Spark plug

Abstract

To provide a spark plug capable of suppressing deformation of a metal shell.SOLUTION: A spark plug 10 includes an insulator 20 formed with a shaft hole 200, a metal shell 50 crimped so as to hold the insulator 20 from the outer peripheral side, a talc material TC filled in an annular space SP between the outer peripheral surface of the insulator 20 and the inner peripheral surface of the metal shell 50, and a first annular member 80 disposed at a position at the end on the side of a center electrode 30 in the annular space SP along a central axis CX of the shaft hole 200. The first annular member 80 includes a fitting contact portion 81 that is a portion that abuts on the inner peripheral surface of the metal shell 50, and becomes a line parallel to the inner peripheral surface of the metal shell 50 in a cross section taken along a plane including the central axis CX.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 internal combustion engines, there has been a demand for smaller spark plugs. For this reason, the width between the two hexagonal faces of the fitting portion, i.e., the width between the two opposing faces of the fitting portion, has become smaller than before. When the width between the two faces 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 (10) 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, a talc material (TC) filled in an annular space (SP) between an outer periphery of the insulator and an inner periphery of the metal shell, a first annular member (80) disposed at an end of the annular space on the center electrode side along the central axis, and a second annular member (90) disposed at an end of the annular space on the opposite side to the center electrode along the central axis. The insulator is formed with a protruding portion (211) that protrudes so that the diameter of the outer periphery increases as it approaches the center electrode side along the central axis and supports the first annular member from the center electrode side. The first annular member has a metal shell abutment portion (81) that abuts against the inner circumferential surface of the metal shell and that, in a cross section when cut along a plane including the central axis, forms a line parallel to the inner circumferential surface of the metal shell.

[0012] When the cross-sectional shape of the first annular member is circular as in the conventional case, the first annular member abuts against the metal shell located outside of it along a line (at a point in the cross section). In this case, the force from the first annular member is concentrated in a narrow area of ​​the metal shell. As a result, the pressure increases, making it easy for the metal shell to deform locally.

[0013] In contrast, in the spark plug having the above configuration, the metal shell abutment portion of the first annular member abuts against the metal shell on the outside of the first annular member with a surface (a line in cross section). In this case, the force from the first annular member is distributed over a wide area of ​​the metal shell. As a result, the pressure is reduced, and deformation of the metal shell can be suppressed. Effect of the Invention

[0014] According to the present disclosure, there is provided an ignition plug capable of suppressing deformation of the metallic shell. [Brief description of the drawings]

[0015] [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 showing a cross-sectional shape of the first annular member. [Figure 4] FIG. 4 is a diagram for explaining a method for manufacturing the first annular member. [Diagram 5] FIG. 5 is a diagram for explaining a problem that may occur in the ignition plug according to the comparative example. [Figure 6] FIG. 6 is a diagram for explaining a problem that may occur in an ignition plug according to another comparative example. [Figure 7] FIG. 7 is a diagram showing forces applied to the metallic shell, the insulator, etc. in the spark plug according to this embodiment. [Figure 8] FIG. 8 is a graph showing the amount of bulging of the width across flats at the fitting portion. [Figure 9] FIG. 9 is a graph showing the extent to which the bulge in the width across flats at the fitting portion is reduced. [Figure 10] FIG. 10 is a diagram showing the position of the first annular member in a modified example of this embodiment. [Figure 11] FIG. 11 is a diagram showing the position of the first annular member in another modified example of this embodiment. [Figure 12] FIG. 12 is a diagram showing another method for forming the first annular member. [Figure 13] FIG. 13 is a diagram showing the shape of a first annular member in yet another modified example of the present embodiment. [Figure 14] FIG. 14 is a diagram showing the shape of a first annular member in yet another modified example of the present embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] 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.

[0017] The configuration of an ignition plug 10 according to a first 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.

[0018] The ignition plug 10 is a device provided in each cylinder of an internal combustion engine (not shown) for igniting fuel 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.

[0019] 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.

[0020] 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.

[0021] The terminal fitting 40 is a metal member held by 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 part serves as an electrode terminal to which a voltage is applied from an external power source (not shown).

[0022] 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."

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] A first annular member 80 is disposed at a position that is an end of the annular space SP on the leading end side (i.e., the center electrode 30 side) along the central axis CX. A second annular member 90 is disposed at a position that is an end of the annular space SP on the rear end side (i.e., the side opposite the center electrode 30) along the central axis CX. Both of these are annular members formed to surround the central axis CX, and are formed of a hard metal material such as carbon steel.

[0032] The cross-sectional shape of the second annular member 90 when cut along a plane including the central axis CX is circular. On the other hand, the cross-sectional shape of the first annular member 80 when cut along a plane including the central axis CX is a shape other than circular, as shown in Fig. 2 etc. Details of the cross-sectional shape will be described later.

[0033] 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.

[0034] 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 80, the talc material TC, and the second annular member 90 are arranged in this order in the annular space SP.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] The configuration of the first annular member 80 and its vicinity will be described with reference to Fig. 2 and other figures. Fig. 2 is an enlarged view of a portion of Fig. 1. In Fig. 2, the reference numeral "210" is attached 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".

[0039] 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 a curved arc protruding toward the tip side. The protrusion 211 supports the first annular member 80 from the tip side.

[0040] 2 indicates the position of the end portion on the rear end side of the protruding portion 211. On the rear end side of the dotted line DL1, the line indicating the outer circumferential surface 210 of the insulator 20 is a straight line extending parallel to the central axis CX.

[0041] 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.

[0042] In the portion of the metallic shell 50 adjacent to the fitting portion 52 on the tip side, i.e., the portion indicated by "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 hereinafter also referred to as the "reduced portion 53."

[0043] The reduced portion 53 continues to the position of the dotted line DL11 shown in Fig. 2. In the portion on the tip side of 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.

[0044] 3 shows a cross-sectional shape of the first annular member 80 when cut along a plane including the central axis CX. As described above, the cross-sectional shape is a shape other than a circle. The first annular member 80 has a metal fitting abutment portion 81, an insulator abutment portion 82, and a recess 83.

[0045] The metal fitting abutment portion 81 is a portion that abuts against the inner peripheral surface 520 of the metal shell 50. The dotted line DL21 in FIG. 3 indicates the position of the portion of the metal fitting abutment portion 81 that is the most forward end side along the central axis CX. The dotted line DL22 in FIG. 3 indicates the position of the portion of the metal fitting abutment portion 81 that is the most rear end side along the central axis CX. The metal fitting abutment portion 81 has a shape that is a line parallel to the inner peripheral surface 520 of the metal shell 50 in a cross section when cut along a plane including the central axis CX as in FIG. 2. Specifically, the metal fitting abutment portion 81 has a shape that is a line parallel to a portion of the inner peripheral surface 520 of the metal shell 50 that faces the metal fitting abutment portion 81 in a cross section when cut along a plane including the central axis CX as in FIG. 2. In this embodiment, the line is a straight line parallel to the central axis CX.

[0046] For this reason, the entire metal fitting abutment portion 81 abuts without any gap against the inner circumferential surface 520 of the metal fitting shell 50. In other words, the metal fitting abutment portion 81 abuts against the metal fitting shell 50 located on the outside thereof over a wide surface (a line in cross section).

[0047] The insulator abutting portion 82 is a portion that abuts against the outer peripheral surface of the protruding portion 211 of the insulator 20. The dotted line DL31 in FIG. 3 indicates the position of the portion of the insulator abutting portion 82 that is the most forward end side along the central axis CX. The dotted line DL32 in FIG. 3 indicates the position of the portion of the insulator abutting portion 82 that is the most rear end side along the central axis CX. The insulator abutting portion 82 has a shape that is a line parallel to the outer peripheral surface of the protruding portion 211 in a cross section when cut along a plane including the central axis CX as in FIG. 2. Specifically, the insulator abutting portion 82 has a shape that is a line parallel to a portion of the outer peripheral surface of the protruding portion 211 that faces the insulator abutting portion 82 in a cross section when cut along a plane including the central axis CX as in FIG. 2. In this embodiment, the line is a curve that protrudes toward the forward end side.

[0048] The recess 83 is a portion of the first annular member 80 that faces the second annular member 90 on the rear end side, and is formed so as to recede in a concave shape toward the tip side.

[0049] 3 is a circumscribing circle that encompasses the cross-sectional shape of the first annular member 80. The length of the line corresponding to the metal fitting contact portion 81 in the cross section of FIG 3 is longer than the radius R of the circle CC.

[0050] The first annular member 80 having the above-described cross-sectional shape can be formed using the method shown in Fig. 4. First, an annular member 80A having a circular cross-sectional shape is prepared. As the annular member 80A, for example, the same one as the second annular member 90 can be used.

[0051] 4(A), the annular member 80A is placed inside a recess 111 provided in the lower mold 110. The recess 111 is a concave groove having a circular ring shape when viewed from above. The shape of the bottom surface S1 of the recess 111 is the same as the shape of the outer circumferential surface of the protrusion 211.

[0052] Next, as shown in FIG. 4B, the upper die 120 is inserted into the recess 111 from above. The shape of the tip surface S2 of the upper die 120 is the same as the shape of the recess 83 and its surroundings in the first annular member 80 shown in FIG. 3. When a force directed downward is further applied to the upper die 120, the annular member 80A is sandwiched between the upper die 120 and the lower die 110 and is plastically deformed. Finally, as shown in FIG. 4C, the tip side portion of the annular member 80A has the same shape as the bottom surface S1 of the recess 111. Also, the shape of the rear end side of the annular member 80A has the same shape as the tip surface S2 of the upper die 120. In this manner, the annular member 80A becomes the first annular member 80.

[0053] As described above, the first annular member 80 is provided with the metal fitting abutment portion 81, the insulator abutment portion 82, and the recess 83 from the initial stage before it receives force from the talc material TC in the annular space SP.

[0054] In order to explain the advantage of the first annular member 80 having the above-mentioned shape, a comparative example similar to the conventional example will first be described. As shown in Fig. 5, in this comparative example, the first annular member 80 has a circular cross-sectional shape similar to that of the second annular member 90. The other configurations of this comparative example are the same as those of this embodiment shown in Fig. 2 etc.

[0055] 5(A) shows the state immediately after the metallic shell 50 is crimped. As described above, when the metallic shell 50 is crimped, a compressive force is applied to the talc material TC. Therefore, the first annular member 80 receives a force in a direction from the talc material TC toward the tip side. The talc material TC also gets into between the first annular member 80 and the protruding portion 211. Therefore, the first annular member 80 receives a force from the talc material TC as indicated by the arrow AR1, in addition to the force in the direction toward the tip side.

[0056] The first annular member 80 is pressed against the protruding portion 211 by a force from the talc material TC. An arrow AR2 in Fig. 5(A) indicates a component of the force that the protruding portion 211 receives from the first annular member 80 along the central axis CX.

[0057] The protruding portion 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 first annular member 80 pressed against the protruding portion 211 tries to move outward along the protruding portion 211, and is pressed against the inner circumferential surface 520 of the metal shell 50. The first annular member 80 is further pressed against the inner circumferential surface 520 by the force indicated by the arrow AR1. The arrow AR3 in Fig. 5(A) indicates the force that the metal shell 50 receives from the first annular member 80. In this way, the first annular member 80 receiving the force from the talc material TC applies a force to the metal shell 50 in a direction to expand it outward.

[0058] In this comparative example and this embodiment, the tip end of the reduced portion 53, i.e., a portion of the metal shell 50 where the thickness is thin, is present near the portion of the metal shell 50 that receives the force from the first annular member 80. Therefore, when the force of the arrow AR3 caused by crimping increases, the metal shell 50 may be deformed as shown in Fig. 5(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. 5(B), the initial shape of the metal shell 50 before deformation is indicated by a dotted line.

[0059] In this comparative example, since the first annular member 80 has a circular cross-sectional shape, the first annular member 80 abuts on the metallic shell 50 located outside of it at a line (at a point in the cross section). For this reason, the force (arrow AR3) from the first annular member 80 is concentrated in a narrow range of the metallic shell 50. Since the pressure received by the metallic shell 50 increases, local deformation of the metallic shell 50 as shown in Fig. 5(B) is more likely to occur.

[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] As a measure to reduce the force indicated by the arrow AR3 in Fig. 5(A) and suppress deformation of the metallic shell 50, it is possible to shape the protrusion as shown in Fig. 6. In the comparative example in Fig. 6, the inclination of the protrusion 211 is gentle, and the portion of the outer circumferential surface of the protrusion 211 that abuts against the first annular member 80 is approximately perpendicular to the central axis CX. In this case, the first annular member 80 pressed against the protrusion 211 is less likely to move outward along the protrusion 211. Therefore, the force (arrow AR3) that the metallic shell 50 receives from the first annular member 80 can be made smaller than in the case of Fig. 5(A).

[0062] 6, however, the protruding portion 211 receives a force (arrow AR2) from the first annular member 80 along the central axis CX perpendicularly. In this case, the load on the protruding portion 211 increases. Depending on the magnitude of the force caused by crimping, a crack CR may occur in the protruding portion 211, as shown in FIG. 6(B). Therefore, in order to suppress deformation of the metallic shell 50, it is not preferable to adopt the configuration of FIG. 6.

[0063] Therefore, in this embodiment, the shape of the first annular member 80 is devised as shown in Fig. 2 etc., to suppress deformation of the metal shell 50 during crimping. Fig. 7 illustrates the state of the metal shell 50 according to this embodiment immediately after crimping in the same manner as Fig. 5(A).

[0064] 5, when the metal shell 50 is crimped, the first annular member 80 receives a force (arrow AR1) from the talc material TC toward the tip side. This force presses the first annular member 80 against the protruding portion 211. The protruding portion 211 of the insulator 20 receives a force indicated by an arrow AR2 from the first annular member 80. Moreover, the inner circumferential surface 520 of the metal shell 50 receives a force indicated by an arrow AR3 from the first annular member 80.

[0065] As described above, in this embodiment, the metal fitting abutment portion 81 provided on the first annular member 80 abuts against the inner circumferential surface 520 of the metal fitting 50 over a wide surface (a line in cross section). In such a configuration, the force (arrow AR3) applied to the metal fitting 50 is distributed from the entire metal fitting abutment portion 81, and the pressure received by the metal fitting 50 is smaller than in the case of Fig. 5(B). As a result, deformation of the metal fitting 50 is suppressed compared to the conventional case.

[0066] Such an effect is more pronounced as the length of the line corresponding to the metal fitting abutment portion 81 in the cross section of Fig. 3 becomes longer. According to experiments conducted by the present inventors, it has been confirmed that the above effect is sufficiently exhibited if the length of the above line is longer than the radius R of the circle CC shown in Fig. 3.

[0067] In this embodiment, the insulator abutting portion 82 provided on the first annular member 80 also abuts over a wide surface (a line in cross section) against the protruding portion 211 of the insulator 20. The force (arrow AR2) applied to the protruding portion 211 is also applied in a dispersed manner from the entire insulator abutting portion 82, and the pressure received by the protruding portion 211 is smaller than in the cases of Fig. 5(B) and Fig. 6(B). As a result, it is also possible to prevent cracks CR from occurring in the protruding portion 211.

[0068] Furthermore, in this embodiment, a recess 83 is formed in a portion of the first annular member 80 on the rear end side. When the recess 83 receives a force from the talc material TC toward the front end side, the first annular member 80 is reliably pressed against the metallic shell 50 and the insulator 20 without any gaps. Therefore, not only the talc material TC but also the first annular member 80 prevents gas from the internal combustion engine from leaking out to the outside.

[0069] FIG. 8 shows the results of measuring the extent to which the two-face width of the fitting portion 52 expands when the metal shell 50 is fixed to the insulator 20 by crimping. The "hard material" shown on the horizontal axis of FIG. 8 indicates the case where the material of the metal shell 50 is relatively hard, specifically, the case where the metal shell 50 is made of a metal material for general cold forging processing and is produced by cold forging. The "soft material" shown on the horizontal axis indicates the case where the material of the metal shell 50 is relatively soft, specifically, the case where the metal shell 50 is made of a metal material for general cutting processing and is produced by cutting. The vertical axis of FIG. 8 indicates the extent to which the two-face width of the fitting portion 52 increases during the process of crimping the metal shell 50. "Th" indicates the upper limit value allowed for the expansion amount of the two-face width. In the configuration of this embodiment, the upper limit value Th is 0.08 mm.

[0070] "A1" and "B1" in Fig. 8 represent the amount of bulging of the two flat width of the fitting portion 52 when a first annular member 80 having a circular cross-sectional shape is used, as in the comparative example in Fig. 5. When the material of the metallic shell 50 is relatively hard (A1), the amount of bulging of the two flat width is 0.07 mm, and when the material of the metallic shell 50 is relatively soft (B1), the amount of bulging of the two flat width is 0.19 mm. Thus, it was confirmed that when the cross-sectional shape of the first annular member 80 is circular, if the material of the metallic shell 50 is soft, the amount of bulging of the two flat width exceeds the upper limit value Th.

[0071] "A2" and "B2" in Fig. 8 represent the amount of bulging of the width across flats of the fitting portion 52 when the first annular member 80 of this embodiment (Fig. 3) is used. When the material of the metallic shell 50 is relatively hard (A2), the amount of bulging of the width across flats is 0.02 mm, and when the material of the metallic shell 50 is relatively soft (B2), the amount of bulging of the width across flats is 0.06 mm. In this way, it was confirmed that when the first annular member 80 of this embodiment is used, the amount of bulging of the width across flats is smaller than the upper limit value Th, regardless of whether the material of the metallic shell 50 is soft or hard.

[0072] The "reduction in bulge" shown on the vertical axis of FIG. 9 indicates the degree to which the bulge is reduced by replacing the first annular member 80 of the comparative example with the first annular member 80 of this embodiment in the case where the metallic shell 50 is produced by cold forging (hard material). In the example of FIG. 8, this "reduction in bulge" is a value obtained by subtracting the bulge amount of "B1" from the bulge amount of "A1", and indicates the magnitude of the effect of adopting the first annular member 80 of this embodiment. FIG. 9 shows an example of the change in the "reduction in bulge" when the two-face width (horizontal axis) of the fitting portion 52 is changed. Note that the letters "M10" and the like attached to each data in FIG. 9 indicate the nominal diameter of the male screw 561.

[0073] 9, when the nominal diameter of the male screw 561 is larger than M12, i.e., when the two-face width of the fitting portion 52 is larger than 16 mm, the rigidity of the fitting portion 52 and its neighboring portions is high, so that the effect of adopting the first annular member 80 of this embodiment is small. On the other hand, when the nominal diameter of the male screw 561 is equal to or smaller than M12, i.e., when the two-face width of the fitting portion 52 is equal to or smaller than 16 mm, the rigidity of the fitting portion 52 and its neighboring portions is low in exchange for the size reduction, so that the effect of adopting the first annular member 80 of this embodiment is large. Thus, it is preferable to adopt the first annular member 80 of this embodiment in the spark plug 10 in which the two-face width of the fitting portion 52 is equal to or smaller than 16 mm.

[0074] As shown in FIG. 2, the first annular member 80 of this embodiment is disposed at a position where its most distal end portion is between dotted line DL13 and dotted line DL12. The first annular member 80 may be disposed at a position different from this. For example, as shown in FIG. 10, the most distal end portion of the first annular member 80 may be disposed at a position where it is between dotted line DL11 and dotted line DL12. Also, as shown in FIG. 11, the most distal end portion of the first annular member 80 may be disposed at a position where it is rearward of the dotted line DL13.

[0075] However, in either case, it is preferable that the first annular member 80 is disposed at a position where its most distal end portion is located rearward of the dotted line DL11. In other words, it is preferable that the position of the most distal end portion along the central axis CX of the reduced portion 53 of the metal shell 50 (i.e., the position of the dotted line DL11 in FIG. 2) is located further forward than the position of the most distal end portion along the central axis CX of the first annular member 80. This is because the outer diameter of the metal shell 50 is smallest at the position of the dotted line DL11, and it is easily deformed even with a small force. By disposing the first annular member 80 in a range that does not overlap with such a position, that is, at a position rearward of the dotted line DL11 in FIG. 2, it is possible to sufficiently suppress the deformation of the metal shell 50.

[0076] As described with reference to Fig. 4, the first annular member 80 of this embodiment is formed by sandwiching the annular member 80A having a circular cross-sectional shape between the lower mold 110 and the upper mold 120. Alternatively, the first annular member 80 may be formed by the method shown in Fig. 12.

[0077] 12, first, an annular member 80B having a triangular cross-sectional shape is prepared. Note that the corners of the triangle in the cross-sectional shape are curved as shown in FIG.

[0078] 12(A), the annular member 80B is disposed inside the annular space SP before the talc material TC is filled in. At this time, a surface of the annular member 80B that forms one side of the triangle is in contact with the inner circumferential surface 520 of the metallic shell 50.

[0079] After that, the upper die 130 is inserted into the annular space SP from above. The shape of the tip surface S12 of the upper die 130 is the same as the shape of the recess 83 and its surroundings in the first annular member 80 shown in FIG. 3. When a force is further applied downward to the upper die 130, the annular member 80B is sandwiched between the tip surface S12 of the upper die 130, the inner peripheral surface 520 of the metallic shell 50, and the protruding portion 211 of the insulator 20, and is plastically deformed. Finally, as shown in FIG. 12(B), the tip side portion of the annular member 80B has the same shape as the outer peripheral surface of the protruding portion 211. Also, the shape of the rear end side of the annular member 80B has the same shape as the tip surface S12 of the upper die 130. The first annular member 80 may be formed from the annular member 80B in this manner.

[0080] The cross-sectional shape of the first annular member 80 is not limited to the cross-sectional shape shown in Fig. 3, and various cross-sectional shapes can be adopted. Below, a number of modified examples that differ from one another in the cross-sectional shape of the first annular member 80 will be described with reference to Fig. 13 and Fig. 14. Fig. 13 and Fig. 14 show cross sections of each modified example taken along a plane including the central axis CX, similar to Fig. 2.

[0081] 13(A), the first annular member 80 does not have a recess 83 formed in a portion facing the second annular member 90 on the rear end side. Instead, a protrusion 84 protruding toward the second annular member 90 is formed in that portion. In this configuration, the thickness of the first annular member 80 is increased, so that it is possible to sufficiently ensure the durability of the first annular member 80 against vibrations and the like.

[0082] In the modified example shown in FIG. 13(B), the first annular member 80 has a shape having a recess 83, but the dimension of the first annular member 80 along the central axis CX is larger than that of the first embodiment. As a result, in this modified example, the metal fitting abutment portion 81 is formed so as to extend to a position on the rear end side of the dotted line DL1. In other words, the metal fitting abutment portion 81 is formed so as to extend to a position on the second annular member 90 side along the central axis CX beyond the range in which the protrusion 211 is formed. In such a configuration, the force applied from the metal fitting abutment portion 81 to the metal shell 50 is distributed over a wider range, making it possible to further suppress deformation of the metal shell 50.

[0083] In this modified example, the insulator abutting portion 82 is also formed to extend to a position on the rear end side of the dotted line DL1. In other words, the insulator abutting portion 82 is formed to extend to a position on the second annular member 90 side along the central axis CX beyond the range in which the protruding portion 211 is formed. In this configuration, the force applied from the insulator abutting portion 82 to the protruding portion 211 is distributed over a wider range, so that it is possible to more reliably prevent cracks CR from occurring in the protruding portion 211.

[0084] In the modified example shown in FIG. 14(C), the shape of the recess 83 of the first annular member 80 has the same curvature as the outer circumferential surface of the protruding portion 211. In the modified example shown in FIG. 14(D), the recess 83 is not formed in the first annular member 80. In this modified example, the shape of the portion of the first annular member 80 facing the second annular member 90 is a flat surface perpendicular to the central axis CX. In the modified example shown in FIG. 14(E), the cross-sectional shape of the first annular member 80 is an oval shape extending along the central axis CX. In each modified example shown in FIG. 14, the first annular member 80 has a metal fitting abutment portion 81 similar to that of the present embodiment, and the entire metal fitting abutment portion 81 abuts against the inner circumferential surface 520 of the metal shell 50. This can provide the same effect as that described above.

[0085] 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]

[0086] 10: Spark plug 20: Insulator 30: Center electrode 50: Main metal fitting 60: Ground electrode 80: First annular member 81: Metal fitting contact part 90: Second annular member 200: Shaft hole 211:Protrusion 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; a first annular member (80) disposed at a position that is an end portion of the annular space on the side of the center electrode along the central axis; a second annular member (90) disposed at an end of the annular space opposite to the central electrode along the central axis, 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; The first annular member is a portion that comes into contact with an inner circumferential surface of the metallic shell, a metal fitting abutment portion (81) that is a line parallel to the inner peripheral surface of the metal fitting in a cross section taken along a plane including the central axis, a recess (83) recessed toward the center electrode side is formed in a portion of the first annular member facing the second annular member.

2. 2. The spark plug according to claim 1, wherein in a cross section taken along a plane including the central axis, the metal fitting abutment portion forms a straight line parallel to the central axis.

3. The first annular member is A portion that abuts against an outer circumferential surface of the protrusion, 3. The spark plug according to claim 1, further comprising an insulator contact portion that is parallel to an outer circumferential surface of said protruding portion in a cross section taken along a plane including said central axis.

4. 4. The spark plug according to claim 3, wherein in a cross section taken along a plane including the central axis, the insulator abutting portion has a curved shape that protrudes toward the center electrode.

5. The insulator abutment portion is 5. The spark plug according to claim 3, wherein the protruding portion is formed to extend along the central axis to a position closer to the second annular member than a range in which the protruding portion is formed.

6. The metal fitting abutment portion is 6. The spark plug according to claim 1, wherein the protruding portion is formed to extend along the central axis to a position closer to the second annular member than a range in which the protruding portion is formed.

7. 7. The spark plug according to claim 1, wherein a portion of the first annular member facing the second annular member has a convex portion protruding toward the second annular member at a position across from the concave portion.

8. The metal shell is a fitting portion (52) that is located on the outer circumferential side of the annular space and that is a portion that fits with a tool when installing the ignition plug; a reduced portion (53) that is adjacent to the fitting portion on the center electrode side and has an outer circumferential surface whose diameter gradually decreases toward the center electrode along the central axis, The position of the reduced portion that is closest to the center electrode along the central axis is 8. The spark plug according to claim 1, wherein the first annular member is disposed at a position closer to the center electrode than a portion of the first annular member that is closest to the center electrode along the central axis.

9. In a cross section of the first annular member cut along a plane including the central axis, 9. The spark plug according to claim 1, wherein a length of a line corresponding to the metal fitting contact portion is longer than a radius (R) of a circumscribing circle (CC) that includes a cross-sectional shape of the first annular member.

10. 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, 10. The spark plug according to claim 1, wherein a width between two opposing faces of said fitting portion is 16 mm or less.

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