JP7632090B2 - Spark plug - Google Patents

Description

This disclosure relates to spark plugs.

For example, an internal combustion engine mounted on a vehicle is provided with a spark plug for igniting fuel. The spark plug has 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 part that fits with a tool such as a plug wrench when attaching the spark plug to the internal combustion engine.

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 on the inside of the fitting, 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 keep the talc within the space.

Patent No. 3502936

When manufacturing the spark plug, the metal shell is tightened against the insulator while the talc material and the pair of annular members are housed in the space. At this time, the talc material on the inside is in a compressed state. The metal shell receives a force from the pressurized talc material in a direction that pushes it outward.

In recent years, there has been a demand for smaller spark plugs due to restrictions on component placement around internal combustion engines. 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, making it easier for the main metal shell to deform due to the force from the talc material.

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

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

The inventors have discovered 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.

The purpose of this disclosure is to provide an ignition plug that can suppress deformation of the metal shell.

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 the outer periphery of the insulator and the inner periphery of the metal shell, a first annular member (80) arranged at the end of the annular space on the center electrode side along the central axis, and a second annular member (90) arranged at the end of the annular space on the opposite side to the center electrode along the central axis. The insulator is provided 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 abutment portion (81) that abuts against the inner peripheral surface of the metal shell and is a line parallel to the inner peripheral surface of the metal shell in a cross section taken along a plane including the central axis.

When the cross-sectional shape of the first annular member is circular, as in the past, the first annular member abuts against the metal shell located outside it in 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 easier for localized deformation of the metal shell to occur.

In contrast, in the spark plug with the above configuration, the metal abutment portion of the first annular member abuts against the metal shell on the outside of it 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.

According to the present disclosure, a spark plug is provided that can suppress deformation of the metal shell.

FIG. 1 is a diagram showing the internal structure of the spark plug according to this embodiment. FIG. 2 is an enlarged view of a portion of the configuration of FIG. FIG. 3 is a diagram showing a cross-sectional shape of the first annular member. FIG. 4 is a diagram for explaining a method for manufacturing the first annular member. FIG. 5 is a diagram for explaining a problem that may occur in the spark plug according to the comparative example. FIG. 6 is a diagram for explaining a problem that may occur in an ignition plug according to another comparative example. FIG. 7 is a diagram showing forces applied to the metallic shell, the insulator, etc. in the spark plug according to this embodiment. FIG. 8 is a graph showing the amount of bulging of the width across flats at the fitting portion. FIG. 9 is a graph showing the extent to which the bulge in the width across flats at the fitting portion is reduced. FIG. 10 is a diagram showing the position of the first annular member in a modified example of this embodiment. FIG. 11 is a diagram showing the position of the first annular member in another modified example of this embodiment. FIG. 12 is a diagram showing another method for forming the first annular member. FIG. 13 is a diagram showing the shape of a first annular member in yet another modified example of this embodiment. FIG. 14 is a diagram showing the shape of a first annular member in yet another modified example of the present embodiment.

The present embodiment will be described below with reference to the attached drawings. To facilitate understanding of the description, the same components in each drawing are denoted by the same reference numerals as much as possible, and duplicate descriptions will be omitted.

The configuration of the spark plug 10 according to the first embodiment will be described with reference to FIG. 1. In FIG. 1, a cross section of the spark plug 10 taken along a plane including the central axis CX (described below) is shown on the left side. However, of the components that make up the spark plug 10, the center electrode 30 and the terminal fitting 40 are shown not in cross section but in their respective external appearances.

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

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.

The center electrode 30 is a metal member held by the insulator 20 at 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 portion 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 portion.

The terminal fitting 40 is a metal member held by the insulator 20 at 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 portion 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).

The side of the insulator 20 where the center electrode 30 is attached along the central axis CX is also referred to as the "tip side" below. 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 side" below.

A resistor 71 is disposed between the terminal metal fitting 40 and the center electrode 30 in the axial hole 200. 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 conductive layers formed of a material in which copper powder is added to powdered glass.

The metal shell 50 is a cylindrical member that is provided to cover part of the insulator 20 from the outer periphery. 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 in this state, it holds the insulator 20. The metal shell 50 has a fitting portion 52, a flange portion 55, and an insertion portion 56.

The fitting portion 52 is a portion that fits with a tool, such as a plug wrench, when installing the spark plug 10 in an internal combustion engine. When viewed along the central axis CX, the shape of the fitting portion 52 is hexagonal. In this embodiment, the width between the two opposing faces of the fitting portion 52 (the so-called "two-face width") is 16 mm.

The flange portion 55 is the 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. In addition, a deformation portion 54 is provided between the flange portion 55 and the fitting portion 52, which will be described later.

The insertion portion 56 is a portion further toward the tip side than the flange portion 55, and is the portion that is inserted into an insertion hole (not shown) formed in the internal combustion engine. A male screw 561 is formed on the outer peripheral surface of the insertion portion 56. When the spark plug 10 is attached to the internal combustion engine, the fitting portion 52 rotates around the central axis CX due to the force received from the tool. As a result, the female screw formed on the inner peripheral surface of the insertion hole and the male screw 561 of the insertion portion 56 screw into each other. This fastens and fixes the spark plug 10 to the internal combustion engine. When the spark plug 10 is attached to the internal combustion engine, the potential of the metal shell 50 becomes the same ground potential as that of the internal combustion engine.

The ground electrode 60 is a metal member formed so as to extend from the tip end of the metal 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 center axis CX. The ground side tip 61 is attached to the part of the ground electrode 60 that faces the discharge tip 31. The gap formed between the ground side tip 61 and the discharge tip 31 is the discharge gap.

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 metal 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 metal shell 50. The crimped portion 51 is a portion of the metal shell 50 that is rearward of the fitting portion 52 and is a portion that deforms toward the inner peripheral side when crimped.

The annular space SP is filled with 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.

A first annular member 80 is disposed in the annular space SP at a position that is the end on the leading end side (i.e., the center electrode 30 side) along the central axis CX. A second annular member 90 is disposed in the annular space SP at a position that is the end on the trailing 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 from a hard metal material such as carbon steel.

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.

The method of 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 annular space SP is in a state where the rear end portion is open to the outside.

A protrusion 562 that protrudes inward is formed on the inner circumferential surface of the insertion portion 56 of the metal shell 50. The insulator 20 inserted inside the metal shell 50 stops with the stepped portion formed on its outer circumferential surface abutting the protrusion 562. After that, the first annular member 80, the talc material TC, and the second annular member 90 are placed in the annular space SP in this order.

Next, a force is applied between the bottom surface of the flange portion 55 (the surface against which the gasket GK abuts) and the tip of the crimped portion 51 in a direction along the central axis CX that compresses them. This force crimps the crimped portion 51, deforming it and displacing it toward the inner periphery as shown in FIG. 1.

The deformation portion 54 formed between the fitting portion 52 and the flange portion 55 is relatively thin-walled and therefore buckles under the above force. This shortens the distance from the crimping portion 51 to the protrusion 562, so that the insulator 20 is pressed strongly against the protrusion 562 by the force through the talc material TC. In this 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.

In the state shown in FIG. 1 after the metal shell 50 has been tightened, 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, so it also functions as a sealing material to prevent gas from the internal combustion engine from leaking out to the rear end.

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."

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 as it moves along the central axis CX toward the tip side (i.e., the center electrode 30 side). In the cross section of FIG. 2, the line showing the outer circumferential surface of the protrusion 211 is an arc-shaped curve that protrudes toward the tip side. The protrusion 211 supports the first annular member 80 from the tip side.

The dotted line DL1 in FIG. 2 indicates the position of the rear end of the protrusion 211. On the rear 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.

In FIG. 2, the reference numeral "520" is attached to the inner peripheral surface of the metal shell 50. Hereinafter, this inner peripheral surface will also be referred to as the "inner peripheral surface 520." In the cross section of FIG. 2, the line indicating the inner peripheral surface 520 of the metal shell 50 is a straight line extending parallel to the central axis CX.

In the portion of the metal shell 50 adjacent to the fitting portion 52 at the tip side, i.e., the portion marked with "symbol 53" in FIG. 2, the diameter of the outer circumferential surface of the metal shell 50 gradually decreases toward the tip side along the central axis CX. Hereinafter, this portion is also referred to as the "reduced portion 53."

The reduced portion 53 continues to the position of the dotted line DL11 shown in FIG. 2. In the portion further toward the tip side than the dotted line DL11, the diameter of the outer peripheral surface of the metal 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 distal portion 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 peripheral 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 peripheral surface of the reduced portion 53 is a straight line.

Figure 3 shows the cross-sectional shape of the first annular member 80 when cut along a plane including the central axis CX. As mentioned 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.

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 center axis CX. The dotted line DL22 in the same figure indicates the position of the portion of the metal fitting abutment portion 81 that is the most rear end side along the center 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 center 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 center axis CX as in FIG. 2. In this embodiment, the line is a straight line parallel to the center axis CX.

Therefore, the entire metal fitting contact portion 81 contacts the inner peripheral surface 520 of the metal shell 50 without any gaps. In other words, the metal fitting contact portion 81 contacts the metal shell 50 on the outside of it over a wide surface (a line in cross section).

The insulator abutment 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 abutment portion 82 that is the most forward end side along the central axis CX. The dotted line DL32 in the same figure indicates the position of the portion of the insulator abutment portion 82 that is the most rear end side along the central axis CX. The insulator abutment 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 abutment portion 82 has a shape that is a line parallel to the portion of the outer peripheral surface of the protruding portion 211 that faces the insulator abutment 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 tip side.

The recess 83 is a portion of the first annular member 80 that faces the second annular member 90 at the rear end and is formed to recess toward the tip end.

The circle CC shown by the dashed line in FIG. 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 abutment portion 81 in the cross section of FIG. 3 is longer than the radius R of the circle CC.

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. The annular member 80A can be, for example, the same as the second annular member 90.

Next, as shown in FIG. 4(A), the annular member 80A is placed inside the recess 111 provided in the lower mold 110. The recess 111 is a concave groove that has 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.

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 undergoes plastic deformation. 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.

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 the force from the talc material TC in the annular space SP.

To explain the advantages of the first annular member 80 having the above-described 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 rest of the configuration of this comparative example is the same as the configuration of this embodiment shown in FIG. 2, etc.

Figure 5 (A) shows the state immediately after the metal shell 50 has been tightened. As described above, when the metal shell 50 is tightened, 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 penetrates between the first annular member 80 and the protruding portion 211. Therefore, in addition to the force toward the tip side, the first annular member 80 also receives a force from the talc material TC as indicated by the arrow AR1.

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

The protrusion 211 is inclined so that the diameter of the outer circumferential surface 210 increases toward the tip along the central axis CX. Therefore, the first annular member 80 pressed against the protrusion 211 tries to move outward along the protrusion 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, which receives force from the talc material TC, applies a force to the metal shell 50 in a direction that pushes it outward.

In this comparative example and this embodiment, the tip end of the reduced portion 53, i.e., the portion of the metal shell 50 where the thickness is thin, is located near the portion of the metal shell 50 that receives the force from the first annular member 80. Therefore, if 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. Note that in FIG. 5(B), the initial shape of the metal shell 50 before deformation is shown by a dotted line.

In this comparative example, the first annular member 80 has a circular cross-sectional shape, so the first annular member 80 abuts the metal shell 50 on its outside in a line (at a point in cross section). For this reason, the force from the first annular member 80 (arrow AR3) is concentrated in a narrow area of the metal shell 50. Because the pressure received by the metal shell 50 increases, localized deformation of the metal shell 50 as shown in FIG. 5(B) is more likely to occur.

If such deformation of the metal shell 50 occurs, when attaching the spark plug 10 to the internal combustion engine, it may be impossible to fit a tool into the fitting portion 52, which may cause problems with fitting with a tool. In addition, the deformation of the metal shell 50 causes the talc material TC to loosen, which may reduce the sealing performance of the talc material TC and allow gas from the internal combustion engine to pass through the talc material TC and leak to the outside.

As a measure to reduce the force indicated by the arrow AR3 in FIG. 5A and suppress deformation of the metal 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 generally perpendicular to the central axis CX. In this case, the first annular member 80 pressed against the protrusion 211 has a smaller tendency to move outward along the protrusion 211. Therefore, the force (arrow AR3) that the metal shell 50 receives from the first annular member 80 can be made smaller than in the case of FIG. 5A.

However, in the comparative example of FIG. 6, the protrusion 211 receives the force (arrow AR2) from the first annular member 80 along the central axis CX perpendicularly. In this case, the burden on the protrusion 211 increases. Depending on the magnitude of the force caused by crimping, a crack CR may occur in the protrusion 211, as shown in FIG. 6(B). Therefore, it is not preferable to adopt the configuration of FIG. 6 in order to suppress deformation of the metal shell 50.

In this embodiment, the shape of the first annular member 80 is designed as shown in FIG. 2, etc., to suppress deformation of the metal shell 50 during crimping. In FIG. 7, the state of the metal shell 50 according to this embodiment immediately after crimping is depicted in the same manner as in FIG. 5(A).

5, when the metal shell 50 is tightened, 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 arrow AR2 from the first annular member 80. In addition, the inner circumferential surface 520 of the metal shell 50 receives a force indicated by arrow AR3 from the first annular member 80.

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

The longer the line corresponding to the metal fitting abutment portion 81 in the cross section of FIG. 3, the greater the effect. According to experiments conducted by the inventors, it has been confirmed that the above effect is fully achieved if the length of the line is longer than the radius R of the circle CC shown in FIG. 3.

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

Furthermore, in this embodiment, a recess 83 is formed in the rear end portion of the first annular member 80. As the recess 83 receives a force from the talc material TC toward the front end, the first annular member 80 is pressed securely against the metal 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 to the outside.

Figure 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 crimped and fixed to the insulator 20. The "hard material" shown on the horizontal axis of Figure 8 represents 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 represents 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 Figure 8 represents the extent to which the two-face width of the fitting portion 52 increases during the process of crimping the metal shell 50. "Th" represents the upper limit value allowed for the amount of expansion of the two-face width. In the configuration of this embodiment, the upper limit value Th is 0.08 mm.

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

"A2" and "B2" in FIG. 8 represent the amount of bulging of the two-face width of the fitting portion 52 when the first annular member 80 of this embodiment (FIG. 3) is used. When the material of the metal shell 50 is relatively hard (A2), the amount of bulging of the two-face width is 0.02 mm, and when the material of the metal shell 50 is relatively soft (B2), the amount of bulging of the two-face width is 0.06 mm. Thus, it was confirmed that when the first annular member 80 of this embodiment is used, the amount of bulging of the two-face width is smaller than the upper limit value Th, regardless of whether the material of the metal shell 50 is soft or hard.

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 when the metal 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 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. The letters such as "M10" attached to each data in FIG. 9 indicate the nominal diameter of the male screw 561.

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 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 M12 or less, i.e., when the two-face width of the fitting portion 52 is 16 mm or less, the rigidity of the fitting portion 52 and its neighboring portions is low in exchange for the compact size, so 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 for an ignition plug 10 in which the two-face width of the fitting portion 52 is 16 mm or less.

As shown in FIG. 2, the first annular member 80 of this embodiment is positioned such that its most distal portion is between dotted line DL13 and dotted line DL12. The first annular member 80 may be positioned in a different position. For example, as shown in FIG. 10, the most distal portion of the first annular member 80 may be positioned between dotted line DL11 and dotted line DL12. Also, as shown in FIG. 11, the most distal portion of the first annular member 80 may be positioned rearward of dotted line DL13.

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 rearward of the dotted line DL11. In other words, it is preferable that the position of the most distal end portion of the reduced portion 53 of the metal shell 50 along the central axis CX (i.e., the position of the dotted line DL11 in FIG. 2) is further forward than the position of the most distal end portion of the first annular member 80 along the central axis CX. This is because the outer diameter of the metal shell 50 is smallest at the position of the dotted line DL11, making it easy to deform 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 deformation of the metal shell 50.

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

In the example of FIG. 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. 12.

As shown in FIG. 12A, the annular member 80B is placed inside the annular space SP before the talc material TC is filled in. At this time, one side of the triangle of the annular member 80B is in contact with the inner peripheral surface 520 of the metal shell 50.

Then, 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 metal 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. In addition, 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.

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, with reference to FIG. 13 and FIG. 14, several modified examples of the cross-sectional shape of the first annular member 80 that differ from each other will be described. In FIG. 13 and FIG. 14, a cross section of each modified example is shown when cut along a plane including the central axis CX, as in FIG. 2.

In the modified example shown in FIG. 13(A), a recess 83 is not formed in the portion of the first annular member 80 facing the second annular member 90 at the rear end. Instead, a protrusion 84 that protrudes 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, etc.

In the modified example shown in FIG. 13(B), the first annular member 80 has a shape with 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 to extend to a position that is rearward of the dotted line DL1. In other words, the metal fitting abutment portion 81 is formed to extend to a position that is closer to the second annular member 90 along the central axis CX than the range in which the protrusion 211 is formed. In this 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.

In addition, in this modified example, the insulator abutment portion 82 is also formed to extend to a position that is rearward of the dotted line DL1. In other words, the insulator abutment portion 82 is formed to extend to a position that is closer to the second annular member 90 along the central axis CX than the range in which the protrusion 211 is formed. In this configuration, the force applied from the insulator abutment portion 82 to the protrusion 211 is distributed over an even wider range, making it possible to more reliably prevent cracks CR from occurring in the protrusion 211.

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 peripheral 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 all of the modified examples shown in FIG. 14, the first annular member 80 has a metal fitting abutment portion 81 similar to that of this embodiment, and the entire metal fitting abutment portion 81 abuts against the inner peripheral surface 520 of the metal shell 50. This can achieve the same effect as that described above.

The present embodiment has been described above with reference to specific examples. However, the present disclosure is not limited to these specific examples. Design modifications to these specific examples made by a person skilled in the art 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, as well as their arrangement, conditions, shape, etc., are not limited to those exemplified and can be modified as appropriate. The elements of each of the above-mentioned specific examples can be combined in different ways as appropriate, as long as no technical contradictions arise.

10: Spark plug 20: Insulator 30: Center electrode 50: Metal shell 60: Ground electrode 80: First annular member 81: Metal abutment portion 90: Second annular member 200: Shaft hole 211: Projection portion SP: Annular space TC: Talc material CX: Center axis

Claims (10)

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