Spark plug

Abstract

To provide a spark plug excellent in durability of a center electrode and voltage resistance of an insulator.SOLUTION: A spark plug 1 has: a cylindrical insulator 2; a center electrode 3 inserted and disposed inside a shaft hole 21 of the insulator; a first conductive seal part 41 which is provided on the outer peripheral side and the base end side of a base end part of the center electrode 3 inside the shaft hole 21; a resistor 5 which is provided on the base end side of the first conductive seal part 41 inside the shaft hole 21; a second conductive seal part 42 which is provided on the base end side of the resistor 5 inside the shaft hole 21; and a stem 6 which closes a base end part of the shaft hole 21. The center electrode 3 is a single member made of a noble metal material or a noble metal alloy material. The center electrode has: a columnar electrode body part 31; and a flange part 32 formed on the base end side of the electrode body part 31. Viewing from a plug axis direction Z, the flange part 32 has an elongated shape. Its length in a longer direction X is longer than the diameter of the electrode body part 31, and its length in a shorter direction is shorter than the diameter of the electrode body part 31.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] A spark plug used as an ignition means for an internal combustion engine has a cylindrical insulator and a center electrode inserted and disposed in its axial hole. As the center electrode, for example, as described in Patent Document 1, a core material having a high thermal conductivity such as Cu is disposed inside an outer material such as Ni, and a noble metal tip is joined to the tip portion. Further, a conductive sealing material is filled in the base end side of the center electrode in the axial hole of the insulator. The sealing material is also filled between the outer peripheral surface of the flange portion provided at the base end portion of the center electrode and the inner wall surface of the axial hole.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the case where a noble metal tip is joined to the tip portion of the center electrode, the durability of the joined portion may be a problem. That is, one end of the spark discharge may move to the joined portion. Then, there is a concern that the joined portion is selectively consumed and, in some cases, the joinability of the noble metal tip to the center electrode is affected.

[0005] In addition, when filling the gap between the outer peripheral surface of the flange portion of the center electrode and the inner wall surface of the axial hole of the insulator with a sealing material, if air bubbles remain in the gap, electric field concentration may occur at the contact portion between the insulator and the air bubbles, and there is a concern that the withstand voltage may decrease.

[0006] The present invention has been made in view of such problems, and aims to provide a spark plug excellent in the durability of a center electrode and the withstand voltage property of an insulator.

Means for Solving the Problems

[0007] One aspect of the present invention includes a cylindrical insulator (2), a center electrode (3) inserted and disposed in the axial hole (21) of the insulator and having a tip exposed from the insulator, a first conductive seal portion (41) disposed on the outer peripheral side and the proximal end side of the proximal end portion of the center electrode in the axial hole, a resistor (5) disposed on the proximal end side of the first conductive seal portion in the axial hole, a second conductive seal portion (42) disposed on the proximal end side of the resistor in the axial hole, a stem (6) disposed on the proximal end side of the second conductive seal portion and closing the proximal end portion of the axial hole, and has, the center electrode is a single member made of a noble metal material or a noble metal alloy material, and has a columnar electrode main body portion (31) and a flange portion (32) formed on the proximal end side of the electrode main body portion, the flange portion has an elongated shape when viewed from the plug axis direction (Z), the length (B) in the longitudinal direction (X) is longer than the diameter (D) of the electrode main body portion, and the length (A) in the short direction orthogonal to the longitudinal direction is shorter than the diameter of the electrode main body portion, in the spark plug (1).

Advantages of the Invention

[0008] In the spark plug of this embodiment, since the center electrode is a single member made of a noble metal material or a noble metal alloy material, it does not have a joint portion such as a welded portion. Therefore, a spark plug excellent in the durability of the center electrode can be obtained.

[0009] Further, when viewed from the plug axis direction, the flange portion has an elongated shape, the length in the longitudinal direction is longer than the diameter of the electrode main body portion, and the length in the short direction orthogonal to the longitudinal direction is shorter than the diameter of the electrode main body portion. Thereby, the center electrode can be disposed at a desired position within the shaft hole, and the withstand voltage of the insulator can be improved. That is, by making the length in the longitudinal direction of the flange portion larger than the diameter of the electrode main body portion, the flange portion can be locked within the shaft hole of the insulator, and the center electrode can be disposed at a desired position within the shaft hole. Further, since the length in the short direction of the flange portion is shorter than the diameter of the electrode main body portion, the gap between the flange portion and the inner wall surface of the shaft hole in the short direction can be increased. Thereby, it is possible to suppress the remaining of bubbles between the outer periphery of the flange portion and the inner wall surface of the shaft hole. As a result, the withstand voltage can be improved.

[0010] As described above, according to the above aspect, it is possible to provide a spark plug excellent in durability of the center electrode and withstand voltage of the insulator. 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 Drawings

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Mode for Carrying Out the Invention

[0012] (Embodiment 1) An embodiment of the spark plug will be described with reference to FIGS. 1 to 16. As shown in FIG. 1, the spark plug 1 of this embodiment includes a cylindrical insulator 2, a center electrode 3, a first conductive seal portion 41, a resistor 5, a second conductive seal portion 42, and a stem 6.

[0013] The center electrode 3 is inserted and disposed in the axial hole 21 of the insulator 2, and the tip thereof is exposed from the insulator 2. The first conductive seal portion 41 is disposed on the outer peripheral side and the proximal end side of the proximal end portion of the center electrode 3 within the axial hole 21. The resistor 5 is disposed on the proximal end side of the first conductive seal portion 41 within the axial hole 21. The second conductive seal portion 42 is disposed on the proximal end side of the resistor 5 within the axial hole 21. The stem 6 is disposed on the proximal end side of the second conductive seal portion 42 and closes the proximal end portion of the axial hole 21.

[0014] The center electrode 3 is a single member made of a noble metal material or a noble metal alloy material. And, as shown in FIGS. 2 to 4, the center electrode 3 has a columnar electrode main body portion 31 and a flange portion 32 formed on the proximal end side of the electrode main body portion 31.

[0015] As shown in FIG. 4, the flange portion 32 has an elongated shape when viewed from the plug axis direction Z. The length B of the flange portion 32 in the longitudinal direction X is longer than the diameter D of the electrode main body portion 31. Also, the length A of the flange portion 32 in the short direction Y orthogonal to the longitudinal direction X is shorter than the diameter D of the electrode main body portion 31. That is, the center electrode 3 has a shape satisfying A < D < B.

[0016] The spark plug 1 is attached to an internal combustion engine such as an automobile engine. As shown in FIG. 1, the spark plug 1 includes a substantially cylindrical mounting fitting 11 that holds an insulator 2 inside. With this mounting fitting 11, the spark plug 1 is attached to the cylinder head of the internal combustion engine.

[0017] In this specification, the penetrating direction of the axial hole 21 of the insulator 2 is referred to as the plug axial direction Z or simply the axial direction Z. In this axial direction Z, the side where the spark plug 1 is exposed to the combustion chamber of the internal combustion engine is referred to as the tip side, and the opposite side is referred to as the base end side.

[0018] The center electrode 3 has its tip protruding from the tip of the insulator 2. Also, a ground electrode 12 is joined to the tip of the mounting fitting 11. A discharge gap G is formed between the center electrode 3 and the ground electrode 12.

[0019] As described above, the center electrode 3 is a single member made of a noble metal material or a noble metal alloy material. As the noble metal material or noble metal alloy material constituting the center electrode 3, for example, Pt (i.e., platinum), Ir (i.e., iridium), Rh (i.e., rhodium), etc., or a noble metal or noble metal alloy containing at least one selected from these noble metals as a main component can be used.

[0020] The noble metal material or noble metal alloy material constituting the center electrode 3 preferably has a Vickers hardness greater than that of a nickel alloy. In particular, the center electrode 3 can be made of a platinum alloy or an iridium alloy.

[0021] Incidentally, as the platinum alloy constituting the center electrode 3, for example, a Pt-Ni alloy, a Pt-Rh alloy, a Pt-Ni-Ir alloy, etc. can be used. In this case, the hardness of the center electrode 3 can be about 350 - 450 HV. Also, as the iridium alloy constituting the center electrode 3, for example, an Ir-Rh alloy, an Ir-Rh-Re alloy, an Ir-Rh-Ta alloy, etc. can be used. In this case, the hardness of the center electrode 3 can be about 400 - 600 HV.

[0022] As shown in FIGS. 2 to 7, the center electrode 3 has a flange portion 32 at its base end portion. The flange portion 32 has a pair of flat surfaces 321 facing in the short side direction Y. Both end portions of the flange portion 32 in the longitudinal direction X are formed by convex curved surfaces 322. When viewed from the plug axis direction Z, the radius of curvature of the convex curved surface 322 of the flange portion 32 is smaller than the radius of curvature of the axis hole 21 of the portion of the axis hole 21 of the insulator 2 where the flange portion 32 is disposed. That is, the radius of curvature of the convex curved surface 322 of the flange portion 32 is smaller than the radius of curvature of the large diameter hole 213 of the axis hole 21 described later.

[0023] As shown in FIG. 4, when the width of the flange portion 32 in the short side direction Y is A and the diameter of the electrode main body portion 31 is D, 0.25 ≦ A / D ≦ 0.75 is satisfied. Also, as shown in FIG. 2, when the protruding width of the flange portion 32 from the electrode main body portion 31 in the longitudinal direction X is C and the diameter of the electrode main body portion 31 is D, C / D ≧ 0.3 is satisfied. Further, when the height of the flange portion 32 in the Z direction is H as shown in FIG. 2, for example, 0.5 ≦ H / D ≦ 5 can be set.

[0024] The diameter D of the electrode main body portion 31 is 0.4 to 1.6 mm. The portion of the electrode main body portion 31 protruding from the tip of the insulator 2 and the portion disposed inside the insulator 2 have the same diameter D. The electrode main body portion 31 has a cylindrical shape with the same diameter D over the entire axial direction Z.

[0025] As shown in FIGS. 1 and 5 to 7, the axis hole 21 of the insulator 2 has a small diameter hole 212 opening at the tip side and a large diameter hole 213 opening at the base end side. A tapered step portion 211 is formed between the small diameter hole 212 and the large diameter hole 213 in the axial direction Z.

[0026] The center electrode 3 is supported by the step portion 211 of the insulator 2 from the tip side with the flange portion 32. And the electrode main body portion 31 of the center electrode 3 is inserted into the small diameter hole 212 of the axis hole 21 of the insulator 2.

[0027] A gap 15 and a gap 150 are formed over the entire circumference between the outer peripheral surface of the flange portion 32 of the central electrode 3 and the inner peripheral surface of the shaft hole 21. Among these gaps 15 and 150, the gap 15 between the end portion of the flange portion 32 in the longitudinal direction X and the inner peripheral surface of the shaft hole 21 is the smallest. The gap 15 between the end portion of the flange portion 32 in the longitudinal direction X and the inner wall surface of the shaft hole 21 is 0.1 mm or more. That is, the distance E in the X direction between the end portion of the flange portion 32 and the inner wall surface of the shaft hole 21 through the gap 15 shown in FIG. 7 is 0.1 mm or more. Among the gaps 15 and 150, the gap 150 of the portion facing the flat surface 321 of the flange portion 32 is larger than the gap 15 at the position facing the end portion of the flange portion 32 in the longitudinal direction X.

[0028] A part of the first conductive seal portion 41 is filled in the gaps 15 and 150. The first conductive seal portion 41 is disposed on the outer peripheral side and the proximal end side of the flange portion 32 of the central electrode 3 in the shaft hole 21 of the insulator 2. As shown in FIG. 1, a resistor 5 is disposed on the proximal end side of the first conductive seal portion 41 in the shaft hole 21. In the shaft hole 21, a stem 6 is disposed on the proximal end side of the resistor 5 via a second conductive seal portion 42.

[0029] The resistor 5 is a member containing a conductive material and is adjusted to a desired resistance value. The resistor 5 electrically connects the central electrode 3 and the stem 6 and has a function of absorbing radio frequency noise. The resistor 5 is composed of, for example, an aggregate in which a conductive material such as a carbon material is dispersed in a base material containing a glass material such as borosilicate glass and an aggregate. Specifically, it is obtained by heat-treating a mixed powder material containing a powder of a conductive material, a glass powder, and an aggregate powder. The mixed powder material before this heat treatment corresponds to the resistor material 50 described later. For example, ceramic powder such as zirconia powder is used as the aggregate powder. The powder of the conductive material can be added, for example, as a carbon-glass mixed powder mainly composed of glass mixed with carbon powder.

[0030] The stem 6 includes a large-diameter terminal portion 62 and a shaft portion 61 having a smaller diameter than this. In the stem 6, the shaft portion 61 is inserted into the shaft hole 21 of the insulator 2, and the terminal portion 62 protrudes to the proximal end side of the insulator 2.

[0031] The first conductive seal portion 41 and the second conductive seal portion 42 are made of, for example, conductive bonding glass. The bonding glass is made of, for example, copper glass obtained by mixing copper powder into glass.

[0032] Next, the manufacturing method of the spark plug 1 of the present embodiment will be described. First, an example of the manufacturing method of the center electrode 3 will be described. A rod-shaped member made of a noble metal alloy is gradually thinned by repeating hot wire drawing using a plurality of types of dies until it reaches a desired diameter. The desired diameter of the wire before cutting at this time is set to 0.4 to 1.6 mm.

[0033] Next, the wire before cutting is cut to a desired length with a wire saw or the like to obtain a straight cylindrical wire 30. As shown in FIGS. 8 and 9, one end of the cut wire 30 is sandwiched between a pair of clamping jigs 18 while being heated and crushed in the Y direction. Thereby, a flat collar portion 32 is formed at one end of the wire 30. Thus, the center electrode 3 including the electrode main body portion 31 and the collar portion 32 is obtained.

[0034] Next, an example of the method of assembling the center electrode 3 and the like to the insulator 2 will be described. First, as shown in FIG. 10, the center electrode 3 is inserted into the small-diameter hole 212 in the axial hole 21 of the insulator 2. The collar portion 32 of the center electrode 3 is locked to the stepped portion 211 of the axial hole 21. In the present embodiment, both the small-diameter hole 212 and the large-diameter hole 213 of the axial hole 21 are cylindrical spaces.

[0035] Next, as shown in FIG. 11, a first conductive glass material 410 is disposed on the proximal end side of the center electrode 3 within the shaft hole 21. Then, as shown in FIG. 12, the first conductive glass material 410 disposed within the shaft hole 21 is pressed toward the distal end side by a pressing jig 19. As a result, the first conductive glass material 410 is compressed on the proximal end side of the center electrode 3. And a part of the first conductive glass material 410 is also filled in the gaps 15, 150 between the flange portion 32 and the inner wall surface of the shaft hole 21. Note that, as the first conductive glass material 410, for example, copper glass powder or the like can be used.

[0036] Next, as shown in FIG. 13, a resistor material 50 is disposed on the proximal end side of the cylindrical body 7 within the shaft hole 21. After the resistor material 50 is disposed within the shaft hole 21, the resistor material 50 is pressed toward the distal end side by a pressing jig 19.

[0037] Next, as shown in FIG. 14, a second conductive glass material 420 is disposed on the proximal end side of the resistor material 50 within the shaft hole 21. The second conductive glass material 420 disposed within the shaft hole 21 is pressed toward the distal end side by a pressing jig 19. As a result, the second conductive glass material 420 is compressed on the proximal end side of the resistor material 50. Also, by this pressing at this time, not only the second conductive glass material 420 is compressed, but also the resistor material 50 and the first conductive glass material 410 disposed on the distal end side thereof are pressed.

[0038] Next, as shown in FIG. 15, the stem 6 is inserted and disposed on the proximal end side of the second conductive glass material 420 within the shaft hole 21. At this stage, a part of the shaft portion 61 of the stem 6 is exposed on the proximal end side of the shaft hole 21.

[0039] Next, while heating and softening the first conductive glass material 410, the resistor material 50, and the second conductive glass material 420, as shown in FIG. 16, pressure is applied to the stem 6 toward the tip side in the axial direction Z. That is, the first conductive glass material 410, the resistor material 50, and the second conductive glass material 420 are heated to about 800 to 900° C., for example. As a result, at least a part of the glass components of the first conductive glass material 410, the resistor material 50, and the second conductive glass material 420 are in a softened state. The first conductive glass material 410, the resistor material 50, and the second conductive glass material 420 in the softened state are also referred to as softened glasses 41G, 5G, and 42G, respectively, for convenience.

[0040] Thereafter, the first conductive glass material 410, the resistor material 50, and the second conductive glass material 420 are cooled and solidified.

[0041] Thereafter, by inserting and fixing the insulator 2 inside the mounting bracket 11, the spark plug 1 shown in FIG. 1 is obtained.

[0042] Next, the operation and effect of this embodiment will be described. In the spark plug 1 of this embodiment, Since the center electrode 3 is a single member made of a noble metal material or a noble metal alloy material, it has no joint such as a welded part. Therefore, a spark plug 1 with excellent durability of the center electrode 3 can be obtained. That is, if the center electrode is a welded noble metal chip to the tip of a base material made of, for example, an Ni alloy, there is concern about the consumption of the joint (welded part) between the base material and the noble metal chip during spark discharge in the discharge gap G. On the other hand, in the spark plug 1 of this embodiment, the center electrode 3 is a single member made of a noble metal material or a noble metal alloy material. Therefore, since there is no joint, there is no such concern as described above.

[0043] Further, the center electrode 3 is a single member made of a noble metal material or a noble metal alloy material. Therefore, it is easy to ensure sufficient hardness and easy to reduce the diameter of the center electrode 3. Further, the center electrode 3 is made of a platinum alloy or an iridium alloy, so that it is easy to ensure high hardness. Therefore, it is easier to reduce the diameter of the center electrode 3.

[0044] By reducing the diameter of the center electrode 3, the axial hole 21 of the insulator 2 can be made thinner. As a result, it is possible to reduce the diameter of the spark plug 1 while ensuring sufficient thickness of the insulator 2. For example, even in the spark plug 1 having a small screw diameter of the mounting fitting 11 of M10 or less, it is possible to sufficiently ensure the insulation performance of the insulator 2.

[0045] Further, the flange portion 32 satisfies A < D < B in relation to the diameter D of the electrode main body portion 31 in terms of the width A and the length B. Thereby, the center electrode 3 can be disposed at a desired position within the axial hole 21, and the withstand voltage of the insulator 2 can be improved. That is, by satisfying D < B, the flange portion 32 can be locked within the axial hole 21 of the insulator 2, and the center electrode 3 can be disposed at a desired position within the axial hole 21. Further, by satisfying A < D, the gap 150 between the flange portion 32 and the inner wall surface of the axial hole 21 in the short-side direction Y can be increased. Thereby, it is possible to suppress the remaining of bubbles in contact with the inner wall surface of the axial hole 21 located on the outer periphery of the flange portion 32. As a result, the withstand voltage can be improved.

[0046] That is, since the shape of the flange portion 32 as viewed from the axial direction Z is the long shape as described above, the gaps 15 and 150 between the flange portion 32 and the inner wall surface of the axial hole 21 are such that only the gap 15 at the portion where the end of the flange portion 32 in the longitudinal direction X faces is narrow, and the other gaps 150 are formed wide. Therefore, the first conductive seal portion 41 can easily enter the gap 15 sufficiently. Further, even if air bubbles F are formed in the narrow gap 15 as shown in FIG. 17 during the manufacturing process, the air bubbles F easily move to the wide gap 150 and hardly remain in the narrow gap 15.

[0047] As shown in Comparative Form 1 in FIG. 18, when the flange portion 932 is formed with the same diameter over the entire circumference of the central electrode 93, a narrow gap 95 will be formed over the entire circumference. Then, if air bubbles F are formed in the gap 95 during the manufacturing process, there will be few escape paths and they are likely to remain. If air bubbles F remain in the narrow gap 95, electric field concentration may occur at the contact portion between the insulator 2 and the air bubbles F, and the withstand voltage may decrease.

[0048] As described above, in this form, the narrow gap 15 is only locally formed. Therefore, as shown in FIG. 17, it is possible to suppress the air bubbles F from easily escaping into the wide gap 150 and causing a decrease in the withstand voltage as described above. Even if air bubbles F remain in the wide gap 150, no electric field concentration will occur as long as the air bubbles F are not in contact with the insulator 2. Furthermore, since the distance between the metal flange portion 32 and the air bubbles F becomes large, there is almost no influence on the withstand voltage.

[0049] Also, both ends of the flange portion 32 in the longitudinal direction X are formed by convex curved surfaces 322. Therefore, even if air bubbles F are formed in the gap 15, the air bubbles F can easily move to the wide gap 150 and are less likely to cause a decrease in the withstand voltage (see FIG. 17).

[0050] When viewed from the plug axis direction Z, the radius of curvature of the convex curved surface 322 of the flange portion 32 is smaller than the radius of curvature of the shaft hole 21 of the portion of the shaft hole 21 where the flange portion 32 is arranged in the insulator 2. Therefore, the gaps 15 between both ends of the flange portion 32 in the longitudinal direction X and the shaft hole 21 have a shape that gradually widens toward both sides in the plug circumferential direction. Therefore, the air bubbles F formed in the gap 15 are more likely to move to the wider gap 150.

[0051] Also, when the width of the flange portion 32 in the short direction Y is A and the diameter of the electrode main body portion 31 is D, 0.25 ≤ A / D ≤ 0.75 is satisfied (see FIG. 4). Thereby, while ensuring the strength of the flange portion 32, a sufficiently wide portion (gap 150) can be provided in the gaps 15 and 150 between the flange portion 32 and the inner wall surface of the shaft hole 21.

[0052] The gap 15 between the end of the flange portion 32 in the longitudinal direction X and the inner wall surface of the shaft hole 21 is 0.1 mm or more. In this case, it becomes easier to prevent air bubbles F from remaining in the gap 15.

[0053] The diameter D of the electrode body portion 31 is 0.4 to 1.6 mm. Thereby, it is possible to sufficiently reduce the diameter of the center electrode 3 and to realize the reduction in diameter of the spark plug 1 while sufficiently ensuring the thickness of the insulator 2. Note that the length B of the flange portion 32 is preferably, for example, 1.8 to 2.4 mm. Thereby, it becomes easier to realize the reduction in diameter of the spark plug 1.

[0054] Further, the flange portion 32 has a pair of flat surfaces 321 facing the short hand direction Y. Therefore, it is easy to secure a large gap 150 between the flange portion 32 and the inner wall surface of the shaft hole 21 in the Y direction.

[0055] The electrode body portion 31 has the same diameter D for the portion protruding from the tip of the insulator 2 and the portion disposed inside the insulator 2. Thereby, it becomes easy to manufacture the center electrode 3 and to realize the reduction in diameter of the spark plug 1.

[0056] Further, the protruding width C of the flange portion 32 from the electrode body portion 31 and the diameter D of the electrode body portion 31 satisfy C / D≧0.3. Thereby, it becomes possible to easily prevent damage to the stepped portion 211 of the shaft hole 21 of the insulator 2.

[0057] As described above, according to this embodiment, it is possible to provide a spark plug excellent in the durability of the center electrode and the withstand voltage of the insulator.

[0058] (Embodiment 2) This embodiment is a form in which the shape of the flange portion 32 as viewed from the axial direction Z is an elliptical shape as shown in FIG. 19. Such an elliptical flange portion 32 can be formed, for example, by making the clamping surface of the clamping jig 18 shown in FIG. 8 into a concave curved surface. 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.

[0059] This embodiment also has the same effects as the first embodiment. It should be noted that the shape of the flange portion 32 may be appropriately changed in addition to those shown in the first and second embodiments.

[0060] (Embodiment 3) As shown in FIG. 20, this embodiment is a spark plug 1 in which the ground electrode 12 is formed in a straight line. That is, in the spark plug 1 of this embodiment, the ground electrode 12 is provided in a straight line from the tip end of the mounting metal fitting 11 toward the oblique tip side.

[0061] The ground electrode 12 is a straight rod-shaped member made of a nickel alloy or the like. One end of the member is joined to the tip of the mounting bracket 11 by welding or the like. The ground electrode 12 protrudes from the joint with the mounting bracket 11 toward the plug center axis PC and is inclined toward the tip side in the axial direction Z. A discharge gap G is formed between the tip of the ground electrode 12 and the tip of the center electrode 3. The rest is the same as in the first embodiment.

[0062] In this embodiment, the center electrode 3 is a single member made of a precious metal material or a precious metal alloy, which more significantly improves durability. This will be described in comparison with a spark plug 9 according to a comparative embodiment 2 shown in Fig. 21. The spark plug 9 of the comparative embodiment 2 has a ground electrode 12 having a similar shape to that of the spark plug 1 of this embodiment, and a center electrode 93 made of a base material 930 and a precious metal tip 933 joined to its tip.

[0063] The center electrode 93, which is composed of a base material 930 and a noble metal chip 933 joined to the tip thereof, has a joint portion 934 therebetween. When the ground electrode 12 is provided linearly from the tip of the mounting bracket 11 toward the diagonal tip side, the distance between the joint portion 934 and the ground electrode 12 is likely to be relatively short. Then, after a spark discharge occurs, a phenomenon is likely to occur in which one end of the discharge is carried by the air flow and reaches the joint portion 934. When one end of the discharge reaches the joint portion 934, the joint portion 934 is likely to be selectively consumed. As a result, there is a concern that gouges or the like may occur in the joint portion 934, and there is a concern that the joinability of the noble metal chip 933 to the base material 930 may be affected.

[0064] On the other hand, in the spark plug 1 of this embodiment, since there is no joint portion in the center electrode 3, there is no such concern as described above. As a result, the durability of the center electrode 3 can be improved. In addition, it has the same operational effects as those of the first embodiment.

[0065] (Experimental Example 1) This example is an example in which, as shown in FIG. 22, the relationship between the width A of the flange portion 32 (see FIG. 4) with respect to the diameter D of the electrode main body portion 31 and the effect of suppressing the remaining bubbles in the narrow gap 15 (see FIG. 17) was examined.

[0066] That is, by the method shown in the first embodiment, while setting the length B of the flange portion 32 to 1.8 mm, spark plugs in which the width A of the flange portion 32 with respect to the diameter D of the electrode main body portion 31, that is, A / D, was variously changed were produced 20 pieces each for each level. Further, while changing the diameter D of the electrode main body portion 31 to 0.4 mm, 1.0 mm, and 1.6 mm, and variously changing the width A as described above, spark plugs were prepared. Note that the height H (see FIG. 2) of the flange portion 32 was set to 2 mm.

[0067] These spark plug samples were non-destructively observed by X-ray CT, and it was confirmed whether or not bubbles remained in the gap 15. A sample in which bubbles remained in the gap 15 was appropriately referred to as a "bubble remaining sample". The number of bubble remaining samples among the 20 pieces for each level was counted. The results are shown in FIG. 22.

[0068] As shown in the figure, regardless of the diameter of the electrode body portion 31, when A / D ≥ 0.8, bubble - remaining samples occurred, while when A / D ≤ 0.75, the number of bubble - remaining samples was zero. From this, it can be seen that by setting A / D ≤ 7.5, the remaining of bubbles can be suppressed.

[0069] (Experimental Example 2) This example is an example in which, as shown in FIG. 23, the relationship between the width A of the flange portion 32 with respect to the diameter D of the electrode body portion 31 (see FIG. 4) and the effect of suppressing the deformation of the flange portion 32 was examined.

[0070] Also in this example, as in Experimental Example 1, various samples were prepared. Then, for each sample, non - destructive observation was performed by X - ray CT to confirm whether there was any bending deformation of the flange portion 32. Samples in which the flange portion 32 had bending deformation were appropriately referred to as "flange - bending samples". The number of flange - bending samples among 20 samples at each level was counted. The results are shown in FIG. 23.

[0071] As shown in the figure, regardless of the diameter of the electrode body portion 31, when A / D ≤ 0.2, flange - bending samples occurred, while when A / D ≥ 0.25, the number of flange - bending samples was zero. From this, it can be seen that by setting A / D ≥ 0.25, the bending deformation of the flange portion 32 can be suppressed.

[0072] (Experimental Example 3) This example is an example in which, as shown in FIG. 24, the relationship between the protruding width C of the flange portion 32 with respect to the diameter D of the electrode body portion 31 (see FIG. 2) and the effect of suppressing the damage of the insulator 2 was examined.

[0073] In this example, while setting the width A of the flange portion 32 to 0.2 mm, spark plugs with various changes in the protruding width C of the flange portion 32 with respect to the diameter D of the electrode body portion 31, that is, C / D, were manufactured 20 pieces each for each level. The rest was the same as in Experimental Example 1.

[0074] These samples of spark plugs were non-destructively observed by X-ray CT to check whether there were any defects such as cracks or the intrusion of the flange portion in the vicinity of the stepped portion 211 of the insulator 2 where the flange portion 32 abutted. Note that the convex corner portion at the inner peripheral end of the stepped portion 211 is a convex corner portion with a curvature radius of 0.05 mm. Samples with defects such as cracks or the intrusion of the flange portion in the vicinity of the stepped portion 211 were appropriately referred to as "stepped portion defective samples". The number of stepped portion defective samples among 20 samples at each level was counted. The results are shown in FIG. 24.

[0075] As shown in the figure, for any diameter of the electrode main body portion 31, when C / D ≤ 0.2, stepped portion defective samples occurred, whereas when C / D ≥ 0.3, the number of stepped portion defective samples was zero. From this, it can be seen that by setting C / D ≥ 0.3, damage to the inner wall surface of the shaft hole 21 of the insulator 2 can be prevented.

[0076] (Experimental Example 4) In this example, as shown in FIG. 25, the relationship between the size of the gap 15 (i.e., the distance E shown in FIG. 7) and the effect of suppressing the remaining bubbles in the gap 15 was investigated.

[0077] In this example, while setting the width A of the flange portion 32 to 0.2 mm and the protruding width C to 0.3 mm, spark plugs with variously changed distances E were manufactured, 20 for each level. The rest was the same as in Experimental Example 1.

[0078] These samples of spark plugs were non-destructively observed by X-ray CT to check whether there were any remaining bubbles in the gap 15 in the same manner as in Experimental Example 1. As a result, the number of bubble remaining samples among 20 samples at each level was counted. The results are shown in FIG. 25.

[0079] As shown in the figure, for any diameter of the electrode main body portion 31, when E ≤ 0.05 mm, bubble remaining samples occurred, whereas when E ≥ 0.1 mm, the number of bubble remaining samples was zero. From this, it can be seen that by setting E ≥ 0.1 mm, the remaining bubbles can be suppressed.

[0080] The present invention is not limited to the above-described embodiments, and can be applied to various embodiments without departing from the gist thereof.

[0081] The features of the present invention are shown as follows. [1] A cylindrical insulator (2), A center electrode (3) that is inserted and disposed in the axial hole (21) of the insulator and whose tip is exposed from the insulator, A first conductive seal portion (41) disposed on the outer peripheral side and the proximal end side of the proximal end portion of the center electrode in the axial hole, A resistor (5) disposed on the proximal end side of the first conductive seal portion in the axial hole, A second conductive seal portion (42) disposed on the proximal end side of the resistor in the axial hole, A stem (6) disposed on the proximal end side of the second conductive seal portion and closing the proximal end portion of the axial hole, and the center electrode is a single member made of a noble metal material or a noble metal alloy material, and has a columnar electrode main body portion (31) and a flange portion (32) formed on the proximal end side of the electrode main body portion, when viewed from the plug axis direction (Z), the flange portion has an elongated shape, the length (B) in the longitudinal direction (X) is longer than the diameter (D) of the electrode main body portion, and the length (A) in the short direction (Y) orthogonal to the longitudinal direction is shorter than the diameter of the electrode main body portion, Spark plug (1). [2] The spark plug according to [1], wherein the flange portion has a pair of flat surfaces facing the short direction. [3] The spark plug according to claim [1] or [2], wherein both ends of the flange portion in the longitudinal direction are formed by convex curved surfaces. [4] The spark plug according to [3], wherein when viewed from the plug axis direction, the radius of curvature of the convex curved surface of the flange portion is smaller than the radius of curvature of the axial hole of the portion of the axial hole of the insulator where the flange portion is disposed. [5] The spark plug according to any one of [1] to [4], wherein when the width in the short side direction of the flange portion is A and the diameter of the electrode main body portion is D, 0.25 ≦ A / D ≦ 0.75 is satisfied. [6] The spark plug according to any one of [1] to [5], wherein the gap between the end portion in the longitudinal direction of the flange portion and the inner wall surface of the shaft hole is 0.1 mm or more. [7] The spark plug according to any one of [1] to [6], wherein the diameter of the electrode main body portion is 0.4 to 1.6 mm. [8] The spark plug according to any one of [1] to [7], wherein the center electrode is made of a platinum alloy. [9] The spark plug according to any one of [1] to [7], wherein the center electrode is made of an iridium alloy.

[10] The spark plug according to any one of [1] to [9], wherein the portion of the electrode main body portion protruding from the tip of the insulator and the portion disposed inside the insulator have the same diameter.

[11] The spark plug according to any one of [1] to

[10] , further comprising a mounting fitting for holding the insulator from the outside and a ground electrode disposed opposite to the tip portion of the center electrode, and the ground electrode is provided linearly from the tip portion of the mounting fitting toward the tip side obliquely.

[12] The spark plug according to any one of [1] to

[11] , wherein when the protruding width of the flange portion from the electrode main body portion in the longitudinal direction is C and the diameter of the electrode main body portion is D, C / D ≧ 0.3 is satisfied.

Explanation of Signs

[0082] 1... Spark plug, 2... Insulator, 21... Shaft hole, 3... Center electrode, 31... Electrode main body portion, 32... Flange portion, 41... First conductive seal portion, 42... Second conductive seal portion, 5... Resistor, 6... Stem, X... Longitudinal direction, Y... Short side direction, Z... Plug axis direction

Claims

1. A cylindrical insulator (2); A center electrode (3) inserted and disposed in the axial hole (21) of the insulator and having a tip exposed from the insulator; A first conductive seal portion (41) disposed on the outer peripheral side and the proximal end side of the proximal end portion of the center electrode in the axial hole; A resistor (5) disposed on the proximal end side of the first conductive seal portion in the axial hole; A second conductive seal portion (42) disposed on the proximal end side of the resistor in the axial hole; A stem (6) disposed on the proximal end side of the second conductive seal portion and closing the proximal end portion of the axial hole; and having The center electrode is a single member made of a noble metal material or a noble metal alloy material, and has a columnar electrode main body portion (31) and a flange portion (32) formed on the proximal end side of the electrode main body portion. The flange portion has an elongated shape when viewed from the plug axis direction (Z), the length (B) in the longitudinal direction (X) is longer than the diameter (D) of the electrode main body portion, and the length (A) in the short direction (Y) orthogonal to the longitudinal direction is shorter than the diameter of the electrode main body portion. A spark plug (1).

2. The spark plug according to claim 1, wherein the flange portion has a pair of flat surfaces facing the short direction.

3. The spark plug according to claim 1 or 2, wherein both ends of the flange portion in the longitudinal direction are formed as convex curved surfaces.

4. The spark plug according to claim 3, wherein when viewed from the plug axis direction, the radius of curvature of the convex curved surface of the flange portion is smaller than the radius of curvature of the axial hole at the portion where the flange portion is disposed in the axial hole of the insulator.

5. The spark plug according to claim 1 or 2, wherein when the width in the short direction of the flange portion is A and the diameter of the electrode main body portion is D, 0.25 ≦ A / D ≦ 0.75 is satisfied.

6. The spark plug according to claim 1 or 2, wherein the gap between the end portion of the flange portion in the longitudinal direction and the inner wall surface of the axial hole is 0.1 mm or more.

7. The spark plug according to claim 1 or 2, wherein the diameter of the electrode main body portion is 0.4 to 1.6 mm.

8. The spark plug according to claim 1 or 2, wherein the center electrode is made of a platinum alloy.

9. The spark plug according to claim 1 or 2, wherein the center electrode is made of an iridium alloy.

10. The spark plug according to claim 1 or 2, wherein the portion of the electrode main body portion protruding from the tip of the insulator and the portion disposed inside the insulator have the same diameter.

11. The spark plug according to claim 1 or 2, further comprising a mounting bracket that holds the insulator from the outside, and a ground electrode disposed opposite to the tip of the center electrode, wherein the ground electrode is linearly provided obliquely toward the tip side from the tip of the mounting bracket.

12. The spark plug according to claim 1 or 2, wherein when the protruding width of the flange portion from the electrode body portion in the longitudinal direction is C and the diameter of the electrode body portion is D, C / D ≥ 0.3 is satisfied.

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