Spark plug

Abstract

To provide an ignition plug which can inhibit deformation of a main body metal fitting.SOLUTION: An ignition plug 10 includes: an insulator 20 formed with a shaft hole 200; a main body metal fitting 50 swaged so as to hold the insulator 20 from the outer periphery side; and a talc material TC filling an annular space SP between an outer peripheral surface of the insulator 20 and an inner peripheral surface of the main body metal fitting 50. A first annular member 81 and a second annular member 82 which contacts with the first annular member 81 from the opposite side of a center electrode 30 are provided at a position, located at a center electrode 30 side end part along a center axis CX of the shaft hole 200, of the annular space SP.SELECTED DRAWING: Figure 2

Description

[Technical field]

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

[0002] For example, an internal combustion engine mounted on a vehicle is provided with a spark plug for igniting fuel. The spark plug includes an insulator that holds a center electrode and a metal shell (housing) that holds the insulator from the outside, and the metal shell is fastened and fixed to the internal combustion engine. A fitting portion is provided on the side of the metal shell, which is a portion that fits with a tool such as a plug wrench when attaching the spark plug to the internal combustion engine.

[0003] As described in the following Patent Document 1, an annular space is formed between the outer peripheral surface of the insulator and the inner peripheral surface of the metal shell, generally inside the fitting portion, and the space is filled with talc, which is powdered talc. The talc increases the impact resistance of the spark plug when the internal combustion engine is in operation, and prevents gas from the internal combustion engine from leaking out to the outside. An annular member is disposed at each of both ends of the space along the central axis of the spark plug to retain the talc within the space. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 3502936 Summary of the Invention [Problem to be solved by the invention]

[0005] During the manufacture of the spark plug, the metal shell is crimped to the insulator with the talc material and the pair of annular members housed in the space. At this time, the inner talc material is in a compressed state. The metal shell receives a force from the pressurized talc material in a direction that pushes it outward.

[0006] In recent years, due to restrictions on component placement around an internal combustion engine, there has been a demand for smaller spark plugs. For this reason, the two-face width of the fitting portion, i.e., the width between the two opposing faces of the fitting portion, has become smaller than before. When the two-face width becomes smaller, the thickness of the fitting portion becomes thinner, and the metal shell becomes more likely to deform due to the force from the talc material.

[0007] If the fitting part of the metal shell is deformed, it may cause problems when fitting the tool when installing the spark plug. In addition, the sealing performance of the talc material may decrease due to deformation of the metal shell, which may allow gas from the internal combustion engine to pass through the talc material and leak to the outside.

[0008] The above-mentioned Patent Document 1 describes that by defining the dimensions such as the length and thickness of the space filled with the talc material, deformation of the metal shell due to the force from the talc material can be suppressed. However, according to experiments etc. conducted by the present inventors, it has become clear that it is difficult to sufficiently suppress deformation of the metal shell by only adopting the configuration described in the above-mentioned Patent Document 1.

[0009] The inventors have found that, depending on the shape of the insulator, the annular member, receiving force from the talc material, applies a force to the metal shell in a direction that pushes it outward, further deforming the metal shell. Patent Document 1 does not take into consideration at all how to suppress deformation of the metal shell due to the force transmitted through the annular member.

[0010] An object of the present disclosure is to provide an ignition plug capable of suppressing deformation of the metallic shell. [Means for solving the problem]

[0011] The spark plug according to the present disclosure includes an insulator (20) having an axial hole (200), a center electrode (30) held by the insulator at one end along the central axis (CX) of the axial hole, a metal shell (50) crimped to hold the insulator from the outer periphery, a ground electrode (60) extending from the metal shell and partially facing the center electrode, and a talc material (TC) filled in an annular space (SP) between the outer periphery of the insulator and the inner periphery of the metal shell. A first annular member (81) and a second annular member (82) abutting against the first annular member from the opposite side to the center electrode are provided in the annular space at an end along the central axis on the center electrode side.

[0012] In the spark plug having the above configuration, the first annular member and the second annular member are disposed in contact with each other at a position in the annular space that is the end portion on the center electrode side along the central axis. In this configuration, the force applied from the annular member to the metallic shell is suppressed compared to a conventional configuration in which a single annular member is disposed at that position. As a result, deformation of the metallic shell can be suppressed more than in the conventional configuration. Effect of the Invention

[0013] According to the present disclosure, there is provided an ignition plug capable of suppressing deformation of the metallic shell. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a diagram showing the internal configuration of the spark plug according to this embodiment. [Diagram 2] FIG. 2 is an enlarged view of a portion of the configuration of FIG. [Diagram 3] FIG. 3 is a diagram for explaining a force applied from the annular member to the metallic shell in the spark plug according to the comparative example. [Figure 4] FIG. 4 is a diagram for explaining the force applied from the annular member to the metallic shell in the spark plug according to the present embodiment. [Diagram 5]FIG. 5 is a diagram showing the relationship between the overlap width between the first annular member and the second annular member and the bulging amount of the two-face width at the fitting portion. [Figure 6] FIG. 6 is a diagram for explaining a force applied from the annular member to the metallic shell in an ignition plug according to a comparative example. [Figure 7] FIG. 7 is a diagram showing the relationship between the overlap width between the first annular member and the second annular member and the angle θ. [Figure 8] FIG. 8 is a diagram for explaining the positions at which the fitting portions are provided. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, the present embodiment will be described with reference to the accompanying drawings. In order to facilitate understanding of the description, the same components in each drawing are denoted by the same reference numerals as much as possible, and duplicated description will be omitted.

[0016] The configuration of an ignition plug 10 according to this embodiment will be described with reference to Fig. 1. In Fig. 1, a cross section of the ignition plug 10 taken along a plane including a central axis CX (described later) is shown on the left side. However, of the components constituting the ignition plug 10, the center electrode 30 and the terminal fitting 40 are shown not in cross section but in their respective external appearances.

[0017] The ignition plug 10 is provided in each cylinder of an internal combustion engine (not shown) and is a device for igniting an air-fuel mixture in the combustion chamber of the cylinder. The ignition plug 10 includes an insulator 20, a center electrode 30, a terminal metal fitting 40, a metal shell 50, and a ground electrode 60.

[0018] The insulator 20 is a cylindrical member made of an insulating material such as alumina. An axial hole 200 is formed in the insulator 20. The axial hole 200 is a through hole formed to pass through the insulator 20 along its central axis. The central axis of the axial hole 200 coincides with the central axis of the insulator 20. The central axis of the axial hole 200 is hereinafter also referred to as the "central axis CX." In a cross section of the insulator 20 cut perpendicularly to the central axis CX, the shape of the axial hole 200 is circular.

[0019] The center electrode 30 is a metal member held by the insulator 20 at a position that is one end of the axial hole 200 along the central axis CX (the lower end in FIG. 1). The center electrode 30 is a rod-shaped member, most of which is disposed inside the axial hole 200. A part of the center electrode 30 protrudes from the axial hole 200 to the outside of the insulator 20, and a discharge tip 31 is attached to the tip of the protruding part.

[0020] The terminal fitting 40 is a metal member held by glass or the like inside the insulator 20 at a position that is the other end of the axial hole 200 along the central axis CX (the upper end in FIG. 1). The terminal fitting 40 is a rod-shaped member, most of which is disposed inside the axial hole 200. A part of the terminal fitting 40 protrudes from the axial hole 200 to the outside of the insulator 20. This protruding portion serves as an electrode terminal to which a voltage is applied from an external power source (not shown).

[0021] In the following, the side of the insulator 20 where the center electrode 30 is attached along the central axis CX is also referred to as the "front end side." In the following, the side of the insulator 20 where the terminal fitting 40 is attached along the central axis CX is also referred to as the "rear end side."

[0022] A resistor 71 is disposed in the axial hole 200 between the terminal metal fitting 40 and the center electrode 30. The resistor 71 is a member disposed to adjust the electrical resistance of the electrical path from the terminal metal fitting 40 to the center electrode 30. The resistor 71 is formed of a material in which a predetermined amount of carbon powder is added to powdered glass and zirconia. The electrical resistance of the resistor 71 is adjusted by the amount of carbon added. By disposing the resistor 71 in the electrical path from the terminal metal fitting 40 to the center electrode 30, the generation of electromagnetic noise caused by the spark discharge of the ignition plug 10 is suppressed. The resistor 71 and the center electrode 30 are electrically connected via a conductive seal layer 72. Similarly, the terminal metal fitting 40 and the resistor 71 are electrically connected via a conductive seal layer 73. Both of the conductive seal layers 72 and 73 are layers having electrical conductivity formed of a material in which copper powder is added to powdered glass.

[0023] The metal shell 50 is a tubular member provided so as to cover a part of the insulator 20 from the outer periphery side. The metal shell 50 is entirely made of metal. As will be described later, the metal shell 50 is fixed to the insulator 20 by crimping, and holds the insulator 20 in this state. The metal shell 50 has a fitting portion 52, a flange portion 55, and an insertion portion 56.

[0024] The fitting portion 52 is a portion that fits with a tool such as a plug wrench when the spark plug 10 is attached to an internal combustion engine. The shape of the fitting portion 52 when viewed along the central axis CX is hexagonal. In this embodiment, the width between two opposing faces of the fitting portion 52 (the so-called "two-face width") is 16 mm. Note that the fitting portion 52 when viewed along the central axis CX may have a Bi-HEX shape.

[0025] The flange portion 55 is a portion that comes into contact with the outer surface of the internal combustion engine via the gasket GK when the spark plug 10 is attached to the internal combustion engine. The flange portion 55 is provided at a position that is closer to the tip side than the fitting portion 52, and protrudes toward the outer periphery. Note that a deformation portion 54 is provided between the flange portion 55 and the fitting portion 52, which will be described later.

[0026] The insertion portion 56 is a portion further toward the tip side than the flange portion 55, and is a portion to be inserted into an insertion hole (not shown) formed in an internal combustion engine. A male screw 561 is formed on the outer circumferential surface of the insertion portion 56. When the spark plug 10 is attached to the internal combustion engine, the fitting portion 52 rotates about the central axis CX due to the force received from a tool. As a result, a female screw formed on the inner circumferential surface of the insertion hole and the male screw 561 of the insertion portion 56 are screwed together. As a result, the spark plug 10 is fastened and fixed to the internal combustion engine. When the spark plug 10 is attached to the internal combustion engine, the potential of the metallic shell 50 becomes the same ground potential as that of the internal combustion engine.

[0027] The ground electrode 60 is a metal member formed to extend from the tip end of the metallic shell 50 toward the tip end. The ground electrode 60 is bent, and a part of it faces the discharge tip 31 of the center electrode 30 along the central axis CX. A ground side tip 61 is attached to the part of the ground electrode 60 facing the discharge tip 31. The gap formed between the ground side tip 61 and the discharge tip 31 is a discharge gap.

[0028] As shown in Fig. 1, inside the fitting portion 52, an annular space SP is formed between the outer peripheral surface of the insulator 20 and the inner peripheral surface of the metallic shell 50. The annular space SP is an annular space formed to surround the central axis CX. The leading end of the annular space SP is defined by a protrusion 211 (see Fig. 2) formed on the outer peripheral surface of the insulator 20. The rear end of the annular space SP is defined by a crimped portion 51 of the metallic shell 50. The crimped portion 51 is a portion of the metallic shell 50 that is rearward of the fitting portion 52 and is a portion that deforms toward the inner peripheral side when crimped.

[0029] The annular space SP is filled with a talc material TC, which is powdered talc. The talc material TC increases the impact resistance of the spark plug 10 when it is installed in the internal combustion engine, and also serves to prevent gases from the internal combustion engine from leaking out to the rear end side.

[0030] An annular member 90 is disposed at a position of the annular space SP that is an end portion on the rear end side (i.e., the side opposite to the center electrode 30) along the central axis CX. A first annular member 81 and a second annular member 82 are disposed in contact with each other at a position of the annular space SP that is an end portion on the front end side (i.e., the side of the center electrode 30) along the central axis CX. The annular member 90, the first annular member 81, and the second annular member 82 are all circular members formed to surround the central axis CX, and are made of a hard metal material such as carbon steel. When cut along a plane including the central axis CX, the cross-sectional shapes of the annular member 90, the first annular member 81, and the second annular member 82 are all circular.

[0031] Thus, in this embodiment, a single annular member 90 is disposed on the rear end side of the talc material TC, while a plurality of annular members (a first annular member 81 and a second annular member 82) are disposed on the front end side of the talc material TC, instead of a single one. The reason for this will be explained later.

[0032] A method for fixing the metal shell 50 to the insulator 20 will be described. First, the insulator 20 is inserted into the metal shell 50 from its rear end. At this time, the crimped portion 51 of the metal shell 50 is not deformed as shown in Fig. 1 and extends generally linearly toward the rear end. In other words, the rear end portion of the annular space SP is open to the outside.

[0033] A protrusion 562 protruding inward is formed on the inner circumferential surface of the insertion portion 56 of the metallic shell 50. The insulator 20 inserted into the metallic shell 50 stops with a stepped portion formed on its outer circumferential surface abutting against the protrusion 562. Thereafter, the first annular member 81, the second annular member 82, the talc material TC, and the annular member 90 are arranged in this order in the annular space SP.

[0034] Next, a force is applied between the bottom surface of flange portion 55 (the surface against which gasket GK abuts) and the tip of crimped portion 51 in a direction along central axis CX to compress them. Due to this force, crimped portion 51 is crimped and deformed, and displaced toward the inner periphery as shown in FIG.

[0035] In addition, since the deformation portion 54 formed between the fitting portion 52 and the flange portion 55 is relatively thin, it buckles due to the above-mentioned force. As a result, the distance from the crimping portion 51 to the projection 562 becomes shorter, and the insulator 20 is strongly pressed against the projection 562 by the force via the talc material TC. In the above-mentioned manner, the metal shell 50 is crimped so as to hold the insulator 20 from the outer periphery, and is fixed to the insulator 20.

[0036] 1 after the metallic shell 50 has been crimped, a compressive force is applied to the talc material TC. In this state, the talc material TC functions as a spring that absorbs vibrations from the internal combustion engine, thereby enhancing the impact resistance of the spark plug 10. In addition, the talc material TC becomes dense when compressed, and therefore also functions as a sealing material that prevents gas from the internal combustion engine from leaking out to the rear end side.

[0037] The configuration of the first annular member 81, the second annular member 82, and the vicinity thereof will be described with reference to Fig. 2. Fig. 2 is an enlarged view of a portion of Fig. 1. In Fig. 2, the reference numeral "210" is given to the outer peripheral surface of the insulator 20. Hereinafter, this outer peripheral surface will also be referred to as the "outer peripheral surface 210".

[0038] A protrusion 211 is formed in the insulator 20 at a position near the end on the tip side of the annular space SP. The protrusion 211 is a protruding portion such that the diameter of the outer circumferential surface 210 increases toward the tip side (i.e., the center electrode 30 side) along the central axis CX. In the cross section of FIG. 2, the line showing the outer circumferential surface of the protrusion 211 is an arc-shaped curve protruding toward the tip side. The protrusion 211 supports the first annular member 81 from the tip side. On the rear end side of the protrusion 211, the line showing the outer circumferential surface 210 of the insulator 20 is a straight line extending parallel to the central axis CX.

[0039] The first annular member 81 is disposed at a position closer to the tip side than the second annular member 82. The center diameter CD1 of the first annular member 81 is larger than the center diameter CD2 of the second annular member 82. It can also be said that the center diameter CD1 is equal to twice the distance from the center of the cross section of the first annular member 81 to the central axis CX in FIG. 2. It can also be said that the center diameter CD2 is equal to twice the distance from the center of the cross section of the second annular member 82 to the central axis CX in FIG. 2.

[0040] In Fig. 2, the reference symbol "520" is attached to the inner circumferential surface of the metallic shell 50. Hereinafter, this inner circumferential surface will also be referred to as "inner circumferential surface 520." In the cross section of Fig. 2, the line indicating the inner circumferential surface 520 of the metallic shell 50 is a straight line extending parallel to the central axis CX.

[0041] 2 is the distance from the outer peripheral surface 210 to the inner peripheral surface 520 along the direction perpendicular to the central axis CX, i.e., the width dimension of the annular space SP at a portion other than the protruding portion 211. "t" shown in Fig. 2 is the distance from the tip of the protruding portion 211 to the inner peripheral surface 520 along the direction perpendicular to the central axis CX, i.e., the width dimension of the gap formed on the tip side of the protruding portion 211.

[0042] 2, the diameter SD1 of the cross-sectional shape of the first annular member 81 is smaller than the above T and larger than the above t. The first annular member 81 abuts against both the outer circumferential surface of the protruding portion 211 and the inner circumferential surface 520 of the metallic shell 50. With this configuration, the talc material TC does not leak out from between the first annular member 81 and the inner circumferential surface 520. Furthermore, the first annular member 81 does not get into the gap formed on the tip side of the protruding portion 211.

[0043] The second annular member 82 is in contact with the first annular member 81 from the side opposite to the center electrode 30 (i.e., from the rear end side). In Fig. 2, the diameter SD2 of the cross-sectional shape of the second annular member 82 is smaller than the diameter SD1 of the cross-sectional shape of the first annular member 81. However, as long as an overlap width OL described later falls within a predetermined range, the diameter SD2 may be larger than the diameter SD1, or the diameters SD2 and SD1 may be equal to each other.

[0044] The second annular member 82 abuts against both the first annular member 81 and the outer circumferential surface 210. The portion of the outer circumferential surface 210 with which the second annular member abuts may be a range where the protruding portion 211 is not formed, or may be a range where the protruding portion 211 is formed.

[0045] 2 indicates the inner diameter of the first annular member 81. Hereinafter, this inner diameter will also be referred to as the "inner diameter ID1." The inner diameter ID1 can also be said to be a dimension equal to twice the distance from the innermost position of the first annular member 81 to the central axis CX.

[0046] 2 indicates the outer diameter of the first annular member 81. Hereinafter, this outer diameter will also be referred to as the "outer diameter OD1." The outer diameter OD1 can also be said to be a dimension equal to twice the distance from the outermost position of the first annular member 81 to the central axis CX. In this embodiment, the outer diameter OD1 is equal to the inner diameter of the inner circumferential surface 520.

[0047] 2 indicates the inner diameter of the second annular member 82. Hereinafter, this inner diameter is also referred to as the "inner diameter ID2." The inner diameter ID2 can also be said to be a dimension equal to twice the distance from the innermost position of the second annular member 82 to the central axis CX. In this embodiment, the inner diameter ID2 is equal to the outer diameter of a portion of the outer circumferential surface 210 where the protrusion 211 is not formed.

[0048] 2 indicates the outer diameter of the second annular member 82. Hereinafter, this outer diameter will also be referred to as the "outer diameter OD2." The outer diameter OD2 can also be said to be a dimension equal to twice the distance from the outermost position of the second annular member 82 to the central axis CX.

[0049] In this embodiment, the outer diameter OD2 of the second annular member 82 is larger than the inner diameter ID1 of the first annular member 81. Therefore, when viewed along the central axis CX, a part of the first annular member 81 and a part of the second annular member 82 overlap each other. The overlap width OL shown in FIG. 2 is the width of the overlapping portion in a direction perpendicular to the central axis CX. The overlap width OL can also be said to be the distance along a direction perpendicular to the central axis CX from the innermost position of the first annular member 81 to the outermost position of the second annular member 82 in a cross section obtained by cutting the ignition plug 10 along a plane including the central axis CX. The overlap width OL is equal to 1 / 2 of the dimension obtained by subtracting the inner diameter ID1 from the outer diameter OD2. In the configuration of this embodiment, the overlap width OL is also equal to a value calculated by the formula (SD2-(T-SD1)).

[0050] The dashed-dotted line DL1 shown in Fig. 2 is an imaginary line passing through both the center of the cross section of the first annular member 81 and the center of the cross section of the second annular member 82. Moreover, the dashed-dotted line CX' shown in Fig. 2 is a straight line parallel to the central axis CX (not shown in Fig. 2). The angle θ shown in Fig. 2 is the angle between the dashed-dotted line DL1 and the dashed-dotted line CX'. The angle θ can also be said to be the angle between the straight line connecting the center of the cross section of the first annular member 81 and the center of the cross section of the second annular member 82 and the central axis CX.

[0051] The cross section shown in Fig. 2 is a cross section of the spark plug 10 taken along a plane that is perpendicular to each of the two opposing faces of the fitting portion 52 and that includes the central axis CX. A dotted line DL52 shown in Fig. 2 represents the outer shape of the fitting portion 52 in a cross section of the spark plug 10 taken along a plane that passes through the apexes of the hexagonal fitting portion 52 and that includes the central axis CX.

[0052] In the portion of the metallic shell 50 adjacent to the fitting portion 52 at the tip side, i.e., the portion marked with the reference symbol "53" in FIG. 2, the diameter of the outer circumferential surface of the metallic shell 50 gradually decreases toward the tip side along the central axis CX. This portion is also referred to as the "reduced portion 53" below. The dotted line DL13 shown in FIG. 2 indicates the position of the hexagonal apex portion that is the most rear end side along the central axis CX of the reduced portion 53, that is, the position of the most rear end side portion of the reduced portion 53 in the cross section indicated by the dotted line DL52. Also, the dotted line DL13' shown in FIG. 2 indicates the position of the hexagonal flat portion that is the most rear end side along the central axis CX of the reduced portion 53, that is, the position of the most rear end side portion of the reduced portion 53 in the cross section of FIG. 2.

[0053] The reduced portion 53 continues to the position of the dotted line DL11 shown in Fig. 2. In the portion further to the tip side than the dotted line DL11, the diameter of the outer circumferential surface of the metallic shell 50 gradually increases toward the tip side along the central axis CX, and is connected to the deformed portion 54 shown in Fig. 1. It can be said that the dotted line DL11 indicates the position of the portion of the reduced portion 53 that is the most tip side along the central axis CX. In the cross section of Fig. 2, in the range from the dotted line DL11 to the dotted line DL12, the line indicating the outer circumferential surface of the reduced portion 53 is an arc-shaped curve. In the range from the dotted line DL12 to the dotted line DL13, the line indicating the outer circumferential surface of the reduced portion 53 is a straight line.

[0054] In order to explain the advantage of arranging two annular members (a first annular member 81 and a second annular member 82) on the tip side of the talc material TC in this embodiment, a comparative example similar to the conventional example will be described first. As shown in Fig. 3, in this comparative example, only a single annular member 80 is arranged on the tip side of the talc material TC. The other configurations of this comparative example are the same as those of this embodiment shown in Fig. 2 etc.

[0055] Fig. 3(A) shows the state immediately after the metal shell 50 is crimped. As described above, when the metal shell 50 is crimped, a compressive force is applied to the talc material TC. Therefore, the annular member 80 receives a force in a direction from the talc material TC toward the tip side. In Fig. 3(A), the force that the annular member 80 receives from the talc material TC is indicated by multiple arrows AR1.

[0056] The annular member 80 is pressed against the protruding portion 211 by the force from the talc material TC. Therefore, the protruding portion 211 receives a force from the annular member 80 in a direction generally toward the tip side. An arrow AR2 in FIG. 3(A) represents the force that the protruding portion 211 receives from the annular member 80.

[0057] The talc material TC also gets into the gap between the annular member 80 and the protruding portion 211. In addition to the force toward the tip side, the annular member 80 receives a force from the talc material TC that has gotten in as described above in a direction toward the outer metallic shell 50. Therefore, the inner circumferential surface 520 of the metallic shell 50 receives a force from the annular member 80 in a direction generally toward the outer circumferential side. The arrow AR3 in FIG. 3(A) represents the force that the inner circumferential surface 520 receives from the annular member 80.

[0058] The protrusion 211 is inclined so that the diameter of the outer circumferential surface 210 increases toward the tip side along the central axis CX. Therefore, the annular member 80 pressed against the protrusion 211 tries to move outward along the protrusion 211, and is pressed even more strongly against the inner circumferential surface 520 of the metallic shell 50. The direction of the force indicated by the arrow AR3 is approximately equal to the direction of a tangent (not shown) that contacts the portion of the protrusion 211 with which the annular member 80 is in contact.

[0059] As described above, the annular member 80, which receives the force from the talc material TC, applies a force to the metal shell 50 in a direction to expand it outward. In this comparative example, the reduced portion 53, i.e., a portion where the thickness of the metal shell 50 is thin, is present in the vicinity of the portion of the metal shell 50 that receives the force from the annular member 80. This is also true in this embodiment. Therefore, when the force of the arrow AR3 due to crimping increases, the metal shell 50 may be deformed as shown in FIG. 3(B). In the example shown in the figure, the outer peripheral surface of the fitting portion 52 is deformed so as to bulge slightly outward. In FIG. 3(B), the initial shape of the metal shell 50 before deformation is shown by a dotted line.

[0060] If such deformation of the metallic shell 50 occurs, when attaching the ignition plug 10 to the internal combustion engine, it may be difficult to fit a tool into the fitting portion 52. In addition, since the talc material TC loosens due to deformation of the metallic shell 50, the sealing performance of the talc material TC may decrease, and gas from the internal combustion engine may pass through the talc material TC and leak to the outside.

[0061] In this embodiment, therefore, the first annular member 81 and the second annular member 82 are arranged in an overlapping manner below the talc material TC, thereby suppressing deformation of the metal shell 50 during crimping. Fig. 4 illustrates the state of the metal shell 50 according to this embodiment immediately after crimping in the same manner as Fig. 3(A).

[0062] 5, in this embodiment, when the metallic shell 50 is crimped, the first annular member 81 and the second annular member 82 each receive a force (arrow AR1) from the talc material TC toward the tip side. The first annular member 81 is pressed against the protruding portion 211 by this force.

[0063] As shown in Fig. 4, in the configuration of this embodiment, the second annular member 82 abuts against the first annular member 81 from the rear end side and the inner circumferential side. Therefore, the part of the annular space SP on the inner circumferential side of the first annular member 81 (the part marked with the reference symbol "SP0" in Fig. 4) is blocked from the rear end side by the second annular member 82, and the talc material TC does not enter this part. Therefore, the magnitude of the force that the second annular member 82 receives from the talc material TC toward the outer circumferential side is smaller than that in the comparative example of Fig. 3(A). As a result, the force (arrow AR3) that the inner circumferential surface 520 receives from the first annular member 81 is also smaller than that in the comparative example of Fig. 3(A).

[0064] In this embodiment, the first annular member 81 is pressed more strongly against the protruding portion 211 by the force from the second annular member 82 on the rear end side. Therefore, the force (arrow AR2) that the protruding portion 211 receives from the first annular member 81 is larger than that in the comparative example of FIG. 3(A).

[0065] In this manner, in the present embodiment, the first annular member 81 and the second annular member 82 are arranged to overlap each other below the talc material TC, thereby changing the balance of the forces indicated by the arrows AR2 and AR3. As a result, the force that the inner circumferential surface 520 receives from the first annular member 81 is suppressed more than in the past, and it is possible to suppress deformation of the metallic shell 50 more than in the past.

[0066] The magnitude of the force that the inner circumferential surface 520 receives from the first annular member 81 varies depending on the respective shapes of the first annular member 81 and the second annular member 82. As a result of conducting experiments on various shapes, the inventors have found that the force varies depending on the overlap width OL (see FIG. 2) described above.

[0067] 5 shows the relationship between the overlap width OL (horizontal axis) and the bulge amount of the two flat width (vertical axis). The "bulge amount of the two flat width" is the increase amount of the two flat width of the fitting portion 52 when the metal shell 50 is crimped and fixed to the insulator 20. The data in FIG. 5 is a plot of the increase amount of the two flat width of the fitting portion 52 while changing the diameter SD2 of the second annular member 82 to various values ​​with the diameter SD1 of the first annular member 81 fixed to 1 mm. Note that each measurement was performed under the condition that the first annular member 81 was in contact with the inner peripheral surface 520 of the metal shell 50 and the second annular member 82 was in contact with the outer peripheral surface 210 of the insulator 20.

[0068] Line 16 in Fig. 5 represents the measured value of the bulge of the two flat width for a sample in which the initial two flat width of the fitting portion 52 is 16 mm. Also, "dW1" in Fig. 5 represents the value of the bulge of the two flat width for a sample in which the initial two flat width of the fitting portion 52 is 16 mm, when the sample has the same comparative example configuration as in Fig. 3. As shown in Fig. 5, when the overlap width OL is in the range of 0.06 mm to 0.88 mm, the bulge of the two flat width is equal to or less than the conventional value (dW1). When the overlap width OL is 0.06 mm and when the overlap width OL is 0.88 mm, the bulge of the two flat width is generally the same value (dW1) as the conventional value.

[0069] Line 14 in Fig. 5 represents the measured value of the bulge of the two flat width for a sample in which the initial two flat width of the fitting portion 52 is 14 mm. Also, "dW2" in Fig. 5 represents the value of the bulge of the two flat width for a sample in which the initial two flat width of the fitting portion 52 is 14 mm, when the sample has a comparative example configuration similar to that of Fig. 3. In this case as well, when the overlap width OL is in the range of 0.06 mm to 0.88 mm, the bulge of the two flat width is below the conventional value (dW2). When the overlap width OL is 0.06 mm and when the overlap width OL is 0.88 mm, the bulge of the two flat width is generally the same value (dW2) as the conventional value.

[0070] When the overlap width OL becomes smaller than 0.06 mm, the bulge of the two-face width becomes larger than in the past. The reason for this is considered to be as follows. In this case, as shown in FIG. 6(A), the second annular member 82 is deeply inserted between the first annular member 81 and the protruding portion 211. As a result, the force that the first annular member 81 receives from the second annular member 82 has a larger component in the direction perpendicular to the central axis CX, as shown by the arrow AR10. As a result, the first annular member 81 is strongly pressed against the inner peripheral surface 520 by the force of the arrow AR3, which is considered to increase the bulge of the two-face width.

[0071] Even when the overlap width OL is greater than 0.88 mm, the bulge of the width across flats becomes larger than in the past. The reason for this is considered to be as follows. In this case, as shown in FIG. 6B, the gap between the second annular member 82 and the outer peripheral surface 210 becomes wider, and the gap is filled with the talc material TC. As a result, the second annular member 82 receives a force from the talc material TC that has entered the gap in a direction toward the outer metallic shell 50. It is considered that the force is transmitted to the inner peripheral surface 520 via the first annular member 81, increasing the bulge of the width across flats.

[0072] As described above, by adjusting the shapes of the first annular member 81 and the second annular member 82 so that the overlap width OL is within the range of 0.06 mm to 0.88 mm, it is possible to suppress deformation of the fitting portion 52 more than ever before. It has been confirmed that the above range for the overlap width OL is the same even when the diameter SD1 of the first annular member 81 is set to a value other than 1 mm. The same is also true when the cross-sectional shape of at least one of the first annular member 81 and the second annular member 82 is not circular.

[0073] In addition, when the cross-sectional shape of each of the first annular member 81 and the second annular member 82 is circular as in this embodiment, the above-mentioned range of the overlap width OL can be expressed as a range for the angle θ shown in FIG. 2. FIG. 7 shows the relationship between the overlap width OL (horizontal axis) and the angle θ (vertical axis). A configuration in which the overlap width OL is 0.06 mm corresponds to a configuration in which the angle θ is 77 degrees. Also, a configuration in which the overlap width OL is 0.88 mm corresponds to a configuration in which the angle θ is 13 degrees. Therefore, if the shapes of each of the first annular member 81 and the second annular member 82 are adjusted so that the angle θ is within the range from 13 degrees to 77 degrees, the deformation of the fitting portion 52 can be suppressed more than in the past.

[0074] If the width across flats of the fitting portion 52 is greater than 16 mm, the rigidity of the fitting portion 52 and its vicinity will be high, and the effect of adopting the configuration in which the first annular member 81 and the second annular member 82 are stacked as in this embodiment will be reduced. On the other hand, if the width across flats of the fitting portion 52 is 16 mm or less, the rigidity of the fitting portion 52 and its vicinity will be reduced in exchange for the size reduction, and the effect of adopting the configuration of this embodiment will be greater. Thus, the configuration of this embodiment is preferably adopted for an ignition plug 10 in which the width across flats of the fitting portion 52 is 16 mm or less.

[0075] Fig. 8 is a cross-section of the ignition plug 10 according to this embodiment, drawn from the same perspective as Fig. 2. The dashed-dotted line DL21 shown in Fig. 8 represents a tangent line that contacts the portion of the protruding portion 211 with which the first annular member 81 abuts.

[0076] When the metallic shell 50 is tightened, the first annular member 81 tends to expand along the outer circumferential surface of the protruding portion 211. For this reason, the direction of the force applied from the first annular member 81 to the inner circumferential surface 520 is the direction along the dashed line DL21, which is the tangent line.

[0077] If the entire reduced portion 53 were located further forward than the dashed dotted line DL21, most of the force along the dashed dotted line DL21 would be applied to the portion of the metal shell 50 with high rigidity (the fitting portion 52), and the metal shell 50 including the fitting portion 52 would not easily deform. In this case, the effect of employing the configuration in which the first annular member 81 and the second annular member 82 are overlapped as in this embodiment is small.

[0078] On the other hand, in this embodiment, as shown in Fig. 8, at least a part of the reduced portion 53 is located rearward of the dashed line DL21. In other words, the fitting portion 52 in this embodiment is formed at a position rearward of the dashed line DL21. In this configuration, the force along the dashed line DL21 is applied to a portion of the metallic shell 50 with low rigidity (the reduced portion 53), so that this portion is easily deformed, and as a result, the fitting portion 52 is also easily deformed. Therefore, in this configuration, it is very effective to adopt a configuration in which the first annular member 81 and the second annular member 82 are overlapped as in this embodiment.

[0079] The dashed line DL22 in FIG. 8 represents a tangent line at the outermost point of the protruding portion 211, that is, a virtual straight line when the shape of the protruding portion 211 is extended further to the outer periphery. In this embodiment, at least a part of the reduced portion 53 is located on the rear end side of the dashed line DL22. In this case, no matter where the first annular member 81 contacts the protruding portion 211, at least a part of the reduced portion 53 is always located on the rear end side of the dashed line DL21. Therefore, as described above, the effect of adopting a configuration in which the first annular member 81 and the second annular member 82 are overlapped as in this embodiment is increased.

[0080] In the above, an example has been described in which the cross-sectional shapes of the first annular member 81 and the second annular member 82 are both circular. However, at least one of the cross-sectional shapes may be a shape other than circular. Even in this case, deformation of the fitting portion 52 can be suppressed by making the outer diameter of the second annular member 82 larger than the inner diameter of the first annular member 81 and restricting the overlap width OL to within a range of 0.06 mm to 0.88 mm.

[0081] Moreover, in the above, an example has been described in which the center diameter CD1 of the first annular member 81 is larger than the center diameter CD2 of the second annular member 82. However, there is no need to be limited to this configuration, and the center diameter CD1 of the first annular member 81 may be smaller than the center diameter CD2 of the second annular member 82. Even in this configuration, it is possible to change the force that the inner circumferential surface 520 receives from the second annular member 82 and suppress deformation of the fitting portion 52.

[0082] The multiple annular members arranged below the talc material TC may include another annular member in addition to the first annular member 81 and the second annular member 82. In other words, a configuration in which three or more annular members are arranged below the talc material TC may be used.

[0083] The present embodiment has been described above with reference to specific examples. However, the present disclosure is not limited to these specific examples. Any design modifications made by a person skilled in the art to these specific examples are also included within the scope of the present disclosure as long as they have the features of the present disclosure. The elements of each of the above-mentioned specific examples and their arrangements, conditions, shapes, etc. are not limited to those exemplified and can be changed as appropriate. The combination of each of the elements of each of the above-mentioned specific examples can be changed as appropriate as long as no technical contradiction occurs. [Explanation of symbols]

[0084] 10: Spark plug 20: Insulator 30: Center electrode 50: Main metal fitting 60: Ground electrode 81: First annular member 82: Second annular member 200: Shaft hole SP: Annular space TC: Talc material CX: Central axis

Claims

1. An insulator (20) having an axial hole (200) formed therein; a center electrode (30) held by the insulator at a position that is one end along a center axis (CX) of the axial hole; a metal shell (50) that is crimped so as to hold the insulator from an outer periphery side; a ground electrode (60) extending from the metallic shell and partially facing the center electrode; a talc material (TC) filled in an annular space (SP) between an outer peripheral surface of the insulator and an inner peripheral surface of the metal shell, At a position of the annular space that is an end portion of the annular space on the side of the center electrode along the central axis, A first annular member (81); a second annular member (82) abutting against the first annular member from an opposite side to the center electrode as viewed in the direction of the central axis.

2. 2. The spark plug of claim 1, wherein a center diameter (CD1) of said first annular member is greater than a center diameter (CD2) of said second annular member.

3. 3. The spark plug according to claim 1, wherein an outer diameter (OD2) of said second annular member is larger than an inner diameter (ID1) of said first annular member.

4. In a cross section taken along a plane including the central axis, 4. The spark plug of claim 3, wherein a distance (OL) from an innermost position of the first annular member to an outermost position of the second annular member in a direction perpendicular to the central axis is within a range of 0.06 mm to 0.88 mm.

5. In a cross section taken along a plane including the central axis, The cross-sectional shape of the first annular member and the cross-sectional shape of the second annular member are both circular, 4. The spark plug according to claim 3, wherein an angle (θ) between the central axis and a straight line connecting a center of a cross section of the first annular member and a center of a cross section of the second annular member is within a range of 13 degrees to 77 degrees.

6. The metal shell is The spark plug has an engagement portion (52) that is located on the outer circumferential side of the annular space and that is engaged with a tool when the spark plug is attached, 6. The spark plug according to claim 1, wherein a width between two opposing faces of said fitting portion is 16 mm or less.

7. The metallic shell is The annular space has an outer circumferential side and a fitting portion that fits with a tool when the spark plug is installed. the insulator is formed with a protruding portion (211) that protrudes along the central axis so that a diameter of an outer circumferential surface increases toward the center electrode side, and that supports the first annular member from the center electrode side, In a cross section taken along a plane including the central axis, The fitting portion is 7. The spark plug according to claim 1, wherein the protrusion is formed at a position on the opposite side to the center electrode than a tangent line (DL21) that contacts a portion of the protrusion with which the first annular member abuts.

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