6.

[0030] Also, as shown in FIGS. 1 and 3, a chip 69 is joined to the protruding end portion 67 of the extended portion 64. Also, a chip 41 is joined to the tip end portion of the center electrode 4. The discharge gap G is formed by the flat base end surface of the chip 69 and the flat tip end surface of the chip 41 facing each other in the Z direction. As shown in FIG. 2, when viewed from the Z direction, the core portion 66 is formed so as not to overlap the chip 69. The chips 41 and 69 can be made of, for example, a noble metal such as iridium or platinum, or an alloy mainly composed of these.

[0031] Also, as shown in FIGS. 1 and 3, the discharge gap G is formed on the tip end side of the tip of the housing 2. That is, the tip end of the center electrode 4 is located on the tip end side of the tip of the housing 2.

[0032] Next, a method for forming the ground electrode 6 in this embodiment will be described. In this embodiment, the ground electrode 6 is formed by bending a rod-shaped electrode material. Specifically, first, as shown in FIG. 6, before assembling the center electrode 4, the insulator 3, and the plug cover 5 to the housing 2, a substantially quadrangular prism-shaped electrode material 60 is joined to the front-end side surface 21 of the housing. When joining the electrode material 60, while setting the longitudinal direction of the electrode material 60 along the Z direction, the base end surface of the electrode material 60 and the front-end side surface 21 of the housing are brought into contact with each other in the Z direction, and welding is performed. Thereafter, the chip 69 is welded to the electrode material 60. Further, if necessary, the length of the electrode material 60 in the Z direction is adjusted by cutting a part of the electrode material 60.

[0033] Next, the insertion jig 91 is inserted into the housing 2 to which the electrode material 60 is joined. At this time, the insertion jig 91 is arranged so that the tip of the insertion jig 91 is positioned on the tip side of the tip of the housing 2. Further, the protruding amount of the insertion jig 91 from the tip of the housing 2 toward the tip side is adjusted according to the height H of the ground electrode 6.

[0034] Thereafter, as shown in FIG. 7, the electrode material 60 joined to the housing 2 is bent inward in the plug diameter direction using the bending jig 92. Specifically, the bending jig 92 has a recess 921 for inserting a part of the electrode material 60. Then, with a part of the electrode material 60 inserted into the recess 921, the electrode material 60 is bent inward in the plug diameter direction.

[0035] Thereafter, as shown in FIG. 8, a part of the bent electrode material 60 is pressed toward the base end side by the hand press 93. Thereby, as shown in FIGS. 1 and 3, the ground electrode 6 having the standing portion 62, the bent portion 63, and the extending portion 64 can be formed.

[0036] After forming the ground electrode 6, the insertion jig 91 is removed, and the insulator 3 that holds the center electrode 4 on the inner peripheral side is assembled to the housing 2. Then, if necessary, the ground electrode 6 fixed to the housing 2 is slightly deformed, and fine adjustment is performed so that the discharge gap G becomes an appropriate distance. Then, the plug cover 5 is joined to the tip of the housing 2. Thus, as shown in FIGS. 1 to 3, the spark plug 1 of this embodiment can be manufactured.

[0037] Next, a method for manufacturing the electrode material 60 to be joined to the housing 2 will be described. In manufacturing the electrode material 60, first, a substantially cylindrical member mainly composed of nickel is subjected to press working to produce a bottomed cylindrical first member 650 that becomes the outer layer portion 65 as shown in FIG. 9. Then, as shown in FIG. 10, a substantially cylindrical clad member 601 is assembled inside the concave portion 651 of the first member 650. The clad member 601 has a cylindrical second member 660 mainly composed of copper that becomes the core portion 66, and a third member 680 mainly composed of nickel that becomes the shaft portion 68. The third member 680 is disposed inside the second member 660. Also, in the clad member 601, the second member 660 and the third member 680 are crimped to each other.

[0038] Next, as shown in FIG. 11, the clad member 601 assembled to the first member 650 is pressed by a pressing jig 94 to crimp the clad member 601 and the first member 650 to each other. Then, annealing is performed on the member composed of the clad member 601 and the first member 650. Next, the annealed member is formed into a substantially quadrangular prism shape using a mold. Then, further annealing is performed on the member that has become a substantially quadrangular prism shape. And the electrode material 60 can be produced by removing unnecessary portions from the annealed member as necessary.

[0039] Next, the operation and effects of this embodiment will be described. The spark plug 1 has a ground electrode 6 having a core portion 66 mainly composed of copper and satisfies the above formula (1). Therefore, the heat of the ground electrode 6 can be easily radiated to the outside, and the heat reception of the ground electrode 6 due to combustion in the main combustion chamber 101 can be suppressed. As a result, overheating of the ground electrode 6 can be suppressed.

[0040] The spark plug 1 of this embodiment ignites the air-fuel mixture in the auxiliary combustion chamber 50 by generating a discharge in the discharge gap G to form a flame. Then, the flame generated in the auxiliary combustion chamber 50 is ejected as a flame jet into the main combustion chamber 101 through the injection holes 51. Thereby, the flame is propagated in the main combustion chamber 101 to burn the air-fuel mixture. Here, due to the influence of cooling by the cylinder 70 and the piston 74 during combustion, the temperature at the center of combustion, that is, near the center of the main combustion chamber 101, tends to be the highest. Therefore, the lower the height H and the smaller the protruding amount of the ground electrode 6 into the main combustion chamber 101, the easier it is to suppress the heat reception of the ground electrode 6. Further, the lower the height H, the shorter the heat dissipation path from the protruding end portion 67 where the temperature particularly tends to be high to the housing tip side surface 21, and the easier it is to suppress overheating of the ground electrode 6. Further, the ground electrode 6 has a core portion 66 mainly composed of copper having a relatively high thermal conductivity. Therefore, the higher the mass ratio Wcu, the easier it is to radiate the heat of the ground electrode 6 to the outside through the housing 2, and the easier it is to suppress overheating of the ground electrode 6. On the other hand, if the height H is made too small, a load is likely to be applied to the joint portion between the housing 2 and the ground electrode 6 when the electrode material 60 is bent, and the manufacturability tends to deteriorate. Further, if the mass ratio Wcu is made too high, it becomes difficult to sufficiently seal the core portion 66 with the outer layer portion 65, and the manufacturability of the ground electrode 6 tends to deteriorate. Therefore, the spark plug 1 of this embodiment satisfies the above formula (1). By adjusting the height H and the mass ratio Wcu within the range of the above formula (1), it is possible to suppress overheating of the ground electrode 6 while ensuring the manufacturability of the ground electrode 6. Therefore, pre-ignition can be suppressed at high load when the operating efficiency of the internal combustion engine is high. As a result, the output and fuel consumption of the internal combustion engine can be improved.

[0041] As described above, the spark plug 1 can easily dissipate the heat of the ground electrode 6 to the outside and suppress the heat reception of the ground electrode 6. Therefore, even if the heat of the bottom wall portion 53 is transmitted to the extended portion 64 through the gap g1 (see FIG. 3), the overheating of the ground electrode 6 can be sufficiently suppressed. In particular, when the gap g1 is small, the heat reception of the ground electrode 6 from the bottom wall portion 53 of the plug cover 5 tends to increase, but the overheating of the ground electrode 6 can be suppressed by the configuration of this embodiment.

[0042] Further, by reducing the height H, the height of the plug cover 5 in the Z direction can also be reduced. That is, the protruding amount of the plug cover 5 into the main combustion chamber can be reduced. Therefore, the distance from the center of the main combustion chamber 101 to the plug cover 5 can be increased, and further, the heat dissipation path from the tip of the plug cover 5 to the housing 2 can be shortened. As a result, the overheating of the plug cover 5 can be suppressed.

[0043] In addition, when the spark plug 1 further satisfies the above formula (2), the heat of the ground electrode 6 can be more easily dissipated to the outside, and the heat reception of the ground electrode 6 can be further suppressed. Therefore, the overheating of the ground electrode 6 can be further suppressed. As a result, even when used as the spark plug 1 for a high-efficiency engine such as a high compression ratio automotive engine or an automotive engine equipped with a supercharger, pre-ignition can be sufficiently suppressed.

[0044] The height H is 1.5 mm or more. Therefore, it is easy to form the ground electrode 6 having the standing portion 62, the bent portion 63, and the extended portion 64. As a result, the productivity of the spark plug 1 can be improved.

[0045] In addition, the core portion 66 is directly fixed to the side surface 21 of the tip of the housing. Therefore, the heat of the ground electrode 6 can be efficiently transmitted to the housing 2. As a result, the overheating of the ground electrode 6 can be further suppressed.

[0046] Further, a core portion 66 is not formed in the protruding end portion 67. Therefore, when welding the chip 69 to the electrode material 60, it is less likely to be affected by the core portion 66 mainly composed of copper. Therefore, it is easy to weld the chip 69 to the electrode material 60. As a result, the productivity of the spark plug 1 can be improved.

[0047] The discharge gap G is formed on the tip side of the tip of the housing 2. Therefore, before fixing the plug cover 5 to the housing 2, it is easy to check the distance of the discharge gap G formed between the ground electrode 6 fixed to the housing 2 and the center electrode 4. Therefore, the adjustment of the discharge gap G can be easily performed. As a result, the productivity of the spark plug 1 can be improved.

[0048] Further, at least a part of the standing portion 62 is disposed inside the cover recess 56. Therefore, it is easy to widen the joining range between the ground electrode 6 and the tip side surface 21 of the housing. That is, the joining range between the ground electrode 6 and the tip side surface 21 of the housing can be widened by the portion where a part of the standing portion 62 is disposed inside the cover recess 56. Therefore, the heat of the ground electrode 6 is more likely to move to the housing 2. As a result, overheating of the ground electrode 6 can be further suppressed.

[0049] The ground electrode 6 has a standing portion 62, a bent portion 63, and an extending portion 64. Therefore, the strength of the joint portion between the ground electrode 6 and the housing 2 can be surely ensured, and overheating of the ground electrode 6 can be further suppressed. That is, in this embodiment, the ground electrode 6 can be fixed to the housing 2 by abutting the base end surface of the rod-shaped electrode material 60 and the tip side surface 21 of the housing in the Z direction and performing welding. Therefore, the ground electrode 6 can be firmly joined to the housing 2. Further, the heat of the ground electrode 6 can be more efficiently dissipated to the outside through the joint portion between the housing 2 and the ground electrode 6.

[0050] The core portion 66 is sealed by the outer layer portion 65 and the housing tip side surface 21. Therefore, it is possible to surely prevent the elution of the core portion 66 mainly composed of copper having a relatively low melting point. As a result, the heat dissipation property of the ground electrode 6 can be surely maintained.

[0051] As described above, according to this embodiment, it is possible to provide the spark plug 1 for an internal combustion engine that can suppress overheating of the ground electrode 6.

[0052] In the above-described Embodiment 1, the ground electrode 6 has a shaft portion 68. However, the ground electrode may be configured not to have a shaft portion.

[0053] (Experimental Example 1) In this example, while the basic structure is the same as that of Embodiment 1, a plurality of spark plugs having different values of the height H and the mass ratio Wcu are used to analyze the relationship between the values of the height H and the mass ratio Wcu and the ignition advance angle from MBT (abbreviation for Minimum Spark Advance for Best Torque) when pre-ignition occurs. Generally, the more the ignition timing is advanced from MBT, the easier it is for pre-ignition to occur. Therefore, in this example, for each internal combustion engine equipped with each spark plug, the ignition timing was gradually advanced from MBT, and the ignition timing at which pre-ignition occurred was analyzed. The test conditions were that the internal combustion engine was a single-cylinder four-stroke engine, the throttle was fully open, and the rotational speed was 6500 rpm.

[0054] Here, when the ignition timing at which pre-ignition occurs advances by 5°CA (abbreviation for crank angle) or more from MBT, it is regarded as a criterion that can sufficiently suppress pre-ignition when used as a spark plug for a general automotive engine. Therefore, from the above analysis results, the relationship between the height H and the mass ratio Wcu that satisfies this criterion was obtained. Also, when the ignition timing at which pre-ignition occurs advances by 10°CA or more from MBT, it is regarded as a criterion that can sufficiently suppress pre-ignition when used as a spark plug for a high-efficiency engine such as a high compression ratio automotive engine or an automotive engine equipped with a supercharger. Therefore, from the above analysis results, the relationship between the height H and the mass ratio Wcu that satisfies this criterion was obtained. Also, in this example, MBT is 20°CA BTDC (abbreviation for before top dead center of compression).

[0055] The graph in Fig. 12 is a graph showing the relationship between the height H and the advance angle amount from MBT for each of the spark plugs with different mass ratios Wcu. In the graph of Fig. 12, the circles and squares are the plotted analysis results of the respective spark plugs. Also, an approximate straight line in these plots is shown in the graph of Fig. 12.

[0056] From the graph in Fig. 12, it can be seen that regardless of the value of the mass ratio Wcu, the smaller the height H, the more the ignition timing at which pre-ignition occurs advances. From this result, it is considered that the shorter the height H, the more the overheating of the plug cover can be suppressed, and pre-ignition can be suppressed.

[0057] Also, from the graph in Fig. 12, it can be seen that regardless of the value of the height H, the larger the value of the mass ratio Wcu, the more the ignition timing at which pre-ignition occurs advances. From this result, it is considered that the larger the value of the mass ratio Wcu, the more the overheating of the plug cover can be suppressed, and pre-ignition can be suppressed.

[0058] Also, from each of the approximate straight lines shown in the graph of FIG. 12, the height H when the advance angle from MBT is 5°CA and the height H when the advance angle from MBT is 10°CA were obtained. And the graph showing the relationship between the obtained height H and the mass ratio Wcu is the graph of FIG. 13. In the graph of FIG. 13, the circles plot the values of the height H obtained from the approximate straight lines of the graph of FIG. 12. Also, an approximate straight line for these plots is shown in the graph of FIG. 13. Here, the equation of the approximate straight line when the advance angle from MBT is 5°CA is the following equation (3). Also, the equation of the approximate straight line when the advance angle from MBT is 10°CA is the following equation (4). H=(2×Wcu / 17)+2.5 ···(3) H=(2×Wcu / 17)+0.5 ···(4)

[0059] Also, in the graph of FIG. 13, the range below the approximate straight line of equation (3) is the combination of the height H and the mass ratio Wcu when the ignition timing at which pre-ignition occurs is advanced by 5°CA or more from MBT. That is, the spark plug of Embodiment 1 that satisfies the above equation (1) can sufficiently suppress pre-ignition when used as a spark plug for a general automotive engine. Also, in the graph of FIG. 13, the range below the approximate straight line of equation (4) is the combination of the height H and the mass ratio Wcu when the ignition timing at which pre-ignition occurs is advanced by 10°CA or more from MBT. That is, the spark plug that satisfies the above equation (2) can sufficiently suppress pre-ignition when used as a spark plug for a high-efficiency engine.

[0060] (Experimental Example 2) In this example, as shown in Table 1 below, using a plurality of spark plugs with different heights H, the relationship between the height H and the manufacturability of the ground electrode was analyzed. Also, in each spark plug, the electrode material serving as the ground electrode had a width of 2.15 mm and a thickness of 1.0 mm. Sample 1 is a spark plug in which the value of the mass ratio Wcu of the ground electrode is 17% by mass while the basic structure is the same as that of Embodiment 1. That is, Sample 1 has a core portion mainly composed of copper. Samples 2 to 5 are spark plugs having a ground electrode without a core portion and a shaft portion. Also, in Samples 2 to 5, other configurations are the same as those of Embodiment 1.

[0061] [Table 1]

[0062] Also, in this example, the evaluation of manufacturability was performed on the bending strength when bending the ground electrode and the strength of the joint between the fixed end of the ground electrode and the side surface of the tip of the housing. Also, for the evaluation of the bending strength, as shown in Table 1, the case where no crack was observed in the bent portion was indicated as "○", and the case where a crack occurred in the bent portion was indicated as "×". Also, for the evaluation of the joint strength, as shown in Table 1, the case where no peeling was observed at the joint between the fixed end of the ground electrode and the side surface of the tip of the housing was indicated as "○", and the case where peeling was observed at the joint was indicated as "×". Also, the determination of manufacturability shown in Table 1 was "○" when the evaluations of both the bending strength and the joint strength were "○", and "×" when at least one of the evaluations of the bending strength and the joint strength was "×". And when the determination in Table 1 was "○", it was judged that there was no problem with the manufacturability.

[0063] From Table 1, for Samples 1, 3 to 5, the determination of manufacturability was "○". On the other hand, for Sample 2, the evaluation of the joint strength was "×", and the determination of manufacturability was "×". Sample 2 and Samples 3 to 5 have the same configuration except for the height H. Therefore, it is considered that in Sample 2, the height H was too low, causing excessive load on the joint, resulting in the evaluation of the joint strength being "×". Also, for Samples 3 to 5 with a height H of 1.5 mm or more, the determination of manufacturability was "○". Therefore, it is considered that by setting the height H to 1.5 mm or more, the manufacturability of the grounding electrode can be surely ensured.

[0064] Also, although Sample 1 has the same height H of 1.3 mm as Sample 2, the evaluation of the joint strength was "○", and the determination of manufacturability was "○". Here, Sample 1 has a core part mainly composed of copper. Therefore, it is presumed that the hardness of the electrode material was relatively low, and the electrode material could be easily bent. Therefore, when bending the electrode material, it is presumed that less load was applied to the joint, resulting in the evaluation of the joint strength being "○". From this result, in the case of a grounding electrode with a core part, it is considered that by setting the height H of the grounding electrode to 1.3 mm or more, the manufacturability of the grounding electrode can be surely ensured. Also, when the height H is 1.5 mm or more, even for Samples 3 to 5 without a core part, since the determination of manufacturability was "○", as in Embodiment 1, by providing a core part and further setting the height H to 1.5 mm or more, it is considered that the manufacturability can be surely improved.

[0065] The present invention is not limited to the above-described embodiments, and can be applied to various embodiments without departing from the gist thereof.

Explanation of Reference Numerals

[0066] 1... Spark plug, 2... Housing, 21... Side surface of the tip of the housing, 3... Insulator, 4... Center electrode, 5... Plug cover, 50... Sub-combustion chamber, 51... Injection hole, 6... Grounding electrode, 61... Fixed end portion, 62... Standing portion, 63... Bending portion, 64... Extended portion, 65... Outer layer portion, 66... Core portion, G... Discharge gap, Z... Axial direction of the plug

Claims

1. A cylindrical insulator (3); A center electrode (4) held on the inner peripheral side of the insulator and exposed from the insulator toward the tip side; A cylindrical housing (2) that holds the insulator on the inner peripheral side; A ground electrode (6) that forms a discharge gap (G) between the center electrode; A plug cover (5) provided at the tip of the housing so as to cover a sub-combustion chamber (50) where the discharge gap is arranged; and has, The plug cover is formed with a nozzle hole (51) that communicates the sub-combustion chamber with the outside, The ground electrode protrudes into the sub-combustion chamber from a fixed end (61) fixed to the housing tip side surface (21) at the tip of the housing, The ground electrode has the fixed end and a standing portion (62) standing from the housing tip side surface toward the tip side, a bent portion (63) bent from the tip of the standing portion toward the inside in the plug diameter direction, and an extending portion (64) extending from the bent portion toward the inside in the plug diameter direction, The ground electrode has an outer layer portion (65) mainly composed of nickel and a core portion (66) arranged inside the outer layer portion and mainly composed of copper, The discharge gap is formed by the tip of the center electrode and the extending portion of the ground electrode facing each other in the plug axis direction (Z), When the height of the ground electrode in the plug axis direction is H mm and the mass ratio of the core portion to the entire ground electrode is Wcu mass%, the following formula (1) is satisfied, The plug cover has a peripheral wall portion (52) that covers the outer peripheral side of the sub-combustion chamber, a bottom wall portion (53) that covers the tip side of the sub-combustion chamber, and a corner portion (54) that connects the tip of the peripheral wall portion and the outer periphery of the bottom wall portion in a curved surface shape, A gap (g1) is formed between the extending portion and the bottom wall portion, and the distance (D1) between the extending portion and the bottom wall portion in the plug axis direction is equal to or less than the thickness (T2) of the plug cover. A spark plug (1) for an internal combustion engine. H ≤ (2 × Wcu / 17) + 2.5... (1)

2. The plug cover has a cover recess (56) formed by a part of the inner peripheral surface (55) retreating outward in the plug diameter direction in the circumferential direction, In the plug cover, the cover recess opens to the base end side, The cover recess is formed from the peripheral wall portion to the corner portion, The spark plug for an internal combustion engine according to claim 1, wherein at least a part of the standing portion is disposed inside the cover recess.

3. A cylindrical insulating insulator (3), A center electrode (4) held on the inner peripheral side of the insulator and exposed from the insulator to the tip side, A cylindrical housing (2) that holds the insulator on the inner peripheral side, A ground electrode (6) that forms a discharge gap (G) between the center electrode, A plug cover (5) provided at the tip of the housing so as to cover the sub-combustion chamber (50) where the discharge gap is arranged, The plug cover is formed with a spray hole (51) that communicates the sub-combustion chamber with the outside, The ground electrode projects into the sub-combustion chamber from a fixed end portion (61) fixed to the housing tip side surface (21) at the tip of the housing, The ground electrode has the fixed end portion, a standing portion (62) standing upright from the housing tip side surface toward the tip side, a bent portion (63) bent inward in the plug diameter direction from the tip of the standing portion, and an extending portion (64) extending inward in the plug diameter direction from the bent portion, The ground electrode has an outer layer portion (65) mainly composed of nickel and a core portion (66) arranged inside the outer layer portion and mainly composed of copper, The discharge gap is formed by the tip portion of the center electrode and the extending portion of the ground electrode facing each other in the plug axis direction (Z), When the height of the ground electrode in the plug axis direction is H mm and the mass ratio of the core portion to the entire ground electrode is Wcu mass%, the following formula (1) is satisfied, The plug cover has a peripheral wall portion (52) that covers the outer peripheral side of the sub-combustion chamber, a bottom wall portion (53) that covers the tip side of the sub-combustion chamber, and a corner portion (54) that connects the tip of the peripheral wall portion and the outer periphery of the bottom wall portion in a curved surface shape, The plug cover has a cover recess (56) formed by a part of the inner peripheral surface (55) retreating outward in the plug diameter direction in the circumferential direction, In the plug cover, the cover recess is open at the base end side, The cover recess is formed from the peripheral wall portion to the corner portion, The spark plug (1) for an internal combustion engine, wherein at least a part of the standing portion is disposed inside the cover recess. H ≦ (2 × Wcu / 17) + 2.5... (1)

4. The spark plug for an internal combustion engine according to any one of claims 1 to 3, wherein the height H is 1.5 mm or more.

5. The spark plug for an internal combustion engine according to any one of claims 1 to 3, further satisfying the following formula (2). H ≦ (2 × Wcu / 17) + 0.5... (2)

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